583513 research-articleXXXX
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〈 Clinical Research 〉 Forefoot Deformity in Rheumatoid Arthritis
Malhar H. Dave, MBBS, MS, Lyndon W. Mason, MB BCh, MRCS, FRCS, and Kartik Hariharan, MB BCh, FRCS
A Comparison of Shod and Unshod Populations Abstract: All reported rheumatoid arthritis (RA) forefoot deformities in the literature thus far have arisen from shoe wearing populations. Our aim in this study was to compare hallucal deformities seen in a shod population with an unshod population. A population comparison was undertaken in 2 specialized foot and ankle units, one in India and one in the United Kingdom. In the shod population, there was 1 hallux varus deformity, 10 without hallucal deformity, and 90 hallux valgus deformities. In contrast, in the unshod population, there were 19 hallux varus deformities and 6 hallux valgus deformities. There was great variability in the lesser toe deformity seen. In the shod population, it was most common to see dorsal subluxation or dislocation, with the fifth toe in a varus position. In the unshod population, the most common lesser toe deformity seen was varus deviation or dislocation. Instability of the metatarsophalangeal joint in the rheumatoid foot predisposes it to significant deformity. In the non– shoe wearing population, intrinsic muscle forces and weight bearing
forces are the most likely determinants of the deformity, with hallux varus being a more common presenting problem. In the shod population, the external forces of shoe wear dictate the direction of deformity. Levels of Evidence: Prognostic Level III: Case control study Keywords: hallux varus; rheumatoid arthritis; shod; unshod; hallux valgus
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involvement of the feet occurred in 91% of females and 85% of males. Michelson et al3 found that the prevalence of foot and ankle symptoms in RA sufferers was related to the duration of systemic illness of the disease and was present in >50% of patients at any time after the diagnosis of RA.3 Although the occurrence of hindfoot pain was the most common problem, the forefoot was a significant
The hallucal deformities reported in RA
Introduction
[rheumatoid arthritis] are a consequence
Rheumatoid arthritis of chronic metatarsophalangeal joint (RA) is a chronic inflammatory disease inflammation . . .” characterized by progressive damage of synovial-lined joints and complaint in a high proportion of variable extra-articular manifestations.1 patients.3,4 RA has a propensity for the small joints Kirkup et al5 described a number of of the hands and feet, which results in a deformities in their analysis of the hallux common occurrence of forefoot in RA, including hallux valgus, deformity. A number of studies have metatarsus primus varus, hallux tortus, reported the incidence of foot ailments hallux rigidus, hallux flexus, “chisel toe,” in RA, with Vainio,2 in a survey involving hallux elevates, hallux varus, and 955 patients affected with RA (618 combined deformities. By far the most females and 337 males), reporting that common forefoot deformity reported in
DOI: 10.1177/1938640015583513. From Abhishek Hospital and Foot and Ankle Centre, Vadodara, Gujarat, India (MHD); Foot and Ankle Unit, University Hospital Aintree, Liverpool, UK (LWM); and Foot and Ankle Unit, Royal Gwent Hospital, Aneurin Bevan University Health Board, Newport, UK (KH). Address correspondence to: Lyndon Mason, MB BCh, MRCS, FRCS, Foot and Ankle Unit, Royal Gwent Hospital, Aneurin Bevan University Health Board, Newport, UK; e-mail: [email protected]. For reprints and permissions queries, please visit SAGE’s Web site at http://www.sagepub.com/journalsPermissions.nav. Copyright © 2015 The Author(s)
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the literature is that of hallux valgus. Kerry et al4 reported an incidence of 65% hallux valgus in 100 patients surveyed with RA in regard to foot problems. Michelson et al3 found, on examination of 99 RA patients, a prevalence of 67% hallux valgus deformities of which 19% were judged to be severe. Coughlin’s6 long-term cohort study on the results of forefoot surgery in chronic RA contained 91% of patients presenting with hallux valgus deformity (43 of 47 feet assessed). Tillman7 found on examination of all metatarsophalangeal joints a lateral deviation or dislocation of 77% of joints, with only 3% medial deviation found, none of which included the first metatarsophalangeal joint. The hallucal deformities reported in RA are a consequence of chronic metatarsophalangeal joint inflammation, which leads to capsular distention and eventually to a loss of capsular and collateral ligament integrity.6 It is likely influenced by other joint changes in the foot, which it is theorized ultimately determines the direction of hallucal deformity.5 External forces, though a great protagonist of hallux valgus deformity in general,8,9 are thought to take a lesser role to the internal factors related to hallucal deformity in RA. All reported RA forefoot deformities in the literature so far have arisen from shoe wearing populations. Our aim in this study was to compare hallucal deformities seen in a shod to an unshod population, our null hypothesis being there was no difference.
documented closed shoe wearing individuals were included in this study. The patients’ medical notes and radiographs were analyzed retrospectively. All measurements were performed according to the guidelines produced by the American Orthopaedic Foot and Ankle Society Ad Hoc Committee on angular measurements.10 The measurements were accomplished using the graphics package present on the hospitals Picture Archiving and Communication System (Carestream Vue PACS, Kodak). Standardized anteroposterior weight bearing radiographs were obtained to measure the hallux valgus and intermetatarsal angles. To minimize bias caused by the interobserver variability, all radiographs were observed by 2 authors independently, and the intraclass coefficient was measured. When discrepancies of greater than 5° existed, a consensus was reached. All lesser toe deformities were noted. Any other deformity or pathology was documented. All data were assessed using SPSS Inc, 20.0 (IBM, New York). Binary data were entered into contingency tables allowing cross-tabulation of the results. For data cells greater than 5, differences were tested using the χ2 test, otherwise Fisher’s exact test was used. Numerical data were tested using a Student t test if parametric or a Mann–Whitney test if nonparametric. A P value of less than .05 was considered statistically significant.
