Two Conditions Caused By Median Nerve Disorders
The median nerve innervates or supplies muscles of the forearm with messages needed for sensation and movement. Compression on the nerve or infection along the nerve can cause a condition known as neuropathy. The affected individual experiences painful symptoms along with numbness. Because the nerve moves through different muscles and ligaments along the course of the arm, median nerve neuropathy can present differently.
In this article, surgeons from the University of Connecticut compare and contrast two specific problems arising from median nerve neuropathies: pronator syndrome (PN) and anterior interosseous nerve syndrome (AIN). The anatomy of the nerve is presented by a written description along with drawings of the nerve as it passes through various soft tissue structures. Understanding where the problem occurs helps the reader understand the clinical presentation.
Pronator syndrome can occur if and when the nerve is compressed in any of several places (e.g., between the two heads of the pronator teres muscle, at the proximal arch of the flexor digitorum surperficialis, at the ligament of Struthers, at the aponeurosis, or at the head of the flexor pollicis longus). Though you may not be familiar with those specific soft tissues, it gives you an idea of how the nerve comes in contact with many and various structures that could put pressure on it.
In the case of anterior interosseous nerve (AIN) syndrome, compression of the median nerve may not be the problem. Instead, there is new evidence that the condition is caused by a neuritis (inflammation of the nerve). The neuritis could be coming from a viral illness, immunizations, strenuous exercise, or pregnancy.
The result of AIN syndrome is a motor paralysis or "palsy" of some or all of the muscles innervated by the median nerve. This is a transient neuritis, which means "temporary" -- given enough time, the nerve will usually recover.
Both of these conditions (pronator syndrome and anterior interosseous syndrome) are fairly rare. So the diagnosis requires a careful patient history, physical examination, and electrodiagnostic and imaging studies. The authors describe similarities and differences in clinical findings that may aid the surgeon in making an accurate diagnosis.
Specific tests that can be done to differentiate one from the other (e.g., pronator compression test, resisted flexion of the middle joint of the middle finger, Tinel sign, Kiloh-Nevin sign, OK sign, weakness of thumb to index finger pinch grip). Each test is described along with a description of what constitutes a positive or negative response.
Once the diagnosis is made, then the next step is developing an appropriate plan-of-care. Conservative (nonoperative) care is recommended for both conditions. Rest, muscle stretching exercises, activity modification, and antiinflammatory medications are tried for at least six months.
Surgery is only advised when nonsurgical intervention is unsuccessful after many, many months (up to a year or more). The exact surgical approach to take remains a point of considerable debate and discussion for both of these conditions. Although there is no formal evidence-based protocol, most surgeons release the median nerve along its entire course in the forearm for both conditions. Any places of restriction or obstruction are removed.
In summary, this article provides surgeons with a starting point for understanding these two conditions caused by impairments of the median nerve. Although much remains a mystery about the causes and best approach to management, this summary gives the surgeon an idea of current knowledge and understanding of both syndromes.
References: Craig M. Rodner, MD, et al. Pronator Syndrome and Anterior Interosseous Nerve Syndrome. In Journal of the American Academy of Orthopaedic Surgeons. May 2013. Vol. 21. No. 5. Pp. 268-275.Back