Radial Mandibular Coronoidectomy in a Basset Hound as a Treatment for Temporomandibular Joint Dysplasia

ABSTRACT

A ‐year‐old Basset Hound, previously diagnosed with temporomandibular joint dysplasia, presented with a 6‐month history of pain during mastication and frequent open‐mouth locking episodes. Oral examination under sedation revealed displacement of the mandible to the left and jaw fixation in an open position. Computed tomography images of the head performed in open and closed positions before and after surgery were obtained. A left partial coronoidectomy was performed using a radial TPLO saw blade, removing bone impingement between the coronoid process and zygomatic arch. The dog was eating soft food a couple of hours after surgery, and no further open‐mouth locking episodes or pain associated with mouth opening were reported up to one year postoperatively. Functional results were achieved using this technique, with a rapid patient recovery.

A one‐year‐old Basset Hound presented with recurrent open‐mouth locking episodes and was diagnosed with temporomandibular joint dysplasia. Two‐position CT imaging was performed and guided surgical planning for partial mandibular coronoidectomy using a radial TPLO saw blade. Postoperative outcome was excellent, with resolution of clinical signs and no recurrence at one‐year follow‐up.

1. Introduction

The temporomandibular joint (TMJ) is a symmetrical synovial joint present in all mammals, serving vital function roles like mastication, communication and overall survival (Lin et al. 2018). TMJ dysplasia is an infrequently reported condition in dogs and cats that results in excessive joint laxity, causing displacement and abnormal contact of the coronoid process with the adjacent zygomatic arch, resulting in pain and open‐locked jaw episodes (Verstraete et al. 2019). This condition is usually congenital or developmental and has been reported sporadically in multiple breeds (Schwarz et al. 2002). Severity of this condition is very variable with inconsistent frequency, duration of open‐mouth locking episodes and radiographic findings (Lantz and Cantwell 1986). In terms of investigations, radiographs of the skull can be performed with changes consistent with caput mandibulae and fossa mandibularis flattening with a hypoplastic or misshapen processus retroarticularis (Lantz and Cantwell 1986). A widened irregular joint space with periarticular osteophytosis and increased obliquity of the articular surface can also be identified (Schwarz et al. 2002). Computed tomography (CT) is the gold standard for the diagnosis of TMJ dysplasia and underlying aetiology (Verstraete et al. 2019), and the addition of a two‐position CT series, with the mouth open and closed, has been reported to assist in surgical planning (Lerer et al. 2014). Treatment options for TMJ dysplasia depend on the cause and severity of clinical signs. Asymptomatic individuals may only require conservative management. However, in cases of progressive intermittent open‐mouth locking episodes and persistent pain, surgical techniques including partial zygomatic arch excision or reduction of the coronoid process height via mandibular coronoidectomy are recommended (Verstraete et al. 2019).

The purpose of this report was to describe the use of consecutive CT imaging studies in open‐ and closed‐mouth positions for surgical planning and postoperative assessment, as well as the long‐term successful outcomes following the use of a radial saw blade for partial mandibular coronoidectomy, achieving a close to normal anatomy of the remaining coronoid process (Video S1).

