Change in cartilage thickness, posttraumatic bone marrow lesions, and joint fluid volumes after acute ACL disruption: a two-year prospective MRI study of sixty-one subjects.

BACKGROUND

Little is known about early morphologic change occurring with an acute injury of the anterior cruciate ligament. Magnetic resonance imaging was used in this study to investigate the two-year change in cartilage thickness, bone marrow lesions, and joint fluid of knees with acute anterior cruciate ligament injury treated surgically or nonsurgically and to identify factors associated with these changes.

METHODS

Sixty-one subjects (sixteen women and forty-five men with a mean age of twenty-six years) with acute anterior cruciate ligament injury to a previously uninjured knee were examined with use of a 1.5-T magnetic resonance imaging scanner at baseline and at three, six, twelve, and twenty-four months after the injury. Thirty-four subjects received rehabilitation and early anterior cruciate ligament reconstruction (a median of 44.5 days after the injury), eleven subjects received rehabilitation and a delayed anterior cruciate ligament reconstruction (408 days), and sixteen received rehabilitation alone. Morphologic measures were obtained from computer-assisted segmentation of magnetic resonance images. Factors tested for association were age, sex, activity level, treatment, and osteochondral fracture at baseline.

RESULTS

After twenty-four months, significant cartilage thinning occurred in the trochlea of the femur (mean, -4.3%; standard response mean = 0.88), whereas significant cartilage thickening occurred in the central medial aspect of the femur (mean, +2.7%; standard response mean = 0.46). A younger age at the time of injury was a risk factor for thickening in the central medial aspect of femur, whereas older age at injury was a risk factor for thinning in the trochlea of the femur. Treatment of the torn anterior cruciate ligament was not related to these changes nor was activity level or an osteochondral fracture at baseline. Posttraumatic bone marrow lesions in the lateral aspect of the tibia resolved completely in fifty-four of fifty-eight knees (median, six months) and lesions in the lateral aspect of the femur resolved completely in forty-four of forty-seven knees (median, three months); however, thirty new bone marrow lesions developed in the lateral aspect of twenty-one knees over the two-year period. None of the factors were related to the development of bone marrow lesions.

CONCLUSIONS

Morphologic change as visualized on magnetic resonance imaging occurs in the knee over the first two years after acute anterior cruciate ligament injury as demonstrated by cartilage thickening (central medial aspect of the femur), cartilage thinning (trochlea of the femur), the resolution of posttraumatic bone marrow lesions in the lateral part of the knee, and the development of new bone marrow lesions laterally. Age and male sex were independent risk factors for change in cartilage morphology.