Assessment of the Potential Role of Preoperative Dental Clearance in Total Joint Arthroplasty Optimization: A Pilot Study.

AIMS AND OBJECTIVES: Periprosthetic joint infection (PJI) is a serious complication after total joint arthroplasty (TJA) and is associated with significant morbidity, mortality, and cost. This pilot study primarily aimed to investigate if preoperative dental screenings would impact the rate of PJI following TJA when compared to historical controls. Secondarily, this study aimed to evaluate the prevalence of dental pathology in patients undergoing TJA. METHODS: Charts from 103 consecutive patients undergoing primary or revision total hip arthroplasty (THA, rTHA) or total knee arthroplasty (TKA, rTKA) by a single surgeon at a single academic institution over a two-year period were reviewed and selected for inclusion. All patients were referred to a dentist for preoperative clearance using a standardized form. The rate of dental pathology before surgery, details of the dental intervention required, and any dental work performed within six months postoperatively were evaluated. The demographic and comorbidity composition of our patient population was also collected. Finally, rates of PJI following each type of TJA were obtained for demographic- and comorbidity-matched historical controls from similar study designs to examine the potential impact of preoperative dental intervention. RESULTS: Of the 103 patients, 31 (30.1%) were found to have preoperative dental pathology. Twenty-eight of these 31 patients (90.3%) required dental intervention prior to surgery. Based on demographic- and comorbidity-matched historical data, we expected two (95% CI (0, 6)) PJI cases for the THA group, 0 (95% CI (0, 2)) PJI cases for the TKA group, two (95% CI (0, 5)) PJI cases for the rTHA group, and two (95% CI (0, 5)) PJI cases for the rTKA group. However, in our study, there were no PJIs after any TJA up to the latest follow-up, which was unlikely for THA, rTHA, and rTKA groups given the calculated Poisson probabilities (9.39%, 15.11%, and 11.26%, respectively). Finding 0 cases was likely for the TKA group given the calculated Poisson probability of 72.61%. CONCLUSIONS: This pilot study demonstrated that preoperative dental screening, which aims to decrease the chance of PJI due to bacteremia, may have an impact on the rate of PJI following THA, rTKA, and rTHA but not TKA based on Poisson probabilities calculated from demographic- and comorbidity-matched historical controls that lacked preoperative dental screening. For THA, rTKA, and rTHA, the Poisson probabilities of observing 0 cases of PJI postoperatively, as was the case in our study, were unlikely, suggesting that some variable in our cohort was decreasing the PJI rate for these groups. However, in the case of TKA, the Poisson probability of observing 0 cases was likely and matched the results of our study, suggesting that no variable in our cohort was affecting the PJI rate for this group. We cannot draw direct conclusions from this retrospective observational study, but the preliminary findings prompt further investigation through an appropriately controlled, blinded, multi-centered, and powered prospective randomized controlled trial.

Quantifying Nanoparticle Ordering Induced by Polymer Crystallization.

It has recently been established that polymer crystallization can preferentially place nanoparticles (NPs) into the amorphous domains of a lamellar semicrystalline morphology. The phenomenology of this process is clear: when the time for NP diffusion is shorter than the crystal growth time, then the NPs are rejected by the growing crystals and placed in the amorphous domains. However, since there is no quantitative characterization of this ordered NP state, we develop a correlation function analysis for small-angle X-ray scattering data, inspired by classical methods used for enunciating the local morphology of lamellar semicrystalline polymers. We show that when the spherulitic growth rate is slower than NP diffusion, then all the NPs are expelled from the crystals. As we increase the crystallization temperature, Tc, the long period characterizing the periodically repeating crystal-amorphous polymer structure, rcc, increases. This results in a smaller number of amorphous domains per unit volume-the number of NPs per amorphous domain thus increases. While the scattering contrast between the pure silica and the polymer is constant, these arguments predict that the apparent contrast between the NP-rich and the polymer-rich domains scale linearly with rcc, as we confirm from our experiments. These facts allow us to posit that the NPs become more efficiently packed in the interlamellar zone with increasing Tc until they form a fully filled monolayer. Above this temperature, NP multilayers form within each of the NP-rich domains. Our analysis approach, therefore, describes NP ordering that is achieved when driven by polymer crystallization.

Mechanisms of Directional Polymer Crystallization.

Zone annealing, a directional crystallization technique originally used for the purification of semiconductors, is applied here to crystalline polymers. Tight control over the final lamellar orientation and thickness of semicrystalline polymers can be obtained by directionally solidifying the material under optimal conditions. It has previously been postulated by Lovinger and Gryte that, at steady state, the crystal growth rate of a polymer undergoing zone annealing is equal to the velocity at which the sample is drawn through the temperature gradient. These researchers further implied that directional crystallization only occurs below a critical velocity, when crystal growth rate dominates over nucleation. Here, we perform an analysis of small-angle X-ray scattering, differential scanning calorimetry, and cross-polarized optical microscopy of zone-annealed poly(ethylene oxide) to examine these conjectures. Our long period data validate the steady-state ansatz, while an analysis of Herman's orientation function confirms the existence of a transitional region around a critical velocity, v crit, where there is a coexistence of oriented and isotropic domains. Below v crit, directional crystallization is achieved, while above v crit, the mechanism more closely resembles that of conventional isotropic isothermal crystallization.

