An investigation of injection techniques for local analgesia of the equine distal tarsus and proximal metatarsus

Review of intra-articular local anaesthetic administration in horses: Clinical indications, cytotoxicity, and outcomes

Equine practitioners frequently inject local anaesthetics (LA) intra-articularly in both diagnosis of lameness and for pain management intra- or post-operatively with synovial endoscopy. Recent reviews of the human and veterinary literature support the concept that chondrotoxicity of LA on joint tissues depends on the type of drug, dose administered, and duration of exposure. The purpose of this review is to summarise the current literature describing intra-articular local anaesthetic use, including both in vitro and in vivo studies, and to draw some comparisons to literature from other species where potential toxicity and duration of effect have been evaluated with the goal of advancing the field's understanding of intra-articular local anaesthetic use in horses, and indicating future directions for the field. The aggregate data available from all species, while generally sparse for horses, indicate that LA are rapidly cleared from the synovial fluid after injection, often within 30 min. In vitro data strongly suggest that lidocaine and bupivacaine are likely more chondrotoxic than other LA, although to what extent is still unknown, and cytotoxicity of LA may be mitigated through concurrent injection with HA, PRP, and drug combinations including nonsteroidal anti-inflammatories and opioids. The current body of in vitro research is not reflective of the in vivo environment, and further in vitro work, if performed, should focus on mimicking the native joint environment, utilising PK data and joint/injection volumes to replicate the native environment more accurately within the joint and the expected exposures to LA.

Radiographic changes of the proximal third metatarsal bone do not predict presence or severity of proximal suspensory desmopathy in a predominately Quarter Horse population

BACKGROUND

Comparison of radiography to magnetic resonance imaging (MRI) can help objectively assess the value and limitations of radiographs in orthopaedic disease processes. The tarsus and proximal suspensory origin of the metatarsus are commonly imaged regions for lameness. The knowledge gained by comparison between imaging modalities will aid in improving accuracy of radiographic interpretation.

OBJECTIVE

To compare the radiographic and MRI findings of the proximal third metatarsal bone (MTIII) and proximal suspensory ligament using MRI as the gold standard.

STUDY DESIGN

Retrospective observational study.

METHODS

Single hindlimbs of 35 horses with radiographic and high-field (3Tesla (3T)) MRI studies were blindly evaluated by two board-certified veterinary radiologists and a radiology resident. Severity and location of the following parameters were assessed: radiographic MTIII sclerosis and lucent regions, MRI endosteal metatarsal sclerosis and bone marrow lesions, plantar cortical proliferation and resorption, and proximal suspensory desmopathy (PSD).

RESULTS

Radiographic osseous changes of MTIII were identified in 54% of limbs, whereas 40% limbs had osseous changes on MRI: 43% of limbs had PSD on MRI. No significant association was found between the presence of radiographic changes in MTIII and PSD on MRI (P = .7). A statistically significant association and positive correlation was found between the severity of radiographic changes and MTIII plantar cortical proliferation and resorption on MRI (P = .01).

MAIN LIMITATIONS

Retrospective study with no histopathology. Ability to correlate findings with lameness was limited by the lack of standardised time intervals between onset of lameness, diagnostic analgesia and advanced imaging.

CONCLUSION

Radiographic bony changes of proximal MTIII do not reliably predict presence or severity of PSD but are associated with osseous changes at the proximal MTIII. The presence of radiographic changes should warrant additional diagnostics in the region prior to making conclusions about the presence or absence of PSD.

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.

Ultrasound-assisted injection of the centrodistal joint in the horse

BACKGROUND

Injection of the centrodistal (CD) joint in the horse is a commonly performed procedure for both diagnostic and therapeutic purposes. This procedure can be technically challenging, and while radiographic guidance has been previously used, ultrasound localised injection of the CD joint has not been described.

OBJECTIVES

The purpose of this study was to explore the feasibility of using ultrasound localisation to increase the accuracy of CD joint injection.

STUDY DESIGN

Experimental method assessment.

METHODS

One operator performed the ultrasound and injection of 24 CD joints in 12 sedated horses. The joints were injected with iohexol (2 ml), sterile saline (1.5 ml) and amikacin (0.5 ml). Dorsoplantar and dorsomedial plantarolateral radiographic projections were obtained immediately after injection to evaluate the presence of contrast material in the CD joint.

