Examination of Skill Acquisition and Grader Bias in a Distal Radius Fracture Fixation Model.

OBJECTIVES: Primary: Assess the ability of faculty graders to predict the objectively measured strength of distal radius fracture fixation. Secondary: Compare resident skill variation and retention related to other knowable training data. DESIGN: Residents were allowed 60 minutes to stabilize a standardized distal radius fracture using an assigned fixed-angle volar plate. Faculty observed and subjectively graded the residents without providing real-time feedback. Objective biomechanical evaluation (construct strength and stiffness) was compared to subjective grades. Resident-specific characteristics (sex, PGY, and ACGME case log) were also used to compare the objective data. SETTING: A simulated operating room in our laboratory. PARTICIPANTS: Post-graduate year 2, 3, 4, and 5 orthopedic residents. RESULTS: Primary: Faculty were not successful at predicting objectively measured fixation, and their subjective scoring suggests confirmation bias as PGY increased. Secondary: Resident year-in-training alone did not predict objective measures (p = 0.53), but was predictive of subjective scores (p < 0.001). Skills learned were not always retained, as 29% of residents objectively failed subsequent to passing. Notably, resident-reported case-specific experience alone was inversely correlated with objective fixation strength. CONCLUSIONS: This testing model enabled the collection of objective and subjective resident skill scores. Faculty graders did not routinely predict objective measures, and their subjective assessment appears biased related to PGY. Also, in vivo case volume alone does not predict objective results. Familiar faculty teaching consistency, and resident grading by external faculty unfamiliar with tested residents, might alter these results.

Radiographic Analysis of Simulated First Dorsal Interosseous and Opponens Pollicis Loading Upon Thumb CMC Joint Subluxation: A Cadaver Study.

BACKGROUND: Therapy programs to treat thumb carpometacarpal (CMC) arthritis may engage selective activation and reeducation of thenar muscles, particularly the first dorsal interosseous (FDI) and opponens pollicis (OP) to reduce subluxation of the joint. We describe the effect of simulated selective activation of the FDI and OP muscles upon radiographic subluxation of the thumb CMC joint. METHODS: In a cadaver model of CMC subluxation, loads were applied to the FDI, the OP, and then concomitantly at 0%, 25%, 50%, 75%, and 100% maximal loads and radial subluxation of the joint and reduction in subluxation was measured. RESULTS: Selective activation of the OP, alone, improved the subluxation ratio (SR) in a dose-dependent manner. Selective activation of FDI, alone, demonstrated minimal effects on SR. Concomitant activation of OP and FDI improved the SR across all loading states, and activation of 75% and greater, when compared with FDI activation alone, resulted in a statistically significant improvement in SR to within 10% of the presubluxed joint. CONCLUSIONS: Concomitant activation of the FDI and OP acts to reduce subluxation of the thumb CMC joint in a dose-dependent fashion. The OP is likely the predominant reducing force. Hand therapy programs that focus on selective strengthening programs likely function in part to encourage patients to activate the easily palpable and easily understood FDI. Concomitant coactivation of the OP may be the major reducing force to elicit clinical and radiographic reduction of subluxation, improved thumb positioning, and reduction of pain and arthritic symptoms.

Development, construct validity, and reproducibility of a mimetic sealed jar measuring the dynamics of opening.

Measurement of the dynamic kinetics involved in opening a jar may enable health care professionals to understand and train individuals in optimal hand/grip mechanics. This technical note details the design, validity, and reproducibility testing of a mimetic jar capable of measuring the forces and moments and isolated digital forces applied to the lid of the jar. An ecological jar instrument was designed with a torque limiter to provide a natural opening mechanism while a six-axis load cell and force sensing resistors recorded the way individuals applied force to the jar and lid during opening of a sealed container. A total of 115 volunteers participated in a validation of the device and an additional 36 participated in repeatability testing. Compared with prior instruments, this mimetic jar provides more force data and a simulated opening experience - making this jar instrument unique. Future studies utilizing the jar designed herein may allow health care professionals to evaluate patients suffering from debilitating osteoarthritis, fibromyalgia or other neuromuscular conditions and offer improvement strategies.

