We used a biodegradable mesh to convert an acetabular defect into a contained defect in six patients at total hip replacement. Their mean age was 61 years (46 to 69). The mean follow-up was 32 months (19 to 50). Before clinical use, the strength retention and hydrolytic in vitro degradation properties of the implants were studied in the laboratory over a two-year period. A successful clinical outcome was determined by the radiological findings and the Harris hip score. All the patients had a satisfactory outcome and no mechanical failures or other complications were observed. No protrusion of any of the impacted grafts was observed beyond the mesh. According to our preliminary laboratory and clinical results the biodegradable mesh is suitable for augmenting uncontained acetabular defects in which the primary stability of the implanted acetabular component is provided by the host bone. In the case of defects of the acetabular floor this new application provides a safe method of preventing graft material from protruding excessively into the pelvis and the mesh seems to tolerate bone-impaction grafting in selected patients with primary and revision total hip replacement.

The effect of cyclic loading on the postoperative fixation stability of a biodegradable ankle plate was tested biomechanically during 12 weeks of hydrolytic degradation. Fracture of the lateral malleolus was simulated, and the parameters of cyclic loading were chosen to represent the physiological conditions during the healing period. Additionally, the effect of cyclic loading on degradation was investigated by measuring the inherent viscosities. In Group I, the cyclic loading was conducted in four phases with gradual increases in estimated walking distance and speed during the healing period. In Group II, cyclic loading was conducted after 12 weeks. Group III was used as a control for inherent viscosity measurements. None of the specimens failed under cyclic loading. No significant differences were found between the loaded groups in any of the parameters measured. Additionally, no significant difference was found in inherent viscosities at 12 weeks. The initial fixation stability provided by the biodegradable ankle plate remains biomechanically unchanged over 12 weeks. Cyclic loading, applied either during or after 12 weeks of hydrolytic degradation, does not seem to have any clinically relevant effect on the fixation stability or the degradation properties. [17][18][19][20] However, use of biodegradable plates to treat lateral malleolar fractures of the ankle is justified as it could make secondary plate removal unnecessary, thereby saving health care resources. 4,[21][22][23] A recent cadaver study 24 showed that a biodegradable ankle plate can provide initial stability comparable to that provided by conventional metallic fixation methods. However, in contrast to metallic devices, the fixation strength of a biodegradable implant is likely to decrease over time due to hydrolytic degradation. Furthermore, physiological loading during bone healing may affect the degradation and strength retention of biodegradable implants. Therefore, our aim was to investigate if a biodegradable plate can withstand cyclic loading and maintain fracture reduction postoperatively until the lateral malleolus fracture has healed. A secondary aim was to investigate whether cyclic loading, applied either during or after a 12-week hydrolytic degradation, has any clinically relevant effect on fixation stability and degradation properties. MATERIALS AND METHODSSolid polyethylene (PE) rods (13 mm diameter) were used as surrogates for human fibulae. Test specimens were created by securing two transversely cut PE rods together with the biodegradable Inion OTPS TM eight-hole ankle plate and Inion OTPS TM 2.8 Â 12 mm screws (Inion Oy, Tampere, Finland) (Fig. 1). The rod heads were placed in contact to resemble fracture reduction. Before fixation, the plates were rejuvenated in water at 708C for 1 min to make them malleable. Thereafter, screw holes were drilled and tapped into the rods through the screw holes of the plates. Each plate was then fixed with eight screws, that is, four screws symmetrically on both sides of the fracture (...

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