PM R 7 (2015) 889-894
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Case Presentation
Lateral Antebrachial Cutaneous Nerve Entrapment After Shoulder Arthroscopy: A Case Report Herbie Yung, MD, Gerritt M. Lagemann, MD, Albert Lin, MD, Steven L. Orebaugh, MD, Megan H. Cortazzo, MD
Abstract The lateral antebrachial cutaneous nerve (LABCN) is a distal sensory branch of the musculocutaneous nerve that innervates the radial aspect of the forearm. Cases of LABCN injury from trauma and chronic compression have been reported. A case of musculocutaneous nerve injury after a biceps tenodesis has also been reported. This case report describes an LABCN injury and forearm pain after a biceps tenodesis procedure. Using a multifaceted diagnostic approach of electrodiagnostics and magnetic resonance neurography, the site of compression was appropriately localized. The patient ultimately achieved relief after a surgical decompression.
Introduction The lateral antebrachial cutaneous nerve (LABCN) is a distal sensory branch of the musculocutaneous nerve. Motor branches of the musculocutaneous nerve innervate the coracobrachialis, biceps, and brachialis in the arm. The LABCN is most commonly found to emerge between the lateral aspect of the biceps tendon and the brachialis at the level of the interepicondylar line [1]. It is typically asymptomatically compressed during pronation and supination with the elbow in extension [2]. Multiple cases of LABCN injury from trauma have been documented, such as antecubital fossa venipuncture [3,4], slam dunking a basketball [5], and olecranon fracture [6]. LABCN injury has also been reported in overuse injury from prolonged elbow flexion during windsurfing [7], and chronic compression injuries have been reported over the antecubital fossa from a camera bag [8] and from a glomus tumor in the forearm [9]. A surgical case series of LABCN injury has been reported related to 2 cases of biceps injuryd1 case of distal biceps attachment avulsion and 1 case of biceps tendon rupture [10]. A case of musculocutaneous nerve entrapment also has been reported after biceps tenodesis and was eventually surgically repaired [11].
This report describes the clinical presentation, electrodiagnostic and radiologic findings, and treatment course in a patient who experienced LABCN entrapment after right shoulder surgery. Case Presentation The patient is a 51-year-old right-handed man presenting with 1.5 years of anterior shoulder pain from tendinopathy of the long head of the biceps, acromioclavicular impingement, and bursitis. His shoulder magnetic resonance imaging scan revealed moderate supraspinatus tendinopathy, a partial infraspinatus tear, mild tendinopathy of the subscapularis, and mild acromioclavicular joint arthrosis. He underwent an arthroscopic right shoulder procedure, including subscapularis repair, open biceps tenodesis, subacromial decompression with formal acromioplasty, and debridement with a bursectomy. Shoulder arthroscopy demonstrated a torn proximal long head of the biceps tendon. Biceps tenodesis was performed given the patient’s young age and active lifestyle. Anesthesia consisted of a right interscalene block under ultrasound guidance, followed by propofol-ketamine sedation in the beach-chair position. The patient’s initial recovery was unremarkable, and he wore a shoulder abduction sling for 4 weeks.
1934-1482/$ - see front matter ª 2015 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2015.03.009
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LABCN Entrapment After Shoulder Arthroscopy
The patient initially presented to the pain clinic 26 days after surgery with worsening pain, which began about 1 week after the surgery. He described the development of a dull, aching, throbbing pain with numbness and tingling in the radial aspect of the right forearm, from the first carpal-metacarpal to the elbow crease but not involving the biceps. The pain was categorized as severe and affected him at night, preventing good-quality sleep. He noted some relief upon taking oral acetaminophen-hydrocodone. Physical examination showed mild right biceps atrophy and a wellhealed surgical incision. He demonstrated 4/5 strength with right elbow flexion limited by pain, 4/5 strength with right wrist flexion and extension, and 5/5 strength in his right hand intrinsics. A shoulder examination was deferred because of postoperative restrictions. Compared with the asymptomatic left side, he had decreased sensation to light touch and pinprick in the radial aspect of the right forearm. The differential diagnoses at that time included upper trunk, lateral cord, or musculocutaneous nerve injury related to the interscalene block, trauma or positioning related to surgery, postsurgical edema with nerve compression, and postsurgical inflammatory neuropathy. Gabapentin, 300 mg 3 times daily, was prescribed at this visit, and use of acetaminophen-hydrocodone was continued. Because a right lateral antebrachial cutaneous nerve injury was suspected, a nerve conduction study (NCS) and concentric needle electromyography (EMG) study were performed 4 weeks after surgery (Tables 1-3), which revealed absent conduction of the right LABCN sensory nerve action potential (SNAP). The LABCN SNAP was elicited on the asymptomatic left side with normal amplitude and velocity. Both medial antebrachial cutaneous nerve SNAPs were present. There was an incidental finding of mild median nerve mononeuropathy at the right wrist. Findings of concentric needle EMG of the right biceps, triceps, brachialis, flexor carpi radialis, and first dorsal interosseous muscle were normal. Slightly increased motor unit action potentials were noted in the right abductor pollicis brevis.