Methods
A total of 126 feet from 87 patients were included in this study. The shod population contained 101 feet from 69 patients, and the unshod population contained 25 feet from 18 patients. Both the sex and side of pathology were similar between groups, with females accounting for 83.2% of patients in the shod group and 96% of patients in the unshod group. There were 66 left feet and 60 right feet included in the study. The mean age of patients in the unshod population was 65.48, and in the shod population it was 65.91. The intraclass correlation coefficient for interobserver
An observational study was undertaken in 2 specialized foot and ankle units, one in India and one in the United Kingdom. All patients suffering from RA and attending for consideration of forefoot surgery from January 2007 to October 2013 were considered for this study. All non–shoe wearing patients presenting to a charity foot and ankle clinic in India with RA forefoot deformities were included in this study. All the patients attending the UK foot and ankle clinic with RA forefoot deformities that were
Results
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variability was 0.956 for the hallux valgus angle and 0.924 for the 1,2 intermetatarsal angle. The definition of hallux valgus deformity is relatively consistent in the literature in regard to hallux valgus angle, where a normal hallux valgus angle is accepted as less than 15°.11 We used 15° valgus angulation of the hallux at the metatarsophalangeal joint for our categorization of normal and hallux valgus deformity. Any degree of varus at the first metatarsophalangeal joint is deemed pathological and was labelled as hallux varus. With this categorization we found in the shod population, there was 1 hallux varus deformity, 10 without hallucal deformity, and 90 feet with varying degrees of hallux valgus deformity. In contrast, in the unshod population, there were 19 hallux varus deformities and 6 hallux valgus deformities. In recording the radiographic parameters, we found in the shod population a mean hallux valgus angle of 34.85° (range −7°to 65°) and a mean 1,2 intermetatarsal angle of 12.79° (range 2° to 27°). In the unshod population, we found a mean hallux valgus angle of −20.72° (range −85° to 63°) and a mean 1,2 intermetatarsal angle of 7.44° (range 2° to 12°). Comparing the means of the shod versus the unshod populations, all radiographic measurements were normally distributed and showed a statistically significant difference on Student’s t test (P < .001). Figure 1 illustrates the difference in hallux valgus angle in shod compared to unshod populations. There was great variability in the lesser toe deformity seen. The results of these observations are contained in Table 1. In the shod population, it was most common to see dorsal subluxation or dislocation, with the fifth toe in a varus position. This has been postulated by us as being due to the external restraint to deformation provided by the shoe preventing varus deformation of the hallux and also preventing the fifth toe deforming into valgus, and thus causing overcrowding of the second, third, and fourth toes. This was seen in 95% (n = 96) of the shod population. In the unshod population, the
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Figure 1. A boxplot comparing hallux valgus angles of shod and unshod populations.
most common lesser toe deformity seen was varus deviation or dislocation. This was present in 80% (n = 20) of the unshod population. Without the medial restraint provided by shoe wear, the deforming forces on the lesser toes are predominantly intrinsic and due to weight bearing forces directed lateral on foot progression during gait. Typical rheumatoid forefoot deformities of shod and unshod patients are seen in Figures 2 and 3.
