Objective
To compare the torsional strength of calf metatarsal bones with defects produced by removal of 2 different implants.
Study Design
In vitro mechanical comparison of paired bones with bicortical defects resulting from the implantation of 2 different external fixation systems: the transfixation pin (TP) and the pin sleeve system (PS).
Sample Population
Neonatal calf metatarsal bones (n = 6 pairs).
Methods
From each pair, 1 bone was surgically instrumented with 2 PS implants and the contralateral bone with 2 TP implants. Implants were removed immediately leaving bicortical defects at identical locations between paired metatarsi. Each bone was tested in torque until failure. The mechanical variables statistically compared were the torsional stiffness, the torque and angle at failure, and work to failure.
Results
For TP and PS constructs, respectively, there were no significant differences between construct types for any of the variables tested. Mean ± SD torsional stiffness: 5.50 ± 2.68 and 5.35 ± 1.79 (Nm/°), P = .75; torque: 57.42 ± 14.84 and 53.43 ± 10.16 (Nm); P = .34; angle at failure: 14.76 ± 4.33 and 15.45 ± 4.84 (°), P = .69; and work to failure 7.45 ± 3.19 and 8.89 ± 3.79 (J), P = .17).
Conclusions
Bicortical defects resulting from the removal of PS and TP implants equally affect the investigated mechanical properties of neonate calf metatarsal bones.
