Neutral Position Research Articles

Antagonistic Feedback Control of Muscle Length Changes for Efficient Involuntary Posture Stabilization.

Simultaneous and cooperative muscle activation results in involuntary posture stabilization in vertebrates. However, the mechanism through which more muscles than joints contribute to this stabilization remains unclear. We developed a computational human body model with 949 muscle action lines and 22 joints and examined muscle activation patterns for stabilizing right upper or lower extremity motions at a neutral body posture (NBP) under gravity using actor-critic reinforcement learning (ACRL). Two feedback control models (FCM), muscle length change (FCM-ML) and joint angle differences, were applied to ACRL with a normalized Gaussian network (ACRL-NGN) or deep deterministic policy gradient. Our findings indicate that among the six control methods, ACRL-NGN with FCM-ML, utilizing solely antagonistic feedback control of muscle length change without relying on synergy pattern control or categorizing muscles as flexors, extensors, agonists, or synergists, achieved the most efficient involuntary NBP stabilization. This finding suggests that vertebrate muscles are fundamentally controlled without categorization of muscles for targeted joint motion and are involuntarily controlled to achieve the NBP, which is the most comfortable posture under gravity. Thus, ACRL-NGN with FCM-ML is suitable for controlling humanoid muscles and enables the development of a comfortable seat design.

Lumbar spine marker placement errors and soft tissue artifact during dynamic flexion/extension and lateral bending in individuals with chronic low back pain

Quantitative in vivo biomechanical assessments are typically performed with optoelectronic motion capture (MoCap) using retroreflective markers attached to skin. This technique inherently contains measurement errors from both marker placement on palpated bony landmarks and skin motion relative to the underlying bone (i.e., soft tissue artifact (STA)). Research on lumbar spine STA is scarce and limited to young, healthy participants in static positions. This study aimed to evaluate static placement errors, lumbar spine STA from MoCap marker clusters (MMC), and linear relationships between STA and patient characteristics. Thirty-nine participants with cLBP performed three trials each of flexion/extension and lateral bending while imaged simultaneously by MoCap (120 Hz) and dynamic biplane radiography DBR (20 Hz). MMCs were placed 29.5 ± 18.0 mm and 27.1 ± 13.4 mm superior to the most prominent aspect of the L1 and L5 spinous process, respectively. L1 relative to L5 STA was larger during flexion/extension (8.6 ± 5.7°) than lateral bending (4.5 ± 2.1°) (p < 0.001). After correcting for marker placement errors, components of the L1 and L5 STA averaged as much as 16.3 mm and 11.4° during flexion/extension, but only 4.0 mm and 4.8° or less during lateral bending. On average, STA for individual L1 and L5 vertebrae increased as participants moved away from the upright neutral position. STA was participant-dependent, however, age and BMI did not model STA well. Given the inaccuracy in marker placement and wide range of patterns of STA, caution is urged when making clinical decisions or when using computational models to estimate spine tissue loading based upon lumbar spine kinematics obtained from skin-mounted markers.

The role of radial head morphology in proximal radioulnar joint congruency during forearm rotation.

Congruency of the proximal radioulnar joint (PRUJ) is important in the rotation of the forearm while any compromise would significantly impair the elbow function. The purpose of this study is to determine the morphological features of the radial head and investigate its role in the congruency of the PRUJ during forearm rotation. The hypothesis is that the PRUJ is more congruent in the maximal pronation and supination positions than in the neutral position. Thirty sets of computed tomography images of the elbow were acquired, and a three-dimensional model of the proximal radius and ulna was generated. The radius of curvature of the radial head and the radial head at the maximal pronation, neutral positions and maximal supination were calculated and compared with a one-way analysis of variance. The point on the radial head contacting the middle point of radial head at the maximal pronation and supination was located at the ends of the semi-major axis of the ellipse, while it was located at one end of the semi-minor axis at neutral position. The radii of curvature of the pronation, neutral and supination points of the radial head were 14.72 ± 1.51, 9.74 ± 1.49 and 14.58 ± 1.70 mm, respectively. The value of the neutral point was significantly smaller than that of the pronation and supination points. This study quantitatively evaluated the morphology of the radial head and suggested that the best congruency of the PRUJ was achieved at maximal pronation and supination, while the neutral position was associated with the least congruency. Basic Science Study.

