ACL Tears Set the Stage for Osteoarthritis

By Cat Perry

Your knees are crucial joints, each held together by a durable but vulnerable network of stabilizing ligaments, tendons, cartilage and bones. Knee ligaments have the especially tough job of keeping thigh bones, the largest in the body, connected to the tibia and fibula. The anterior cruciate ligament (ACL), along with other knee ligaments, helps guard against front-to-back (and back-to-front) motions. But sudden stops, twists or pivots, in addition to hyperextension or impact, can stretch it beyond its normal range of motion, leading to a tear or sprain of the ACL or the meniscus, a thin cartilage in the knee. About 100,000 to 200,000 people in the United States experience ACL tears annually, and it’s most often, but not exclusively, young athletes, with higher rates among women than men. Half of these people opt for ACL reconstruction surgery, or ligamentoplasty.

Once ruptured, an ACL cannot regrow or heal back to normal on its own. The two primary treatment options are ACL reconstructive surgery and physical therapy (PT), but there’s a catch: Despite the undeniable benefits of these treatments, they don’t prevent the eventual development of OA, which occurs in up to 87% of those who sustain an ACL tear. So how can you reduce your risk for post-traumatic osteoarthritis (PTOA)?

Why Do ACL Tears Lead to Osteoarthritis?

“We know that patients are at increased risk of developing OA in the knee after an ACL injury,” says Drew A. Lansdown, MD, assistant professor in residence, Sports Medicine & Shoulder Surgery, at University of California, San Francisco. PTOA, a progressive, chronic condition, “is thought to be multifactorial, resulting from the impact on the cartilage at the time of initial injury, an inflammatory cascade that starts after injury, alterations in joint biomechanics due to ACL deficiency, associated meniscus injuries and other factors,” he explains. In fact, concurrent damage to the meniscus happens in 25% to 45% of those with ACL rupture, and studies point to the combination of ACL and meniscal damage as one of the most important predictors for developing PTOA.

Treatment Options

PHYSICAL THERAPY

Physical therapy helps patients work on “strengthening, balance and control of the knee, hip and core muscles,” explains Dr. Lansdown. On its own, PT can be effective for some people, especially those whose jobs and activities don’t include “pivoting or twisting activities, and [who] stick with in-line activities [like] walking, cycling, swimming, etc.,” he adds. For them, PT alone may provide knee function that’s comparable to those who have reconstruction surgery, according to research in New England Journal of Medicine (NEJM). Analyses in the Cochrane Database of Systematic Reviews show similar patterns: Those who opt for PT have seemingly similar knee function two and five years out compared with those who choose ACL reconstruction.

However, in the NEJM study, 30% of those who did not initially opt for surgery did have ACL reconstruction within six months. And in the Cochrane review, many PT patients had ongoing rupture symptoms, such as knee swelling, instability and “locking,” so 39% ended up having reconstruction after two years, and 51% within five years.

“With physical therapy [alone], the torn ACL will often scar to surrounding structures in the knee, but it won't heal back to its normal anatomic location,” Dr. Lansdown says. This may lead to biomechanics that increase joint strain. “While some patients can eventually get back to these higher-level activities, it is less predictable with non-operative treatment, and then these patients are at risk for recurrent instability and additional meniscus/cartilage injuries if they do go back to higher-level activities.” So ACL reconstruction is typically preferred over PT alone.

ACL RECONSTRUCTION SURGERY

“The current gold standard for surgical treatment is ACL reconstruction, where a tendon graft is used to replace the ACL,” Dr. Lansdown says. Those who choose ACL surgery tend to have fewer ACL rupture symptoms afterward, a more predictable return to activities and maybe even less risk of developing OA compared to those with untreated ruptures.

While various tendons may be used for the graft, hamstring and quadriceps tendons (which connect the respective muscles to bone) show especially positive outcomes. Medical literature indicates the best time for ACL reconstruction surgery is at least three weeks after the injury and is best followed by physical therapy to rebuild hamstring and quad strength. In a small study of active patients over age 60 with non-arthritic knees, ACL surgery showed positive results for functional recovery while not increasing the development of knee deterioration, and most patients returned to pre-surgery levels of activity.   

Again, the meniscus may be key: If you have significant meniscus damage during an ACL injury, having a total meniscectomy (or surgical removal of the torn meniscus) at the same time as ACL surgery can reduce your risk for developing PTOA by 7% to 61% compared to those with deficient ACLs who have just partial meniscectomy.

However, gait analysis of ACL surgery patients reveals an altered joint loading pattern and biomechanics compared with healthy patients, which may contribute to the development of PTOA. And large study analyses done in the Journal of Athletic Training adds to evidence that surgery patients have relatively similar occurrences of osteoarthritis compared to those who do not have surgery.

The surgical option chosen least is ACL repair. In this procedure ACL sutures are used to sew the ligament back together. However, the sutures often fail over time. 

THE FUTURE OF ACL TREATMENT OPTIONS

There are also treatments for OA that target inflammatory pathways. In animal studies, dead cells in the joint area were removed to promote a healthy environment, and medications that inhibit inflammation or boost antioxidants have also been tested. These show a slowing of progression with PTOA; however, there is not enough evidence to support using these treatments in humans.

A wide range of complementary treatments are being tested in humans, including cryotherapy to reduce inflammation, gene therapy and weight loss to decrease joint loading. Investigations into regenerative medicine to treat knee OA are also ongoing. Examples include regrowing cartilage; or using platelet-rich plasma to boost collagen and reduce inflammation. Cell-based therapies like using mesenchymal stromal cells (generated from your own bone marrow or fat tissue) are also in the early stages of being studied for lowering OA pain and improving cartilage quality. So there is a lot of room for further research into ACL injury therapies that help reduce OA risk.

Despite the risk of developing OA, surgery is the treatment of choice. “Current research does show overall similar rates of OA with or without surgical treatment,” Dr. Lansdown says. “While surgery at this point does not seem able to change the risk of developing OA, it does allow for lower risk of subsequent injury to the meniscus and cartilage, which is also important.”

It is best to have detailed and forward-looking conversations with your doctor and physical therapist. Together you can develop a multi-layered treatment plan that could help you prevent or minimize OA and optimize your long-term health.

Published May 21, 2021