The consequences of anterior femoral notching in total knee arthroplasty -A biomechanical study

Background: Notching of the anterior femoral cortex during total knee arthr oplasty has been implicated as a cause of subsequent periprosthetic supraco ndylar femoral fracture, However, other than observational clinical data, n o reliable association between these events has been established, to our kn owledge, The purpose of the present study was to investigate the biomechani cal effects of notching of the anterior femoral cortex. Methods: The femoral component of a total knee replacement was implanted in twelve matched pairs of human cadaveric femora; one specimen in each pair had preservation of the anterior femoral cortex, and the other had a full-t hickness cortical defect created just proximal to the anterior flange of th e femoral component, The pairs were then subjected to either bending or tor sional loading to failure, Both the fracture pattern and the quantitative l oad to failure were analyzed. Two matched pairs were excluded from the anal ysis because of inadvertent fracture during placement of the component. Results: Following the application of a bending load, femora with notching of the anterior femoral cortex sustained a short oblique fracture that orig inated at the cortical defect proximal to the femoral component and femora, without notching had a midshaft fracture. In contrast, notching of the ante rior femoral cortex had no effect on the fracture pattern that was observed after the application of a torsional load. The mean load to failure was si gnificantly reduced by notching in both testing modes, Notching decreased b ending strength from 11,813 to 9690 newtons (18 percent; p = 0.0034), and i t decreased torsional strength from 134.7 to 81.8 newton-meters (39.2 perce nt; p = 0.01). Conclusions: Biomechanical testing demonstrated that notching of the anteri or femoral cortex significantly lessens the load to failure following total knee arthroplasty and influences the subsequent fracture pattern. These ef fects are manifested in different ways under the two loading conditions: th e fracture pattern is altered under bending load, and there is a greater qu antitative decrease in load to failure with torsional loading. Clinical Relevance: Weakening of the femur by notching of the anterior cort ex after total knee arthroplasty may warrant alteration in the customary po stoperative regimen for these patients, Manipulation of a total knee replac ement,vith a notched anterior femoral cortex should probably be avoided.