Since the 1980s, bioabsorbable implants have been increasingly utilized for fracture fixation and also for other orthopaedic procedures, including ligament reconstruction, meniscal repair, rotator cuff repair, and shoulder labral lesion repair1-4. The majority of bioabsorbable materials for implants are monopolymers or copolymers of polylactic acid (PLA) (including a levorotatory [PLLA] and a dextrorotatory [PDLLA] configuration), polyglycolic acid (PGA), and polydioxanone (PDS)3,4. The foreign-body reactions related to polyglycolic acid usually have emerged one to four months after implantation and have been well documented in the literature1,3,5. However, the in vivo degradation time of the stereoisomeric form of polylactic acid copolymers is much longer6. In contrast to polyglycolic acid, the tissue responses associated with polylactic acid (PLLA or PDLLA) are much less common5.
From June 2005 to December 2009, seventy-eight distal radial fractures were treated with these implants at our hospital. Three patients (4%) had a late foreign-body reaction twenty-one months after fixation. Debridement and removal of the remaining implant was curative in all three patients. Histopathological examination showed a nonspecific foreign-body reaction, and the retrieved particles were confirmed as polylactic acid polymers with use of Fourier transform infrared spectroscopy. The patients were informed that data concerning their cases would be submitted for publication, and they consented.
CASE 1. A forty-eight-year-old woman sustained a closed, left distal radial fracture with intra-articular involvement when she slipped and fell in December 2005. She had no known systemic diseases and reported no allergies. Two weeks after the injury, she underwent open reduction and internal fixation with a bioabsorbable plate and screws (Inion OTPS Volar Radius Plates; Inion Oy, Tampere, Finland) (Fig. 1) through a volar radial (Henry) approach between the flexor carpi radialis tendon and the radial artery7. The postoperative course was unremarkable.
In September 2007, twenty months after the procedure, the patient noted a gradually enlarging mass on the volar side of the wrist. She also complained of wrist soreness and finger tingling and was suspected of having carpal tunnel syndrome. The mass was soft, nonmovable, and elastic in character. Deep palpation exacerbated the pain. Magnetic resonance imaging showed a healed distal radial fracture that was accompanied by an oval 1.0 × 0.6 × 2.2-cm mass lying within the wrist flexor tendons (Fig. 1, D, E, and F). Laboratory data were within normal limits (C-reactive protein level [CRP], 0.03 mg/dL; erythrocyte sedimentation rate [ESR], 9 mm/hr; white blood-cell count [WBC], 5170/mm3).
Operative exploration was carried out in December 2007, two years after the initial operation. Intraoperatively, 7 mL of a cloudy fluid that had collected along the volar side of the distal part of the radius was drained. The fluid was accompanied by several fragments of a whitish material (Fig. 2). The surrounding tissue was erythematous and swollen. The wound was thoroughly debrided. Previous screw holes in the diaphyseal area were still clearly visible, but the metaphyseal area screw holes could not be identified. Intraoperative Gram staining and cultures were negative. Later histopathological analysis revealed a nonspecific foreign-body reaction (Fig. 3, A), and the retrieved particles disclosed polylactic acid polymers under Fourier transform infrared spectroscopy (Fig. 4). There was no evidence of infection or malignancy. At the time of the latest follow-up examination, in May 2010, neither wrist tenderness nor finger tingling was noted. Radiographs revealed that the screw holes had filled in.
CASE 2. A fifty-year-old woman sustained a closed, right intra-articular distal radial fracture. The patient had no known systemic diseases and reported no allergies. She underwent open reduction and internal fixation with a bioabsorbable plate and screws (Inion OTPS) through a volar radial approach7. The postoperative course was unremarkable.
In August 2009, the patient reported a prominent, painful mass, 2 cm in diameter, overlying the distal part of the radius, just beneath the surgical scar. She also noted occasional tingling in her fingers. The mass was soft, immobile, and elastic in character. Application of pressure exacerbated the pain and numbness. Magnetic resonance imaging showed a healed distal radial fracture accompanied by a soft-tissue mass that had infiltrated between the flexor tendons and the distal part of the radius. Laboratory data were within the normal range (CRP, 0.05 mg/dL; ESR, 10 mm/hr; WBC, 5460/mm3).
