Shock-Absorbing Effects of Various Padding Conditions in Improving Efficacy of Wrist Guards

The use of wrist guards has limited efficacy in preventing wrist injuries during falling in many sports activities. The objectives of this study were to measure the ground reaction force of the hand under simulated impact of the forearm and hand complex with different padding conditions of wrist guards and to analyze their impact force attenuation and maximum energy absorption for improved functional efficiency. A total of 15 subjects, wearing a commercial wrist guard, participated in a cable-released hand impact experiment to test four different conditions on the volar aspect of the hand, which include a wrist guard without a volar splint (bare hand), with a volar splint (normal use), with a volar splint and additional viscoelastic polymeric padding, and a volar splint and additional air cell padding. The ground reaction force and acceleration of the hand were measured using a force platform mounted on an anti-vibration table and a miniature accelerometer, respectively. Additional padding on the bare hand could substantially improve the maximum energy absorption by more than 39%, with no differences with each other. However, only the air cell padding could simultaneously improve the impact force attenuation by 32% compared with the bare hand impact without compromising the maximum energy absorption. It is recommended that common wrist guard design should provide more compliant padding in the volar aspect to improve the impact force attenuation through optimal material selection and design.

Key Points

• The controversial efficacy of wrist guards in preventing wrist injuries during falling was tested through investigation of their impact force attenuation and maximum energy absorption from the measured ground reaction force of the hand under simulated impact of the forearm and hand complex with four different padding conditions of wrist guards: a wrist guard without a volar splint (bare hand), with a volar splint (normal use), with a volar splint and additional viscoelastic polymeric padding, and a volar splint and additional air cell padding.
• In general, padding on the bare hand could improve the maximum energy absorption by more than 39%, while only the air cell padding could simultaneously attenuate the peak impact force by 32% without compromising the maximum energy absorption.
• Common wrist guard design requires more compliant padding in the volar aspect to improve the impact force attenuation, which should be done through optimal material selection and design.

Key words: Accidental falls direction, wrist injuries, prevention, fractures     

A2 and A4 Flexor Pulley Biomechanical Analysis: Comparison among Gender and Digit

Rock climbing has become increasingly more popular in the USA over the past two decades. Accordingly, with increased participation comes an increase in climbing-related injuries. Rooks et al noted that three-quarters of elite and recreational climbers will suffer upper extremity injuries, approximately 60% involving the hand or wrist and 40% divided evenly between the shoulder and elbow. Most of these injures will be strains, microtrauma, and tendonitis; however, 30–50% represent trauma to the proximal interphalangeal region. The purpose of this study was to investigate the biomechanical properties of the A2 and A4 pulley and compare biomechanical properties among gender and digit. A specially designed materials testing machine, shown in the included figure, measured maximum breaking load, displacement and stiffness of the A2 and A4 pulleys of ten cadaveric hands using an S hook to apply a steady force until complete pulley rupture. The A2 and A4 biomechanical properties of breaking load, displacement, and stiffness did not significantly differ among the index, middle, ring, and little fingers. Additionally, there was no significant difference in A2 or A4 pulley biomechanics between male and female specimens. The A2 and A4 pulleys among differing digits and genders have similar biomechanical properties in regards to maximum breaking load, displacement, and stiffness.     

Explicit Finite Element Models Accurately Predict Subject-Specific and Velocity-Dependent Kinetics of Sideways Fall Impact

The majority of hip fractures in the elderly are the result of a fall from standing or from a lower height. Current injury models focus mostly on femur strength while neglecting subject-specific loading. This article presents an injury modeling strategy for hip fractures related to sideways falls that takes subject-specific impact loading into account. Finite element models (FEMs) of the human body were used to predict the experienced load and the femoral strength in a single model. We validated these models for their predicted peak force, effective pelvic stiffness, and fracture status against matching ex vivo sideways fall impacts (n = 11) with a trochanter velocity of 3.1 m/s. Furthermore, they were compared to sideways impacts of volunteers with lower impact velocities that were previously conducted by other groups. Good agreement was found between the ex vivo experiments and the FEMs with respect to peak force (root mean square error [RMSE] = 10.7%, R² = 0.85) and effective pelvic stiffness (R² = 0.92, RMSE = 12.9%). The FEMs were predictive of the fracture status for 10 out of 11 specimens. Compared to the volunteer experiments from low height, the FEMs overestimated the peak force by 25% for low BMI subjects and 8% for high BMI subjects. The effective pelvic stiffness values that were derived from the FEMs were comparable to those derived from impacts with volunteers. The force attenuation from the impact surface to the femur ranged between 27% and 54% and was highly dependent on soft tissue thickness (R² = 0.86). The energy balance in the FEMS showed that at the time of peak force 79% to 93% of the total energy is either kinetic or was transformed to soft tissue deformation. The presented FEMs allow for direct discrimination between fracture and nonfracture outcome for sideways falls and bridge the gap between impact testing with volunteers and impact conditions representative of real life falls. © 2019 American Society for Bone and Mineral Research.     

