Nerve Reconstruction Research Articles

End-to-Side Cross-face Nerve Graft for Mental Nerve Reconstruction after Segmental Mandibulectomy.

The traditional technique for mental never reconstruction after segmental mandibulectomy is to bridge the gap between the proximal end of the inferior alveolar nerve (IAN) and the mental nerve stump. However, it often presents significant challenges. In cases of proximal IAN stump is close to skull base or kept inside the remaining mandible body and ramus, approaching the proximal end of the IAN can be very challenging.To overcome the limitation, a novel technique of cross-face mental nerve re-innervation with end-to-side coaptation to the contralateral mental nerve has been developed. This procedure involves preparing the recipient site before mandibulectomy, harvesting a donor nerve, preparing the contralateral mental nerve for end-to-side neurorrhaphy, and performing cross-face reinnervation after flap inset. The technique utilizes end-to-side coaptation to connect the nerve graft to the contralateral mental nerve.This new technique overcomes challenges posed by traditional methods, offering advantages such as shorter nerve grafts, easier coaptation due to superficial nerve position, and reduced risk of interference with second-stage dental surgeries. Initial outcomes have been promising, with all patients showing sensation recovery above S3 and no significant interference with contralateral mental nerve function.This innovative approach provides a solution for patients undergoing segmental mandibulectomy and has potential applications in restoring sensation lost due to various causes. It opens new possibilities for nerve rehabilitation and warrants further investigation through larger clinical trials to validate its efficacy and explore its potential in other nerve repair scenarios.

Human dorsal root ganglia are either preserved or completely lost after deafferentation by brachial plexus injury

BackgroundPlexus injury results in lifelong suffering from flaccid paralysis, sensory loss, and intractable pain. For this clinical problem, regenerative medicine concepts set high expectations. However, it is largely unknown how dorsal root ganglia (DRG) are affected by accidental deafferentation. MethodsHere, we phenotyped DRG of a clinically and MRI-characterised cohort of 13 patients with plexus injury. Avulsed DRG were collected during reconstructive nerve surgery. For control, we used DRG from forensic autopsy. The cellular composition of the DRG was analysed in histopathological slices with multicolour high-resolution immunohistochemistry, tile microscopy, and deep-learning-based bioimage analysis. We then sequenced the bulk RNA of corresponding DRG slices. ResultsIn about half of the patients we found loss of the typical DRG units consisting of neurones and satellite glial cells. The DRG cells were replaced by mesodermal/connective tissue. In the remaining patients, the cellular units were well preserved. Preoperative plexus MRI neurography was not able to distinguish the two types. Patients with ‘neuronal preservation’ had less maximum pain than patients with ‘neuronal loss’. Arm function improved after nerve reconstruction, but severe pain persisted. Transcriptome analysis of preserved DRGs revealed expression of subtype-specific sensory neurone marker genes, but downregulation of neuronal attributes. Furthermore, they showed signs of ongoing inflammation and connective tissue remodelling. ConclusionsPatients with plexus injury separate into two groups with either neuronal preservation or neuronal loss. The former could benefit from anti-inflammatory therapy. For the latter, studies should explore mechanisms of neuronal loss especially for regenerative approaches. Clinical trial registrationDRKS00017266.

One Size Does Not Fit All: Prediction of Nerve Length in Implant-based Nipple-Areola Complex Neurotization.

Breast reconstruction with sensory restoration is gaining recognition as an important goal. Successful reinnervation has been shown in autologous reconstruction but not widely studied in implant-based reconstruction (IBR). This article describes our technique for nipple-areola complex (NAC) neurotization to predict maximal nerve length. We also propose a novel equation that can be utilized preoperatively to estimate the total nerve length required for NAC neurotization. This is a retrospective study of patients who underwent nerve reconstruction with IBR between April 2021 and May 2022. An equation based on the arc length of a circle was utilized to predict the total nerve length required. Postoperative assessment of sensation was performed at 3, 6, and 12 months using Semmes-Weinstein monofilament testing in all four breast quadrants and the NAC. Patients completed the Breast-Q Sensation Module preoperatively and at 3, 6, and 12 months. NAC neurotization was performed in 58 patients undergoing IBR. The average length of intercostal nerve (ICN) harvested was 5.3 cm for staged reconstructions and 5.6 cm for direct-to-implant reconstruction. The average total nerve length (allograft + mobilized ICN) was 12.3 cm. On average, 6.9 cm of nerve allograft was used. The mean difference between total nerve length and predicted nerve length was 0.47 cm (range -3.5 to 4.6 cm). There was a significant improvement in sensory monofilament values measured in all four breast quadrants and the NAC between 3 to 6 and 6 to 12 months postoperatively. A thorough understanding of sensory anatomy and precise surgical techniques are essential to perform NAC neurotization successfully. Our early results suggest the positive impact of breast sensation on patient quality of life.

