Demonstration of central conduction time and neuroplastic changes after cervical lordosis rehabilitation in asymptomatic subjects: a randomized, placebo-controlled trial

A randomized controlled study was conducted to evaluate the effect of rehabilitation of the cervical sagittal configuration on sensorimotor integration and central conduction time in an asymptomatic population. Eighty (32 female) participants with radiographic cervical hypolordosis and anterior head translation posture were randomly assigned to either a control or an experimental group. The experimental group received the Denneroll cervical traction while the control group received a placebo treatment. Interventions were applied 3 × per week for 10 weeks. Outcome measures included radiographic measured anterior head translation distance, cervical lordosis (posterior bodies of C2–C7), central somatosensory conduction time (latency) (N13–N20), and amplitudes of potentials for spinal N13, brainstem P14, parietal N20 and P27, and frontal N30. Outcomes were obtained at: baseline, after 10 weeks of intervention, and at 3 months follow up. After 10 weeks and 3-months, between-group analyses revealed statistically significant differences between the groups for the following measured variables: lordosis C2–C7, anterior head translation, amplitudes of spinal N13, brainstem P14, parietal N20 and P27, frontal N30 potentials (P < 0.001), and conduction time N13–N20 (P = 0.004). Significant correlation between the sagittal alignment and measured variables were found (P < 0.005). These findings indicate restoration of cervical sagittal alignment has a direct influence on the central conduction time in an asymptomatic population.

Neural Interruption by Unilateral Labyrinthectomy Biases the Directional Preference of Otolith-Related Vestibular Neurons

Background: The directional preference of otolith-related vestibular neurons elucidates the neuroanatomical link of labyrinths, but few direct experimental data have been provided. Methods: The directional preference of otolith-related vestibular neurons was measured in the vestibular nucleus using chemically induced unilateral labyrinthectomy (UL). For the model evaluation, static and dynamic behavioral tests as well as a histological test were performed. Extracellular neural activity was recorded for the neuronal responses to the horizontal head rotation and the linear head translation. Results: Seventy-seven neuronal activities were recorded, and the total population was divided into three groups: left UL (20), sham (35), and right UL (22). Based on directional preference, two sub-groups were again classified as contra- and ipsi-preferred neurons. There was no significance in the number of those sub-groups (contra-, 15/35, 43%; ipsi-, 20/35, 57%) in the sham (p = 0.155). However, more ipsi-preferred neurons (19/22, 86%) were observed after right UL (p = 6.056 × 10−5), while left UL caused more contra-preferred neurons (13/20, 65%) (p = 0.058). In particular, the convergent neurons mainly led this biased difference (ipsi-, 100% after right UL and contra-, 89% after left UL) (p < 0.002). Conclusions: The directional preference of the neurons depended on the side of the lesion, and its dominance was mainly led by the convergent neurons.

A new quantitative evaluation system for distal radioulnar joint instability using a three-dimensional electromagnetic sensor

Background The accurate assessment of distal radioulnar joint (DRUJ) instability is still challenging as there is no established objective evaluation method. This study aimed to develop a noninvasive measurement method using a three-dimensional electromagnetic sensor system (EMS) to quantitatively assess and characterize the normal DRUJ movement in healthy volunteers. Methods The DRUJ movement was mimicked using both a block model and saw bone. Movement of the models was measured by EMS, and the accuracy and reproducibility of the measurements were assessed. In vivo measurement was performed in a sitting position with the elbow flexed and the forearm pronated. One sensor each was attached to the distal radial shaft and the ulnar head. The examiners fixed the distal radius and the carpal bones, moved the ulnar head from the dorsal to the volar side and measured the dorsovolar translation. The volar translation was measured by EMS and ultrasonography, and the correlation coefficient was calculated. The dorsovolar translation was evaluated in 14 healthy volunteers (7 men and 7 women) by three hand surgeons. The intraclass and inter-rater correlation coefficients (ICCs), the differences between the dominant and non-dominant sides and between men and women were assessed. Results The accuracy and reproducibility assessment results of the EMS showed high accuracy and reproducibility. In the comparison between EMS and ultrasonography, the correlation coefficient was 0.920 (p = 0.16 × 10-3). The ICC (1,5) for the intra-rater reliability was 0.856, and the ICC (2,5) for inter-rater reliability was 0.868. The mean ulnar head translation and difference between dominant and non-dominant sides were 6.00 ± 1.16 mm (mean ± SD) and − 0.12 ± 0.40 mm, respectively. There were no significant differences between any of the parameters. Conclusions A new measurement method using EMS could evaluate DRUJ movement with high accuracy, reproducibility, and intra- and inter-rater reliability. In healthy volunteers, the dorsovolar ulnar head translation was 6.00 mm. The difference between the dominant and non-dominant sides was < 1.0 mm with no significant difference. EMS provided an objective, non-invasive, real-time assessment of dynamic changes in the DRUJ. These findings could be useful in the treatment of patients with DRUJ instability.

