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Instability of the forearm is a complex problem that leads to pain and limited motions. Up to this time, no universal consensus has yet been reached as regards the optimal treatment for forearm instability. In some cases, conservative treatments are recommended for forearm instability injuries. However, quantitative studies on the conservative treatment of forearm instability are lacking. The present study developed a finite element model of the forearm to investigate the contribution of the distal radioulnar joint stabilizer on forearm stability. The stabilizer was designed to provide stability between the radius and ulna. The forearm model with and without the stabilizer was tested using the pure transverse separation and radial pull test for the different ligament sectioned models. The percentage contribution of the stabilizer and ligament structures resisting the load on the forearm was estimated. For the transverse stability of the forearm, the central band resisted approximately 50% of the total transverse load. In the longitudinal instability, the interosseous membrane resisted approximately 70% of the axial load. With the stabilizer, models showed that the stabilizer provided the transverse stability and resisted almost 1/4 of the total transverse load in the ligament sectioned models. The stabilizer provided transverse stability and reduced the loading on the ligaments. We suggested that a stabilizer can be applied in the conservative management of patients who do not have the gross longitudinal instability with the interosseous membrane and the triangular fibrocartilage complex disruption.

In golf, the trunk and pelvis kinematic variables are often related to measures of performance due to the highly complex and multi-joint movements involved in swings. However, it is unclear how specific body segments or joints contributed to the golf performance parameters. Therefore, the purpose of this study was to identify the key joints, including those of the upper and lower trunk, that are associated with golf performance parameters, such as X-Factor and pelvis motion. A motion capture system was used to obtain three-dimensional kinematics of golf swings performed by 10 low handicap male golfers. Based on regression analysis, right knee adduction, right shoulder external rotation and left elbow extension in ball address to top of the backswing and left knee adduction and lower trunk right bending with left rotation in top of the backswing to end of follow-through were presented as predictor variables for the X-Factor. For pelvis movement, a greater number of joint angles were associated with pelvis posterior tilt during backswing and pelvis motion to target with right rotation during downswing/follow-through. This study provides fundamental details of the movement mechanisms of major joints, as well as their relationships with performance parameters. Such understanding can be combined with training to improve the golfing skill and prevent possible injuries.

The push-off mechanism to generate forward movement in skating has been analyzed by using high-speed cameras and specially designed skates because it is closely related to skater performance. However, using high-speed cameras for such an investigation, it is hard to measure the three-dimensional push-off force, and a skate with strain gauges is difficult to implement in the real competitions. In this study, we provided a new method to evaluate the three-dimensional push-off angle in short-track speed skating based on motion analysis using a wearable motion analysis system with inertial measurement unit sensors to avoid using a special skate or specific equipment insert into the skate for measurement of push-off force. The estimated push-off angle based on motion analysis data was very close to that based on push-off force with a small root mean square difference less than 6% when using the lateral marker in the left leg and the medial marker in the right leg regardless of skating phase. These results indicated that the push-off angle estimation based on motion analysis data using a wearable motion capture system of inertial measurement unit sensors could be acceptable for realistic situations. The proposed method was shown to be feasible during short-track speed skating. This study is meaningful because it can provide a more acceptable push-off angle estimation in real competitive situations.

Understanding the mechanism of injury involved in lateral ankle sprain is essential to prevent injury, to establish surgical repair and reconstruction, and to plan reliable rehabilitation protocols. Most studies for lateral ankle sprain posit that ankle inversion, internal rotation, and plantarflexion are involved in the mechanism of injury. However, recent studies indicated that ankle dorsiflexion also plays an important role in the lateral ankle sprain mechanism. In this study, the contributions of ankle plantarflexion and dorsiflexion on the ankle joint were evaluated under complex combinations of internal and inversion moments. A multibody ankle joint model including 24 ligaments was developed and validated against two experimental cadaveric studies. The effects of ankle plantarflexion (up to 60°) and dorsiflexion (up to 30°) on the lateral ankle sprain mechanism under ankle inversion moment coupled with internal rotational moment were investigated using the validated model. Lateral ankle sprain injuries can occur during ankle dorsiflexion, in which the calcaneofibular ligament and anterior talofibular ligament tears may occur associated with excessive inversion and internal rotational moment, respectively. Various combinations of inversion and internal moment may lead to anterior talofibular ligament injuries at early ankle plantarflexion, while the inversion moment acts as a primary factor to tear the anterior talofibular ligament in early plantarflexion. It is better to consider inversion and internal rotation as primary factors of the lateral ankle sprain mechanism, while plantarflexion or dorsiflexion can be secondary factor. This information will help to clarify the lateral ankle sprain mechanism of injury.