RESULTS

The CD joint was successfully injected in 17/24 joints, representing a 70.8% accuracy.

MAIN LIMITATIONS

The horses used in this study were from the University research herd, and not clinical cases. One investigator performed all the ultrasonography and CD joint injections.

CONCLUSIONS

The use of ultrasound localisation could improve success of CD joint injection as well as improve the learning curve of less experienced practitioners learning this procedure.

In vitro evaluation of a medial approach for intra-articular injection of the tarsometatarsal joints of horses

OBJECTIVE

To develop a reliable method for injection of the tarsometatarsal (TMT) joint of horses through a medial approach and to characterize anatomy of the synovial recesses of the TMT joint with CT.

SAMPLE

13 pairs of fresh cadaveric equine tarsi.

PROCEDURES

TMT joints were assessed with radiography and CT. Twelve pairs of TMT joints were assigned to an experienced veterinarian (8 joints) or veterinary student (16 joints) for injection with contrast medium through a medial or a lateral approach. Every TMT joint was then reexamined radiographically and with CT to assess diffusion of contrast medium. The number of attempts for the lateral and medial approaches between and within investigators was evaluated, which included evaluation of the diffusion of contrast solution in relation to the approach used.

RESULTS

All 24 TMT joints were successfully injected, as confirmed with radiography and CT. There was no significant difference in the number of attempts between the medial and lateral approaches and between investigators. No significant difference was detected in the distribution of contrast medium in each synovial recess between the medial and lateral approaches.

CONCLUSIONS AND CLINICAL RELEVANCE

The medial approach described here for injection of the TMT joint of horses was highly reliable. It involved use of an easily palpable anatomic landmark on the mediodistal aspect of the TMT joint. An established alternative method for injection of the TMT joint may be useful in clinical practice for diagnostic and therapeutic purposes, although a medial approach may increase risk of injury to veterinarians.

Comparing the clinical success rate of the dorsolateral approach to the medial approach for injection of the centrodistal joint in the horse

BACKGROUND

Centrodistal joint injection is an important component of lameness evaluation and treatment. Successful injection is poor for the medial approach. The dorsolateral approach is an alternative but has not been validated with contrast medium. Radiograph-guidance has not been studied to determine its necessity or benefit for either approach.

OBJECTIVES

To determine if the dorsolateral approach to the centrodistal joint is more successful than the medial approach. To determine if radiograph-guidance is beneficial.

STUDY DESIGN

Prospective, randomised study.

METHODS

Three operators injected 98 centrodistal joints in total, each horse served as its own control. In Phase 1, injections were performed by standard technique. In the Phase 2, operators were allowed to use radiography to assist needle placement. Contrast deposition was evaluated by a single radiologist.

RESULTS

Without radiographic assistance, 10/25 (40%) joints were successfully injected using either the medial or dorsolateral approach. With radiographic assistance, 19/24 (79%) joints were successfully injected using the medial approach, 11/24 (46%) joints were successfully injected using the dorsolateral approach.

MAIN LIMITATIONS

The population consisted of aged horses representing a variety of breeds with existing osteoarthritis, and multiple operators were recruited.

CONCLUSIONS

The dorsolateral approach was equivalent to the medial approach when traditional injection techniques were used. Radiograph-guidance improved success of the medial approach, but not the dorsolateral approach. Many injections performed from the dorsolateral approach (32/49; 65%) resulted in extensive perivascular subcutaneous contrast deposition after infiltration into the tarsal canal. Further research is needed to improve injection success of the centrodistal joint when using the dorsolateral approach.

The relationship between sagittal hoof conformation and hindlimb lameness in the horse

BACKGROUND

Lameness can be multifactorial and may result from the accumulation of multiple seemingly unrelated causes. The identification of factors associated with lameness could be one method to decrease incidence of lameness and prolong the equine athlete's competitive life.

OBJECTIVES

To determine if there is an association between hoof balance in the sagittal plane and hindlimb lameness.

STUDY DESIGN

Case-control study.

METHODS

Eighty client-owned horses with hindlimb lameness (cases) and 80 horses with no detectable hindlimb lameness (controls) were prospectively enroled following lameness evaluation as either cases (lameness localised with regional anaesthesia) or controls (no hindlimb lameness). Lameness cases were divided based on location (stifle, tarsus, proximal metatarsus and other sites). Lateromedial radiographs were performed on hind hooves and plantar angle of the distal phalanx (PADP) was determined. The prevalence of negative/neutral PADP and median PADPs were calculated. Conditional logistic regression and Wilcoxon signed rank tests were used to analyse PADPs, and odds ratios were calculated. Significance was set at P<0.05.

