Volar percutaneous screw fixation of the scaphoid: a cadaveric study

Rethinking Scaphoid Fixation

Scaphoid fixation, whether for acute injuries or nonunion, is made challenging by the small and intra-articular nature of the most commonly fractured carpal bone. The purpose of this article is to review the techniques to simplify scaphoid fixation and to optimize healing and early return to activity.

Deviations in positioning variable pitch screws- scaphoid waist fractures

INTRODUCTION

Operative therapy using a headless cannulated variable pitch compression screw is the gold standard for the treatment of instable scaphoid fractures.

HYPOTHESIS

Deviation from the central placement is associated with a loss of stability and stiffness.

MATERIAL AND METHODS

An artificial bone model was manufactured and different screw positions (central, 10° and 20° to the long axis) were assessed. A shearing test with axial force on the 45° flexed scaphoid was applied.

RESULTS

The inserted variable pitch screw showed the highest stiffness and failure force in a position in the long axis. At 10 degrees, a slight decrease in stiffness (32.7N/mm±9.3N/mm) and failure force (41.6N±13.2N) was observed, while a significant reduction in stiffness (29.3N/mm±4.6N/mm) and failure force (50.3N±19.5N) was measured at 20 degrees.

DISCUSSION

Deviations in the angle of insertion of the compression screw cause loss in failure force, thus deviations from the central placement is associated with less stability and stiffness.

LEVEL OF PROOF

Controlled laboratory study (basic science study, biomechanical testing).

Biomechanical Strength of Retrograde Fixation in Proximal Third Scaphoid Fractures

Background: Current techniques for fixation of proximal pole scaphoid fractures utilize antegrade fixation via a dorsal approach endangering the delicate vascular supply of the dorsal scaphoid. Volar and dorsal approaches demonstrate equivalent clinical outcomes in scaphoid wrist fractures, but no study has evaluated the biomechanical strength for fractures of the proximal pole. This study compares biomechanical strength of antegrade and retrograde fixation for fractures of the proximal pole of the scaphoid. Methods: A simulated proximal pole scaphoid fracture was produced in 22 matched cadaveric scaphoids, which were then assigned randomly to either antegrade or retrograde fixation with a cannulated headless compression screw. Cyclic loading and load to failure testing were performed and screw length, number of cycles, and maximum load sustained were recorded. Results: There were no significant differences in average screw length (25.5 mm vs 25.6 mm, P = .934), average number of cyclic loading cycles (3738 vs 3847, P = .552), average load to failure (348 N vs 371 N, P = .357), and number of catastrophic failures observed between the antegrade and retrograde fixation groups (3 in each). Practical equivalence between the 2 groups was calculated and the 2 groups were demonstrated to be practically equivalent (upper threshold P = .010). Conclusions: For this model of proximal pole scaphoid wrist fractures, antegrade and retrograde screw configuration have been proven to be equivalent in terms of biomechanical strength. With further clinical study, we hope surgeons will be able to make their decision for fixation technique based on approaches to bone grafting, concern for tenuous blood supply, and surgeon preference without fear of poor biomechanical properties.

Management of Scaphoid Fractures

LEARNING OBJECTIVES

After reading this article, the participant should be able to: 1. Understand the epidemiology, classification, and anatomy pertinent to the scaphoid. 2. Appropriately evaluate a patient with suspected scaphoid fracture, including appropriate imaging. 3. Understand the indications for operative treatment of scaphoid fractures, and be familiar with the various surgical approaches. 4. Describe the treatment options for scaphoid nonunion and avascular necrosis of the proximal pole.

SUMMARY

The goal of this continuing medical education module is to present the preoperative assessment and the formation and execution of a surgical treatment plan for acute fractures of the scaphoid. In addition, secondary surgical options for treatment of scaphoid nonunion and avascular necrosis are discussed.

Transtrapezial Approach for Fixation of Acute Scaphoid Fractures: Rationale, Surgical Techniques, and Results: AAOS Exhibit Selection

The ideal position for a screw used for scaphoid fixation is central. The purpose of this study was to compare the current volar percutaneous approaches used for scaphoid fracture fixation, explore different options to improve central screw placement, and describe our experience with the transtrapezial approach.