Tendon pain - what are the mechanisms behind it?

OBJECTIVES: Management of chronic tendon pain is difficult and controversial. This is due to poor knowledge of the underlying pathophysiology of chronic tendon pain, priorly known as tendinitis but now termed tendinopathy. The objective of this topical review was to synthesize evolving information of mechanisms in tendon pain, using a comprehensive search of the available literature on this topic. CONTENT: This review found no correlations between tendon degeneration, collagen separation or neovascularization and chronic tendon pain. The synthesis demonstrated that chronic tendon pain, however, is characterized by excessive nerve sprouting with ingrowth in the tendon proper, which corresponds to alterations oberserved also in other connective tissues of chronic pain conditions. Healthy, painfree tendons are devoid of nerve fibers in the tendon proper, while innervation is confined to tendon surrounding structures, such as sheaths. Chronic painful tendons exhibit elevated amounts of pain neuromediators, such as glutamate and substance p as well as up-regulated expression and excitability of pain receptors, such as the glutamate receptor NMDAR1 and the SP receptor NK1, found on ingrown nerves and immune cells. Increasing evidence indicates that mast cells serve as an important link between the peripheral nervous system and the immune systems resulting in so called neurogenic inflammation. SUMMARY: Chronic painful tendons exhibit (1) protracted ingrowth of sensory nerves (2) elevated pain mediator levels and (3) up-regulated expression and excitability of pain receptors, participating in (4) neuro-immune pathways involved in pain regulation. Current treatments that entail the highest scientific evidence to mitigate chronic tendon pain include eccentric exercises and extracorporeal shockwave, which both target peripheral neoinnervation aiming at nerve regeneration. OUTLOOK: Potential mechanism-based pharmacological treatment approaches could be developed by blocking promotors of nerve ingrowth, such as NGF, and promoting inhibitors of nerve ingrowth, like semaphorins, as well as blocking glutamate-NMDA-receptor pathways, which are prominent in chronic tendon pain.

Function of peripheral nerves in the development and healing of tendon and bone.

Although the functions of the peripheral nervous system in whole body homeostasis and sensation have been understood for many years, recent investigation has uncovered new roles for innervation in the musculoskeletal system. This review centers on advances regarding the function of nerves in the development and repair of two connected tissues: tendon and bone. Innervation in healthy tendons is generally confined to the tendon sheaths, and tendon-bone attachment units are typically aneural. In contrast to tendon, bone is an innervated and vascularized structure. Historically, the function of abundant peripheral nerves in bone has been limited to pain and some non-painful sensory perception in disease and injury. Indeed, much of our understanding of peripheral nerves in tendons, bones, and entheses is limited to the source and type of innervation in healthy and injured tissues. However, more recent studies have made important observations regarding the appearance, type, and innervation patterns of nerves during embryonic and postnatal development and in response to injury, which suggest a more expansive role for peripheral nerves in the formation of musculoskeletal tissues. Indeed, tendons and bones develop in a close spatiotemporal relationship in the embryonic mesoderm. Models of limb denervation have shed light on the importance of sensory innervation in bone and to a lesser extent, tendon development, and more recent work has unraveled key nerve signaling pathways. Furthermore, loss of sensory innervation also impairs healing of bone fractures and may contribute to chronic tendinopathy. However, more study is required to translate our knowledge of peripheral nerves to therapeutic strategies to combat bone and tendon diseases.

