Instability of total hip replacement: A clinical study and determination of its risk factors

Rev Esp Cir Ortop Traumatol. 2015 Jul-Aug;59(4):287-94. doi: 10.1016/j.recot.2014.12.004. Epub 2015 Jan 28.
[Article in English, Spanish]

Abstract

Objectives: To determine the risk factors associated with prosthetic dislocation and simulate a finite element model to determine the safe range of movement of various inclination and anteversion cup positions.

Material and methods: Retrospective Case Control study with 46 dislocated patients from 1994 to 2011.

Control group: 83 randomly selected patients. Dislocation risk factors described in the literature were collected. A prosthetic model was simulated using finite elements with 28, 32, 36 mm heads, and a 52 mm cup. Acetabular position was 25°, 40°, and 60° tilt and with 0°, 15° and 25° anteversion. In extension of 0° and flexion of 90°, internal and external rotation was applied to analyze the range of movement, maximum resisting moment, and stress distribution in the acetabulum to impingement and dislocation.

Results: There was greater dislocation in older patients (p=0.002). Higher dislocation in fractures than in osteoarthritis (p=0.001). Less anteversion in dislocated patients (p=0.043). Longer femoral neck in dislocated patients (p=0.002). Finite element model: lower dislocation when there is more anteversion, tilt and bigger femoral heads.

Discussion-conclusions: Advanced age and fractures are the major risk factors for dislocation. "Safe zone" of movement for dislocation avoidance is 40°-60° tilt and 15°-25° anteversion. Both the defect and excess of soft tissue tension predispose to dislocation. Bigger femoral heads are more stable.

Keywords: Anteversion; Anteversión; Dislocation; Elementos finitos; Finite elements; Inestabilidad; Instability; Luxación; Prótesis total de cadera; Total hip arthroplasty.

MeSH terms

  • Aged
  • Arthroplasty, Replacement, Hip*
  • Case-Control Studies
  • Female
  • Finite Element Analysis
  • Follow-Up Studies
  • Hip Joint / physiopathology
  • Hip Prosthesis*
  • Humans
  • Joint Dislocations / etiology*
  • Joint Dislocations / physiopathology
  • Male
  • Middle Aged
  • Prosthesis Design
  • Prosthesis Failure / etiology*
  • Range of Motion, Articular
  • Retrospective Studies
  • Risk Factors