Predictors of Radiographic Knee Osteoarthritis After Anterior Cruciate Ligament Reconstruction.

Li RT, Lorenz S, Xu Y, Harner CD, Fu FH, Irrgang JJ.  Am J Sports Med. 2011 Oct 21. [Epub ahead of print]

Over the past few months, SMR had several posts highlighting that individuals with a history of knee injury are at greater risk for knee osteoarthritis (OA) even if they undergo surgeries like anterior cruciate ligament (ACL) reconstructions (see below). As clinicians we must strive to reduce the risk of knee OA for our injured patients.  Unfortunately, it is unclear which variables might predict individuals who will develop knee OA after an injury. Therefore, Li et al. tried to determine the prevalence of knee OA after a single-bundle ACL reconstruction and to identify factors that predict the development of knee OA.  This study was a secondary analysis derived from a study that assessed outcomes among 422 patients that underwent a single-bundle ACL reconstruction (Kowalchuk et al 2009). The current study focused on 249 patients that were entered in a research database and had physical examination and radiographic data. All of the ACL reconstructions were performed by one of two surgeons using the same surgical method.  One orthopaedic surgeon scored the radiographic knee OA severity in medial and lateral tibiofemoral compartments as well as patellofemoral joints. The authors evaluated numerous potential risk factors: 1) patient characteristics (e.g., age, sex, body mass index [BMI], occupation), 2) surgical variables (e.g., concurrent meniscal tears, chondral lesions, graft type/placement), and 3) other factors (e.g., length of time between injury and surgery, length of follow-up time, need for revision surgery). The average time between surgery and follow-up was 7.9 years (range: 2.1 to 20.3 years) and on average patients were 26.4 years of age at the time of surgery. Between 25% and 32% of participants had radiographic evidence of knee OA in the medial or lateral tibiofemoral compartment or patellofemoral joint. In the final statistical models, four predictors were associated with increased odds of developing knee OA: pre-operative high BMI, medial chondral lesions, concurrent medial meniscectomy, and length of follow-up. Overall, predicting knee OA development based on these four predictors had a sensitivity of 60.2% (chance of positively diagnosing a patient who has pathology) and a specificity of 70.4% (chance of correctly identifying a healthy patient).

This is a helpful study for identifying predictors to identify patients that may develop knee OA after a single-bundle ACL reconstruction. While the authors state that this model is not ready to be used in clinics to predict knee OA development it does provide us helpful information. Not surprisingly concurrent injuries (i.e., cartilage lesions and meniscal damage) were risk factors for knee OA since these injuries further complicate the adverse biomechanical and biochemical changes associated with ACL injuries. It is also not surprising that the length of follow-up was related to knee OA development. It is possible that all joints with a history of trauma may be on a path towards knee OA but some might get to OA faster than other joints. If provided a long enough time perhaps all of these joints would progress to knee OA without a disease modifying or risk modifying intervention. Finally, there is the issue of high BMI which has been suggested as risk factor for knee OA. It is important for future studies to untangle whether the risk is associated with high body mass or high body fat percentage (or both). Regardless, BMI is the only predictor from this study that is modifiable. This highlights the need for us to educate our patients with a history of knee injuries that they are at increased risk for knee OA and therefore should reduce their other risk factors for knee OA by maintaining a healthy lifestyle as they age (e.g., remain physically active, maintain a healthy body weight).  Have you ever discussed the risks of knee OA with your patients with a history of knee injuries? If so, how do you advise them?

Written by: Jeffrey Driban

Li RT, Lorenz S, Xu Y, Harner CD, Fu FH, & Irrgang JJ (2011). Predictors of Radiographic Knee Osteoarthritis After Anterior Cruciate Ligament Reconstruction. The American Journal of Sports Medicine PMID: 22021585