Anatomical Study of the Axillary Nerve: Description of a Surgical Blind Zone

A Surgical Framework for the Management of Incomplete Axillary Nerve Injuries

BACKGROUND

 Axillary nerve injury is the most common nerve injury affecting shoulder function. Nerve repair, grafting, and/or end-to-end nerve transfers are used to reconstruct complete neurotmetic axillary nerve injuries. While many incomplete axillary nerve injuries self-resolve, axonotmetic injuries are unpredictable, and incomplete recovery occurs. Similarly, recovery may be further inhibited by superimposed compression neuropathy at the quadrangular space. The current framework for managing incomplete axillary injuries typically does not include surgery.

METHODS

 This study is a retrospective analysis of 23 consecutive patients with incomplete axillary nerve palsy who underwent quadrangular space decompression with additional selective medial triceps to axillary end-to-side nerve transfers in 7 patients between 2015 and 2019. Primary outcome variables included the proportion of patients with shoulder abduction M3 or greater as measured on the Medical Research Council (MRC) scale, and shoulder pain measured on a Visual Analogue Scale (VAS). Secondary outcome variables included pre- and postoperative Disabilities of the Arm, Shoulder, and Hand Questionnaire (DASH) scores.

RESULTS

 A total of 23 patients met the inclusion criteria and underwent nerve surgery a mean 10.7 months after injury. Nineteen (83%) patients achieved MRC grade 3 shoulder abduction or greater after intervention, compared with only 4 (17%) patients preoperatively (p = 0.001). There was a significant decrease in VAS shoulder pain scores of 4.2 ± 2.5 preoperatively to 1.9 ± 2.4 postoperatively (p < 0.001). The DASH scores also decreased significantly from 48.8 ± 19.0 preoperatively to 30.7 ± 20.4 postoperatively (p < 0.001). Total follow-up was 17.3 ± 4.3 months.

CONCLUSION

 A surgical framework is presented for the appropriate diagnosis and surgical management of incomplete axillary nerve injury. Quadrangular space decompression with or without selective medial triceps to axillary end-to-side nerve transfers is associated with improvement in shoulder abduction strength, pain, and DASH scores in patients with incomplete axillary nerve palsy.

The surgical anatomy of the axillary approach for nerve transfer procedures targeting the axillary nerve

PURPOSE

The exact relational anatomy for the anterior axillary approach, targeting the axillary nerve for nerve transfers/grafts, has not been fully investigated. Therefore, this study aimed to dissect and document the gross anatomy surrounding this approach, specifically regarding the axillary nerve and its branches.

METHODS

Fifty-one formalin-fixed cadavers (98 axilla) were bilaterally dissected simulating the axillary approach. Measurements were taken to quantify distances between identifiable anatomical landmarks and relevant neurovascular structures encountered during this approach. The musculo-arterial triangle, described by Bertelli et al., to aid in identification on localization of the axillary nerve, was also assessed.

RESULTS

From the origin of the axillary nerve till (1) latissimus dorsi was 62.3 ± 10.7 mm and till (2) its division into anterior and posterior branches was 38.8 ± 9.6 mm. The origin of the teres minor branch along the posterior division of the axillary nerve was recorded as 6.4 ± 2.9 mm in females and 7.4 ± 2.8 mm in males. The musculo-arterial triangle reliably identified the axillary nerve in only 60.2% of the sample.

CONCLUSION

The results clearly demonstrate that the axillary nerve and its divisions can be easily identified with this approach. The proximal axillary nerve, however, was situated deep and therefore challenging to expose. The musculo-arterial triangle was relatively successful in localising the axillary nerve, however, more consistent landmarks such as the latissimus dorsi, subscapularis, and quadrangular space have been suggested. The axillary approach may serve as a reliable and safe method to reach the axillary nerve and its divisions, allowing for adequate exposure when considering a nerve transfer or graft.

A multidisciplinary approach to the management of brachial plexus injuries: experience from the Mayo Clinic over 100 years

A multidisciplinary brachial plexus clinic has been a relatively new concept, offering different surgical speciality perspectives on the treatment of brachial plexus injuries. The resulting collaborative effort has proven to be greater than the sum of its parts. In this review, the history, philosophy of care, development/implementation and impact of a creation of a multidisciplinary brachial plexus team at the Mayo Clinic are detailed.

