FITT Odyssey: A Scoping Review of Exercise Programs for Managing Rotator Cuff Related Shoulder Pain.

OBJECTIVE: To summarize the FITT (frequency, intensity, time, type) components of exercise programs included in randomized controlled trials (RCTs) that compared 2 or more programs for managing rotator cuff related shoulder pain (RCRSP). DESIGN: Scoping review. LITERATURE SEARCH: Electronic searches were conducted up to May 2023. STUDY SELECTION CRITERIA: RCTs comparing the effects of 2 or more types of exercise programs, differing in prescription according to the FITT principle, in people with RCRSP. DATA SYNTHESIS: We extracted data from each trial report so that we could answer items 1-10 and 13-15 from the Consensus on Exercise Reporting Template (CERT). Descriptive analysis of the exercise programs was performed by summarising and presenting the FITT characteristics, and other relevant CERT characteristics (material, provider, delivery, tailoring). RESULTS: FITT characteristics from 46 exercise programs included in 22 trials were extracted. The exercise programs were divided into 4 categories (defined in accordance to the original authors' description and proposed rationale): motor control (n=8), scapula-focused (n=7), eccentric (n=8), and non-specific exercise programs (n=28). Five programs were allocated to 2 different categories. The different program types had similar parameters. Exercise programs frequency ranged from 2 to 7 times per week, dose ranged from 1 to 3 sets and 4 to 30 repetitions per sets and exercise program duration ranged from 4 to 16 weeks. CONCLUSION: There was considerable variability in the parameters used to prescribe exercises for RCRSP. Clinicians seeking guidance on FITT parameters derived from trials should do so cautiously because there was no one size-fits-all approach.

Reliability and validity of the medial standing overhead arm reach (SOAR) test as a measure of functional hip adduction motion.

OBJECTIVE: The Posterior Standing Overhead Arm Reach (SOAR) test has been previously reported as a reliable clinical measure of closed chain hip extension motion. The proposed Medial SOAR test expands on that testing approach to provide a similar measure of functional hip adduction motion. This was a preliminary intrarater and interrater reliability and validity study of the Medial SOAR test as a measure of functional hip adduction. DESIGN: Cross-sectional. SETTING: University motion analysis laboratory. PARTICIPANTS: Fifty hips were assessed in 25 (22 female) asymptomatic participants (mean age = 23.4 years, SD = 0.8). MAIN MEASURES: Maximum hip adduction during the Medial SOAR test was measured with a standard goniometer independently by two examiners. The test was also performed using three-dimensional motion capture. The intrarater and interrater reliability of the goniometric measure was determined using intraclass correlation coefficients, and the relationship between measures obtained via goniometry and three-dimensional motion capture was assessed with Pearson correlations and Bland-Altman analysis. RESULTS: Intrarater reliability (ICC2,3) was 0.88 (95% CI = 0.80-0.92) for Examiner 1 and 0.87 (95% CI = 0.79-0.92) for Examiner 2. The standard error of measurement and minimal detectable change were less than 3.0°. Interrater reliability demonstrated an intraclass correlation coefficient = 0.62 (95% CI = 0.28-0.79). Pearson correlations were significant with low-to-moderate associations (r = 0.49, P < 0.001; r = 0.24, P = 0.045). CONCLUSIONS: Similar to the previously reported Posterior SOAR test, the Medial SOAR test demonstrated acceptable intrarater and interrater reliability, along with low-to-moderate associations with three-dimensional motion capture. The Medial SOAR test has the potential to provide a reliable and accurate assessment of closed chain hip adduction.

Management of chronic musculoskeletal pain in an adult with Down syndrome using a modified pain neuroscience approach: a case report.

