Impact of Screw Length on Proximal Scaphoid Fracture Biomechanics

Abstract

Background Proximal scaphoid fractures display high nonunion rates and increased revision cases. Waist fracture fixation involves maximizing screw length within the cortex; however, the optimal screw length for proximal scaphoid fractures remains unknown. Purpose The main purpose of this article is to compare stiffness and ultimate load for proximal scaphoid fracture fixation of various headless compression screw lengths. Methods Eighteen scaphoids underwent an osteotomy simulating a 7 mm oblique proximal fracture. Screws of three lengths (10, 18, and 24 mm) were randomly assigned for fixation. Each specimen underwent cyclic loading with stiffness calculated during the last loading cycle. Specimens that withstood cyclic loading were loaded to failure. Results No significant difference in stiffness between screw lengths was found. Ultimate load was significantly impacted by the screw length. A significant difference in ultimate load between a 10 and 24 mm screw was found; however, no significant difference occurred in ultimate load between an 18 and 24 mm screw. Conclusions No significant difference in stiffness between all groups could be due to similarities in purchase in the proximal aspect. The 10 mm screw withstanding less ultimate load compared to the 24 mm screw could be due to the 10 mm screw gaining less purchase on either side of the fracture site compared to the 24 mm screw. Lack of significant difference in ultimate load between the 18 and 24 mm screw could be occurring because the fracture site is closer to the 18 mm screw midpoint, as distal threads are engaged closer to the fracture. Clinical Relevance Maximizing screw length may not provide superior fixation biomechanically compared with fixation utilizing a 6 mm shorter screw for proximal scaphoid fractures.

Normative Radiographic Measurements of Scaphoid in a Sample Indian Population

“…It is crucial to find the best screw sizes for surgical outcomes, especially in patients with scaphoid nonunion, where we use a radiograph of the normal side to evaluate screw length. 1,2 In surgical cases, the inserted guidewire measures scaphoid 5.5 (0.9) 5.5 (0.9) 5.5 (0.9) 0.9 SL ratio 1.9 (0.2) 1.9 (0.2) 1.9 (0. 2), and 5.5 (0.9) mm.…”

“…Knowledge of the standard lengths and widths of the scaphoid at different levels may be beneficial for inventory management in the operating room during scaphoid fracture management, in instances where screw placement is required, and in nonunion. 1,2 Several measurements and indices, such as the scapholunate (SL) angle, the scaphoid lunate ratio, and the SL gap, have been used to quantify and diagnose carpal instability. [3][4][5] The radioscaphoid angle has been recognized as a quantifiable measure for assessing outcomes in intercarpal arthrodesis.…”

“…Knowledge of the standard lengths and widths of the scaphoid at different levels may be beneficial for inventory management in the operating room during scaphoid fracture management, in instances where screw placement is required, and in nonunion. 1 2…”

Biomechanical Comparison of Different Volar Screw Placements for Horizontal Oblique Scaphoid Fractures

“…This resulted in a shorter screw in this study that could affect the fixation strength. However, Patel et al demonstrated maximizing screw length may not provide superior fixation for proximal scaphoid fractures [20]. Therefore, a 2 mm gap at the fracture site that simulated a scaphoid waist fracture may have been the reason for inferior fixation strength.…”

Pull-out forces of headless compression screws in variations of synthetic bone models imitating different types of scaphoid fractures in good bone quality

“…Headless compression screws represent the current gold standard in the surgical treatment of scaphoid fractures and non-unions [4][5][6]. High failure rates have been in part attributed to insufficient screw characteristics and unfavourable placement [5][6][7]. The technical features of the screw determine the tensile force that is required to reach the point of failure to screw pull-out [3].…”