TDK conference 2018

In 1898, Hultkrantz had also shown a distinct orientation to the collagen fibers at the articular surface of cartilage and postulated that this structural preference was related to the directional variation in stiffness and strength characteristics of the tissue. This orientation of split lines in cartilage was thought to be similar to Langer’s lines, which are reflective of lines of tension in the skin. These findings would suggest that all cartilage surfaces have a unique orientation of stress lines, which are designed to resist the tensile forces that are generated on the joint surface during motion and weight bearing. In a previous study (Below et al., 2002) a "split line" method was developed, which has been successfully adapted to mapping the cartilage surface split-lines for several species. In dogs, Böttcher et al. described the collagen fiber network layout of the stifle joint (2009).

The aim of the present research was to map the collagen fibers in the top layer of the cartilage surface of the distal part of the femur using macroscopic and x-ray diagnostics, and thus provide new data for the biomechanical and structural knowledge of equine knee joints.

A total of 32 equine distal femur samples were examined. The medial and lateral femur condyles and the femur trochlea were evaluated. The quality of the hyalin cartilage was scanned macroscopically and the samples were scored based on the classification of ICRS (International Cartilage Regeneration&Joint Preservation Society). The surface lines were visualized using split-line method, and with digital camera (D3100, Nikon) pictures were taken from multiple views of the samples. The images were examined with special regard to collagen fibers. We also investigated the altered fiber orientation of the abnormal hyaline cartilage.

Another part of the research was the radiological examination of the preparations with digital X-ray equipment (Visiovet Medizintechnik) in latero-medial and caudo-cranial settings. The images were examined by three independent experts for signs of osteoarthritis.

Assessing the trochlear hyaline cartilage there were visible lesions in 6 cases (18,7%) in a total of 32 samples. 14 medial femoral condyles (43.8%) and 8 lateral femoral condyles (25%) showed some lesions. The collagen fiber orientation in the intact hyaline-covered areas showed similar pattern, especially in the central part of the medial femur condyle and the lateral and medial part of the trochlea, where collagen fibers are aligned in a uniformly transverse direction. Collagen fibers in the intertrochlear region tend to be longitudinal. At the presence of cartilage damage the orientation of collagen fibers is modified and occasionally becomes irregular.

A total of eight preparations showed osteoarthritis-like lesions (25%). Samples that showed cartilage surface degeneration in native examination significantly presented more osteoarthritis-like lesions radiologically (P <0.05).