Mineralization can be an incidental ultrasonographic finding in equine tendons and ligaments

Tendon/ligament mineralization is recognized in horses but information regarding its clinical significance is limited. The aims of this observational study were to report the structures most commonly affected by ultrasonographically detectable mineralization and, for these, determine frequency of diagnosis and key clinical features. Cases presented at our hospital in April 1999–April 2013 and September 2014–November 2015 were included: a total of 27 horses (22 retrospective, five prospective). Mineralizations were most common in deep digital flexor tendons (10) and suspensory ligament branches (eight), representing 10% and 7% (estimated), respectively, of horses diagnosed with injuries to these structures during the study. Two deep digital flexor tendon and three suspensory ligament branch cases showed bilateral mineralization. Deep digital flexor tendon mineralization was restricted to the digital flexor tendon sheath, most commonly in the proximal sheath (±sesamoidean canal), and seven of 10 cases involved hindlimbs. Suspensory ligament branch mineralization was visible in the same ultrasound window as the proximal sesamoid bones in 10/11 limbs and six of eight cases involved forelimbs. Previous corticosteroid medication was a feature of one deep digital flexor tendon and one suspensory ligament branch case. Mineralization was associated with lameness in some but not all limbs. Mineralized foci within the deep digital flexor tendon preceded hypoechoic lesion formation in two limbs. Of the cases with deep digital flexor tendon or suspensory ligament branch injury only, one of three and two of three cases, respectively, became sound. Findings indicated that tendon/ligament mineralization can be associated with lameness in some horses, but can also be an incidental finding.     

Myofibroblasts in the accessory ligament (distal check ligament) and the deep digital flexor tendon of foals

OBJECTIVE: To demonstrate myofibroblasts in the accessory ligament of the deep digital flexor tendon (ie, distal check ligament) and deep digital flexor tendon of clinically normal foals. SAMPLE POPULATION: Tissue specimens from 25 foals that were necropsied for reasons unrelated to this study and unrelated to musculoskeletal disease. PROCEDURE: The distal check ligament and deep digital flexor tendon of both forelimbs were examined histologically. Myofibroblasts were identified by immunohistochemical staining specific for alpha-smooth muscle actin (alpha-SMA). RESULTS: Most of the cells in the distal check ligament and deep digital flexor tendon of all foals stained positive for alpha-SMA. CONCLUSION AND CLINICAL RELEVANCE: Myofibroblasts made up most of the cells in the distal check ligament and deep digital flexor tendon of clinically normal foals. These cells have contractile ability and therefore, may play a role in flexure contracture of these tendons. The ability of tetracycline to chelate calcium or decrease the expression of the contractile protein alpha-smooth muscle actin could inhibit the myofibroblasts' ability to contract, thus providing a rationale for tetracycline administration as a treatment of distal interphalangeal joint flexor deformity in foals.     

MAGNETIC RESONANCE IMAGING FEATURES OF PROXIMAL METACARPAL AND METATARSAL INJURIES IN THE HORSE

Magnetic resonance (MR) imaging abnormalities in horses with lameness localized to the proximal metacarpal or metatarsal region have not been described. To accomplish that, the medical records of 45 horses evaluated with MR imaging that had lameness localized to either the proximal metacarpal or metatarsal region were reviewed. Abnormalities observed in the proximal suspensory ligament or the accessory ligament of the deep digital flexor tendon included abnormal high signal, enlargement, or alteration in shape. Twenty-three horses had proximal suspensory ligament desmitis (13 hindlimb, 10 forelimb). Sixteen horses had desmitis of the accessory ligament of the deep digital flexor tendon. One horse had desmitis of the proximal suspensory ligament and the accessory ligament of the deep digital flexor tendon on the same limb and one horse had desmitis of the proximal suspensory ligament on one forelimb and desmitis of the accessory ligament of the deep digital flexor tendon on the other forelimb. Four horses did not have abnormalities in the proximal suspensory ligament or accessory ligament of the deep digital flexor tendon. Eighty percent of horses with forelimb proximal suspensory ligament desmitis and 69% of horses with hindlimb proximal suspensory ligament desmitis returned to their intended use. Sixty-three percent of horses with desmitis of the accessory ligament of the deep digital flexor tendon were able to return to their intended use. MR imaging is a valuable diagnostic modality that allows diagnosis of injury in horses with lameness localized to the proximal metacarpal and metatarsal regions. The ability to accurately diagnose the source of lameness is important in selecting treatment that will maximize the chance to return to performance.     

