In vitro biomechanical comparison of a plate-rod combination-construct and an interlocking nail-construct for experimentally induced gap fractures in canine tibiae

OBJECTIVE: To compare structural properties of a plate-rod combination-bone construct (PRCbc) and interlocking nail-bone construct (ILNbc) by use of an experimentally induced gap fracture in canine tibiae. SAMPLE POPULATION: 12 paired canine tibiae. PROCEDURE: Specimens were implanted with a plate-rod combination consisting of a 3.5-mm, limited-contact, dynamic-compression plate combined with an intramedullary rod or 6-mm interlocking nail. Ostectomy (removal of 10-mm segment) was performed. Paired constructs were loaded for bending, compression, or torsion measurements (4 constructs/group). Compliance was determined by fitting regression lines to the load-position curves at low (initial compliance) and high (terminal compliance) loads. RESULTS: Bending compliances did not differ significantly between constructs. For the ILNbc, initial compliance was greater than terminal compliance in compression and torsion. Initial compliance and terminal compliance for the PRCbc were similar in compression and torsion. Initial compliance in compression and torsion was greater for the ILNbc, compared with initial compliance for the PRCbc. Maximum deformations in bending and compression were similar between constructs; however, maximum torsional angle was significantly greater for the ILNbc, compared with values for the PRCbc. CONCLUSIONS AND CLINICAL RELEVANCE: The study documented that for an experimentally induced gap fracture in canine tibiae, a plate-rod combination is a significantly less compliant fixation method in torsion and compression, compared with an interlocking nail. Considering the deleterious effects of torsional deformation on bone healing, a plate-rod combination may represent a biomechanically superior fixation method, compared with an interlocking nail, for the treatment of dogs with comminuted tibial diaphyseal fractures.