At our 1-week follow-up visit (5 weeks after surgery), the patient had experienced no relief from use of gabapentin, 300 mg 3 times daily, and use of this drug was subsequently discontinued. At this time, he was no longer immobilized in the shoulder abduction sling and began outpatient physical therapy for range of motion and strengthening. An ultrasound-guided right LABCN perineural injection was proposed for therapeutic relief; the patient agreed to undergo this procedure. Using a 12-MHz linear probe, the LABCN was identified at the elbow (Figure 1). A 22-gauge, 3.5-inch needle was advanced to the nerve, and a 10-mL solution of 10-mg methylprednisolone acetate (Depo-Medrol) and 1% preservative-free lidocaine was injected. After the injection, the patient reported subjective numbness and decreased pain in the distribution of the nerve in the radial aspect of the forearm. He was also provided with a compound cream containing 5% lidocaine, 10% ketamine, and 6% gabapentin. At the next follow-up visit 3 weeks later (8 weeks after surgery), the patient continued to have the same pain in the right radial forearm distribution. He had received mild relief from the injection for only 1 day. At this time, 10 mg of oral amitriptyline every evening and 250 mg of daily oral magnesium were added to his regimen of acetaminophen-hydrocodone and compound cream. He noted that the compound cream had provided some pain relief but that it wore off rather quickly. The formulation was adjusted to include 10% ketamine, 10% gabapentin, 2% cyclobenzaprine, 0.2% clonidine, 5% magnesium, and 2% bupivacaine. At 3.5 months after surgery, the patient continued to have ongoing pain and was considering surgical intervention after conservative treatments had failed. He underwent dedicated magnetic resonance (MR) neurography of the right elbow (Signa 1.5T HDX, GE, Milwaukee, WI) with series consisting of small field of view, thin-slice axial T1 (repetition time [TR] 550 ms, echo time [TE] 13 ms, number of excitations [NEX] ¼ 1, field of view ¼ 180 mm, matrix ¼ 256 192, slice thickness/gap ¼ 3/0 mm) and short Tau inversion recovery (STIR) (TR 5917 ms, TE 23 ms, TI ¼ 160 ms, NEX ¼ 1, field of view ¼ 180 mm,
Table 1 Sensory nerve conduction studies showing absent conduction of the left antebrachial cutaneous nerve Nerve
Onset Latency
Peak Latency
Amplitude
Segment
Latency Difference
Distance
Conduction Velocity
R median R radial R median R ulnar R ulnar R LABC R MABC L median L radial L LABC L MABC
2.7 ms 1.7 ms 3.0 ms 2.0 ms 2.0 ms No response 2.3 ms 2.1 ms 2.0 ms 2.3 ms 2.0 ms
3.2 ms 2.4 ms 3.6 ms 2.6 ms 2.7 ms No response 2.7 ms 2.8 ms 2.6 ms 2.6 ms 2.5 ms
11 mV 5 mV 10 mV 6 mV 24 mV No response 8 mV 20 mV 6 mV 8 mV 20 mV
Wrist-thumb Wrist-thumb Wrist-digit IV Wrist-digit IV Wrist-digit V Forearm-elbow Forearm-elbow Wrist-thumb Wrist-thumb Forearm-elbow Forearm-elbow
2.7 ms 1.7 ms 3.0 ms 2.0 ms 2.0 ms No response 2.3 ms 2.1 ms 2.0 ms 2.3 ms 2.0 ms
100 100 130 130 110 120 120 100 100 120 120
37 m/s 59 m/s 43 m/s 65 m/s 55 m/s No response 52 m/s 48 m/s 50 m/s 53 m/s 60 m/s
R ¼ right; LABC ¼ lateral antebrachial cutaneous; MABC ¼ medial antebrachial cutaneous; L ¼ left.
mm mm mm mm mm mm mm mm mm mm mm
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Table 2 Motor nerve conduction studies showing normal median and ulnar nerve conductions Nerve R median Wrist Elbow R Ulnar Wrist Below elbow Above elbow Axilla
Latency
Amplitude
Segment
Latency Difference
Distance
Conduction Velocity
3.8 ms 8.9 ms
11.5 mV 10.9 mV
Wrist-abductor pollicis brevis Wrist-elbow
3.8 ms 5.1 ms
55 mm 272 mm
53 m/s
2.1 6.3 7.8 9.3
12.6 11.4 10.6 10.1
Wrist-abductor digiti minimi Wrist-below elbow Below elbow-above elbow Above elbow-axilla
2.1 4.2 1.5 1.5
55 mm 235 mm 80 mm 100 mm
56 m/s 52 m/s 68 m/s
ms ms ms ms
mV mV mV mV
ms ms ms ms
R ¼ right.
matrix ¼ 256 192, slice thickness/gap ¼ 3/0 mm). The imaging showed that the LABCN was focally displaced posteriorly and also showed a focally increased internal T2 signal as it passed deep to the biceps brachii distal muscle and myotendinous junction (Figure 2). These findings indicated entrapment of the nerve by the biceps myotendinous junction and secondary nerve inflammation. The patient was referred to an orthopedic hand surgeon for evaluation for LABCN decompression. At 4 months after his initial surgery, the patient underwent a surgical decompression in the right elbow with excision of fascia over the biceps tendon. A 3-cm incision was made at the right distal lateral upper arm between the biceps brachii and the brachialis. The right lateral antebrachial cutaneous nerve was identified beneath the biceps (Figure 3). The fascia was identified at the musculotendinous junction and incised to relieve the compression of the nerve (Figure 4). One week later upon telephone follow-up, the patient reported that he was doing very well and was pleased with the results of the surgery. Three months after surgery, the patient reported that his symptoms were largely resolved with only mild numbness and paresthesias in the distal radial aspect of the right wrist. Discussion To our knowledge, this is the first reported case of lateral antebrachial cutaneous nerve entrapment
following proximal biceps tenodesis. We attempted a therapeutic ultrasound-guided perineural injection that unfortunately only provided minimal relief. In addition to traditional electromyographic diagnosis, we used MR neurography as an adjunct tool to identify nerve entrapment. This is also the first reported case of LABCN entrapment identified through use of MR neurography. Electrodiagnostic Studies Diagnoses in most reported cases of LABCN compression are made from nerve conduction studies showing absent sensory conduction of the LABCN [4-7]. In a case series of 23 patients [10], electrodiagnostic studies resulted in positive findings for all 23 patients. In our case, a nerve conduction study was the initial diagnostic test and showed absent nerve conduction on the affected side with intact nerve conduction in the unaffected side. Needle EMG of 2 muscles with motor branch innervations from the musculocutaneous nerve (biceps brachii and brachialis) revealed no abnormalities, decreasing the likelihood of musculocutaneous nerve involvement. Clinical findings of right elbow flexor weakness and atrophy were likely due to postoperative immobilization. Normal median sensory nerve conduction to the thumb would be unusual if the upper trunk or lateral cord of the brachial plexus was involved [12]. Normal needle EMG of the flexor carpi radialis also
Table 3 Needle electromyography examination showing normal studies of 2 muscles with motor branch innervation from the musculocutaneous nerve (biceps brachii and brachialis) Spontaneous Activity Muscle
Insertional Activity
R R R R
Normal Normal Normal Normal
biceps brachii triceps Brachii brachialis flexor carpi radialis R abductor pollicis brevis R first dorsal interosseous
Volitional MUAPs
Volitional Activity
Fibs
Positive Waves
Duration
Amplitude
Polyphasics
Hz
limits limits limits limits
0 0 0 0
0 0 0 0
Normal Normal Normal Normal
Normal Normal Normal Normal
limits limits limits limits
0 0 0 0
Normal Normal Normal Normal
Normal limits
0
0
Normal limits
0
Normal limits
Normal limits
Normal limits
Normal limits
0
0
Normal limits
Slightly increased Normal limits
0
Normal limits
Normal limits
Normal limits
limits limits limits limits
MUAPs ¼ motor unit action potentials; Fibs ¼ fibrillations; R ¼ right.
