Relationship between the Branching Patterns of the Radial Nerve and Supinator Muscle

The posterior interosseous nerve (PIN) innervates the posterior compartment muscle of the forearm and is a continuation of the deep branch of the radial nerve. The anatomic descriptions of PIN vary among different authors. This study investigated the distribution patterns of PIN and its relationships to the supinator muscle. This study investigated which nerves innervate the posterior compartment muscles of the forearm, the radial nerve, and the PIN, using 28 nonembalmed limbs. Also, the points where the muscle attaches to the bone were investigated. The measured variables in this study were measured from the most prominent point of the lateral epicondyle of the humerus (LEH) to the most distal point of the radius styloid process. For each specimen, the distance between the above two points was assumed to be 100%. The measurement variables were the attachment area of the supinator and branching points from the radial nerve. The attachment points of the supinator to the radius and ulna were 47.9 % ± 3.6 % and 31.5 % ± 5.2 % , respectively, from the LEH. In 67.9% of the specimens, the brachioradialis and extensor carpi radialis longus (ECRL) were innervated by the radial nerve before superficial nerve branching, and the extensor carpi radialis brevis (ECRB) innervated the deep branch of the radial nerve. In 21.4% of the limbs, the nerve innervating the ECRB branched at the same point as the superficial branch of the radial nerve, whereas it branched from the radial nerve in 7.1% of the limbs. In 3.6% of the limbs, the deep branch of the radial nerve branched to innervate the ECRL. PIN was identified as a large branch without divisions in 10.7% and as a deep branch innervating the extensor digitorum in 14.3% of the limbs. The anatomic findings of this study would aid in the diagnosis of PIN syndromes.

Right radial nerve decompression for refractory radial tunnel syndrome

Background: Radial tunnel syndrome arises due to compression of the radial nerve through the radial tunnel.[1,5] The radial nerve divides into superficial and deep branches in the forearm. The deep branch travels posteriorly through the heads of the supinator where compression commonly occurs.[3,9,7] This syndrome results in pain in the hand and forearm with no motor weakness.[8] This condition can be treated conservatively with splinting and anti-inflammatory medication.[2,4,6] For cases of refractory radial tunnel syndrome, surgical management can be considered. Herein, we have presented a step-by-step video guide on how to perform a radial nerve decompression with a review of the relevant anatomy and surgical considerations. Case Description: A 68-year-old right-handed woman presented to the Mayo Clinic (Scottsdale, AZ) with the right elbow pain which radiated to the forearm causing significant difficulties with daily tasks. She had been dealing with worsening symptoms for 4 months. The patient’s history of gardening and clinical presentation allowed for diagnosis of radial tunnel syndrome. After conservative measures failed and other differential diagnoses were excluded, surgical decompression was recommended to treat her symptoms. The patient’s right arm was marked preoperatively between the brachioradialis and extensor carpi radialis longus (ECRL) muscles. The posterior cutaneous nerve of the forearm was identified which allowed for the determination of the interval between the brachioradialis and ECRL. Separation of the two muscles allowed for the identification of the radial sensory nerve. A nerve stimulator was used to confirm the sensory nature of this nerve. The nerve to the extensor carpi radialis brevis (ECRB) was identified and retracted with a vessel loop. Dorsal to the nerve to the ECRB is the posterior interosseous nerve (PIN), which was identified and retracted with a vessel loop. The fascia of the ECRB was divided both longitudinally and transversely and the supinator below was identified. The supinator muscle was carefully divided to further decompress the PIN. Informed consent for publication of this material was obtained from the patient. Conclusion: The patient tolerated the procedure well and reported significantly reduced pain at 7-month follow-up. To the best of our knowledge, video tutorials on this procedure have not been published. This video can serve as an educational guide for peripheral nerve specialists dealing with similar lesions.

