Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement.

OBJECTIVES: The objective of this study was to characterize the effect of rifampin incorporation into poly(methyl methacrylate) (PMMA) bone cement. While incompatibilities between the two materials have been previously noted, we sought to identify and quantify the cause of rifampin's effects, including alterations in curing properties, mechanical strength, and residual monomer content. METHODS: Four cement groups were prepared using commercial PMMA bone cement: a control; one with 1 g of rifampin; and one each with equimolar amounts of ascorbic acid or hydroquinone relative to the amount of rifampin added. The handling properties, setting time, exothermic output, and monomer loss were measured throughout curing. The mechanical strength of each group was tested over 14 days. A radical scavenging assay was used to assess the scavenging abilities of rifampin and its individual moieties. RESULTS: Compared with control, the rifampin-incorporated cement had a prolonged setting time and a reduction in exothermic output during polymerization. The rifampin cement showed significantly reduced strength and was below the orthopaedic weight-bearing threshold of 70 MPa. Based on the radical scavenging assay and strength tests, the hydroquinone structure within rifampin was identified as the polymerization inhibitor. CONCLUSION: The incorporation of rifampin into PMMA bone cement interferes with the cement's radical polymerization. This interference is due to the hydroquinone moiety within rifampin. This combination alters the cement's handling and curing properties, and lowers the strength below the threshold for weight-bearing applications. Additionally, the incomplete polymerization leads to increased toxic monomer output, which discourages its use even in non-weight-bearing applications.Cite this article: G. A. Funk, E. M. Menuey, K. A. Cole, T. P. Schuman, K. V. Kilway, T. E. McIff. Radical scavenging of poly(methyl methacrylate) bone cement by rifampin and clinically relevant properties of the rifampin-loaded cement. Bone Joint Res 2019;8:81-89. DOI: 10.1302/2046-3758.82.BJR-2018-0170.R2.

Improved gold chloride staining method for anatomical analysis of sensory nerve endings in the shoulder capsule and labrum as examples of loose and dense fibrous tissues.

Consistency in gold chloride staining is essential for anatomical analysis of sensory nerve endings. The gold chloride stain for this purpose has been modified by many investigators, but often yields inconsistent staining, which makes it difficult to differentiate structures and to determine nerve ending distribution in large tissue samples. We introduce additional steps and major changes to the modified Gairns' protocol. We controlled the temperature and mixing rate during tissue staining to achieve consistent staining and complete solution penetration. We subjected samples to sucrose dehydration to improve cutting efficiency. We then exposed samples to a solution containing lemon juice, formic acid and paraformaldehyde to produce optimal tissue transparency with minimal tissue deformity. We extended the time for gold chloride impregnation 1.5 fold. Gold chloride was reduced in the labrum using 25% formic acid in water for 18 h and in the capsule using 25% formic acid in citrate phosphate buffer for 2 h. Citrate binds gold nanoparticles, which minimizes aggregation in the tissue. We stored samples in fresh ultrapure water at 4° C to slow reduction and to maintain color contrast in the tissue. Tissue samples were embedded in Tissue Tek and sectioned at 80 and 100 µm instead of using glycerin and teasing the tissue apart as in Gairns' modified gold chloride method. We attached sections directly to gelatin subbed slides after sectioning with a cryostat. The slides then were processed and coverslipped with Permount. Staining consistency was demonstrated throughout the tissue sections and neural structures were clearly identifiable.

The effect of accuracy of implantation on range of movement of the Scandinavian Total Ankle Replacement.

When performing the Scandinavian Total Ankle Replacement (STAR), the positioning of the talar component and the selection of mobile-bearing thickness are critical. A biomechanical experiment was undertaken to establish the effects of these variables on the range of movement (ROM) of the ankle. Six cadaver ankles containing a specially-modified STAR prosthesis were subjected to ROM determination, under weight-bearing conditions, while monitoring the strain in the peri-ankle ligaments. Each specimen was tested with the talar component positions in neutral, as well as 3 and 6 mm of anterior and posterior displacement. The sequence was repeated with an anatomical bearing thickness, as well as at 2 mm reduced and increased thicknesses. The movement limits were defined as 10% strain in any ligament, bearing lift-off from the talar component or limitations of the hardware. Both anterior talar component displacement and bearing thickness reduction caused a decrease in plantar flexion, which was associated with bearing lift-off. With increased bearing thickness, posterior displacement of the talar component decreased plantar flexion, whereas anterior displacement decreased dorsiflexion.

The effect of agility ankle prosthesis misalignment on the peri-ankle ligaments.

In the Agility total ankle replacement system, motion is constrained by the implant's articulating surfaces and the peri-ankle ligaments. The effects of plausibly occurring implant malpositioning on peri-ankle ligament functional extension during walking were explored in this study. The intent was to determine whether certain ligaments could serve as guides to assist in proper component positioning at implantation. Using a cadaver preparation with simulated physiologic motion and loading, we monitored change of ligament length of the anterior talofibular, posterior talofibular, calcaneofibular, and tibiocalcaneal ligaments resulting from controlled malpositioning of the tibial component relative to a neutral position. During a simulated walking cycle, effects of mediolateral and anterior/posterior translation, internal and external rotation, inversion and eversion, and elevation of the component were evaluated. In all cases, tibial component displacement from the neutral position caused atypical length change in one or more of the peri-ankle ligaments. In particular, anterior/posterior displacement significantly changed the lengthening behavior of all four tested ligaments. The anterior talofibular ligament was sensitive to transverse plane displacements, whereas the tibiocalcaneal ligament was sensitive to coronal plane displacements. For the Agility prosthesis, these two ligaments seem to be sensitive guides for tibial component positioning at implantation.

Total ankle replacement revisited.

The surgical treatment of painful, end-stage ankle arthritis includes ankle arthrodesis and total ankle replacement. In the past decade, total ankle replacement has become a viable alternative to ankle arthrodesis. Modern implant designs either involve a syndesmosis fusion and resurfacing of the medial and lateral recesses of the ankle joint or the use of a 3-component, mobile bearing implant. In limited clinical series, the early results of both these prosthetic design approaches are encouraging. In selected patients, ankle arthroplasty is an effective approach to relieving pain and improving function. The purposes of this paper are to review the clinical results from total ankle replacement and ankle arthrodesis; discuss indications, contraindications, design features, postoperative rehabilitation, and initial results for the major current total ankle designs; and present concepts for future total ankle development. In particular, this article explores the advantages and concerns with 2 prevalent but different design approaches. It also discusses future directions for total ankle replacement.