It’s a fact that half of all patients who have anterior cruciate ligament (ACL) surgery end up with knee osteoarthritis. Why does this happen and who does it affect? If the predictive factors and patients at risk can be identified, it might be possible to put a stop to this problem. In an effort to find some answers, a group of Australian physical therapists identify, test, and follow 56 patients who had ACL surgery. All of the patients were younger than 40 years old and had a complete ACL rupture.
They used a variety of ways to measure and track results over a period of six years. Joint laxity (looseness) was measured using a special device called the KT-1000 arthrometer. Another tool was used to measure muscle strength. The involved knee was compared to the other (uninvolved) side. Each patient filled out a survey with questions about return-to-sports. They reported on type of sports participation, level of competition, intensity (how often they played), and duration (how long they played).
X-rays were taken to confirm the presence (and severity) of tibiofemoral and patellofemoral arthritis. Joint space, presence of osteophytes (bone spurs), and any obvious arthritic changes of the cartilage-bone interface were noted. The tibiofemoral joint is located between the lower leg bone (tibia or shin) and the thigh bone (femur). The patellofemoral joint is where the patella (kneecap) moves up and down over the femur.
Other studies have shown us clearly now that aging is a factor in the development of knee osteoarthritis — and so is a previous knee injury. In fact, any time the knee ligaments (like the anterior cruciate ligament) or the meniscus (cartilage) is damaged in a knee injury, the chances that person will develop knee osteoarthritis go up by 10. That means they are 10 times more likely to have knee arthritis compared with someone the same age who never injured the knee.
Anyone with both a ligament AND a meniscus injury has a 70 per cent chance of developing knee problems later. Most of these injuries are sports-related in the younger age group. Athletes involved in cutting sports or activities that include sharp pivoting movements of the lower leg or sudden changes in direction are the group who have the highest number of ACL tears.
For this group of patients, the therapists also paid attention to what kind of ACL reconstruction was done. Some patients had a bone-patellar tendon-bone graft, while the others had a hamstrings graft. No one had a meniscectomy (removal of the meniscus cartilage. When the meniscus was damaged, a repair was done instead. Only one surgeon was involved in performing the procedures. The graft tissue was reattached exactly where the anatomical ACL pulled away from the bone. That spot is called the footprint of the ligament.
Additional information was gathered that might be linked with results such as how much time passed between the injury and the surgery, age at the time of surgery, and whether or not there was chondral damage. Chondral damage refers to part of the joint articular (surface) cartilage being pulled away with the ligament when it detached from the bone.
The good news is that 96 per cent of the patients were satisfied with the results. They had a stable knee joint and were able to go back to competitive play in their sports activities. The downside is that true to form, half the group had signs of osteoarthritis. The patients who had a hamstring graft had the highest incidence of arthritis. In fact, twice as many people in the hamstring group had developed knee arthritis compared with the patellar tendon graft group. However, the patellar tendon group was more likely to have more severe osteoarthritis (rated as moderate) compared with only mild arthritis in the hamstring group.
Dividing results by groups based on location of the arthritis, members of the tibiofemoral group who developed arthritis were more likely to have had a meniscectomy and chondral damage compared with those individuals who did not develop arthritis. Muscle weakness of the quadriceps and an imbalance between quadriceps and hamstrings had a significant effect in predicting the development of arthritis later. Patients in the patellofemoral arthritis group had more meniscal and chondral damage than those without arthritis but the arthritic group were also older at the time of surgery (30 years old and older).
It makes sense that losing the meniscus leads to problems later. The meniscus is designed to absorb shock. It also evens out the two joint surfaces so they can slide and glide against each other smoothly. Without the meniscus, the contact pressure and load on the joint increase thus speeding up degenerative changes that ultimately lead to arthritis. Likewise, disruption of the chondral surface leading to osteoarthritis is easy to understand. With pits and holes in the surface, every movement wears away the joint protection needed for normal knee motion.
The reason for hamstring grafts being linked with onset of osteoarthritis is unclear. More study is needed to understand this factor more completely. Older age might be part of the accelerated joint destruction because joint remodeling for healing and recovery are less effective as we age. It’s likely that the older adults already had a degenerative process starting even before the injury occurred. The injury and age-related decline in remodeling processes seem to be two strikes against normal healing.
The authors conclude that the biggest predictors of arthritis after ACL reconstruction surgery are meniscal damage (and removal) along with cartilage (chondral) disruption (where the joint surface meets the underlying bone). Type of graft, age of the patient at the time of surgery, and leg muscle weakness/imbalance are additional factors that can influence the final outcome of surgery. Addressing these risk factors before and after surgery may reduce the high rates of osteoarthritis following ACL reconstructive surgery.