Kinetics and kinematics of the equine hind limb: in vivo tendon strain and joint kinematics

Strains of the suspensory ligament and deep digital flexor, superficial digital flexor, and long digital extensor tendons in the equine (pony) hind limb were recorded in vivo, using implanted strain gauges consisting of silicone rubber tubes filled with mercury. The relationship between strain gauge signals and tendon strains was obtained from tension-strain tests performed on isolated tendons after death of the ponies. During normal walking, maximal tendon strain (elongation over initial length, relative to the length of the structures at first ground contact) was 3.1% in the suspensory ligament and 3.4%, 2.3%, and 0.3% in the deep digital flexor, the superficial digital flexor, and the long digital extensor tendons, respectively. Changes (that occurred during walking) in the distance from origin to insertion of these musculotendinous structures were computed from limb geometric configuration and limb conformation. Maximal increase in origin to insertion length was 3.1% in the suspensory ligament and 2%, 1.6%, and 1.5% in the deep digital flexor, superficial digital flexor, and long digital extensor musculotendinous structures, respectively. The differences in strain, comparing the entire musculotendinous structure and its tendon, were explained by muscular contraction or relaxation.     

Dorsal subluxation of the proximal interphalangeal joint in the pelvic limb of three horses

In horses, dorsal subluxation of the proximal interphalangeal joint in the pelvic limb, which realigned when weight was applied to the limb, improved following surgery. Improvement was observed, if not immediately, at least within two weeks after treatment. The severity and duration of the condition appear to be important considerations in predicting the time necessary for resolution of the condition following surgery. Treatment consisted of surgical resection of a small segment of the medial head of the deep digital flexor tendon in the pelvic limb. The section removed was positioned distal to the tarsus, at the level prior to the tendon joining the main portion of the deep digital flexor tendon. Previously, a surgical treatment was described in which a portion of the accessory ligament (distal check ligament) of the deep digital flexor muscle was resected. Because the medial head is much stronger than the accessory ligament, resection of the tendon of the medial head provides more release of tension to allow stretching of the deep digital flexor muscle tendon.     

Kinetics and kinematics of the equine hind limb: in vivo tendon loads and force plate measurements in ponies

Loads on the suspensory ligament, deep digital flexor tendon, superficial digital flexor tendon, and long digital extensor tendon of the equine hind limb were determined in ponies by use of implanted strain gauges consisting of silicone rubber tubes filled with mercury. Recordings were made simultaneously with force plate measurements and high-speed film recordings while the ponies were walking. The relationship between strain gauge signals and tendon loads was obtained from tension-strain tests performed after death of the ponies. The suspensory ligament and the 2 digital flexor tendons were loaded during the stance phase, and the extensor tendon was loaded mainly during the swing phase. The loading pattern of the suspensory ligament, with peak loads of 4.6 N/kg of body weight, correlated well with the vertical component of the ground reaction force. Maximal loading of the deep digital flexor tendon was observed during the second half of the stance phase, with peak values of 6.7 N/kg. The superficial digital flexor tendon was loaded maximally at the beginning of the stance phase, with a peak load of 4.1 N/kg, and the long digital extensor tendon was loaded maximally during the swing phase, with a peak load of 0.3 N/kg. Recordings made from this procedure for calibration of the strain gauge signals to tendon load and tendon strain, in combination with the force plate measurements, enabled verification of the results by torque analysis of the lower portion of the hind limb, using the vector of the ground reaction force, limb conformation, and limb geometric configuration. Torque analysis of the lower extremity indicated that the determined tendon loads were in agreement with the recorded ground reaction forces.     

Identification of surgically-induced longitudinal lesions of the equine deep digital flexor tendon in the digital flexor tendon sheath using contrast-enhanced ultrasonography: an ex-vivo pilot study

Background

Longitudinal tears in the lateral aspect of the deep digital flexor tendon are the most common causes of pain localised to the equine digital flexor tendon sheath. However conventional ultrasonographic techniques provide limited information about acute lesions. Ultrasonographic contrast agents are newly developed materials that have contributed to advancement in human diagnostic imaging. They are currently approved for intravenous use in human and animal models. In this study we described intrathecal use in the horse. This study was undertaken to evaluate the reliability of standard and angle contrast-enhanced ultrasonography to detect and characterize surgically-induced longitudinal lesions in the deep digital flexor tendons.In this pilot study surgically-induced lesions were created in the lateral aspect of the deep digital flexor tendon within the digital flexor tendon sheath in 10 isolated equine limbs to generate a replicable model for naturally occurring lesions. Another 10 specimens were sham operated. All the limbs were examined ultrasonographically before and shortly after the intrasynovial injection of an ultrasound contrast agent containing stabilised microbubbles. The images were blindly evaluated to detect the ability to identify surgically-created lesions. The deep digital flexor tendons were dissected and a series of slices were obtained. The depth of longitudinal defects identified with contrast-enhanced ultrasound scans was compared to the real extent of the lesions measured in the corresponding gross tendon sections.

