Given the accumulating evidence linking anterior cruciate ligament injury to early-onset osteoarthritis, one might reason that surgical repair of the injured joint would decrease that risk. But too often that isn’t the case. This two-part series explores the complicated ways, both negative and positive, that surgery can influence OA risk.
By Cary Groner, Lower Extremity Review June 2012
Orthopedists and athletic trainers typically understand that the long-term consequences of anterior cruciate ligament (ACL) injury may include osteoarthritis. The meniscal damage frequently associated with ACL rupture and surgery to address that damage both compound the risk.1 Nevertheless, the biomechanical and chemical processes that lead from a torn ACL to degenerative joint disease are only now being elucidated, and many clinicians still disagree about what’s going on and what to do about it.
Contentious issues include the nature of the initial injury to cartilage and subchondral bone; if biochemical processes or stabilization issues are more to blame for OA; whether surgical intervention is superior to conservative care in preventing the progression from the initial ligament injury to osteoarthritis; and, when ACL reconstruction is done, whether certain approaches are superior to others for stabilizing the joint and reducing OA risk.
“This is a problem we thought we had under control, but it turns out we don’t,” said Jonathan Chang, MD, a clinical associate professor of orthopedics at the University of Southern California in Los Angeles. “In sports medicine we are looking for new directions to see if there is a way to stanch what looks potentially like a coming epidemic of arthritis in reconstructed knees. At the moment, we’re just trying to get a handle on how big the problem is, and what some of the risk factors are.”
According to Stefan Lohmander, MD, a professor in the Department of Orthopedics at Lund University in Sweden, dealing with an ACL tear involves two stages.
“First is what happens at the moment of acute injury, and second is what happens down the road,” he said. “Researchers are trying to find out if there are interventions we could do in the first hours or days after injury, similar to how we intervene when someone is having a heart attack or a stroke. Then later, when the biomechanics and dynamic movements of the joint are not normal, what can we do? If we can’t put it right again, then every remaining step in the individual’s lifetime will put an abnormal load onto the knee joint.”
Scope of the problem
Ten to 20 years after an ACL injury or meniscal tear, some studies report that roughly half of patients have osteoarthritis. Other research suggests even higher rates. For example, in a cohort of 19 elite athletes with untreated ACL ruptures who were symptomatically stable, all had meniscectomies by 20 years; by 35 years all had degenerative changes associated with OA, and eight (42%) had undergone total knee replacement.
Clinicians and researchers do agree on the rough parameters of the physical catastrophe. The initial ACL rupture damages the cartilage of the tibial plateau and the lateral femoral condyle; this appears to trigger cytokine and protease cascades in the joint, which increases the catabolism of chondrocytes. Postrupture knee instability may further damage the meniscus and the articular cartilage, particularly in the medial compartment, where most OA occurs.
Research shows that by 10 years, all patients with an untreated ACL rupture will have a medial meniscal tear, though this includes those who incurred meniscal damage at the initial injury. That damage, particularly loss of the posterior horn of the meniscus, increases the anterior displacement of the tibia on the femur, concentrates the axial load in specific areas, and increases shear forces. Not everyone with a meniscal injury will develop OA, of course, but about half do by 20 years post-injury, and the risk is affected by factors including the presence of finger osteoarthritis (a hereditary marker for generalized OA), obesity, and sex.
In a 2007 paper in the American Journal of Sports Medicine (AJSM), Lohmander summarized in three categories the reasons for the variation in reported long-term OA outcomes in patients with ACL and/or meniscal tears. The first category includes the injury itself, reconstructive surgery and rehab, return to sport, chronic instability, and later injuries associated with these variables. The second category comprises the individual’s activity level, strength, body mass index (BMI) and personality. The third consideration is that the way OA is diagnosed and assessed—for example, using x-ray, magnetic resonance imaging (MRI), or patient symptom scores—can produce inconsistent results.
To cut or not to cut
Experts have long debated the relative value of ACL reconstruction in preventing OA. Much of the research suggests that it has a protective effect; for example, in one study of patients with reconstructed knees at 20 years follow up, the reported risk of osteoarthritis ranged from 14% to 26% with a normal medial meniscus and up to 37% after meniscectomy. By contrast, those with untreated ruptures developed OA 60% to 100% of the time.
