Biomechanical in vitro evaluation of the effect of cyclic loading on the postoperative fixation stability and degradation of a biodegradable ankle plate

Abstract

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 (...

Interfacial Sliding Properties of Bone Screw Materials and Their Effect on Screw Fixation Strength

“…In vitro fatigue testing of fracture fixation is typically performed for biodegradable materials in an environment simulating human body conditions (30). However, fatigue tests can also reveal the long-term interfacial behavior of metallic implants like bone screws and fixation plates with novel surfaces and coatings, and thus, they should be considered.…”

Evaluation of the Fatigue Performance and Degradability of Resorbable PLDLLA-TMC Osteofixations

“…Minimal decrease of retention strength should be expected in titanium (not mentioning the unfortunate drawbacks of titanium plates) [28-35]. Vaananen et al [11]. examine the hydrolytic stability of an ankle plate made from identical material over 12 weeks.…”

“…Although an elaborate approximation, loading does not correspond to the permanent intermittent complex loading that occurs in-situ . The loading patterns chosen by Vaananen [11]. are possibly representative for the loading situation of a plate used for fixation in the leg, but is certainly not applicable to the jaw, as permanent movement in swallowing of saliva and speaking occurs, even if no loading by hard food chewing occurs.…”

“…Complete disintegration is sought after 3 months of stable fixation and should cause no local irritation of tissues [9,10]. The biodegradation of polymers used in resorbable osteofixations has been demonstrated in many laboratory in-vitro and in-vivo animal studies [11-16], but only few in-situ patient studies have been reported [17,18]. These latter studies have some limitations, such as small number of explants and the results being applicable only to the specific polymer used for fabricating the osteosyntheses.…”

“…This polymer has the advantage to be less brittle in handling, due to the addition of TMC. In 2.5 mm strength, PLDLLA-TMC is also more stable than other available polymer osteofixations [11,15]. PLDLLA-6TMC so far has only been investigated for degradation in-vitro (laboratory experimentation) and in-vivo (animals), not in-situ (patients) [11,15].…”