A computer model to simulate patellar biomechanics following total knee replacement: the effects of femoral component alignment.

OBJECTIVE: The objective of this study is to analyze the biomechanics of the patellar component following total knee replacement. More specifically we investigated the effect of displacing the femoral component of an Insall-Burstein II total knee replacement on the patellar tracking and patello-femoral contact pressures. DESIGN: We used a validated computer simulation of the knee joint to virtually insert the femoral component with the following four types of placements: (1) no misplacement, (2) 5 degrees of internal rotation, (3) 5 degrees of external rotation and (4) 5 degrees of flexion rotation. The patellar 3D tracking and patello-femoral contact pressures were computed for each femoral component placement as a function of knee flexion angle. BACKGROUND: Complications at the patello-femoral joint are the among most frequent following total knee replacement. RESULTS: Femoral component placement unevenly affected the associated patellar tracking: a 5 degrees internal rotation tilted and rotated the patella laterally by about 5 degrees throughout knee flexion. A 5 degrees external rotation of the femoral component had less effect on patellar tracking. A rotation of 5 degrees in flexion primarily caused patellar rotation (5-10 degrees lateral rotation). Femoral component malalignment had only minor effects on the peak pressure distributions at the patello-femoral interface. CONCLUSION:These results suggest that femoral component positioning primarily affects patellar tracking, with a possible threat for patellar subluxation under external rotation of the femoral component. RELEVANCE: Precise alignment of the prosthetic components is difficult to control during total knee replacement due to the lack of precise anatomical landmarks in the human knee joint. Consequently, the position of each prosthetic component may differ from the ideal one suggested by the manufacturer. Improper alignment of the prosthetic components during total knee replacement may lead to premature implant failure

Displacements of the tibial tuberosity. Effects of the surgical parameters.

A three-dimensional computer model is used, based on the finite element method, to investigate the effects of 1-, 1.5-, and 2-cm tibial tubercle elevations and of 0.5- and 1-cm medial displacements of the tuberosity, performed with different bone shingles. Patellar kinematics and patellofemoral interface peak pressure, between 45 degrees and 135 degrees of passive knee flexion, are compared for these different surgical parameters with those of a normal knee not surgically treated. The shingle lengths of 3, 5, 7, and 10 cm have little influence on the results. Augmenting tubercle medializations decrease the lateral peak pressure but result in an overpressure of the medial facet that is 154% of the normal peak value. With knee flexion between 45 degrees and 60 degrees, increasing tubercle elevations decreases later and medial peak pressures. With flexion of more than 60 degrees, increasing elevations decrease the lateral peak pressure, but they augment and even cause overpressure on the medial facet. An overpressure on the lateral facet also is seen in midrange knee flexion (75 degrees-90 degrees) for all tubercle elevation values. Increasing tubercle elevations and medializations appear to be the predominant parameters from a biomechanical point of view

Reflexology and bronchial asthma

AbstractMany asthma patients seek alternative or adjunctive therapies. One such modality is reflexology, whereby finger pressure is applied to certain parts of the body. The aim of the study was to examine the popular claim that reflexology treatment benefits bronchial asthma. Ten weeks of active or simulated (placebo) reflexology given by an experienced reflexologist, were compared in an otherwise blind, controlled trial of 20+20 outpatients with asthma.Objective lung function tests (peak flow morning and evening, and weekly spirometry at the clinic) did not change. Subjective scores (describing symptoms,β2 -inhalations and quality of life) and also bronchial sensitivity to histamine improved on both regimens, but no differences were found between groups receiving active or placebo reflexology. However, a trend in favour of reflexology became significant when a supplementary analysis of symptom diaries was carried out. It was accompanied by a significant pattern compatible with subconscious un-blinding, in that patients tended to guess which treatment they had been receiving.No evidence was found that reflexology has a specific effect on asthma beyond placebo influence