In Vitro Wear of a Novel Vitamin E Crosslinked Polyethylene Lumbar Total Joint Replacement.

Background: A novel, lumbar total joint replacement (TJR) design has been developed to treat degeneration across all three columns of the lumbar spine (anterior, middle, and posterior columns). Thus far, there has been no in vitro studies that establish the preclinical safety profile of the vitamin E-stabilized highly crosslinked polyethylene (VE-HXLPE) lumbar TJR relative to historical lumbar anterior disc replacement for the known risks of wear and impingement faced by all motion preserving designs for the lumbar spine.

Questions/purpose: In this study we asked, (1) what is the wear performance of the VE-HXLPE lumbar TJR under ideal, clean conditions? (2) Is the wear performance of VE-HXLPE in lumbar TJR sensitive to more aggressive, abrasive conditions? (3) How does the VE-HXLPE lumbar TJR perform under impingement conditions?

Method: A lumbar TJR with bilateral VE-HXLPE superior bearings and CoCr inferior bearings was evaluated under clean, impingement, and abrasive conditions.

Do Articular Surfaces of Dual Mobility Hips Have More Wear and Friction? An In Vitro Investigation.

Background: Larger head-to-neck ratio of dual mobility (DM) hip arthroplasties provide greater range of motion/less risk of dislocation, but raise concerns for high wear and friction. We measured in vitro, the wear rates of contemporary DM hips with highly cross-linked ultra high molecular weight polyethylene (UHWMPE), where it came from, and their frictional torques.

Methods: Hip simulators were used to compare the wear of DM to fixed-bearing (FB) designs of 2 different implants.

Ceramic Wear Particles: Can They Be Retrieved In Vivo and Duplicated In Vitro?

Background: Little is known about retrieved zirconia platelet toughened alumina (ZPTA) wear particles from ceramic-on-ceramic (COC) total hip arthroplasty. Our objectives were to evaluate clinically retrieved wear particles from explanted periprosthetic hip tissues and to analyze the characteristics of in vitro-generated ZPTA wear particles.

Methods: Periprosthetic tissue and explants were received for 3 patients who underwent a total hip replacement of ZPTA COC head and liner.

Thermal Localization Improves the Interlayer Adhesion and Structural Integrity of 3D printed PEEK Lumbar Spinal Cages.

Additive manufacturing (AM) is a potential application for polyetheretherketone (PEEK) spinal interbody fusion cages, which were introduced as an alternative to titanium cages because of their biocompatibility, radiolucency and strength. However, AM of PEEK is challenging due to high melting temperature and thermal gradient. Although fused filament fabrication (FFF) techniques have been shown to 3D print PEEK, layer delamination was identified in PEEK cages printed with a first generation FFF PEEK printer [1].

Does annealing improve the interlayer adhesion and structural integrity of FFF 3D printed PEEK lumbar spinal cages?

Polyaryletheretherketone (PEEK) has been commonly used for interbody fusion devices because of its biocompatibility, radiolucency, durability, and strength. Although the technology of PEEK Additive Manufacturing (AM) is rapidly developing, post-processing techniques of 3D printed PEEK remain poorly understood. AM of PEEK has been challenging because of its high melt temperature (over 340 °C) and requires specialized equipment which was not commercially available until recently.

Structure-Property Relationships for 3D printed PEEK Intervertebral Lumbar Cages Produced using Fused Filament Fabrication.

Recent advances in additive manufacturing technology now enable fused filament fabrication (FFF) of Polyetheretherketone (PEEK). A standardized lumbar fusion cage design was 3D printed with different speeds of the print head nozzle to investigate whether 3D printed PEEK cages exhibit sufficient material properties for lumbar fusion applications. It was observed that the compressive and shear strength of the 3D printed cages were 63-71% of the machined cages, whereas the torsion strength was 92%.

Are PEEK-on-Ceramic Bearings an Option for Total Disc Arthroplasty? An In Vitro Tribology Study.

