Dissectional Orientation: Morphological Variations of Teres Minor Muscle and its Nerve Supply

SUMMARY: The teres minor is one of the rotator cuff muscles that comprise the superior margin of the quadrangular space. Quadrangular space syndrome (QSS) refers to the entrapment or compression of the axillary nerve and the posterior humeral circumflex artery in the quadrangular space, often caused by injuries, dislocation of the shoulder joint, etc. Patients who fail the primary conservative treatments and have persistent symptoms and no pain relief for at least six months would be considered for surgical interventions for QSS. This cadaveric study of 17 cadavers (males: 9 and females: 8) was conducted in the Gross Anatomy Laboratory at the Department of Anatomy, Faculty of Medicine Siriraj Hospital, Mahidol University. The cadavers were preserved in a 10 % formaldehyde solution and obtained ethical approval by the ethical commission of the Siriraj Institutional Review Board. The morphology of the teres minor muscle-tendon junction, the bifurcation type of the axillary nerve, and the length and number of the terminal branches of the nerve to the teres minor were documented. Specimens with quadrangular space contents and surrounding muscles that had been destroyed were excluded from the study. The results showed that 47.06 % of the specimens had type A bifurcation, 47.06 % had type B bifurcation, and the remaining 5.88 % had type C bifurcation. It was observed that 58.82 % had nonclassic muscle-tendon morphology, while 41.18 % were classic. The average length of the terminal branches of the nerve to the teres minor in males was 1.13 cm, with the majority having two branches. For females, many showed one terminal branch with an average length of 0.97 cm. Understanding the differences in anatomical variations can allow for a personalized treatment plan prior to quadrangular space syndrome surgical procedures and improve the recovery of postsurgical interventions for patients.

El músculo redondo menor es uno de los músculos del manguito rotador que comprende el margen superior del espacio cuadrangular. El síndrome del espacio cuadrangular (QSS) se refiere al atrapamiento o compresión del nervio axilar y la arteria circunfleja humeral posterior en el espacio cuadrangular, a menudo causado por lesiones, dislocación de la articulación humeral, entre otros. En los pacientes en los que fracasan los tratamientos conservadores primarios y presentan síntomas persistentes y ningún alivio del dolor durante al menos seis meses se considerarían para intervenciones quirúrgicas para QSS. Este estudio cadavérico de 17 cadáveres (hombres: 9 y mujeres: 8) se llevó a cabo en el Laboratorio de Anatomía Macroscópica del Departamento de Anatomía de la Facultad de Medicina del Hospital Siriraj de la Universidad Mahidol. Los cadáveres se conservaron en una solución de formaldehído al 10 % y obtuvieron la aprobación ética de la comisión ética de la Junta de Revisión Institucional de Siriraj. Se documentó la morfología de la unión músculo-tendón del músculo redondo menor, el tipo de bifurcación del nervio axilar y la longitud y el número de las ramas terminales del nervio para el músculo redondo menor. Se excluyeron del estudio los especímenes con contenido de espacios cuadrangulares y músculos circundantes que habían sido destruidos. Los resultados mostraron que el 47,06 % de los especímenes presentó bifurcación tipo A, el 47,06 % una bifurcación tipo B y el 5,88 % restante una bifurcación tipo C. Se observó que el 58,82 % presentaba una morfología músculo-tendinosa no clásica, mientras que el 41,18 % era clásica. La longitud pmedia de los ramos terminales del nervio hasta el músculo redondo menor en los hombres era de 1,13 cm, y la mayoría tenía dos ramos. En el caso de las mujeres, mostraron un ramo terminal con una longitud promedio de 0,97 cm. Comprender las diferencias en las variaciones anatómicas puede permitir un plan de tratamiento personalizado antes de los procedimientos quirúrgicos del síndrome del espacio cuadrangular y mejorar la recupe- ración de las intervenciones posquirúrgicas de los pacientes.

Sonoanatomy and an ultrasound scanning protocol of the intramuscular innervation pattern of the infraspinatus muscle.

INTRODUCTION: Botulinum neurotoxin injection is a valuable treatment method for patients with myofascial pain syndrome in the infraspinatus muscle. However, there is no botulinum neurotoxin injection guideline, and the most appropriate injection site based on topographical anatomic information for this injection to effectively treat myofascial pain syndrome in the infraspinatus muscle is unclear. The purpose of this study was to evaluate the intramuscular nerve terminal of the infraspinatus muscle and to suggest the most efficient botulinum neurotoxin injection sites. METHODS: This study used 5 formalin-embalmed and 10 fresh frozen cadavers with a mean age of 78.9 years. Sihler's staining was applied to evaluate the intramuscular nerve terminal of the infraspinatus muscle. The ultrasound scanning of the infraspinatus muscle was performed based on the surface landmarks and internal structures near the scapular region. RESULTS: The intramuscular nerve terminal was mostly observed in the medial third area of the infraspinatus muscle. The deltoid tubercle, inferior angle, and acromion of the scapula are useful as surface landmarks to scan the infraspinatus muscle. DISCUSSION: The proposed injection sites based on the intramuscular nerve terminal and surface landmarks can be regarded as accurate locations to reach the cluster area of the intramuscular nerve terminal and each compartment of the infraspinatus muscle to manage the myofascial pain syndrome in the infraspinatus muscle.

