Wear Performance of Total Ankle Replacements: Standard's, Improved Material's and Long Term Performance

Background:

There is little knowledge about wear performance of total ankle arthroplasties (TAR). However, revisions rates are high for TAR [1] and wear associated revisions are frequent [2].

Therefore, the aim of this study is

1. (1)

   To test the wear behavior of a TAR using a biomechanically valid testing scenario.

2. (2)

   To test the influence of an alternative ceramic tibial component.

3. (3)

   To test the long term wear performance of TAR.

Material and Methods:

In the first part of this study the HINTEGRA (Smith & Nephew) TAR has been used for wear testing. Wear testing was performed on a modified AMTI knee simulator. Level walking according to a previous described testing standard [see abstract: Development of a force controlled testing scenario for total ankle replacements] has been used. Level walking was simulated in three clinical relevant situations, first simulating the reduced loading after implantation, secondly simulating an increasing range of motion and at last a loading pattern orientating at the loadings in the native/healthy joint. Every simulation was run for 3 million cycles, resulting in 9 million total cycles.

In the second part of this study the metal tibial plateau was replaced by a ceramic tibial component (Biolox® Delta, CeramTec). Simulation was run, as described above, for additional 9 million cycles. Termed as a long term test, in total 18 million cycles of testing are performed.

Results:

When simulating level walking with loadings assumed after implantation a wear rate of 19.5 ± 1,49 mg/Mc has been determined. Increasing the range of motion lead to a wear rate of 18.0 ± 2,56 mg/Mc and simulating loading as assumed in a healthy joint, a wear rate of 23.8 ± 1,47 mg/Mc was determined. When replacing the metal tibial component by a ceramic tray the wear rate decreased between 20–30% dependent on the tested scenario. No delamination occurred during 18 millon cycles of testing.

Conclusion:

In this study, high wear rates for TAR were determined. Compared to standardized wear testing of total knee replacements in our laboratory the wear rate of TAR was approximately 2.5 times increased. Ceramics seem to be an option to decrease the wear rate. The high wear rate of the polyethylene may be a factor contributing to the high revision rates seen in TARs.