Abstract
Distal femoral malunion can have significant consequences because deformity at this level alters knee loading via its longest lever arm. Even relatively small magnitudes of malunion may lead to varus or valgus shift of the mechanical axis, creating abnormal compartmental contact pressures and external moments. This may lead to activity related pain and accelerated joint degeneration. Although distal femoral fractures account for only 0.5% of all skeletal injuries, they include high energy injuries in young patients, low energy mechanisms in older patients and a subgroup of periprosthetic injuries. Metaphyseal comminution and medial cortical deficiency may lead to fixation failure, particularly in poor quality bone. Malunion remains a concern even with modern fixation devices and may present with progressive varus and fixed flexion deformity of the knee associated with limb shortening. This review describes the principles governing diagnosis, deformity analysis and surgical correction of distal femoral malunion, integrating contemporary evidence with established deformity correction techniques. Emphasis is placed on the execution of the planned corrective osteotomy and fixation. Pathomechanical analysis shows that distal femoral deformity modifies both the location and magnitude of the knee's functional loading axis. Each component of deformity contributes to abnormal joint forces and the effects of multiplanar deformity may be summative. Accurate deformity correction therefore incorporates analysis of calibrated AP & Lateral long leg radiographs with the knee in maximum extension, clinical examination to assess joint range and stability, as well as a complete assessment of the torsional profile which may include cross sectional imaging. A surgical plan is then selected according to anatomical and functional requirements. Successful correction requires precise deformity analysis and accurate reproduction in theatre of the simulated deformity correction, whichever surgical technique is selected. When executed accurately, surgery corrects the coronal, sagittal and axial planes of the deformity and normalises load transmission through the knee joint. This commonly improves symptoms and facilitates arthroplasty if required. Distal femoral malunion should be addressed with meticulous deformity analysis, simulation of correction and accurate execution of the preoperative plan in surgery. Modern fracture fixation implants, techniques and education have not eliminated malunion, therefore attention to detail is important in preventing malunion during the management of distal femoral fractures.