Diffusion of radiodense contrast medium after perineural injection of the palmar digital nerves

Computed tomographic evaluation of the proximity of needles placed for perineural anesthesia of the palmar digital nerves to synovial structures in the foot: an ex vivo study

Background

Potential synovial penetration following palmar digital nerve blocks has not been investigated.

Objectives

To evaluate the proximity of needles placed for palmar digital nerve blocks to nearby synovial structures using computed tomography (CT).

Study design

Descriptive observational study.

Methods

In 18 cadaver forelimbs, sequential injection of the navicular bursa (NB), distal interphalangeal joint (DIPJ) and digital flexor tendon sheath (DFTS) was performed using 3, 5 and 10 mL diluted radiodense contrast medium, respectively. After each synovial injection, 25 gage needles were placed over the palmar digital nerves at the proximal aspect of the ungular cartilages (distal injections) and 1 cm further proximally (proximal injections), and CT examination was performed. Subsequently, needles were removed, and the synovial structures further distended with the same volume as for the first injection. Perineural needle placement and image acquisition were repeated. The distance between the needle tip and adjacent synovial structures was measured (mm) in reconstructed images. Results were analyzed in separate general linear mixed models, to determine the effect of needle position and synovial distension on the distance from the tip of the needle to the NB, DFTS and DIPJ.

Results

Synovial penetration was confirmed following 12/420 (3%) needle placements (NB n = 5, 1 after proximal and 4 after distal injections; DIPJ n = 2, DFTS n = 2, NB or DIPJ n = 3, all after distal injections). The mean distance from the needle tip to the NB and DIPJ was significantly smaller after the second distension (NB: p = 0.025; DIPJ: p < 0.001) and with the distal needle placements (NB: p < 0.001; DIPJ: p < 0.001). For the DFTS, the distance from the needle tip was significantly smaller with the proximal needle placements (p = 0.001).

Main limitations

Ex-vivo study.

Conclusion

There is a small risk of synovial penetration when performing palmar digital nerve blocks, especially when distension of adjacent synovial structures is present.

Low-field magnetic resonance imaging of sagittal groove disease of the proximal phalanx in non-racing sport horses

BACKGROUND

Injuries of the sagittal groove of the proximal phalanx (P1) in equine athletes are considered to predominantly occur due to chronic bone stress overload.

OBJECTIVES

To describe the range of abnormalities that is present in the sagittal groove in a large group of horses diagnosed with sagittal groove disease (SGD) on low-field MRI.

STUDY DESIGN

Retrospective, cross-sectional.

METHODS

Medical records were searched to identify initial MRI images of horses diagnosed with SGD and these were blindly evaluated using a semi-quantitative grading scheme and novel SGD MRI classification system reflecting potential pathways of pathological progression and severity of stress injury.

RESULTS

A total of 132 limbs from 111 horses were included in the study; predominantly warmbloods competing in showjumping (n = 83) and dressage (n = 18). SGD MRI classifications were: 0 (normal, n = 0), 1 (small subchondral defect, n = 2), 2 (osseous densification, n = 28), 3 (subchondral microfissure with osseous densification, n = 7), 4 (bone oedema-like signal within the subchondral ± trabecular bone and ± subchondral microfissure or demineralisation, n = 72), 5 (incomplete macrofissure/fracture, n = 23) and 6 (complete fracture, n = 0). Classification 4c (bone oedema-like signal with demineralisation) and 5 had higher proportions in the plantar third of hindlimbs (3% and 10%, respectively) compared with forelimbs (0% and 0%, respectively). SGD classification and extent of bone oedema-like signal were not significantly different between lame (n = 116) and non-lame limbs (n = 16) (both p > 0.05). Periosteal new bone and oedema-like signal were identified (either confidently or suspected) at the dorsoproximal aspect of P1 in 25% and 39% of limbs, respectively.

MAIN LIMITATIONS

Inclusion via diagnoses in original MRI reports, variable clinical history, small size of some classification groups.

CONCLUSIONS

The presence or absence of lameness is not a dependable measure of the severity of SGD. The periosteal oedema-like signal of P1 has not previously been described in MRI of SGD and further supports the concept of bone stress injury.

Prevalence and clinical significance of increasing head height asymmetry as a measure of forelimb lameness in horses when trotting in a straight line after palmar digital nerve block

BACKGROUND

Some horses increase in forelimb lameness, measured as vertical head height asymmetry, or differences in maximums and minimums of head heights (HDmax, HDmin), after a palmar digital nerve (PDN) block. The prevalence of this finding, or what it means clinically, has not been reported in peer-reviewed literature.

OBJECTIVES

To estimate the prevalence of increasing head height asymmetry after a PDN block and determine if this is associated with cause of forelimb lameness.

STUDY DESIGN

Retrospective case series.

METHODS

Head height asymmetry, normalised to expected vertical head displacement, from inertial-sensor data collections of all horses evaluated for forelimb lameness while trotting in a straight line at two different clinics were screened for cases that had an initial PDN block and then another more proximal block in the same limb during the same lameness evaluation. Medical records of the screened cases (n = 213) were evaluated to determine the cause of lameness. Prevalence of increasing head height asymmetry was calculated. Differences in lameness amplitude between groups of cases that remained unchanged (Group 1), that increased (Group 2), and that decreased (Group 3) in head height asymmetry before and after the initial PDN block were compared (Kruskal-Wallis). Determination of the location of the cause of lameness and final diagnoses of cases were compared between Group 1 and Group 2 (chi-squared tests of independence).

RESULTS

The PDN block increased head height asymmetry at a prevalence of 32.5% (95% CI = 24.5%-41.5%) and 13.8% (95% CI = 7.3%-22.9%), in clinic 1 and 2, respectively. Increasing head height asymmetry after an initial PDN block did not predict localization of the cause of forelimb lameness or specific diagnosis (p = 0.1), other than indicating that it is unlikely to be in the foot (p = 0.02).

