Abstract
Patella and extensor mechanism injuries are common injuries and are generally managed with some degree of immobilisation and partial weight bearing to facilitate healing. The aim of this project was to determine the type of immobilisation or splintage during partial weight bearing that results in minimal forces acting through the extensor mechanism.
Gait analysis studies were performed on eight healthy male subjects mobilising partially weight bearing. Measurements were taken for six types of immobilisation: locked at 0, 10, 20, 30 degrees and unlocked in an orthotic knee brace, and without a brace. The ground reaction force, knee joint angle and the knee flexion moment were measured using Qualisys Track Manager and Visual 3D Software. The extensor mechanism moment and the extensor mechanism force were calculated using static equilibrium equations and documented data. A one-way analysis of variance statistical test was performed to determine the statistical significance of the differences between the six types of immobilisation.
There was a direct relationship between the knee flex-ion angle and the extensor mechanism force. The extensor mechanism force at 0 degrees of immobilisation was significantly lower than that for 20 and 30 degrees (p< 0.05). The increase in the extensor mechanism moment arm with increasing knee flexion was not suf-ficient to offset the increase in the extensor mechanism force caused by the increase in the knee flexion moment. The results also showed that the knee flexion angle does not always correspond with the angle set at the knee brace; however they did exhibit a direct relationship.
These results have important implications for the management of patients with patella and extensor mechanism injuries. The results suggest that improvements in knee brace design to allow 0 degrees of knee flexion, rather than the 10 degrees as seen in this study, are likely to result in significantly reduced extensor mechanism tensile forces.
Correspondence should be addressed to Mr Carlos Wigderowitz, Senior Lecturer, University Department of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Dundee DD1 9SY.
