Traumatic Complete Separation of the Anconeal Process in a 1-year-old French Bulldog with an Ununited Anconeal Process

Abstract

A 1-year-old 13.5 kg male neutered French bulldog presented for acute left thoracic limb non-weight-bearing lameness following minor trauma. Orthopaedic examination revealed left elbow joint effusion and discomfort on elbow manipulation, particularly in extension. Computed tomography showed separation of the left anconeal process, incomplete fusion of the right anconeal process, and bilateral humeroulnar incongruity. Elbow arthroscopy confirmed complete separation of the left anconeal process. The fragment was removed via caudolateral arthrotomy. Histopathology of the excised fragment demonstrated organized fibrosis and multifocal bone proliferation extending along the separation line, consistent with traumatic separation secondary to an ununited anconeal process. On follow-up examination 4 weeks postoperatively, there was a mild left thoracic limb lameness that had completely resolved by 5-month postoperative. No lameness was reported at long-term follow-up (20 months postoperative).

 

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Keywords

ununited anconeal process - anconeal process separation - French bulldog

Introduction

Ununited anconeal process (UAP) is a developmental disorder of the elbow joint, observed in young growing dogs, particularly large breed dogs though small breeds have been reported.[1] [2] UAP is characterized by the failure of the anconeal process to fuse with the proximal ulnar metaphysis by 4 to 5 months of age.[1] Clinically affected dogs commonly present between 5 and 12 months of age with chronic, mild to moderate weight-bearing lameness that may be exacerbated by exercise.[2] The pathophysiology and underlying cause for UAP is incompletely understood, with proposed explanations that include trauma, metabolic, genetic, rapid/prolonged periods of growth in large-breed dogs, trochlear notch dysplasia, and radioulnar incongruity.[2]

Traumatic fracture of the anconeal process is a much rarer clinical presentation. It is defined as traumatic fracture of a normal anconeal process or traumatic separation of the process that was stably attached with fibrous or fibrocartilaginous tissue rather than bone due to incomplete fusion.[2] There are few reports of traumatic anconeal process fracture in the veterinary literature; three case reports in large breed dogs and a single case report of two cats.[3] [4] [5] [6] In two of the case reports in dogs, one on a 12-month-old boxer and the other on a 12-month German Shepherd, the authors hypothesized that the traumatic fracture was secondary to an underlying UAP though histology was not performed.[3] [5] A recent report of suspected traumatic anconeal fracture in a 14-month-old boxer included histopathology on the excised fragment, which demonstrated the possibility of an isolated anconeal fracture in the absence of preexisting pathology.[4] Medl and Hurter described two cases of traumatic anconeal fracture in a 3- and 5-year-old female spayed domestic shorthair. The authors concluded that major trauma was necessary to fracture the anconeal process in cats.[6]

Traumatic fracture or separation of the anconeal process has not been previously reported in small or medium breed dogs. The objective of this report was to describe a case of traumatic anconeal process separation secondary to incomplete fusion of the anconeal process in a 1-year-old male neutered French Bulldog. In this report we use the term “separation” rather than “fracture,” as it may be more appropriate given the suspected incomplete fusion of the anconeal process. We describe comprehensive clinical, diagnostic, and surgical findings with regular orthopaedic and sports medicine rehabilitation follow-up.

 

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Case Description

A 1-year-old 13.5 kg castrated male French bulldog presented to the emergency department of a small animal referral hospital for acute left thoracic limb lameness after jumping off the couch. The dog was non-weight-bearing on the left thoracic limb at the time of examination. Survey radiographs performed at the time of consultation did not reveal any obvious pathology. Over the following 8 weeks, the dog was managed conservatively, including periods of activity restriction and two 7-day courses of an oral non-steroidal anti-inflammatory drug (Meloxicam 0.1 mg/kg once daily: Metacam 0.5mg/mL, Boehringer Ingelheim Animal Health Australia Pty. Ltd., New South Wales, Australia). The dog was reported to continue to be non-weight-bearing on the limb with occasional periods of toe-touching lameness.

The dog presented for specialist surgery referral 8 weeks following the onset of lameness. On physical examination, the dog was bright, alert, and responsive with normal vital parameters. The dog was non-weight-bearing on the left thoracic limb at a walk. There was appreciable atrophy of the proximal thoracic limb musculature relative to the right and discomfort on elbow manipulation, notably in extension. There was palpable left elbow joint effusion, particularly on the caudolateral aspect. The remainder of the orthopaedic examination was within normal limits.