Discussion The classical clinical picture of the forefoot in RA, known as pied douloureux des rhumatisants, presents with lowering of the medial arch, broadening of the forefoot, hallux valgus, and clawing with dorsal subluxation of the lesser toes.12 Varus deformity is also common in the little toe.13 This traditional description has originated solely from the shoe wearing literature. It is generally accepted that synovitis is the precipitating event of this destructive
process of RA in foot pathology.6,12 The synovitis ultimately results in the loss of joint stability as it causes distension of the capsule and ligaments combined with the pannus-related erosions at the insertions of the ligaments.6,12 In the lesser toes, the deformity is a consequence of distal displacement of the plantar fat pad with uncovering of the metatarsal head by lengthening of the plantar plate. As the deformity progresses there is an imbalance in the intrinsic and extrinsic musculature, with extension contracture and plantar plate adhesion. In this study, we found this to be true of 89% of the shod population; however, only 24% of the unshod population presented with this deformity. Alternatively, 76% of the unshod population presented with hallux varus. We thus have been forced to reject our null hypothesis. The comparison of shod versus unshod populations has illustrated the importance of external influences on the direction of forefoot deformity. Hallux varus has only been reported rarely in
association with RA.5,14,15 However, this study has demonstrated the high prevalence of hallux varus deformity in a population who are not influenced by the external pressures of shoe wear. In the shoe wearing population, a closed toe box acts as a barrier to any varus deformity, in contrast deviating the great toe into a valgus position. It is well described that the incidence of hallux valgus in shod compared to unshod populations is significantly greater.8,16 Unlike the normal population, the instability experienced in chronic RA results in an unsplinted hallux to deviate medially, influenced by the intrinsic and extrinsic imbalance and the forces of weight bearing. To our knowledge, there are no comparisons of shod and unshod populations in the literature involving RA subjects. Extrapolating biomechanical comparative studies to this population, Kadambande et al17 found that although there was no difference in intrinsic muscle function in the forefoot in shod and unshod populations, a much greater pliability was found in the forefoot of non–shoe wearing group. D’Août et al’s18 comparative study on barefoot Indians from the city of Bangalore and Caucasian subjects from Belgium found lower peak pressures in the unshod subjects than in their Western peers. The habitual barefoot Indians distributed pressures more evenly in time, by applying low pressures over a longer period of time instead of high pressures over a short period. This is partly explained by the flatter initial foot placement in this population. Through these studies, it is possible to theorize that the unshod group experiences lower forefoot pressures; however, no pedobarographic differences were apparent to explain why the force direction in the propulsive phase of gait may cause the development of hallux varus. Gastrocnemius tightness, common to RA, arises either as a consequence or is a major contributor to the development of pes planus deformity. A midtarsal break occurs as the transverse tarsal joint (talanavicular and calcaneocuboid joint) is unlocked and dorsiflexion occurs primarily at this
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Table 1. Observed Lesser Toe Deformity. Population Shod
Unshod
Lesser Toe Deformity
Number
Lateral deviation 2/3/4/5
1
Lateral deviation 2/3/4, medial 5
3
Dorsal subluxation 2/3/4/5
7
Dorsal subluxation 2/3/4, medial 5
45
Dorsolateral dislocation 2/3/4, medial 5
35
Dorsolateral dislocation 2/3, dorsal subluxation 4, medial 5
6
Dorsal dislocation 2, lateral deviation 3/4/5
4
Medial deviation 2/3/4/5
6
Lateral deviation 2/3/4/5
1
Medial deviation 2, lateral deviation 3/4/5
3
Dorsomedial subluxation/dislocation 2/3/4/5 Dorsolateral dislocation 2/3/4, medial 5
14 1
Figure 2. Hallux valgus with overcrowding of the second, third, and fourth toes with varus deformity of the fifth toe in a shoe wearing patient suffering from RA.
level. With a tight gastrocnemius, excessive force is required in an attempt to get the medial aspect of the heel to
the ground, and through this a midfoot (midtarsal) break is much more likely in an already hypermobile midfoot. Those
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feet that do display a midfoot break have significantly more medial weight transfer (pronation),19 which may explain the abnormal transfer of weight bearing forces to the hallux and the first metatarsal. If this force transmission exits lateral to the forces expected in the propulsive phase of a normal foot (ie, between the first and second metatarsals)20 then the hallux will be pushed medial. In the shod populations the toe box prevents varus deformation; however, in the unshod population without any medial buttress there is no restriction to such forces. Some studies have proposed non–shoe wearing as a cause of idiopathic hallux varus even without pathology, although noting that this occurrence was rare. Joseph et al21 studied 30 cases of idiopathic hallux varus, and described 5 cases in an Indian unshod population and attributed the deformity solely to the lack of shoe wear by these individuals. Joseph et al22 followed this study with an analysis of 69 cases of hallux varus in an Indian population; this time 8 cases were deemed as a consequence of RA. Of these 8 cases all involved midtarsal degenerative changes, and it was concluded that both intrinsic and extrinsic muscle imbalance was the basis of the varus deformity.22 In the later study the authors noted a zigzag appearance of the foot in RA, very typical to the midfoot break described in the studies by DeSilva and Gill.19 This was compared to the ulnar drift in the rheumatoid hand as a consequence of the supination and radial deviation of the carpus off the ulnar.23 We also noted a reduction in the 1,2 intermetatarsal angle in the unshod population compared to the shod population, with abduction of the forefoot (ie, the metatarsals laterally deviate) in keeping with the Z-deformity described by Joseph et al.22 The long extrinsic muscle pull in this deformity will naturally pull the toes into a varus position, although in the shoe wearing population this is prevented due to the external pressure provided by the shoe. External forces in the shod population heavily influence lesser toe deformities. Overcrowding of the lesser toes is
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Figure 3. Clinical and radiological images of hallux varus with varus subluxation/dislocation of the lesser toes in a non–shoe wearing patient with RA.
