Navigated total knee arthroplasty with the fluoroscopic medtronic system

Abstract

Total knee arthroplasty has become a predictable and reliable surgical procedure. Correct positioning of the components is a key factor in this success. Component mal-position can cause pain [14], limited range of motion [6], instability [22], polyethylene wear and loosening of the implant [11, 30]. In the earlier days of total knee arthroplasty, much attention was given to the correction of limb alignment as the detrimental effects of remaining mal-alignment were obvious and well documented, both clinically [1, 2, 11, 13, 16, 22- 24, 28, 33, 37] and bio-mechanically [3, 12, 15]. With the improvement in surgical training and better instrumentation systems, correct positioning of the components evolved to a routine procedure. Over the last decade, alignment issues received less attention in the orthopaedic literature, but remains a threat to the patient undergoing TKA. A round table and multi-centre evaluation of the French orthopedic community concluded that 31% of the patients with major pre-operative coronal mal-alignment displayed a deviation of the mechanical axis of more than 5° post-operatively.[7] Jeffery et al. [17] noted good post-operative coronal alignment (mechanical axis deviation of less than 3°) in 2/3 of their total knee arthroplasties. In 1/3 of the operated knees, mechanical axis deviation in the coronal plane was found. These knees had a mechanical loosening rate of 24% at eight years, as opposed to 3% mechanical loosening for normally aligned knees.Both image-less and image-based systems have been evaluated and results of prospective randomized trials showed better coronal and sagittal alignment for the patients operated with CAS than for patients operated with conventional instruments [5, 9, 31, 36] With the help of a fluoroscopy based CAS system we assessed two variables. We checked the accuracy of the calculation of the kinematic centre of rotation of the hip and compared the outcome between the patients that underwent TKA with and without image based computer assistance [36].Sharkey et al. [30] showed recently that mal-alignment and mal-position of components still play a significant role in the failure mechanism of modern knee prostheses. A new factor was recently introduced. Increasing interest in minimally invasive surgery (MIS) dramatically reduced the surgical exposure. Surgeons undergo pressure from peers, industry and patients to follow this new trend [8]. The reduction of the surgical exposure limits the ability of the surgeon to find the usual anatomic landmarks that are used for component positioning. Also, as the soft tissues are less spread, positioning and fixation of the cutting blocks can be tedious. It is clear that MIS carries the risk of increased surgical error, even in the hands of experienced surgeons. Computer assisted surgery was developed before the big wave of MIS hit the orthopaedic community. Two mainstream technologies prevailed: image-less CAS and imagebased CAS, the latter being most often combined with fluoroscopy in total knee surgery. The typical characteristic of image based CAS is that the system can create the spatial link between the image and the anatomical landmarks, the defined virtual points, planes and axes. This extra information under the form of a fluoroscopic image allows the surgeon to double check the information relating to the important reference planes and axes. However, these systems do have a significant disadvantage. The image intensifier is an alien tool in total knee arthroplasty. It is bulky, needs draping and poses a potential risk for microbiological contamination. It also increases surgical time and carries a potential radiation hazard. The image-less systems do not have these disadvantages: they are cheaper, easier to use, less bulky, and create no radiation hazard. © 2007 Springer Medizin Verlag Heidelberg.