In a prospective randomised clinical study acetabular components were implanted either freehand (n = 30) or using CT-based (n = 30) or imageless navigation (n = 30). The position of the component was determined post-operatively on CT scans of the pelvis.

Following conventional freehand placement of the acetabular component, only 14 of the 30 were within the safe zone as defined by Lewinnek et al (40° inclination sd 10°; 15° anteversion sd 10°). After computer-assisted navigation 25 of 30 acetabular components (CT-based) and 28 of 30 components (imageless) were positioned within this limit (overall p < 0.001). No significant differences were observed between CT-based and imageless navigation (p = 0.23); both showed a significant reduction in variation of the position of the acetabular component compared with conventional freehand arthroplasty (p < 0.001). The duration of the operation was increased by eight minutes with imageless and by 17 minutes with CT-based navigation.

Imageless navigation proved as reliable as that using CT in positioning the acetabular component.

Aim: To determine the pattern of gene expression induced in cultured human chondrocytes in response to compressive mechanical loads.

Methods: Chondrocytes were obtained from tissue discarded at the time of a number of total knee replacements and where established in primary cell culture. The cultured chondrocytes were then subjected to compressive and tensile loads using a Flexcell machine. The RNA was subsequently extracted from these chondrocytes and the alterations in gene expression determined using the Affymetrix Gene Array machine.

Results: Intended as an in vitro model for Osteoarthritis, it was found that mechanical stimulation of human chondrocytes caused a significant alteration in the expression of a number of classes of compounds. These included enzymes, inflammatory mediators and structural proteins.

Conclusions: This study identified several interesting candidate genes whose expression was significantly altered after being exposed to a laboratory model for osteoarthrosis. Further study of these genes and their expression may lead to important clinical applications.