Preoperative Diagnostics

Complete blood count and serum biochemistry were within reference intervals. The dog underwent helical multi-detector computed tomography (CT; GE MEDICAL SYSTEMS Revolution EVO 64 slice) evaluation of the thoracic limbs and cervical spine, including both unenhanced and contrast-enhanced sequences. The scan parameters were tailored to the dog's size and conformation. All studies were reviewed by a board-certified radiologist (XX) in conjunction with a board-certified surgeon (XX).

Both thoracic limbs had changes consistent with humeroulnar incongruity, medial coronoid blunting with sclerosis, and bilateral elbow degenerative joint disease. There was no evidence of radioulnar incongruity in either limb. In the right thoracic limb, there was evidence of incomplete fusion of anconeal process, described as a caudomedial cleft in the caudal portion of the anconeal process ([Fig. 1A]). Mild irregular margination of the radial incisure of the medial coronoid process irregularity of the apex and mild to moderate osteophyte formation of the medial coronoid process and medial humeral epicondyle were also noted. In the left elbow, there was a large ovoid bone fragment within the supratrochlear foramen measuring approximately 1.06 × 0.62 cm with cortical and trabecular bone definition separated from the ulna by a 0.21-cm gap. An ununited anconeal process with separation was prioritized given the findings in the right limb ([Fig. 1B, C]). Additionally, there was moderate subtrochlear sclerosis, irregular margination of the apex, and radial incisure of the medial coronoid process with moderate to osteophyte formation of the medial coronoid process, medial humeral epicondyle, and cranioproximal radial head. Mild fluid distention of the elbow synovial capsule was noted.

Fig. 1 Three-dimensional reconstruction of the right elbow (A) and multiple-plane reconstruction of computed tomography (CT) scan of the left (B, C) elbow. (A) A cleft is noted along the caudomedial aspect of the right anconeal process. This region is indicated by a red arrow. (B) The abnormal left anconeal process has a concave cranial border which is blunted and irregularly margined (white arrow). Cranial to this there is an approximately 0.21-cm length separation from the ulna (asterisk). (C) There is a large ovoid bone attenuating structure, consistent with free anconeal fragment, present within the supratrochlear foramen (asterisk). The fragment has an irregular caudal margin and measures approximately (1.06 cm × 0.62 cm).

Arthrocentesis was performed for the left elbow and submitted for cytological examination by a board-certified pathologist (XX). A Wright–Giemsa stained smear of joint fluid was highly cellular with a dense mucinous protein background and a mild diffuse scattering of erythrocytes. Nucleated cells were predominantly large mononuclear cells (macrophages/synovial lining cells, 76%), with moderately scattered small lymphocytes (21%), and scant nondegenerate neutrophils (3%). These cytological findings were consistent with a traumatic or degenerative arthropathy as can be seen with acute or chronic trauma to the articular surface.

 

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Surgery

The dog was premedicated with methadone (Ilium Methadone, Troy laboratories Pty. Ltd., New South Wales, Australia; 0.3 mg/kg), acepromazine (A.C.P.2, Ceva Animal Health Pty Ltd., New South Wales, Australia; 0.01 mg/kg), and medetomidine (Ilium Medetomidine, Troy laboratories Pty. Ltd., New South Wales, Australia; 0.005 mg/kg) administered as an intramuscular injection. The dog was induced with propofol (Propofol 1%, B Braun Australia Pty. Ltd., New South Wales, Australia; 2.8 mg/kg intravenously), intubated and maintained with inhalation isoflurane anaesthesia (Isothesia NXT, Provet AU, Queensland, Australia). A local proximal radial, ulnar, median, and musculocutaneous nerve block was performed by a board-certified specialist veterinary anaesthetist using bupivacaine (bupivacaine, Pfizer, New South Wales, Australia; 1 mg/kg). Antibiotic prophylaxis was administered at anaesthetic induction and every 90 minutes of surgical time (Cefazolin-AFT, AFT Pharmaceuticals, New South Wales, Australia; 22 mg/kg q90m).

