ULTRASONOGRAPHIC EVALUATION OF TARSOCRURAL JOINT CARTILAGE IN NORMAL ADULT HORSES

Ultrasonographic examination of the tarsus was performed on four clinically and radiographically normal limbs of adult horses. Particular attention was paid to the articular cartilage surfaces of the trochlear ridges of the talus and the distal intermediate ridge of the tibia. Two separate measurements of articular cartilage thickness were acquired from a longitudinal view at each site. Anatomy was confirmed with post mortem dissection. Ultrasonography was found to be a practical method for imaging the articular cartilage over the trochlear ridges of the talus and distal intermediate ridge of the tibia. The cartilage appeared as a hypoechoic band overlying the hyperechoic subchondral bone. The mean cartilage thickness over the lateral and medial trochlear ridges of the talus and the distal intermediate ridge of the tibia were 0.57 mm, 0.58 mm and 0.7 mm respectively. These measurements may have value for comparison to thickened cartilage and lesions of osteochondrosis and abnormally thinned cartilage of osteoarthritis. Ultrasound examination was not helpful in evaluating the proximal and distal intertarsal and tarsometatarsal joints, the close proximity of the articular surfaces obscured visualization of the articular cartilage.     

Comparison of radiography and ultrasonography to detect osteochondrosis lesions in the tarsocrural joint: A prospective study

Reasons for performing study: Lesions located on the medial malleolus of the tarsocrural joint can be difficult to image radiographically. Ultrasonography allows evaluation of articular cartilage and subchondral bone. Objectives: To compare dorso30° lateral‐plantaromedial‐oblique (DL‐PlMO) and dorso45° views to detect lesions on the medial malleolus, to validate the use of ultrasonography to show lesions in the tarsocrural joint and to compare its sensitivity to radiography. Methods: Tarsocrural joints (n = 111) with osteochondrosis were evaluated ultrasonographically and radiographically prior to arthroscopic lesion debridement. A complete radiographic examination was made and the best view to detect each lesion recorded. Longitudinal and transverse ultrasonography of the dorsal aspect of the joint was performed and the best scan plane to image each lesion recorded. Results: There were 94 joints with lesions on the distal intermediate ridge of tibia, 24 with lesions on the medial malleolus, and 4 with lesions on the lateral trochlear ridge. The sensitivity of radiography to detect lesions on the medial malleolus and distal intermediate ridge of tibia was 71 and 96%, respectively. Eighty‐two percent of lesions on the medial malleolus were better imaged on dorso30° view. The sensitivity of ultrasonography to detect lesions on the medial malleolus and distal intermediate ridge of tibia was 83 and 98%, respectively. Ultrasonography was significantly more sensitive than radiography to detect lesions on the medial malleolus and distal intermediate ridge of tibia. Conclusion: Dorso30° lateral‐plantaromedial‐oblique view was the best to image lesions on the medial malleolus. Ultrasonography was a valuable diagnostic tool to diagnose lesions in the tarsocrural joint and was more sensitive than radiography for lesions located on the medial malleolus and distal intermediate ridge of tibia. Clinical relevance: Radiographic examination should include a dorso30° view for detection of lesions on the medial malleolus and ultrasonography should be considered to diagnose osteochondrosis in the tarsocrural joints.     

Arthroscopic removal of fractures of the lateral malleolus of the tibia in the tarsocrural joint: A retrospective study of 13 cases

There is limited information on the treatment of lateral malleolus (LM) fractures in the horse, with no previously published case series for the outcome following arthroscopic removal of such fractures. This report reviews and evaluates findings of a retrospective study of 13 horses admitted to a private equine referral hospital over a 10 year period (1999–2009) that underwent arthroscopic removal of fractures of the LM. Hospital records were reviewed and details including patient history, aetiology of the fracture and limb affected, results of all diagnostic tests and surgical reports were documented. Performance information concerning Thoroughbred horses that went onto race post operatively was collected using an online database. Owners and trainers were contacted regarding the return to performance for non‐Thoroughbred cases or those that did not go onto race post operatively. Of the 13 horses presented, 12 were Thoroughbreds, 9 of which were National Hunt racehorses and 3 were Flat racehorses. The other horse in the study was used for general purpose riding. All cases presented with an acute unilateral fracture. Eleven of the 13 had >6 months post operative follow‐up and all were nonlame. Of the 12 Thoroughbreds, 10 have raced again, a total of 104 times (median 5 times). The median time from surgery to return to racing was 241 days (180–366 days). It is concluded that horses with fractures of the LM have an excellent prognosis for return to full athletic performance following arthroscopic debridement; and that arthroscopic fragment removal is an appropriate treatment method for fractures of the LM.     

Haematuria in two geldings caused by osteochondroma of the os pubis: Case reports and anatomic study of the os pubis in 41 cadaveric pelvises

Exostosis of the os pubis causing haematuria, and potentially cystorrhexis, in horses has not been described in the literature. In this study, 2 geldings that suffered from exercise‐induced haematuria caused by an osteochondroma of the os pubis, and the assessment of 41 cadaveric pubic bones are reported on. The anatomy of the os pubis is highly variable. The prevalence of exostosis in the os pubis appears to be higher in male horses. Palpation and ultrasonography of the pelvis per rectum and cystoscopy are valuable diagnostic tools. Depending on the extent of changes in the bladder wall, surgical removal of the exostosis should be considered in order to prevent cystorrhexis. In horses that present with haematuria, closer assessment of the os pubis for the presence of an exostosis is warranted.     

Clinical, radiological and ultrasonographic features, treatment and outcome in 22 horses with caudal distal radial osteochondromata

Reasons for performing study: Although a well recognised clinical entity, only small numbers of osteochondromata on the caudal distal radius have previously been published and its occurrence in young racing Thoroughbreds has not previously been reported. Identification and management of associated lesions in the deep digital flexor tendon have received scant attention in the literature. Hypothesis: Osteochondromata of the caudal distal radius occur commonly in young racing Thoroughbreds. They vary in size and location, sagittally and proximodistally, but the majority cause impingement damage to the deep digital flexor tendon. Methods: Case records and diagnostic images of horses with osteochondromata of the caudal distal radius were reviewed retrospectively and follow‐up information obtained. Results: Twenty‐five osteochondromata were identified in 22 horses, 19 of which were Thoroughbreds. All osteochondromata were metaphyseal. Twenty‐two were in the middle one‐third of the bone and laceration of the adjacent deep digital flexor tendon was identified in 21 limbs. Treatment in all cases consisted of removal of the osteochondroma with debridement of the deep digital flexor tendon when this was affected. All horses returned to work and none exhibited any evidence of recurrence. Conclusion: Osteochondromata of the caudal distal radius occur in young racing Thoroughbreds but are also identified in other horses. They have a consistent metaphyseal location and most are found in the middle one‐third of the radius. Size varies, but most cause laceration of the adjacent deep digital flexor tendon. Treatment by removal of the mass and debridement of the tendon is associated with a good prognosis. Potential relevance: Osteochondromata of the caudal distal radius are an important cause of tenosynovitis of the carpal sheath of the digital flexor tendons in young racing Thoroughbreds. When present in the most common location of the middle one‐third of the bone, they are likely to cause impingement damage to the deep digital flexor tendon. Tenoscopic surgery offers a good prognosis.     

Intra-articular stabilisation of the equine cricoarytenoid joint

Reasons for performing study: The success of laryngoplasty is limited by abduction loss in the early post operative period. Objective: To determine the efficacy of polymethylmethacrylate (PMMA) in stabilising the cricoarytenoid joint (CAJ) and reducing the force on the laryngoplasty suture. Hypothesis: Injection into the cricoarytenoid joint resists the forces produced by physiological laryngeal air flows and pressures thereby reducing the force experienced by the laryngoplasty suture. Methods: Ten cadaver larynges were collected at necropsy and PMMA was injected into one CAJ at selected random. Each larynx was subjected to physiological conditions with with constant (static) or cycling (dynamic) flow. The specimens were tested sequentially in each of 4 conditions: 1) bilateral full abduction (Control 1); 2) transection of the suture on the side without PMMA; 3) bilateral abduction achieved by replacing the suture (Control 2); and 4) cutting the suture on the PMMA side. Tracheal pressure and flow and pressure in the flow chamber were recorded using pressure and flow transducers. The strain experienced by each suture during bilateral abduction (Controls 1 and 2) was measured. Statistical comparison of the 4 conditions was performed using a mixed effect model with Tukey's post hoc test for multiple comparisons. The strain gauge data were analysed by paired comparison of the regression slopes. Results: In the static and dynamic states, tracheal pressure increased and tracheal flow decreased when the suture on the non‐cement side was cut (P<0.05). There was no significant difference in any outcome measure between PMMA injected into the CAJ and bilaterally abducted specimens (Controls 1 and 2) for either condition. The rate of increase in strain with increasing translaryngeal pressure was significantly less on the suture with PMMA placed in the CAJ (P = 0.03). Conclusions: These data provide strong evidence that injecting PMMA into the CAJ resists the collapsing effect of physiological airflows and pressures in vitro and reduces the force experienced by the laryngoplasty suture during maximal abduction. Potential relevance: Augmentation of prosthetic laryngoplasty with this technique may reduce arytenoid abduction loss in the early post operative period.     

Diagnostic analgesia of the equine digit

Analgesia usually occurs within 5 min after administration of local anaesthetic solution into joints or around nerves in the distal portion of the limb. Gait should be assessed within 10 min after diagnostic regional analgesia of the distal portion of the limb because rapid diffusion of anaesthetic solution can result in anaesthesia of other nerve branches, thus confusing results of the examination. A palmar digital nerve block (PDNB) anaesthetises most of the foot, including the distal interphalangeal (DIP) joint (coffin joint), rather than just the palmar half of the foot, as was once commonly believed. To avoid partially anaesthetising the proximal interphalangeal joint (pastern joint), the palmar digital nerves should be anaesthetised near or distal to the proximal margin of the collateral cartilages. Clinicians should be aware that an abaxial sesamoid nerve block (ASNB) may ameliorate or abolish pain within the metacarpo/metatarso‐phalangeal joint (fetlock joint). Mepivacaine administered into the DIP joint desensitises the DIP joint and probably the palmar digital nerves to also cause anaesthesia of the navicular bursa, the navicular bone, the toe region of the sole, the digital portion of the deep digital flexor tendon (DDFT) and the distal portions of the collateral ligaments of the DIP joint. When a large volume of mepivacaine HCl (e.g. 10 ml) is administered, the heel region of the sole may also be desensitised. Only a small percentage of horses with disease of the collateral ligament(s) of the DIP joint show a significant improvement in lameness after intra‐articular analgesia of the DIP joint, and no horse is likely to improve after intrabursal analgesia of the navicular bursa. A PDNB, however, improves lameness substantially in most horses that are lame because of disease of the collateral ligament(s) of the DIP joint, and all affected horses are likely to become sound after an abaxial sesamoid nerve block. The degree of improvement in lameness associated with injury to one or both collateral ligaments of the DIP joint after PDNB is determined by the extent of the injury and the level at which the palmar digital nerves are anaesthetised. The further proximal the level of the injury within the collateral ligament, the less likely that lameness is ameliorated by analgesia of the DIP joint or a PDNB. Verschooten's technique appears to be the most accurate technique for centesis of the navicular bursa. Even though analgesia of the DIP joint results in analgesia of the navicular bursa, analgesia of the navicular bursa does not result in analgesia of the DIP joint. Pain arising from the DIP joint can probably be excluded as a cause of lameness when lameness is attenuated by analgesia of the navicular bursa. Analgesia of the digital flexor tendon sheath (DFTS) is likely to desensitise only structures that are contained within or border on the sheath itself (i.e. the superficial and deep digital flexor tendons, the straight and oblique distal sesamoidean ligaments, the annular ligaments of the fetlock and pastern, and the portion of the DDFT that lies within the foot). Because lameness caused by disease of the DDFT within the foot may fail to improve appreciably after analgesia of the palmar digital nerves, the DIP joint, or the navicular bursa, a portion of the DDFT within the foot and distal to the DFTS probably receives its sensory supply from more proximal deep branches of the medial and lateral palmar digital nerves that enter the DFTS. Performing intrathecal analgesia of the DFTS on horses with lameness that is unchanged after anaesthesia of the palmar digital nerves but resolves after an ASNB, may be useful in localising lameness to that portion of the DDFT that lies within the foot. Resolution of lameness after intrathecal analgesia of the DFTS justifies suspicion of a lesion within the digital portion of the DDFT or within structures contained within the DFTS. The belief that concurrent or sequential intra‐articular administration of medication substantially increases the risk of joint infection or that inflammation caused by the local anaesthetic solution may dampen the therapeutic response to intra‐articular medication appears to be unfounded.