To describe outcomes of horses with temporohyoid osteoarthropathy (THO) treated with partial ceratohyoidectomy.
10 client-owned horses
Medical records from 2 institutions were examined for records of horses with THO treated with partial ceratohyoidectomy between 2010 and 2021. History, signalment, clinical signs, diagnostics, medications, and surgery-related details were recorded. Horses with a minimum of 6 months follow-up were recruited for neurologic and imaging examinations in the hospital or field where radiography of the basihyoid-ceratohyoid articulation were performed along with CT, when available.
10 horses with THO were included (9 unilateral; 1 bilateral). Nine planned partial ceratohyoidectomies were performed in 8 horses, whereas 2 horses had preoperatively planned complete ceratohyoidectomies transitioned to partial ceratohyoidectomies during surgery due to intraoperative complications. Postoperative complications occurred mostly in transitioned surgeries (obstructed airway, tongue mobility issues, and incisional hemorrhage), whereas only 1 horse with a planned ceratohyoidectomy had postoperative complication of rhabdomyolysis. All complications resolved before hospital discharge. Neurologic signs improved in all 10 horses, with 2 showing complete resolution. Nine horses were available for radiographic follow-up, 6 of which also had head CT scans. A space between the ceratohyoid and basihyoid bones was measurable on radiography in all 9 horses, and was confirmed on CT. Three horses demonstrated proliferation of either ceratohyoid or basihyoid bones. The 9 horses with unilateral disease returned to previous work, and the horse with bilateral disease was retired.
Partial ceratohyoidectomy is a surgical option for treatment of THO that provides similar clinical outcomes to published reports on ceratohyoidectomy.
To describe outcomes of horses with temporohyoid osteoarthropathy (THO) treated with partial ceratohyoidectomy.
10 client-owned horses
Medical records from 2 institutions were examined for records of horses with THO treated with partial ceratohyoidectomy between 2010 and 2021. History, signalment, clinical signs, diagnostics, medications, and surgery-related details were recorded. Horses with a minimum of 6 months follow-up were recruited for neurologic and imaging examinations in the hospital or field where radiography of the basihyoid-ceratohyoid articulation were performed along with CT, when available.
10 horses with THO were included (9 unilateral; 1 bilateral). Nine planned partial ceratohyoidectomies were performed in 8 horses, whereas 2 horses had preoperatively planned complete ceratohyoidectomies transitioned to partial ceratohyoidectomies during surgery due to intraoperative complications. Postoperative complications occurred mostly in transitioned surgeries (obstructed airway, tongue mobility issues, and incisional hemorrhage), whereas only 1 horse with a planned ceratohyoidectomy had postoperative complication of rhabdomyolysis. All complications resolved before hospital discharge. Neurologic signs improved in all 10 horses, with 2 showing complete resolution. Nine horses were available for radiographic follow-up, 6 of which also had head CT scans. A space between the ceratohyoid and basihyoid bones was measurable on radiography in all 9 horses, and was confirmed on CT. Three horses demonstrated proliferation of either ceratohyoid or basihyoid bones. The 9 horses with unilateral disease returned to previous work, and the horse with bilateral disease was retired.
Partial ceratohyoidectomy is a surgical option for treatment of THO that provides similar clinical outcomes to published reports on ceratohyoidectomy.
