Are Intramedullary Implants Used for Midfoot Charcot Fit for Female Metatarsals?

Category: Midfoot/Forefoot; Basic Sciences/Biologics Introduction/Purpose: Radiological assessments of metatarsal biometrics have been documented in few studies and often lack direct clinical significance. The narrower diameter of female metatarsals could be an impediment for intramedullary implant suitability. This investigation examines the radiological morphometry of female metatarsals to assess the diameter fitness of intramedullary implants used for midfoot Charcot fusion. Methods: Foot roentgenograms of 143 female patients in the standing position were collected for radiological assessment. Initially, basic biometric parameters were determined at the level of the metatarsal neck. Cortical thickness was derived by subtracting the inner width from the outer width measurements. Following a hypothetical reaming, mean values of inner width, outer width, and cortical thickness were assessed for fitness estimation. Implant fitness was considered satisfactory if either a) the inner width was below the threshold of 6mm, and/or b) the cortical thickness was below the threshold of 2mm (1 mm on each side of the cortex). Additional examination was performed using the lower quartile values for further analysis. Results: The findings revealed that: a) the mean inner width of M5 was significantly greater compared to M2, M3 and M4 (p ˂ 0.00001), while no significant difference was observed among the median metatarsals, and b) M2 exhibited a significantly higher outer width than M3 and M4 (p ˂ 0.00001), with no difference observed with M5. According to the predefined threshold values, the estimated width fitness values (after hypothetical reaming) for accepting implant diameter were deemed inadequate for M2, M3 and M4, and the estimated cortical thickness values deemed inadequate for M3, M4 and M5. Conclusion: Our study indicates, for the first time, a discrepancy in the inner width of the lateral metatarsals at the neck level concerning commercially available Charcot-specific intramedullary implants for female patients. This mismatch suggests an increased vulnerability to cortex fractures at the metatarsal neck and potential implant migration. If a critical width is identified, utilizing smaller implant diameters or opting for a proximal insertion at the base of the metatarsals might present more suitable alternatives.