Measurement of insertion torque of tapered external fixation pins: A comparison between two experimental models.

The aim of this study was to compare an in vitro versus an ex vivo experimental model to test the insertion torque of two different types of external fixation pins. A torque measuring machine was developed in order to perform accurate measurements. Forty tapered pins made of stainless steel were utilized. Half of the pins were plasma-spray coated with hydroxyapatite (HA) and the other half remained uncoated. For the in vitro model 20 cylinders were used that were made of synthetic polymer according to ASTM standards. For the ex vivo model 10 fresh femora harvested from adult sheep were used. All the pins were implanted after predrilling, and insertion torque was measured. Statistical analysis of the in vitro versus the ex vivo model showed significant differences in both coated (p < 0. 0005) and uncoated (p = 0.002) external fixation pins. These results may be due to the surface roughness that caused significant friction between the HA coating and the polyvinylchloride in the in vitro model. The significant difference between the in vitro and ex vivo results lead us to state that the in vitro model does not realistically simulate the behavior of external fixation pins implanted in bone.

Surgical treatment of isolated forearm non-union with segmental bone loss.

Twenty-four isolated radius and ulna non-unions with segmental bone loss were operated on. Nine non-unions were in the radius, 15 in the ulna. The surgical technique consisted of removal of the necrotic bone, filling of the bone defect with an intercalary bone graft and internal fixation with a cortical bone graft fixed opposite to a plate. The average length of bone defect after freshening of the bone ends was 3.6 cm (range 2-10.5 cm). The average length of follow-up was 90 months. In 23 cases union was achieved. In three cases a postoperative infection developed. Resolution of the infection after surgical debridement was achieved in two of these patients, while recurrent infection caused failure of the treatment in the third patient. Statistical analysis revealed a shorter healing time (p = 0.031) in the ulna non-unions (12.5 +/- 3.0 weeks) compared with the radius non-unions (16.4 +/- 4.2 weeks). Functional results were classed as excellent in 10 patients, satisfactory in six, unsatisfactory in seven and failure in one.