Kinematics of valgus bracing for medial gonarthrosis: technical report

OBJECTIVE: To determine whether a valgus knee brace altered the alignment of the shank segment with respect to the thigh segment of patients with medial gonarthrosis of the knee. DESIGN: Twelve (subject) x 2 (brace condition) x 2 (speed) repeated measures design. METHODS: Twelve male subjects (mean age 55 yr, SD 5 yr) who were prescribed a valgus knee brace for medial gonarthrosis walked on a treadmill at normal (mean 1.5 m/s, SD 0.3 m/s) and fast walking speed (mean 2.1 m/s, SD 0.2 m/s) while filmed by two gen-locked video cameras. Flexion, coronal and axial rotation angles of the thigh and shank segments in a global co-ordinate system were determined from kinematic data of reflective markers on the affected leg. Data were calibrated with respect to the standing 'no-brace' condition and averaged over five step cycles at four specific points in time during the stance phase. RESULTS: The brace had no effect on thigh coronal angle but reduced shank coronal angle at toe-off (statistically significant). The brace also prevented full extension (statistically significant) during mid-stance by resisting valgus forces in the coronal plane transmitted though the brace's helical strap. This same strap was believed to be responsible for axial forces that created statistically significant external rotation of the thigh axial angle throughout the stance phase and internal rotation of the shank axial angle during knee extension at heel strike and mid-stance. The brace hinge may explain the unexpected external rotation of the shank axial angle that accompanied knee flexion. CONCLUSION: This study demonstrated that the brace altered the kinematics in all three planes of motion and transmitted forces from one plane to another. This study also indicates that the subject-brace interaction was more complex in nature than initially anticipated. RELEVANCE: Clinical evidence suggests that there can be a reduction of knee pain by wearing a valgus brace for medial gonarthrosis and that the brace alters the orientation of thigh and shank segments during gait in such a manner to reduce the inter-joint pressure of the afflicted compartment. Therefore a biomechanical analysis of a possible kinematic effect was warranted.