The role of bone morphology of the greater tuberosity and lateral acromion on subacromial space during scaption: a three-dimensional dynamic simulation analysis.

BACKGROUND: The bone morphology of the greater tuberosity and lateral acromion plays a central role in subacromial impingement syndrome. The critical shoulder angle (CSA) and greater tuberosity angle (GTA) are two-dimensional measurement parameters that have been validated to evaluate it radiologically. These markers are, however, static and don't consider the dynamic effect of glenohumeral motion. OBJECTIVES: This study aimed to better understand the biomechanics in subacromial impingement with a dynamic simulation based on a validated 3D biomechanical model coupling joint kinematics and 3D reconstructed computed tomography. STUDY DESIGN & METHODS: Sixty-one patients were included in this study: a case group of 44 patients with degenerative rotator cuff tears involving only the supraspinatus, and a control group of 17 without a rotator cuff tear. Patients with previous surgeries, traumatic cuff tears, and cuff tear arthropathy were excluded. CSA, GTA, and impingement-free range of motion (IF-ROM) of the glenohumeral joint in scaption were calculated. Correlation tests were used to determine the relationship between ROM and CSA, GTA, and combined CSA and GTA values. RESULTS: CSA and GTA were significantly higher in the rotator cuff tear group (p = 0.001 and < 0.001), while IF-ROM was significantly higher in the control group (p = 0.001). There was no overall correlation between CSA and GTA (R = 0.02, p = 0.8). Individual correlation between both angles with IF-ROM was negatively weak for CSA (R = -0.4, p < 0.001) and negatively moderate for GTA and IF-ROM (R = -0.5, p < 0.001). However, combining both angles resulted in a negatively high correlation with IF-ROM (R = -0.7, p < 0.001). CONCLUSION: Subacromial space narrowing during scaption is highly correlated to the cumulative values of GTA and CSA. These findings suggest that the combined bony morphology of the lateral acromion and greater tuberosity plays an important role in subacromial impingement. LEVEL OF EVIDENCE: III.

Three-dimensional reconstruction and virtual reposition of fragments compared to two dimensional measurements of midshaft clavicle fracture shortening.

BACKGROUND: Midshaft clavicle fracture shortening measurement is a reported key element for indication to surgical management and reporting of clinical trials. Determination of pre-fracture clavicle length for shortening measurement remains an unresolved issue. The purpose of the study was to assess accuracy of a novel technique of three-dimensional reconstruction and virtual reposition of bone fragments (3D-VR) for determination of pre-fracture clavicle length and measurement of shortening. METHODS: Accuracy of 3D-VR measurements was assessed using 5 synthetic bone clavicle fracture models. Measurements were compared between caliper and 3D-VR technique measurements. Correlation between 3D-VR and 2D measurements on standard radiographs was assessed on a cohort of 20 midshaft fractures. Four different methods for 2D measurements were assessed. RESULTS: Mean difference between caliper measurements and 3D-VR was 0.74 mm (95CI = - 2.51;3.98) (p = 0.56) on synthetic fracture models. Mean differences between 3D-VR and standard radiograph shortening measurement methods were 11.95 mm (95CI = 7.44;16.46) for method 1 (Jeray et al.) and 9.28 mm (95CI = 4.77;13.79) for method 2 (Smekal et al.) (p < 0.05). Differences were - 1.02 mm (95CI = - 5.53;3.48) for method 3 (Silva et al.) and - 2.04 mm (95CI = - 6.55;2.47) for method 4 (own method). Interobserver correlation ranged between 0.85 and 0.99. A false positive threshold of 20 mm was measured by the two observers in 25% of the case according to method of method 1, 30-35% with method 2, 15% with method 3 et al. and 5-10% with the method 4. CONCLUSION: 3D VR is accurate in measuring midshaft clavicle fracture length and shortening. Two dimensional measurements may be used for approximation of clavicular shortening.

Sexual activity after total hip arthroplasty: a motion capture study.

