Accuracy of fluoroscopic examination in the treatment of Bennett's fracture

Abstract

Background: Restoration of joint congruity is an important factor for the prevention of subsequent arthritis in patients with Bennett's fracture. Surgical treatment of Bennett's fracture is thus generally recommended for displaced intra-articular fractures to the proximal aspect of the thumb metacarpal. Fluoroscopic examination is used to evaluate the adequacy of closed reduction after pinning of Bennett's fracture. The purpose of this study was to determine the accuracy of fluoroscopy to determine the reduction of Bennett's fractures.

Methods: A model was created, to mimic a Bennett's fracture utilizing ten fresh-frozen cadaveric hands. An oblique cut was made in the proximal aspect of the thumb metacarpal using an oscillating saw. The small oblique fragment involved 1/4-1/3 of the joint surface was then shifted in position creating a step-off or gap at the fracture site. An anatomical reduction model, gap models (1 mm, 2 mm, 3 mm), and step-off models (1 mm, 2 mm, 3 mm) were created using percutaneous fixation with two 1.0 mm Kirschner wires for each cadaveric hand. Fluoroscopic assessment then took place and was reviewed by 2 attending hand surgeons blinded to the actual position. Their estimated fluoroscopic position was then compared to the actual displacement.

Results: The step-off and gap on fluoroscopic examination showed a significant difference compared to the step-off and gap from direct visualization. The frequency of underestimation for the 3 mm displacement models from the fluoroscopic examination was 60%. The frequency for overestimated was 9% for the models in which displacement was within 2 mm (0, 1, 2 mm).

Conclusions: The assessment of articular gap and step-off using PA (postero-anterior), AP (antero-posterior), and lateral view of fluoroscopic examination is not accurate as compared to the examination by direct visualization. Surgeons need to be aware that PA, AP and lateral view of fluoroscopic examination alone may not be sufficient to judge the final position of a reduced Bennett's fracture. Other methods such as live fluoroscopy in multiple different planes, 3-dimensional fluoroscopy or arthroscopic examination should be considered.

Keywords: Bennett’s fracture; Fluoroscopy; Gap; Reduction; Step-off.

Fig. 1

a: fresh-frozen preserved cadaver forearm was used; b-d 1 mm Kirschner wires were used to judge the displacement of fractures from 1 mm to 3 mm

Fig. 2

a: anatomy reduction models; b:1 mm step-off model; c: 2 mm step-off model; d: 3 mm step-off model; e: fluoroscopy image of (a); f: fluoroscopy image of (b); g fluoroscopy image of (c); h: fluoroscopy image of (d)

Fig. 3

a: anatomy reduction model; b: 1 mm gap model; c: 2 mm gap model; d: 3 mm gap model; e: fluoroscopy image of (a); f: fluoroscopy image of (b); g fluoroscopy image of (c); h: fluoroscopy image of (d)

Fig. 4

The difference between direct view and fluoroscopic view. a: 3 mm step-off model; b: fluoroscopic view of (a); c: 3 mm gap model; (d): fluoroscopic view of (c)