Background Osteoarthritis (OA) is the most common rheumatic disorder world-wide. The disease affects multiple structures inside the joint, including the articular cartilage, the calcified cartilage, and the subchondral bone. The calcified cartilage compartment plays a key-region role in the development or progression of OA. However the pathophysiology of OA is not yet fully understood (1). Especially a full characterization of the three-dimensional appearance of the calcified cartilage compartment in aging and in OA has not yet been performed.
Objectives The aim of the study was to compare volume and surface area of the calcified cartilage compartment in osteoarthritis and healthy human femoral heads.
Methods 20 human femoral heads were collected from 20 old OA patients upon a joint-replacement operation for end-stage OA. Moreover, a total of 25 femoral heads were collected from healthy young and old deceased individuals. The applied microscopic techniques were based on design-based stereology with systematic uniform random sampling, vertical sections and the Cavalieri’s estimator (2-3). The femoral head was rotated around a vertical axis and sawn into 7-mm-thick slices. Every slice was cut into two halves, embedded in methylmethacrylate, cut into 7-µm-thick slices, and stained with May-Grünwald Toluidine blue. Quantitative microscopic techniques were applied in order to quantify the volume and surface areas of both the entire femoral head and the calcified cartilage compartment in human femoral heads.
Results Both the volume and the surface area of the entire femoral head were significantly larger in the OA patients (volume 48.9 ± 12.1 cm3, surface area 51.7 ± 8.11 cm2) (p<0.05) than in the age-matched old individuals (volume 39.4 ± 13.1 cm3, surface area 40.7 ± 12.5 cm2). Furthermore, the volume of the calcified cartilage compartment was significantly larger in the OA patients (0.74 ± 0.29 cm3) than in the age-matched individuals (0.45 ± 0.17 cm3) (p<0.01), and the difference was significant even when correcting for the relatively larger femoral head in the OA patients. Both the upper and lower surface areas of the calcified cartilage were significantly larger in the OA patients (tidemark: 48.7 ± 10.4 cm2, cement line: 83.7 ± 24.8 cm2) than in the age-matched healthy individuals (tidemark: 40.3 ± 12.5 cm2, cement line: 61.7 ± 17.7 cm2) (p<0.05)
Conclusions The volume and surface areas of the calcified cartilage compartment in the human femoral head were significantly larger in the OA patients compared with age-matched normal individuals. These findings indicate that the calcified cartilage compartment may play a role in the pathophysiology of OA.
Oegema TR, Jr, Carpenter RJ, Hofmeister F, Thompson RC, Jr. The interaction of the zone of calcified cartilage and subchondral bone in osteoarthritis. Microsc Res Tech. 1997 May 15;37(4):324-32.
Baddeley AJ, Gundersen HJG, Cruz-Orive LM. Estimation of surface area from vertical sections. J Microsc. 1986 Jun;142(Pt 3):259-76.
Gundersen HJG, Jensen EB. The efficiency of systematic sampling in stereology and its prediction. J Microsc. 1987 Sep;147(Pt 3):229-63.
Disclosure of Interest None Declared