Single versus double retrograde intramedullary nail technique for treatment of displaced proximal humeral fractures in children: A retrospective cohort study

Background

Highly displaced proximal humeral fractures in children with low remodeling potential need to be reduced and fixed. The use of two flexible retrograde nails became the most popular fixation technique due to the excellent functional outcome, the low complication rates, and the possibility of early mobilization. A modified single retrograde technique has been suggested by the authors to address the main disadvantage of this technique, the long operative duration. The aim of this study was to compare these techniques in terms of efficacy, and clinical and radiological outcomes.

Methods

We performed a retrospective, monocentric study. Two groups of patients were defined: One was treated with the standard flexible retrograde double nail technique and the other with the modified single nail technique. The demographic and fracture characteristics were similar in both groups and the postoperative immobilization with a simple sling for 2 weeks. We compared the surgical duration for the initial fixation and hardware removal procedures. The Quick Disabilities of the Arm, Shoulder, and Hand score, the secondary displacement at 1-week follow-up, the radiological union at 6-week follow-up, and the perioperative and short-term complications were also assessed for both groups.

Results

The surgical duration of the initial fixation procedure was significantly shorter in single nail technique group (p = 0.005). The percentage of excellent Quick Disabilities of the Arm, Shoulder, and Hand score (0) was similar in the two groups (p = 0.98). No secondary displacement was reported for the double nail technique group. In only one patient from the single nail technique group, we detected a secondary displacement at the first week control which did not need reoperation. In both groups, fractures were healed on the 6-week radiologic control. No cases of infection, superficial skin irritation, neurological damage, or complications related to implant removal were reported in both groups.

Conclusions

The single nail technique of fixation proximal humeral fractures in children addresses the disadvantage of long surgical times, described until today, with the double nail technique without compromising the excellent functional and radiological short-term outcomes.

Level of evidence

level III.

Elastic Resistance and Shoulder Movement Patterns: An Analysis of Reaching Tasks Based on Proprioception

This study departs from the conventional research on horizontal plane reach movements by examining human motor control strategies in vertical plane elastic load reach movements conducted without visual feedback. Here, participants performed shoulder presses with elastic resistances at low, moderate, and high intensities without access to visual information about their hand position, relying exclusively on proprioceptive feedback and synchronizing their movements with a metronome set at a 3 s interval. The results revealed consistent performance symmetry across different intensities in terms of the reach speed (p = 0.254-0.736), return speed (p = 0.205-0.882), and movement distance (p = 0.480-0.919). This discovery underscores the human capacity to uphold bilateral symmetry in movement execution when relying solely on proprioception. Furthermore, this study observed an asymmetric velocity profile where the reach duration remained consistent irrespective of the load (1.15 s), whereas the return duration increased with higher loads (1.39 s-1.45 s). These findings suggest that, in the absence of visual feedback, the asymmetric velocity profile does not result from the execution of the action but rather represents a deliberate deceleration post-reach aimed at achieving the target position as generated by the brain's internal model. These findings hold significant implications for interpreting rehabilitation approaches under settings devoid of visual feedback.

Joint mobility as a bridge between form and function

Joints enable nearly all vertebrate animal motion, from feeding to locomotion. However, despite well over a century of arthrological research, we still understand very little about how the structure of joints relates to the kinematics they exhibit in life. This Commentary discusses the value of joint mobility as a lens through which to study articular form and function. By independently exploring form-mobility and mobility-function relationships and integrating the insights gained, we can develop a deep understanding of the strength and causality of articular form-function relationships. In turn, we will better illuminate the basics of 'how joints work' and be well positioned to tackle comparative investigations of the diverse repertoire of vertebrate animal motion.

