Radial Tunnel Syndrome: Case Report and Comprehensive Critical Review of a Compression Neuropathy Surrounded by Controversy

Abstract

Radial tunnel syndrome (RTS) is an uncommon controversial entity thought to cause chronic lateral proximal forearm pain due to compression of the deep branch of the radial nerve, without paralysis or sensory changes. Diagnostic confusion for pain conditions in this region results from inconsistent definitions, terminology, tests, and descriptions in the literature of RTS and “tennis elbow,” or lateral epicondylitis. A case of bilateral RTS with signs discordant with traditionally used clinical diagnostic tests was successfully relieved with surgical decompression and led us to perform a comprehensive critical review of the condition. We delineate the controversy surrounding its diagnosis and aim to facilitate appropriate management and identify other areas for further study in this controversial condition. Clinical validity and evidence of anatomical rationale for the traditionally used Maudsley’s provocative test is unclear in diagnosis of RTS or in chronic lateral elbow pain, if at all. Neither imaging nor electrophysiological studies contribute to a clinical diagnosis which is supported by short-term improvement after an injection with long-acting local anesthetic and corticosteroid. Accurate diagnosis and treatment of RTS can significantly improve quality of life, but validity and evidence for traditional clinical tests and definitions must be clarified.

Introduction

The challenge to diagnose chronic lateral elbow and forearm pain is well recognized. Similar symptoms can make it difficult to differentiate between diagnoses. Imprecise language which historically referred to pain in this region such as “tennis elbow,” “chronic tennis-elbow,” or “resistant tennis elbow” further complicates understanding. The current accepted definition of “tennis elbow” is lateral epicondylitis, a degenerative tendinopathy.^1-3 Radial tunnel syndrome (RTS) is an alternative described cause of pain. Its postulated pathogenesis is compression of the deep branch of the radial nerve, viz the posterior interosseous nerve (PIN), within the radial tunnel. Radial tunnel syndrome has been reported as the most common entrapment neuropathy of the radial nerve, ⁴ accounting for up to 1% to 2% of peripheral nerve entrapments in the upper limb. ⁵ Other reports cite a rare annual incidence of PIN compression neuropathies at 3 in 100 000. ⁶ Affected populations are associated with repetitive work, especially in forearm pronation and supination, heavy lifting, precedent trauma, racquet sports, and occupations such as manual workers, homemakers, machine operators, musicians, and professionals among others.

Unlike pain syndromes caused by mixed nerves such as carpal and cubital tunnel syndromes caused by the median and the ulnar nerves, respectively, nomenclature of manifestations of radial nerve entrapment is further confused by inconsistent descriptions of pain, and there is no accepted reference standard for its diagnosis. ⁷ Controversially, some question the existence of pain conditions resulting from compression of the primarily “motor” PIN.^8,9 Posterior interosseous nerve compression can also result in palsy of the PIN-innervated musculature, labeled PIN syndrome, although a clear distinction is not always made between RTS and PIN syndrome.^10-12

By deduction, a lack of clarity in understanding and nomenclature can result in misdiagnosis, incorrect treatment, or treatment failure that at best does not alleviate nor improve symptoms but at worst can cause harm.

Method

The following case of long-standing bilateral lateral proximal forearm pain was successfully treated with surgical radial tunnel decompression, despite signs being discordant with traditional clinical diagnostic tests for RTS. Search of the PubMed database to March 2020 was subsequently conducted with the search terms “radial tunnel” OR “posterior interosseous nerve syndrome.”

A 60-year-old right-handed civil construction educator presented with a 6-year history of bilateral focal pain and tenderness just distal to the lateral epicondyle. This interfered with daily activities including his work which involved physical labor, domestic activities such as chopping firewood, and especially his preferred leisurely pastime of golf.

Neither resisted middle finger extension nor resisted active supination in elbow extension aggravated pain. Despite tenderness over the radial tunnel, there was no tenderness over the lateral epicondyle itself. There was no weakness or atrophy of PIN-innervated muscles.

One of 5 previous electrophysiological studies found a minor abnormality of the left ulnar nerve which was decompressed by another surgeon. This unfortunately worsened his symptoms. His symptoms were occasionally suggestive of carpal tunnel syndrome, despite normal nerve conduction studies. Ultrasound-guided carpal tunnel cortisone injection was ineffective. Neck magnetic resonance imaging was normal. Acupuncture was ineffective. Ultrasound-guided corticosteroid and local anesthetic injection around the right PIN produced a dramatic improvement for a few days.

A presumptive diagnosis of RTS was made. With full informed consent, the patient requested surgical exploration of the more symptomatic right side.

