radiographs revealed a tibiofemoral angle at 7° of valgus (Figure 5A) and that the mechanical axis of the right lower extremity was passing through the center of the knee (Figure 5B). Figure 3. A 14-mm custom-made angled polyethylene insert with an 8-mm lateral buildup similar to the 16-mm insert used in our case.
TKA may require additional techniques for exposure, the addition of augments for implants, and increased levels of implant constraint.11 Studies of isolated polyethylene exchange, however, have described low complication rates; minimal loss of motion; failure rates between 9% and 29%, principally for aseptic loosening; technically easier procedures compared with component revisions; and shorter operating times.5,6,13-15 However, the main indication for isolated polyethylene exchange in most of these studies, unlike our case, was osteolysis rather than malalignment or instability, which contributes to the elevated rates of aseptic loosening.
Figure 4. Radiographs of the right knee obtained at the time of revision surgery show well-fixed tibial and femoral components. (A) An anteroposterior view. (B) A lateral view.
Discussion As little as 5° of valgus has been shown to increase strain in the medial collateral ligament to levels approaching the failure limit, with maximum strain occurring at 60° of flexion.8 Higher failure rates have been associated in valgus alignment greater than 7.4° compared with neutral alignment (failure rates, 1.4% vs 0.6%).4 Additionally, valgus malalignment after TKA can result in higher strain in the tibia (which may predispose patients to aseptic loosening) than either neutral or varus malalignment because the lateral compartment contains less stiff cancellous bone than the medial compartment.9 Valgus malalignment may also contribute to altered patellofemoral mechanics, including patellofemoral instability, possibly leading to anterior knee pain.10 Both coronal varus and valgus malalignment have been shown to result in chronic instability, particularly in full extension of the knee.2 The risks of revision TKA include infection, stiffness, bone loss, neurovascular complications, and damage to the extensor mechanism.11,12 Postoperative pain, recovery, and rehabilitation may be problematic.5 Moreover, revision
Figure 5. Postoperative standing hip-to-ankle radiographs show correction of malalignment. (A) Improvement in the tibiofemoral angle to 7° of valgus. (B) The mechanical axis that passes through the center of the right knee joint comparable to the left knee joint.
Although Shaw and Murray16 first reported the use of angled inserts to correct deformity in 1978, little information on custom-made angled polyethylene inserts is available. In a study by Sah et al,17 angled polyethylene insert exchange was used to treat excessive posterior slope, with excellent outcomes. Subsequently, Sah et al6 used angled polyethylene insert exchange in nine patients with coronal plane deformities caused by tibial component malposition, with similar excellent results. These findings are encouraging, but data on the longevity of these implants, extent of correction, and complications remain limited. Although the importance of coronal alignment after TKA is well described, revision TKA to correct valgus
Case Report
55