| The Surgical Technologist | AUGUST 2022 352 Kostretzis et al. Kinematic Alignment Total Knee Revision FIGURE 2 | The inverse tangent of the augment’s thickness over the implant’s width can be used to approximate the angular correction given by apposing the component with a unilateral augment to a uniformly flat bone surface. In a purely mathematical sense, the augment would first contact a flat surface at point A. However, from a practical point of view, because of the use of cement and partial impaction in cancellous bone, using point A to calculate the angular correction would overestimate the correction. Thus point B, in the middle of the augment, was assumed to be where a flat plane would intersect the augment. The length of the segment BC was subtracted from the width of the implant in the calculations. each femoral component size are provided in Table 2. Posterior augments were utilized in a similar fashion to achieve the desired rotational alignment for the femoral component. The resulting rotational angular corrections are the same as the coronal angular corrections for the distal femoral augments already described in Table 2. If less angular correction is required, the selected augment will be combined intra-operatively with a bone resection (1–3 mm). Table 3 summarizes common problems encountered with failed primary arthroplasties and how to address them during rKA revision. Surgical Technique to Apply rKA in the Revision Setting The rKA TKA revision aims to recreate the pre-arthritic native knee anatomy and soft tissues laxities. To confirm or optimize our preoperative plan, at surgical exposure, a careful knee examination is performed to assess soft tissues laxity, knee range of motion, and the position, orientation, and fixation of the implant. After removing the implant and bone loss assessment, we used a distal femoral cutting jig connected to an intramedullary rod kept loose in the metaphysis (not deeply inserted, to avoid a tight fit in the diaphysis). We performed the distal femoral refreshing cuts including the planned supplemental bone resection and/or metallic augments to modify the mDFA adjust the joint line level when required (Table 2). In practice, a 5-mm augment angulates the component by 5◦. When dealing with the smallest sizes, this angle would be closer to 6◦ and 4◦ with the largest components. Using an anterior referenced 4-in-1 femoral cutting block of the appropriate size, and positioned to correct any malrotation, we performed the anterior, chamfer, posterior, and posterior stabilized (PS) box cuts. Then, we performed the proximal tibial refreshing cuts using a cutting jig connected to an intramedullary rod kept loose in the metaphysis. Tibial cut orientation included the planned supplemental bone resection and/or metallic augments to modify Frontiers in Surgery | www.frontiersin.org 4 August 2021 | Volume 8 | Article 721379
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