Motion, and Patient-Reported Outcomes

Objectives: Patients with irreparable rotator cuff tears (RCT) exhibit functional limitations believed to be caused by superior migration of the humerus1,2. One viable treatment is superior capsule reconstruction (SCR). SCR has been shown to restore stability of the glenohumeral (GH) joint in cadavers1, but its effectiveness at controlling in vivo humeral motion is unknown. Outcomes are typically evaluated through standard clinical radiographs to assess acromial-humeral distance (AHD), and patient-reported outcomes (PROs) such as ASES and Visual Analog Scale3. Reported changes in AHD are inconsistent, with some studies reporting an increase in AHD of 2.6 to 3.2 mm4,5, while other studies reported no significant change in AHD after SCR6,7. Additionally, AHD does not account for anterior-posterior translations of the humeral head and clinical radiographs cannot assess dynamic translation of the humerus during arm abduction. The aim of this study was to determine the in vivo effect of SCR on in vivo glenohumeral arthrokinematics during scapular abduction, and to compare these results to PROs. We hypothesized that static and dynamic AHD would increase, humeral head location on the glenoid would be more inferior at corresponding abduction angles after SCR, and changes in humeral head translation or AHD would correlate with increased GH abduction range of motion and improved PROs. Methods: Ten patients (8M, 2F, age 63 ± 7 years) with irreparable RCT provided informed consent to participate in this prospective IRB-approved study. ASES, DASH, and WORC surveys were completed before (PRE) and 1-year (1YR-POST) after SCR. Synchronized biplane radiographs of the shoulder were collected PRE and 1YR-POST at 50 images/s while patients performed 3 trials of scapular plane arm abduction. Biplane radiographs were also collected during a static neutral trial where the participants placed their hand on their lap. Six degree of freedom GH and scapular kinematics were determined with sub-millimeter accuracy by matching subject-specific CT-based bone models of the humerus and scapula to radiographs using a validated volumetric tracking technique8. AHD was calculated as the minimum distance between the acromion and the humerus at 10° increments of GH abduction and averaged throughout the motion. Humeral head translation, defined as the relative translation of the center of the humeral head compared to the center of the glenoid, was calculated at 10° increments of GH abduction and expressed as averages in the superior/inferior (SI) and anterior/posterior (AP) directions. Differences between PRE and 1YR-POST static AHD, average dynamic humeral head location, PROs, and maximum GH abduction were evaluated using a paired t-test. A Pearson correlation was used to determine associations between static AHD and average humeral head location, and both PROs and maximum GH abduction. Significance was set at p < 0.05 for all tests. Results: There was no difference in static AHD from PRE (5.3±1.6mm) to 1YR-POST (4.6±1.6mm) while the average dynamic AHD during GH abduction decreased from 2.7±1.2mm PRE to 2.3±1.0mm 1YR-POST (Figure 1). Static AHD was larger than the average dynamic AHD both PRE and 1YR-POST (Figure 1). The average position of the humeral head during abduction moved 1.5% of the glenoid height superior from PRE to 1YR-POST and 1.7% of the glenoid width anterior from PRE to 1YR-POST (Figure 2). ASES, WORC, and DASH scores significantly improved from PRE to 1YR-POST and maximum GH abduction significantly increased from PRE (78.1±23.1°) to 1YR-POST (93.9±12.3°) (Table 1). Interestingly, there was a positive correlation between the AP humeral head location and DASH score PRE such that a higher DASH score was associated with the humeral head being more anterior (R = 0.767). No other associations were found between either average humeral head locations or AHD and either PROs or maximum GH abduction at both time points as well as the changes in those measures between time points (all R < 0.67). Conclusions: Static AHD, as measured clinically, may not be a good representation of dynamic AHD during scapular abduction given the differences between the static and dynamic AHD measurements at similar abduction angles. Additionally, our in vivo kinematics findings are not consistent with prior results of a cadaver-based biomechanical study of SCR as we found were minute changes in the SI humeral head position, with a 0.4mm more superior humeral head position following SCR. Regardless, patient-reported qualitative outcomes and maximum GH abduction all improved significantly. This suggests clinical outcomes after SCR may be influenced by mechanisms other than restoration of humeral head translation. Future in vivo studies are needed to evaluate the kinematic mechanisms behind improved PROs after SCR. [Table: see text]