Development of a disposable force-sensing glove for clinicians and demonstration of its force measurements on patients during rehabilitation following anterior cruciate ligament reconstruction surgery.

For many clinicians, their effectiveness is dependent on the magnitude of forces they manually apply to their patients. However, current state-of-the-art care strategies lack quantitative feedback, making it difficult to provide consistent care over time and among multiple clinicians. To provide real-time quantitative feedback to clinicians, we have developed a disposable glove with a force sensor embedded in the fingertips or palm. The sensor is based on the fiber-optic bendloss effect whereby light intensity from an infrared source is attenuated as the fiber is bent between a series of corrugated teeth. The sensor fabricated has a very low profile (10×7×1 mm) and has demonstrated high sensitivity, accuracy, range, and durability. Force feedback up to 90 N with an average force threshold at 0.19 N and average sensor resolution at 0.05 N has been demonstrated. A preliminary clinical study has also been conducted with anterior cruciate ligament reconstruction patients who show significant range of motion improvement when treated with the force-sensing glove.

Pulmonary function tests correlated with thoracic volumes in adolescent idiopathic scoliosis.

Scoliosis deformity has been linked with deleterious changes in the thoracic cavity that affect pulmonary function. The causal relationship between spinal deformity and pulmonary function has yet to be fully defined. It has been hypothesized that deformity correction improves pulmonary function by restoring both respiratory muscle efficiency and increasing the space available to the lungs. This research aims to correlate pulmonary function and thoracic volume before and after scoliosis correction. Retrospective correlational analysis between thoracic volume modeling from plain x-rays and pulmonary function tests was conducted. Adolescent idiopathic scoliosis patients enrolled in a multicenter database were sorted by pre-operative Total Lung Capacities (TLC) % predicted values from their Pulmonary Function Tests (PFT). Ten patients with the best and ten patients with the worst TLC values were included. Modeled thoracic volume and TLC values were compared before and 2 years after surgery. Scoliosis correction resulted in an increase in the thoracic volume for patients with the worst initial TLCs (11.7%) and those with the best initial TLCs (12.5%). The adolescents with the most severe pulmonary restriction prior to surgery strongly correlated with post-operative change in total lung capacity and thoracic volume (r2 = 0.839; p < 0.001). The mean increase in thoracic volume in this group was 373.1 cm3 (11.7%) which correlated with a 21.2% improvement in TLC. Scoliosis correction in adolescents was found to increase thoracic volume and is strongly correlated with improved TLC in cases with severe restrictive pulmonary function, but no correlation was found in cases with normal pulmonary function. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:175-182, 2017.

Adolescent Idiopathic Scoliosis Thoracic Volume Modeling: The Effect of Surgical Correction.

BACKGROUND: Scoliosis has been shown to have detrimental effects on pulmonary function, traditionally measured by pulmonary function tests, which is theorized to be correlated to the distortion of the spine and thorax. The changes in thoracic volume with surgical correction have not been well quantified. This study seeks to define the effect of surgical correction on thoracic volume in patients with adolescent idiopathic scoliosis. METHODS: Images were obtained from adolescents with idiopathic scoliosis enrolled in a multicenter database (Prospective Pediatric Scoliosis Study). A convenience sample of patients with Lenke type 1 curves with a complete data set meeting specific parameters was used. Blender v2.63a software was used to construct a 3-dimensional (3D) computational model of the spine from 2-dimensional calibrated radiographs. To accomplish this, the 3D thorax model was deformed to match the calibrated radiographs. The thorax volume was then calculated in cubic centimeters using Mimics v15 software. RESULTS: The results using this computational modeling technique demonstrated that surgical correction resulted in decreased curve measurement as determined by Cobb method, and increased postoperative thoracic volume as expected. Thoracic volume significantly increased by a mean of 567 mm (P<0.001). The percent change in thoracic volume after surgical correction averaged 40% (range, 3% to 87%). The smaller the baseline volume, the greater the change in volume postoperatively (r=-0.86).Evaluation of postoperative data demonstrated that spinal curve measurement as determined by Cobb method was significantly reduced from a mean of 69 degrees (range, 50 to 96 degrees) preoperatively to 27 degrees (range, 13 to 33 degrees) postoperatively (P<0.001). CONCLUSIONS: This pilot study demonstrates methodologic plausibility for measuring 3D changes in thoracic volumes using 2-dimensional imaging. This is an assessment of the novel modeling technique, to be used in larger future studies to assess clinical significance. LEVEL OF EVIDENCE: Level 3-retrospective comparison of prospectively collected data.

