**2.4. Component selection**

During preoperating planning, the orthopedic surgeon selects the implant. The selection should be carried out based on the clinical evaluation and the radiological measurements, but the final decision should be taken during the operation and after the knee bone cuts and soft-tissue balancing. That is why valgus knee surgeons always have plane A and plane B in the prosthesis selection (constrained component, VVC or classical), especially in severe deformed knees.

Preferably, in proper restored soft-tissue balancing, a minimally constrained component can be implanted. Nevertheless, if significant deformity necessitates posterior cruciate ligament (PCL) sacrifice for soft-tissue balancing, the majority of surgeons agree that a more constrained posteriorly stabilized (PS) component must be used [6]. PS knee components provide some degree of posterior stabilization as well as protection against posteromedial, posterolateral, straight medial, or straight lateral translation, but it will not protect against residual medial laxity, which is one of the major considerations in achieving proper balance in VD knees [9, 10, 18].

The debated issue between posterior-stabilized (PS) and cruciate-retaining (CR) implants in VD is that the PCL is often contracted and it may limit the deformity correction [10, 21]. It is true that in specific cases, the deformity correction with an intact PCL may be difficult to be obtained, as the PCL is a secondary stabilizer [22, 23]. Above and beyond, the PS design is more stable than a CR one due to the post-cam mechanism, and the PS design allows greater lateralization of the femoral and tibial components that improves the patella tracking and minimizes the necessity performing a lateral retinacula release [1, 2]. For these reasons, in VD knees, some orthopedic surgeons prefer a contracted PCL with a PS design as simplest as to stabilize it by using a CR implant [6].

McAuley et al. also presented that CR implants could be used in a wide range of VD osteoarthritic knees and that survival is improved when the LCL and/or the popliteus tendon are preserved. Release of both the PCL and popliteus is one of the two factors that made revision resulting from wear, osteolysis, or instability more likely, whereas, release of both the LCL and popliteus increased the likelihood of revision by 19.9 times due to more mediolateral laxity [24].

A debated issue is the amount of constraint needed to balance a VD knee. Favorito et al. proposed that the surgeons should resist the temptation, if possible, of a more highly constrained prosthesis. Although a highly constrained component may be necessary in difficult revision cases, they are infrequently necessary for primary arthroplasties [6]. In severe VD knees, the problem is that the PCL may be stretched or elongated, which means nonfunctional and these knees require either an ultra-congruent (VVC or hinged) or PC component.

Additionally, in extremely deficient lateral femoral condyle valgus knees, the usage of component augmentation blocks may be required. That is because the lateral femoral condyle may have had little or no distal femoral bone resected or, similarly, little to no bone resected from the chamfer and posterior cuts; then component augmentation blocks may be required [4, 6]. Nevertheless, if press-fit femoral component is being performed, then as long as native bone is resting on the medial-posterior side of the chamfer cuts, then the remaining lateral defect can be filled with autograft bone taken from other cuts during the procedure [1, 6].
