Research Review by Dr. Shawn Thistle©

Date:

Mar. 2008

Review Title:

Nerve Entrapment Syndromes of the Elbow

Study Titles:

  1. Robertson C, Saratsiotis J. A review of compressive ulnar neuropathy at the elbow. JMPT 2005; 28: 345.e1-345.e18.
  2. Tsai P, Steinberg DR. Median and radial nerve compression about the elbow. J Bone Joint Surg (Br) 2008; 90-A(2): 420-428.

Summary:

This review will focus on compressive neuropathies about the elbow. Each of the three main nerves of the arm (median, ulnar, radial) can become entrapped in various anatomical regions and structures. The prudent clinician should be confident in identifying and differentiating the clinical presentations of various entrapment neuropathies of the elbow, as well as palpating and treating the involved tissues.

Those who practice Active Release Techniques® or similar soft tissue treatments will espouse their efficacy for treating these conditions, in the absence of supporting scientific evidence. For the most part, this anecdotal evidence is all we have to rely on for these conditions, so specific treatment will not be discussed until higher level evidence emerges.

In this review, each nerve will be dealt with separately, outlining relevant anatomy, and clinical considerations for each nerve’s entrapment neuropathies at the elbow.

MEDIAN NERVE

Anatomy:
  • formed from the medial and lateral cords of the brachial plexus, containing fibers from C6-T1
  • the lateral cord contributes mostly sensory fibers from C5-6 while the medial cord contributes mostly motor fibers from C8-T1
  • from the axilla, the nerve courses lateral to the brachial artery to the elbow
  • in the middle of the brachium, the nerve crosses the brachial artery to lie medial to it, after which both pass under the lacertus fibrosus, and enter the antecubital region medial to the biceps tendon (anterior to brachioradialis)
  • the nerve then passes under the humeral head of the pronator teres, and subsequently between the humero-ulnar and radial portions of flexor digitorum superficialis (under the proximal arch of the muscle belly, which can become fibrotic in some patients)
  • the last major branch of the median nerve, the anterior interosseous nerve (AIN), branches approximately 4cm distal to the medial epichondyle of the humerus, and runs along the interosseous membrane of the forearm, supplying motor innervation to the pronator quadratus, flexor digitorum profundus, and flexor pollicus longus
Anterior Interosseous Nerve Syndrome
  • normally presents with isolated palsy of the flexor pollicus longus and/or the radial aspect of flexor digitorum profundus (and/or pronator quadratus)
  • patient will complain of weakness of pinch – affecting activities such as writing and manipulating small objects
  • there may be a antecedent episode of insidious forearm pain followed by progressive hand weakness
  • repetitive elbow flexion and pronation are proposed mechanisms of injury
  • clinically, look for inability to flex the interphalangeal joint of the thumb (and perhaps index finger), and inability to make the “OK” sign
  • pronator quadratus weakness will be difficult to isolate due to normal function or pronator teres (can be partially eliminated by testing pronation with elbow fully flexed)
Pronator Syndrome
  • known as the great mimic of carpal tunnel syndrome (CTS)
  • associated with pain and paresthesia of the lateral 3½ digits, becoming worse with certain activities
  • true CTS is more likely to present with night pain
  • the median nerve may be tender over the wrist and elbow in both conditions
  • examination may reveal diminished sensation over the distribution of the palmar cutaneous nerve (which branches proximal to the carpal tunnel, therefore preserving its function in true CTS, but not in pronator syndrome due to the more proximal entrapment)
  • Phalen’s test should be negative, but Tinel’s over the nerve at the pronator could be positive in pronator syndrome
  • additional specific entrapment sites about the elbow can include the ligament of Struthers (originating from the suprachodylar eminence to the humeral shaft), lacertus fibrosus, and fibrous arch of the flexor digitorum superficialis
  • suspect lacertus fibrosus involvement if pain is recreated with resisted elbow flexion/forearm supination
  • a positive middle finger flexion test may identify flexor digitorum superficialis involvement
RADIAL NERVE