Anatomic landmarks for arthroscopic suprascapular nerve decompression.

PURPOSE: Arthroscopic suprascapular nerve (SSN) decompression has become a more frequently utilized procedure in the treatment of SSN entrapment and has gained popularity over recent years. Despite increasing technical notes and outcomes information regarding this technique, there remains a paucity of data with respect to clear anatomic guidelines for teaching this procedure. The purpose of this study was to provide guidelines that are visible arthroscopically and palpable externally to allow safer and more efficient surgery for arthroscopic decompression by analysing the superior scapular anatomy with respect to local landmarks. METHODS: A cadaveric study was used to examine neurovascular structural measurements obtained in twelve cadavera with 23 usable shoulders. Arthroscopic dissection of the pertinent anatomy as determined by previously described approaches was followed by meticulous open regional dissection and measurements of the local landmarks. RESULTS: Measurements of the pertinent arthroscopic anatomy with respect to local landmarks of the superior shoulder were recorded in 23 shoulders and are included herein. Measurements taken arthroscopically on 22 shoulders revealed that the lateral insertion of the transverse suprascapular ligament to the acromioclavicular joint was 3.6 cm (SD 0.5 cm). One of the anatomic measurements on open dissection had a significant correlation with our subject's demographics and was found between cadaveric height and the linear distance from the lateral acromion to the suprascapular notch (mean distance = 66.53 ± 5.30 mm; Pearson's correlation = 0.739; p = 0.006). CONCLUSIONS: This cadaveric study describes meaningful landmarks and their measurements, which are identifiable arthroscopically and enable safer surgery in this area. Using these numbers, surgeons can know that it is safe to bluntly dissect to 2.5 cm medial to the acromioclavicular joint (and 5 cm medial to the palpable lateral acromion) before dissection is likely to encounter the SSN or artery. This knowledge will allow surgeons to learn this surgical technique, and for surgical educators to safely teach dissection and release in this uncommonly accessed anatomic region.

Comparison of nonnavigated and 3-dimensional image-based computer navigated balloon kyphoplasty.

Balloon kyphoplasty is a common treatment for osteoporotic and pathologic compression fractures. Advantages include minimal tissue disruption, quick recovery, pain relief, and in some cases prevention of progressive sagittal deformity. The benefit of image-based navigation in kyphoplasty has not been established. The goal of this study was to determine whether there is a difference between fluoroscopy-guided balloon kyphoplasty and 3-dimensional image-based navigation in terms of needle malposition rate, cement leakage rate, and radiation exposure time. The authors compared navigated and nonnavigated needle placement in 30 balloon kyphoplasty procedures (47 levels). Intraoperative 3-dimensional image-based navigation was used for needle placement in 21 cases (36 levels); conventional 2-dimensional fluoroscopy was used in the other 9 cases (11 levels). The 2 groups were compared for rates of needle malposition and cement leakage as well as radiation exposure time. Three of 11 (27%) nonnavigated cases were complicated by a malpositioned needle, and 2 of these had to be repositioned. The navigated group had a significantly lower malposition rate (1 of 36; 3%; P=.04). The overall rate of cement leakage was also similar in both groups (P=.29). Radiation exposure time was similar in both groups (navigated, 98 s/level; nonnavigated, 125 s/level; P=.10). Navigated kyphoplasty procedures did not differ significantly from nonnavigated procedures except in terms of needle malposition rate, where navigation may have decreased the need for needle repositioning.