A unique case of mid-tendonpalmaris longus muscle - dissection presentation and literature review

The palmaris longus (PL) muscle is one of five muscles that originates from the common flexor tendon, which attaches at the medial epicondyle of the humerus, and has its own insertion distally into the palmar aponeurosis. Although the PL contributes minimal biomechanical function, its wide anatomic variation can produce pathologies in the forearm and wrist such as median nerve entrapment. The present work describes a unique case of a PL distally migrated muscle belly with wide tendon both proximal and distal not noted in other anatomical or surgical reference materials. Here-in, the current case is compared to previously re-ported PL variations and their documented frequencies by region and ethnicity. Key findings include several studies showing Caucasian populations with greater than 25% frequencies of absent PL, compared to 4-6% in African regions. Potential explanations for this finding include evolutionary adaptations associated with manual labor and need for increased grip strength. In addition, the considerations of abnormal PL in surgical procedures inclusive of challenges in graft procedures that might present with such anatomic variations of the PL are examined

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Anatomical variations and innervation patterns of the superior oblique muscle.

GOAL: The location and anatomical relationships of the superior oblique muscle make surgical intervention difficult. The aim of the present paper was therefore to supplement existing anatomical descriptions of this muscle. Its anatomical variability is particularly emphasized, including variations in muscle and tendon size and details of the innervation pattern. MATERIALS AND METHODS: The study was conducted on 78 orbits from 39 adult human cadavers of both sexes (18 males and 21 females). The roof and upper part of the medial and lateral walls of the orbit were carefully removed, which allowed the superior oblique muscle and trochlear nerve to be exposed along their entire course. Sihler's stain was applied to visualize the intramuscular distribution of the trochlear nerve. RESULTS: The length of the muscle between the origin and trochlea ranged from 37.8 to 56.5mm, the length of the tendinous expansion ranged from 16.3 to 22.8mm, and the width of the scleral insertion of the muscle's tendon ranged from 5.4 to 9.6mm. In two cadavers, accessory muscular slips connecting the levator palpebrae superioris muscle to the trochlea of the superior oblique muscle were present unilaterally. The distance from the level of the trochlea attachment to the anteriormost endings of the intramuscular branches varied from 17.2 to 21.5mm. CONCLUSIONS: The intramuscular nervous branches of the trochlear nerve form a tree-like pattern. Unexpected anatomical variations such as accessory muscular bands could be relevant during orbital imaging or surgeries.

Percutaneous Tendon Needling without Ultrasonography for Lateral Epicondylitis.

Percutaneous ultrasonic tendon needling has been used to treat persistent lateral epicondylitis, and its efficacy has been demonstrated. However, whether ultrasonography is necessary remains unclear. The purpose of this retrospective study was to evaluate the efficacy of percutaneous tendon needling without ultrasonography for lateral epicondylitis. A total of 36 patients who underwent tendon needling without ultrasonography for lateral epicondylitis were retrospectively included in the study. The tendinotic lesion was needled by fenestration approximately 20-30 times without sonographic assistance. The Visual Analogue Scale (VAS) pain score, the grip strength, and success rates were assessed at baseline and at 1, 3, 6, and 12 months after treatment. The Nirschl tennis elbow score was evaluated at baseline and at 6 and 12 months after the needling procedure. The mean VAS pain score and grip strength at 3, 6, and 12 months significantly improved compared to the baseline values. At 6 and 12 months, the success rates had significantly increased compared to the rates at 1 month. The mean Nirschl scores at 6 and 12 months were significantly better than the baseline value. No severe complications were observed during the study period. Percutaneous tendon needling without ultrasonography is a simple and safe technique. The procedure is effective for lateral epicondylitis that is unresponsive to conventional conservative treatments.

Morphology and innervation of brachioradialis and flexor carpi radialis and their utility in tendon transfer surgeries: A Cadaveric Study.