In short-track speed skating, the three-dimensional kinematics of the lower extremities during the whole skating cycle have not been studied. Kinematic parameters of the lower extremities during skating are presented as joint angles versus time. However, the angle-time presentation is not sufficient to describe the relationship between multi-joint movement patterns. Thus, angle-angle presentations were developed and used to describe interjoint coordination in sport activities. In this study, 15 professional male skaters' full body motion data were recorded using a wearable motion capture system during short-track speed skating. We investigated the three-dimensional kinematics of the lower extremities and then established the interjoint coordination between hip-knee and knee-ankle for both legs during the whole skating cycle. The results demonstrate the relationship between multi-joint movements during different phases of short-track speed skating. This study provides fundamentals of the movement mechanism of the lower extremities that can be integrated with physiotherapy to improve skating posture and prevent injuries from repetitive stress since physiological characteristics play an important role in skating performance.

Myelopathy in the cervical spine due to cervical ossification of the posterior longitudinal ligament could be induced by static compression and/or dynamic factors. It has been suggested that dynamic factors need to be considered when planning and performing the decompression surgery on patients with the ossification of the posterior longitudinal ligament. A finite element model of the C2-C7 cervical spine in the neutral position was developed and used to generate flexion and extension of the cervical spine. The segmental ossification of the posterior longitudinal ligament on the C5 was assumed, and laminectomy was performed on C4-C6 according to a conventional surgical technique. For various occupying ratios of the ossified ligament between 20% and 60%, von-Mises stresses, maximum principal strains in the spinal cord, and cross-sectional area of the cord were investigated in the pre-operative and laminectomy models under flexion, neutral position, and extension. The results were consistent with previous experimental and computational studies in terms of stress, strain, and cross-sectional area. Flexion leads to higher stresses and strains in the cord than the neutral position and extension, even after decompression surgery. These higher stresses and strains might be generated by residual compression occurring at the segment with the ossification of the posterior longitudinal ligament. This study provides fundamental information under different neck positions regarding biomechanical characteristics of the spinal cord in cervical ossification of the posterior longitudinal ligament.

Ossification of the posterior longitudinal ligament is a common cause of the cervical myelopathy due to compression of the spinal cord. Patients with ossification of the posterior longitudinal ligament usually require the decompression surgery, and there is a need to better understand the optimal surgical extent with which sufficient decompression without excessive posterior shifting can be achieved. However, few quantitative studies have clarified this optimal extent for decompression of cervical ossification of the posterior longitudinal ligament. We used finite element modeling of the cervical spine and spinal cord to investigate the effect of posterior decompression extent for continuous-type cervical ossification of the posterior longitudinal ligament on changes in stress, strain, and posterior shifting that occur with three different surgical methods (laminectomy, laminoplasty, and hemilaminectomy). As posterior decompression extended, stress and strain in the spinal cord decreased and posterior shifting of the cord increased. The location of the decompression extent also influenced shifting. Laminectomy and laminoplasty were very similar in terms of decompression results, and both were superior to hemilaminectomy in all parameters tested. Decompression to the extents of C3-C6 and C3-C7 of laminectomy and laminoplasty could be considered sufficient with respect to decompression itself. Our findings provide fundamental information regarding the treatment of cervical ossification of the posterior longitudinal ligament and can be applied to patient-specific surgical planning., (© IMechE 2016.)

