Relationship of Retropatellar Knee Cartilage and Subchondral Patellar Bone During the Course of Osteoarthritis

Background. Rotational and shearing forces/stress as well as varying relationships between subchondral bone and retropatellar cartilage result in specific dysregulated bone remodeling of this joint section. Material and methods. Using immunohistochemistry and real-time polymerase chain reaction (RT-PCR) human retropatellar cartilage was investigated for expression of key molecules of the extracellular matrix and cartilage composition. Results were correlated with 3D microcomputed tomography of underlying subchondral bone. 129 serial medial and lateral patella facet samples of patients undergoing implantation of total knee endoprosthesis of areas showing mild (Group A, ICRS 1b) respectively advanced (Group B, ICRS 3a/3b) (43 each) osteoarthritis according to the histological-histochemical grading system (HHGS) were compared with 23 healthy biopsies. Results. Periarticular subchondral bone analysis of OA samples showed sclerosis, altered trabecular structures and inflammatory-like infiltration. A decrease of trabecular number but increase of the bone volume fraction was observed in group B accompanied by subchondral bone resorption pits and enchondral ossification. Greater differences were found within the first mm of subchondral bone. Trabecular Thickness grew slightly in group A to increase most pronounced at the medial facet in group B representing cartilage graded ICRS 3a/3b (HHGS 11.7 points). The medial patella site in group B showed the highest increase in the ratio between expression values for the genes Col1A1 and the reference gene. The medial facet presented higher amounts and increased magnitude of variance in facet shape and size. Conclusions. 1. Comparable OA prevalence on the medial compared to the lateral patellar facet was shown. 2. Cartilage degeneration severity is correlated with bone volume fraction (BV/TV). 3. In total knee arthropla - sty and TKA revision surgery subchondral bone adressing techniques such as micro-fracturing and Bone-Grafting should be considered in non-resurfacing techniques. 4. Reconstructive techniques such as Matrix-induced ACI (MACI) or Osteochondral autograft transplantation must address state of subchondral patellar bone.