INTRODUCTION: The Brachioradialis (BR) muscle flap is easy to harvest, provides a stable coverage to the cubital fossa as it is well vascularized. The BR andflexor carpi radialis (FCR) tendons are utilized in tendon transfer to restore the normal hand function. Therefore, the present study describes the morphology of the muscle bellies and the tendons of BR and FCR along with their pattern of innervation. MATERIALS AND METHODS: The study was carried out on 27 upper limbs of formalin-fixed, adult human cadavers. Length and width of the bellies of BR and FCR were measured. The number of motor branches and their distances from the bi-epicondylar line was measured. RESULTS: The mean lengths of BR and FCR bellies were 21.22±2.18cm and 16.15±2.39cm, and the lengths of their tendons were, 12.67±1.13cm and 12.48±1.72cm respectively. BR received a single motor branch in 19 upper limbs. However, FCR received single motor branch in 25 limbs as a common trunk. One upper limb received three motor branches to BR, and two upper limbs received two motor branches to FCR. The most proximal and distal branches to the BR were ranged between 6.3-2.2cm proximal to the bi-epicondylar line. Those to the FCR were ranged between 3.5-6.9cm distal to the bi-epicondylar line. CONCLUSION: The motor branches to the BR and FCR are variable in their origin, and the knowledge of such variations is essential for identifying them while performing selective neurotomy surgeries.

How to visualize the innervation pattern in tendons: A methodical guide.

BACKGROUND: Tendon pathologies are common and several data suggests that the peripheral nervous system is involved in this disorder. Immunohistochemistry (IHC) is one of the pillars to characterize nervous structures and their implication in the pathogenesis of chronic tendon pain. Most commonly, formalin-fixed, paraffin-embedded (FFPE) tendons are used for immunohistochemical characterization of the innervation. However, FFPE specimens exhibit major disadvantages: First, antigens (proteins) are masked and antigen retrieval is necessary to restore antigenicity. Second, FFPE specimens involve immunolabeling with enzyme-conjugated antibodies but this approach has limitations when multiple antigens are of interest simultaneously. Consequently, there is a demand in the orthopedic community for an alternative immunohistochemical approach to visualize tendon innervations. RESULTS: Here, we present a guide how to visualize tendon innervation. This guide couples paraformaldehyde fixation, cryo-embedding, immunofluorescence, and confocal laser scanning microscopy. We demonstrate the utility of our approach in the long head of the biceps tendon. For nerve fiber characterization, we used different neuronal markers including antibodies against neurofilament, protein gene product 9.5, calcitonin gene related peptide, and substance P. We show that it is possible to collect high quality, multicolor images of the innervation pattern of tendons. To map immunolabeled structures and the anatomical structures of the tendon fluorescence images and bright field images were merged. CONCLUSION: For the orthopedic community our approach might be a convenient research tool to simultaneously utilize multiple neuronal markers on the same tissue section and to define with greater accuracy the heterogeneity of tendon innervation.

Reinnervation of Extrinsic Finger Flexors and Brachioradialis 22 and 36 Months Following Traumatic Pan-Brachial Plexopathy: A Case Report.

A 25-year-old man sustained a right-sided brachial plexus injury from a high-velocity motocross accident. Physical examination and electromyography were consistent with a pan-brachial plexopathy with no evidence of axonal continuity. The patient underwent a spinal accessory to suprascapular nerve transfer and an intercostal to musculocutaneous nerve transfer with interpositional sural nerve grafts. He recovered MRC 4/5 elbow flexion and MRC 2/5 shoulder abduction and external rotation. Twenty-two months post-injury the patient displayed a flicker of flexion of his flexor pollicis longus and flexor digitorum profundus to his index finger - he went on to recover a functional pinch. Thirty-six months post-injury the patient displayed a flicker of contraction in brachioradialis with motor unit potentials on electromyography. This case demonstrates that some patients may have capacity for functional recovery after prolonged denervation and highlights the potential impact of anatomical anomalies in the assessment and treatment of peripheral nerve injuries.

Innervation of flexor hallucis longus muscle: an anatomical study for selective neurotomy.