limits limits limits limits
Recruitment
Rate
Normal Normal Normal Normal
Normal Normal Normal Normal
limits limits limits limits
limits limits limits limits
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LABCN Entrapment After Shoulder Arthroscopy
et al in 2004 [10]. Two patients in a case series by Dailiana et al [2] were diagnosed solely with local anesthetic nerve block. Our case is the first reported case in which ultrasound was used to locate the nerve prior to injection of medication. We decided to pursue a perineural injection of corticosteroid for therapeutic relief as part of a conservative management plan. Ultrasound was preferred rather than a blind injection to better locate the nerve given its small caliber and to accurately provide relief at the source of pain. The injection provided pain relief in the affected region, but it only provided short-term relief. MR Neurography
Figure 1. Longitudinal view of the lateral antebrachial cutaneous nerve (LABCN) and ultrasound-guided perineural injection using a 12-MHz linear probe and 22-gauge needle. With the elbow in extension, the needle is inserted distal to proximal into the biceps at the level of the elbow prior to the injection of medication.
reduces the likelihood of C6 nerve root involvement. The slightly increased motor unit action potentials of the abductor pollicis brevis is a secondary, incidental finding of median mononeuropathy at the wrist. Ultrasound-Guided Perineural Injection Blind diagnostic anesthetic nerve block of the lateral antebrachial cutaneous nerve was successfully performed in 17 of 19 healthy volunteers in a study by Olson in 1969 [13]. Diagnostic anesthetic nerve block was also successfully performed in 23 patients in a study by Naam
MR neurography uses high-resolution, thin-slice imaging to visualize nerve plexuses and peripheral nerves directly along their course. In peripheral neuropathy, it has shown greatest utility in identifying focal areas of nerve entrapment and compression [14], for example, in cases of cubital tunnel and Guyon canal syndromes for the ulnar nerve and in carpal tunnel syndrome for the median nerve [15,16]. When compared with standard MR protocols, the very thin slice, high-resolution images allow better identification of small nerve course on T1 imaging, and fat-suppression techniques such as STIR imaging allow better identification of subtle abnormalities of nerve edema, structure, and fascicular structure [16-19]. In addition to identifying the site of nerve entrapment or injury, MR neurography potentially can show the nature and extent of the underlying diseasedfor example, in cases of trauma, inflammation, or tumor. Exact protocols vary, but our institution uses 3mm-thick slices and a small field of view to create inplane spatial resolution of slightly less than 1 mm. As a small peripheral nerve, the LABCN is therefore at
Figure 2. Consecutive axial inferior-to-superior thin-slice short Tau inversion recovery images through the elbow show the lateral antebrachial cutaneous nerve (straight arrows) entrapped beneath the distal biceps muscle and biceps myotendinous junction (curved arrows). The nerve at the site of entrapment has T2 hyperintense signal for a nerve of this size, a finding suggesting local inflammation within the nerve (although abnormal nerve T2 signal in isolation can be a spurious finding). Imaging was performed with the elbow flexed and the shoulder fully abducted because the patient could not tolerate imaging with the standard extended elbow and adducted shoulder. The brachialis (*) and brachioradialis (**) muscles are labeled to orient the viewer.
H. Yung et al. / PM R 7 (2015) 889-894
Figure 3. Intraoperative photograph with the elbow extended and the forearm supinated demonstrating biceps tendon (straight arrow) compression of the lateral antebrachial cutaneous nerve (block arrow).
the lower size limit of anatomic structures that can be accurately identified by MR neurography. As image resolution and quality continue to improve, MR neurography is emerging as a valuable adjunct tool in evaluation of peripheral neuropathy when more established diagnostic tools such as EMG and NCS do not fully answer the clinical question, such as in this case, in which imaging was used to localize precisely the anatomic site of nerve entrapment. To our knowledge, this is the first use of MR neurography to identify entrapment of the lateral antebrachial cutaneous nerve and a rare successful use of MR neurography in general to identify disease in a nerve of such small caliber. Treatment Options In one case of traumatic LABCN compression, nonsteroidal anti-inflammatory drugs did not improve symptoms [5], whereas in another case of chronic
Figure 4. Intraoperative photograph after debridement demonstrating relieved compression of the lateral antebrachial cutaneous nerve (arrow).
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overuse compression, the symptoms were completely resolved with a short course of tapering oral steroids [7]. The patient declined a trial of oral steroids because of potential systemic adverse effects. In unique cases such as compression by tumor [9] and olecranon fossa fracture [6], relief was provided by surgical decompression. In a surgical case series by Dailiana et al [2] in 9 patients with LABCN compression at the elbow, 2 patients responded to conservative management consisting of immobilization, while 7 underwent surgical treatment, with 6 of the 7 patients receiving full relief. In a study by Naam et al [10], 16 patients with LABCN compression underwent surgical decompression after conservative treatment failed. Of the 16 who underwent surgical treatment, 14 had complete relief, 1 had persistent mild discomfort, and 1 had intermittent pain only with activities. In the case presented here, the patient had little to no relief from oral and topical neuromodulators or from postoperative physical therapy for shoulder range of motion and strengthening. An ultrasoundguided perineural injection provided only temporary relief. Definitive relief was only obtained after surgical decompression. In a previously reported case of musculocutaneous nerve entrapment after biceps tenodesis by Ma et al [11], the musculocutaneous nerve was compressed proximally and stretched around the tenodesed long head of the biceps. The authors reported surgical treatment as musculocutaneous nerve exploration with proximal and distal extension of the previous surgical incision and retenodesis of the long head of the biceps tendon. The patient initially presented with significantly reduced elbow flexion strength (2/5) and atrophy. EMG performed at 2 months demonstrated musculocutaneous nerve injury. After 5 months of conservative treatment, the patient underwent surgical exploration, which revealed the musculocutaneous nerve wrapped around the long head of the biceps [11]. In our case, the patient demonstrated mild elbow flexion weakness (4/5), with normal EMG findings in the biceps and brachialis. The site of nerve entrapment was specifically localized distally to the biceps myotendinous junction, which was then used to assist in further surgical planning. Intramuscular access was obtained with a much smaller, 3-cm entry incision at the distal upper arm, rather than a much larger incision needed for nerve exploration, allowing for fewer complications and quicker postoperative recovery. The cause of the LABCN entrapment is likely from the tension created by the distal biceps tendon when the proximal long head tendon is repositioned during the tenodesis. Shoulder arthroscopy demonstrated a frayed and torn proximal long head tendon. A tenotomy was performed prior to reattachment onto the humerus. This effective shortening of the biceps tendon may have created enough tension to entrap the LABCN distally.
