Biomechanical stability of abductor pollicis longus muscles with variable numbers of tendinous insertions

Abstract

Background: In the course of a study of different variants of the tendon of the abductor pollicis longus (APL) muscle, the unusual finding of a tendon with six subdivisions was observed in the first compartment. Using this preparation and others with various numbers of tendons (2, 3, 4, and 6), we intended to establish whether the multitendoned muscles increased the strength of the thumb.Methods: Fifty-two upper extremities were examined with attention to the tendons of the APL muscle. The strain on each tendon was biomechanically determined using a microcomputer and potentiometer. The stress was measured continuously and plotted against strain.Results: Following treatment with elastase, it is seen that the significance of changes in stability and Young's modulus is inversely proportional to the number of tendons arising from the APL.Conclusions: Division of the tendon into several parts leads to better mechanical distribution of stress and extension on thumb abduction. In addition, palmar-flexion in the wrist may be supported. Anat.

Anatomical variation of abductor pollicis longus in Indian population

“…Variation in the anatomy of the APL muscle plays an essential role to understand the different disease processes associated with it and their treatment. 28 32 37 38 Usually, APL originates from the posterior surface of radius, ulna and the interosseous membrane. In the lower third of the forearm, the APL and EPB occupy the most lateral compartment of the extensor retinaculum in a single synovial sheath, crossing superficial to the radial styloid process.…”

“…Different authors have studied the variation of APL tendon. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 39 40 41 42 43 44 45 46 47 48 49 But only few reports are available from the Indian subcontinent. 9 14 30 31 46 47 48 49 There seems to be an ethnical variation in the origin, insertion, and arrangement of these tendons.…”

“… 1 Multiple tendinous insertion of APL has been reported by many authors. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 The anatomical variation may remain asymptomatic or may present with painful conditions like de Quervain tenosynovitis (DQT). 2 5 6 19 The treatment of such condition in severe cases involves either an injection therapy or surgical decompression of the first extensor compartment.…”

“… 33 34 35 36 The other clinical implications of multiple tendinous slips insertion of APL is its association with first carpo-metacarpal arthritis or subluxation and its use as a tendon graft. 28 32 37 38 It seems essential to understand the anatomic variation of APL by the orthopedic surgeons as it has been associated with many orthopedic conditions. This cadaveric study was designed to look for tendinous variations of APL in the Indian population.…”