Arthroscopy:
The Journal of Arthroscopic
and Related
Published by Raven Press, Ltd. 0 1992 Arthroscopy
Surgery
&X3):385-390
Association of North America
Technical
Midcarpal Arthroscopy:
Note
Anatomy and Technique
Steven F. Viegas, M.D.
Summary: Wrist arthroscopy has had a dramatic impact in both evaluation and treatment of a variety of wrist problems. Wrist arthroscopy has typically meant arthroscopy of the proximal wrist joint; however, midcarpal joint arthroscopy is becoming a routine part of a complete arthroscopic examination of the wrist. Specific indications, pertinent anatomy, and a clear technique for performing a midcarpal arthroscopy is not well documented in the literature. This article attempts to offer some insight on these issues. Key Words: Wrist-Midcarpal joint.
Arthroscopy of the knee has certainly become an accepted standard of care. Wrist arthroscopy, specifically of the radiocarpal joint, has been gaining popularity, although admittedly it is still in its relative infancy. Arthroscopy of the midcarpal joint is even less commonly performed. In the few pamphlets and/or manuals offering assistance to arthroscopists of the wrist joints, the midcarpal joint is often mentioned only in passing, with little more than anecdotal information provided on the basic anatomy and arthroscopic techniques. Only one previously published article directly addressed midcarpal arthroscopy (1). Recently, additional information was published, further elucidating the variable anatomy of the midcarpal joint and some of the pathology commonly noted in this portion of the wrist (2,3). I attempt to review the basic bone and soft tissue anatomy, the arthroscopic techniques, common pathology, and some operative arthroscopic techniques relating to the midcarpal joint (Fig. 1).
ANATOMY The midcarpal joint is a common joint comprised of seven bones. The distal aspect of the joint consists of the trapezium, the trapezoid, the capitate, and the hamate; the proximal aspect consists of the triquetrum, the lunate, and the scaphoid. Recently, two types of lunate have been described. Type I, which occurs in -35% of wrists, has a distal surface of the lunate which is a simple concave surface that articulates only with the capitate (3). Associated with this type of a lunate is a hamate and capitate whose proximal poles form a smooth curve, broken only by the capitohamate (CH) joint. In this type of wrist, the CH joint generally lines up with the lunatotriquetral joint. Type II lunates, which occur in -65% of wrists, articulate primarily with the capitate but also articulate with the hamate by a separate facet. In these wrists, the proximal pole of the hamate extends proximally beyond the curve of the proximal pole of the capitate, and the CH joint line runs into the ridge in the lunate formed by the intersection of the hamate and capitate facets of the lunate (Fig. 2). The size of hamate facet of the lunate varies from 1 to 6 mm. Chondral lesions and arthrosis at the proximal pole of the hamate, which were not identifiable radiographically, were commonly noted in individuals aged ~50 years but only in association with a type II lunate (2,3) (Fig. 3).
From the Department of Orthopaedic Surgery, University of Texas Medical Branch-Galveston, Galveston, Texas, U.S.A. Address correspondence and reprint requests to Steven F. Viegas M.D., Department of Orthopaedic Surgery, University of Texas Medical Branch-Galveston, 6.136 McCullough Bldg. (G92). Galveston, Texas 77550, U.S.A. Presented at the AAOS Instructional Course Lecture 130 at the 58th Annual Meeting of the American Academy of Orthopaedic Surgeons, Anaheim, California, March 7-12, 1991.
385
386
S. F. VIEGAS
1A
FIG. 1. Three-dimensional reconstructed image of a cadaver wrist that has been graphically manipulated to (A) “explode” the midcarpal joint and (B) manipulate the bones to visualize the proximal aspect of the distal carpal row and the distal aspect of the proximal carpal row. Radius, R; ulna, U; scaphoid, S; lunate, L; triquetrum, T; pisiform, P; hamate, H; capitate, C; trapezoid, Td; trapezium, Tm; first metacarpal, 1; second metacarpal, 2; third metacarpal, 3; fourth metacarpal, 4; fifth metacarpal 5.
