Sarah L. Pownder

BioCartilage Improves Cartilage Repair Compared With Microfracture Alone in an Equine Model of Full-Thickness Cartilage Loss:

Background: Microfracture (MFx) remains a dominant treatment strategy for symptomatic articular cartilage defects. Biologic scaffold adjuncts, such as particulated allograft articular cartilage (BioCartilage) combined with platelet-rich plasma (PRP), offer promise in improving clinical outcomes as an adjunct to MFx. Purpose: To evaluate the safety, biocompatibility, and efficacy of BioCartilage and PRP for cartilage repair in a preclinical equine model of full-thickness articular cartilage loss. Study Design: Controlled laboratory study. Methods: Two 10-mm-diameter full-thickness cartilage defects were created in 5 horses in the trochlear ridge of both knees: one proximal (high load) and another distal (low load). Complete blood counts were performed on each peripheral blood and resultant PRP sample. In each horse, one knee received MFx with BioCartilage + PRP, and the other knee received MFx alone. Horses were euthanized at 13 months. Outcomes were assessed with serial arthroscopy, magnetic resonance imaging (MRI), micro–computed tomography (micro-CT), and histology. Statistics were performed using a mixed-effects model with response variable contrasts. Results: No complications occurred. PRP generated in all subjects yielded an increase in platelet fold of 3.8 ± 4.7. Leukocyte concentration decreased in PRP samples by an average fold change of 5 ± 0.1. The overall International Cartilage Repair Society repair score in both the proximal and distal defects was significantly higher (better) in the BioCartilage group compared with MFx (proximal BioCartilage: 7.4 ± 0.51, MFx 4.8 ± 0.1, P = .041; distal BioCartilage: 5.6 ± 0.98, MFx 2.6 ± 1.5, P = .022). BioCartilage-treated proximal defects demonstrated improved histologic scores for repair-host integration (BioCartilage, 96 ± 9; MFx, 68 ± 18; P = .02), base integration (BioCartilage, 100 ± 0; MFx, 70 ± 37; P = .04), and formation of collagen type II (BioCartilage, 82 ± 8; MFx, 58 ± 11; P = .05) compared with the positive control. On MRI, T2 relaxation time was significantly shorter (better) in the superficial region of BioCartilage-treated distal defects compared with MFx (P = .05). There were no significant differences between BioCartilage and MFx on micro-CT analysis. Conclusion: BioCartilage with PRP safely improved cartilage repair compared with MFx alone in an equine model of articular cartilage defects up to 13 months after implantation. Clinical Relevance: The 1-year results of BioCartilage + PRP suggest that homologous allograft tissue provides a safe and effective augmentation of traditional MFx.

Ultrashort echo imaging of cyclically loaded rabbit patellar tendon

Tendinopathy affects individuals who perform repetitive joint motion. Magnetic resonance imaging (MRI) is frequently used to qualitatively assess tendon health, but quantitative evaluation of inherent MRI properties of loaded tendon has been limited. This study evaluated the effect of cyclic loading on T₂* values of fresh and frozen rabbit patellar tendons using ultra short echo (UTE) MRI. Eight fresh and 8 frozen rabbit lower extremities had MR scans acquired for tendon T₂* evaluation. The tendons were then manually cyclically loaded for 100 cycles to 45 N at approximately 1 Hz. The MR scanning was repeated to reassess the T₂* values. Analyses were performed to detect differences of tendon [Formula: see text] values between fresh and frozen samples prior to and after loading, and to detect changes of tendon T₂* values between the unloaded and loaded configurations. No difference of T₂* was found between the fresh and frozen samples prior to or after loading, p=0.8 and p=0.1, respectively. The tendons had significantly shorter T₂* values, p=0.023, and reduced T₂* variability, p=0.04, after cyclic loading. Histologic evaluation confirmed no induced tendon damage from loading. Shorter T₂* , from stronger spin-spin interactions, may be attributed to greater tissue organization from uncrimping of collagen fibrils and lateral contraction of the tendon during loading. Cyclic tensile loading of tissue reduces patellar tendon T₂* values and may provide a quantitative metric to assess tissue organization.

