A systematic scoping review found that mechanically aligned total knee arthroplasty remains supported by the most extensive long-term survivorship evidence, while long-term data for personalized alignment strategies remain limited. The researchers emphasized that it is uncertain whether poorer outcomes reported with unintended varus or valgus component positioning in mechanically aligned total knee arthroplasty also apply to the deliberate nonneutral positioning used in some personalized approaches.
The review included 51 studies encompassing 7,944 patients who underwent 9,687 primary total knee arthroplasties. The researchers searched studies published from January 1946 through February 2025, although no eligible studies were identified before 2006. Eligible studies reported postoperative tibial or femoral coronal alignment measured on long-leg standing radiographs or supine computed tomography scanograms and included survivorship outcomes with at least 12 months of follow-up. Mean follow-up was approximately 4.6 years. Most studies were retrospective, single-center, and single-surgeon series.
The primary outcome was all-cause aseptic revision. Because of heterogeneity in study design, alignment measurement methods, and outcome reporting, the researchers did not perform a meta-analysis and instead conducted a qualitative synthesis.
Most studies evaluated mechanical alignment, although personalized alignment techniques — including unrestricted kinematic alignment, restricted kinematic alignment, modified kinematic alignment, functional alignment, adjusted mechanical alignment, and anatomical alignment — were also represented. Among 48 studies reporting outcomes for a defined alignment philosophy, 33 reported 100% aseptic survivorship at final follow-up, while 4 reported survivorship below 95%.
Among 32 studies reporting mechanical alignment outcomes, short-term aseptic survivorship was 96.5% to 100%, including in several reports involving patients with preoperative varus deformity. Similar findings were reported in midterm studies. Nine studies provided long-term follow-up beyond 10 years, and 5 of those studies associated nonneutral tibial or femoral component positioning with lower survivorship.
In those long-term studies, survivorship ranged from 74.2% to 79.3% with increased tibial varus, 90% with increased femoral varus, and 83.3% with femoral valgus. In one study, increasing varus alignment was associated with a 5.8-fold increase in the aseptic revision rate compared with neutral alignment.
However, the long-term varus findings were not uniform. Four long-term mechanical-alignment studies reported 97.2% to 100% survivorship even with varus tibial components. The researchers also noted that radiostereometric analysis data suggested no overall difference in tibial component migration between kinematic and mechanical alignment and that the amount of migration was minimal in some analyses. In addition, some retrieval data implicated overall limb varus more strongly than isolated component varus. These conflicting findings suggest that the relationship between coronal component position and long-term failure remains incompletely understood.
The researchers also evaluated 26 studies of personalized alignment techniques, most commonly kinematic alignment. Twelve kinematic-alignment studies reported short-term survivorship ranging from 95.9% to 100% across unrestricted, restricted, and modified approaches. Two single-surgeon studies with more than 10 years of follow-up reported survivorship of 98.4% to 99%.
However, 2 studies raised concerns about early-to-midterm revision risk with kinematic alignment. One case-control study of restricted kinematic alignment reported a 16% aseptic failure rate at 3 years compared with 2% in a mechanically aligned comparator group. Another study reported a 2.2-fold increased revision hazard compared with national registry controls at follow-up of up to 8 years. The review noted that neither study reported whether revised cases occurred in alignment outliers, limiting interpretation of the revision signal.
The review also highlighted concerns related to valgus component malalignment. Several kinematic-alignment and registry studies associated femoral and/or tibial valgus with elevated rates of patellofemoral complications, including maltracking, erosion, and stiffness. The researchers noted that patellofemoral problems following total knee arthroplasty are multifactorial, involving trochlear geometry, component rotation, soft-tissue balance, and implant design, but coronal and axial plane changes inherent to many personalized philosophies may contribute.
In subgroup analyses, studies involving patients with varus knees showed survivorship ranging from 97% to 100% across alignment philosophies and follow-up durations. In studies involving patients with valgus knees, mechanically aligned total knee arthroplasty achieved 100% short-term survivorship, while 1 functional-alignment study reported 98% survivorship at 18 months, with failures limited to alignment outliers exceeding predefined boundaries.
The researchers cautioned that the evidence base had several important limitations. Most included studies were small, retrospective, and lacked comparator groups. Only 5 studies included more than 500 total knee arthroplasties, and long-term data for personalized alignment were limited to 2 single-surgeon kinematic-alignment series. No long-term data were available for adjusted mechanical alignment, functional alignment, or anatomical alignment.
The review did not establish safe thresholds for coronal varus or valgus alignment. Many studies did not clearly report reasons for revision, making it difficult to determine whether failures were directly attributable to alignment. The researchers also noted that most included studies used cemented fixation and a limited number of implant designs, which may limit generalizability to contemporary cementless and more conforming prostheses. The review focused on static coronal alignment and did not assess dynamic, 3-dimensional, sagittal, or axial alignment factors. It also prioritized survivorship and did not evaluate potential advantages of personalized alignment in patient-reported function, satisfaction, or kinematics.
Disclosures: Disclosure forms are available with the online version of the article. The review protocol was prospectively registered in PROSPERO.
Source: JBJS Open Access
