Abstract The extensor complex of the finger metacarpophalangeal (MCP) joint is composed of the extensor digitorum communis (EDC), sagittal band (SB), and loose connective tissue (LCT) underlying the extensor tendon. The purpose of this study is to evaluate the relative contributions of the EDC, SB, and LCT to finger MCP joint extension. Six fresh-frozen specimens were used. A 3 kg weight was affixed to the finger extensor tendons and a 1.5 kg weight affixed to the finger flexor tendons. MCP joint extension was measured at baseline and following serial sectioning of the EDC, SB, and LCT (group 1) or SB, EDC, and LCT (group 2). Sectioning of the EDC was performed distal to the SB. MCP joint extension was reported as the relative angular difference from baseline. From a baseline of MCP hyperextension, sectioning of the EDC first led to a decrease in MCP extension of 9 degrees, with no further decrease in MCP extension following release of the SB. In contrast, sectioning of the SB first led to a decrease in MCP extension of 15 degrees from baseline, with an additional decrease in MCP extension of 6 degrees following release of the EDC. There was no significant difference in MCP extension between sectioning of the SB or EDC first. Final sectioning of the LCT caused a further decrease in MCP extension by an average additional 12 degrees. LCT originated from the palmar surface of the extensor mechanism and inserted upon the dorsal joint capsule, which itself then inserted onto the dorsal base of the proximal phalanx. In the biomechanics of MCP joint extension, there is no statistical difference between sectioning of SB and the EDC. Additionally, the LCT is an additional MCP joint extensor in the absence of the SB and the EDC distal to the SB.
Arvind et al. (Wed,) studied this question.
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