RESULTS

The mean PADP was significantly smaller in cases compared to controls. The mean PADP was significantly smaller in horses with lameness localised to tarsus and proximal suspensory, but not the stifle. Lameness in horses was associated with a negative/neutral PADP (Odds ratio [OR] 3.87, 95% confidence interval [95% CI] 1.97-7.61, P<0.01), with lameness localised to the tarsus (OR 4.98, 95% CI 1.34-18.54, P = 0.01) and proximal suspensory (OR 5.16, 95% CI 1.11-23.89, P = 0.03) being associated with a negative/neutral PADP.

MAIN LIMITATIONS

It is unknown whether the negative/neutral PADP contributed to lameness or lameness resulted in lower PADP.

CONCLUSIONS

Horses with hindlimb lameness localised to the distal tarsus and proximal metatarsus, but not the stifle, were more likely to have negative/neutral PADPs. Corrective farriery to improve PADP may be investigated further as one component in the treatment of hindlimb lameness localised to regions proximal to the foot. The Summary is available in Portuguese - see Supporting Information.

Comparison of Metzenbaum scissors and Y-shaped fasciotome for deep metatarsal fasciotomy for the treatment of proximal suspensory ligament desmopathy in horses

OBJECTIVE

To quantitate the iatrogenic injury associated with deep plantar metatarsal fasciotomy performed with Metzenbaum scissors compared with a Y-shaped fasciotome.

STUDY DESIGN

Experimental ex vivo surgical study.

STUDY POPULATION

Cadaveric hind limbs (n = 20) from 10 sound thoroughbred racehorses.

METHODS

A plantar metatarsal fasciotomy was performed, extending from the proximal extent of the deep metatarsal fascia, distally. Hind limbs were randomly assigned to 2 groups, undergoing fasciotomy with straight Metzenbaum scissors (n = 10) or a Y-shaped fasciotome (n = 10). Magnetic resonance imaging was performed before and after surgery to identify the maximal depth of any iatrogenic trauma. Gross examination of the surgical site included measuring the length of the incision in the deep metatarsal fascia and localizing iatrogenic trauma sustained by the plantar aspect of the proximal suspensory ligament (PSL) during the procedure.

RESULTS

Iatrogenic injury to the PSL was identified in 6 of 10 and 9 of 10 specimens prepared with the fasciotome and Metzenbaum scissors, respectively (P = .03), and was most commonly located in the distal third of the fascial incision. Differences between the length of incision (P = .02) and the maximal depth of signal (P = .03) for incisions created with Metzenbaum scissors or a fasciotome were identified.

CONCLUSION

The use of a fasciotome resulted in longer fascial incisions and less severe iatrogenic trauma to the PSL compared with using Metzenbaum scissors.

CLINICAL SIGNIFICANCE

A Y-shaped fasciotome may be the preferred surgical instrument for successful desmopathy of the PSL fasciotomy because a greater release of compartmental pressure is possible through a longer incision with minimal iatrogenic trauma to the underlying PSL.

Is anaesthesia of the deep branch of the lateral plantar nerve specific for the diagnosis of proximal metatarsal pain in the horse?

OBJECTIVES

To investigate the specificity of anaesthesia of the deep branch of the lateral plantar nerve (DB-LPN).

METHODS

Twenty horses had DB-LPN anaesthesia performed by a single injection technique as part of a lameness investigation. The mechanical nociceptive threshold (NT) was measured using a handheld force meter at six points on the lateral aspect of the limb: before diagnostic anaesthesia (T0), and at 15 (T15) and 30 (T30) minutes post anaesthesia. Paired t-tests were performed and significance was set at p <0.05. In addition, ten cadaveric limbs were injected with 2.5 ml new methylene blue solution using a single injection technique to evaluate the extent of dye diffusion within the proximal metatarsal region.