BACKGROUND: The aim of the study was to describe the innervation of flexor hallucis longus (FHL) and obtain its surgical coordinates to facilitate selective neurotomy. MATERIALS AND METHODS: Fifteen embalmed lower limbs of adults were studied. Anatomical dissections to isolate the innervating branches of FHL were performed. Distance between the supplying nerve of FHL, including both its origin and termination, and the medial malleolus were obtained, providing anatomical coordinates beneficial for surgery. RESULTS: In all cases, FHL was innervated by only one branch, which originated from the tibial nerve. Mean distance between the medial malleolus and the nervous branch origin was 21.39 ± 3.05 cm. Mean distance between the medial malleolus and the nervous branch termination was 12.7 ± 1.59 cm. Length of the nervous branch innervating FHL was proportional to the length of the leg, measuring 8.69 ± 2.45 cm. All nerves were located 15-17.4 cm above the medial malleolus. CONCLUSIONS: This anatomical study traced valuable surgical coordinates useful for performing selective peripheral neurotomy on the nerve branch innervating the FHL.

Sympathetic Innervation and Adrenergic Receptors in Equine Deep Digital Flexor Tendinopathy: Preliminary Results.

The aim of this study was to delineate the pattern of sympathetic innervation in the suprasesamoidean region of the deep digital flexor tendon (DDFT) in horses with tendinopathy by immunohistochemical labelling for tyrosine hydroxylase (TH) and α-1 adrenergic receptor (α1-AR). Twelve forelimbs were obtained from 10 horses with DDFT tendinopathy and six feet obtained from six horses were used as healthy controls. Post-mortem radiographic, ultrasonographic and gross examinations were performed on the suprasesamoidean area of the DDFT to assess the presence of tendinopathy. Longitudinal sections were collected and processed. Lesions were classified as core lesions, dorsal border lesions and parasagittal oblique splits. Immunohistochemistry was performed and the degree of immunoreaction was classified as absent, mild or marked. Seven core lesions, four dorsal border lesions and one parasagittal oblique split were identified. There was no increased expression of sympathetic innervation in samples with a dorsal border lesion of the DDFT compared with healthy samples. In contrast, core lesions showed increased expression of α1-AR and reduced expression of TH, which supports the hypothesis of a compensatory imbalance between the sympathetic mediator and the sympathetic receptors as a cause or effect of structural damage. In addition, adrenergic activation could stimulate cell proliferation and differentiation within these lesions.

Normal tendon reflexes despite absent sensory nerve action potentials in CANVAS: a neurophysiological study.

CANVAS is a recently defined progressive ataxic syndrome with impairment of vestibular, somatosensory and cerebellar function due to atrophic degeneration of dorsal root ganglia and dorsal columns, of cranial nerve somatosensory ganglia, of vestibular ganglia and vestibular nerves and of cerebellar Purkinje cells. While all patients eventually develop sensory impairment in a non-length dependent pattern and lose sensory nerve action potentials, some retain their tendon reflexes. Here we study 5 CANVAS patients with absent sensory nerve action potentials but intact, even brisk Achilles tendon reflexes and, in 4, preserved H reflexes in the upper and lower limbs. These findings imply that dorsal root ganglion neurons subserving cutaneous afferents more vulnerable than those subserving muscle afferents. Our findings have a clinical message: preservation of the Achilles tendon jerk does not exclude a large fibre peripheral neuronopathy.

Impact of Targeted Assistance of Multiarticular Finger Musculotendons on the Coordination of Finger Muscles During Isometric Force Production.

Neurological injuries often cause degraded motor control. While rehabilitation efforts typically focus on movement kinematics, abnormal muscle activation patterns are often the primary source of impairment. Muscle-based therapies are likely more effective than joint-based therapy. In this paper, we examined the feasibility of biomimetic input mimicking the action of human musculotendons in altering hand muscle coordination. Twelve healthy subjects produced a submaximal isometric dorsal fingertip force, while a custom actuator provided assistance mirroring the actions of either the extrinsic extensor or the intrinsic muscles of the index finger. The biomimetic inputs reduced the activation level of all task-related muscles, but the degree of change was different across the muscles, resulting in significant changes in their coordination (co-contraction ratios) and force-electromyography correlations. Each biomimetic assistance particularly increased the neural coupling between its targeted muscle and the antagonist muscle. Subjects appeared to fully take advantage of the assistance, as they provided minimal level of effort to achieve the task goal. The targeted biomimetic assistance may be used to retrain activation patterns post-stroke by effectively modulating connectivity between the muscles in the functional context and could be beneficial to restore hand function and reduce disability.