On orthopedic surgical skill prediction--the limited value of traditional testing.

OBJECTIVES: Primary: to assess the utility of our distal radius fracture repair model as a tool for examining residents' surgical skills. Secondary: to compare the residents' ability to achieve specific biomechanically measured fracture stability with traditional test scores. DESIGN: Our laboratory pioneered a model that measures biomechanical qualities of a repaired distal radius fracture. Before participation, all residents to be tested completed specified knowledge examinations. During the laboratory exercise, proctors observed each resident and completed Objective Structured Assessment of Technical Skills forms. At the completion of the laboratory, each specimen was tested biomechanically. Written examinations were completed in a proctored setting and computer examinations at home following the honor system. The laboratory exercise had adequate space and materials and allowed 60 minutes to complete the procedure. Residents had equal access to x-ray imaging. SETTING: The examination environment of the study resembled an operating room. PARTICIPANTS: Postgraduate years 3 and 4 orthopedic residents in our program were asked to participate. The institutional review board reviewed and approved the study as exempt. RESULTS: Fracture repair constructs capable of resisting loads expected during rehabilitation were created by approximately half the residents tested. However, traditional written and computer-based testing methods failed to predict which resident's fracture construct would pass the biomechanical testing. Prior in vivo similar case experience was not predictive. CONCLUSIONS: The idea that "book smart does not equal street smart" applies to the tested model. To measure surgical skill acquisition and increase public safety related to surgery, it will be necessary to employ new and specific examination methods that identify the skill to be acquired and test the acquisition of this skill as precisely as possible.

Altered helical axis patterns of the lumbar spine indicate increased instability with disc degeneration.

Although the causes of low back pain are poorly defined and indistinct, degeneration of the intervertebral disc is most often implicated as the origin of pain. The biochemical and mechanical changes associated with degeneration result in the discs' inability to maintain structure and function, leading to spinal instability and ultimately pain. Traditionally, a clinical exam assessing functional range-of-motion coupled with T2-weighted MRI revealing disc morphology are used to evaluate spinal health; however, these subjective measures fail to correlate well with pain or provide useful patient stratification. Therefore, improved quantification of spinal motion and objective MRI measures of disc health are necessary. An instantaneous helical axis (IHA) approach provides rich temporal three-dimensional data describing the pathway of motion, which is easily visualized. Eighteen cadaveric osteoligamentous lumbar spines (L4-5) from throughout the degenerative spectrum were tested in a pure moment fashion. IHA were calculated for flexion-extension and lateral bending. A correlational study design was used to determine the relationship between disc measurements from quantitative T2* MRI and IHA metrics. Increased instability and out-of-plane rotation with diminished disc health was observed during lateral bending, but not flexion-extension. This new analysis strategy examines the entire pathway of motion, rather than simplifying spinal kinematics to its terminal ends of motion and provides a more sensitive kinematic measurement of disc health. Ultimately, through the use of 3D dynamic fluoroscopy or similar methods, a patient's functional IHA in lateral bending may be measured and used to assess their disc health for diagnosis, progression tracking, and treatment evaluation.

Combining displacement field and grip force information to determine mechanical properties of planar tissue with complicated geometry.