In September 2009, at the time of surgery, a yellowish turbid fluid collection was noted volar to the radius and was excised. Histopathological analysis revealed a nonspecific foreign-body reaction (Fig. 3, B). At the time of the latest follow-up examination, in May 2010, no wrist tenderness, finger tingling, wound swelling, or erythema was noted.
CASE 3. A healthy thirty-eight-year-old man with no history of allergies sustained a right distal radial fracture in October 2006. He underwent open reduction and internal fixation with a bioabsorbable plate and screws (Inion OTPS) through a volar radial approach7. The postoperative course was unremarkable.
He had noted a gradually enlarging soft-tissue mass adjacent to the previous surgical scar beginning in June 2008, twenty months after the operation. Examination revealed a lobulated, soft, elastic, nonmovable 3 × 2-cm mass. When pressure was applied, there was mild discomfort. Aspiration produced 1 mL of yellowish turbid fluid. Gram staining and cultures were negative. Ultrasonography revealed a hypoechoic and anechoic mass, nearly 3.5 × 2.2 cm in size, volar to the distal part of the radius. Magnetic resonance imaging showed a healed intra-articular distal radial fracture with an accumulation of fluid on the volar surface of the radius. All laboratory data were normal (CRP, 0.06 mg/dL; ESR, 9 mm/hr; WBC, 5820/mm3).
In July 2008, operative treatment was carried out following a preoperative diagnosis of infection. A yellowish cystic mass measuring 4 × 2 cm was noted. Approximately 12 mL of cloudy fluid was drained, accompanied by several clear to whitish particles. The surrounding tissue was edematous. The mass was excised, and histologic analysis revealed a nonspecific foreign-body reaction. The collected particles were sent for Fourier transform infrared spectroscopy and were shown to be compatible with polylactic acid polymers (Fig. 4). There was no evidence of infection or malignancy. At an outpatient visit in March 2010, the wound had fully healed without any complications.
Unstable distal radial fractures are often surgically treated. Treatment with metallic implants may require a second operation to remove the implants. Bioabsorbable implants have several advantages over traditional metallic implants, including reduced stress shielding and a decreased rate of secondary surgery. The physiochemical characteristics of biodegradable implants make them appealing1,4,8. However, one of the major concerns of bioabsorbable implants is their strength. With the advances in bioengineering, the strength of bioabsorbable implants is now similar to that of metal implants. Nieminen et al.9 evaluated the mechanical strength of bioabsorbable implants in a sheep study and concluded that the implants maintained adequate strength throughout the fracture-healing period. Buijs et al.10 found similar torsion and side-bending stiffness in association with bioabsorbable implants and 1.5-mm titanium plates, although the titanium plate had better tensile strength and stiffness. Another prospective, randomized, single-blinded clinical study compared bioabsorbable and metal plates for the treatment of distal radial fractures and identified no significant differences in functional outcomes11.
Although there have been encouraging results, there is still no consensus on the ideal composition of bioabsorbable implants. Different manufacturers use different protocols and compositions to produce each product, and usually these data are not readily available, for proprietary reasons. Among these components, the most common are polyglycolic acid, polylactic acid, the isomers PLLA and PDLLA, a copolymer of polyglycolic acid and polylactic acid (PLGA), polydioxanone, and trimethylene carbonate (TMC)1,3,4. Most of the biomaterials degrade primarily by hydrolysis, in vitro, with the release of their respective monomers, and they finally are excreted as carbon dioxide and water1,4,6. However, in vivo, the condition of degradation not only depends on the composition of the biomaterial itself but also is strongly influenced by the shape and size of the implants, the site of implantation, and the surrounding environment. Thus, it is difficult to identify risk factors and to devise solutions for the foreign-body reaction. According to the manufacturer, the implants that we used gradually lose their strength during an eighteen to forty-six-week period while bone-healing occurs. The strength of the implant is completely lost in six to nine months, and bioresorption takes place over in two to four years12.