PHRENIC NERVE RECONSTRUCTION WITH SHORT-TERM DIAPHRAGM PACING CORRECTS DIAPHRAGM PARALYSIS DUE TO INTRATHORACIC NERVE INJURY.

Symptomatic diaphragm paralysis and subsequent pulmonary debilitation has been shown to occur following phrenic nerve injury within the thoracic cavity. In this study, we investigate the effectiveness of intrathoracic reconstruction of the phrenic nerve combined with short-term diaphragm pacing in restoring diaphragm function. A retrospective review of 34 consecutive patients who underwent intrathoracic phrenic nerve reconstruction and diaphragm pacing for symptomatic diaphragm paralysis was performed. Inclusion criteria included confirmation of diaphragm paralysis on chest fluoroscopy, BMI <40, Age <75, and presence of functional motor units on EMG testing. Surgical treatment consisted of intrathoracic phrenic nerve reconstruction with simultaneous implantation of a diaphragm pacemaker. 34 patients met inclusion criteria, including: 23 males and 11 females with an average age of 46 and average BMI of 28.5 kg/m2. Thirty patients (88%) reported improvement in respiratory function. FVC and FEV1 values improved by 15% (p=0.02) and 14% (p=0.049), respectively. A 375% increase in diaphragm motor amplitude was observed, from 0.04mV to 0.19mV (p=0.02). Radiographic improvement in resting diaphragm position and contraction was demonstrated in 71% of patients. Complications included pacemaker site infection (5%), cardiac arrythmia (5%), and asymptomatic abdominal bulge (3%). Intrathoracic phrenic nerve reconstruction with short-term diaphragm pacing is a safe and effective surgical treatment that improves diaphragm function and alleviates symptoms of respiratory insufficiency in patients with diaphragmatic paralysis following intrathoracic phrenic nerve injury. This approach should be considered as part of the treatment algorithm for this patient population.

Digital nerve reconstruction with a new composite silk fibroin nerve conduit.

Peripheral nerve injuries often require bridging when direct repair is not feasible. Nerve autografts are the gold standard, but they can lead to donor site morbidity. Silk fibroin-based nerve conduits, like the novel SILKBridge, offer a promising alternative. This pilot study evaluates the mid-term outcomes of the first in-human digital nerve reconstruction using the SILKBridge, focusing on sensory recovery, complication rates, patient-reported outcomes, and biological integration. This study included four patients with digital nerve defects reconstructed using the SILKBridge. Clinical assessments included two-point discrimination, Semmes-Weinstein monofilament testing, and pain evaluation using the Numeric Rating Scale. Sonographic assessments were also performed to evaluate the conduit's biointegration and potential complications. At a mean follow-up of 32 months, all patients demonstrated satisfactory sensory recovery and reported minimal to no pain. Sonographic assessments confirmed effective biointegration with no signs of inflammation or scarring. The mid-term evaluation of the first in-human digital nerve reconstruction with the SILKBridge revealed safety, efficiency, and favorable biocompatibility properties. Further studies with larger cohorts are needed to validate these findings and compare them with other nerve repair methods.

Surgical Considerations in the Management of Constriction Ring Syndrome.

