Bioabsorbable Implants For Flatfoot: Can They Work?
What The Studies Reveal About The Efficacy Of Bioabsorable Implants
Various authors have reported a wide range of applications for bioabsorbable implants in the literature, including the use of these modalities in osteotomies, fractures and arthrodeses. However, the surgeon must remember that in comparison to traditional metal implants, bioabsorbables possess inferior mechanical properties.18 Therefore, surgeons should reserve the use of these implants for instances when minimal load and stress will be applied, when healing will occur before the implant loses significant strength, and when surgeons would remove the implant under normal circumstances.9 Medial malleolar fractures and syndesmotic injuries are currently the most accepted applications for absorbable fixation. Bucholz, et. al., randomized 155 patients with displaced medial malleolar fractures.19 They managed one group with 4.0 mm stainless steel fixation while managing the other group with 4.0 mm PLA screw fixation. There was no significant difference between the groups in terms of fracture healing, postoperative complications or functional results. In addition, at an average follow-up of 37 months, no inflammatory reactions occurred in the PLA group. Hovis, et. al., followed 23 patients with PLLA screw fixation of syndesmotic injuries for an average of 34 months.18 All patients returned to pre-injury levels of activity within the time of follow-up. There were no reactions to the absorbable material and no secondary procedures were required. The authors conclude that PLLA screws are ideal for fixation of these injuries because compression is not required in syndesmotic repairs. Thordarson, et. al., compared bioabsorbable fixation to stainless steel screw fixation of syndesmotic injuries in pronation-external rotation ankle fractures.20 In a randomized study, the authors utilized fixation with a 4.5 mm PLA screw for 17 patients and employed a 4.5 mm stainless steel screw for 15 patients. After 11 months, all fractures healed uneventfully. In addition, there were no wound complications, no radiographic osteolytic changes and no inflammatory reactions in the PLA group. The Lisfranc injury represents another clinical scenario in which approximation has more vital importance than compression. These injuries also typically require hardware removal after standard open reduction internal fixation (ORIF) with metal implants. Accordingly, Lisfranc injuries seem extremely conducive to bioabsorbable fixation. Thordarson and Hurvitz used PLA screws in 14 patients with Lisfranc fractures/dislocations.21 There was no loss of reduction after an average 20-month follow-up. There were also no reports of soft tissue or bone reaction to the implants. Within a 10-year period, Rokkanen, et. al., performed a total of 2,500 orthopedic procedures using bioabsorbable materials.22 They reported fixation failure in 3.7 percent of the patients with PGA implant cases and encountered non-infectious inflammatory reactions in 2.3 percent of patients with PGA implants. The reaction appeared postoperatively at two to three months. However, no reactions occurred with the use of PLA implants. Bioabsorbable implant use in pediatric patients is still under debate. Researchers published an experimental study on the effect of PDS implants placed across the growth plate of rabbits in 1989.23 A transphyseal 2.0 mm PDS implant showed no permanent growth disturbance and no histomorphometric change in comparison to a control. Böstman, et. al., published a study of PGA pins in treating 71 fractures in skeletally immature patients. According to the study, 87 percent of patients experienced anatomic healing until union.17 Still, the authors recommended long-term clinical studies before widespread use becomes commonplace for pediatric patients. However, keep in mind that these studies dealt with implanting devices into bone as opposed to soft tissues.