Articular Cartilage Defects: The Neglected Factor in ACL Injuries and Return to Sport

Anterior cruciate ligament (ACL) pathology is the third most common knee injury (accounting for 25.4%) in high school athletes.¹ The total number of ACL ruptures is estimated at nearly 250,000 per year² and a subsequent surgical reconstruction is performed in nearly 125,000 patients.³ ACL injuries and the following surgical/rehabilitative principles have received ample attention in the literature over the years; however, one factor is often overlooked.

Chondral damage often accompanies ACL ruptures

Articular cartilage defects, although less common than meniscal pathology, were found in 30% of knees that recently underwent ACL reconstruction, according to a recent systematic review by Flanigan et al.⁴ Similarly, in an arthroscopic evaluation of 378 knees following acute ACL rupture, 163 patients (43%) had evidence of a concomitant full-thickness articular cartilage lesion.⁵

In another study, 146 of 663 (19.1%) patients showed evidence of at least one chondral lesion with the majority (41%) localized to the medial femoral condyle.⁶ Among patients with a chondral lesion, 80% had a meniscal lesion and the primary ACL rupture in the same compartment. Moreover, 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 higher at > 5 years.

A concomitant chondral lesion was present in 36% of ACL ruptures documented in a retrospective analysis of over 25,000 knee arthroscopies.⁷ A much smaller retrospective analysis of 1,000 knee arthroscopies found an associated ACL rupture in 26% of chondral defects.⁸

ACL-R may be aggravating articular cartilage damage

Although ACL reconstruction failure and revisions are typically rare – only 2-6% of all surgeries⁹ – the revisions may be causing additional articular cartilage damage.

Borchers et al evaluated cartilage defects during primary and revision ACL reconstruction.¹⁰ They found a higher 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, chondral injuries occur more often in individuals who have undergone ACL reconstruction, especially a revision.

Does chondral damage affect patient outcomes and return to sport?

Although limited research was dedicated to this question, substantial preliminary evidence suggests that chondral damage does lead to inferior patient outcomes – especially in cases of full-thickness cartilage lesions.

Defect size matters

Røtterud et al evaluated the varying patient-reported outcomes following ACL reconstruction between patients with no additional defects and those with concomitant full-thickness chondral defects or meniscal pathology.¹¹

A total of 3,674 patients were assessed on 5 subscales of Knee Injury and Osteoarthritis Outcome Score (KOOS):

• Pain
• Other symptoms
• Function in daily living
• Function in sport and recreation
• Knee related Quality of life.¹²

At the 2-year follow-up, patients with full-thickness cartilage lesions reported lower crude mean values for all of the KOOS subscales compared with those without cartilage lesions.

Patients with lesions ≥ 2 cm² in diameter also reported poorer outcomes, but the differences were below statistical significance.

Somewhat surprisingly, patient-perceived outcomes remained at the same level in patients with meniscal pathology and smaller chondral lesions (grades I/II) and those without any 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.

Focal cartilage damage can be worse than ACL-deficiency

In a cross-sectional study, Heir et al further identified the extreme patient-perceived deficits in individuals with focal cartilage damage.¹³ The patient complaints were worse than with ACL-deficiency and the quality of life was affected as much as in patients scheduled for total knee replacement.

So even though full-thickness chondral lesions are not nearly as common as meniscal pathology, we should still consider them in patients recovering from ACL reconstruction because they can hurt the patient-perceived outcomes.

MRI underestimates chondral defects

Two studies suggest significant chondral defects may be underestimated or missed altogether due to unreliable pre-operative imaging.

In his study, Campbell et al tried to determine how accurately radiologists can estimate the size of chondral defects in the knee via pre-operative MRI evaluation.¹⁴ In the 92 cartilage defects imaged, radiologists underestimated lesions by about 1.04 cm² in diameter compared to intra-operative findings.

Imaging of medial femoral condyle and femoral trochlea was particularly unreliable, underestimating defects by 92.0% and 82.8%, respectively. This raises serious concerns since most chondral defects associated with ACL-R occur at the medial femoral condyle (see above).

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 due 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.

MRI has only 45% specificity in chondral lesions

To further support the potential for underrated chondral lesions, Figueroa et al reported specificity of only 45% when MRI had was used to rule in a chondral lesion.¹⁵

This data should raise red flags for therapists and orthopedic surgeons alike. Just because imaging is negative, does not mean we can definitively rule out a chondral lesion as a differential diagnosis or contributory factor.

Return to sport after ACL-R and chondral changes

The above findings indicate that we should consider the potential cartilage damage when planning a patient’s return to sport.

Poorer chondral resiliency after ACL-R

Van Ginckel et al evaluated 15 patients treated with isolated ACL reconstruction compared with 15 matched controls.¹⁶ 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.

Post-injury chondral thickness changes

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.¹⁷ At twenty-four months, cartilage in the femoral trochlea became significantly thinner compared to the thickening of the central medial aspect of the femur.

Consider morphological changes during the return to sport

The morphological changes to the articular cartilage described above show that we need to understand the biomechanical and neurophysiological changes associated with return to sport following ACL reconstruction. We should keep both short-term (6 months) and long-term (24 months) changes in the back of our minds and pay special attention to the short-term cartilaginous thinning seen in these patients despite the lack of radiological and/or arthroscopic evidence of chondral lesions. We must handle return to sport delicately to avoid the potential osteoarthritic changes down the road despite the continual pressures from the athlete and coaching staff.

Most importantly, we don’t know if what we do in rehabilitation can positively OR negatively impact this process. It may be that the “dye” is cast with the initial injury OR we may be able to alter the progression – time will tell.