Intersection Syndrome

Etiology

The first dorsal compartment of the wrist is comprised of the abductor pollicis longus and extensor pollicis brevis. These tendons have a unique anatomical pathway proximally in which they cross over the second dorsal compartment tendons just proximal to the extensor retinaculum and radial styloid. The second dorsal compartment of the wrist comprises the extensor carpi radialis brevis and extensor carpi radialis longus.[1][2][4]

Epidemiology

Intersection syndrome is typically the result of repetitive extension and flexion exercises or activities. This syndrome is commonly seen in sporting activities such as rowing or canoeing, skiing, racquet sports, and horseback riding. There is no significant difference in injury patterns found in men versus women.[1][4][2]

Pathophysiology

The repetitive extension-flexion results in a friction injury at the crossover junction of the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis) and the second dorsal compartment (extensor carpi radialis brevis/extensor carpi radialis longus) tendons leading to an inflammatory response and subsequently tenosynovitis. The presentation is typically one in which the patient complains of pain or tenderness over the dorsal aspect of the wrist proximal to the radial styloid. On examination, swelling and palpable crepitus with wrist or thumb extension may also occur.[2][4]

History and Physical

Intersection syndrome was first described in the literature by Alfred-Armand-Louis-Marie Velpeau, a French anatomist and surgeon, in 1841. He is also credited for the first accurate description of leukemia. The term intersection syndrome was first coined by James H Dobyns in 1978 at the Mayo Clinic. Although the accepted vernacular is intersection syndrome, it has been described in the medical literature by many other names: oarsmen wrist, crossover syndrome, squeaker wrist, abductor pollicis longus bursitis, abductor pollicis longus syndrome, subcutaneous polymyositis, and peritendinitis crepitans.[1][2]

Evaluation

Intersection syndrome is a clinical diagnosis, although a musculoskeletal ultrasound can easily confirm it. The initial steps for diagnosis include a focused physical exam of the elbow, wrist, and hand.[1][2][5] As with all musculoskeletal exams, clinicians must have a structured approach that includes inspection, a range of motion, palpation, muscle testing, and other special tests. Each joint above and below the injury should be tested in all motions. Look for swelling over the distal forearm as some cases can present with a palpable finding on exam 4 to 6 cm proximal to the Lister tubercle. Crepitus is a prevalent finding on the exam over the site of irritation. This is a finding that is specific to intersection syndrome. As the 2 dorsal compartments cross, the pronation and supination movements create friction, resulting in the examination finding of crepitus. Pronation is typically found more uncomfortable than supination.[1][2][5]

Resisted pronation that leads to the patient's pain, along with the palpable finding of crepitus 2 to 3 cm proximal to the radial styloid, can differentiate tenosynovitis of De Quarvein syndrome from intersection syndrome. De Quarvein syndrome is a condition that also involves the first dorsal compartment of the wrist extensors and affects the anatomy below the radial styloid. The Finkelstein maneuver is used to test for De Quarvein syndrome.[1][2]

Plain film imaging and computed tomography do not help diagnose intersection syndrome. Magnetic resonance imaging (MRI) provides excellent soft tissue images and aids in diagnosis, although MRI would not be an efficient or cost-saving choice.[4][3] Ultrasound technology has pushed musculoskeletal medicine forward in both diagnosis and treatment provided by physicians. Some say it can be as specific as MRI in the hands of the skilled user. Remember, as in most musculoskeletal conditions, the anatomy is mostly superficial. Therefore, a linear ultrasound probe is utilized. When observing intersection syndrome under ultrasound, 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, which are on top of each other. This represents swelling or edema as caused by friction. There also may be a thickening of the tendon sheaths.[3][5]

Treatment / Management

Treatment is conservative management with rest and activity modification. Corticosteroid injection has shown significant improvement and is a known next-best step if little or no improvement has been made with other conservative treatments.[1][2] Nonsteroidal anti-inflammatory drugs (NSAIDs) may be useful for acute injury and pain relief. Common NSAIDs are ibuprofen, naproxen, meloxicam, or diclofenac.[2] Acetaminophen may also be used for pain relief. Typically, rest and activity modification is more effective than medication therapy; ice is also an effective treatment. A temporary splint for protection and comfort at night may also be beneficial. There is no compelling evidence-based rehabilitation protocol for intersection syndrome at this time. Clinicians may consider using eccentric strengthening and stretching for rehab protocols.(B3)

When conservative measures are ineffective, corticosteroid injection under ultrasound guidance can be used. Confirm the diagnosis using the ultrasound visualization technique noted in the evaluation process. The typical injection is a 1-to-1 mixture of a corticosteroid and anesthetic (0.5 mL to 1 mL of steroid, triamcinolone 40 mg/1 mL, and a local anesthetic of choice at 0.5 mL to 1 mL). A 23- to 25-gauge needle at 1 to 1.5 inches is preferred.[5]

Using the in-plane or out-of-plane needle injection technique, guide the needle to where the first dorsal compartment (abductor pollicis longus and extensor pollicis brevis) is crossed over the second dorsal compartment (extensor carpi radialis brevis/extensor carpi radialis longus).[5] 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 solidify the diagnosis. The steroid takes time to reach its full potential. Rehabilitation exercises may be used in tandem with the injection after days 3 to 5. Additionally, prolotherapy is another injectable option that is also performed under ultrasound guidance with the same technique as steroids. The basis of prolotherapy is to minimize the adverse event profile of steroids and produce similar outcomes for improvements in pain and function. Prolotherapy uses an anesthetic, usually lidocaine, and a mixture of dextrose in sterile water (5%-20%). Prolotherapy is thought to create a proinflammatory state, which triggers the release of growth factors and, ultimately, collagen deposition, leading to tissue strengthening.[5] In rare, recalcitrant cases, surgical debridement and release are indicated.

Differential Diagnosis

The differential diagnoses for intersection syndrome include the following: 

• Boutonniere defect
• Drummer wrist
• Dupuytren contracture
• Extensor digitorum tenosynovitis
• Jammed finger
• Jersey finger
• Mallet finger
• Metacarpophalangeal ligament rupture
• Ring avulsion injury
• Scaphoid fracture