Preoperative Prediction of the Scaphoid Screw Length for the Fixation of Fractures Using MRI Measurements of Finger Phalanges

Introduction: Scaphoid fractures are one of the most common carpal bone fractures, with most fractures involving the waist. When surgery is indicated, internal fixation with screws is the standard method for the fixation of these fractures. Accurate length and trajectory of the screw are two crucial parameters essential for optimal internal fixation. Determining the accurate screw length required for fixation can be challenging, especially in an intraoperative setting. Preoperative determination of the screw length can improve surgical precision, thereby contributing to an improved functional outcome. This study investigates a novel approach using magnetic resonance imaging (MRI) measurements of the little, ring, middle, and index finger middle phalanges to preoperatively predict the screw length used for scaphoid fracture fixation. Methods: This retrospective observational study included an analysis of 30 MRIs of the wrist and hand. The MRI protocol for wrist and hand was unified for all the patients to ensure consistency and reproducibility. All MRIs were performed by a single experienced radiologist using a high-field 1.5 Tesla MRI scanner. The axial lengths of the bones were calculated on T1-weighted coronal MRI slices using the Meddiff Rispacs DICOM viewer software. A line was drawn from the condyles of the phalanx to the base of the phalanx to measure the maximum axial length of the middle phalanx. The maximum axial length of the scaphoid was measured from the proximal pole to the distal articular surface along the fracture fixation axis. The measurements were performed by a consultant orthopedic hand surgeon and a qualified orthopedic senior resident to minimize inter-observer errors. A musculoskeletal radiologist further analyzed the measurements. Pearson's correlation coefficient was used to determine the relationship between the scaphoid length and the lengths of the middle phalanges. Paired t-tests were applied with the level of significance set at p < 0.05. Linear regression was performed to develop a predictive equation for scaphoid length based on the middle phalanx measurements. Results: The mean scaphoid length was 1.96 cm. The mean lengths of the middle phalanges of the little, ring, middle, and index fingers were 1.66 cm, 2.05 cm, 2.29 cm, and 1.79 cm, respectively. Using the paired t-test, a significant positive correlation was found between the scaphoid length and middle phalanx length of all fingers (p < 0.001), with the strongest correlation observed with the length of the middle phalanx of the ring finger (r = 0.861). The regression equation for predicting scaphoid length based on the middle phalanx of the middle finger was: y = 0.665 + 0.565x (study power 90%). Conclusion: MRI measurements of the middle phalanx, particularly of the ring finger, offer a reliable method for predicting scaphoid screw length preoperatively. This approach can improve surgical planning, precision, and potentially patient outcomes without increasing additional costs.