title: The effects of necrotic lesion size and orientation of the femoral component on stress alterations in the proximal femur in hip resurfacing - a finite element simulation.
abstract: BACKGROUND
  Due to the advantages of its bone-conserving nature, hip resurface arthroplasty (HRA) has recently gained the interest of orthopedic surgeons for the treatment of young and active patients who have osteonerosis of the femoral head. However, in long-term follow-up studies after HRA, narrowing of the femoral neck has often been found, which may lead to fracture. This phenomenon has been attributed to the stress alteration (stress shielding). Studies addressing the effects of necrotic size and the orientation of the implant on stress alterations are lacking.
  
  
  METHODS
  Computed tomography images of a standard composite femur were used to create a three-dimensional finite-element (FE) intact femur model. Based on the intact model, FE models simulating four different levels of necrotic regions (0°, 60°, 100°, 115°) and three different implant insertion angles (varus 10°, neutral, valgus 10°) were created. The von Mises stress distributions and the displacement of the stem tip of each model were analyzed and compared for loading conditions that simulated a single-legged stance.
  
  
  RESULTS
  Stress shielding occurred at the femoral neck after HRA. More severe stress shielding and an increased displacement of the stem tip were found for femoral heads that had a wider necrotic lesion. From a biomechanics perspective, the results were consistent with clinical evidence of femoral neck narrowing after HRA. In addition, a varus orientation of the implant resulted in a larger displacement of the stem tip, which could lead to an increased risk of implant loosening.
  
  
  CONCLUSIONS
  A femoral head with a wide necrotic lesion combined with a varus orientation of the prosthesis increases the risk of femoral neck narrowing and implant loosening following HRA.
authors.forename: Ching-Lung
authors.initials: CL
authors.lastname: Tai
authors.forename: Yung-Chou
authors.initials: YC
authors.lastname: Chen
authors.affiliation: Department of Orthopaedic Surgery, Chang Gung Memorial Hospital, Chang Gung University College of Medicine, Taoyuan, Taiwan. hsiehph@adm.cgmh.org.tw.
authors.forename: Pang-Hsin
authors.initials: PH
authors.lastname: Hsieh
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005271:Femur Head Necrosis / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D006801:Humans; D008953:Models, Anatomic; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome
references.citation: World J Orthop. 2013 Apr 18;4(2):75-9
references.pmid: 23610755
references.citation: J Bone Joint Surg Br. 2007 Nov;89(11):1431-8
references.pmid: 17998177
references.citation: J Arthroplasty. 2001 Dec;16(8 Suppl 1):134-9
references.pmid: 11742465
references.citation: Clin Orthop Relat Res. 1993 Jun;(291):171-84
references.pmid: 8504596
references.citation: J Bone Joint Surg Am. 2004 Jan;86(1):28-39
references.pmid: 14711942
references.citation: Int Orthop. 2005 Aug;29(4):224-8
references.pmid: 15856230
references.citation: J Bone Joint Surg Br. 1995 Nov;77(6):875-80
references.pmid: 7593098
references.citation: J Arthroplasty. 2008 Dec;23(8):1105-9
references.pmid: 18534469
references.citation: J Arthroplasty. 2010 Jun;25(4):522-8
references.pmid: 19520546
references.citation: J Orthop Res. 2008 Apr;26(4):453-9
references.pmid: 17972335
references.citation: Proc Inst Mech Eng H. 2006 Feb;220(2):289-97
references.pmid: 16669395
references.citation: J Bone Joint Surg Br. 2006 Aug;88(8):1110-5
references.pmid: 16877617
references.citation: Clin Orthop Relat Res. 2006 Dec;453:110-4
references.pmid: 17006372
references.citation: J Biomech. 1995 Sep;28(9):1067-78
references.pmid: 7559676
references.citation: Orthop Clin North Am. 2005 Apr;36(2):125-34, vii
references.pmid: 15833450
references.citation: J Bone Joint Surg Br. 2009 Jan;91(1):124-30
references.pmid: 19092017
references.citation: Clin Biomech (Bristol, Avon). 2007 Aug;22(7):780-6
references.pmid: 17544555
references.citation: Clin Orthop Relat Res. 2010 Feb;468(2):375-81
references.pmid: 19756906
references.citation: Chin Med J (Engl). 2012 Nov;125(22):4061-5
references.pmid: 23158143
references.citation: Clin Biomech (Bristol, Avon). 2014 Apr;29(4):412-7
references.pmid: 24629519
references.citation: Proc Inst Mech Eng H. 2006 Feb;220(2):333-44
references.pmid: 16669399
references.citation: J Bone Joint Surg Am. 2004 Sep;86(9):1874-7
references.pmid: 15342747
references.citation: Rev Chir Orthop Reparatrice Appar Mot. 2008 Dec;94(8):715-30
references.pmid: 19070714
references.citation: Orthop Clin North Am. 2005 Apr;36(2):203-13, ix
references.pmid: 15833458
references.citation: J Arthroplasty. 2000 Jun;15(4):505-11
references.pmid: 10884212
references.citation: J Am Acad Orthop Surg. 2006 Aug;14(8):454-63
references.pmid: 16885477
references.citation: Orthop Clin North Am. 2005 Apr;36(2):231-42, x
references.pmid: 15833461