Surgical Treatment of Iatrogenic Nerve Injury Following Arthroscopic Capsulolabral Repair

PURPOSE

Case reports of nerve injuries following arthroscopic capsulolabral repair emphasize the proximity of major nerves to the glenoid. This study describes preoperative localization using nerve-sensitive magnetic resonance imaging in a small cohort of patients with iatrogenic nerve injuries following arthroscopic capsulolabral repair and the outcomes of nerve repair in these patients.

METHODS

Cases of iatrogenic nerve injury following arthroscopic capsulolabral repair referred to 2 surgeons from January 2017 to December 2019 were identified. Clinical charts, electrodiagnostic testing, magnetic resonance imaging studies, and operative reports were reviewed.

RESULTS

Four cases of iatrogenic nerve injury were identified. The time to presentation to our institution ranged from 2 weeks to 8 years. The axillary nerves in 3 cases were tethered by a suture at the inferior glenoid, whereas 1 case had a suture tied around the radial and median nerves inferior to the glenohumeral joint capsule. One case underwent excision and nerve transfer, 1 underwent excision and nerve repair, and 2 underwent suture removal and neurolysis. Open and arthroscopic approaches, including a recently described approach to the axillary nerve in the "blind zone," were used. Three cases demonstrated good recovery of all affected motor and sensory functions after surgery. At the 10-month follow-up, 1 case had persistent weakness, but there was evidence of axonal regeneration on electrodiagnostic testing.

CONCLUSIONS

Arthroscopic capsulolabral repair places regional nerves, particularly the axillary nerve, at risk owing to their proximity to the joint capsule and inferior glenoid. Patients with neuropathic pain in the distribution of affected nerves with corresponding sensorimotor loss following arthroscopic capsulolabral surgery should undergo focused magnetic resonance imaging with nerve-sensitive sequences and electrodiagnostic testing to localize the injury. The use of multiple surgical windows to the axillary nerve in the "blind zone" enables full visualization for neurolysis, suture removal, and nerve repair or transfer.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic V.

Definition of a Risk Zone for the Axillary Nerve Based on Superficial Landmarks

BACKGROUND

The aim of this study was to investigate the axillary nerve's location along superficial anatomical landmarks, and to define a convenient risk zone.

METHODS

A total of 123 upper extremities were evaluated. After dissection of the axillary nerve, the vertical distance between the upper border of the anterolateral edge of the acromion and the proximal border of the nerve was measured. Furthermore, the interval between the proximal border and the distal border of the axillary nerve's branches was evaluated. The interval between the distal border of the branches and the most distal part of the lateral humeral epicondyle was measured. The distance between the anterolateral edge of the acromion and the lateral humeral epicondyle was evaluated. Measurements were expressed as proportions with respect to the distance between the acromion and the lateral humeral epicondyle.

RESULTS

The distance between the acromion and the proximal border of the axillary nerve's branches was at a height of 10 percent of the distance between the acromion and the lateral humeral epicondyle, starting from the acromion (90 percent when starting from the lateral humeral epicondyle). The interval between the proximal and distal margins of the axillary nerve's branches was between 10 percent and 30 to 35 percent of this interval, starting from the acromion (65 to 70 percent when starting from the lateral humeral epicondyle).

CONCLUSIONS

The authors were able to locate the branches of the axillary nerve at an interval between 10 and 35 percent of the distance between the acromion and the lateral humeral epicondyle, starting from the acromion. This makes the proximal third of this distance an easily applicable risk zone during shoulder surgery.

Feasibility of arthroscopic decompression of the axillary nerve in the quadrilateral space: Cadaver study

INTRODUCTION

Axillary nerve compression is a rare, but disabling condition. The three main causes are quadrilateral space syndrome among young athletes, compression due to an inferior glenohumeral osteophyte in early osteoarthritis and isolated teres minor atrophy secondary to triceps hypertrophy. The diagnosis is clinical, but may be reinforced by an electromyogram or corticosteroid injection. The usual surgical treatment is open nerve decompression using a posterior approach. Arthroscopy is a less invasive approach that should be useful in theory.

HYPOTHESIS

Arthroscopic decompression of the axillary nerve is safe and less invasive than open techniques.

MATERIAL AND METHODS

Arthroscopic nerve decompression was performed as described by PJ Millet and TR Gaskill on 10 shoulders from 6 frozen cadavers. An open posterior approach was then made to verify the effectiveness of the nerve decompression.

