The role of arthroscopy in perilunate injuries

Relevant anatomy and biomechanics

A pure perilunate injury involves a dislocation of the carpus from the lunate, and constitutes a purely ligamentous injury to the wrist. Pure perilunate dislocations are considered lesser arc injuries because the traumatic force results in a circular disruption of ligaments close to the body of the lunate. Greater arc injuries occur when the force takes a path of greater circumference around the lunate. Greater arc perilunate fracture dislocations usually involve the scaphoid, but also may include fractures of the radial styloid, ulnar styloid, capitate, and triquetrum in any combination. Of perilunate dislocations, greater arc injuries are more common, with approximately two-thirds of perilunate dislocations classified as greater arc injuries.

Perilunate injuries are a spectrum of carpal injuries that are the result of high-energy trauma. The mechanism of injury is typically hyperextension, ulnar deviation, and intercarpal supination of the wrist. This can occur with a fall on to the thenar eminence, where the weight of the body rotates over the fixed point on the ground, causing ulnar deviation and supination of the carpus. If the force is of sufficient magnitude, there will be a pattern of progressive perilunate instability as described by Mayfield et al. Their classic description of carpal instability was derived from their observations following sudden loading experiments on cadaver specimens when the wrist was loaded in extension, radial deviation, and carpal bone supination. This specific position produced a predictable pattern of injuries. In stage I, with forced wrist hyperextension, the extrinsic palmar and dorsal ligaments tightly stabilize the lunate, and the force is concentrated on the scapholunate interosseous ligament (SLIL), which progressively tears in a palmar-to-dorsal direction. In stage II, increasing force also disrupts the extrinsic ligaments including the scaphocapitate (SC) and radioscaphocapitate (RSC) ligaments, leading to a dorsal dislocation of the capitate. With further deformation, the lunotriquetral interosseous ligament (LTIL) ruptures in stage III. In stage IV, the lunate is forced volarly and dislocates into the carpal tunnel through the space of Poirier.

In greater arc injuries, the force transmission results in a variable pattern of fractures, which can include a radial styloid avulsion or a fracture of the scaphoid, capitate, triquetrum, or ulnar styloid. The most common pattern is a transscaphoid perilunate fracture dislocation. The scaphoid may fracture at any level, including at the proximal pole. The SC syndrome consists of a fracture of the scaphoid and the capitate. The capitate fracture can occur through the body ( Fig. 13.1 A–B) or the neck due to a direct impact of the capitate against the dorsal lip of the radius. As the distal fragment relocates, the proximal fragment rotates 90 to 180 degrees. There may also be a fracture of the triquetrum, which is usually a sagittal split through the body of the triquetrum or an avulsion fracture of the proximal pole ( Fig. 13.2 A–E). Fractures of the radial or ulnar styloid ( Fig. 13.3 A–D) are usually avulsion fractures but may include a tear of the RSC/long radiolunate ligaments (LRL) and/or the triangular fibrocartilage complex (TFCC).

Herzberg recently drew attention to the existence of an occult perilunate injury, which he has termed PLIND for perilunate injuries, nondislocated. The concept of the PLIND lesion is consistent with a lesser arc, greater arc, and translunate type of injury. He presented 11 patients with acute perilunate injuries where the capitate either had spontaneously reduced after dislocation or had never been dislocated. One case was missed and treated as an isolated displaced scaphoid fracture, which led to a very poor short-term result. The common features of a PLIND lesion include a history of high-energy trauma combined with the physical findings of marked wrist swelling and diffuse wrist tenderness that is suggestive of a more global injury. The primarily common radiographic feature is a coronal perilunate-type path of injury on the posteroanterior (PA) view, but no dislocation of the capitate from the lunate in the sagittal plane ( Fig. 13.4 A–D). A good clue is the presence of midcarpal osteochondral loose bodies. A CT scan and/or MRI should be performed in this case to better evaluate the bony injuries. Herzberg recommends wrist arthroscopy to confirm the diagnosis of a PLIND  lesion when there is a high index of suspicion ( Video 13-1 ). Bain et al. described a perilunate translunate injury that appears to be a variant of a PLIND lesion. There is also no true dislocation of the capitate from the fractured lunate but the arc of injury in the coronal plane travels within and around the lunate ( Fig. 13.5 A–C). The arc may extend into the SLIL or LTIL or extend through the carpal bones, which could include a transscaphoid, translunate perilunate injury.