Posterior interosseous neuropathy: distinguishing from a proximal radial neuropathy

The posterior interosseous nerve is the terminal motor branch of the radial nerve that innervates the extensor carpi ulnaris and the extensors of the thumb and fingers. We describe a case of a posterior interosseous neuropathy presenting with the typical ‘finger drop’ and partial ‘wrist drop’. We focus on the clinical signs that distinguish it from a more proximal radial neuropathy, clarified by nerve conduction studies and needle electromyography. Multimodal imaging of the forearm did not identify a compressive lesion. Persistent symptoms prompted surgical exploration 5 years after initial onset. It identified compression of the posterior interosseous nerve in the region of the arcade of Frohse and leash of Henry. The sites were decompressed and concurrent salvage secondary reconstructive tendon transfers were required in view of the severe axonal loss with minimal chance of functional reinnervation.

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 Palsy Caused by a Ganglion of the Arcade of Frohse

A 51-year-old male who is right-handed visited the outpatient for right fingers-drop. The patient's fingers, including thumb, were not extended on metacarpophalangeal joint. The active motion of the right wrist was available. The electromyography and nerve conduction velocity study were consistent with the posterior interosseous neuropathy. Further evaluation was done with the magnetic resonance imaging for finding the space-occupying lesion or any possible soft tissue lesion around the radial nerve pathway. On magnetic resonance imaging, the ganglion cyst, which was about 1.8 cm in diameter, was observed on the proximal part of the superficial layer of the supinator muscle (Arcade of Frohse). The surgical excision was done on the base of ganglion cyst at the base of stalk of cyst which looked to be connected with proximal radioulnar joint capsule. The palsy had completely resolved when the patient was observed on the outpatient department a month after the operation.

Transbrachioradialis Approach to the Radial Tunnel: An Anatomic Study of 5 Potential Compression Sites

Background: Recent anatomic studies have failed to demonstrate a single utilitarian approach to intraoperative identification and surgical release of all 5 potential sites of posterior interosseous nerve (PIN) compression in the radial tunnel. This study examines if a single incision brachioradialis-splitting approach without the use of additional anatomic windows is capable of adequately exposing the entire length of the radial tunnel, including all 5 sites of PIN compression to allow for adequate release. Methods: Ten fresh frozen cadaver forearms (6 female, 4 male) were dissected utilizing a curvilinear 7 cm incision over the brachioradialis. The muscle belly was split via simple blunt retraction, exposing the radial tunnel. The PIN was identified and mobilized at 5 compression sites: radiocapitellar joint (RCJ), radial recurrent vessels (Leash of Henry), fibrous medioproximal edge of extensor carpe radialis brevis, arcade of Frohse, and distal edge of supinator. Results: The PIN was identified and effectively released in all specimens without difficulty from this single approach. All 5 sites of compression were visible and accessible through the brachioradialis-split approach. Specifically, there was no difficulty in identifying and releasing the PIN at the distal edge of supinator. Conclusions: Radial tunnel syndrome is defined as PIN compression within the radial tunnel spanning from the fibrous RCJ to the distal edge of the supinator. A single brachioradialis-splitting approach is adequate for complete visualization and release of all compression sites of the radial tunnel. Utilizing this technique allows for surgical access and ease as well as minimizing necessity for additional windows or multiple incisions.