Is Dry Needling of the Supinator a Safe Procedure? A Potential Treatment for Lateral Epicondylalgia or Radial Tunnel Syndrome. A Cadaveric Study

The supinator muscle is involved in two pain conditions of the forearm and wrist: lateral epicondylalgia and radial tunnel syndrome. Its close anatomical relationship with the radial nerve at the arcade of Frohse encourages research on dry needling approaches. Our aim was to determine if a solid filiform needle safely penetrates the supinator muscle during the clinical application of dry needling. Needle insertion of the supinator muscle was conducted in ten cryopreserved forearm specimens with a 30 × 0.32 mm filiform needle. With the forearm pronated, the needle was inserted perpendicular into the skin at the dorsal aspect of the forearm at a point located 4cm distal to the lateral epicondyle. The needle was advanced to a depth judged to be in the supinator muscle. Safety was assessed by measuring the distance from the needle to the surrounding neurovascular bundles of the radial nerve. Accurate needle penetration of the supinator muscle was observed in 100% of the forearms (needle penetration:16.4 ± 2.7 mm 95% CI 14.5 mm to 18.3 mm). No neurovascular bundle of the radial nerve was pierced in any of the specimen’s forearms. The distances from the tip of the needle were 7.8 ± 2.9 mm (95% CI 5.7 mm to 9.8 mm) to the deep branch of the radial nerve and 8.6 ± 4.3 mm (95% CI 5.5 mm to 11.7 mm) to the superficial branch of the radial nerve. The results from this cadaveric study support the assumption that needling of the supinator muscle can be accurately and safely conducted by an experienced clinician.

Supinator to Posterior Interosseous Nerve Transfer for Restoration of Finger Extension

BACKGROUND Cervical spinal cord injuries result in a severe loss of function and independence. The primary goal for these patients is the restoration of hand function. Nerve transfers have recently become a powerful intervention to restore the ability to grasp and release objects. The supinator muscle, although a suboptimal tendon transfer donor, serves as an ideal distal nerve donor for reconstructive strategies of the hand. This transfer is also applicable to lower brachial plexus injuries. OBJECTIVE To describe the supinator to posterior interosseous nerve transfer with the goal of restoring finger extension following spinal cord or lower brachial plexus injury. METHODS Nerve branches to the supinator muscle are transferred to the posterior interosseous nerve supplying the finger extensor muscles in the forearm. RESULTS The supinator to posterior interosseous nerve transfer is effective in restoring finger extension following spinal cord or lower brachial plexus injury. CONCLUSION This procedure represents an optimal nerve transfer as the donor nerve is adjacent to the target nerve and its associated muscles. The supinator muscle is innervated by the C5-6 nerve roots and is often available in cases of cervical SCI and injuries of the lower brachial plexus. Additionally, supination function is retained by supination action of the biceps muscle.

Morphological Classification of Arch of Frohse and Its Implication in Compression of Deep Branch of Radial Nerve

BACKGROUND Arcade of Frohse (AF) is a tendinous superior margin of superficial layer of supinator muscle which was first described by Frohse and Frankel in 1908. Since then it has been studied by many authors and held accountable as one of the essential components for compression of deep branch of radial nerve (DBRN) which leads to radial tunnel syndrome. Considering AF as an important element of compression, we made an attempt to classify it on the basis of its shape and to find out if any particular shape has a predominant role in compression of the nerve. We also observed the structure of superior and inferior margin of the supinator muscle. METHODS This study was conducted among 80 (70 males and 10 females) formalin fixed upper limbs present in the Department of Anatomy. The limbs were maintained in supine with slightly flexed position and dissection was performed to expose the supinator muscle. The proximal and distal borders of supinator muscles were examined meticulously with the help of magnified lens. The morphometric measurements were taken with the help of a digital caliper. RESULTS The FA is classified into four categories as loop, high arc, low arch and linear shaped. The most frequent shape observed was arch shaped (high and low arch) about 66%, followed by loop shaped (30%) and least was linear shaped (2.5%). On the basis of structure, the proximal and distal margin of supinator muscle was reported to be tendinous in majority of the cases. The distance of the AF from the fixed reproducible anatomical landmark like inter epicondylar line (IEL) was measured and the average distance found was 3.36 cm. CONCLUSIONS Knowledge of different shapes would aid surgeons and radiologists for better approach towards diagnosis and management of supinator syndrome. The morphometric finding can be useful for surgeons to locate the superior margin of supinator (AF) in surgical procedures for decompression of DBRN in supinator syndrome. KEY WORDS Arcade of Frohse, Inter Epicondylar Line, Supinator Muscle, Deep Branch of Radial Nerve and Radial Tunnel Syndrome