Moment arms of the deltoid, infraspinatus and teres minor muscles for movements with high range of motion: A cadaveric study

BACKGROUND

Moment arms are an indicator of the role of the muscles in joint actuation. An excursion method is often used to calculate them, even though it provides 1D results. As shoulder movement occurs in three dimensions (combination of flexion, abduction and axial rotation), moment arms should be given in 3D. Our objective was to assess the 3D moment arms of the rotator cuff (infraspinatus and teres minor) and deltoid muscles for movements with high arm elevation.

METHODS

The 3D moment arms (components in plane of elevation, elevation and axial rotation) were assessed using a geometric method, enabling to calculate the moment arms in 3D, on five fresh post-mortem human shoulders. Movement with high range of motion were performed (including overhead movement). The humerus was elevated until it reaches its maximal posture in different elevation plane (flexion, scaption, abduction and elevation in a plane 30° posterior to frontal plane).

FINDINGS

We found that the anterior deltoid was a depressor and contributes to move the elevation plane anteriorly. The median deltoid was a great elevator and the posterior deltoid mostly acted in moving the elevation plane posteriorly. The infraspinatus and teres minor were the greatest external rotator of the shoulder. The position of the glenohumeral joint induces changes in the muscular moment arms. The maximal shoulder elevation was 144° (performed in the scapular plane).

INTERPRETATION

The knowledge of 3D moment arms for different arm elevations might help surgeons in planning tendon reconstructive surgery and help validate musculoskeletal models.

Paleobiological reconstructions of articular function require all six degrees of freedom

Paleobiologists typically exclude impossible joint poses from reconstructions of extinct animals by estimating the rotational range of motion (ROM) of fossil joints. However, this ubiquitous practice carries the assumption that osteological estimates of ROM consistently overestimate true joint mobility. Because studies founded on ROM-based exclusion have contributed substantially to our understanding of functional and locomotor evolution, it is critical that this assumption be tested. Here, we evaluate whether ROM-based exclusion is, as currently implemented, a reliable strategy. We measured the true mobilities of five intact cadaveric joints using marker-based X-ray Reconstruction of Moving Morphology and compared them to virtual osteological estimates of ROM made allowing (a) only all three rotational, (b) all three rotational and one translational, and (c) all three rotational and all three translational degrees of freedom. We found that allowing combinations of motions in all six degrees of freedom is necessary to ensure that true mobility is always successfully captured. In other words, failing to include joint translations in ROM analyses results in the erroneous exclusion of many joint poses that are possible in life. We therefore suggest that the functional and evolutionary conclusions of existing paleobiological reconstructions may be weakened or even overturned when all six degrees of freedom are considered. We offer an expanded methodological framework for virtual ROM estimation including joint translations and outline recommendations for future ROM-based exclusion studies.

Low elbow mobility indicates unique forelimb posture and function in a giant extinct marsupial

Joint mobility is a key factor in determining the functional capacity of tetrapod limbs, and is important in palaeobiological reconstructions of extinct animals. Recent advances have been made in quantifying osteological joint mobility using virtual computational methods; however, these approaches generally focus on the proximal limb joints and have seldom been applied to fossil mammals. Palorchestes azael is an enigmatic, extinct ~1000 kg marsupial with no close living relatives, whose functional ecology within Australian Pleistocene environments is poorly understood. Most intriguing is its flattened elbow morphology, which has long been assumed to indicate very low mobility at this important joint. Here, we tested elbow mobility via virtual range of motion (ROM) mapping and helical axis analysis, to quantitatively explore the limits of Palorchestes' elbow movement and compare this with their living and extinct relatives, as well as extant mammals that may represent functional analogues. We find that Palorchestes had the lowest elbow mobility among mammals sampled, even when afforded joint translations in addition to rotational degrees of freedom. This indicates that Palorchestes was limited to crouched forelimb postures, something highly unusual for mammals of this size. Coupled flexion and abduction created a skewed primary axis of movement at the elbow, suggesting an abducted forelimb posture and humeral rotation gait that is not found among marsupials and unlike that seen in any large mammals alive today. This work introduces new quantitative methods and demonstrates the utility of comparative ROM mapping approaches, highlighting that Palorchestes' forelimb function was unlike its contemporaneous relatives and appears to lack clear functional analogues among living mammals.

