OBJECTIVE: To develop a bone fixation nut (PFO) for the purpose of increasing the internal osteosynthesis stability. METHODS: 16 fresh cadavers were used (32 proximal humeral extremities), eight male and eight female, mean age of 60.56 years. In each of the 16 cadavers, the humerus of one of the arms was fixated with a PFO-plate-screw system, and the contralateral was fixated with the plate-screw-nut system made of conventional metal. A load was applied on the system and measured by a torquemeter till one of the elements failed (polyethylene nut, conventional nut, or bone). The load individually used by 20 orthopedists to tighten the screws till the point they believed that the system was stable was measured. All of the results were noted down and statistically evaluated. RESULTS: In the evaluation of the mean load used to tighten the screws, in routine fixations, individually, by 20 experienced orthopedists, a mean load of 3.18 N.m was found, this load being lower than the strength of the PFO-plate-screw system, that was 6.37 N.m. Failure of the system in the bone with the PFO occurred in three cases and failure of the system with the metal nut occurred in 10 cases. CONCLUSION: The PFO nut showed to be less aggressive to the bone than the conventional metal nut, and presented a lower incidence of bone fracture. The mean load applied by the orthopedist is not sufficient to break the nut and lead to a system failure.
Osteoporosis; Shoulder fractures; Orthopedic fixation devices; Cadaver