Effect of compliant flooring on impact force during falls on the hip.

Compliant flooring represents a promising but understudied strategy for reducing impact force and hip fracture risk due to falls in high-risk environments such as nursing homes, hospitals, gymnasiums, and senior centers. We conducted "pelvis release experiments" with young women (n=15) to determine whether floor stiffness influences peak hip impact force during safe, low-height falls. During the trials, we used a pelvic sling and electromagnet to lift and instantly release the participant from a height of 5 cm above a force plate, which measured the force applied to the hip region during impact. Trials were conducted for rigid floor conditions and with layers of ethylene vinyl acetate foam rubber overlying the floor that we regarded as firm (1.5-cm thick; stiffness=263 kN/m), semifirm (4.5-cm thick; stiffness=95 kN/m), semisoft (7.5-cm thick; stiffness=67 kN/m), and soft (10.5-cm thick; stiffness=59 kN/m). When compared to the rigid condition, peak hip impact force averaged 8% lower in the firm condition and 15% lower in the semifirm condition. Peak forces were not significantly different between the semifirm, semisoft, and soft floor conditions, indicating that a 4.5 cm-thick foam mat provides nearly the same force attenuation as a 10.5 cm-thick mat. These results support the need for laboratory experiments to measure the effect of floor stiffness on postural stability and for clinical trials to determine the effect of compliant flooring on hip fracture incidence in high-risk environments.     

The lateral impaction of the shoulder

17 patients had radiographic demonstration of injury to the clavicle, scapula and ribs from an impact delivered to the lateral shoulder. The study included 13 males and 4 females whose ages ranged from 18 to 83 years (average 45 years). Most injuries were sustained in falls or motor vehicle accidents. Analysis of these cases suggests a biomechanical hypothesis concerning the transmission of the impact forces within the shoulder girdle. According to this hypothesis, the impaction force applied to the lateral shoulder is transmitted from outside inward following two paths. The anterior and superior path passes through the acromio-clavicular joint, the clavicle, the costo-clavicular joint and the sterno-clavicular joint. The posterior and inferior path is transmitted within the gleno-humeral joint, the scapula and the scapulo-thoracic joint. Major impacting force is required to disrupt the anterior and posterior arches of the shoulder girdle. When both of these supporting structures are damaged, the patient is at risk for more serious injuries, including disruption of the thorax, shoulder joint, brachial plexus and neck.     

The effect of forearm posture on wrist flexion in computer workers with chronic upper extremity musculoskeletal disorders

Background  

Occupational computer use has been associated with upper extremity musculoskeletal disorders (UEMSDs), but the etiology and pathophysiology of some of these disorders are poorly understood. Various theories attribute the symptoms to biomechanical and/or psychosocial stressors. The results of several clinical studies suggest that elevated antagonist muscle tension may be a biomechanical stress factor. Affected computer users often exhibit limited wrist range of motion, particularly wrist flexion, which has been attributed to increased extensor muscle tension, rather than to pain symptoms. Recreational or domestic activities requiring extremes of wrist flexion may produce injurious stress on the wrist joint and muscles, the symptoms of which are then exacerbated by computer use. As these activities may involve a variety of forearm postures, we examined whether changes in forearm posture have an effect on pain reports during wrist flexion, or whether pain would have a limiting effect on flexion angle.     

