Quantitative magnetic resonance imaging and histological hoof wall assessment of 3-year-old Quarter Horses.

BACKGROUND: Few noninvasive methods are available for equine hoof wall evaluation. The highly organised wall structures and composition of proteoglycans and collagens may make this region amenable to quantitative MRI (qMRI) techniques of T1ρ and T2 mapping to identify pathology related to proteoglycan content and collagen organisation respectively. OBJECTIVE: To establish normative T1ρ and T2 values of the equine hoof wall of 3-year-old Quarter Horses with histological comparison. STUDY DESIGN: Cadaveric anatomical study. METHODS: Six cadaveric left thoracic feet from 3-year-old racing Quarter Horses with no reported lameness were evaluated using T1ρ and T2 mapping. Mapping was performed at six regions of interest at the toe of each hoof including proximal and distal regions of the inner epidermis, stratum lamellatum and corium. Histology was evaluated for standard hoof morphology and proteoglycan staining. RESULTS: T2 values of the stratum lamellatum and corium were similar (42.9 [95% CI: 41.6-44.2] ms and 44 [95% CI: 42.7-45.3] ms respectively), but both were significantly different to the inner epidermis (35.8 [95% CI: 34.5-37.1] ms, P<0.001). T1ρ values for the inner epidermis, stratum lamellatum and corium were significantly different (25.1 [95% CI: 23.1-27.1] ms, 44.4 [95% CI: 42.4-46.4] ms and 50.1 [95% CI: 48.1-52.1] ms, respectively, P<0.001). Histology demonstrated normal organised morphology. Proteoglycan staining was only visible in the stratum lamellatum and corium. MAIN LIMITATIONS: Cadaveric study with frozen samples used. CONCLUSIONS: Variation of qMRI metrics through the depth of the equine hoof wall was found. Although the highly ordered environment of collagen may contribute to T2 values, there was lack of evidence to support proteoglycan content as a major contributor of T1ρ values. It is possible T1ρ values had a greater dependence on total water content as the lowest values were seen in the epidermis. Additional research using qMRI is needed to determine mapping values in different disease states.

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.

Correlation of meniscal T2* with multiphoton microscopy, and change of articular cartilage T2 in an ovine model of meniscal repair.

OBJECTIVE: To correlate meniscal T2* relaxation times using ultra-short echo time (UTE) magnetic resonance imaging (MRI) with quantitative microscopic methods, and to determine the effect of meniscal repair on post-operative cartilage T2 values. DESIGN: A medial meniscal tear was created and repaired in the anterior horn of one limb of 28 crossbred mature ewes. MR scans for morphological evaluation, meniscal T2* values, and cartilage T2 values were acquired at 0, 4 and 8 months post-operatively for the Tear and Non-Op limb. Samples of menisci from both limbs were analyzed using multiphoton microscopy (MPM) analysis and biomechanical testing. RESULTS: Significantly prolonged meniscal T2* values were found in repaired limbs than in control limbs, P < 0.0001. No regional differences of T2* were detected for either the repaired or control limbs in the anterior horn. Repaired limbs had prolonged cartilage T2 values, primarily anteriorly, and tended to have lower biomechanical force to failure at 8 months than Non-Op limbs. MPM autofluorescence and second harmonic generation data correlated with T2* values at 8 months (ρ = -0.48, P = 0.06). CONCLUSIONS: T2* mapping is sensitive to detecting temporal and zonal differences of meniscal structure and composition. Meniscal MPM and cartilage T2 values indicate changes in tissue integrity in the presence of meniscal repair.

Computed tomography of temporal bone fractures and temporal region anatomy in horses.

BACKGROUND: In people, specific classifications of temporal bone fractures are associated with clinical signs and prognosis. In horses, similar classifications have not been evaluated and might be useful establishing prognosis or understanding pathogenesis of certain types of trauma. HYPOTHESIS/OBJECTIVES: We hypothesized associations between temporal bone fracture location and orientation in horses detected during computed tomography (CT) and frequency of facial nerve (CN7) deficit, vestibulocochlear nerve (CN8) deficit, or temporohyoid osteoarthropathy (THO). Complex temporal region anatomy may confound fracture identification, and consequently a description of normal anatomy was included. ANIMALS: All horses undergoing temporal region CT at our hospital between July 1998 and May 2008. METHODS: Data were collected retrospectively, examiners were blinded, and relationships were investigated among temporal bone fractures, ipsilateral THO, ipsilateral CN7, or ipsilateral CN8 deficits by Chi-square or Fischer's exact tests. Seventy-nine horses had CT examinations of the temporal region (158 temporal bones). RESULTS: Sixteen temporal bone fractures were detected in 14 horses. Cranial nerve deficits were seen with fractures in all parts of the temporal bone (petrosal, squamous, and temporal) and, temporal bone fractures were associated with CN7 and CN8 deficits and THO. No investigated fracture classification scheme, however, was associated with specific cranial nerve deficits. CONCLUSIONS AND CLINICAL IMPORTANCE: Without knowledge of the regional anatomy, normal structures may be mistaken for a temporal bone fracture or vice versa. Although no fracture classification scheme was associated with the assessed clinical signs, simple descriptive terminology (location and orientation) is recommended for reporting and facilitating future comparisons.