Aseptic loosening and other wear-related complications are one of the most frequent late reasons for revision of total knee arthroplasty (TKA). Periprosthetic osteolysis (PPOL) predates aseptic loosening in many cases indicating the clinical significance of this pathogenic mechanism. A variety of implant-, surgery-, and host-related factors have been delineated to explain the development of PPOL. These factors influence the development of PPOL due to changes in mechanical stresses within the vicinity of the prosthetic device, excessive wear of the polyethylene liner, and joint fluid pressure and flow acting on the peri-implant bone. The process of aseptic loosening is initially governed by factors such as implant/limb alignment, device fixation quality, and muscle coordination/strength. Later large numbers of wear particles detached from TKAs trigger and perpetuate particle disease, as highlighted by progressive growth of inflammatory/granulomatous tissue around the joint cavity. An increased accumulation of osteoclasts at the bone-implant interface, an impairment of osteoblast function, mechanical stresses, and an increased production of joint fluid contribute to bone resorption and subsequent loosening of the implant. In addition, hypersensitivity and adverse reactions to metal debris may contribute to aseptic TKA failure but should be determined more precisely. Patient activity level appears to be the most important factor when the long-term development of PPOL is considered. Surgical technique, implant design, and material factors are the most important preventative factors because they influence both the generation of wear debris and excessive mechanical stresses. New generations of bearing surfaces and designs for TKA should carefully address these important issues in extensive preclinical studies. Currently, there is little evidence that PPOL can be prevented with pharmacological interventions.

Objective. To compare the knee joint loading patterns in individuals with differing radiographic grades of knee osteoarthritis (OA) for characterization of the mechanical implications of different structural states, and to compare the knee adduction angular impulse, a measure of gait complementary to the commonly used peak knee adduction moment.Methods. Asymptomatic subjects (those without knee OA) having a Kellgren/Lawrence (K/L) radiographic severity grade of 0 or 1 (n ‫؍‬ 28) and subjects with symptomatic knee OA having K/L grades of 2 (n ‫؍‬ 66) or 3 (n ‫؍‬ 23) were recruited. Gait analysis was used to calculate the peak external knee adduction moment and the external knee adduction angular impulse for the whole stance and for the 4 subdivisions of stance.Results. Both the peak knee adduction moment and the knee adduction angular impulse increased with K/L radiographic grade (P < 0.05). However, only the knee adduction angular impulse differed between subjects with moderate (grade 3) and those with mild (grade 2) radiographic knee OA (P < 0.05).Conclusion. The differences between mild and moderate symptomatic radiographic knee OA are not only structural but also functional, based on the magnitude of load in the medial knee joint. Moreover, knee adduction angular impulse provides additional information beyond that available from the peak knee adduction moment, and may therefore be an important gait parameter to include in OA research. These findings are important for our understanding of the pathophysiologic mechanisms of OA.The peak external joint moments determined by gait analysis are surrogate markers of the effects of contact load on an individual's joints. In particular, in the knee, the external adduction moment is the primary predictor of load distribution across the tibial plateau (1) and is a main determinant of clinical outcomes following surgical intervention to correct varus deformity (2). Individuals with symptomatic radiographic knee osteoarthritis (OA) have higher-than-normal peak external knee adduction moments during walking (3-8).The peak external knee adduction moment has been implicated in progression of radiographic OA (9) and has been identified as a marker of disease severity (8,10), when individuals with OA radiographic severity grades Յ2 are compared with those with grades Ն3, using the Kellgren and Lawrence (K/L) scale (11). In addition, when the first and second peak external knee adduction moments, occurring during midstance and terminal stance, respectively, were compared in healthy controls and in individuals with less or more severe OA, the first peak was higher than normal regardless of disease severity, whereas the second peak was higher than normal only in those with more severe OA (8).As a measure of knee load, the peak external knee adduction moment reflects only a single time point during stance and is independent of the duration of the stance phase of gait. Because individuals with OA ambulate at slower speeds (3) and exhibit a prolonged stance phase as compared with hea...

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Arthritis is a leading cause of disability, and when nonoperative methods have failed, a prosthetic implant is a cost-effective and clinically successful treatment. Metal-on-metal replacements are an attractive implant technology, a lower-wear alternative to metal-on-polyethylene devices. Relatively little is known about how sliding occurs in these implants, except that proteins play a critical role and that there is a tribological layer on the metal surface. We report evidence for graphitic material in the tribological layer in metal-on-metal hip replacements retrieved from patients. As graphite is a solid lubricant, its presence helps to explain why these components exhibit low wear and suggests methods of improving their performance; simultaneously, this raises the issue of the physiological effects of graphitic wear debris.

Objective. The relationship between knee pain and radiographic evidence of knee osteoarthritis (OA) is notoriously imperfect. In particular, conditions that distinguish individuals with symptoms from those with comparable radiographic involvement who remain asymptomatic are unclear. We investigated dynamic loading across the knee in individuals with mild radiographic OA who were distinguished by the presence or absence of knee pain. Methods. Subjects were recruited into 3 groups: symptomatic with a Kellgren/Lawrence (K/L) grade of 2 (n ‫؍‬ 52), asymptomatic with a K/L grade of 2 (n ‫؍‬ 19), and asymptomatic with a K/L grade of 0 or 1 (n ‫؍‬ 37), the latter representing a normal comparator group. Dynamic knee loading was assessed with gait analysis, and both the peak external knee adduction moment and the knee adduction angular impulse were determined. Results. Peak knee adduction moment and knee adduction angular impulse were 19% and 30% higher, respectively, in symptomatic K/L grade 2 individuals than in asymptomatic individuals with the same radiographic grade (P < 0.05). Conversely, the asymptomatic K/L grade 2 group did not differ from the K/L grade 0 -1 normal comparator group (P ‫؍‬ 1.00). Conclusion. Among individuals with mild radiographic knee OA (K/L grade 2), those who are symptomatic have significantly higher medial compartment loads than those who are asymptomatic, whereas those who are asymptomatic do not differ from normal controls (asymptomatic K/L grade 0 or 1). These findings suggest a biomechanical component to the distinction between asymptomatic and symptomatic radiographic OA, which may be pathophysiologically important.