The midcarpal joint is generally restricted even with distraction so that the arthroscope cannot be passed sufficiently palmar to visualize the palmar capsule and ligaments. However, when possible, four ligaments may be seen. They are (a) the palmar ligament which runs between the scaphoid tuberosity and the trapezia1 ridge (4), which is reinforced by and often difficult to separate from the flexor carpi
radialis tendon sheath (Fig. 4), (b) the scaphocapitate portion of the radioscaphocapitate (SC) ligament which runs from the palmar ulnar portion of the scaphoid tubercle to the palmar midcapitate surface, (c) the triquetrocapitate ligament, a strong structure that originates from the palmar radial half of the triquetrum, and travels obliquely in a radial direction where it forms a sling palmar to the prox-
FIG. 2. Type I (A) and type II (B) carpal morphology.
Arthroscopy,
Vol. 8, No. 3, 1992
MIDCARPAL
FIG. 3. A cadaver wrist with arthrosis at the proximal pole of the hamate, common in wrists with a type II carpal morphology. Capitate. C; hamate, H; arthrosis (arrow).
imal end of the hamate and runs ulnar to the thin palmar capsule that represents the space of Poirier, and (d) the triquetrohamate (TH) ligament, which arises from the palmar ulnar side of the triquetrum, adjacent to the triquetrocapitate ligament, and attaches to the palmar ulnar portion of the waist of the hamate, proximal to the hamate hook (Fig. 5).
387
ARTHROSCOPY
articular surface on the distal pole of the scaphoid. Keeping to the ulnar side of the extensor pollicis longus tendon will usually maintain a safe margin between the normal course of the radial artery and the STT portal. The extensor pollicis longus tendon can be rather mobile at the level of the STT joint. Therefore, one must be careful not to displace the tendon radially while establishing the STT portal; otherwise, the radial artery could be at risk of injury. The ulnar aspect of the extensor carpi radialis longus tendon can also be used as a guide for the STT portal. At this level, it is a less mobile tendon than the extensor pollicis longus tendon and therefore perhaps more reliable; however, it is less easily palpated and identified. Care should be taken in the development of the STT portal to avoid harming the small branches of the sensory branch of the radial nerve. The other accessory portal is on the ulnar aspect of the wrist and enters the TH joint, just ulnar to the extensor carpi ulnaris tendon. This is an excellent portal for an inflow or outflow canula and can also be used as a portal for a probe or instrument to access the TH joint, including the proximal pole of the hamate.
PORTALS Four portals have been shown to be useful in the midcarpal space (Fig. 6). The portal most commonly used in midcarpal arthroscopy is the radial midcarpal portal (RMC), which is located -1 cm distal to the 34 radiocarpal arthroscopy portal and in line with the radial margin of the third metacarpal. Through this portal, the arthroscope enters the joint between the capitate and the concave surface of the scaphoid. A second portal in the midcarpal space is the ulnar midcarpal portal (UMC), which is located on the midaxial line of the fourth metacarpal and enters the joint at the four-corner intersection between the lunate, triquetrum, hamate, and capitate in the wrist with a type I lunate. In a wrist with a type II lunate, this portal should enter directly over the lunatotriquetral (LT) joint and under the proximal pole of the hamate. The UMC portal is of increased importance in a wrist with a type II lunate because the existence of a large lunatohamate articulation can sometimes make it difficult to sweep the arthroscope ulnar to see the triquetrohamate joint from the RMC portal. There are two accessory portals. One is on the radial side of the midcarpal space and enters the scaphotrapeziotrapezoid (STT) joint. This portal is located just to the ulnar side of the extensor pollicis longus tendon, at the level of the
ARTHROSCOPY TECHNIQUE It is often helpful to have a posteroanterior (PA) radiograph of the wrist available for viewing in the operating room to assess the particular lunate and midcarpal morphology. Aided by the radiograph, which is almost a 1: 1 template, one should mark anatomic landmarks on the skin. Some type of suspension or distraction device should be used to hold the hand and arm. The midcarpal joint can be distended with 3-5 ml fluid through any of the portals. First, the RMC should be established. Preparation of the RMC portal, and any wrist arthroscopy portal, should involve a careful skin incision followed by controlled blunt dissection to the capsule with a blunt trochar or a hemostat. The arthroscope sleeve should be introduced with a tapered trochar using a twisting motion. The index finger should be placed on the trochar sleeve close to the tip of the trochar to avoid an inadvertent and sudden plunge into the joint which may damage the articular surfaces. The obturator will enter the midcarpal joint between the scaphoid and the capitate. Normally there is no communication between the radiocarpal and midcarpal spaces. The obturator should be removed gently to allow the sheath to fill with fluid with the sheath inclined so that any bubbles escape proximally. Arthroscopy.