Superior Capsule Reconstruction With a 3 mm–Thick Dermal Allograft Partially Restores Glenohumeral Stability in Massive Posterosuperior Rotator Cuff Deficiency: A Dynamic Robotic Shoulder Model

Background: Superior capsule reconstruction (SCR) has been shown to improve shoulder function and reduce pain in patients with isolated irreparable supraspinatus tendon tears. However, the effects of SCR on biomechanics in a shoulder with an extensive posterosuperior rotator cuff tear pattern remain unknown. Purpose/Hypothesis: The purpose was to (1) establish a dynamic robotic shoulder model, (2) assess the influence of rotator cuff tear patterns, and (3) assess the effects of SCR on superior humeral head translation after a posterosuperior rotator cuff tear. It was hypothesized that a posterosuperior rotator cuff tear would increase superior humeral head translation when compared with the intact and supraspinatus tendon–deficient state and that SCR would reduce superior humeral head translation in shoulders with massive rotator cuff tears involving the supraspinatus and infraspinatus tendons. Study Design: Controlled laboratory study. Methods: Twelve fresh-frozen cadaveric shoulders were tested using a robotic arm. Kinematic testing was performed in 4 conditions: (1) intact, (2) simulated irreparable supraspinatus tendon tear, (3) simulated irreparable supra- and infraspinatus tendon tear, and (4) SCR using a 3 mm–thick dermal allograft (DA). Kinematic testing consisted of static 40-N superior force tests at 0°, 30°, 60°, and 90° of abduction and dynamic flexion, abduction, and scaption motions. In each test, the superior translation of the humeral head was reported. Results: In static testing, SCR significantly reduced humeral superior translation compared with rotator cuff tear at all abduction angles. SCR restored the superior stability back to native at 60° and 90° of abduction, but the humeral head remained significantly and superiorly translated at neutral position and at 30° of abduction. The results of dynamic testing showed a significantly increased superior translation in the injured state at lower elevation angles, which diminished at higher elevation, becoming nonsignificant at elevation >75°. SCR reduced the magnitude of superior translation across all elevation angles, but translation remained significantly different from the intact state up to 60° of elevation. Conclusion: Massive posterosuperior rotator cuff tears increased superior glenohumeral translation when compared with the intact and supraspinatus tendon–insufficient rotator cuff states. SCR using a 3-mm DA partially restored the superior stability of the glenohumeral joint even in the presence of a simulated massive posterosuperior rotator cuff tear in a static and dynamic robotic shoulder model. Clinical Relevance: The biomechanical performance concerning glenohumeral stability after SCR in shoulders with large posterosuperior rotator cuff tears is unclear and may affect clinical outcomes in daily practice.

A new quantitative evaluation system for distal radioulnar joint instability using a three-dimensional electromagnetic sensor

Background The accurate assessment of distal radioulnar joint (DRUJ) instability is still challenging as there is no established objective evaluation method. This study aimed to develop a noninvasive measurement method using a three-dimensional electromagnetic sensor system (EMS) to quantitatively assess and characterize the normal DRUJ movement in healthy volunteers. Methods The DRUJ movement was mimicked using both a block model and saw bone. Movement of the models was measured by EMS, and the accuracy and reproducibility of the measurements were assessed. The movement was evaluated in 14 healthy volunteers (7 men and 7 women) by three hand surgeons. Measurement was done in a sitting position with the elbow flexed and the forearm pronated. One sensor each was attached to the distal radial shaft and the ulnar head. The examiners fixed the distal radius and moved the ulnar head from the dorsal to the volar side, measuring the dorsovolar ulnar head translation. The intraclass and interrater correlation coefficients (ICCs) were calculated using the average values of the measurements. The differences between the dominant and non-dominant sides and between men and women were also assessed. Results The accuracy and reproducibility assessment results of the EMS showed high accuracy and reproducibility. The ICC (1,5) for the intra-rater reliability was 0.856, and the ICC (2,5) for inter-rater reliability was 0.868. The mean ulnar head translation and difference between dominant and non-dominant sides were 6.00 ± 1.16 mm (Mean ± SD) and -0.12 ± 0.40 mm, respectively. There were no significant differences between any of the parameters.Conclusions A new measurement method using EMS could evaluate DRUJ movement with high accuracy, reproducibility, and intra- and inter-rater reliability. In healthy volunteers, the dorsovolar ulnar head translation was 6.00 mm. The difference between the dominant and non-dominant sides was < 1.0 mm with no significant difference. EMS provided an objective, non-invasive, real-time assessment of dynamic changes in the DRUJ. These findings could be useful in the treatment of patients with DRUJ instability.