Musculoskeletal ultrasound diagnosis of quadrilateral space syndrome: A case report.

INTRODUCTION: Quadrilateral space syndrome (QSS) is a peripheral nerve entrapment disease, which can be misdiagnosed in clinic. In the past, QSS was mainly diagnosed by clinical symptoms combined with magnetic resonance imaging (MRI), electromyography (EMG), and arterial angiography. There are few reports on the diagnosis of QSS by musculoskeletal ultrasound (MSKUS) combined with clinical symptoms. PATIENT CONCERNS: A middle-aged female patient had posterolateral pain and numbness in her right shoulder for 2 months. DIAGNOSES: At first, she was diagnosed as suprascapular nerve entrapment, while EMG of suprascapular nerve and axillary nerve indicated that nerve conduction was normal. Then, MRI was performed, showing the shoulder had no abnormalities, and EMG and arterial angiography of upper limb showed no abnormalities too. Finally, she was diagnosed as QSS according to MSKUS and lidocaine block test. INTERVENTIONS: Two sealing treatments of axillary nerve block in quadrilateral space under the guidance of MSKUS were performed. OUTCOMES: After 2 treatments, the pain and numbness in her shoulder disappeared, and her shoulder could move normally. There was no recurrence after 3 months of follow-up. CONCLUSION: MSKUS is an effective method to diagnose QSS. It is fast, convenient and inexpensive, and is worth popularizing in clinic.

Anatomy of the nerves to the teres minor and the long head of the triceps brachii for electromyography.

BACKGROUND: We investigated the branching pattern and topographic anatomy of the nerves to the teres minor (Tm) and the long head of the triceps brachii (LHT) in relation to reference lines extending between surface landmarks, to identify the innervation patterns of, and the optimal needle placement points within, the Tm and the LHT. METHODS: The anatomical courses of the nerves to the Tm and the LHT were investigated in 37 upper limbs of fresh-frozen cadavers. Distances from the acromion to nerve penetration points, and crossing points of reference lines with the Tm and LHT were measured in 27 cadaveric upper limbs. RESULTS: The Tm was innervated by the axillary nerve in all specimens in three patterns, and the LHT was innervated exclusively by the radial nerve. Our dissection and measurements indicate that the midpoint of the reference line from the acromion to the inferior angle of the scapula is the optimal needle insertion point for the Tm. The target point for the LHT appears to be the one-third point of the reference line from the acromion to the medial epicondyle, or the two-thirds point of the reference line from the acromion to the axillary fold. CONCLUSIONS: We investigated the branching pattern of the nerves to the Tm and the LHT and propose optimal needle placement points for electromyography of the Tm and LHT.

Suprascapular nerve decompression in addition to rotator cuff repair: a prospective, randomized observational trial.

BACKGROUND: Tear and retraction of the supraspinatus (SS) and infraspinatus (IS) musculotendinous units and/or their repair may be associated with traction damage to the suprascapular nerve, potentially responsible for pain or weakness of the rotator cuff (RC). Arthroscopic release of the transverse scapular ligament at the suprascapular notch has been advocated to prevent or treat suprascapular nerve impairment associated with RC retraction and/or repair. The effect of this procedure on preoperative normal nerve function is, however, not well studied.We hypothesize that (1) decompression of the suprascapular nerve without preoperative pathologic neurophysiological findings will not improve clinical or imaging outcome and (2) suprascapular decompression will not measurably change suprascapular nerve function. METHODS: Nineteen consecutive patients with a magnetic resonance arthrography documented RC tear involving SS and IS but normal preoperative electromyography (EMG)/nerve conduction studies of the SS and IS were enrolled in a prospective, controlled trial involving RC repair with or without suprascapular nerve decompression at the suprascapular notch. Nine patients were randomized to undergo, and 10 not to undergo, a decompression of the suprascapular nerve. Patients were assessed clinically (Constant score, mobility, pain, strength, subjective shoulder value), with magnetic resonance imaging and neurophysiology preoperatively and at 3- and 12-month follow-up. RESULTS: There was no clinically relevant difference between the release and the non-release group in any clinical parameter at any time point. At magnetic resonance imaging, there was a slightly greater increase of fatty infiltration of the IS in the release group without any other differences between the 2 groups. Electromyographically, there were no pathologic findings in the non-release group at any time point. Conversely, 3 of the 9 patients of the release group showed pathologic EMG findings at 3 months, of whom 2 had recovered fully and 1 only partially at 12 months. CONCLUSION: In the presence of normal EMG findings, suprascapular nerve release added to arthroscopic RC repair is not associated with any clinical benefit, but with electromyographically documented, postoperative impairment of nerve function in 1 of 3 cases. Suprascapular nerve release does not therefore seem to be justified as an adjunct to RC repair if preoperative EMG findings document normal suprascapular nerve function. Based on these findings, the ongoing prospective randomized trial was terminated.

