ABSTRACT
Osteochondrosis is a common disease that has been described in several farm and pet species as well as in some wildlife species, including captive roan antelope (Hippotragus equinus), a giraffe (Giraffa camelopardalis reticulata), snow leopard (Panthera uncia), and free-ranging wild boar (Sus scrofa ferus). It has not previously been confirmed in gray wolves (Canis lupus lupus). Postmortem radiographs of three free-ranging, juvenile sibling wolves revealed osteochondrosis in at least one of the glenohumeral joints (GHJs) in all individuals. Whole-body computed tomography and computed tomographic arthrography of both GHJs were performed in one case and suggested bilateral osteochondrosis lesions of the humeral head without cartilage flap formation. Cytologic examination of synovial fluid from the GHJs of this wolf was consistent with degenerative arthropathy. Macroscopic and histopathologic examination of the GHJs confirmed the presence of osteochondrosis manifesta in both males and the female. The identification of this condition highlights the importance of considering osteochondrosis in the differential diagnosis of lameness in both captive and free-ranging wolf populations.
Osteochondrosis (OC) is defined as an endochondral ossification disorder. It is characterized by focal thickening of the articular cartilage extending into the subchondral bone (Ytrehus et al. 2007), thought to be caused by a failure of blood supply to the growing cartilage (Carlson et al. 1989, 1991; Ekman and Carlson 1998; Ytrehus et al. 2004).
Osteochondrosis encompasses a wide range of continuous lesions, divided into the three subcategories: OC latens, describing focal ischemic lesions confined to epiphyseal cartilage; OC manifesta, whereby retention of necrotic cartilage is found in the subchondral bone, indicating a delayed endochondral ossification; and OC dissecans (OCD; also known as osteochondritis dissecans), characterized by cleft formation through the articular cartilage surface (Ytrehus et al. 2007). On imaging, only two subcategories can be distinguished: OC manifesta, which is characterized by a change in the shape of the subchondral bone; and OCD, in which there is a complete fissure through the cartilage, producing a flap, chondral, or osteochondral fragment (Morgan et al. 2000; Pollard and Phillips 2018). Osteochondrosis commonly affects young animals, with multiple risk factors including rapid growth, diet, trauma, and genetic and anatomic factors proposed (Ytrehus et al. 2007).
Pet and farmed species, such as dogs, horses, and pigs, are frequently affected by OC (Ytrehus et al. 2007), often associated with lameness. In contrast, description of OC in wildlife species is rare; it has been reported in captive roan antelope (Hippotragus equinus; Johnson et al. 2008), a reticulated giraffe (Giraffa camelopardalis reticulata; Basu et al. 2016), snow leopards (Panthera uncia; Herrin et al. 2012; Huckins et al. 2018), and in free-ranging wild boar (Sus scrofa ferus; Etterlin et al. 2017). In free-ranging canids, to date OCD-like lesions have been recorded in the glenoid cavity in one dingo (Canis lupus dingo; Lawier et al. 2015) and the mandible of four of 392 examined gray wolf skulls (Canis lupus lupus; Döring et al. 2018).
In domestic dogs, OC frequently affects the caudocentral aspect of the humeral head, as well as the humeral trochlea, femoral condyles and trochlea, and talus (Pollard and Phillips 2018). The primary screening method is radiography (Kippenes and Johnston 1998), with the addition of computed tomography (CT), particularly CT arthrography, if lesions are not visible (Kippenes and Johnston 1998). Magnetic resonance imaging offers the best diagnostic imaging sensitivity for humeroscapular OC diagnosis (Wall et al. 2015). The clinical gold standard remains shoulder arthroscopy, although histopathologic assessment is regarded as the overall gold standard; the latter can only be performed in dead animals (van Bree and Van Ryssen 1998).
In Switzerland, wolves are a federally protected species (Swiss Federal Hunting Act). According to the “Swiss Wolf Concept,” a law enforcement aid, every wolf found dead or shot until summer 2023 was submitted to the Institute for Fish and Wildlife Health of the Vetsuisse Faculty, University of Bern, Switzerland to undergo a standardized postmortem examination, including a full-body radiograph.
