Intersection Syndrome

Etiology

Intersection syndrome typically results from repetitive wrist extension and flexion exercises or activities.[6] This repetitive motion is believed to cause friction at the intersection point of the first and second dorsal compartments, leading to localized inflammation and, ultimately, painful tenosynovitis.[7][8]

Epidemiology

This relatively rare syndrome has a purported incidence of less than 1 in 100,000 patients annually and is more commonly observed in athletes participating in activities such as rowing or canoeing, skiing, racquet sports, and horseback riding.[9][10] Studies have found no significant difference in injury patterns between men and women.[1][3][2]

Pathophysiology

In the dorsal forearm, the abductor pollicis longus and extensor pollicis brevis intercept the extensor carpi radialis brevis and extensor carpi radialis longus at approximately 60°.[11] Friction at this site between the muscle bellies of these first compartment structures and the tendons of the second compartment results from repetitive wrist flexion, extension, and, to a certain extent, pronation.[12] Over time, this friction creates a progressive inflammatory response that leads to tenosynovitis. 

History and Physical

Clinical History of Intersection Syndrome

A careful and methodical approach to history-taking and physical examination can often lead to a diagnosis of intersection syndrome. Patients with this condition typically present with pain over the dorsal wrist and dorso-radial distal forearm; a history of repetitive wrist motion associated with work or recreational activities may also be present. 

Physical Examination Findings of Intersection Syndrome 

The physical examination should begin with a focused assessment of the elbow, forearm, and wrist.[1][2][13] As with all musculoskeletal examinations, clinicians must have a structured approach that includes inspection, range of motion, palpation, muscle testing, and other provocative tests. Each joint above and below the site of concern should be assessed.

The hallmark finding is tenderness to palpation along the dorso-radial distal forearm, approximately 4 to 6 cm proximal to Lister tubercle. Associated swelling may be noted at this site. In addition, crepitus at the distal forearm may be palpable with resisted wrist and thumb extension, another finding fairly specific to intersection syndrome.

 De Quervain Tenosynovitis Versus Intersection Syndrome

The aforementioned clinical findings aid in differentiating intersection syndrome from de Quervain tenosynovitis, a more common tenosynovitis of the first dorsal compartment, which presents with tenderness to palpation at the radial styloid (more distal than the site of tenderness in intersection syndrome) and no crepitus. Furthermore, patients with de Quervain tenosynovitis may have a positive Finkelstein test, which is described as pain along the radial aspect of the wrist with thumb flexion and wrist ulnar deviation. Careful attention to these distinguishing features is essential to avoid misdiagnosing intersection syndrome as de Quervain tenosynovitis. 

Evaluation

Although intersection syndrome is typically considered a clinical diagnosis, imaging studies can be used as adjunctive tools when the history and physical examination findings are equivocal. 

Diagnostic Imaging Studies

Magnetic resonance imaging (MRI) of the forearm provides soft tissue images and can aid diagnosis.[3][4][14][15] Fluid-sensitive sequences, such as short tau inversion recovery and fat-suppressed proton density, may demonstrate peritendinous fluid or edema in the first and second dorsal compartments, as well as possible tendinosis and muscle edema. 

Ultrasound has also been used as an alternative imaging modality.[4][13][16][17][18] However, its accuracy depends heavily on the skill and experience of the ultrasonographer. As in many musculoskeletal conditions, the anatomy relevant to intersection syndrome is fairly superficial. Therefore, a linear ultrasound probe should be utilized. When evaluating for intersection syndrome under ultrasound guidance, the ideal image is in the transverse plane on the short axis. The finding correlating to the diagnosis is a hypoechoic area between the 2 dorsal compartments, indicating swelling or edema caused by friction. A thickening of the tendon sheaths may also be observed.[13]

Although forearm and wrist radiographs can be obtained to confirm the absence of bony pathology, they are not typically necessary to diagnose intersection syndrome.

Treatment / Management

Conservative Management

The recommended treatment of intersection syndrome predominantly includes nonoperative modalities. First-line conservative approaches, such as a period of rest and activity modification, aim to mitigate repetitive wrist motion and, therefore, minimize friction at the junction between the first and second dorsal compartments. Nonsteroidal anti-inflammatory drugs, such as ibuprofen, naproxen, meloxicam, and diclofenac, may be effective for managing acute injury and pain relief.[2] In addition, immobilization with a wrist brace or splint in a neutral position and wrist stretching and eccentric strengthening exercises can provide relief.

Pharmacologic Management

When conservative measures do not resolve or adequately improve symptoms, second-line treatment with corticosteroid injections can be performed with or without ultrasound guidance.[1][2][19][20] Although many different injectable combinations have been described, the typical injection is a 1:1 mixture of a corticosteroid and anesthetic, such as 0.5 mL to 1 mL of triamcinolone 40 mg/mL and 0.5 mL to 1 mL of a local anesthetic. A 23- to 25-gauge needle measuring 1 to 1.5 inches in length is preferred.[13](B3)

Using the in-plane or out-of-plane needle injection technique, the needle should be guided to the intersection where the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis) is crossed over by the second dorsal compartment (extensor carpi radialis brevis and extensor carpi radialis longus) at the point of maximal tenderness.[13] After the injection, the patient should pronate and supinate the wrist while the clinician observes for crepitus and tenderness with palpation. Resolution of the pain can help further confirm the diagnosis. The steroid requires time to achieve its full potential, which may take several weeks following injection. Rehabilitation exercises can be introduced in tandem with the injection after 3 to 5 days.

Surgical Management

In rare, refractory cases, surgical intervention with debridement and release of the second dorsal compartment is indicated. This procedure may be performed under local or regional anesthesia. A slightly curvilinear longitudinal incision is centered at the intersection between the first and second dorsal compartments, approximately 6 cm proximal to Lister tubercle.

Blunt dissection is then carried down through the subcutaneous tissues until the roof of the second dorsal compartment is visualized. This roof is then completely incised along its entire length to decompress and release the extensor carpi radialis brevis and extensor carpi radialis longus tendons. Any surrounding inflamed tenosynovium is also carefully excised while preserving the integrity of the tendons. A concomitant first dorsal compartment release can also be considered through the same incision, with attention to preserving the superficial radial nerve. Following this, the incision is copiously irrigated with normal saline, the skin is closed with the suture of choice for the surgeon, and a sterile dressing with a splint is applied. 

Differential Diagnosis

The differential diagnoses for intersection syndrome include: 

• De Quervain tenosynovitis [21]
• Extensor pollicis longus tendon rupture
• Extensor digitorum tenosynovitis
• Dorsal wrist ganglion cysts [22]
• Wartenberg syndrome [23]
• Scaphoid fracture [24]
• Scapholunate ligament injury [25]

Prognosis

Although definitive outcome data with respect to intersection syndrome are lacking in the literature, the majority of patients experience resolution of their symptoms with nonoperative treatment.[11] In particular, resolution of crepitus with active tendon loading typically indicates safe return to high-intensity activities. In addition, a worse postoperative course and poorer outcomes are associated with the presence of tendon sheath fibrosis and adhesions.

Complications

Complications associated with intersection syndrome and its treatment include persistent dorsal forearm and wrist pain, along with progressive stiffness in more refractory cases, potentially impacting daily activities and occupational function. Moreover, potential adverse effects due to steroid injections can occur, including fat atrophy, skin depigmentation, transient increases in blood glucose levels, particularly in diabetic patients, and, if performed repeatedly, extensor tendon damage or rupture. Postoperative complications may manifest as wound infections, extensor tendon lacerations, radial nerve injury, and incomplete relief or persistent symptoms.