The use of a patch to augment rotator cuff surgery - A survey of UK shoulder and elbow surgeons.

BACKGROUND: Rotator cuff tears are a common cause of shoulder pain and can result in prolonged periods of pain, disability and absence from work. Rotator cuff repair surgery is increasingly used in an attempt to resolve symptoms but has failure rates of around 40%. There is a pressing need to improve the outcome of rotator cuff repairs. Patch augmentation increasingly being used within the NHS in an attempt to reduce repair failures. The aim of this survey was to determine current UK practice and opinion relating to the factors that influence choice of patch, current patient selection and willingness to assist with generation of improved evidence. METHODS: An online survey was sent to the surgeon members of the British Elbow and Shoulder Society (BESS). Questions covered respondent demographics, experience with patches, indications for patch augmentation and willingness to be involved in a randomised trial of patch augmented rotator cuff surgery. RESULTS: The response rate was 105/550 (19%). 58% of respondents had used a patch to augment rotator cuff surgery. 70% of patch users had undertaken an augmented repair within the last 6 months. A wide surgical experience in augmentation was reported (ranging 1 to 200 implants used). However, most surgeons reported low volume usage, with a median of 5 rotator cuff augmentation procedures performed. At least 10 different products had been used. Most of the patches used were constructed from human decellularised dermis tissue, although porcine derived and synthetic based patches had also been used. Only 3-5% stated they would undertake an augmented repair for small tears across ages, whereas 28-40% and 19-59% would do so for large or massive tears respectively. When assessing patient suitability, patient age seemed relevant only for those with large and massive tears. Half of the surgeons reported an interest in taking part in a randomised controlled trial (RCT) evaluating the role of patch augmentation for rotator cuff surgery, with a further 22% of respondent's undecided. CONCLUSIONS: A variety of patches have been used by surgeons to augment rotator cuff repair with a wide range of operator experience. There was substantial uncertainty about which patch to use and differing views on which patients were most suitable. There is a clear need for robust clinical evaluation and further research in this area.

Localization of the centers of intramuscular nerve dense regions of the rotator cuff muscles: a guide for botulinum toxin A injection for spasticity accompanied by shoulder pain / Localización de los centros de las regiones densas del nervio intramuscular de los músculos del manguito rotador: una guía para la inyección de toxina botulínica A por espasticidad con dolor de hombro

To accurately localize the centers of intramuscular nerve dense regions (CINDRs) of rotator cuff muscles. Twenty adult cadavers were used. The curves on skin connecting the superior angle of scapula with the acromion, and with the inferior angle of scapula were designed as the horizontal (H) and longitudinal (L) reference lines, respectively. One side of the rotator cuff muscles were removed and subjected to Sihler's staining to show intramuscular nerve dense regions, and the contralateral muscles' CINDRs were labeled with barium sulfate and scanned by computed tomography (to determine body surface projection points (P)). The intersection of the longitudinal line from point P to line H, and that of the horizontal line from point P to line L, were recorded as PH and PL, respectively. The projection of CINDRs on the anterior body surface across the saggital plane was defined as P' and the line connecting P to P' was recorded as Line PP'. Percentage positions of CINDRs of PH and PL on lines H and L, and the depths on line PP' were determined under the Syngo system. Two, four, one, and one CINDRs were identified in supraspinatus, infraspinatus, teres minor, and subscapularis muscles, respectively. The positions of PH of these CINDRs on the H-line are as follows: supraspinatus, 25.43 % and 26.59 %; infraspinatus, 53.85 %, 34.63 %, 35.96 % and 58.17 %; teres minor, 74.50 %; and subscapularis, 20.33 %. The PL on the L-line: supraspinatus, 11.09 % and 14.83 %; infraspinatus, 21.59 %, 27.93 %, 48.55 % and 57.52 %; teres minor, 68.28 %; and subscapularis, 52.82 %. The depth on line PP': supraspinatus, 24.83 % and 25.40 %; infraspinatus, 21.55 %, 16.10 %, 10.01 % and 8.14 %; teres minor, 13.27 %; and subscapularis, 22.88 %. The identification of these CINDRs should provide the optimal target position for injecting botulinum toxin A to treat rotator cuff muscles spasticity accompanied by shoulder pain and to improve the efficiency and efficacy of blocking target localization.

