title: Protrusio After Medial Acetabular Wall Breach in Total Hip Arthroplasty.
abstract: BACKGROUND
  Medial protrusio is a recognized complication of total hip arthroplasty, but it is not known if a medial wall breach during cup implantation increases the risk. We thus investigated the effect of up to a 2 cm defect in the medial acetabular wall in a cadaveric model. Separately, we investigated the ability of acetabular screws to rescue the construct.
  
  
  METHODS
  Nine human fresh-frozen hemipelves were reamed medially to create the defect, implanted with acetabular cups, and then loaded to failure. The nine contralateral hemipelves were reamed in a standard fashion and served as controls. Separately, nine hemipelves with a medial defect were augmented with two acetabular screws each, then loaded to failure, with the contralateral side as a control. Load-to-failure, stiffness, and energy were recorded.
  
  
  RESULTS
  The presence of a medial wall defect decreased the load-to-failure by a mean of 26% (5710 v. 4221 N, p=0.024). The addition of two acetabular screws did not rescue the construct (mean 27% decrease, 4082 v. 2985 N, p=0.024). The majority of specimens failed in a supra-physiologic range of force. Bone density correlated with failure loads (R(2) range of 0.54-0.78), and osteoporotic specimens were more likely to fail at a physiologic range, consistent with forces experienced during minor stumbles or falls.
  
  
  CONCLUSIONS
  Osteoporotic patients with a medial wall defect after hip arthroplasty may be susceptible to fracture during activities of daily living. Protected weight bearing with an assistive device may be reasonable in order to minimize fall risk until cup ingrowth is achieved.
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics , Iowa City, IA , USA.
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Martin
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics , Iowa City, IA , USA ; Department of Biomedical Engineering, University of Iowa , Iowa City, IA , USA.
authors.forename: Anneliese D
authors.initials: AD
authors.lastname: Heiner
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics , Iowa City, IA , USA.
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Baer
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics , Iowa City, IA , USA.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Pugely
authors.affiliation: Department of Orthopaedic Surgery and Rehabilitation, University of Iowa Hospitals and Clinics , Iowa City, IA , USA ; Department of Orthopaedic Surgery, VA Medical Center , Iowa City, IA , USA.
authors.forename: Nicolas O
authors.initials: NO
authors.lastname: Noiseux
mesh_terms: D000077:Acetabulum / Q000473:pathology* / Q000601:surgery*; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000379:methods; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005260:Female; D006622:Hip Prosthesis; D006801:Humans; D007593:Joint Instability / Q000209:etiology* / Q000503:physiopathology; D008297:Male; D011475:Prosthesis Failure; D018570:Risk Assessment