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LABCN Entrapment After Shoulder Arthroscopy
Conclusion This case report describes lateral antebrachial nerve entrapment after proximal biceps tenodesis. The clinical diagnosis was confirmed by a combination of electrodiagnostics and MR neurography. After failure of conservative treatment, including nonsteroidal antiinflammatory and neuromodulating medications and a perineural corticosteroid injection, a surgical decompression of a compressed LABCN resolved the symptoms. The source of compression is likely from the tension created at the distal biceps tendon during the tenodesis. Electrodiagnostics were used to identify the LABCN as the source of pain, but its precise location of entrapment was still unclear. In this novel case MR neurography was used to localize precisely a smallcaliber peripheral nerve and its site of entrapment at the elbow, allowing for accurate, less invasive surgical decompression. Although it is a rare complication, peripheral nerve entrapment after biceps tenodesis should be considered in patients with radial forearm pain. Video Gallery: To view the online video, use your smartphone camera QR Reader App to scan and capture this QR Code, text GS5ULW to 64842, or visit www.pmrjournal.org to locate this video content. URL: http://www.pmrjournal.org/article/ S1934-1482(15)00140-9/addons
References 1. Bourne MH, Wood MB, Carmichael SW. Locating the lateral antebrachial cutaneous nerve. Los Angeles, CA: Presentation at the Sixteenth Annual Meeting of the American Association for Hand Surgery; October 23-26, 1986. 2. Dailiana ZH, Roulot E, Le Vet D. Surgical treatment of compression of the lateral antebrachial cutaneous nerve. J Bone Joint Surg 2000;82-B:420-423.
3. Yuan RT, Cohen MJ. Lateral antebrachial cutaneous nerve injury as a complication of phlebotomy. Plast Reconstr Surg 1985;76:299-300. 4. Sitik TP, Foye PM, Nadler SF, Brachman GO. Phlebotomy-related lateral antebrachial cutaneous nerve injury. Am J Phys Med Rehabil 2001;90:230-234. 5. Gillingham BL, Mack GR. Compression of the lateral antebrachial cutaneous nerve by the biceps tendon. J Shoulder Elbow Surg 1996;5:330-332. 6. Belzille E, Cloutier D, Foy S. Entrapment of the lateral antebrachial cutaneous nerve exiting through the forearm fascia. J Hand Surg 2001;26A:64-67. 7. Jablecki CK. Lateral antebrachial cutaneous neuropathy in a windsurfer. Muscle Nerve 1999;22:944-945. 8. Narasanagi SS. Compression of the lateral cutaneous nerve of forearm. Neurology India 1972;20:224-225. 9. Van Der Lei B, Damen A, Van Valkenburg E. Compression of the lateral cutaneous nerve of the forearm by a glomus tumour. J Hand Surg 1982;22-B:71-72. 10. Naam NH, Massoud HA. Painful entrapment of the lateral antebrachial cutaneous nerve at the elbow. J Hand Surg 2004;29A:1148-1153. 11. Ma H, Heest AV, Glisson C, Patel S. Musculocutaneous nerve entrapment: An unusual complication after biceps tenodesis. Am J Sports Med 2009;37:2467-2469. 12. Ferrante ME. Brachial plexopathies: Classification, causes and consequences. Muscle Nerve 2004;30:547-568. 13. Olson IA. The origin of the lateral cutaneous nerve of forearm and its anaesthesia for modified brachial plexus block. J Anat 1969; 105:381-382. 14. Chhabra A, Williams EH, Wang KC, Dellon AL, Carrino JA. MR neurography of neuromas related to nerve injury and entrapment with surgical correlation. Am J Neuroradiol 2010;31:1363-1368. 15. Cudlip SA, Howe FA, Clifton A, Schwartz MS, Bell BA. Magnetic resonance neurography studies of the median nerve before and after carpal tunnel decompression. J Neurosurg 2002;96: 1046-1051. 16. Chalian M, Behzadi AH, Williams EH, Shores JT, Chhabra A. Highresolution magnetic resonance neurography in upper extremity neuropathy. Neuroimag Clin N Am 2014;24:109-125. 17. Cudlip SA, Howe FA, Griffiths JR, Bell BA. Magnetic resonance neurography of peripheral nerve following experimental crush injury, and correlation with functional deficit. J Neurosurg 2002; 96:755-759. 18. Chhabra A, Andreisek G. Magnetic Resonance Neurography. New Delhi: Jaypee Brothers Medical Publishers; 2012. 19. Chin CT. Nerve and Vascular Injuries in Sports Medicine. New York, NY: Springer; 2009.
Disclosure H.Y. Department of Physical Medicine and Rehabilitation, University of Pittsburgh Medical Center, Suite 201, 3471 Fifth Ave, Pittsburgh, PA 15213. Address correspondence to: H.Y.; e-mail: [email protected] Disclosure: nothing to disclose G.M.L. Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose A.L. Department of Orthopedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose
S.L.O. Department of Anesthesia, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosures outside this publication: royalties, Lippincott, Williams, & Wilkins; travel/accommodations/meeting expenses unrelated to activities listed, NYSORA and ASRA M.H.C. Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose Submitted for publication September 25, 2014; accepted March 10, 2015.