Con el objetivo de localizar con precisión los centros de las regiones densas del nervio intramuscular (CRDNI) de los músculos del manguito rotador, se utilizaron veinte cadáveres adultos. Las curvas en la piel que conectan el ángulo superior de la escápula con el acromion y con el ángulo inferior de la escápula se determinaron como líneas de referencia horizontales (H) y longitudinales (L), respectivamente. Se extrajo de un lado los músculos del manguito rotador y se sometió a la tinción de Sihler para mostrar regiones densas de nervios intramusculares, y los CRDNI de los músculos contralaterales se marcaron con sulfato de bario y se escanearon mediante tomografía computarizada (para determinar los puntos de proyección de la superficie corporal (P)). La intersección de la línea longitudinal desde el punto P a la línea H, y de la línea horizontal desde el punto P a la línea L, se registraron como PH y PL, respectivamente. La proyección de CRDNI en la superficie del cuerpo anterior a través del plano sagital se definió como P 'y la línea que conecta P a P' se registró como Línea PP '. Las posiciones porcentuales de los CRDNI de PH y PL en las líneas H y L, y las profundidades en la línea PP 'se determinaron bajo el sistema Syngo. Se identificaron dos, cuatro, uno y un CINDR en los músculos supraespinoso, infraespinoso, redondo menor y subescapular, respectivamente. Las posiciones de PH de estos CRDNI en la línea H son las siguientes: supraespinoso, 25,43 % y 26.59 %; infraspinatus, 53,85 %, 34,63 %, 35,96 % y 58,17 %; redondo menor, 74,50 %; y subescapular, 20,33 %. El PL en la línea L: supraespinoso, 11.09 % y 14.83 %; infraspinatus, 21,59 %, 27,93 %, 48,55 % y 57,52 %; redondo menor, 68.28 %; y subescapular, 52,82 %. La profundidad en la línea PP ': supraespinoso, 24,83 % y 25,40 %; infraspinatus, 21,55 %, 16,10 %, 10,01 % y 8,14 %; redondo menor, 13.27 %; y subescapularis, 22,88 %. La identificación de estos CRDNI debería proporcionar la posición objetivo óptima para inyectar la toxina botulínica A para tratar la espasticidad de los músculos del manguito rotador acompañada de dolor en el hombro y para mejorar la eficiencia y la eficacia del bloqueo de la localización del objetivo.

Effect of suprascapular nerve injury on rotator cuff enthesis.

BACKGROUND: Numerous reports have shown that retracted rotator cuff tears may cause suprascapular nerve injury, and nerve injury causes atrophy and fat accumulation in the rotator cuff muscles. However, the effect of suprascapular nerve injury on rotator cuff enthesis has not been directly defined. This study aimed to investigate the effect of suprascapular nerve injury on rotator cuff enthesis. METHODS: Twenty-four Wistar albino rats underwent bilateral transection of the suprascapular nerve. Additional 6 rats were used as the sham group. Bilateral supraspinatus and infraspinatus entheses were examined after 1, 4, 8, and 12 weeks of nerve transection. Histomorphometric analyses were performed for each zone of enthesis. RESULTS: Compared with normal enthesis, significant and consistent decrease in cellularity were observed in the tendon and bone at all time points (P < .001). Collagen bundle diameter in the tendon also decreased in a similar manner (P < .001). Apart from the tendon and bone zones, fibrocartilage and calcified fibrocartilage zones showed similar response, and significant decrease in cellularity was observed 8 weeks after nerve transection (P < .001). CONCLUSION: This study identifies suprascapular nerve injury as an underlying mechanism leading to compromise of the rotator cuff enthesis structure. Suprascapular nerve injury may be considered as an etiologic factor for the impaired healing after repair of a massive tear.

Origen del nervio subescapular inferior, patrones de ramificación y su contribución a la inervación del músculo subescapular / Origin of the inferior subscapular nerve, branching patterns and its contribution to the subscapular muscle innervation

El nervio subescapular inferior (NSI) inerva parcialmente al músculo subescapular (MSe) e inerva también al músculo redondo mayor (MRM). Diversas publicaciones determinan amplia variación en su origen en el Plexo Braquial (PB), pero existe poca evidencia de estas variaciones y del patrón de inervación del MSe y MRM en individuos latinoamericanos. El propósito de este estudio fue describir el origen del NSI en el PB, determinar número de ramos que le entrega al MSe y los patrones de ramificación. Se utilizaron 30 miembros superiores de individuos adultos, Brasileños; 13 del lado derecho y 17 del izquierdo, fijados en formaldehido al 10 %. Se disecaron las regiones axilares para exponer el fascículo posterior del plexo braquial (FPPB) y sus ramos. Se determinó si el origen del NSI era individual o procedía de un tronco común. Se cuantificó el número de ramos para el MSe, estableciendo patrones de ramificación. El NSI y sus ramos se agruparon según su origen y ramificación. En 3 de los casos (10 %) el NSI procedía de un tronco común con el nervio toracodorsal (NTD), 2 del lado izquierdo (6,6 %) y 1 del derecho (3,3 %); en 27 casos (90 %) procedía del nervio axilar (NAx), 15 del lado izquierdo (50 %) y 12 del derecho (40 %). En ningún caso, el origen fue directo del FPPB. Además, se cuantificó el número de ramos que aportaba a la inervación del MSe, observándose un promedio de 4 ramos (de 1 a 8 ramos) para el MSe. Se identificaron 4 patrones de ramificación del NSI hacia el MSe y el MRM. Tanto el origen como la distribución del NSI presentaron variaciones. Los datos aportados complementarán los conocimientos para la correcta enseñanza, el oportuno diagnóstico y la buena práctica quirúrgica de la zona axilar.

