One measure of joint rehabilitation after injury is the degree to which joint range of motion is restored. The early prediction of the rehabilitated range of motion is made difficult because injured joints are often immobilized due to swelling, pain or casting. A method was developed to calculate the joint positions which exhibited high congruity from a single 3D MRI. The method was applied to the subtalar joint, and a screw axis fitted through this congruous range of motion (CROM). The orientation of the CROM screw axis was 200 from the ROM screw axis and exhibited more supination-pronation movement than the ROM.
Displaced intra-articular calcaneal fractures (DIACF) are fractures which disrupt the posterior facet of the subtalar joint. Their outcome is mixed and difficult to predict. Ten patients with DIACF had a CROM screw axis calculated for both their injured and contralateral subtalar joints from MRIs taken within 6 weeks of the injury. After 12 to 14 months, their DIACF were assessed by the Rowe score (Rowe, 1963), the SF-36 (Ware et at. (1992), two patient self-assessments (Hildebrand et at., 1996), and a new radiologic score based on a one-year MRI. The amount of supination-pronation movement of the CROM screw axis was significantly correlated with all but one of the outcome measures of the DIACF (p < 0.05).
The MRI survey of displaced intra-articular calcaneal fractures was developed both as an assessment of the CROM and to challenge the published observations that radiologic findings are not correlated with DIACF outcome (Pozo, 1984). The MRI survey divided the injury pathologies into three parts: (I) the cartilage and bony pathologies of the subtalar joint; (ii) the cartilage and bony pathologies of the nearby joints (talonavicular, calcaneocuboid and talocrural); and (iii) the soft tissue pathologies. The assessment was compared to standard measures of the DIACF and found to correlate significantly. In addition, the MRI assessment of both the subtalar joint and the soft tissue correlated with the outcome measures. It was concluded that imaging of DIACF fractures yields relevant information about DIACF outcome.