Background: Most contemporary total disc replacements (TDRs) use conventional orthopaedic bearing couples such as ultrahigh-molecular-weight polyethylene (polyethylene) and cobalt-chromium (CoCr). Cervical total disc replacements incorporating polyetheretherketone (PEEK) bearings (specifically PEEK-on-PEEK bearings) have been previously investigated, but little is known about PEEK-on-ceramic bearings for TDR.

Questions/purposes: (1) What is the tribologic behavior of a PEEK-on-ceramic bearing for cervical TDR under idealized, clean wear test conditions? (2) How does the PEEK-on-ceramic design perform under impingement conditions? (3) How is the PEEK-on-ceramic bearing affected by abrasive wear? (4) Is the particle morphology from PEEK-on-ceramic bearings for TDRs affected by adverse wear scenarios?

Methods: PEEK-on-ceramic cervical TDR bearings were subjected to a 10 million cycle ideal wear test based on ASTM F2423 and ISO 181912-1 using a six-station spine wear simulator (MTS, Eden Prairie, MN, USA) with 5 g/L bovine serum concentration at 23° ± 2° C (ambient temperature).

Factors Affecting Lethal Isotherms During Cryoablation Procedures.

Background: Creating appropriately-sized, lethal isotherms during cryoablation of renal tumors is critical in order to achieve sufficiently-sized zones of cell death. To ensure adequate cell death in target treatment locations, surgeons must carefully select the type, size, location, and number of probes to be used, as well as various probe operating parameters.

Objective: The current study investigates the effects of probe type, operating pressure, and clinical method on the resulting sizes of isotherms in an in vitro gelatin model.

The Biotribology of PEEK-on-HXLPE Bearings Is Comparable to Traditional Bearings on a Multidirectional Pin-on-disk Tester.

Background: All-polymer bearings involving polyetheretherketone (PEEK) have been proposed for orthopaedic applications because they may reduce stress shielding, reduce weight of the implants, reduce wear and risk of osteolysis, and prevent release of metal ions by replacing the metal articulating components. Little is known about the biotribology of all-polymer PEEK bearings, including the effects of cross-shear, which are relevant for implant longevity, especially in the hip, and increased temperature that may affect lubricant proteins and, hence, lubrication in the joint.

Questions/purposes: Using pin-on-disk in vitro testing, we asked: (1) Can all-polymer bearing couples involving PEEK have a comparable or lower wear rate than highly crosslinked UHMWPE (HXLPE) on CoCr bearing couples? (2) Is the wear rate of PEEK bearing couples affected by the amount of cross-shear? (3) Is there a difference in wear mechanism and surface morphology for all-polymer bearing surfaces compared with UHMWPE (HXLPE) on CoCr?

Methods: We simultaneously tested a total of 100 pin-on-disk couples (n = 10 per bearing couple) consisting of three traditional metal-on-UHMWPE and seven polymer-on-polymer bearings for 2 million cycles under physiologically relevant conditions and in accordance with ASTM F732.

Development of a clinically relevant impingement test method for a mobile bearing lumbar total disc replacement.

Background Context: Total disc arthroplasty is an alternative therapy to spinal fusion for the treatment of neck or low back pain and is hypothesized to reduce the risk of disease progression to the adjacent spinal levels. Radiographic and retrieval analyses of various total disc replacements (TDRs) have shown evidence of impingement damage. Impingement of TDRs can occur when the device reaches the limits of its functional range of motion, causing contact between peripheral regions of the device.

Bench Models for Assessing the Mechanics of Mitral Valve Repair and Percutaneous Surgery.

Rapid preclinical evaluations of mitral valve (MV) mechanics are currently best facilitated by bench models of the left ventricle (LV). This review aims to provide a comprehensive assessment of these models to aid interpretation of their resulting data, inform future experimental evaluations, and further the translation of results to procedure and device development. For this review, two types of experimental bench models were evaluated.

