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: Radial Head Arthroplasty is considered the treatment of choice for unreconstructable radial head fractures. Short-term results in the current literatue are promising. Due to the lack of long-term results, radial head arthroplasty is looked at critically by many surgeons. In our the study we provide the 8.4 years results after treatment with the floating radial head prosthesis by Judet (Tornier, France).

Methods: In our department 19 patients were treated with bipolar radial head arthroplasty between 1997 and 2001. 11 prostheses were implantated primary and 6 secondary. The other two were implanted because of a loosening of a prior implanted prosthesis and one after resection of a vast chondrosarcoma. 12 of these patients − 10 men and 2 women – were now examined retrospectively after 101 months (78–132).

Results: 6 Patients were treated primary, 5 secondary and one was treated because of a vast chondrosarcoma. There were 5 proximal ulna fractures and 8 processus coronoideus fractures as concomitant injuries of the elbow. Following complications were seen: 2 dislocations, 2 capitellar erosions and 4 cases of heterotopic ossifications. According to the Mayo Elbow Performance Score 4 patients achieved an excellent result, 7 a good, and one a satisfactory result. The mean DASH was 13.7 (0–44). No differences were seen between primary and secondary implantation. The flexion arc was 123° (110–140°), the extension deficit was 20° (0–40°), pronation 61° (30–90°) and supination 62° (40–90°).

Conclusion: Our 8.4 years results show that radial head arthroplasty with Judet’s bipolar prosthesis leads to mostly excellent and good – subjective as well as objective – results.

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.

The science of tribology concerning hip arthroplasty has mainly dealt with total endoprostheses, whereas measurement values of hemiendoprosthetic implants are rare. The small amount of experimental tribologic data concerning hemiendoprosthetic implants in the form of pendulum trials, animal experiments, in-vivo measurements on human hip joints and pin on disc studies will be reviewed in the following work. The reported frictional coefficients in these studies were between 0,014-0,07. In order to test the friction coefficients of different femur head hemiendoprostheses (ceramic-cobalt chrome – and titanium heads and bipolar endoprostheses) against fresh cadaveric acetabula, the HEPFlEx-hip simulator (Hemi-EndoProsthesis Flexion Extension) was developed. In the simulator, the various hemiendoprosthetic heads are placed on a special cone and tested against a human cadaver acetabulum cast in MCP 47 woodmetal. The plane of movement of the apparatus is uniaxial with a rotating movement of +/− 35 degrees. The force is produced pneumatically dynamic with amounts of up to 5 kN. Newborn calf serum served as a lubricant. Preliminary results showed that the mean friction coefficient at 3 kN loading was μ=0.032–0.07 for ceramic against cartilage and μ=0.024–0.153 for metal against cartilage.