Temporohyoid osteoarthropathy (THO) is a disease affecting the temporohyoid joint (articulation of the stylohyoid and petrous temporal bone) with proposed causes including progressive otitis media and interna, nonseptic osteoarthritis, and guttural pouch infection. 1,2 Clinical signs of THO include facial nerve deficits observed as an ear droop, muzzle deviation, decreased upper eyelid function, and corneal ulceration from decreased tear production as well as vestibulocochlear nerve deficits observed by a head tilt, nystagmus, circling and ataxia. 3–6 More subtle clinical signs can include head shaking, ear rubbing, behavioral changes, and changes in ability to masticate. 2,5 In affected horses with infectious otitis media, fracture of the petrous temporal bone can result in meningoencephalitis. 2
Surgical treatment for THO has been shown to improve prognosis and increase the possibility of recovery in patients performing athletic activities when compared to medical management alone. 3,7 Three surgical procedures have been described for horses with THO, all performed on the hyoid apparatus to reduce force placed on the temporohyoid joint, therefore, lowering risk for petrous temporal bone fracture. 8–10 Partial stylohyoidostectomy involves removing a segment of stylohyoid bone and requires meticulous dissection to avoid neurovascular structures during the approach. 8 Intraoperative complications can include transection of the lingual vessels or damage to the hypoglossal nerve due to proximity of these structures to the stylohyoid bone. 8 Regrowth of the stylohyoid bone segment as early as 6 months after the surgery has been reported due to incomplete removal of the periosteum. 9 Because of this complication, ceratohyoidectomy was described by Pease et al. 9 as an alternative surgical intervention.
A ceratohyoidectomy is performed under general anesthesia, or standing sedation, and consists of disarticulating the ceratohyoid bone from the basihyoid and stylohyoid bones and removing it entirely. 9,11 Postoperative bone union is unlikely with this procedure due to exposure of cartilage at the articulation sites of the basihyoid bone and stylohyoid bone and complete removal of the ceratohyoid periosteum eliminating the scaffold for bone regrowth. 9 Regardless of anesthetic technique used, intraoperative complications can occur when disarticulating the ceratohyoid bone from the stylohyoid bone including hemorrhage from damage to lingual vessels as well as problems swallowing and masticating after injury or transection of the hypoglossal nerve. 3,7,11 An outcome of returning to previous performance, ranging from 20% (1/5) 12 to 100% (4/4) 11 and complete resolution of clinical signs ranging from 27% (4/15) 7 to 48% (12/25) 3 has been seen in horses that have undergone a ceratohyoidectomy. Because of these outcomes, this has become the preferred surgical method over partial stylohyoidostectomy.
More recently, disarticulation of the ceratohyoid bone from the basihyoid bone in 6 horses performed under standing sedation and local block was described. 10 This approach demonstrated no intraoperative or postoperative complications and reported resolution of clinical signs for 50% (3/6) of horses and return to previous or greater level of work for 80% (5/6). 10 However, follow-up time was limited and reported by owners.
Hemorrhage and iatrogenic damage to neural structures are serious intraoperative complications encountered by most of the previously described techniques. 3,7,11 The objective of the study reported here was to describe outcomes of horses with THO treated with partial ceratohyoidectomy. We hypothesized that the clinical outcome would be similar to previous reports for a ceratohyoidectomy. 3,7,11–13
Medical records from 2010 to February 2021 at the University of Minnesota and Universidad Andres Bello were searched for horses diagnosed with THO (right, left, or bilateral) based on clinical signs, radiography, CT, or guttural pouch endoscopy, alone, or in combination. Horses treated surgically were further examined with a focus on those treated with partial ceratohyoidectomy, which was defined as any procedure where only a portion of the ceratohyoid was removed. Therefore, this could include a preoperatively planned partial ceratohyoidectomy, or a procedure converted to a partial ceratohyoidectomy from a preoperatively planned complete ceratohyoidectomy during surgery due to complications during dissection. Admitting history, signalment, clinical signs, duration, diagnostics performed preoperatively, affected side, medications administered, surgical time, hospital duration, duration of medical management prior to surgery, intra- and postoperative complications, and discharge medications were obtained from records. Median and range were calculated when appropriate. After medical record review, horses treated by partial ceratohyoidectomy were only included if surgical intervention was greater than, or equal to, 6 months prior. These horses were prospectively recruited for a postoperative neurologic examination and diagnostic imaging. Postoperative examinations were performed in accordance with the University of Minnesota’s Institutional Animal Care and Use Committee with owner consent.
