Progressive loss of implant fixation in a preclinical rat model of cemented knee arthroplasty

Friend or foe? Inflammation and the foreign body response to orthopedic biomaterials

The use of biomaterials and implants for joint replacement, fracture fixation, spinal stabilization and other orthopedic indications has revolutionized patient care by reliably decreasing pain and improving function. These surgical procedures always invoke an acute inflammatory reaction initially, that in most cases, readily subsides. Occasionally, chronic inflammation around the implant develops and persists; this results in unremitting pain and compromises function. The etiology of chronic inflammation may be specific, such as with infection, or be unknown. The histological hallmarks of chronic inflammation include activated macrophages, fibroblasts, T cell subsets, and other cells of the innate immune system. The presence of cells of the adaptive immune system usually indicates allergic reactions to metallic haptens. A foreign body reaction is composed of activated macrophages, giant cells, fibroblasts, and other cells often distributed in a characteristic histological arrangement; this reaction is usually due to particulate debris and other byproducts from the biomaterials used in the implant. Both chronic inflammation and the foreign body response have adverse biological effects on the integration of the implant with the surrounding tissues. Strategies to mitigate chronic inflammation and the foreign body response will enhance the initial incorporation and longevity of the implant, and thereby, improve long-term pain relief and overall function for the patient. The seminal research performed in the laboratory of Dr. James Anderson and co-workers has provided an inspirational and driving force for our laboratory's work on the interactions and crosstalk among cells of the mesenchymal, immune, and vascular lineages, and orthopedic biomaterials. Dr. Anderson's delineation of the fundamental biologic processes and mechanisms underlying acute and chronic inflammation, the foreign body response, resolution, and eventual functional integration of implants in different organ systems has provided researchers with a strategic approach to the use of biomaterials to improve health in numerous clinical scenarios.

Peri-operative zoledronic acid attenuates peri-prosthetic osteolysis in a rat model of cemented knee replacement

Progressive osteolysis can occur at the cement-bone interface of joint replacements and the associated loss of fixation can lead to clinical loosening. We previously developed a rat hemiarthroplasty model that exhibited progressive loss of fixation with the development of cement-bone gaps under the tibial tray that mimicked patterns found in human arthroplasty retrievals. Here we explored the ability of a bisphosphonate (zoledronic acid, ZA) to attenuate cement-bone osteolysis and maintain implant stability. Sprague-Dawley rats (n = 59) received a poly(methylmethacrylate) cemented tibial component and were followed for up to 12 weeks. Treatment groups included peri-operative administration of ZA (ZA group), administration of ZA at 6 weeks postop (late ZA group), or vehicle (Veh group). There was a 60% reduction in the rate of cement-bone gap formation for the ZA group (0.15 mm3/week) compared to Veh group (0.38 mm3/week, p = 0.016). Late ZA prevented further progression of gap formation but did not reverse bone loss to the level achieved in the ZA group. Micromotion from five times body weight toggle loading was positively correlated with cement-bone gap volume (p = 0.009) and negatively correlated with the amount of cement in the metaphysis (p = 0.005). Reduced new bone formation and enduring nonviable bone in the epiphysis for the ZA group were found. This suggests that low bone turnover in the epiphysis may suppress the early catabolic response due to implantation, thereby maintaining better fixation in the epiphysis. This preclinical model presents compelling supporting data documenting improved maintenance of the cement-bone fixation with the use of peri-operative bisphosphonates.

Roles of inflammatory cell infiltrate in periprosthetic osteolysis

Classically, particle-induced periprosthetic osteolysis at the implant-bone interface has explained the aseptic loosening of joint replacement. This response is preceded by triggering both the innate and acquired immune response with subsequent activation of osteoclasts, the bone-resorbing cells. Although particle-induced periprosthetic osteolysis has been considered a foreign body chronic inflammation mediated by myelomonocytic-derived cells, current reports describe wide heterogeneous inflammatory cells infiltrating the periprosthetic tissues. This review aims to discuss the role of those non-myelomonocytic cells in periprosthetic tissues exposed to wear particles by showing original data. Specifically, we discuss the role of T cells (CD3+, CD4+, and CD8+) and B cells (CD20+) coexisting with CD68+/TRAP- multinucleated giant cells associated with both polyethylene and metallic particles infiltrating retrieved periprosthetic membranes. This review contributes valuable insight to support the complex cell and molecular mechanisms behind the aseptic loosening theories of orthopedic implants.

