Negative intra-articular pressure (IAP) is a passive stabilizer during joint movement. In contrast to that of large joints, the IAP within the metacarpophalangeal (MCP) joint has not been well studied. The objective of this study was to evaluate the biomechanics of the MCP joint in terms of load-displacement relation and IAP during the application of long-axis distraction to fresh cadaver specimens. Nine fresh MCP joints specimens from four hands were used. A long-axis distraction load of 16 kg was applied to the cadaver MCP joint before and after venting of the joint capsule. In addition to load-displacement data, a pressure transducer was used to measure the IAP of the MCP joint during loading. After venting the capsule, significant increases were found in displacement at a load of 16 kg (4.60 ± 0.80 mm in an intact MCP joint and 5.22 ± 0.97 mm in a vented MCP joint) and in displacement at the cross-point (3.44 ± 0.82 and 4.01 ± 0.81 mm). No significant difference was found in the displacement difference between a load of 16 kg and the cross-point (1.16 ± 0.26 and 1.20 ± 0.33 mm) as well as stiffness at the terminal range under both the intact and venting conditions (12.59 ± 2.53 and 12.28 ± 2.70 kg/mm). The IAP decreased dramatically during the 5% to 10% total distraction of load. It was found that negative IAP of the MCP joint contributes significantly to initial stability.
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