Histopathological changes in the human posterior cruciate ligament during aging and osteoarthritis: correlations with anterior cruciate ligament and cartilage changes

Abstract

Objectives: To determine the histological patterns of posterior cruciate ligament (PCL) degeneration during aging and in relation to changes in articular cartilage and anterior cruciate ligament (ACL) across the entire adult age spectrum.

Methods: Human knee joints (n=120 from 65 donors) were processed within 72 h of postmortem. Articular cartilage surfaces were graded macroscopically. Each PCL was histologically evaluated for inflammation, mucinous changes, chondroid metaplasia, cystic changes and orientation of collagen fibres. The severity of PCL degeneration was classified as normal, mild, moderate or severe. PCL scores were compared to ACL and cartilage scores from the same knees.

Results: All knees had intact PCL. Histologically, 6% were normal, 76% showed mild, 12% moderate and 9% severe degeneration. Fibre disorientation was the most prevalent and severe change. Histological grades of PCL and ACL correlated, but significantly fewer PCL than ACL showed severe changes. There was a weaker correlation between aging and total histological PCL scores (R=0.26) compared to aging and ACL scores (R=0.42). ACL scores correlated with cartilage scores (R=0.54) while PCL scores increased with the severity of osteoarthritis from grades 0 to III but not between osteoarthritis grades III-IV (R=0.32). In knees with ruptured ACL, the PCL scores correlated with cartilage scores of the lateral compartment.

Conclusions: PCL histopathological changes were less severe than in the ACL. PCL degeneration was associated with ACL and cartilage damage. The lack of correlation with age indicates independent pathways for PCL versus ACL degeneration.

Figure 1

Bivariate scatterplots of total PCL, total ACL, and total cartilage scores, and associated ages. Also depicted are the LOESS regressions (smoothers), indicative of increasing scores with age. Spearman’s correlations r between age and total PCL (left panel), total ACL (middle panel), and total cartilage scores (right panel) are 0.26 (95% confidence interval 0.08 to 0.42), 0.42 (95% CI 0.23 to 0.58), and 0.75 (95% CI 0.66 to 0.82) respectively.

Figure 2

Total and specific PCL and ACL scores versus cartilage grade. Valuess depicted are the mean ligament scores at each specific cartilage grade, separately for PCL and ACL. Total PCL and ACL histological score (A), inflammation (B), mucoid changes (C), chondroid changes (D), cystic changes (E) and fiber orientation (F). Mean total and component ACL and PCL scores tended to increase with increasing OA grade: total scores, F_4,111 = 11.42, p<0.001; inflammation, F_4,111 = 2.63, p=0.038; mucoid, F_4,111 = 4.34, p=0.027; chondroid, F_4,111 = 2.54, p=0.044; cystic changes, F_4,111 = 4.36, p=0.0026; fiber orientation, F_4,111 = 11.10, p<0.001.

Figure 3

Total and specific PCL and ACL scores versus age. Ages were divided into 4 quartiles; within each quartile, means and associated 95% confidence intervals of total and specific histological scores are shown, separately for PCL (red) and ACL (blue). Total PCL and ACL histological score (A), inflammation (B), mucoid changes (C), chondroid changes (D), cystic changes (E) and fiber orientation (F). In paired analyses, ACL inflammation scores were found to be significantly higher than the corresponding PCL scores (t₁₁₆ = 3.63, p<0.001), and PCL chondroid metaplasia scores were significantly greater than their ACL counterparts (t₁₁₅ = −2.71, p=0.009). No significant pairwise differences between ACL and PCL scores were found with inflammation, mucoid degeneration, fiber organization, or total scores.

Figure 4

Total and specific PCL and ACL scores in donors younger than 45 years (n=9) with normal cartilage (grade 0).