2. Case History

A one‐year‐old, male intact Basset Hound was represented at the referral centre for further assessment and treatment of a previously diagnosed TMJ dysplasia. Clinical signs included pain while masticating, daily episodes of open‐mouth locking jaw associated with yawning. The patient was initially referred at 6‐month‐old, with a history of a ‘click’ sound when yawning but no open‐mouth locking episodes. A radiographic survey was previously performed, revealing incongruence of the left and right TMJs, flattened mandibular condyles and shallow mandibular fossae. The patient was sedated with medetomidine (Sedastart; AnimalCare Ltd., UK) (5 µg/kg intravenously) and butorphanol (Butador; Chanelle Pharma, Ireland) (0.3 mg/kg intravenously) for oral examination and diagnostic imaging. The CT images were acquired with the animal in the sternal position, pre‐ and postcontrast (Omnipaque 350 mg/mL100mL Iohexol Injection Solution, 2 mL/kg intravenously) with a neutral closed‐mouth position (SOMATOM Scope; version syngoCT VC40, Siemens). The CT scan was performed in axial mode using 130 kV and 160 mA, with a slice thickness of 1.0 mm, an acquisition matrix of 512 × 512 and a pitch of 0.8. Additionally, an open‐mouth series was acquired using an intraoral tape roll. The DICOM images were evaluated using specialised software (Horos DICOM Viewer) and identified bilateral shallow mandibular fossae and TMJs incongruency (left worse than the right); the medial part of the condyle of the left mandible was enlarged and showed increased attenuation. The position of the coronoid processes was asymmetrical and changed in relation to the zygomatic arches between the open‐ and closed‐mouth series. At initial presentation, no treatment was recommended due to the growing process and minimal clinical signs. However, 6 months after initial presentation, multiple open‐mouth locking episodes associated with pain were observed. The dog managed a spontaneous reduction with repeated yawning. Parameters of the physical examination were unremarkable. Oral examination under sedation (identical sedation as the previous visit) revealed subluxation of the TMJ. While the mandible was displaced to the left and the mouth was wide open, the jaw could be locked in the open position. A ‘click’ and crepitus were identified on manipulation in both joints and was associated with discomfort. Contrast CT scans, repeated with the mouth in closed and open positions (Figures 1 and 2), identified ongoing bilateral TMJ dysplasia associated with left TMJ subluxation in an open‐mouth position and remodelling of the left mandibular condyle. Additionally, proximity between the left coronoid process and zygomatic bone was identified in an open‐mouth position with further remodelling of the associated osseous margins, which explained the intermittent jaw‐locking episodes. Similar but less pronounced changes were observed on the right side. No major asymmetry or muscle atrophy was identified.

FIGURE 1.

Computed tomographic images of the TMJs preoperatively, transverse view (a) showing the asymmetry and sagittal view of the left TMJ (b). The left mandibular condyle is enlarged and misshapen medially with mild heterogeneous hyperattenuation. A focal, smoothly marginated concave defect is visible at the ventromedial aspect of the left mandibular condyle, delineated by a discontinuous mineralized rim and containing a mineral attenuating fragment.

FIGURE 2.

3D reconstruction of CT images obtained with an open‐ and closed‐mouth position at 6 months of age (a, b), 1 year of age—preoperatively (c, d) and postoperatively (e, f).

Surgical treatment was planned for the following day. The dog was premedicated with dexmedetomidine (Dexdomitor; Zoetis UK Limited) (3 µg/kg intramuscularly) and methadone (Synthadon; Animalcare Ltd., UK) (0.3 mg/kg intramuscularly). General anaesthesia was induced with propofol (Propofol‐Lipuro Vet; Virbac UK) (2 mg/kg) and ketamine (Ketabel; Bela‐Pharm GmbH&Co. KG, UK) (2 mg/kg) and maintained after endotracheal intubation with isoflurane and oxygen. Once induced, a caudal mandibular nerve (inferior alveolar nerve) block and an infraorbital nerve block using a total 1 mg/kg of bupivacaine (Marcain; AstraZeneca UK Limited) perineurally. A ventrolateral approach to the zygomatic arch was performed. The masseter muscle was disinserted from the coronoid process of the mandible. There was severe remodelling of the cranial dorsal tip of the coronoid and the medial aspect of the cranial zygomatic arch, showing an appearance of a pseudo‐joint. Once the remodelled coronoid was exposed, a circular cut (using an 18‐mm radial TPLO blade) of the coronoid process tip was performed (Figure 3). Intraoperative mouth opening and closing confirmed the resolution of the impingement of the coronoid process with the zygomatic arch. Closure was achieved in three layers, with the muscles and fascia closed in one layer, followed by the subcutaneous tissue and skin. Postoperative CT scan confirmed satisfactory reduction of the mandibular coronoid process height without any further impingement identified in the open position. The dog was hospitalised for 4 days in total while receiving investigations, surgical treatment and postoperative care with fluid therapy, paracetamol (Paracetamol Kabi; Fresenius Kabi, Ireland) (10 mg/kg intravenously q12hrs), methadone (Synthadon; Animalcare Ltd., UK) (0.2 mg/kg intravenously q6hrs) and gabapentin (Neurosil; Teva UK Ltd., UK) (10 mg/kg orally q8hrs). The dog was able to eat soft food immediately after surgery without any signs of discomfort, pain or open‐mouth locking episodes. The dog was discharged the following day, recommending soft diet, avoidance of rough playing and chewing toys and a course of meloxicam (Loxicom; Norbrook Ltd., UK) (0.1 mg/kg orally q24hrs) for 14 days and gabapentin (Gabapentin Rosemount; Jenson R+ Ltd., Ireland) (15 mg/kg q12hrs) for 21 days. At the 2‐week postoperative assessment, the dog was doing well without reported pain or jaw locking episodes. Physical examination was within normal limits. No further diagnostics were performed, and the dog was discharged without any further treatment. At 1‐year follow‐up, the referring veterinarian reported no further open‐mouth locking episodes, or pain or discomfort while eating or playing.