Relative risk of impingement and joint instability during sexual activities after total hip arthroplasty (THA) has never been objectively investigated. Hip range of motion necessary to perform sexual positions is unknown. A motion capture study with two volunteers was performed. 12 common sexual positions were captured and relevant hip joint kinematics calculated. The recorded data were applied to prosthetic hip 3D models to evaluate impingement and joint instability during motion. To explore the effect of acetabular component positioning, nine acetabular cup positions were tested. Four sexual positions for women requiring intensive flexion (> 95°) caused prosthetic impingements (associated with posterior instability) at 6 cup positions. Bony impingements (associated with anterior instability) occurred during one sexual position for men requiring high degree of external rotation (> 40°) combined with extension and adduction at all cup positions. This study hence indicates that some sexual positions could be potentially at risk after THA, particularly for women.

Computer-Aided Intra-Operatory Positioning of an MRgHIFU Applicator Dedicated to Abdominal Thermal Therapy Using Particle Swarm Optimization.

PURPOSE: Transducer positioning for liver ablation by magnetic resonance-guided high-intensity focused ultrasound (MRgHIFU) is challenging due to the presence of air-filled organs or bones on the beam path. This paper presents a software tool developed to optimize the positioning of a HIFU transducer dedicated to abdominal thermal therapy, to maximize the treatment's efficiency while minimizing the near-field risk. METHODS: A software tool was developed to determine the theoretical optimal position (TOP) of the transducer based on the minimization of a cost function using the particle swarm optimization (PSO). After an initialization phase and a manual segmentation of the abdomen of 5 pigs, the program randomly generates particles with 2 degrees of freedom and iteratively minimizes the cost function of the particles considering 3 parameters weighted according to their criticality. New particles are generated around the best position obtained at the previous step and the process is repeated until the optimal position of the transducer is reached. MR imaging data from in vivo HIFU ablation in pig livers was used for ground truth comparison between the TOP and the experimental position (EP). RESULTS: As compared to the manual EP, the rotation difference with the TOP was on average -3.1 ± 7.1° and the distance difference was on average -7.1 ± 5.4 mm. The computational time to suggest the TOP was 20s. The software tool is modulable and demonstrated consistency and robustness when repeating the calculation and changing the initial position of the transducer.

Extreme hip motion in professional ballet dancers: dynamic and morphological evaluation based on magnetic resonance imaging.

OBJECTIVE: To determine the prevalence of femoroacetabular impingement (FAI) of the cam or pincer type based on magnetic resonance imaging (MRI) in a group of adult female professional ballet dancers, and to quantify, in vivo, the range of motion (ROM) and congruence of the hip joint in the splits position. MATERIALS AND METHODS: Institutional review board approval and informed consent from each volunteer were obtained. Thirty symptomatic or asymptomatic adult female professional ballet dancers (59 hips) and 14 asymptomatic non-dancer adult women (28 hips, control group) were included in the present study. All subjects underwent MRI in the supine position, while, for the dancers, additional images were acquired in the splits position. Labral abnormalities, cartilage lesions, and osseous abnormalities of the acetabular rim were assessed at six positions around the acetabulum. A morphological analysis, consisting of the measurement of the α angle, acetabular depth, and acetabular version, was performed. For the dancers, ROM and congruency of the hip joint in the splits position were measured. RESULTS: Acetabular cartilage lesions greater than 5 mm were significantly more frequent in dancer's hips than in control hips (28.8 vs 7.1%, p = 0.026), and were mostly present at the superior position in dancers. Distribution of labral lesions between the dancers and the control group showed substantially more pronounced labral lesions at the superior, posterosuperior, and anterosuperior positions in dancers (54 lesions in 28 dancer's hips vs 10 lesions in 8 control hips). Herniation pits were found significantly more often (p = 0.002) in dancer's hips (n = 31, 52.5%), 25 of them being located in a superior position. A cam-type morphology was found for one dancer and a retroverted hip was noted for one control. Femoroacetabular subluxations were observed in the splits position (mean: 2.05 mm). CONCLUSION: The prevalence of typical FAI of the cam or pincer type was low in this selected population of professional ballet dancers. The lesions' distribution, mostly superior, could be explained by a "pincer-like" mechanism of impingement with subluxation in relation to extreme movements performed by the dancers during their daily activities.

Correlation of clinical and magnetic resonance imaging findings in hips of elite female ballet dancers.