RESULTS

Compared with T0, there was a significant decrease in NT for all points combined at T15 (p = 0.008) and also at T30 (p = 0.007). There was a significant decrease in NT at T15 on the lateral third metatarsal bone (p = 0.012). At T30 there was a significant decrease in NT at the lateral sesamoid (p = 0.007), lateral third metatarsal bone (p = 0.031), and mid metatarsus (p = 0.033). Four out of 20 horses had a NT greater than 10 N at the lateral heel bulb at T30. In the cadaveric limbs, the total diffusion distance for all limbs (mean ± SD) was 70.4 ± 20.5 mm. Dye surrounded the DB-LPN in all limbs and the lateral plantar nerve (LPN) in nine out of 10 limbs.

CLINICAL SIGNIFICANCE

Concurrent anaesthesia of the LPN is likely to occur when DB-LPN anaesthesia is performed using a single injection technique.

Computed tomographic features of lesions detected in horses with tarsal lameness

REASONS FOR PERFORMING STUDY

Tarsal pain is a common cause of hindlimb lameness in horses. Diagnosis can usually be made with radiography and ultrasonography; however, in some cases, these techniques are inconclusive and additional imaging is necessary. No studies describing computed tomography (CT) features of different tarsal lesions in horses with tarsal lameness are reported.

OBJECTIVES

Our aims were as follows: 1) to characterise CT abnormalities in horses with tarsal lameness; 2) to compare CT findings with those from other imaging techniques; and 3) to assess whether CT can help to diagnose tarsal pathology.

STUDY DESIGN

Retrospective case series.

METHODS

Computed tomography of the tarsus was performed on 15 horses (n = 17 joints) with tarsal lameness. The horses were divided into 3 groups depending on the reason for CT examination, as follows: 1) other imaging techniques were inconclusive; 2) evaluation of a fracture; or 3) other imaging techniques showed tarsal lesions, and CT was performed to assess whether additional lesions were present.

RESULTS

Group 1 included 7 horses. Lesions detected with CT included subchondral cyst-like lesions (2 horses); an osteolytic lesion in the cochlea tibiae (one horse); degenerative changes of the distal tarsal joints (2 horses); osteolytic lesions tarsometatarsal joint (one horse); and sclerosis of the third tarsal bone with a lesion of the tarsometatarsal interosseous ligament (one horse). In this group, CT provided information on the character and extent of the lesion that was not available with other imaging techniques. Computed tomography revealed more information about the extent and complexity of the fracture than radiography in Group 2, whereas CT did not provide extra information in Group 3.

CONCLUSIONS

Focal lesions located between the tarsal bone surfaces are difficult or even impossible to detect with radiography and ultrasonography, but they can be detected and characterised with CT.

POTENTIAL RELEVANCE

Computed tomography of the tarsus should be considered when radiography and ultrasonography are inconclusive, or for further evaluation of tarsal fractures.

Management of hindlimb proximal suspensory desmopathy by neurectomy of the deep branch of the lateral plantar nerve and plantar fasciotomy: 155 horses (2003-2008)

REASONS FOR PERFORMING STUDY

Neurectomy of the deep branch of the lateral plantar nerve and plantar fasciotomy have become accepted as methods of treatment of proximal suspensory desmopathy (PSD), but there are limited long-term studies documenting the outcome.

OBJECTIVES

To describe long-term follow-up in horses with PSD alone or with other injuries contributing to lameness and poor performance, including complications, following neurectomy and fasciotomy.

METHODS

Follow-up information was acquired for 155 horses that had undergone neurectomy and fasciotomy for treatment of PSD between 2003 and 2008. Success was classified as a horse having been in full work for >1 year post operatively. Horses were divided into 3 groups on the basis of the results of clinical assessment and diagnostic analgesia. Horses in Group 1 had primary PSD and no other musculoskeletal problem. Horses in Group 2 had primary PSD in association with straight hock conformation and/or hyperextension of the metatarsophalangeal joint. Horses in Group 3 had PSD and other problems contributing to lameness or poor performance.

RESULTS

In Group 1, 70 of 90 horses (77.8%) had a successful outcome, whereas in Group 3, 23 of 52 horses (44.2%) returned to full function for >1 year. Complications included iatrogenic damage to the plantar aspect of the suspensory ligament, seroma formation, residual curb-like swellings and the development of white hairs. All horses in Group 2 remained lame.

CONCLUSIONS AND CLINICAL RELEVANCE

There is a role for neurectomy of the deep branch of the lateral plantar nerve and plantar fasciotomy for long-term management of hindlimb PSD, but a prerequisite for successful management requires recognition of risk factors for poor outcome including conformation features of straight hock or fetlock hyperextension.

