Pronator Teres Syndrome (PTS) is a compression neuropathy characterized by the physical squeezing of the median nerve in the upper forearm, a location higher up the arm than the wrist. The median nerve controls sensation and movement in parts of the hand and forearm, so its compression causes various symptoms. Because its symptoms often mimic those of the more widely known Carpal Tunnel Syndrome, PTS is frequently misdiagnosed.
Anatomical Location and Compression Mechanism
The median nerve enters the forearm, passing through or near the pronator teres muscle, which rotates the forearm so the palm faces down. This muscle typically consists of two distinct heads: a larger humeral head and a smaller ulnar head. In most people, the median nerve travels directly between these two muscle heads, creating a narrow passageway.
Compression occurs when the space between these heads is reduced. Repetitive or forceful forearm rotation and gripping, such as during certain sports or manual labor, can cause the pronator teres muscle to enlarge (hypertrophy), tightening this passageway. Other structures can also contribute to compression, including the lacertus fibrosus or the fibrous arch of the flexor digitorum superficialis muscle. The pressure on the nerve causes irritation, leading to characteristic symptoms.
Recognizing the Physical Symptoms
Patients with Pronator Teres Syndrome typically experience a deep, aching pain located in the upper forearm. This discomfort often worsens with repetitive activities involving forceful forearm rotation, such as turning a screwdriver or opening a jar. Tenderness is often felt when pressing directly over the pronator teres muscle.
Nerve compression also causes sensory changes in the hand, including numbness and tingling (paresthesias). These sensations affect the skin supplied by the median nerve: the thumb, index finger, middle finger, and the radial half of the ring finger. Unlike other nerve entrapment conditions, symptoms are usually more prominent during the day with activity and typically do not cause nighttime waking.
Motor symptoms can also develop, resulting in weakness in the muscles of the hand and forearm controlled by the median nerve. Patients may notice reduced grip strength or difficulty with fine motor tasks, such as buttoning a shirt or using small tools. This weakness can lead to clumsiness or a tendency to drop objects.
Key Differences from Carpal Tunnel Syndrome
Pronator Teres Syndrome (PTS) is commonly confused with Carpal Tunnel Syndrome (CTS) because both involve median nerve compression, but the location differs. The primary distinctions involve the location of maximum pain, changes in palm sensation, and the response to specific physical tests. In PTS, maximum tenderness and pain are located in the upper forearm near the elbow, a location not typically affected by CTS.
A significant distinguishing factor is sensation in the palm. The palmar cutaneous nerve, which supplies sensation to the palm, separates from the main median nerve before it enters the carpal tunnel at the wrist. Therefore, in isolated CTS, palm sensation remains normal, but the higher compression of PTS can affect this branch, leading to numbness or tingling in the palm.
Provocative physical tests further differentiate the conditions. A specific maneuver where the clinician resists the patient’s attempt to turn their palm down while extending the elbow often reproduces pain in PTS, but not in CTS. Furthermore, a positive Tinel’s sign—a tingling sensation when the nerve is tapped—will be located over the pronator teres muscle for PTS, but over the wrist for CTS.
Conservative and Surgical Treatment Options
Initial management focuses on conservative, non-surgical approaches to reduce nerve irritation and inflammation. Rest and activity modification are advised, involving avoidance of the repetitive, forceful forearm rotation and gripping that exacerbate symptoms. Non-steroidal anti-inflammatory drugs (NSAIDs) may be used to decrease pain and swelling around the nerve.
Physical therapy is an important part of conservative treatment, incorporating gentle stretching exercises and nerve gliding techniques. A splint may be recommended temporarily to support the elbow and wrist in a neutral position, reducing tension on the nerve. Corticosteroid injections near the compressed nerve are sometimes considered for temporary relief if symptoms persist after several weeks of initial treatment.
If conservative management fails to provide relief after three to six months, surgical decompression may be necessary. The goal of surgery is to relieve pressure on the median nerve by releasing the structures that are squeezing it. This procedure involves surgically releasing the tight fascia and the head of the pronator teres muscle to ensure the nerve has an open pathway. Following surgery, patients typically undergo rehabilitation to restore strength and full mobility.