Regional variations in human patellar trabecular architecture and the structure of the quadriceps enthesis: a cadaveric study.

We investigated whether there were regional differences in the quadriceps enthesis and the patella bone structure that could suggest unequal force transmission to the patella. Quadriceps tendon enthesis was removed by cutting the patellae transversally in the middle and the quadriceps tendon approximately 1 cm from the bone. Tissues were post-fixed, decalcified, dehydrated through and embedded in paraffin wax. Serial longitudinal sections were cut, mounted on glass slides at 1-mm intervals and slides were stained. Trabecular architecture was analysed from digital images taken from the histological slides, and regional differences at the enthesis in the thickness of the uncalcified fibrocartilage and the cortical zone of calcified tissue (calcified cartilage and lamellar bone) were evaluated. At the quadriceps enthesis, the thickness of the cortical zone of calcified tissue was significantly greater in the central part of the enthesis than medially and laterally. The trabeculae were thicker in the central and lateral parts compared with the medial region. Similarly, the zone of uncalcified fibrocartilage was thicker laterally and centrally than medially. Bone structure and the thickness of uncalcified fibrocartilage presented a similarity between the centre and the lateral parts; however, the medial side was different. We suggest that the mechanical stress at the proximal quadriceps tendon enthesis is higher laterally and centrally compared with medially. This could induce a lateral patellar translation, which is potentially a risk factor for knee osteoarthritis.