Performing planar biaxial testing and using nominal stress-strain curves for soft-tissue characterization is most suitable when (1) the test produces homogeneous strain fields, (2) fibers are aligned with the coordinate axes, and (3) strains are measured far from boundaries. Some tissue types [such as lamellae of the annulus fibrosus (AF)] may not allow for these conditions to be met due to their natural geometry and constitution. The objective of this work was to develop and test a method utilizing a surface displacement field, grip force-stretch data, and finite-element (FE) modeling to facilitate analysis of such complex samples. We evaluated the method by regressing a simple structural model to simulated and experimental data. Three different tissues with different characteristics were used: Superficial pectoralis major (SPM) (anisotropic, aligned with axes), facet capsular ligament (FCL) (anisotropic, aligned with axes, bone attached), and a lamella from the AF (anisotropic, aligned off-axis, bone attached). We found that the surface displacement field or the grip force-stretch data information alone is insufficient to determine a unique parameter set. Utilizing both data types provided tight confidence regions (CRs) of the regressed parameters and low parameter sensitivity to initial guess. This combined fitting approach provided robust characterization of tissues with varying fiber orientations and boundaries and is applicable to tissues that are poorly suited to standard biaxial testing. The structural model, a set of C++ finite-element routines, and a Matlab routine to do the fitting based on a set of force/displacement data is provided in the on-line supplementary material.

Quantitative T2* (T2 star) relaxation times predict site specific proteoglycan content and residual mechanics of the intervertebral disc throughout degeneration.

Degeneration alters the biochemical composition of the disc, affecting the mechanical integrity leading to spinal instability. Quantitative T2* MRI probes water mobility within the macromolecular network, a potentially more sensitive assessment of disc health. We determined the relationship between T2* relaxation time and proteoglycan content, collagen content, and compressive mechanics throughout the degenerative spectrum. Eighteen human cadaveric lumbar (L4-L5) discs were imaged using T2* MRI. The T2* relaxation time at five locations (nucleous pulposus or NP, anterior annulus fibrosis or AF, posterior AF, inner AF, and outer AF) was correlated with sulfated-glycosaminoglycan (s-GAG) content, hydroxyproline content, and residual stress and strain at each location. T2* relaxation times were significantly correlated with s-GAG contents in all test locations and were particularly strong in the NP (r = 0.944; p < 0.001) and inner AF (r = 0.782; p < 0.001). T2* relaxation times were also significantly correlated with both residual stresses and excised strains in the NP (r = 0.857; p < 0.001: r = 0.816; p < 0.001), inner AF (r = 0.535; p = 0.022: r = 0.516; p = 0.028), and outer AF (r = 0.668; p = 0.002: r = 0.458; p = 0.041). These strong correlations highlight T2* MRI's ability to predict the biochemical and mechanical health of the disc. T2* MRI assessment of disc health is a clinically viable tool showing promise as a biomarker for distinguishing degenerative changes.

Quantification of continuous in vivo flexion-extension kinematics and intervertebral strains.

PURPOSE: Healthy subjects performed lumbar flexion and were assessed by video fluoroscopy to measure the in vivo kinematics of the lower lumbar motion segments. METHODS: Fifteen healthy subjects (8 male, 7 female, 28 ± 10 years) performed lumbar flexion and extension back to neutral while their vertebrae were imaged. The sagittal plane vertebral margins of L3-S1 were identified. Lumbar angle, segmental margin strains, axial displacements, anterior-posterior (A-P) translations, and segmental rotations over the course of flexion were measured. RESULTS: L4-L5 had the largest posterior margin Green strain (65%). Each segment displayed more axial displacement than A-P translation. Peak vertebral angulation occurred at approximately 75% of peak flexion during the extension phase. CONCLUSION: L4-L5 exhibited the largest anterior and posterior margin strains (29 and 65%, respectively). Strains in the disc during in vivo lumbar flexion are due to both angular rotation and linear translation.

The low-anterolateral portal for arthroscopic biceps tenodesis: description of technique and cadaveric study.

