1994 Project Reports | Contents | Previous | Next | Home
Biomechanical Evaluation of Fracture Fixation Methods
SS Schmidt, MS; AJ Irish, MS; JG Vachsevanos, BS; Gary S Beaupré, PhD; J Csongrati, MD; C Comstock, MD; MCH van der Meulen, PhD; SB Goodman, MD
Overview - Although many kinds of fractures can be treated using non- operative approaches (casts, splints), surgical treatment and the use of fixation hardware is necessary for certain types of injuries. Operative treatment is generally chosen for several reasons including: failure of non- operative methods; contraindications to non operative methods; fracture or disruption of joint surfaces; and the presence of multiple fractures. Fracture fixation devices are used to maintain fracture alignment, allow use of the injured limb sooner, and protect the healing tissue from reinjury. For a given fracture, there are often several fixation methods and devices among which the orthopedic surgeon must choose. The optimal choice is a function of many variables, including the stabilization required, the presence of soft tissue injuries, and the ease of surgery.
Mechanical testing has become a common tool to evaluate the performance of internal fixation devices. Physiological loads are applied to the hardware and its mechanical stability is measured. Our laboratory has used this technique to assess the performance of a variety of existing orthopaedic implants and as a tool for the design and evaluation of new hardware.
Recently we have undertaken two studies in this area. The first examined methods of plate fixation for femoral fractures occurring below hip implants. The second study evaluated internal fixation techniques used to stabilize pelvic fractures at the sacroiliac joint.
Cerclage Plating
SS Schmidt, MS; AJ Irish, MS; JG Vachsevanos, BS; GS Beaupré, PhD; J Csongradi, MD
Fixation of a femoral shaft fracture can be complicated if the patient has an underlying artificial hip implant (Figure 1a). The attachment of plates with screws is not recommended near the implant as the screws may cause stress concentrations in the cement, damage the prostheses, or fail to anchor in weak, osteoporotic bone, common in elderly patients. An alternative to screw plating is cerclage wire plating, where the plate is secured to the bone by wires that wrap around the bone and plate (Figure 1b). Although inherently less stiff than screw plating, cerclage plating can circumvent the difficulties associated with the use of screws. The results of our study indicate that the use of an inexpensive plate insert to secure the cerclage wire to the plate can significantly improve fixation stability and strength.
Figure 1: (a) Illustration of femoral shaft fracture located at the tip
of hip implant. (b) Cerclage wire plating of femoral fracture distal to
implant.
Pelvic Fracture Fixation
CP Comstock, MD; MCH van der Meulen, PhD; SB Goodman, MD Optimal management of unstable fractures and dislocations of the pelvis is an unresolved issue. These fractures result from high energy trauma from motor vehicle accidents, severe falls or industrial accidents, and are often accompanied by multiple trauma. Pelvic fractures frequently unstable due to the disruption of ligaments in addition to the fracture. Few studies have examined the most appropriate pelvic stabilization. Anterior fixation has been shown to be insufficient, and posterior screws or bars may be preferable. However, the posterior surgical procedures are difficult and may require extensive soft tissue dissection. The stiffness of four different pelvic fixations for unstable sacroiliac fractures was compared (Figure 2). Sacroiliac screws, either alone or combined with posterior sacral bars, were found to be significantly stiffer in compression and torsion than posterior sacral bars alone or anterior sacroiliac plates (Figure 3).
|
Figure 2. Schematic of four different fixation methods investigated. Anterior view (a) sacral plates. Posterior view (b) sacroiliac (SI) bars, (c) SI screws, and (d) bars and screws combined. |
| Figure 3. Pelvic structural stiffness under compressive and torsional loading. Values reported as mean stiffness (per cent of intact) +/- SD. |  |
Republished from the 1994 Rehabilitation R&D Center Progress Report. For
current information about this project, contact
Gary Beaupré.