Anthropomorphic simulations of falls,shakes, and inflicted impacts in infants

OBJECT: Rotational loading conditions have been shown to produce subdural hemorrhage and diffuse axonal injury. No experimental data are available with which to compare the rotational response of the head of an infant during accidental and inflicted head injuries. The authors sought to compare rotational deceleration sustained by the head among free falls, from different heights onto different surfaces, with those sustained during shaking and inflicted impact. METHODS: An anthropomorphic surrogate of a 1.5-month-old human infant was constructed and used to simulate falls from 0.3 m (1 ft), 0.9 m (3 ft), and 1.5 m (5 ft), as well as vigorous shaking and inflicted head impact. During falls, the surrogate experienced occipital contact against a concrete surface, carpet pad, or foam mattress. For shakes, investigators repeatedly shook the surrogate in an anteroposterior plane; inflicted impact was defined as the terminal portion of a vigorous shake, in which the surrogate's occiput made contact with a rigid or padded surface. Rotational velocity was recorded directly and the maximum (peak-peak) change in angular velocity (delta theta(max)) and the peak angular acceleration (theta(max)) were calculated. Analysis of variance revealed significant increases in the delta theta(max) and theta(max) associated with falls onto harder surfaces and from higher heights. During inflicted impacts against rigid surfaces, the delta theta(max) and theta(max) were significantly greater than those measured under all other conditions. CONCLUSIONS: Vigorous shakes of this infant model produced rotational responses similar to those resulting from minor falls, but inflicted impacts produced responses that were significantly higher than even a 1.5-m fall onto concrete. Because larger accelerations are associated with an increasing likelihood of injury, the findings indicate that inflicted impacts against hard surfaces are more likely to be associated with inertial brain injuries than falls from a height less than 1.5 m or from shaking.     

Changes in in vivo knee loading with a variable‐stiffness intervention shoe correlate with changes in the knee adduction moment

External knee adduction moment can be reduced using footwear interventions, but the exact changes in in vivo medial joint loading remain unknown. An instrumented knee replacement was used to assess changes in in vivo medial joint loading in a single patient walking with a variable‐stiffness intervention shoe. We hypothesized that during walking with a load modifying variable‐stiffness shoe intervention: (1) the first peak knee adduction moment will be reduced compared to a subject's personal shoes; (2) the first peak in vivo medial contact force will be reduced compared to personal shoes; and (3) the reduction in knee adduction moment will be correlated with the reduction in medial contact force. The instrumentation included a motion capture system, force plate, and the instrumented knee prosthesis. The intervention shoe reduced the first peak knee adduction moment (13.3%, p = 0.011) and medial compartment joint contact force (12.3%; p = 0.008) compared to the personal shoe. The change in first peak knee adduction moment was significantly correlated with the change in first peak medial contact force (R² = 0.67, p = 0.007). Thus, for a single subject with a total knee prosthesis the variable‐stiffness shoe reduces loading on the affected compartment of the joint. The reductions in the external knee adduction moment are indicative of reductions in in vivo medial compressive force with this intervention. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:1548–1553, 2010     

Effect of displacement of fractures of the greater tuberosity on the mechanics of the shoulder

Using a dynamic biomechanical model of malunion of the shoulder, we have determined the change in deltoid force required for abduction with various combinations of superior and posterior displacement of fractures of the greater tuberosity of the humerus. We tested eight fresh human cadaver shoulders in a dynamic shoulder-testing apparatus during cycles of glenohumeral abduction from 0 degrees to 90 degrees. The greater tuberosities were osteotomised and stabilised to represent malunion with combinations of superior and posterior displacements of 1 cm and less. The peak force was measured for each displacement in each specimen and statistically compared with values of no displacement using a repeated-measures analysis of variance. The abduction force was significantly increased by 16% (p = 0.006) and 27% (p = 0.0001) by superior displacements of 0.5 cm and 1 cm, respectively, while combined superior and posterior displacement of 1 cm gave an increase in force of 29% (p = 0.001). While treatment criteria for acceptable residual displacement of the greater tuberosity are widely used, there is little information on the direct biomechanical effects of displacement on shoulder mechanics. Although the results of conservative treatment are influenced by a number of factors, including associated injuries, rehabilitation and the pre-existing function of the shoulder, our data suggest that small amounts of residual displacement may alter the balance of forces required to elevate the arm at the glenohumeral joint.     