Distribution of radiodense contrast medium after perineural injection of the palmar and palmar metacarpal nerves (low 4-point nerve block): an in vivo and ex vivo study in horses

REASONS FOR PERFORMING STUDY

Evidence-based information is limited on distribution of local anaesthetic solution following perineural analgesia of the palmar (Pa) and palmar metacarpal (PaM) nerves in the distal aspect of the metacarpal (Mc) region ('low 4-point nerve block').

OBJECTIVES

To demonstrate the potential distribution of local anaesthetic solution after a low 4-point nerve block using a radiographic contrast model.

METHODS

A radiodense contrast medium was injected subcutaneously over the medial or the lateral Pa nerve at the junction of the proximal three-quarters and distal quarter of the Mc region (Pa injection) and over the ipsilateral PaM nerve immediately distal to the distal aspect of the second or fourth Mc bones (PaM injection) in both forelimbs of 10 mature horses free from lameness. Radiographs were obtained 0, 10 and 20 min after injection and analysed subjectively and objectively. Methylene blue and a radiodense contrast medium were injected in 20 cadaver limbs using the same techniques. Radiographs were obtained and the limbs dissected.

RESULTS

After 31/40 (77.5%) Pa injections, the pattern of the contrast medium suggested distribution in the neurovascular bundle. There was significant proximal diffusion with time, but the main contrast medium patch never progressed proximal to the mid-Mc region. The radiological appearance of 2 limbs suggested that contrast medium was present in the digital flexor tendon sheath (DFTS). After PaM injections, the contrast medium was distributed diffusely around the injection site in the majority of the limbs. In cadaver limbs, after Pa injections, the contrast medium and the dye were distributed in the neurovascular bundle in 8/20 (40%) limbs and in the DFTS in 6/20 (30%) of limbs. After PaM injections, the contrast and dye were distributed diffusely around the injection site in 9/20 (45%) limbs and showed diffuse and tubular distribution in 11/20 (55%) limbs.

CONCLUSIONS AND POTENTIAL RELEVANCE

Proximal diffusion of local anaesthetic solution after a low 4-point nerve block is unlikely to be responsible for decreasing lameness caused by pain in the proximal Mc region. The DFTS may be penetrated inadvertently when performing a low 4-point nerve block.

Tiludronate infusion in the treatment of bone spavin: a double blind placebo-controlled trial

REASONS FOR PERFORMING STUDY

Tiludronate regulates bone remodelling through a decrease of the resorptive process and should therefore ameliorate the remodelling processes active in osteoarthritis of the distal tarsal joints ('bone spavin') and alleviate pain associated with abnormal bone lysis.

OBJECTIVE

To confirm the efficacy of tiludronate, administered as a single infusion at a dose of 1 mg/kg bwt, in the treatment of bone spavin in the horse.

METHODS

A double blind placebo controlled trial on 108 clinical cases of bone spavin was undertaken. The lameness score of the lamest limb was assessed following distal tarsal analgesia of the contralateral limb and followed-up using the same procedure throughout the study. Bone spavin in the lamest limb was confirmed by distal tarsal analgesia and radiography. Horses were treated at Day 0 and reassessed 60 days later after controlled exercise. A second nonblinded treatment was given to unresponsive horses and all horses were re-examined at Day 120. Exercise levels were recorded at each examination.

RESULTS

Eighty-seven horses completed the trial as per the protocol. The tiludronate horses were significantly less lame than the placebo horses (P = 0.0318). Horses treated at Day 60 with tiludronate showed further improvement in lameness at Day 120 (P = 0.0096 and P = 0.0034 for horses treated with tiludronate and placebo at Day 0, respectively). The only significant difference in radiographic findings between tiludronate and placebo was for presence of periarticular osteophytes (P = 0.006).

CONCLUSIONS

Tiludronate treatment is proven to be effective in bone spavin in horses in association with a controlled exercise programme.

CLINICAL RELEVANCE

Tiludronate in combination with controlled exercise offers an alternate medical treatment for bone spavin.

Concentration of methylprednisolone in the centrodistal joint after administration of methylprednisolone acetate in the tarsometatarsal joint

REASONS FOR PERFORMING STUDY

The centrodistal (CD) and tarsometatarsal (TMT) joints are often injected individually with a corticosteroid to resolve lameness caused by osteoarthritis (OA). There are no data available regarding diffusion of methylprednisolone (MP) from the TMT joint to the CD joint.

