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PRONATOR SYNDROME

Introduction

Compression neuropathy of the median nerve in the proximal forearm was first termed “pronator syndrome” in 1951 by Dr. Seyffarth. The classic definition describes entrapment of the median nerve where it passes between the two heads of the pronator teres muscle. Abnormal anatomic structures, such as a schwannoma or ganglion cyst, may also cause pronator syndrome-like symptoms, but this is rare. Patients experience aching pain in the proximal forearm and weakness of muscles innervated by the median nerve. The diagnosis is made clinically, yet clinical findings are inconsistent.1,2 Pronator syndrom is a difficult diagnosis to make with certainty because of the lack of level I evidence to describe the basis of this diagnosis and treatment for it.3

Pathophysiology

  • There are three categories of nerve injury:
    • Neurapraxia: least severe; focal damage of the myelin fibers around the axon (axon and connective tissue sheath are not disrupted); days to weeks in duration
    • Axonotmesis: more severe; axon is injured; regeneration possible, but typically requires months, and recovery is often incomplete
    • Neurotmesis: complete disruption of the axon; recovery unlikely
  • Degree of injury depends on severity and duration of compression

Related Anatomy

  • Besides the two heads of the pronator teres muscle, there are four additional sites of potential compression:
    • Lacertus fibrosis (bicipital aponeurosis)
    • Ligament of Struthers (extending from a supracondylar process to the medial epicondyle)
    • Anomalous muscles such as an accessory head of the flexor pollicis longus (FPL)
    • Flexor digitorum superficialis (FDS) arch
  • The FDS arch is believed to be one of the more common sites of compression in pronator syndrome
  • At the level of the lacertus fibrosus, the median nerve passes through a “tunnel”
  • Median nerve branches also deep to a “superficialis arcade”

Incidence and Related Conditions

  • Pronator syndrome represents <1% of all median nerve entrapment disorders, but is the second most common cause after carpal tunnel syndrome (CTS).
  • The disorder is often confused with CTS because symptoms are similar.
  • Pronator syndrome is four times more likely to affect middle aged women than men, which suggests anatomic anomalies rather than overuse as causative.

Differential Diagnosis

  • Anterior interosseous nerve (AIN) syndrome
  • Carpal tunnel syndrome
  • Cervical radiculopathy
  • Double-crush syndrome
  • Thoracic outlet syndrome
ICD-10 Codes

  • PRONATOR SYNDROME

    Diagnostic Guide Name

    PRONATOR SYNDROME

    ICD 10 Diagnosis, Single Code, Left Code, Right Code and Bilateral Code

    DIAGNOSISSINGLE CODE ONLYLEFTRIGHTBILATERAL (If Available)
    PRONATOR SYNDROME G56.12G56.11 

    ICD-10 Reference

    Reproduced from the International statistical classification of diseases and related health problems, 10th revision, Fifth edition, 2016. Geneva, World Health Organization, 2016 https://apps.who.int/iris/handle/10665/246208

Symptoms
Transient paresthesias in the hand (over the thenar eminence, thumb, and three fingers—but not little finger)
Loss of pinch strength, loss of fine motor skills, and a sense of clumsiness (dropping objects)
Absence of nighttime pain (pain present in patients with CTS)
Decreased sensation in the distribution of median nerve’s palmar cutaneous branch, particularly over the thenar eminence (sensation normal in patients with CTS)
Typical History

40- to 50-year-old aged women will complain of aching pain and weakness of the proximal forearm and possibly tingling and numbness of the hand. She may report a history of activities requiring repetitive pronation of the forearm, especially with the elbow extended. Such activities include chopping wood, playing racquet sports, rowing, weight-lifting, throwing, and repeatedly using a screwdriver or cleaning fish. Symptom onset may be described as insidious or acute.  