PURPOSE: Arthroscopic biceps tenodesis surgery is an important procedure for the correction of biceps tendonitis or in conjunction with rotator cuff repair with biceps symptoms. Recent trends have developed in placing the biceps tendon lower in the bicipital groove for a tenodesis. However, a more distal biceps tenodesis location is technically challenging when carried out arthroscopically with standard posterior and lateral portals. We aimed to establish the safety of a low-anterolateral portal location for direct access to the lowest aspect of the bicipital groove. METHODS: An anatomical study design was used to examine portal to neurovascular structural measurements in 23 cadaveric shoulders. These shoulders had undergone low-anterolateral portal placement over the inferior most aspect of the bicipital groove as determined by palpation and direct arthroscopic visualization. No arthroscopic irrigation was performed. Following this, the shoulders underwent open dissection with the cannula in place to evaluate for any potential damage to any portion of the axillary nerve. RESULTS: All of the resultant portals in this study provided direct access to the inferior most aspect of the bicipital groove, and the dissection revealed that the portal was touching a small distal axillary nerve branch on the undersurface of the anterior deltoid in nearly half of the shoulders. CONCLUSIONS: The placement of a low-anterolateral portal for arthroscopic biceps tenodesis at the distal bicipital groove does not produce significant neurovascular damage; the portal trajectory comes close to distal anterior branches of the axillary nerve. Given these findings, this portal should be placed bluntly to best protect these underlying neurovascular structures.

Disc degeneration assessed by quantitative T2* (T2 star) correlated with functional lumbar mechanics.

STUDY DESIGN: Experimental correlation study design to quantify features of disc health, including signal intensity and distinction between the annulus fibrosus and nucleus pulposus, with T2* magnetic resonance imaging (MRI) and correlate with the functional mechanics in corresponding motion segments. OBJECTIVE: Establish the relationship between disc health assessed by quantitative T2* MRI and functional lumbar mechanics. SUMMARY OF BACKGROUND DATA: Degeneration leads to altered biochemistry in the disc, affecting the mechanical competence. Clinical routine MRI sequences are not adequate in detecting early changes in degeneration and fails to correlate with pain or improve patient stratification. Quantitative T2* relaxation time mapping probes biochemical features and may offer more sensitivity in assessing disc degeneration. METHODS: Cadaveric lumbar spines were imaged using quantitative T2* mapping, as well as conventional T2-weighted MRI sequences. Discs were graded by the Pfirrmann scale, and features of disc health, including signal intensity (T2* intensity area) and distinction between the annulus fibrosus and nucleus pulposus (transition zone slope), were quantified by T2*. Each motion segment was subjected to pure moment bending to determine range of motion (ROM), neutral zone (NZ), and bending stiffness. RESULTS: T2* intensity area and transition zone slope were significantly correlated with flexion ROM (P = 0.015; P = 0.002), ratio of NZ/ROM (P = 0.010; P = 0.028), and stiffness (P = 0.044; P = 0.026), as well as lateral bending NZ/ROM (P = 0.005; P = 0.010) and stiffness (P = 0.022; P = 0.029). T2* intensity area was also correlated with lateral bending ROM (P = 0.023). Pfirrmann grade was only correlated with lateral bending NZ/ROM (P = 0.001) and stiffness (P = 0.007). CONCLUSION: T2* mapping is a sensitive quantitative method capable of detecting changes associated with disc degeneration. Features of disc health quantified with T2* predicted altered functional mechanics of the lumbar spine better than traditional Pfirrmann grading. This new methodology and analysis technique may enhance the assessment of degeneration and enable greater patient stratification for therapeutic strategies. LEVEL OF EVIDENCE: N/A.

Instantaneous helical axis methodology to identify aberrant neck motion.

