Measurement of surface contact area of the ankle joint

OBJECTIVE: To determine the distribution of contact area of the ankle joint with axial loading and in positions of maximal dorsiflexion, plantar flexion, supination, and pronation. We also tested the effects of extrinsic tendon loading and arch instability. DESIGN: Nine cadaveric feet were studied in the intact condition and following transection of ligaments to create arch instability. BACKGROUND: Assessment of ankle contact in various joint positions and degrees of instability is difficult to accomplish with conventional methods. METHODS: Displacement of the talus relative to the tibia was measured with a magnetic tracking device and tibiotalar joint contact from proximity calculations of digitized joint surfaces. RESULTS: Contact area did not change significantly from unloaded condition to 667 N load condition in the medial, central, and lateral zones. Central zone contact area decreased in plantar flexion by an average of 324 mm(2) (SD, 165 mm(2)) (P = 0.0004). Medial zone contact area decreased in plantar flexion by a mean of 55 mm(2) (SD, 28 mm(2)) (P = 0.0004), decreased in pronation by an average of 42 mm(2) (SD, 36 mm(2)) (P = 0.0086), and increased in supination by an average of 20 mm(2) (SD, 26 mm(2)) (P = 0.0430). Lateral zone contact decreased in plantar flexion by a mean of 124 mm(2) (SD, 57 mm(2)) (P = 0.0002). CONCLUSIONS: In plantar flexion, there was a decrease in contact area. Loading extrinsic tendons to the foot did not significantly increase ankle contact area, but arch instability caused a decrease in central and lateral zone contact area. RELEVANCE: This technique was used to assess joint contact characteristics in various loading conditions and will be useful for evaluating the extent to which treatment for ankle or hindfoot problems such as bracing or reconstruction operations restores normal joint contact.