Abstract
Introduction
Complications related to the patellofemoral joint continue to be a substantial source of patient morbidity, causing anterior knee pain, instability, and dysfunction following total knee arthroplasty. One of the principle factors affecting patellofemoral outcomes may be trochlear design. The optimal design is currently unknown. The purpose of the present study was to study patellofemoral joint contact by analysing areas of wear in retrieved femoral components of three modern designs.
Materials and Methods
Eighteen retrieved femoral components featuring three different designs (constant radius of rotation, multiple radii of rotation, and multiple radii of rotation with built-in external rotation design) were matched on the basis of time-in-vivo, age, BMI and gender. All implants were cobalt chrome, posterior stabilized, cemented components with fixed bearing design with a resurfaced patella. Trochlear wear and surface damage were assessed using visual inspection, low-magnification light microscopy, and light profilometry.
Results
Six implants from each group were successfully matched and were used for the topographical analysis. The femoral components were closely matched on the basis of time-in-vivo (TIV) (2.4 years±1.2), age (71.6 years±11.3), and BMI (33.0 kg/m2±7.0). There were 9 males and 9 females in the sample. Infection was the most common reason for revision (n=14) followed by instability (n=3) and loosening (n=1). There were no significant differences in TIV, age, and BMI between the groups (p=0.366, p=0.829, and p=0.586, respectively). When compared with unused, reference components, both the retrieved constant radius implants (p<0.05) and multiple radii implants (p<0.05) were significantly rougher than the new components. The retrieved components with multiple radii and built-in external rotation were not substantially rougher than the reference component (p>0.05). Visual inspection of the femoral components showed evidence of damage in all implant types. Modes of damage included scratches, striation, pitting, and delamination. No significant differences between the groups were found with respect to overall damage and wear on visual inspection (p=0.480). However, light profilometry analysis showed significantly increased roughness of multiple radii components compared to constant radius or multiple radii components with built-in external rotation (p<0.05). This was particularly significant in the proximal middle (p=0.045) and medial zones of the trochlea (p=0.017).
Conclusions
All retrieved femoral components show evidence of damage in the trochlear area. While retrieved constant radius and multiple radii components showed increased wear compared to new components, retrieved components with multiple radii and built-in external rotation did not differ significantly from their new state. Retrieved multiple radii components appeared to have increased roughness compared with constant radius or multiple radii with built-in external rotation, particularly in the proximal zones of the trochlea. The long term effects of increased trochlear roughness requires further investigation and correlation with clinical outcomes. As the volume and patient demands for total knee arthroplasty increase, a greater understanding of the effect of trochlear design on clinical outcomes is warranted.
