gms | German Medical Science

Objectives: In TKA, the femoral component's prosthetic trochlear groove (PTG) is 6° lateral from vertical to approximate the quadriceps line of force (QLF). A PTG that medially deviates relative to the QLF does not coincide with the patient’s Q-angle.

Figure 1 [Fig. 1]

It is unknown whether a medial deviation is more frequent in kinematic alignment (KA) than mechanical alignment (MA) and whether KA patients with medial deviation have a lower Forgotten Joint Score (FJS) and Oxford Knee Score (OKS).

Methods: The study extracted 147 patients from a database with 4-year FJS and OKS, and a CT scanogram showing the pelvis and anterior inferior iliac spines, a limb with a KA TKA, and a native (i.e., healthy) opposite limb. MA of the femoral component was simulated on the limb opposite the KA TKA. Scanogram measurements determined the PTG-QLF angle.

Results: Eighty-six percent of the PTGs deviated medially after KA TKA, and 21%, 17%, and 8% after the simulation of MA TKA using reported mean and standard deviation values for manual, patient-specific, and robotic instrumentation. For the 126 KA TKAs with medial deviation, the median 83 and 46 points FJS and OKS were 17 and 1 point lower than those patients with lateral deviation (p < 0.0001, p = 0.0053).

Conclusion: In most patients with KA TKA and some with MA TKA, the 6° PTG is too narrow to coincide with the Q-angle. These findings suggest that the PTG of the flange on the femoral component should be redesigned with a broader angle than 6° and then clinically evaluated.