Positive Tests, Exams or Signs
Work-up Options
Treatment Options
Conservative
  • Activity modification
  • Injection of an anti-inflammatory medication or short course of oral steroids
  • Physical therapy
  • Splinting with elbow at 90° 
  • Posture work station modification
  • Assessment of results at 3–6 months before making a decision about surgery
Operative

Surgery entails decompression of the median nerve

  • Traditional:
    • Large, S-shaped incision
    • All possible points of nerve compression from distal third of the arm through the proximal third of the forearm should be released completely.
    • Technically demanding and includes release of lacertus fibrosis, ligament of struthers, FDS arch and any other compressive structure that can be safely released.
  • Procedures also include minimally invasive, via a mini-open procedure or endoscopy:
    • Release of lacertus fibrosus
  • Conscious surgery with local lidocaine-epinephrine infiltration and no tourniquet
  • Immediate mobilization encouraged
    • Release of fibrous arcade of superficialis muscles, located ~7 cm distal to elbow crease
  • For tumor etiology such a lipoma or ganglion, do surgical decompression and removal of the mass 
CPT Codes for Treatment Options

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Complications
  • Traditional approach: excessive scar tissue; wound infection
  • Injury to branches of medial antebrachial cutaneous nerve
Outcomes
  • Most outcomes are from small retrospective case series where the objectivity of diagnostic process is limited. 1-3
  • Conservative treatment: ~50% of patients experience symptom resolution within 4 months
  • General decompression: good to excellent results reported by ≥90% of patients
    • Symptom resolution may be complete in only 55%
    • Satisfactory outcomes in both endoscopically assisted decompression and mini-open decompression
  • Minimally invasive: release of lacertus fibrosus
    • Patients with no manual labor return to work 1–2 days postoperatively.
    • Statistically significant postoperative improvement in Disabilities of the Arm, Shoulder, and Hand Questionnaire (DASH) scores
Key Educational Points
  • A ganglion cyst at the elbow can cause pronator syndrome.
  • Forearm sensation is normal in pronator syndrome, and sensation of the digits may also be normal.
  • False-negative and false-positive NCS results are common for this condition.
  • The risk for recurrent median nerve entrapment is low. 
  • Like radial tunnel syndrome, pronator syndrom versus a purely clinical diagnosis, there is variability in the diagnostic criteria for this diagnosis.
  • Positive nerve conduction studies have not correlated with successful patient outcomes.3
  • The pronator syndrome diagnosis can be supported by sveral clinical maneuvers including:
    1. Pain and paresthesias with resisted pronation with forearm in neutral.
    2. Pain with resisted elbow flexion in 120-130° of flexion in supination.
    3. Pain or paresthesias with resisted middle finger flexion.
    4. Paresthesias of the affected hand only when pressure applied to bilateral pronator muscle bellies.
References

New Articles

  1. Hagert E. Clinical diagnosis and wide-awake surgical treatment of proximal median nerve entrapment at the elbow: a prospective study. Hand (NY) 2013;8:41–6. PMID: 24426891
  2. Guo B, Wang A. Median nerve compression at the fibrous arch of the flexor digitorum superficialis: an anatomic study of the pronator syndrome. Hand (NY) 2014;9:466–70. PMID: 25414606

Reviews

  1. Strohl AB, Zelouf DS. Ulnar tunnel syndrome, radial tunnel syndrome, anterior interosseous nerve syndrome, and pronator syndrome. J Am Acad Orthop Surg 2017;25(1):e1-10. PMID: 27902538
  2. Kowalska B, Sudol-Szopinska I. Ultrasound assessment on selected peripheral nerve pathologies. Part I: Entrapment neuropathies of the upper limb – excluding carpal tunnel syndrome. J Ultrason 2012;12(50):307-18. PMID: 26674101
  3. Presciutti S, Rodner CM. Pronator syndrome. J Hand Surg Am. 2011; 36A: 907-909

Classics

  1. Morris HH, Peters BH. Pronator syndrome: clinical and electrophysiological features in seven cases. J Neurol Neurosurg Psychiatr 1976;39:461-4. PMID: 932765
  2. Solnitzky O. Pronator syndrome: compression neuropathy of the median nerve at level of pronator teres muscle. Georgetown Med Bull 1960;13:232-8. PMID: 13832639
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