Design of a first metatarsophalangeal joint simulator.

BACKGROUND

The use of total first metatarsophalangeal joint (MPJ) arthroplasty to treat patients in which the pain, due to a pathological joint, has not been relieved with a conservative method or for which the disease or disorder is at an advanced stage, is popular. Although meta-analysis of clinical results indicates that this surgical option is efficacious, there are problems with implant failure due to wear of the components. Although there is a plethora of designs of this type of implant in clinical use, there are no literature reports on total first MPJ simulators, which may be used to evaluate, for example, the wear rate of a total first MPJ implant.

METHODS

We designed such a simulator, guided by the biomechanics of the joint. Thus, for example, the implant under test will be articulated at least 40° dorsiflexion, under a 600 N loading, at 1 Hz. Furthermore, the testing stations will be configured to allow testing of any type of first MPJ implant. We also performed a finite element analysis (FEA) study of a model of an articulating station, subjected to a quasi-static load of 1200 N.

RESULTS

For an articulating station, (1) the highest von Mises stress occurred at the implant-fixture interface; and (2), for the other parts, the minimum factor of safety, against elastic failure, is approximately 9.

CONCLUSIONS

The designed joint simulator is mechanically sound and may be used for wear testing of any type of first MPJ implant.