FIGURE 3.

Intraoperative images: Radial saw blade use (a), radial osteotomy of the coronoid process (b) and resected coronoid process (c).

3. Discussion

To our knowledge, this is the first case report describing the use of a two‐position CT imaging series of the head, at 6 months and 1 year of age, both pre‐ and postoperatively, following partial mandibular coronoidectomy. Using CT images to diagnose TMJ dysplasia, support decision‐making, plan surgical treatment and assess functional outcomes was essential in this case, particularly for selecting the appropriate size of the radial saw blade and estimating the portion to be removed. This is the first case reporting the use of a radial saw blade to perform mandibular coronoidectomy. This simple modification of the osteotomy line shape can achieve similar results with less morbidity by preserving the zygomatic arch and associated soft tissue structures (Lantz 2012). This cut shape may have avoided the need for further osteoplasty, thus minimising morbidity and surgical time.

Skull radiographs were traditionally used to confirm TMJ dysplasia in dogs with a history of oral sensitivity or locking episodes (Schwarz et al. 2002). However, evidence of widened joint spaces and signs of degenerative joint disease may not always be present. Advanced imaging, such as skull CT scan, can give more detailed information (Bar‐Am et al. 2008; Lerer et al. 2014). Two‐position CT imaging (mouth open/closed) in our case provided further details, specifically on defining the coronoid process portion to remove for clinical resolution. The selection of the TPLO saw blade diameter was guided by preoperative CT and was confirmed intraoperatively based on surgical exposure and visualisation of the resection margins. Two‐position CT imaging, under general anaesthesia, was previously reported to diagnose a dog with TMJ dysplasia (Lerer et al. 2014). However, it was not reported and used for surgical planning. Villamizar‐Martinez et al. documented CT morphologic features of the TMJ and presented a method for joint congruency measurements in dogs (2016). Unfortunately, in this study, the dogs’ mouths remained partially opened by the presence of the endotracheal tube between the maxillary and mandibular incisors (Lerer et al. 2014). The preoperative CT scans in our case were performed under sedation, avoiding the need for an endotracheal tube and allowing perfect mouth occlusion. Lantz (2012) presented an algorithmic approach to the surgical decision‐making for the treatment of TMJ dysplasia, which was based on history, clinical observation, oral manipulation and radiographic findings. The use of two‐position CT series under sedation could help with specific and appropriate surgical intervention.