BACKGROUND: Neck pain afflicts 30-50% of the U.S. population annually; however we currently have poor diagnostic differentiation techniques to inform individualized treatment. Planar neck kinematics has been shown to be correlated with neck pain, but neck motion is much more complex than pure planar activities. Our objective was to define a methodology for determining aberrant neck kinematics and assess it. METHODS: We examined a complex neck kinematic activity of neck circumduction and computed the pathway of motion using the instantaneous helical axis approach in 81 patients with non-specific neck pain and in 20 non-matched symptom free subjects. Neck circumduction, or rolling of the head, represents a complex neck kinematic activity, investigating the innate coupled motion of the cervical spine at the end ranges of motion in all directions. Instance of discontinuities in the helical axis patterns, or folds, were identified and labeled as occurrences of aberrant motion. FINDINGS: The instances of aberrant motion, or folds, which are nearly non-existent in the healthy sample group, are present in both the pre- and post-treatment neck pain patients. Following a treatment intervention of the symptomatic patients, pain and neck disability index decreased significantly (P<0.001) concomitant with a decrease in the number of folds (P=0.021). INTERPRETATION: The present study highlights a new technique using an instantaneous helical axis approach to detect subtle abnormalities in the pathway of motion of the head about the trunk, during a neck circumduction exercise.

An image-based gait simulation study of tarsal kinematics in women with hallux valgus.

BACKGROUND: Although not well understood, foot kinematics are changed with hallux valgus. OBJECTIVE: The purpose of this study was to examine tarsal kinematics in women with hallux valgus deformity. DESIGN: A prospective, cross-sectional design was used. METHODS: Twenty women with (n=10) and without (n=10) deformity participated. Data were acquired with the use of a magnetic resonance scanner. Participants were posed standing to simulate gait, with images reconstructed into virtual bone datasets. Measures taken described foot posture (hallux angle, intermetatarsal angle, arch angle). With the use of additional computer processes, the image sequence was then registered across gait conditions to compute relative tarsal position angles, first-ray angles, and helical axis parameters decomposed into X, Y, and Z components. An analysis of variance model compared kinematics between groups and across conditions. Multiple regression analysis assessed the relationship of arch angle, navicular position, and inclination of the first-ray axis. RESULTS: Both the hallux and intermetatarsal angles were larger with deformity; arch angle was not different between groups. The calcaneus was everted by ≥6.6 degrees, and the first ray adducted (F=44.17) by ≥9.3 degrees across conditions with deformity. There was an interaction (F=5.06) for the first-ray axis. Follow-up comparisons detected increased inclination of the first-ray axis over middle stance compared with late stance in the group with deformity. LIMITATIONS: Gait was simulated, kinetics were not measured, and sample size was small. CONCLUSIONS: There were group differences. Eversion of the calcaneus and adduction of the first ray were increased, and the first-ray axis was inclined 24 degrees over middle stance in women with deformity compared with 6 degrees in control participants. Results may identify risk factors of hallux valgus and inform nonoperative treatment (orthoses, exercise) strategies.

Developmental biomechanics of the human cervical spine.

Head and neck injuries, the leading cause of death for children in the U.S., are difficult to diagnose, treat, and prevent because of a critical void in our understanding of the biomechanical response of the immature cervical spine. The objective of this study was to investigate the functional and failure biomechanics of the cervical spine across multiple axes of loading throughout maturation. A correlational study design was used to examine the relationships governing spinal maturation and biomechanical flexibility curves and tolerance data using a cadaver human in vitro model. Eleven human cadaver cervical spines from across the developmental spectrum (2-28 years) were dissected into segments (C1-C2, C3-C5, and C6-C7) for biomechanical testing. Non-destructive flexibility tests were performed in tension, compression, flexion, extension, lateral bending, and axial rotation. After measuring their intact biomechanical responses, each segment group was failed in different modes to measure the tissue tolerance in tension (C1-C2), compression (C3-C5), and extension (C5-C6). Classical injury patterns were observed in all of the specimens tested. Both the functional (p<0.014) and failure (p<0.0001) mechanics exhibited significant relationships with age. Nonlinear flexibility curves described the functional response of the cervical spine throughout maturation and elucidated age, spinal level, and mode of loading specificity. These data support our understanding of the child cervical spine from a developmental perspective and facilitate the generation of injury prevention or management schema for the mitigation of child spine injuries and their deleterious effects.

The biomechanics of a multilevel lumbar spine hybrid using nucleus replacement in conjunction with fusion.

