On the Necessity of a Customized Knee Spacer in Peri-Prosthetic Joint Infection Treatment: 3D Numerical Simulation Results

Abstract

Peri-prosthetic joint infections (PJIs) dramatically affect human health, as they are associated with high morbidity and mortality rates. Two-stage revision arthroplasty is currently the gold standard treatment for PJI and consists of infected implant removal, an accurate debridement, and placement of antimicrobial impregnated poly-methyl-metha-acrylate (PMMA) spacer. The use of antibiotic-loaded PMMA (ALPMMA) spacers have showed a success rate that ranges from 85% to 100%. ALPMMA spacers, currently available on the market, demonstrate a series of disadvantages, closely linked to a low propensity to customize, seen as the ability to adapt to the patients’ anatomical characteristics, with consequential increase of surgical complexity, surgery duration, and post-operative complications. Conventionally, ALPMMA spacers are available only in three or four standard sizes, with the impossibility of guaranteeing the perfect matching of ALPMMA spacers with residual bone (no further bone loss) and gap filling. In this paper, a 3D model of an ALPMMA spacer is introduced to evaluate the cause- effect link between the geometric characteristics and the correlated clinical improvements. The result is a multivariable-oriented design able to effectively manage the size, alignment, stability, and the patients’ anatomical matching. The preliminary numerical results, obtained by using an “ad hoc” 3D virtual planning simulator, clearly point out that to restore the joint line, the mechanical and rotational alignment and the surgeon’s control on the thicknesses (distal and posterior thicknesses) of the ALPMMA spacer is mandatory. The numerical simulations campaign involved nineteen patients grouped in three different scenarios (Case N° 1, Case N° 2 and Case N° 3) whose 3D bone models were obtained through an appropriate data management strategy. Each scenario is characterized by a different incidence rate. In particular, the observed rates of occurrence are, respectively, equal to 17% (Case N° 1), 74% (Case N° 2), and 10% (Case N° 3).

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

“…In the following, a not exhaustive list of drawbacks associated with the common used ALPMMA spacers are reported, such as: (I) both femoral-tibial and femoral-patellar instability; (II) the possibility of developing important contractures in flexion; (III) frailty and subsequent breaking of the implant, especially with high doses of antibiotic; (IV) the difficulty of managing malalignments on the three planes of space (frontal, sagittal, and transversal) and bone defects whether segmental or cavitary (affecting articular surfaces, metaphysis, and diaphysis). The aforementioned weaknesses may be overcome through the designing of a patient-tailored ALPMMA spacer with specific features to mitigate the above mentioned drawbacks [ 27 ]. The objective is to introduce the additive manufacturing approach in the orthopedic field as a powerful tool to effectively manage the PJI.…”

Articulating spacers: what are available and how to utilize them?

“…3D printing technology allows for rapid prototyping based on each individual’s unique anatomical configuration, thereby improving the match between components and joints. Previous evaluation of 3D models of spacers by using an " ad hoc " virtual planning simulator revealed a strong correlation between the geometric characteristics of the spacer and clinical improvement [ 66 ]. In recent years, 3D printing-based spacers have been proposed to enhance joint function and stability [ 67 ].…”