Review Question - QID 220057

The patient in Figure A presents with a varus deformity, whereas the patient in Figure B presents with a valgus deformity and evidence of lateral femoral condyle hypoplasia. In cases where a hypoplastic lateral femoral condyle exists, it is not uncommon to require an increased amount of external rotation of the femoral component relative to the posterior condylar axis (PCA) to achieve an appropriate cut with a balanced flexion gap and prevent postoperative patellofemoral maltracking (Answer 1).

Patellofemoral alignment is a critical consideration in total knee arthroplasty (TKA), particularly in valgus knee deformities with a hypoplastic lateral femoral condyle. Achieving proper alignment involves careful attention to the Q-angle, which is influenced by the positioning and rotation of the femoral, tibial, and patellar components. Surgeons must be especially cautious when using the PCA as a reference in these cases, as lateral femoral condyle hypoplasia can lead to inadvertent internal rotation of the femoral component, increasing the risk of patellar maltracking. Key factors in ensuring appropriate patellofemoral tracking include avoiding internal rotation of the femoral component, ensuring the tibial component is centered with appropriate rotation, and avoiding lateral placement of the patellar component. Typically, when appropriate external rotation of the femoral component is achieved, the posterior medial condyle resection should be thicker than the posterior lateral condyle resection. Proper patellofemoral alignment, with particular attention to the unique challenges posed by a hypoplastic lateral femoral condyle, is crucial for optimizing patient outcomes and minimizing the risk of complications in TKA.

Brooks reviewed the seven bone cuts involved in a typical TKA: distal, anterior, and posterior femur cuts, anterior and posterior chamfer cuts, tibia cuts, and patella cuts, emphasizing that each cut impacts the others and the overall outcome. They highlight the importance of the distal femoral cut for overall alignment and the anterior femoral cut for component rotation, which affects patellar tracking and gap balancing. Brooks concluded that surgeons should avoid ligamentous injury during these cuts, aim for a 3-degree posterior slope for the tibial cut with particular focus on tibial rotation, and ensure the patella cut is not too deep, with component placement tending medial and superior for optimal results.

Scott reviewed the methods for determining femoral and tibial component rotation in total knee arthroplasty (TKA) and their influence on knee kinematics and surgical outcomes. The author found that while at least four methods exist for determining femoral rotation and three for tibial rotation, each with its advocates and varying effects on flexion gap determination and patellofemoral tracking, there is a lack of consensus on the best method. The author concluded that achieving a rotationally congruent articulation during weight-bearing is crucial, and surgeons must be knowledgeable about the various methods and their potential impact on TKA outcomes.

Figure A demonstrates the AP, lateral, and “sunrise” radiographs of a patient with tricompartmental osteoarthritis and varus knee deformity. Figure B demonstrates the same radiographic views of a patient with tricompartmental osteoarthritis and valgus knee deformity, with suspicion of lateral femoral condyle hypoplasia.

Incorrect Answers:
Answer choice B: This choice is incorrect, as patients with valgus knee deformities typically require greater amounts of external, rather than internal, rotation of their femoral component. Furthermore, internal rotation of the femoral component would more likely have detrimental effects on patellofemoral tracking
Answer choice C: The trans-sulcus axis, also known as “Whiteside’s Line,” may be used as a reference for the determination of femoral component rotation. However, regardless of the reference line utilized intraoperatively, in cases of lateral femoral condyle hypoplasia with valgus deformity, more external, rather than internal, rotation of the femoral component relative to the PCA would be expected compared to a case with varus deformity.
Answer choices D and E: In cases of severe bone loss, augments may be required to achieve stable flexion and extension gaps while allowing for bone preservation in the knee's less worn areas. In the cases above, if posterior augments were to be required, it is most likely that patient “B” would require posterior lateral augments.