PURPOSE: To understand why professional female ballet dancers often complain of inguinal pain and experience early hip osteoarthritis (OA). Goals were to examine clinical and advanced imaging findings in the hips of dancers compared with those in a matched cohort of nondancers and to assess the femoral head translation in the forward split position using magnetic resonance imaging (MRI). METHODS: Twenty professional female ballet dancers and 14 active healthy female individuals matched for age (control group) completed a questionnaire on hip pain and underwent hip examination with impingement tests and measurement of passive hip range of motion (ROM). All had a pelvic 1.5 T MRI in the back-lying position to assess femoroacetabular morphologic features and lesions. For the dancers, additional MR images were acquired in the split position to evaluate femoroacetabular congruency. RESULTS: Twelve of 20 dancers complained of groin pain only while dancing; controls were asymptomatic. Dancers' passive hip ROM was normal. No differences in α neck angle, acetabular depth, acetabular version, and femoral neck anteversion were found between dancers and controls. MRI of dancers while performing splits showed a mean femoral head subluxation of 2.05 mm. MRI of dancers' hips showed labral tears, cartilage thinning, and herniation pits, located in superior and posterosuperior positions. Lesions were the same for symptomatic and asymptomatic dancers. Controls had proportionally the same number of labral lesions but in an anterosuperior position. They also had 2 to 3 times fewer cartilage lesions and pits than did dancers. CONCLUSIONS: The results of our study are consistent with our hypothesis that repetitive extreme movements can cause femoral head subluxations and femoroacetabular abutments in female ballet dancers with normal hip morphologic features, which could result in early OA. Pathologic changes seen on MRI were symptomatic in less than two thirds of the dancers. LEVEL OF EVIDENCE: Level IV, therapeutic case series.

Physics-based character animation and human motor control.

Motor neuroscience and physics-based character animation (PBCA) approach human and humanoid control from different perspectives. The primary goal of PBCA is to control the movement of a ragdoll (humanoid or animal) applying forces and torques within a physical simulation. The primary goal of motor neuroscience is to understand the contribution of different parts of the nervous system to generate coordinated movements. We review the functional principles and the functional anatomy of human motor control and the main strategies used in PBCA. We then explore common research points by discussing the functional anatomy and ongoing debates in motor neuroscience from the perspective of PBCA. We also suggest there are several benefits to be found in studying sensorimotor integration and human-character coordination through closer collaboration between these two fields.

On the Plausibility of Virtual Body Animation Features in Virtual Reality.

We present two experiments to assess the relative impact of different levels of body animation fidelity on plausibility illusion (Psi). The first experiment presents a virtual character that is not controlled by the user ( n=13), while the second experiment presents a user-controlled virtual avatar ( n=24, all male). Psi concerns how realistic and coherent the events in a virtual environment look and feel and is part of Slater's proposition of two orthogonal components of presence in virtual reality (VR). In the experiments, the face, hands, upper and lower bodies of the character or self-avatar were manipulated to present different degrees of animation fidelity, such as no animation, procedural animation, and motion captured animation. Participants started the experiment experiencing the best animation configuration. Then, animation features were reduced to limit the amount of captured information made available to the system. Participants had to move from this basic animation configuration towards a more complete one, and declare when the avatar animation realism felt equivalent to the initial and most complete configuration, which could happen before all animation features were maxed out. Participants in the self-avatar experiment were also asked to rate how each animation feature affected their sense of control of the virtual body. We found that a virtual body with upper and lower body animated using eight tracked rigid bodies and inverse kinematics (IK) was often perceived as equivalent to a professional capture pipeline relying on 53 markers. Compared to what standard VR kits in the market are offering, i.e., a tracked headset and two hand controllers, we found that foot tracking, followed by mouth animation and finger tracking, were the features that added the most to the sense of control of a self-representing avatar. In addition, these features were often among the first to be improved in both experiments.

Playing the mirror game in virtual reality with an autonomous character.

