bs_bs_banner
Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12203
Descriptive Clinical Reports
Frontal plane fractures of the accessory carpal bone and implications for the carpal sheath of the digital flexor tendons G. J. MINSHALL and I. M. WRIGHT* Newmarket Equine Hospital, Newmarket, Suffolk, UK. *Correspondence email: [email protected]; Received: 31.03.13; Accepted: 11.10.13
Summary Reasons for performing study: Accurate radiological and ultrasonographic descriptions of frontal plane fractures of the accessory carpal bone (ACB) are lacking, and implications of these fractures for the carpal sheath and its contents have not previously been reported. Objectives: Aims were as follows: 1) to describe the location and radiological features of frontal plane fractures of the ACB; 2) to document communication of displaced fractures with the carpal sheath and consequent injury to the deep digital flexor tendon (DDFT); 3) to describe ultrasonographic identification of lesions; and 4) to report tenoscopic evaluation and treatment. Study design: Retrospective case series. Methods: Analysis of frontal plane fractures of the ACB referred to a single hospital between 2006 and 2012, including review of radiographic, ultrasonographic and tenoscopic images. Results: Nine fractures were identified, of which 8 displaced fractures all communicated with the carpal sheath. Comminuted fragments and/or protruding fracture margins lacerated the lateral margin of the enclosed DDFT. This was identifiable ultrasonographically and confirmed at tenoscopy in 7 cases. Treatment in these horses consisted of removal of torn tendon tissue together with fragmentation and protuberant fracture edges, and 7 of 7 cases returned to work. One horse with a nondisplaced fracture was managed with immobilisation; the fracture healed, and the horse returned to work. One horse with a displaced fracture was retired to stud. Conclusions: Frontal plane fractures of the ACB occur palmar to the groove in its lateral margin for the tendon of insertion of ulnaris lateralis. Comminuted fragments can displace distally within the carpal sheath to a mid-metacarpal level or abaxially to lie extrathecally, lateral to the parent bone. Displaced fractures communicate with the carpal sheath and traumatise the DDFT. Keywords: horse; accessory carpal bone; fracture; deep digital flexor tendon; carpal sheath
Introduction The accessory carpal bone (ACB) is one of 7 consistent equine carpal bones. It articulates proximally with the radius and distally with the ulnar carpal bone; both articulations forming part of the antebrachiocarpal joint [1,2]. The bone has a discoid shape [1], concave medially and convex laterally. The medial surface is covered by fibrocartilage, is intrathecal with respect to the carpal sheath of the digital flexor tendons (carpal sheath) and forms the lateral margin of the carpal canal [3]. The lateral surface is irregular. It is indented by a broad groove in the dorsal half of the bone. This has a slight proximopalmar–dorsodistal orientation, occupies the proximal two-thirds of the bone and carries a tendon of insertion of ulnaris lateralis (extensor carpi ulnaris). It has been determined that the centre of the groove is located at a point 28% of the dorsopalmar length of the bone [4]. Two carpal flexor muscles insert on the ACB. Flexor carpi ulnaris inserts proximally. Ulnaris lateralis inserts at 2 points: on the lateral surface of the proximal margin of the ACB and via an ensheathed tendon that runs in the lateral groove of the bone to the proximal border of the fourth metacarpal bone. The ACB is anchored by 4 ligaments: the accessorio-ulnar, accessorio-ulnar carpal, accessorio-quartal and accessorio-metacarpal ligaments [1]. All are substantial and transmit the forces generated by the lever arm of the ACB from the carpal flexor muscles that insert upon it. The flexor retinaculum is a transverse ligament that extends from the palmar margin of the ACB to the medial palmar carpus, thus creating the carpal canal. A fibrous band from the ACB is also said to attach to the lateral digital extensor tendon [2]. Fractures of the ACB are well recognised but uncommon [5–8]. The largest published series comprised 19 cases accumulated over a period of 21 years [4]. They are considered to be most common in jumping horses [4,6,8] but can occur in all breeds [9,10]. Although fragmentation of the articular surfaces has been recognised [11–13], all authors agree that the most common fractures of the ACB are in a frontal (dorsal) plane and are complete [4,9,12,14,15]. This is a retrospective study of frontal plane fractures of the ACB referred to a single hospital. The objectives are as follows: 1) to describe the Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
location and radiological features of frontal plane fractures of the ACB; 2) to document communication of displaced fractures with the carpal sheath and consequent injury to the deep digital flexor tendon (DDFT); 3) to describe ultrasonographic identification of lesions; and 4) to report tenoscopic evaluation and treatment.
Materials and methods Medical records of all horses referred to Newmarket Equine Hospital with radiographically confirmed fractures of an ACB between September 2006 and September 2012 were reviewed, and cases with proximodistally complete fractures in a frontal plane were selected for further evaluation. Data retrieved included age, breed, gender and use of horses, history and clinical findings. Diagnostic information including radiographs, ultrasonographs and tenoscopic images and recordings were reviewed. The same radiographic equipment, data retrieval system and digital measuring program (Synapse V3.2.1)a were used throughout the study period, which permitted consistent measurements to be made within the group. The dorsopalmar location of fractures was expressed as the percentage length of the dorsal fragment as described previously [4] (Fig 1a), in order to determine the fracture location with respect to the groove for the tendon of insertion of ulnaris lateralis. In 7 cases, ultrasonography of the carpal sheath was performed using a hospital-based machine (Vivid 3)b, with linear and curved array transducers (10 MHz). Following clipping and skin preparation, the carpal sheath was imaged in its entirety. For imaging of extra-articular margins of the ACB and the metacarpal portion of the carpal sheath, a stand-off pad was employed with the linear array transducer. The linear and curved array transducers were used to image proximal structures. The linear array transducer was used with the limb in a weightbearing position. The curved array transducer was used with the limb weightbearing, to provide a wide field of view, and with the limb partially flexed (160–170°), in varying caudomedial-craniolateral oblique directions, for assessment of the DDFT and axial margin of the ACB.
579
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
these horses there was distension of the carpal sheath. The carpal sheath was not distended in the nondisplaced frontal plane fracture. Three carpi exhibited visible dorsopalmar shortening and/or axial deviation of the palmar aspect of the ACB. Instability and crepitus were palpable in all 8 displaced fractures.
a)
Radiography x
Y
b)
All horses underwent radiographic examination, which included lateromedial, dorsopalmar, dorsolateral–palmaromedial oblique, dorsomedial–palmarolateral oblique and, in all but one case, flexed lateromedial projections of the affected carpus. One fracture was simple and nondisplaced; the remainder were all displaced and, to varying degrees, comminuted. Comminuted fragments were of varying sizes and had varying degrees of displacement. Small fragments were identified within the soft tissues as far distal as the middle one-third of the palmar metacarpus in 5 horses (Fig 2). In 4 horses, comminuted fragments were sufficiently far displaced laterally at the level of the ACB to be identified abaxial to the normal margins of the bone in dorsopalmar projections (Fig 3). The largest comminuted fragments originated from the distal margin in 5 horses, proximal margin in one horse and proximal and distal margins in one horse. The large distal fragments were consistently of triangular shape in lateromedial projections, with the apex oriented proximally. In one horse, a substantial proximodistal fragment extended from the proximal to the distal margins of the ACB between the principal dorsal and palmar fragments. In this case, the palmar fragments were displaced distally in a rotational manner. In the remaining 8 cases, proximodistal alignment was maintained. Carpal flexion resulted in further dorsopalmar fracture displacement in 7 cases (Fig 1b); it was not performed in one animal and did not induce fragment distraction in the nondisplaced case. Flexion also resulted in distal displacement of the palmar fragments in 4 horses, while in one case there was slight proximal displacement of the palmar fragment. The dorsal fragments were between 40 and 56% (mean 46%) of the bones’ dorsopalmar length as previously described and determined [4] (Fig 1a). There was no radiological evidence of involvement of the articular surfaces in any case.