A Single Retrograde Intramedullary Nail Technique for Treatment of Displaced Proximal Humeral Fractures in Children: Case Series and Review of the Literature

Displaced proximal humeral fractures in older children with low remodeling potential need to be reduced and fixed. There are many options for stabilization, including external fixation, rigid internal fixation with screws and plates, percutaneous pinning, and flexible intramedullary nailing. The use of 2 flexible retrograde nails, originated at the University of Nancy, France, became the most popular technique in Europe. The aim of this study was to describe and assess a modified, single retrograde nail technique to treat fractures of the proximal part of the humerus.

Methods

We performed a retrospective monocentric study. From June 2016 to May 2019, a modified retrograde nail technique with 1 prebent nail was used for the management of 21 consecutive children with a closed displaced proximal humeral fracture. Demographic and surgical data were collected. The surgical technique is similar to the classic elastic stable intramedullary nailing, but only 1 nail is used. The average surgical time and perioperative complications were used as criteria for the feasibility of this technique. Radiographs were obtained preoperatively; at 1, 4, and 6 weeks postoperatively; and after implant removal at an average of 4.2 months postoperatively. The clinical outcomes were assessed on the basis of the shoulder range of motion documented in the medical records and by using the French edition of the QuickDASH (shortened version of the Disabilities of the Arm, Shoulder and Hand [DASH] questionnaire) evaluation scale at the time of implant removal.

Results

Nineteen patients with a mean age of 12.6 years and a mean follow-up of 6 months were included in the study. The mean surgical time was 49 minutes. The single intramedullary nail technique provided a satisfactory reduction of all fractures. No perioperative complication occurred. In 1 case, partial loss of reduction was observed on the first-week control radiograph. All patients had a healed fracture, no deficits, excellent results according to the QuickDASH score, a normal range of motion, and excellent strength of the shoulder joint at the time of implant removal (at a mean of 4.2 months).

Conclusions

The current study confirms the feasibility and efficacy of the single retrograde intramedullary nail technique to treat displaced proximal humeral fractures in children.

Level of Evidence

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

An Inertial Measurement Unit-Based Wireless System for Shoulder Motion Assessment in Patients with Cervical Spinal Cord Injury: A Validation Pilot Study in a Clinical Setting

Residual motion of upper limbs in individuals who experienced cervical spinal cord injury (CSCI) is vital to achieve functional independence. Several interventions were developed to restore shoulder range of motion (ROM) in CSCI patients. However, shoulder ROM assessment in clinical practice is commonly limited to use of a simple goniometer. Conventional goniometric measurements are operator-dependent and require significant time and effort. Therefore, innovative technology for supporting medical personnel in objectively and reliably measuring the efficacy of treatments for shoulder ROM in CSCI patients would be extremely desirable. This study evaluated the validity of a customized wireless wearable sensors (Inertial Measurement Units-IMUs) system for shoulder ROM assessment in CSCI patients in clinical setting. Eight CSCI patients and eight healthy controls performed four shoulder movements (forward flexion, abduction, and internal and external rotation) with dominant arm. Every movement was evaluated with a goniometer by different testers and with the IMU system at the same time. Validity was evaluated by comparing IMUs and goniometer measurements using Intraclass Correlation Coefficient (ICC) and Limits of Agreement (LOA). inter-tester reliability of IMUs and goniometer measurements was also investigated. Preliminary results provide essential information on the accuracy of the proposed wireless wearable sensors system in acquiring objective measurements of the shoulder movements in CSCI patients.

