SLR - February 2013 - Bullock
Reference: Noh J. H., Roh Y. H., Yang B. G., Kim S. W., Lee J. S., & Oh M. K. Outcomes of operative treatment of unstable ankle fractures: a comparison of metallic and biodegradable implants J Bone Joint Surg Am, 2012; 94(22):e166, 1-7.
Scientific Literature Review
Reviewed by: Mark Bullock, DPM
Residency Program: St. John Hospital and Medical Center
Podiatric Relevance:
Hardware pain is a common postoperative complication in the foot and ankle due to limited soft tissue coverage. This is particularly evident with ankle fractures where several studies demonstrate high rates of hardware removal postoperatively. Biodegradable synthetic polymers were developed in part to eliminate hardware removal and the associated risks. Additional benefits of biodegradable implants include reducing the stress shielding and image interference caused by the metallic implants. Unfortunately, most research to date reporting outcomes of bioabsorbable implants on malleolar fractures lacks a comparison group.
Methods:
The study is a prospective trial where patients with unstable ankle fractures were randomized into one of two treatment groups. Group one utilized metallic fixatives while group two utilized biodegradable polylevolactic acid implants for both medial and lateral malleolar fractures. Three-point-five millimeter and 4.0 mm screws were used in group one for lateral plate fixation compared with 3.1 mm and 4.5 mm screws in group two. Four-point-five millimeter screws were used in both groups for medial malleolar fractures. Outcomes included time to fracture union, nonunions, and clinical scores (AOFAS/SMFA dysfunction/bother index) up until 12 months. Baseline SMFA dysfunction and bother index scores were taken retrospectively.
Results:
Fifty-three of 56 patients in group one and 49/53 patients in group two completed the 12 month follow-up. AOFAS clinical scores at 12 months were lower with biodegradable implants, 84.3 vs 87.5 (p=0.004). Time to lateral malleolar fracture union was delayed with biodegradable implants, 17.6 weeks vs 15.8 weeks (p=0.002). Use of biodegradable implants significantly delayed operative time, 56.4 minutes vs 30.2 minutes. Of the twelve medial malleolar fractures that required biodegradable screw fixation, six lost reduction but healed uneventfully. Subjective complaints of prominence and mild tenderness were less common with biodegradable implants, 12/49 patients versus 17/53 patients.
Conclusions:
Results of the study suggest significant limitations with current bioabsorbable plate-screw constructs. An additional 26.2 minutes were spent in the operating room due to a need for tapping with a narrow pitch, precise measurements, precise reduction and additional periosteal stripping of the lateral malleolus. Delayed osseous healing was not pronounced and had minimal effect on clinical outcomes but could theoretically increase the risk of non-union. It is uncertain whether the delayed healing time was caused by fixation strength, increased periosteal stripping and/or different screw sizes as they are all confounding variables. Further studies are needed comparing biodegradable screws to metallic screws in isolation because the absorbable screws lost initial reduction of the medial malleolar fracture in half of cases.