Analyzing the History of Falls in Patients with Severe Knee Osteoarthritis

Background

One out of three adults over the age of 65 years and one out of two over the age of 80 falls annually. Fall risk increases for older adults with severe knee osteoarthritis, a matter that should be further researched. The main purpose of this study was to investigate the history of falls including frequency, mechanism and location of falls, activity during falling and injuries sustained from falls examining at the same time their physical status. The secondary purpose was to determine the effect of age, gender, chronic diseases, social environment, pain elsewhere in the body and components of health related quality of life such as pain, stiffness, physical function, and dynamic stability on falls frequency in older adults aged 65 years and older with severe knee osteoarthritis.

Methods

An observational longitudinal study was conducted on 68 patients (11 males and 57 females) scheduled for total knee replacement due to severe knee osteoarthritis (grade 3 or 4) and knee pain lasting at least one year or more. Patients were personally interviewed for fall history and asked to complete self-administered questionnaires, such as the 36-item Short Form Health Survey (SF-36) and the Western Ontario and McMaster Universities Arthritis Index (WOMAC), and physical performance test was performed.

Results

The frequency of falls was 63.2% for the past year. The majority of falls took place during walking (89.23%). The main cause of falling was stumbling (41.54%). There was a high rate of injurious falling (29.3%). The time patients needed to complete the physical performance test implied the presence of disability and frailty. The high rates of fall risk, the high disability levels, and the low quality of life were confirmed by questionnaires and the mobility test.

Conclusions

Patients with severe knee osteoarthritis were at greater risk of falling, as compared to healthy older adults. Pain, stiffness, limited physical ability, reduced muscle strength, all consequences of severe knee osteoarthritis, restricted patient''s quality of life and increased the fall risk. Therefore, patients with severe knee osteoarthritis should not postpone having total knee replacement, since it was clear that they would face more complicated matters when combining with fractures other serious injuries and disability.     

Cervical intervertebral disc injury during simulated frontal impact

Cervical disc injury due to frontal impact has been observed in both clinical and biomechanical investigations; however, there is a lack of data that elucidate the mechanisms of disc injury during these collisions. The goals of the current study were to determine the peak dynamic disc annular tissue strain and disc shear strain during simulated frontal impact of the whole human cervical spine model with muscle force replication at 4 g, 6 g, 8 g and 10 g horizontal accelerations of the T1 vertebra. These data were compared with those obtained during physiological loading, and with previously reported rear impact data. Peak disc shear strain and peak annular tissue strain during frontal impact exceeded (p<0.05) corresponding physiological limits at the C2–C3 intervertebral level, beginning at 4 g and 6 g, respectively. These subsequently spread throughout the entire cervical spine at 10 g, with the exception of C4–C5. The C5–C6 intervertebral level was at high risk for injury during both frontal and rear impacts, while during frontal impact, in addition to C5–C6, subfailure injuries were likely at superior intervertebral levels, including C2–C3. The disc injuries occurred at lower impact accelerations during rear impact as compared with frontal impact. The subfailure injuries of the cervical intervertebral disc that occur during frontal impact may lead to the chronic symptoms reported by patients, such as head and neck pain.     

Do Both Areal BMD and Injurious Falls Explain the Higher Incidence of Fractures in Women than in Men?

The higher incidence of fractures in women than in men is generally attributed to the lower areal bone mineral density (areal BMD, g/cm²) of the former. The purpose of the present study was to investigate both areal BMD and injurious falls as risk factors for fractures. In a first cohort, areal BMD was measured in 5,131 men and women (age range 40–95 years). In a second cohort, consisting of 26,565 men and women (age range 40–69 years), a health survey was conducted including questions about lifestyle and medication. Main outcome measures included validated prospective injurious falls and fractures in both cohorts. The higher areal BMD and femoral neck BMD in men compared to women (P < 0.001) were explained by a higher diameter of the femoral neck. Importantly, the diameter of the femoral neck was not associated with fractures in either sex (hazard ratio [HR] 0.94–1.04, P > 0.05 for all), suggesting that a higher areal BMD and lower incidence of osteoporosis in men do not explain their lower incidence of fractures. In contrast, women were more prone to sustain injurious falls than men in both cohorts investigated (HR for women = 1.61 and 1.84, P < 0.001 for both), resulting in a higher incidence of fractures (HR for women = 2.24 and 2.36, P < 0.001 for both). The number of injurious falls and fractures occurring each month during the study period showed a very strong correlation in both women (r = 0.95, P < 0.00001) and men (r = 0.97, P < 0.00001). In summary, low areal BMD, and thus osteoporosis, may not explain the higher fracture incidence in women than in men. Instead, a higher incidence of injurious falls in women was strongly associated with the higher fracture risk.     