Results

On October 4, 2019, under general anesthesia and tourniquet control, exploration, decompression, and neurolysis was performed via the posterior (dorsal) approach (Figures 1a and 1b).^13,14

Figure 1.

(a) Divided belly of the right superficial head of S with retraction of EDC ulnarly and ECRB radially via the posterior (dorsal approach) and (b) closer view of constriction of PIN at the level of the arcade of Frohse (proximal edge superficial supinator muscle belly). The tips of the tenotomy scissors indicate constriction.

Note. S = supinator; EDC = extensor digitorum communis; ECRB = extensor carpi radialis brevis; PIN = posterior interosseous nerve.

Intraoperatively, constriction of the PIN was identified at the arcade of Frohse (Figure 1b). Slight indentation in the superficial surface of the nerve was more palpable than visible. At postoperative review 3 weeks later, the patient’s right forearm was pain-free and he requested exploration of the now more symptomatic left side. He also reported a successful return to playing golf.

A similar procedure was performed on the left forearm 7 weeks later (Figures 2a-2e).

Figure 2.

(a) Skin marking for posterior approach; (b, c) dissection proceeds between extensor digitorum communis and extensor carpi radialis brevis; and (d, e) the striped muscle belly of the superficial head of supinator is seen and carefully divided along its length revealing the posterior interosseous nerve.

This time, division of the superficial supinator belly revealed slight PIN compression at the muscle’s distal edge.

At 4 and 2 months after the procedures, respectively, of the right and left forearms, the patient was pain-free; this was maintained at 12-month follow-up. Maudsley’s middle finger test remains negative. ¹⁵ The patient reports that his golfing handicap, which before surgery was at 15, is now close to par.

The PubMed database search yielded 199 results. All 24 foreign language articles were excluded as those were clearly irrelevant or unable to be retrieved. A further 7 articles were identified as relevant in the reference list of some of the 90 articles obtained, resulting in review of 97 articles. One systematic review looking at interventions for treating RTS was identified. ¹⁰ A further limited search was performed on review articles related to lateral epicondylitis and Maudsley’s test.

Discussion

Anatomy

The radial nerve bifurcates into a superficial sensory and a primarily motor deep branch (PIN) within 3 cm of the elbow joint proximally or distally. The superficial branch continues beneath the brachioradialis, while the PIN passes through the radial tunnel which is approximately 5 cm long from the level of the radial head to the distal edge of the superficial head (belly) of the supinator.^6,16 The radial tunnel walls are medially, the brachialis and biceps tendon; anterolaterally, the mobile wad of the brachioradialis, extensor carpi radialis longus (ECRL), and extensor carpi radialis brevis (ECRB); posteriorly the floor is the capitellum of the humerus and the capsule of the radiocapitellar joint continued by the deep head of supinator distally; and the radial recurrent vessels, superficial supinator head, and brachialis form a roof anteriorly.^15-17

Five described levels of PIN entrapment within the radial tunnel are as follows: ⁶

1. Anterior to the radiocapitellar joint between the brachialis and brachioradialis,

2. Level of recurrent radial vessels (leash of Henry) and radial neck,

3. Leading tendinous edge of the ECRB medial proximal border,

4. Fibrous proximal edge of the superficial head of supinator (arcade of Frohse),

5. Distal edge of the superficial supinator head.

An anatomical study showed that the PIN is in fact a mixed nerve, motor for the extensor muscles of the forearm, and sensory and proprioceptive for the posterior capsule of the wrist joint. ¹⁸

Surgery

Described approaches to the radial tunnel include dorsal, anterolateral, anterior, and transbrachioradialis,^12,19 with similarities between the transbrachioradialis and anterior approaches. ²⁰

Dorsal (posterior approach)

This is senior author’s (B.R.J.) preferred approach and is described above.

Anterior approach

A curvilinear incision is made 3 cm lateral to the biceps tendon protecting the lateral cutaneous nerve of the forearm. Brachioradialis muscle is longitudinally split as the radial head is approached identifying the radial nerve. The tendinous portion of ECRB is divided transversely as well as the entire superficial part of supinator and any potentially compressive branches of the recurrent radial artery.^15,16

Confusing Nomenclature

Radial tunnel syndrome as an alternative diagnosis to lateral epicondylitis was first presented in 1883 in an article “Lawn-Tennis Elbow.” ²¹ As our understanding develops, most would agree they are separate entities. However, definitions in the literature are inconsistent and terms are used interchangeably which confuses the entities actually being referred to. Despite the definition of “tennis elbow” being lateral epicondylitis,^1-3 even as recently as 2010, some describe it as being “tendinogenic, articular or neurogenic” in etiology. ²² We will explore another example below of definition causing confusion in diagnosis, a provocative maneuver referred to as “Maudsley’s test.”