HYPOTHESIS

A therapeutic concentration of MP diffuses into the CD joint after methylprednisolone acetate (MPA) is administered into the TMT joint.

OBJECTIVE

To measure the concentration of MP in the CD joint after MPA was administered into the TMT joint.

METHODS

MPA was administered into a TMT joint of 16 horses. At different times, the ipsilateral CD joint of these horses was injected with a small amount of saline and recovered saline was measured for concentration of MP using high performance liquid chromatography.

RESULTS

Six hours after administration of MPA into the TMT joint, a therapeutic concentration of MP was found in all 10 CD joints sampled at this time.

CONCLUSIONS

Horses with pain arising from the distal 2 joints of the hock can be treated by administering MPA into the TMT joint alone.

POTENTIAL RELEVANCE

Administering MPA into the TMT joint only, to treat OA of the distal 2 hock joints, reduces the difficulties and risks associated with centesis of the CD joint.

Chemical arthrodesis of the distal tarsal joints using sodium monoiodoacetate in 104 horses

OBJECTIVE

To evaluate chemical arthrodesis using sodium monoiodoacetate for treatment of degenerative joint disease of the tarsometatarsal and distal intertarsal joints.

DESIGN

Retrospective clinical study.

METHOD

Horses were diagnosed with degenerative joint disease of one or more of the tarsometatarsal or distal intertarsal joints based on history, lameness examination, radiographic findings and, in some cases, response to intra-articular anaesthesia or medication. Intra-articular injections of sodium monoiodoacetate were performed using 23 gauge needles in the sedated, standing horse. Positive contrast arthrography of the distal intertarsal joint was performed in all horses to evaluate needle placement and the presence or absence of communication with other synovial structures. The mean intra-articular dose of sodium monoiodoacetate was 192 mg. Horses were subject to a graded exercise program commencing 7 to 10 days after treatment. Where possible, follow up lameness examination and radiography was performed at 3, 6, 12 and 24 months after treatment.

RESULTS

At 3, 6, 12 and 24 months after treatment, respectively, 0/57, 14/55, 41/50, and 29/34 of horses were sound. At 3, 6, 12 and 24 months after treatment, respectively, 5/55, 24/38, 26/30 and 18/18 of horses had radiographic evidence of ankylosis of treated joints. Post injection pain was marked in 6.7% of horses and significant complications requiring further treatment occurred in 3.8% of horses.

CONCLUSIONS

Chemical arthrodesis using sodium monoiodoacetate was an effective treatment method for degenerative joint disease of the distal tarsal joints. The technique was performed in the sedated standing horse and required minimal equipment. Results were comparable to those achieved following surgical arthrodesis. The risk of significant complications was minimised through good technique using an appropriate injection volume and concentration.

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

The purpose of this study was to describe ultrasonographic changes of the equine palmar metacarpal area attributed to the infiltration of local anesthetic solution and to determine whether these changes were noted immediately or at 24 h. The palmar metacarpal region of one forelimb in each of six horses was examined ultrasonographically with a 10-MHz linear array transducer and a 7.5-MHz curvilinear transducer. Transverse and longitudinal images were recorded at 5-cm intervals distal to the accessory carpal bone. High and low palmar and palmar metacarpal nerve blocks were performed with a 2% mepivacaine hydrochloride solution. Ultrasonographic examinations similar to the initial examination then were performed immediately, 1 h and 24 h postinjection. Cross-sectional area and mean pixel value were determined for the superficial and deep digital flexor tendons, the accessory ligament of the deep digital flexor tendon, the suspensory ligament, and the suspensory branches at each level and time period. Subjective ultrasonographic changes also were noted. No significant difference was noted in the cross-sectional area or mean pixel value of any structure at any level or time period compared to baseline. Subjective changes in the tendons and ligaments were not noted. There was mild hypoechoic swelling of the surrounding soft tissues and gas in the region of the injections. Gas could interfere with the evaluation of the origin of the suspensory ligament and the proximal portion of the accessory ligament of the deep digital flexor tendon within the first hour but was not detectable ultrasonographically at 24 h. Based on these findings, if gas interferes with an ultrasonographic examination performed temporally close to perineural anesthesia, a repeat examination at 24 h is recommended.

