Lansdowne JL, Sinnott MT, Déjardin LM, Ting D, Haut RC.
Department of Small Animal Clinical Sciences, College of Veterinary Medicine, Michigan State University, East Lansing, MI 48824, USA.

Vet Surg. 2007 Jun;36(4):368-77. 

OBJECTIVE: To compare standard interlocking nails (ILN) with a newly designed ILN featuring an angle-stable locking mechanism (ILNn).

STUDY DESIGN: Six experimental groups.

SAMPLE POPULATION: Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.

METHODS: Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared (P<.05).

RESULTS: Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained approximately 2 x the torsional deformation of the bolted ones (approximately 36 degrees [ILN6s] versus approximately 18 degrees [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (approximately 8 degrees) and bending (approximately 4 degrees) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.

CONCLUSIONS: Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.

CLINICAL RELEVANCE: The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing.