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Changes in the dimension of the suspensory apparatus are used to diagnose pathological changes and to evaluate the process of healing since pathological changes, in shape and structure, cannot always reliably be differentiated from normal findings. The individually very differing amount of muscle fibres in the origin and body of the suspensory ligament causes an ultrasonographic image with very variable echogenicity. Also, anastomoses, overlaying tendons and ligaments cause artifacts in all parts of the suspensory apparatus except in the oblique sesamoidean ligament.
The purpose of this study was to investigate the precision of ultrasonographic measurements of the origin, body and branches of the suspensory ligament and of the straight and oblique distal sesamoidean ligaments in equine fore- and hindlimbs. In addition, in the origin of the suspensory ligament different techniques for dimensional measurement were evaluated.
14 sound horses (six Standardbreds, six Arabian mix breeds, one Warmblood and one Quarter horse) in age between 5 - 28 years underwent ultrasonographic examination of all four limbs by two operators. Longitudinal and transverse ultrasonographic images, acquired with a linear probe (12 MHz), were used to measure depth, width, circumference and crosssectional area at locations determined by anatomical features. In the origin of the suspensory ligament additionally a microconvex probe (8 MHz) was used. Also, in the origin of the suspensory ligament in the forelimbs with flexed limb position additional images were acquired using a linear and a microconvex probe. Two operators examined each animal sonographically twice with an interval of at least one day. The scans were saved and measured in the scanners archive. Inter- and intraoperator variability was evaluated using agreement indices and 95% limits of agreement (Bland und Altmann, 1986).
Measurements in the longitudinal image at the origin and the branches of the suspensory ligament were the more reliable of the measurements. In the transverse image the measurement of the circumference from the suspensory ligaments branches and the straight sesamoidean ligament in the distal pastern can also be considered reliable. All measurements of the suspensory ligament body and the oblique sesamoidean ligaments had low reliability.
The reliability of measurements of the size of the suspensory apparatus should be considered when making clinical judgements from ultrasonographic images.