BACKGROUND: The use of pain neuroscience education (PNE) in the management of chronic musculoskeletal pain is well documented in the literature for the adult population. However, the use of this component within the larger biopsychosocial approach has not been examined in adults with intellectual disabilities. The purpose of this case report is to describe the utilization of a PNE approach combined with exercise in the physical therapy management of chronic musculoskeletal pain in an adult with Down syndrome. CASE DESCRIPTION: The patient was a 40-year-old man with Down syndrome who presented with chronic low back pain that affected his sleep, participation at work, and social activities. Modified metaphors were used to assist the patient in understanding his pain experience as part of a multi-modal program that included exercise and aquatic therapy. OUTCOMES: Upon concluding 11 weeks of treatment, the patient returned to his prior work schedule and social activities with a pain rating at worst of 3/10 on the numeric pain rating scale with only occasional pain episodes. His disability score on the Oswestry Disability Index improved by 39% relative to baseline. DISCUSSION: The findings demonstrate how utilizing PNE within a physical therapy plan of care was used in the management of chronic musculoskeletal pain to improve function in an adult with Down syndrome.

A preliminary study of the reliability and validity of the Posterior Standing Overhead Arm Reach (SOAR) test as a measure of functional hip extension motion.

BACKGROUND: Current clinical tests do not provide a method to reliably measure closed chain hip extension. We developed the Posterior Standing Overhead Arm Reach (SOAR) test for this purpose. OBJECTIVES: This was a preliminary intrarater and interrater reliability and validity study of the Posterior SOAR test as a measure of functional hip extension. DESIGN: Cross-sectional. METHOD: Hip extension on the Posterior SOAR test was measured with a standard goniometer independently by two examiners. The test was then repeated using three-dimensional (3D) motion capture. Intraclass correlation coefficients (ICC) were used to determine the intrarater and interrater reliability of the goniometric measure and Pearson correlations were used to assess the relationship between measures obtained via goniometry and 3D motion capture. RESULTS: Fifty hips were assessed in 25 (14 female, 11 male) asymptomatic participants (mean age = 24.0 years, SD = 1.1). Intrarater reliability (ICC2,3) was 0.80 (95% CI = 0.68-0.88) for Examiner 1 and 0.77 (95% CI = 0.64-0.86) for Examiner 2, indicating excellent reliability. The standard error of the measure (SEM90) ranged from 2.5° to 3.0° with a minimal detectable change (MDC90) of 3.5° to 4.2°. Interrater reliability was good with ICC = 0.65 (95% CI = 0.36-0.80). Pearson correlations were significant with low to moderate associations (r = 0.36, P = 0.009; r = 0.51, P < 0.001). CONCLUSIONS: The Posterior SOAR test demonstrated excellent intrarater reliability, good interrater reliability, and low to moderate associations with 3D motion capture. The Posterior SOAR test has the potential to provide a reliable and accurate assessment of closed chain hip extension.

Reliability of the beighton score and impact of generalized joint mobility and resting scapular position on Median Neurodynamic Test 1.

INTRODUCTION: There is a lack of understanding of the impact of generalized joint mobility, joint hypermobility, and resting scapular position on neurodynamic testing of the median nerve. The objectives of the study were to determine: 1) the reliability of the Beighton score (BS) with and without the cutoff score for general joint hypermobility (GJH); 2) if there are differences in the Median Neurodynamic Test 1 (MNT 1) based on the Beighton cutoff score for GJH; 3) if there are differences in the MNT 1 based on an assessment of resting scapular position; 4) if there are relationships between the BS with and without the cutoff score for GJH, resting scapular position, and MNT 1. METHODS: Testing was performed by two testers at two-time intervals at least 1 week apart. The population of interest was healthy asymptomatic adults. The outcome measures included the BS, resting scapular position, and MNT 1. RESULTS: Intraclass correlation coefficients (ICC2,1) were 0.52 for intertester reliability at visit 1 and 0.86 at visit 2, with intratester reliability of 0.88 for Tester 1 and 0.71 for Tester 2 for the BS. Intertester prevalence-adjusted bias-adjusted kappa (PABAK) values for the Beighton GJH cutoff scores were 0.80-0.84 and 0.80 to 0.92 for intratester reliability. There were no statistically significant differences or relationships for any of the other variables of interest. CONCLUSION: Joint mobility and resting scapular position are not confounding variables when performing MNT 1 in an asymptomatic population.

