AUGUST 2022 | The Surgical Technologist | 353 Kostretzis et al. Kinematic Alignment Total Knee Revision TABLE 1 | Estimated angular correction given by apposing a tibial component with a unilateral augment to a uniformly flat bone surface. Tibia size # Tibia width (mm) Augment thickness (mm) Angular correction (degrees) 1 61 5 5.8 2 64 5 5.5 3 67 5 5.3 4 70 5 5.1 5 74 5 4.8 6 77 5 4.6 7 80 5 4.4 8 85 5 4.2 1 61 10 11.5 2 64 10 11.0 3 67 10 10.5 4 70 10 10.0 5 74 10 9.5 6 77 10 9.1 7 80 10 8.8 8 85 10 8.3 TABLE 2 | Estimated angular correction given by apposing a femoral component with a unilateral augment to a uniformly flat bone surface. Femur size # Femur width (mm) Augment thickness (mm) Angular correction (degrees) 1 59 5 5.8 2 62 5 5.5 3 65 5 5.3 4 68 5 5.1 5 71 5 4.8 6 74 5 4.6 7 77 5 4.5 8 80 5 4.3 1 59 10 11.5 2 62 10 11.0 3 65 10 10.5 4 68 10 10.0 5 71 10 9.6 6 74 10 9.2 7 77 10 8.9 8 80 10 8.5 1 59 15 17.0 2 62 15 16.2 3 65 15 15.5 4 68 15 14.9 5 71 15 14.2 6 74 15 13.7 7 77 15 13.2 8 80 15 12.7 Distal augments are available in 5, 10, and 15mm sizes. Posterior augments are available in 5 and 10mm sizes only. TABLE 3 | Encountered problems specific to mechanically aligned primary arthroplasties revised with the rKA protocol and their solution. Problem Diagnosis Plausible solution Coronal malalignment of the femoral component 1) AP standing long leg x-ray 2) Preoperative x-rays 3) Contralateral knee anatomy 1) Medial distal femoral augment to correct excessive varisation from native anatomy common in MA. 2) Lateral distal femoral augment to correct excessive valgisation from native anatomy Coronal malalignment of the tibial component 1) AP standing long leg x-ray 2) Preoperative x-rays 3) Contralateral knee anatomy 1) Lateral tibial augment to correct excessive valgisation from native anatomy common in MA 2) Medial tibial augment to correct excessive varisation from native anatomy. Femoral axial malalignment 1) CT-Scan of the TKA 1) Posterior medial femoral augment to correct systematic external rotation in MA 2) Posterior lateral augment to correct excessive internal rotation from native anatomy. Anterior overstuffing of the femoral component 1) Lateral x-ray of the knee 2) CT-Scan of the TKA 1) Medial and lateral posterior augments to posteriorize the femur 2) Larger medial femoral augment than lateral to correct excessive external rotation the mPTA when required while keeping the tibial slope neutral (Table 1). With trial implants in place, the collateral ligaments’ laxities in 10◦ of flexion are assessed to determine the polyethylene thickness and serve as an indicator for achieving a planned coronal alignment (goal is 1–2 mm of medial and 2–3 mm of lateral joint opening). Next, the medial and lateral flexion gaps are assessed (goal is 2–3 mm of medial and 3–4 mm of lateral joint opening). If present, hyperlaxity is addressed by increasing the femoral size, using posterior augments. In cases of significant mediolateral imbalances (>4 mm difference) or gross flexion instability with the larger femoral component compatible with the selected tibial size, a varus-valgus constrained liner (TS) was used. Such imbalances were present in cases with longstanding soft tissue changes: ligament stretching or contractures where complete capsulectomy and debridement was required to obtain satisfactory ROM. Lastly, the patella was left intact if well tracking or revised if resurfaced with malposition or under resection. RESULTS Indications for performing knee revision are presented in Table 4. All interventions included both femoral and tibial components revision, except for one case where only the femoral component was revised for aseptic loosening. Cemented stems were used for both the femur and tibia in 28 (65%) cases, for the femur alone in 13 (30%) cases, and no stems in two cases. The Frontiers in Surgery | www.frontiersin.org 5 August 2021 | Volume 8 | Article 721379
RkJQdWJsaXNoZXIy MTExMDc1