primarily the causative factor in the deformities seen in the shod population, which in time progresses from deviation to subluxation and then finally to dislocation. The unshod population commonly used open toed sandals with a Y-shaped strap, which is a possible external force preventing lateral deviation of the hallux or even pushing the hallux into varus. This theory, however, does not explain the medial deviation of the lesser toes. As previously discussed, in the unshod population the extrinsic muscle tendons are deviated medially and in combination with inherent joint instability, the lesser toes drift medially progressing to dislocation in time. On the analysis of the information available to us from our observations and from the existing literature, we have postulated the possible pathomechanics of the creation of hallux varus in an unshod population. It is reiterated that this proposed mechanism of deformation has not been validated and further research is required to do so. The lack of restraint against varus deforming forces
on the hallux in unshod RA allows progressive varus angulation of the hallux. This may be a self-propagating phenomenon with varusization of the hallux increasing supination of the foot and causing it to lateral load further, increasing the deforming intrinsic forces. The use of “flip flop” type footwear or walking bare footed may further contribute to the deforming forces and its central “Y” strap may prevent valgus deformation of the hallux by acting as a splint. A tight gastrocnemius and a midfoot break that is thought to produce some of the deforming force in creating hallux valgus in shod RA might well play the opposite role in unshod RA patients in creating a hallucal varusizing influence. A possible explanation for the lesser toe deformity in addition is that the lesser toes “followed” the hallux into a varus deformity, which was further propagated by increasing supination and lateral loading of the foot in propulsive gait. The intrinsic muscles are known to act in a more prehensile manner in the unshod foot to allow for gripping functions in the unshod foot.24 This has
also been studied in sand walking,25 where the foot was significantly more prehensile. The ability of the foot to spread by being more pliable has also been alluded to previously. All of these factors may be implicated in creating a multifactorial and complex pathomechanism to explain the deformity of hallux varus in unshod RA patients. This investigation was an observational study. There are several limitations to the study. First, there was a mismatch in the population numbers in each group with the shod population having quadruple the number of patients than the unshod group. This was due to patient attendance in the study time frame, with much greater numbers attending the UK department than the one in India. This may have produced bias but was unavoidable. The severity of pathology seen in the India clinic was much greater than that seen in the UK clinic. This sets up a possible regression toward the mean error. The patient group in India might have been more self-selecting than in the UK clinic as only patients with severe pathology and symptoms may have presented to a private clinic as opposed to significantly larger numbers in the UK clinic. This may also be as a result of footwear requirements being more exacting in UK patient populations due to weather and the habituation of shod status: in contrast, unshod feet could possibly tolerated greater degrees of deformity as there was no compulsion to put these feet into conforming footwear. In addition, the cost of medical care in India may have had an influence on the types of patients coming to a private clinic in India. The socioeconomic status was not investigated as part of the study. Racial factors may play a role in the development of hallux varus in RA in unshod populations. This has not been investigated as part of this study. Last, the alignment of the hindfoot, the characteristics of the walking surface, and variations of footwear in the shod population are all factors that have not been included in the observations of this study. While we agree that it may play a
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role in the deformity produced we believe that the factors that we have mentioned in our study are compelling ones that play a signification role in deformity creation in the rheumatoid forefoot. In conclusion, instability of the metatarsophalangeal joint in the rheumatoid foot predisposes it to significant deformity. External forces of shoe wear may dictate the deformity, with hallux valgus being the most likely scenario in a shoe wearing patient. In the non–shoe wearing population, intrinsic forces and weight bearing forces determine the deformity, with hallux varus being more commonly encountered as the presenting symptom in the unshod rheumatoid foot.
References
5. Kirkup JR, Vidigal E, Jacoby RK. The hallux and rheumatoid arthritis. Acta Orthop Scand. 1977;44:527-544. 6. Coughlin MJ. Rheumatoid forefoot reconstruction. A long-term follow-up study. J Bone Joint Surg Am. 2000;82: 322-341. 7. Tillman K. The Rheumatoid Foot: Diagnosis, Pathomechanics, and Treatment. New York, NY: Georg Thieme; 1979. 8. Sim-Fook L, Hodgson AR. A comparison of foot forms among the non-shoe and shoewearing Chinese population. J Bone Joint Surg Am. 1958;40:1058-1062. 9. Perera AM, Mason L, Stephens MM. The pathogenesis of hallux valgus. J Bone Joint Surg Am. 2011;93:1650-1661. 10. Coughlin MJ, Saltzman CL, Nunley JAI. Angular measurements in the evaluation of hallux valgus deformities: a report of the Ad Hoc Committee of the American Orthopaedic Foot and Ankle Society on Angular Measurements. Foot Ankle Int. 2002;23:68-74. 11. Easley ME, Trnka HJ. Current concepts review: hallux valgus part 1: pathomechanics, clinical assessment, and nonoperative management. Foot Ankle Int. 2007;28:654-659.
1. Grassi W, De Angelis R, Lamanna G, Cervini C. The clinical features of rheumatoid arthritis. Eur J Radiol. 1998;27(suppl 1):S18-S24. 2. Vainio S. The rheumatoid foot: a clinical study with pathological and roentgenological comment. Ann Chir Gynaecol Fenn Suppl. 1956;45(1, suppl 2):1-107.
12. Louwerens JWK, Schrier JCM. Rheumatoid forefoot deformity: pathophysiology, evaluation and operative treatment options. Int Orthop. 2013;37:1719-1729. 13. Trieb K. Management of the foot in rheumatoid arthritis. J Bone Joint Surg Br. 2005;87:1171-1177.