The evaluation of rotational lateral ankle laxity in gravity stress position by ultrasonography: normative value in uninjured ankles

BackgroundThe evaluation of lateral ankle laxity remains challenging when diagnosing chronic lateral ankle instability (CLAI). Several studies have reported that internal rotation of the talus as an indicator of rotational lateral ankle laxity (RLAL) increases in patients with CLAI. However, there is no established method for detecting and evaluating the RLAL. This study aimed to report a novel method for evaluating the RLAL in the gravity stress position by measuring the talofibular distance (TFD) using ultrasonography (US) and show the normative value of the TFD.MethodsThe TFDs in the subjects with healthy ankles were prospectively measured 10 mm distal to the ankle joint in the neutral ankle position and gravity stress position using US. The differences in the TFD between the two ankle positions were evaluated. The differences in the TFD by gender and ankle laterality were also evaluated.ResultsA total of 52 healthy ankles of 28 subjects (mean age, 24.0 ± 1.6; male/female, 12/16) were finally included. There was a significant difference in the TFD between the neutral ankle position (6.9 ± 0.9 mm) and gravity stress position (9.0 ± 0.9 mm) (p < 0.001). The mean difference in the TFD between the two ankle positions was 2.1 ± 0.6 mm. There were no significant differences in the TFD by gender and ankle laterality.ConclusionsThe present study reported a novel US method for evaluating RLAL by applying gravity stress and the normative value of the TFD.

Effect of Posterior Decompression on the Spinal Cord of Thoracic Ossification of the Posterior Longitudinal Ligament: A Finite Element Analysis

Thoracic ossification of the posterior longitudinal ligament (T-OPLL) causes myelopathy. Although posterior decompression for T-OPLL has shown positive results, patients with kyphotic curvatures often endure poor outcomes. Posterior decompression with fusion (PDF) has demonstrated better results compared to posterior decompression alone. This study aims to evaluate the effects of the posterior procedures for T-OPLL. A 3-dimensional finite element model of the C2-T12 spine, created from medical images, was used to develop the following T3-T4 OPLL compression models: an intact model (no surgery), 25% canal occupancy ratio (COR) OPLL, a discontinuous 25% COR OPLL, a continuous 50% COR OPLL, and a discontinuous 50% COR OPLL. These models were analyzed to evaluate the effects of posterior decompression (laminectomy [LN]) with varied fixation lengths (LN T3-T4, PDF T3-T4, LN T2-T5, and PDF T2-T5) in neutral, flexion, and extension positions. Increased discontinuity in OPLL led to increased stress on the spinal cord. Posterior decompression reduced spinal cord stress in the neutral posture. However, in flexion and extension, spinal cord stress increased for LN T3-T4, LN T2-T5, and PDF T3-T4 compared to the neutral posture. Notably, PDF T2-T5 prevented an increase in spinal cord stress during these motions. Effective management of intervertebral mobility and the appropriate length of decompression are crucial for addressing the thickness and mobility of T-OPLL.

Measuring the outward migration of the nasotracheal tube at vocal cords with head and neck extension: a novel approach using a flexible bronchoscope in patients undergoing head and neck oncosurgery.

Head and neck extension achieves optimal surgical exposure during head and neck oncosurgeries. However, it can lead to cephalad migration of the tracheal tube, causing complications. Preventing shallow intubation is essential, especially in patients with difficult airway. Using an innovative technique, we aimed to measure the proximal migration of the nasotracheal tube at the vocal cords on neck extension in patients with difficult airway. We enrolled 60 adult patients undergoing head and neck oncosurgeries with a mouth opening of less than 1.5 cm. After nasotracheal intubation using a flexible bronchoscope (FB), the FB was introduced into the adjacent nostril and maneuvered to reach the glottis. The FB was used to view and align the intubation depth mark (IDM) on the tracheal tube (TT) with the vocal cords in the neutral position. The outward migration of the TT at the vocal cords with a 30° to 40° neck extension was measured using the same maneuver. Also, the TT tip-to-carina distance was noted in both neutral and extension using FB. The mean proximal migration of the TT at the vocal cords during neck extension was 3±0.3 mm. The TT tip-to-carina distance increased by a mean of 20±7 mm with extension. The proximal migration contributed 15%, whereas elongation of the trachea contributed 85% to this increase. The major contributing factor for the increase in TT tip-to-carina distance on neck extension was tracheal elongation rather than outward migration of the TT at vocal cords.