A Modified Arthroscopic Outside-in Shoulder Release Approach for Severe Shoulder Stiffness

Objective

Arthroscopic release is effective for patients with shoulder stiffness, but the traditional inside-out procedure cannot effectively alleviate the mobility of some severe stiff shoulder and even cause itrogenic injuries sometimes. The aim of this study is to evaluate the clinical efficacy and advantages of a modified outside-in shoulder release approach for severe shoulder stiffness.

Methods

Included in this retrospective study were 15 patients (five male and 10 female) with severe shoulder stiffness who underwent modified outside-in shoulder release surgery at our hospital between June 2019 and March 2021. Of them, 10 patients had a primary frozen shoulder and five had secondary shoulder stiffness, involving the right shoulder in six cases and the left shoulder in nine cases. The mean age of the 15 patients was 56.7 (34–69) years. The patients were instructed to exercise passively from second-day post-operation and enhance the rehabilitation exercise gradually. All patients received a range of motion (ROM) examination before and after surgery. The American Shoulder and Elbow Surgeon's Score (ASES), Constant Score (CS), and Visual Analog Scale (VAS) score for pain were recorded. All data were tested by normal distribution first and then by paired T test, otherwise by Wilcoxon rank sum test.

Results

The mean follow-up period was 18.2 (12–33) months. Compared with the preoperative value, the mean ASES score at the final follow-up improved from 38.4 ± 7.37 to 88.13 ± 6.33 points; the mean CS score from 43.27 ± 6.71 to 78.74 ± 6.93 points; the mean VAS score from 5.07 ± 1.03 to 0.81 ± 0.83 points; forward flexion from 81.93° ± 11.45° to 156.73° ± 9.12°; abduction from 65.93° ± 16.82° to 144.80° ± 8.83°; neutral external rotation from 13.53° ± 10.38° to 51.20° ± 4.77°; internal rotation from the buttock to waist (L3), all showing a significant difference (P < 0.0001). No serious complication was observed in any patient during the postoperative follow-up periods.

Conclusion

The present study has demonstrated that the modified arthroscopic outside-in shoulder release approach can improve ROM of patients and alleviate pain effectively, proving it to be an appropriate surgical option for the treatment of severe shoulder stiffness.     

Assessment of Bone Fragility in Patients With Multiple Myeloma Using QCT‐Based Finite Element Modeling

Multiple myeloma (MM) is a malignant plasma cell disease associated with severe bone destruction. Surgical intervention is often required to prevent vertebral body collapse and resulting neurological complications; however, its necessity is determined by measuring lesion size or number, without considering bone biomechanics. Finite element (FE) modeling, which simulates the physiological loading, may improve the prediction of fragility. To test this, we developed a quantitative computed tomography (QCT)‐based FE model of the vertebra and applied it to a dataset of MM patients with and without prevalent fracture. FE models were generated from vertebral QCT scans of the T₁₂ (T₁₁ if T₁₂ was fractured) of 104 MM patients, 45 with fracture and 59 without, using a low‐dose scan protocol (1.5 mm slice thickness, 4.0 to 6.5 mSv effective dose). A calibration phantom enabled the conversion of the CT Hounsfield units to FE material properties. Compressive loading of the vertebral body was simulated and the stiffness, yield load, and work to yield determined. To compare the parameters between fracture and nonfracture groups, t tests were used, and standardized odds ratios (sOR, normalized to standard deviation) and 95% confidence intervals were calculated. FE parameters were compared to mineral and structural parameters using linear regression. Patients with fracture showed lower vertebral stiffness (–15.2%; p = 0.010; sOR = 1.73; 95% CI, 1.11 to 2.70), yield force (–21.5%; p = 0.002; sOR = 2.09; 95% CI, 1.27 to 3.43), and work to yield (–27.4%; p = 0.001; sOR = 2.28; 95% CI, 1.33 to 3.92) compared to nonfracture patients. All parameters correlated significantly with vBMD (stiffness: R² = 0.57, yield force: R² = 0.59, work to yield: R² = 0.50, p < 0.001), BV/TV (stiffness: R² = 0.56, yield force: R² = 0.58, work to yield: R² = 0.49, p < 0.001), and Tb.Sp (stiffness: R² = 0.51, yield force: R² = 0.53, work to yield: R² = 0.45, p < 0.001). FE modeling identified MM patients with compromised mechanical integrity of the vertebra. Higher sOR values were obtained for the biomechanical compared to structural or mineral measures, suggesting that FE modeling improves fragility assessment in these patients. © 2016 American Society for Bone and Mineral Research.     

