Abstract
Introduction
As the population continues to grow and age, the incidence of revision total knee replacement (RTKR) is expected to rise significantly. Modularity within revision total knee systems is common, and recognition of modular junctions as an important source adverse local tissue reaction (ALTR) has not yet been fully described in the literature. In both hips and knees, ALTR may be caused by wear debris from articulating surfaces, stress shielding, and other classic areas of focus, but now attention is shifting towards the role of corrosion products from modular junctions. In severe cases, junctions can become welded together creating significant hurdles in revisions and potentially altered biomechanics in vivo. In view of these issues, the present study was undertaken: (i) to examine the level of damage observed in modular junctions of total knee prostheses obtained at revision, (ii) to correlate the severity of surface damage to the design and composition of the mating components, and (iii) to associate patient demographics and comorbidities with the spectrum of corrosion and fretting seen in retrieved implants.
Methods
117 TKR components from 76 patients were examined after retrieval from revision procedures performed at a single institution. Patient demographics and clinical data were compiled. The retrievals consisted of 57 femoral components and 60 tibial components from a diverse range of manufacturers. The implants were disassembled manually, or in a mechanical testing machine if cold welded, and separated into groups based on mating material type. Modular junctions were then examined using stereomicroscopy (Wild) at magnifications of X6 to X31. Upon inspection, damage on the male component was graded using modified Goldberg scales for corrosion and fretting (Table 1). Factors associated with trunnions having damage scores of 3 or higher were evaluated using standard statistical procedures to determine the susceptibility for corrosion of each junction type and location.
Results
Approximately two-thirds (64%) of trunnions had corrosion scores of 3 or higher. As seen in chart 1, junctions containing titanium alloys were the most susceptible to corrosion with the femoral component being the most prevalent. The most severe cases of corrosion (score of 5) were seen in mixed metal junctions in the femur (24%) and TiAlV/TiAlV junctions in the tibia (27%). Fretting was most frequently observed (73%) in tibial components with TiAlV/TiAlV junctions, over half of which were level 4. A disturbing finding was that 15% of modular junctions with a TiAlV component were cold welded and could only be disassembled using a mechanical testing machine. The femoral component tended to incur more severe levels of corrosion damage than that of the tibia for other material combinations.
Conclusions
In TKR, modular junctions formed by one or more TiAlV components are the most susceptible to corrosive attack and fretting. Moreover, the most severe corrosion and fretting cases (score of 5 or 4, respectively) were only seen in the presence of a TiAlV component.
