Journal of experimental orthopaedics · 2026
Joint line obliquity change was associated with femoral and tibial resection patterns and smaller final flexion imbalance after robot-assisted total knee arthroplasty.
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Morita Yugo, Shin Jonggu, El-Hassan Mohammed, Shichman Ittai, Long William J, Sculco Peter K
Аннотация
PURPOSE: Associations between preoperative-to-post-operative changes in arithmetic hip-knee-ankle angle (aHKA) and joint line obliquity (JLO) and final balance after robot-assisted total knee arthroplasty (TKA) were evaluated. Relationships with resection redistribution and tibial-varus reduction were also examined.
METHODS: A retrospective single-surgeon series of 402 primary robot-assisted TKAs was analysed. Preoperative and post-operative aHKA, JLO and coronal plane alignment of the knee (CPAK) type were determined from full-length radiographs. Final extension and flexion imbalance and laxity ranges after trial implantation were the primary outcomes. Signed and absolute changes were assessed in multivariable models; resection redistribution and a varus-only tibial-boundary subgroup were examined in supportive analyses.
RESULTS: A change in CPAK type was observed in 300 knees (74.6%), including a JLO-zone change in 221 (55.0%). Greater ΔJLO was associated with smaller final flexion imbalance (β = -0.060; p < 0.001) and a narrower final extension laxity range (β = -0.055; p = 0.002). Corresponding associations were found for |ΔJLO| (β = -0.046; p = 0.018 and β = -0.070; p = 0.004). Neither signed nor absolute aHKA change was associated with final extension or flexion imbalance. In varus knees, tibial-varus reduction was associated with greater JLO and aHKA changes, coronal femoral adjustment and smaller final flexion imbalance. Neither |ΔaHKA| nor |ΔJLO| was associated with improvement in the Knee injury and Osteoarthritis Outcome Score for Joint Replacement.
CONCLUSIONS: Greater JLO change was associated with smaller final flexion imbalance and a narrower extension laxity range rather than impaired balance. In varus knees, JLO change accompanied tibial-varus reduction and coordinated femoral adjustment. JLO change may therefore reflect specific aspects of the final balancing state rather than an unintended deviation from the native phenotype.
LEVEL OF EVIDENCE: Level III, retrospective cohort study.
METHODS: A retrospective single-surgeon series of 402 primary robot-assisted TKAs was analysed. Preoperative and post-operative aHKA, JLO and coronal plane alignment of the knee (CPAK) type were determined from full-length radiographs. Final extension and flexion imbalance and laxity ranges after trial implantation were the primary outcomes. Signed and absolute changes were assessed in multivariable models; resection redistribution and a varus-only tibial-boundary subgroup were examined in supportive analyses.
RESULTS: A change in CPAK type was observed in 300 knees (74.6%), including a JLO-zone change in 221 (55.0%). Greater ΔJLO was associated with smaller final flexion imbalance (β = -0.060; p < 0.001) and a narrower final extension laxity range (β = -0.055; p = 0.002). Corresponding associations were found for |ΔJLO| (β = -0.046; p = 0.018 and β = -0.070; p = 0.004). Neither signed nor absolute aHKA change was associated with final extension or flexion imbalance. In varus knees, tibial-varus reduction was associated with greater JLO and aHKA changes, coronal femoral adjustment and smaller final flexion imbalance. Neither |ΔaHKA| nor |ΔJLO| was associated with improvement in the Knee injury and Osteoarthritis Outcome Score for Joint Replacement.
CONCLUSIONS: Greater JLO change was associated with smaller final flexion imbalance and a narrower extension laxity range rather than impaired balance. In varus knees, JLO change accompanied tibial-varus reduction and coordinated femoral adjustment. JLO change may therefore reflect specific aspects of the final balancing state rather than an unintended deviation from the native phenotype.
LEVEL OF EVIDENCE: Level III, retrospective cohort study.