Comparison of two reinforcement rings for primary total hip arthroplasty addressing displaced acetabular fractures: a biomechanical analysis

Archives of Orthopaedic and Trauma Surgery https://doi.org/10.1007/s00402-020-03433-3 TRAUMA SURGERY Comparison of two reinforcement rings for primary total hip arthroplasty addressing displaced acetabular fractures: a biomechanical analysis Johannes Becker1,2 · M. Winkler2 · C. von Rueden1,3 · E. Bliven2 · P. Augat2,3 · H. Resch4 Received: 7 November 2019 © The Author(s) 2020 Abstract Introduction Aim of this study was to biomechanically compare two different acetabular cup fixation constructs in terms of fracture fixation for displaced acetabular fractures involving the anterior column with hemitransverse fracture under partial and full weight-bearing conditions. Methods Two different reinforcement rings designed as cages for primary THA were biomechanically tested in terms of managing a complex acetabular fracture. Single-leg stance cyclic loading was performed to assess fracture gap movement and fragment rotation. Twelve hemi pelvis Sawbones were divided into two groups: primary THA with acetabulum roof reinforcement plate (ARRP) (n = 6) and primary THA with Burch–Schneider reinforcement cage (BSRC) (n = 6). Results During loading under partial weight-bearing (250 N) fracture gap movement tended to be larger in the BSRC group as compared to the ARRP group. Under full weight-bearing conditions, the ARRP showed 60% significantly less motion (p = 0.035) of the os ilium to os ischii gap compared to BSRC. Fracture gap movements between the os ilium and spina iliaca fragments were significantly reduced by 76% (p = 0.048) for ARRP in contrast to BSRC. The ARRP group also demonstrated significantly less movement in the fracture gaps os ischii to quadrilateral plate (62% reduction, p = 0.009) and quadrilateral plate to spina iliaca (87% reduction, p < 0.001). Significantly less rotational movement of the quadrilateral plate to the os ilium was exhibited by the ARRP group (p = 0.015). Conclusions The presented acetabulum roof-reinforcement plate (ARRP) provides stable conditions at the acetabular component with adequate stabilization of a displaced acetabular fracture. Keywords Displaced acetabular fracture · Hip arthroplasty · Acetabulum roof reinforcement plate · Burch–Schneider reinforcement cage Introduction Johannes Becker and M. Winkler contributed equally to the manuscript. * Johannes Becker johannes.becker@klinikum‑gap.de 1 Department of Trauma Surgery, BG Unfallklinik Murnau, Murnau, Germany 2 Institute for Biomechanics, BG Unfallklinik Murnau, Murnau, Germany 3 Institute for Biomechanics, Paracelsus Medical University, Salzburg, Austria 4 Department of Traumatology and Sports Medicine, Paracelsus Medical University, Salzburg, Austria The incidence of anterior column fractures combined with hemitransverse (ACPHT) fractures tremendously increases due to an aging society. Such fractures involve displacement of the quadrilateral plate (QLP) and are often associated with a higher degree of comminution and impaction in patients with osteoporotic bone quality [15, 23, 25, 42]. Stable fixation and anatomical reduction of this “key” fragment is mandatory, but also very challenging due to reduced bone quality [23, 27, 42]. Primary total hip arthroplasty (THA) and the use of cages for joint reconstruction offer the advantage of stable fixation and the possibility of immediate postoperative mobilization with full weight-bearing [4, 26, 29–31, 34, 43]. In the past, only a few biomechanical studies have analyzed the stability of acetabular fracture reconstruction 13 Vol.:(0123456789) Archives of Orthopaedic and Trauma Surgery methods underlining the necessity of stable osteosynthesis to prevent re-displacement of the QLP [6, 24]. However, the lack of homogeneity in biomechanical test set-ups aggravates comparison under full weight-bearing conditions [6, 7, 10, 17, 22, 24, 33, 36]. In particular no comparative biomechanical data has been made available regarding cages designed for primary THA which address displaced acetabular fractures in the elderly. This study compares two different reinforcement cages for displaced acetabular fractures providing fixation of the acetabular roof. Designed as a defect implant for revision surgery in hip bone defects, the Burch–Schneider reinforcement cage (BSRC) aims to restore the anatomical rotational center of the hip [40]. The fixation of the BSRC is achieved by trabecular screws which may become challenging in the case of multi-fragmental fractures due to reduced options for screw placement. On the other hand, the newly designed acetabulum roof-reinforcement plate (ARRP) is intended as a fracture fixation cage and offers multiple options for the insertion of fixed-angle stable screws [29, 30]. We hypothesize that the acetabulum roof-reinforcement plate offers higher biomechanical stability in comparison to the Burch–Schneider reinforcement cage in terms of prevention of quadrilateral plate protrusion and fracture gap movements under partial and full weight-bearing conditions. Materials and methods Specimens and preparation The study was conducted using synthetic hemi pelvises (3405 left pelvis-partial, 4th Generation, Sawbones, Malmö, Sweden). A CT scan of one synthetic hemi pelvis bone was performed and DICOM data of the scan was segmented. After data segmentation, a negative of the prepared hemi pelvis model was used to create a virtual sawing template. This template was 3D printed with PolyJet technology. Using this template, an anterior column combined with posterior hemitransverse (ACPHT) fracture with additional break out of the quadrilateral plate (Fig. 1) was reproducibly cut in twelve synthetic bones with an oscillating saw, as according to Culemann et al. [6]. Two groups of six hemi pelvis Sawbones each were created and prepared for cyclic loading: ARRP, primary THA with Acetabulum Roof Reinforcement Plate (41medical AG, Bettlach, Switzerland) and BSRC, primary THA with Burch-Schneider Reinforcement Cage (Zimmer Biomet Deutschland GmbH, Freiburg i. Breisgau, Germany). Prior to testing, specimens were attached to an artificial sacrum that consisted of a polyurethane cast (RenCast FC 53 A/B, Gößl + Pfaff GmbH, Karlskron/Brautlach, Germany) which was used to create an equal load distribution 13 Fig. 1  Fracture of the anterior column combined with a posterior hemi transverse fracture and additional break out of the quadrilateral plate. Fracture lines were achieved using an oscillating saw and a 3D-printed template between the servohydraulic testing machine and synthetic bone, mimicking the sacroiliac joint. For correct placing of the sacrum substitute, anatomical correlations and geometric dimensions of a fourth generation Sawbones sacrum (3405, Sawbones, Malmö, Sweden) corresponding to the hemi pelvis were used for manufacturing. The connection between sacrum and hemi pelvis was secured using three threaded rods (M8) with corresponding nuts. The artificial sacrum was reused for each test sample. Implant confi (...truncated)