Independent of the preoperative coronal deformity, adjusted mechanical alignment leads in a high percentage to non-anatomical tibial and femoral bone cuts

Abstract

PurposeThe technique of adjusted mechanical alignment (AMA) in total knee arthroplasty (TKA) has been described to achieve alignment and balancing goals in varus knees in a high percentage, albeit at the price of non‐anatomical bone cuts. The purpose of this study was to analyze (1) whether AMA achieves similar alignment and balancing results in different types of deformity and (2) whether they can be achieved without altering the native anatomy. MethodsA series of 1000 patients with hip–knee–ankle (HKA) angles from 165° to 195° were analyzed. All patients were operated using AMA technique. According to the preoperative HKA angle, three groups of knee phenotypes (varus, straight, valgus) were defined. The bone cuts were analyzed for being anatomic (< 2 mm deviation of individual joint surface) or non‐anatomic (> 4 mm deviation of individual joint surface). ResultsAMA reached the goals for postoperative HKA in over 93% in every group (varus: 636 cases, 94%, straight: 191 cases, 98%, valgus: 123 cases, 98%). In 0° extension, the gaps were balanced in varus knees in 654 cases (96%), in straight knees in 189 cases (97%) and in valgus knees in 117 cases (94%). A balanced flexion gap was found in a similar number of cases (varus: 657 cases, 97%, straight: 191 cases, 98%, valgus: 119 cases, 95%). In the varus group, non‐anatomical cuts were performed at the medial tibia (89%) and the lateral posterior femur (59%). The straight group showed similar values and distribution for non‐anatomical cuts (medial tibia: 73%; lateral posterior femur 58%). Valgus knees showed a different distribution of values, being non‐anatomical at the lateral tibia (74%), distal lateral femur (67%) and posterior lateral femur (43%). ConclusionIn all knee phenotypes, the AMA goals were achieved in a high percentage by altering the patients’ native anatomy. In varus knees, the alignment was corrected by non‐anatomical cuts at the medial tibia, and in valgus knees at the lateral tibia and the lateral distal femur. All phenotypes showed non‐anatomical resections on the posterior lateral condyle in approximately 50% of cases. Level of evidenceIII.

Definitions and consequences of current alignment techniques and phenotypes in total knee arthroplasty (TKA) – there is no winner yet

“…Image reproduced from original work with permission from Dr. Jonathan Vigdorchik extent of soft tissue releases, the approach of adjusted mechanical alignment (AMA) was introduced [34,35]. This technique involves performing a tibial cut still perpendicular to the mechanical axis, but the distal femoral cut can be adjusted by up to 3° in either varus or valgus direction, contingent upon the individual extension gap difference [33,36]. An intentional varus cut in AMA serves as an integral component of the balancing technique, when removal of osteophytes and capsular release fail to achieve a balanced extension gap [37].…”

“…A drawback associated with MA pertains to the substantial requirement of soft tissue release, especially in cases of severe deformities, necessitating extensive ligament release to attain balanced gaps [33]. To mitigate the extent of soft tissue releases, the approach of adjusted mechanical alignment (AMA) was introduced [34, 35].…”

“…However, a noteworthy disadvantage is that the cut of the distal femur may be non‐anatomical in certain patients, as some patients have a constitutional valgus of the femur [38, 39]. It is evident that AMA does not truly qualify as a personalized alignment technique, as it fails to consistently restore constitutional alignment in the majority of cases [33, 36].…”

Higher satisfaction and function scores in restricted kinematic alignment versus mechanical alignment with medial pivot design total knee arthroplasty: A prospective randomised controlled trial

“…The disadvantages of this technique include the need for soft tissue release, as well as ignoring the joint line height and obliquity, which can have negative biomechanical consequences [22,24,36]. With the advent of modern surgical techniques such as patientspecific instruments (PSI) or robotic-assisted TKA, it seems sensible to consider the individual knee anatomy of patients in the surgical technique, particularly taking into account the great variability of the femoral and tibial anatomy in osteoarthritic and nonosteoarthritic patients [10,12,18].…”

Robotic‐assisted mechanically aligned total knee arthroplasty does not lead to better clinical and radiological outcomes when compared to conventional TKA: a systematic review and meta‐analysis of randomized controlled trials

“…Total knee arthroplasty (TKA) does not lead to similarly convincing results as total hip arthroplasty (THA), which has been considered “the treatment of the century” [31]. The reason why TKA results are inferior to THA are manifold and may be related to the following factors: complexity of knee joint anatomy, different kinematics, surgical indication, periprosthetic knee infections, unclear targets for components positioning and alignment, problems in reliably executing the surgery, patellar maltracking, and demanding soft‐tissue balancing techniques [18, 20, 35, 53, 54]. Moreover, the number of revision surgery is increasing significantly due to the rapidly growing number of primary implantations, mainly because of infection and instability [7, 30, 40].…”