Scintigraphy and Positron Emission Tomography (PET) are both nuclear medicine imaging techniques, providing functional information of the imaged areas. Scintigraphy is a two-dimensional projected imaging technique that was introduced in equine imaging in the late 1970s. Scintigraphy allows imaging of large body parts and can cover multiple areas, remaining the only technique commonly used in horses for whole body imaging. PET is a cross-sectional imaging technique, first used in horses in 2015, allowing higher resolution three-dimensional functional imaging of the equine distal limb. This manuscript will cover current use and values of these two modalities in equine lameness diagnosis.

Positron Emission Tomography (PET) is an imaging technique that provides functional information, in addition to structural information obtained with computed tomography (CT). The most common application is cancer staging, using 18F-Fluorodeoxyglucose (18F-FDG), a radioactive analog of glucose. Although limited data are available in the veterinary literature, human studies have demonstrated benefit with the addition of PET both for assessment of the primary tumor and for detection of metastatic disease. 18F-FDG PET appears to be more accurate at detecting the margin of oral neoplasia, in particular for tumors arising from highly vascularized tissue, such as the lingual and laryngeal areas. 18F-FDG PET has a high sensitivity for the detection of lymph node metastasis, however the specificity is variable between studies. Tracers beyond 18F-FDG can also be used for oncology imaging. 18F-Fluoride (18F-NaF) is an excellent osseous tracer, useful in assessing bone involvement of primary tumors or osseous metastasis. Other specific tracers can be used to assess cell proliferation or hypoxia for tumor characterization. 18F-FDG is also an excellent tracer for detection of inflammation. Human studies have demonstrated its value for the assessment of periodontitis and dental implant infection. 18F-NaF has been used to assess disorders of the temporomandibular joint in the human literature, demonstrating good correlation with arthralgia and therapeutic outcome. Both 18F-NaF and 18F-FDG had good concordance with localization of cervical pain in people. PET will likely have a growing role in veterinary medicine not only for oncologic imaging but also for assessment of inflammation and pain.

A 20-year-old Quarter horse gelding was referred for evaluation of an acute onset non-weight-bearing right forelimb lameness. Marked soft tissue swelling was apparent over the right scapula and shoulder region; no crepitus was palpable. A complete transverse fracture of the scapular neck was suspected based on ultrasonography and radiographs were obtained to confirm the presumptive diagnosis. A complete, oblique fracture of the right scapular neck with mild cranial and proximal displacement of the distal fragment was detected. Computed tomography of the upper right forelimb was performed post-mortem; lytic bony destruction of the scapular neck with a secondary pathologic fracture was observed. The lesion was considered most likely neoplastic. At necropsy a complete, comminuted fracture of the right scapula was confirmed, secondary to neoplastic invasion of the bone. A solitary, dorsally located, neoplastic mass was also observed within the parenchyma of the right caudal lung. Histopathologically, the lung and scapula lesions were similar, characteristic of a well-differentiated pulmonary carcinoma.

Previously published myelographic studies do not report findings at the junction between the seventh cervical (C7) and first thoracic vertebrae (T1). Modern digital radiographic equipment allows improved visualization of C7-T1. Based on clinical experience, we hypothesized that 50% reduction of the dorsal myelographic column or 20% reduction of the dural diameter, criteria commonly used as a supportive finding for spinal cord compression in the cervical vertebral column, do not apply at C7-T1. A myelographic study was performed on 12 healthy, neurologically normal horses. Our hypothesis was confirmed; using established criteria eight of 12 horses would have been classified as having evidence of spinal cord compression at C7-T1. The dorsal myelographic column reduction at C7-T1 was 48 ± 12%, while the C6-C7 dorsal myelographic column reduction was 33 ± 17% (mean ± standard deviation) (P = 0.010). The dural diameter reduction at C7-T1 (22.0 ± 6.7%) was significantly greater than the dural diameter reduction at C6-C7 (13.2 ± 9.5%) (P = 0.0007). Further measurements and comparisons suggested that the apparent greater reduction of dorsal myelographic column and dural diameter at C7-T1 was due to larger intravertebral measurements at C7 rather than smaller intervertebral values at C7-T1. Based on these findings, alternative criteria should be used at C7-T1 when assessing clinical cases for cervical stenotic myelopathy. Reduction of the dorsal myelographic column by 60% or of the dural diameter by 30% would avoid high numbers of false positive myelographic cases at C7-T1.

A 16-year-old, Quarter Horse mare was presented for a 3/5 right hind lameness associated with osteoarthritis of the talocalcaneal joint (TCLJ). Positron emission tomography (PET) and computed tomography (CT) demonstrated marked increased uptake of 18F-sodium fluoride and bone remodeling at the medial facet of the TCLJ, respectively. Under general anesthesia 2 cortical screws (4.5 and 5.5 mm) were placed in neutral fashion via an arthrotomy from dorsomedial to plantaromedial through the medial facet of the TCLJ followed by copious lavage of the tarsocrural joint. Eight weeks after surgery, observable effusion of the tarsocrural joint was present and lameness had worsened. Radiographic examination revealed a fragmented medial malleolus of the tibia, likely secondary to repetitive trauma of the screw heads during tarsal flexion. Repeated CT showed partial fusion of the TCLJ. Both screws were removed and the tarsocrural joint was thoroughly lavaged arthroscopically. At a 20-month recheck the lameness had not improved, and ultrasound examination revealed severe thickening of the TCLJ capsule. Recheck examination 48 mo after surgery showed complete fusion of the TCLJ and resolution of the lameness. Key clinical message: Diagnosis of osteoarthritis of the TCLJ is challenging. Management by arthrodesis using a dorsomedial approach can result in fragmentation of the medial malleolus, with secondary synovitis and capsulitis of the tarsocrural joint.

