Postoperative full leg radiographs exhibit less residual coronal varus deformity compared to intraoperative measurements in robotic arm-assisted total knee arthroplasty with the MAKO™ system

Abstract

Purpose Robotic arm-assisted total knee arthroplasty (raTKA), currently a major trend in knee arthroplasty, aims to improve the accuracy of implant positioning and limb alignment. However, it is unclear whether and to what extent manual radiographic and navigation measurements with the MAKO™ system correlate. Nonetheless, a high agreement would be crucial to reliably achieve the desired limb alignment. Methods Thirty-six consecutive patients with osteoarthritis and a slight-to-moderate varus deformity undergoing raTKA were prospectively included in this study. Prior to surgery and at follow-up, a full leg radiograph (FLR) under weight-bearing conditions was performed. In addition, a computed tomography (CT) scan was conducted for preoperative planning. The hip–knee–ankle angle (HKA), mechanical lateral distal femur angle (mLDFA), mechanical medial proximal tibial angle (mMPTA) and joint line convergence angle (JLCA) were measured in the preoperative and follow-up FLR as well as in the CT scout (without weight-bearing) by three independent raters. Furthermore, the HKA was intraoperatively assessed with the MAKO™ system before and after raTKA. Results Significantly higher HKA values were identified for intraoperative deformity assessment using the MAKO system compared to the preoperative FLR and CT scouts (p = 0.006; p = 0.05). Intraoperative assessment of the HKA with final implants showed a mean residual varus deformity of 3.2° ± 1.9°, whereas a significantly lower residual varus deformity of 1.4° ± 1.9° was identified in the postoperative FLR (p < 0.001). The mMPTA was significantly higher in the preoperative FLR than in the CT scouts (p < 0.001). Intraoperatively, the mMPTA was adjusted to a mean of 87.5° ± 0.9° with final implants, while significantly higher values were measured in postoperative FLRs (p < 0.001). Concerning the mLDFA, no significant differences could be identified. Conclusion The clinical importance of this study lies in the finding that there is a difference between residual varus deformity measured intraoperatively with the MAKO™ system and those measured in postoperative FLRs. This has implications for preoperative planning as well as intraoperative fine-tuning of the implant position during raTKA to avoid overcorrection of knees with slight-to-moderate varus osteoarthritis. Level of evidence Level IV.

Discrepancies in Coronal Alignment Measurements between Full-length Weight-bearing Radiographs and Computed Tomography in Robotic Arm-assisted Total Knee Arthroplasty with the Mako System

“…These ndings are consistent with our results. Glowalla et al studied differences in the knee alignment determined between postoperative FLWBR and CT measurements and found less varus positioning of the tibial component on postoperative FLWBR than on intraoperative measurements made with the Mako system 19 . They suggested that careful preoperative planning and ne-tuned adjustments of the component position in robotic armassisted TKA are necessary to prevent excessive overcorrection in varus knee osteoarthritis.…”

“…The discrepancy in determining the MA as well as the weight-bearing condition between preoperative FLWBR and CT to assess knee joint alignment may result in a mismatch in coronal alignment between the intraoperative values and postoperative results 15,17,18 . Glowalla et al have recently reported that there was a discrepancy between the residual varus deformity assessed intraoperatively with the Mako system and that evaluated with postoperative FLWBR 19 . They recommended careful preoperative planning in robotic arm-assisted TKA to prevent excessive overcorrection in varus knee osteoarthritis.…”

High degree of alignment precision associated with total knee arthroplasty performed using a surgical robot or handheld navigation

“…Although the ability to precisely cut the distal femur and proximal tibia is an important aspect of TKA technique, this study does not evaluate other intraoperative variables such as component rotation, component sizing, and joint line restoration. Particularly for robotic‐assisted TKAs, it is important to note that small differences may occur between measurements obtained from the robotic platform and those obtained from postoperative radiographs [8]. Patient outcomes were outside of the scope of this study and not evaluated.…”

Robotic‐arm assisted total knee arthroplasty is associated with comparable functional outcomes but improved forgotten joint scores compared with conventional manual total knee arthroplasty at five‐year follow‐up

“…Recently, Glowalla et al reviewed radiological outcomes in 36 patients undergoing RO TKA and reported a statistically significant difference in residual deformity as measured with the intraoperative robotic system of 3.2° ± 1.9° and postoperative full leg radiographs of 1.4° ± 1.9°. [16] However, the clinical significance of these radiological differences remains unknown and intraoperative images were taken in the supine position while postoperative full leg radiographs were taken in the standing position.…”