Surgical management of constriction ring syndrome (CRS) is individualised due to the heterogenic presentation of the condition. CRS includes constriction rings, acrosyndactyly, nubbins and short digits. Involvement of more than one limb is common and children often need multiple surgeries. Each limb may need staged surgeries. If the child has vascular or lymphatic compromise secondary to a constriction ring, the ring needs to be excised and released in the first few days of life. The rings are released using multiple big Z-plasties in one or two stages. Nerve palsy associated with the rings need early intervention. Tendon transfers may be advised when nerve procedures like neurolysis and nerve reconstruction fail. Acrosyndactyly can be corrected with separation of the fused fingertips. At times, the web is more distal than usual and requires web deepening using partial syndactyly separation techniques and may need full thickness skin grafting. Complex type of acrosyndactyly is difficult to treat as it needs proper planning and staged surgical correction to achieve a five-digit hand. Separation of the syndactyly with web deepening gives more functional length and independence to the digits. The short fingers, especially the thumb, need reconstruction. Non-vascularised toe phalangeal transfer or a microvascular toe transfer can reconstruct a missing digit. Level of Evidence: Level V (Therapeutic).

Current Concepts of the Management of Painful Traumatic Peripheral Nerve Neuromas

Painful neuromas are a complex clinical condition that results in notable disability and functional impairment after injury to a peripheral nerve. When regenerating axons lack a distal target, they form a stump neuroma. Up to 60% of neuromas are painful because of mechanical sensitivity and crosstalk between nerve fibers. Clinical evaluation includes a thorough history and physical examination followed by directed diagnostic imaging and procedures to assess pain generators and their effect on quality of life. Nonsurgical management options may include pharmacological interventions, desensitization strategies, injections, and therapies to reduce pain perception and improve function. Surgical interventions, such as nerve reconstruction by direct repair or grafting, redirection to alternative targets, and containment of regenerating axons by relocation into innervated tissues or in grafts, are considered when conservative measures fail. A comprehensive and individualized treatment plan is crucial for optimizing patient outcomes with painful neuromas. The plan should consider the underlying pathology, pain generators, and psychosocial factors contributing to the patient's pain.

Robotic microsurgery for pediatric peripheral nerve surgery

The technology of microsurgical robotic systems has shown potential benefit during the last decade for a variety of microsurgical procedures, such as vascular anastomoses, lymphatic anastomoses or nerve coaptation. At the same time, peripheral nerve surgery has produced ever more sophisticated nerve transfers in which the smallest nerve structures are connected to each other. Following obstetric brachial plexus injuries, nerve reconstruction surgery is often required in the first few years of life in order to improve the function of the affected arm, including nerve transfers to denervated muscles, which enable reinnervation of target muscles. In pediatric patients, these donor-nerve structures are even smaller than in adults, which further increases the demands to the microsurgeon. In this publication, we show the possible applications, capabilities and limitations of a dedicated microsurgical robotic system for nerve transfers in pediatric patients.

Alginate Use in Orthopedics and Peripheral Nerve Repair: A Systematic Review.

The use of alginate, a derivative of seaweed, has been proposed for multiple orthopedic indications. We aimed to review the current use of alginate in orthopedics and to focus on the future applications of alginate for peripheral nerve repair. A comprehensive literature search was performed to identify biomechanical, laboratory, animal, and human studies where alginate has been utilized for orthopedic or nerve repair indications. A systematic review of orthopedic indications was conducted for safety and efficacy, and a specific focus was placed on alginate for use in peripheral nerve repair and reconstruction. Thirty-two studies were identified. Alginate has a strong history and safety profile for usage in orthopedic surgery. Its primary usage has been for the repair of articular cartilage, although it has also been used for disc regeneration of the lumbar spine and for cushioning joints in osteoarthritis. The primary indication in peripheral nerve repair is to create an environment that encourages Schwann cell migration and repair in nerve injuries while blocking fibrotic scar tissue formation by inhibiting the activity of fibroblasts. Alginate hydrogel may serve as a potential conduit for nerve regeneration in nerve injuries with small to medium-sized gaps.

Surgery for facial palsy in the hands of otorhinolaryngologists: a population-based study.

