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Dorsal and Volar Surgical Approaches to the Metacarpophalangeal Joint: A Comparative Anatomic Study.

BACKGROUND
We compared 3 surgical approaches to the MP joint: a dorsal extensor tendon-splitting approach, a dorsal extensor tendon-reflecting parasagittal approach, and the volar A1 pulley approach. We quantitatively compared each of these approaches by measuring the amount of articular cartilage exposed on the base of the proximal phalanx. We hypothesize that visualization of the articular cartilage of the proximal phalangeal base is enhanced with the volar approach.


METHODS
The MP joints of the 32 available digits were randomly assigned to 1 of 3 surgical approaches: extensor tendon splitting (A), extensor tendon reflecting (B), or volar approach (C). After each approach, the visible articular surface of the base of the proximal phalanx was stained with methylene blue. The MP joints were then disarticulated, and the proximal phalanges were digitally mapped using a 3-dimensional digitizer. Three-dimensional computer software was used to analyze and calculate the dyed exposed surface area and total surface area of each specimen.


RESULTS
The mean % exposed joint surface area for the dorsal extensor splitting, dorsal extensor reflecting and volar approaches were 62%, 67% (over the dorsal side of the proximal phalanx) and 54% (over the volar side of the proximal phalanx), respectively. Multiple linear regression showed statistical significance for a smaller percentage of articular surface area exposed with the volar approach. However, this was not clinically significant. A significant association was found between location in the small finger and greater % exposed joint surface, compared to approaches in the index finger. In all volar approach specimens, the collateral insertion site was visible, but not in the dorsal approach specimens.


CONCLUSIONS
Knowledge of the limits of each exposure is essential for planning the most appropriate surgical approach. The A1 pulley approach provided greater access to the volar 50% of the joint and collateral ligament insertion without violating the extensor mechanism. The amount of joint surface visualized through all 3 approaches was not significantly different. However, based on the accessibility to the collateral ligament insertion site among three different approaches, we recommend the volar A1 pulley approach for treatment of avulsion fractures of the base of the proximal phalanx. For other injuries of the MP joint, including the intra-articular proximal phalanx base fractures, and metacarpal head fractures, the dorsal approaches are still indicated.