Results

Contrast-enhanced ultrasonography with both angle and standard approach provided a significant higher proportion of correct diagnoses compared to standard and angle contrast ultrasonography (p < 0.01). Contrast-enhanced ultrasonography reliably estimated the depth of surgically-induced longitudinal lesions in the deep digital flexor tendons.

Conclusion

Contrast-enhanced ultrasound of the digital flexor tendon sheath could be an effective tool to detect intrasynovial longitudinal tears of the deep digital flexor tendon, although an in vivo study is required to confirm these results for naturally occurring lesions.     

EVALUATION OF THE EQUINE DIGITAL FLEXOR TENDON SHEATH USING DIAGNOSTIC ULTRASOUND AND CONTRAST RADIOGRAPHY

This study was designed to evaluate the normal anatomy of the digital flexor tendon sheath using contrast radiography and diagnostic ultrasound. Iodinated contrast medium was injected into eight cadaver limbs and the limbs immediately frozen. Lateromedial and dorsopalmar/plantar radiographs were made. These limps were then cut transversely and proximal to distal radiographs of each slab were made. This cross sectional contrast methodology allowed the visualization of the relative size and shape of the superficial and deep digital flexor tendons as well as the potential space taken by effusions of the digital flexor tendon sheath.
The second part of the study used twelve live animals with normal digital flexor tendon sheaths. Ultrasonographic measurement of the structures of the digital flexor tendon sheath at each level were compiled. This documented the ability of diagnostic ultrasound to image: 1) the superficial and deep digital flexor tendons, 2) the proximal and distal ring of the manica flexoria , 3) the straight and oblique sesamoidean ligaments, and 4) the mesotendinous attachments to the superficial and deep flexor tendons. Iodinated contrast medium was then injected into the digital flexor tendon sheath and the ultrasonography repeated. These images were compared with those obtained from contrast radiography and prosections of twenty normal limbs. The iodinated contrast medium enhanced sonographic imaging of the structures of the digital tendon sheath, particularly the abaxial borders of the superficial digital flexor tendon branches and the mesotendinous attachments to the superficial and deep digital flexor tendons.     

Minimally invasive desmotomy of the accessory ligament of the deep digital flexor tendon in horses

This retrospective study describes ultrasound guided desmotomy of the accessory ligament of the deep digital flexor tendon in 35 cases, and a modification of this procedure using an adapted surgical instrument. The procedure was successful in 97% of cases. Wound healing was excellent in all except 4 cases. Corrective shoeing prior to surgery contributes to success. The procedure can be performed on the standing horse and offers the advantages of minimally invasive surgery which include: reduced incision length, reduced morbidity and improved cosmetic outcome. The adapted surgical instrument can be an alternative to isolate the ligament under ultrasound guidance.     

Tenoscopic Anatomy of the Equine Carpal Flexor Synovial Sheath

Objective —To describe the tenoscopic anatomy of the carpal sheath of the flexor tendons (carpal sheath) viewed from a lateral approach.
Study Design —Tenoscopic observation of structures within the carpal sheath subsequently confirmed by dissection.
Animals or Sample Population—12 equine cadaveric forelimbs.
Methods —The limbs were positioned lateral side up with the carpus slightly flexed. After distention of the carpal sheath, a portal for the arthroscope was made approximately 3 cm proximal to the distal radial physis and 2.5 cm caudal to the radius between the tendons of the ulnaris lateralis and lateral digital extensor muscles.
Results —A lateral tenoscopic approach was adequate to identify all structures within the carpal sheath. From proximal to distal, structures identified using this approach were the radial head of the deep digital flexor muscle, accessory ligament of the tendon of the superficial digital flexor muscle, distal radial physis, tendons of the superficial and deep digital flexor muscles, accessory carpal bone, antebrachiocarpal and middle carpal joints, and vincula of the tendon of the deep digital flexor muscle.
Conclusions —A lateral tenoscopic approach offered an easy, repeatable entry into the carpal sheath and allowed good observation of all structures within the sheath except for the medial borders of the tendons of the deep and superficial digital flexor muscles.
Clinical Relevance —Applications of a lateral tenoscopic approach to the carpal sheath include diagnostic procedures, lavage and synovial resection for septic tenosynovitis, desmotomy of the accessory ligament of the tendon of the superficial digital flexor muscle for flexural deformity or tendinitis, and removal of osteochondromas from the distal radial metaphysis.     