The left elbow joint was distended with 5 mL of saline at a point immediately cranial and distal to the medial epicondylar crest to establish an arthroscopy port (1.9-mm, 30 arthroscope; Synergy HD arthroscopic system; Arthrex Vet Systems) in this location. An egress port was then successfully established in the caudomedial joint pouch. Arthroscopy revealed partial thickness cartilage fibrillation on the humeral trochlea, consistent with a grade 2 Modified Outerbridge[7] ([Fig. 2]). The separated anconeal fragment described on the CT was readily visible and was mobile on probing, further supporting a diagnosis of complete separation. There was mild to moderate synovitis in the region of the medial coronoid. Humeroulnar incongruity was subjectively appreciated through elbow range of motion.

Fig. 2 Intra-articular structures of the caudal left elbow joint as seen via the caudomedial arthroscopic portal. (A) Trochlear notch, (B) completely separated anconeal process, and (C) humeral trochlea.

The procedure was converted to a left caudolateral elbow arthrotomy for fragment removal. A skin incision was made using a no. 15 scalpel blade beginning at the level of the distal humerus following the caudolateral edge of the bone distally. At the level of the lateral humeral epicondyle, the incision was made to curve between the epicondylar crest and the tuber olecranon and continued distally along the ulna in line with the anconeus muscle. The subcutaneous fat and fascia were incised on the same line as the skin incision and elevated from the deep brachial fascia to allow retraction of the skin margins. The anconeus muscle was then elevated cranially and proximally using a periosteal elevator. The joint was cleanly entered by making an incision into the joint beneath the anconeus muscle at the anticipated level of the anconeal process. The fragmented anconeal process was located and elevated using a periosteal elevator, grasped with a curved haemostat and successfully removed ([Fig. 3A, B]). The joint capsule and anconeal fascia/periosteum were opposed in multiple cruciate sutures using 3–0 polydioxanone suture followed by the antebrachial fasci and subcutaneous tissue in a simple continuous buried fashion and finally the skin in an intradermal pattern, both using 3–0 glyconate suture. No intraoperative complications were experienced.

Fig. 3 Gross dimensions (A) and stereozoom microscopic appearance (B) of the left anconeal process fragment removed via left caudolateral elbow arthrotomy.

 

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Postoperative Diagnostics

Immediate postoperative CT confirmed complete removal of the anconeal fragment ([Fig. 4]). Recovery from anesthesia was uneventful, and postoperative analgesia was provided with Methadone (Ilium Methadone, Troy laboratories Pty. Ltd., New South Wales, Australia; 0.2 mg/kg IV every 4 hours as needed) and a single dose of a nonsteroidal anti-inflammatory (Meloxicam, Metacam 5 mg/mL, Boehringer Ingelheim Animal Health Australia Pty. Ltd. New South Wales, Australia; 0.1 mg/kg) IV injection upon recovery.

Fig. 4 Frontal (A) and sagittal plane (B) reconstruction of the postoperative computed tomography scan of the left elbow, confirming successful removal of the separated anconeal process fragment (asterisk).

Macroscopically, the removed fragment was a completely separated cartilage capped piece of trabecular bone measuring 9 × 8 × 6 mm ([Fig. 3A, B]). On histopathological evaluation at 40× magnification, there was a band of organizing fibrosis and mild multifocal bone proliferation extending along the separation line ([Fig. 5]). The separation line of the anconeal process had a paler band of fibrous tissue and fibrocartilage below thickened trabeculae of bone. The histopathological conclusion was consistent with an acute traumatic separation of the anconeal process secondary to an underlying UAP.

Fig. 5 Hematoxylin and eosin (H&E)-stained light microscopic histopathological image of the anconeal fragment at 40× magnification. The separation line of the anconeal process has a paler band of fibrous tissue and fibrocartilage (*) below thickened trabeculae of bone. Scale bar = 200 µm.

 

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Follow-up

On the day following surgery, the dog was weight-bearing on the operated limb at the walk and offloading the limb while standing. The dog was discharged 1 day postoperatively with oral analgesia (Meloxicam, Metacam 5mg/mL, Boehringer Ingelheim Animal Health Australia Pty. Ltd. NSW, Australia; 0.1 mg/kg once daily) and trazodone (Trazodone HCL, BOVA, NSW, Australia; 7 mg/kg three times daily). At home, exercise instructions were limited to leashed elimination walks of 5- to 10-minute duration, two to three times daily for the first 2 weeks, followed by progressive return to function as directed by follow-up examinations.