The Latest Lessons Learned from Retrieval Analyses of Ultra-High Molecular Weight Polyethylene, Metal-on-Metal, and Alternative Bearing Total Disc Replacements.

Knowledge regarding the in vivo performance and periposthetic tissue response of cervical and lumbar total disc replacements (TDRs) continues to expand. This review addresses the following four main questions: 1) What are the latest lessons learned from polyethylene in large joints and how are they relevant to current TDRs? 2) What are the latest lessons learned regarding adverse local tissue reactions from metal-on-metal, CoCr bearings in large joints and how are they relevant to current TDRs? 3) What advancements have been made in understanding the in vivo performance of alternative biomaterials, such as stainless steel and polycarbonate urethane, for TDRs in the past five years? 4) How has retrieval analysis of all these various artificial disc bearing technologies advanced the state of the art in preclinical testing of TDRs? The study of explanted artificial discs and their associated tissues can help inform bearing selection as well as the design of future generations of disc arthroplasty. Analyzing retrieved artificial discs is also essential for validating preclinical test methods.

Comparison of in vivo and simulator-retrieved metal-on-metal cervical disc replacements.

Background: Cervical disc arthroplasty is regarded as a promising treatment for myelopathy and radiculopathy as an alternative to cervical spine fusion. On the basis of 2-year clinical data for the PRESTIGE(®) Cervical Disc (Medtronic, Memphis, Tennessee), the Food and Drug Administration recommended conditional approval in September 2006 and final approval in July 2007; however, relatively little is known about its wear and damage modes in vivo. The main objective was to analyze the tribological findings of the PRESTIGE(®) Cervical Disc.

In vivo deformation, surface damage, and biostability of retrieved Dynesys systems.

Study Design: Retrospective retrieval analysis.

Objective: To evaluate wear, deformation and biodegradation within retrieved polycarbonate urethane (PCU) components of Dynesys systems.

Summary Of Background Data: The Dynesys Dynamic Stabilization System (Zimmer Spine) consists of pedicle screws (Ti alloy), polycarbonate urethane (PCU) spacers, and a polyethylene-terephthalate cord.

Deformation of metal-backed acetabular components and the impact of liner thickness in a cadaveric model.

Shell deformation of resurfacing and all-metal modular cups following press-fit implantation has been reported, but not for conventional metal-backed cups with polyethylene liners. The deformation of acetabular components with historical and thin polyethylene inserts after press-fit insertion was evaluated using a cadaveric model. All shells and liners deformed upon implantation.

Retrieval analysis of a ProDisc-L total disc replacement.

Study Design: We retrieved a functioning ProDisc-L total disc replacement and associated tissues at 16 months of service life.

Objective: To analyze a previously unreported mode of implant malpositioning, wear mechanisms, and polyethylene locking mechanism, and to study retrieved periprosthetic tissues.

Summary Of Background Data: The clinical performance of polyethylene in the context of total disc replacements remains poorly understood.

Accelerated aqueous aging simulation of in vivo oxidation for gamma-sterilized UHMWPE.

In vivo oxidation of gamma air-sterilized ultrahigh-molecular-weight polyethylene (UHMWPE) has been observed when joint replacement hip and knee components are explanted during revision surgery. The purpose of the present study was to extend a previously published accelerated aging protocol for gamma-sterilized UHMWPE. Unsterilized and gamma-sterilized GUR 1150 resin samples were aged in phosphate-buffered saline (PBS) at 40 or 50 degrees C for up to 52 weeks.

Analysis of a retrieved polyethylene total disc replacement component.

Background Context: Although total disc replacements have been performed in Europe since the 1980s, this type of surgery is still new in the United States. The clinical performance of polyethylene in total disc replacements is still not well understood.

Purpose: To describe the wear, surface damage, oxidation and mechanical properties in an explanted polyethylene total disc replacement component.