Vol. 8, No. 3, 1992
S. F. VIEGAS 4A
FIG. 4. A cadaver wrist demonstrating (A) the palmar scaphotrapezial ligament complex/flexor carpi radialis tendon sheath (arrow), and (B) the flexor carpi radialis tendon (open arrow) visible on transection of that structure. Scaphoid, S; trapezium, Tm; trapezoid, Td; capitate, C; hamate, H; triquetrum, T.
An arthroscope with a diameter of 1.7-2.7 mm is suggested; I prefer a 1.7- or a 1.9-mm video arthroscope. Irrigation with lactated Ringer’s or normal saline solution is acceptable, and gravity irrigation is usually satisfactory for diagnostic arthroscopy of the midcarpal joint. One begins examination of the midcarpal joint with the arthroscope in the radial midcarpal portal. The order in which the surfaces are inspected does not matter, so long as all of them are inspected. Generally, one begins the examination by sweeping up the concave surface of the scaphoid to the scaphaid/trapezoid/trapezium joint, seeking areas of chondromalacia or arthrosis on the distal pole of the scaphoid. In the STT joint, the trapezoid is in the foreground (dorsal) and the trapezium is in the background (palmar) (Fig. 7). Considerable degenerative changes may exist in the STT joint. Bubbles
frequently collect here and may impair visualization of the STT joint. To evacuate them or to debride the STT joint, one should establish the STT portal. The STT portal is located just ulnar to the EPL tendon, which will provide protection for the radial artery. Bubbles may be evacuated through this portal by inserting a 21-gauge needle into the STT joint. This portal can be dilated to allow access to debride the joint with a small motorized shaver. One continues to examine the midcarpal joint by going back down over the convex surface of the capitate in an ulnar direction; the scapholunate interval can be visualized across the capitate articular surface. The stability of the scapholunate joint can be assessed dynamically by performing the scaphoid stress test while visualizing the scapholunate joint arthroscopically. It is often easier to assess the scapholunate joint from the midcarpal joint than
5A,B
FIG. 5. A cadaver wrist dissected to demonstrate (A) the synovial fold of tissue that lies between the triquetrohamate (th) ligament and the triquetrocapitate (tc) ligament, to which the probe is pointing. B: Once that synovial fold has been resected, the individual th and the tc ligaments can be more easily identified. Hamate, H; capitate, C; triquetrum, T; lunate L.
Arthroscopy,
Vol. 8, No. 3. 1992
MIDCARPAL
n
TH
STT
UMC
RMC
EDC
I
FIG. 6. Location of the four midcarpal portals. Radial midcarpal portal, RMC; ulnar midcarpal portal, UMC; scaphotrapeziotrapezoid portal, STT; triquetrohamate portal, TH; extensor carpi ulnaris ECU: extensor digiti quintii, EDQ; extensor digitorum communis, EDC; extensor pollicis longis, EPL; extensor carpi radialis brevis, ECRB; extensor carpi radialis longus, ECRL.
from the radiocarpal joint owing to the absence of overlying or degenerative ligaments at the midcarpal aspect of the scapholunate joint. Once the scapholunate joint is assessed, one should then visualize the lunate noticing whether there are one or two distal articular facets on the lunate (i.e., type I vs.