A Practical Guide to Measuring Ex vivo Joint Mobility Using XROMM

X-Ray Reconstruction of Moving Morphology (XROMM), though traditionally used for studies of in vivo skeletal kinematics, can also be used to precisely and accurately measure ex vivo range of motion from cadaveric manipulations. The workflow for these studies is holistically similar to the in vivo XROMM workflow but presents several unique challenges. This paper aims to serve as a practical guide by walking through each step of the ex vivo XROMM process: how to acquire and prepare cadaveric specimens, how to manipulate specimens to collect X-ray data, and how to use these data to compute joint rotational mobility. Along the way, it offers recommendations for best practices and for avoiding common pitfalls to ensure a successful study.

A coordinate-system-independent method for comparing joint rotational mobilities

Three-dimensional studies of range of motion currently plot joint poses in a 'Euler space' whose axes are angles measured in the joint's three rotational degrees of freedom. Researchers then compute the volume of a pose cloud to measure rotational mobility. However, pairs of poses that are equally different from one another in orientation are not always plotted equally far apart in Euler space. This distortion causes a single joint's mobility to change when measured based on different joint coordinate systems and precludes fair comparison among joints. Here, we present two alternative spaces inspired by a 16th century map projection - cosine-corrected and sine-corrected Euler spaces - that allow coordinate-system-independent comparison of joint rotational mobility. When tested with data from a bird hip joint, cosine-corrected Euler space demonstrated a 10-fold reduction in variation among mobilities measured from three joint coordinate systems. This new quantitative framework enables previously intractable, comparative studies of articular function.

Influence of glenohumeral joint muscle insertion on moment arms using a finite element model

Accurate muscle geometry is essential to estimate moment arms in musculoskeletal models. Given the complex interactions between shoulder structures, we hypothesized that finite element (FE) modelling is suitable to obtain physiological muscle trajectory. A FE glenohumeral joint model was developed based on medical imaging. Moment arms were computed and compared to literature and MRI-based estimation. Our FE model produces moment arms consistent with the literature and with MRI data (max 17 mm differences). The inferior and superior fibres of a same muscle can have opposite action; predictions of moment arms are sensitive to muscle insertion (up to 20 mm variation).

Influence of humeral abduction angle on axial rotation and contact area at the glenohumeral joint

BACKGROUND

Although the elevation angle of the arm affects the range of rotation, it has not been evaluated up to the maximal abduction angle. In this study we conducted an evaluation up to maximal abduction and determined the contact patterns at the glenohumeral (GH) joint.

METHODS

Fourteen healthy volunteers (12 men and 2 women; mean age, 26.9 years) with normal shoulders (14 right and 8 left) were instructed to rotate their shoulders at 0°, 90°, 135°, and maximal abduction for each shoulder at a time. Using 2-dimensional and 3-dimensional single-plane image registration, the internal rotation (IR), external rotation (ER), and range of motion (ROM; ie, axial rotations) at the thoracohumeral (TH) and GH joints, and the contribution ratio (%ROM = GH-ROM/TH-ROM) were calculated for each abduction. The glenoid position with respect to the humeral head was also analyzed.

RESULTS

The TH-IR and TH-ER shifted toward an ER with increasing abduction angle, whereas the TH-ROM significantly decreased except at abduction between 0° and 90° (P < .001). The GH-IR and GH-ROM significantly decreased except at abduction between 0° and 90° (P < .001), but the GH-ER remained constant regardless of the abduction. The contribution ratio exceeded 80% for every abduction angle. The glenoid moved on the central and posterior areas of the humeral head at 0° and 90° abduction, respectively, and on the posterosuperior and anterosuperior areas at 135° and maximal abduction, respectively.

CONCLUSION

Our results provide new knowledge about wide axial rotation up to maximal abduction and constant GH-ER at any abduction.