366 Critical Airway Closing Pressures in the Sniffing Versus the Neutral Head Position in a Novel, Human Cadaveric Airway Model

366 Critical Airway Closing Pressures in the Sniffing Versus the Neutral Head Position in a Novel, Human Cadaveric Airway Model

Influence of Changing Hip Position on Electromyographic Activities of Selected Trunk Muscles During Bridging Exercises in Healthy Subjects: A Cross-Sectional Study

Objective: The purpose of this study was to investigate how rectus abdominis, external oblique (EO), internal oblique (IO), erector spinae, multifidus (MF), and gluteus maximus (GMax) muscle activities change with different hip positions during back and side bridging exercises. MethodsThirty-six healthy individuals participated in this cross-sectional study and performed 6 exercises including back bridging (BB) in neutral hip position, BB with internal rotation, BB with external rotation (BB + ER), side bridging with hips in neutral (SB), side bridging with hips in flexion (SB + HF), and side bridging with hips in extension (SB + HE). Muscle activity was observed using surface electromyography, normalized using maximum voluntary isometric contraction. Repeated-measures 1-way analysis of variance compared muscle readings for each position. ResultsBack bridging with internal rotation showed significant differences in EO (P = .01) and IO (P < .001) compared with other BB positions. Multifidus and GMax differed significantly in BB + ER (P = .04). Side bridging exhibited significant differences in EO (P = .02; P < .001) and IO (P < .001) compared with the other 2 SB positions, with peak in SB + HF. Erector spinae, MF, and GMax also differed significantly (P < .001, P = .02, P < .001, respectively) with peak in SB + HE. ConclusionThe findings revealed that EO and IO muscles were most active during BB with internal rotation, whereas the MF and GMax muscles were most active during BB + ER. In terms of SB, the EO and IO muscles were most active with either SB + HF or SB + HE, whereas the erector spinae, MF, and GMax muscles were most active with SB + HE.

Elbow kinematics with increased lengthening of a radial head arthroplasty evaluated with dynamic radiostereometric analysis.

The aim of this study was to evaluate the kinematics of the elbow following increasing length of the radius with implantation of radial head arthroplasties (RHAs) using dynamic radiostereometry (dRSA). Eight human donor arms were examined by dRSA during motor-controlled flexion and extension of the elbow with the forearm in an unloaded neutral position, and in pronation and supination with and without a 10 N valgus or varus load, respectively. The elbows were examined before and after RHA with stem lengths of anatomical size, + 2 mm, and + 4 mm. The ligaments were maintained intact by using a step-cut lateral humeral epicondylar osteotomy, allowing the RHAs to be repeatedly exchanged. Bone models were obtained from CT scans, and specialized software was used to match these models with the dRSA recordings. The flexion kinematics of the elbow were described using anatomical coordinate systems to define translations and rotations with six degrees of freedom. The greatest kinematic changes in the elbows were seen with the longest, + 4 mm, implant, which imposed a mean joint distraction of 2.8 mm in the radiohumeral joint and of 1.1 mm in the ulnohumeral joint, an increased mean varus angle of up to 2.4° for both the radius and the ulna, a mean shift of the radius of 2.0 mm in the ulnar direction, and a mean shift of the ulna of 1.0 mm posteriorly. The kinematics of the elbow deviated increasingly from those of the native joint with a 2 mm to a 4 mm lengthening of the radius. This confirms the importance of restoring the natural length of the radius when undertaking RHA.

Efficiency assessment of intelligent patient-specific instrumentation in total knee arthroplasty: a prospective randomized controlled trial

BackgroundIn total knee arthroplasty (TKA), the practical use of patient-specific instrumentation (PSI) has been reported previously with both advantage and disadvantage. The application of artificial intelligent (AI) forces overwhelmingly development of medical industries, while the impact of AI on PSI efficiency remains unknown. Thus, this study aimed to assess the efficiency of Intelligent-PSI (i-PSI) in TKA, compared with the conventional instrumentation-TKA (CI).Methods102 late-stage OA patients who met inclusive criteria were recruited in this prospective randomized controlled trial and separated into two groups (i-PSI vs. CI). In both groups, an AI preoperative planning engine was applied for surgery decision making. In CI group, conventional instrumentation was applied for bony resection, while resection of i-PSI group was completed with i-PSI. A convolutional neural network was applied to automatically process computer tomography images and thus produced i-PSI. With the help of three-dimension printing, the workflow of production was largely simplified. AI-driven preoperative planning guided resection and alignment decisions. Resection measurement, perioperative radiography and perioperative clinical outcomes were analyzed to verify efficiency of i-PSI.ResultsIn resection outcomes, smaller deviation of lateral and medial distal femoral resection were found in i-PSI group than CI group (P = 0.032 and 0.035), while no difference was found in other resection planes. In radiography outcomes, postoperative coronal alignments of i-PSI group, including postoperative Hip–knee–ankle axis (HKA) (P = 0.025), postoperative HKA outliners (P = 0.042), Femoral coronal alignment (FCA) (P = 0.019) and Joint line convergence angle (JLCA) (P = 0.043) showed closer to neutral position than CI group. Moreover, Femoral sagittal alignment (FSA) of i-PSI group showed closer to neutral position than CI group(P = 0.005). No difference was found in other alignments. In clinical outcomes, i-PSI group seemed to cost more surgical time than CI group (P = 0.027), while others showed no differences between the two groups.ConclusionIntelligent Patient-specific Instrumentation in TKA achieved simplified production flow than conventional PSI, while also showed more accurate resection, improved synthesis position and limb alignment than conventional instrumentation. Above all, this study proved that i-PSI being an applicable and promising tool in TKA.

