One Third of ACL Ruptures Heal Naturally; Outcomes Uncertain

VIENNA — Nearly one third of anterior cruciate ligament (ACL) injuries appear to heal without surgery, according to an analysis of three-dimensional MRI data taken from the NACOX study, presented as a late-breaking poster at the recent World Congress on Osteoarthritis (OARSI) 2024 Annual Meeting.

At 2 years after injury, three-dimensional MRI showed that 13 of 43 (30%) knees had evidence of normal, continuous ACL fibers. Moreover, a further 14 (33%) knees had a continuous ACL fiber structure following rehabilitation alone. ACL fibers were partly (16%) or completely (21%) ruptured in the remainder of cases.

“If you think of the ACL like a rope, when there is continuity, it means those fibers have rejoined,” study coauthor Stephanie Filbay, PhD, an associate professor at The University of Melbourne in Melbourne, Australia, told Medscape Medical News.

Stephanie Filbay

“Within that, there’s a few variations of healing that we’re seeing. Some look like they’ve never been injured, while some have rejoined but appear thinner or longer than a normal ACL,” Filbay said.

She added: “What all this research is showing is that it’s happening at a much higher rate than we thought possible. And in some of the studies, it looks like ACL healing is associated with very favorable outcomes.”

At OARSI 2024, Filbay presented additional data from her and others’ research on the relationships between ACL healing and long-term functional outcomes and osteoarthritis (OA) incidence in comparisons between patients’ treatment pathways: Early ACL surgery, rehabilitation followed by delayed surgery, or rehabilitation only.

Healing Without Surgery

The idea that the ACL can heal without surgery is relatively recent and perhaps still not widely accepted as a concept, as Filbay explained during a plenary lecture at OARSI 2024.

Filbay explained that the ideal management of ACL injury depends on the severity of knee injury and whether someone’s knee is stable after trying nonsurgical management. Results of the ACL SNNAP trial, for example, have suggested that surgical reconstruction is superior to a rehabilitation strategy for managing non-acute ACL injuries where there are persistent symptoms of instability.

However, there have been two trials — COMPARE performed in the Netherlands and KANON performed in Sweden — that found that early surgery was no better than a strategy of initial rehabilitation with the option of having a delayed ACL surgery if needed.

What Happens Long Term?

Posttraumatic OA is a well-known long-term consequence of ACL injury. According to a recent meta-analysis, there is a sevenfold increased risk for OA comparing people who have and have not had an ACL injury.

ACL injury also results in OA occurring at an earlier age than in people with OA who have not had an ACL injury. This has been shown to progress at a faster rate and be associated with a longer period of disability, Filbay said.

But does the ACL really heal? Filbay thinks that it does and has been involved in several studies that have used MRI to look at how the ACL may do so.

In a recently published paper, Filbay and colleagues reported the findings from a secondary analysis of the KANON trial and found that nearly one in three (30%) of the participants who had been randomized to optional delayed surgery had MRI evidence of healing at 2 years. But when they excluded people who had delayed surgery, 53% of people managed by rehabilitation alone had evidence of healing.

The evaluation also found that those who had a healed vs non-healed ligament had better results using the Knee Injury and Osteoarthritis Outcome Score (KOOS), and that there were better outcomes at 2 years among those with ACL healing vs those who had early or delayed ACL surgery.

ACL Continuity and Long-Term Outcomes

At OARSI 2024, Filbay and colleagues reported an even longer-term secondary analysis of the KANON trial on the relationship between ACL healing at 5 years and outcomes at 11 years. The results were first reported in NEJM Evidence.

Filbay reported that participants with ACL continuity on MRI at 5 years actually had worse patient-reported outcomes 11 years later than those who were managed with early or delayed ACL reconstruction.

“This does not align with previous findings suggesting better 2-year outcomes compared to the surgically managed groups,” Filbay said.

However, people with ACL continuity following rehabilitation did seem to show numerically similar or fewer signs of radiographic OA at 11 years vs the surgical groups.

Radiographic OA of the tibiofemoral joint (TFJ) or patellofemoral joint (PFJ) at 11 years was observed in a respective 14% and 21% of people with ACL continuity at 5 years (n = 14) and in 22% and 11% of people with ACL discontinuity at 5 years in the rehabilitation alone group.

By comparison, radiographic OA of the TFJ or PFJ at 11 years was seen in a respective 23% and 35% of people who had rehabilitation with delayed surgery (n = 26) and in 18% and 41% of those who had early surgery (n = 49).

These are descriptive results, Filbay said, because the numbers were too small to do a statistical analysis. Further, larger, longitudinal studies will be needed.

Posttraumatic OA After ACL Surgery

Elsewhere at OARSI 2024, Matthew Harkey, PhD, and colleagues from Michigan State University, East Lansing, Michigan, reported data showing that nearly two thirds of people who undergo surgical reconstruction have symptoms at 6 months that could be indicative of early knee OA.

Knee symptoms indicative of OA declined to 53% at 12 months and 45% at 24 months.

“It’s a bit complex — we can’t outright say arthritis is developing, but there’s a large group of patients whose symptoms linger long after surgery,” Harkey said in a press release.

“Often, clinicians assume that these postoperative symptoms will naturally improve as patients reengage with their usual activities. However, what we’re seeing suggests these symptoms persist and likely require a targeted approach to manage or improve them,” Harkey said.

The analysis used data on 3752 individuals aged 14-40 years who were enrolled in the New Zealand ACL Registry and who completed the KOOS at 6, 12, and 24 months after having ACL reconstruction.

Harkey and team reported that one in three people had persistent early OA symptoms at 2 years, while 23% had no early OA symptoms at any timepoint.

The studies were independently supported. Filbay and Harkey had no relevant financial relationships to report.

Filbay and colleagues have developed a treatment decision aid for individuals who have sustained an ACL injury. This provides information on the different treatment options available and how they compare.

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