title: Does High Hip Center Decrease Range of Motion in Total Hip Arthroplasty? A Computer Simulation Study.
abstract: High placement of a cementless acetabular cup is often required to have sufficient bone coverage in hip dysplasia. We examined whether a high hip center decreases the postoperative range of motion (ROM) in total hip arthroplasty.
  
  
  
  Using a computer software, ROM and bone coverage were examined in 32 patients with unilateral osteoarthritis of the hip with Crowe type II or III hip dysplasia. The cup was placed at the anatomic hip center and moved vertically in 5-mm increments. Vertical center of rotation (V-COR) was defined as the distance from the head center to the interteardrop line. The required ROM was defined as flexion  ≥110°, internal rotation (IR) at 90° flexion ≥30°, extension ≥30°, and external rotation ≥30°. We determined the V-COR to satisfy the required ROM and cup center-edge angle (Cup-CE) ≥0°.
  
  
  
  Only 40.6% of the patients satisfied Cup-CE ≥0° at the anatomic hip center. Bone coverage increased with the peak at 30, 35 mm of V-COR (90.6% satisfied Cup-CE ≥0°) and decreased at ≥40 mm. Higher V-COR resulted in lower range of flexion and IR, but increased the range of extension and external rotation. The cutoff value from the receiver-operating characteristic curve for both flexion and IR was a V-COR of 35 mm.
  
  
  
  The higher hip center gained more bone coverage but decreased the range of hip flexion and IR. Acceptable V-COR in hip dysplasia was around 35 mm, about 20 mm above the true hip center, in terms of ROM.
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Keisuke
authors.initials: K
authors.lastname: Komiyama
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Nakashima
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Masanobu
authors.initials: M
authors.lastname: Hirata
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Hara
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Kohno
authors.affiliation: Department of Orthopedic Surgery, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D000077:Acetabulum / Q000601:surgery; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip; D003198:Computer Simulation; D005260:Female; D006618:Hip Dislocation, Congenital / Q000150:complications / Q000601:surgery*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D015207:Osteoarthritis, Hip / Q000209:etiology / Q000601:surgery*; D016059:Range of Motion, Articular; D012399:Rotation
keywords: computer simulation; high hip center; hip dysplasia; range of motion; total hip arthroplasty