title: Range of motion in a modular femoral stem system with a variety of neck options.
abstract: Modular femoral stem systems decouple leg length, offset, and version. The hip ROM and type of impingement for 162 femoral head/neck combinations were measured at four extreme hip positions in a Sawbones pelvis and femur to identify constructs that lead to early impingement. Hip ROM increased in all positions with increasing head size and neck length. We identified a new type of impingement created by the build-up of the proximal femoral stem: femoral stem on acetabular liner impingement. Seventy percent of neutral neck options achieved our definition of acceptable ROM. In general, when utilizing a modular femoral stem, surgeons can minimize impingement by choosing the longest femoral neck that does not over-lengthen the limb, using the largest femoral head accommodated by the cup, and avoiding neck version unless the cup or stem is malaligned.
authors.affiliation: Arthroplasty, Orthopaedic Surgery, Massachusetts General Hospital, Los Gatos, California.
authors.forename: Sanaz
authors.initials: S
authors.lastname: Hariri
authors.forename: Sungwook
authors.initials: S
authors.lastname: Chun
authors.forename: James B
authors.initials: JB
authors.lastname: Cowan
authors.forename: Charles
authors.initials: C
authors.lastname: Bragdon
authors.forename: Henrik
authors.initials: H
authors.lastname: Malchau
authors.forename: Harry E
authors.initials: HE
authors.lastname: Rubash
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D005269:Femur / Q000601:surgery*; D006622:Hip Prosthesis; D011474:Prosthesis Design; D016059:Range of Motion, Articular
keywords: biomechanics; dislocation; impingement; modular femoral neck; total hip arthroplasty