title: The influence of resection height on proximal femoral strain patterns after Metha short stem hip arthroplasty: an experimental study on composite femora.
abstract: OBJECTIVE
  The number of candidates for a total hip arthroplasty (THA) is steadily increasing, while the average patient age is decreasing for primary THA. The rise in THA is mainly due to excellent clinical outcomes and the extended longevity of modern implants. Short stem arthroplasties with predominantly metaphyseal fixation such as the Metha® stem are suggested for young patients. It is hypothesised that the more physiological load transfer of these devices reduces stress shielding, which in turn may reduce the risk of aseptic loosening. However, patients with femoral deformities often require a deviation of the resection height. To this end, our aim was to evaluate how resection height influences strain patterns in order to characterise possible limits for short stem implantation.
  
  
  METHODS
  Biomechanical testing using ten strain gauges on synthetic bone illustrated the strain patterns of three different resection heights (0, +5 and +10 mm) for the Metha stem.
  
  
  RESULTS
  The greatest differences in strains were displayed at the "high" (most proximal) resection height (+10 mm) when compared to the non-implanted strain pattern. At the medial calcar, the strain was 143% for +10 mm, 96% for +5 mm and 94% for 0 mm. Overall, discrepancies were less for deeper resections.
  
  
  CONCLUSIONS
  The deeper the resection, the more similar the strain patterns are when compared to a non-implanted synthetic bone. Changes in strain patterns are induced by variation in the varus/valgus positioning of the implant and by different offsets.
authors.affiliation: Department of Orthopaedic Surgery, Hannover Medical School, Anna-von-Borries-Str. 1-7, 30625, Hannover, Germany. Thilo.floerkemeier@annastift.de
authors.forename: Thilo
authors.initials: T
authors.lastname: Floerkemeier
authors.forename: Jens
authors.initials: J
authors.lastname: Gronewold
authors.forename: Sebastian
authors.initials: S
authors.lastname: Berner
authors.forename: Gavin
authors.initials: G
authors.lastname: Olender
authors.forename: Christof
authors.initials: C
authors.lastname: Hurschler
authors.forename: Henning
authors.initials: H
authors.lastname: Windhagen
authors.forename: Gabriela
authors.initials: G
authors.lastname: von Lewinski
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001696:Biomechanical Phenomena; D005269:Femur / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D013314:Stress, Mechanical