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Case Presentation
Lateral Antebrachial Cutaneous Nerve Entrapment After Shoulder Arthroscopy: A Case Report Herbie Yung, MD, Gerritt M. Lagemann, MD, Albert Lin, MD, Steven L. Orebaugh, MD, Megan H. Cortazzo, MD
Abstract The lateral antebrachial cutaneous nerve (LABCN) is a distal sensory branch of the musculocutaneous nerve that innervates the radial aspect of the forearm. Cases of LABCN injury from trauma and chronic compression have been reported. A case of musculocutaneous nerve injury after a biceps tenodesis has also been reported. This case report describes an LABCN injury and forearm pain after a biceps tenodesis procedure. Using a multifaceted diagnostic approach of electrodiagnostics and magnetic resonance neurography, the site of compression was appropriately localized. The patient ultimately achieved relief after a surgical decompression.
Introduction The lateral antebrachial cutaneous nerve (LABCN) is a distal sensory branch of the musculocutaneous nerve. Motor branches of the musculocutaneous nerve innervate the coracobrachialis, biceps, and brachialis in the arm. The LABCN is most commonly found to emerge between the lateral aspect of the biceps tendon and the brachialis at the level of the interepicondylar line [1]. It is typically asymptomatically compressed during pronation and supination with the elbow in extension [2]. Multiple cases of LABCN injury from trauma have been documented, such as antecubital fossa venipuncture [3,4], slam dunking a basketball [5], and olecranon fracture [6]. LABCN injury has also been reported in overuse injury from prolonged elbow flexion during windsurfing [7], and chronic compression injuries have been reported over the antecubital fossa from a camera bag [8] and from a glomus tumor in the forearm [9]. A surgical case series of LABCN injury has been reported related to 2 cases of biceps injuryd1 case of distal biceps attachment avulsion and 1 case of biceps tendon rupture [10]. A case of musculocutaneous nerve entrapment also has been reported after biceps tenodesis and was eventually surgically repaired [11].
This report describes the clinical presentation, electrodiagnostic and radiologic findings, and treatment course in a patient who experienced LABCN entrapment after right shoulder surgery. Case Presentation The patient is a 51-year-old right-handed man presenting with 1.5 years of anterior shoulder pain from tendinopathy of the long head of the biceps, acromioclavicular impingement, and bursitis. His shoulder magnetic resonance imaging scan revealed moderate supraspinatus tendinopathy, a partial infraspinatus tear, mild tendinopathy of the subscapularis, and mild acromioclavicular joint arthrosis. He underwent an arthroscopic right shoulder procedure, including subscapularis repair, open biceps tenodesis, subacromial decompression with formal acromioplasty, and debridement with a bursectomy. Shoulder arthroscopy demonstrated a torn proximal long head of the biceps tendon. Biceps tenodesis was performed given the patient’s young age and active lifestyle. Anesthesia consisted of a right interscalene block under ultrasound guidance, followed by propofol-ketamine sedation in the beach-chair position. The patient’s initial recovery was unremarkable, and he wore a shoulder abduction sling for 4 weeks.
1934-1482/$ - see front matter ª 2015 by the American Academy of Physical Medicine and Rehabilitation http://dx.doi.org/10.1016/j.pmrj.2015.03.009
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LABCN Entrapment After Shoulder Arthroscopy
The patient initially presented to the pain clinic 26 days after surgery with worsening pain, which began about 1 week after the surgery. He described the development of a dull, aching, throbbing pain with numbness and tingling in the radial aspect of the right forearm, from the first carpal-metacarpal to the elbow crease but not involving the biceps. The pain was categorized as severe and affected him at night, preventing good-quality sleep. He noted some relief upon taking oral acetaminophen-hydrocodone. Physical examination showed mild right biceps atrophy and a wellhealed surgical incision. He demonstrated 4/5 strength with right elbow flexion limited by pain, 4/5 strength with right wrist flexion and extension, and 5/5 strength in his right hand intrinsics. A shoulder examination was deferred because of postoperative restrictions. Compared with the asymptomatic left side, he had decreased sensation to light touch and pinprick in the radial aspect of the right forearm. The differential diagnoses at that time included upper trunk, lateral cord, or musculocutaneous nerve injury related to the interscalene block, trauma or positioning related to surgery, postsurgical edema with nerve compression, and postsurgical inflammatory neuropathy. Gabapentin, 300 mg 3 times daily, was prescribed at this visit, and use of acetaminophen-hydrocodone was continued. Because a right lateral antebrachial cutaneous nerve injury was suspected, a nerve conduction study (NCS) and concentric needle electromyography (EMG) study were performed 4 weeks after surgery (Tables 1-3), which revealed absent conduction of the right LABCN sensory nerve action potential (SNAP). The LABCN SNAP was elicited on the asymptomatic left side with normal amplitude and velocity. Both medial antebrachial cutaneous nerve SNAPs were present. There was an incidental finding of mild median nerve mononeuropathy at the right wrist. Findings of concentric needle EMG of the right biceps, triceps, brachialis, flexor carpi radialis, and first dorsal interosseous muscle were normal. Slightly increased motor unit action potentials were noted in the right abductor pollicis brevis.
