Plantar plate pathology is associated with erosive disease in the painful forefoot of patients with rheumatoid arthritis.

BACKGROUND: Disease-related foot pathology is recognised to have a significant impact on mobility and functional capacity in the majority of patients with rheumatoid arthritis (RA). The forefoot is widely affected and the metatarsophalangeal (MTP) joints are the most common site of symptoms. The plantar plates are the fibrocartilaginous distal attachments of the plantar fascia inserting into the five proximal phalanges. Together with the transverse metatarsal ligament they prevent splaying of the forefoot and subluxation of the MTP joints. Damage to the plantar plates is a plausible mechanism therefore, through which the forefoot presentation, commonly described as 'walking on pebbles', may develop in patients with RA. The aims of this study were to investigate the relationship between plantar plate pathology and clinical, biomechanical and plain radiography findings in the painful forefoot of patients with RA. Secondly, to compare plantar plate pathology at the symptomatic lesser (2nd-5th) MTP joints in patients with RA, with a group of healthy age and gender matched control subjects without foot pain. METHODS: In 41 patients with RA and ten control subjects the forefoot was imaged using 3T MRI. Intermediate weighted fat-suppressed sagittal and short axis sequences were acquired through the lesser MTP joints. Images were read prospectively by two radiologists and consensus reached. Plantar plate pathology in patients with RA was compared with control subjects. Multivariable multilevel modelling was used to assess the association between plantar plate pathology and the clinical, biomechanical and plain radiography findings. RESULTS: There were significant differences between control subjects and patients with RA in the presence of plantar plate pathology at the lesser MTP joints. No substantive or statistically significant associations were found between plantar plate pathology and clinical and biomechanical findings. The presence of plantar plate pathology was independently associated with an increase in the odds of erosion (OR = 52.50 [8.38-326.97], p < 0.001). CONCLUSION: The distribution of plantar plate pathology at the lesser MTP joints in healthy control subjects differs to that seen in patients with RA who have the consequence of inflammatory disease in the forefoot. Longitudinal follow-up is required to determine the mechanism and presentation of plantar plate pathology in the painful forefoot of patients with RA.

MRI appearances of the femur following bone graft harvesting using the Reamer-Irrigator-Aspirator.

The reamer-irrigator-aspirator is increasingly being used to harvest autologous bone graft from the femur. The purpose of this study was to investigate the extent of neo-vascularisation and new bone formation that occurs within the medulla following the procedure, and determine if new bone formation would potentially allow a repeat bone harvest in those individuals subsequently requiring further bone graft. Eleven patients who had undergone femoral bone harvest were examined with MRI. The nature of the tissue within the medulla and the extent of neo-vascularisation were assessed. MRI was performed between 3 months and 28 months following bone graft harvest, mean 14 months. Intense vascularisation of the endostial cortical surface and neo-vascularisation of the haematoma within the canal occurred as soon as 3 months following bone harvest. From as early as 14 months the tissue was replaced by normal intramedullary bone. The formation of new bone within the medullary canal gives the potential for a repeat reaming, should further bone graft be required at a later date.

Anatomical location of erosions at the metatarsophalangeal joints in patients with rheumatoid arthritis.

OBJECTIVE: The aim of this study was to identify the anatomical location of erosions at the MTP joints in patients with RA using high-resolution 3T MRI. METHODS: In 24 patients with RA, the more symptomatic forefoot was imaged using 3T MRI. T1-weighted, intermediate-weighted and T2-weighted fat-suppressed sequences were acquired through the MTP joints, together with three-dimensional volumetric interpolated breath-hold examination (3D VIBE) and T1-weighted fat-suppressed post-gadolinium contrast sequences. Images were scored for bone erosion in the distal and proximal part of the MTP joints using the RA MRI scoring (RAMRIS) system. The base of the proximal phalanx and the head of the metatarsal were divided into quadrants to determine the location of erosions (octants) in the dorsal-medial, dorsal-lateral, plantar-medial and plantar-lateral regions. RESULTS: Seventeen females and seven males with a mean age of 55.5 years and disease duration of 10.6 years (range 0.6-36) were included. Eighteen patients were RF positive, the mean 44-joint DAS for CRP and ESR (DAS44CRP and DAS44ESR) were 2.5 (s.d. 0.8) and 2.6 (s.d. 0.9), respectively. In this cohort of patients with RA, irrespective of MTP joint location, octants located in the proximal part (metatarsal) of the joint and the plantar aspect of the joint were more eroded. CONCLUSION: This is the first study to report the anatomical location of erosions at the MTP joints in patients with RA. We noted that erosions were more commonly seen on the plantar aspect of the metatarsal head in RA, supporting the hypothesis of a relationship between biomechanical demands and bone changes in the forefoot.

