Knee OA risk factors after ACL reconstruction.

Factors Involved in the Development of Osteoarthritis After Anterior Cruciate Ligament Surgery. 
Keays, S., Newcombe, P., Bullock-Saxton, J., Bullock, M. and Keays, A.  American Journal of Sports Medicine, 2010; 38, 455 – 463.
http://www.ncbi.nlm.nih.gov/pubmed/20051501

The most commonly affected joint by osteoarthritis is knee joint. Knee trauma has been associated with increased risk of knee OA development. ACL rupture and meniscal lesions are one of the most commonly suggested factors triggering the onset of OA. Some research findings report that half of the ACL – reconstructed knees will suffer from OA. Knowledge of the factors involved in the pathogenesis of this condition after ACL reconstruction could lead to improved preventive and therapeutic management. Thus, authors conducted this study to identify risk factors for knee OA development after ACL reconstruction.

The variables assessed were quadriceps strength, hamstring strength, quadriceps-to-hamstring strength ratios, knee joint stability, associated injury to the meniscus or chondral surface, time delay between injury and surgery, age at the time of surgery, type of graft used, and postsurgery sport. Fifty-six subjects with anterior cruciate ligament reconstruction were followed for 6 years after surgery. Assessment included KT-1000 arthrometer testing, isokinetic strength testing, a return-to-sport questionnaire, and a radiograph assessment.
Study results revealed that twenty-seven patients (48%) had developed tibiofemoral OA, with 7 patients (12%) having moderate tibiofemoral OA and 20 patients (36%) having mild OA. In addition, 20 patients (36%) had developed mild patellofemoral OA. Inclusion of meniscectomy in the surgery, presence of chondral damage observed at the time of surgery, patellar tendon grafting, quadriceps strength measured at 60 deg/s and quadriceps/hamstring strength ratio measured at 60 deg/s.  were predictors of tibiofemoral OA. Meniscectomy, chondral damage, and age at the time of surgery demonstrated a trend toward patellofemoral OA.
Meniscectomy was found to be one of two most significant predictors for tibiofemoral and patellofemoral OA. While tibiofemoral OA onset is not surprising, authors provide explanation to the patellofemoral OA appearance. According to them, decreased tibiofemoral joint space associated with a meniscectomy changes the relationship of the patellar to the femoral trochlea which potentially triggers OA development.
Damage to the cartilage was the second most significant predictor for both tibio- and patellofemoral OA. Authors reference to other studies where “increased concentration of chondrodestructive cytokines and decreased concentration of chondroprotective cytokines present in the ACL-ruptured knee” has been provided as a potential causation of OA in the patellofemoral and tibiofemoral articular surfaces.
Older patients at the time of the surgery were more prone to develop OA changes in the patellofemoral joint but not in the tibiofemoral joint. This could be explained with that degenretaive processes speed up with increasing age and OA is a process of not only of degeneration but also of wear and remodeling and those remodeling processes decrease with age.
Inbalance between quadriceps and hamstring strength ratio has been reported to be the predictor for tibiofemoral joint OA changes. It could be attributed to uneven joint loading which might be present at the time of muscles imbalance. The posteromedial aspect of the joint may be increasingly loaded due to the development of a flexion contracture in the knee joint as it is the case when quadriceps weakness relative to hamstring is present. Furthermore, if both the quadriceps and hamstring muscles are tight, as is often the case in weak muscles and in disproportionately strong muscles, there could be increased compression in the joint, according to authors.
Based on the findings, authors suggest that in clinically unstable knees, ACL surgery should not be delayed unnecessarily so as to avoid any secondary meniscal and chondral injury. In addition, there is some evidence that STG may be the graft of choice. Importantly, physiotherapists should focus on restoring dynamic stability in the ACL deficient knee to avoid further damage and should ensure a restored quadriceps-to-hamstring ratio before and after surgery.