The computational modeling approach has commonly been used to predict knee joint contact forces, muscle forces, and ligament loads during activities of daily living. Knowledge of these forces has several potential applications, for example, within design of equipment to protect the knee joint from injury and to plan adequate rehabilitation protocols, although clinical applications of computational models are still evolving and one of the limiting factors is model validation. The objective of this study was to extend previous modeling technique and to improve the validity of the model prediction using publicly available data set of the fifth "Grand Challenge Competition to Predict In Vivo Knee Loads." A two-stage modeling approach, which combines conventional inverse dynamic analysis (the first stage) with a multi-body subject-specific lower limb model (the second stage), was used to calculate medial and lateral compartment contact forces. The validation was performed by direct comparison of model predictions and experimental measurement of medial and lateral compartment contact forces during normal and turning gait. The model predictions of both medial and lateral contact forces showed strong correlations with experimental measurements in normal gait (r = 0.75 and 0.71) and in turning gait trials (r = 0.86 and 0.72), even though the current technique over-estimated medial compartment contact forces in swing phase. The correlation coefficient, Sprague and Geers metrics, and root mean squared error indicated that the lateral contact forces were predicted better than medial contact forces in comparison with the experimental measurements during both normal and turning gait trials., (© IMechE 2016.)

Accurate measurement of the center of rotation of the knee joint is indispensable for prediction of joint kinematics and kinetics in musculoskeletal models. However, no study has yet identified the knee center of rotations during several daily activities before and after high tibial osteotomy surgery, which is one surgical option for treating knee osteoarthritis. In this study, an estimation method for determining the knee joint center of rotation was developed by applying the optimal common shape technique and symmetrical axis of rotation approach techniques to motion-capture data and validated for typical activities (walking, squatting, climbing up stairs, walking down stairs) of 10 normal subjects. The locations of knee joint center of rotations for injured and contralateral knees of eight subjects with osteoarthritis, both before and after high tibial osteotomy surgery, were then calculated during walking. It was shown that high tibial osteotomy surgery improved the knee joint center of rotation since the center of rotations for the injured knee after high tibial osteotomy surgery were significantly closer to those of the normal healthy population. The difference between the injured and contralateral knees was also generally reduced after surgery, demonstrating increased symmetry. These results indicate that symmetry in both knees can be recovered in many cases after high tibial osteotomy surgery. Moreover, the recovery of center of rotation in the injured knee was prior to that of symmetry. This study has the potential to provide fundamental information that can be applied to understand abnormal kinematics in patients, diagnose knee joint disease, and design a novel implants for knee joint surgeries., (© IMechE 2015.)

Heterotopic ossification is one of the possible complications following cervical total disk replacement. Although there are numerous hypotheses regarding the etiology of heterotopic ossification, the main causes of heterotopic ossification remain unknown. In this study, we hypothesize that heterotopic ossification formation is related to external loading in the cervical vertebrae after total disk replacement. A two-dimensional finite element model of a cervical vertebra treated by total disk replacement in the sagittal plane was developed. The bone adaptation process of heterotopic ossification was simulated based on strain energy density under both compressive and shear forces. Different types of heterotopic ossification formation were analyzed according to the directions of forces. Two distinct types of heterotopic ossification following cervical total disk replacement were predicted, which was consistent with previous clinical studies. Type 1 heterotopic ossification was observed in the posterior upper part of the vertebra under compressive forces, while type 2 heterotopic ossification was detected mostly in the anterior upper part under shear forces. In addition, heterotopic ossification formation enhanced the strain energy distribution, which is known to be related to bone remodeling. This article presents the effects of different mechanical loading conditions on the occurrence of heterotopic ossification following cervical total disk replacement, and the results may be useful for the design of artificial disks that minimize heterotopic ossification.

It has been reported that posterolateral corner structures, including the lateral collateral ligament, the popliteus tendon, and the popliteofibular ligament, may play important roles in reducing external rotational and posterior translational instabilities. However, there are few studies focusing on the quantitative influence of posterolateral corner structures on knee joint stability, due to the difficulty of controlling experimental conditions. In this study, a knee model that included posterolateral corner structures was developed. It was validated by comparison to previous experimental studies using the posterior drawer test, dial test, and varus stress test. The posterior translation, external rotation, and varus rotation were then predicted in order to investigate the contribution of posterolateral corner structures to translational and rotational stabilities. Our results indicate that posterolateral corner structures, including the popliteofibular ligament and the popliteus tendon, could contribute to posterior translational and external rotational stabilities, as clinical observations had suggested. Therefore, the addition of posterolateral corner structures to knee joint models may improve the utility of such models.