Modern facial surgery can improve eye closure and address facial functional and emotional expression disabilities in case of severe acute facial paralysis with low probability of recovery and in cases of chronic flaccid facial paralysis. Reports on outcome typically originate from specialized tertiary care centers, whereas population-based data from routine care beyond specialized centers is sparse. Therefore, patients' characteristics, surgical techniques, postoperative complications, and patients' satisfaction with the final outcome were analyzed for all inpatients with facial paralysis undergoing facial surgery in Thuringia, a federal state in Germany, between 2006 and 2022. 260 patients (female 41.5%; median age 65 years) were included. On average, the surgery rate was higher for men than for women (0.83 ± 0.39 versus 0.58 ± 0.24 per 100,000 population per year). For first surgery, static procedures were dominating (67.3%), followed by dynamic reconstruction (13.8%), and combined static and dynamic reconstructions (13.5%). The most frequent type of surgery was upper lid weight loading (38.5%), hypoglossal-facial jump nerve suture (17.3%), and facial-facial interpositional graft suture (16.9%). Bleeding/hematoma formation needing revision surgery was the most frequent complication (6.2%). Overall, 70.4% of the patients were satisfied with the final result. The satisfaction was higher if the target was to improve eye closure (65.2%) or to improve upper face function (65.3%) than to improve the lower face function (53.3%). If facial nerve reconstruction surgery and/or upper lid weight placement was performed, the satisfaction was significantly higher. If revision surgery was needed to improve the result, the satisfaction was significantly lower.

The Use of Grayscale Muscle Ultrasound to Indicate Muscle Recovery After Peripheral Nerve Reconstruction.

This study aimed to validate the use of grayscale muscle ultrasound by measuring echo intensity to longitudinally evaluate functional muscle reinnervation in a rabbit peroneal nerve defect model. Eighteen New Zealand White rabbits underwent a 30-mm peroneal nerve reconstruction with autografts or decellularized allografts. Ultrasound measurements of tibialis anterior muscles were performed before surgery and at 4, 8, 12, 16, 20, and 24 weeks postoperatively and included cross-sectional muscle area, mean gray value (MGV), and mean gray value normalized for area (MGVA). At 24 weeks, functional motor recovery was evaluated with isometric tetanic force (ITF) and compound muscle action potential (CMAP). MGVA data was compared with ITF and CMAP measurements by calculating the Spearman correlation coefficient. Muscle area (Left/Right Ratio (L/R)) of autografts was superior to allografts at 4, 12, 16, 20 and 24 weeks (p<0.03 for all comparisons). MGVs of the operated side were significantly higher for autografts at 4, 8, and 12 weeks and at 12, 16, 20, and 24 weeks for allografts (p<0.01 for all comparisons), compared to their unoperated sides. Similar patterns were seen in both groups for MGVA (operated versus control side). MGVA (L/R) demonstrated a strong correlation with ITF (L/R) for autografts (ρ = -0.7) and allografts (ρ = -0.87), but inconsistent with CMAPs (L/R). Quantitative muscle ultrasound demonstrated a reliable, non-invasive tool for evaluating motor recovery in a rabbit peroneal nerve reconstruction model. Clinical translation could provide valuable insights into muscle health and structural changes following nerve reconstruction.

Ancient cervical vagal schwannoma and an interposition great auricular to vagus nerve graft

Introduction: Schwannomas of the cervical vagus nerve are exceedingly rare and have a myriad of clinical presentations depending on the tumor size and its proximity to neurovascular structures. We report a rare case of a cervical vagal schwannoma that was successfully treated with en bloc resection and reconstruction with a great auricular to vagus nerve graft. Case Report: A 42-year-old male presented with an asymptomatic, right lateral neck mass. Magnetic resonance imaging revealed a lesion 2.4 cm × 1.4 cm × 4.0 cm in size, located between the carotid arteries and internal jugular vein displacing the internal carotid artery anteromedially. En bloc resection of the lesion and reconstruction of the vagus nerve with a great auricular interposition graft was performed. Conclusion: Vagal schwannomas are rare, benign neurogenic tumors. Complete surgical excision is the mainstay of treatment. When a safe surgical plane cannot be identified between the neurogenic tumor and the main nerve trunk, en bloc resection with reconstruction should be considered.

Modern Possibilities for Reconstruction of Nerves of the Head and Neck

The main etiological factors of nerve damage to the head and neck include injuries, oncological diseases, iatrogenic injuries during surgical interventions. An important task of treatment is to restore the lost function of the nervous head and neck, the functions of which certainly determine the quality of life of the patient. The article presents modern methods of nerve reconstruction of the head and neck. The methods of reconstructive surgery of the facial, trigeminal, inferior alveolar, lingual, recurrent laryngeal nerves are described. This article also describes the types of rehabilitation after reconstructive operations on the nerves of the head and neck using pharmacological and non-pharmacological treatment methods such as botulinum therapy, neuromuscular retraining, taping, post-isometric relaxation, acupuncture, phonophoresis, gymnastics.