Anatomy:
  • terminal branch of the posterior cord, containing fibers from C5-8
  • from the axilla, the nerve passes through the triangular space to the posterior aspect of the brachium, coursing along the anterior aspect of the lateral head of the triceps
  • from there, the nerve travels along the spiral groove of the humerus before emerging under the proximal brachioradialis and on top of brachialis
  • under the cover of extensor carpi radialis brevis and longus, the nerve branches into the superficial sensory branch and the posterior interosseous nerve (PIN) – this occurs proximal to the radial tunnel
  • the superficial sensory branch continues distally under brachioradialis
  • the PIN crosses the elbow and lies in fatty tissue anterior to the radiocapitellar joint, before entering the radial tunnel
  • potential entrapment sites include fibrous bands between the brachioradialis and radiocapitellar joint capsule, the proximal edge of the supinator (also called the Arcade of Frohse), distal edge of the supinator, branches of the radial recurrent artery, and the underside of extensor carpi radialis brevis
  • the PIN innervates the extensor carpi radialis brevis and supinator (before entering the radial tunnel), the extensor carpi ulnaris, extensor digitorum communis, and extensor digiti minimi (with a superficial branch arising under the distal supinator), and the abductor pollicus longus, extensor pollicus brevis/longus, and extensor indicis proprius (with a deeper branch arising under the distal supinator)
Posterior Interosseous Nerve (PIN) Syndrome
  • patient may present with a transient episode of forearm pain which precedes insidious extensor muscle weakness
  • although PIN palsy is normally complete, individual digits may be spared
  • muscles of the mobile wad are spared as they are innervated more proximally
  • main symptom of this syndrome is motor deficit
Radial Tunnel Syndrome
  • caused by compression of the PIN in the proximal forearm
  • main clinical characteristic is proximal dorsal forearm pain
  • symptoms may occur at night or be aggravated by repetitive motions involving pronation/supination of the forearm, maximal wrist flexion-extension, or elbow extension
  • symptoms may overlap with those of lateral epichondylalgia or extensor tendinopathy (commonly called Tennis Elbow)
  • actual motor involvement is rare in this syndrome
  • it is estimated that 5% of patients with Tennis Elbow have RTS while 50% of patients with RTS have concomitant Tennis Elbow
  • the most common finding is tenderness over the mobile wad and radial tunnel (versus over the lateral epichondyle in Tennis Elbow)
  • the middle finger extension test may be useful for identifying RTS, but remains controversial
ULNAR NERVE

Anatomy
  • terminal branch of the medial cord of the brachial plexus, containing C8-T1 (and occasionally C7) nerve roots
  • descends along medial aspect of the arm, where it pierces the medial intermuscular septum at the border of the triceps and brachialis muscles where it enters the posterior compartment of the arm
  • the nerve passes through the cubital tunnel, the most common area of entrapment
  • distal to the cubital tunnel, the nerve travels to the flexor compartment of the forearm via the medial epichondylar groove of the distal humerus, where it emerges between the two heads of flexor carpi ulnaris
  • during elbow flexion, the medial collateral ligament bulges inward, which narrows the cubital tunnel
  • terminal branches include two cutaneous branches: the dorsal cutaneous branch to the ulnar side of the hand (4th/5th digits), and a palmar cutaneous branch; and a deep motor branch which innervates the hypothenar muscles, 4th/5th lumbricals, all interossei muscules, adductor pollicus, and the deep head of flexor pollicus brevis
  • common entrapment sites for the ulnar nerve at the elbow include: 1) medial intermuscular septum (Arcade of Struthers); 2) ulnar groove; 3) cubital tunnel; 4) between the two heads of the flexor carpi ulnaris
Cubital Tunnel Syndrome
  • used to refer to entrapment at the arcuate ligament of Osborne (which forms the roof of the cubital tunnel), but now is used to described entrapment at any of the four sites listed above
  • can include both motor and sensory abnormalities
  • can be caused by external trauma, pressure/compression, bony or scar tissue impingement, myofascial irregularities, soft tissue masses etc.
  • patients generally report paresthesias radiating distally to the ulnar aspect of the hand, sometimes coupled with pain at the medial elbow/forearm
  • paresthesia may be more pronounced at night, due to sleeping with the elbow in a flexed position, which tensions the nerve
  • weakness starts with clumsiness and reduced dexterity in the hand, with progression to weakness of grip and pinch (identified clinically with Froment’s sign – which attempts to isolate the adductor pollicus)
  • atrophy of the intrinsic hand muscles may be noted when compared to other side
  • “clawing” of the 4th and 5th fingers may be present (better known as “claw hand” or “benediction posture”), which results from paralysis of the lumbrical and interosseous muscles
  • patients will not be able to flex the metacarpophalangeal joints, and should have difficulty making a fist with ulnar aspect of hand
  • other clinical signs include the inability to oppose the 5th finger to the thumb or make an “o”, positive Froment’s sign, positive Tinnel’s sign at medial epichondylar groove, positive pressure provocation at the elbow (manual pressure applied to ulnar nerve proximal to cubital tunnel with elbow flexed 20° and forearm supinated – can also be repeated with elbow in full flexion which is then called the “combined pressure provocation test”)

Conclusions & Practical Application:

Nerve entrapment syndromes at the elbow are relatively common. Recognizing distinguishing signs and symptoms of various entrapment syndromes can help the clinician direct treatment appropriately. In recalcitrant or progressive cases that do not respond to treatment, referral for nerve conduction testing or surgical consultation may be required, regardless of which nerve is involved.

Unfortunately, the literature to date does little but suggest that a course of conservative treatment be attempted before this step is taken, rather than providing specific treatment guidelines. It goes without saying that further research is required. The practicing clinician should bear in mind that even well written case series would represent valuable additions to the literature.