Scapular movement impairments in individuals with subacromial pain syndrome based on scapular assistance test and scapula reposition test outcomes.

BACKGROUND: Individuals with subacromial pain present with a variety of contributing impairments related to the movement problem. The scapular assistance test (SAT) and scapula reposition test (SRT) are proposed to identify shoulder pain related to abnormal scapular movement or position. It remains unknown if scapular movement related impairments are present in those with positive tests. OBJECTIVES: To determine if scapular motion related impairments differ based on the result of the SAT or SRT in individuals with subacromial pain syndrome. DESIGN: Cross-sectional METHOD: Sixty individuals with subacromial pain syndrome were included. Prior to obtaining results of the SAT and SRT, a single examiner measured scapular upward rotation and posterior tilt active and passive motion, pectoralis minor length, and strength of the middle trapezius, lower trapezius, and serratus anterior. Dynamic scapular motion was qualitatively assessed with the Scapular Dyskinesis Test. The Mann-Whitney U test assessed for differences based on the outcome of the SAT and SRT. RESULTS: There was a significant difference (P = .023) in pectoralis minor length for the SAT. Participants with a positive SAT had decreased muscle length compared to those who tested negative. There were no significant differences in scapular motion or strength based on the result of either the SAT or SRT. CONCLUSIONS: A positive SAT was associated with greater pectoralis minor length impairment, but not muscle strength or mobility. The SRT did not identify greater impairments in any of the scapular movement related impairments assessed. Individuals may vary in contributing impairments related to SAT or SRT results.

Agreement and reliability of a symptom modification test cluster for patients with subacromial pain syndrome.

OBJECTIVES: To identify if a plausible theoretical construct exists for a test cluster in a group of patients with subacromial pain syndrome presenting with glenohumeral internal rotation deficit (GIRD); determine the intertester agreement and reliability of the proposed test cluster; determine if there are any meaningful relationships between the test cluster and the component tests for the entire sample; and determine if there are any differences in disability on the Dutch version of the shoulder pain and disability index between participants with a positive and negative test cluster. METHODS: This study is a retrospective secondary analysis of data that were collected to determine the interrater agreement and reliability of clinical tests for assessment of patients with shoulder pain in primary care. RESULTS: The test cluster total agreement and negative specific agreement was 87.8 and 90.4%, respectively. The prevalence-adjusted bias-adjusted kappa for the test cluster was substantial at 0.76. There were statistically significant meaningful relationships (≥0.50) between GIRD and the test cluster for Tester A (Phi = 0.71, p < .01) and Tester B (Phi = 0.82, p < .01). No differences in disability were identified between those with a positive and negative test cluster. CONCLUSION: The test cluster described in this study may be a reliable means of identifying a subgroup of patients with subacromial pain syndrome related to GIRD. Future research should look to validate this test cluster prospectively.

COMPARATIVE ANALYSIS OF HIP MUSCLE ACTIVATION DURING CLOSED-CHAIN REHABILITATION EXERCISES IN RUNNERS.

