A biomechanical modelof the arthrosis of the hip joint - biomed 2011

The hip joint has been investigated in depth, but causes of algic (pain) phenomena, especially those apparently located at the knee (referred pain), still remain unclear. Using a bi-dimensional multi-body model we investigated the effect of arthrosis on the kinematic of the hip joint and its relationship to pain. The bone was modeled as a rigid structure whereas the capsule and cartilage were assumed to be deformable. The effects of arthrosis were simulated as reduction of the thickness of the deformable tissues and increased friction. The extension velocity of the rectus femori and the trajectory of the instantaneous center of rotation (ICR) were examined for both physiological conditions and advanced degrees of arthrosis.In physiological conditions, results show that the extension velocity of the muscle has slight irregularities but is nevertheless continuous. The presence of arthrosis leads to a localized increase in friction and the model shows a migration of the location of the ICR toward the acetabulum. Changes in the ICR due to irregular surface friction, cartilage erosion as well as lack of synovial fluid, which in normal conditions ensures boundary film lubrication, induce discontinuities in the extension velocity of the muscle which are detected by the proprioceptive system (e.g. Golgi tendon organ) generating algic phenomena.The results of the model confirmed these findings and how hip arthrosis, in producing changes in the extension velocity of the muscle and in the kinematic of the movement, results in muscle and tendon pain around the knee.