A preliminary study determining the feasibility of electromagnetic tracking for kinematics at the ankle joint complex

Objective. To determine the feasibility of using electromagnetic tracking (EMT) for quantifying three-dimensional kinematics at the ankle; joint complex (AJC). Methods. AJC kinematics were recorded in 10 normal healthy adults, and 10 rheumatoid arthritis patients presenting with AJC instability and deformity who were undergoing footwear and orthotic intervention. Results. Kinematics in normal subjects had strong face validity, curve shape showing moderate (n = 9), good (n = 8) or excellent (n = 4) agreement with data from seven published studies. The range of motion about the x-axis (15.2 degrees) was similar to reference values (17.0 degrees), but our technique underestimated rotations about the y- (8.1 degrees vs 14.0 degrees) and z-axes (7.7 degrees vs 12.2 degrees). In the rheumatoid arthritis pronated foot group, eversion and internal rotation during the stance phase of gait were between 2 and 5 times greater than for normal subjects. The use of a corrective fool orthosis in this group restored normal kinematics, reducing maximum eversion and internal rotation by 57 and 68%, respectively. Conclusion. A new technique for measuring kinematics at the AJC is described. Based upon the findings of this pilot study, EMT may be useful for diagnosing AJC dysfunction and quantifying the mechanical efficacy of footwear and, orthosis interventions.