| Thumb opposition is a special function of human being, and one of three important manual functions. Dysfunction of thumb opposition caused by any reasons can affect manual functions badly, so it must be reconstructed. The curative effect of transferring ECU to EPL to reconstruct thumb opposition was good by reported issues. But we found the effects of some patients were not satisfied enough because of the dysfunction of thumb extension after operation. Because EPL is the main tendon of thumb extension, we thought that it may be better if EPL was replaced by EPB. So we carried out this study to find the possibility of transferring ECP to EPB to opponensplasty. Objective: To study the anatomical characteristics of OpP and AbPB and the routes of EPB, EPL, and ECU. To set up anatomical model of transferring ECU to EPB to restore thumb opposition and analyze biomechanical characteristics of that tendon transfer in order to establish a new method of reconstruction of thumb opposition which according with the biomechanics of human thumb. Method: Thenar muscles, ECU, EPB, and EPL were anatomized in 20 fresh forearm cadavers. The origin, insertion and fibrous direction of thenar muscles were observed, OpP and AbPB mainly; and the length of ECU and EPB were measured. Anatomical models of transferring ECU to EPB to restore thumb opposition were set up in specimens: the tendon of EPB was transferred to ECU at the volar surface of the wrist after routing around EPL tendon. The relation between the direction of tendon transfer and AbPB was observed and the farthest distance between interphalangeal joint of thumb and 3rd metacarpophalangeal joint was measured after tendon transfer. The biomechanical analysis was also done after transferring ECU to EPB. Result: 1. Anatomical results (1) AbPB was the most superficial layer of the thenar eminence, radial to FPB. It arose from radial aspect of distal edge of flexor retinaculum, ridge of trapezium, tubercle of scaphoid, and attached to radial aspect of articular capsule of metacarpal joint, radial sesamoid, dorsal digital expansion of thumb. The direction of fibres was the same to the axis of 1st metacarpal bone. OpP was deeper to AbPB and superficial head of FPB. It arose from flexor retinaculum and trapezium, attached to the whole radial edge of 1st metacarpal bone. The direction of fibres was 45°～55°angled with 1st metacarpal bone. (2) ECU lied in dorsal forearm. It arose from lateral epicondyle, forearm fascia, posterior edge of ulna. Fibres run downwards posterior to ulna, and the tendon under the extensor retinaculum, and attached to thedorsal base of 5th metacarpal bone. The length of tendon was (7.888±0.865) cm. EPB arose from posterior radius and interosseous membrane. Fibres run down obliquely extending to a long tendon, lateral to AbPL, attaching to the dorsal base of proximal phalanx of thumb. Its insertion was invariable, its tendon was little thinner than EPL, 3 of 20 forearm specimens (15%) were excessively thin. The length of EPB was (10.413±0.512) cm. EPL located in the middle of posterior compartment of forearm. It arose from posterior ulna and interosseous membrane. Fibres ran down obliquely extending to a long tendon, over the ECRL and ECRB, through extensor retinaculum, oblique to dorsal thumb, attaching to base of distal phalanx of thumb. (3) After transferring ECU to EPB, the opposition position of the thumb was good. The direction of tendon transferred was consistent to AbPB, but not the same, so there was a pronating effect after tendon transfer. The farthest distance between interphalangeal joint of thumb and 3rd metacarpophalangeal joint was (5.941±0.766) cm after tendon transfer. 2. Biomechanical analysis (1) Fibres of AbPB were along the axis of 1st metacarpal bone. When AbPB contracted, it mainly abducts the thumb, at the same time, it can also pronate and extend thumb weakly. The pronation of the thumb was mainly caused by OpP. Fibres of OpP was 45°～55°angled with 1st metacarpal bone. When OpP contracted, itcan make 1st metacarpal bone abducted and pronated, and the latter was primary. This motion was the basis of thumb opposition. (2) The power of ECU was strong enough, and the EPB was located at posterior of thumb metacarpal joint, ridial to EPL. After transferring ECU to EPB, the direction of tendon transferred was consistent to AbPB. The component of forces along AbPB (parallel to 1st metacarpal bone) could make thumb abduct, and the other one upright to 1st metacarpal bone could make thumb pronate. Conclusions: 1. The action of thumb opposition included thumb abduction, pronation and flexion, at last thumb tip contacting to little finger tip. It was abduction and pronation that were most important in this process. Thumb abduction was carried out by AbPB, but thumb pronation which made the thumb go around from upright to parallel to palm at coronal plane was made by OpP. We must not only keep tendon transferred consisting to AbPB, but also think much of reconstruction of OpP. 2. In all kinds of methods for reconstruction of thumb opposition, radial abduction of thumb usually well restored after operation. But the angle of pronation was not enough; the curative effect was not quite satisfied. ECU had constant anatomical position, sufficient length and strength. The direction of transferred ECU to EPB tendon was consistent with that of AbPB. One component of forces along AbPB (parallel to 1st metacarpal bone) could make thumb abduct, and the other one perpendicular to 1st... |
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