At our 1-week follow-up visit (5 weeks after surgery), the patient had experienced no relief from use of gabapentin, 300 mg 3 times daily, and use of this drug was subsequently discontinued. At this time, he was no longer immobilized in the shoulder abduction sling and began outpatient physical therapy for range of motion and strengthening. An ultrasound-guided right LABCN perineural injection was proposed for therapeutic relief; the patient agreed to undergo this procedure. Using a 12-MHz linear probe, the LABCN was identified at the elbow (Figure 1). A 22-gauge, 3.5-inch needle was advanced to the nerve, and a 10-mL solution of 10-mg methylprednisolone acetate (Depo-Medrol) and 1% preservative-free lidocaine was injected. After the injection, the patient reported subjective numbness and decreased pain in the distribution of the nerve in the radial aspect of the forearm. He was also provided with a compound cream containing 5% lidocaine, 10% ketamine, and 6% gabapentin. At the next follow-up visit 3 weeks later (8 weeks after surgery), the patient continued to have the same pain in the right radial forearm distribution. He had received mild relief from the injection for only 1 day. At this time, 10 mg of oral amitriptyline every evening and 250 mg of daily oral magnesium were added to his regimen of acetaminophen-hydrocodone and compound cream. He noted that the compound cream had provided some pain relief but that it wore off rather quickly. The formulation was adjusted to include 10% ketamine, 10% gabapentin, 2% cyclobenzaprine, 0.2% clonidine, 5% magnesium, and 2% bupivacaine. At 3.5 months after surgery, the patient continued to have ongoing pain and was considering surgical intervention after conservative treatments had failed. He underwent dedicated magnetic resonance (MR) neurography of the right elbow (Signa 1.5T HDX, GE, Milwaukee, WI) with series consisting of small field of view, thin-slice axial T1 (repetition time [TR] 550 ms, echo time [TE] 13 ms, number of excitations [NEX] ¼ 1, field of view ¼ 180 mm, matrix ¼ 256 192, slice thickness/gap ¼ 3/0 mm) and short Tau inversion recovery (STIR) (TR 5917 ms, TE 23 ms, TI ¼ 160 ms, NEX ¼ 1, field of view ¼ 180 mm,
Table 1 Sensory nerve conduction studies showing absent conduction of the left antebrachial cutaneous nerve Nerve
Onset Latency
Peak Latency
Amplitude
Segment
Latency Difference
Distance
Conduction Velocity
R median R radial R median R ulnar R ulnar R LABC R MABC L median L radial L LABC L MABC
2.7 ms 1.7 ms 3.0 ms 2.0 ms 2.0 ms No response 2.3 ms 2.1 ms 2.0 ms 2.3 ms 2.0 ms
3.2 ms 2.4 ms 3.6 ms 2.6 ms 2.7 ms No response 2.7 ms 2.8 ms 2.6 ms 2.6 ms 2.5 ms
11 mV 5 mV 10 mV 6 mV 24 mV No response 8 mV 20 mV 6 mV 8 mV 20 mV
Wrist-thumb Wrist-thumb Wrist-digit IV Wrist-digit IV Wrist-digit V Forearm-elbow Forearm-elbow Wrist-thumb Wrist-thumb Forearm-elbow Forearm-elbow
2.7 ms 1.7 ms 3.0 ms 2.0 ms 2.0 ms No response 2.3 ms 2.1 ms 2.0 ms 2.3 ms 2.0 ms
100 100 130 130 110 120 120 100 100 120 120
37 m/s 59 m/s 43 m/s 65 m/s 55 m/s No response 52 m/s 48 m/s 50 m/s 53 m/s 60 m/s
R ¼ right; LABC ¼ lateral antebrachial cutaneous; MABC ¼ medial antebrachial cutaneous; L ¼ left.
mm mm mm mm mm mm mm mm mm mm mm
H. Yung et al. / PM R 7 (2015) 889-894
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Table 2 Motor nerve conduction studies showing normal median and ulnar nerve conductions Nerve R median Wrist Elbow R Ulnar Wrist Below elbow Above elbow Axilla
Latency
Amplitude
Segment
Latency Difference
Distance
Conduction Velocity
3.8 ms 8.9 ms
11.5 mV 10.9 mV
Wrist-abductor pollicis brevis Wrist-elbow
3.8 ms 5.1 ms
55 mm 272 mm
53 m/s
2.1 6.3 7.8 9.3
12.6 11.4 10.6 10.1
Wrist-abductor digiti minimi Wrist-below elbow Below elbow-above elbow Above elbow-axilla
2.1 4.2 1.5 1.5
55 mm 235 mm 80 mm 100 mm
56 m/s 52 m/s 68 m/s
ms ms ms ms
mV mV mV mV
ms ms ms ms
R ¼ right.
matrix ¼ 256 192, slice thickness/gap ¼ 3/0 mm). The imaging showed that the LABCN was focally displaced posteriorly and also showed a focally increased internal T2 signal as it passed deep to the biceps brachii distal muscle and myotendinous junction (Figure 2). These findings indicated entrapment of the nerve by the biceps myotendinous junction and secondary nerve inflammation. The patient was referred to an orthopedic hand surgeon for evaluation for LABCN decompression. At 4 months after his initial surgery, the patient underwent a surgical decompression in the right elbow with excision of fascia over the biceps tendon. A 3-cm incision was made at the right distal lateral upper arm between the biceps brachii and the brachialis. The right lateral antebrachial cutaneous nerve was identified beneath the biceps (Figure 3). The fascia was identified at the musculotendinous junction and incised to relieve the compression of the nerve (Figure 4). One week later upon telephone follow-up, the patient reported that he was doing very well and was pleased with the results of the surgery. Three months after surgery, the patient reported that his symptoms were largely resolved with only mild numbness and paresthesias in the distal radial aspect of the right wrist. Discussion To our knowledge, this is the first reported case of lateral antebrachial cutaneous nerve entrapment
following proximal biceps tenodesis. We attempted a therapeutic ultrasound-guided perineural injection that unfortunately only provided minimal relief. In addition to traditional electromyographic diagnosis, we used MR neurography as an adjunct tool to identify nerve entrapment. This is also the first reported case of LABCN entrapment identified through use of MR neurography. Electrodiagnostic Studies Diagnoses in most reported cases of LABCN compression are made from nerve conduction studies showing absent sensory conduction of the LABCN [4-7]. In a case series of 23 patients [10], electrodiagnostic studies resulted in positive findings for all 23 patients. In our case, a nerve conduction study was the initial diagnostic test and showed absent nerve conduction on the affected side with intact nerve conduction in the unaffected side. Needle EMG of 2 muscles with motor branch innervations from the musculocutaneous nerve (biceps brachii and brachialis) revealed no abnormalities, decreasing the likelihood of musculocutaneous nerve involvement. Clinical findings of right elbow flexor weakness and atrophy were likely due to postoperative immobilization. Normal median sensory nerve conduction to the thumb would be unusual if the upper trunk or lateral cord of the brachial plexus was involved [12]. Normal needle EMG of the flexor carpi radialis also
Table 3 Needle electromyography examination showing normal studies of 2 muscles with motor branch innervation from the musculocutaneous nerve (biceps brachii and brachialis) Spontaneous Activity Muscle
Insertional Activity
R R R R
Normal Normal Normal Normal
biceps brachii triceps Brachii brachialis flexor carpi radialis R abductor pollicis brevis R first dorsal interosseous
Volitional MUAPs
Volitional Activity
Fibs
Positive Waves
Duration
Amplitude
Polyphasics
Hz
limits limits limits limits
0 0 0 0
0 0 0 0
Normal Normal Normal Normal
Normal Normal Normal Normal
limits limits limits limits
0 0 0 0
Normal Normal Normal Normal
Normal limits
0
0
Normal limits
0
Normal limits
Normal limits
Normal limits
Normal limits
0
0
Normal limits
Slightly increased Normal limits
0
Normal limits
Normal limits
Normal limits
limits limits limits limits
MUAPs ¼ motor unit action potentials; Fibs ¼ fibrillations; R ¼ right.
