掌骨および指骨骨折の治療：髄内スクリュー法

Metacarpal and phalangeal fractures are among the most common fractures that upper-extremity surgeons encounter, accounting for 30% of all hand fractures^1,2. These particular fractures can be treated either operatively or nonoperatively, according to the amounts of displacement, malrotation, and shortening¹. Operative treatment includes the use of Kirschner wire fixation, intramedullary screws, plate-and-screw constructs, or interfragmentary screws. Multiple studies have demonstrated superior biomechanical strength and early active range of motion with use of intramedullary screws for the treatment of unstable metacarpal and phalangeal fractures^3-7. This minimally invasive technique is designed for unstable metacarpal or phalangeal shaft and neck fractures to allow early active motion. Furthermore, intramedullary placement of implants avoids hardware prominence and extensive soft-tissue stripping, which can impact tendon gliding and postoperative range of motion.

Metacarpal fractures can be treated with 3.6 or 4.0-mm intramedullary screws according to the canal diameter. The fracture is reduced by closed means or a limited open reduction. With the metacarpophalangeal joint flexed, the guidewire is inserted into the dorsal third of the metacarpal head through the articular cartilage and driven past the fracture site to the desired depth. A small stab incision is made, and the depth gauge is placed against the metacarpal head. The cannulated drill is placed over the guidewire, and the canal is drilled on the oscillate setting. A screw of the appropriate diameter and length is then placed over the wire, and its position is confirmed under fluoroscopy. Phalangeal fractures are treated with one or two 2-mm screws, inserted antegrade or retrograde according to the fracture location and orientation. The fracture is reduced, and the dual-diameter guidewire is passed through the long axis of the canal to the level of the far cortex (typically at the phalangeal base). A stab incision is made, and the depth gauge is inserted down to bone. The dual-diameter guidepin measures 1.6 mm in diameter on one half and 0.8 mm on the other half. The 1.6-mm portion of the guidewire is then driven out of the far cortex such that the smaller-diameter segment spans the fracture site and remains in the bone. The screw is then placed over the guidewire. A second screw may be placed in a V or X pattern with use of a similar technique.

Alternatives to this procedure include nonoperative treatment, Kirschner wire fixation, plate-and-screw constructs, interfragmentary compression screws, and intramedullary headless compression screws.

Although many metacarpal and phalangeal fractures may be treated by closed means, a number of fractures require surgical fixation. Melone discussed that 10% of phalangeal and metacarpal fractures are either irreducible by closed means or unsuitable for percutaneous pinning⁸. The more common historical complications related to these fractures include stiffness and infection. Page and Stern cited a 35% complication rate with plate-and-screw fixation, including a 19% major complication rate⁶. Percutaneous Kirschner wire fixation is an alternative technique for fixation that is less invasive than open reduction and internal fixation procedures. Belsky et al. assessed 100 phalangeal fractures treated with use of Kirschner wire fixation and found favorable postoperative range of motion⁹. Botte et al. reported an 18% pin complication rate, most commonly infection, pin migration, and pin loosening¹⁰. The use of intramedullary screws allows for minimally invasive fixation that is similar to the use of headless compression screws. The non-compressive design of intramedullary screws avoids shortening in oblique or comminuted fractures. The various length options and differential diameter design allow intramedullary cortical thread engagement to facilitate early active motion. Not all fractures are suitable for intramedullary screw fixation, and there are certainly risks associated with its use. The articular surface can be violated, as the starting point lies at the dorsal third of the articular surface. Although we have not yet seen postoperative degenerative changes, this is a theoretical risk. There is also a risk of subsidence of screws used to treat distal fractures, if the screw is not in the subchondral bone.

Preoperative evaluation of canal diameter is helpful to determine the appropriate screw diameter. The ring finger metacarpal typically has the narrowest canal, and a 3.6-mm screw is thus typically utilized. Most other fingers can accommodate a 4.0-mm screw. Anatomy can vary, however.Ensure that the depth gauge is flush against the bone, confirmed on fluoroscopy. We typically subtract 5 mm from the measured length; however, this is dependent on fracture location.Prior to drilling, advance the guidewire into the far cortex in order to avoid guidewire pullout when the cannulated drill is removed.In some cases, tight isthmal fit of the screw can make screw progression difficult. If excessive torque is encountered, back out the implant 2 to 3 turns before continuing (similar to tapping).Ensure that the screw is buried under the articular surface. This is especially important in more distal fractures, in which purchase in subchondral bone is important in avoiding subsidence. In these fractures, a larger incision is often made in order to directly visualize the screw position.When attempting to place crossed screws into a proximal phalanx, sequential advancement of the screws (i.e., alternating screw progression across the isthmus of the canal) can allow for easier screw passage when both guidewires are across the fracture site.To gauge the stability of phalangeal shaft fractures, we apply varus/valgus and flexion/extension stress while using dynamic fluoroscopy after the first screw is inserted. If unstable, a second screw is inserted according to the previously described technique.

K-wire = Kirschner wireMCP = metacarpophalangealAP = anteroposteriorCMC = carpometacarpal.