All patients were administered broad-spectrum antimicrobials and a non-steroidal anti-inflammatory (flunixin meglumine, 1.1 mg/kg, IV, q 12 h). The combination of antimicrobials used, and administration duration were reported in the medical record and were chosen by each clinician. If horses had medical management initiated with antimicrobials, the medications did not change for surgery (Supplementary Table S1). If there were no antimicrobials administered prior to surgery, cefazolin sodium (11 mg/kg, IV) or potassium penicillin (22,000 U/kg, IV) and gentamicin (6.6 mg/kg, IV) were administered 45 minutes prior to surgical incision and continued for a median of 3 days (range, 3 to 10 days). A tetanus toxoid vaccine was administered intramuscularly prior to surgery if it had not been administered within the last 6 months.
All partial ceratohyoidectomies were performed using the approach previously described for complete ceratohyoidectomy. 9 If the surgery was a planned partial ceratohyoidectomy the free end of the ceratohyoid bone was grasped with a towel clamp after disarticulation from the basihyoid bone using cartilage scissors. Care was taken to avoid excessive motion of the ceratohyoid bone to prevent iatrogenic trauma to the temporohyoid joint. One or 2 passes were made with bone rongeurs to remove the distal aspect of the ceratohyoid bone. The bone removed was estimated anywhere from 0.5 to 1 cm by measuring the piece or pieces on a #3 scalpel blade handle. A bone rasp was used to ensure all edges of the remaining ceratohyoid bone were smooth. Two absorbable gelatin sponges (Surgifoam) were placed over the remaining ceratohyoid bone, and the bone was released into its normal position. If the surgery was converted from a preoperatively planned complete ceratohyoidectomy to a partial ceratohyoidectomy because of complications that arose during dissection toward the ceratohyoid-stylohyoid articulation, the surgeon stopped further dissection and instead removed the distal aspect of the ceratohyoid bone after disarticulation from the basihyoid bone similar to what is described above. Prior to closure, adequate hemostasis was verified, and the surgical site was lavaged with sterile saline (0.9% NaCl) solution. The incision was closed in 3 layers with the use of 2-0 polyglecaprone suture.
Horses were discharged based on clinician assessment and were prescribed antimicrobials (trimethoprim sulfamethoxazole, 25 mg/kg, PO, q 12 h for 1 to 4 weeks) and NSAIDS (flunixin meglumine, 1.1 mg/kg, PO, q 12 h for 5 days; Supplementary Table S1). Stall rest for 4 weeks, followed by paddock rest for 4 weeks was recommended. It was recommended to have a veterinarian recheck the horse prior to turning the horse out in a paddock.
Postoperative follow-up evaluations were performed by veterinarians either in the respective hospital or in the field and included radiography of the sites of former basihyoid-ceratohyoid articulations for all surviving horses, standing CT (with sedation) of the head with focus on the hyoid apparatus for horses evaluated in a hospital, and neurologic examinations for all horses. Postoperative neurologic examinations included subjective evaluation of cranial nerves, behavior and mental status, head posture and coordination, presence of muscle atrophy, skin sensation, local cervical reflex, vertebral column movement, tail tone and perineal reflex, hearing, and analysis of gait and posture such as the presence of ataxia, paresis, hypometria, or hypermetria, alone or in combination. 14 Ataxia was graded on a scale 14 of 0 (no ataxia present) to 5 (down and unable to stand) as described by the modified Mayhew scale. Except for Horse 1, all neurologic examinations were performed by or had videos reviewed by 1 board-certified large animal internist (AWB) either in person (n = 5) or by recorded video (n = 4) where 3 examinations were performed by a large animal internal medicine resident (LH) trained under the internist and 1 performed by a large animal surgery resident (FH). The internist was asked to not reference patient records prior to the neurologic examination and their findings were described. Horse 1 died prior to review of medical records but did have a neurologic examination performed by another board-certified internist at the University of Minnesota 21 months after surgery; the clinical findings were transcribed from the medical record.
