ArticleBMC musculoskeletal disorders2026
Robot-assisted mechanically aligned total knee arthroplasty: comparing early outcomes between varus and non-varus knees, and between CPAK Type I and Type IV subtypes.
Article in BMC musculoskeletal disorders, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
objectiveThis study aims to compare early pain relief and functional recovery between varus and non-varus phenotypes following robot-assisted mechanically aligned total knee arthroplasty (MA-TKA), with a specific focus on the two most common varus subtypes: Type I and Type IV.
methodsA retrospective analysis was performed on 124 patients who underwent primary unilateral robot-assisted MA-TKA. Patients were classified according to the Coronal Plane Alignment of the Knee (CPAK) classification based on preoperative arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO). Based on aHKA, patients were categorized into a varus group (CPAK Types I, IV, and VII, n = 93) and a non-varus group (neutral and valgus phenotypes, n = 31). Within the varus cohort, the two most prevalent subtypes - Type I (n = 64) and Type IV (n = 27) - were compared; Type VII (n = 2) was excluded from subtype-specific analyses due to small sample size. Patient-reported outcomes (VAS pain, KSS clinical/function, WOMAC) were evaluated preoperatively and at 1, 3, and 6 months postoperatively. Radiographic parameters (aHKA, MPTA, LDFA, JLO) were measured preoperatively and at 1 month.
resultsPreoperatively, the varus group had a significantly lower aHKA than the non-varus group (- 6.9° ± 2.4° vs. -0.1° ± 1.1°, p < 0.001). Postoperatively, both groups achieved neutral mechanical alignment with no significant difference in aHKA (p = 0.231). However, residual joint line obliquity differed significantly between Type I and Type IV knees (176.2° ± 0.2° vs. 179.3° ± 0.3°, p < 0.001). Non-varus patients had significantly better functional recovery at 1 month than varus patients (KSS‑Function: 60.5 ± 2.8 vs. 53.8 ± 3.1, p = 0.042; WOMAC: 36.2 ± 1.9 vs. 43.0 ± 2.3, p < 0.001), and these differences attenuated by 6 months. Within the varus subgroup, Type IV patients had lower 1‑month VAS scores and higher KSS‑Function scores than Type I patients (VAS: 3.5 ± 0.4 vs. 4.2 ± 0.4, p = 0.018; KSS‑Function: 55.0 ± 2.5 vs. 53.3 ± 2.9, p = 0.039).
conclusionsPreoperative CPAK phenotype is associated with early recovery after robot-assisted MA‑TKA. Non-varus patients had higher 1‑month KSS‑Function scores than varus patients. Among varus knees, Type IV patients had lower 1‑month VAS scores and higher 1‑month KSS‑Function scores than Type I patients, whereas Type I knees retained greater residual postoperative joint line obliquity. Distinguishing varus subtypes may help refine prognostic expectations and guide individualized alignment strategies.
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