Optimizing MRI for imaging peripheral arthritis.

MRI is increasingly used for the assessment of both inflammatory arthritis and osteoarthritis. The wide variety of MRI systems in use ranges from low-field, low-cost extremity units to whole-body high-field 7-T systems, each with different strengths for specific applications. The availability of dedicated radiofrequency phased-array coils allows the rapid acquisition of high-resolution images of one or more peripheral joints. MRI is uniquely flexible in its ability to manipulate image contrast, and individual MR sequences may be combined into protocols to sensitively visualize multiple features of arthritis including synovitis, bone marrow lesions, erosions, cartilage changes, and tendinopathy. Careful choice of the imaging parameters allows images to be generated with optimal quality while minimizing unwanted artifacts. Finally, there are many novel MRI techniques that can quantify disease levels in arthritis in tissues including synovitis and cartilage.

Magnetic resonance arthrography of lesser metatarsophalangeal joints in patients with rheumatoid arthritis: relationship to clinical, biomechanical, and radiographic variables.

OBJECTIVE: Our exploratory study of painful lesser metatarsophalangeal (MTP) joints in patients with rheumatoid arthritis (RA) primarily aimed to compare the clinical, biomechanical, and plain radiography findings with magnetic resonance (MR) arthrography findings. Our secondary aim was to compare standard unenhanced MR with MR arthrography in imaging the lesser MTP joints in RA. METHODS: In 15 patients with RA, the more symptomatic forefoot was imaged using 3T MR imaging. Proton density fat-suppressed images were acquired through the lesser MTP joints prior to arthrography. Under ultrasound guidance, contrast agent was injected into 2 lesser MTP joints. T1-weighted fat-suppressed sequences were subsequently acquired. The MR images were read by 2 musculoskeletal radiologists and consensus was reached. Spearman's correlation coefficient was used to assess the association between abnormalities seen on MR arthrography and the clinical, biomechanical, and plain radiography findings. RESULTS: MR arthrography demonstrated pathology at 18 of 28 lesser MTP joints (64%) examined in patients with RA. MR arthrography abnormalities were associated with RA disease duration, forefoot deformity, Larsen score, subluxation, and peak plantar pressure. Unenhanced MR had a sensitivity of 78% and specificity of 90% for detecting pathology compared to MR arthrography. CONCLUSION: Capsule and plantar plate pathology occurs in the painful forefoot of patients with RA and is associated with features of disease and deformity at the lesser MTP joints. Compared with MR arthrography, standard MR imaging was highly specific and moderately sensitive for diagnosing lesser MTP joint pathology in patients with RA.

MRI identifies plantar plate pathology in the forefoot of patients with rheumatoid arthritis.

Previous cadaveric studies have suggested that forefoot deformities at the metatarsophalangeal (MTP) joints in patients with rheumatoid arthritis (RA) might result from the failure of the ligamentous system and displacement of the plantar plates. This study aimed to examine the relationship between plantar plate pathology and the rheumatoid arthritis magnetic resonance imaging score (RAMRIS) of the lesser (second to fifth) MTP joints in patients with RA using high-resolution 3 T magnetic resonance imaging (MRI). In 24 patients with RA, the forefoot was imaged using 3 T MRI. Proton density fat-suppressed, T2-weighted fat-suppressed and T1-weighted post gadolinium sequences were acquired through 96 lesser MTP joints. Images were scored for synovitis, bone marrow oedema and bone erosion using the RAMRIS system and the plantar plates were assessed for pathology. Seventeen females and 7 males with a mean age of 55.5 years (range 37-71) and disease duration of 10.6 years (range 0.6-36) took part in the study. Plantar plate pathology was most frequently demonstrated on MRI at the fifth MTP joint. An association was demonstrated between plantar plate pathology and RAMRIS-reported synovitis, bone marrow oedema and bone erosion at the fourth and fifth MTP joints. In patients with RA, 3 T MRI demonstrates that plantar plate pathology at the lesser MTP joints is associated with features of disease severity. Plantar plate pathology is more common at the fourth and fifth MTP joints in subjects with RA in contrast to the predilection for the second MTP reported previously in subjects without RA.

