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Patient-Specific “Safe Zones” Reduce the Rate of Dislocation after Total Hip Arthroplasty

7 pagesPublished: October 27, 2019

Abstract

INTRODUCTION: Most dislocations have been shown to occur within Lewinnek’s proposed safe zone (LSZ) for cup inclination (40°±10°) and anteversion (15°±10°). Using a functional and dynamic simulation that accounts for individual patient anatomy and variations in pelvic tilt, we created a patient-specific target orientation for the acetabular cup. The purposes of this study were to: (1) compare pre-operative acetabular cup parameters using this novel dynamic imaging sequence to the LSZ, and (2) describe rates of dislocation in patients whose pre-operative acetabular cup parameters were determined using dynamic imaging sequences.
METHODS: We retrospectively reviewed 1,500 consecutive, primary THAs that underwent dynamic sitting and standing pre-operative acetabular cup planning. Using these inputs, we modeled an optimal cup position for each patient. Inclination, anteversion, pelvic tilt, pelvic incidence, lumbar flexion angles, and rates of dislocation were analyzed.

RESULTS: Mean age of patients was 63 years. Mean pelvic tilt was 4.7o when supine, -0.3o when standing, and -0.7o when flex-seated. Mean pelvic incidence was 54o and mean lumbar flexion was 43o. Mean inclination was 40° and mean anteversion was 24°. Only 56% of the dynamically planned cups were within the LSZ (p<0.05). Mean inclination and anteversion difference between dynamic and LSZ was 1.3o and 8.9o, respectively. Only 0.5% of dynamically planned cups dislocated post-operatively, all were within LSZ.
DISCUSSION: Acetabular cup positioning in patient-specific safe zones reduces the rate of dislocation after THA. Historical target parameters for cup inclination and anteversion significantly differ to target values obtained with the use of functional imaging.

Keyphrases: dislocation, Dynamic radiographs, Functional radiographs, Lewinnek safe zone, patient-specific, Safe Zone, THA, total hip arthroplasty

In: Patrick Meere and Ferdinando Rodriguez Y Baena (editors). CAOS 2019. The 19th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery, vol 3, pages 402--408

Links:
BibTeX entry
@inproceedings{CAOS2019:Patient_Specific_Safe_Zones_Reduce,
  author    = {Jonathan Vigdorchik and Zlatan Cizmic and David Novikov and Michael Bradley and Michael Miranda and David Watson and Douglas Dennis and Stefan Kreuzer},
  title     = {Patient-Specific "Safe Zones" Reduce the Rate of Dislocation after Total Hip Arthroplasty},
  booktitle = {CAOS 2019. The 19th Annual Meeting of the International Society for Computer Assisted Orthopaedic Surgery},
  editor    = {Patrick Meere and Ferdinando Rodriguez Y Baena},
  series    = {EPiC Series in Health Sciences},
  volume    = {3},
  pages     = {402--408},
  year      = {2019},
  publisher = {EasyChair},
  bibsource = {EasyChair, https://easychair.org},
  issn      = {2398-5305},
  url       = {https://easychair.org/publications/paper/FS9r},
  doi       = {10.29007/17jm}}
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