Effects of Linear Visual-Vestibular Conflict on Presence, Perceived Scene Stability and Cybersickness in the Oculus Go and Oculus Quest

Humans rely on multiple senses to perceive their self-motion in the real world. For example, a sideways linear head translation can be sensed either by lamellar optic flow of the visual scene projected on the retina of the eye or by stimulation of vestibular hair cell receptors found in the otolith macula of the inner ear. Mismatches in visual and vestibular information can induce cybersickness during head-mounted display (HMD) based virtual reality (VR). In this pilot study, participants were immersed in a virtual environment using two recent consumer-grade HMDs: the Oculus Go (3DOF angular only head tracking) and the Oculus Quest (6DOF angular and linear head tracking). On each trial they generated horizontal linear head oscillations along the interaural axis at a rate of 0.5 Hz. This head movement should generate greater sensory conflict when viewing the virtual environment on the Oculus Go (compared to the Quest) due to the absence of linear tracking. We found that perceived scene instability always increased with the degree of linear visual-vestibular conflict. However, cybersickness was not experienced by 7/14 participants, but was experienced by the remaining participants in at least one of the stereoscopic viewing conditions (six of whom also reported cybersickness in monoscopic viewing conditions). No statistical difference in spatial presence was found across conditions, suggesting that participants could tolerate considerable scene instability while retaining the feeling of being there in the virtual environment. Levels of perceived scene instability, spatial presence and cybersickness were found to be similar between the Oculus Go and the Oculus Quest with linear tracking disabled. The limited effect of linear coupling on cybersickness, compared with its strong effect on perceived scene instability, suggests that perceived scene instability may not always be associated with cybersickness. However, perceived scene instability does appear to provide explanatory power over the cybersickness observed in stereoscopic viewing conditions.

A biomechanical analysis of ischiofemoral impingement in a cadaver model

Ischiofemoral impingement (IFI) occurs due to the diminishing of space between the ischium and lesser trochanter. During a robotic hip study, one hip presented with indications of IFI, an opportunity to explore the pathophysiology and treatment strategies for this unusual condition. This specimen underwent kinematic tests in two states: (i) native lesser trochanter and (ii) resected lesser trochanter. The ‘Resected lesser trochanter’ state was found to increase the hip range of motion and decrease femoral head translation by eliminating contact between the femur and pelvis. These results suggest that lesser trochanteric resection would provide physical benefit for IFI patients.

Contributions of the Capsule and Labrum to Hip Mechanics in the Context of Hip Microinstability

Background: Hip microinstability and labral pathology are commonly treated conditions with increasing research emphasis. To date, there is limited understanding of the biomechanical effects of the hip capsule and labrum on controlling femoral head motion. Purpose/Hypothesis: The purpose of this study was to determine the relative role of anterior capsular laxity and labral insufficiency in atraumatic hip microinstability. Our hypotheses were that (1) labral tears in a capsular intact state will have a minimal effect on femoral head motion and (2) the capsule and labrum work synergistically in controlling hip stability. Study Design: Controlled laboratory study. Methods: Twelve paired hip specimens from 6 cadaveric pelvises (age, 18-41 years) met the inclusion criteria. Specimens were stripped of all soft tissue except the hip capsule and labrum, then aligned, cut, and potted using a custom jig. A materials testing system was used to cyclically stretch the anterior hip capsule in extension and external rotation, while rotating about the mechanical axis of the hip. Labral insufficiency was created with a combined radial and chondrolabral tear under direct visualization. A motion tracking system was used to record hip internal-external rotation and displacement of the femoral head relative to the acetabulum in the anterior-posterior, medial-lateral, and superior-inferior directions. Testing variables included baseline, postventing, postcapsular stretching, and postlabral insufficiency. Results: When comparing the vented state with each experimental pathologic state, increases in femoral head motion were noted in both the capsular laxity state and the labral insufficiency state. The combined labral insufficiency and capsular laxity state produced statistically significant increases ( P < .001) in femoral head translation compared with the vented state in all planes of motion. Conclusion: Both the anterior capsule and labrum play a role in hip stability. In this study, the anterior hip capsule was the primary stabilizer to femoral head translation, but labral tears in the setting of capsular laxity produced the most significant increases in femoral head translation. Clinical Relevance: This study provides a physiologic biomechanical assessment of the hip constraints in the setting of hip microinstability. It also sheds light on the importance of the hip capsule in the management of labral tears. Our study demonstrates that labral tears in isolation provide minimal changes in femoral head translation, but in the setting of a deficient capsule, significant increases in femoral head translation are seen, which may result in joint-related symptoms.