Introduction

Osteochondrosis is a common disorder of growth cartilage in domestic animals and humans.¹ When osteochondrosis progresses to the formation of a cartilaginous flap, clinical signs typically develop and the term osteochondritis dissecans is used. In dogs, articular osteochondrosis is commonly seen in the caudal central aspect of the humeral head, the medial aspect of the distal humeral condyle, the medial and the lateral distal femoral condyles, and the medial and lateral trochlear ridges of the talus.¹ Osteochondrosis of the glenoid cavity has been described in humans, pigs, and horses.^2–7 In dogs, a case of osseous cyst-like lesion of the glenoid cavity that was conservatively treated has been reported.⁸ The case reported here is distinct from that previously reported for three reasons: (1) The subchondral bone defect involving the glenoid cavity was associated with a cartilage flap, indicating that it was an osteochondritis dissecans condition. (2) The lesion was associated with a partial nonunion of the supraglenoid tubercle. (3) The lesion was treated surgically with a good outcome.

Case Report

A 5 mo old English setter was presented for a 10-day history of left forelimb lameness that worsened after exercise. Clinical findings included mild left forelimb lameness, pain upon palpation of the caudolateral part of the shoulder, and reluctance to extend the shoulder. Palpation of the supraglenoid tubercle area, abduction and flexion of the shoulder, and biceps compression test were normal. Physical examination of the right shoulder was unremarkable.

Orthogonal radiographic views of both shoulders were obtained under sedation (butorphanol^a 0.3 mg/kg IV and medetomidine^b 10 µg/kg IV). The mediolateral view of the left shoulder demonstrated an ill-defined subchondral lucency surrounded by sclerosis in the mid-glenoid cavity. The proximo-dorsal part of the supraglenoid tubercle was irregular. The mediolateral view of the right shoulder revealed a similar but smaller lucency along the subchondral bone of the mid-glenoid cavity.

Computed tomography (CT) scans of both shoulders were acquired. A CT arthrography of the left shoulder was performed at the same time. A subchondral bone defect was delineated in the central part of the glenoid cavity of the left shoulder with surrounding bone sclerosis (Figure 1A). This defect measured 8 × 9 × 3 mm, and the density (170 ± 21 HU) was consistent with thickened cartilage. On CT arthrography, this lesion was separated from the subchondral bone by the contrast medium, indicating cartilage fissure and flap formation (Figure 1B). These findings suggested osteochondritis dissecans on the left glenoid cavity. A small subchondral bone cyst (1.5 mm diameter) was also noted proximally to the defect. The supraglenoid tubercle was irregular and partially separated from the remaining scapula by a transverse fissure (Figure 1A). This finding suggested abnormal ossification of the supraglenoid tubercle. The CT scan of the right shoulder revealed a similar but smaller subchondral bone defect measuring 5 × 5 × 2 mm and small subchondral bone cysts. Evaluation of the right shoulder with CT arthrography was offered but declined by the owner due to the absence of overt lameness.

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After aseptic preparation of the left shoulder, a 30° oblique 2.7 mm arthroscope^c was inserted through a lateral portal and a palpation hook was inserted through a caudolateral portal. A large, fissured, and loosely attached flap of cartilage was apparent on inspection of the articular surface and the glenoid cavity (Figure 2A). Palpation led to spontaneous bleeding from the bone bed. A deep, anfractuous sinus lined with softened, wrinkled cartilage was observed on the caudal border of the cartilage flap. The palpation hook was replaced with a 35° oblique plasma-mediated bipolar radiofrequency ablation wand^d. The cartilage flap was then completely disintegrated in situ until small areas of bleeding were observed on the exposed bone bed (Figure 2B). Postoperative analgesia was provided with intravenous boluses of morphine^e (0.2 mg/kg q 4 hr for 12 hr) and intravenous administration of meloxicam^f (0.2 mg/kg). The dog was able to walk and was discharged the following day with a 10-day course of meloxicam^g (0.1 mg/kg q 24 hr). Exercise restriction was recommended for 4 wk. Arthroscopy of the right shoulder was also declined by the owner.

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The postoperative follow-up examinations revealed persistence of a mild weight-bearing lameness at 2 wk, which was further reduced at 6 wk and resolved at 3 mo postoperatively. The physical examinations at 3 and 18 mo postoperatively were unremarkable. At 18 mo postoperatively, the dog had returned to full activity, including hunting, and no lameness was apparent. Follow-up radiographs at 18 mo revealed mild osteophytosis, fusion of the supraglenoid tubercle, and healing of the subchondral bone defect on the left shoulder (Figure 3). The glenoid defect on the right shoulder had also healed.

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Discussion

This case report describes a case of presumed osteochondritis dissecans of the glenoid cavity in a 5 mo old English setter. As mentioned previously, only one case of a lesion of the mid-glenoid cavity has been reported in a 6 mo old Labrador retriever.⁸

In our case, CT and CT arthrography provided additional information to the survey radiographs, such as the extent of the cartilage flap, small subchondral bone cysts, and incomplete fusion of the supraglenoid tubercle.