The inferior subscapular nerve (ISN) partially innervates the subscapular muscle (SbM) and also innervates the teres major muscle (TMM). Several publications determine wide variation in their origin from Brachial Plexus (BP), but there is little evidence of these variations and the innervation pattern of SbM and TMMin Latin American individuals. The purpose of this study was to describe the origin of the ISN from PB, to determine the number of branches that it gives to the SbM and the branching patterns. 30 upper limbs of cadavers of the Brazilian adult individuals were used; 13 on the right side and 17 on the left, fixed in 10 % formaldehyde. The axillary regions were dissected to expose the posterior fascicle of the brachial plexus (PFBP) and its branches. It was determined whether the origin of the NSI was individual or came from a common trunk. The number of branches for the SbM was quantified, establishing branching patterns. The ISN and its branches were grouped according to their origin and branching. In 3 of the cases (10 %) the ISN came from a common trunk with the thoracodorsal nerve (TDN), 2 from the left side (6.6 %) and 1 from the right side (3.3 %); in 27 cases (90 %) it came from the axillary nerve (AxN), 15 from the left side (50 %) and 12 from the right side (40 %). In no case, the origin was direct from the PFBP. In addition, the number of branches that contributed to the innervation of the SbM was quantified, with an average of 4 branches (from 1 to 8 branches) being observed for the SbM. Four branching patterns of the ISN towards the SbM and the TMM were identified. Both the origin and the distribution of the ISN presented many variations. The data provided will complement the knowledge for proper teaching, timely diagnosis and good surgical practice of the axillary area.

Arthroscopic rotator cuff repair with or without suprascapular nerve decompression in posterosuperior massive rotator cuff tears.

PURPOSE: The purpose of this study was to compare clinical outcomes of the arthroscopic rotator cuff repair (ARCR) in posterosuperior massive rotator cuff tears with or without arthroscopic suprascapular nerve (SSN) decompression in terms of arthroscopic release of the transverse scapular ligament. METHODS: Patients with a minimum follow-up of 24 months who underwent complete repair of torn rotator cuff involving a complete full-thickness tear of the supraspinatus and the infraspinatus were retrospectively evaluated. A total of 31 patients were treated with SSN decompression (group 1), and 36 patients were treated without SSN decompression (group 2). The clinical and functional outcomes were evaluated using the University of California, Los Angeles (UCLA) score, active range of motion (flexion and external rotation), and a visual analog scale (VAS) for pain. Repair integrity and fatty infiltration of the repaired cuff were examined by MRI. RESULTS: There was no significant difference between both groups across all measured at final follow-up: UCLA scores were 30.8 in group 1 and 30.8 in group 2 (p = 0.58); VAS scores were 14 mm and 13 mm, respectively (p = 0.35); active flexion angle were 149° and 153°, respectively (p = 0.35); and external rotation angles were 41° and 42°, respectively (p = 0.85). There were no significant differences in the re-tear rate (42% in group 1 and 33% in group 2, P = 0.75) and post-operative fatty infiltration scores of supraspinatus (P = 0.28) and infraspinatus (P = 0.37) in both groups. CONCLUSIONS: The functional outcomes and healing rate did not differ significantly between the groups with or without SSN decompression treated with arthroscopic cuff repair for massive RCT. At the short-term follow-up, SSN decompression was not found to have significantly affected the outcome of ARCR for posterosuperior massive RCT.

Quadrilateral space syndrome: The forgotten differential.

The quadrilateral space is bounded by the teres minor superiorly, the teres major inferiorly, the long head of the triceps medially and the shaft of the humerus laterally. The axillary nerve and posterior circumflex humeral artery pass through this space to enter the posterior compartment of the upper arm. Quadrilateral space syndrome (QSS) is caused by entrapment of the axillary nerve or its main branches and/or the posterior circumflex humeral artery in the quadrilateral space by internal or external compression. QSS can often be difficult to diagnose, given that patients may present with non-specific symptoms. As such, patients may be misdiagnosed with more common disorders of the shoulder. We report a case of QSS masquerading initially as rotator cuff pathology with positive impingement signs.

Intraoperative neuromonitoring during reverse shoulder arthroplasty.

