Polyethylene-Based Knee Spacer for Infection Control: Design Concept and Pre-Clinical In Vitro Validations

Oxidized Zirconium Bearing Surface Failure in Total Knee Arthroplasty: A Unique Case Report of Isolated Medial Compartment with Catastrophic Results

Introduction

Oxidized Zirconium (OXINIUM™) is a metal alloy with a ceramic surface, utilized to increase the longevity of knee and hip implantations and reduce polyethylene wear. Polyethylene-based spacers are effective in infection control and prosthetic stability. Therefore, understanding the interactions between the polyethylene spacer and metallic counterparts is essential in surgical decision-making. Furthermore, understanding how patients may present when catastrophic failure of these components arises is imperative. Herein, we present a unique case of atraumatic OXINIUM™ wear in a middle-aged female after uneventful primary total knee arthroplasty (TKA), highlighting atypical clinical features and addressing the surgical management of this unexpected implant failure.

Case Report

A 51-year-old African American female presented from an outside facility with persistent left knee pain after undergoing a TKA with a Smith and Nephew OXINIUM™ coated knee. The patient presented to the senior author's clinic with worsening symptoms 2-year postoperatively from her primary left TKA by another surgeon. After a thorough work-up which was essentially unremarkable-3 years from her initial surgery - the recommendation was made for surgical revision given clinical concern for instability. During the initial surgical approach, significant sparking of the tissue was noted on the use of electrocautery. Once the capsule was dissected, black synovial fluid with soft tissue involvement was noted. Intraoperative analysis of the polyethylene spacer revealed disintegration in the medial compartment with loss of the zirconium coating along the femoral component. There was no evidence of polyethylene spacer wear within the lateral compartment. The primary components were explanted and replaced with a nickel-free implant. Following revision, the patient reported complete resolution of her symptoms with improvement in active range of motion.

Conclusion

This case illustrates a unique presentation of atraumatic prosthetic surface coating failure after an uneventful primary TKA with well-aligned post-operative radiographs. Instability in the posterior stabilized total knee caused the polyethylene liner to come out of place, causing articulation of femoral and tibial components, creating the metal debris. Patients who present with persistent symptoms-of unknown etiology - after primary TKA should be considered for enhanced screenings and early surgical intervention.

Preliminary tribological results of a new total temporary hip joint prosthesis spacer

Temporary antibiotic-loaded cement spacers are widely used for treating chronic periprosthetic hip infections. The aim of this study is to evaluate the short-term tribological performance of ultra-high-molecular-weight polyethylene (UHMWPE) and (60Co) gamma-irradiated cross-linked UHMWPE (XLPE) self-mated systems as frictional pairs for temporary total hip spacers. A three-axial hip joint simulator, FIME II, was used to test the UHMWPE and XLPE self-mated systems under variable load profiles. A fetal bovine serum solution was used as a lubricant. After simulation tests, wear measurements of damaged coupled surfaces were made with a coordinate measuring machine. Finally, surfaces were characterized with scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and nanoindentation tests. The mass loss test results for UHMWPE were 11.91 ± 3.43 mg for the cups and 4.57 ± 0.92 mg for the heads. Whereas, the results for XLPE showed a significant reduction, with mean mass loss values of 6.59 ± 0.14 mg for the cups and 2.82 ± 0.59 mg for the heads, suggesting the viability of the self-mated XLPE contact pair for a temporary total hip spacer.

A Customized Knee Antibiotic-Loaded PMMA Spacer: A Preliminary Design Analysis

A preliminary design of customized antibiotic-loaded poly-methyl-methacrylate (ALPMMA) spacer characterized by an appropriate footprint according to the specific patient’s anatomy and a reliable mechanical response to severe functional loads (i.e., level walking and 45° bent knee) is reported. The targeted virtual prototyping process takes origin from a novel patented 3D geometrical conceptualization characterized by added customization features and it is validated by a preliminary FEM-based analysis. Mechanical and thermomechanical properties of the antibiotic-doped orthopedic PMMA cement, which will be used for the future prototype manufacturing, were measured experimentally by testing samples taken during a real day-running orthopedic surgery and manufactured according to the surgeon protocol. FEM analysis results indicate that small area is subjected to intensive stresses, validating the proposed geometry from the mechanical point of view, under the two loading scenarios, moreover the value of safety margins results positive, and this is representative of the lower stress magnitude compared to the critical material limits. The experimental data confirm that the presence of antibiotic will last during the surgeon period moreover, the temperature dependent modulus of the bone cement is slightly affected by the body range temperature whereas it will drastically drop for higher temperature out the range of interest. A complete customization, according to a patient anatomy, and the corresponding real prototype spacer will be manufactured by 3D printing techniques, and it will be validated by destructive testing during the second stage of this activity before commercialization.