Perceptual-motor synchronisation in human groups is crucial in many activities, from musical ensembles to sports teams. To this aim, the mirror game, where partners are asked to imitate each other's movements or gestures, is one of the best available experimental paradigms to study how humans engage in joint tasks and how they tend to synchronise their behaviour. However, to date, virtual reality characters do not engage in motor synchronisation with human users. In this work, we explored to what extent an autonomous virtual character and a human that play the mirror game in virtual reality can synchronise their behaviour. We created a full-body version of the mirror game with an autonomous virtual character, whose movements were driven by a model based on coupled oscillators. Participants engaged in a joint imitation task with a virtual player animated with one of three options: a model that included a small coupling, a model with no coupling, or another human. Behavioural measures and subjective reports suggest that participants were unable to distinguish the condition of small coupling from the engagement with an avatar driven by another human participant.

A Novel Concept of a Phased-Array HIFU Transducer Optimized for MR-Guided Hepatic Ablation: Embodiment and First In-Vivo Studies.

Purpose: High-intensity focused ultrasound (HIFU) is challenging in the liver due to the respiratory motion and risks of near-/far-field burns, particularly on the ribs. We implemented a novel design of a HIFU phased-array transducer, dedicated to transcostal hepatic thermo-ablation. Due to its large acoustic window and strong focusing, the transducer should perform safely for this application. Material and Methods: The new HIFU transducer is composed of 256 elements distributed on 5 concentric segments of a specific radius (either 100, 111, or 125 mm). It has been optimally shaped to fit the abdominal wall. The shape and size of the acoustic elements were optimized for the largest emitting surface and the lowest symmetry. Calibration tests have been conducted on tissue-mimicking gels under 3-T magnetic resonance (MR) guidance. In-vivo MR-guided HIFU treatment was conducted in two pigs, aiming to create thermal ablation deep in the liver without significant side effects. Imaging follow-up was performed at D0 and D7. Sacrifice and post-mortem macroscopic examination occurred at D7, with the ablated tissue being fixed for pathology. Results: The device showed -3-dB focusing capacities in a volume of 27 × 46 × 50 mm3 as compared with the numerical simulation volume of 18 × 48 × 60 mm3. The shape of the focal area was in millimeter-range agreement with the numerical simulations. No interference was detected between the HIFU sonication and the MR acquisition. In vivo, the temperature elevation in perivascular liver parenchyma reached 28°C above physiological temperature, within one breath-hold. The lesion was visible on Gd contrast-enhanced MRI sequences and post-mortem examination. The non-perfused volume was found in pig #1 and pig #2 of 8/11, 6/8, and 7/7 mm along the LR, AP, and HF directions, respectively. No rib burns or other near-field side effects were visually observed on post-mortem gross examination. High-resolution contrast-enhanced 3D MRI indicated a minor lesion on the sternum. Conclusion: The performance of this new HIFU transducer has been demonstrated in vitro and in vivo. The transducer meets the requirement to perform thermal lesions in deep tissues, without the need for rib-sparing means.

In vivo static and dynamic lengthening measurements of the posterior cruciate ligament at high knee flexion angles.

PURPOSE: Rehabilitation is an important aspect of both non-operative and operative treatments of knee ligament tear. Posterior cruciate ligament (PCL) non-operative treatment consists of a step-by-step rehabilitation protocol and is well described. It goes from rest (phase I) to strengthening exercises (phase IV). More specific and high-intensity exercises such as cutting, sidestepping or jumps are, however, not described in detail, as no in vivo data exist to tell how these exercises constrain the ligaments and whether they have the same effect on all of them, in particular regarding lengthening. The goal of this study was to measure the ligament lengthening in static knee flexion based on 3D reconstructions from magnetic resonance imaging (MRI) and from motion capture and ligament simulation during dynamic exercises. METHODS: The knee of nine volunteers was first imaged in a closed-bore MRI scanner at various static knee flexion angles (up to 110°), and the corresponding lengthening of the PCL and the other major knee ligaments was measured. Then, the volunteers underwent motion capture of the knee where dynamic exercises (sitting, jumping, sidestepping, etc.) were recorded. For each exercise, knee ligament elongation was simulated and evaluated. RESULTS: According to the MRI scans, maximal lengthening occurred at 110° of flexion in the anterior cruciate ligament and 90° of flexion in the PCL. Daily living movements such as sitting were predicted to elongate the cruciate ligaments, whereas they shortened the collateral ligaments. More active movements such as jumping put the most constrain to cruciate ligaments. CONCLUSION: This study provides interesting insights into a tailored postoperative regimen. In particular, knowing the knee ligament lengthening during dynamic exercises can help better define the last stages of the rehabilitation protocol, and hence provide a safe return to play.

