Pain on the ulnar side of the wrist is a common cause of loss of function in the upper extremity. Acute injury and chronic degeneration present differently. Because of the anatomical overlap, complex differential diagnosis, and varying treatment outcomes, the ulnar aspect of the wrist is considered the “black box” of the wrist, and its pathology can be compared to that of low back pain. Common causes of ulnar carpal pain include tears of the triangular fibrocartilage complex, ulnar carpal impingement syndrome, and tears of the lunar triangular ligament. The ulnar aspect of the wrist consists of a number of important structures and maintains stability, allowing dynamic motion and producing a strong grip through ulnar deviation. The intrinsic ligaments include the cephalic hook ligament and the lunotriquetral ligament. The lunotriquetral ligament is a “C” shaped ligament with a dorsal, a palmar, and a central region. The palmar portion of the meniscal triangle ligament is considered to be the most structurally important and the most common site of tear compared to the central and dorsal portions. The external ligaments include the ulnar deltoid ligament and the ulnar meniscal ligament. These ligaments maintain the stability of the distal ulna and the palmar aspect of the carpus. Their fibers begin at the triangular fibrocartilage complex and ulnar styloid process and insert into the palmar portion of the semilunar, triangular, and semilunar triangular ligaments. The triangular fibrocartilage complex is a fibrocartilage structure that contributes to the stability of the inferior ulnar radial joint. It includes the triangular fibrocartilage (articular disc), the palmar and dorsal radial ulnar ligaments, the meniscal homologue, the ulnar collateral ligament, and the tendon sheath of the ulnar carpal extensor tendon. The ulnar collateral ligament begins at the base of the ulnar styloid process and is an insufficiently defined articular capsule structure. The meniscal homologue extends from the discoid portion of the triangular fibrocartilage complex to the triangular bone, lunate bone, and fifth metacarpal. The blood supply to the triangular fibrocartilage complex is supplied by the terminal portion of the anterior and posterior interosseous arteries, with good peripheral blood supply but poor central and radial portions. Anatomical understanding suggests repair of the peripheral portion of the tear and removal of the central and radial portions of the tear. Clinical presentation An etiologically accurate diagnosis of lateral ulnar carpal pain requires a thorough history, a detailed physical examination, and a precise interpretation of the appropriate diagnostic tests. Lateral ulnar wrist pain can be classified as acute injury, chronic strain injury, and chronic degeneration. Acute injuries include falls from heights, sprains, and uneven mechanical loading. Injuries to the inferior ulnar radial joint and deltoid fibrocartilage complex are usually due to an axial loading type of force during excessive rotation forward. Typical injuries to the semilunar deltoid ligament are caused by wrist hyperextension. With a dislocation of the inferior ulnar radial joint, the patient may hear a ringing sound and immediately see a deformity. However a stable injury to the meniscal deltoid ligament and deltoid fibrocartilage complex may result in a persistent low grade pain after the initial injury. Chronic strain injuries include tendinitis of the ulnar carpal extensors and ulnar carpal flexors. Presentation in these cases may be painless, although an acute injury may lead to chronic tendonitis. When the mechanics of using the wrist are altered, the history may include a new movement of the wrist or a change in an existing movement. The history in the case of chronic degeneration may have an old injury, a fracture of the elbow, wrist, hand or a systemic inflammatory disease. It is capable of occurring after a distal radius fracture, an elbow fracture with radial head injury, or as a result of anatomic variation. Chronic degenerative deltoid fibrocartilage complex injury may be due to an injury in the distant past, inferior ulnar radial joint lesions, inflammatory lesions such as pseudogout.