MAIN LIMITATIONS

Study samples consisted primarily of Warmbloods (clinic 1) and Quarter Horses (clinic 2). Analysis of blocking induced changes was limited to straight line trot only.

CONCLUSIONS

Increasing head height asymmetry after PDN block is common during forelimb lameness evaluations. Other than indicating that the cause of lameness is more proximal in the blocked forelimb, this does not help determine the final diagnosis.

When radiography and ultrasonography are not enough: the use of computed tomography and magnetic resonance imaging for equine lameness cases

MRI and CT have enhanced our diagnostic abilities for equine lameness beyond what is available using radiography and ultrasonography. This has allowed veterinarians to better prognosticate and treat lameness conditions, improving patient outcomes. This article discusses the basic principles behind MRI and CT, their advantages and disadvantages, the different types of equipment available for clinical use in horses, the typical diagnostic workup prior to pursuing advanced imaging, and common regions where MRI and CT are used clinically. The companion Currents in One Health by Spriet, AJVR, July 2022, discusses even more advanced equine imaging in the form of positron emission tomography. Combined, these future directions of MRI, CT, and positron emission tomography may include improved ability to image standing horses or screen for injury prevention.

Conservative versus surgical treatment of 21 sports horses with osseous trauma in the proximal phalangeal sagittal groove diagnosed by low-field MRI

OBJECTIVE

To compare the outcome following conservative vs surgical management of sports horses with a diagnosis of subchondral bone trauma of the proximal aspect of the proximal phalanx (PP) by low-field MRI.

STUDY DESIGN

Retrospective case series.

ANIMALS

Twenty-one mature sports horses with evidence of high water signal within the proximal sagittal groove of the PP according to low-field MRI of the fetlock, with no definitive radiographic evidence of fracture.

METHODS

Medical records (2010-2017) of horses admitted to 2 referral hospitals were reviewed. Historical, clinical, radiographic, and MRI findings and treatment choice were recorded. Conservative management consisted of confinement to a stall followed by gradual reintroduction to exercise. Surgical management consisted of cortical screw fixation across the proximal aspect of the PP. Long-term outcome was determined by telephone questionnaire or by clinical records review. Fisher's exact test was used to compare outcome between the 2 treatment groups.

RESULTS

Follow-up was available in 17 of 21 horses in the study, including 8 horses treated conservatively and 9 treated surgically. No difference in outcome was detected in this study; 4 of 8 horses were sound after conservative management, and 5 of 9 horses were sound after surgery (P > .99).

CONCLUSION

Approximately half of the horses that had a diagnosis of osseous trauma within the proximal aspect of PP returned to athletic activity, regardless of conservative or surgical management.

CLINICAL SIGNIFICANCE

The prognosis for return to athletic functions in horses with osseous trauma within the proximal aspect of the PP is guarded.

The effect of a compression bandage on the distribution of radiodense contrast medium after palmar digital nerve blocks

BACKGROUND

Studies have shown proximal diffusion of injected drugs in perineural blocks; such diffusion may affect specificity of the nerve block.

OBJECTIVES

To investigate the effect of a compression bandage applied to the pastern region on proximal diffusion of contrast medium injected over the palmar digital nerves.

STUDY DESIGN

Experimental study, randomised cross-over design.

METHODS

Radiodense contrast medium was injected over the lateral and medial palmar digital nerves of the left front limb of nine mature horses. Each horse was injected on two separate occasions, once with a 5 cm wide compression bandage applied proximal to the injection site and once without. The order of the two treatments was randomised with a wash-out period between treatments of at least 7 days. Radiographs were obtained at 5, 10, 20 and 30 min and distribution of the contrast column assessed.

RESULTS

Proximal distribution of the contrast medium was significantly reduced (P<0.01) with compression bandage. Furthermore, the compression bandage inhibited lymphatic drainage of the injected contrast medium.

MAIN LIMITATIONS

Clinical effect of the differences in diffusion length was not assessed.

CONCLUSIONS

The compression bandage reduced proximal diffusion and lymphatic drainage of contrast material causing it to stay localised around the injection site. Use of compression bandages could thus result in increased specificity of the nerve block and potentially prolong its effect.

Mechanical nociceptive thresholds of dorsal laminae in horses after local anaesthesia of the palmar digital nerves or dorsal branches of the digital nerve

We examined the hypothesis that the palmar digital nerves (PDNs), but not the dorsal branches (DBs) of the digital nerves, innervate the sensitive dorsal laminae of the equine foot by evaluating the effects of perineural anaesthesia of the PDNs and DBs separately on pain sensation evoked via mechanical stimulation of the dorsal laminae and other regions of the equine foot. Six clinically normal mares were used in a crossover design. A portable dynamometer was used to evaluate mechanical nociceptive thresholds at different points on the dorsal laminae, bulbs of the heel, coronary band and sole before and after the horses underwent perineural injection of PDNs or DBs with a local anaesthetic solution (treated group) or an isotonic saline solution (control group). Cornified tissue was removed from the sole and the dorsal aspect of the hoof wall before evaluations of mechanical nociceptive thresholds. Anaesthetising PDNs distal to the DBs increased mechanical nociceptive thresholds compared to baseline values (P <0.001) at sites assessed in the dorsal laminae, sole, and the bulbs of the heels. Anaesthetising DBs increased mechanical nociceptive thresholds compared to baseline values (P <0.01) only at sites assessed at the most proximal aspect of the foot (i.e., coronary band sites). In conclusion, PDNs, not DBs, are primarily responsible for pain signal transmission evoked by pressure in the dorsal laminae of the foot of clinically normal horses.