3. Michelson J, Easley M, Wigley FM, Hellmann D. Foot and ankle problems in rheumatoid arthritis. Foot Ankle Int. 1994;15:608-613. 4. Kerry RM, Holt GM, Stockley I. The foot in chronic rheumatoid arthritis: a continuing problem. Foot. 1994;4:201-203.
14. Donley BG. Acquired hallux varus. Foot Ankle Int. 1997;18:586-592. 15. Shrader JA, Siegel KL. Nonoperative management of functional hallux limitus
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in a patient with rheumatoid arthritis. Phys Ther. 2003;83:831-843. 16. Shine IB. Incidence of hallux valgus in a partially shoe-wearing community. Br Med J. 1965;1:1648-1650. 17. Kadambande S, Khurana A, Debnath U, Bansal M, Hariharan K. Comparative anthropometric analysis of shod and unshod feet. Foot. 2006;16:188-191. 18. D’Août K, Pataky TC, De Clercq D, Aerts P. The effects of habitual footwear use: foot shape and function in native barefoot walkers. Footwear Sci. 2009;1:81-94. 19. DeSilva JM, Gill SV. Brief communication: a midtarsal (midfoot) break in the human foot. Am J Phys Anthropol. 2013;151: 495-499. 20. Morton DJ. The Human Foot. New York, NY: Columbia University Press; 1935. 21. Joseph B, Jacob T, Chacko V. Hallux varus—a study of thirty cases. J Foot Surg. 1984;23:392-397. 22. Joseph B, Chacko V, Abraham T, Jacob M. Pathomechanics of congenital and acquired hallux varus: a clinical and anatomical study. Foot Ankle. 1987;8: 137-143. 23. Pahle JA, Raunio P. The influence of wrist position on finger deviation in the rheumatoid hand. A clinical and radiological study. J Bone Joint Surg Br. 1969;51:664-676. 24. Stewart SF. Footgear—its history, uses and abuses. Clin Orthop Relat Res. 1972;88: 119-130. 25. Lejeune TM, Willems PA, Heglund NC. Mechanics and energetics of human locomotion on sand. J Exp Biol. 1998;201(pt 13):2071-2080.
FASXXX10.1177/1938640015583513Foot & Ankle SpecialistFoot & Ankle Specialist
vol. XX / no. X
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〈 Clinical Research 〉 Forefoot Deformity in Rheumatoid Arthritis
Malhar H. Dave, MBBS, MS, Lyndon W. Mason, MB BCh, MRCS, FRCS, and Kartik Hariharan, MB BCh, FRCS
A Comparison of Shod and Unshod Populations Abstract: All reported rheumatoid arthritis (RA) forefoot deformities in the literature thus far have arisen from shoe wearing populations. Our aim in this study was to compare hallucal deformities seen in a shod population with an unshod population. A population comparison was undertaken in 2 specialized foot and ankle units, one in India and one in the United Kingdom. In the shod population, there was 1 hallux varus deformity, 10 without hallucal deformity, and 90 hallux valgus deformities. In contrast, in the unshod population, there were 19 hallux varus deformities and 6 hallux valgus deformities. There was great variability in the lesser toe deformity seen. In the shod population, it was most common to see dorsal subluxation or dislocation, with the fifth toe in a varus position. In the unshod population, the most common lesser toe deformity seen was varus deviation or dislocation. Instability of the metatarsophalangeal joint in the rheumatoid foot predisposes it to significant deformity. In the non– shoe wearing population, intrinsic muscle forces and weight bearing
forces are the most likely determinants of the deformity, with hallux varus being a more common presenting problem. In the shod population, the external forces of shoe wear dictate the direction of deformity. Levels of Evidence: Prognostic Level III: Case control study Keywords: hallux varus; rheumatoid arthritis; shod; unshod; hallux valgus
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involvement of the feet occurred in 91% of females and 85% of males. Michelson et al3 found that the prevalence of foot and ankle symptoms in RA sufferers was related to the duration of systemic illness of the disease and was present in >50% of patients at any time after the diagnosis of RA.3 Although the occurrence of hindfoot pain was the most common problem, the forefoot was a significant
The hallucal deformities reported in RA
Introduction
[rheumatoid arthritis] are a consequence
Rheumatoid arthritis of chronic metatarsophalangeal joint (RA) is a chronic inflammatory disease inflammation . . .” characterized by progressive damage of synovial-lined joints and complaint in a high proportion of variable extra-articular manifestations.1 patients.3,4 RA has a propensity for the small joints Kirkup et al5 described a number of of the hands and feet, which results in a deformities in their analysis of the hallux common occurrence of forefoot in RA, including hallux valgus, deformity. A number of studies have metatarsus primus varus, hallux tortus, reported the incidence of foot ailments hallux rigidus, hallux flexus, “chisel toe,” in RA, with Vainio,2 in a survey involving hallux elevates, hallux varus, and 955 patients affected with RA (618 combined deformities. By far the most females and 337 males), reporting that common forefoot deformity reported in
DOI: 10.1177/1938640015583513. From Abhishek Hospital and Foot and Ankle Centre, Vadodara, Gujarat, India (MHD); Foot and Ankle Unit, University Hospital Aintree, Liverpool, UK (LWM); and Foot and Ankle Unit, Royal Gwent Hospital, Aneurin Bevan University Health Board, Newport, UK (KH). Address correspondence to: Lyndon Mason, MB BCh, MRCS, FRCS, Foot and Ankle Unit, Royal Gwent Hospital, Aneurin Bevan University Health Board, Newport, UK; e-mail: [email protected]. For reprints and permissions queries, please visit SAGE’s Web site at http://www.sagepub.com/journalsPermissions.nav. Copyright © 2015 The Author(s)