Fig 1: Lateromedial a) and flexed lateromedial b) radiographic projections of one horse with a complete frontal plane fracture of the accessory carpal bone. The dorsopalmar location of fractures was expressed as X/X + Y × 100%. In this case, the fracture is comminuted in its distal one-half. Carpal flexion results in fragment distraction and increases malalignment.
Tenoscopy of the carpal sheath (7 horses) was performed under general anaesthesia, with horses in dorsal recumbency and the limb slightly flexed. A standard proximolateral arthroscope portal was employed [3].
Results Clinical details Seventeen cases were identified with radiographically confirmed fractures of the ACB, of which 9 suffered proximodistally complete fractures in a frontal plane. These occurred in horses aged from 3 to 11 years. There were 8 Thoroughbreds and one Thoroughbred cross; one entire male, 7 geldings and one female. Two horses were used for flat racing, 6 for jump racing and one for eventing. One horse used for flat racing sustained a frontal plane fracture during racing and the other after escaping from handlers and jumping a gate. In horses used for jump racing, 3 fractures occurred following falls and 3 during racing without falling. The event horse fell at a crosscountry jump. Fractures occurred in 4 left and 5 right limbs. Horses presented between 1 day and 11 months following injury. Seven fractures presented within days of injury, and all these horses were lame at the walk; one horse presented 9 weeks post injury and also was lame at the walk; and in one animal referred after 11 months, lameness was rated at a level of 3–4/10 at the trot. Eight of 9 fractures were displaced, and in all of
580
Fig 2: Lateromedial radiograph demonstrating multiple fragments displaced to a mid-metacarpal level (circled) from a comminuted frontal plane fracture of the accessory carpal bone. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
Ultrasonography Ultrasonography was performed in 6 horses with displaced fractures and one horse with a nondisplaced fracture. In all cases with displaced fractures, ultrasonography identified communication of the fracture with the distended carpal sheath and revealed defects in the lateral margin of the DDFT adjacent to the fracture. The defects in the tendons corresponded to the shape of the protruding fracture margins and/or fragments (Fig 4a). Fragments were visible in the distal sheath in 4 cases. One case in which this was radiographically evident did not undergo ultrasonography.
Treatment The case with a simple, nondisplaced fracture was managed by standing application of a sleeve cast from proximal antebrachium to distal metacarpus, to maintain the carpus in an extended position. This was maintained for 32 days. Bandages of decreasing bulk were then applied for a further 2 weeks. The horse received a total of 8 weeks box rest followed by 8 weeks of progressively increasing walking exercise and then a similar period of gradually increasing trotting exercise. Following diagnosis, the owners of the single mare in this series decided to retire the animal for breeding purposes, and a conservative approach was therefore undertaken. The limb was maintained in extension by application of a dorsal splint extending from proximal antebrachium to distal metacarpus. This was changed at 5–7 day intervals and maintained for 4 weeks. A total of 6 weeks box rest was given, and this was followed by 4 weeks of increasing walking exercise before allowing paddock turnout. The remaining 7 horses underwent tenoscopy of the carpal sheath. Six sheaths contained sanguinous fluid, the exception being seen in the horse in which the fracture had occurred 11 months previously. This and the second most chronic case (which had fractured 9 weeks prior to referral)
Fig 3: Dorsopalmar radiograph with lateral displacement of comminuted fragments (arrows) from a frontal plane fracture of the accessory carpal bone.
c)
a) D SDFT
Pa
DDFT DDFT
Fig 4: a) Ultrasonograph obtained using a curved array transducer with the carpus slightly flexed. Abbreviations and symbols: DDFT = deep digital flexor tendon; SDFT = superficial digital flexor tendon; white arrow, palmar protrusion of a fragment from the fractured accessory carpal bone; black arrow, defect in the DDFT corresponding in shape and location to the protruding fragment; and arrowheads, irregular echogenic material associated with the lateral margin of the DDFT. b), c) and d) Tenoscopic images of the fracture imaged in a). b) Strands of fibrous tissue (FT) bridge the dorsal (D) and palmar (Pa) fracture fragments. Torn fibres from the lateral margin of the DDFT are suspended in the irrigating fluid. c) Extension of the carpus produces closure of the fracture gap and further protrusion of the dorsal fragment into the carpal sheath. d) The protuberant spike of bone has been removed (arrows) together with the torn DDFT. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
d)
b)
D FT Pa Pa FT
DDFT
D
DDFT
581
Accessory carpal bone fractures and implications for the carpal sheath
F
DDFT
Fig 5: Tenoscopic image of an acute case with a sharp comminuted fragment (F) protruding from the fracture and lacerating the lateral margin of the DDFT. Further small fragments (arrows) are seen displaced distally within the carpal sheath. DDFT = deep digital flexor tendon.
had deposits of brown pigment, consistent with haemosiderin, throughout the synovium. All fractures created defects in the fibrocartilage surface of the ACB and communicated with the carpal sheaths. Loose osseous debris over and above fragments previously recognised radiographically was found in 4 horses. The lateral margin of the DDFT adjacent to the fracture was irregularly lacerated in all 7 cases, with disrupted fibres extruded into the sheath lumen and suspended in the irrigating fluid (Fig 4b, c). All tears were aligned with the ACB fracture and, with the carpus slightly flexed for arthroscopic access, the tears extended a short distance proximal to this. Sharp, unstable comminuted fragments were present in and adjacent to the fracture in 5 horses (Fig 5). Incongruent fracture margins produced sharp osseous edges, which protruded into the sheath in 5 horses. Two of these also had protuberant comminuted fragments. The 3 others included the longstanding fracture. In this case, organised fibrous tissue bridged the fracture gap (Fig 4b) between dorsal and palmar fragments. In all cases, carpal flexion resulted in fragment distraction and on extension the fracture gap closed (Fig 4c). Carpal extension also resulted in increased protrusion of fragments and/or incongruent fracture margins into the sheath and resulted in visible impingement on the lacerated DDFT. Impinging ‘spikes’ originated from the dorsal fragment in 3 horses, palmar fragment in one horse and a central fragment in one horse. In all cases, impinging, comminuted fragments and fracture margins were removed using instrument portals between the arthroscope and ACB. In 3 horses, an additional portal was created through the fracture gap. This required increasing the degree of carpal flexion in order to distract dorsal and palmar fragments. It also facilitated retrieval of laterally displaced fragments. Fragment removal was achieved with 3 × 10, 4 × 10 and 6 mm × 10 mm arthroscopic rongeursc. In most cases, no soft tissue dissection was required. Some fragments, particularly in the distal half of the ACB, required prior resection of ligament attachments, which was achieved with straight and curved fixed-blade meniscectomy knivesd and scissorse. Blood clots and other debris were cleared from the fracture using a motorised synovial resectorf, in an oscillating mode with suction applied. Protuberant spikes of the ACB that impinged on the DDFT were removed with a motorised burrf. The torn and extruded DDFT fibres were removed using a synovial resectorf (Fig 4d). Displaced fragments that had migrated into the distal sheath remained in this location at surgery and were identified loosely adherent, with blood clots, to the sheath wall and DDFT. These were removed using 2 and 3 mm arthroscopic rongeursc through an instrument portal created close to the distal sheath reflection. In one horse, comminuted fragments situated between the principal dorsal and palmar fragments were partly covered by hyaline cartilage. On removal, the caudal articular surface of the ulnar carpal bone was visible through the fractured ACB. At the end of procedures, sheaths were lavaged to remove all visible particulate debris and evacuated. Skin portals were closed with simple interrupted sutures of 3 metric monofilament polyamideg. The limbs were
582
G. J. Minshall and I. M. Wright
then protected with elasticated dressings (Pressage)h (n = 4) or sleeve casts (n = 3), which extended from proximal antebrachium to distal metacarpus, with the carpus in an extended position. Horses with casts received hand-assisted recoveries from anaesthesia to ensure that the cast limb was maintained in a protracted position. Animals with bandages recovered unassisted. All horses received perioperative antimicrobials that commenced presurgery and were administered for 1–7 days (mean 3 days) post operatively. The horse that received antimicrobial drugs for 7 days had an open wound over a hind pastern sustained in the same fall as the accessory carpal bone fracture. All horses received preoperative phenylbutazone (Equipalazone;i 4 mg/kg bwt i.v.), which was continued either i.v. or orally for 2–28 days (mean 17 days) post operatively. Sutures were removed between 10 and 14 days after surgery. Bandages were changed as necessary and maintained for between 2 and 3 weeks. Casts were maintained for 1 week (n = 1) or 3 weeks (n = 2), followed by reducing bandage support over the next 2–3 weeks. Horses were confined to their stables for between 1 and 8 weeks (mean 4.8 weeks) post surgery. Walking exercise then commenced and increased in time over the following 4–8 weeks (mean 7 weeks). Exercise thereafter varied as determined by racing/competition seasons.
