Anterior cruciate ligament changes in the human knee joint in aging and osteoarthritis

Abstract

Objective: The development and patterns of spontaneous age-related changes in the anterior cruciate ligament (ACL) and their relationship to articular cartilage degeneration are not well characterized. This study was undertaken to investigate the types and temporal sequence of age-related ACL changes and to determine their correlation with cartilage lesion patterns at all stages of osteoarthritis (OA) development in human knee joints without prior joint trauma.

Methods: Human knee joints (n = 120 from 65 donors ages 23-92) were obtained at autopsy, and ACLs and cartilage were graded macroscopically and histologically. Inflammation surrounding the ACL was assessed separately.

Results: Histologic ACL substance scores and ligament sheath inflammation scores increased with age. Collagen fiber disorganization was the earliest and most prevalent change. The severity of mucoid degeneration and chondroid metaplasia in the ACL increased with the development of cartilage lesions. A correlation between ACL degeneration and cartilage degeneration was observed, especially in the medial compartment of the knee joint.

Conclusion: Our findings indicate that ACL degeneration is highly prevalent in knees with cartilage defects and may even precede cartilage changes. Hence, ACL deficiencies may not only be important in posttraumatic OA, but may also be a feature associated with knee OA pathogenesis in general.

Figure 1

A. ACL macroscopic scores versus age. The mean age of donors with normal ACL was significantly less than that of donors with abnormal ACL and that of donors with ruptured ACL. Each ACL was treated as a separate unit for analysis. Values are the mean + SD. * = p< 0.05, ** = p<0.01. B. ACL microscopic scores versus age. The total ACL score, which is the sum of all histological changes within the ACL increased with donor age. Each data point represents one knee.

Figure 2. Macroscopic changes in ACL versus cartilage changes

Macroscopic changes in ACL correlated with cartilage degeneration, especially in the medial femoral condyle, compared to the other compartments of the knee joint. Within each compartment, all pairwise comparisons of normalized cartilage scores among the three ACL categories were statistically significant [at p<0.05 from the nonparametric Dwass-Steel-Critchlow-Fligner procedure], with the exceptions of abnormal vs. ruptured, in the trochlea, medial tibia, and lateral tibia. Values are the mean + SD. * = p<0.05.

Figure 3. Histological changes in ACL versus cartilage changes

The relationship of total ACL score versus cartilage scores in knee compartments was analyzed. ACL degeneration correlated with cartilage degeneration, especially in the medial compartments, compared to the lateral compartments of the knee joint.

Figure 4. Severity of ACL changes versus cartilage degeneration

There were no normal ACL in knees with Grade II, III and IV cartilage (mild, moderate and severe cartilage degeneration), while there were also degenerated ACL in Grade 0 and I (normal and minimal cartilage degeneration).

Figure 5. Aging-related prevalence of histopathological abnormalities in ACL

For each histological abnormality, the percentage per age decade of ACL that had scores indicating pathologic change was calculated. The earliest change and most prevalent change is collagen fiber disorganization. Calcium deposition is the latest and least prevalent change. A relatively high percentage of young donors already have mucoid degeneration, which does not increase with age. Inflammation, chondroid metaplasia, cystic changes and ligament sheath inflammation also increase with age.