In vivo dynamic migration of the posterior interosseous nerve across various elbow and forearm positions.

The posterior interosseous nerve (PIN) is at risk of iatrogenic nerve injury during elbow surgery when using a lateral or posterolateral approach. Results of cadaveric studies indicated that maintaining forearm pronation throughout the surgery can help move the PIN away from the surgical window. However, in vivo dynamic migration of the PIN in response to changes in the elbow and forearm position is unclear. This study aimed to clarify the in vivo dynamic migration pattern of the PIN in response to changes in the elbow and forearm position using ultrasound imaging. This study included 43 upper extremities of 22 healthy volunteers (16 females; mean age, 29 years). Using ultrasound imaging, we measured the shortest distance from the radial head (RH) to the point where the PIN crossed the lateral aspect of the radial axis in six positions of the elbow and forearm: 90° forearm supination, 90° pronation, and neutral forearm position, each at 135° of elbow flexion and 0° of elbow extension. The RH-to-nerve distance was greater during elbow extension than during elbow flexion regardless of the forearm position. However, the maximum migration distance was 3.5 mm when transitioning from elbow extension and forearm pronation (25.1 mm) to elbow flexion and forearm supination (21.6 mm). Although forearm pronation may help move the PIN away from the surgical window, care should be taken not to injure the nerve when performing elbow surgery using a lateral or posterolateral approach. Level of evidence: Level III.

Subtalar joint pronation: Who is the real enemy, presence or severity: A cross-sectional study?

The study aims to compare static and dynamic postural stability, navicular drop, dorsiflexion range of motion, and jumping performance of individuals with neutral, prone, and hyperprone foot postures. Forty-eight participants between the ages of 18 and 40, were categorized into neutral (n=16), prone (n=16), and hyperprone (n=16) according to foot posture index (FPI). Static and dynamic postural control evaluations (with the Biodex Balance System SD), navicular drop test (NDT) weight-bearing lunge test, countermovement jump test without arm swing, and drop vertical jump tests have been completed. In the results, the average age of participants in the NG, PG, and HPG are 22.31 ± 2.75, 23.87± 3.72, and 22.37 ± 1.28 years and BMI are 22.6 ± 3, 23.4 ± 3.8, and 21.4 ± 2.24 (kg/m²), respectively. The demographic data of the participants showed a homogeneous distribution. There were no significant differences in none of the outcomes except the NDT. Navicular drop amount is positively correlated by the subtalar joint pronation. An increase in subtalar joint pronation does not have a significant effect on static and dynamic stability, jump performance, or dorsiflexion range of motion in healthy individuals.

No dog in this fight: Interrogating Ethiopia’s calculated neutrality towards the Russia-Ukraine war

ABSTRACT Ethiopia has officially adopted a neutral position in the Russia-Ukraine war in line with the principles of the Non-Aligned Movement (NAM). Despite the centrality of sovereignty and territorial integrity in Ethiopia’s foreign policy, the government has avoided publicly castigating Russia for its assault on Ukraine’s sovereignty. This stance constitutes a sovereignty paradox when viewed in light of Ethiopia’s demonstrated commitment to its own sovereignty which has seen it fight three wars against Italy, Somalia and Eritrea, and the country’s advocacy to institutionalize sovereignty norms at the global level. This contribution argues that Addis Ababa’s reliance on Moscow’s arms supplies and its diplomatic cover in the United Nations Security Council in the context of the Tigrayan conflict compromised its ability to defend the principle of sovereignty.