To obtain postoperative follow-up imaging, each patient was sedated with detomidine hydrochloride to effect (0.01 to 0.02 mg/kg, IV). Radiographic examinations were centered over the basihyoid bone and included a right dorsal–left ventral oblique view made 10° to 15° dorsal to the plane of interest (Rt10-15D–LeVO) for horses that had undergone right-sided partial ceratohyoidectomy and a left dorsal–right ventral oblique view made at 10° to 15° dorsal to the plane of interest (Le10-15D–RtVO) for those that had undergone left-sided partial ceratohyoidectomy. To subjectively evaluate if a space was observed between the ceratohyoid and basihyoid bone on the surgical side, radiographs were reviewed by a board-certified large animal surgeon (NE) and large animal surgical resident (ADB). Since a variable amount of bone was removed at surgery and the fact that no space is present in normal unaffected basihyoid-ceratohyoid articulations, the evaluators simply came to a consensus about whether a space was present or absent. A standing multi-slice helical CT (EQUINA by ASTO CT) scan was performed when possible. The head was imaged from nose to first articulating cervical vertebrae. CT images were reviewed, and findings were reported by a board-certified radiologist as would occur with any clinical patient that was presented to these institutions. One investigator (ADB) obtained measurements of the spaces between the ceratohyoid bones and basihyoid bones. Measurements (VuePACS v12.2.5.3000126; Phillips) were taken from the most distal aspect of the remaining ceratohyoid bone to the basihyoid bone on the lateral oblique radiograph and on sagittal plane multiplanar reconstruction (MPR) CT images.
At follow-up, owners were asked if their horse returned to its previous level of work prior to surgery and if they were satisfied with the result of the surgical procedure.
Results were reported as numbers, percentages, medians, and ranges. Calculations were made with the use of available software (Excel 16.66.1; Microsoft).
Twenty-one horses were diagnosed with THO with 11 having a partial ceratohyoidectomy, 4 managed medically, 3 having a ceratohyoidectomy, and 3 subject to euthanasia. Eleven horses had the left side affected, 8 had the right side affected, and 2 had bilateral disease. Ten of the 11 horses with a partial ceratohyoidectomy performed met the inclusion criteria where surgery was performed at least 6 months prior. These 10 horses included 7 females and 3 geldings and the following breeds: 6 American Quarter Horses, and 1 each of a Tennessee Walking Horse, Morgan Horse, Thoroughbred, and a Warmblood (Supplementary Table S2). Horses were used for jumping, roping, working cattle, barrel racing, therapeutic riding, trail riding, western pleasure, or dressage. Median age was 12.5 years (range, 5 to 23 years), and the median duration between onset of clinical signs and presentation was 14 days (range, ≤ 3 hours to 2.5 months). The most common reported clinical signs at presentation included facial nerve deficits (8/10), evidence of vestibulocochlear nerve deficits (7/10) with (4/7) or without (3/7) vestibular ataxia, and a combination of cranial nerve VII and VIII neurologic deficits (5/10; Supplementary Table S3). All 10 horses initially had unilateral clinical signs, and surgery was performed on the side with associated clinical signs. Five horses had the left side treated, 4 had the right side treated and 1 had both sides treated. Four months after undergoing left-sided partial ceratohyoidectomy, Horse 9 (14-year-old Quarter Horse gelding) had developed neurologic signs of cranial nerve VII and VIII on the right side and underwent right-sided partial ceratohyoidectomy. Thus, 11 partial ceratohyoidectomies had been performed in total.