To our knowledge, most previously reported tissue reactions have been associated with ankle fracture treatment13-15. The ankle joint has less soft-tissue coverage and more osseous prominence than the volar surface of the distal part of the radius, which may result in poorer implant concealment and slower degradation and may lead to the accumulation of breakdown products and tissue irritation2,5,11,15. This idea is supported by comparing our rate of foreign-body reaction (4%) with those in previous reports of distal radial fractures that were treated with bioabsorbable dorsal plates (23%; three of thirteen)11 and ankle fractures (8%; four of fifty)15. In addition, Ambrose and Clanton1 and Bostman and Pihlajamaki2,5 reported the vascularity of the local tissue and the volume of the implanted polymer as possible risk factors for foreign-body reaction because a sufficient debris-clearing capacity of the tissue probably is essential to prevent the accumulation of a local overload of polymeric degradation particles1,2,5. The volar surface of the distal part of the radius generally is regarded as an area with a good vascular supply and soft-tissue coverage7. A previous report revealed the relatively low rate of foreign-body reaction associated with volar plates (0%; zero of six)11.
According to one report, the geometry of the implants influences reaction rates, with screws and serrated bolts showing a higher prevalence of adverse tissue reactions than pins and rods5. On the basis of our limited experience, we believe that the plate system, which has a larger mean volume than rods or pins, may increase the possibility of foreign-body reaction, despite good local tissue vascularity.
Generally, the timing of the foreign-body reaction is thought to be related to the final stage of polymer degradation; thus, a shorter degradation time may decrease the possibility of adverse foreign-body reaction1. According to the data acquired from the manufacturer, the composition of the implants used in our patients included copolymers of TMC, PLLA, and PDLLA, and the degradation time is approximately four to nine months12. This degradation profile is slightly shorter than that of other similar composite products1. In our three cases, the second surgical intervention occurred at an average of twenty-one months after implantation. The time course of degradation was much longer than previously anticipated, and the specimens were later confirmed to have a high content of lactic acid polymers, findings that were compatible with those of previous reports1,2,6.
Despite the occurrence of foreign-body reactions, all three fractures healed before the reaction occurred. Thus, it seems that the soft-tissue reactions do not impair bone-healing. Also, the tissue reaction was consistent and showed an aseptic, nonspecific inflammatory reaction with multinucleated giant cells. Polymeric debris was often visible along with an occasional osteolytic reaction2,3.
Clinically, complications associated with resorbable implants can present with varying levels of severity, ranging from mild fluid accumulation to sinus formation to irreversible soft-tissue damage1,4. The reported prevalence of inflammatory reactions has been low, and the reactions themselves have been so mild that the effects on long-term outcome were negligible5. In a few studies, however, the reactions were moderate to severe and necessitated second operations5.
Our study had several limitations. First, the rate of foreign-body reaction in our series (4%) was higher than that in an earlier report (0.2%; one of 491)5 but was lower than those in reports of distal radial fractures treated with bioabsorbable dorsal plates (23%; three of thirteen)11 or ankle fractures (8%; four of fifty)15. This finding suggests that different anatomical sites have varying rates of foreign-body reaction. However, with a limited number of cases involving distal radial fractures and with no control group, the risk factors for foreign-body reaction cannot be assessed. Second, a polylactic acid-induced foreign-body reaction may occur several years after the original operation, and a higher rate of loss to follow-up can be anticipated, resulting in an underestimation of the reaction rate. Longer follow-up is warranted to clarify the prevalence of polylactic acid-related foreign-body reactions.
We have used bioabsorbable implants for the treatment of distal radial fractures for several years, and most of the patients were symptom-free after implantation. Bone union and functional recovery usually were achieved in approximately two to three months and were not adversely affected by polylactic acid-induced foreign-body reaction. The prevalence of foreign-body reaction is low, but foreign-body reaction can occur several years after the original operation and will require further treatment.
Investigation performed at Far-Eastern Memorial Hospital, National Taiwan University & Hospital, and Mackay Memorial Hospital, Taipei, Taiwan
Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.