Diagnostic imaging of the equine tarsal region using radiography and ultrasonography. Part 2: Bony disorders

Ultrasonography of the normal donkey tarsus (equus asinus)

Tarsal joint illness is a frequent source of hind limb lameness due to the complex anatomy of the region and the presence of numerous bony and soft tissue structures. Proper lameness diagnosis aims to discover the structure provoking lameness. Ultrasonography documents valuable information of soft tissues and characterizes soft tissue injuries that have heretofore been difficult to obtain either noninvasively or via radiography. The objectives of the current study were to develop and describe a standardized ultrasonographic protocol for investigation of the tarsal region in donkeys. The donkey tarsal anatomy was investigated in 5 cadavers and the tarsi of 11 healthy lameness free adult donkeys were echographically investigated. The dorsal, plantar, lateral and medial aspects of the tarsal region were substantially evaluated at four anatomical landmarks in both the longitudinal and horizontal planes using a multi-frequency 5-12 MHz linear transducer. Sonoanatomy of the extensor and flexor tarsal tendons, collateral and plantar ligaments, and synovial pouches was delineated and described. Systematic echography of the tarsal region allowed accurate localization and thorough exploration of various soft tissues of clinical interest in the donkey tarsus. Sonograms provided in this study should serve as a reference database for tarsal ultrasonography in clinical circumstances.

Impact of periarticular osteophytes of the distal tarsus diagnosed in nonlame yearling Standardbred horses on racing performance

OBJECTIVE

The aim of this study was to identify the radiographic prevalence of periarticular osteophytes of the distal tarsus in nonlame yearling Standardbred horses, and to evaluate its potential impact on race performance.

STUDY DESIGN

Cross-sectional cohort study.

ANIMALS

Client-owned yearling Standardbred horses (n = 416).

METHODS

Bilateral tarsal radiographs were available from all horses for review. Osteophytes were measured on radiographs using clinical visualization software and categorized by size. Racing records were obtained from the United States Trotting Association. Regression analysis was used to determine associations between presence or size of periarticular osteophytes and performance parameters with sex and gait covariates.

RESULTS

Of 416 Standardbred yearlings without clinical lameness, 113 (27.1%) had distal tarsal periarticular osteophytes. Regression analyses revealed few associations between the presence of periarticular osteophytes and performance parameters. Affected horses had fewer starts at 4 years of age (incident rate ratio [IRR] 0.92, p = .01) and fewer lifetime starts (IRR 0.95, p = .003), but the effect size was small. Within the affected group, osteophyte size was only associated with number of starts at 3 (IRR 0.67, p < .0001). Sex and gait affected many performance parameters.

CONCLUSION

The prevalence of distal tarsal periarticular osteophytes was similar to that in other breeds. Periarticular osteophytes of the distal tarsus appeared to be a largely incidental finding in nonlame yearling Standardbreds intended for harness racing.

CLINICAL SIGNIFICANCE

Distal tarsal periarticular osteophytes in young, nonlame Standardbred horses should affect racing potential only minimally. This is in contrast to reports from other disciplines.

Radiographic anatomy of the equine distal tibia

The radiographic anatomy of the equine distal tibia is complex and is not widely described in the current literature. Superimposition and radiographic similarities between the different osseous structures of the equine distal tibia can make it difficult for anatomic localization of pathology. The purpose of this prospective, descriptive, anatomic study was to detail the normal anatomy of the equine distal tibia using routine radiographic projections and CT of the equine tarsus. Radiographic identification of the different osseous protuberances of the distal tibia on three cadaveric limbs was achieved using radiopaque markers and evaluation of multiplanar and 3D CT reconstructions to create anatomical maps. It was found that the lateral malleolus is composed of cranial and caudal protuberances that are superimposed over the intermediate cochlear ridge of the distal tibia on the lateromedial, dorsal 45° lateral-plantaromedial, and dorsal 65° medial-plantarolateral oblique views, thereby hindering visualization of the cranial protuberance of the lateral malleolus. The medial malleolus is a simple rounded protuberance with discrete margins. On the dorsal 65° medial-plantarolateral oblique, the medial malleolus is ill-defined due to superimposition with the talus. The intermediate cochlear ridge of the distal tibia extends in a craniolateral to caudomedial direction, with its cranial protuberance largely superimposed with the calcaneus and talus on the dorsoplantar view. In summary, the distal tibial anatomy is complex and a thorough anatomical reference is necessary when reviewing radiographs of the equine tarsus for pathology. A plantaro 15° distal 85° lateral-dorsoproximomedial oblique projection is proposed to isolate all distal tibial protuberances.

Radiographic method for evaluation of tarsus morphometry

The equine tarsus is the most common area of the hind limb associated with lameness. Tarsal function is probably directly related to its conformation. Previous conformational measurement methods and radiological data are either limited or too specific to explain the complex tarsus conformation in different loading conditions. This study aimed to develop a consistent method to evaluate equine tarsal conformation from lateromedial radiographs. Twenty cadaveric hind limbs from 15 adult horses of different breeds were cut at the distal one third of the tibia. Hind limbs mounted in a loading rig and positioned with the metatarsus vertical were digitally radiographed. The zero-degree lateromedial (ZLM) was defined by vertical and horizontal landmarks including overlapping of the lateral and medial trochlea of the talus and a contact point between the dorsal edges of lateral and medial borders of the distal central tarsal bone. Radiographs missing these features were retaken to achieve consistent ZLM views. Specific radiographic features were selected as landmarks to develop tarsal parameters based on their clarity and their being consistently identifiable. The intra-rater repeatability of ten measurable morphometric parameters was evaluated with each radiograph measured twice with an interval of at least one month and Bland-Altman plots developed from this data. Repeat measurements did not differ significantly (Intraclass correlation coefficients (ICC) ranged from 0.731-0.966). This study provides a base for evaluation of the tarsal conformation by radiography.

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.

Arthroscopically accessible anatomy of the tarsal collateral ligaments in the horse

OBJECTIVE

To describe the arthroscopically accessible anatomy of the tarsal collateral ligaments in the horse.

STUDY DESIGN

Descriptive study.

ANIMALS

Cadaveric equine hind limbs (n = 24) obtained from horses without tarsal disease.

METHODS

Two pairs of tarsal joints were used to obtain silicone models of the tarsocrural joint and dissect the tarsal collateral ligaments (CLs). Ten pairs of tarsocrural joints had arthroscopic exploration and the accessible parts of the tarsal CLs were marked with an arthroscopic hook knife. Subsequently, the limbs were dissected and the marked positions were allocated to the specific parts of the CLs.

RESULTS

Ipsilateral arthroscope and instrument portals were used in each pouch of the tarsocrural joint. Via the plantaromedial pouch, the superficial (2/20 limbs), middle (7), deep (6) or both middle and deep (3) short medial CL and the long medial CL (14) were reached. Access via the plantarolateral pouch allowed manipulation of the deep short lateral CL (20/20 limbs) and the long lateral CL (20). Dorsally, arthroscopy via the dorsomedial pouch gave access to the deep short medial CL (20/20 limbs), while the superficial (9) or middle (10) or both superficial and middle (1) short lateral CL could be reached via the dorsolateral joint recess.

CONCLUSIONS

Limited parts of the tarsal CLs can be observed or manipulated arthroscopically in normal equine tarsocrural joints.