Effect of perineural anesthesia on the ultrasonographic appearance of equine palmar metacarpal structures

Non-weight bearing ultrasonographic examination allows the diagnosis of longitudinal fiber disruption (split) in equine suspensory ligament branches not visible on weight bearing examination

When evaluating suspensory ligament branch splits, there is a discrepancy between high field MRI findings and weight bearing ultrasonographic imaging characteristics. In this descriptive and retrospective case series, ultrasonographic examination was performed on suspensory ligament branches with the limbs in weight bearing and non-weight bearing positions. Suspensory ligament branch splits were defined as linear regions of decreased echogenicity when imaged with the limb in a weight bearing position that increased in size and became anechoic with the limb in a non-weight bearing position. This appearance was considered an indication of pathologic change in the branch. A total of 62 suspensory ligament branches were included in the study from 37 horses, with 14 partial splits, 11 intrasubstance splits, and 14 complete splits of which two had extension of fetlock synovial fluid and synovial membrane through the split. Recheck ultrasonographic examinations performed in eight horses up to 14 months following the initial examination demonstrated persistence of the split in two horses, partial resolution in five horses, and complete resolution in one horse. Ultrasonographic examination using the non-weight bearing approach proved valuable for increasing the lesion conspicuity as compared to the weight bearing images. Certain abnormalities, such as longitudinal fiber disruption (split) in suspensory ligament branches may only be evident when imaged non-weight bearing. The use of this technique provides a more accurate representation of lesion severity and allows for monitoring over time. A longitudinal study is necessary to determine the clinical relevance of suspensory ligament branch splits.

The effects of perineural and intrasynovial anaesthesia of the equine foot on subsequent magnetic resonance images

REASONS FOR PERFORMING STUDY

Artefacts caused by regional anaesthesia can influence image interpretation of ultrasonography and nuclear scintigraphy. Perineural and intrasynovial anaesthesia are commonly performed prior to magnetic resonance imaging (MRI); and the effects on MR images, if any, are unknown.

OBJECTIVES

To determine if perineural and intrasynovial anaesthesia of structures in the equine foot cause iatrogenic changes detectable with MRI.

METHODS

A baseline MRI examination of both front feet was performed on 15 horses, 2-6 days prior to mepivacaine injection adjacent to the lateral and medial palmar digital nerves, and into the podotrochlear bursa, digital flexor tendon sheath and distal interphalangeal joint of one randomly assigned forelimb. Magnetic resonance imaging was repeated at 24 and 72 h post injection; then qualitative and quantitative assessments of MRI findings were performed.

RESULTS

Magnetic resonance imaging findings associated with the palmar digital nerves, podotrochlear bursa and distal interphalangeal joint at 24 and 72 h after mepivacaine injection did not alter significantly from those at baseline. Compared with baseline, a significant increase in synovial fluid volume of the digital flexor tendon sheath was detected with MRI at 24 and 72 h post injection.

CONCLUSIONS

Perineural anaesthesia of the palmar digital nerves and intrasynovial anaesthesia of the podotrochlear or distal interphalangeal joint did not interfere with the interpretation of MR images acquired at 24 or 72 h after injection. However, intrasynovial anaesthesia of the digital flexor tendon sheath caused an iatrogenic increase in synovial fluid, detectable on MR images for at least 72 h.

POTENTIAL RELEVANCE

Although a definite time frame for resolution of digital flexor tendon sheath distension was not determined, we recommend waiting more than 3 days between intrasynovial anaesthesia of the digital flexor tendon sheath and evaluation with MRI.