Summary

The risk of mechanical failure is greatly increased if the spacer is <200% of the size of the segmental defect or if insufficient amount of spacer is inserted into residual bone.

Abstract

Background

Periprosthetic joint infection (PJI) can prove a challenging complication of any arthroplasty procedure. We reviewed our use of static antibiotic loaded cement spacers (ABLCs) for staged management of PJI where segmental bone loss, ligamentous instability or soft tissue defects necessitate a static construct. We reviewed factors contributing to their failure and techniques to avoid these complications when using ABLCs in this context.

Methods

Retrospective analysis of 94 patients undergoing first-stage revision of an infected knee prosthesis between 2007 to 2020 at a single institution. Radiographs and clinical records were used to analyse and classify causes and incidence of static spacer failure. Two-sided Student’s t-tests were used to assess continuous variables and Pearson’s Chi-squared was used to compare categorical values. Kaplan Meier survival function and log-rank tests were used to compare survival rates over time. A p-value of <0.05 was considered statistically significant.

Results

Of the 94 cases there were 19 primary total knee replacements (TKRs), 10 revision TKRs (Varus-valgus constraint), 20 hinged TKRs, 1 arthrodesis (nail), 1 failed spacer (performed elsewhere), 21 distal femoral endoprosthetic replacements and 22 proximal tibial replacements. 35 of 94 (37.2%) had spacer related complications, of which 26/35 complications (74.3%) were because of mechanical failure of the spacer construct. Risk factors for internal failure were a construct where the total intramedullary spacer length was <200% of the central osseous defect (p=0.0085), where proximal or distal intraosseous spacer contact of less than 10% and the requirement of a tibial tubercle osteotomy for tibial component extraction (p=0.0046). Incidence of spacer complication significantly increased the time to second stage on mean 157 days (range 42 – 458) without complications versus 227 days (11-528) with complications (p=0.014).

Conclusion

The failure rate of antibiotic loaded cement spacers with segmental osseous defects is much higher than anticipated. Complications of the spacer significantly increased the time to second stage. The risk of mechanical failure is greatly increased if the spacer is <200% of the size of the segmental defect or if insufficient amount of spacer is inserted into residual bone. This serves as a guide for surgeons to avoid mechanical complications with static spacers.