Clinical and Biomechanical Evaluation of Mid-Level Constrained and Posterior-Stabilized Polyethylene Inserts in Primary Total Knee Arthroplasty: An Analysis of 12,674 Cases

J Arthroplasty. 2024 Jun;39(6):1518-1523. doi: 10.1016/j.arth.2023.12.018. Epub 2023 Dec 14.

Abstract

Background: Mid-level constraint polyethylene designs provide additional stability in total knee arthroplasty (TKA). The purposes of this study were to (1) compare the survivorship and reason for revision between mid-level inserts and posterior-stabilized (PS) used in primary TKA and (2) evaluate the biomechanical constraint characteristics of mid-level inserts.

Methods: We reviewed all cases of primary TKA performed at our institution from 2016 to 2019 using either PS or mid-level constrained inserts from 1 of 6 manufacturers. Data elements included patient demographics, implants, reasons for revision, and whether a manipulation under anesthesia was performed. We performed finite element analyses to quantify the varus/valgus and axial-rotation constraint of each mid-level constrained insert. A one-to-one propensity score matching was conducted between the patients with mid-level and PS inserts to match for variables, which yielded 2 cohorts of 3,479 patients.

Results: For 9,163 PS and 3,511 mid-level TKAs, survivorship free from all-cause revision was estimated up to 5 years and was lower for mid-level than PS inserts (92.7 versus 94.1%, respectively, P = .004). When comparing each company's mid-level insert to the same manufacturer's PS insert, we found no differences in all-cause revision rates (P ≥ .91) or revisions for mechanical problems (P ≥ .97). Using propensity score matching between mid-level and PS groups, no significant differences were found in rates of manipulation under anesthesia (P = .72), all-cause revision (P = .12), revision for aseptic loosening (P = .07), and revision for instability (P = .45). Finite element modeling demonstrated a range in varus/valgus constraint from ±1.1 to >5°, and a range in axial-rotation constraint from ±1.5 to ±11.5° among mid-level inserts.

Conclusions: Despite wide biomechanical variations in varus/valgus and axial-rotation constraint, we found minimal differences in early survivorship rates between PS and mid-level constrained knees.

Keywords: biomechanics; knee implants; mid-level constraint; polyethylene insert; total knee arthroplasty.

MeSH terms

  • Aged
  • Aged, 80 and over
  • Arthroplasty, Replacement, Knee* / instrumentation
  • Arthroplasty, Replacement, Knee* / methods
  • Biomechanical Phenomena
  • Female
  • Finite Element Analysis
  • Humans
  • Knee Joint / physiopathology
  • Knee Joint / surgery
  • Knee Prosthesis*
  • Male
  • Middle Aged
  • Polyethylene*
  • Prosthesis Design*
  • Prosthesis Failure*
  • Reoperation* / statistics & numerical data
  • Retrospective Studies