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Rotation of the cervical spine beyond its normal range of motion is a leading cause of fall-related spinal cord injuries (SCIs) in older adults. This rotation is constrained, in part, by the spinal ligaments. The experimentally measured properties of these ligaments are tabulated in literature, including sex-specific properties; however, their influence on the rotation kinematics of the cervical spine has not been compared. We examined how different mechanical properties of spinal ligaments, including sex-specific properties, affected the rotational kinematics of the cervical spine using finite element analysis (FEA). Ligament properties most influenced the rotation of the lower cervical spine, with increased ligament stiffness reducing rotation. Ligament deformation remained mostly in the toe region of their force-displacement curves, emphasizing the need to incorporate non-linear ligament behavior in FEA. Predictions made using one set of experimental properties (Property 1) better-matched experimental kinematic data. Using sex-specific properties had a moderate effect (6% in extension, –3% in flexion) on rotation, with a greater impact on extension. Ligament properties also affected the segmental distribution of rotation, causing a variability of 3–21% at different levels. We emphasized the need to incorporate tailored approaches to FEA to obtain clinically relevant results when modeling flexion/extension rotation.

The purpose of this scoping review was to outline the current gait interventions used in biomechanics-based research focused on persons with autism spectrum disorder. A review of articles was conducted using the PRISMA methodology for reporting guidance with an a priori PICO framework. The selected articles were identified, reviewed, evaluated for risk of bias, and used to group biomechanics-based gait interventions that have been implemented in research involving persons with autism spectrum disorder. Titles and abstracts of 573 articles were reviewed; seven articles describing gait interventions met the inclusionary criteria. The interventions reported in the literature were hippotherapy, weighted vests, and exercise programs. Additional orthopedic interventions (serial casting and foot orthoses) were utilized for individuals who primarily walk on their forefoot. Findings from this review reveal changes in spatiotemporal characteristics post-hippotherapy, changes in ground reaction forces and foot pressures after participation in exercise intervention programs, and no change in parameters via weighted vests. For persons with autism spectrum disorder who are forefoot strikers, the use of serial casting and foot orthoses reportedly improved the overall kinematic and spatiotemporal parameters during gait.

An AO type C2 distal radius fracture was simulated in a cadaver model by creating a metaphyseal defect of 5 mm and an intra-articular defect of 2 mm. Five different methods of plate osteosynthesis were tested biomechanically in each of six fresh cadaveric hands. Biomechanical testing suggested that cement augmented plating plus screws in the distal fragment was the strongest. Dorsal and volar plating plus screws on both sides of the distal fragment had the same effect of restoring stiffness and load transmission pattern as fixation with double plating plus volar screws alone. Fixation with plating plus dorsal screws was significantly weaker than these three methods, and double buttress plating with no screws in the distal fragments was the weakest.

Introduction: To identify the strongest peak load resistance among four mallet finger fracture fixation methods (Kirschner wire, pull-out wire, tension-band wiring and the JuggerKnot™ (Biomet) soft anchor fixation).

Methods: Fixation techniques were assigned among 24 specimens from six cadaveric human hands in a randomized block fashion. Peak load resistance was tested at 30°, 45° and 60° of flexion of the distal interphalangeal joint.

Results: The mean peak load of tension-band wiring was 67.8 N at 60° of flexion which was most superior. The JuggerKnot™ fixation had mean peak loads of 13.35 N (30°), 22.51 N (45°) and 32.96 N (60°). No complications of implant failure or fragmentation of the dorsal fragment was noted.

Conclusions: Tension-band wiring was the strongest fixation method but was most prominent on the skin surface as seen in three specimens. The JuggerKnot™ soft anchor fixation had similar peak load resistance as k-wire fixation and pull-out wiring.

