Gross and ultrasonographic anatomy of the carpal flexor tendon sheath in horses

Desensitisation of the distal forelimb following intrathecal anaesthesia of the carpal sheath in horses

BACKGROUND

The effect of intrathecal anaesthesia of the carpal sheath on distal forelimb sensitivity in horses remains unknown.

OBJECTIVES

To assess the effect of carpal sheath anaesthesia on skin sensitivity of the distal forelimb and to determine potential locations for desensitisation of palmar nerves.

STUDY DESIGN

In vivo experimental and descriptive anatomical studies.

METHODS

Mepivacaine hydrochloride 2% (0.6 mg/kg) was injected unilaterally in the carpal sheath of 8 horses. Mechanical nociception of the distal forelimb was measured with a dynamometer and compared with the control limb at t_0, t_15, t_30, t_60, t_90, t₁₂₀ and t_180 minutes . Additionally, the carpal sheath of 10 pairs of cadaveric limbs was injected with latex and potential locations for anaesthetic diffusion to the neighbouring nerves were identified during longitudinal dissection (one limb) and in 3-cm-thick transverse cuts (opposite limb).

RESULTS

Six of 8 horses (75%) were completely desensitised at the level of both heel bulbs. Anaesthetic injection was not smooth in the 2 horses without desensitisation. Desensitisation started between 30 and 60 minutes in 67% of desensitised heel bulbs (8/12), and 50% (6/12) of them were still completely desensitised at 180 minutes. Cadaveric specimens revealed close proximity between the sheath and the medial palmar nerve as it travels inside the mesotenon of the digital flexor tendons in the carpal region and with both palmar nerves at the proximal metacarpal region.

MAIN LIMITATIONS

Skin mechanical nociception does not necessarily correlate with deep pain but remains the main clinical tool used by practitioners to assess distal limb anaesthesia.

CONCLUSIONS

Intrathecal anaesthesia of the carpal sheath led to distal limb skin desensitisation through diffusion to the palmar nerves at 2 possible locations. Carpal sheath anaesthesia should be interpreted within 15 minutes following injection and anaesthetic blocks distal to the carpus should be delayed for more than 3 hours following carpal sheath anaesthesia.

Diagnostic tenoscopy of the carpal sheath with a needle arthroscope in standing sedated horses

OBJECTIVE

To investigate the use of a needle arthroscope for diagnostic tenoscopy of the carpal sheath in standing horses.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Six forelimbs for the cadaveric part of the study and six horses for the in vivo part of the study.

METHODS

Six cadaveric limbs were used to perform carpal sheath tenoscopy with a 1.2-mm-diameter needle arthroscope (65 and 100 mm long), followed by tenoscopy with a 4-mm arthroscope through a standard proximolateral approach. Then, unilateral standing carpal sheath tenoscopy was performed in six healthy sedated horses with a 65-mm-long needle arthroscope. Limbs were maintained in flexion during the procedure by using a custom-made splint and base. Degree of tenoscopic evaluation, safety, horse tolerance, and complications were recorded.

RESULTS

Visibility at the most distal aspect of the sheath was absent for the needle arthroscopes vs a standard arthroscope. The maneuverability with a 65-mm needle arthroscope was excellent and allowed exhaustive visualization of the proximal region of the carpal sheath in cadaveric limbs and standing horses (six of six). However, visualization of the intertendinous recess was partial in most horses (four of six) vs cadavers (complete in six of six) because of remaining flexor tendon tension in standing horses. No major complications were encountered.

CONCLUSION

Standing carpal sheath tenoscopy allowed a safe and thorough evaluation of most structures in the proximal region of the sheath and offers an alternative diagnostic technique.

CLINICAL SIGNIFICANCE

Horses with unrewarding results after traditional imaging or that require an accurate diagnosis before treatment may benefit from this alternative procedure.

