No abstract

Wolff׳s Law suggests that the orientation of trabeculae in human bone changes in response to altered loading patterns. The aim of this study was to investigate trabecular orientation in both the femur and tibia and to compare this with the mechanical axis of the leg. The study involved analysis of radiographs from patients with osteoarthritis of the knee (n=91). For each patient, the trabecular orientation in both the distal femur and proximal tibia was measured from a standard anteroposterior radiograph of the knee and the mechanical axis of the leg was calculated from a long leg view taken while weight bearing. There was a significant correlation between the mechanical axis and the trabecular orientation in each of the regions considered in the femur (r=-0.41, -0.30, 0.52, and 0.23) and tibia (r=-0.27 and 0.31). Multiple regression analysis, with mechanical axis as the dependent variable, produced an R(2) of 0.62. Greater trabecular anisotropy (i.e. greater alignment) was observed in the medial femur and tibia compared to the lateral side (p<0.01). The results give an insight into the trabecular changes that may take place during development of osteoarthritis and following surgery. In particular, we propose that the orientation of the trabeculae in both the distal femur and proximal tibia will reflect the angle of mechanical loading through the knee.

No abstract

In the experience curve concept set forth by the National Aeronautics and Space Administration (NASA), production time falls by a set percentage every time cumulative production doubles. NASA has established benchmark figures for different manufacturing processes, and we have used these figures in analyzing our first 240 navigated total knee arthroplasties for varus knees. Our experience curve was 93% (P < .001), which is similar to the experience curve (90%) for processes consisting of 25% hand assembly and 75% machining. We suggest that the experience curve may provide a guide for comparing different surgical teams and navigation systems and for resource allocation.

There is currently a lack of a 'Gold Standard' for quantification and modelling of the Pivot Shift test (PST) in anterior cruciate ligament (ACL) deficient knees. A sudden change in state resulting from a small change in a parameter is characteristic of systems that can be modelled using catastrophe theory. Analysis of data obtained from 50 consecutive navigated ACL reconstructions demonstrated statistically significant (p &lt; 0.01) fitting with a cusp type model of catastrophic failure. Modelling the PST as a Cusp catastrophe may enable true evidence based decisions as to which ACL deficient knees should have surgery and guide the decisions as to the optimum type of surgery required. It may also influence the position of the reconstructed ligaments and allow objective comparisons of different ligament types and surgical techniques.