Bone mineral density changes in the knee following anterior cruciate ligament rupture.

OBJECTIVE: The pathophysiology of anterior cruciate ligament (ACL) rupture leading to knee osteoarthritis (OA) remains largely unknown. It seems that bone loss occurs after ACL rupture. The purpose of our study was to determine bone mineral density (BMD) changes in the knee after ACL rupture during 2-year follow-up period and to compare BMD changes between the injured and healthy contralateral knee.

DESIGN: Patients were included in an observational prospective follow-up study within 6 months after ACL trauma and evaluated for 2 years. Patients were treated operatively or non-operatively. At baseline and at the one- and 2-year follow-ups, BMD was measured in six regions of the tibia and femur for both knees (medial, central, lateral) using a Dual-energy X-ray Absorptiometry (DXA) scanner.

RESULTS: One hundred forty-one patients were included, with the following characteristics: 66% were male, median age at baseline was 25.3 (inter-quartile range 11.3) years, and 63% were treated operatively. After 1 year, BMD was significantly lower in all regions of the injured knee of the operatively treated patients compared to baseline. After 2 years, BMD was significantly increased, but remained lower than the baseline levels. In all regions for all measurements, the mean BMD was significantly lower in the injured knee than in the healthy contralateral knee.

CONCLUSIONS: During a 2-year follow-up period after ACL rupture, the BMD level in the injured knee was found to be lower than in the healthy contralateral knee. In operatively treated patients, the BMD decreased in the first year and increased in the second follow-up year.