The medium-term follow-up was managed by a board-certified specialist in Sports Medicine and Rehabilitation (XX). On examination at the routine 2-week postoperative examination, the dog exhibited a moderate left thoracic limb lameness but remained comfortable through passive range of motion of the left elbow. The plan was amended to include physiotherapy exercises and the dog completed 10 weekly sessions of hydrotherapy in the underwater treadmill. The dog was reevaluated 5 weeks postoperatively. Orthopaedic examination revealed a mild left thoracic limb lameness with no overt discomfort through full range of motion of the left elbow, including in extension. On examination at 5 months postoperatively, there was complete resolution of the left thoracic limb lameness, and the dog had returned to normal unrestricted activity. At telephone follow-up 20 months postoperatively, the owner reported normal activity and no lameness even after exuberant exercise.

 

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Discussion

This report describes the clinical, diagnostic, and surgical findings with regular orthopaedic and sports medicine rehabilitation follow-up in a 1-year-old male neutered French Bulldog following acute, traumatic, complete separation of the anconeal process. Histopathology and CT findings were suggestive of bilateral incomplete fusion of the anconeal process prior to minor trauma on the left thoracic limb that resulted in traumatic anconeal process separation. This report discusses the aetiopathogenesis of UAP and a possible link with traumatic anconeal process separation in a dog, supported by a comprehensive diagnostic and therapeutic approach.

UAP is most commonly observed in 5- to 12-month-old medium-large breed dogs such as German Shepherds and hound breeds.[2] Depending on the breed, the ossification centre of the anconeal process mineralizes between 10 and 16 weeks of age with complete fusion to the ulna by approximately 20 weeks.[2] The underlying pathogenesis remains poorly understood, with proposed mechanisms including inherited developmental anomalies, metabolic defects, nutritional deficiencies, genetic disturbance of normal growth-stimulating hormones, and traumatic episodes.[2] Clinically, dogs with UAP often present with a mild to moderate weight-bearing lameness; however, the dog in this report had no prior history of lameness. It is possible that a mild bilateral thoracic limb lameness may have gone unnoticed by the owner as the preoperative CT described a caudomedial cleft in the contralateral anconeal process, suggestive of incomplete fusion of the anconeal process, with secondary osteoarthritic changes.

We speculate that a fatigue “fracture” or separation occurred in this case, with minor trauma (jumping off the couch) resulting in acute complete separation through weakened fibrous or fibrocartilaginous tissue that exists in dogs with UAP. Separation may be a more appropriate term given the suspicion for incomplete fusion of the anconeal process. With the limb in extension during landing, the anconeal process may have been entrapped by the epicondylar ridges, creating a shearing force resulting in separation along the weakened UAP.[4] This was also suspected in two previous case reports in dogs with a history of minor trauma; however, a histological diagnosis was lacking.[3] [5] In this dog, histological examination of the excised fragment reported a band of organizing fibrosis and mild multifocal bone proliferation extending along the separation line. This is consistent with a more chronic process; bone remodelling and secondary healing following the initial separation, which is suspected to have occurred 8 weeks prior to the diagnosis and surgery. The histology findings could also be consistent with incomplete fusion of the anconeal process, which was noted on the contralateral side. In comparison, the two previous reports in cats and one in a dog, describe an anconeal fracture through radiographically normal bone following major motor vehicle trauma.[4] [6] Histology was performed in the canine case; a 14-month-old Boxer, where the fracture line was described as sharp/straight with a thin surface layer of disorganized haemorrhage and other features consistent with an acute response to trauma.[4] An association between UAP and anconeal fracture has only previously been histologically documented in swine by Kincaid and Lidvall.[8] In that study, histopathology on the elbows of five pigs with anconeal process fractures revealed a composition of fibrous connective tissue and fibrocartilage, similar to the histopathology findings in this case. Additionally, there was proliferation of subperiosteal bone noted at the base of the anconeal process, which formed a “buttress callus.”[8] A similar finding was appreciated in our case described as mildly to moderately thickened bone trabeculae towards the separation line. Given the uncertainty in defining this as a fracture due to the presence of fibrous/fibrocartilaginous tissue, we have used the term “acute traumatic complete separation” of the anconeal process.