limits limits limits limits
Recruitment
Rate
Normal Normal Normal Normal
Normal Normal Normal Normal
limits limits limits limits
limits limits limits limits
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LABCN Entrapment After Shoulder Arthroscopy
et al in 2004 [10]. Two patients in a case series by Dailiana et al [2] were diagnosed solely with local anesthetic nerve block. Our case is the first reported case in which ultrasound was used to locate the nerve prior to injection of medication. We decided to pursue a perineural injection of corticosteroid for therapeutic relief as part of a conservative management plan. Ultrasound was preferred rather than a blind injection to better locate the nerve given its small caliber and to accurately provide relief at the source of pain. The injection provided pain relief in the affected region, but it only provided short-term relief. MR Neurography
Figure 1. Longitudinal view of the lateral antebrachial cutaneous nerve (LABCN) and ultrasound-guided perineural injection using a 12-MHz linear probe and 22-gauge needle. With the elbow in extension, the needle is inserted distal to proximal into the biceps at the level of the elbow prior to the injection of medication.
reduces the likelihood of C6 nerve root involvement. The slightly increased motor unit action potentials of the abductor pollicis brevis is a secondary, incidental finding of median mononeuropathy at the wrist. Ultrasound-Guided Perineural Injection Blind diagnostic anesthetic nerve block of the lateral antebrachial cutaneous nerve was successfully performed in 17 of 19 healthy volunteers in a study by Olson in 1969 [13]. Diagnostic anesthetic nerve block was also successfully performed in 23 patients in a study by Naam
MR neurography uses high-resolution, thin-slice imaging to visualize nerve plexuses and peripheral nerves directly along their course. In peripheral neuropathy, it has shown greatest utility in identifying focal areas of nerve entrapment and compression [14], for example, in cases of cubital tunnel and Guyon canal syndromes for the ulnar nerve and in carpal tunnel syndrome for the median nerve [15,16]. When compared with standard MR protocols, the very thin slice, high-resolution images allow better identification of small nerve course on T1 imaging, and fat-suppression techniques such as STIR imaging allow better identification of subtle abnormalities of nerve edema, structure, and fascicular structure [16-19]. In addition to identifying the site of nerve entrapment or injury, MR neurography potentially can show the nature and extent of the underlying diseasedfor example, in cases of trauma, inflammation, or tumor. Exact protocols vary, but our institution uses 3mm-thick slices and a small field of view to create inplane spatial resolution of slightly less than 1 mm. As a small peripheral nerve, the LABCN is therefore at
Figure 2. Consecutive axial inferior-to-superior thin-slice short Tau inversion recovery images through the elbow show the lateral antebrachial cutaneous nerve (straight arrows) entrapped beneath the distal biceps muscle and biceps myotendinous junction (curved arrows). The nerve at the site of entrapment has T2 hyperintense signal for a nerve of this size, a finding suggesting local inflammation within the nerve (although abnormal nerve T2 signal in isolation can be a spurious finding). Imaging was performed with the elbow flexed and the shoulder fully abducted because the patient could not tolerate imaging with the standard extended elbow and adducted shoulder. The brachialis (*) and brachioradialis (**) muscles are labeled to orient the viewer.
H. Yung et al. / PM R 7 (2015) 889-894
Figure 3. Intraoperative photograph with the elbow extended and the forearm supinated demonstrating biceps tendon (straight arrow) compression of the lateral antebrachial cutaneous nerve (block arrow).
the lower size limit of anatomic structures that can be accurately identified by MR neurography. As image resolution and quality continue to improve, MR neurography is emerging as a valuable adjunct tool in evaluation of peripheral neuropathy when more established diagnostic tools such as EMG and NCS do not fully answer the clinical question, such as in this case, in which imaging was used to localize precisely the anatomic site of nerve entrapment. To our knowledge, this is the first use of MR neurography to identify entrapment of the lateral antebrachial cutaneous nerve and a rare successful use of MR neurography in general to identify disease in a nerve of such small caliber. Treatment Options In one case of traumatic LABCN compression, nonsteroidal anti-inflammatory drugs did not improve symptoms [5], whereas in another case of chronic
Figure 4. Intraoperative photograph after debridement demonstrating relieved compression of the lateral antebrachial cutaneous nerve (arrow).
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overuse compression, the symptoms were completely resolved with a short course of tapering oral steroids [7]. The patient declined a trial of oral steroids because of potential systemic adverse effects. In unique cases such as compression by tumor [9] and olecranon fossa fracture [6], relief was provided by surgical decompression. In a surgical case series by Dailiana et al [2] in 9 patients with LABCN compression at the elbow, 2 patients responded to conservative management consisting of immobilization, while 7 underwent surgical treatment, with 6 of the 7 patients receiving full relief. In a study by Naam et al [10], 16 patients with LABCN compression underwent surgical decompression after conservative treatment failed. Of the 16 who underwent surgical treatment, 14 had complete relief, 1 had persistent mild discomfort, and 1 had intermittent pain only with activities. In the case presented here, the patient had little to no relief from oral and topical neuromodulators or from postoperative physical therapy for shoulder range of motion and strengthening. An ultrasoundguided perineural injection provided only temporary relief. Definitive relief was only obtained after surgical decompression. In a previously reported case of musculocutaneous nerve entrapment after biceps tenodesis by Ma et al [11], the musculocutaneous nerve was compressed proximally and stretched around the tenodesed long head of the biceps. The authors reported surgical treatment as musculocutaneous nerve exploration with proximal and distal extension of the previous surgical incision and retenodesis of the long head of the biceps tendon. The patient initially presented with significantly reduced elbow flexion strength (2/5) and atrophy. EMG performed at 2 months demonstrated musculocutaneous nerve injury. After 5 months of conservative treatment, the patient underwent surgical exploration, which revealed the musculocutaneous nerve wrapped around the long head of the biceps [11]. In our case, the patient demonstrated mild elbow flexion weakness (4/5), with normal EMG findings in the biceps and brachialis. The site of nerve entrapment was specifically localized distally to the biceps myotendinous junction, which was then used to assist in further surgical planning. Intramuscular access was obtained with a much smaller, 3-cm entry incision at the distal upper arm, rather than a much larger incision needed for nerve exploration, allowing for fewer complications and quicker postoperative recovery. The cause of the LABCN entrapment is likely from the tension created by the distal biceps tendon when the proximal long head tendon is repositioned during the tenodesis. Shoulder arthroscopy demonstrated a frayed and torn proximal long head tendon. A tenotomy was performed prior to reattachment onto the humerus. This effective shortening of the biceps tendon may have created enough tension to entrap the LABCN distally.