Purpose: This study assesses the influence of A2 pulley integrity on the strength of the repair. Method: Part 1- The flexor digitorum profundus (FDP) tendons of 72 Cobb chicken feet were severed and repaired in the region of the A2 pulley using a modified Kessler core suture and an epitendinous suture. The A2 pulley was either left intact, divided for 50% of its length, or divided in its entirety. The distal interphalangeal joint was fixed at a position of 20°, 40° or 60° of joint flexion. The load to failure, integrity of the A2 pulley and the site of tendon failure were analysed. Part 2- A further 32 chicken feet were used to exclude the effects of freezing and thawing on results and to analyse differences when using a core suture only. Results: No difference in failure load between any of the test groups or subgroups was identified. The integrity of the A2 pulley was preserved in all specimens. The most common cause of failure was distal suture pull-out. Discussion: This study does not demonstrate that release of the A2 pulley provides an advantage in increasing tendon repair strength. Division of 50% of the A2 pulley does not predispose to pulley rupture. Flexor tendon repair strength did not alter with distal interphalangeal joint flexion between 20° and 60°. Clinical Relevance: The findings of this study do not support division of the A2 pulley to prevent flexor tendon repair failure if repair methods of appropriate strength are utilised.

The quantitative effects of fixed femoral rotation on the patellofemoral joint were assessed in canines in vitro and in vivo. For the in vitro study, ten canine knees were examined in neutral and 30 degrees of internal and external fixed femoral rotations. Fuji film was inserted into the patellofemoral joint and quadriceps loading was simulated at 60 and 90 degrees of knee flexion. There was significant increase in patellofemoral contact pressures on the contralateral facets of the patella with 30 degrees of fixed femoral rotation at both knee flexion angles (p < 0.05). For the in vivo study, 12 skeletally mature mongrel dogs were subjected to either internal or external bilateral femoral rotational deformity of 30 degrees. Three animals served as controls. Biomechanical evaluation of the articular cartilage showed a statistically significant decrease for both the unrelaxed and relaxed apparent shear modulus at six months for both internal and external femoral rotations (p < 0.05) in comparison to the control. In vivo results from fixed femoral rotation on the patellofemoral joint correlate with that expected from in vitro biomechanical results. The results from this study suggest that rotational deformity of the femur should be corrected within six months to prevent patellofemoral joint arthrosis.

As age, experience and common sense look at biomechanical, hormonal, genetic and other roles in bone physiology and its disorders, two questions can arise: (a) How did we fail? (b) How could we make it better? The acerbic Sam Johnson said that to teach new things, we should use examples of already known ones. If so, an analogy might help to clarify this article's message for people who work with bones and their disorders.

Assume this: (a) Mythical physiologists were taught that renal physiology depends on "kidney cells" but were taught nothing about nephrons; (b) so they explained renal health and disorders in those terms. (c) For many decades, they "knew" that view was correct (as the ancients "knew" the world was flat). (d) But then others described nephrons and some errors their properties revealed in those views about renal physiology; (e) so controversies began.

Today, an analogous situation confronts real biomechanicians and physiologists. (i) Most of them were taught that osteoblasts and osteoclasts (bone's "effector cells") explain bone physiology without "nephron-equivalent" input, so they explained bone disorders and mechanical effects in those terms. (ii) Yet nephron-equivalent mechanisms and functions, including biomechanical ones, in bones have the same operational relationship to their cells, health and disorders as nephrons and their functions do to renal cells, health and disorders. (iii) Adding that knowledge to former views led to the Utah paradigm of skeletal physiology. It also revealed errors in many former views about bone physiology; (iv) so real controversies have begun.

Biomechanicians, physiologists, clinicians and pharmacologists from whom poor interdisciplinary communication hid that paradigm could think the view in (i) above remains valid, and keep analyzing data and designing studies within its constraints.

Like Wegner's idea of plate tectonics in geology, the Utah paradigm came before its field was ready, so others fought it. But while the plate-tectonics war was won, it has just begun for the Utah paradigm. This article reviews how such things could apply to bone and some of their implications. Its conclusion offers succinct answers to the italicized questions above.

Here, we suggest that new ideas and knowledge about "osteoporosis" reveal necessary new directions for future work. To explain, by 1999, five studies involving a total of 1827 healthy humans from two to over 80 years of age supported this proposal in the Utah paradigm of skeletal physiology: Momentary muscle strength strongly influences and may dominate control of the biologic mechanisms that determine the postnatal strength of load-bearing bones. That italicized proposal differed so much from former views that before 1999, few people thought it deserved testing in humans. The above five studies did finally test it, and they support it.