Quantitative magnetization transfer ultrashort echo time imaging of the Achilles tendon.

Ultrashort echo time imaging allows the short T(2) Achilles tendon to be directly visualized with MRI. Radiofrequency saturation 1 kHz or less off-resonance has been used previously to improve image contrast. In this study, magnetization transfer was investigated in the Achilles tendon of eight normal volunteers and one patient with psoriatic arthritis. 2D Ultrashort echo time images were acquired using saturation pulses 2-100 kHz off-resonance at 4 pulse powers. On-resonance saturation recovery images were also obtained to estimate T(1). The results were fitted to a two compartment quantitative magnetization transfer model. The estimated bound proton fraction for the eight healthy volunteers was 21.0 ± 1.2% (mean ± standard deviation) compared to 16.4% in the patient with psoriatic arthritis (P < 0.05). The T(2) of the bound protons was measured as 6.1 ± 0.3 µsec in the healthy volunteers and 6.0 µsec in the patient. This technique appears clinically feasible and may be useful for assessing the collagen and water changes which occur in Achilles tendinopathy.

MRI for the assessment and monitoring of RA--what can it tell us?

The past 15 years has seen an exponential rise in the use of MRI for the assessment of rheumatoid arthritis (RA). In this Perspectives article, we review the current and potential future role of MRI in the diagnosis, prognosis and monitoring of RA. We also review the impact of MRI research on the understanding of disease mechanisms. In our view, the pivotal role of synovitis in RA and its predilection for sonographically accessible joints makes it likely that MRI will be used diagnostically in joints that are inaccessible to ultrasonography or where the differential diagnosis is unclear. Additionally, MRI will probably assume an even more prominent role in clinical trials where the aim of therapy is the complete ablation of synovitis. Given the ever-increasing sophistication of MRI, we anticipate that it will continue to be a key research tool in the coming years.

Changes underlying the dynamic contrast-enhanced MRI response to treatment in rheumatoid arthritis.

OBJECTIVE: Dynamic contrast-enhanced MRI of patients with rheumatoid arthritis has shown a decrease in the early enhancement rate (EER) of synovitis after treatment. The purpose of this work was to investigate the underlying changes. METHODS: 3D dynamic contrast-enhanced images were acquired from 13 patients before and 1-2 weeks after anti-TNF alpha treatment. The EER of the inflamed synovium was measured. The T1 relaxation time of the synovitis was calculated from images at different flip angles. The time course of the arrival of gadolinium at the radial artery was determined. The gadolinium enhancement of the inflamed synovium was modeled to calculate the fractional plasma volume (vp), the fractional extravascular, extracellular fluid volume (ve), and the volume transfer constant (Ktrans). Pre- and post-treatment values were compared and the dependence of the EER on each parameter was assessed. RESULTS: There was a decrease in the EER measured over 26 s after treatment (29%, p = 0.002). Reductions in T1 (12%, p = 0.001), Ktrans (31%, p = 0.002), and vp (43%, p = 0.01) contributed to this; however, the EER was relatively insensitive to changes in ve. CONCLUSIONS: The decrease in EER after anti-TNF alpha treatment is largely caused by reductions in the volume transfer constant Ktrans, the fractional plasma volume vp, and the T1 relaxation time. Only the contributions from Ktrans and vp directly reflect synovial vascularity.

Pharmacokinetic modeling of dynamic contrast-enhanced MRI of the hand and wrist in rheumatoid arthritis and the response to anti-tumor necrosis factor-alpha therapy.

