Intramedullary Threaded Nail Fixation Versus Plate and Screw Construct in Metacarpal Neck Fractures: A Biomechanical Study.

BACKGROUND: Indicated surgical management of metacarpal neck fractures varies with techniques, including Kirschner wire fixation, plate fixation, intramedullary fixation, and headless compression screw fixation, without demonstrated superiority. This study compares intramedullary threaded nail (ITN) fixation with a locking plate construct. METHODS: Index through small finger metacarpals were harvested from 10 embalmed cadavers. After application of appropriate exclusion criteria, remaining metacarpals underwent neck fracture creation by a three-point load to failure. Eight samples were randomly allocated to fixation with ITN fixation, and six were stabilized with a 2.3-mm seven-hole locking plate. Samples were then subjected to a second round of biomechanical testing using the same apparatus. Ultimate load between the intact tissue and the subsequently stabilized fracture was analyzed with a paired Student t -test. Percentage change in ultimate load in the intact tissue and stabilized tissue was calculated, and the magnitude of relative difference between the two groups was analyzed using unpaired Student t -tests. Statistical difference was defined by a P value of < 0.05. RESULTS: Both groups demonstrated the ability to handle a biomechanical load; however, both were significantly weaker than the intact tissue (paired Student t -test p ITN-fixed versus p ITN-intact = 0.006; p plate-fixed versus p plate-intact = 0.002). ITN samples demonstrated a higher load to failure (unpaired Student t -test p ITN-fixed versus p plate-fixed = 0.039). CONCLUSION: ITN provides a biomechanically stronger fixation constructed for vertically oriented metacarpal neck fractures compared with locking plate fixation. Both ITN and locking plate constructs provide stabilization capable of tolerating a biomechanical load; however, both fixation modalities are weaker than the native tissue.

Commonly used adjuvants (liquid soap, foam sanitizer, or ultrasound gel) do not improve strength or curing time of fiberglass cast material.

BACKGROUND: Bone fractures are one of the most common injuries in the USA. Fiberglass tape is a commonly used casting material, and many medical professionals apply adjuvants including liquid hand soap, foam sanitizers, and ultrasound gel in the hopes of improving outcomes relating to ease of molding and eventual strength, lamination, and smoothness of cast material. However, the efficacy of these agents to improve fiberglass cast mechanics has not been scientifically evaluated. The purpose of this study was to assess the mechanical effects of commonly used adjuvants on fiberglass cast materials. METHODS: Studies compared regularly shaped samples of water-activated, untreated fiberglass tape (Ossur Techform Premium) to water-activated fiberglass tape treated with one of three commonly used adjuvants (liquid soap, foam hand sanitizer, or ultrasound gel) during lamination. Material stiffness, yield stress, and ultimate load were measured by 3-point bending. RESULTS: These studies demonstrated that that liquid soap and ultrasound gel did not affect fiberglass tape mechanical properties, but alcohol-based foam sanitizer significantly reduced stiffness (- 32.8%), yield stress (- 33.6%), and ultimate load (- 31.0%) of the cast material as compared to the control group. Regression slopes were not significantly different between groups, suggesting that no adjuvants improved material curing time. CONCLUSIONS: These data suggest that the application of adjuvants is not beneficial and potentially harmful to fiberglass cast behavior. Despite the widespread practice of adjuvant application by medical professionals during casting, results from the current study suggest that use of these agents for structural enhancement of fiberglass casts is not beneficial and should largely be discouraged.