The problem with assessing such statistics is the time lag between injury (with or without surgery) and the appearance of either radiographic or symptomatic osteoarthritis. It’s a little like astronomers viewing a star, knowing that the light reaching their eyes was actually set in motion millions of years before. Clinicians are now seeing the results of surgeries performed two or three decades ago, when techniques were less refined.
“Prior to the late 1980s, football players didn’t want to get their ACLs reconstructed because it was an open procedure followed by six weeks in a cast, and it was six months before you could walk,” said Leo Pinczewski, MD, an associate professor of orthopedics at the University of Notre Dame in Sydney, Australia. “A combination of the surgery, and the fact that the patients lost their menisci, led to a hundred percent incidence of osteoarthritis at ten years. I was almost ready to give up ACL surgery, because even though we were making our patients more stable and allowing them a higher level of activity, we were abetting the development of osteoarthritis.”
The advent of arthroscopic surgery changed all that, Pinczewski said.
“Between 1988 and 1992, I did eighteen hundred bone-patellar tendon-bone [BPTB] reconstructions, and we could use interference screws to fix the graft. That meant we could get rid of casts and bracing and get patients moving straight away,” he said. “We found that if you operated on the ACL before the patient damaged their meniscus or articular cartilage due to instability, it took a lot longer to develop any arthritis, and not everyone did. Now we know that patients who have surgery within four months of their ACL injury have significantly less osteoarthritis at fifteen years than those who have their surgery later than four months [unpublished data]. The longer you wait, the more meniscal and articular cartilage damage there is.”
James Murray, MD, an orthopedic knee specialist at the Avon Orthopaedic Center and Frenchay Hospital in North Bristol, UK, agreed that the four-month window to surgery is important.
“When you have an unstable knee with rotational laxity, the chance of damaging the meniscus is higher on the medial side, and meniscal injury after untreated ACL injury is roughly one percent per month,” he said. “People who’ve had nonoperative treatment of ACLs progress to medial arthritis.”
Naturally, not everyone in the field concurs. In 2010, Lohmander, Richard Frobell, PhD, and their colleagues published a paper in The New England Journal of Medicine that provoked a lively exchange of letters to the editor in that and other journals. The paper concluded that a strategy of rehabilitation with early ACL reconstruction wasn’t any better than rehab plus optional delayed reconstruction in affecting an array of two-year outcomes, including pain, symptoms, function in sports, and knee-related quality of life.
Detractors took issue with several aspects of the study. Not the least of these was that, of the 59 subjects in the optional delayed-reconstruction group, 23 ultimately chose to have ACL reconstruction, at an average of about a year after randomization.
Of course, two years isn’t enough time to glean much information about OA risk, and the authors didn’t evaluate this variable directly. However, critics noted that in a pivot-shift test, just 47% of the delayed group scored normal, versus 75% of those in the immediate surgery group. Because pivot shift is a measure of stability that may affect later OA risk, the statistic could have implications for osteoarthritis prevention. Nevertheless, in one of the responses to the letters regarding their article, Lohmander and his colleagues wrote, “there is insufficient evidence to show whether ACL reconstruction is associated with less or more post-injury osteoarthritis compared with nonsurgical treatment.”
Lohmander is polite, soft-spoken, and composed when discussing his research; you don’t get the feeling you’re talking to a firebrand with an ax to grind. His point is simply about evidence.
“There will be continued development in terms of finding the optimal way to reconstruct the ACL and rehabilitate patients, whether they have a surgical reconstruction or not,” he told LER. “I think our study provides the best evidence so far, but that doesn’t mean it’s the last word.”
The long-term consequence of anterior cruciate ligament and meniscus injuries: osteoarthritis, Lohmander LS, Englund PM, Dahl LL, Roos EM. Am J Sports Med. 2007 Oct;35(10):1756-69. Epub 2007 Aug 29.
ACL reconstruction and risk of knee OA, Part 2 in Lower Extermity Review
Early ACL surgery could lower risk of associated knee damage in Lower Extremity Review
Patellofemoral osteoarthritis 15 years after anterior cruciate ligament injury-a prospective cohort study, Neuman P, Kostogiannis I, Fridén T, Roos H, Dahlberg LE, Englund M. Osteoarthritis Cartilage. 2009 Mar;17(3):284-90. doi: 10.1016/j.joca.2008.07.005. Epub 2008 Sep 3.
Combined knee joint geometry measurements provided more information on ACL injury risk in Healio Orthopedics Today