A study found that maintaining patients' preoperative knee alignment during total knee arthroplasty, rather than pursuing neutral mechanical alignment, may be associated with improved patient-reported outcomes.
In the study, published in The Bone & Joint Journal, investigators analyzed 284 knees in 231 patients who underwent primary total knee arthroplasty for osteoarthritis between 2013 and 2019. The study population included patients with a mean age of 74.0 years (standard deviation [SD] = 8.0) and mean body mass index of 26.7 kg/m² (SD = 4.4). The cohort comprised 238 knees in females and 46 in males, with Kellgren-Lawrence grades of 3 (89 knees) and 4 (195 knees). The mean postoperative follow-up was 55 months.
The investigators found that changing patients' varus/valgus alignment from pre- to postoperative states emerged as a significant negative predictive factor for both the Knee injury and Osteoarthritis Outcome Score–12 and Forgotten Joint Score–12 (FJS-12). Additionally, postoperative apex proximal joint line obliquity (JLO) was identified as a negative predictor for both the Knee Society Score 2011 (KSS 2011) and KOOS-12.
Using the Coronal Plane Alignment of the Knee (CPAK) classification system, the investigators documented that preoperatively, phenotype I (varus alignment with apex distal JLO) predominated in 55% of cases (155 knees). Postoperatively, phenotype V (neutral alignment with neutral JLO) became most common, occurring in 26% of cases (73 knees), followed by phenotypes II and IV at 16% each (45 knees), and phenotype VI at 14% (39 knees).
All procedures utilized a medial parapatellar approach without navigation and included patellar resurfacing. Surgeons employed either Persona PS (150 knees) or Journey II BCS (134 knees) implants.
Cases avoiding negative CPAK factors—specifically maintaining preoperative alignment and avoiding postoperative apex proximal JLO—demonstrated improved outcomes:
- KSS 2011 scores: 131 vs 124 points (P = .030)
- KOOS-12 scores: 75 vs 69 points (P = .005)
- FJS-12 scores: 55 vs 48 points (P = .019).
Despite using mechanical alignment technique targeting neutral alignment in all cases, the desired neutral alignment was not achieved in 54% of knees (n = 154/284).
Multivariable regression analyses revealed female sex as a negative predictor for KSS 2011 (β = –7.2, P = .005) and FJS-12 (β = –3.0, P = .003). The Persona PS implant was associated with lower FJS-12 scores (β = –5.3, P = .006).
The study's limitations included varying postoperative follow-up intervals, evaluation limited to the coronal plane, and insufficient cases for certain phenotypes. The research was supported by grants from the Ogata Memorial Foundation, Inc. and the Medical Care Education Research.
One investigator reported receiving study-related grants from the Ogata Memorial Foundation and Medical Care Education Research, while another disclosed unrelated research grants from Zimmer Biomet.
