title: Source of the slippage in the universal joints of the Hoffmann external fixator.
abstract: An investigation was conducted to determine what improvements in the resistance to slippage could be obtained in selected interfaces (rod/clip torsional, cheek/bowl and cheek/clip) of the Hoffmann external fixator. The modification involved changing the standard wing-nut clamp for a bolt with a thread of 7 mm and a 1 mm pitch and placing an FAG 28-303 thrust-bearing (needle roller and cage assembly) between the bolt and the cheek. The results showed a significant improvement in the slippage values of all interfaces; increases of approximately six times were obtained at all torque values of the wing-nut clamp or fastener tested. Such improvements would markedly increase the reliability of external fixation systems and thus reduce the incidence of loss-of-reduction of fracture due to slippage of the universal joint.
authors.affiliation: Orthopaedic Research Laboratory, University Hospital, University of Western Ontario, London, Canada.
authors.forename: F L
authors.initials: FL
authors.lastname: Drijber
authors.forename: J B
authors.initials: JB
authors.lastname: Finlay
authors.forename: T K
authors.initials: TK
authors.lastname: Moroz
authors.forename: C H
authors.initials: CH
authors.lastname: Rorabeck
mesh_terms: D004868:Equipment Failure; D005592:Fracture Fixation / Q000295:instrumentation*; D006801:Humans; D008433:Mathematics; D012399:Rotation; D013314:Stress, Mechanical; D013718:Tensile Strength