RESULTS

The axillary nerve and its branches, the circumflex artery and the triceps were always sufficiently released in the space below the joint capsule. When the joints were subsequently opened by a posterior approach, complete nerve decompression was confirmed in all cases with no iatrogenic lesions.

DISCUSSION

The good results of this study are encouraging, but should be supplemented with a comparative study in patients of open versus arthroscopic axillary nerve release.

CONCLUSION

We think this arthroscopic technique is a good option for treating axillary nerve compressions. The complication risk is expected to be low.

LEVEL OF EVIDENCE

IV.

Outcomes of Microneurolysis of Hourglass Constrictions in Chronic Neuralgic Amyotrophy

PURPOSE

Wide variability in the recovery of patients affected by neuralgic amyotrophy (NA) is recognized, with up to 30% experiencing residual motor deficits. Using magnetic resonance imaging and ultrasound (US), we identified hourglass constrictions (HGCs) in all affected nerves of patients with chronic motor paralysis from NA. We hypothesized that chronic NA patients undergoing microsurgical epineurolysis and perineurolysis of constrictions would experience greater recovery compared with patients managed nonsurgically.

METHODS

We treated 24 patients with chronic motor palsy from NA and HGCs identified on magnetic resonance imaging and US either with microsurgical epineurolysis and perineurolysis of HGCs (11 of 24) or nonsurgically (13 of 24). Muscle strength (both groups) and electrodiagnostic testing (EDX) (operative group) was performed before and after surgery. Preoperative EDX confirmed muscle denervation in the distribution of affected nerve(s). All patients met criteria for microneurolysis: 12 months without improvement since onset or failure of clinical and EDX improvement after 6 months documented by 3 successive examinations, each at least 6 weeks apart.

RESULTS

Mean time from onset to surgery was 12.5 ± 4.0 months. Average time to most recent post-onset follow-up occurred at 27.3 months (range, 18-42 months; 15 nerves). Average time to latest follow-up among nonsurgical patients was 33.6 months (range, 18-108 months; 16 nerves). Constrictions involved individual fascicular groups (FCs) of the median nerve and the suprascapular, axillary and radial nerves proper (HGCs). Nine of 11 operative patients experienced clinical recovery compared with 3 of 13 nonsurgical patients. EMG revealed significant motor unit recovery from axonal regeneration in the operative group.

CONCLUSIONS

Microsurgical epineurolysis and perineurolysis of FCs and HGCs was associated with significantly improved clinical and nerve regeneration at an average follow-up of 14.8 months compared with nonsurgical management. We recommend microneurolysis of HGCs and FCs as a treatment option for patients with chronic NA who have failed to improve with nonsurgical treatment.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Overcoming the Axillary Nerve Blind Spot Through the Deltopectoral and Axillary Approaches: A Cadaveric Study

PURPOSE

The aim of this study was to evaluate the feasibility of exploring the axillary nerve (AN) at the 6 o'clock position (blind spot) using the deltopectoral approach, with the interval lateral to the conjoint tendon (CJT) or combined with the axillary approach.

METHODS

Four ANs were dissected combining the deltopectoral approach-medial to the CJ (A), the deltopectoral approach-lateral to the CJT (B) and the axillary approach (C) in 3 sequences: A-B-C, B-A-C, and C-B-A. After the first approach was completed, the proximal and distal margins were marked. Additional exposure with the second and third approaches and the 6 o'clock position were also marked. Then, the AN was excised and the amount of exposed nerve with the 3 approaches was measured.

RESULTS

The deltopectoral approach-medial to the conjoint tendon did not allow exposure of the AN at the 6 o'clock position. Six o'clock position exposure was accomplished using the lateral interval of the deltopectoral and the axillary approaches. A deltopectoral approach lateral to the CJT allowed exploration of the AN at the blind spot, but not the terminal branches. The axillary approach was able to expose the AN at the 6 o'clock position, the terminal branches, but not the nerve-muscle junction. Combining the 3 approaches exposed 81% to 94% of the total length of the AN.

CONCLUSIONS

The deltopectoral approach allowed visualization of the AN at the 6 o'clock position when explored lateral to the CJT. The axillary approach allowed visualization of the terminal branches of the AN and the 6 o'clock position of the glenoid.

CLINICAL RELEVANCE

The deltopectoral approach lateral to the conjoint tendon allows the surgeon to assess continuity of the AN at the 6-o'clock position and to perform a neurolysis. If nerve repair, nerve grafting, or nerve transfer is attempted, a combination of the 3 approaches could be used.

