Lisfranc Stability after Fixation with Magnesium-Based Biodegradable Screws; a Weightbearing CT Assessment of a Biodegradable Implant

Research Type: Level 5 - Case report, Expert opinion, Personal observation Introduction/Purpose: Unstable Lisfranc injuries compromise the tarsometatarsal complex, necessitating surgical stabilization. Traditional fixation often requires secondary hardware removal, prompting interest in biodegradable alternatives. Moreover, when assessing with radiographs or CT scans, metal implants impose artifacts on the images. Magnesium-based biodegradable screws offer biodegradability while providing sufficient strength for the fixation and no blockade of the radiology imaging. This study aims to evaluate the stability of Lisfranc joint after fixation with magnesium based biodegradable screws using weightbearing CT (WBCT) scans in a cadaver model of Lisfranc instability. The surgeons were also asked about the difficulty of using such screws compared to their experience with metal screws. Methods: Lisfranc instability was induced in twelve cadaveric specimens. The baseline measurements of the Lisfranc volume and area as well as post-instability measurements were obtained using WBCT under 75kg weight. These measurements were conducted after fixation of the Lisfranc using 3.5 mm magnesium-based biodegradable partly threaded screws (RemeOs, Bioretec, Finland). The area and volume of the Lisfranc joint was measured based on a report by Bhimani et al. (2021). Paired t-tests were used to compare the measurements at each stage with significance set at p < 0.05. Proper screw trajectory was ensured to prevent malalignment. The surgeons also commented on the difficultly of the procedures as bad, mediocre, and good. Results: As expected, we observed significant increases in areas and volumes compared in the injured state compared to the intact states (Table 1). The measurements we also significantly different between the post-fixation and unstable state (Table 1). No screw loosening was observed. The difficulty rate of the surgery was set as “good” by the surgeons in all the cases. While Xray can hardly show the location of these screws, WBCT can depict the trajectory of the screws very well without any artifact. Conclusion: Magnesium-based biodegradable screws provided effective stabilization of the Lisfranc complex based on WBCT assessment; however, we did not conduct other biomechanical studies on them. Nevertheless, literature advocates for these implants biomechanically. Their performance appears comparable to traditional fixation, although further studies are needed to confirm equivalency. The biodegradable nature of these screws eliminates the need for hardware removal, presenting a promising alternative for such midfoot injuries. Further studies are suggested to assess for short- and long-term possible adverse effects of these novel implants.