Mechanical Loosening of Total Knee Arthroplasty
In the process of evaluating possible risk factors for failure of total knee arthroplasty, multiple studies have attempted to identify patient characteristics that may predispose one to a poor result. During this process, a number of such characteristics
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Mechanical Loosening of Total Knee Arthroplasty Paul Lombardi, Alexander Miric, Thomas P. Sculco The Hospital for Special Surgery - New York
Patient Factors In the process of evaluating possible risk factors for failure of total knee arthroplasty, multiple studies have attempted to identify patient characteristics that may predispose one to a poor result. During this process, a number of such characteristics have been suggested to affect the outcome of total knee arthroplasty, and evidence has been presented to support and refute each one of these assertions. In general, these patient characteristics can be divided into two broad categories: a) those related to patient demand, and b) those related to the quality of the bone. Factors studied in regard to patient demand on the prosthesis include the patient's age, weight, and activity level. Factors studied in regard to the bone quality include the patient's primary diagnosis, medical condition, sex and degree of preoperative joint deformity. Patient Demands
Since failure at the bone/cement interface constitutes a large portion of mechanical failures after total knee arthroplasty, it stands to reason that increased stress at this interface may be associated with an increase in the rate of implant loosening . The activity level of the patient has been referred to by a number of authors as an important consideration prior to performing a total knee arthroplasty. However, difficulties with quantifying a specific patient's activity level have limited the amount of data collected with respect to the effect of this vari able on arthroplasty outcome. Consequently, there is little in the literature directly addressT. P. Sculco et al. (eds.), Knee Arthroplasty © Springer-Verlag/Wien 2001
ing this assertion. Mintz, et aI., after an arthroscopic evaluation of worn polyethylene components, noted the influence of activity level on wear rates . However, no evaluation of the patient's level of activity is mentioned. In fact, one study that attempted to correlate outcome with a preoperative ambulation rating failed to find any relation between the two. More often, age has been used as an indicator for level of activity. In a review of 32 knee arthroplasty revisions, Tsao, et al. cited decreased age as a significant predictor of an increased risk of failure. Although this view has been shared by others (l), it is not shared by all (4). Ahlberg and Lunden (6), for example, failed to find a link between age and risk of revision in their review of revised knee arthroplasties . While it would seem self-evident that younger patients would place higher demands on a prosthetic knee, in turn, leading to earlier failure, it is not clear that such a direct relationship exists. Since a patient's body weight is related to the joint reactive forces transmitted through the weight bearing joints, it has been studied as a possible factor in the failure of a knee arthroplasty. This factor is especially significant in light of the number of obese patients undergoing total knee arthroplasty. Bostman
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