BACKGROUND: The aim of this study was to evaluate the risk of nerve injury with neuromonitoring during reverse total shoulder arthroplasty. MATERIALS: This study included 15 shoulders of 15 patients (11 females and 4 males) who underwent reverse total shoulder arthroplasty. The mean age was 74.8 ± 4.4 years. Nine shoulders had cuff tear arthropathy, 4 had massive rotator cuff tears, 2 had osteoarthritis, and 1 had rheumatoid arthritis. The somatosensory evoked potentials of the median nerve, transcranial motor evoked potentials, and free-electromyograms from 6 upper-extremity muscles were measured intraoperatively. We defined a nerve alert as 50% amplitude attenuation or 10% latency prolongation of the somatosensory evoked potentials and transcranial motor evoked potentials and sustained neurotonic discharge on free-electromyogram. RESULTS: Thirty-one alerts were recorded in 11 patients. The axillary nerve was associated with 17 alerts. Eleven alerts occurred during the glenoid procedure and 5 alerts occurred during the humeral procedure. One patient who did not recover from the alert of the axillary nerve had clinically incomplete paralysis of the deltoid muscle. CONCLUSION: The present findings suggest that the axillary nerve was the nerve most frequently exposed to the risk of injury, especially during glenoid and humeral implantation.

Characterization of an anatomic safe zone surrounding the lower subscapular nerve during an open deltopectoral approach.

BACKGROUND: Due to anatomic variance in subscapular nerve innervation patterns, it is theorized that the dysfunction of the subscapularis could be the result of iatrogenic denervation during mobilization of the subscapularis while exposing the anterior glenohumeral joint in anterior surgical approaches. The purpose of this study was to describe innervation patterns of the subscapularis and to characterize a safe zone when conducting an anterior surgical approach. METHODS: The study used 6 human cadaveric shoulder specimens (12 shoulders total). A deltopectoral approach was used to expose the axillary nerve back to the posterior cord of the brachial plexus and reveal the origins of the upper and lower subscapularis nerves. An anatomic safe zone was characterized by measuring distances from both the upper and lower subscapularis nerve insertions with respect to that of the lateral border of the conjoint tendon, the bicipital groove, superior border of the subscapularis, and the axillary nerve (for the lower subscapular nerve only) with the arm in 30° abduction. RESULTS: The anatomic safe zone of the subscapular nerves medial to the conjoint tendon is less than 32 mm. In relation to the axillary nerve, the safe zone is less than 10 mm inferiorly and 15 mm medially. CONCLUSIONS: This described safe zone with respect to the lateral border of the conjoint tendon and axillary nerve is aimed to provide guidance to reduce iatrogenic injury of the subscapular nerves during anterior shoulder exposure. Extra care should be undertaken while dissecting past this safe zone to prevent iatrogenic subscapular nerve injury.

Intramuscular innervation of the subscapularis muscle and its clinical implication for the BoNT injection: An anatomical study using the modified Sihler's staining.

Shoulder pain is commonly associated with spasticity of the rotator cuff muscles including the subscapularis (SSC). The aim of this study was to elucidate the intramuscular innervation pattern of the SSC using the modified Sihler's staining technique to facilitate the targeting of botulinum neurotoxin (BoNT) injections to alleviate shoulder spasticity. Ten SSC specimens (mean age, 81.5 years) were used in this study. Modified Sihler's staining was used to clarify the muscle and to stain the intramuscular nerves. Their extramuscular and intramuscular innervation patterns were examined. The upper subscapular, lower subscapular, thoracodorsal, and axillary nerves (USN, LSN, TDN, and AXN) innervated the SSC in 100%, 80%, 20%, and 40% of specimens, respectively. There was an anastomosis between the USN and LSN in the central portion of the SSC in more than half of the cases. The USN innervated the overall portion of the muscle. In contrast, the additional branches from the TDN and AXN innervated the inferior SSC portion. The superficial branches of the USN were mostly distributed in the superior SSC portion while the deep branches were distributed in the inferior portion. As a major intramuscular nerve within the SSC, the USN should be targeted by a BoNT injection. Regarding the USN distribution, the aim should be to spread the BoNT injectate within the central SSC portion. For supplementary injection to the AXN, the lateral approach would be more appropriate than alternatives. A physician performing a BoNT injection should consider the intramuscular innervation of the SSC portion. Clin. Anat. 32:110-116, 2019. © 2018 Wiley Periodicals, Inc.

Proposed surgical technique to facilitate targeted reinnervation of the infraspinatus: A cadaveric feasibility study.