BACKGROUND: Increased hip adduction and internal rotation during the early stance phase of running have been linked to an increased risk of lower extremity injury. Both the gluteus maximus (GMAX) and gluteus medius (GMED) eccentrically control these motions. GMAX and GMED activation levels during commonly used rehabilitation exercises requires further exploration. HYPOTHESIS/PURPOSE: The purpose of this study was to compare peak surface electromyography (sEMG) amplitudes of GMAX and GMED between three closed-chain rehabilitation exercises: bilateral hip external rotation with resistance band (BER), forward lunge with resistance band (FL), and single-leg rotational squat (SLS). It was hypothesized that the FL would elicit greater peak amplitude in the GMAX and GMED than SLS and BER. STUDY DESIGN: Descriptive, observational cohort study. METHODS: Twenty-two healthy runners (14 male, 8 female) had sEMG electrodes placed bilaterally on GMAX and GMED. Participants completed three repetitions each of BER, FL, and SLS exercises with sEMG data normalized to the maximal amplitude recorded at each muscle during the running trial (% MRC). Seven inertial measurement units affixed to the lower extremity measured joint kinematics to enable the exercises to be split into eccentric and concentric phases respectively. RESULTS: There were no significant differences between exercises during the eccentric phases with all peak amplitudes for GMAX and GMED being less than < 30% MRC. Both the SLS (GMAX: 48.2 ± 45.2% MRC, p = 0.019; GMED: 39.3 ± 24.8% MRC, p < .001) and FL (GMAX: 65.8 ± 58.9% MRC, p < .001; GMED: 52.2 ± 34.9% MRC, p<.001) elicited significantly greater peak amplitudes than BER (GMAX: 21.7 ± 22.3% MRC; GMED: 22.8 ± 21.2% MRC) during the concentric phase. CONCLUSION: Running related injuries have been linked to deficits in GMAX and GMED activation and strength. When averaged bilaterally across 22 healthy runners, peak GMAX and GMED amplitudes during three weight bearing exercises were less than 70% MRC. All three exercises had comparable eccentric peak amplitudes; however, the BER exercise produced a significantly reduced GMAX and GMED amplitude during the concentric phase versus the FL and SLS. The FL and SLS appear equally effective at eliciting peak GMAX and GMED activation. LEVEL OF EVIDENCE: 3.

Agreement and Reliability of Median Neurodynamic Test 1 and Resting Scapular Position.

OBJECTIVE: The purposes of this study were to determine whether there are differences between the dominant and nondominant arms for the Median Neurodynamic Test 1 (MNT 1); whether there are differences between men and women on the MNT 1; the reliability of an assessment of resting scapular position; the reliability of the MNT 1; and the frequency and percentage of sensory responses that are present during the MNT 1 in the asymptomatic population. METHODS: This was a reliability and agreement study. It included asymptomatic students enrolled in the college of health professions and the college of nursing at a university. The Mann-Whitney U was used to determine whether there were any differences between the dominant and nondominant sides and between sexes for elbow extension range of motion and for sensory responses on the numeric pain rating scale when performing the MNT 1. A χ2 analysis was used to determine whether there were any differences between sexes and between dominant and nondominant upper extremities for sensory-response location, sensory-response type, and structural differentiation for raters 1 and 2. The intraclass correlation coefficient (ICC2,3) was used to determine the intertester and intratester reliability for the degrees of elbow extension attained during testing. RESULTS: Reliability for degrees of elbow extension and strength of the sensory response was excellent (ICC2,3 ˃ 0.75) and substantial (κ ≥ 0.68), respectively. Resting scapular position and all other components of the MNT 1 demonstrated statistically significant side-to-side differences and κ values ranging from 0.23 to 0.88. CONCLUSION: Elbow extension and magnitude of sensory response are reliable components of the MNT 1 that are not different between the dominant and nondominant sides in the asymptomatic population.

Non-thrust cervical manipulations reduce short-term pain and decrease systolic blood pressure during intervention in mechanical neck pain: a randomized clinical trial.