Relationship between neuropathy proximal to the suprascapular nerve and rotator cuff tear in a rodent model.

BACKGROUND: Rotator cuff tears are believed to coexist with cervical spine lesions. In cases of preexisting neuropathy, such as cervical spine lesions, fatty degeneration has likely already occurred due to the neuropathy. In these cases, rotator cuff tear is thought to occur easily because of preexisting extensive fatty degeneration and degeneration of the tendons due to neuropathy. This study aimed to evaluate the effects of paralysis due to neuropathy proximal to the suprascapular nerve on the supraspinatus and infraspinatus tendons using a rat model of brachial plexus paralysis. METHODS: This study included fifteen, 8-week-old Sprague-Dawley rats. The left shoulder was included in the paralysis group and the contralateral shoulder constituted the sham group. Biomechanical testing (evaluated maximum tear force, maximum displacement and Young's modulus) (n = 10) and histological analyses (n = 5) (using the Bonar scale) were performed at 12 weeks postoperatively to confirm the degeneration of the tendon. RESULTS: The mean maximum tear force was significantly lower in the paralysis group than in the sham group (P = 0.008), indicating that rotator cuff tears occurred with a lower force in the paralysis group. Additionally, the average Young's modulus was significantly greater in the paralysis group than in the sham group (P = 0.003), indicating that the rotator cuff muscle became hard and inflexible in the paralysis group. The Bonar scales of the histological analyses were significantly higher in the paralysis group (total score = 7.04 ± 0.61) than the sham group (total score = 0) (p < 0.0001). CONCLUSIONS: If neuropathy of proximal to the suprascapular nerve, such as cervical spine or brachial plexus lesion, exists, weakness and degeneration of the rotator cuff tendon and stiffness of the rotator cuff muscle develop. Neuropathy is likely a cause of rotator cuff tears.

Defining the Anatomy of the Tendinous Intersections of the Rectus Abdominis Muscle and Their Clinical Implications in Functional Muscle Neurotization.

PURPOSE: Little is known about the definitive course of the tendinous intersections from anterior to posterior through the rectus abdominis (RA) muscle. The implications of a full thickness intersection may have effects on the ability to neurotize the RA. We hypothesized that these tendinous inscriptions would be fully adherent to the anterior rectus sheath, but there would be an incomplete penetrance into the posterior surface, thereby allowing for muscle fibers and neurovascular structures to run the entire course of the RA muscle. METHODS: Fifty-five cadaveric, hemiabdominal walls were evaluated. Measurements were taken of RA muscle thickness, depth of penetrance of the tendinous intersections, and intersection thickness. RESULTS: Of the 32 cadavers, 2 had 4 paired tendinous intersections and the remaining 30 cadavers had 3 paired tendinous intersections. Rectus abdominis muscle belly tended to be thicker at midbelly, between intersections than at the level of the corresponding intersection. A total of 168 tendinous intersections were assessed. Thirty (18%) of these inscriptions proved to be full thickness extending from anterior rectus sheath to posterior rectus sheath without any intervening muscle or neurovascular structures. Twenty-three (42%) of the 55 hemiabdomens assessed had at least one full-thickness tendinous intersection. CONCLUSIONS: The majority of RA muscles have 3 paired tendinous intersections. Most intersections are incomplete and only encompass the anterior rectus sheath. However, there may be a higher percentage of full-thickness intersections than previously appreciated and the clinical relevance behind these remains unclear.

Morphology and relationships of the biceps brachii and brachialis with the musculocutaneous nerve.

