Advantages of custom made prosthesis are the 3D-Planing and correction of the head position using the best possible form fit. Considering these properties we examined several off the shelf systems if they can fulfil the requirements to form fit and head position. By using our fit program we simulated the implantation of five different off the shelf systems in more than 200 individual reconstructed femora. The data of these bones were used for constructing a custom made implant, so the best form fit and head position could be compared with the result of the fit. All of the patients were younger than 65 years. The data of the off the shelf prostheses systems came from 3D measurement. All systems were described as anatomical. The fit program is an optimization program which can implant a 3D prosthesis model in a reconstructed 3D femur by variation of all six special parameters simultaneously. Compared to the demands of our custom implants, the results of the virtual implantation of the off the shelf systems, are more or less unsatisfactory. Depending on the acceptable tolerance of the limits in offset, leg lengthening and anteversion up to 50% of the patients could not be treated with a single off the shelf system, when the best form fit was reached sufficiently. Using the results of this examination we enlarged our custom-made prosthesis system with six different sizes of an anatomical like off the shelf prostheses. By perfoming the same fit simulation with our new implants we found that more than 70% of our patients could be treated with this implant sufficiently, when using the same limits. A good correspondence was found between the computer fit, which was calculated in advance, and the postoperative situation. The combined system of custom and off the shelf prostheses in addition with our 3D planning system based on CT examination, leads to new way of choosing the best implant for a single patient. If the virtual implantation of an off the shelf system does not give a satisfying result, the custom-made CTX prosthesis will be chosen for this patient.
The mobile bearing knee system has been designed to combine high stability and kinetic function with or without the posterior cruciate ligament. In this kontext the MBK-system is mainly qualified for patients with sufficient kollateral ligaments. Regarding to the origin anatomy a special attachment of the articulating surface allows an anterior-posterior movement of 4,5 mm and a rotation of 53 degrees. The sagital scape of the femoral component guarantees concruency to the articulating surface throughout a range of motion from 5 degress extension to 105 degress flexion. According to this fact high stresses to polyethylene with the consequence of an increase of attrition could be reduced. From May 1997 to June 2001 236 mobile bearing knees were implanted in 220 patients. In June 2000 100 patients with 1 to 2 year follow up were investigated clinically and radiologically. The Knee Society Score was used for the clinical assessment. By using a special study questionaire pre-, intra- and postoperative data were collected. Overall results in the first cases with 1 to 2 year follow up were good to excellent. Over 90% of the whole study group represented a plain increase of score values pre- to postoperatively. Regarding to the first 100 implantations postoperative complications were seen in 3 cases (1 deep vein thrombosis, 1 fixed flexion deformity, 1 sub-luxation of the patella). Intraoperative complications were noticed by one patient because of an uncomplicated tibial fissure. One re-admission was necessary in 1 case because of a traumatic patella fracture. A reduction of pain was noticed in 89,2% after 1 year, in 100% after 2 years. In case of the radiological follow up no signs of loosening or implant failure were seen. Till June 2001 we had 2 more complications. One TKR has been revisised because of infection. One tibial component was changed because of instability and malrotation. The first results in 100 cemented mobile bearing knees were very encouraging. All patients with 1 to 2 year follw up represented good clinical and radiological results. Mechanical implant failures were not seen in any cases.
In Revision-THR the great variability of acetabular defects requires a revision-cup-system, which enables the surgeon to treat even extensive unexspected bone losses with a load stable reconstruction during the surgery. For these cases a modular revision support cup (MRS-Titan) has been developed. It allows the reconstruction of the geometric rotation centre and prevents the applied autologous or homologous bone graft in the healing phase from overlaoding. Beyond that an individual adjustment of the differently large flexible straps guarantees the solid anchoring of the revision support cup to the vital bone. The individual anatomy can be preserved in every case of acetabular destruction due to the high range of modularity the system provides. Because of the intraoperatively synthesis of all parts of the MRS-cup the approach and the traumatization of the soft tissue can be minimized. Since 1995 we implanted 95 MRS-Titan-cups out of 250 which were implanted world wide. In all cases a stable anchoring of the implant has been reached. We will report about our own follow-up and complications. In 4 MRS revisions a revitalized acetabular bone graft has been found able to host a noncemented hemispherical cup in three cases.