Evaluation of a tenoscopic approach for desmotomy of the accessory ligament of the deep digital flexor tendon in horses

Objective: To develop a tenoscopic approach for desmotomy of the accessory ligament of the deep digital flexor tendon (AL‐DDFT) in horses. Study Design: Experimental. Animals: Cadaveric forelimbs (n=10) and 4 forelimbs from 2 horses anesthetized for terminal teaching procedures, and 12 forelimbs of 6 experimental horses. Methods: Saline distention of the carpal flexor sheath facilitated insertion of an arthroscope into the distal medial aspect of the sheath between the AL‐DDFT and deep digital flexor tendon (DDFT). Location of an instrument portal on the lateral aspect of the metacarpus was identified with a needle. The lateral aspect of the AL‐DDFT was transected and the arthroscope and instrument were switched to transect the remaining fibers on the medial aspect. Cadaveric specimens were dissected for evaluation. Experimental horses were monitored for 30 days postoperatively. Results: Minor complications including incomplete division of the AL‐DDFT and shallow incision into the suspensory ligament were observed in some cadaver specimens. The AL‐DDFT was completely transected in all experimental horses with no suspensory ligament damage. Mean±SD surgical time (incision to skin closure) was 28.3±11.8 minutes. On ultrasonographic examination, transection of the AL‐DDFT was complete in all experimental horses. Minor DDFT fiber disruption was noted in 1 limb during ultrasound examination at day 30. Conclusions: A tenoscopic approach through the carpal flexor sheath provided adequate access for desmotomy of the AL‐DDFT.     

Ultrasonographic Evaluation of the Distal Extremity

Despite the increasing use of magnetic resonance imaging (MRI), ultrasound remains a valuable tool to diagnose injuries that cause distal extremity lameness in the horse. The key to a successful examination is a strong knowledge of anatomy in combination with proper ultrasonographic technique and the patience and dedication to learn these skills. Similar to all imaging modalities, it is equally important to recognize and consider the limitations of ultrasound in this region so that findings can be interpreted appropriately. Ultrasound can be used to diagnose injuries to the deep digital flexor tendon (DDFT), straight distal sesamoidean ligament and branches of the superficial digital flexor tendon using standard pastern ultrasonographic technique. The addition of newer techniques to image the DDFT at the level of P2, the navicular bursa and the collateral sesamoidean ligament can enhance the diagnostic utility of ultrasound in horses with distal extremity lameness. Although visibility is limited, ultrasound can be used to diagnose collateral ligament injuries of the coffin joint in many affected horses. Transcuneal imaging may be useful in some horses to detect abnormalities of the distal sesamoidean impar ligament and navicular bone, but evaluation of the DDFT is limited. Ultrasound should be considered in all horses with distal extremity lameness, regardless of the ability to perform advanced imaging procedures. Information gained is often complementary to other imaging modalities and may provide the basis for recheck examination purposes.     

Acquired flexural deformity of the metacarpophalangeal joint in five horses associated with tendonous damage in the palmar metacarpus.

Five cases of acquired flexural deformity of the metacarpophalangeal joint (MCPJ) in older horses and ponies were studied. The mean age of affected horses was 14-8 years. Four deformities developed following desmitis of the accessory ligament of the deep digital flexor tendon (ALDDFT) and superficial digital flexor tendon (SDFT) and one following tendonitis of the SDFT alone. All cases were markedly lame and demonstrated variable degrees of flexural deformity. Ultrasonographic examination was performed on all cases which revealed extensive adhesion formation between the ALDDFT and SDFT and reduced cross-sectional area of the deep digital flexor tendon in each case. A variety of treatments were unsuccessfully employed to treat this condition. The prognosis for acquired flexural deformity of the MCPJ in old horses following tendonous damage in the palmar metacarpus is likely to be poor.     

