Togher C, Hyer C, Berlet G, Thompson J, Perkins J
Orthopedic Foot & Ankle Center, Worthington, United States
BACKGROUND:
The integration of porous coating into the newer generation of implants theoretically increases the chances of osseous ingrowth and survivorship in total ankle replacements. Alternatively, literature in hip replacement surgery has demonstrated increased rates of stress shielding, aseptic loosening, thigh pain, and cystic formation around stemmed femoral implants extensively coated with porous surfaces. While some ankle prostheses have integrated porous coating technology with stemmed tibial implants, there is little to no research investigating the potential negative effects this may have on periprosthetic cystic formation secondary to a stress shielding effect.
METHODS
Our study identified 11 patients who underwent total ankle arthroplasty via a smooth-stemmed tibial prosthesis and matched these patients based on implant age with patients who received fully porous-coated tibial implants. We then identified 39 supplemental patients for a total of 50 fully porous-coated tibial implants. Radiographs were compared for postoperative rates of backside loosening and cystic formation secondary to stress shielding between the groups. Relative risk for reoperation between the smooth and porous-coated implants was also investigated.
RESULTS
While the smooth-stem group showed no rates of backside cystic formation or stress shielding, the follow-up matched porous-coated group showed a rate of 63.3% of cystic formation and potential loosening secondary to stress shielding observed on final radiographic follow up (P < 0.01). Relative risk for reoperation in was 0.74.
CONCLUSION
This data shows that there is some consistency with the hip arthroplasty literature suggesting an increased risk for stress shielding in fully porous-coated stemmed tibial implants compared to smooth-stemmed tibial implants in total ankle arthroplasty, although there is a low reoperation rate associated with these findings.