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the literature is that of hallux valgus. Kerry et al4 reported an incidence of 65% hallux valgus in 100 patients surveyed with RA in regard to foot problems. Michelson et al3 found, on examination of 99 RA patients, a prevalence of 67% hallux valgus deformities of which 19% were judged to be severe. Coughlin’s6 long-term cohort study on the results of forefoot surgery in chronic RA contained 91% of patients presenting with hallux valgus deformity (43 of 47 feet assessed). Tillman7 found on examination of all metatarsophalangeal joints a lateral deviation or dislocation of 77% of joints, with only 3% medial deviation found, none of which included the first metatarsophalangeal joint. The hallucal deformities reported in RA are a consequence of chronic metatarsophalangeal joint inflammation, which leads to capsular distention and eventually to a loss of capsular and collateral ligament integrity.6 It is likely influenced by other joint changes in the foot, which it is theorized ultimately determines the direction of hallucal deformity.5 External forces, though a great protagonist of hallux valgus deformity in general,8,9 are thought to take a lesser role to the internal factors related to hallucal deformity in RA. All reported RA forefoot deformities in the literature so far have arisen from shoe wearing populations. Our aim in this study was to compare hallucal deformities seen in a shod to an unshod population, our null hypothesis being there was no difference.
documented closed shoe wearing individuals were included in this study. The patients’ medical notes and radiographs were analyzed retrospectively. All measurements were performed according to the guidelines produced by the American Orthopaedic Foot and Ankle Society Ad Hoc Committee on angular measurements.10 The measurements were accomplished using the graphics package present on the hospitals Picture Archiving and Communication System (Carestream Vue PACS, Kodak). Standardized anteroposterior weight bearing radiographs were obtained to measure the hallux valgus and intermetatarsal angles. To minimize bias caused by the interobserver variability, all radiographs were observed by 2 authors independently, and the intraclass coefficient was measured. When discrepancies of greater than 5° existed, a consensus was reached. All lesser toe deformities were noted. Any other deformity or pathology was documented. All data were assessed using SPSS Inc, 20.0 (IBM, New York). Binary data were entered into contingency tables allowing cross-tabulation of the results. For data cells greater than 5, differences were tested using the χ2 test, otherwise Fisher’s exact test was used. Numerical data were tested using a Student t test if parametric or a Mann–Whitney test if nonparametric. A P value of less than .05 was considered statistically significant.
Methods
A total of 126 feet from 87 patients were included in this study. The shod population contained 101 feet from 69 patients, and the unshod population contained 25 feet from 18 patients. Both the sex and side of pathology were similar between groups, with females accounting for 83.2% of patients in the shod group and 96% of patients in the unshod group. There were 66 left feet and 60 right feet included in the study. The mean age of patients in the unshod population was 65.48, and in the shod population it was 65.91. The intraclass correlation coefficient for interobserver
An observational study was undertaken in 2 specialized foot and ankle units, one in India and one in the United Kingdom. All patients suffering from RA and attending for consideration of forefoot surgery from January 2007 to October 2013 were considered for this study. All non–shoe wearing patients presenting to a charity foot and ankle clinic in India with RA forefoot deformities were included in this study. All the patients attending the UK foot and ankle clinic with RA forefoot deformities that were
Results
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variability was 0.956 for the hallux valgus angle and 0.924 for the 1,2 intermetatarsal angle. The definition of hallux valgus deformity is relatively consistent in the literature in regard to hallux valgus angle, where a normal hallux valgus angle is accepted as less than 15°.11 We used 15° valgus angulation of the hallux at the metatarsophalangeal joint for our categorization of normal and hallux valgus deformity. Any degree of varus at the first metatarsophalangeal joint is deemed pathological and was labelled as hallux varus. With this categorization we found in the shod population, there was 1 hallux varus deformity, 10 without hallucal deformity, and 90 feet with varying degrees of hallux valgus deformity. In contrast, in the unshod population, there were 19 hallux varus deformities and 6 hallux valgus deformities. In recording the radiographic parameters, we found in the shod population a mean hallux valgus angle of 34.85° (range −7°to 65°) and a mean 1,2 intermetatarsal angle of 12.79° (range 2° to 27°). In the unshod population, we found a mean hallux valgus angle of −20.72° (range −85° to 63°) and a mean 1,2 intermetatarsal angle of 7.44° (range 2° to 12°). Comparing the means of the shod versus the unshod populations, all radiographic measurements were normally distributed and showed a statistically significant difference on Student’s t test (P < .001). Figure 1 illustrates the difference in hallux valgus angle in shod compared to unshod populations. There was great variability in the lesser toe deformity seen. The results of these observations are contained in Table 1. In the shod population, it was most common to see dorsal subluxation or dislocation, with the fifth toe in a varus position. This has been postulated by us as being due to the external restraint to deformation provided by the shoe preventing varus deformation of the hallux and also preventing the fifth toe deforming into valgus, and thus causing overcrowding of the second, third, and fourth toes. This was seen in 95% (n = 96) of the shod population. In the unshod population, the
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Figure 1. A boxplot comparing hallux valgus angles of shod and unshod populations.
most common lesser toe deformity seen was varus deviation or dislocation. This was present in 80% (n = 20) of the unshod population. Without the medial restraint provided by shoe wear, the deforming forces on the lesser toes are predominantly intrinsic and due to weight bearing forces directed lateral on foot progression during gait. Typical rheumatoid forefoot deformities of shod and unshod patients are seen in Figures 2 and 3.
