SLR - July 2019 - Clay B. Shumway

The Relationship Between Polyethylene Insert Size and Complications in Total Ankle Replacement

Reference: Cottom, JM., et al. "The Relationship Between Polyethylene Insert Size and Complications in Total Ankle Replacement." Foot & ankle specialist (2018): 1938640018787044.

Reviewed By: Clay B. Shumway, DPM
Residency Program: East Liverpool City Hospital – East Liverpool, OH

Podiatric Relevance: Total Ankle Replacement has become increasingly more common due to improvement in surgeons' experience and improvement in technology. Indications are being stretched and oft times varus and valgus deformity is being corrected at the same time as the ankle arthroplasty. Larger poly inserts are typically used in these deformity correction cases when more bone needs to be removed. The larger polys used are usually 10 mm or greater in thickness. This study compares the complication rate in 63 patients with a poly less than 10 mm in thickness vs. 47 patients with a poly 10 mm or greater.     

Methods: A level IV retrospective comparative study reviewing charts of patients who had TAA from 2012 to 2017. Exclusions were lost to follow up, AVN of the talus, septic arthritis, or periarticular osteomyelitis. Also, patients undergoing revision TAR or ankle fusion take down were not included. Patients were placed in two groups, with group one having a poly less than 10 mm and group two having a poly 10 mm or greater. Demographics, poly size, implant used, concomitant procedures, complications, revision rates, failure rates and patient-reported outcomes were recorded. Complications were anything that required return to OR within first 90 days of surgery. All TAA were performed by author James Cottom. Fischer exact test was used for comparing categorical variables.

Results: Of the 221 patients undergoing TAR from 2012-2017 100 patients were available for f/u. avg. follow up was 31.3 months STAR prosthesis was used in 74 patients, Salto XT in 15, Cadence in three, and Infinity in eight. Group one complication rate was 11.1 percent and group two was 16.2 percent. This was not statistically significant. Complications for group one included five wound dehiscences, one periprosthetic fracture, one required poly swap after aseptic loosening, and one required poly swap with gutter debridement. No implant failures in group one. Group two complications included two wound dehiscences, two had deep infection requiring removal of implant, one had removal of implant, placement of antibiotic spacer and then successful reimplantation, one had a poly swap. Group one AOFAS scores were 83.3 and group two 82. Foot function index score in group one was 15.7 and for group two was 22.3.

Conclusions: Larger poly inserts had a higher complication rate likely from cases being more complex involving deformity correction. This was not statistically significant. Patient reported outcomes were similar. This is the first study to compare poly size to complication rates. A study by Pijls showed better outcomes with larger poly sizes. Poly wear is a concern in the ankle with forces up to five times body weight being transmitted through the joint. Kobayashi found that synovial fluid analysis for poly particle size similar to total knee arthroplasties. Two ankles in group one and one in group two required poly swap due to wear in this study. A three-piece mobile bearing implant may accommodate for the various rotational forces in the ankle. The did not compare the different implants used or the two-piece vs three-piece implants. 

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