Jan Egil Brattgjerd1, Martin Loferer2, Sanyalak Niratisairak3, Harald Steen4, Knut Strømsøe5. 1. Division of Orthopaedic Surgery, Biomechanics Lab, Oslo University Hospital, Pb. 4950 Nydalen, 0424 Oslo, Norway; Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Pb. 1171 Blindern, 0318 Oslo, Norway. Electronic address: j.e.brattgjerd@medisin.uio.no. 2. Endolab Mechanical Engineering GmbH, Seb.-Tiefenthaler Str. 13, D-83101 Thansau, Rosenheim, Germany. 3. Division of Orthopaedic Surgery, Biomechanics Lab, Oslo University Hospital, Pb. 4950 Nydalen, 0424 Oslo, Norway; Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Pb. 1171 Blindern, 0318 Oslo, Norway. 4. Division of Orthopaedic Surgery, Biomechanics Lab, Oslo University Hospital, Pb. 4950 Nydalen, 0424 Oslo, Norway. 5. Institute of Clinical Medicine, Faculty of Medicine, University of Oslo, Pb. 1171 Blindern, 0318 Oslo, Norway.
Abstract
BACKGROUND: In undisplaced femoral neck fractures, internal fixation remains the main treatment, with mechanical failure as a frequent complication. As torsional stable fixation promotes femoral neck fracture healing, the Hansson Pinloc® System with a plate interlocking pins, was developed from the original hook pins. Since its effect on torsional stability is undocumented, the novel implant was compared with the original configurations. METHODS: Forty-two proximal femur models custom made of two blocks of polyurethane foam were tested. The medial block simulated the cancellous head, while the lateral was laminated with a glass fiber filled epoxy sheet simulating trochanteric cortical bone. Two hollow metal cylinders with a circumferential ball bearing in between mimicked the neck, with a perpendicular fracture in the middle. Fractures were fixated by two or three independent pins or by five configurations involving the interlocking plate (two pins with an optional peg in a small plate, or three pins in a small, medium or large plate). Six torsional tests were performed on each configuration to calculate torsional stiffness, torque at failure and failure energy. FINDINGS: The novel configurations improved parameters up to an average of 12.0 (stiffness), 19.3 (torque) and 19.9 (energy) times higher than the original two pins (P < 0.001). The plate, its size and its triangular configuration improved all parameters (P = 0.03), the plate being most effective, also preventing permanent failure (P < 0.001). INTERPRETATION: The novel plate design with its pin configuration enhanced torsional stability. To reveal clinical relevance a clinical study is planned.
BACKGROUND: In undisplaced femoral neck fractures, internal fixation remains the main treatment, with mechanical failure as a frequent complication. As torsional stable fixation promotes femoral neck fracture healing, the Hansson Pinloc® System with a plate interlocking pins, was developed from the original hook pins. Since its effect on torsional stability is undocumented, the novel implant was compared with the original configurations. METHODS: Forty-two proximal femur models custom made of two blocks of polyurethane foam were tested. The medial block simulated the cancellous head, while the lateral was laminated with a glass fiber filled epoxy sheet simulating trochanteric cortical bone. Two hollow metal cylinders with a circumferential ball bearing in between mimicked the neck, with a perpendicular fracture in the middle. Fractures were fixated by two or three independent pins or by five configurations involving the interlocking plate (two pins with an optional peg in a small plate, or three pins in a small, medium or large plate). Six torsional tests were performed on each configuration to calculate torsional stiffness, torque at failure and failure energy. FINDINGS: The novel configurations improved parameters up to an average of 12.0 (stiffness), 19.3 (torque) and 19.9 (energy) times higher than the original two pins (P < 0.001). The plate, its size and its triangular configuration improved all parameters (P = 0.03), the plate being most effective, also preventing permanent failure (P < 0.001). INTERPRETATION: The novel plate design with its pin configuration enhanced torsional stability. To reveal clinical relevance a clinical study is planned.
Authors: Kristine Kalland; Henrik Åberg; Anna Berggren; Michael Ullman; Greta Snellman; Kenneth B Jonsson; Torsten Johansson Journal: Acta Orthop Date: 2019-08-27 Impact factor: 3.717