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LABCN Entrapment After Shoulder Arthroscopy
Conclusion This case report describes lateral antebrachial nerve entrapment after proximal biceps tenodesis. The clinical diagnosis was confirmed by a combination of electrodiagnostics and MR neurography. After failure of conservative treatment, including nonsteroidal antiinflammatory and neuromodulating medications and a perineural corticosteroid injection, a surgical decompression of a compressed LABCN resolved the symptoms. The source of compression is likely from the tension created at the distal biceps tendon during the tenodesis. Electrodiagnostics were used to identify the LABCN as the source of pain, but its precise location of entrapment was still unclear. In this novel case MR neurography was used to localize precisely a smallcaliber peripheral nerve and its site of entrapment at the elbow, allowing for accurate, less invasive surgical decompression. Although it is a rare complication, peripheral nerve entrapment after biceps tenodesis should be considered in patients with radial forearm pain. Video Gallery: To view the online video, use your smartphone camera QR Reader App to scan and capture this QR Code, text GS5ULW to 64842, or visit www.pmrjournal.org to locate this video content. URL: http://www.pmrjournal.org/article/ S1934-1482(15)00140-9/addons
References 1. Bourne MH, Wood MB, Carmichael SW. Locating the lateral antebrachial cutaneous nerve. Los Angeles, CA: Presentation at the Sixteenth Annual Meeting of the American Association for Hand Surgery; October 23-26, 1986. 2. Dailiana ZH, Roulot E, Le Vet D. Surgical treatment of compression of the lateral antebrachial cutaneous nerve. J Bone Joint Surg 2000;82-B:420-423.
3. Yuan RT, Cohen MJ. Lateral antebrachial cutaneous nerve injury as a complication of phlebotomy. Plast Reconstr Surg 1985;76:299-300. 4. Sitik TP, Foye PM, Nadler SF, Brachman GO. Phlebotomy-related lateral antebrachial cutaneous nerve injury. Am J Phys Med Rehabil 2001;90:230-234. 5. Gillingham BL, Mack GR. Compression of the lateral antebrachial cutaneous nerve by the biceps tendon. J Shoulder Elbow Surg 1996;5:330-332. 6. Belzille E, Cloutier D, Foy S. Entrapment of the lateral antebrachial cutaneous nerve exiting through the forearm fascia. J Hand Surg 2001;26A:64-67. 7. Jablecki CK. Lateral antebrachial cutaneous neuropathy in a windsurfer. Muscle Nerve 1999;22:944-945. 8. Narasanagi SS. Compression of the lateral cutaneous nerve of forearm. Neurology India 1972;20:224-225. 9. Van Der Lei B, Damen A, Van Valkenburg E. Compression of the lateral cutaneous nerve of the forearm by a glomus tumour. J Hand Surg 1982;22-B:71-72. 10. Naam NH, Massoud HA. Painful entrapment of the lateral antebrachial cutaneous nerve at the elbow. J Hand Surg 2004;29A:1148-1153. 11. Ma H, Heest AV, Glisson C, Patel S. Musculocutaneous nerve entrapment: An unusual complication after biceps tenodesis. Am J Sports Med 2009;37:2467-2469. 12. Ferrante ME. Brachial plexopathies: Classification, causes and consequences. Muscle Nerve 2004;30:547-568. 13. Olson IA. The origin of the lateral cutaneous nerve of forearm and its anaesthesia for modified brachial plexus block. J Anat 1969; 105:381-382. 14. Chhabra A, Williams EH, Wang KC, Dellon AL, Carrino JA. MR neurography of neuromas related to nerve injury and entrapment with surgical correlation. Am J Neuroradiol 2010;31:1363-1368. 15. Cudlip SA, Howe FA, Clifton A, Schwartz MS, Bell BA. Magnetic resonance neurography studies of the median nerve before and after carpal tunnel decompression. J Neurosurg 2002;96: 1046-1051. 16. Chalian M, Behzadi AH, Williams EH, Shores JT, Chhabra A. Highresolution magnetic resonance neurography in upper extremity neuropathy. Neuroimag Clin N Am 2014;24:109-125. 17. Cudlip SA, Howe FA, Griffiths JR, Bell BA. Magnetic resonance neurography of peripheral nerve following experimental crush injury, and correlation with functional deficit. J Neurosurg 2002; 96:755-759. 18. Chhabra A, Andreisek G. Magnetic Resonance Neurography. New Delhi: Jaypee Brothers Medical Publishers; 2012. 19. Chin CT. Nerve and Vascular Injuries in Sports Medicine. New York, NY: Springer; 2009.
Disclosure H.Y. Department of Physical Medicine and Rehabilitation, University of Pittsburgh Medical Center, Suite 201, 3471 Fifth Ave, Pittsburgh, PA 15213. Address correspondence to: H.Y.; e-mail: [email protected] Disclosure: nothing to disclose G.M.L. Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose A.L. Department of Orthopedic Surgery, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose
S.L.O. Department of Anesthesia, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosures outside this publication: royalties, Lippincott, Williams, & Wilkins; travel/accommodations/meeting expenses unrelated to activities listed, NYSORA and ASRA M.H.C. Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA Disclosure: nothing to disclose Submitted for publication September 25, 2014; accepted March 10, 2015.
