Background: The purpose of this study was to compare the stability of the 2.4 mm palmar locking compression plate (LCP) and a new intramedullary nail-plate-hybrid Targon DR (TDR) for dorsally comminuted distal radius fractures.

Methods: An extraarticular 10 mm dorsally open wedge osteotomy was created in 8 pairs of fresh frozen distal radii to simulate an AO-A3-fracture. The fractures were stabilized with one of the fixation constructs. The specimens were loaded axially with 200 N and dorsal-excentically with 150 N. Cyclic loading with 2000 cycles as well as loading to failure were performed under axial loading.

Results: Axial loading revealed that intramedullary osteosynthesis (Targon DR: 369N/mm) was significantly (p=0.017) stiffer than plate osteosynthesis (LCP: 131 N/mm). With 214 N/mm the intramedullary nail was also more stable during dorsal excentric loading than the LCP with 51 N/mm (p=0.012). After the 2000 cycles of axial loading with 150 N the Targon group was still significant stiffer than the LCP group under both loading patterns. Neither group showed a significant change in stiffness after the 2000 cycles. The Targon DR group even showed a slight increase with 435,22 N/mm (p = 0.161), while the LCP group showed a slight decrease with 122.24 N/mm (p = 0.575) during axial loading. Under dorsal excentric loading the Targon group was still significant stiffer with 212.46 N/mm than the LCP group with 44.96 N/mm (p=0.012). The load to failure tests demonstrated again the superiority of intramedullary nailing (625N) when compared to plate osteosynthesis (403N) (p< 0.025).

Conclusions: The study shows that both implants are able to withstand physiological loads occuring under unloaded wrist motion. Neither implant showed a significant loss of stability after 2000 cycles long-term loading. Intramedullary nailing with the Targon DR of a distal A3 radial fracture is biomechanically more stable than volar fixed angle plating with the 2.4 mm LCP under axial and dorsal-excentric loads in our experimental setup.

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.

The purpose of this study was to evaluate the clinical outcome of a hydroxyapatite (HA)-coated tapered stem and to assess bone remodelling of the proximal femur using quantitative computed tomography osteodensitometry.

Fifty consecutive hips were managed with total hip replacement using the Cerafit Multicone H-A.C. stem with HA coating and the Cerafit Triradius-M press-fit cup (Ceraver Osteal, Paris, France). The mean follow-up was 3 years (range, 2.9 to 4 years). Current criteria were used for clinical and radiological assessment.

Forty-nine hips (98%) were clinically rated good or excellent. The mean preoperative Harris Hip Score was rated 57, and it has improved to 96 at the time of follow-up. The radiographs showed stable fixation by bone ingrowth in all hips. Fifteen patients (15 hips) were eligible for osteodensitometry. The mean decrease of the overall bone density (BD) in the metaphyseal portion of the femur 3 years after insertion of the stem was rated 14.21%, and the mean decrease of the cortical BD was rated 15.52%. The mean decrease of the overall BD in the diaphyseal portion of the femoral component was rated 10.00%, and the mean decrease of cortical BD was rated 7.76%. Little changes were observed underneath the tip of the stem.

The clinical and radiological outcomes of the tapered stem with HA coating at a mean follow-up of 3 years compares favourably with other reports. Results of osteodensitometry show less proximal femur BD loss in comparison to similar investigations performed using uncemented stems.