Bone shape variability within a specific population has been seldom investigated and used to optimize implant design. There is insufficient anatomical fitting of the existing prebend periarticular plates for the distal fibula. We developed a methodology for design of orthopaedic implants that fit a maximum percentage of the target population, both in terms of geometry and biomechanical stability. In co-operation with an implant manufacturer and different academic institutions, a virtual bone database has been developed that contains anatomical data of more than 1000 CT datasets with the implemented possibility to generate idealized implant fits for different anatomical sites. This program (Stryker Virtual Bone Database (VBD) is able to generate statistical anatomical shapes for different populations like age groups or ethnical groups. Based on this, an implant for the distal fibula has been developed (VariAx Distal Lateral Fibula Locking Plate) for distal fibula fracture treatment. Aim of this study was to develop and validate an implant that is optimized for the specific anatomical area. It should be precontoured and still fit to the majority of patients sustaining a distal fibular fracture. Another objective was to create a distally tapered design as there is less soft tissue cover in that anatomic area. ProE CAD system was used in combination with the Bone Database (VBDB) to evaluate the bone shape of the target population plate shape. Several bones (from CT scans) have been used in a first validation process in comparison with an implant already available on the market (SPS Fibula Plate). Additionally, the results have been verified with a bone fitting study which was conducted in collaboration with the Maurice E. Müller Institute (MEM) in Bern/Switzerland. In a second step, the finished implant design was validated against statistical bone shapes of populations of different ethical origin. The comparison of the new Plate's shape with real bone data confirmed that the neutral form does cope with the anatomic situation laterally which means that no systematic pre-bending of the plate is required. Comparing with a conventional implant, the new implant could have been implanted unbend in 6 of 7 cases of virtual matching with real patient datasets compared to none with the conventional implant. The validation of statistical datasets of different ethnical origin (Caucasian, Asian) showed no statistical difference of implant mismatch.Materials & Methods
Results
The degeneration of the adjacent segment in lumbar spine with spondylodesis is well known, though the exact incidence and the mechanism is not clear. Several implants with semi rigid or dynamic behavior are available to reduce the biomechanical loads and to prevent an adjacent segment disease (ASD). Randomized controlled trials are not published. We investigated the biomechanical influence of dynamic and semi rigid implants on the adjacent segment in cadaver lumbar spine with monosegmental fusion (MF). 14 fresh cadaver lumbar spines were prepared; capsules and ligaments were kept intact. Pure rotanional moments of ±7.5 Nm were applied with a Zwick 1456 universal testing machine without preload in lateral bending and flexion/extension. The intradiscal pressure (IDP) and the range of motion (ROM) were measured in the segments L2/3 and L3/4 in following situations: in the native spine, monosegmental fusion L4/5 (MF), MF with dynamic rod to L3/4 (Dynabolt), MF with interspinous implant L3/4 (Coflex), and semi rigid fusion with PEEK rod (CD Horizon Legacy) L3-L5.Introduction
Materials and Methods