Objectives: To evaluate the association of resting blood pressure with pain response and evaluate the cardiovascular effects of anterior-to-posterior [AP] versus lateral [LAT] techniques of cervical spine non-thrust manipulation [NTM].Methods: Forty-three (23 females) participants with non-chronic neck pain (mean age 29.00 ± SD 9.09 years) randomly received AP or LAT NTM to the cervical spine. Blood pressure and heart rate were measured before, during, and after the intervention. Disability and pain were measured pre- and post-intervention.Results: Resting systolic blood pressure (SBP) was significantly associated with average pain reduction two days later on univariate and multivariate analyses (coefficients -0.029 ± SD 0.013, p = 0.036; -0.026 ± 0.012, p = 0.032).No significant differences existed between AP and LAT NTM groups in disability, pain reduction, and cardiovascular variables. The decrease in 'worst neck pain' rating 2-days post-intervention was clinically significant within the AP (mean -2.43 ± SD 2.66) group. Mixed-effect model ANOVA revealed a significant change in SBP over time (estimate -1.94 ± SD 0.70, p = 0.007).Discussion: This spinal NTM study was the first to relate resting SBP with short-term pain reduction, demonstrating SBP-related hypoalgesia. In normotensive individuals with unilateral non-chronic neck pain, each 10 mmHg higher resting SBP was associated with a 0.29-unit decrease in average pain at follow-up when holding baseline pain constant.AP and LAT NTM equally reduced short-term pain and decreased SBP during-intervention, suggesting SBP-sympathoinhibition. These techniques have previously been shown to be sympatho-excitatory when delivered under different dosage parameters. SBP's mediating and moderating role should be investigated."Level of Evidence: 1b."

The Comparative Effects of Upper Thoracic Spine Thrust Manipulation Techniques in Individuals With Subacromial Pain Syndrome: A Randomized Clinical Trial.

BACKGROUND: Subacromial pain syndrome (SPS) accounts for as much as 44% of shoulder pain encountered by physical therapists. Thoracic spine thrust manipulation (TSTM) is effective in the short term for improving pain and function in individuals with SPS, but its mechanisms remain elusive. Furthermore, it is unknown whether individuals with SPS respond differently based on the TSTM technique received. OBJECTIVES: To compare the immediate effects of a supine TSTM, seated TSTM, and sham manipulation on the primary outcomes of self-reported pain, function, and satisfaction and secondary biomechanical impairments examined in individuals with SPS. METHODS: Participants in this randomized clinical trial were randomized to receive a seated TSTM (n = 20), supine TSTM (n = 20), or sham manipulation (n = 20). The primary outcomes of self-reported pain, function, and satisfaction were measured via the Penn Shoulder Score. Secondary outcomes were changes in scapular upward rotation and posterior tilt; peak force generated in tests for the middle trapezius, lower trapezius, and serratus anterior; and pectoralis minor muscle length. Impairment measures were immediately reassessed, and the Penn Shoulder Score was reassessed after 48 hours. RESULTS: There were no significant between-group differences in immediate or short-term follow-up outcomes. CONCLUSION: Two TSTM techniques resulted in no differences in pain, satisfaction, and function when compared to a sham manipulation. Thoracic spine thrust manipulation did not have an immediate effect on the scapular impairments examined. LEVEL OF EVIDENCE: Therapy, level 1. J Orthop Sports Phys Ther 2019;49(10):716-724. Epub 12 Mar 2019. doi:10.2519/jospt.2019.8484.

Immediate Effects of Thoracic Spine Thrust Manipulation on Neurodynamic Mobility.

