Change in cartilage thickness, posttraumatic bone marrow lesions, and joint fluid volumes after ACL disruption: A two-year prospective MRI study of sixty-one subjects.
Frobell RB. J Bone Joint Surg Am. 2011; 93: 1096-1103: doi:10.2106/JBJSJ.00929.
Anterior cruciate ligament (ACL) tears commonly occur and sideline athletes for a portion of their season or off-season training.   Short-term ACL tears are often managed with surgery, and the majority of athletes return to full participation in less than one year.  The long-term consequences of an ACL tear are not as favorable, and include the increased risk of knee osteoarthritis (OA).   However, very few studies have evaluated structural changes associated with ACL tears and the related treatments.  The purpose of this magnetic resonance imaging (MRI) study was to investigate the changes in cartilage thickness, posttraumatic bone marrow lesions, and joint fluid over 2 years following an ACL tear.   This study includes patients from a larger study comparing nonsurgical and surgical ACL treatments. Sixty-one participants (average age = 26 years) had MRIs at baseline, 3 months, 6 months, 1 year, and 2 years post ACL tear. Intervention strategies to manage the ACL tears included 34 patients with rehabilitation plus an early ACL reconstruction (typically 40 to 52 days after the injury), 16 with rehabilitation only, and 11 with rehabilitation and a delayed ACL reconstruction (typically over a year after the injury). The delayed ACL reconstructions were performed if patients, originally assigned to the rehabilitation only group, had symptomatic instability and were willing to undergo surgery.  Immediately after injury, 95% of knees had a posttraumatic bone marrow lesion (bone bruise) in the lateral tibia and 77% had a lesion in the lateral femur (they did not measure these lesions in the medial knee).  About 93% of the posttraumatic bone marrow lesions completely resolved within one year.  They also found that 34% of the participants developed new bone marrow lesions in the lateral knee over the 2-year follow-up period (possibly a sign of overloading the joint).  Regardless of intervention or physical activity level, cartilage changes were evident in the central medial femoral cartilage, trochlea, and posterior aspect of the medial and lateral femoral cartilage over the first 2 years after ACL injuries.  The changes in cartilage and formation of new bone marrow lesions are often associated with OA and the changes in trochlea cartilage were greater than what is normally seen in patients with knee OA. 
This study is important because it is one of the first studies to describe the structural changes that follow an ACL tear.  Both the changes in cartilage thickness and the appearance of new bone marrow lesions is concerning since these are findings often associated with knee OA. The author acknowledges that the small sample size prevented him from comparing surgical techniques or meniscal status.  Furthermore, MRI data is lacking among young healthy knees which makes it challenging to compare this study to healthy knees. Regardless, these findings complement a recently MRI study by Neuman et al that indicated that patients with ACL tears had altered knee cartilage composition. It is of an important note that once structural changes occur, we have no interventions to stop the knee from developing OA.  Some studies have suggested that biochemical changes in the joint occur after an ACL injury (Lohmander et al 1999) and precede structural changes.  Changes in biochemical markers may serve as warning signs for impending structural changes. It would be interesting to see a similarly designed study that collects biochemical markers from the synovial fluid at the same time points as the MRI to monitor these changes together.  These MRI and biochemical studies after knee injuries may influence our intervention strategies (e.g., how to treat specific patients).  Long-term it appears that it does not matter whether or not an athlete has surgery but it would be helpful to see studies similar to this one with a larger sample size.  Has anyone noticed more athletes being managed without surgery?  Are the short-term results in non-surgical return to play as favorable as the athletes that decide to have surgery?
Written by: Nicole Cattano
Reviewed by: Jeffrey Driban
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