Discussion The classical clinical picture of the forefoot in RA, known as pied douloureux des rhumatisants, presents with lowering of the medial arch, broadening of the forefoot, hallux valgus, and clawing with dorsal subluxation of the lesser toes.12 Varus deformity is also common in the little toe.13 This traditional description has originated solely from the shoe wearing literature. It is generally accepted that synovitis is the precipitating event of this destructive
process of RA in foot pathology.6,12 The synovitis ultimately results in the loss of joint stability as it causes distension of the capsule and ligaments combined with the pannus-related erosions at the insertions of the ligaments.6,12 In the lesser toes, the deformity is a consequence of distal displacement of the plantar fat pad with uncovering of the metatarsal head by lengthening of the plantar plate. As the deformity progresses there is an imbalance in the intrinsic and extrinsic musculature, with extension contracture and plantar plate adhesion. In this study, we found this to be true of 89% of the shod population; however, only 24% of the unshod population presented with this deformity. Alternatively, 76% of the unshod population presented with hallux varus. We thus have been forced to reject our null hypothesis. The comparison of shod versus unshod populations has illustrated the importance of external influences on the direction of forefoot deformity. Hallux varus has only been reported rarely in
association with RA.5,14,15 However, this study has demonstrated the high prevalence of hallux varus deformity in a population who are not influenced by the external pressures of shoe wear. In the shoe wearing population, a closed toe box acts as a barrier to any varus deformity, in contrast deviating the great toe into a valgus position. It is well described that the incidence of hallux valgus in shod compared to unshod populations is significantly greater.8,16 Unlike the normal population, the instability experienced in chronic RA results in an unsplinted hallux to deviate medially, influenced by the intrinsic and extrinsic imbalance and the forces of weight bearing. To our knowledge, there are no comparisons of shod and unshod populations in the literature involving RA subjects. Extrapolating biomechanical comparative studies to this population, Kadambande et al17 found that although there was no difference in intrinsic muscle function in the forefoot in shod and unshod populations, a much greater pliability was found in the forefoot of non–shoe wearing group. D’Août et al’s18 comparative study on barefoot Indians from the city of Bangalore and Caucasian subjects from Belgium found lower peak pressures in the unshod subjects than in their Western peers. The habitual barefoot Indians distributed pressures more evenly in time, by applying low pressures over a longer period of time instead of high pressures over a short period. This is partly explained by the flatter initial foot placement in this population. Through these studies, it is possible to theorize that the unshod group experiences lower forefoot pressures; however, no pedobarographic differences were apparent to explain why the force direction in the propulsive phase of gait may cause the development of hallux varus. Gastrocnemius tightness, common to RA, arises either as a consequence or is a major contributor to the development of pes planus deformity. A midtarsal break occurs as the transverse tarsal joint (talanavicular and calcaneocuboid joint) is unlocked and dorsiflexion occurs primarily at this
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Table 1. Observed Lesser Toe Deformity. Population Shod
Unshod
Lesser Toe Deformity
Number
Lateral deviation 2/3/4/5
1
Lateral deviation 2/3/4, medial 5
3
Dorsal subluxation 2/3/4/5
7
Dorsal subluxation 2/3/4, medial 5
45
Dorsolateral dislocation 2/3/4, medial 5
35
Dorsolateral dislocation 2/3, dorsal subluxation 4, medial 5
6
Dorsal dislocation 2, lateral deviation 3/4/5
4
Medial deviation 2/3/4/5
6
Lateral deviation 2/3/4/5
1
Medial deviation 2, lateral deviation 3/4/5
3
Dorsomedial subluxation/dislocation 2/3/4/5 Dorsolateral dislocation 2/3/4, medial 5
14 1
Figure 2. Hallux valgus with overcrowding of the second, third, and fourth toes with varus deformity of the fifth toe in a shoe wearing patient suffering from RA.