OBJECTIVE: The purpose of this study was to investigate the immediate effects of thoracic spine thrust manipulation (TSM) on the upper limb provocation test (ULPT) and seated slump test (SST) in individuals with identified neurodynamic mobility impairments. A secondary aim was to determine if correlation existed between the perception of effect and improvements in neurodynamic mobility following a thrust manipulation compared with mobilization. METHODS: A pretest-posttest experimental design randomized 48 adults into 2 groups: TSM or mobilization. Participants with identified neurodynamic mobility impairment as assessed with the ULPT or SST received a pre-assigned intervention (TSM, n = 64 limbs; mobilization, n = 66 limbs). Perception of effect was assessed to determine its influence on outcome. Repeated-measures analysis of variance was used to examine the effects of intervention, and Fisher's exact test and independent t tests were used to determine the influence of perception. RESULTS: Both the ULPT (P < .001) and SST (P < .001) revealed improvements at posttest regardless of intervention. The ULPT effect sizes for TSM (d = 0.70) and mobilization (d = 0.69) groups were medium. For the SST, the effect size for the TSM group (d = 0.53) was medium, whereas that for the mobilization group (d = 0.26) was small. Participants in the mobilization group with positive perception had significantly greater (P < .05) mean neurodynamic mobility changes than those with a negative perception. CONCLUSIONS: Neurodynamic mobility impairment improved regardless of intervention. The magnitude of change was greater in the ULPT than SST. Although both interventions appeared to yield similar outcomes, individuals who received mobilization and expressed a positive perception of effect exhibited significantly greater changes in neurodynamic mobility than those without a positive perception.

The immediate cardiovascular response to joint mobilization of the neck - A randomized, placebo-controlled trial in pain-free adults.

BACKGROUND: Some normotensive patients can have a spike in resting systolic blood pressure (SBP) in response to acute neck pain. Applying the typical dosage of mobilization may potentially result in a sympatho-excitatory response, further increasing resting SBP. Therefore, there is a need to explore other dosage regimens that could result in a decrease in SBP. OBJECTIVES: To compare the blood pressure (BP) and heart rate (HR) response of pain-free, normotensive adults when receiving unilateral posterior-to-anterior mobilization (PA) applied to the neck versus its corresponding placebo (PA-P). STUDY DESIGN: Double-Blind, Randomized Clinical Trial. METHODS: 44 (18 females) healthy, pain-free participants (mean age, 23.8 ± 3.04 years) were randomly allocated to 1 of 2 groups. Group 1 received a PA-P in which light touch was applied to the right 6th cervical vertebra. Group 2 received a PA to the same location. BP and HR were measured prior to, during, and after the application of PA or PA-P. A mixed-effect model of repeated measure analysis was used for statistical analysis. RESULTS: During-intervention, the PA group had a significant reduction in SBP, while the placebo group had an increase in SBP. The change in SBP during-intervention was significantly different between the PA and the placebo group (p-value = 0.003). There were no significant between-group differences found for HR and diastolic BP (DBP). The overall group-by-time interaction was statistically significant for SBP (p-value = 0.01). CONCLUSIONS: When compared to placebo, the dosage of applied PA resulted in a small, short-lived drop in SBP not exceeding the minimal detectable change. Trial registered at Germanctr.de (DRKS00005095).

4D XCAT phantom for multimodality imaging research.

PURPOSE: The authors develop the 4D extended cardiac-torso (XCAT) phantom for multimodality imaging research. METHODS: Highly detailed whole-body anatomies for the adult male and female were defined in the XCAT using nonuniform rational B-spline (NURBS) and subdivision surfaces based on segmentation of the Visible Male and Female anatomical datasets from the National Library of Medicine as well as patient datasets. Using the flexibility of these surfaces, the Visible Human anatomies were transformed to match body measurements and organ volumes for a 50th percentile (height and weight) male and female. The desired body measurements for the models were obtained using the PEOPLESIZE program that contains anthropometric dimensions categorized from 1st to the 99th percentile for US adults. The desired organ volumes were determined from ICRP Publication 89 [ICRP, "Basic anatomical and physiological data for use in radiological protection: reference values," ICRP Publication 89 (International Commission on Radiological Protection, New York, NY, 2002)]. The male and female anatomies serve as standard templates upon which anatomical variations may be modeled in the XCAT through user-defined parameters. Parametrized models for the cardiac and respiratory motions were also incorporated into the XCAT based on high-resolution cardiac- and respiratory-gated multislice CT data. To demonstrate the usefulness of the phantom, the authors show example simulation studies in PET, SPECT, and CT using publicly available simulation packages. RESULTS: As demonstrated in the pilot studies, the 4D XCAT (which includes thousands of anatomical structures) can produce realistic imaging data when combined with accurate models of the imaging process. With the flexibility of the NURBS surface primitives, any number of different anatomies, cardiac or respiratory motions or patterns, and spatial resolutions can be simulated to perform imaging research. CONCLUSIONS: With the ability to produce realistic, predictive 3D and 4D imaging data from populations of normal and abnormal patients under various imaging parameters, the authors conclude that the XCAT provides an important tool in imaging research to evaluate and improve imaging devices and techniques. In the field of x-ray CT, the phantom may also provide the necessary foundation with which to optimize clinical CT applications in terms of image quality versus radiation dose, an area of research that is becoming more significant with the growing use of CT.