In October and November 2022, three juvenile gray wolf siblings, two males (M1, M2) and one female (F1), from a pack in eastern Switzerland were legally shot as part of a population regulation measure and submitted to the Vetsuisse Faculty for postmortem examination. Their ages were estimated by correlation of dental evaluation (Gipson et al. 2000), radiographic, and reproductive organ findings. After the findings in these wolves the carcasses of their sire (M3) and grandsire (M4), submitted in March 2023 and November 2022, respectively, were subjected to additional screening for OC.
All five animals underwent full-body laterolateral radiographs, plus mediolateral radiographs of the glenohumeral joint (GHJ). One wolf (M1) underwent full-body CT and CT arthrography of the GHJ (with a 16-slice multidetector CT, Philips Brilliance 16, Philips Medical Systems BV, Best, Netherlands) using the following parameters: 120 kV, 180 mA, 0.8-mm slice thickness, pitch of 0.5. The CT was followed by cytologic examination of the obtained synovial fluid. Direct smears and cytocentrifuge preparations of the synovial fluid were stained with Wright–Giemsa stain (Hematek, Siemens, Switzerland) and microscopically examined for cellularity and cellular morphology. Fluid volume was insufficient to perform an automated total nucleated cell count or protein measurement. All wolves underwent a macroscopic examination using a standardized postmortem protocol, modified for taxidermy purposes. After consulting with the submitter, permission was granted to examine the GHJs of the three siblings and the sire, including opening the joints and humeral head removal. In the case of the grandsire (M4), joints could not be opened because of taxidermal use.
Histopathologic examination was performed bilaterally on the humeral heads of all three siblings where macroscopic changes were detected by visual inspection and radiology. Calcified hard bone tissue was cut into 5- to 6-mm-thick pieces using a diamond saw, then fixed in 4% neutral buffered formaldehyde solution for at least 48 h. Tissues were decalcified following Kristensen's protocol (Kristensen 1948) using Kristensen solution (produced in-house) at 37 C in a shaker (Edmund Bühler GmbH, Bodelshausen, Germany). Once sufficiently softened (30–48 h), bone sections were embedded in paraffin, cut at 4-μm thickness, and stained with H&E for histopathologic evaluation.
The signalments and findings in the musculoskeletal system of the five wolves are summarized in Tables 1 and 2 respectively. Radiographic findings included a bilateral concave indentation of the subchondral bone at caudal third of the humeral head of M1, with lengths of 11.9 mm and 12.7 mm on the left and right sides, respectively. The defects demonstrated irregular margination and were surrounded by mild subchondral bone sclerosis. This led to the radiologic diagnosis of bilateral GHJ OC. In F1, flattening of the caudal third of the humeral head and a mild irregular subchondral bone surface were noted, which were more pronounced on the right than on the left side (Fig. 1 A, B). Similar mild flattening was noted in the right humeral head of M2, but no radiographic changes were observed in the left GHJ of M2, nor in the GHJ of M3 or M4. This led to the suspicion of osteochondrosis lesions of the humeral head, affecting both forelimbs in F1 as well as the right forelimb in M2.
Mediolateral radiographs of the left (A) and right (B) glenohumeral joints (GHJs) of F1, a juvenile female European gray wolf (Canis lupus lupus) from Switzerland. A flattening of the caudal third of the humeral head and a mild irregular subchondral bone surface are noted (arrows), being more pronounced on the left than on the right side. Sagittal multiplanar computed tomographic reconstructions of the left GHJ before (C) and after arthrography (E) and right GHJ before (D) and after arthrography (F) of M1, a juvenile male European gray wolf from Switzerland. At the mid- to caudal third of the humeral head there is a large (left more pronounced than right) semilunar-shaped subchondral bone defect visible (arrows), demonstrating mildly irregular margins and surrounded by mild, ill-defined sclerosis. The contrast (E, F) outlines a smooth, intact, and convex-shaped articular cartilage covering the subchondral defects in both GHJs, compatible with osteochondrosis. Multiple intra-articular gas inclusions (due to the contrast injection) are visible.