FIG. 7. Arthroscopic view of the scaphoid-trapezium-trapezoid joint as viewed through the STT portal. Scaphoid, S; trapezium, Tm; trapezoid, Td. The outlines of the carpal bones have been enhanced to facilitate recognition.
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ARTHROSCOPY
type II). One can then look down at the lunatotriquetral joint and the articular surface of the triquetrum. The lunatotriquetral joint can be assessed just as the scapholunate was assessed. Any laxity between the triquetrum and the hamate should be evaluated. The TH joint is a saddle-shaped joint that is normally quite tight. In general, if it is possible to see across that joint and visualize the volar capsule between the triquetrum and the hamate, some degree of midcarpal laxity, if not instability, is present. By sweeping the arthroscope back to the TH portion of the midcarpal joint the light from the scope will facilitate establishing the UMC and/or the TH portal. Insertion of a 21-gauge needle and observation of its entry internally will help confirm optimal UMC or TH portal location. The standard technique should be followed to establish a UMC and/or a TH portal. Often, a normal fold of synovial tissue lies at the dorsal and/or palmar aspect of the lunatotriquetral joint. Working back in a radial direction, looking at the distal carpal row, one should inspect the proximal pole of the hamate and the articular surface of the capitate. One should then extend the patient’s wrist slightly and look in a dorsoulnar distal direction to visualize the attachment of the dorsal capsule to the distal carpal row and assess whether the dorsal capsule has avulsed from the hamate and/or from the capitate. In this situation, it may be possible actually to look up into the carpometacarpal joints of the fourth and fifth rays. OPERATIVE PROCEDURES Midcarpal arthroscopy can allow access to and excision of chondral lesions in the midcarpal joint. The articulation between the scaphoid and the trapezoid and the trapezium is a common location for development of chondral lesions and/or arthrosis. The proximal pole of the hamate is another common location for similar lesions. These lesions in the midcarpal joint can be visualized and treated arthroscopically with a combination of small hand instruments and/or small motorized shaver/debridement systems, but specific indications and long-term outcomes are still being determined. Anatomic reduction of the scapholunate joint and the lunatotriquetral joints are often best evaluated from the midcarpal joint. Arthroscopically assisted reduction and percutaneous fixation of scapholunate and lunatotriquetral dissociations are being Arthroscopy.
Vol. 8. No. 3. 1992
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S. F. VIEGAS
performed. In cases of acute lunatotriquetral or scapholunate dissociation, anatomic reduction and multiple pin fixation for 6-8 weeks has been performed to stabilize the proximal carpal row. Reduction and pinning can be assisted by radiocarpal and midcarpal arthroscopy. Multiple 0.045inch diameter K-wires can be placed across the unstable scapholunate and/or lunatotriquetral joint. The bore of a 145gauge needle can be used as a cannula to protect small cutaneous nerve branches during percutaneous placement of the K-wires (T. Whipple, personal communication, 1990). CONCLUSIONS Arthroscopy of the midcarpal joint of the wrist is a relatively new procedure made possible by the advances and miniaturization of arthroscopic instrumentation. Only recently has even the basic
Arthroscopy,
Vol. 8, No. 3, 1992
variability in the normal anatomy of the midcarpal joint been delineated. Midcarpal arthroscopy is becoming a routine part of a complete diagnostic wrist arthroscopy and is offering good visualization of midcarpal anatomy and new opportunities for arthroscopic treatment of midcarpal and proximal wrist joint pathology.
REFERENCES 1. Toby EB, Poehling GG, Koman AL. Midcarpal arthroscopy. Surg Rounds Orthop 1989;3:23-7. 2. Viegas SF. The lunohamate articulation of the midcarpal joint. Arthroscopy 1990;6:5-10. 3. Viegas SF, Wagner K, Patterson RM, Peterson P. The medial (hamate) facet of the lunate. J Hand Surg [Am] 1990; 15564-571. 4. Drewniany JJ, Palmer AK, Flatt AE. The scaphotrapezial ligament complex: an anatomic and biomechanical study. J Hand Surg [Am] 1985;10:492-8.