Deflection estimation of reinforced concrete beams using long-gauge optic sensors

Deflection is a crucial indicator in structural health monitoring, directly impacting the service life, safety, and economic viability of structures. However, current indirect methods for measuring deflection, such as multi-element FBG sensors or accelerometers, often have limitations. While they may be suitable for flexure-dominated reinforced concrete (RC) specimens in the elastic stage, they neglect the significant influence of nonlinearity and shear deformation. This paper introduces a new approach for estimating the deflection of reinforced concrete (RC) beams using distributed long-gauge optic sensors. The method tackles the limitations of current methods by incorporating the crucial factors of shear deformation, neutral axis position variation and shear stiffness degradation. Experimental studies are first conducted to validate the accuracy and stability of long-gauge optic sensors in small-scale RC members. Algorithms are then utilized the measurement data to estimate the deflection. The results demonstrate the excellent performance of long-gauge optic sensors in measuring shear deformation and vertical deflection of RC beams, as evidenced by comparisons with LVDT measurements. Additionally, a method for decoupling flexural and shear deformation is proposed. This method offers a preliminary assessment of the reinforced concrete (RC) beam type by quantifying the relative significance of shear deformation.

Dynamics-based protein network features accurately discriminate neutral and rheostat positions

In some proteins, a unique class of nonconserved positions is characterized by their ability to generate diverse functional outcomes through single amino acid substitutions. Due to their ability to tune protein function, accurately identifying such “rheostat” positions is crucial for protein design, for understanding the impact of mutations observed in humans, and for predicting the evolution of pathogen drug resistance. However, identifying rheostat positions has been challenging, due—in part—to the absence of a clear structural relationship with binding sites. In this study, experimental data from our previous study of the Escherichia coli lactose repressor protein (LacI) was used to identify rheostat positions for which mutations tune in vivo EC50 for the allosteric ligand “IPTG.” We next used the rheostat assignments to test the hypothesis that rheostat positions have unique dynamic features that will enable their identification. To that end, we integrated all-atom molecular dynamics simulations with perturbation residue response analysis. Results first revealed distinct dynamic behavior in IPTG-bound LacI compared with apo LacI, which was consistent with IPTG’s role as an allosteric inducer. Next, we used a variety of dynamic features to build a classification model that discriminates experimentally characterized rheostat positions in LacI from positions with other types of substitution outcomes. In parallel, we built a second classifier model based on the 3D structural “static” network features of LacI. In comparative studies, the dynamic model better identified rheostat positions that were >8 Å from the binding site. In summary, our study provides insights into the dynamic characteristics of rheostat positions and suggests that models built on dynamic features may be useful for predicting the locations of rheostat positions in a wide range of proteins.

Bow Hunter Phenomenon From Advanced Cerebrovascular Disease Treated With Subclavian Artery Stenting and Carotid Endarterectomy.

Bow Hunter syndrome (BHS) is a rare disorder characterized by mechanical occlusion of the vertebral artery (VA) during neck rotation, resulting in symptomatic, transient, and positional vertebrobasilar insufficiency. We describe a case of a 76-year-old female who presented with dizziness and right ear tinnitus triggered by right head rotation. Her symptoms would immediately resolve upon returning her head to the neutral position. CT angiogram showed 80% stenosis of the left subclavian artery origin, 50%-70% stenosis of the proximal right internal carotid artery (ICA), and near occlusive stenoses of the origins of the bilateral VAs. After failing conservative management, the patient was treated with left subclavian artery stenting, followed by a right carotid endarterectomy (CEA) 6weeks later. Follow-up at 1month showed resolution of paroxysmal symptoms and no neurological sequelae. To our knowledge, there have not yet been reported cases of patients with concurrent BHS, subclavian artery stenosis, and carotid artery stenosis. We suggest that global revascularization via subclavian artery stenting and CEA may be considered as treatment for patients with BHS complicated by other cerebrovascular disease secondary to stenoses of the ICA and subclavian artery. This approach obviates the need for more complex surgery or endovascular intervention of the VA.