If true, its implications would affect many things. In part, they include (A), genetic effects on bone strength and "mass", muscle and "osteoporosis"; (B) the pathogenesis, diagnosis, classification, prevention and management of "osteoporosis"; (C) the things osteoporosis-oriented basic, clinical and pharmaceutical research should study; (D) the absorptiometric methods and animal models used to study the disorder; (E) which research projects would receive preferred funding; (F) and the content of future texts, review articles, classroom lectures and many osteoporosis-oriented meetings.

Many might find some of those implications dubious. While we will respect such doubts, this article describes some of those implications so others can exploit them and/or help to resolve any disagreements they may cause. Because they depend on the Utah paradigm of skeletal physiology, some of its pertinent features must be summarized.

Functional electrical stimulation (FES) standing system can enable the paraplegics to achieve the standing position for functional activities in daily living. FES standing system is usually applied by stimulating the knee extensor muscles. The hip joints are in hyperextension and the ankle joints remain free. Therefore, the knee joint control is the key point of the FES standing control system.

Traditional open-loop control often induces high knee end-velocity (KEV) when the subject reaches the upright position. In this work, the reducing of KEV by closed-loop control was addressed. An on/off feedback control based on mechanical energy conservation was developed to control the knee extensors and flexors. The result was compared to the open loop controlled standing up in a mechanically simulative experiment. It is concluded that the on/off control strategy can reduce the KEV more efficiently when compared to the open-loop control. Proportional-integral-derivative (PID) position controlled standing up was also studied and compared with the on/off control system. The PID controller was found to be capable of reducing KEV to a level lower than that of the on/off control, whereas its instability for knee control was also found.

This study evaluated the influence of head mass on the acceleration of the head and neck complex in automobile rear-end collisions using a three-dimensional finite element method. The geometry of the finite element model is based on a cervical (C2–7) motion segment of a 20-year-old man that was obtained by computed tomography. Four types of models were prepared by changing the parameters of mass for an examination of the effects of head mass. Simulated loads were applied at the lower end of the C7 vertebra, with the axial direction constrained. Each model was loaded, and the head acceleration and distribution of von Mises stress were analyzed. Stress was observed to concentrate on the C2/3, C5/6 and C6/7 intervertebral discs. With a large head mass, the delay of the initial rise of the acceleration curve was large and the value of acceleration was small. On the contrary, when the head mass was small, the acceleration curve started to rise earlier. The acceleration curve of the model with the head mass of 1.0 kg was the closest to that of the experiments by Severy. Head mass is an important factor which influences the dynamic response of the head in rear-end collisions.

The scope of serial studies into the kinematics of the cervical vertebrae, have been limited by the methods available for imaging. Plain radiography has been one of the main methods by which data has been collected. The widespread use of this method has, however, been restricted by factors including exposure to ionizing radiation and magnification errors. With the advent of Interventional Magnetic Resonance (iMR) scanners, however, the authors sought to determine the utility of an iMR scanner in obtaining functional images of the cervical vertebrae, from which repeatable measurements of vertebral kinematics can be collected.

20 healthy volunteers (mean age 25.4 ± 3.7 years) were recruited. They had their cervical vertebrae scanned in three positions: neutral, flexed and extended. Sagittal images were obtained for each subject from between the level of the C2 vertebra to the T1 vertebra and measurements of inter-segmental motion were made, using established clinical methodology.

Clear images of the cervical vertebrae were obtained in all positions from which measures of motion were made. Greatest angular motions were found to occur in the mid-cervical level, C4/C5. Non-osseous structures, including the intervertebral discs and nerve roots were well visualized.

Our results suggest that iMR scanning may have an important role in the imaging of cervical spine and its associated structures. It offers a modality that allows the determination of both normal and abnormal kinematics on a large scale.