Medical management was initiated in 7 horses for a median of 3 days (range, 2 to 15 days) prior to surgery (Supplementary Table S1). Medical management included ceftiofur sodium (2.2 mg/kg, IM, q 12 h; n = 1 horse), trimethoprim sulfamethoxazole (25 mg/kg, PO, q 12 h; 1), cefazolin (11 mg/kg, IV, q 8 h; 1), gentamicin (6.6 mg/kg, IV, g 24 hours; 1), flunixin meglumine (1.1 mg/kg, IV, q12h; 7), dexamethasone (0.05 to 0.1 mg/kg, IV or IM, q 24 h; 3), vitamin E supplementation (5,000 U, PO, q 24 h; 4), or neomycin-polymyxin B sulfate-bacitracin zinc ophthalmic ointment (q 4 h; 6), alone or in combination. Medications were based on clinician preference and owner decisions.
Horses underwent general anesthesia for 10 of the 11 partial ceratohyoidectomies, with 1 procedure performed with standing sedation achieved with continuous rate infusion of detomidine hydrochloride (0.005 to 0.01 mg/kg/h) and local anesthesia (2% lidocaine, 10 mL, subcutaneously). Two horses (Horse 1 and 2) had a presurgical plan of complete ceratohyoidectomy but due to intraoperative complications a partial ceratohyoidectomy was performed. A planned partial ceratohyoidectomy was performed in 8 horses (9 procedures in total). After failed attempts to control hemorrhage in Horse 1, the visible ceratohyoid bone was removed with rongeurs and the surgical site was closed and packed with lap sponges. Packing was removed the day after surgery and a bandage covering the incision remained in place for 7 days. Horse 2 had hyoid apparatus asymmetry and dorsomedial deviation of the ceratohyoid-stylohyoid articulation on the affected side making it difficult to access the ceratohyoid-stylohyoid articulation during surgery. After failed attempts to expose the proximal aspect of the ceratohyoid bone articulation with the stylohyoid, the surgeon converted the surgery to a partial ceratohyoidectomy. Four different board-certified veterinary surgeons (NE, MM, JMY, FB) performed the procedures, and 1 surgeon (NE) performed most procedures (6/11). The median surgical time was 90 minutes (range, 50 to 180 minutes; Supplementary Table S2). The only intraoperative complication was severe hemorrhage observed in Horse 1. Immediate postoperative complications included an obstructed upper airway that led to an emergency tracheostomy in recovery and lack of tongue mobility (Horse 1), frank blood exiting the incision when the horse was fed after surgery, which resolved with a pressure bandage within 2 hours (Horse 2), and rhabdomyolysis that resolved within 36 hours with medical treatment (Horse 10). The tongue mobility and respiratory obstruction for Horse 1 both resolved within 3 days and the tracheotomy site was left to heal by second intention with no long-term effects. All horses survived to hospital discharge with a median hospitalization duration of 7 days (range, 4 to 24 days; Supplementary Table S1).
For horses with only 1 side affected, median follow-up was 14 months (range, 6 to 44 months). Follow-up for Horse 9, who had bilateral disease, occurred 7 months after the second surgery (11 months from the first surgery). All horses had improved neurologic signs, and 2 horses (Horse 4 and Horse 10) had complete resolution of signs (Supplementary Table S3). Of the 8 horses with facial nerve clinical signs, 7 showed improvement, with 1 horse having no change. Of the 4 horses with vestibular ataxia, 2 had resolution of signs and 2 improved. Other vestibular signs (head tilt, horizontal nystagmus, circling) resolved for 4 of the 7 horses that initially had evidence of vestibulocochlear nerve deficits, and the remaining 3 of these 7 horses showed improvement. Nine of 10 horses returned to their previous reported level of work. One horse (Horse 9) that underwent a partial ceratohyoidectomy on both ceratohyoid bones was retired due to residual deficits.