BACKGROUND CONTEXT: Degenerative disc disease is commonly a multilevel pathology with varying deterioration severity. The use of fusion on multiple levels can significantly affect functionality and has been linked to persistent adjacent disc degeneration. A hybrid approach of fusion and nucleus replacement (NR) has been suggested as a solution for mildly degenerated yet painful levels adjacent to fusion. PURPOSE: To compare the biomechanical metrics of different hybrid implant constructs, hypothesizing that an NR+fusion hybrid would be similar to a single-level fusion and perform more naturally compared with a two-level fusion. STUDY DESIGN: A cadaveric in vitro repeated-measures study was performed to evaluate a multilevel lumbar NR+fusion hybrid. METHODS: Eight cadaveric spines (L3-S1) were tested in a Spine Kinetic Simulator (Instron, Norwood, MA, USA). Pure moments of 8 Nm were applied in flexion/extension, lateral bending, and axial rotation as well as compression loading. Specimens were tested intact; fused (using transforaminal lumbar interbody fusion instrumentation with posterior rods) at L5-S1; with a nuclectomy at L4-L5 including fusion at L5-S1; with NR at L4-L5 including fusion at L5-S1; and finally with a two-level fusion spanning L4-S1. Repeated-measures analysis of variance and corrected t tests were used to statistically compare outcomes. RESULTS: The NR+fusion hybrid and single-level fusion exhibited no statistical differences for range of motion (ROM), stiffness, neutral zone, and intradiscal pressure in all loading directions. Compared with two-level fusion, the hybrid affords the construct 41.9% more ROM on average. Two-level fusion stiffness was statistically higher than all other constructs and resulted in significantly lower ROM in flexion, extension, and lateral bending. The hybrid construct produced approximately half of the L3-L4 adjacent-level pressures as the two-level fusion case while generating similar pressures to the single-level fusion case. CONCLUSIONS: These data portend more natural functional outcomes and fewer adjacent disc complications for a multilevel NR+fusion hybrid compared with the classical two-level fusion.

Adaptations of mouse skeletal muscle to low-intensity vibration training.

PURPOSE: We tested the hypothesis that low-intensity vibration training in mice improves contractile function of hindlimb skeletal muscles and promotes exercise-related cellular adaptations. METHODS: We subjected C57BL/6J mice to 6 wk, 5 d·wk, 15 min·d of sham or low-intensity vibration (45 Hz, 1.0g) while housed in traditional cages (Sham-Active, n = 8; Vibrated-Active, n = 10) or in small cages to restrict physical activity (Sham-Restricted, n = 8; Vibrated-Restricted, n = 8). Contractile function and resistance to fatigue were tested in vivo (anterior and posterior crural muscles) and ex vivo on the soleus muscle. Tibialis anterior and soleus muscles were evaluated histologically for alterations in oxidative metabolism, capillarity, and fiber types. Epididymal fat pad and hindlimb muscle masses were measured. Two-way ANOVAs were used to determine the effects of vibration and physical inactivity. RESULTS: Vibration training resulted in a 10% increase in maximal isometric torque (P = 0.038) and 16% faster maximal rate of relaxation (P = 0.030) of the anterior crural muscles. Posterior crural muscles were unaffected by vibration, except greater rates of contraction in Vibrated-Restricted mice compared with Vibrated-Active and Sham-Restricted mice (P = 0.022). Soleus muscle maximal isometric tetanic force tended to be greater (P = 0.057), and maximal relaxation was 20% faster (P = 0.005) in vibrated compared with sham mice. The restriction of physical activity induced muscle weakness but was not required for vibration to be effective in improving strength or relaxation. Vibration training did not affect muscle fatigability or any indicator of cellular adaptation investigated (P ≥ 0.431). Fat pad but not hindlimb muscle masses were affected by vibration training. CONCLUSION: Vibration training in mice improved muscle contractility, specifically strength and relaxation rates, with no indication of adverse effects to muscle function or cellular adaptations.