There were no features on arthrocentesis, CT, or histology of the anconeal bone fragment that defined a cause for the incomplete fusion of the anconeal process. Joint fluid cytology was not able to provide a specific diagnosis or suggestion for underlying cause other than being consistent with a traumatic or degenerative arthropathy associated with trauma. We can only speculate in this case. A congenital and/or developmental disorder, such as shortened ulna or deformity of the ulnar semilunar notch, may have placed abnormal stresses on the anconeal physis, preventing complete fusion. This is of interest as canine elbow dysplasia is reported to primarily affect medium-large breeds, although smaller chondrodystrophic breeds such as the Dachshund and French bulldog, have also been reported.[2] [9] [10] Yet, to the best of the authors' knowledge, UAP, a subset of canine elbow dysplasia, has not been previously reported in the French bulldog, while medial coronoid disease and elbow incongruity have.[11]

Asymmetric widening of the humeroulnar joint was seen bilaterally on CT. On arthroscopic examination, a grade 2 Modified Outerbridge cartilage lesion was noted on the humeral trochlea, which may be suggestive of humeroanconeal incongruity. Humeroanconeal incongruity was documented arthroscopically by Danielski and Yeadon in a controlled clinical study in spaniel breed dogs with humeral intracondylar fissures (HIF).[12] The authors described a humeroanconeal cartilaginous lesion on the caudal humeral condyle and proposed it to be associated with focal humeroanconeal incongruity defined as mechanical impingement of the anconeal process within the olecranon fossa.[12] Arthroscopy findings in this dog revealed a similar cartilage lesion, supportive of humeroanconeal incongruity that may have contributed to anconeal process separation when the dog landed with the limb extended to cause focal impingement of the anconeal process on the olecranon fossa.[12] In this case, no HIF was noted on CT or arthroscopically, which contrasts with the findings by Danielski and Yeadon where the cartilage lesion was found in all dogs with HIF but in no dogs without HIF.[12] This may reflect a form of elbow incongruity unique to the French bulldog. The same authors recently reported partial or complete HIF healing following bioblique dynamic proximal ulnar osteotomy in spaniel breed dogs, supporting their theory of humeroanconeal incongruity in the pathogenesis of HIF.[13] Future research is warranted to determine if incomplete anconeal process fusion could be improved with correction of humeroanconeal incongruity by proximal ulnar osteotomy.

Current treatment recommendations for dogs with a UAP include fragment excision, lag-screw fixation, proximal ulnar osteotomy and a combination of the latter.[2] A consensus for recommended management of traumatic anconeal process fracture with possible underlying UAP in dogs is lacking owing to the rarity of this presentation. In this case, fragment excision was preferred over open reduction and internal fixation due to the elapsed time since original injury, small fragment size and its hypoattenuating/demineralized appearance on CT. The postoperative CT confirmed complete fragment removal with the described surgical technique and histology definitively diagnosed the suspected bone pathology. The dog had a good clinical outcome with resolution of left thoracic limb lameness at the 5-month postoperative follow-up exam and as reported by the owner at 20-month postoperative. In two of the previous case reports in dogs and the single report of two cats with traumatic anconeal process fracture, fragment removal resulted in an excellent outcome with resolution of lameness and return to function.[3] [4] [6] A successful outcome was reported with lag screw fixation in a 1-year-old German Shepherd for traumatic anconeal process fracture.[5]

In this dog and all other published cases, mediolateral and craniocaudal radiographic elbow projections were nondiagnostic for anconeal process separation due to superimposition of the humeral condyles. To increase radiographic sensitivity, a flexed mediolateral view has been previously recommended and was reported as diagnostic in the case of the 14-month-old boxer.[4] This could have been used in our case report and may have yielded a diagnosis at initial presentation; however, ultimately CT was invaluable in identifying pathology bilaterally and providing a more global assessment of the elbow joints preoperatively and documenting complete fragment removal postoperatively.

 

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Conclusion

This case report described acute, traumatic, complete separation of the anconeal process in a 1-year-old French Bulldog and successful clinical outcome following fragment removal. CT, surgical, and histopathology findings were supportive of incomplete fusion of the anconceal process that likely predisposed the process to separation following low-energy trauma. Clinicians should consider the possibility of ununited anconeal process in cases of traumatic anconeal fracture/separation.

 

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Conflict of Interest

None declared.

Acknowledgments

None.

Authors' Contributions

L.M. contributed to the literature review and wrote/reviewed the manuscript. J.C. contributed to the case management, literature review, and review/revision of the manuscript. A.A. reported on the imaging findings related to the case and provided CT images. B.C. managed medium and long-term follow-up case management. S.Y. reported on the cytology and histopathology findings related to the case and provided relevant images. J.S. was the primary surgeon/clinician for case management and reviewed the manuscript. All authors reviewed and approved the final version of the manuscript.

• References

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Publication History

Received: 26 August 2024

Accepted: 29 December 2024

Article published online:
25 March 2025