Biomechanical analysis of fixed bearing and mobile bearing total knee prostheses

Urwin, Samuel (2014) Biomechanical analysis of fixed bearing and mobile bearing total knee prostheses. Doctoral thesis, Northumbria University.

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Abstract

In total knee replacement (TKR) surgery, mobile bearing (MB) total knee prostheses were designed to more closely mimic the function of the normal knee than traditional fixed bearing (FB) designs by allowing axial mobility between the polyethylene insert and tibial tray. Despite the hypothetical benefits of the MB design, few studies have objectively analysed knee biomechanics during activities of daily living (ADLs) in the laboratory compared to FB designs. This thesis aimed to substantiate the theoretical advantages of MB implantation during ADLs in the laboratory as well as during free living conditions, in addition to investigating previous claims of instability in MB knees. Sixteen patients undergoing primary unilateral total knee replacement (TKR) surgery were randomised to receive either a FB (n=8) or MB (n=8) total knee prosthesis and were tested at pre-surgery, three months post-surgery, and nine months post-surgery using three dimensional motion analysis in the laboratory and electrogoniometry and accelerometry during free living conditions. No differences were found between FB and MB groups during walking at post-surgery that could not be explained by differences at pre-surgery. There were also no differences between FB and MB groups during the more biomechanically demanding activities of stair negotiation and sit to stand and stand to sit activities, as well as no differences during free living conditions away from the laboratory. There appears to be no evidence based rationale for the widespread use of MBs with regards to optimising knee function during ADLs. This thesis was the first to compare FB and MB designs using the same implant range, posterior cruciate ligament (PCL) scenario, posterior stabilising strategy, and patella strategy over a range of ADLs, as well as being the first to combine testing in the laboratory with testing during free living conditions away from the laboratory.

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