Mediolateral radiographs of the left (A) and right (B) glenohumeral joints (GHJs) of F1, a juvenile female European gray wolf (Canis lupus lupus) from Switzerland. A flattening of the caudal third of the humeral head and a mild irregular subchondral bone surface are noted (arrows), being more pronounced on the left than on the right side. Sagittal multiplanar computed tomographic reconstructions of the left GHJ before (C) and after arthrography (E) and right GHJ before (D) and after arthrography (F) of M1, a juvenile male European gray wolf from Switzerland. At the mid- to caudal third of the humeral head there is a large (left more pronounced than right) semilunar-shaped subchondral bone defect visible (arrows), demonstrating mildly irregular margins and surrounded by mild, ill-defined sclerosis. The contrast (E, F) outlines a smooth, intact, and convex-shaped articular cartilage covering the subchondral defects in both GHJs, compatible with osteochondrosis. Multiple intra-articular gas inclusions (due to the contrast injection) are visible.
Signalment, nutritional status, and additional pathologic findings observed on full-body radiographs of five related gray wolves (Canis lupus lupus), three juvenile siblings (female F1, males M1 and M2) and their sire (M3) and grandsire (M4). The wolves were legally shot in Switzerland in 2022 and 2023. Osteochondrosis was observed in the three immature siblings (F1, M1 and M2).

Radiologic, macroscopic, and histopathologic findings in the humeral heads of five related gray wolves (Canis lupus lupus). The wolves, three juvenile siblings (female F1, males M1 and M2) and their sire M3 and grandsire M4, were legally shot in Switzerland in 2022 and 2023. The radiologic and macroscopic descriptions report the appearance of the caudal aspects of the humeral head in the wolves.

Native CT of the entire body as well as CT arthrography of both GHJs was performed in M1. At the mid- to caudal third of the right humeral head, a large semilunar-shaped subchondral bone defect was visible, demonstrating mildly irregular margins (Fig. 1D). The latter was surrounded by mild ill-defined sclerosis. On the left humeral head, a larger lesion with the same characteristics as on the right side was observed (Fig. 1C). After arthrography, the contrast outlined a smooth, intact, convex-shaped articular cartilage covering the subchondral defects in both GHJs (Fig. 1E, F). Multiple intra-articular gas inclusions were visible and associated with the contrast injection, but did not hamper the evaluation. These findings were suggestive of OC lesions of the GHJs. The remainder of the skeleton was unremarkable.
Synovial fluid of the GHJ of M1 was sampled before performing arthrography. On cytologic examination it was pale straw colored and slightly cloudy, with high viscosity. Approximately six to eight nucleated cells were found per 40× high-power fields in thin areas (normal for dogs: ≤2; Fernandes 2020), with minimal blood contamination. Cells were all large mononuclear cells, predominantly synoviocytes or monocytes, occasionally in small clumps, with <5% vacuolated macrophages. Occasional osteoclasts were also seen. Taken together, cytologic findings were consistent with a degenerative arthropathy and exposure of subchondral bone (Fig. 2).
Cytologic preparations of glenohumeral synovial fluid taken postmortem from M1, a juvenile male European gray wolf (Canis lupus lupus) from Switzerland (Wright–Giemsa stain). Direct smear showing mildly increased numbers of synoviocytes with occasional clumping (magnification 400×). Inset: Cytocentrifuge preparation of synovoial fluid showing an osteoclase (magnification 1,000× oil).
Cytologic preparations of glenohumeral synovial fluid taken postmortem from M1, a juvenile male European gray wolf (Canis lupus lupus) from Switzerland (Wright–Giemsa stain). Direct smear showing mildly increased numbers of synoviocytes with occasional clumping (magnification 400×). Inset: Cytocentrifuge preparation of synovoial fluid showing an osteoclase (magnification 1,000× oil).