Follow-up radiography was performed for 9 of 10 horses (10 of the 11 procedures; Supplementary Table S4). The remaining horse (Horse 1) did not undergo follow-up radiographic examination because it was euthanized 40 months after surgery for reasons unrelated to THO (colic). Radiography revealed that all 9 horses had a visible space that could be measured (median, 0.7 cm; range, 0.7 to 3.6 cm) between the basihyoid and remaining ceratohyoid bone on the operated side or sides (Figure 1). Six horses also underwent standing CT at follow-up examination. The visible space between the distal remnant of the ceratohyoid and basihyoid bones had a median length of 0.6 cm (range, 0.5 to 3.7 cm). Proliferation of the ceratohyoid bone was observed in 2 horses (Horse 4 and 10), and proliferation of the basihyoid was present in 1 (Horse 6; Figure 2).
Partial ceratohyoidectomy is a surgical option, in standing or anesthetized patients, for horses diagnosed with THO and can provide a similar clinical outcome when compared to what has been previously reported for complete ceratohyoidectomy. 3,7,11–13,15 There were no intraoperative complications for those horses in which a planned partial ceratohyoidectomy was performed. No bone proliferation of the ceratohyoid was visible on postoperative radiography, but CT revealed ceratohyoid or basihyoid proliferation in 3 of the 6 horses that received postoperative CT scans. When bone proliferation did occur, it was not complete and did not appear to have any effect on improvement of clinical signs.
Horse 1 and Horse 2 were planned to have complete ceratohyoidectomies, however, due to complications that arose during attempts to expose the ceratohyoid-stylohyoid articulation, a partial ceratohyoidectomy was performed to minimize morbidity from further dissection. In Horse 1, hemorrhage was encountered when dissecting the ceratohyoid from the stylohyoid bone articulation obstructing visibility of the surgical field, similar to what has been reported as a main intraoperative complication of complete ceratohyoidectomy. 3,7,11 Due to hemorrhage and packing the area with lap sponges, this patient experienced life-threatening airway obstruction in recovery, likely due to hematoma formation, as previously seen in other reports. 3,7,11 Although there was no mention of excessive hemorrhage in the surgery report of Horse 2, it is likely that there was a small amount of ongoing hemorrhage from the dissection that led to a buildup of pressure around the incision that eventually exited the incision when more movement of the area commenced with feeding. Even though the procedures in both horses were more invasive than the planned partial ceratohyoidectomies and complications occurred during and after surgery, the resolution of the complications and functional outcome of the surgery were similar to the planned procedures after 6 months, which is why they were included in the present study. It is important to note that more ceratohyoid bone was removed since more of it was exposed due to deeper dissection. These horses demonstrate that surgeons can convert a preoperatively planned complete ceratohyoidectomy to a partial ceratohyoidectomy during surgery if complications arise and still achieve comparable results.
No intraoperative hemorrhage or postoperative neuropathies were observed in the 9 planned partial ceratohyoidectomy surgeries which was better than previous reports of complete ceratohyoidectomy procedures in which 6.7% (1/15), 7 18.5% (5/27), 3 and 50% (2/4) 11 of horses intraoperative hemorrhage or postoperative neuropathies. It was likely that fewer intraoperative complications in the present study, compared to previous studies, 3,7,11 were due to elimination of deep dissection to the ceratohyoid-stylohyoid articulation that is also observed in the reported standing disarticulation of the ceratohyoid from the basihyoid bone. 10 Neurovascular structures including the hypoglossal nerve, lingual branches of the mandibular nerve, glossopharyngeal nerve and lingual artery adjacent to this articulation make hemorrhage and iatrogenic trauma to neural structures possible, leading to postoperative neuropathy of the tongue. 9 The only complication observed in this group of horses was postoperative rhabdomyolysis in recovery (Horse 10), likely due horse size (653 kgs) and prolonged time on the table (3 hours).
