Collateral Ligament Laxity of the Finger Metacarpophalangeal Joints: An In Vivo Study

PurposeTo assess the normal degree of laxity of the collateral ligaments (CLs) of the finger metacarpophalangeal (MCP) joints and to compare side-to-side differences in CL laxity.MethodsOne hundred subjects had measurements of the degree of laxity in the radial (RCL) and ulnar (UCL) collateral ligaments of the MCP joints of each digit on both hands with the joints at neutral and at 30° and 90° of flexion using a custom-made measuring device. Statistical analysis was performed to assess both the difference in laxity for each ligament at each position of flexion and between sides for analogous ligaments (eg, the right index RCL at neutral compared to the left index RCL at neutral).ResultsThere was a significant decrease in laxity for all ligaments between neutral (mean, 24° laxity) and 90° of flexion (mean, 15° laxity). There was a side-to-side difference between the RCL of all digits in extension (mean, 3°) and the index RCL in flexion (2°). These differences were statistically significant but clinically minimal. There were no side-to-side differences between any of the other ligaments at any position.ConclusionsFinger MCP joint CL stability increases with increasing flexion of the joint. There is little to no difference between analogous ligaments on either hand of the subject when tested in the same position of MCP joint flexion. Knowledge of the average degree of MCP joint CL laxity can be helpful in assessing a potentially injured joint. A patient’s contralateral, uninjured side can be used to determine that individual’s normal laxity and a substantial increase from this on an injured digit can indicate CL rupture.Type of study/level of evidenceDiagnostic II.