Carpal instability and its biomechanics have always been evolving due to the advancement in the field of radiology and arthroscopy. Lunate plays a pivotal role and acts like an intercalated segment in carpal stability, loss of anchorage of this key structure cause intercalated segment instability. Volar intercalated segment instability is a less common manifestation of dissociative carpal instability. We report of a case of post traumatic acute static volar instability.

13‑year‑boy had sustained distal one‑third radius and ulna fracture after fall on an outstretched hand. Open reduction and K‑wire fixation was performed for both bone fracture forearm (Fig. 1). Implants were removed after 4 weeks (Fig. 2).

He noticed restriction of dorsiflexion of wrist, while other movements normal. Serial X‑rays showed a loss of normal alignment of radio‑lunate in comparison with the opposite (Fig. 3, 4).

Initial X‑ray showed normal alignment of carpus before reduction. Serial radiographs during follow‑up showed a volar facing lunate with alteration of scapholunate and lunatocapitate angle and was diagnosed with a volar intercalated lunate instability (Fig. 5). The patient was put on strict rehabilitation protocol and the dorsiflexion improved from 0‑10° to 0‑40°. At 1 year follow‑up patient is still having restriction of dorsiflexion (Fig. 6) with volar lunate instability (Fig. 5). The patient is being planned for further procedure.

Carpal instability should be considered as a differential in patients presenting with chronic wrist pain and restricted movements following trauma. Reagan et al. classified carpal instability into four categories and lunato‑triquetral ligament is involved in stage three which leads to volar lunate instability ^[1]. Lunate instability is further divided into static or dynamic and acute or chronic. VISI is a condition in which there is pathologic volar flexion of the lunate, with or without a similar posture of the other proximal row carpal bones. Palmar flexion instability is less commonly recognized ^[1]. VISI is commonly seen in rheumatoid arthritis. Lunato‑triquetral ligament attrition due to congenital ligamentous laxity causes VISI. Posttraumatic volar lunate instability is an entity that can be missed during the initial traumatic event because of its subtle nature ^[2]. Posttraumatic carpal stability diagnosed at the earliest avoids advanced surgical procedures such as reconstruction and fusion of joint ^[3]. Earlier management prevents functional morbidity of wrist. Lunate instability in plain radiograph can be diagnosed with the alteration of various angles namely the loss of scapholunate angle, loss of alignment between the lunate, capitate and radius and increase in the capitolunate angle. Treatment options include from closed reduction and K‑wire fixation, dorsal capsulodesis, tenodesis, arthroscopic or open repair with reconstruction and finally arthrodesis ^[4]. Few cases have been reported in literature ^[5]. VISI is a missed injury in our case associated distal radius and ulna fracture ^[6]. This injury could be subtle in nature before reduction and fixation that led to delay in diagnosis or iatrogenic in nature after reduction of the fracture.

Wrist function is a complex interaction of various biomechanics involving the carpal bones, ligaments and the distal radio-ulnar complex. Awareness of carpal instability associated with fractures or injuries around the wrist is needed by the treating surgeon to avoid delay in diagnosis and treatment.

To suspect volar intercalated segment instability following a wrist injury and also following reduction with k wire fixation. Follow up of patient at regular intervals to prevent morbidity due to this deformity.