Knee injuries resulting in anterior cruciate ligament (ACL) tears are fairly common -- especially in athletes and sports participants. With full tears, ACL reconstruction is usually required. Most athletes are concerned with how soon can they get back into action on the court or in the field. An equally important question is: how well does the new ACL hold up over time? Is osteoarthritis inevitable?

To find out, this group of sports physiotherapists and orthopedic surgeons performed a long-term (15-year) study of patients who had an ACL injury. Some of the patients had just the ACL tear. Others had additional damage done at the same time (e.g., meniscal injury, cartilage lesions, other ligament damage).

Everyone in both groups had an ACL reconstruction surgery. The goal of surgery was to restore stability and function of the knee joint. Without the ACL to hold the two bones of the knee together (the femur or thigh bone and the tibia, the lower leg bone), the tibia can slide too far forward away from the femur.

The graft used to replace the ruptured ACL was taken from the patellar tendon (just below the knee cap). This graft procedure is called a bone-patellar tendon bone (BPTB) autograft. Autograft means the graft tissue came from the patient's own knee.

It should be noted that the patients who had additional injuries to the same knee may or may not have had those injuries repaired at the time of the ACL surgery. For example in some cases, meniscal tears were repaired, removed, or left alone. Anyone with chondral (cartilage) lesions may have had the edges shaved down to smooth the area, but full repair was not made.

Results for these two groups were compared in terms of motion, function, strength, and activity level. Everyone was followed early on (six months after surgery, one year later, two years later) and then rechecked at 10 and 15 years after the procedure.

X-rays were used to document any signs of osteoarthritis. Narrowing of the joint space, presence of bone spurs, and deformity of the bones at the joint were evaluated to grade the severity of arthritic changes.

One thing that makes this study different from others like it is the way they looked at osteoarthritis. Most studies just report how many patients developed osteoarthritis down the road after ACL surgery. In this study, they compared how many patients had signs of arthritis on X-ray without symptoms and how many had visible changes with symptoms. Pain was the primary symptom used to say whether or not the patient had symptomatic radiographs (X-rays).

The authors also took a closer look at how additional injuries affected function. In other words, they compared patients with ACL, meniscal, and/or cartilage damage to those who had just an isolated ACL tear. How did their X-rays look 10 to 15 years later? Which group had more symptoms of arthritis?

Because they were looking at so many different findings, it might be easier to show you the results in a list:

Two-thirds of the patients had combined injuries; one-third had an isolated ACL injury.

Three-fourths of the patients (74 per cent) had X-ray evidence of osteoarthritis.

More patients in the combined injury group had osteoarthritis (and more severe arthritis) compared to the isolated ACL injury group.

There was no difference between the two groups in terms of symptomatic radiographs.

Slightly less than 10 per cent of the patients reinjured their ACL grafts during the 15 year follow-up.

Two-thirds of the all the patients in both groups went back to sports activities after rehab

Everyone in both groups (isolated ACL injury and combined injuries) had more than normal knee joint laxity (looseness) during the follow-up period.

There was no significant differences in strength or function between the two groups.

What can we conclude from these findings? First, the good news. Knee function is improved and maintained for a long time after ACL reconstruction surgery. Improved knee function can be expected for patients with an isolated ACL injury as well as for those who have combined injuries.

Now the possible downside. Osteoarthritis is common after these surgeries. ACL reconstruction surgery does not prevent osteoarthritis. Patients with isolated ACL injuries tend to have mild arthritic changes. Patients with combined injuries are more likely to develop moderate to severe osteoarthritis.

What we don't know is why some people develop more arthritis than others and why some patients have pain with their arthritic changes and others don't. The next step in researching this topic is to look for risk factors for developing osteoarthritis. Discovering predictive factors of who will have arthritis might help surgeons find ways to prevent this natural progression of events.

Reference: Britt Elin Øiestad, PT, MSc, et al. Knee Function and Prevalence of Knee Osteoarthritis After Anterior Cruciate Ligament Reconstruction. In The American Journal of Sports Medicine. November 2010. Vol. 38. No. 11. Pp. 2201-2210.