Like authors had postulated in the preceding decades, Roles and Maudsley described a pain condition attributed to PIN entrapment in the radial tunnel in 1972. They first used the now commonly accepted terminology RTS, but concurrently named it “resistant tennis elbow” as distinct from traditional “tennis elbow” (lateral epicondylitis). ¹⁵ Many cite this article and label a provocative test they used, resisted middle finger extension which elicited immediate pain in the affected area in the proximal radial forearm, as “Maudsley’s test” in relation to RTS presumably from compression of the nerve at the radial tunnel.^1,16,23 However, others describe Maudsley’s test as an indicator for lateral epicondylitis.^2,24 This differs from the original authors’ test description and reasoning, as it was not for diagnosis of “tennis elbow” but rather as a tool to select suitable patients who might benefit from operative decompression of the “radial tunnel syndrome”; they postulated the pain was caused by PIN compression by tightened fascial origin of ECRB and was elicited in all 36 patients in their series. ¹⁵

Lister et al reported Maudsley’s test to be 1 of the 3 pathognomonic indicators of RTS. ¹⁶ Others have concurred it is a useful diagnostic test.^23,25 Others have found it unreliable.^5,26,27

Werner’s series found no relationship between positive preoperative Maudsley’s test and intraoperative observations of a fascial extension or arch from the ECRB crossing the nerve, and demonstrated better results when Maudsley’s test was negative. ²⁶ In 39 of 67 cases where the middle finger test was positive, there was a fascial extension from ECRB, compared with 15 of 23 cases where the test was negative. No convincing PIN compression by this extension was found, nor any nerve alterations observed at or under it. Furthermore, results after decompression were no different whether or not the nerve was crossed by ECRB.

Another study demonstrated 11 patients with positive Maudsley’s test lacked evidence of PIN compression by ECRB and concluded the provocative test did not reliably indicate ECRB impingement. ²⁷

Without referring to these articles, an anatomical study in 2002 hypothesized that a positive Maudsley’s test was more likely to indicate pathology of the extensor digitorum communis (EDC), rather than compression of the PIN by ECRB or disease within the ECRB itself. ²⁴ In 13 specimens, they demonstrated that muscle fibers of the middle finger component of EDC extend to the lateral epicondyle. ²⁴ The hypothesis that EDC is implicated in Maudsley’s test may be supported by the Nirschl group that concluded the pathoanatomy of lateral epicondylitis to be angiofibroblastic tendinosis; although primarily involving ECRB, it secondarily involved EDC from observations in greater than 1000 cases of lateral epicondylitis. ³ These studies bring the diagnostic accuracy of Maudsley’s test in diagnosing RTS into question, and its clinical value is therefore unclear.

Adding confusion, another example of inconsistency in language is reference to RTS as “supinator syndrome.” ⁵ Some call radial nerve entrapment at the cubital fossa “posterior interosseous nerve syndrome or supinator syndrome.” ²⁸ Another example of a confusing description of “tennis elbow,” inconsistent with lateral epicondylitis, is as follows:

during extension of the elbow with the forearm, in pronation and the wrist in flexion, the position adopted at the end of a tennis service, the tendinous edges of the supinator and extensor carpi radialis brevis encroach on the radial nerve . . . ²⁸

Roles and Maudsley cursorily mentioned features of weak grip and occasional paresthesia in the superficial radial nerve distribution among their study population, ¹⁵ which differs from our current understanding of true RTS which is nonparetic. ¹⁰ Some authors dispute the existence of RTS and believe the name should be reserved for true neurogenic cases with neurologic deficit and weakness in the distribution of the PIN. ²⁹

Clinical Examination

Roles and Maudsley reported RTS presents with symptoms of “pain and tenderness over the lateral epicondyle of the humerus and pain on passive stretching of the extensor muscles and on resisted extension of the fingers,” but failed conventional treatment for lateral epicondylitis after “reasonable” time. ¹⁵ They described 2 provocative tests to identify and select patients for operative decompression: (1) Maudsley’s test, expounded above; and (2) local tenderness along the radial nerve in front of the radial head compared with the contralateral side.

