Treatment of Trans-Scaphoid Perilunate Injuries of the Wrist using a Nitinol Staple for Fixation

The effi cacy of staples for treating scaphoid fractures has been well documented, however its application in perilunate injuries has not be well elucidated [1]. The purpose of this paper is to review the technique of treating perilunate fractures with a nitinol staple. We have used this technique in 18 patients to treat 19 perilunate fractures at a Level 1 Trauma Center and have obtained satisfactory clinical results.


Introduction
The effi cacy of staples for treating scaphoid fractures has been well documented, however its application in perilunate injuries has not be well elucidated [1]. The purpose of this paper is to review the technique of treating perilunate fractures with a nitinol staple. We have used this technique in 18 patients to treat 19 perilunate fractures at a Level 1 Trauma Center and have obtained satisfactory clinical results.
Perilunate fracture dislocations are uncommon, but usually occur in young patients who sustain high energy trauma or falls on outstretched hands. Mayfi eld fi rst described the mechanism of perilunate dislocation occurring with extension, ulnar deviation, and intercarpal supination [2]. This sequence of events leading to the injury has been described as a fourstep process, starting with a radial force passing through the scaphoid causing a fracture, transmission of the force through the lunocapitate joint causing the lunate to project through the space of Poirier, dislocation of the other carpal bones around the lunate, and disruption of the lunotriquetral joint [3,4]. The lunate, however, remains attached to the short radiolunate ligament, allowing surgical access to the lunate via the carpal tunnel.
The diagnosis of this complex injury may be missed in up to 25% of the patients, and up to 50% of patients may present with acute carpal tunnel symptoms [5][6][7]. Early diagnosis and treatment is essential to avoid long term disability, as delayed treatment is associated with poor outcomes [5,8,9].
Treatment of perilunate fracture dislocations of the wrist is a challenging problem for patients and the hand surgeons [10,11]. Various surgical treatment options have been advocated, including a volar approach, dorsal approach, and combined approaches to address all of the injured structures on the palmar and dorsal aspects of the wrist [11][12][13][14][15][16][17][18][19].
One of the clinical sequelae resulting from treatment of this injury is the degree of stiffness that occurs in the fi ngers and wrist after prolonged immobilization following surgical repair of the bone and ligaments [20]. Many patients require extensive rehabilitation to obtain a functional range of motion after the structures are healed [21].
In our experience, a combined approach and repair of all of the involved structures, has resulted in dissatisfaction with the outcome due to the amount of time the patients require to regain function. Additionally, the limited range of motion that is fi nally achieved by these patients was often suboptimal for performing even basic activities of daily living [22].
The current approach described for treatment of these trans-scaphoid perilunate injuries is one that is practical and allows for stable fi xation of the scaphoid fracture, reduction of the lunate, decompression of the carpal tunnel, and repair of the rent involving the palmar ligaments including the radioscaphocapitate and ulnocapitate ligaments.

Relevant anatomy
The volar surface of the scaphoid is concave, and therefore the scaphoid tends to volar fl ex, creating a humpback deformity. A scaphoid fracture may collapse to a humpback deformity due to shortening of the volar cortical length and can cause dorsal intercalated segment instability (DISI) [23].
Placing fi xation on the palmar aspect of the scaphoid helps to prevent the humpback deformity, in essence, acting as an I-beam to counteract the deformity forces.
Intrinsic and extrinsic ligaments provide support and stability to the wrist, with the volar ligaments being more important stabilizers than the dorsal ligaments.
The scapholunate ligament is one of the important volar ligaments and is the primary stabilizer of the scapholunate joint (and wrist). The space of Poirier is a weakened area of the volar wrist capsule, at the proximal capitate, between the radioscaphocapitate and the long radiolunate ligaments ( Figure 1). This is an intrinsically weak region, especially with the wrist in hyperextension that allows the lunate to undergo palmar fl exion and dislocation into the carpal tunnel.

Indications/Contraindications
Since the majority of trans-scaphoid perilunate fracture dislocations result from high energy injuries, such as falls from heights and motor vehicle accidents, a comprehensive evaluation for other major injuries should be performed following the ABC's of trauma. The initial evaluation of the injured wrist should include assessment of open wounds, edema or deformity, and alignment with the forearm. An examination of the peripheral nerves, particularly the median nerve, is essential considering the high association with acute carpal tunnel syndrome [24].
Radiographic evaluation should include a postero-anterior (PA) and true lateral views (Figure 2). On a PA view with a perilunate dislocation, the carpal height ratio will be less than 0.5 and there can be overlap of the lunate and capitate, and one may see a disruption in Gilula's lines ( Figure 3). The pie in the sky sign may also be visualized on the PA view, which is a triangular appearance of the lunate due to its palmar fl exed posture. On the lateral view with a perilunate injury, the lunate may or may not be positioned in the lunate fossa colinear with the radius, depending on the stage of the dislocation (Figure 4).
Early reduction is essential to reduce pressure on the median nerve and surrounding soft tissues. Factors that have been shown to infl uence outcomes include open injury, delay in diagnosis and treatment, and non-anatomical reduction [5].

Postoperative management and rehabilitation
Rehabilitation:Patients return in 10-14 days following surgery for removal of the post-operative dressing, wound check, and radiographs (Figure 7). A short arm thumb spica cast is applied for an additional 3-4 weeks. Patients are encouraged to move shoulder, elbow, forearm and fi ngers (Figure 8). A CT scan is obtained at 3 months following the surgery. Patient works on range of motion of the fi ngers and wrist in therapy, as well as modalities for pain ( Figure 9). We use a conventional push-up as a good indicator of clinical union ( Figure 10).
Those with scapholunate advanced collaspsed (SLAC) or scapholunate nonunion advanced collapse (SNAC) wrist tend to avoid this motion by modifying their push-ups with a closed fi st or by performing them on their fi ngertips.

Expected outcomes and complications
The single volar approach has allowed for earlier mobilization and decreased stiffness over the combined dorsal and volar approach. The volar approach also allows for easier repair of the more important stabilizing ligaments of the wrist, as well as release of the carpal tunnel compared to the dorsal approach.
Although this repair requires a large incision, we have not seen complications due to large incision size, including restenosis of the carpal tunnel in our experience. Volar operative approach is also less disruptive of the blood fl ow to the proximal pole of the scaphoid. Performing the surgery with the staple (scaple) allows for easy insertion, constant compression at the fracture site, and prevents the humpback deformity of the scaphoid.
One major disadvantage associated with the use of the nitinol staple for these grossly unstable injuries is the fact that a skilled surgical assistant is often required to maintain the reduction of the scaphoid while the surgeon inserts the staple.
Alternatively, provisional fi xation can sometimes be obtained with smooth k-wires to allow for insertion of the staple, but a skilled surgical assistant is usually better for maintaining the reduction while the scaphoid is drilled and the staple is inserted. Other potential complications of the trans-scaphoid perilunate injury include post traumatic arthritis, non-union, carpal instability, and carpal malalignment [5,811,21,22].