Stress radiography for osteoarthritis of the knee: a new technique.

Stress radiographs have been used for several years to detect the amount of varus/valgus knee laxity and to evaluate the degree of compartmental involvement in degenerative osteoarthritis. However, the popularity of these radiographic methods has been affected by their technical limits due to the x-ray exposure for the personnel involved and the variability of the stress forces applied. A device was developed with the aim to create a constant varus or valgus stress force to the knee with the patient in a supine position. The device does not require personal assistance during the actual film taking. Sixty consecutive patients where included in the study and measured prior to their total knee replacement. All patients had standard weight-bearing AP and lateral views as well as stress views in varus and valgus. Both knees were examined in full extension and 30° of flexion. The joint space width in both the lateral and medial compartments were measured and subsequently compared with the standard weight-bearing films. A significant decrease in joint space distance in the affected compartment was found in the stress radiographs compared with the standard weight-bearing views. The medial compartment was best examined with the knee extended and varus stress force (P < 0.001) and for the lateral compartment 30° of flexion proved to be more efficient (P < 0.01). In conclusion, this stress radiographic device offers a possibility to enhance the varus/valgus force in a standardized way compared to standard weight-bearing views of the knee. The reliability and reproducibility is high. It is suitable for clinical practice and a valuable tool in research.