Follow-up examinations The horse with the simple, nondisplaced fracture was re-evaluated radiographically at 32 days (cast removal). This demonstrated irregular resorption at the fracture margins with evidence of bridging callus. There was also irregular new bone proximally, adjacent to the fracture. Radiographs taken 5 months after injury demonstrated good fracture healing, with bridging bone along the whole of its length. The fracture plane was discernible only as an ill-defined zone of reduced opacity. Trabecular bone bridged the previous defect throughout. The new bone on the proximal margin had reduced in quantity and was now smoothly marginated and organised. Radiographs of the mare managed conservatively were taken after 6 weeks. At this point, osseous resorption had resulted in a radiologically wider fracture gap that increased further in flexed lateromedial projections, demonstrating persistent instability. One surgically managed horse re-presented 7 months after surgery when lameness and distension of the carpal sheath recurred in training. At this time, there was also slight distension of the antebrachiocarpal joint. Radiographs confirmed previous fragment removal, with 3 principal fracture fragments remaining in situ. A defect in the distal articular surface of the dorsal fragment of the ACB was now also identified (this was the horse from which an articular fragment was removed). Ultrasonography revealed a 7 mm osseous protuberance impinging on the lateral margin of the DDFT. The horse underwent a second tenoscopic procedure, which revealed further laceration of the lateral margin of the DDFT. There was an adjacent protuberant ‘spike’ of bone emanating from the middle fragment of the ACB and, when the carpus was extended, this protruded into the DDFT. The fragment size precluded removal. The protuberant ‘spike’ only was therefore smoothed until congruent with the remaining fracture fragments and adjacent fibrous scar tissue using a motorised burr. The torn tendon fibres were removed, before closure and application of an elasticated dressing as reported previously. The animal received perioperative i.v. phenylbutazone (Equipalazone)i and antimicrobial medication for 24 h. Dressings and sutures were removed 12 days post operatively. The horse received 2 weeks of box rest, followed by 10 weeks of increasing walking before free paddock exercise.
Case outcomes The horse with the simple, nondisplaced fracture returned to full work as an eventer but was killed in an accident 11 months post injury. The animal with the complete fracture that was managed conservatively achieved paddock soundness and was used as a broodmare. All 7 horses treated surgically returned to training and racing. Their first races were between 10 and 20 months (mean 12 months) after surgery. They had an aggregate of 67 runs before surgery for 9 wins and 23 places; post surgery, they had 45 runs for 8 wins and 12 places. The horse that underwent 2 surgeries has run once, 20 months after the second surgery. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
Discussion A number of proposed aetiologies have been raised. Some authors consider fractures of the ACB to be the result of external trauma [9,14], including falls causing entrapment between metacarpus and caudal radius [4,9,16]. However, as most frontal plane fractures of the ACB occur during exercise, others have considered abnormal loading likely to be part of the aetiology [7,10,11]. In the present study, there was an equal division in histories between horses that had sustained falls and those that had not, which suggests that entrapment is not the sole or dominant aetiology. Previous authors have recognised the presence of crepitus in some cases [9], which was consistent with all displaced fractures in the present series. References to distension of the carpal sheath in horses with frontal plane fractures of the ACB have been made previously [4,6,10,14] without comment on its significance. Observations on the present series highlight the importance of distension of the carpal sheath as a consistent clinical signal of intrathecal trauma with displaced frontal plane fractures. Lateromedial radiographs have been considered the most useful projection for fracture evaluation [4,6], but the observations from the reported horses support a comprehensive radiographic assessment. Dorsopalmar projections were necessary to identify laterally displaced fragments. The fracture distraction produced in flexed lateromedial projections permits more complete identification and quantification of comminution and assessment of instability. Additionally, lateromedial radiographs including the middle one-third of the metacarpus are necessary to identify distally displaced fragments with the carpal sheath. In the largest series of ACB fractures in the literature, 17 of the 19 were in a frontal plane at approximately the midpoint of the bone, which was determined to be palmar to the groove for the tendon of ulnaris lateralis [4]. Despite this, subsequent authors continue to report that frontal plane fractures occur through this groove [9]. The measurements made in this study support the conclusions of Barr et al. [4]. Previously, there has been little documentation of displacement or instability as recorded in the present series [10,14]. In the only comparable series in the literature, 13 of 17 frontal plane fractures were comminuted. Fragmentation was described as proximal in 5, distal in one and both proximal and distal in 7 horses [4]. However, there was no further information regarding size or location. Displacement of fragments distally within the carpal sheath and laterally in an extrathecal location, as recognised in the present cases, has not previously been reported or the implications recognised. A number of authors have recognised the potential for fractures of the ACB to compromise the carpal canal, although none considered the potential for impingement of fracture fragments on the enclosed tendons. Ultrasonographic evaluation has not previously been reported. Previous authors recognised the potential for development of carpal canal syndrome subsequent to fractures of the ACB [3,6,9,14]. This has been ascribed to increased pressure within the carpal canal [17] or expansion of a fibrous response around healing fractures [9]. The results presented indicate that all displaced frontal plane fractures of the ACB communicate with the carpal sheath. This is anatomically logical. Displaced fragments and/or fracture margins also protrude intrathecally and lacerate the lateral margin of the DDFT. These features explain the presence of carpal sheath distension with such fractures and, using the techniques described, both can be reliably identified ultrasonographically. Conservative management with a goal of developing a fibrocartilaginous nonunion has long been recognised as the treatment of choice for frontal plane fractures of the ACB irrespective of configuration [4,9,10,14,15,18,19]. In one series, follow-up was reported for 11 horses at 6 months to 7 years post injury, all of which were reported to be sound. Seven of these were competitive, including 6 racing, of which 3 won and one was placed, 2 were used for breeding, one for hunting and one was in light work [4]. Division of the posterior carpal annular ligament (carpal retinaculum) was reported in 2 horses with longstanding fractures of the ACB. One raced post surgery and the other returned to hunting [17]. There have been few reported attempts at surgical repair of frontal plane fractures [7,15,20]. Bone shape and fracture location have generally been considered to preclude safe repair, and this has not been adopted into clinical practice [10]. The results of the present study support this premise and suggest that accurate reconstruction of displaced fractures is rarely possible. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
The clinical, radiological, ultrasonographic and tenoscopic findings reported for the present series suggest that removal of displaced fragments and/or protruding fracture margins that lacerate the adjacent DDFT together with displaced osseous debris and damaged tendon fibres is logical. One author considered immobilisation important and suggested that a tube cast may be contributory [11]. This study has shown that extension of the carpus closes the fracture gap in frontal plane fractures of the ACB and, providing protruding fragments have been removed, should limit trauma to the DDFT. On this basis, cast immobilisation was employed in 3 later cases following risks/benefits evaluation, taking into consideration the horse’s temperament and the requirement for assisted recovery. A sleeve (tube) cast was employed in the single simple, nondisplaced fracture in this series. Healing has not previously been recorded in frontal plane fractures of the ACB. It has been reported in a single transverse fracture, treated by confinement only [21]. In the 23 years since the last published series of frontal plane fractures of the ACB, there have been substantial developments in diagnostic imaging, including the advent of digital radiography together with ultrasonography [22] and tenoscopy [3,23] of the carpal sheath. As documented in this paper, these have contributed to greater understanding of the injury, particularly when combined with dynamic assessment of lesions. The principal conclusions from this study are that, as previously reported, frontal plane fractures of the ACB do not occur through the lateral groove in the bone for the tendon of insertion of ulnaris lateralis [4]. Displaced fractures will, de facto, communicate with the carpal sheath. Comminuted fragments may displace as far distally as the mid-metacarpus. Laceration of the DDFT is a common, previously unreported consequence of displaced frontal plane fractures of the ACB that can be detected ultrasonographically. Tenoscopy of the carpal sheath permits removal of displaced and impinging fracture fragments and/or protuberant fracture margins, other intrathecal fragments and lacerated tendon tissue.