Restoration of shoulder lateral rotation remains a significant challenge following brachial plexus injury. Transfer of the accessory nerve to suprascapular nerve (SSN) has been widely performed, although with generally poor outcomes for lateral rotation. A recent report suggested a selective infraspinatus reinnervation technique using a radial nerve branch for SSN transfer. This cadaveric study was performed in 7 specimens (14 shoulders). We present technical modifications to achieve additional length to the recipient nerve (suprascapular) that would facilitate direct repair. Key elements of the technique are (1) isolation of the SSN immediately distal to its motor branch to supraspinatus near the superior transverse scapular ligament; and (2) delivery of the transected SSN through the spinoglenoid notch and deep to the infraspinatus for emergence in the infraspinatus-teres minor interval. Nerve overlap of at least 21 mm was observed in all 14 dissected shoulders between the harvested SSN and radial nerve branches. The mean nerve overlap between harvested branches was 26 mm (range 21-32 mm). The mean harvested SSN length was 59 mm (range 46-80 mm). The mean length of the harvested radial nerve branch was 72 mm (range 65-85 mm). No measurements were significantly different between left and right shoulders or between males and females (smallest P value = 0.1249). Nerve diameter of the two harvested branches was judged to be appropriately compatible for surgical coaptation in all 14 dissected shoulders. We present a variation on a described technique to increase recipient suprascapular nerve length. Additional length of the recipient nerve is achieved through utilization of a more proximal dissection of the suprascapular nerve near the level of the superior transverse scapular ligament and delivering the nerve through the teres minor-infraspinatus interval. These surgical modifications are of clinical interest when selective reinnervation of the infraspinatus muscle is considered. We believe such a targeted approach can potentially increase shoulder lateral rotation function. Clin. Anat. 32:131-136, 2019. © 2018 Wiley Periodicals, Inc.

Cadaveric Dissection of the Axillary Nerve: An Investigation of Extra-Muscular and Intra-Muscular Branching Patterns.

BACKGROUND: Variations in the axillary nerve branching patterns have been reported. The aim of the study is to investigate the extra- and intra-muscular course of the axillary nerve and quantify the regional innervation of the deltoid. METHODS: In fresh frozen specimens, the origin of the axillary nerve from the posterior cord of the brachial plexus and its extra- and intra-muscular course were identified. Muscle dimensions, branching patterns and the distance from the axillary nerve origin to major branches were measured. The weights of muscle segments supplied by major branches of the axillary nerve were recorded. RESULTS: Twenty-three cadaveric dissections were completed. The axillary nerve bifurcated within the quadrangular space in all cases. The mean distance from the origin to bifurcation of the axillary nerve was 39 ± 13 mm; from axillary nerve bifurcation to the teres minor branch was 13 ± 6 mm; and from axillary nerve bifurcation to the middle branch of anterior division was 26 ± 11 mm. The nerve to teres minor and superior lateral brachial cutaneous nerve originated from the posterior division or common trunk in all cases. No fibrous raphe were identified separating anterior, middle and posterior deltoid segments. The anterior division of axillary nerve supplied 85 ± 4% of the deltoid muscle (by weight). The posterior division supplied 15 ± 4% of the deltoid muscle (by weight). The posterior deltoid was supplied by both anterior and posterior divisions in 91.3% of cases. CONCLUSIONS: This study demonstrates a consistent branching pattern of the axillary nerve. The anterior division of the axillary nerve innervates all three deltoid segments in most instances (85% of the deltoid by weight). This study supports the concept of re-innervation of the anterior division alone in isolated axillary nerve injuries.

Reversal of Fatty Infiltration After Suprascapular Nerve Compression Release Is Dependent on UCP1 Expression in Mice.

BACKGROUND: In large rotator cuff tears, retraction of the supraspinatus muscle creates suprascapular nerve traction and compression. However, suprascapular nerve transection, when used in previous models, is different from chronic compression of the suprascapular nerve in patients. To define the role of suprascapular nerve chronic injury in rotator cuff muscle atrophy and fatty infiltration, we developed a novel reversible suprascapular nerve compression mouse model. QUESTIONS/PURPOSES: We asked: (1) Can suprascapular nerve injury be induced by compression but reversed after compression release? (2) Can muscle fatty infiltration be induced by suprascapular nerve compression and reversed after compression release? (3) Is white fat browning involved in fatty infiltration resorption? METHODS: Mice in a common strain of C57BL/6J were randomly assigned to suprascapular nerve transection (n = 10), nerve compression (n = 10), nerve compression and release (n = 10), or sham control (n = 10) groups. To study the role or white fat browning on muscle fatty infiltration, additional UCP1 reporter mice (n = 4 for nerve compression and n = 4 for nerve compression release) and knockout mice (n = 4 for nerve compression and n = 4 for nerve compression release) were used. Nerve injury was testified using osmium tetroxide staining and neural muscular junction staining and then semiquantified by counting the degenerating axons and disrupted junctions. Muscle fatty infiltration was evaluated using Oil Red O staining and then semiquantified by measuring the area fraction of fat. Immunofluorescent and Oil Red O staining on UCP1 transgenic mice was conducted to testify whether white fat browning was involved in fatty infiltration resorption. Ratios of UCP1 positively stained area and fat area to muscle cross-section area were measured to semiquantify UCP1 expression and fatty infiltration in muscle by blinded reviewers. Analysis of variance with Tukey post hoc comparisons was used for statistical analysis between groups. RESULTS: Suprascapular nerve injury was induced by compression but reversed after release. The ratios of degenerating axons were: sham control: 6% ± 3% (95% confidence interval [CI], 3%-10%); nerve compression: 58% ± 10% (95% CI, 45%-70% versus sham, p < 0.001); and nerve compression and release: 15% ± 9% (95% CI, 5%-26% versus sham, p = 0.050). The supraspinatus muscle percentage area of fatty infiltration increased after 6 weeks of nerve compression (19% ± 1%; 95% CI, 18%-20%; p < 0.001) but showed no difference after compression release for 6 weeks (5% ± 3%; 95% CI, 1%-10%; p = 0.054) compared with sham (2% ± 1%; 95% CI, 1%-3%). However, the fat area fraction in UCP1 knockout mice did not change after nerve compression release (6% ± 1%; 95% CI, 4%-8% at 2 weeks after compression and 5% ± 0.32%; 95% CI, 4%-6% after 2 weeks of release; p = 0.1095). CONCLUSIONS: We developed a clinically relevant, reversible suprascapular nerve compression mouse model. Fatty infiltration resorption after compression release was mediated through white fat browning. CLINICAL RELEVANCE: If the mechanism of browning of white fat in rotator cuff muscle fatty infiltration can be confirmed in humans, a UCP1 agonist may be an effective treatment for patients with suprascapular nerve injury.

