Ovine Femur Research Articles

Femoral Press-Fit Fixation of the Hamstring Tendons for Anterior Cruciate Ligament Reconstruction

Background Press-fit fixation of patellar tendon–bone anterior cruciate ligament autografts is an interesting technique because no hardware is necessary. For hamstring tendon grafts, no biomechanical data exist of a press-fit procedure. Hypothesis Press-fit femoral fixation of hamstring tendons is mechanically equivalent to press-fit patellar tendon–bone fixation. Study Design Controlled laboratory study. Methods Patellar and hamstring tendons of 30 human cadavers (age, 53.8 ± 18.0 years) were used. An outside-in press-fit fixation with a knot in the semitendinosus and gracilis tendons and an inside-out and outside-in fixation with the tendons wrapped around a bone block were compared with patellar tendon–bone press-fit fixation in 30 ovine femora. Constructs were cyclically strained and then loaded until failure. Maximum load to failure, stiffness, and elongation during failure testing and cyclical loading were investigated. Results The maximum load to failure was 561 ± 309 N for the patellar tendon, 599 ± 234 N for the semitendinosus/gracilis tendons knot construct, 678 ± 231 for the semitendinosus/gracilis tendons bone construct inserted outside in, and 339 ± 236 for the semitendinosus/gracilis tendons bone construct inserted inside out (inferior to the others; analysis of variance, Dunn test, P < .01). Stiffness of the constructs averaged 134 ± 32 N/mm for the patellar tendon, 124 ± 21 N/mm for the knot construct, 118 ± 27 N/mm for the outside-in fixation, and 117 ± 23 N/mm for inside-out fixation. Elongation during initial cyclical loading was 0.7 ± 0.6 mm for the patellar tendon, 1.6 ± 0.5 mm for the knot construct, 1.9 ± 1.2 mm for the outside-in fixation, and 1.9 ± 0.9 mm for the inside-out fixation (significantly larger for all semitendinosus/gracilis tendon techniques, P < .05). Conclusions Failure loads for the semitendinosus/gracilis tendons bone construct inserted outside in and the semitendinosus/gracilis tendons knot construct were within the confidence interval of the patellar tendon press-fit fixation. All semitendinosus/gracilis tendon graft techniques exhibited larger elongation during initial cyclical loading than the patellar tendon graft. There was no difference in stiffness between all techniques. Clinical Relevance Two of the 3 hamstring press-fit fixation techniques showed loads to failure similar to the patellar tendon fixation. Preconditioning of the constructs is critical. These results must be interpreted with care because of high standard deviations.

Limb lengthening by diaphyseal corticotomy, callus distraction, and dynamic axial fixation. An experimental study in the ovine femur.

Limb lengthening of the left femur was performed in 12 sheep, 7-8 months of age. After weakening of the cortex by drill holes, a controlled fracture was created in the diaphysis. The bone segments were fixed in reduced position using a unilateral external fixation device. The fixator was left in neutral position for 10 days postoperatively when lengthening started. By means of daily distraction at a rate of 1.0 mm once a day for 3 weeks, an average lengthening of 1.9 cm (11.9%) was obtained. Two weeks after distraction had been discontinued, distinct callus bridging of the lengthening zone was confirmed radiographically in all animals. At this time the rigid state of fixation was converted to a system allowing axial compression by loading in half the animals. The other half of the animals served as controls with the fixator remaining unchanged. The external device was left on until 5 weeks after the end of distraction. At this time the animals were killed. Both femora of all animals were tested mechanically in torsion. The average ultimate torsional strength of the elongated femur compared with control was 71% in the group with dynamic axial fixation and 65% in the control group. No significant difference in relative strength of the tested bones in the two groups was found. We conclude that intermittent axial compression by loading during consolidation had no significant effect on the bone-healing process evaluated by radiography and mechanical testing.