According to Swenson et al, the third most common knee injury in high school aged athletes is pathology associated with the anterior cruciate ligament (ACL) at 25.4%. Additionally, Griffin et al estimated that the total number of ACL ruptures per year approaches nearly 250,000 and a subsequent surgical reconstrucaton is perfromed in nearly 125,000 patients (Kim et al). This injury and the following surgical/rehabilitative principles have been given substantial attention in the literature over the years, however there is one factor that is often overlooked.
Articular cartilage defects, while not as prevalent as meniscal pathology, have been found in 30% of knees that recently underwent ACL reconstruction according to the findings of a recent systematic review published by Flanigan et al. Additionally, Maffulli et al found similar results in an arthroscopic evaluation of 378 knees following acute rupture of the ACL where 163 patients (43%) had evidence of a concomitant full-thickness articular cartilage lesion. Once again, in a similar study, Tandogen et al determined that 146/663 (19.1%) patients showed evidence of at least one chondral lesion with the majority being localized to the medial femoral condyle (41%). Of the patients who presented with a chondral lesion, 80% had a meniscal lesion in addition to the primary ACL rupture in the same compartment. Also, they found that the odds of having a serious chondral lesion (grade III/IV) were 2.7 times higher at 2 to 5 years post-injury and 12.6 times more likely at > 5 years. In a retrospective analysis of over 25,000 knee arthroscopies, Widuchowski et al found that a concomitant chondral lesion was present in 36% of ACL ruptures documented. In a much smaller, albeit similar, study Hjelle et al found an associated ACL rupture in 26% of chondral defects after conducting a retrospective analysis of 1,000 knee arthroscopies. While ACL reconstruction failure and the following revisions are typically rare at an incidence of only 2-6% of all surgeries (Spindler et al), it appears that this revision leads to an increase in articular cartilage damage. Borchers et al evaluated the presence of cartilage defects in patients during primary and revision ACL reconstruction. They found an increased odds ratio of grade III and IV chondral lesions in revision compared with primary ACL reconstruction in the lateral and patellar-trochlear compartments. Based on this data, there does seem to be a higher incidence of chondral injuries in individuals who have undergone ACL reconstruction and especially in those who have undergone a revision, but does this underlying concomitant pathology effect the patient’s outcomes or their eventual return to sport?
While there has not been a great deal of research devoted to this question, there is substantial preliminary evidence that chondral damage does lead to inferior patient outcomes. Røtterud et al evaluated the varying patient-reported outcomes following ACL reconstruction between patients with no additional defects and those with concommitent full-thickness chondral defects or meniscal pathology. After evaluating the Knee Injury and Osteoarthritis Outcome Score (KOOS) of 3,674 patients, those with full-thickness cartilage lesions reported lower crude mean values for all of the KOOS subscales compared with those patients without cartilage lesions at the 2-year follow-up. There were also worse outcomes in those patients with lesions ≥ 2 cm2 in diameter, but these differences were small and did not reach statistical significance. Also, somewhat surprisingly, meniscal pathology and less substantial chondral lesions (grades I/II) did not yield inferior patient-perceived outcomes compared to those without additional intra-articular lesions. Based on these findings, patients with full-thickness cartilage damage reported more pain and symptoms, impaired function in activities of daily living, sports, recreation, and reduced knee-related quality of life compared to those without concomitant chondral damage. Heir et al completed a cross-sectional study that further identified the extreme patient-perceived deficits of individuals presenting with focal cartilage damage. They found that complaints are worse than those of ACL-deficient patients, and quality of life is affected to the same extent as in patients scheduled for total knee replacement. This body of evidence demonstrates that while full-thickness chondral lesions are not nearly as common as meniscal pathology, they still must be considered in patients recovering from ACL reconstruction based on their detrimental impact on the patient’s perceived therapeutic outcome.
Another very important and under appreciated factor must also be considered in rehabilitation status-post ACL reconstruction. Campbell et al conducted a very important study with concerning results. They attempted to determine the ability of radiologists to accurately estimate the size of chondral defects of the knee via pre-operative MRI evaluation. Of the 92 total cartilage defects imaged, the radiological findings indicated lesions that were approximately 1.04 cm2 smaller in diameter than what was found intra-operatively. Areas of specific concern were the medial femoral condyle and femoral trochlea, which were underestimated by 92.0% and 82.8%, respectively. This is especially concerning since the majority of chondral defects associated with ACL reconstruction are localized to the medial femoral condyle. Further, when all compartments were averaged together, MRI imaging underestimated chondral defects by 70%… And this is in high grade defects. This leads us to believe that significant chondral defects are potentially underestimated or missed altogether secondary to unreliable pre-operative imaging. While this study was not focused primarily on patients undergoing treatment for ACL pathology, it does give us information on the underestimation of cartilage defects. To further support the potential for under-reported chondral lesions, Figueroa et al reported specificity of only 45% when MRI was utilized to rule in a chondral lesion. This information should give caution to therapists and orthopedic surgeons alike. Just because imaging is negative, does not mean that a chondral lesion can be definitively ruled out as a differential diagnosis or contributory factor.
These findings indicate the need to take potential cartilage damage into consideration when planning you patient’s return to sport. Van Ginckel et al evaluated fifteen patients treated with isolated ACL reconstruction compared with 15 matched controls. Each patient received a 3-T MRI cartilage evaluation (3-D volume/thickness documented), biochemical composition (T2/T2* mapping), and functional assessment. Patient function was determined by recording in vivo deformation (including recovery) after a 30 minute run. Patients recovering from an isolated ACL reconstruction demonstrated diminished quality and in vivo cartilaginous resiliency compared with controls. In a similar study, Frobell et al performed diagnostic 1.5-T MRI evaluation at baseline, three, six, twelve, and twenty-four months post-injury. At twenty-four months, significant cartilage thinning occurred in the femoral trochlea compared to thickening localized to the central medial aspect of the femur. The morphological changes to the articular cartilage found in these two studies shows the need to understand the biomechanical and neurophysiological changes associated with return to sport following ACL reconstruction. Both short-term (6 months) and long-term (24 months) changes have been identified and must be in the back of the treating clinician’s mind. Specific attention should be paid to the short-term cartilaginous thinning that can be seen in these patients despite the lack of radiological and/or arthroscopic evidence of chondral lesions. While there are typically continual pressures from the athlete and coaching staff, return to sport must be handled delicately to avoid the potential for long-term osteoarthritic changes down the road.