Peripheral nerve grafting

Peripheral nerve lesions often lead to significant and permanent loss of motor and sensory function. The aim of peripheral nerve grafting is to bridge nerve defects. When tension-free nerve repair is not possible, peripheral nerve grafting is indicated. Local infection, insufficient soft tissue coverage, significant muscle atrophy or joint contraction in case of "motor" nerve grafting, lack of microsurgical instruments or experience, life-threatening injuries. Exposure and preparation of the nerve stumps. Choosing and preparation of the donor nerve. Approximation. Nerve repair. Nerve reconstruction must always be tension-free as nerve repair with tension frequently leads to disruption of nerve healing and poor functional outcome. Autologous nerve grafting from various donor sites leads to excellent functional results with little sensory deficits at the donor regions. Limited immobilization, physiotherapy, ergotherapy, regular clinical and neurological assessments. Outcome of peripheral nerve grafting may, for example, depend on defect length, caliber and quality of the injured nerve, quality of the donor nerve, microsurgical expertise of the surgeon, time of reconstruction, and age of the patient.

Technical Strategies and Learning Curve in Robotic-assisted Peripheral Nerve Surgery.

Robotic-assisted peripheral nerve surgery (RASPN) has emerged as a promising advancement in microsurgery, offering enhanced precision and tremor reduction for nerve coaptations. This study investigated the largest published patient collective in RASPN and provided specific technical aspects, operative setups, and a learning curve. Data collection involved creating a prospective database that recorded surgical details such as surgery type, duration, nerve coaptation time, and number of stitches. The experienced surgeon first underwent a 12-hour training program utilizing the Symani robot system in combination with optical magnification tools before using the system clinically. The study included 19 patients who underwent robot-assisted peripheral nerve reconstruction. The cohort included six men (31.6%) and 13 women (68.4%), with an average age of 53.8 ± 18.4 years. The procedures included nerve transfers, targeted muscle reinnervation, neurotized free flaps, and autologous nerve grafts. Learning curve analysis revealed no significant reduction in time per stitch over the initial nine coaptations (4.9 ± 0.5 min) compared with the last 10 coaptations (5.5 ± 1.5 min). The learning curve for RASPN was compared with early experiences with other surgical robots, emphasizing the importance of surgical proficiency and assistant training. Obstacles such as instrument grip strength and blood clot formation were highlighted, and suggestions for future advancements were proposed. RASPN presents an exciting opportunity to enhance precision; however, ongoing research and optimization are necessary to fully harness its benefits.

Peripheral Nerve Blocks as a Predictor of Nerve Reconstruction Success After Major Limb Amputation.

Postamputation pain is a spectrum of debilitating sensations that impacts millions of people in the United States. While the development of postamputation pain, including phantom limb pain (PLP), is multifactorial, it has been associated with disorganized axonal sprouting, resulting in a neuroma and subsequent central nervous system changes. Nerve reconstruction surgeries, such as regenerative peripheral nerve interface (RPNI) and targeted muscle reinnervation (TMR), provide transected nerve fibers with proper target organs for reinnervationand have been shown to significantly reduce PLP. This case series aims to describe perioperative peripheral nerve blocks as a diagnostic tool for identifying patients who would benefit from RPNI or TMR. We conducted a retrospective search of patients who underwent major extremity amputation and who received a diagnostic peripheral nerve block before undergoing reconstructive nerve surgery (TMR and/or RPNI). Six patients (58-80 years old) with below-knee amputations (BKA) were examined. All patients experienced a reduction in postamputation pain (PAP), specifically PLP, after a diagnostic peripheral nerve block (PNB). The average time between amputation and revision surgery was approximately two years (Mean: 22.35 months). Following surgical intervention, all patientsreported a reduction in PLP episodes after nerve reconstruction surgery. Two patients no longer reported PLP.Ambulation rates also improved following revision (50% vs 83%). PNBs can be used as an effective diagnostic tool to identify patients that will significantly benefit from amputation revisions with TMR or RPNI.

Comment On: Rethinking Oncologic Facial Nerve Reconstruction in the Acute Phase through Classification of the Level of Injury.

Comment On: Rethinking Oncologic Facial Nerve Reconstruction in the Acute Phase through Classification of the Level of Injury.