Ultrasonographic examination of the distal podotrochlear apparatus of the horse: A transcuneal approach

In the diagnostic work‐up of lameness originating from the foot, ultrasonographic examination is an essential complement to radiography for the detection of soft tissue lesions of the podotrochlear apparatus (PTA). The infrasesamoidean part of the deep digital flexor tendon, distal sesamoidean ligament and distal sesamoid bone can be accurately assessed using a transcuneal approach. This paper describes the ultrasonographic technique and presents normal and abnormal ultrasound images of the infrasesamoidean part of the PTA.     

Aseptic tenosynovitis of the carpal flexor sheath caused by rupture of the accessory ligament of the deep digital flexor tendon

A mare was evaluated for acute left forelimb lameness with effusion of the carpal flexor sheath. No osseous abnormalities were noted during radiographic examination. Significant disruption of the accessory ligament of the deep digital flexor tendon was seen during ultrasonographic examination. Carpal sheath effusion and lameness resolved after medical treatment.     

Model formulation and determination of in vitro parameters of a noninvasive method to calculate flexor tendon forces in the equine forelimb

OBJECTIVE: To describe a method to calculate flexor tendon forces on the basis of inverse dynamic analysis and an in vitro model of the equine forelimb and to quantify parameters for the model. SAMPLE POPULATION: 38 forelimbs of 23 horses that each had an estimated body mass of > or = 500 kg. PROCEDURE: Longitudinal limb sections were used to determine the lines of action of the tendons. Additionally, limb and tendon loading experiments were performed to determine mechanical properties of the flexor tendons. RESULTS: The study quantified the parameters for a pulley model to describe the lines of action. Furthermore, relationships between force and strain of the flexor tendons and between fetlock joint angle and suspensory ligament strain were determined, and the ultimate strength of the tendons was measured. CONCLUSION AND CLINICAL RELEVANCE: The model enables noninvasive determination of forces in the suspensory ligament, superficial digital flexor tendon, and distal part of the deep digital flexor (DDF) tendon. In addition, it provides a noninvasive measure of loading of the accessory ligament of the DDF tendon for within-subject comparisons. However, before application, the method should be validated. The model could become an important tool for use in research of the cause, prevention, and treatment of tendon injuries in horses.     

CHARACTERIZATION OF THE MAGIC ANGLE EFFECT IN THE EQUINE DEEP DIGITAL FLEXOR TENDON USING A LOW-FIELD MAGNETIC RESONANCE SYSTEM

Three isolated equine limbs were imaged with a low-field magnetic resonance system with a vertical magnetic field. Each limb was scanned in multiple positions with mild variation of the angle between the magnetic field and the long axis of the limb. When the long axis of the limb was not perpendicular to the magnetic field, a linear hyperintense signal was present at the palmar aspect of one of the deep digital flexor tendon lobes, at the level of the navicular bone and collateral sesamoidean ligaments, in proton density and T1-weighted pulse sequences. With increased angulation of the limb, the palmar hyperintense signal extended farther distally and proximally and additional signal hyperintensity was present at the dorsal aspect of the distal part of the other lobe of the deep digital flexor tendon. Increased signal intensity was also present in the collateral ligament of the distal interphalangeal joint on the same side as the palmar hyperintense signal in the tendon. The changes in the deep digital flexor tendon are due to the specific orientation of fibers at the palmar and dorsal aspect of the tendon, which is responsible for focal manifestation of the magic angle effect. Careful positioning of the limb perpendicular to the magnetic field can prevent this phenomenon. The association of palmar increased signal intensity in the deep digital flexor tendon with increased signal in the collateral ligament of the distal interphalangeal joint on the same side should be recognized as manifestations of the magic angle effect.     

USE OF CONTRAST-ENHANCED COMPUTED TOMOGRAPHY TO ASSESS ANGIOGENESIS IN DEEP DIGITAL FLEXOR TENDONOPATHY IN A HORSE

We compared contrast-enhanced computed tomography (CT) and high field magnetic resonance (MR) imaging in a horse with deep digital flexor tendonopathy. Lesions in the distal extremity were documented grossly and histopathologically. In contrast-enhanced CT, the deep digital flexor tendon lesions were markedly contrast enhancing with evidence of angiogenesis in the core and dorsal border lesions. The lesion morphology was clearly delineated on MR imaging, but without contrast media angiogenesis cannot be identified. Gross examination, histopathologic examination, and CD31 immunohistochemistry confirmed the tendonopathy and an increased presence of small blood vessels. In this horse, deep digital flexor tendon lesions appeared similarly on contrast-enhanced CT and MR imaging. Contrast-enhanced CT may be an alternative to MR imaging for assessing tendon and ligament injury in the digit of the horse.