Does increased femoral component size options reduce anterior femoral notching in total knee replacement?

Total knee arthroplasty (TKA) is currently the best option for management of advanced knee arthritis for patients who have exhausted conservative management. There have been significant implant design improvements and this is a continuing process to help the surgeon replicate patient anatomy and kinematics. Amongst the many variables in implantation to achieve a well-functioning TKA, getting optimal femoral component sizing is one. Every implant system has certain discreet implant sizes and the surgeon has to strive to obtain the best fit possible for the patient and attain a well aligned and stable TKA. The aim of this study was to assess the frequency of various femoral component sizes being implanted with a system which has 2.5 mm antero-posterior increment between sizes, and to assess the incidence of anterior femoral notching when using a posterior referencing system.

A retrospective analysis of 739 TKAs implanted in 532 patients between January 2013 and January 2016 at a single center using a single posterior stabilized implant system was done. Patient demographics and femur component size used was obtained from hospital patient records. Immediate post-operative radiographs were analyzed to look for anterior femoral notching and presence of this was classified according to Tayside classification. A telephonic follow up at minimum 2 tears post-surgery was done to interview for occurrence of supracondylar femur fracture or revision for any other causes.

There were 207 bilateral and 325 unilateral TKAs performed in 532 patients during the study period. There were 245 males and 287 females with an average age of 61.3 years (43-81 years, SD = 7.2). The most commonly used femoral component was 60 mm and an intermediate size prosthesis was used in 43.11% patients. The incidence of femoral notching ranged from 0 to 6.3%. No patient had sustained a supracondylar condylar fracture at minimum 2 years follow up.

The availability of a larger number of femoral components in a TKA system allows the surgeon the modularity to choose and obtain the best fit possible. Restoration of posterior condylar offset, preventing anterior notching, medio-lateral overhang and patellofemoral joint stuffing are greatly dependent on correct femoral component sizing. The findings from our study underscore the need to use an implant system with as many femoral size options as possible with lesser increments in between sizes to minimize anterior femoral notching when using a posterior referencing technique.