Biomechanics of the first ray. Part IV: The effect of selected medial column arthrodeses. A three-dimensional kinematic analysis in a cadaver model

This study is the fourth in a series of investigations on the biomechanics of the first ray, this part focusing on open kinetic chain range of motion simulating the clinicai examination. Segmental sagittal range of motion of the medial column was measured on intact cadaver specimens and compared to various simulated medial column arthrodesis patterns. These arthrodeses included the first metatarsocuneiform, first metatarsocuneiform-intercuneiform, naviculocuneiform, and talonavicular joints. The specimens were mounted to a test apparatus that was comprised of a modified ankle-foot orthosis which held the ankle and rearfoot in fixed neutral position. Additionally, the lesser metatarsus was affixed to the test apparatus while the first ray was left free to be manipulated via a carbon fiber rod attached to a pneumatic actuator. A 24.5-N (5.5-lb) sagittal plane load was applied to the first ray while the specimen was held rigidly in the apparatus. The first ray was manipulated using a repeated measures design. Data were collected for each osseous segment of the medial column using a radiowave tracking system. Kinematic data were collected and statistically analyzed. Results demonstrated in intact specimens that the naviculocuneiform, first metatarsocuneiform, and talonavicular joints contributed an average of 50%, 41 %, and 9% of total first ray sagittal plane range of motion, respectively. Furthermore, first ray range of motion was significantly reduced with all of the simulated arthrodeses of the medial column (p < .05). These findings suggest that first ray range of motion when evaluated clinically is a blend of motions of joints comprising the medial column.