Valgus knee injuries: evaluation and documentation using a simple technique of stress radiography

Clinical assessment of post traumatic ligament laxity is subjective. Stress radiographs provide an objective and permanent record of the laxity. We describe a simple method of stress radiography to help evaluate and to document valgus knee injuries. In this study we have correlated the X-ray findings with those at arthroscopy. No specialised equipment is required and radiation exposure to the patient and the surgeon is minimal. With the patient under general anaesthesia the injured and the normal knee are firmly bound together. A valgus stress is applied to both the knees simultaneously and a radiograph is taken. The opening of the medial joint space is measured as in the figure 1, i.e. the perpendicular distance between the tangent drawn to the subchondral bone of the femoral condyles, and the most medial point of the tibial plateau. The opening of the medial joint space provides a direct measure of valgus laxity. The ratio of the medial joint opening to the normal knee is calculated. A ratio of two or more is indicative of an associated anterior or posterior cruciate ligament rupture in addition to medial collateral ligament injury.