Authors’ declaration of interests No competing interests have been declared.
Ethical animal research Ethical review not required by this journal: retrospective clinical study.
Sources of funding None.
Acknowledgements The authors gratefully acknowledge the assistance of Dr Till Hoermann for translating the German literature.
Authorship The authors contributed equally to design, execution, analysis and interpretation, preparation and final approval of the manuscript.
Manufacturers’ addresses a
Fujifilm Medial Systems, Stanford, Connecticut, USA. GE Medical Healthcare, Chalfont St Giles, Buckinghamshire, UK. c Scanlon, St Paul, Minnesota, USA. d Karl Storz, Tuttlingen, Germany. e Sontec, Centennial, Colorado, USA. f Dyonics/Smith & Nephew Endoscopy, Godmanchester, Cambridgeshire, UK. g Ethicon, Edinburgh, UK. h Jupiter Products, Cardiff, UK. i Arnolds, Shrewsbury, Shropshire, UK. b
583
Accessory carpal bone fractures and implications for the carpal sheath
References 1. Sisson, R. (1975) Equine syndesmology. In: The Anatomy of Domestic Animals, Ed: R. Getty, W.B. Saunders, Philadelphia, Pennsylvania. pp 349375. 2. Kainer, R.A. and Fails, A.D. (2011) Functional anatomy of the equine musculoskeletal system. In: Adams and Stashak’s Lameness in Horses, 6th edn., Ed: G.M. Baxter, Blackwell Publishing Ltd, Ames, Iowa. pp 3-72. 3. McIlwraith, C.W., Nixon, A.J., Wright, I.M. and Boening, K.J. (2005) Tenoscopy. In: Diagnostic and Surgical Arthroscopy in the Horse, 3rd edn., Elsevier, Edinburgh. pp 365-408. 4. Barr, A.R.S., Sinnott, M.J.A. and Denny, H.R. (1990) Fractures of the accessory carpal bone in the horse. Vet. Rec. 126, 432-434. 5. Radue, P. (1981) Carpal tunnel syndrome due to fracture of the accessory carpal bone. Vet. Clin. N. Am.: Equine Pract. 3, 8-18. 6. Dyson, S.J. (1990) Fractures of the accessory carpal bone. Equine Vet. Educ. 2, 188-190. 7. Rikjenhuizen, A.B.M. and Nemeth, F. (1994) Accessory carpal bone fractures in the horse. Vet. Quart. 16, S101-S103. 8. Launois, T., Vandekeybus, L., Desbrosse, F. and Perrin, R. (2002) Dorsal 80° proximal 30° lateral-palmarodistal medial oblique view for screw fixation of the accessory carpal bone. J. Equine Vet. Sci. 22, 265-270. 9. Kawcak, C. (2011) The carpus. In: Adams and Stashak’s Lameness in Horses, 6th edn., Ed: G.M. Baxter, Blackwell Publishing Ltd, Ames, Iowa. pp 680-686. 10. Ruggles, A.J. (2012) The Carpus. In: Equine Surgery, 4th edn., Eds: J.A. Auer and J.A. Stick, Elsevier, St Louis, Missouri. pp 1347-1363. 11. Auer, J. (1980) Diseases of the carpus. Vet. Clin. N. Am.: Large Anim. Pract. 2, 81-99. 12. Wyburn, R.S. and Goulden, B.E. (1974) Fractures of the equine carpus: a report on 57 cases. N. Z. Vet. J. 22, 133-142.
584
G. J. Minshall and I. M. Wright
13. Higgins, J.L., Spike-Pierce, D.L. and Bramlage, L.R. (2010) Racing prognosis of thoroughbred yearlings with dorsal proximal accessory carpal bone fragments. Proc. Am. Ass. Equine Practnrs. 56, 402. 14. Ross, M.W. (2011) The carpus. In: Diagnosis and Management of Lameness in the Horse, 2nd edn., Eds: M.W. Ross and S.J. Dyson, Elsevier, St Louis, Missouri. pp 426-449. 15. Easley, K.J. and Schneider, J.E. (1981) Evaluation of a surgical technique for repair of equine accessory carpal bone fractures. J. Am. Vet. Med. Ass. 178, 219-223. 16. Munroe, G.A. and Cauvin, E. (1997) Surgical treatment of a comminuted articular fracture of the accessory carpal bone in a thoroughbred horse. Vet. Rec. 141, 47-49. 17. Mackay-Smith, M.P., Cushing, L.S. and Leslie, J.A. (1972) “Carpal Canal” syndrome in horses. J. Am. Vet. Med. Ass. 160, 993-997. 18. Adams, O.R. (1966) Lameness in Horses, Lea & Febiger, Philadelphia, Pennsylvania. 19. von Freudenberg, F. (1985) Logetronographie der Röntgenbilder, ein Hilfsmittel beim Studium der Fraktur des Os carpi accessorium beim Pferd und zur Beurteilung des Behandlungsergebnisses. Berl. Münch. Tierärztl. Wochenschr. 98, 160-166. 20. Vidovic, A. and Nikolai, V. (2005) Fallbericht über die operative Versorgung einer Fraktur des Os carpi accessorium bei einem Rennpferd. Prakt. Tierarzt. 86, 406-410. 21. Carson, D.M. (1990) The osseous repair of a horizontal fracture of the accessory carpal bone in a Thoroughbred racehorse. Equine Vet. Educ. 2, 173-176. 22. Cauvin, E.R.J., Munroe, G.A., Boswell, J. and Boyd, J.S. (1997) Gross and ultrasonographic anatomy of the carpal flexor tendons sheath in horses. Vet. Rec. 141, 489-495. 23. Southwood, L.L., Stashak, T.S. and Kainer, R.A. (1998) Tenoscopic anatomy of the equine carpal flexor synovial sheath. Vet. Surg. 27, 150-157.
Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
Equine Veterinary Journal ISSN 0425-1644 DOI: 10.1111/evj.12203
Descriptive Clinical Reports
Frontal plane fractures of the accessory carpal bone and implications for the carpal sheath of the digital flexor tendons G. J. MINSHALL and I. M. WRIGHT* Newmarket Equine Hospital, Newmarket, Suffolk, UK. *Correspondence email: [email protected]; Received: 31.03.13; Accepted: 11.10.13
Summary Reasons for performing study: Accurate radiological and ultrasonographic descriptions of frontal plane fractures of the accessory carpal bone (ACB) are lacking, and implications of these fractures for the carpal sheath and its contents have not previously been reported. Objectives: Aims were as follows: 1) to describe the location and radiological features of frontal plane fractures of the ACB; 2) to document communication of displaced fractures with the carpal sheath and consequent injury to the deep digital flexor tendon (DDFT); 3) to describe ultrasonographic identification of lesions; and 4) to report tenoscopic evaluation and treatment. Study design: Retrospective case series. Methods: Analysis of frontal plane fractures of the ACB referred to a single hospital between 2006 and 2012, including review of radiographic, ultrasonographic and tenoscopic images. Results: Nine fractures were identified, of which 8 displaced fractures all communicated with the carpal sheath. Comminuted fragments and/or protruding fracture margins lacerated the lateral margin of the enclosed DDFT. This was identifiable ultrasonographically and confirmed at tenoscopy in 7 cases. Treatment in these horses consisted of removal of torn tendon tissue together with fragmentation and protuberant fracture edges, and 7 of 7 cases returned to work. One horse with a nondisplaced fracture was managed with immobilisation; the fracture healed, and the horse returned to work. One horse with a displaced fracture was retired to stud. Conclusions: Frontal plane fractures of the ACB occur palmar to the groove in its lateral margin for the tendon of insertion of ulnaris lateralis. Comminuted fragments can displace distally within the carpal sheath to a mid-metacarpal level or abaxially to lie extrathecally, lateral to the parent bone. Displaced fractures communicate with the carpal sheath and traumatise the DDFT. Keywords: horse; accessory carpal bone; fracture; deep digital flexor tendon; carpal sheath
Introduction The accessory carpal bone (ACB) is one of 7 consistent equine carpal bones. It articulates proximally with the radius and distally with the ulnar carpal bone; both articulations forming part of the antebrachiocarpal joint [1,2]. The bone has a discoid shape [1], concave medially and convex laterally. The medial surface is covered by fibrocartilage, is intrathecal with respect to the carpal sheath of the digital flexor tendons (carpal sheath) and forms the lateral margin of the carpal canal [3]. The lateral surface is irregular. It is indented by a broad groove in the dorsal half of the bone. This has a slight proximopalmar–dorsodistal orientation, occupies the proximal two-thirds of the bone and carries a tendon of insertion of ulnaris lateralis (extensor carpi ulnaris). It has been determined that the centre of the groove is located at a point 28% of the dorsopalmar length of the bone [4]. Two carpal flexor muscles insert on the ACB. Flexor carpi ulnaris inserts proximally. Ulnaris lateralis inserts at 2 points: on the lateral surface of the proximal margin of the ACB and via an ensheathed tendon that runs in the lateral groove of the bone to the proximal border of the fourth metacarpal bone. The ACB is anchored by 4 ligaments: the accessorio-ulnar, accessorio-ulnar carpal, accessorio-quartal and accessorio-metacarpal ligaments [1]. All are substantial and transmit the forces generated by the lever arm of the ACB from the carpal flexor muscles that insert upon it. The flexor retinaculum is a transverse ligament that extends from the palmar margin of the ACB to the medial palmar carpus, thus creating the carpal canal. A fibrous band from the ACB is also said to attach to the lateral digital extensor tendon [2]. Fractures of the ACB are well recognised but uncommon [5–8]. The largest published series comprised 19 cases accumulated over a period of 21 years [4]. They are considered to be most common in jumping horses [4,6,8] but can occur in all breeds [9,10]. Although fragmentation of the articular surfaces has been recognised [11–13], all authors agree that the most common fractures of the ACB are in a frontal (dorsal) plane and are complete [4,9,12,14,15]. This is a retrospective study of frontal plane fractures of the ACB referred to a single hospital. The objectives are as follows: 1) to describe the Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
location and radiological features of frontal plane fractures of the ACB; 2) to document communication of displaced fractures with the carpal sheath and consequent injury to the deep digital flexor tendon (DDFT); 3) to describe ultrasonographic identification of lesions; and 4) to report tenoscopic evaluation and treatment.
Materials and methods Medical records of all horses referred to Newmarket Equine Hospital with radiographically confirmed fractures of an ACB between September 2006 and September 2012 were reviewed, and cases with proximodistally complete fractures in a frontal plane were selected for further evaluation. Data retrieved included age, breed, gender and use of horses, history and clinical findings. Diagnostic information including radiographs, ultrasonographs and tenoscopic images and recordings were reviewed. The same radiographic equipment, data retrieval system and digital measuring program (Synapse V3.2.1)a were used throughout the study period, which permitted consistent measurements to be made within the group. The dorsopalmar location of fractures was expressed as the percentage length of the dorsal fragment as described previously [4] (Fig 1a), in order to determine the fracture location with respect to the groove for the tendon of insertion of ulnaris lateralis. In 7 cases, ultrasonography of the carpal sheath was performed using a hospital-based machine (Vivid 3)b, with linear and curved array transducers (10 MHz). Following clipping and skin preparation, the carpal sheath was imaged in its entirety. For imaging of extra-articular margins of the ACB and the metacarpal portion of the carpal sheath, a stand-off pad was employed with the linear array transducer. The linear and curved array transducers were used to image proximal structures. The linear array transducer was used with the limb in a weightbearing position. The curved array transducer was used with the limb weightbearing, to provide a wide field of view, and with the limb partially flexed (160–170°), in varying caudomedial-craniolateral oblique directions, for assessment of the DDFT and axial margin of the ACB.
579
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
these horses there was distension of the carpal sheath. The carpal sheath was not distended in the nondisplaced frontal plane fracture. Three carpi exhibited visible dorsopalmar shortening and/or axial deviation of the palmar aspect of the ACB. Instability and crepitus were palpable in all 8 displaced fractures.
a)
Radiography x
Y
b)
All horses underwent radiographic examination, which included lateromedial, dorsopalmar, dorsolateral–palmaromedial oblique, dorsomedial–palmarolateral oblique and, in all but one case, flexed lateromedial projections of the affected carpus. One fracture was simple and nondisplaced; the remainder were all displaced and, to varying degrees, comminuted. Comminuted fragments were of varying sizes and had varying degrees of displacement. Small fragments were identified within the soft tissues as far distal as the middle one-third of the palmar metacarpus in 5 horses (Fig 2). In 4 horses, comminuted fragments were sufficiently far displaced laterally at the level of the ACB to be identified abaxial to the normal margins of the bone in dorsopalmar projections (Fig 3). The largest comminuted fragments originated from the distal margin in 5 horses, proximal margin in one horse and proximal and distal margins in one horse. The large distal fragments were consistently of triangular shape in lateromedial projections, with the apex oriented proximally. In one horse, a substantial proximodistal fragment extended from the proximal to the distal margins of the ACB between the principal dorsal and palmar fragments. In this case, the palmar fragments were displaced distally in a rotational manner. In the remaining 8 cases, proximodistal alignment was maintained. Carpal flexion resulted in further dorsopalmar fracture displacement in 7 cases (Fig 1b); it was not performed in one animal and did not induce fragment distraction in the nondisplaced case. Flexion also resulted in distal displacement of the palmar fragments in 4 horses, while in one case there was slight proximal displacement of the palmar fragment. The dorsal fragments were between 40 and 56% (mean 46%) of the bones’ dorsopalmar length as previously described and determined [4] (Fig 1a). There was no radiological evidence of involvement of the articular surfaces in any case.
