Dorsal intercalated segment instability

Dorsal Intercalated Segment Instability (DISI) is a condition affecting the alignment and stability of the carpal bones in the wrist, specifically the lunate and scaphoid bones. This condition is characterized by a dorsal tilt of the lunate when viewed in a lateral radiograph of the wrist. DISI is often a consequence of a scapholunate ligament injury, which can result from trauma such as a fall on an outstretched hand. This condition is significant because it can lead to chronic wrist pain, decreased range of motion, and long-term complications such as osteoarthritis if not properly managed.

Etiology

DISI most commonly occurs following a traumatic event that leads to the disruption of the scapholunate ligament, one of the key stabilizers of the wrist. This ligament injury allows for abnormal motion between the scaphoid and lunate bones, with the scaphoid flexing volarly (towards the palm) and the lunate extending dorsally (towards the back of the hand). Other causes may include non-traumatic conditions such as ligament laxity or degenerative changes within the wrist.

Pathophysiology

The normal biomechanics of the wrist are disrupted in DISI due to the altered position of the lunate, which is tilted dorsally. This dorsal tilt is measured as an increased scapholunate angle on lateral radiographs, typically greater than 70 degrees. The disruption in the alignment of the carpal bones leads to abnormal load distribution across the wrist, which can accelerate degenerative changes and contribute to the development of carpal instability and osteoarthritis.

Clinical Presentation

Patients with DISI often present with dorsal wrist pain, especially with wrist extension or when bearing weight on the affected hand. There may also be a decrease in wrist range of motion, particularly in flexion and radial deviation. In some cases, a visible deformity or a palpable gap between the scaphoid and lunate bones can be detected.

Diagnosis

The diagnosis of DISI is primarily based on clinical examination and confirmed through imaging studies. Lateral radiographs of the wrist are essential for assessing the scapholunate angle and identifying the dorsal tilt of the lunate. Advanced imaging techniques such as MRI or CT scan may be used to evaluate the integrity of the scapholunate ligament and the extent of any associated injuries or degenerative changes.

Treatment

Treatment options for DISI vary depending on the severity of the condition and the presence of associated injuries. Non-surgical management may include immobilization with a splint or cast, anti-inflammatory medications, and hand therapy to restore range of motion and strength. Surgical intervention may be necessary in cases of significant instability, persistent symptoms, or when conservative measures fail. Surgical options include ligament repair or reconstruction, and in severe cases, carpal fusion procedures.

Prognosis

The prognosis for patients with DISI depends on the severity of the ligament injury and the timeliness of intervention. Early diagnosis and appropriate management can lead to favorable outcomes, with restoration of wrist function and alleviation of pain. However, untreated or chronic DISI can lead to progressive wrist instability, decreased function, and osteoarthritis.