INTRODUCTION: Major anatomical textbooks generally state that the biceps brachii muscle (BB) is composed of long and short heads, whereas the brachialis muscle (BR) consists of a single head. However, the numbers of heads comprising the BB and the BR are very variable. The purpose of this study was to investigate how the branching patterns of the musculocutaneous nerve (MC) influence the number of heads of the BB and the BR. MATERIALS AND METHODS: Morphological examinations of the BB and MC were conducted using cadavers of 22 Japanese individuals, and morphological examinations of the BR and the MC were conducted in 9 of those 22 individuals. RESULTS: A three-headed BB was observed in 7 of the 22 specimens (31.8%). Most of these specimens showed a Type III branch pattern (after penetrating the long head or the short head, the MC innervated the supernumerary head or communicated with the main root again). The number of BR heads was categorized into three types: Type A, two heads (superficial and deep heads, 22.2%); Type B, three or four heads (two or three superficial heads and one deep head, 44.4%); and Type C, multiple heads (33.3%). Among these categories, branches of the MC in Type A specimens were most simple. CONCLUSION: A supernumerary head of the BB seemed to be present if the MC penetrates it. The BR basically consists of superficial and deep heads, and the number of superficial heads is affected by branches of the MC.

Effects of muscle action type on corticospinal excitability and triceps surae muscle-tendon mechanics.

This study investigated whether the specific motor control strategy reported for eccentric muscle actions is dependent on muscle mechanical behavior. Motor evoked potentials, Hoffman reflex (H-reflex), fascicle length, pennation angle, and fascicle velocity of soleus muscle were compared between isometric and two eccentric conditions. Ten volunteers performed maximal plantarflexion trials in isometric, slow eccentric (25°/s), and fast eccentric (100°/s) conditions, each in a different randomized testing session. H-reflex normalized by the preceding M wave (H/M) was depressed in both eccentric conditions compared with isometric ( P < 0.001), while no differences in fascicle length and pennation angle were found among conditions. Furthermore, although the fast eccentric condition had greater fascicle velocity than slow eccentric ( P = 0.001), there were no differences in H/M. There were no differences in motor evoked potential size between conditions, and silent period was shorter for both eccentric conditions compared with isometric ( P = 0.009). Taken together, the present results corroborate the hypothesis that the central nervous system has an unique activation strategy during eccentric muscle actions and suggest that sensory feedback does not play an important role in modulating these muscle actions. NEW & NOTEWORTHY The present study provides new insight into the motor control of eccentric muscle actions. It was demonstrated that task-dependent corticospinal excitability modulation does not seem to depend on sensory information processing. These findings support the hypothesis that the central nervous system has a unique activation strategy during eccentric muscle actions.

Neurofilament distribution in the superior labrum and the long head of the biceps tendon.

BACKGROUND: The postoperative course after arthroscopic superior labrum anterior to posterior (SLAP) repair using suture anchors is accompanied by a prolonged period of pain, which might be caused by constriction of nerve fibres. The purpose was to histologically investigate the distribution of neurofilament in the superior labrum and the long head of the biceps tendon (LHBT), i.e. the location of type II SLAP lesions. METHODS: Ten LHBTs including the superior labrum were dissected from fresh human specimen and immunohistochemically stained against neurofilament (NF). All slides were scanned at high resolution and converted into tagged image file format, and regions of interest (ROIs) were defined as follows: ROI I-superior labrum anterior to the LHBT origin, ROI II-mid-portion of the superior labrum at the origin of the LHBT, ROI III-superior labrum posterior to the LHBT origin and ROI IV-the most proximal part of the LHBT before its attachment to the superior labrum. The entire images were automatically segmented according to the defined ROIs and measured using a programmed algorithm specifically created for this purpose. The NF-positive cells were counted, and their total size and the area of other tissue were measured separately for the different ROIs. RESULTS: Distribution of NF-positive cells in absolute numbers revealed a clear but insignificantly higher amount in favour of ROI I, representing the superior labrum anterior to the LHBT origin. Setting ROI I at 100%, a significant difference could be seen compared to ROI III, representing the superior labrum posterior to the LHBT origin (ROI I vs. ROI III with a p value < 0.05). CONCLUSIONS: Summarizing, the density of neurofilament is inhomogeneously distributed throughout the superior labrum with the highest number of neurofilament in the anterior superior labrum. Thus, suture placement in type II SLAP repair could play an important role for the postoperative pain-related outcome.

