Interfragmentary displacement has a main effect on callus formation in fracture healing. To test whether compressive or distractive displacements have a more pronounced effect on new bone formation, a sheep osteotomy model was created whereby the gap tissue was subjected to constant bending displacement. A diaphyseal osteotomy with a gap of 2 mm was created in 18 sheep tibiae and stabilized with a special unilateral actuator-driven external fixator. Two experimental groups with six sheep each received either 10 or 1000 cycles evenly distributed over 24 h. The third group of six sheep served as a control group without actively induced displacement. The amount and direction of cyclic displacement was kept constant throughout the observation period, resulting in 50% compressive and 50'%) distractive displacement within the osteotomy gap. At sacrifice, six weeks after surgery, bending stiffness was measured and new bone formation was assessed radiologically and microradiographically. In all cycled groups, the amount of periosteal callus formation was up to 25 times greater on the compression compared to the distraction side (p < 0.001). The application of the higher number of daily cycles resulted in an up to 10-fold greater amount of periosteal new bone formation on the compression side ( p < 0.012), while the difference on the distraction side was not significant. Ten cycles applied a day were sufficient to create an abundant periosteal callus on the compression side. In the 1000 cycle group, bending stiffness revealed slightly lower values but the difference was not significant. Solid periosteal bridging of the gap was observed in two sheep in the control group, whereas bridging in the cycled groups was observed exclusively at the medullary side. In conclusion, cyclic compressive displacements were found to be superior over distractive displacements. A higher number of enforced and maintained compressive displacements enhanced periosteal callus formation but did not allow bony bridging of the gap.

The intramedullary load carriers were biomechanically superior when compared to the plating systems in the fracture model presented here. Supplementary, the Sirus Nail showed higher stiffness values than the PHN. However, the latter are gaining in importance due to the possibility of minimal invasive implantation. Whether this will be associated with functional advantages requires further clinical investigation.

In the presented prospective study 35 consecutive patients with displaced 3- and 4-part fractures of the proximal humerus, including fracture dislocations, were treated with a fixator plate comprising angular stability between May 2001 and December 2002. After 18.5 (8-29) months 31 (89%) fractures were available for follow-up. Good and very good results were obtained in 64%. A poor result was documented in 23%. 64% of the patients had no or mild pain, 71% were able to abduct the arm over 90 degrees . Fracture classification according to Neer and AO had no influence on the outcome, with a mean Constant Score of 76 points. Partial avascular necrosis (AVN) of the humeral head was seen in 16% of all cases representing 4% of the fractures without dislocation and 80% of the fracture dislocations. Fracture dislocation (p=0.02) and AVN (p=0.005) had a negative effect on the Constant Score, with AVN being a predictor for a high level of pain (p=0.04). Secondary dislocation of the greater tuberosity was seen in two patients, loosening of screws in one patient and a fracture below the plate in another one. Secondary dislocation or loss of reduction of the head was not recorded. Angle stable plate fixation with tension band wiring of the tuberosities is an effective and safe option to treat this difficult fractures, also in elderly patients with osteoporotic bone. Because 40% of the 4-part fractures with fracture dislocation yielded a satisfactory or better result, the plate fixator with angular stability may be an alternative to prosthetic replacement in selected cases.

Indirect MR arthrography with supplementary images obtained with patients in the ABER position significantly improved sensitivity and increased diagnostic confidence for partial-thickness tears of the supraspinatus tendon. Interobserver agreement was improved for both full- and partial-thickness tears.