Occult Osteochondral Lesions After ACL Rupture: Six-Year MRI Follow-up Study
Abstract & commentary
Synopsis: The initial ligament injury produced some irreversible changes in the knee with persistent marrow changes. The altered load-bearing properties of subchondral bone may then contribute to subsequent changes in the overlying articular cartilage.
Source: Faber KJ, et al. Occult osteochondral lesions after anterior cruciate ligament rupture: Six-year magnetic resonance imaging follow-up study. Am J Sports Med 1999; 27(4):489-494.
Faber and colleagues studied 23 patients who had anterior cruciate ligament (ACL) rupture that was associated with normal appearing x-rays and a finding of an occult osteochondral lesion demonstrated by magnetic resonance imaging (MRI). Patients were eliminated from the study if, at the time of the original arthroscopy, they were found to have any visible evidence of articular cartilage damage of any type.
Patients were then evaluated six years after their initial injury and ACL reconstruction. They underwent a Mohtadi quality of life outcome measurement, as well as clinical examination, MRI, and KT-1000 evaluation.
The index and follow-up MRIs were compared and evaluated for cartilage thinning and any changes in the marrow signal. A significant number of patients had cartilage thinning that was in juxtaposition to the injury site, noticed on the original MRI scan. These marrow signal changes persisted in 65% of the patients. When Faber et al compared the clinical outcomes, as well as the KT-1000 results, there was no significant change in the measurements between the groups that had a persistent marrow change and those that did not. They conclude that the initial injury produced some irreversible changes in the knee with persistent marrow changes. The altered load-bearing properties of subchondral bone may then contribute to subsequent changes in the overlying articular cartilage. Faber et al admit to a few shortcomings with the study in that they were unable to study as many patients as they would have liked. Because their numbers were small, there was no control group.
Comment by James P. Tasto, MD
We still do not fully understand the natural history of the ACL-deficient knee, with or without surgical intervention.1 Since the advent of MRI, we have noticed a rather large number of patients who have subsequent articular cartilage damage with and without arthroscopic corroboration. Vellet et al showed that one year after an ACL injury, approximately 66% of patients have persistent osteochondral changes on their MRI scans.2 Rosen et al suggested in their review that the majority of these lesions resolved.3
MRI technology is advancing to the point where we can now appreciate more subtle changes in the articular cartilage and, therefore, there can be overall characterization of our preoperative and postoperative assessment of the myriad of injuries that occur during an ACL rupture. We do not know if the initial insult at the time of ACL injury is responsible for subsequent cartilage thinning, or if this is the result of the changes in the subchondral bone and load-bearing capacity. We also do not know if our ACL reconstruction plays a role in reducing the incidence of these changes over the long term, or if it has no bearing and the die was cast during the initial injury. It will be of interest to see if subsequent studies can demonstrate the 15- to 20-year follow-up and attempt to correlate the MRI findings with early arthritic changes.
References
1. Daniel DM, et al. Fate of the ACL-injured patient. A prospective outcome study. Am J Sports Med 1994; 22:632-644.
2. Vellet AD, et al. Occult posttraumatic osteochondral lesions of the knee: Prevalence, classification, and short-term sequelae evaluated with MR imaging. Radiology 1991;178:271-276.
3. Rosen MA, et al. Occult osseous lesions documented by magnetic resonance imaging associated with anterior cruciate ligament ruptures. Arthroscopy 1991;7:45-51.
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