In previous reports, a positive clinical outcome has been reported as return to previous use, 3,7,10,11 complete resolution 3,10,12 or improved clinical signs. 3,10,12,13 In the current study, only 2 of 10 horses fully recovered from their clinical signs, which is comparable, but slightly lower than previous studies that reported 4/15, 7 (2/5), 12 12/25, 3 and 3/6 13 horses having complete resolution of clinical signs. It has been previously reported that some patients’ clinical signs do not improve with surgical intervention 3,7,12,13 and that it can take up to 2 years to have complete resolution or improvement of clinical signs in cases managed medically. 5 Considering the median time to follow-up was 14 months, there is a possibility that given more time, more horses could have obtained clinical resolution. It should be emphasized that residual cranial nerve deficits after surgery are not surprising in these cases, 3,7 and when present, they were no worse. Residual cranial nerve deficits should not affect quality of life of the horse, as long as the eye is protected, whereas residual ataxia would; ataxia was improved after surgery in all unilaterally affected horses in the present study. Another consideration is that in previous studies clinical improvement was determined by the primary veterinarian or owner 3,7,10–13 whereas all horses in the current study had follow-up neurologic examinations performed or reviewed by a board-certified veterinary internist, which may result in greater reporting of clinical signs. Nonetheless, all horses had improvement in clinical signs with 9 returning to their previous level of performance. This return to performance is better than previous ceratohyoidectomy reports where 1/5, 12 13/20, 3 and 8/10 7 of horses returned to previous work but is less than that reported by Racine et al 11 where all 4 horses with standing procedures returned to previous work levels.
It has previously been reported that bilateral THO is prevalent and more readily diagnosed on CT. 16 In the current study, Horse 9 was the only horse diagnosed with bilateral disease via standing CT on initial presentation. However, clinical signs were unilateral so a left partial ceratohyoidectomy was initially performed. Four months after surgery the horse returned with right-sided clinical signs and a right-sided partial ceratohyoidectomy was performed. A retrospective case series states 4 horses having bilateral complete ceratohyoidectomy performed, with 3 of them having surgery on both sides at the same time, and 1 horse returning 6 months later to have the procedure performed on the opposite side. 3 Complete ceratohyoidectomy has also been described as a staged bilateral procedure in 1 case report, where successful return to full function was accomplished within 10 months of the second procedure. 17 Similar to this report, 6 weeks after the second surgery Horse 9 appeared to be doing well and the owners turned him out in a small paddock. When seen later that day, the horse had facial trauma and was severely ataxic with a more obvious head tilt to the right. It was assumed that the patient had slipped on ice, aggravating current pathology with subsequent return of clinical signs, but it is also possible that his ataxia was not improved which is why he slipped. There was evidence of both left and right-sided residual deficits observed at the seventh month recheck after the second surgery (11 months after the first). The owners elected to retire the horse.
To the author’s knowledge there are no studies examining postoperative imaging of the head following ceratohyoidectomy in horses diagnosed with THO. Therefore, all horses, except Horse 1, had follow-up imaging performed. Radiography was performed for all 9 since they are available to most veterinarians. The authors assumed surgeons would most often interpret follow-up radiography, which could be viewed as a limitation of the present study since radiographic images were not interpreted by a radiologist and bias could have been present. Radiographs were evaluated to see whether ceratohyoid bone proliferation occurred after excising the distal aspect of the bone and whether bone proliferation would alter the clinical outcome due to reconnections of the ceratohyoid-basihyoid bones. The median radiographic space of 0.7 cm measured at follow-up coincided with the approximate space created at surgery (0.5 to 1 cm), suggesting minimal proliferation. However, it is important to note, that detail on radiographic images of the basihyoid area is difficult to assess due to bone and soft tissue overlap, whereas CT can provide greater detail for THO in 3-D. 16 For 3 horses, CT demonstrated more proliferation than did radiography (Figure 2), but clinical signs still improved. This proliferation may have occurred due to movement of the ceratohyoid remnant during chewing and swallowing, or from iatrogenic trauma sustained during disarticulation of the ceratohyoid from the basihyoid bone. It is unknown whether there is a need to cover the cut end of the ceratohyoid bone to prevent proliferation. Pease et al 9 described suturing the ceratohyoid, hyoglossus and sternohyoideus muscles over the cut end of the basihyoid bone after removing the ceratohyoid. Muscle bellies were not sutured over the cut end of the ceratohyoid bone in the current study, but absorbable gelatin sponges were placed in the gap created between the remaining ceratohyoid and basihyoid bones. It is unknown whether gelatin sponges would have any positive or negative effect on bone proliferation or if muscle belly coverage would have prevented the proliferation identified on CT. Nonetheless, reconnection of the ceratohyoid and basihyoid bone did not occur in the current study.