A Mobile based Decision Support System for Postural Evaluation of Agricultural Activities with Rapid Entire Body Assessment (REBA)

Agriculture is an unorganized sector and it is a very high drudgery prone profession due to the absence of awareness and entry of advanced agricultural technologies. Many farming activities and operations are carried out by farm workers in the agriculture sector, where they are subject to very poor working conditions which can lead to physical and mental stress. Workers in agriculture experience musculoskeletal disorders in various body parts throughout various agricultural operations. These problems are caused by heavy work loads, repetitive movements, uncomfortable postures, prolonged periods of time spent in neutral or unsupported positions and the use of conventional equipment and implements that are not ergonomically built. The ergonomic risk factors present in the workplace can be examined using various evaluation instruments to ascertain the workers abilities and drawbacks. The work-related risks are measured using the scientifically validated posture assessment instruments. Rapid entire body assessment (REBA) is a technique that assess a person’s complete body including wrists, fore arms, elbows, shoulders, neck, trunk, back, legs and knees. It uses a systematic process to find the postural musculoskeletal disorders and risks associated with the job tasks. A mobile application is developed to assess the agricultural activities on the basis of physiological analysis and postural analysis using REBA ergonomics technique. The application evaluates the drudgery involved in the agricultural work by using physical assessment followed by postural ergonomics methods and provide recommendation of correct posture to avoid developing musculoskeletal disorders.

Development of the humeral head offset index for control of humeral torsion

BackgroundControl of humeral torsion can present a challenge, especially intraoperatively during closed reduction and fixation of humeral shaft fractures or 2-part surgical neck fractures of the proximal humerus. The objective of this study is to develop and validate an indirect method for the assessment of humeral torsion using an index that is linearly correlated with rotational arm position and can be derived from only a single plain radiographic image of the proximal humerus.MethodsThe Humeral Head Offset Index (HHOI) is calculated as the ratio of the medial and lateral offset of the humeral head measured from the outer cortices of the shaft on a plain radiographic or fluoroscopic image. The relationship of HHOI with humeral torsion was first verified on a sawbone model with radiopaque characteristics under fluoroscopic control. Different degrees of retroversion were simulated through manual rotation of the humerus with a digital protractor in 5° increments until 40° internally rotated and then in 5° increments until 40° externally rotated from the neutral position. The same procedure was subsequently performed digitally on Digitally Reconstructed Radiographs (DRRs) from computed tomography (CT) dataset of the sawbone. Next, the HHOI index was applied to eight randomly selected patients with total humerus CT using the same method. Spearman’s rho was calculated for the bivariate analysis of correlation between the simulated degree of retroversion and the HHOI. Strength of correlation was classified according to Koo and Li. Interrater and intrarater reliability of three blinded observers with repetition of measurement after three months were analyzed by assessing the intraclass correlation coefficient (ICC).ResultsBoth in the sawbone model and in DRRs, we demonstrated a high to very high significant linear correlation between simulated retroversion and the HHOI. ICC values demonstrated excellent interrater reliability and excellent intrarater reliability for measurement of the HHOI.ConclusionsThe HHOI is a new, simple, reliable index that has a linear relationship to the rotation of the humerus and can therefore allow an indirect control of humeral torsion in comparison to the contralateral side.

A review of ergonomic positions to improve musculoskeletal distress in hepatobiliary pancreatic surgeons according to open, laparoscopic, and robotic surgeries.

Advances in surgical ergonomics are essential for the performance, health, and career longevity of surgeons. Many surgeons experience work-related musculoskeletal disorders (WMSDs) resulting from various surgical modalities, including open, laparoscopic, and robotic surgeries. To prevent WMSDs, individual differences may exist depending on the surgical method; however, the key is to maintain a neutral posture, and avoid static postures. This review aims to summarize the concepts of ergonomics and WMSDs; identify the ergonomic challenges of open, laparoscopic, and robotic surgeries; and discuss ergonomic recommendations to improve them.

Direct Suturing of Ulnar or Median Nerve Defects in High-Degree Elbow Flexion: An Experimental Cadaver Study

The aim of this study is to determine the maximum loss of median and ulnar nerve substances that can be treated by direct suture in elbow flexion and to quantify this elbow flexion. The other objective is to determine the participation of the wrist position in this direct suture in elbow flexion. We performed an experimental study on 6 ulnar nerve lesions and 6 median nerve lesions. For each defect, a direct tensionless suture was performed with elbow flexion and in three different positions of the wrist (wrist extension, neutral position, and wrist flexion). A 90° elbow flexion allowed direct suturing of defects up to 40 mm in the 3 positions of the wrist. A bowstringing effect (i.e., increase of the perpendicular distance of the nerve from the axis of rotation of the elbow) was noted starting from 25 mm of nerve defect. Wrist extension placed tension on the nerve suture for both nerves. The results of this first anatomical study clarified the conditions for direct suturing of ulnar and median nerve defects in the flexed elbow position and flexed wrist position. This is an approach to consider for limited nerve defects to the elbow or when allograft harvesting is to be avoided.