level. With a tight gastrocnemius, excessive force is required in an attempt to get the medial aspect of the heel to
the ground, and through this a midfoot (midtarsal) break is much more likely in an already hypermobile midfoot. Those
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feet that do display a midfoot break have significantly more medial weight transfer (pronation),19 which may explain the abnormal transfer of weight bearing forces to the hallux and the first metatarsal. If this force transmission exits lateral to the forces expected in the propulsive phase of a normal foot (ie, between the first and second metatarsals)20 then the hallux will be pushed medial. In the shod populations the toe box prevents varus deformation; however, in the unshod population without any medial buttress there is no restriction to such forces. Some studies have proposed non–shoe wearing as a cause of idiopathic hallux varus even without pathology, although noting that this occurrence was rare. Joseph et al21 studied 30 cases of idiopathic hallux varus, and described 5 cases in an Indian unshod population and attributed the deformity solely to the lack of shoe wear by these individuals. Joseph et al22 followed this study with an analysis of 69 cases of hallux varus in an Indian population; this time 8 cases were deemed as a consequence of RA. Of these 8 cases all involved midtarsal degenerative changes, and it was concluded that both intrinsic and extrinsic muscle imbalance was the basis of the varus deformity.22 In the later study the authors noted a zigzag appearance of the foot in RA, very typical to the midfoot break described in the studies by DeSilva and Gill.19 This was compared to the ulnar drift in the rheumatoid hand as a consequence of the supination and radial deviation of the carpus off the ulnar.23 We also noted a reduction in the 1,2 intermetatarsal angle in the unshod population compared to the shod population, with abduction of the forefoot (ie, the metatarsals laterally deviate) in keeping with the Z-deformity described by Joseph et al.22 The long extrinsic muscle pull in this deformity will naturally pull the toes into a varus position, although in the shoe wearing population this is prevented due to the external pressure provided by the shoe. External forces in the shod population heavily influence lesser toe deformities. Overcrowding of the lesser toes is
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Figure 3. Clinical and radiological images of hallux varus with varus subluxation/dislocation of the lesser toes in a non–shoe wearing patient with RA.
primarily the causative factor in the deformities seen in the shod population, which in time progresses from deviation to subluxation and then finally to dislocation. The unshod population commonly used open toed sandals with a Y-shaped strap, which is a possible external force preventing lateral deviation of the hallux or even pushing the hallux into varus. This theory, however, does not explain the medial deviation of the lesser toes. As previously discussed, in the unshod population the extrinsic muscle tendons are deviated medially and in combination with inherent joint instability, the lesser toes drift medially progressing to dislocation in time. On the analysis of the information available to us from our observations and from the existing literature, we have postulated the possible pathomechanics of the creation of hallux varus in an unshod population. It is reiterated that this proposed mechanism of deformation has not been validated and further research is required to do so. The lack of restraint against varus deforming forces
on the hallux in unshod RA allows progressive varus angulation of the hallux. This may be a self-propagating phenomenon with varusization of the hallux increasing supination of the foot and causing it to lateral load further, increasing the deforming intrinsic forces. The use of “flip flop” type footwear or walking bare footed may further contribute to the deforming forces and its central “Y” strap may prevent valgus deformation of the hallux by acting as a splint. A tight gastrocnemius and a midfoot break that is thought to produce some of the deforming force in creating hallux valgus in shod RA might well play the opposite role in unshod RA patients in creating a hallucal varusizing influence. A possible explanation for the lesser toe deformity in addition is that the lesser toes “followed” the hallux into a varus deformity, which was further propagated by increasing supination and lateral loading of the foot in propulsive gait. The intrinsic muscles are known to act in a more prehensile manner in the unshod foot to allow for gripping functions in the unshod foot.24 This has
also been studied in sand walking,25 where the foot was significantly more prehensile. The ability of the foot to spread by being more pliable has also been alluded to previously. All of these factors may be implicated in creating a multifactorial and complex pathomechanism to explain the deformity of hallux varus in unshod RA patients. This investigation was an observational study. There are several limitations to the study. First, there was a mismatch in the population numbers in each group with the shod population having quadruple the number of patients than the unshod group. This was due to patient attendance in the study time frame, with much greater numbers attending the UK department than the one in India. This may have produced bias but was unavoidable. The severity of pathology seen in the India clinic was much greater than that seen in the UK clinic. This sets up a possible regression toward the mean error. The patient group in India might have been more self-selecting than in the UK clinic as only patients with severe pathology and symptoms may have presented to a private clinic as opposed to significantly larger numbers in the UK clinic. This may also be as a result of footwear requirements being more exacting in UK patient populations due to weather and the habituation of shod status: in contrast, unshod feet could possibly tolerated greater degrees of deformity as there was no compulsion to put these feet into conforming footwear. In addition, the cost of medical care in India may have had an influence on the types of patients coming to a private clinic in India. The socioeconomic status was not investigated as part of the study. Racial factors may play a role in the development of hallux varus in RA in unshod populations. This has not been investigated as part of this study. Last, the alignment of the hindfoot, the characteristics of the walking surface, and variations of footwear in the shod population are all factors that have not been included in the observations of this study. While we agree that it may play a
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role in the deformity produced we believe that the factors that we have mentioned in our study are compelling ones that play a signification role in deformity creation in the rheumatoid forefoot. In conclusion, instability of the metatarsophalangeal joint in the rheumatoid foot predisposes it to significant deformity. External forces of shoe wear may dictate the deformity, with hallux valgus being the most likely scenario in a shoe wearing patient. In the non–shoe wearing population, intrinsic forces and weight bearing forces determine the deformity, with hallux varus being more commonly encountered as the presenting symptom in the unshod rheumatoid foot.
References
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