Shoulder Motion Analysis During Codman Pendulum Exercises.

PURPOSE: To quantify shoulder motion during Codman pendulum exercises. METHODS: Shoulder kinematics were analyzed in 17 healthy volunteers using a validated biomechanical model coupling patient-specific imaging and motion capture. Participants were instructed to perform medio-lateral, antero-posterior and circular pendulum exercises. Glenohumeral (GH), scapulothoracic (ST), thoracohumeral (TH) ROM and overall exercise amplitude were calculated for each sequence. Linear regression analyses were carried out to determine association between different components of shoulder motion. RESULTS: Mean overall exercise amplitude was 40.59±11.24° (range, 25.38 to 70.25°) for medio-lateral exercises, 46.5±22.02° (range, 20.68 to 100.24°) for antero-posterior exercises, and 20.28±7.13° (range, 10.9 to 35.49°) for circular exercises. Mean GH and ST involvement remained minimal, ranging from 6.74 to 13.81°, and 1.5° to 5.12°, respectively. There was no significant correlation between overall exercise amplitude and GH (R = 0.31, p = 0.01) or ST ROM (adjusted R2 = 0.57, p < 0.001), but a moderate correlation with TH ROM (R = 0.73, p < 0.001). CONCLUSION: This study demonstrates that Codman pendulum exercises depend mainly on truncal movement and produce very little movement in the GH and ST joints. Although they may be a safe way to promote early general stretching of the upper limb, they may be of limited further use in restoring passive shoulder ROM. CLINICAL RELEVANCE: This study quantifies motion during frequently administered shoulder rehabilitation exercises and shows that they do not produce significant movement in the shoulder. Their use in restoring passive range of motion is thus questionable.

Scapulothoracic Alignment Alterations in Patients with Walch Type B Osteoarthritis: An In Vivo Dynamic Analysis and Prospective Comparative Study.

BACKGROUND: Kinematic changes of the scapulothoracic joint may influence the relative position of the glenoid fossa and, consequently, the glenohumeral joint. As the alignment of the scapula relative to the thorax differs between individuals, such variability may be another factor in the development of posterior head subluxation. The purpose of this study was to compare scapulothoracic alignment in pathologic type B shoulders with contralateral healthy shoulders. METHODS: Seven adult volunteers with unilateral type B glenohumeral osteoarthritis (OA) underwent bilateral computed tomography (CT) scans of the shoulders and arms. A patient-specific, three-dimensional measurement technique that coupled medical imaging (i.e., CT) and optical motion capture was used. RESULTS: The scapulothoracic distance at the trigonum was 75 ± 15 mm for pathologic shoulders and 78 ± 11 mm for healthy shoulders (p = 0.583), while at the inferior angle, it was 102 ± 18 mm for pathologic shoulders and 108 ± 12 mm for healthy shoulders (p = 0.466). CONCLUSION: Scapula positioning at a resting position did not differ between pathologic and healthy shoulders. However, pathologic shoulders tended to be limited in maximal glenohumeral motion and exhibited greater anterior tilt of the scapula in internal rotation at 90 degrees, which may be adaptive to the restricted glenohumeral motion.

Acromioplasty during repair of rotator cuff tears removes only half of the impinging acromial bone.