Posterior interosseous nerve entrapment by intramuscular lipoma arising from the supinator muscle - a case report

Background: Lipomas are benign, slow-growing tumors frequently subcutaneous and asymptomatic, intramuscular lipoma constituting a rare subtype. However, a lipoma occurring nearby the proximal radius may cause posterior interosseous nerve (PIN) entrapment. Case presentation: We described an uncommon case of a 45-year-old-man with a history of progressive, painless proximal right (dominant) forearm swelling for 4 months associated with PIN entrapment syndrome, presenting as fingers extension weakness. Intramuscular lipoma was observed in the supinator muscle in the magnetic resonance imaging (MRI). Lipoma surgical excision and release of the PIN through proximal forearm direct anterior approach was performed. Results: The histopathological examination confirmed the diagnosis of benign intramuscular lipoma. The follow-up of the patient showed full recovery within three months postoperatively. Discussion: Intramuscular lipoma is rare; however, it could originate from supinator muscle in the forearm, presenting with vague pain and could lead to compression of nearby neurovascular structures such as the PIN. Clinical evaluation and imaging studies, especially MRI, are crucial for diagnosis. If neural compression is evident, surgical resection is mandatory. Conclusion: Intramuscular lipoma entrapping PIN is rare and requires early clinical diagnosis confirmed by imaging and neurophysiological studies, surgical excision being the method of choice for optimum functional outcomes.

Minimal Damage to the Supinator Muscle After the Double-Incision Technique for Distal Biceps Tendon Repair

Background: The effect of the double-incision technique on the supinator muscle is unclear. Purpose: The aim of this study was to quantify fatty atrophy of the supinator muscle and map the area of muscle damage. Study Design: Case series; Level of evidence, 4. Methods: A total of 19 male patients (median age, 43 years) who underwent distal biceps tendon repair were included in the analysis. Patients with a minimum of 12 months of follow-up were included. The following variables were analyzed: range of motion; shortened version of Disabilities of the Arm, Shoulder and Hand (QuickDASH) score; Summary Outcome Determination (SOD) score; and isokinetic peak force and endurance in supination. Quantitative analysis and mapping of fatty infiltration of the supinator muscle were based on the calculation of proton density fat fraction on magnetic resonance imaging scans of both elbows using the IDEAL (Iterative Decomposition of Echoes of Asymmetrical Length) sequence. Results: At an average follow-up of 24 months (range, 12-64 months), the median SOD score was 9.0 (95% CI, 7.8-9.4), and the mean QuickDASH score was 6.7 (95% CI, 0.0-14.1). A difference of 17% in peak torque was measured between repaired and nonrepaired elbows (repaired elbow: 9.7 N·m; nonrepaired elbow: 11.7 N·m; P = .11). Endurance was better in the repaired elbow than the nonrepaired elbow (8.4% vs 14.9% work fatigue, respectively; P = .02). The average fat fraction of the supinator muscle was 19% (95% CI, 16%-21%) in repaired elbows and 14% (95% CI, 13%-16%) in contralateral elbows ( P = .04). The increase in fat fraction was located in a limited area between the radius and ulna at the level of the bicipital tuberosity. Conclusion: The assessment of the supinator muscle showed a limited increase in fat fraction between the radius and ulna at the level of the bicipital tuberosity. No significant effect on supination strength was highlighted.