A stem revision system was developed by a group of orthopedic surgeons and bioengineers. Implant specific instruments have been created to make the operation as easy as possible. The stem of the MRP prosthesis is conical and forged of a Titanium Aluminium Niobium alloy. It consists of 2 modular elements, a diaphysical and a trochantical part that can be supplemented by a head. Stem lengths from 140 mm and 200 mm are aviable with different length of diaphysical and prolongation elements so that each stem length could be realized in small steps. Also the anchoring of th diaphysical prosthesis elements in the bone makes a free construction of the total prosthesis to the femur with choice of the length and a variable adjustment of the rotation position of the neck of the femur prosthesis. Eight longitudinal ridges on the stem elements guarantee a rotation stability and the curved stems allow a reconstruction of the physiological antecurvation of th thigh also in case of fractures and segmental resections. Since 1993 the members of the clinical working team implanted 1500 MRP prosthesis. We think that the best way for an optimal anchoring is the preservation of a great deal of the solid bone structures also in the section of the primary anchoring with partial bone resorption. The proximal anchoring of the femoral isthmus up to the middle third of the femur guarantees the most reliable long-term results. Indications for revision operations are given by resorptive bone defects up to a considerable bone loss on the proximal femur, for intraoperative stem fractures, for primary subtrochantar long distance fractures with simultaneous coxarthritis and for defect zones after bone tumor treatments. The very variable new design facilitates the revision operation and shortens the operation time. The MRP prosthesis is able to bridge mechanically stable, damaged or missing parts of the proximal femur with revision operations and it makes an immediate partial loading possible for the patient. Defected zones of the bone fill with bone structures as a basis for the local anchored musculature. The modularity of the prosthesis lightens the revision operation.
With 3D CT data of proximal femora it is possible to develop a computer programme for optimising femoral component fit and simulation of implantation. The implantation of the femoral stem can be simulated with any femoral component that has cortical press fit. Five different currently used femoral components were virtually “implanted” in over 200 different femoral bone data. Optimal femoral fit was defined, when the component showed best diaphyseal and metaphyseal congruent contact with all CT data available. Position of neck and head were secondary, since an optimal press fit situation had priority in our set-up. Best fit was considered taken cortical contact and reconstruction of joint geometry into account. There were numerous failures in all tested standard components, when correct angle of antetorsion, off-set, and leg length were expected. There were considerably better results with the use of CTX standard prosthesis (CTX-S). The data of this study indicate a high proportion of less optimal fit with femoral standard components tested in this series. Indication for choosing CTX-S femoral components is dependent upon the individual geometry of dysplastic hip joint and the simulation results of standard components using the VIP method.
The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from machining has been realised in order to overcome this limitations. The „All-in-One Milling-Tool“ achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under control by navigation. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive facilitated alignment und resection steps and the documentation of planned and actual implant position.
The disadvantages of sawing for precise bone cuts are well known: untrue cuts, heat and metal wear. The main limiting factors of available milling devices are the difficult handling and high costs, especially if the devices are based on a robot. Supported by clinical users and mechanical engineers a milling concept adopted from industrial machining has been realised in order to overcome this limitations. The “All-in-One Milling-Tool” achieves the same precision of a robot by a mechanically guided milling resection far below the necessary investment for a robot. Once fixed at the femur, the device allows all femural and tibial resections. Three methods are provided for the alignment of the resection planes and will be discussed: intramedullary adjustment, 3D CT-based planning and intramedullar performance as well as the performance under navigation control. All versions are based on a handheld resection and guarantee a visual and haptical feedback for the surgeon. The use of navigation has the advantage of the accurate transfer of the 3D plan into the OR, the interactive guided and facilitated alignment und resection steps and the documentation of planned and actual implant position.
