Injury risk of interphalangeal and metacarpophalangeal joints under impact loading

Injuries to the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of the hand are particularly disabling. However, current standards for hand protection from blunt impact are not based on quantitative measures of the likelihood of damage to the tissues. The aim of this study was to evaluate the probability of injury of the MCP and PIP joints of the human hand due to blunt impact. Impact testing was conducted on 21 fresh-frozen cadaveric hands. Unconstrained motion at every joint was allowed. All hands were imaged with computed tomography and dissected post-impact to quantify injury. An injury-risk curve was developed for each joint using a Weibull distribution with dorsal impact force as the predictive variable. The injury risks for PIP joints were similar, as were those for MCP joints. The risk of injury of the MCP joints from a given applied force was significantly greater than that of the PIP joints (p = 0.0006). The axial forces with a 50% injury risk for the MCP and PIP joints were 3.0 and 4.2 kN, respectively. This is the first study to have investigated the injury tolerance of the MCP and PIP joints. The proposed injury curves can be used for assessing the likelihood of tissue damage, for designing targeted protective solutions such as gloves, and for developing more biofidelic standards for assessing these solutions.