Exploration of the axillary nerve through an open posterior endoscopic-assisted (OPEA) approach: First clinical experience

INTRODUCTION

Previous studies have described a segment of the axillary nerve (AN) that cannot be surgically explored through the deltopectoral and posterior surgical open approaches (blind zone). We present the first two cases using an endoscopic-assisted approach to explore the AN through a posterior approach.

MATERIAL AND METHODS

Two patients were evaluated, in whom clinical, electrodiagnostic testing, and MRI could not localize the level of the AN dysfunction. An open posterior endoscopic-assisted (OPEA) approach was performed 4 and 9 months after injury in an attempt to visualize all segments of the AN. Photographs and videos were taken to evaluate the intraoperative visualization of the AN and provide long-term clinical follow-up.

RESULTS

Almost the entire AN was visualized with the scope through the OPEA approach, avoiding the deltopectoral approach. No AN lesion was found during the nerve exploration. A triceps branch to AN transfer, using the previous posterior approach, was performed. Patients in both groups achieved a deltoid muscle function of BMRC grade 4 after 24 and 9 months, respectively.

CONCLUSION

The exploration of the AN through the OPEA approach was a useful strategy to visualize the blind zone of the AN without requiring the addition of a deltopectoral approach. We believe this novel technique has a role in selected cases of AN injury.

Unusual anatomic variant of the axillary nerve challenging the deltopectoral approach to the shoulder: a case report

Background

The deltopectoral approach is a well-described surgical approach to the proximal humerus and glenohumeral joint. One of the structures at risk during this approach is the axillary nerve. Typically, the axillary nerve arises off the posterior cord of the brachial plexus and courses lateral to the proximal humerus and inferior to the glenohumeral joint, exiting the axilla through the quadrangular space. We describe a case of an aberrant axillary nerve, coursing anteriorly across the glenohumeral joint within the deltopectoral groove encountered during a reverse total shoulder arthroplasty.

Case presentation

A 73-year-old female presented complaining of atraumatic progressive right shoulder pain of several months duration. Clinical and radiographic findings were consistent with advanced rotator cuff arthropathy. After failing appropriate non-operative treatment, the patient elected to undergo reverse total shoulder arthroplasty. During the deltopectoral approach to the glenohumeral joint, the axillary nerve was found to be coursing deep to the cephalic vein within the deltopectoral interval. The nerve was isolated and protected, and the glenohumeral joint was accessed via a small window in the anterior deltoid muscle. The remainder of the procedure was performed without complication. The patient was found to be healing well and with normal axillary nerve function at 4-month follow-up.

Conclusions

Neurologic lesions are well-documented complications of reverse total shoulder arthroplasty. The integrity of the axillary nerve is of particular importance to reverse total shoulder arthroplasty as it innervates the deltoid and post-operative function of the extremity is dependent upon a functioning deltoid muscle. Extreme care must be taken to avoid insult to the axillary nerve and any aberrant paths it may course around the glenohumeral joint.

Arthroscopic-assisted exploration of the axillary nerve through a posterior open approach: A novel technique

INTRODUCTION

Previous studies have described a segment of the axillary nerve (AN) that cannot be surgically explored through standard open surgical approaches (blind zone). This study aimed to evaluate the feasibility of combining the standard posterior approach to the AN by using an arthroscope to visualize all segments of the AN.

MATERIAL AND METHODS

Four fresh-frozen shoulders in two adult human torsos were included in the study. A standard posterior approach was performed on each shoulder, and a dry arthroscopy was performed through the surgical opening in an attempt to visualize all the segments of the AN. A surgical clip was placed at the most proximal and anterior segment of the AN that could be visualized with the arthroscope. A standard open deltopectoral approach was then performed to determine the exact location of the surgical clip and its relation to the origin of the AN.

RESULTS

All segments of the AN (including the blind zone) were visualized from the quadrilateral space to their origin from the posterior cord in all four specimens. The surgical clip was found at an average of 1 cm (range from 0.5 to 1.5 cm) from the origin of the AN from the posterior cord.

CONCLUSIONS

This cadaveric study shows that it is feasible to visualize all segments of the AN (including the blind zone) using this novel approach that combines the use of the standard posterior approach to the AN with dry arthroscopic exploration. Clinical studies are necessary to evaluate the utility of this novel approach.