The Journal of Arthroscopic
and Related
Published by Raven Press, Ltd. 0 1992 Arthroscopy
Surgery
&X3):385-390
Association of North America
Technical
Midcarpal Arthroscopy:
Note
Anatomy and Technique
Steven F. Viegas, M.D.
Summary: Wrist arthroscopy has had a dramatic impact in both evaluation and treatment of a variety of wrist problems. Wrist arthroscopy has typically meant arthroscopy of the proximal wrist joint; however, midcarpal joint arthroscopy is becoming a routine part of a complete arthroscopic examination of the wrist. Specific indications, pertinent anatomy, and a clear technique for performing a midcarpal arthroscopy is not well documented in the literature. This article attempts to offer some insight on these issues. Key Words: Wrist-Midcarpal joint.
Arthroscopy of the knee has certainly become an accepted standard of care. Wrist arthroscopy, specifically of the radiocarpal joint, has been gaining popularity, although admittedly it is still in its relative infancy. Arthroscopy of the midcarpal joint is even less commonly performed. In the few pamphlets and/or manuals offering assistance to arthroscopists of the wrist joints, the midcarpal joint is often mentioned only in passing, with little more than anecdotal information provided on the basic anatomy and arthroscopic techniques. Only one previously published article directly addressed midcarpal arthroscopy (1). Recently, additional information was published, further elucidating the variable anatomy of the midcarpal joint and some of the pathology commonly noted in this portion of the wrist (2,3). I attempt to review the basic bone and soft tissue anatomy, the arthroscopic techniques, common pathology, and some operative arthroscopic techniques relating to the midcarpal joint (Fig. 1).
ANATOMY The midcarpal joint is a common joint comprised of seven bones. The distal aspect of the joint consists of the trapezium, the trapezoid, the capitate, and the hamate; the proximal aspect consists of the triquetrum, the lunate, and the scaphoid. Recently, two types of lunate have been described. Type I, which occurs in -35% of wrists, has a distal surface of the lunate which is a simple concave surface that articulates only with the capitate (3). Associated with this type of a lunate is a hamate and capitate whose proximal poles form a smooth curve, broken only by the capitohamate (CH) joint. In this type of wrist, the CH joint generally lines up with the lunatotriquetral joint. Type II lunates, which occur in -65% of wrists, articulate primarily with the capitate but also articulate with the hamate by a separate facet. In these wrists, the proximal pole of the hamate extends proximally beyond the curve of the proximal pole of the capitate, and the CH joint line runs into the ridge in the lunate formed by the intersection of the hamate and capitate facets of the lunate (Fig. 2). The size of hamate facet of the lunate varies from 1 to 6 mm. Chondral lesions and arthrosis at the proximal pole of the hamate, which were not identifiable radiographically, were commonly noted in individuals aged ~50 years but only in association with a type II lunate (2,3) (Fig. 3).
From the Department of Orthopaedic Surgery, University of Texas Medical Branch-Galveston, Galveston, Texas, U.S.A. Address correspondence and reprint requests to Steven F. Viegas M.D., Department of Orthopaedic Surgery, University of Texas Medical Branch-Galveston, 6.136 McCullough Bldg. (G92). Galveston, Texas 77550, U.S.A. Presented at the AAOS Instructional Course Lecture 130 at the 58th Annual Meeting of the American Academy of Orthopaedic Surgeons, Anaheim, California, March 7-12, 1991.
385
386
S. F. VIEGAS
1A
FIG. 1. Three-dimensional reconstructed image of a cadaver wrist that has been graphically manipulated to (A) “explode” the midcarpal joint and (B) manipulate the bones to visualize the proximal aspect of the distal carpal row and the distal aspect of the proximal carpal row. Radius, R; ulna, U; scaphoid, S; lunate, L; triquetrum, T; pisiform, P; hamate, H; capitate, C; trapezoid, Td; trapezium, Tm; first metacarpal, 1; second metacarpal, 2; third metacarpal, 3; fourth metacarpal, 4; fifth metacarpal 5.