Surgical treatments previously described for TMJ dysplasia include plication of the stretched TMJ capsule (Thomas 1979) and partial or complete zygomatic arch ostectomy (Stewart et al. 1975). While mandibular condylectomy has been described by Bennett in 1986, it is currently not recommended because of the risk of exacerbating mandibular instability (Verstraete et al. 2019). Coronoidectomy has been described in conjunction with partial zygomatic arch excision (Lantz 2012). Partial zygomatic arch excision was not required to be performed in this case and avoided associated complications. In refractory cases, an alternative option would be total replacement of the diseased joint to prevent further open‐mouth locking episodes and instability. TMJ replacement has been used in human medicine for end‐stage joint diseases (Speculand 2009; Wolford et al. 2015; Yoda et al. 2020), and a recent study has evaluated its potential in dogs and cats (Arzi et al. 2024).

Decision‐making for TMJ dysplasia cases is based on age, degree and cause of ‘locking’ episodes (Lantz and Cantwell 1986). In this case, surgical intervention was warranted due to progressive worsening and presence of open‐mouth locking episodes. Two‐position CT imaging performed under sedation showed degenerative changes and variable positioning of the left coronoid process in open‐and closed‐mouth series. In the open‐mouth position, it is displaced rostroventrally with subsequent close apposition between its rostral margins and the left zygomatic bone rostroventral aspect. At that level of contact, the opposing margins were moderately remodelled, displaying irregular thickening, flattening and moderate heterogenicity with irregular peripheral defects and moderate patchy sclerosis, which were more severe compared to the initial examination.

An oscillating radial saw blade was used, achieving a close to normal anatomical shape of the remaining coronoid process, minimising anaesthesia and operating time and surgical morbidity. TPLO saw blades and oscillating saws are widely available and commonly used due to their cost‐effectiveness, accessibility and efficiency. In contrast, piezoelectric bone cutting instruments, while offering superior precision, selective tissue cutting and reduced bleeding, are less commonly found in hospitals due to their higher cost and specialised learning curve (Verstraete et al. 2019). While a TPLO saw blade offers short surgical time and accessibility, its use for mandibular coronoidectomy carries risks of major injury to vessels, nerves, and soft tissues. Careful technique, appropriate instrument selection and intraoperative vigilance are essential to prevent these complications. Alternative techniques such as piezoelectric bone cutting or high‐speed burr osteotomy offer greater precision and safety by minimising soft tissue trauma, making them preferable in cases where preservation of delicate structures is paramount (Verstraete et al. 2019). However, they are less likely to be used because of their cost and poor availability.

A caudal mandibular nerve block was performed to provide regional analgesia to the surgical site. However, adding a maxillary nerve block would have provided more adequate analgesia; although systemic perioperative analgesia was added using methadone as premedication and ketamine as an induction agent, no requirement for additional adjunctive analgesia was identified.

In this case, the combination of a two‐position imaging modality and using a radial saw for surgical technique could bring successful outcomes and prevent arthroplasty.

Author Contributions

Elena Rappa: writing – original draft, data curation, literature review. Bruno Santos: case management, clinical investigation. Marie‐Pauline Maurin: conceptualization, surgical planning, supervision. All authors read and approved the final manuscript.

Ethics Statement

This case report was conducted in compliance with ethical standards for veterinary care and welfare. The owners of the animal provided informed consent for all diagnostic and therapeutic procedures as well as use of clinical notes and imaging for research purposes and possible future contact.

Conflicts of Interest

The authors declare no conflicts of interest.

Peer Review

The peer review history for this article is available at https://www.webofscience.com/api/gateway/wos/peer‐review/10.1002/vms3.70492.

Supporting information

Supporting File: vms370492‐sup‐0001‐videoS1.MOV

Rappa, E. , Santos B., and Maurin M.‐P.. 2025. “Radial Mandibular Coronoidectomy in a Basset Hound as a Treatment for Temporomandibular Joint Dysplasia.” Veterinary Medicine and Science 11, no. 5: 11, e70492. 10.1002/vms3.70492

Data Availability Statement

No new data were generated or analysed in this study.