Bone Nanomechanical Properties and Relationship to Bone Turnover and Architecture in Patients With Atypical Femur Fractures: A Prospective Nested Case-Control Study

Atypical femur fractures (AFFs) are well-established serious complication of long-term bisphosphonate and denosumab therapy in patients with osteopenia or osteoporosis. To elucidate underlying mechanism(s) for the development of AFF, we performed a nested case-control study to investigate bone tissue nanomechanical properties and prevailing bone microstructure and tissue-level remodeling status as assessed by bone histomorphometry. We hypothesized that there would be differences in nanomechanical properties between patients with and without AFF and that bone microstructure and remodeling would be related to nanomechanical properties. Thirty-two full-thickness transiliac bone biopsies were obtained from age- and sex-matched patients on long-term bisphosphonate therapy with (n = 16) and without an AFF (n = 16). Standard histomorphometric measurements were made in each sample on three different bone envelopes (cancellous, intracortical, and endosteal). Iliac bone wall thickness was significantly lower on all three bone surfaces in patients with AFF than in those without AFF. Surface-based bone formation rate was suppressed similarly in both groups in comparison to healthy premenopausal and postmenopausal women, with no significant difference between the two groups. Nanoindentation was used to assess material properties of cortical and cancellous bone separately. Elastic modulus was higher in cortical than in cancellous bone in patients with AFF as well as compared to the elastic modulus of cortical bone from non-AFF patients. However, the elastic modulus of the cancellous bone was not different between AFF and non-AFF groups or between cortical and cancellous bone of non-AFF patients. Resistance to plastic deformation was decreased in cortical bone in both AFF and non-AFF groups compared to cancellous bone, but to a greater extent in AFF patients. We conclude that long-term bisphosphonate therapy is associated with prolonged suppression of bone turnover resulting in altered cortical remodeling and tissue nanomechanical properties leading to AFF

Fatigue testing of three peristernal median sternotomy closure techniques

Failure of a sternotomy closure because of closure system fatigue is a complication that may result in dehiscence and put the individual at risk for serious complications. The purpose of this study was to assess the fatigue performance of three peristernal median sternotomy closure techniques (figure-of-eight stainless-steel wires, figure-of-eight stainless-steel cables, or Pectofix Dynamic Sternal Fixation [DSF] stainless-steel plates) in order to quantify the potential risk of fatigue failure of these devices when subject to cyclic loads in physiologically relevant loading directions

Fatigue strength of common tibial intramedullary nail distal locking screws

Premature failure of either the nail and/or locking screws with unstable fracture patterns may lead to angulation, shortening, malunion, and IM nail migration. Up to thirty percent of all unreamed nail locking screws can break after initial weight bearing is allowed at 8–10 weeks if union has not occurred. The primary problem this presents is hardware removal during revision surgery. The purposes of our study was to evaluate the relative fatigue resistance of distal locking screws and bolts from representative manufacturers of tibial IM nail systems, and develop a relative risk assessment of screws and materials used. Evaluations included quantitative and qualitative measures of the relative performance of these screws

A Biomechanical Comparison of Three Sternotomy Closure Techniques

Background. A biomechanical study of three sternotomy closuretechniques (figure-of-eight stainless-steel wires, PectofixDynamic Sternal Fixation [DSF] stainless-steel plates, and figure-of-eightstainless-steel cables) was conducted to compare strength andstiffness variables in three clinically relevant loading modes(anterior-posterior shear, longitudinal shear, and lateral distraction). Methods. All tests were conducted on polyurethane foam sternalmodels that simulate the properties of cancellous bone. Eachmodel was divided longitudinally and reconstructed using oneof the sternotomy closure repair techniques. Tests were performedusing a materials testing system that applies a continuouslyincreasing amount of force in one direction to the model untilit catastrophically breaks. A total of six trials of each fixationtype in each of three test groups were prepared and tested,for a total of 54 tests. Strength and stiffness variables aswell as a post-yield analysis of failure were evaluated. Results. Sternums repaired using the DSF plate system are amore rigid construct than sternums repaired using the stainless-steelwires or cables in the distraction and transverse shear modesand they are not significantly different from sternums repairedwith wires or cables in the longitudinal shear mode. The DSFplate system offers a 25% improvement in resistance to failure(yield) compared to wires when a transverse shear force is appliedto the model. The cable system had a higher resistance to failurethan the wires in all modes although the differences were notstatistically significant. Additionally, the DSF plate systemprovides substantial reduction of the implant’s cuttinginto the sternal model under loading as evidenced by the post-yielddisplacement when compared with either cables or wires for thedistraction and longitudinal shear modes. For the transverseshear mode, the cables or wires would completely fail at theload for which cutting begins for the DSF. Conclusions. Both the DSF plate system and the stainless-steelcable system offer important advantages over figure-of-eightwire for sternal closure

Armature position sensor for a relay

A sensor for use with high-power solenoid-actuated relays, and for detecting and signalling relay armature position and hence the actuation state of the relay. The sensor is external to a sealed chamber in which the relay contacts and armature system are positioned, and includes a permanent magnet, the flux path of which includes the relay armature and base. Armature movement to close the relay alters the flux path to operate a reed switch adjacent the magnet, and the condition of the reed switch signals the unactuated or actuated state of the relay

Osteon interfacial strength and histomorphometry of equine cortical bone

The interfacial strength of secondary osteons from the diaphysis of the Thoroughbred equine third metacarpal was evaluated using the fiber pushout test. The pushout was performed on 300–500 mm sections of 4x4x15mm bone blocks machined from four anatomic regions of the cortex. Pushout strength was evaluated from proximal to distal location within the diaphysis on four osteon types classified under polarized light on adjacent histologic sections from each block. The shear strength of the interfaces were estimated from shear lag theory. Differences were found in the interfacial strength of osteons based on appearance under polarized light with bright field having the highest interfacial strength (40.3 MPa). The lowest strength was found in the dark field osteons (22.8 MPa). The dorsal region had the highest shear strength and toughness compared to all other regions. The cement line and interlamellar interfaces are similar in strength, but exhibit regional dependence—specifically, the palmar region strength is less (17.5 MPa) than the osteon interlamellar interfaces (30.4 MPa) and osteon type dependent (alternating significantly weaker than other types). Histomorphometry revealed significant regional differences (po0:0001) in osteon area fraction among the four osteon types as well as differences in the osteon diameter (p ¼ 0:01), with dorsal regions having larger osteons (170 mm) than the palmar region (151 mm). Fatigue life and fracture toughness of Haversian bone are reported in the literature to be regionally dependent and are known to be associated with osteon pullout—an osteon interfacial phenomenon. Therefore, the results presented in this study are important to further the understanding of the mechanisms of fragility and damage accumulation in cortical bone