Upper Extremity Innervation Patterns and Clinical Implications for Nerve and Tendon Transfer.

BACKGROUND: The authors previously studied the intramuscular innervation of 150 upper limb muscles and demonstrated that certain patterns of intramuscular innervation allowed muscles to be split into compartments with independent function. This study aims to determine the location, extramuscular course, and number of motor nerve branches of upper limb peripheral nerves. The authors want to combine this information with their previous work to create a blueprint of upper limb neuromuscular anatomy that would be useful in reconstructive surgery. METHODS: Ten fresh frozen cadaveric upper limbs were dissected. The origin of branches from the peripheral nerve trunk, their course, and the number of motor nerves per muscle were determined. The authors reviewed all the images of the Sihler-stained muscles from their earlier study. RESULTS: Motor nerve branches arise at the intersection of nerve trunk and muscle belly and are clustered near the origin of muscle groups. Two patterns of extramuscular innervation were noted, with one group having a single motor nerve and another group with consistently more than one motor nerve. A modified classification of muscles was proposed based on the orientation of muscle fibers to the long axis of the limb, the number of muscle compartments, and the number of heads of origin or the tendons of insertion. CONCLUSIONS: Motor nerve clusters can be located based on fixed anatomical landmarks. Muscles with multiple motor nerves have morphology that allows them to be split into individual compartments. The authors created a muscle and nerve blueprint that helps in planning nerve and split muscle transfers.

Review: Emerging concepts in the pathogenesis of tendinopathy.

Tendinopathy is a common clinical problem and has a significant disease burden attached, not only in terms of health care costs, but also for patients directly in terms of time off work and impact upon quality of life. Controversy surrounds the pathogenesis of tendinopathy, however the recent systematic analysis of the evidence has demonstrated that many of the claims of an absence of inflammation in tendinopathy were more based around belief than robust scientific data. This review is a summary of the emerging research in this topical area, with a particular focus on the role of neuronal regulation and inflammation in tendinopathy.

Nerve supply of the subscapularis during anterior shoulder surgery: definition of a potential risk area.

PURPOSE: The purpose of the study was to evaluate the position of the subscapular nerves relative to surgical landmarks during exposure and to analyze the pattern of innervation of the subscapularis to avoid injury during anterior shoulder surgery. METHODS: 20 embalmed human cadaveric shoulder specimens were used in the study. The muscular insertions of the subscapular nerves were marked and their closest branches to the musculotendinous junction and the coracoid process were measured in horizontal and vertical distances. In addition, the innervation pattern of each specimen was documented. RESULTS: 14/20 specimens showed an innervation of the subscapularis with an upper, middle and lower subscapular nerve branch. Even though the nerve branches were in average more than 2 cm medial to the musculotendinous junction, minimal distances of 1.1-1.3 cm were found. The mean vertical distance as measured from the medial base of the coracoid to the nerve innervation point into the muscle was 0.7 cm for the upper nerve branch, 2.2 cm for the middle nerve branch and 4.4 cm for the lower nerve branch. CONCLUSIONS: The subscapularis has a variable nerve supply, which increases the risk of muscle denervation during open shoulder surgery. Dissection or release should be avoided at the anterior aspect of the subscapularis muscle more than 1 cm medial to the musculotendinous junction. In approaches with a horizontal incision of the subscapularis, splitting should be performed at a vertical distance of 3.2-3.6 cm to the coracoid base to avoid iatrogenic subscapular nerve injuries.