Impact of Valgus vs Varus Mechanical Axis Correction During Primary Total Knee Arthroplasty on Postoperative Periarticular Bone Mineral Density

J Arthroplasty. 2021 May;36(5):1792-1798. doi: 10.1016/j.arth.2020.12.011. Epub 2020 Dec 13.

Abstract

Background: Knee periarticular bone mineral density (BMD) is influenced by limb malalignment. The purpose of this study is to determine if the nature and magnitude of alignment correction (ΔAlign°) performed during primary total knee arthroplasty (TKA) had an impact on BMD at the metaphysis of the distal femur (DFmr) and proximal tibia (PTb).

Methods: Seventy-one patients (male = 37 |female = 34; age: 65 ± 2 years) underwent full-length standing X-rays and knee-specific BMD measurements using dual-energy X-ray absorptiometry before and 3 and 6 months following TKA. A t-test was used to compare baseline demographics and knee-specific BMD measures (medial/lateral DFmr/PTb) between patients with preoperative valgus (VAL, N = 18) and varus (VAR, N = 53) malalignment. Pearson correlation analysis was used to determine if ΔAlign° correlated with site-specific knee BMD changes. A 2 (varus/valgus) by 3 (time) analysis of variance was used to compare site-specific BMD (%ΔBMD) changes following TKA. Type I error was set at α = 0.05 for all analyses.

Results: VAR patients had higher preoperative BMD for medial measurement at both the DFmr (VAR: 1.17 ± 0.06 g/cm2; VAL: 1.00 ± 0.09 g/cm2) and PTb (VAR: 1.41 ± 0.07 g/cm2; VAL: 1.29 ± 0.14 g/cm2) (P < .05). ΔAlign° and %ΔBMD were correlated on the medial side of the DFmr (r = 0.393, P < .05) and lateral/medial BMD ratio at the PTb (r = -0.670, P < .01) in VAL patients. Only VAL patients had significant %ΔBMD changes at 6 months postoperative with increases on the medial side only for the DFmr and PTb (+4%-8%, P < .05).

Conclusion: Valgus patients exhibited reduced medial BMD at DFmr and PTb and showed sustained improvements 6 months postsurgery. Mechanical axis correction may be clinically impactful to bone remodeling when correcting valgus malalignment.

Level of evidence: Level II, prospective cohort study.

Keywords: bone mineral density; dual-energy X-ray absorptiometry; mechanical axis; total knee arthroplasty; valgus.

MeSH terms

  • Aged
  • Arthroplasty, Replacement, Knee* / adverse effects
  • Bone Density
  • Female
  • Humans
  • Knee Joint / diagnostic imaging
  • Knee Joint / surgery
  • Male
  • Middle Aged
  • Osteoarthritis, Knee* / surgery
  • Prospective Studies
  • Tibia / diagnostic imaging
  • Tibia / surgery