Comparison of Three Methods to Quantify Repair Cartilage Collagen Orientation

Objective: The aim of this study was to determine if the noninvasive or minimally invasive and nondestructive imaging techniques of quantitative T2-mapping or multiphoton microscopy (MPM) respectively, could detect differences in cartilage collagen orientation similar to polarized light microscopy (PLM). It was hypothesized that MRI, MPM, and PLM would all detect quantitative differences between repair and normal cartilage tissue. Methods: Osteochondral defects in the medial femoral condyle were created and repaired in 5 mature goats. Postmortem, MRI with T2-mapping and histology were performed. T2 maps were generated and a mean T2 value was calculated for each region of interest. Histologic slides were assessed using MPM with measurements of autocorrelation ellipticity, and by PLM with application of a validated scoring method. Collagen orientation using each of the 3 modalities (T2-mapping, MPM, and PLM) was measured in the center of the repair tissue and compared to remote, normal cartilage. Results: MRI, MPM, and PLM were able to detect a significant difference between repair and normal cartilage (n = 5). The average T2 value was longer for repair tissue (41.43 ± 9.81 ms) compared with normal cartilage (27.12 ± 14.22 ms; P = 0.04); MPM autocorrelation ellipticity was higher in fibrous tissue (3.75 ± 1.17) compared with normal cartilage (2.24 ± 0.51; P = 0.01); the average PLM score for repair tissue was lower (1.6 ± 1.02) than the score for remote normal cartilage (4.4 ± 0.42; P = 0.002). The strongest correlation among the methods was between MRI and PLM (r = −0.76; P = 0.01), followed by MPM and PLM (r = −0.58; P = 0.08), with the weakest correlation shown between MRI and MPM (r = 0.35; P = 0.31). Conclusion: All 3 imaging methods quantitatively measured differences in collagen orientation between repair and normal cartilage, but at very different levels of resolution. PLM is destructive to tissue and requires euthanasia, but because MPM can be used arthroscopically, both T2-mapping and MPM can be performed in vivo, offering nondestructive means to assess collagen orientation that could be used to obtain longitudinal data in cartilage repair studies.

High-Resolution Methods for Diagnosing Cartilage Damage In Vivo

Advances in current clinical modalities, including magnetic resonance imaging and computed tomography, allow for earlier diagnoses of cartilage damage that could mitigate progression to osteoarthritis. However, current imaging modalities do not detect submicrometer damage. Developments in in vivo or arthroscopic techniques, including optical coherence tomography, ultrasonography, bioelectricity including streaming potential measurement, noninvasive electroarthrography, and multiphoton microscopy can detect damage at an earlier time point, but they are limited by a lack of penetration and the ability to assess an entire joint. This article reviews current advancements in clinical and developing modalities that can aid in the early diagnosis of cartilage injury and facilitate studies of interventional therapeutics.

Magnetic resonance imaging of an equine fracture model containing stainless steel metal implants.