A survey of human shoulder functional kinematic representations

In this survey, we review the field of human shoulder functional kinematic representations. The central question of this review is to evaluate whether the current approaches in shoulder kinematics can meet the high-reliability computational challenge. This challenge is posed by applications such as robot-assisted rehabilitation. Currently, the role of kinematic representations in such applications has been mostly overlooked. Therefore, we have systematically searched and summarised the existing literature on shoulder kinematics. The shoulder is an important functional joint, and its large range of motion (ROM) poses several mathematical and practical challenges. Frequently, in kinematic analysis, the role of the shoulder articulation is approximated to a ball-and-socket joint. Following the high-reliability computational challenge, our review challenges this inappropriate use of reductionism. Therefore, we propose that this challenge could be met by kinematic representations, that are redundant, that use an active interpretation and that emphasise on functional understanding.

Development of a 3D workspace shoulder assessment tool incorporating electromyography and an inertial measurement unit-a preliminary study

Traditional shoulder range of movement (ROM) measurement tools suffer from inaccuracy or from long experimental setup times. Recently, it has been demonstrated that relatively low-cost wearable inertial measurement unit (IMU) sensors can overcome many of the limitations of traditional motion tracking systems. The aim of this study is to develop and evaluate a single IMU combined with an electromyography (EMG) sensor to monitor the 3D reachable workspace with simultaneous measurement of deltoid muscle activity across the shoulder ROM. Six volunteer subjects with healthy shoulders and one participant with a ‘frozen’ shoulder were recruited to the study. Arm movement in 3D space was plotted in spherical coordinates while the relative EMG intensity of any arm position is presented graphically. The results showed that there was an average ROM surface area of 27291 ± 538 deg² among all six healthy individuals and a ROM surface area of 13571 ± 308 deg² for the subject with frozen shoulder. All three sections of the deltoid show greater EMG activity at higher elevation angles. Using such tools enables individuals, surgeons and physiotherapists to measure the maximum envelope of motion in conjunction with muscle activity in order to provide an objective assessment of shoulder performance in the voluntary 3D workspace.

Graphical abstract

Finite element models of the human shoulder complex: a review of their clinical implications and modelling techniques

The human shoulder is a complicated musculoskeletal structure and is a perfect compromise between mobility and stability. The objective of this paper is to provide a thorough review of previous finite element (FE) studies in biomechanics of the human shoulder complex. Those FE studies to investigate shoulder biomechanics have been reviewed according to the physiological and clinical problems addressed: glenohumeral joint stability, rotator cuff tears, joint capsular and labral defects and shoulder arthroplasty. The major findings, limitations, potential clinical applications and modelling techniques of those FE studies are critically discussed. The main challenges faced in order to accurately represent the realistic physiological functions of the shoulder mechanism in FE simulations involve (1) subject-specific representation of the anisotropic nonhomogeneous material properties of the shoulder tissues in both healthy and pathological conditions; (2) definition of boundary and loading conditions based on individualised physiological data; (3) more comprehensive modelling describing the whole shoulder complex including appropriate three-dimensional (3D) representation of all major shoulder hard tissues and soft tissues and their delicate interactions; (4) rigorous in vivo experimental validation of FE simulation results. Fully validated shoulder FE models would greatly enhance our understanding of the aetiology of shoulder disorders, and hence facilitate the development of more efficient clinical diagnoses, non-surgical and surgical treatments, as well as shoulder orthotics and prosthetics. © 2016 The Authors. International Journal for Numerical Methods in Biomedical Engineering published by John Wiley & Sons Ltd.

Mechanical risk of rotator cuff repair failure during passive movements: A simulation-based study

BACKGROUND

Despite improvements in rotator cuff surgery techniques, re-tear rate remains above 20% and increases with tear severity. Mechanical stresses to failure of repaired tendons have been reported. While optimal immobilization postures were proposed to minimize this stress, post-operative rehabilitation protocols have never been assessed with respect to these values. Purpose was to use musculoskeletal simulation to predict when the stress in repaired tendons exceeds safety limits during passive movements. Hence, guidelines could be provided towards safer post-operative exercises.

