Posterior Interosseous Nerve Syndrome

What is Posterior Interosseous Nerve Syndrome?

• Posterior interosseous nerve (PIN) syndrome is a specific type of radial nerve entrapment neuropathy.
  

  • The posterior interosseous nerve (PIN) is a branch of the radial nerve that primarily provides motor innervation to the extensor muscles of the forearm.
    

  • PINS is characterized by weakness or paralysis of these muscles, leading to difficulty in extending the fingers and thumb, while wrist extension remains intact due to the preservation of the extensor carpi radialis longus and brevis muscles [Dang & Rodner, 2009; Wegiel et al, 2023; Baumer et al, 2016].

What are common causes of Posterior Interosseous Nerve Syndrome?

• Common causes of posterior interosseous nerve syndrome (PINS) include:
  • Mechanical compression: This can occur due to anatomical structures such as the supinator muscle or pathological entities like ganglion cysts [Sigamoney et al, 2017; Dang & Rodner, 2009].
  • Parsonage-Turner syndrome: Also known as neuralgic amyotrophy, this inflammatory condition can affect the posterior interosseous nerve [Sigamoney et al, 2017].
  • Spontaneous "hourglass" constriction: This refers to intrinsic constriction within the nerve fascicles, which can occur without an obvious external compressive force [Sigamoney et al, 2017].
    
  • Diabetes: Diabetic patients may develop fascicular constriction within the radial nerve, leading to PINS [Kim et al, 2021].

Who is at risk of Posterior Interosseous Nerve Syndrome?

• Populations most at risk for developing posterior interosseous nerve syndrome (PINS) include:
  • Individuals with Diabetes: Diabetic patients are at increased risk for both radial neuritis and PINS due to the higher likelihood of developing neuralgic amyotrophy and fascicular constriction within the radial nerve [Kim et al, 2021].
  • Patients with Rheumatoid Arthritis: Rheumatoid arthritis can lead to PINS due to inflammatory synovitis affecting the elbow joint, which can compress the posterior interosseous nerve [Malipeddi et al, 2011].
  • Occupational Groups with High Biomechanical Exposure: Construction workers and other occupations involving forceful handgrip work and exposure to hand-arm vibration are at increased risk for radial nerve entrapment [Jackson et al, 2019].
  • Elderly Men: Radial neuropathy is more frequent in older men, particularly those aged 75-84 years, likely due to increased susceptibility to compressive neuropathies [Latinovic et al, 2006].
  • Pediatric Populations: Children and adolescents, especially those with traumatic injuries, are at risk for radial neuropathy, often localized at the posterior interosseous nerve or distal main radial trunk [Karakis et al, 2018].
  • Wheelchair Users: Individuals who use wheelchairs are at risk for radial neuropathy due to compression between the spiral groove of the humerus and hard surfaces of the wheelchair [Moore, 2009].

What are the symptoms of Interosseous Nerve Syndrome?

• Posterior interosseous nerve syndrome (PINS) is characterized by motor deficits without sensory loss.
  

  • The primary symptom is weakness or paralysis of the extensor muscles of the forearm, leading to difficulty in extending the fingers and thumb.
    

  • Wrist extension is usually preserved, but there may be radial deviation due to the intact function of the extensor carpi radialis longus and brevis muscles.
    

  • Patients may also report pain in the forearm, particularly around the elbow, which can precede the onset of motor symptoms [Kim et al, 2021; Sigamoney et al, 2017; Akane et al, 2016].

  • This can severely limit the ability to perform tasks that require finger extension, such as opening jars, writing, or using tools. Despite the preservation of wrist extension, the inability to extend the fingers can significantly hinder hand function and ADLs. Patients with PINS may also experience pain around the elbow, which can further limit their functional abilities [Kim et al, 2021].

What are the treatment options for Posterior Interosseous Nerve Syndrome?

NON-SURGICAL TREATMENTS

• Initial treatment includes rest, activity modification, and splinting to reduce nerve irritation.
  

  • Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) and corticosteroids can help reduce inflammation and pain. Neuropathic pain may be managed with medications such as pregabalin, carbamazepine, or duloxetine [Chrestian, 2020; Kim et al, 2021].

  • Occupational Therapy: This can help patients adapt to functional limitations and improve their ability to perform activities of daily living (ADLs) [Chrestian, 2020; Kim et al, 2021].

  • Injections: Several types of injections are available for treating radial neuritis and posterior interosseous nerve syndrome (PINS), each with distinct mechanisms of action and potential benefits:

    • Corticosteroid Injections: These are commonly used to reduce inflammation and pain. Corticosteroids inhibit inflammatory cytokines and reduce nerve swelling, which can alleviate compression and improve symptoms. They are often used in combination with local anesthetics for immediate pain relief [Buntragulpoontawee et al, 2020; Norbury & Nazarian, 2019].

    • Hydrodissection: Normal saline or local anesthetics can mechanically separate the nerve from surrounding tissues, reducing compression. This technique is often combined with other injectates like corticosteroids, prolotherapy or biologic injections to enhance therapeutic effects [Buntragulpoontawee et al, 2020; Norbury & Nazarian, 2019].

    • Prolotherapy Perineural Injection Therapy with 5% Dextrose (D5W): Perineural injection with D5W is an emerging therapy for entrapment neuropathies. Dextrose is thought to reduce neurogenic inflammation and promote tissue healing. Studies have shown that D5W injections can provide significant pain relief and functional improvement in peripheral nerve entrapments. Ultrasound-guided perineural injection with dextrose (5% dextrose) has been reported to improve sensory and motor functions in cases of radial nerve palsy [Buntragulpoontawee et al, 2020; Chen et al, 2018; Azizi et al, 2025].

    • Platelet-Rich Plasma (PRP): PRP injections involve using a concentration of the patient's own platelets to promote healing. PRP contains growth factors that can enhance tissue repair and reduce inflammation. It has shown favorable outcomes in treating entrapment neuropathies, including improved pain and function [Buntragulpoontawee et al, 2020].

SURGICAL

• Surgical Intervention: Surgery is indicated for compressive lesions or if there is no improvement with conservative treatment after 6 weeks. Surgical options include decompression, neurolysis, neurorrhaphy, and nerve grafting, depending on the severity and cause of the nerve entrapment [Carter & Weiss, 2015; McGraw, 2019; Wu et al, 2014].
  

REFERENCES

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