Exchange Lifetimes of the Bound Polymer Layer on Silica Nanoparticles.

Understanding the structure and dynamics of the bound polymer layer (BL) that forms on favorably interacting nanoparticles (NPs) is critical to revealing the mechanisms responsible for material property enhancements in polymer nanocomposites (PNCs). Here we use small angle neutron scattering to probe the temporal persistence of this BL in the canonical case of poly(2-vinylpyridine) (P2VP) mixed with silica NPs at two representative temperatures. We have observed almost no long-term reorganization at 150 °C (∼Tg,P2VP + 50 °C), but a notable reduction in the BL thickness at 175 °C. We believe that this apparently strong temperature dependence arises from the polyvalency of the binding of a single P2VP chain to a NP. Thus, while the adsorption-desorption process of a single segment is an activated process that occurs over a broad temperature range, the cooperative nature of requiring multiple segments to desorb converts this into a process that occurs over a seemingly narrow temperature range.

Nanoparticle Organization by Growing Polyethylene Crystal Fronts.

We investigate the crystallization-induced ordering of C18 grafted 14 nm diameter spherical silica nanoparticles (NPs) in a short chain (Mw = 4 kDa, DM ≈ 2.3) polyethylene and a commercial high-density polyethylene (Mw = 152 kDa, DM ≈ 3.2) matrix. For slow isothermal crystallization of the low molecular weight matrix, the NPs segregate into the interlamellar regions. This result establishes the generality of our earlier work on poly(ethylene oxide) based materials and suggests that crystallization can be used to control NP dispersion across different polymer classes. The incompatibility between the particles and the matrix in the Mw = 152 kDa results in a competition between filler organization and filler agglomeration. The mechanical properties improve due to the addition of NPs and are further enhanced by particle organization, even for the case of the macrophase-separated mixtures in the Mw = 152 kDa matrix. In contrast, dielectric behavior is strongly affected by the scale of NP organization, with the lower molecular weight matrix showing more significant increases in permittivity due to the local scale of NP ordering.

Effects of Hairy Nanoparticles on Polymer Crystallization Kinetics.

We previously showed that nanoparticles (NPs) could be ordered into structures by using the growth rate of polymer crystals as the control variable. In particular, for slow enough spherulitic growth fronts, the NPs grafted with amorphous polymer chains are selectively moved into the interlamellar, interfibrillar, and interspherulitic zones of a lamellar morphology, specifically going from interlamellar to interspherulitic with progressively decreasing crystal growth rates. Here, we examine the effect of NP polymer grafting density on crystallization kinetics. We find that while crystal nucleation is practically unaffected by the presence of the NPs, spherulitic growth, final crystallinity, and melting point values decrease uniformly as the volume fraction of the crystallizable polymer, poly(ethylene oxide) or PEO, ϕPEO, decreases. A surprising aspect here is that these results are apparently unaffected by variations in the relative amounts of the amorphous polymer graft and silica NPs at constant ϕ, implying that chemical details of the amorphous defect apparently only play a secondary role. We therefore propose that the grafted NPs in this size range only provide geometrical confinement effects which serve to set the crystal growth rates and melting point depressions without causing any changes to crystallization mechanisms.

Tunable Multiscale Nanoparticle Ordering by Polymer Crystallization.

While ∼75% of commercially utilized polymers are semicrystalline, the generally low mechanical modulus of these materials, especially for those possessing a glass transition temperature below room temperature, restricts their use for structural applications. Our focus in this paper is to address this deficiency through the controlled, multiscale assembly of nanoparticles (NPs), in particular by leveraging the kinetics of polymer crystallization. This process yields a multiscale NP structure that is templated by the lamellar semicrystalline polymer morphology and spans NPs engulfed by the growing crystals, NPs ordered into layers in the interlamellar zone [spacing of [Formula: see text] (10-100 nm)], and NPs assembled into fractal objects at the interfibrillar scale, [Formula: see text] (1-10 µm). The relative fraction of NPs in this hierarchy is readily manipulated by the crystallization speed. Adding NPs usually increases the Young's modulus of the polymer, but the effects of multiscale ordering are nearly an order of magnitude larger than those for a state where the NPs are not ordered, i.e., randomly dispersed in the matrix. Since the material's fracture toughness remains practically unaffected in this process, this assembly strategy allows us to create high modulus materials that retain the attractive high toughness and low density of polymers.