BACKGROUND: To date, there is no consensus on when and how to perform acromioplasty during rotator cuff repair (RCR). We aimed to determine the volume of impinging bone removed during acromioplasty and whether it influences postoperative range of motion (ROM) and clinical scores after RCR. METHODS: Preoperative and postoperative computed tomography scans of 57 shoulders that underwent RCR were used to reconstruct scapula models to simulate volumes of impinging acromial bone preoperatively and then compare them to the volumes of bone resected postoperatively to calculate the proportions of desired (ideal) vs. unnecessary (excess) resections. All patients were evaluated preoperatively and at 6 months to assess ROM and functional scores. RESULTS: The volume of impinging bone identified was 3.5 ± 2.3 cm3, of which 1.6 ± 1.2 cm3 (50% ± 27%) was removed during acromioplasty. The volume of impinging bone identified was not correlated with preoperative critical shoulder angle (r = 0.025, P = .853), nor with glenoid inclination (r = -0.024, P = .857). The volume of bone removed was 3.7 ± 2.2 cm3, of which 2.1 ± 1.6 cm3 (53% ± 24%) were unnecessary resections. Multivariable analyses revealed that more extensive removal of impinging bone significantly improved internal rotation with the arm at 90° of abduction (beta, 27.5, P = .048) but did not affect other shoulder movements or clinical scores. CONCLUSIONS: Acromioplasty removed only 50% of the estimated volume of impinging acromial bone. More extensive removal of impinging bone significantly improved internal rotation with the arm at 90° of abduction.

Guided versus freehand acromioplasty during rotator cuff repair. A randomized prospective study.

INTRODUCTION: There is no consensus on how to perform acromioplasty, particularly regarding the level and extent of bone resection, which depend on scapular and humeral morphologies. HYPOTHESIS: We aimed to determine whether computer-assisted acromioplasty planning helps surgeons remove impinging bone, reduce unnecessary resections, and improve short-term outcomes of rotator cuff tears (RCR). PATIENTS AND METHODS: We randomized 64 patients undergoing RCR of full-thickness supraspinatus tears into two groups: 'guided acromioplasty' (GA) and 'freehand acromioplasty' (FA). The pre- and post-operative scapula models were reconstructed using computed-tomography scans to quantify impinging bone removal, unnecessary bone resections, and identify zones of acromial bone removal. All patients were evaluated preoperatively and at 6 months to assess their range of motion (ROM), functional scores and tendon integrity using ultrasound. RESULTS: The two groups did not differ in demographics, clinical or morphologic characteristics. Compared to FA, GA tended to lower impinging bone removal (55±26% vs. 43±27%, p=0.087) and to increase unnecessary resection of the total bone removed (49±22% vs. 57±27%, p=0.248). GA resulted in significant anterior under-resection, while FA resulted in significant medial over-resection. Clinical outcomes and ROM improved significantly for all patients, except for internal rotation in the GA group. There were no other significant differences between the two groups, neither in terms of post-operative scores nor in terms of clinical net improvements, nor tendon repair integrity. CONCLUSIONS: This computer-assisted planning for acromioplasty during RCR proved no benefits in terms of bone removal, tendon healing, or clinical outcomes. Nonetheless such planning tools could help less experienced surgeons improve the efficacy of acromioplasty. LEVEL OF PROOF: I, Randomized controlled trial (Therapeutic study).

A hand-eye calibration method for augmented reality applied to computer-assisted orthopedic surgery.

BACKGROUND: Augmented reality (AR) allows the surgeon to represent holographic patient-specific anatomical information and surgical instruments in the physical world. To correctly superimpose virtual and physical objects, a hand-eye (HE) calibration method for mapping the virtual and physical spaces was proposed. METHODS: Mathematical relationships between the virtual camera and the physical space were derived. Finally, the accuracy and robustness of the proposed HE calibration method were qualitatively and quantitatively evaluated. RESULTS: The proposed calibration method allows us to determine an optimal invariant spatiotemporal mapping between the virtual camera and the physical space. CONCLUSION: Qualitatively and quantitatively reliable and accurate estimates for the physical-virtual mapping transformation were verified. Consequently, imaging data and surgical instruments holograms can be precisely represented in the physical space.

Effect of critical shoulder angle, glenoid lateralization, and humeral inclination on range of movement in reverse shoulder arthroplasty.