Fig 1: Lateromedial a) and flexed lateromedial b) radiographic projections of one horse with a complete frontal plane fracture of the accessory carpal bone. The dorsopalmar location of fractures was expressed as X/X + Y × 100%. In this case, the fracture is comminuted in its distal one-half. Carpal flexion results in fragment distraction and increases malalignment.
Tenoscopy of the carpal sheath (7 horses) was performed under general anaesthesia, with horses in dorsal recumbency and the limb slightly flexed. A standard proximolateral arthroscope portal was employed [3].
Results Clinical details Seventeen cases were identified with radiographically confirmed fractures of the ACB, of which 9 suffered proximodistally complete fractures in a frontal plane. These occurred in horses aged from 3 to 11 years. There were 8 Thoroughbreds and one Thoroughbred cross; one entire male, 7 geldings and one female. Two horses were used for flat racing, 6 for jump racing and one for eventing. One horse used for flat racing sustained a frontal plane fracture during racing and the other after escaping from handlers and jumping a gate. In horses used for jump racing, 3 fractures occurred following falls and 3 during racing without falling. The event horse fell at a crosscountry jump. Fractures occurred in 4 left and 5 right limbs. Horses presented between 1 day and 11 months following injury. Seven fractures presented within days of injury, and all these horses were lame at the walk; one horse presented 9 weeks post injury and also was lame at the walk; and in one animal referred after 11 months, lameness was rated at a level of 3–4/10 at the trot. Eight of 9 fractures were displaced, and in all of
580
Fig 2: Lateromedial radiograph demonstrating multiple fragments displaced to a mid-metacarpal level (circled) from a comminuted frontal plane fracture of the accessory carpal bone. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
Ultrasonography Ultrasonography was performed in 6 horses with displaced fractures and one horse with a nondisplaced fracture. In all cases with displaced fractures, ultrasonography identified communication of the fracture with the distended carpal sheath and revealed defects in the lateral margin of the DDFT adjacent to the fracture. The defects in the tendons corresponded to the shape of the protruding fracture margins and/or fragments (Fig 4a). Fragments were visible in the distal sheath in 4 cases. One case in which this was radiographically evident did not undergo ultrasonography.
Treatment The case with a simple, nondisplaced fracture was managed by standing application of a sleeve cast from proximal antebrachium to distal metacarpus, to maintain the carpus in an extended position. This was maintained for 32 days. Bandages of decreasing bulk were then applied for a further 2 weeks. The horse received a total of 8 weeks box rest followed by 8 weeks of progressively increasing walking exercise and then a similar period of gradually increasing trotting exercise. Following diagnosis, the owners of the single mare in this series decided to retire the animal for breeding purposes, and a conservative approach was therefore undertaken. The limb was maintained in extension by application of a dorsal splint extending from proximal antebrachium to distal metacarpus. This was changed at 5–7 day intervals and maintained for 4 weeks. A total of 6 weeks box rest was given, and this was followed by 4 weeks of increasing walking exercise before allowing paddock turnout. The remaining 7 horses underwent tenoscopy of the carpal sheath. Six sheaths contained sanguinous fluid, the exception being seen in the horse in which the fracture had occurred 11 months previously. This and the second most chronic case (which had fractured 9 weeks prior to referral)
Fig 3: Dorsopalmar radiograph with lateral displacement of comminuted fragments (arrows) from a frontal plane fracture of the accessory carpal bone.
c)
a) D SDFT
Pa
DDFT DDFT
Fig 4: a) Ultrasonograph obtained using a curved array transducer with the carpus slightly flexed. Abbreviations and symbols: DDFT = deep digital flexor tendon; SDFT = superficial digital flexor tendon; white arrow, palmar protrusion of a fragment from the fractured accessory carpal bone; black arrow, defect in the DDFT corresponding in shape and location to the protruding fragment; and arrowheads, irregular echogenic material associated with the lateral margin of the DDFT. b), c) and d) Tenoscopic images of the fracture imaged in a). b) Strands of fibrous tissue (FT) bridge the dorsal (D) and palmar (Pa) fracture fragments. Torn fibres from the lateral margin of the DDFT are suspended in the irrigating fluid. c) Extension of the carpus produces closure of the fracture gap and further protrusion of the dorsal fragment into the carpal sheath. d) The protuberant spike of bone has been removed (arrows) together with the torn DDFT. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
d)
b)
D FT Pa Pa FT
DDFT
D
DDFT
581
Accessory carpal bone fractures and implications for the carpal sheath
F
DDFT
Fig 5: Tenoscopic image of an acute case with a sharp comminuted fragment (F) protruding from the fracture and lacerating the lateral margin of the DDFT. Further small fragments (arrows) are seen displaced distally within the carpal sheath. DDFT = deep digital flexor tendon.
had deposits of brown pigment, consistent with haemosiderin, throughout the synovium. All fractures created defects in the fibrocartilage surface of the ACB and communicated with the carpal sheaths. Loose osseous debris over and above fragments previously recognised radiographically was found in 4 horses. The lateral margin of the DDFT adjacent to the fracture was irregularly lacerated in all 7 cases, with disrupted fibres extruded into the sheath lumen and suspended in the irrigating fluid (Fig 4b, c). All tears were aligned with the ACB fracture and, with the carpus slightly flexed for arthroscopic access, the tears extended a short distance proximal to this. Sharp, unstable comminuted fragments were present in and adjacent to the fracture in 5 horses (Fig 5). Incongruent fracture margins produced sharp osseous edges, which protruded into the sheath in 5 horses. Two of these also had protuberant comminuted fragments. The 3 others included the longstanding fracture. In this case, organised fibrous tissue bridged the fracture gap (Fig 4b) between dorsal and palmar fragments. In all cases, carpal flexion resulted in fragment distraction and on extension the fracture gap closed (Fig 4c). Carpal extension also resulted in increased protrusion of fragments and/or incongruent fracture margins into the sheath and resulted in visible impingement on the lacerated DDFT. Impinging ‘spikes’ originated from the dorsal fragment in 3 horses, palmar fragment in one horse and a central fragment in one horse. In all cases, impinging, comminuted fragments and fracture margins were removed using instrument portals between the arthroscope and ACB. In 3 horses, an additional portal was created through the fracture gap. This required increasing the degree of carpal flexion in order to distract dorsal and palmar fragments. It also facilitated retrieval of laterally displaced fragments. Fragment removal was achieved with 3 × 10, 4 × 10 and 6 mm × 10 mm arthroscopic rongeursc. In most cases, no soft tissue dissection was required. Some fragments, particularly in the distal half of the ACB, required prior resection of ligament attachments, which was achieved with straight and curved fixed-blade meniscectomy knivesd and scissorse. Blood clots and other debris were cleared from the fracture using a motorised synovial resectorf, in an oscillating mode with suction applied. Protuberant spikes of the ACB that impinged on the DDFT were removed with a motorised burrf. The torn and extruded DDFT fibres were removed using a synovial resectorf (Fig 4d). Displaced fragments that had migrated into the distal sheath remained in this location at surgery and were identified loosely adherent, with blood clots, to the sheath wall and DDFT. These were removed using 2 and 3 mm arthroscopic rongeursc through an instrument portal created close to the distal sheath reflection. In one horse, comminuted fragments situated between the principal dorsal and palmar fragments were partly covered by hyaline cartilage. On removal, the caudal articular surface of the ulnar carpal bone was visible through the fractured ACB. At the end of procedures, sheaths were lavaged to remove all visible particulate debris and evacuated. Skin portals were closed with simple interrupted sutures of 3 metric monofilament polyamideg. The limbs were
582
G. J. Minshall and I. M. Wright
then protected with elasticated dressings (Pressage)h (n = 4) or sleeve casts (n = 3), which extended from proximal antebrachium to distal metacarpus, with the carpus in an extended position. Horses with casts received hand-assisted recoveries from anaesthesia to ensure that the cast limb was maintained in a protracted position. Animals with bandages recovered unassisted. All horses received perioperative antimicrobials that commenced presurgery and were administered for 1–7 days (mean 3 days) post operatively. The horse that received antimicrobial drugs for 7 days had an open wound over a hind pastern sustained in the same fall as the accessory carpal bone fracture. All horses received preoperative phenylbutazone (Equipalazone;i 4 mg/kg bwt i.v.), which was continued either i.v. or orally for 2–28 days (mean 17 days) post operatively. Sutures were removed between 10 and 14 days after surgery. Bandages were changed as necessary and maintained for between 2 and 3 weeks. Casts were maintained for 1 week (n = 1) or 3 weeks (n = 2), followed by reducing bandage support over the next 2–3 weeks. Horses were confined to their stables for between 1 and 8 weeks (mean 4.8 weeks) post surgery. Walking exercise then commenced and increased in time over the following 4–8 weeks (mean 7 weeks). Exercise thereafter varied as determined by racing/competition seasons.