REASONS FOR PERFORMING STUDY Post operative imaging in subjects with orthopaedic implants is challenging across all modalities. Magnetic resonance imaging (MRI) is preferred to assess human post operative musculoskeletal complications, as soft tissue and bones are evaluated without using ionising radiation. However, with conventional MRI pulse sequences, metal creates susceptibility artefact that distorts anatomy. Assessment of the post operative equine patient is arguably more challenging due to the volume of metal present, and MRI is often not performed in horses with implants. Novel pulse sequences such as multiacquisition variable resonance image combination (MAVRIC) now provide improved visibility in the vicinity of surgical-grade implants and offer an option for imaging horses with metal implants. OBJECTIVES To compare conspicuity of regional anatomy in an equine fracture-repair model using MAVRIC, narrow receiver bandwidth (NBW) fast spin echo (FSE), and wide receiver bandwidth (WBW) FSE sequences. STUDY DESIGN Nonrandomised in vitro experiment. METHODS MAVRIC, NBW FSE and WBW FSE were performed on 9 cadaveric distal limbs with fractures and stainless steel implants in the third metacarpal bone and proximal phalanx. Objective measures of artefact reduction were performed by calculating the total artefact area in each transverse image as a percentage of the total anatomic area. The number of transverse images in which fracture lines were visible was tabulated for each sequence. Regional soft tissue conspicuity was assessed subjectively. RESULTS Overall anatomic delineation was improved using MAVRIC compared with NBW FSE; delineation of structures closest to the metal implants was improved using MAVRIC compared with WBW FSE and NBW FSE. Total artefact area was the highest for NBW FSE and lowest for MAVRIC; the total number of transverse slices with a visible fracture line was highest in MAVRIC and lowest in NBW FSE. CONCLUSION MAVRIC and WBW FSE are feasible additions to minimise artefact around implants.

The effect of freeze-thawing on magnetic resonance imaging T 2 * of freshly harvested bovine patellar tendon

BACKGROUND Analysis of fresh specimens in research studies is ideal; however, it is often necessary to freeze samples for evaluation at a later time. Limited evaluation of the effect of freeze-thawing of tendon tissue samples on inherent magnetic resonance imaging (MRI) parameters, such as ultrashort echo time (UTE) T2* values, have been performed to date. METHODS This study performed UTE MRI on 14 bovine patellar tendons at harvest and after four consecutive freeze-thaw cycles. RESULTS Results demonstrated a small but significant reduction (12%) in tendon T2* values after the first freeze thaw cycle, but not after successive cycles. Tendons from juvenile animals with open physis had a significant reduction of T2* following a single freeze thaw cycle, P<0.0001. CONCLUSIONS The results of this study emphasize the importance of using uniform tendon storage protocols when using UTE MRI in preclinical models.

An in vivo model of a mechanically-induced bone marrow lesion

Bone marrow lesions (BMLs) are radiologic abnormalities in magnetic resonance images of subchondral bone that are correlated with osteoarthritis. Little is known about the physiologic processes within a BML, although BMLs are associated with mechanical stress, bone tissue microdamage and increased bone remodeling. Here we establish a rabbit model to study the pathophysiology of BMLs. We hypothesized that in vivo loads that generate microdamage in cancellous bone would also create BMLs and increase bone remodeling. In vivo cyclic loading (0.2-2.0 MPa in compression for 10,000 cycles at 2 Hz) was applied to epiphyseal cancellous bone in the distal femurs of New Zealand white rabbits (n=3, right limb loaded, left limb controls experienced surgery but no loading). Magnetic resonance images were collected using short tau inversion recovery (STIR) and T1 weighted sequences at 1 and 2 weeks after surgery/loading and histological analysis of the BML was performed after euthanasia to examine tissue microdamage and remodeling. Loaded limbs displayed BMLs while control limbs showed only a small BML-like signal caused by surgery. Histological analysis of the BML at 2 weeks after loading showed increased tissue microdamage (p=0.03) and bone resorption (p=0.01) as compared to controls. The model described here displays the hallmarks of load-induced BMLs, supporting the use of the model to examine changes in bone during the development, progression and treatment of BMLs.

Two-Year Evaluation of Osteochondral Repair with a Novel Biphasic Graft Saturated in Bone Marrow in an Equine Model:

Objective To evaluate a biphasic cartilage repair device (CRD) for feasibility of arthroscopic implantation, safety, biocompatibility, and efficacy for long-term repair of large osteochondral defects. Methods The CRD was press-fit into defects (10 mm diameter, 10 mm deep) created in the femoral trochlea of 12 horses. In the contralateral limb, 10 mm diameter full-thickness chondral defects were treated with microfracture (MFX). Radiographs were obtained pre- and postoperatively, and at 4, 12, and 24 months. Repeat arthroscopy was performed at 4 and 12 months. Gross assessment, histology, mechanical testing, and magnetic resonance imaging (MRI) were performed at 24 months. Results The CRD was easily placed arthroscopically. There was no evidence of joint infection, inflammation, or degeneration. CRD-treated defects had significantly more sclerosis compared to MFX early (P = 0.0006), but was not different at 24 months. CRD had better arthroscopic scores at 4 months compared to MFX (P = 0.0069). At 24 months, there was no difference in repair tissue on histology or mechanical testing. Based on MRI, CRD repair tissue had less proteoglycan (deep P = 0.027, superficial P = 0.015) and less organized collagen (deep P = 0.028) compared to MFX. Cartilage surrounding MFX defects had more fissures compared to CRD. Conclusion The repair tissue formed after CRD treatment of a large osteochondral lesion is fibrocartilage similar to that formed in simple chondral defects treated with MFX. The CRD can be easily placed arthroscopically, is safe, and biocompatible for 24 months. The CRD results in improved early arthroscopic repair scores and may limit fissure formation in adjacent cartilage.

Quantitative Magnetic Resonance Imaging and Histological Comparison of Normal Canine Menisci

OBJECTIVE  The purpose of this observational study was to establish normative data for the canine menisci using magnetic resonance imaging (MRI). METHODS  Ten fresh stifles from five normal male Beagles were obtained from animals with no known lameness. Conventional MRI and ultrashort echo time (UTE) imaging were performed and T2* values calculated. Five stifles were assessed histologically. RESULTS  The caudal horn of the medial meniscus had significantly prolonged T2* values (4.6 ± 1.27 ms; p = 0.002) as compared with the cranial horn of the medial meniscus (3.25 ± 0.86 ms), and the cranial (3.06 ± 0.54 ms) and caudal (3.64 ± 0.72 ms) horns of the lateral meniscus. Histology demonstrated normal tibial, femoral, interior and peripheral meniscal margins, and normal cellularity. The medial meniscus was noted to be obliquely oriented to the scan plane compared with the relatively perpendicular orientation of the lateral meniscus as compared with the bore of the magnet in a limb-extended orientation. CLINICAL SIGNIFICANCE  Variability of MRI UTE T2* is seen in the normal canine meniscus, with prolongation of the caudal horn, medial meniscus. Prolongation may be due to magic angle effects, as the medial meniscus of the Beagle is not perpendicular to the axis of the main magnetic field. Canine meniscal injury is a common sequela to cruciate tear, and detecting meniscal damage is important for directing patient care. The non-invasive quantitative MRI technique of UTE imaging can be used for the evaluation of collagen orientation, while acknowledging inherent regions of prolongation.

Nonarticular osseous cyst‐like lesions of the intermedioradial carpal bone may be incidental magnetic resonance imaging findings in dogs

As magnetic resonance imaging (MRI) becomes more readily available and more frequently utilized in the assessment of canine carpal lameness, both normal variations and early pathologic conditions must be recognized to optimize patient care and provide accurate diagnosis. On cross sectional studies of the canine carpus, cyst-like lesions have been detected at the dorsolateral aspect of the intermedioradial carpal bone. The cross-sectional imaging and histologic properties of these lesions have not been described. The purpose of this observational study is to evaluate the MRI and histologic features of these cyst-like lesions in a cohort of clinically sound dogs. It was hypothesized that the lesions would show features similar to intraosseous ganglion cysts of the human wrist. Twenty-five cadaveric canine carpi were obtained and a total of 13 lesions were detected on MRI. Based on MRI, six carpi with lesions of varying size and one normal carpus were submitted for histological evaluation. Five of the abnormal carpi had nonarticular cyst-like lesions; one specimen with a positive magnetic resonance image for a cyst-like lesion had no cyst-like lesion on histology. Conspicuity of a medium-size lesion as evaluated on radiographs was poor. Given the presence of these nonarticular cyst-like lesions in a population of clinically sound patients, their clinical importance is uncertain. The development of these lesions may relate to altered mechanics or genetic predispositions, requiring additional study.