Dynamic contrast-enhanced MRI (DCE-MRI) of the hand and wrist was performed in 11 patients with rheumatoid arthritis twice before and once 2 weeks after treatment with anti-tumor necrosis factor (TNF)-alpha therapy. A rapid, T1-weighted 3D spoiled gradient echo (SPGR) sequence was used for the dynamic imaging. T1 estimation was performed using similar images obtained at different flip angles. The relative radiofrequency field was estimated from the known T1 of the periarticular fatty marrow. The arterial input function (AIF) was measured at each examination, and normalized to the expected plasma concentration to reduce partial volume effects. Synovial enhancement was modeled to yield values for Ktrans, ve, and vp. Ktrans and ve showed good reproducibility. There was a significant decrease of about 20% in Ktrans after 2 weeks of treatment. This study demonstrates the potential of DCE-MRI and pharmacokinetic modeling to study early changes in inflammatory activity in rheumatoid arthritis following treatment.

Immobilized enzyme reactor chromatography: optimization of protein retention and enzyme activity in monolithic silica stationary phases.

Our group recently reported on the application of protein-doped monolithic silica columns for immobilized enzyme reactor chromatography, which allowed screening of enzyme inhibitors present in mixtures using mass spectrometry for detection. The enzyme was immobilized by entrapment within a bimodal meso/macroporous silica material prepared by a biocompatible sol-gel processing route. While such columns proved to be useful for applications such as screening of protein-ligand interactions, significant amounts of entrapped proteins leached from the columns owing to the high proportion of macropores within the materials. Herein, we describe a detailed study of factors affecting the morphology of protein-doped bioaffinity columns and demonstrate that specific pH values and concentrations of poly(ethylene glycol) can be used to prepare essentially mesoporous columns that retain over 80% of initially loaded enzyme in an active and accessible form and yet still retain sufficient porosity to allow pressure-driven flow in the low muL/min range. Using the enzyme gamma-glutamyl transpeptidase (gamma-GT), we further evaluated the catalytic constants of the enzyme entrapped in capillary columns with different silica morphologies as a function of flowrate and backpressure using the enzyme reactor assay mode. It was found that the apparent activity of the enzyme was highest in mesoporous columns that retained high levels of enzyme. In such columns, enzyme activity increased by approximately 2-fold with increases in both flowrate (from 250 to 1000 nL/min) and backpressure generated (from 500 to 2100 psi) during the chromatographic activity assay owing to increases in k(cat) and decreases in K(M), switching from diffusion controlled to reaction controlled conditions at ca. 2000 psi. These results suggest that columns with minimal macropore volumes (<5%) are advantageous for the entrapment of soluble proteins for bioaffinity and bioreactor chromatography.

Inhibitor screening using immobilized enzyme reactor chromatography/mass spectrometry.

We describe the coupling of capillary-scale monolithic enzyme reactor columns directly to a tandem mass spectrometer for screening of enzyme inhibitors. A two-channel nanoLC system is used to continuously infuse substrate or substrate/inhibitor mixtures through the column, allowing continuous variation of inhibitor concentration by simply altering the ratio of flow from the two pumps. In the absence of inhibitor, infusion of substrate leads to formation of product, and both substrate and product ions can be simultaneously monitored in a quantitative manner by MS/MS. The presence of inhibitor leads to a decrease in product and an increase in substrate concentration in the column eluent. Knowing the product/substrate ratio and the total analyte concentration (P + S), the concentration of product eluting, and hence the relative enzyme activity, can be determined. Both IC50 and KI values can then be obtained by direct MS detection of the effect of inhibitors on relative activity. Inhibitor screening is demonstrated using reusable, sol-gel derived, monolithic capillary columns containing adenosine deaminase, directly interfaced to ESI-MS/MS. On-column enzyme activity was assessed by monitoring inosine and adenosine elution. It is shown that the method can be used for automated screening of the effects of compound mixtures on ADA activity and to determine the KI value of the known inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine, even when the compound is present within a mixture.

Capillary-scale monolithic immunoaffinity columns for immunoextraction with in-line laser-induced fluorescence detection.

