Introduction: This study was initiated to evaluate cortical and cancellous bone density (BD) changes of the acetabulum after cemented and uncemented total hip arthroplasty (THA) using computer tomography (CT)-assisted osteodensitometry in-vivo.

Materials and Methods: 15 cemented ZCA Pfannen cups (Zimmer, USA) (age 78 years) and 21 press-fit Trilogy cups (Zimmer, USA) (age 72 years) were implanted by one surgeon. All hips were investigated by a standardized CT-mode (slice thickness 2 mm, table feed 5 mm, extended CT-scale). 6 CT-scans at the level of the cup and 4 scans above the dome of the cup were analyzed 2 weeks and 2 years after surgery. Cancellous and cortical bone mineral density (BMD) (CaHA mg/ml) were elaborated with a special software tool (CAPPA postOP, CAS Innovations AG, Erlangen).

Results: 2 years after index operation cemented cups showed mild cancellous BD loss (−8% to −20%) and no significant cortical BD changes cranial, significant cortical (−4% to −20%) and cancellous (−16% to −44%) BD loss ventral and no significant BD changes dorsal to the cup.

For press-fit cups we observed highly significant (p< 0,01) cancellous BD loss in all sectors (−17% to −53%), cortical BD loss ventral and dorsal to the cup (−12% to −23%) and very limited BD loss cranial (−4% to −13%) to the cup.

Conclusions CT-assisted osteodensitometry allows a thorough assessment of the actabular bone in-vivo. Different patterns of stress shielding were observed for cemented and press-fit cups. For the press-fit cup high BD loss for both cortical and cancellous bone was observed in all areas adjacent to the pelvic implant, except for cortical BD at the acetabular dome, suggesting fixation of the cup in the cranial cortical bone. Comparetively less BD loss was seen for cemented cups in all sectors, especially for cancellous bone, suggesting a more physiological stress transfer to both cortical and cancellous pelvic bone.

Introduction: The aim of this study was to analyze the periprosthetic bone remodeling of the femoral component after implantation of an uncemented taper-design stem using CT-assisted osteodensitometry. This method allows accurate three-dimensional evaluation of cortical and cancellous bone with high resolution.

Material and methods: We followed 21 consecutive Patients with osteoarthritis who received primary total hip replacement using 21 uncemented three-dimensionally shaped taper stems (TiAl6V4-Cerafit, Ceraver, France). CT-evaluation was performed 2 weeks, 1 and 6 years post-op. Bone mineral density (BMD) [mg/ml] was determined separately for both cortical and cancellous bone using a special software.

Results: Mean decrease of cortical BMD in the proximal (metaphyseal) area 6 years post-op was −25%, (1 year post-op −15%). Only slight changes of BMD were observed in the distal (diaphyseal) area. Cancellous BMD decreased progressively from −26% 1 year post-op to −49% 6 years after index operation in the proximal area. Cortical bone density loss was lower and non-progressive at the diaphysis (Ø −7% 1 year, −9% 6 years post-OP) and the distal region (Ø −6% 1 year, −4% 6 years post-OP) of the stem. All stems showed no signs of loosening on plain radiography and good clinical results according to the Harris hip score.

Conclusion: Computertomography assisted osteoden-sitometry is the only method which allows discrimination between periprosthetic cortical and cancellous bone density changes in vivo. The analyzed uncemented stem is anchored at the diaphysis and distal region. Due to the changed biomechanical loading after stem implantation, progressive proximal cancellous bone density loss was measured for the first time in vivo. Its role in the pathogenesis of implant loosening is still unknown and needs to be further elucidated.

Background: The aim of this prospective multi-center study was to evaluate the clinical and radiological results of a total of 314 uncemented femoral stem revisions using the modular MRP-titanium system.

Methods: 305 patients (111 males, 194 females, mean age 67.7) with 314 MRP-titanium systems were followed-up for a meantime of 3.2 years (1 to 9 years). Pre- and post-operatively all patients were clinically documented using the Harris hip score. Radiologically, the preoperative bony defects were assessed by the Paprosky classification. Post-operatively, periprosthetic bone remodeling was evaluated on the basis of radiographic evidence of bone apposition or resorption.

The modular MRP-titanium system has proven to be valuable in quite problematic cases of hip revision arthroplasty with extensive femoral defects. The system allows intraoperative adaptation of implant length and antetorsion angle to the actual situation, a feature not provided by non-modular femoral revision implants.

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.

Aims: Prospective multi-center study to evaluate the mid-term results of 280 uncemented femoral stem revisions using the modular MRP-Titan system. Methods: 273 patients with 280 MRP-Titan systems, follow-up for a mean time of 3 years (1 to 8 years). Harris hip score for clinical evaluation, bony defect classification according to Paprosky [163 cases (58%) with type 2B, 2C and 3]. Results: Three aseptic loosenings (1%), three septic loosenings (1%), one additional re-revision because of periprosthetic fracture. Postoperative dislocations occurred in 23 cases (8%), 17 of these (6%) were managed by closed or open reposition without changing the implant. In 6 cases (2%) the antetorsion angle of the modular prosthesis neck was altered. Harris hip score: 38 points preoperatively, 85 points at the last follow-up postoperatively. In 18 cases (6.4%) radiolucient lines were seen, but with no progression and no migration of the stems. The overall survival-rate after 8 years of follow-up was 92%. Conclusions: The modular MRP-Titan system has proven to be valuable in quite problematic cases of hip revision arthroplasty with extensive femoral defects. The system allows intraoperative adaptation of implant length and antetorsion angle to the actual situation, a feature not provided by non-modular femoral revision implants.

Aim: Can comparable results be obtained regarding the postoperative improvement of range of motion using ßexionosteotomy alone in comparison to the three-dimensional corrective osteotomy. Material and Methods: 16 patients after SCFE were analyzed (7 female, 9 male). A computer program for simulation of movement and osteotomy developed by the authors, served for study execution. According to 3D-reconstruction of the computer tomography data the physiological range was determined by ßexion, abduction and internal rotation. The three-dimensional osteotomy was compared with the onedimensional ßexionosteotomy. Both inter-trochanteric osteotomy techniques were simulated and the improvements of the movement range were assessed and compared. Results: The average slipping and thus correction angles measured inferior 25.5¡ (range: 7.5¡–51.0¡) and posterior 52.0¡ (range: 29.0¡– 78.5¡). After the simulation of osteotomy by Southwick the angle of ßexion was 61.3¡ (improvement: 41.4¡), of abduction 60.3¡ (improvement: 42.9¡) and interior rotation of 70.1¡ (improvement: 52.6¡). The ßexionsosteotomy after Grifþth achieved a ßexion of 66.7¡ (improvement: 46.8¡), an abduction of 41.1¡ (improvement: 23.7¡) and an internal rotation of 57.4¡ (improvement: 40.0¡). Conclusion: The improvement of the free movement range after ßexion osteotomy is comparable, with three-dimensional osteotomy after Southwick with the exception of the abduction angle.