The midcarpal joint is generally restricted even with distraction so that the arthroscope cannot be passed sufficiently palmar to visualize the palmar capsule and ligaments. However, when possible, four ligaments may be seen. They are (a) the palmar ligament which runs between the scaphoid tuberosity and the trapezia1 ridge (4), which is reinforced by and often difficult to separate from the flexor carpi
radialis tendon sheath (Fig. 4), (b) the scaphocapitate portion of the radioscaphocapitate (SC) ligament which runs from the palmar ulnar portion of the scaphoid tubercle to the palmar midcapitate surface, (c) the triquetrocapitate ligament, a strong structure that originates from the palmar radial half of the triquetrum, and travels obliquely in a radial direction where it forms a sling palmar to the prox-
FIG. 2. Type I (A) and type II (B) carpal morphology.
Arthroscopy,
Vol. 8, No. 3, 1992
MIDCARPAL
FIG. 3. A cadaver wrist with arthrosis at the proximal pole of the hamate, common in wrists with a type II carpal morphology. Capitate. C; hamate, H; arthrosis (arrow).
imal end of the hamate and runs ulnar to the thin palmar capsule that represents the space of Poirier, and (d) the triquetrohamate (TH) ligament, which arises from the palmar ulnar side of the triquetrum, adjacent to the triquetrocapitate ligament, and attaches to the palmar ulnar portion of the waist of the hamate, proximal to the hamate hook (Fig. 5).
387
ARTHROSCOPY
articular surface on the distal pole of the scaphoid. Keeping to the ulnar side of the extensor pollicis longus tendon will usually maintain a safe margin between the normal course of the radial artery and the STT portal. The extensor pollicis longus tendon can be rather mobile at the level of the STT joint. Therefore, one must be careful not to displace the tendon radially while establishing the STT portal; otherwise, the radial artery could be at risk of injury. The ulnar aspect of the extensor carpi radialis longus tendon can also be used as a guide for the STT portal. At this level, it is a less mobile tendon than the extensor pollicis longus tendon and therefore perhaps more reliable; however, it is less easily palpated and identified. Care should be taken in the development of the STT portal to avoid harming the small branches of the sensory branch of the radial nerve. The other accessory portal is on the ulnar aspect of the wrist and enters the TH joint, just ulnar to the extensor carpi ulnaris tendon. This is an excellent portal for an inflow or outflow canula and can also be used as a portal for a probe or instrument to access the TH joint, including the proximal pole of the hamate.
PORTALS Four portals have been shown to be useful in the midcarpal space (Fig. 6). The portal most commonly used in midcarpal arthroscopy is the radial midcarpal portal (RMC), which is located -1 cm distal to the 34 radiocarpal arthroscopy portal and in line with the radial margin of the third metacarpal. Through this portal, the arthroscope enters the joint between the capitate and the concave surface of the scaphoid. A second portal in the midcarpal space is the ulnar midcarpal portal (UMC), which is located on the midaxial line of the fourth metacarpal and enters the joint at the four-corner intersection between the lunate, triquetrum, hamate, and capitate in the wrist with a type I lunate. In a wrist with a type II lunate, this portal should enter directly over the lunatotriquetral (LT) joint and under the proximal pole of the hamate. The UMC portal is of increased importance in a wrist with a type II lunate because the existence of a large lunatohamate articulation can sometimes make it difficult to sweep the arthroscope ulnar to see the triquetrohamate joint from the RMC portal. There are two accessory portals. One is on the radial side of the midcarpal space and enters the scaphotrapeziotrapezoid (STT) joint. This portal is located just to the ulnar side of the extensor pollicis longus tendon, at the level of the
ARTHROSCOPY TECHNIQUE It is often helpful to have a posteroanterior (PA) radiograph of the wrist available for viewing in the operating room to assess the particular lunate and midcarpal morphology. Aided by the radiograph, which is almost a 1: 1 template, one should mark anatomic landmarks on the skin. Some type of suspension or distraction device should be used to hold the hand and arm. The midcarpal joint can be distended with 3-5 ml fluid through any of the portals. First, the RMC should be established. Preparation of the RMC portal, and any wrist arthroscopy portal, should involve a careful skin incision followed by controlled blunt dissection to the capsule with a blunt trochar or a hemostat. The arthroscope sleeve should be introduced with a tapered trochar using a twisting motion. The index finger should be placed on the trochar sleeve close to the tip of the trochar to avoid an inadvertent and sudden plunge into the joint which may damage the articular surfaces. The obturator will enter the midcarpal joint between the scaphoid and the capitate. Normally there is no communication between the radiocarpal and midcarpal spaces. The obturator should be removed gently to allow the sheath to fill with fluid with the sheath inclined so that any bubbles escape proximally. Arthroscopy.