Another less invasive surgery was described where the ceratohyoid was disarticulated from the basihyoid bone using standing sedation and local block. 10 This surgical technique was reported to release the ceratohyoid bone creating a 1- to 2-cm space between the ceratohyoid and basihyoid bones measured by digital palpation at surgery. 10 The authors have experienced a similar hyoid release when disarticulating the ceratohyoid bone from the basihyoid bone during the procedure described in the current study but also felt it was important to remove part of the ceratohyoid bone. Results of both of these relatively non-invasive techniques suggest that the release that is created by disarticulation of the ceratohyoid and basihyoid bones likely alters the force placed on the hyoid apparatus such that inflammation can be attenuated. This is demonstrated by the short-term improvement in 3 of 6 horses within a 30- to 60-day follow-up period 10 as well as the long-term improvement in all 10 horses in the present study, compared to more invasive surgeries. 3,7,11–13
Regardless whether surgery is performed, it is important to control potential infections and resultant pain and inflammation when treating THO to mitigate clinical signs. Infections may be hard to diagnose when extending from otitis media or interna, hemorrhage associated with stylohyoid bone fracture, or fracture of the petrous temporal bone. 2,5,18 Therefore, systemic and local anti-inflammatories as well as broad-spectrum antimicrobials are initiated days before or just prior to surgery. In the current study, the combination, initiation, and duration of broad-spectrum antimicrobials were determined by the attending clinician based on severity and variation of clinical signs present, with consideration of owner economics. This resulted in 1 of 4 different broad-spectrum antimicrobial combinations being administered to an individual (Supplementary Table S1). Upon discharge, the broad-spectrum antimicrobial prescribed was changed in most horses to achieve high owner compliance. Broad-spectrum antimicrobials have been reported for medical management of THO for a duration ranging from 5 days to 6 weeks. 3,5,12 It is unknown to what extent the medical treatment or particular antimicrobial combination used in the current study contributed to the positive outcome; however, it has been reported that surgery has an increased prognosis for survival when compared to medical treatment alone. 3
The current study had some limitations. A limited number of horses were enrolled, which is a reflection of the number of horses that present with THO to the institutions participating in the present study. One horse had already died prior to our recruiting horses for follow-up examination; however, data for this horse were included because follow-up neurologic examination was achieved by a board-certified internist 21 months after the procedure. Not all horses had follow-up neurologic examinations performed in person as some were reviewed by video (4 horses). This may have led to less accurate results but were still likely more detailed than other reports where the owner or primary veterinarian provided clinical outcome data. 3,7,10–12 The neurologic examinations performed did not objectively test for hearing loss since necessary equipment was not available. Not all horses were able to return to the hospital and undergo CT, limiting potential detail that could be gained compared to radiography. For the measurement between the basihyoid and ceratohyoid bones of interest, magnification was not accounted for meaning there was likely error in the actual measurement, but the authors were simply attempting to see if the space at follow-up was similar to the amount of bone removed at surgery.
In conclusion, the present study demonstrated that partial ceratohyoidectomy is a surgical option for treatment of THO and provides similar clinical outcome as the complete ceratohyoidectomy technique previously reported. 3,7,11–13 Partial ceratohyoidectomy is feasible in the standing or anesthetized patient. Even if bone proliferation occurs by 6 months after surgery, a measurable space between the ceratohyoid and basihyoid bone remains without return of original clinical signs.
Supplementary materials are posted online at the journal website: avmajournals.avma.org
