Gross anatomical observations of the palmar

RESEARCH PAPER

Gross anatomical observations of the palmar interossei muscles in humans: A cadaveric study Mamatha Hosapatna, Radhakrishnan Periyasamy, Antony Sylvan D’Souza, Sushma Rama Kotian Department of Anatomy, Kasturba Medical College, Manipal University, India Correspondence address: Sushma RK, Department of Anatomy, Kasturba Medical College, Manipal University, India. Email: [email protected] DOI: 10.5455/jcer.201333

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ABSTRACT Objectives: The interossei muscles of the hand provide a foundation for all the intrinsic hand movements. They occupy the intervals between the metacarpal bones and are divided into a palmar and dorsal set. The palmar interossei are smaller than dorsal interossei and lie on the palmar surface of the metacarpal bones rather than between them. The present study aimed to evaluate the number and variations in the palmar interosseous muscles. Methods: Thirty hands from 15 human cadavers (10 males and 5 females, of age ranging from 50 to 65 years) in the Department of Anatomy, Kasturba Medical College, Manipal were studied to explore the prevalence of palmar interosseous. Results: The palmar interossei showed variations, i.e., bipennate, hypertrophied muscle and absence of first palmar interossei. These findings are rare and are less reported. The study also agrees upon the prevalence of four palmar interossei as suggested by different studies. The nerve supply to the interossei when traced was normal in all the specimens and was provided by the deep branch of the ulnar nerve. Conclusion: Ample knowledge of the possible variations in these muscles is very essential for clinicians and surgeons dealing with fractures, stiff joints, claw toe or tendon transfers. Key words: Adduction, intrinsic muscle, metacarpals, palmar interossei, tendon transfer

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INTRODUCTION The human hand is a complex anatomic entity consisting of many muscles, nerves and vessels, thus providing a special ability to perform accurate and meticulous movements. A series of robotic facsimiles of human hands have been developed, but none have approached the range of functions of the original. These functions are attributed to the exclusive muscular arrangement of the hand. The interossei constitute one such series of small muscles located deep in the intermetacarpal spaces of the hand. The interosseus muscles lie between the metacarpal bones and are covered dorsally and ventrally by fasciae attached to the metacarpals. In each interspace there are two muscles, a dorsal and a palmar interosseus.

The anatomy and number of palmar interossei (PI), remains controversial. Historically, a majority of anatomists have held that there are three PI which serve to adduct digits II, IV, and V.[1-3] However over the years the presence of the first i.e., pollical palmar interossei muscle (PPIM) has been documented.[4-7] A clear understanding of the intrinsic muscles of the hand is relevant and important in the treatment of stiff joints and congenital anomalies such as camptodactyly and in the reinsertion of the intrinsic muscles during index finger pollicisation and other reconstructive surgeries.

MATERIALS AND METHODS Thirty hands from 15 human cadavers (10 males and 5 females, of age ranging from 50 to 65 years) in the

Journal of Clinical & Experimental ResearchSeptember-December 2013Volume 1Issue 3

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Hosapatna, et al.: Variations of the palmar interossei muscles in humans

Department of Anatomy, Kasturba Medical College, Manipal, were studied to explore the prevalence of PI muscles. The hands were meticulously dissected and the PI were cleaned and exposed. The muscles were made evident by defining their attachments and were distinguished from the dorsal interossei by placing a string in between. The nerve supply to the interossei was also traced. The observations were photographed, recorded and tabulated.

RESULTS

Figure 2: Arrow pointing the presence of bipennate 2nd and 3rd palmar interossei arising from the adjacent metacarpal bones.

Out of the 30 hands dissected, 22 (73.33%) showed the presence of the PPIM, bilaterally in eight cases and unilaterally in the remaining six cases [Figure 1a]. The PPIM differentiated from the fibers of adductor polices and flexor policis brewis based on its attachments. The remaining eight specimens (26.67%) showed the presence of only three PI [Figure 1b].

Figure 3: Arrow showing the hypertrophied and bipennate 1st Palmar interosseus muscle (PI). Figure 1: Showing the presence of four (1a) and three (1b) palmar interossei (PI). Arrow pointing the absence of the 1st palmar interosseus muscle. 1st, 2nd, 3rd, 4th- First, second, third and fourth palmar interossei respectively.

Furthermore, the PI also showed notable and significant variations as enlisted below: 

Bipennate origin of the PI in 9 (30%) specimens [Figure 2].

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Hypertrophied and bipennate 1st PI in 2 specimens (6.7%) [Figure 3].

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Additional slips from the different PI in 5 specimens (16.60%) [Figure 4].

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Interestingly, one hand showed the coexistence of three different variations, i.e., absence of first PI, an additional slip from the 2nd PI to the index finger and bipennate origin of the 2nd PI [Figure 5].

Figure 4: Showing the presence of additional slips from the 2nd palmar interosseus muscle to the middle finger.

