Physical Examination
The test most commonly used to test for intrinsic contracture is the intrinsic tightness (Bunnell) test. The examiner holds the metacarpophalangeal (MCP) joints in extension while passively flexing the interphalangeal (IP) joints. The IP joints are then passively flexed with the MCP joints held in flexion.
If IP joint flexion is blocked or lessened when the MCP joint is extended in comparison with when it is flexed, the result is positive and there is tightness of the intrinsic muscles. In contrast, if extensor contracture is present at the proximal IP (PIP) joint, then PIP joint flexion is greater with MCP joint extension.
In some circumstances, the intrinsic tightness test may not be reliable in diagnosing intrinsic contracture. IP joint stiffness and capsular or intra-articular adhesions can mask underlying intrinsic muscle tightness. In these situations, IP joint flexion may be decreased regardless of the position of the MCP joint.
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The metacarpal head is uniquely shaped in that it is ovoid in the sagittal plane, and it widens from the dorsal to the volar dimension. The collateral ligaments are eccentrically mounted dorsal to the axis of rotation of the metacarpophalangeal joint. This anatomy causes variable degrees of tightness on the collateral ligaments based on the position of the joint by a camlike effect. When the joint is in extension, the collateral ligaments are lax. In flexion, the collateral ligaments span a greater distance and are tight.
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Proximal interphalangeal (PIP) joint collateral ligaments originate close to the axis of rotation, providing a smaller change in length with joint position and providing lateral stability. The PIP joint ranges in only 1 plane, and its trochlear shape also adds to its lateral stability.
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Edema is the initial response to any insult to the hand and leads to adverse sequelae. Joint stiffness develops as intra-articular hematoma and fluid accumulate within the synovial space, distending the capsule. Increased fluid content within the articular capsule and collateral ligaments effectively shortens these structures, favoring extension.
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With injury, checkreins form at the IP joints. Checkreins are collagenous bands connecting the lateral sides of the proximal volar plate to the assembly lines on the volar lateral surfaces of the phalanx. Assembly lines are the 2 ridges along the volar lateral surfaces of the phalanx to which are attached volar ligamentous structures, such as the flexor sheath, Cleland and Grayson ligaments, and the oblique retinacular ligaments of Landsmeer.