Follow-up examinations The horse with the simple, nondisplaced fracture was re-evaluated radiographically at 32 days (cast removal). This demonstrated irregular resorption at the fracture margins with evidence of bridging callus. There was also irregular new bone proximally, adjacent to the fracture. Radiographs taken 5 months after injury demonstrated good fracture healing, with bridging bone along the whole of its length. The fracture plane was discernible only as an ill-defined zone of reduced opacity. Trabecular bone bridged the previous defect throughout. The new bone on the proximal margin had reduced in quantity and was now smoothly marginated and organised. Radiographs of the mare managed conservatively were taken after 6 weeks. At this point, osseous resorption had resulted in a radiologically wider fracture gap that increased further in flexed lateromedial projections, demonstrating persistent instability. One surgically managed horse re-presented 7 months after surgery when lameness and distension of the carpal sheath recurred in training. At this time, there was also slight distension of the antebrachiocarpal joint. Radiographs confirmed previous fragment removal, with 3 principal fracture fragments remaining in situ. A defect in the distal articular surface of the dorsal fragment of the ACB was now also identified (this was the horse from which an articular fragment was removed). Ultrasonography revealed a 7 mm osseous protuberance impinging on the lateral margin of the DDFT. The horse underwent a second tenoscopic procedure, which revealed further laceration of the lateral margin of the DDFT. There was an adjacent protuberant ‘spike’ of bone emanating from the middle fragment of the ACB and, when the carpus was extended, this protruded into the DDFT. The fragment size precluded removal. The protuberant ‘spike’ only was therefore smoothed until congruent with the remaining fracture fragments and adjacent fibrous scar tissue using a motorised burr. The torn tendon fibres were removed, before closure and application of an elasticated dressing as reported previously. The animal received perioperative i.v. phenylbutazone (Equipalazone)i and antimicrobial medication for 24 h. Dressings and sutures were removed 12 days post operatively. The horse received 2 weeks of box rest, followed by 10 weeks of increasing walking before free paddock exercise.
Case outcomes The horse with the simple, nondisplaced fracture returned to full work as an eventer but was killed in an accident 11 months post injury. The animal with the complete fracture that was managed conservatively achieved paddock soundness and was used as a broodmare. All 7 horses treated surgically returned to training and racing. Their first races were between 10 and 20 months (mean 12 months) after surgery. They had an aggregate of 67 runs before surgery for 9 wins and 23 places; post surgery, they had 45 runs for 8 wins and 12 places. The horse that underwent 2 surgeries has run once, 20 months after the second surgery. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
Accessory carpal bone fractures and implications for the carpal sheath
G. J. Minshall and I. M. Wright
Discussion A number of proposed aetiologies have been raised. Some authors consider fractures of the ACB to be the result of external trauma [9,14], including falls causing entrapment between metacarpus and caudal radius [4,9,16]. However, as most frontal plane fractures of the ACB occur during exercise, others have considered abnormal loading likely to be part of the aetiology [7,10,11]. In the present study, there was an equal division in histories between horses that had sustained falls and those that had not, which suggests that entrapment is not the sole or dominant aetiology. Previous authors have recognised the presence of crepitus in some cases [9], which was consistent with all displaced fractures in the present series. References to distension of the carpal sheath in horses with frontal plane fractures of the ACB have been made previously [4,6,10,14] without comment on its significance. Observations on the present series highlight the importance of distension of the carpal sheath as a consistent clinical signal of intrathecal trauma with displaced frontal plane fractures. Lateromedial radiographs have been considered the most useful projection for fracture evaluation [4,6], but the observations from the reported horses support a comprehensive radiographic assessment. Dorsopalmar projections were necessary to identify laterally displaced fragments. The fracture distraction produced in flexed lateromedial projections permits more complete identification and quantification of comminution and assessment of instability. Additionally, lateromedial radiographs including the middle one-third of the metacarpus are necessary to identify distally displaced fragments with the carpal sheath. In the largest series of ACB fractures in the literature, 17 of the 19 were in a frontal plane at approximately the midpoint of the bone, which was determined to be palmar to the groove for the tendon of ulnaris lateralis [4]. Despite this, subsequent authors continue to report that frontal plane fractures occur through this groove [9]. The measurements made in this study support the conclusions of Barr et al. [4]. Previously, there has been little documentation of displacement or instability as recorded in the present series [10,14]. In the only comparable series in the literature, 13 of 17 frontal plane fractures were comminuted. Fragmentation was described as proximal in 5, distal in one and both proximal and distal in 7 horses [4]. However, there was no further information regarding size or location. Displacement of fragments distally within the carpal sheath and laterally in an extrathecal location, as recognised in the present cases, has not previously been reported or the implications recognised. A number of authors have recognised the potential for fractures of the ACB to compromise the carpal canal, although none considered the potential for impingement of fracture fragments on the enclosed tendons. Ultrasonographic evaluation has not previously been reported. Previous authors recognised the potential for development of carpal canal syndrome subsequent to fractures of the ACB [3,6,9,14]. This has been ascribed to increased pressure within the carpal canal [17] or expansion of a fibrous response around healing fractures [9]. The results presented indicate that all displaced frontal plane fractures of the ACB communicate with the carpal sheath. This is anatomically logical. Displaced fragments and/or fracture margins also protrude intrathecally and lacerate the lateral margin of the DDFT. These features explain the presence of carpal sheath distension with such fractures and, using the techniques described, both can be reliably identified ultrasonographically. Conservative management with a goal of developing a fibrocartilaginous nonunion has long been recognised as the treatment of choice for frontal plane fractures of the ACB irrespective of configuration [4,9,10,14,15,18,19]. In one series, follow-up was reported for 11 horses at 6 months to 7 years post injury, all of which were reported to be sound. Seven of these were competitive, including 6 racing, of which 3 won and one was placed, 2 were used for breeding, one for hunting and one was in light work [4]. Division of the posterior carpal annular ligament (carpal retinaculum) was reported in 2 horses with longstanding fractures of the ACB. One raced post surgery and the other returned to hunting [17]. There have been few reported attempts at surgical repair of frontal plane fractures [7,15,20]. Bone shape and fracture location have generally been considered to preclude safe repair, and this has not been adopted into clinical practice [10]. The results of the present study support this premise and suggest that accurate reconstruction of displaced fractures is rarely possible. Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
The clinical, radiological, ultrasonographic and tenoscopic findings reported for the present series suggest that removal of displaced fragments and/or protruding fracture margins that lacerate the adjacent DDFT together with displaced osseous debris and damaged tendon fibres is logical. One author considered immobilisation important and suggested that a tube cast may be contributory [11]. This study has shown that extension of the carpus closes the fracture gap in frontal plane fractures of the ACB and, providing protruding fragments have been removed, should limit trauma to the DDFT. On this basis, cast immobilisation was employed in 3 later cases following risks/benefits evaluation, taking into consideration the horse’s temperament and the requirement for assisted recovery. A sleeve (tube) cast was employed in the single simple, nondisplaced fracture in this series. Healing has not previously been recorded in frontal plane fractures of the ACB. It has been reported in a single transverse fracture, treated by confinement only [21]. In the 23 years since the last published series of frontal plane fractures of the ACB, there have been substantial developments in diagnostic imaging, including the advent of digital radiography together with ultrasonography [22] and tenoscopy [3,23] of the carpal sheath. As documented in this paper, these have contributed to greater understanding of the injury, particularly when combined with dynamic assessment of lesions. The principal conclusions from this study are that, as previously reported, frontal plane fractures of the ACB do not occur through the lateral groove in the bone for the tendon of insertion of ulnaris lateralis [4]. Displaced fractures will, de facto, communicate with the carpal sheath. Comminuted fragments may displace as far distally as the mid-metacarpus. Laceration of the DDFT is a common, previously unreported consequence of displaced frontal plane fractures of the ACB that can be detected ultrasonographically. Tenoscopy of the carpal sheath permits removal of displaced and impinging fracture fragments and/or protuberant fracture margins, other intrathecal fragments and lacerated tendon tissue.