Hagert’s group concluded that the following 3 characteristics, if present, indicate a nonparetic PIN entrapment at the arcade of Frohse, and not lateral epicondylitis: (1) night pain; (2) local tenderness 5 cm distal to the lateral epicondyle, irrespective of lateral epicondyle tenderness; and (3) indirect pain induced by supination against resistance. ³⁰

Lister described 3 pathognomonic signs: (1) severe tenderness over the radial nerve through the mobile wad at and just distal to the radial head; (2) positive Maudsley’s test; and (3) similar pain on resisted supination of the extended forearm. ¹⁶ Pain was exacerbated by repetitive movement involving forearm pronation and wrist flexion.

Werner described similar but slightly different criteria of clinical diagnosis: proximal radial forearm pain, aggravated by work but present at rest; and intense tenderness over the PIN, especially under the arcade of Frohse. ²⁶ One-third of the reported cases had a nontender epicondyle, and in most cases, there was pain on active supination and pronation against resistance. Interestingly in one-third of the cases, Maudsley’s test was negative and when positive, maximal pain was usually located over the lateral epicondyle. Surgical results were better when the epicondyle was not tender and when Maudsley’s test was negative. Werner also found equally good results when Maudsley’s test was negative as when a positive Maudsley’s test was combined with a nontender epicondyle.

In another series, all 49 patients described localized tenderness over the radial tunnel rather than the lateral epicondyle, 46 had pain on resisted supination, and 36 of 49 had positive Maudsley’s test. ³¹ Eight of 10 patients who had greater than 75% pain relief after diagnostic anesthetic injections to the radial tunnel had good surgical results.^23,31 Other authors find PIN anesthetic blockade useful, but they have encountered false-positive cases. ³² In another series, all patients received local anesthetic blockade of the radial tunnel with complete or partial relief of symptoms, although those with coexisting lateral epicondylitis did not experience relief from their epicondylitis symptoms. ¹¹ Other studies have also used relief of symptoms with infiltration of cortisone and lidocaine in the radial tunnel to support diagnosis of RTS.^33,34

Interestingly, our patient presented with absence of some of these classically described signs above. Of Lister’s signs, our patient only had the tenderness distal to the radial head. Maudsley’s test was negative on multiple occasions which, like other studies, questions its utility in diagnosis.^5,11,26,27 Instead, the examination clues that led to the diagnosis were pain over the radial tunnel, absence of tenderness over lateral epicondyle itself, and elicitation of pain on resisted supination of forearm in elbow flexion, rather than in extension. Although some have written that resisted supination of the forearm should be performed with the elbow fully extended to negate the supinator force of biceps brachii, ²³ others have reasoned that by flexing the elbow to 90° and fully pronating the forearm, pain is reproduced on resisting active supination as the proximal edge of supinator is compressed against the PIN. ¹⁷

Other Investigations

Majority of studies describe a lack of abnormalities found on medical imaging and electrodiagnostic testing.^{13,19,23,27,32} Some dispute RTS as a true condition based on negative electrodiagnostic testing.^8,35 Others reason that a normal test does not exclude RTS and that despite normal studies at rest or forced supination, resisted supination of the forearm caused a significantly higher occurrence of latency prolongation in the PIN in patients with RTS compared with normal controls.^23,36

Rationale for Operative Intervention

All but 3 of Roles and Maudsley’s series of 38 cases had a good or excellent postoperative result. This and subsequent studies have shown the arcade of Frohse is the most common site of nerve compression.^15,27,37

Nineteen of 20 cases treated surgically by the Lister group had symptomatic relief with an average follow-up of 29.8 months. ¹⁶ That same year, Werner published a series where 73 of 90 cases had good or excellent results. ²⁶ Of the 17 fair and poor cases, he reasoned that some were probably misinterpreted as nerve entrapments; 7 cases did not have compression observed at surgery.

In 1980, the Werner group demonstrated pressure of 40 to 50 mmHg exerted on the PIN by the superficial head of supinator during passive stretch of the muscle, and this pressure increased almost 4-fold with active muscle contraction. ³⁶ Citing experimental studies that demonstrated reduction in nerve venous blood flow at 20 to 30 mmHg and ischemia at 60 to 80 mmHg, the Werner group theorized physiological changes behind RTS. Epineural vessels sensitive to low compression forces might be injured resulting in epineural edema followed by fibrosis, and the increases in connective tissue due to ischemia may cause mechanical sensitivity of nerve fibers, especially the numerous thin afferent fibers mediating pain sensation. Sixteen of 90 operative cases from their 1979 article demonstrated indentations combined with proximal swelling of the nerve at the intersection between the PIN and arcade of Frohse. ²⁶

Another case series demonstrated symptom relief in 14 of the 15 cases of RTS treated operatively. ²⁵