Highly aligned electroactive ultrafine fibers promote the differentiation of mesenchymal stem cells into Schwann-like cells for nerve regeneration

This study investigates the efficacy of a novel tissue-engineered scaffold for nerve repair and functional reconstruction following injury. Utilizing stable jet electrospinning, we fabricated aligned ultrafine fibers from dopamine and poly(L-lactic acid) (PLLA), further developing a biomimetic, oriented, and electroactive scaffold comprising poly(pyrrole) (PPy), polydopamine (PDA), and PLLA through dual in situ polymerizations. The scaffold demonstrated enhanced cell adhesion and reactive oxygen species (ROS) scavenging capabilities and promoted the differentiation of mesenchymal stem cells (MSCs) into Schwann-like cells, essential for nerve regeneration. In vivo assessments revealed significant peripheral nerve regeneration in 10 mm sciatic nerve defects in rats, with observations made 12 weeks post-transplantation. This included facilitated myelination and increased muscle density on the injured side, leading to improved motor function recovery. Our results suggest that the aligned PPy/PDA/PLLA fibrous scaffold offers a promising approach for promoting the differentiation of MSCs into Schwann-like cells conducive to nerve regeneration and represents a significant advancement in nerve repair technologies. This study provides a foundational basis for future research into tissue-engineered solutions for nerve damage, potentially impacting clinical strategies for nerve reconstruction.

Feasibility of a cross-face reconstruction of the mental nerve—A cadaveric simulation study with histomorphometric analysis

IntroductionThe inevitable sacrifice of the inferior alveolar nerve (IAN) during oncologic resections results in substantial sensory impairment, impacting crucial functions such as speech, saliva retention, and mastication. This study investigates the feasibility of sensory restoration through cross-face reconstruction of the mental nerve via a contralateral mental nerve branch. MethodsThe cross-face reconstruction procedure was simulated in five formalin-fixed cadavers for both sides to evaluate the anatomic fundamentals and the nerve gap between the mental nerve main trunk and the transferred contralateral mental nerve branch. Furthermore, a histomorphometric analysis was performed to assess cross-sectional area and axon counts. ResultsThe mean gap distance between the main mental nerve trunk and the transferred contralateral branch was 15.3mm. End-to-end coaptation was achieved in 9 out of 10 simulations. The mean cross-sectional area was 0.996 mm2 at the main mental nerve trunk and 0.253mm2 at the coaptation site of the nerve branch. The mean donor-to-recipient axon ratio was found to be 0.3:1. ConclusionThe cadaveric simulation demonstrates the feasibility of a cross-face reconstruction of the mental nerve with only minimal gapping. Advantages of the proposed technique include the use of shorter nerve grafts, minimizing donor site morbidity and enabling fast reinnervation. This technique may offer a promising method for enhancing the quality of life for a patient group with increasing survival rates and life expectancy.

Free functional gracilis transfer for reconstruction of isolated anterior deltoid atrophy following surgical proximal humerus fixation

BackgroundPalsy of the clavicular head of the deltoid is a complication after surgical fixation of proximal humerus fractures. Flexion of the shoulder joint may be impaired as a result. Additionally, patients may complain of joint instability, visible atrophy and pain. Where nerve reconstruction is not possible, muscle transfers remain as secondary reconstructive procedures. MethodsThree patients suffering from anterior deltoid palsy after proximal humerus fixation received a free functional gracilis transfer to the shoulder. Postoperatively, patients underwent biofeedback-based rehabilitation. Before and after the intervention, subjective complaints, pain level and active range of motion (ROM) were recorded. At the final follow-up patients completed a Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire. ResultsThe surgery was successful in all patients with first muscle signals registered through sEMG approximately four months postoperatively. At the latest follow-up (> 3 years), the patients showed improved shoulder stability and pain scores. In two patients with preoperative restrictions, active ROM improved. The DASH score showed minimal to no disability in two patients and moderate disability in the third. Two patients voiced satisfaction with the restoration of the ventral bulk of the shoulder. ConclusionsThe free functional gracilis muscle transfer is a novel approach for secondary reconstruction in patients with anterior deltoid atrophy who don’t qualify for nerve intervention. It addresses shoulder instability and pain and may improve active ROM. The addition of fresh muscle tissue to the ventral shoulder can improve its natural contour and prevent protrusion of the humeral head.