A bimodal meso/macroporous monolithic silica capillary column containing an entrapped antibody was prepared by a biocompatible sol-gel process and used for nanoflow immunoaffinity chromatography and immunoextraction studies. Stationary phases were prepared by combining the protein-compatible silane precursor diglycerylsilane with an aqueous solution containing 10,000 Da poly(ethylene glycol) and the antibody. An analytical method was developed that was capable of determining both the dissociation constant and binding site content for the anti-fluorescein antibody within the stationary phase. The assay showed that while the antibody residing in macropores was easily removed, approximately 20% of initially loaded antibody remained active and accessible after several washes, consistent with the antibody being entrapped within the mesopores of the sol-gel matrix. The dissociation constants for fluorescein binding to the anti-fluorescein antibody were similar in solution and in the meso/macroporous silica, indicating that the entrapped antibody retained its native conformation within such a matrix. The mixture was loaded into a 250-microm-i.d. fused-silica capillary where the polymer phase separated from the silica followed by gelation of the silica. The capillary-scale immunoaffinity columns could be operated at low back pressure using a syringe pump and were capable of performing chromatographic separations that were dependent on the presence of the antibody within the stationary phase. Such columns could also be operated using in-line laser-induced fluorescence detection. The use of the capillary-scale monolithic columns for on-column immunoextraction and preconcentration is also demonstrated.

Capillary-scale frontal affinity chromatography/MALDI tandem mass spectrometry using protein-doped monolithic silica columns.

Frontal affinity chromatography (FAC) interfaced with electrospray mass spectrometry (ESI-MS) has been reported as a potential method for screening of compound mixtures against immobilized target proteins. However, the interfacing of bioaffinity columns to ESI-MS requires that the eluent that passes through the protein-loaded column have a relatively low ionic strength to produce a stable spray. Such low ionic strength solvents can cause serious problems with protein stability and may also affect binding constants and lead to high nonspecific binding to the column. Herein, we report on the interfacing of bioaffinity columns to matrix-assisted laser desorption/ionization (MALDI) MS/MS as a new platform for FAC/MS studies. Capillary columns containing a monolithic silica material with entrapped dihydrofolate reductase were used for frontal affinity chromatography of small-molecule mixtures. The output from the column was combined with a second stream containing alpha-cyano-hydoxycinnamic acid in methanol and was deposited using a nebulizer-assisted electrospray method onto a conventional MALDI plate that moved relative to the column via a computer-controlled x-y stage, creating a semipermanent record of the FAC run. The use of MALDI MS/MS allowed for buffers with significantly higher ionic strength to be used for FAC studies, which reduced nonspecific binding of ionic compounds and allowed for better retention of protein activity over multiple runs. Following deposition, MALDI analysis required only a fraction of the chromatographic run time, and the deposited track could be rerun multiple times to optimize ionization parameters and allow signal averaging to improve the signal-to-noise ratio. Furthermore, high levels of potential inhibitors could be detected via MALDI with limited ion suppression effects. Both MALDI- and ESI-based analysis showed similar retention of inhibitors present in compound mixtures when using identical ionic strength conditions. The results show that FAC/MALDI-MS should provide advantages over FAC/ESI-MS for high-throughput screening of compound mixtures.

Protein-doped monolithic silica columns for capillary liquid chromatography prepared by the sol-gel method: applications to frontal affinity chromatography.

The development of bioaffinity chromatography columns that are based on the entrapment of biomolecules within the pores of sol-gel-derived monolithic silica is reported. Monolithic nanoflow columns are formed by mixing the protein-compatible silica precursor diglycerylsilane with a buffered aqueous solution containing poly(ethylene oxide) (PEO, MW 10,000) and the protein of interest and then loading this mixture into a fused-silica capillary (150-250-microm i.d.). Spinodal decomposition of the PEO-doped sol into two distinct phases prior to the gelation of the silica results in a bimodal pore distribution that produces large macropores (>0.1 microm), to allow good flow of eluent with minimal back pressure, and mesopores (approximately 3-5-nm diameter) that retain a significant fraction of the entrapped protein. Addition of low levels of (3-aminopropyl)triethoxysilane is shown to minimize nonselective interactions of analytes with the column material, resulting in a column that is able to retain small molecules by virtue of their interaction with the entrapped biomolecules. Such columns are shown to be suitable for pressure-driven liquid chromatography and can be operated at relatively high flow rates (up to 500 microL x min(-1)) or with low back pressures (<100 psi) when used at flow rates of 5-10 microL x min(-1). The clinically relevant enzyme dihydrofolate reductase was entrapped within the bioaffinity columns and was used to screen mixtures of small molecules using frontal affinity chromatography with mass spectrometric detection. Inhibitors present in compound mixtures were retained via bioaffinity interactions, with the retention time being dependent on both the ligand concentration and the affinity of the ligand for the protein. The results suggest that such columns may find use in high-throughput screening of compound mixtures.