Morphological Analysis of Metacarpal Shafts With Respect to Retrograde Intramedullary Headless Screw Fixation

Abstract

Background: The use of retrograde intramedullary headless compression screw fixation for metacarpal neck and shaft fractures has been described in the literature. The purpose of this study was to perform a computed tomography (CT)-based morphological analysis of metacarpal size to help surgeons anticipate expected hardware needs. Methods: In all, 108 consecutive hand CT scans were evaluated for the medullary diameter in the volar-dorsal and radial-ulnar planes at the narrowest point of the canal, as well as for the distance from the articular surface to this point. Results were then analyzed by finger and by sex. Results: The ring finger had the smallest average medullary canal diameter for both men and women (2.7 and 2.6 mm, respectively); the small finger had the largest average diameter (3.9 mm) for men and the middle finger (3.6 mm) for women. Radial-ulnar was the rate-limiting dimension in the index, middle, and ring fingers, whereas volar-dorsal was the smallest dimension in the small finger, regardless of sex. Medullary diameter tended to be larger in patients aged more than 50 years. More than 50% of fingers have diameters >3.0 mm, and at least 40% of index, middle, and small fingers have diameters >3.5 mm, which are common diameters of commercially available headless compression screws. Conclusions: When preparing to perform open reduction internal fixation of a metacarpal using retrograde intramedullary headless compression screws, the surgeon needs to be prepared with screws of larger diameters to optimize fixation. Screws of larger diameters are needed to achieve endosteal purchase, regardless of sex.

Keywords: compression; computed; dimensions; fracture; headless; intramedullary; metacarpal; screw; tomography.

Figure 1.

(a) Anteroposterior radiograph of a left hand of a 31-year-old male patient demonstrating a left fifth metacarpal distal shaft fracture with approximately 60° of apex dorsal angulation, and (b) postoperative image of the same patient following open reduction internal fixation using a standard 4.0-mm Acutrack 2 headless compression screw (Acumed, Hillsboro, Oregon)

Figure 2.

Computed tomographic measurements of the metacarpal using Philips IntelliSpace PACS Enterprise. Image (a) represents an axial cut depicting the measurement performed to determine the (A) volar-dorsal and (B) radial-ulnar measurement at the narrowest part of the metacarpal shaft. Image (b) represents a coronal cut depicting the measurement performed to determine the (A) length from the metacarpal head to the narrowest point of the metacarpal shaft.

Figure 3.

Histogram plots depicting the distribution of diameters at the narrowest point of the intramedullary canal for the (a) index, (b) middle, (c) ring, and (d) small metacarpals.