Biomechanical Consequences of Nail Insertion Point and Anterior Cortical Perforation for Antegrade Femoral Nailing

Biomechanical properties of artificial bones made by Sawbones: A review

Biomedical engineers and physicists frequently use human or animal bone for orthopaedic biomechanics research because they are excellent approximations of living bone. But, there are drawbacks to biological bone, like degradation over time, ethical concerns, high financial costs, inter-specimen variability, storage requirements, supplier sourcing, transportation rules, etc. Consequently, since the late 1980s, the Sawbones® company has been one of the world's largest suppliers of artificial bones for biomechanical testing that counteract many disadvantages of biological bone. There have been many published reports using these bone analogs for research on joint replacement, bone fracture fixation, spine surgery, etc. But, there exists no prior review paper on these artificial bones that gives a comprehensive and in-depth look at the numerical data of interest to biomedical engineers and physicists. Thus, this paper critically reviews 25 years of English-language studies on the biomechanical properties of these artificial bones that (a) characterized unknown or unreported values, (b) validated them against biological bone, and/or (c) optimized different design parameters. This survey of data, advantages, disadvantages, and knowledge gaps will hopefully be useful to biomedical engineers and physicists in developing mechanical testing protocols and computational finite element models.

Biomechanical comparison of the undercut thread design versus conventional buttress thread for the lag screw of the dynamic hip screw system

Objective: To compare the fixation stability of the lag screw with a undercut thread design for the dynamic hip screw (DHS) system versus the lag screw with the conventional buttress thread. Methods: The lag screws with the undercut thread (a flat crest feature, a tip-facing undercut feature) and buttress thread were both manufactured. Fixation stability was investigated using cyclic compressive biomechanical testing on custom osteoporotic femoral head sawbone. The forces required for the same vertical displacement in the two types of lag screw were collected to evaluate the resistance to migration. Varus angle was measured on X-ray images to assess the ability in preventing varus collapse. Finite element analysis (FEA) was performed to analyze the stress and strain distribution at the bone-screw interface of the two types of lag screws. Results: The biomechanical test demonstrated that the force required to achieve the same vertical displacement of the lag screw with the undercut thread was significantly larger than the lag screw with conventional buttress thread (p < 0.05). The average varus angles generated by the undercut and buttress threads were 3.38 ± 0.51° and 5.76 ± 0.38°, respectively (p < 0.05). The FEA revealed that the region of high-stress concentration in the bone surrounding the undercut thread was smaller than that surrounding the buttress thread. Conclusion: The proposed DHS system lag screw with the undercut thread had higher migration resistance and superior fixation stability than the lag screw with the conventional buttress thread.