A 2-component cadaveric biomechanical study looked at the role of supinator in the pathogenesis of chronic lateral elbow pain. ³⁸ One experiment looked at the relative contribution of each extensor muscle to tensile force at the common extensor origin. Using a force transducer inserted in the common extensor tendon at the usual site of clinical tenderness in lateral epicondylitis, they sequentially applied tension to each of the ECRB, EDC, superficial head of supinator, extensor carpi ulnaris (ECU), and ECRL muscles. Extensor carpi radialis brevis and EDC produced the largest increases in mean tensile force, followed by supinator. Contributions of ECRL and ECU were not significant. The authors concluded that supinator may play a role in lateral epicondylitis and may need to be addressed in addition to EDC and ECRB in treatment of epicondylitis. The second experiment measured radial tunnel pressure changes with different wrist and elbow positions by using an angioplasty catheter inserted along the PIN in the radial tunnel, and the effects of sequential musculotendinous release. The radial tunnel pressure reduced with release of the superficial head of supinator most significantly, especially with the hand in a pronated and flexed position. They concluded that lateral epicondylitis and RTS are conditions which can be difficult to separate and may coexist in some cases and that release of the superficial head of supinator would reduce tensile force at the common extensor tendon origin and also reduce pressure within the radial tunnel. Others have suggested that RTS can occur simultaneously in up to 5% of patients with lateral epicondylitis. ¹

Cases with greater than 1 compression site have been reported. ²⁷

Outcomes

The only systematic review published regarding interventions for RTS found that no randomized controlled trials or controlled clinical trials were available. ¹⁰ Of 21 eligible case review articles from 1979 to 1999, only 6 met their criteria of being high-quality articles for analysis.^{15,16,26,27,30,33} The 6 articles evaluated effectiveness of surgical decompression but not of conservative management. The review found, therefore, a tendency for the effectiveness of surgical decompression in patients with RTS and unknown effectiveness of conservative treatment. It also found a lack of protocol in diagnosing RTS.

Reported outcomes vary in the literature with surgery reported to improve symptoms in 67% to 93% of patients.^10,13,19 Reasons for such varied outcomes may be because imprecise definitions of “radial tunnel syndrome” can lead to ill-conceived surgery. ³⁹ Some studies have reported incidence of coexistence of RTS and lateral epicondylitis. Of patients with RTS, it is reported that between 18% and 43% also have lateral epicondylitis, and outcomes have been reported to be less satisfactory compared with patients without lateral epicondylitis.^11,27,31,37 Others have reported less favorable outcomes in patients claiming compensation,^5,11,31 although this is not always the case. ²⁷

Recently, a study looked at the utility of a single injection of lignocaine and betamethasone into an area of maximal tenderness in the mobile wad of 35 patients with RTS. ⁴⁰ A visual analogue score for pain and the Quick Disabilities of the Arm, Shoulder, and Hand (qDASH) score were used as baseline measures and at 1 year. Although the article reports most patients had benefit, it is difficult to draw firm conclusions from the study due to a significant number having coexistent conditions including lateral epicondylitis, cubital tunnel syndrome, carpal tunnel syndrome, and fibromyalgia affecting the same limb, and potentially the qDASH score. Eight patients (35%) who had no improvement went on to have surgical decompression of the PIN, but no comment is made on their postoperative course. Limitations cited by the authors include a lack of ultrasound guidance to confirm injection within the radial tunnel itself and a lack of a control group. A high proportion of patients (78%) also were observed to have clinical lateral epicondylitis within the same arm.

Conclusion

Radial tunnel syndrome should be considered in patients presenting with chronic lateral proximal forearm pain and as an alternative diagnosis to lateral epicondylitis. Our summary of recommendations based on our review can be found in Figure 3. In addition, clinical validity and evidence of anatomical rationale for the traditionally used Maudsley’s provocative test is unclear and warrants further investigation to clarify its use and value in diagnosis of RTS or in chronic lateral elbow pain, if at all. Literature surrounding the conditions of RTS and lateral epicondylitis would benefit from more consistency in nomenclature and definition. Effectiveness of conservative measures is unclear but may be of benefit and warrants further study. Surgical management often leads to satisfactory outcomes if the diagnosis is accurate, and the patient receives appropriate targeted treatment, but can lead to poor outcomes if not.

Figure 3.

Authors’ current recommendations based on comprehensive critical review of radial tunnel syndrome.

Note. RTS = radial tunnel syndrome; PIN = posterior interosseous nerve; SBRN = superficial branch radial nerve.