RESUMEN
PURPOSE: The purpose of this study was to compare the effect of varying screw lengths on load to failure and retention of the dorsal ulnar corner fragment after fixation of comminuted intra-articular distal radius fractures in a cadaveric model. METHODS: Twenty-four fresh frozen cadaveric forearms were subjected to a standardized distal radius osteotomy to mimic an intra-articular fracture pattern. Dual X-ray absorptiometry scans were performed to ensure minimal variability in bone density. All fractures were fixed with a volar locking plate and distal locking screws. Three different lengths of distal locking screws were used in each group of eight specimens to simulate the clinical decision of different distal screw lengths. The screw lengths tested were bicortical, 100% of the width of the bone but unicortical, and 75% of the width of the bone and unicortical. All specimens were preconditioned with cyclic axial loading and then axially loaded using matching acrylic resin molds to clinical failure and fragment displacement as detected by a motion analysis system. Retention or loss of the dorsal ulnar corner fragment during loading was recorded as a binary variable. RESULTS: Between the three groups, there were no statistically significant differences in precycling stiffness, postcycling stiffness, load at 2 mm displacement of the dorsal ulnar corner, or force at failure. The group with 75% length screws had a significantly higher loss of reduction of the dorsal ulnar corner (86%) compared with the other groups (0%). CONCLUSIONS: Varying screw lengths did not affect the stiffness or overall loads to failure of axially loaded specimens. However, the 75% length screws did not reliably secure the dorsal ulnar corner fragments. Although this did not significantly affect the overall load to failure of the construct, displacement of this fragment may have implications for rotation of the forearm through the distal radioulnar joint. CLINICAL RELEVANCE: Surgeons should consider the utilization of full-length unicortical locking screws to ensure adequate fixation of the dorsal ulnar corner. TYPE OF STUDY/LEVEL OF EVIDENCE: Biomechanical study V.
RESUMEN
The fracture behavior of bone is critically important for evaluating its mechanical competence and ability to resist fractures. Fracture toughness is an intrinsic material property that quantifies a material's ability to withstand crack propagation under controlled conditions. However, properly conducting fracture toughness testing requires the access to calibrated mechanical load frames and the destructive testing of bone samples, and therefore fracture toughness tests are clinically impractical. Impact microindentation mimicks certain aspects of fracture toughness measurements, but its relationship with fracture toughness remains unknown. In this study, we aimed to compare measurements of notched fracture toughness and impact microindentation in fresh and boiled bovine bone. Skeletally mature bovine bone specimens (n = 48) were prepared, and half of them were boiled to denature the organic matrix, while the other half remained preserved in frozen conditions. All samples underwent a notched fracture toughness test to determine their resistance to crack initiation (KIC) and an impact microindentation test using the OsteoProbe to obtain the Bone Material Strength index (BMSi). Boiling the bone samples increased the denatured collagen content, while mineral density and porosity remained unaffected. The boiled bones also showed significant reduction in both KIC (P < .0001) and the average BMSi (P < .0001), leading to impaired resistance of bone to crack propagation. Remarkably, the average BMSi exhibited a high correlation with KIC (r = 0.86; P < .001). A ranked order difference analysis confirmed the excellent agreement between the 2 measures. This study provides the first evidence that impact microindentation could serve as a surrogate measure for bone fracture behavior. The potential of impact microindentation to assess bone fracture resistance with minimal sample disruption could offer valuable insights into bone health without the need for cumbersome testing equipment and sample destruction.
RESUMEN
The fracture behavior of bone is critically important for assessing its mechanical competence and ability to resist fractures. Fracture toughness, which quantifies a material's resistance to crack propagation under controlled geometry, is regarded as the gold standard for evaluating a material's resistance to fracture. However properly conducting this test requires access to calibrated mechanical load frames the destruction of the bone samples, making it impractical for obtaining clinical measurement of bone fracture. Impact microindentation offers a potential alternative by mimicking certain aspects of fracture toughness measurements, but its relationship with mechanistic fracture toughness remains unknown. In this study, we aimed to compare measurements of notched fracture toughness and impact microindentation in fresh and boiled bovine bone. Skeletally mature bovine bone specimens (n=48) were prepared, and half of them were boiled to denature the organic matrix, while the other half remained preserved in frozen conditions. Notched fracture toughness tests were conducted on all samples to determine Initiation toughness (KIC), and an impact microindentation test using the OsteoProbe was performed to obtain the Bone Material Strength index. Boiling the bone samples resulted increased the denatured collagen without affecting mineral density or porosity. The boiled bones also showed significant reduction in both KIC (p < 0.0001) and the average Bone Material Strength index (p < 0.0001), leading to impaired resistance of bone to crack propagation. Remarkably, the average Bone Material Strength index exhibited a high correlation with KIC (r = 0.86; p < 0.001). The ranked order difference analysis confirmed excellent agreement between the two measures. This study provides the first evidence that impact microindentation could serve as a surrogate measure for bone fracture behavior. The potential of impact microindentation to non-destructively assess bone fracture resistance could offer valuable insights into bone health without the need for elaborate testing equipment and sample destruction.