Authors’ declaration of interests No competing interests have been declared.
Ethical animal research Ethical review not required by this journal: retrospective clinical study.
Sources of funding None.
Acknowledgements The authors gratefully acknowledge the assistance of Dr Till Hoermann for translating the German literature.
Authorship The authors contributed equally to design, execution, analysis and interpretation, preparation and final approval of the manuscript.
Manufacturers’ addresses a
Fujifilm Medial Systems, Stanford, Connecticut, USA. GE Medical Healthcare, Chalfont St Giles, Buckinghamshire, UK. c Scanlon, St Paul, Minnesota, USA. d Karl Storz, Tuttlingen, Germany. e Sontec, Centennial, Colorado, USA. f Dyonics/Smith & Nephew Endoscopy, Godmanchester, Cambridgeshire, UK. g Ethicon, Edinburgh, UK. h Jupiter Products, Cardiff, UK. i Arnolds, Shrewsbury, Shropshire, UK. b
583
Accessory carpal bone fractures and implications for the carpal sheath
References 1. Sisson, R. (1975) Equine syndesmology. In: The Anatomy of Domestic Animals, Ed: R. Getty, W.B. Saunders, Philadelphia, Pennsylvania. pp 349375. 2. Kainer, R.A. and Fails, A.D. (2011) Functional anatomy of the equine musculoskeletal system. In: Adams and Stashak’s Lameness in Horses, 6th edn., Ed: G.M. Baxter, Blackwell Publishing Ltd, Ames, Iowa. pp 3-72. 3. McIlwraith, C.W., Nixon, A.J., Wright, I.M. and Boening, K.J. (2005) Tenoscopy. In: Diagnostic and Surgical Arthroscopy in the Horse, 3rd edn., Elsevier, Edinburgh. pp 365-408. 4. Barr, A.R.S., Sinnott, M.J.A. and Denny, H.R. (1990) Fractures of the accessory carpal bone in the horse. Vet. Rec. 126, 432-434. 5. Radue, P. (1981) Carpal tunnel syndrome due to fracture of the accessory carpal bone. Vet. Clin. N. Am.: Equine Pract. 3, 8-18. 6. Dyson, S.J. (1990) Fractures of the accessory carpal bone. Equine Vet. Educ. 2, 188-190. 7. Rikjenhuizen, A.B.M. and Nemeth, F. (1994) Accessory carpal bone fractures in the horse. Vet. Quart. 16, S101-S103. 8. Launois, T., Vandekeybus, L., Desbrosse, F. and Perrin, R. (2002) Dorsal 80° proximal 30° lateral-palmarodistal medial oblique view for screw fixation of the accessory carpal bone. J. Equine Vet. Sci. 22, 265-270. 9. Kawcak, C. (2011) The carpus. In: Adams and Stashak’s Lameness in Horses, 6th edn., Ed: G.M. Baxter, Blackwell Publishing Ltd, Ames, Iowa. pp 680-686. 10. Ruggles, A.J. (2012) The Carpus. In: Equine Surgery, 4th edn., Eds: J.A. Auer and J.A. Stick, Elsevier, St Louis, Missouri. pp 1347-1363. 11. Auer, J. (1980) Diseases of the carpus. Vet. Clin. N. Am.: Large Anim. Pract. 2, 81-99. 12. Wyburn, R.S. and Goulden, B.E. (1974) Fractures of the equine carpus: a report on 57 cases. N. Z. Vet. J. 22, 133-142.
584
G. J. Minshall and I. M. Wright
13. Higgins, J.L., Spike-Pierce, D.L. and Bramlage, L.R. (2010) Racing prognosis of thoroughbred yearlings with dorsal proximal accessory carpal bone fragments. Proc. Am. Ass. Equine Practnrs. 56, 402. 14. Ross, M.W. (2011) The carpus. In: Diagnosis and Management of Lameness in the Horse, 2nd edn., Eds: M.W. Ross and S.J. Dyson, Elsevier, St Louis, Missouri. pp 426-449. 15. Easley, K.J. and Schneider, J.E. (1981) Evaluation of a surgical technique for repair of equine accessory carpal bone fractures. J. Am. Vet. Med. Ass. 178, 219-223. 16. Munroe, G.A. and Cauvin, E. (1997) Surgical treatment of a comminuted articular fracture of the accessory carpal bone in a thoroughbred horse. Vet. Rec. 141, 47-49. 17. Mackay-Smith, M.P., Cushing, L.S. and Leslie, J.A. (1972) “Carpal Canal” syndrome in horses. J. Am. Vet. Med. Ass. 160, 993-997. 18. Adams, O.R. (1966) Lameness in Horses, Lea & Febiger, Philadelphia, Pennsylvania. 19. von Freudenberg, F. (1985) Logetronographie der Röntgenbilder, ein Hilfsmittel beim Studium der Fraktur des Os carpi accessorium beim Pferd und zur Beurteilung des Behandlungsergebnisses. Berl. Münch. Tierärztl. Wochenschr. 98, 160-166. 20. Vidovic, A. and Nikolai, V. (2005) Fallbericht über die operative Versorgung einer Fraktur des Os carpi accessorium bei einem Rennpferd. Prakt. Tierarzt. 86, 406-410. 21. Carson, D.M. (1990) The osseous repair of a horizontal fracture of the accessory carpal bone in a Thoroughbred racehorse. Equine Vet. Educ. 2, 173-176. 22. Cauvin, E.R.J., Munroe, G.A., Boswell, J. and Boyd, J.S. (1997) Gross and ultrasonographic anatomy of the carpal flexor tendons sheath in horses. Vet. Rec. 141, 489-495. 23. Southwood, L.L., Stashak, T.S. and Kainer, R.A. (1998) Tenoscopic anatomy of the equine carpal flexor synovial sheath. Vet. Surg. 27, 150-157.
Equine Veterinary Journal 46 (2014) 579–584 © 2013 EVJ Ltd
