34th Annual Scientific Meeting proceedings

Surgical challenges of Poll Evil and fistulous withers
The cranial and caudal nuchal and supraspinous bursae are all closely related to het funicular part of the nuchal ligament and respectively C1 (atlas), C2 (axis) and the highest spinous processes of the first cranial thoracic vertebrae.^1,2,4,7,13 The congenital presence of some bursae is not completely clear. The supraspinous bursa is reported to be consistently present, but the presence of the cranial and caudal nuchal bursae vary. Some state that the cranial nuchal bursa is present in every horse, but others dispute this. There is more agreement on facultative presence of the caudal nuchal bursa in literature.^{1,2,4,7,9,10,12,13}

Except for the anatomical region, the clinical presentation of a bursitis of the cranial and caudal bursae is quite comparable. It starts generally with an asymmetric swelling which can be painful on palpation and can decrease range of movement (ROM) of the neck. In general, a cranial nuchal bursitis is more frequently encountered than a bursitis of the caudal nuchal bursa.^2,4,7 In most of the cases the skin is intact and no fistula is visible in contrast to patients with a supraspinous bursitis. The amount of swelling in these nuchal bursitis cases does not resemble the clinical impairment of neck ROM of a patient. So horses with minor swelling can show clear symptoms of decreased movement and pain and others with clear swelling do not show any or minor symptoms, irrespective of the time the swelling occurred.² The degree of pain and swelling can be used to differentiate between an acute or a chronic bursitis but still there is a lot of variation possible. Besides the mentioned symptoms of neck stiffness and an extended neck, head shaking, reluctance to work were also observed in these bursitis cases.^2,4,7 With diagnostic imaging similar impressions can be noted when these bursae are examined, i.e., the severity of radiographic or ultrasonographic findings do not go hand in hand with clinical symptoms.^2,4,7 Advanced imaging methods as CT and MRI do give a more complete view of the diseased area, and could also be very helpful in the therapeutic approach.^2,4,7

An acute bursitis of the supraspinous bursa can initially go unnoticed because of the less clearer clinical signs of the deeper localized bursa which is covered by several muscles. Patients are more often presented with a fistula i.e., the chronic stage.^9,10,12

The exact pathogenesis for all these three bursitis is still not completely understood.^{2,4, 9,10,11,12,14} Historically, Brucella spp. were mentioned in several bursitis reports and everybody should be aware that brucellosis is a zoonosis.^{2,3,7,9,10,11,12,14} There are large differences between publications regarding Brucella spp. because of the geographical presence/ absence of Brucellosis all around the world. It is important to realize that for equines a Brucella test has not been validated yet and therefore results need to be interpreted carefully.⁵ Besides Brucella spp. several other pathogens can be cultured, but also here it should be noted that cultures can be negative even if there is a fistulous tract.^{2,4,5,7,10,11,12}

For the cranial and caudal bursa Onchocerca spp. and trauma have also been mentioned. Trauma due to tack is reported.^1,7 In vivo research did also show that a hyperflexed head-neck position compared to normal position increased pressure at the level of cranial and caudal nuchal bursa, 4 to 3 times respectively.⁶ The assumption of a clinical relation between hyperflexion and bursitis has not been proven yet.⁶

In cases with a supraspinous bursitis/ fistulous withers the harvesting of representative culture can be even more challenging. Is not advised to sample from  the fistulous tract. Besides Brucella spp. several other pathogens have also been described in literature. ^9,10,12 Also trauma has been reported frequently as a cause for this type of bursitis. Especially in working horses tack that doesn’t fit properly can result in severe damage.^9,10,12

Treatment of choice in nonseptic cranial and caudal nuchal bursitis is bursoscopy and debridement.^2,7 Bursoscopy of bursae that were treated medically first seem to have a poorer outcome.² In fistulous bursae complete resection of the diseased tissue with second intention wound healing has been reported to be successfully.⁴ For both surgical treatments additional surgeries can be necessary to resolve the problem completely. Medical treatment of both representations seems not to resolve these problems.

In cases with supraspinous bursitis/ fistulous withers complete resection of all diseased tissue (soft and bony tissues) with drainage ventrally of the rhomboideus muscle together with preservation of the dorsoscapular ligament are important for success.^8,9,12 Unfortunately, even when these steps are followed some horses require additional surgical interventions. This surgery is preferred in the standing patient so both sides can be approached easily, optimal ventral drainage can be achieved. And because the patient is standing the dorsoscapular ligament is under tension and can be preserved more easily.^8,12 

Conclusion
Surgery is the best option in cases with a cranial, caudal or supraspinous bursitis.  ‘Early’ bursoscopic debridement of nonseptic cranial and caudal bursitis was most successful compared to medication only or bursae that were medicated earlier before a bursoscopy was performed. Cases with a fistula/ septic cranial bursitis can be successful resected completely without recurrence. In cases with a fistulous withers complete resection in the standing horses is advised so an adequate ventral drainage can be achieved together with the preservation of the dorsoscapular ligament. Recurrence has to be anticipated, because in all these bursitis cases this is a recognized and often reported complication.

References

1. Abuja, et al. The cranial nuchal bursa: Anatomy, ultrasonography, magnetic resonance imaging and endoscopic approach, EVJ, 46, 2014
2. Bergren, et al. Diagnosis, treatment and outcome of cranial nuchal bursitis in 30 horses, EVJ, 50, 2018
3. Cárdenas, et al. Characterization and evolution of countries affected by bovine brucellosis (1996-2014), Transboundary and Emerging Diseases, 66, 2019
4. Corraretti, et al. Treatment of fistulous cranial nuchal bursitis by complete surgical resection in two horses, EVE, 35, 2023
5. Dorneles, et al. Equine Brucellosis: Current understanding and challenges. J Eq Vet Science, 127, 2023
6. Dippel, et al. An equine cadaver study investigating the relationship between cervical flexion, nuchal ligament elongation and pressure at the first and second cervical vertebra. Vet Jour, 252, 2019
7. Garcia-López, et al. Diagnosis and management of cranial and caudal nuchal bursitis in four horses. JAVMA, 237, 2010
8. Garrett. Anatomy of the dorsoscapular ligament of horses, JAVMA, 196, 1990
9. Gaughan, et al. Fistulous withers in horses: 14 cases (1978-1987), JAVMA, 193, 1988
10. Guard. Fistula of the withers, North Am Vet, 13, 1932
11. Guarin, et al. Case report: nuchal bursitis associated with Borrelia burgdorferi infection in a horse. Frontiers Vet Science, 8, 2021
12. Hawkins and Fessler. Treatment of supraspinous bursitis by the use of debridement in standing horses: 10 cases (1968-1999), JAVMA, 217, 2000
13. Sisson. Equine Syndesmology, In Getty, R (Ed.) Sisson and Grossman’s The Anatomy of the Domestic Animals 5^th edition
14. Schramme and Schumacher. Management of bursitis. In Auer and Stick (Ed.) Equine Surgery 5^th edition