Summary

Ultrastatic spacer is a two nail construct that provides stable fixation during treatment of periprosthetic infections after total knee arthroplasty.

Abstract

Introduction

Prosthetic joint infection (PJI) is a rare but devastating complication after total knee arthroplasty (TKA). While guidelines clearly recommend treatment to include removal of the infected hardware and placement of an antibiotic impregnated spacer to maintain the patient’s leg length, the most stable construct for knee arthrodesis has not been established. Therefore, we sought to describe our technique evaluate the outcomes when using an ultrastatic spacer to treat PJI after TKA.

Methods

We retrospectively reviewed 11 patients who underwent placement of an ultrastatic spacer between 10/29/2020 and 3/23/2022. All patients were indicated for placement of the ultrastatic spacer for periprosthetic infection after TKA. Medical records were reviewed for demographics, infectious organism, antibiotic therapy, complications, outcomes, and if patient underwent additional revision surgeries.
The ultrastatic spacer was constructed using a retrograde femoral and antegrade tibial nail that overlap to span the knee joint. The nails were tied together using 16-guage wire. Antibiotic cement impregnated with three grams of tobramycin and five grams of vancomycin were then hand impacted into the bone defects and to span the knee joint.

Results

Mean age at time of implantation was 62.6 years and 81.8 percent (%) of patients were male. 90.9% of patients required placement of a right ultrastatic spacer. Infectious etiologies were identified in eight patients: three patients with staphylococcus epidermidis, one with methicillin-sensitive staphylococcus aureus (MSSA), one with methicillin-resistant staphylococcus aureus, one with Enterobacter cloacae, one with a combination of MSSA, cutibacterium acnes, and mold, and one with a combination of staphylococcus epidermidis, Enterobacter cloacae, and pseudomonas stutzeri. Three patients’ cultures did not grow any organisms, but intraoperative findings were consistent with periprosthetic infection. Postoperatively, all patients received an antibiotic regimen based on microbiology sensitivity testing.
Four patients cleared their PJI and underwent revision TKA or distal femoral replacement. Three of those patients continue to have no evidence of their periprosthetic infection and remain on chronic antibiotic suppressive therapy, while one patient had recurrence of MSSA in the setting of a quadriceps rupture. One additional patient also cleared the PJI and underwent permanent fixation with a modular knee arthrodesis due to loss of his extensor mechanism not amenable to repair. Four patients underwent revision of the ultrastatic spacer due to persistent PJI. Two of these patients were revised to another ultrastatic spacer and two patients underwent implantation of an antibiotic cement spacer with single nail construction. Two patients still have their ultrastatic spacer implanted at most recent follow-up. Average time that the ultrastatic spacer was implanted in each patient was 182.36 days.

Discussion

The ultrastatic spacer provides stable fixation for patients with a PJI after TKA with a mean time to revision of 182.36 days. In combination with systemic antibiotic therapy, the ultrastatic spacer successful at resolving 45.45% of PJI. Surgeons should be aware that the ultrastatic spacer is a viable option for treatment of PJI and the technique for implantation.