前下后上型齿突骨折螺钉内固定的生物力学研究

目的：评价前下后上型齿突骨折螺钉内固定的生物力学效果。方法：收集20具新鲜成人上颈椎标本,分为3组,模拟齿突Ⅱ型骨折模型,骨折线为前下后上,截骨角度分别为0°6具,17°8具,25°6具,并进行齿突螺钉固定。进行旋入力矩、最大轴向拔出力和刚度测试。结果：各组最大螺钉旋入力矩、抗拔出力差异无统计学意义。骨折端错位程度随着截骨角度的增加而增加,在17°组平均移位1.61mm,25°组平均移位2.88mm。抗扭转力矩随着截骨角度的增加而增加。各组剪切刚度差异无统计学意义。结论：一定角度范围内的前下后上型骨折可使用齿突螺钉固定进行治疗。     

Cost description of clinical examination and MRI in wrist ligament injuries

Objective: The total number and cost of wrist MRIs in the catchment area of the Västra Götaland Region in Sweden (population 1 723 000) during 1 year was analysed, together with the number and content of referrals.

Methods: Six radiology departments reported the numbers and rate of all MRI investigations intended to diagnose wrist ligament injuries (n?=?411) and other injuries to the wrist.

Results: The additional cost of the difference between MRIs and a clinical examination by a hand surgeon, plus indirect costs for patients with suspected wrist ligament injuries, was calculated as 957 000 euros.

Conclusions: It is recommended that MRI should only be used in patients in whom there are clinical difficulties in terms of diagnosing wrist ligament injuries. It is suggested that patients with suspected wrist ligament injuries should be referred directly to an experienced hand surgeon, capable of performing a standardised wrist examination and, when needed, diagnostic arthroscopy and final treatment. The proposed algorithm for the diagnosis and treatment of suspected wrist ligament injuries presented in the present study could save time for the patient and for the radiology departments, as well as reducing costs. The ability to implement the early and appropriate treatment of acute ligament injuries could be improved at the same time.     

Joint Kinetics to Assess the Influence of the Racket on a Tennis Player’s Shoulder

This study aimed at investigating the influence of three rackets on shoulder net joint moments, power and muscle activity during the flat tennis serve under field- conditions. A 6-camera Eagle^® motion analysis system, operating at 256 Hz, captured racket and dominant upper limb kinematics of the serve in five tennis players under three racket conditions (A: low mass, high balance and polar moment, B: low three moments of inertia, and C: high mass, swingweight and twistweight). The electromyographic activity of six trunk and arm muscles was simultaneously recorded. Shoulder net joint moments and power were computed by 3D inverse dynamics. The results showed that greater shoulder joint power and internal/external rotation peak moments were found to accelerate and decelerate racket A in comparison with the racket C. Moreover, serving with the racket A resulted in less activity in latissimus dorsi muscle during the acceleration phase, and biceps brachii muscle during the follow-through phase when compared with racket C. These initial findings encourage studying the biomechanical measurements to quantify the loads on the body during play in order to reduce them, and then prevent shoulder injuries. Racket specifications may be a critical point for coaches who train players suffering from shoulder pain and chronic upper limb injuries should be considered in relation to the racket specifications of the players.

