Ligament-tension-guided versus fixed-angle distal femoral coronal target selection in primary total knee arthroplasty using a manual alignment workflow: a retrospective cohort study

BACKGROUND: Distal femoral resection is a determinant of coronal alignment and extension-gap symmetry in total knee arthroplasty (TKA). Conventional intramedullary (IM) alignment relies on a fixed femoral canal-referenced valgus angle, which can be affected by anatomical variability and does not account for extension-gap ligament tension. By contrast, a ligament-tension-guided extramedullary (EM) workflow preserves the femoral canal and uses full-extension tension feedback rather than a preset angle to guide coronal positioning. METHODS: This single-centre retrospective cohort study analysed 76 unilateral primary TKAs performed by a single senior surgeon between September 2019 and January 2024 (EM, n = 37; IM, n = 39). In the EM group, coronal guide positioning was based on full-extension tension feedback without a preset valgus angle, whereas the IM group used conventional intramedullary alignment with a fixed 6° femoral canal-referenced valgus setting. The primary outcome was coronal precision, defined as the absolute deviation of the mechanical lateral distal femoral angle (mLDFA) from 90° on standardised full-length weight-bearing radiographs 6 weeks postoperatively. Prespecified secondary outcomes were mLDFA within ± 3° of 90°, intraoperative visible blood loss, distal femoral resection-step time, and haemoglobin (Hb) decrease within 24 h. RESULTS: Compared with conventional IM alignment, the EM workflow was associated with greater coronal precision, with a smaller absolute deviation of the mLDFA from the 90° target (P = 0.016) and a higher proportion of knees within ± 3° of target (P = 0.020). Intraoperative visible blood loss and haemoglobin decrease within 24 h were lower in the EM group (both P < 0.001), whilst distal femoral resection-step time was comparable (P = 0.235). Exploratory early recovery measures were favourable in the EM group and should be interpreted cautiously. At 12 months, KSS and WOMAC scores, complication rates, and revision-free status were comparable, and no revision was required in either group. CONCLUSIONS: In primary TKA, ligament-tension-guided EM distal femoral resection was associated with greater coronal precision and a lower perioperative bleeding burden than fixed-angle IM alignment, without clear between-group differences in 12-month clinical outcomes. These findings support prospective evaluation of tension-informed coronal target selection.