Purpose: According to the Ottawa rules, x-rays are not needed after knee trauma unless one or more of the following clinical criteria are present: age over 55 years, pain at palpation of the head of the fibula, pain at palpation of the anterior aspect of the patella, impossible knee flexion beyond 90°, inability to walk four steps immediately after trauma and at the emergency consultation. We conducted a prospective study in a consecutive series of patients to check the validity of this rule in daily practice.

Materials and methods: From December 2001 to January 2002, we included all patients consulting in an emergency situation for recent trauma involving only the knee joint. We excluded patients aged less than ten years, wounds without trauma, trauma more than two days before consultation, and patients with a history of trauma involving the same knee. An emergency physical exam was performed in all cases with identification of the study criteria. Standard x-rays (AP and lateral view in the supine position) were obtained for all patients. The patients and the x-rays were seen later by a senior orthopaedic surgeon and a senior radiologist who noted the presence of fracture requiring specific therapeutic management. The sensitivity, specificity and positive and negative predictive values of the Ottawa rule were determined for search for fracture.

Results: One hundred thirty-eight patients met the inclusion criteria during the study period. The sensitivity and negative predictive value of the Ottawa rule were 100%; the specificity was 36%, and the positive predictive value was 25%. Nineteen fractures (14%) requiring specific therapeutic management were identified: all patients had at least one positive sign. Seventy-six patients (55%) without fracture had at least one positive sign. Forty-three patients (31%) without fracture did not have any positive sign. The x-rays were not contributive for these patients.

Discussion and conclusion: This study demonstrated the validity of the Ottawa rule in the clinical setting of our practice. With widespread use of this rule, approximately one-third of the x-rays performed for recent trauma involving the knee alone could be avoided.