The placement of artificial disks can alter the center of rotation and kinematic pattern; therefore, forces in the spine during the motion will be affected as a result. The relationship between the location of joint center of artificial disks and forces in the spinal components is not investigated. A musculoskeletal model of the spine was developed, and three location cases of center of rotation were investigated varying 5 mm anteriorly and posteriorly from the default center. Resultant joint forces, ligament forces, facet forces, and muscle forces for each case were predicted during sagittal motion. No considerable difference was observed for joint force (maximum 14%). Anterior shift of center of rotation induced the most ligament forces (200 N) and facet forces (130 N) among the three cases. Posterior and anterior shifts of centers of rotation from the default location caused considerable changes in muscle forces, respectively: 108% and 70% of increase in multifidi muscle and 157% and 187% of increase in short segmental muscle. This study showed that the centers of rotation due to the design and the surgical placement of artificial disk can affect the kinetic results in the spine.

Recently, novel polymers, including polyetheretherketone and carbon fibre reinforced polymer, have been used for spinal implants. Because the in vitro experimental test uses metal blocks with different material properties from those of polymer cages in standard test protocols for prediction of the mechanical performance, it is necessary to analyse the influence of various experimental conditions, such as the material of the blocks. In this study, the compressive stiffness of spinal cages was investigated for different materials (polyetheretherketone, carbon fibre reinforced polymer, and titanium) under simulations of the mechanical experimental tests and the in vivo situation based on finite element analysis. The stiffness was affected by shapes of cage as well as experimental conditions, such as the load application method or fixation block. In the open cages, the polymer cages showed a greater dependence on the experimental situation than the metal cages. Hence, it may be necessary to consider the experimental conditions during in vitro mechanical tests for the stiffness evaluation of spinal cages made of novel polymers to obtain results relevant for an in vivo situation.

Breakage of screws has been one of the most common complications in spinal fixation systems. However, no studies have examined the breakage risk of pedicle screw fixation systems that use flexible rods, even though flexible rods are currently being used for dynamic stabilization. In this study, the risk of breakage of screws for the rods with various flexibilities in pedicle screw fixation systems is investigated by calculating the von Mises stress as a breakage risk factor using finite element analysis. Three-dimensional finite element models of the lumbar spine with posterior one-level spinal fixations at L4-L5 using four types of rod (a straight rod, a 4 mm spring rod, a 3 mm spring rod, and a 2 mm spring rod) were developed. The von Mises stresses in both the pedicle screws and the rods were analysed under flexion, extension, lateral bending, and torsion moments of 10 Nm with a follower load of 400 N. The maximum von Mises stress, which was concentrated on the neck region of the pedicle screw, decreased as the flexibility of the rod increased. However, the ratio of the maximum stress in the rod to the yield stress increased substantially when a highly flexible rod was used. Thus, the level of rod flexibility should be considered carefully when using flexible rods for dynamic stabilization because the intersegmental motion facilitated by the flexible rod results in rod breakage.

The load-carrying capacity of the spine has been experimentally shown to increase substantially when the resultant force of all loads applied on the spine is directed in accordance to its curvature, which is called a 'follower load (FL)'. However, there have been few studies to investigate the muscle forces producing the FL owing to the difficulty of the relevant experimental measurements. This study investigated whether trunk muscle activations could be found for transmitting an external load within a range of FL direction. A two-dimensional finite element model of a lumbar spine and 117 pairs of trunk muscles was developed in the sagittal plane. An optimization technique was utilized to estimate the muscle forces generating the FL and the corresponding responses of the lumbar spine under two loading cases: the upright neutral standing posture and the posture holding 200 N in the hands. For each loading case, the muscle forces required to generate the FL could be found and the corresponding responses of the lumbar spine validated that the FL could increase the load-carrying capacity. The results showed that the FL could be produced in vivo by trunk muscles to increase the load-carrying capacity.