Vol. 8, No. 3, 1992
S. F. VIEGAS 4A
FIG. 4. A cadaver wrist demonstrating (A) the palmar scaphotrapezial ligament complex/flexor carpi radialis tendon sheath (arrow), and (B) the flexor carpi radialis tendon (open arrow) visible on transection of that structure. Scaphoid, S; trapezium, Tm; trapezoid, Td; capitate, C; hamate, H; triquetrum, T.
An arthroscope with a diameter of 1.7-2.7 mm is suggested; I prefer a 1.7- or a 1.9-mm video arthroscope. Irrigation with lactated Ringer’s or normal saline solution is acceptable, and gravity irrigation is usually satisfactory for diagnostic arthroscopy of the midcarpal joint. One begins examination of the midcarpal joint with the arthroscope in the radial midcarpal portal. The order in which the surfaces are inspected does not matter, so long as all of them are inspected. Generally, one begins the examination by sweeping up the concave surface of the scaphoid to the scaphaid/trapezoid/trapezium joint, seeking areas of chondromalacia or arthrosis on the distal pole of the scaphoid. In the STT joint, the trapezoid is in the foreground (dorsal) and the trapezium is in the background (palmar) (Fig. 7). Considerable degenerative changes may exist in the STT joint. Bubbles
frequently collect here and may impair visualization of the STT joint. To evacuate them or to debride the STT joint, one should establish the STT portal. The STT portal is located just ulnar to the EPL tendon, which will provide protection for the radial artery. Bubbles may be evacuated through this portal by inserting a 21-gauge needle into the STT joint. This portal can be dilated to allow access to debride the joint with a small motorized shaver. One continues to examine the midcarpal joint by going back down over the convex surface of the capitate in an ulnar direction; the scapholunate interval can be visualized across the capitate articular surface. The stability of the scapholunate joint can be assessed dynamically by performing the scaphoid stress test while visualizing the scapholunate joint arthroscopically. It is often easier to assess the scapholunate joint from the midcarpal joint than
5A,B
FIG. 5. A cadaver wrist dissected to demonstrate (A) the synovial fold of tissue that lies between the triquetrohamate (th) ligament and the triquetrocapitate (tc) ligament, to which the probe is pointing. B: Once that synovial fold has been resected, the individual th and the tc ligaments can be more easily identified. Hamate, H; capitate, C; triquetrum, T; lunate L.
Arthroscopy,
Vol. 8, No. 3. 1992
MIDCARPAL
n
TH
STT
UMC
RMC
EDC
I
FIG. 6. Location of the four midcarpal portals. Radial midcarpal portal, RMC; ulnar midcarpal portal, UMC; scaphotrapeziotrapezoid portal, STT; triquetrohamate portal, TH; extensor carpi ulnaris ECU: extensor digiti quintii, EDQ; extensor digitorum communis, EDC; extensor pollicis longis, EPL; extensor carpi radialis brevis, ECRB; extensor carpi radialis longus, ECRL.
from the radiocarpal joint owing to the absence of overlying or degenerative ligaments at the midcarpal aspect of the scapholunate joint. Once the scapholunate joint is assessed, one should then visualize the lunate noticing whether there are one or two distal articular facets on the lunate (i.e., type I vs.