Bisphosphonates' use and risk of aseptic loosening following total hip arthroplasty: a systematic review

Purpose

The main indication of bisphosphonates (BPs) is osteoporosis treatment. However, there is growing interest in the peri- and postoperative use of BPs to mitigate total hip arthroplasty (THA) aseptic loosening (AL) risk. This systematic review aimed to evaluate the implant survival and the AL rate in patients with elective THA receiving BPs compared to those that do not receive BPs. Secondary outcomes included the comparison of revision rate, postoperative complications, and patients' functional scores.

Methods

This systematic review was conducted under the PRISMA 2020 guidelines with a pre-registered PROSPERO protocol. Three engines and grey literature were searched up until May 2022. Randomized and nonrandomized controlled trials and comparative cohort studies assessing BP and control therapy impact on THA survival were included.

Results

Twelve studies embraced the inclusion criteria. A total of 99 678 patients and 99 696 THAs were included; 10 025 patients received BPs (BP group), and 89 129 made up the control group. The overall revision and AL rates were lower in the BP group (2.17% and 1.85%) than in the control group (4.06% and 3.2%). Periprosthetic fracture (PPF) cases were higher in the BP group (0.24%) than in the control group (0.04%); however, the majority of PPF cases were derived from a single study. Further complication risk was similar between groups. Most studies reported comparable functional scores between groups.

Conclusion

BP treatment after elective THA seems to reduce the overall revision and AL risk. Other complications' risk and functional scores were similar between groups. Further high-quality studies are needed to validate the results due to the multifactorial AL pathogenesis.

Potential for supraphysiologic fluid shear stresses in a rat cemented knee replacement model

The mechano-biologic environment associated with aseptic loosening of cemented joint replacements is not fully understood. The goal of this study was to use a preclinical rat knee arthroplasty model to explore the changes in cement-bone morphology and micromotion that occur with in vivo service. Narrow gaps between cement and bone under the tibial tray were present at early time points, and with even small magnitude micromotion, resulted in large micromotion-to-gap width ratios. These data were then used to develop models of fluid flow in the cement-bone gaps to estimate potential for high fluid shear stress (FSS). Modeling results revealed supraphysiologic (>4 Pa) FSS were possible, particularly for cases in which eccentric loading applied to the implant and if the fluid in the gap consisted of marrow or synovial fluid. The early, high FSS environment, could cause fluid-induced periprosthetic osteolysis locally, resulting in progressive loss of cement-bone fixation.

Novel Tuning of PMMA Orthopedic Bone Cement Using TBB Initiator: Effect of Bone Cement Extracts on Bioactivity of Osteoblasts and Osteoclasts

Bone cement containing benzoyl peroxide (BPO) as a polymerization initiator are commonly used to fix orthopedic metal implants. However, toxic complications caused by bone cement are a clinically significant problem. Poly (methyl methacrylate) tri-n-butylborane (PMMA-TBB), a newly developed material containing TBB as a polymerization initiator, was found to be more biocompatible than conventional PMMA-BPO bone cements due to reduced free radical generation during polymerization. However, free radicals might not be the only determinant of cytotoxicity. Here, we evaluated the response and functional phenotypes of cells exposed to extracts derived from different bone cements. Bone cement extracts were prepared from two commercial PMMA-BPO cements and an experimental PMMA-TBB. Rat bone marrow-derived osteoblasts and osteoclasts were cultured in a medium supplemented with bone cement extracts. More osteoblasts survived and attached to the culture dish with PMMA-TBB extract than in the culture with PMMA-BPO extracts. Osteoblast proliferation and differentiation were higher in the culture with PMMA-TBB extract. The number of TRAP-positive multinucleated cells was significantly lower in the culture with PMMA-TBB extract. There was no difference in osteoclast-related gene expression in response to different bone cement extracts. In conclusion, PMMA-TBB extract was less toxic to osteoblasts than PMMA-BPO extracts. Although extracts from the different cement types did not affect osteoclast function, PMMA-TBB extract seemed to reduce osteoclastogenesis, a possible further advantage of PMMA-TBB cement. These implied that the reduced radical generation during polymerization is not the only determinant for the improved biocompatibility of PMMA-TBB and that the post-polymerization chemical elution may also be important.