KNEE Structured oralexamination question9: Malalignment of total knee replacement (TKR) components

EXAMINER: Have a look at this image. What can you see?

(Figure 3.8.)

CANDIDATE: This is a CT scan of the distal femur showing an axial view of the femoral component of TKR. There is a lot of metal artifact.

EXAMINER: Why do you think a CT scan was done for this patient?

CANDIDATE: CT scan can be performed following TKR to check for loosening or malalignment of the components.

EXAMINER: What do you think of the alignment of this femoral component?

CANDIDATE: The angle formed by the surgical transepicondylar axis and the posterior condylar axis show the femoral component is internally rotated.

EXAMINER: Good. What problems can arise from internal rotation of the femoral component?

CANDIDATE: Rotational alignment of the tibial and femoral component plays an important role in TKR. Once correct frontal alignment and proper soft tissue balancing have been achieved, the rotational placement of the components represents the ‘third dimension’ in knee TKR. Femoral component malposition has been implicated in patellofemoral

Figures 3.8 CT axial view of TKR.

maltracking following TKR, which is associated with anterior knee pain, subluxation, fracture, wear, and aseptic loosening. It has been suggested that rotating-platform mobile bearings compensate for malrotation between the tibial and femoral components and may, therefore, reduce any associated patellofemoral maltracking. Internal rotation of femoral component by resection of excessive amounts of posterior lateral femoral condyle or insufficient resection of the posterior medial femoral condyle moves the anterior femoral patellar groove portion of the femoral component medially, making it more difficult for a relatively laterally placed patella to be captured by the patellofemoral groove. In addition, internal rotation of the femoral component results in tight flexion gap on the medial side of the knee.

Nicoll D, Rowley DI. Internal rotational error of the tibial component is a major cause of pain after total knee replacement. J Bone Joint Surg Br 2010;92-B:1238–1244.