FIG. 7. Arthroscopic view of the scaphoid-trapezium-trapezoid joint as viewed through the STT portal. Scaphoid, S; trapezium, Tm; trapezoid, Td. The outlines of the carpal bones have been enhanced to facilitate recognition.
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type II). One can then look down at the lunatotriquetral joint and the articular surface of the triquetrum. The lunatotriquetral joint can be assessed just as the scapholunate was assessed. Any laxity between the triquetrum and the hamate should be evaluated. The TH joint is a saddle-shaped joint that is normally quite tight. In general, if it is possible to see across that joint and visualize the volar capsule between the triquetrum and the hamate, some degree of midcarpal laxity, if not instability, is present. By sweeping the arthroscope back to the TH portion of the midcarpal joint the light from the scope will facilitate establishing the UMC and/or the TH portal. Insertion of a 21-gauge needle and observation of its entry internally will help confirm optimal UMC or TH portal location. The standard technique should be followed to establish a UMC and/or a TH portal. Often, a normal fold of synovial tissue lies at the dorsal and/or palmar aspect of the lunatotriquetral joint. Working back in a radial direction, looking at the distal carpal row, one should inspect the proximal pole of the hamate and the articular surface of the capitate. One should then extend the patient’s wrist slightly and look in a dorsoulnar distal direction to visualize the attachment of the dorsal capsule to the distal carpal row and assess whether the dorsal capsule has avulsed from the hamate and/or from the capitate. In this situation, it may be possible actually to look up into the carpometacarpal joints of the fourth and fifth rays. OPERATIVE PROCEDURES Midcarpal arthroscopy can allow access to and excision of chondral lesions in the midcarpal joint. The articulation between the scaphoid and the trapezoid and the trapezium is a common location for development of chondral lesions and/or arthrosis. The proximal pole of the hamate is another common location for similar lesions. These lesions in the midcarpal joint can be visualized and treated arthroscopically with a combination of small hand instruments and/or small motorized shaver/debridement systems, but specific indications and long-term outcomes are still being determined. Anatomic reduction of the scapholunate joint and the lunatotriquetral joints are often best evaluated from the midcarpal joint. Arthroscopically assisted reduction and percutaneous fixation of scapholunate and lunatotriquetral dissociations are being Arthroscopy.
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performed. In cases of acute lunatotriquetral or scapholunate dissociation, anatomic reduction and multiple pin fixation for 6-8 weeks has been performed to stabilize the proximal carpal row. Reduction and pinning can be assisted by radiocarpal and midcarpal arthroscopy. Multiple 0.045inch diameter K-wires can be placed across the unstable scapholunate and/or lunatotriquetral joint. The bore of a 145gauge needle can be used as a cannula to protect small cutaneous nerve branches during percutaneous placement of the K-wires (T. Whipple, personal communication, 1990). CONCLUSIONS Arthroscopy of the midcarpal joint of the wrist is a relatively new procedure made possible by the advances and miniaturization of arthroscopic instrumentation. Only recently has even the basic
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variability in the normal anatomy of the midcarpal joint been delineated. Midcarpal arthroscopy is becoming a routine part of a complete diagnostic wrist arthroscopy and is offering good visualization of midcarpal anatomy and new opportunities for arthroscopic treatment of midcarpal and proximal wrist joint pathology.
REFERENCES 1. Toby EB, Poehling GG, Koman AL. Midcarpal arthroscopy. Surg Rounds Orthop 1989;3:23-7. 2. Viegas SF. The lunohamate articulation of the midcarpal joint. Arthroscopy 1990;6:5-10. 3. Viegas SF, Wagner K, Patterson RM, Peterson P. The medial (hamate) facet of the lunate. J Hand Surg [Am] 1990; 15564-571. 4. Drewniany JJ, Palmer AK, Flatt AE. The scaphotrapezial ligament complex: an anatomic and biomechanical study. J Hand Surg [Am] 1985;10:492-8.