A detailed three-dimensional head-neck (C0–C7) finite element (FE) model developed based on the actual geometry of an embalmed human cadaver specimen was exercised to dictate the motions of the cervical spine under dynamic loadings. The predicted results analyzed under vertex drop impact were compared against experimental study to validate the FE model. The validated C0–C7 FE model was then further analyzed to investigate the response of the whole head-neck complex under 10G-ejection condition. From the simulation of ejection process, obvious hyper-flexion of the head-neck complex could be found. The peak flexion angles of all the lower motion segments were beyond physiological tolerance indicating a potential injury in these regions. Furthermore, the stress values in the spine were also related to the magnitudes of rotation of the motion segments. During the acceleration onset stage, the maximum stresses in the bone components were low. After that, the stress values increased sharply into the dangerous range with increased rotational angles. The effect of muscles in alleviating the potential damage in the neck is significant. It was implied that it is important for pilots to stiffen the neck before ejection to avoid severe cervical injury.

A detailed three-dimensional head-neck (C0–C7) finite element (FE) model developed previously based on the actual geometry of a cadaveric specimen was used to characterize the whiplash phenomenon of the head-neck region during rear-end collision. A maximum rear impact pulse of 8.5 G of acceleration was applied to C7. The effects of a headrest on the responses of head-neck complex were also discussed. The study demonstrates the effectiveness of the current C0–C7 FE model in characterizing the gross responses of human cervical spine under whiplash. The results showed that during whiplash, the lower cervical levels, especially the C6–C7, experience hyperextension in the early phase of acceleration. The whole cervical spine is at risk of extension injuries rather than flexion injuries in whiplash. The use of a proper headrest can effectively reduce the cervical spine from extension injury during the acceleration phase of cervical spine in whiplash.

Large allograft bones are commonly used in limb salvage procedures for the reconstruction of bone defects after resection of a bone tumor. A V-shaped osteotomy may perform better than the traditional transverse osteotomy as it increases the stability of the docking site and increases the contact area between an allograft and the host cortex. The aim of this study is to investigate the biomechanical properties of a V-shaped docking site of different angles.

orcine femurs with 45°, 60° or 90° V-shaped osteotomy were first tested with 1000 N compression, followed by 2 and 5 Nm torque. The torsional stiffness of the 45° specimen group at 5 Nm torque was significantly higher (P<0.05) than the 90° group. Therefore, our results show that 45° V-shaped osteotomy is found to be the most stable docking angle.

Thoracolumbar burst fracture is one of the most common and most studied injuries of the spine. Radiography and quantitative discomanometry have previously demonstrated that intervertebral discs adjacent to a burst fracture were disrupted; however, there have been conflicting data on the properties of the next-adjacent discs. Also, no data exists on the localization of injury within each disc. The objective of this study is to use an in vitro biomechanical design to examine the flexibility differences of intervertebral discs adjacent and next-adjacent to burst fracture vertebrae. Ten cadaveric thoracolumbar (T11–L3) spines with L1 burst fracture included adjacent (T12–L1, L1–L2) and next-adjacent (T11–T12, L2–L3) intervertebral discs. The bending flexibilities (μm/N) of each disc under 50 N of compression were determined at 25 points: the center point, along with the combinations of three radii (1 cm, 2 cm, 3 cm) and eight angles. The overall flexibility of each disc and the presence of any regional differences were then evaluated. Across all radii, the T11μT12 disc was statistically less flexible than the other three discs (p < 0.01). The difference between the flexibilities of the average anterior region and the average posterior region was significant at many 2-cm and all 3-cm radii; this difference was greater in the T12–L1 disc than in any of the other three discs. Thus, the upper next-adjacent intervertebral disc (T11–T12) was not as susceptible to mechanical disruption as were the other three discs. The anterior region of each disc may also have a higher propensity for mechanical disruption than the posterior region, especially at larger radii.

Most of the biomechanical experiments, which validate vertebral finite-element models, deal with vertebral bodies in axial compression. In standing position, gravity loads can induce bending on the last thoracic and first lumbar vertebrae. Hence, the purpose of the study was to evaluate the strength of vertebrae submitted to anterior bending. The boundary conditions were carefully assessed for further validation of finite-element models. Fifteen vertebrae (T11–L2) were tested until failure. The load was applied on the anterior part of the vertebral body and distributed to the whole vertebral body through a polymethylmetacrylate layer. The 3D position of the origin of the force relative to the vertebra was assessed using a motion-capture system and 3D reconstructions of the testing device. The mean failure load was equal to 2098 N. Ninety-five percent of the vertebrae failed through a vertical displacement smaller than 1.5 mm. Rotations were weak during the test (< 1°), therefore the protocol can be simplified by removing the motion capture system if the initial 3D origin of the load is known. To our knowledge, it is the first protocol that quantifies the strength of whole vertebrae under anterior bending. It collects with accuracy all the data necessary for one-to-one vertebral finite-element model validations.