Clinical implications of orbital volume change in the management of isolated and zygomaticomaxillary complex-associated orbital floor injuries.

BACKGROUND: Orbital floor injuries can occur in isolation or in association with zygomaticomaxillary complex fractures. Volumetric computed tomographic measurements of affected orbits are investigated for utility in guiding management in these two groups. METHODS: The medical records of all patients with craniomaxillofacial injuries (2003 to 2005) were reviewed. Of 522 total patients, 45 patients had isolated orbital floor fractures, 13 of whom underwent repair (29 percent), and 64 had zygomaticomaxillary complex fractures, 36 of whom underwent reconstruction (56 percent) and 10 of whom underwent orbital floor repair (16 percent). Radiographic criteria for floor exploration included 50 percent area fracture in isolated injuries and 10-mm estimated zygomaticomaxillary complex compression in zygomaticomaxillary complex-associated floor injuries. Volume measurements of the affected orbits were obtained and compared with the uninjured contralateral orbit. RESULTS: Before treatment in the operative zygomaticomaxillary complex group, there was an average decrease in orbital volume of 18.3 percent. In the isolated orbital floor group, there was an average increase in orbital volume of 28.3 percent. CONCLUSIONS: Zygomaticomaxillary complex-associated orbital floor injuries can be compressive injuries associated with loss of volume, whereas isolated injuries generally result in volume expansion. Radiographic criteria are often considered in the decision to proceed with orbital floor exploration to avoid late enophthalmos. The literature suggests that a 20 percent change in orbital volume results in perceptible deformity. Therefore, a radiographic criterion of 50 percent floor area (28 percent volume increase) in isolated injuries may be too stringent; an estimated 10 mm of compression (18.3 percent volume change) is a reasonable operative criterion for floor exploration in zygomaticomaxillary complex-associated injuries.

Mechanisms underlying reversal of motor unit activation order in electrically evoked contractions after spinal cord injury.

Extracellular stimulation normally activates larger-diameter axons, innervating motor units producing higher force, at lower stimulation intensities than required to activate small-diameter axons innervating motor units producing low force. However, activation of weaker thenar motor units at lower stimulation intensities than required to activate strong motor units has been reported during extracellular stimulation of the median nerve in persons with chronic cervical spinal cord injury. We used a computational model that reproduced this experiment to identify the potential mechanisms for the observed reversal of the inverse recruitment order, including preferential death of large motoneurons, demyelination and remyelination, and denervation and reinnervation of muscle fibers. Five sets of simulations assessed these mechanisms with seven simulated subjects. Preferential reinnervation, with small-diameter axons reinnervating more abandoned muscle fibers than larger-diameter axons, accounted for the apparent reversal of the inverse recruitment order observed previously. Preferential death of larger axons enhanced the reversal, but alone could not account for the observed reversal. Further, demyelination and remyelination, even in an extreme case and when combined with preferential death of large motoneurons, could not reproduce the reversal of inverse recruitment order. Thus, the apparent reversal of the inverse recruitment order was not a reversal of activation order across different diameter nerve fibers, but rather was a consequence of the redistributed force-generating capacity of the motor units resulting from denervation and reinnervation.