The influence of tenoscopic approaches on radiocarpal joint perforation during carpal sheath tenoscopy in horses

OBJECTIVE

To report the frequency of radiocarpal joint (RCJ) perforation during two proximolateral carpal sheath (CS) approaches and to investigate whether the presence or absence of a natural communication between the RCJ and CS.

STUDY DESIGN

Experimental, randomized, controlled study.

SAMPLE POPULATION

Twelve adult horses and 12 cadaver front limbs.

METHODS

Proximolateral CS tenoscopy was performed on both carpi of 12 horses under general anaesthesia. Limbs were randomly assigned into two groups. In group 1, the instrument portal was centered at the level of the distal radial physeal remnant (PR). In group 2, the instrument portal was centered 2 cm proximal to the PR. Immediately after tenoscopy, dye-coloured fluid was instilled arthroscopically into the dorsolateral RCJ, and the open tenoscopic portals were evaluated for leakage. Twelve cadaver front limbs were examined for naturally occuring RCJ and CS communication by using positive-contrast computed tomography (CT). Frequency of perforations were compared with McNemar's test for two matched proportions.

RESULTS

In group 1, 10 of 12 RCJ were perforated during tenoscopy, and, in group 2, four of 12 RCJ were perforated (P = 0.03). No diffusion of contrast from the RCJ to the CS was detected by CT.

CONCLUSION

Perforation of the RCJ was common when CS instrument portals were placed at the level of the PR. No natural communication was detected between the RCJ and CS.

CLINICAL SIGNIFICANCE

Carpal sheath tenoscopic instrument portals may need to be placed >2 cm proximal to the PR to prevent inadvertent RCJ perforation, especially in horses undergoing tenoscopic treatment of a septic CS.

In search of clinical truths: equine and comparative studies of anatomy

The importance of correlating anatomical studies with diagnostic and therapeutic approaches in practice has long been recognised. Such studies in the horse have, until recently, lagged behind this discipline in human medicine and surgery. Clinical techniques by which this correlation is achieved include radiography, ultrasound, computed tomography and magnetic resonance imaging. This review presents published literature on the subject and, in addition, describes the part played by plastination, a recently developed technique for the preservation of biological specimens. In this, tissue fluids and part of the lipids are replaced by certain polymers yielding specimens that can be handled without gloves, do not smell or decay, and even retain microscopic properties of the original sample. The technique has proved to be a useful tool to correct previously presented anatomical descriptions and is one now favoured by human surgeons. Studies of the horse employing this technique include those of the temporomandibular joint and tarsus. The aim of the review is to stimulate further correlations of anatomical structure and equine medical and surgical procedures, thereby advancing knowledge and understanding in practice and teaching.

Ultrasonography of peripheral nerves in the normal adult horse

A study of the ultrasonographic appearance and size of the sciatic, tibial, peroneal, suprascapular, radial, median, and ulnar nerves and a comparison with the anatomic size and location of these nerves in the normal adult horse is reported. Cadavers and live horses were studied. Landmarks for localization and techniques for nerve identification are described. The depth and diameter of each nerve at various locations and the success rate in imaging each nerve are reported. Statistically significant correlations were found between anatomically and ultrasonographically measured nerve depths and diameters. The success rate in identifying nerves was 70% in the live horses and 49% in cadavers, with the deep peroneal nerve being the easiest to identify. Some applications of this technique in horses are discussed.

Ultrasonographic anatomy of the accessory ligament of the superficial digital flexor tendon in horses

The ultrasonographic anatomy of the accessory ligament of the superficial digital flexor tendon (AL-SDFT) in the horse is presented. Comparison between anatomical sections of isolated limbs and ultrasound scans of the distal antebrachium in sound horses enabled the authors to establish the normal reference ultrasonographic images of this structure. The AL-SDFT inserts 7-14 cm above the antebrachiocarpal joint on the palmaromedial aspect of the radius. Ultrasonographically it appears as an uniformly echogenic structure located deep to the median artery. The knowledge of ultrasonographic anatomy is essential for identification of abnormal images and assessment of AL-SDFT damage.