Desmitis of the oblique distal sesamoidean ligaments (ODSL) is caused by hyperextension of the metacarpophalangeal/metatarsophalangeal joint and has been described as a significant cause of lameness in racehorses. In this study, three Thoroughbred racehorses (age range: 3-6 years) were diagnosed with desmitis of the forelimb ODSL using standing low-field magnetic resonance imaging (sMRI). Radiography and ultrasonography were inconclusive with regard to a definitive diagnosis. For all horses, the sMRI characteristics included increased signal intensity within the medial ODSL on T1-weighted gradient echo, T2-weighted fast spin echo and short tau inversion recovery fast spin echo images, which use a fat suppression technique. Effusion of the digital flexor tendon sheath was also clearly visible on sMRI. Following rest and controlled exercise for roughly 3 months, two horses successfully returned to racing within 5 months. Our findings support the use of sMRI for diagnosing ODSL injuries in Thoroughbred racehorses.

Objective

To evaluate the diagnostic value of still images of needle arthroscopy (SNAR), still images of traditional arthroscopy (STAR), and computed tomography (CT) to diagnose medial coronoid process (MCP) pathology.

Study design

Prospective clinical trial.

Animals

Dogs (n = 17) presented for evaluation of elbow dysplasia.

Methods

For each case, two SNAR and STAR images of the MCP were reviewed independently and in random order by three board-certified surgeons. Computed tomographic images were reviewed by one board-certified radiologist. Reviewers were blinded to surgical and clinical findings. Surgical findings from real-time TAR with palpation were used as the gold standard. Receiver operating characteristic (ROC) curves and concordance statistics tests for the diagnostic accuracy of MCP fissure, MCP fragment, medial compartment condition, and cartilage score were calculated.

Results

Images of 27 elbows joints were reviewed. For MCP fissure detection, areas under the ROC curves for CT (0.84), STAR (0.73), and SNAR (0.57) did not differ. For the detection of MCP fragment, STAR had a larger area under the ROC curve (0.93) compared with SNAR (0.74, P = .015) and CT (0.54, P < .001). Still images of TAR and SNAR had comparable concordance for cartilage score (0.80 and 0.77, respectively) and medial compartment pathology (0.80 and 0.73, respectively).

Conclusion

Still images of NAR, STAR, and CT had similar diagnostic value to identify MCP fissures. Still images of TAR was superior to SNAR and CT to identify MCP fragments.

Clinical significance

The diagnostic accuracy of SNAR varied on the basis of the coronoid lesion being evaluated.

Objective

 The aim of this study was to assess bone density, bone architecture and clinical function of canine nonunion distal appendicular long bone fractures with a defect treated with fixation, compression-resistant matrix and recombinant human bone morphogenetic protein-2 (rhBMP-2).

Study design

 Prospective cohort study with dogs at least 1-year post treatment. Computed tomography was performed and quantitative measurements from previous fracture sites were compared with measurements from contralateral limbs. Subjective evaluation included gait assessment and palpation.

Results

 Six patients met the inclusion criteria. The rhBMP-2 treated bone exhibited higher density at the periphery and lower density in the centre, similar to the contralateral limb. All patients were weight bearing on the treated limb and all fractures were healed.

Conclusion

 The rhBMP-2-treated bone underwent restoration of normal architecture and density. Acceptable limb function was present in all patients. The results of this study can serve as a basis for long-term response in treating nonunion fractures in veterinary patients.

Background

It is currently unknown if the intrathecal administration of a high dose of allogeneic mesenchymal stem cells (MSCs) is safe, how MSCs migrate throughout the vertebral canal after intrathecal administration, and whether MSCs are able to home to a site of injury. The aims of the study were: 1) to evaluate the safety of intrathecal injection of 100 million allogeneic adipose-derived MSCs (ASCs); 2) to assess the distribution of ASCs after atlanto-occipital (AO) and lumbosacral (LS) injection in healthy horses; and 3) to determine if ASCs homed to the site of injury in neurologically diseased horses.

Methods

Six healthy horses received 100 × 10⁶ allogeneic ASCs via AO (n = 3) or LS injection (n = 3). For two of these horses, ASCs were radiolabeled with technetium and injected AO (n = 1) or LS (n = 1). Neurological examinations were performed daily, and blood and cerebrospinal fluid (CSF) were evaluated prior to and at 30 days after injection. Scintigraphic images were obtained immediately postinjection and at 30 mins, 1 h, 5 h, and 24 h after injection. Three horses with cervical vertebral compressive myelopathy (CVCM) received 100 × 10⁶ allogeneic ASCs labeled with green fluorescent protein (GFP) via AO injection and were euthanized 1-2 weeks after injection for a full nervous system necropsy. CSF parameters were compared using a paired student's t test.

Results

There were no significant alterations in blood, CSF, or neurological examinations at any point after either AO or LS ASC injections into healthy horses. The radioactive signal could be identified all the way to the lumbar area after AO ASC injection. After LS injection, the signal extended caudally but only a minimal radioactive signal extended further cranially. GFP-labeled ASCs were not present at the site of disease at either 1 or 2 weeks following intrathecal administration.

Conclusions

The intrathecal injection of allogeneic ASCs was safe and easy to perform in horses. The AO administration of ASCs resulted in better distribution within the entire subarachnoid space in healthy horses. ASCs could not be found after 7 or 15 days of injection at the site of injury in horses with CVCM.