DISCUSSION The interossei constitute a series of small muscles located deep in the intermetacarpal spaces of the hand and are subdivided on anatomical and functional grounds into dorsal and palmar interossei. Dorsal interossei take a bipennate origin from adjacent metacarpals and function primarily to abduct the digits at the metacarpophalangeal joints. In contrast, PI are unipennate and function to adduct the digits. PI arises from the anterior border of the


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shaft of the first, second, fourth and fifth metacarpals and encroaches on the surface facing the axial line of the hand. The first arises near the base, the others from the three-fourth of the shaft. The fibre bundles of each muscle converge in a penniform manner and are inserted, with few exceptions, wholly into the extensor expansions on the axial side of the corresponding digit. The interossei are occasionally doubled or may be absent in one or more spaces.[8]

years, several studies have verified the observation of this muscle.[4, 6, 7] Previous classical studies published during the end of the nineteenth century, described these variations: Wood found this variation in three consecutive years i.e., two out of 32 hands[10]; 3 out of 36[11] and 8 out of 36.[12] Therefore the muscle was found in 13 out of 104 subjects (12.5%). Macalister [13] and Le Double [14] also reported the similar descriptions with similar incidences. Recently, Susman and his co-workers reported the presence of PPIM in two distinct populations. A South African population with an incidence of 85% and European-American population with 87%.[7] This was in general agreement with the 80% of the reported specimens by Fahrer[6] and 91% of the cases as documented by Peter et al.[15]

Figure 5: Showing the coexistence of three different variations i.e., the absence of 1st palmar interossei, bipennate origin of the 2 nd palmar interossei and additional slip from the 2nd palmar interossei to the index finger.

In a study by Eladoumikdachi and his co-workers [9], 38% of PI had more than one head. This may indicate complexity of the interossei. The present study also showed bipennate origin of the PI and the existence of hypertrophied and bipennate 1st PI [Figure 3]. Presence of additional slips from the PI may also indicate intricacy of the muscle fibers concerned with fine movements of the hand. The present study has revealed the presence of additional slips from the different PI [Figure 4]. This finding is however rare and is not reported elsewhere. Although anatomists generally agree upon the presence of four PI muscles in the human hand, questions about the existence of the PPIM have persisted. Henle first suggested the presence of four PI, when he described a muscle originating and inserting on the thumb as interosseous primus volaris.[5] Over the

In the present study, 73.33% showed the presence of the PPIM. These lines of evidence, all independently contribute to the fact that the PPIM is present in majority of the human hands. There are three major schools of thought regarding the origin of the PPIM. The first suggests that the PPIM is a portion of adductor pollicis.[16-17] Another group suggests that these muscle fibres are a part of the deep head of flexor pollicis brevis.[18-19] The third group however proposes that the PPIM is a distinct muscle belonging to the series of the PI.[20] Authors have demonstrated that the PPIM is distinct from the adductor pollicis, the major differentiating feature being the origin of the PPIM exclusively from the first metacarpal. The adductor pollicis on the other hand originates from the trapezium, trapezoid, capitate as well as from the bases of 2nd and 3rd metacarpals respectively.[7] Authors have also suggested that the muscle fibres of PI are not associated with deep head of flexor pollicis brewis either. This being attributed to their different areas of origin (the latter being on the carpal bones), diverse insertions (the latter into the ulnar sesamoid), and the position of the PPIM deep to the flexor pollicis brevis in the palm.[20] Despite various references to a PPIM in nonhuman primates, there is no solid evidence of a PPIM in


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monkeys or apes.[21-22] The PPIM could probably differentiated due tool behaviour in hominids thereby contributing to the intricate movements. The occurrence of the PPIM therefore be unique to humans.

have early hand may

ACKNOWLEDGEMENTS We are grateful to the cadaver donors who have selflessly consented to donate their bodies for the purpose of medical research and education.

The functional significance of the PPIM may be dealt with two alternatives. Based on its position relative to the first metacarpophalangeal joint, it might function like other PI in adducting the thumb (or assisting the adductor pollicis in this action) while simultaneously extending the pollical interphalangeal joint. However, based on its relatively small size and minimal physiological cross section, it is unlikely that much force is produced by the PPIM. Another possible function of the PPIM is that it is part of a parallel muscle combination (PMC). As such, the PPIM may assume the role of a ‘‘kinesiological monitor’’ providing sensory feedback about thumb position.[23]

REFERENCES

Electromyographic studies, detailed histological and PMC analysis may however be useful in truly distinguishing PPIM from other deep palmar muscles.

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Environmental or genetic factors may not be completely responsible for the rare absence of the PPIM both unilaterally and bilaterally, but it is likely that both factors play some role in the course of development. The interossei (and the digits they act upon) become differentiated between the 6th and 8th weeks of embryonic life as programmed cell death separates the hand plate into distinct digital rays. In the course of development the interossei muscles develop and assume their designated function thereby contributing to the smooth and prehensile movement characteristic of the human hand. Electromyographical studies may reveal an altered pattern in the case of such variant patterns of the PI as reported in the present study. Additionally, the PPIM is extensively used for various reconstructive surgeries. They are used as transposition flaps and even to reconstruct and recreate the function of adductor pollicis. Therefore the observed variations in the present study may be helpful for the clinicians and surgeons to plan the treatment regime.

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Cite this article as: Hosapatna M, Periyasamy R, D’Souza AS, Kotian SR. Gross anatomical observations of the palmar interossei muscles in humans: A cadaveric study. J Clin Exp Res 2013;1:5357. Source of Support: Nil, Conflicts of Interest: None declared


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