Long-Term Outcome of Brachial Plexus Reimplantation After Complete Brachial Plexus Avulsion Injury.

BACKGROUND: Complete brachial plexus avulsion injury is a severe disabling injury due to traction to the brachial plexus. Brachial plexus reimplantation is an emerging surgical technique for the management of complete brachial plexus avulsion injury. OBJECTIVE: We assessed the functional recovery in 15 patients who underwent brachial plexus reimplantation surgery after complete brachial plexus avulsion injury with clinical examination and electrophysiological testing. METHODS: We included all patients who underwent brachial plexus reimplantation in our institution between 1997 and 2010. Patients were assessed with detailed motor and sensory clinical examination and motor and sensory electrophysiological tests. RESULTS: We found that patients who had reimplantation surgery demonstrated an improvement in Medical Research Council power in the deltoid, pectoralis, and infraspinatous muscles and global Medical Research Council score. Eight patients achieved at least grade 3 MRC power in at least one muscle group of the arm. Improved reinnervation by electromyelography criteria was found in infraspinatous, biceps, and triceps muscles. There was evidence of ongoing innervation in 3 patients. Sensory testing in affected dermatomes also showed better recovery at C5, C6, and T1 dermatomes. The best recovery was seen in the C5 dermatome. CONCLUSIONS: Our results demonstrate a definite but limited improvement in motor and sensory recovery after reimplantation surgery in patients with complete brachial plexus injury. We hypothesize that further improvement may be achieved by using regenerative cell technologies at the time of repair.

Evaluation of infraspinatus reinnervation and function following spinal accessory nerve to suprascapular nerve transfer in adult traumatic brachial plexus injuries.

PURPOSE: Our objective was to determine the prevalence and quality of restored external rotation (ER) in adult brachial plexus injury (BPI) patients who underwent spinal accessory nerve (SAN) to suprascapular nerve (SSN) transfer, and to identify patient and injury factors that may influence results. METHODS: Fifty-one adult traumatic BPI patients who underwent SAN to SSN transfer between 2000 and 2013, all treated less than 1 year after injury with >1 year follow-up. The primary outcome measured was shoulder ER. The outcomes we utilized included "clinically useful ER" (motion ≥ -35° with ≥MRC 2 strength), modified British Medical Research Council (MRC) grading, and electromyographic (EMG) reinnervation. RESULTS: EMG evidence of re-innervation was found in 85% of patients. Surgery resulted in improved ER in 41% (21/51) of shoulders at an average of 28 months follow-up. Of these, only 31% (17/51) had clinically useful ER. The average ER active range of motion was 12° from full internal rotation (Range: -60° to 90°) and MRC grade 2.2 (2-4). The only predictor of ER improvement was an isolated upper trunk (C5-C6) injury. Improved ER was clinically evident in 76%, 37% and 26% of upper trunk (UT), C5-C6-C7 and panplexus injuries, respectively (P < 0.03). CONCLUSIONS: Although 85% had EMG signs of recovery, the SAN to SSN transfer failed to provide useful recovery of ER through reinnervation of the infraspinatus muscle in injuries involving more levels than a C5-C6 root/upper trunk pattern. In patients with greater than C5-6 level injuries alternatives to SAN to SSN transfer should be considered to restore shoulder ER. © 2016 Wiley Periodicals, Inc. Microsurgery 37:365-370, 2017.