Intramedullary Headless Compression Screw Fixation Technique of Metacarpal Fractures

The video demonstrates the fixation technique. Open reduction due to presence of fracture callous was required followed by placement of a cannulated headless compression screw (Depuy Synthes, West Chester, PA).

1. WHAT ARE THE INDICATION, ALTERNATIVES, AND BENEFITS OF INTRAMEDULLARY SCREW FIXATION?

2.  HOW IS IMF PERFORMED?

3. WHAT ARE IMPORTANT PREOPERATIVE AND POSTOPERATIVE CONSIDERATIONS?

4.  WHAT ARE OTHER APPLICATIONS OF IMF SCREWS IN THE HAND?

Metacarpal fractures can be fixated with K-wire, plating, and IMF. K-wires have the benefit of low cost and speed but comes at great cost of joint stiffness as wires prevent early joint motion post-operatively, risk of infection, and require patient compliance in removal and hand therapy.¹ Plating has the benefit of stable fixation allowing early range of motion at the expense of more extensive soft tissue dissection, surgery duration, and increased cost.² IMF has the benefits of minimal incision, stable fixation to allow early range of motion, limited reliance on non-cooperative patients, and shortened duration of surgery.³

IMF screws are designed to be compressive and non-compressive due to its variable threaded and fully threaded construct, respectively. In transverse fractures and short oblique fractures (< 2 times the shaft diameter), the compression screws are indicated. Fully threaded screws are useful for comminuted and long oblique fractures (>2 times the shaft diameter) because metacarpal shortening and fracture fragment migration is avoided secondary to compression.⁴

Contraindications to IMF screws include patients with head-splitting fractures due to the risk of worsening the fracture with placement of the screw. Infected and pediatric fractures with open physes are also absolute contraindications.⁵

The operation is performed under regional block with sedation or under general anesthesia. After prep, if rapid reduction cannot be obtained in a closed manner, then an open reduction is performed. A 1.5-cm longitudinal incision is made dorsally over the metacarpal head. The metacarpal head is exposed by splitting the extensor tendon longitudinally. In this patient a bony malunion had to be disrupted and callus removed prior to reduction, so a longer incision was made. Prior to driving the guide wire, the appropriately sized screw is overlaid over the bone and fluoroscopy is used to confirm appropriate sizing. The appropriate guide wire is driven into the dorsal 1/3 of metacarpal head and advanced retrograde to the level of fracture under fluoroscopic guidance. The fracture is reduced, and the K-wire is advanced across the fracture site to the base of metacarpal. The flexion cascade is evaluated for absence of malrotation. The K-wire is then advanced through the carpometacarpal joint to avoid inadvertent removal when reaming over the wire. The metacarpal is drilled just past the fracture site while ensuring that the narrowest part of the canal is reamed in order to accommodate the screw threads. A countersink is used to allow the screw head to be seated in subchondral bone. In order to prevent rotational deformity during screw placement, the fingers are all flexed into the palm to set the appropriate flexion cascade and prevent malrotation. The screw is then hand driven with the fingers flexed. The surgeon should confirm screw placement under fluoroscopy and again check for malrotation. The guidewire is then removed. Extensor tendon and skin are closed.

The key to successful IMF is selection of the screw to be used preoperatively based on radiographs of the hand. The metacarpal length and inner diameter of isthmus (most narrow portion) are measured on posteroanterior view in millimeters. The surgeon should be mindful that each metacarpal has consistent differences in width, as the ring finger has the narrowest isthmus at average of 2.6 mm and small finger largest at 3.6 mm. The width of the narrowest part of the isthmus is the most important factor to guide the choice of the appropriately sized screw to ensure contact between screw and bone without causing blowout. Screw length is recommended to be at least 4-6 mm shorter than full bone length. Measurements of the K-wire are performed, and 4-6 mm are generally subtracted to get final screw length (for partially threaded screws, measurements must accommodate for the distal threads to be placed past the fracture line).

A bulky soft dressing is placed immediately postoperative and removed between 3-5 day for early range of motion to begin. There is no need for rigid immobilization if good purchase is achieved. The patient is expected to reach full range of motion by 4 weeks and start strengthening and progressively heavier activities in 4-8 weeks. Unlimited unrestricted usage is recommended by 8 weeks.

The use of compression screws has been well published in treating carpal bone fractures, especially the scaphoid.⁶ Due to the compromised vascularity of the scaphoid proximal pole due to retrograde vascular anatomy, compression at the site of fracture is critical to prevent nonunion and avascular necrosis.⁷ On the other hand, metacarpal and phalangeal bones have the ability to heal without need for compression by evidence of healing through hand splinting in minimally displaced fractures. Many studies have demonstrated excellent results in IMF of proximal and middle phalanx fractures.⁸ IMF screws are a great option in phalanx fractures as PIPJ stiffness is a significant complication that can be avoided with early range of motion as part of this technique. Joint stiffness that results from K-wires can be debilitating to patients and require months of therapy to reverse, often with range of motion that is never at preoperative state.⁹ In contrast to preoperative measurements of metacarpal bone on posteroanterior view, phalanx measurements should be done on lateral view. Anterograde screw placement is common with access through extensor hood and central slip for proximal and middle phalanxes, respectively.

Affiliations: Division of Plastic and Reconstructive Surgery, Department of Surgery, Rutgers/New Jersey, Medical School, Newark, NJ

Correspondence: John Chao, MD; jac807@njms.rutgers.edu

Disclosures: None of the authors have any conflicts of interest to disclose.