A reliable assessment of the osteochondral lesion and demonstration of cartilage fissure and flap could also have been obtained via MRI, which appears to be the most useful diagnostic tool for osteochondrosis and osteochondritis dissecans of the humeral head in dogs.⁹ Ultrasonography could also have been used in our case. This modality is able to demonstrate lesions such as focal increased thickness and irregularity of the articular cartilage but can be associated with false-positive diagnoses.⁹ Ultrasonography is recommended only as an ancillary modality.⁹

The subchondral bone defect in the middle of the glenoid cavity was presumed to be a lesion of osteochondritis dissecans based on the cartilage flap formation. However, no definitive diagnosis could be determined from the histopathological analysis because the cartilage flap was disintegrated in situ. In a case series of 32 immature dogs with shoulder subchondral lesions, Lande et al. described a dog with imaging findings similar to the case reported here.⁸ In both cases, an oval lucent defect was found bilaterally in the mid-aspect of the glenoid cavity, with surrounding bone sclerosis. Even though the imaging findings were similar, Lande reported a case of osteochondrosis, whereas a cartilage flap was observed in the case presented here.

Subchondral bone cysts are rarely found in dogs and have been associated with osteoarthritis or osteochondrosis.^10,11 In contrast, subchondral bone cysts are commonly found in young racehorses in which a clear association of subchondral bone cysts with osteochondrosis and osteochondritis dissecans has been demonstrated.¹² A common etiopathogenesis involving failure of the blood supply to epiphyseal cartilage and ischemic chondronecrosis has been described.¹³ In horses, subchondral bone cysts can appear as irregular and multilobular areas when small and tend to become more spherical when large. In all cases, an opening is found showing communication of the cyst with the synovial cavity.¹² Similarities with the case reported here include the subchondral location of the cyst, the presence of an opening detected on arthroscopy, and the association with a presumed lesion of osteochondritis dissecans. In horses, incidental or small subchondral bone cysts may be left untreated.¹⁴ However, larger cysts and clinically affected horses benefit from cyst curettage and grafting.¹⁴ Reported grafting materials include cancellous bone, allogeneic chondrocytes with insulin-like growth factor, and bone substitute alone or in combination with platelet-rich plasma or bone marrow aspirate concentrate.¹⁴

Fusion of the supraglenoid tubercle occurs around 5 mo of age in the dog.¹⁵ The case reported here presented an abnormal ossification of the supraglenoid tubercle in association with the presumed glenoid osteochondritis dissecans. Separation of the left supraglenoid tubercle was incomplete. The fragment was considered stable and complete fusion was noted after conservative treatment. Abnormal ossification of the supraglenoid tubercle and cranial and mid-glenoid cavity resembling ostochondrosis, as seen in the case reported here, has already been described in an 8 mo old English setter by De Simone et al.¹⁶ In De Simone’s case report, the histopathologic findings obtained after core biopsy of the glenoid cavity were consistent with osteochondrosis or focal chondrodysplasia.¹⁶ However, this lesion was not associated with an osseous cyst-like lesion or cartilage flap in the center of the glenoid cavity, as observed in the case we report here.

Surgery has been shown to be the treatment of choice of humeral head osteochondritis dissecans in dogs and horses.^6,7,17 Surgery typically involves arthroscopic removal of the fragment and cartilage debridement until bleeding of the subchondral bone is obtained.^6,7,17 In the case reported here, portals for arthroscope, egress cannula, and instrument were placed as described for treatment of shoulder osteochondritis involving the humeral head.¹⁷ The 30° oblique vision of the arthroscope allowed complete evaluation of the glenoid cavity. Access to all parts of the glenoid cavity was easily achieved. Treatment of osteochondritis dissecans of the glenoid cavity did not appear to be more technically demanding than that of the humeral head. In the case reported here, removal of the fragment was achieved in situ by plasma-mediated bipolar radiofrequency ablation. With this method, there was no need for portal enlargement or multiple instrument removal and replacement in the portal. Cartilage removal and debridement were performed by introducing a single instrument. Limitations of plasma-mediated bipolar radiofrequency ablation include the cost of the equipment, the loss of the cartilage flap for histopathology, and possible inadvertent damage to surrounding structures. Plasma-mediated bipolar radiofrequency ablation causes volumetric removal of tissue at low temperatures ranging from 60°C to 80°C, with minimal collateral damage.¹⁸ Moreover, during arthroscopic removal of the cartilage, thermal damage to peripheral cartilage is limited by the constant influx of fluids.

In the case reported here, surgical removal of the cartilage flap on the left shoulder led to a favorable outcome. Although no specific conclusion can be drawn from this single case of presumed osteochondritis dissecans of the glenoid cavity, surgical treatment for osteochondritis dissecans is generally considered to be beneficial.¹ No specific treatment of the subchondral bone cysts found in our case was deemed necessary in view of their small size.

An evaluation of cartilage status on the right shoulder could have been obtained with CT arthrography, MRI, or arthroscopy.⁹ The owner declined further examination of the right shoulder based on the lack of clinical signs. The subsequent excellent outcome and absence of osteoarthritis on the right shoulder may indicate that surgery was not necessary on the right side.

Conclusion

In summary, this case report describes a form of osteochondrosis of the center of the glenoid cavity. A cartilage fissure and subchondral bone cysts were discerned by CT. Although lifelong follow-up was not available, arthroscopic radiofrequency ablation of the cartilaginous flap and curettage of the lesion led to a favorable outcome.