Navigated, gap-balanced, adjusted mechanical alignment achieves alignment and balancing goals in a very high percentage but with partially non-anatomical resections

Abstract

Purpose Navigated, gap-balanced adjusted mechanical alignment (AMA) including a 0° varus tibial cut and modiication of angles and resections of the femoral cuts to obtain optimal balance accepting minor axis deviations. Objectives of this study were (1) to analyse to what extent AMA achieves the goals for leg alignment and gap balance, and ( 2) in what percentage non-anatomical cuts are needed to achieve these goals. Methods Out of 1000 total knee arthroplasties (TKA) all varus knees (hip-knee-ankle (HKA) angle < 178°; n = 680) were included. All surgeries were performed as computer assisted surgery (CAS) in AMA technique. CAS data at the end of surgery were analysed with respect to HKA and gap-sizes. All bone cuts were quantiied. Depending on the amount of deformity, a subgroup analysis was performed. It was analysed whether the amount of deformity inluences the non-anatomical cuts by correlation analysis. Results AMA reached the goals for postoperative HKA (3° corridor) in 636 cases (93.5%). While extension and lexion gap balance were achieved in more than 653 cases (96%), lexion and extension gap size were equalled in 615 knees (90.4%). The resections of the lateral tibia plateau and distal and posterior medial femoral condyle were anatomical (Tibia: 7.0 ± 1.7 mm; medial condyle distal: 7.8 ± 1.4 mm; medial posterior: 8.2 ± 1.8 mm). The number of non-anatomical resections for those cuts were low; 67 (9.9%); 24 (3.5%); 32 (4.7%). For the medial tibia plateau and the lateral posterior condyle, the cuts were non-anatomical in a high percentage of cases; Tibia: 606 (89.1%), lateral posterior condyle: 398 (58.5%). Moderate but signiicant correlations were found between resection diferences and amount of deformity (medio-lateral: tibia: 0.399; distal femur: 0.310; posterior femur: 0.167). No correlations were found between resection diferences and gap values. Conclusion AMA reaches the intended target for HKA and gap balance in over 612 (90%) of cases and maintains the medial femoral condyle anatomically. Non-anatomical tibial resection causes increased external rotation of the femoral component and by that non-anatomical cut of the posterior lateral condyle. Nonanatomical resections of AMA might be one reason for the persisting high rate of unsatisied patients after TKA. Anatomical and individual alignment philosophies might help to reduce this rate of dissatisfaction.

Functional alignment achieves a more balanced total knee arthroplasty than either mechanical alignment or kinematic alignment prior to soft tissue releases

“…A surgeon’s ability to assess a balanced TKA is poor [ 7 , 16 ], even by experienced surgeons [ 18 ]. A balanced knee has previously been defined as a gap differential of ≤ 2 mm [ 8 ].…”

Alignment analysis of Brainlab knee 3 navigation-guided total knee arthroplasty using the adjusted mechanical method

“…In the ideal condition of the lower limb's mechanical alignment, LDFA and MPTA are both 90°. Considering the constitutional varus of the knee joint at 3° in most people, a slight varus MPTA between 87° and 88° was shown to be more physiologic ( 3 ). In our study, there was no statistically significant difference between postoperative LDFA and preoperational LDFA, while there was a statistically significant difference between postoperative MPTA and preoperational MPTA.…”

“…In recent years, with the rapid development of artificial intelligence, computer navigation technology has been applied in TKA to improve the accuracy of prosthesis positions. Compared with traditional manual surgery, it significantly improves the lower limb alignment, reduces the wear and loosening rate of the prosthesis, increases the prosthesis survival rate, and accelerates the postoperative rehabilitation process (2)(3)(4).…”

Verasense sensor-assisted total knee arthroplasty showed no difference in range of motion, reoperation rate or functional outcomes when compared to manually balanced total knee arthroplasty: a systematic review

“…Achieving optimal clinical and functional outcomes after total knee arthroplasty (TKA) depends on a number of factors such as leg alignment, orientation of the components, as well as adequate soft tissue balancing [ 2 , 9 , 21 , 24 ]. Assessing soft tissue balance is challenging for the surgeon, as the perceived “feeling for balance” is influenced by several elements such as surgical experience, patients’ body mass index (BMI), gender, soft tissue laxity, the degree of joint contracture, as well as the fitness level of the surgeon [ 14 ].…”