OBJECTIVES: To date, no study has considered the impact of acromial morphology on shoulder range of movement (ROM). The purpose of our study was to evaluate the effects of lateralization of the centre of rotation (COR) and neck-shaft angle (NSA) on shoulder ROM after reverse shoulder arthroplasty (RSA) in patients with different scapular morphologies. METHODS: 3D computer models were constructed from CT scans of 12 patients with a critical shoulder angle (CSA) of 25°, 30°, 35°, and 40°. For each model, shoulder ROM was evaluated at a NSA of 135° and 145°, and lateralization of 0 mm, 5 mm, and 10 mm for seven standardized movements: glenohumeral abduction, adduction, forward flexion, extension, internal rotation with the arm at 90° of abduction, as well as external rotation with the arm at 10° and 90° of abduction. RESULTS: CSA did not seem to influence ROM in any of the models, but greater lateralization achieved greater ROM for all movements in all configurations. Internal and external rotation at 90° of abduction were impossible in most configurations, except in models with a CSA of 25°. CONCLUSION: Postoperative ROM following RSA depends on multiple patient and surgical factors. This study, based on computer simulation, suggests that CSA has no influence on ROM after RSA, while lateralization increases ROM in all configurations. Furthermore, increasing subacromial space is important to grant sufficient rotation at 90° of abduction. In summary, increased lateralization of the COR and increased subacromial space improve ROM in all CSA configurations.Cite this article: A. Lädermann, E. Tay, P. Collin, S. Piotton, C-H Chiu, A. Michelet, C. Charbonnier. Effect of critical shoulder angle, glenoid lateralization, and humeral inclination on range of movement in reverse shoulder arthroplasty. Bone Joint Res 2019;8:378-386. DOI: 10.1302/2046-3758.88.BJR-2018-0293.R1.

Sexual Activities as Risk Factors of Rotator Cuff Lesions: A Prospective Cohort Study.

The aim of this study was to analyze the occurrence of rotator cuff impingement due to reduction of subacromial space height during complex shoulder motion to determine safety of sexual activities. The hypothesis was that such activities could be deleterious if not performed with precaution. To use a patient-specific 3D measurement technique coupling medical imaging and optical motion capture to evaluate the safety of various sexual positions according to subacromial compression. Descriptive laboratory study. A volunteer couple underwent Magnetic Resonance Imaging (MRI) and motion capture of their shoulders. Five common active and passive sexual positions were evaluated. Significant differences in subacromial space height were observed between the different performed actions. All active sexual positions requiring important pressure on the hands or elbows (e.g., scorpio) or weight lifting (e.g., superman) caused subacromial impingement. No subacromial impingement was however observed during passive sexual activities (e.g., basset hound). This study indicates that some sexual positions could potentially place the rotator cuff at risk. Such high-tech investigation shows promise in the areas of cause, intervention and education. The present findings may assist health professionals in providing them with preventive measures and is highly relevant for decision-making regarding health promoting initiatives.

Shoulder strengthening exercises adapted to specific shoulder pathologies can be selected using new simulation techniques: a pilot study.

PURPOSE: Shoulder strength training exercises represent a major component of rehabilitation protocols designed for conservative or postsurgical management of shoulder pathologies. Numerous methods are described for exercising each shoulder muscle or muscle group. Limited information is available to assess potential deleterious effects of individual methods with respect to specific shoulder pathologies. Thus, the goal of this pilot study was to use a patient-specific 3D measurement technique coupling medical imaging and optical motion capture for evaluation of a set of shoulder strength training exercises regarding glenohumeral, labral and subacromial compression, as well as elongation of the rotator cuff muscles. METHODS: One volunteer underwent magnetic resonance imaging (MRI) and motion capture of the shoulder. Motion data from the volunteer were recorded during three passive rehabilitation exercises and twenty-nine strengthening exercises targeting eleven of the most frequently trained shoulder muscles or muscle groups and using four different techniques when available. For each exercise, glenohumeral and labral compression, subacromial space height and rotator cuff muscles elongation were measured on the entire range of motion. RESULTS: Significant differences in glenohumeral, subacromial and labral compressions were observed between sets of exercises targeting individual shoulder muscles. Muscle lengths computed by simulation compared to MRI measurements showed differences of 0-5%. CONCLUSIONS: This study represents the first screening of shoulder strengthening exercises to identify potential deleterious effects on the shoulder joint. Motion capture combined with medical imaging allows for reliable assessment of glenohumeral, labral and subacromial compression, as well as muscle-tendon elongation during shoulder strength training exercises.