Acute rotational trauma to the knee: poor agreement between clinical assessment and magnetic resonance imaging findings

Objectives: To determine the incidence of anterior cruciate ligament (ACL) injuries in the general population; the pathology associated with a knee sprain verified by magnetic resonance imaging (MRI); and the agreement between clinical findings and MRI. Material and methods: Inclusion criterion was an acute rotational trauma to the knee associated with effusion. One hundred and fifty‐nine consecutive patients, mean age 27 years and 36% women, were included after clinical assessment at the orthopedic emergency unit. Patients were referred to an MRI examination (1.0 or 1.5 T) performed within a median of 8 days of the initial visit. Results: The annual incidence of MRI verified ACL injuries was 0.81/1000 inhabitants aged 10–64 years. Fifty‐six percent ( n =89) of those included had sustained an ACL injury of whom 38% had an associated medial meniscus tear. There was a poor agreement between initial clinical antero‐posterior laxity and MRI verified presence of an ACL tear (κ 0.281). Every second patellar dislocation was diagnosed as a ligament injury. Conclusion: Our findings indicate that the incidence of ACL injuries is higher than previously described. We also show that the first clinical examination after an acute knee trauma has a low diagnostic value. Further assessment with MRI improves the chances of a correct diagnosis of intraarticular pathology and is recommended in the early phase after a rotational knee trauma.