Diffusion of mepivacaine between adjacent synovial structures in the horse. Part 2: tarsus and stifle

This paper tests the hypothesis that the local analgesic agent mepivacaine diffuses between adjacent equine synovial structures in the hindlimb and with greater frequency than latex, gelatine dye or contrast media. We report the incidence of diffusion of mepivacaine between the tarsometatarsal, centrodistal and tarsocrural joints, and the 3 synovial compartments of the stifle in 33 fresh equine cadavers. The tarsometatarsal joint and one synovial compartment of the stifle in the left limb and the centrodistal joint and a different synovial compartment of the stifle in the right limbs were injected with mepivacaine. Following flexion and extension of the limb, synovial fluid was aspirated from the noninjected centrodistal and tarsometatarsal joints and the tarsocrural joints of the hock and the noninjected compartments of the stifle. Concentrations of mepivacaine in these samples were assayed using an enzyme linked immunosorbent assay. For samples obtained by dilution of synovial fluid the concentration of mepivacaine was determined by comparing the concentration of urea in the diluted synovial fluid and the concentrations of the serum urea. Mepivacaine was detected in 25/25 (100%) adjacent tarsometatarsal and centrodistal joints after diffusion in both directions, in 23/25 (92%) of tarsocrural joints after diffusion from tarsometatarsal joints and in 22/25 (88%) tarsocrural joints after diffusion from centrodistal joints in the hocks. Diffusion from the femoropatellar to medial and lateral femorotibial joints and between the medial and lateral femorotibial joints in both directions were 20/20 (100%). Diffusion from the lateral femorotibial to the femoropatellar joint was 18/20 (90%) and from the medial femorotibial to femoropatellar joints 17/20 (85%). Mepivacaine was detected at concentrations >0.3 mg/l in a proportion of samples ranging from 15/25 (60%) in the tarsocrural joint following tarsometatarsal joint injection to 18/20 (90%) in the lateral femorotibial joint after femoropatellar joint injection. At mepivacaine concentrations >100 mg/l, detection ranged from 3/20 (15%) in the lateral femorotibial joint from the medial femorotibial joint to 19/25 (76%) in the centrodistal joint from the tarsometatarsal joint. At mepivacaine concentrations >300 mg/l, detection ranged from 1/25 (4%) in the tarsocrural joint from the tarsometatarsal joint to 16/25 (64%) in the from centrodistal joint the tarsometatarsal joint. The results show greater diffusion of mepivacaine between these adjacent synovial structures than assumed from previous anatomical, latex injection and contrast arthrographic studies. Therefore, commonly performed intrasynovial local analgesic techniques in the hindlimb of the horse are not as specific as first thought.

Suspensory ligament desmitis

The gross and functional anatomy of the suspensory ligament (SL) and its ultrasonographic variability are described. Injuries of the suspensory apparatus are divided into lesions confined to the proximal one third of the metacarpus or metatarsus (proximal suspensory desmitis and avulsion fractures), lesions of the body, and branch lesions. Complete breakdown injuries are also discussed. In view of the close association of the SL, the second, third, and fourth metacarpal or metatarsal bones, and the proximal sesamoid bones, associated bony lesions are also considered.

Proximal suspensory desmitis in the hindlimb: 42 cases

Proximal suspensory desmitis of the hindlimb was diagnosed using local analgesic techniques and ultrasonography in 42 horses. Subtarsal analgesia resulted in substantial improvement in lameness in 36 of 41 horses in which local analgesic techniques were used. In the remaining five horses lameness was improved by perineural analgesia of the tibial nerve (three) or the tibial and fibular nerves. Intra-articular analgesia of the tarso-metatarsal joint produced a similar degree of improvement in two of 24 horses in which lameness had been improved by subtarsal analgesia. Ultrasonographic abnormalities of the proximal one third of the suspensory ligament of the lame limb only were detected in 36 of the 37 unilaterally lame horses. Abnormalities were detected in both suspensory ligaments in the five bilaterally lame horses and in one horse with unilateral lameness. Radiographic abnormalities of the proximal aspect of the third metatarsal bone of the lame or lamer limb were detected in 23 horses. Four horses have been in full work for more than 1 year without recurrent lameness. Two other horses resumed full work but had lameness due to another cause. Six horses are in light work despite mild lameness. Sixteen horses have been retired or humanely destroyed due to persistent or recurrent lameness.