Key Points

• Light racket required more joint power than heavy one to achieve similar post impact ball velocity.
• Serving with a light racket resulted in higher shoulder internal and external rotation moments than using a heavy one for similar performance.
• Chronic shoulder pain should encourage coaches to check for potentially inappropriate racket specifications of their players.

Key words: EMG, inverse dynamics, joint power, joint moment, tennis serve     

Predictors of proximal tibia anterior shear force during a vertical stop‐jump

Anterior cruciate ligament (ACL) continues to be a significant medical issue for athletes participating in sports and recreational activities. Biomechanical analyses have determined that anterior shear force is the most direct loading mechanism of the ACL and a probable component of noncontact ACL injury. The purpose of this study was to examine the biomechanical predictors of proximal tibia anterior shear force during a stop‐jump task. A biomechanical and electromyographic (EMG) analysis of the knee was conducted while subjects performed a vertical stop‐jump task. The task was chosen to simulate an athletic maneuver that included a landing with a sharp deceleration and a change in direction. The final regression model indicated that posterior ground reaction force, external knee flexion moment, knee flexion angle, integrated EMG activity of the vastus lateralis, and sex (female) would significantly predict proximal tibia anterior shear force (p < 0.0001, R² = 0.8609). Knee flexion moment had the greatest influence on proximal tibia anterior shear force. The mathematical relationships elucidated in the current study support previous clinical and basic science research examining noncontact ACL injuries. This data provides important evidence for clinicians who are examining the risk factors for these injuries and developing/validating training programs to reduce the incidence of injury. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1589–1597, 2007     

Biomechanical tolerance of whole lumbar spines in straightened posture subjected to axial acceleration

Quantification of biomechanical tolerance is necessary for injury prediction and protection of vehicular occupants. This study experimentally quantified lumbar spine axial tolerance during accelerative environments simulating a variety of military and civilian scenarios. Intact human lumbar spines (T12‐L5) were dynamically loaded using a custom‐built drop tower. Twenty‐three specimens were tested at sub‐failure and failure levels consisting of peak axial forces between 2.6 and 7.9 kN and corresponding peak accelerations between 7 and 57 g. Military aircraft ejection and helicopter crashes fall within these high axial acceleration ranges. Testing was stopped following injury detection. Both peak force and acceleration were significant (p < 0.0001) injury predictors. Injury probability curves using parametric survival analysis were created for peak acceleration and peak force. Fifty‐percent probability of injury (95%CI) for force and acceleration were 4.5 (3.9–5.2 kN), and 16 (13–19 g). A majority of injuries affected the L1 spinal level. Peak axial forces and accelerations were greater for specimens that sustained multiple injuries or injuries at L2–L5 spinal levels. In general, force‐based tolerance was consistent with previous shorter‐segment lumbar spine testing (3–5 vertebrae), although studies incorporating isolated vertebral bodies reported higher tolerance attributable to a different injury mechanism involving structural failure of the cortical shell. This study identified novel outcomes with regard to injury patterns, wherein more violent exposures produced more injuries in the caudal lumbar spine. This caudal migration was likely attributable to increased injury tolerance at lower lumbar spinal levels and a faster inertial mass recruitment process for high rate load application. Published 2017. This article is a U.S. Government work and is in the public domain in the USA. J Orthop Res 36:1747–1756, 2018.     

Comparative study of carpal tunnel compliance in the human,dog, rabbit,and rat

The purpose of this study was to measure the compliance of the carpal tunnel in candidate animal models of carpal tunnel syndrome (CTS), by measuring the resistance when passing a tapered metal rod through the carpal tunnel. Forepaws from 10 dogs, 10 rabbits, and 10 rats with intact carpal tunnels, and 10 fresh frozen human wrist cadavers were used. The slopes of the linear part of the force‐displacement curve (a measure of stiffness), normal force, and increasing area ratio (InAR) were significantly different among the four species (p < 0.05). Post hoc analysis indicated that the mean slopes for the human carpal tunnel were the largest, indicating the least compliance, whereas those of the rat were the least (p < 0.05). The features of the compliance for the dog carpal tunnel were closest to the human. The development of animal models of CTS should consider the compliance of the carpal tunnel, as it will be more difficult to increase pressure in a more compliant tunnel. © 2009 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 28:652–656, 2010