Purpose. The primary objective of the study was to determine a way to obtain subject-specific body dimensions. The aim was then to develop linear statistical models for estimating human body geometry from a small number of body measurements. Methods. Internal (bone dimensions) and external (body) measurements were collected on 64 healthy adults representative of three morphotypes. Simple and multiple linear regression models between external and internal body dimensions were then obtained and assessed. Results. The statistical analysis provided 184 anthropometrical models which allow estimation of subject-specific external and internal data from 10 external dimensions that can be easily measured on any subject. Among them, 62 models had a 2SEE (i.e. twice the Standard Error of Estimate) lower than 10%. Conclusion. This study proposes a non-invasive approach to estimate both external and internal body dimensions.

Pain is routinely implicated as a factor when considering impaired movement in injured populations. Movement velocity is often considered during the rehabilitation process; unfortunately our understanding of pain's impact on shoulder movement velocity in rotator cuff tear patients is less understood. Therefore, the purpose of this study was to test the hypothesis that there would be an increase in peak and mean shoulder elevation velocities following the decrease of shoulder pain in rotator cuff tear patients, regardless of tear size. Fifteen subjects with full-thickness rotator cuff tears (RCT) performed humeral elevation and lowering in three planes before and after receiving a lidocaine injection to relieve pain. Pain was assessed using a visual analog scale. Humeral elevation velocity data were collected using an electromagnetic tracking system. A significant reduction in pain (pre-injection 3.53 ± 1.99; post-injection 1.23 ± 1.43) resulted in significant increases in maximum and mean humeral elevation velocities. Mean shoulder elevation and lowering velocities increased 15.10 ± 2.45% while maximum shoulder movement velocities increased 12.77 ± 3.93%. Furthermore, no significant relationships were noted between tear size and movement velocity. These significant increases in movement velocity provide evidence to further support the notion that human motion can be inhibited by injury-associated pain, and that by reducing that pain through clinical interventions, human movement can be impacted in a positive fashion.

Gender, lifting loads, and flexed trunk postures are three risk factors associated with low back pain. Previous studies have not found gender differences in effective trunk stiffness (intrinsic stiffness plus reflex response) using force perturbations, but these measures may have been confounded by differences in trunk kinematics between males and females. The purpose of this study was to investigate the effects of gender, trunk extensor preload, and trunk flexion angle on intrinsic trunk stiffness using position perturbations, which have the potential to eliminate kinematic differences between research subjects and to separate intrinsic stiffness from reflex responses. A total of 13 males and 12 females were exposed to sudden, small trunk flexion position perturbations with two trunk extension preloads (0 and 30% maximum) and three trunk flexion angles (0, 20, and 40 degrees). Data collected during position perturbations were used along with a two degree of freedom model of the trunk and connecting elements to estimate intrinsic trunk stiffness. Intrinsic stiffness was lower in females compared to males, and increased with increasing preload and trunk flexion angle. Intrinsic stiffness increased more substantially among males with increasing preload and trunk angle, and effects of trunk angle were diminished with a preload. A lower intrinsic stiffness and smaller increases with preload and trunk angle, may contribute to the increased rate of occupational LBP and injury among females.

In order to better understand the behavior of the total wrist implant systems, finite element analysis (FEA) was used to model the articular surfaces of two unconstrained total wrist arthroplasty (TWA) devices. After creating models based on manufacturer specifications, simulations of flexion, extension, radial deviation, ulnar deviation and circumduction were run with simulated moments from surrounding tendons under displacement control. In addition, simulations were run under positioning that represented a pronated and supinated forearm as well as unstable conditions. Understanding implant behavior and capabilities as related to the shape of the articular surfaces is important for proper prescription of implants as well as determining future directions for the design of arthroplasty devices.