Predictors of Posterior Cruciate Ligament Degeneration in Osteoarthritic Knees

Purpose: To evaluate the tibial articular cartilage and histology of the posterior cruciate ligament (PCL) in osteoarthritic knees so as to determine predictors of PCL degeneration.

Methods: 23 advanced osteoarthritic knees (mean patient age, 61 years) treated with total knee arthroplasty (TKA) were prospectively studied. The Knee Society Score was assessed. Osteoarthritic changes on radiographs were graded as mild, moderate, or severe. Tibial articular cartilage erosion was assessed. The appearance of both cruciate ligaments was classified as normal, abnormal (thinner and sclerotic), or ruptured. Both ligaments were examined histologically for degenerative changes. Each degenerative change of the PCL was graded by 2 histopathologists twice separately. Higher scores indicated more severe degeneration.

Results: Of the 23 knees, the gross appearance of the anterior cruciate ligaments (ACLs) was normal in 6, abnormal in 11, and ruptured in 6. Histologically, the PCLs were normal in 4, minimally degenerated in 2, mildly in 8, moderately in 5, and severely in 4. The predominant degenerative change was the presence of loose fibrous tissue. ACL appearance correlated positively with PCL degeneration (r=0.883, p=0.001). The mean Knee Society Score was 24 (range, 0-43), and the mean function score was 30 (range, 5-55). PCL degeneration correlated positively with the Knee Society Score (r=0.565, p=0.02) but not with the function score (r=0.061, p=0.447). Anteroposterior instability correlated positively with PCL degeneration (r=0.691, p=0.01). Erosion in the lateral tibiofemoral compartment and ACL insufficiency were indicators of PCL degeneration (despite a normal appearance). Inter-observer reliability and intra-observer reproducibility were 0.82 and 0.87, respectively.

Conclusion: The Knee Society Score, anteroposterior instability, ACL appearance, and erosion in the lateral tibiofemoral compartment are predictors of PCL degeneration and can help decide on the optimal type of TKA implant (PCL-retaining vs. PCL-sacrificing design).