METHODS

Sixteen healthy participants volunteered in passive three-dimensional shoulder range-of-motion and passive rehabilitation exercises assessment. Stress in all rotator cuff tendons was predicted during each movement by means of a musculoskeletal model using simulations with different type and size of tears. Safety stress thresholds were defined based on repaired tendon loads to failure reported in the literature and used to discriminate safe from unsafe ranges-of-motion.

FINDINGS

Increased tear size and multiple tendons tear decreased safe range-of-motion. Mostly, glenohumeral elevations below 38°, above 65°, or performed with the arm held in internal rotation cause excessive stresses in most types and sizes of injury during abduction, scaption or flexion. Larger safe amplitudes of elevation are found in scapular plane for supraspinatus alone, supraspinatus plus infraspinatus, and supraspinatus plus subscapularis tears.

INTERPRETATION

This study reinforces that passive early rehabilitation exercises could contribute to re-tear due to excessive stresses. Recommendations arising from this study, for instance to keep the arm externally rotated during elevation in case of supraspinatus or supraspinatus plus infraspinatus tear, could help prevent re-tear.

Assessment of the glenohumeral joint's active and passive axial rotational range

BACKGROUND

Assessment of the range of axial rotation of the glenohumeral joint will improve understanding of shoulder function, with applications in shoulder rehabilitation and sports medicine. However, there is currently no complete description of motion of the joint. The study aimed to develop a reliable protocol to quantify the internal and external axial rotations of the glenohumeral joint during active and passive motion at multiple humeral positions.

METHODS

Optical motion tracking was used to collect kinematic data from 20 healthy subjects. The humerus was positioned at 60°, 90°, and 120° of humerothoracic elevation in the coronal, scapular, and sagittal planes. Internal and external rotations were measured at each position for active and passive motion, where intrasubject standard deviations were used to assess variations in internal-external rotations.

RESULTS

The protocol showed intrasubject variability in the axial rotational range of <5° for active and passive rotations at all humeral positions. Maximum internal rotation was shown to be dependent on humeral position, where a reduced range was measured in the sagittal plane (P < .001) and at 120° elevations (P < .001). Conversely, maximum external rotations were not affected by humeral position.

CONCLUSION

The results describe normal ranges of internal-external rotation of the glenohumeral joint at multiple humeral positions. The protocol's low variability means that it could be used to test whether shoulder pathologic conditions lead to changes in axial rotational range at specific humeral positions.

Glenohumeral translations during range-of-motion movements, activities of daily living, and sports activities in healthy participants

BACKGROUND

Glenohumeral translations have been mainly investigated during static poses while shoulder rehabilitation exercises, activities of daily living, and sports activities are dynamic. Our objective was to assess glenohumeral translations during shoulder rehabilitation exercises, activities of daily living, and sports activities to provide a preliminary analysis of glenohumeral arthrokinematics in a broad range of dynamic tasks.

METHODS

Glenohumeral translations were computed from trajectories of markers fitted to intracortical pins inserted into the scapula and the humerus. Two participants (P1 and P2) performed full range-of-motion movements including maximum arm elevations and internal-external rotations rehabilitation exercises, six activities of daily living, and five sports activities.

FINDINGS

During range-of-motion movements, maximum upward translation was 7.5mm (P1) and 4.7mm (P2). Upward translation during elevations was smaller with the arm internally (3.6mm (P1) and 2.9mm (P2)) than neutrally (4.2mm (P1) and 3.7mm (P2)) and externally rotated (4.3mm (P1) and 4.3mm (P2)). For activities of daily living and sports activities, only anterior translation during reach axilla for P1 and upward translation during ball throwing for P2 were larger than the translation measured during range-of-motion movements (108% and 114%, respectively).

INTERPRETATION

While previous electromyography-based studies recommended external rotation during arm elevation to minimize upward translation, measures of glenohumeral translations suggest that internal rotation may be better. Similar amplitude of translation during ROM movement and sports activities suggests that large excursions of the humeral head may be caused not only by fast movements, but also by large amplitude movements.