u-HA/PLLA composites are mainly used to treat fractures of the upper extremities [8, 17]. Unstable metacarpal fractures are commonly treated by open reduction and internal fixation using rigid devices, such as titanium plates [2, 3]. However, these implants are often associated with high complication rates [5, 6]. u-HA/PLLA bioabsorbable implants have been introduced as a reliable alternative to titanium plates. These absorbable implants are designed to provide several clinical advantages compared to metallic implants [8]. Firstly, mesh sheets made from u-HA/PLLA are very thin (0.7 mm thickness); therefore, the associated risk of soft tissue irritation is lower than that of titanium plates. Secondly, mesh sheets are malleable and can be placed in the best possible position to cover a fracture according to the fracture pattern. Furthermore, there are many screw holes in the mesh sheets. Therefore, surgeons have more flexibility for screw placement. The u-HA/PLLA material also serves as a good alternative for patients allergic to metal. Above all, there is no need to remove the u-HA/PLLA bioabsorbable plates.
It has already been demonstrated that u-HA/PLLA bioabsorbable plate constructs have sufficient mechanical strength to stabilize metacarpal fractures [8]. The bending strength and stiffness of semi-tubular and one-third tubular bioabsorbable plate constructs were comparable to those of titanium plates. Further, the strengths of plates were shown to remain comparable to that of cortical bone for 6 months [11], which is more than the 3–4 months required for bone healing. In fact, good clinical results using bioabsorbable plates to repair metacarpal fractures have been reported [8]. In these studies, bioabsorbable plates were used to repair diaphyseal and proximal fractures. Fractures near the joints should be handled with care, because bioabsorbable plates have no locking system, and there is a large amount of cancellous bone in the proximal metacarpal bone near joints. Therefore, there is a possibility that screws may fall out or loosen. In addition, tapping must be performed to fix screws, and care must be taken to avoid tightening screws too strongly because the shear strength of bioabsorbable screws is weaker than that of titanium screws, and they may twist as a result of breakage between the screw shaft and head. In these cases, a rescue technique may be used to cauterize the screw stump using an electrosurgical knife to integrate it within the bioabsorbable plate. In the past, breakage of screw heads occurred in a small number of our patients; however, this complication has not recently occurred.
Delayed foreign body reactions such as inflammation and persistent swelling have been reported occasionally in the oral and maxillofacial surgical fields [13]. These are thought to be caused by mechanical irritation due to protrusion of screws that had not been degraded, and inflammatory reactions that occur throughout the process of degradation and absorption. In orthopedic literature, one study with mean follow-up period of 45.7 months (range, 34–61 months) showed that foreign body reactions did occur in four of nine patients that required second procedures to remove implants [18]. In this study, no implant-specific complications were reported, which indicates that operation site likely affects surgical outcomes. In oral and maxillofacial surgery, the presence of oral bacteria cannot be ignored [19]. In fact, the surgical site infection frequency of hand fractures was reported to be 1% [20], whereas that of mandibular closed fractures was reported to be 1.4–33.4% [21, 22]. The surgery was performed as described to prevent mechanical irritation, however, other factors were unknown.
In this study, two cases yielded low Q-DASH scores. One case had limited range of motion. There were no physical findings that suggested adhesion of the extensor tendon, and there were no abnormalities observed, such as screw protrusion. Postoperative therapy was more likely to affect the observed outcome than technical problems. In another case, poor recovery of grip strength ratio was observed; however, the patient had multiple fractures which could have led to poor level of recovery.
In this study, in the case of metacarpal fractures, we found that the process of bioabsorption might be completed in about 8 years. Previous studies conducted on wrist arthritis using four-corner fusion for scapholunate advanced collapse and scaphoid nonunion advanced collapse using bioabsorbable plates indicate that it took significantly fewer years (approximately 5 years) for absorption to take place after surgery [23]. These results suggest that the speed of absorption depends on the location of surgical intervention. We speculate that the less cancellous nature of metacarpal bones may be a factor that contributes to the differences observed between metacarpal and four-corner fusion absorption rates. However, there are no studies that have demonstrated that absorption speeds of implants within the bone differ from those placed outside the bone. This study suggests that cancellous bone volume may contribute to differences in plate bioabsorption rates.
This study had three limitations. Firstly, this study assessed a case series retrospectively, and the sample size was limited to six patients. Therefore, more cases should be included in future studies. Secondly, as mentioned above, no true locking system exists, and there is a possibility that screws may have fall out or loosen. In this study, there were no cases where screws backed out. Thirdly, control group was not included in this study. In spite of these limitations, one of the strengths of this study is long-term follow-up and the results of this study suggest that the use of bioabsorbable plates is an useful option for the treatment of displaced metacarpal fractures.