At postmortem examination, M1 had good nutritional status, whereas M2 and F1 had moderate and poor nutritional status, respectively. In all three siblings, moderately demarcated white foci were observed in the articular cartilage on the caudal articular surfaces of both humeral heads (Table 2). A sagittal section of the humeral head showed an irregular thickening of the articular cartilage that extended sharply into the primary cancellous bone (Fig. 3A, B). The maximal thickness of the observed cartilage changes in the humeral heads of the examined animals are presented in Table 2. In unaffected areas, the cartilage width was 0.1 cm in all three siblings. Additional musculoskeletal changes included a healed malunited left radius fracture and osteopenia in F1, a chronic Salter-Harris type 1 fracture of the left femur in M2 and a chronic oblique right olecranon fracture in M3. Opening the GHJ of the sire revealed normal thickness and regular appearance of the cartilage layer in both humeral heads.
Macroscopic and histopathologic findings in M1 and M2, two juvenile male European gray wolf (Canis lupus lupus) siblings from Switzerland, diagnosed with osteochondrosis manifesta. (A) Caudal view on the left and right humeral heads of M1, which exhibit each a focal, poorly demarcated opaque area at their caudal aspects (arrows). (B) Sagittal cut of the left and right humeral head reveals a focal, irregular thickening of up to 5 mm of the articular cartilage corresponding to the opaque areas (arrows). (C) Articular cartilage of the left humeral head of M1: a large cone-shaped focus of retained cartilage extends into the subchondral bone (arrowheads), indicative of an endochondral ossification failure (H&E, magnification 40×). (D) Articular cartilage of the right humeral head of 2: necrotic cartilage canals (asterisk) are visible within and at the border of the areas of ischemic chondronecrosis (arrowheads) in the subchondral bone, which also shows signs of remodeling with presence of osteoclasts, osteoblasts and fibroblasts (H&E, magnification 100×).
Macroscopic and histopathologic findings in M1 and M2, two juvenile male European gray wolf (Canis lupus lupus) siblings from Switzerland, diagnosed with osteochondrosis manifesta. (A) Caudal view on the left and right humeral heads of M1, which exhibit each a focal, poorly demarcated opaque area at their caudal aspects (arrows). (B) Sagittal cut of the left and right humeral head reveals a focal, irregular thickening of up to 5 mm of the articular cartilage corresponding to the opaque areas (arrows). (C) Articular cartilage of the left humeral head of M1: a large cone-shaped focus of retained cartilage extends into the subchondral bone (arrowheads), indicative of an endochondral ossification failure (H&E, magnification 40×). (D) Articular cartilage of the right humeral head of 2: necrotic cartilage canals (asterisk) are visible within and at the border of the areas of ischemic chondronecrosis (arrowheads) in the subchondral bone, which also shows signs of remodeling with presence of osteoclasts, osteoblasts and fibroblasts (H&E, magnification 100×).
Histopathologic examination revealed focal or multifocal necrotic cartilage canals associated with surrounding areas of necrotic cartilage in the epiphyseal growth cartilage of both humerus heads of all three siblings. In the female, the thickening appeared flattened, with beginning retention of cartilage. In both males, lesions were more progressed, whereby clear, cone-shaped foci of retained cartilage extending into the subchondral bone were observed (Fig. 3C, D). On the right humeral head in M1, the subchondral bone showed remodeling with osteoclasts, osteoblasts, and fibroblasts. A cleft present in the growing cartilage did not extend to the articular surface. In the left humeral head, three areas of cartilage retention were observed. Similarly, the right humeral head in M2 exhibited a cleft in the growing cartilage, which did not extend to the surface of the joint. On both sides, there was evidence of remodeling in the subchondral bone, with osteoclasts, osteoblasts, and fibroblasts evident, and multifocal disturbance of the primary trabecula. Summarized, these findings were suggestive of OC manifesta. Histopathology was not performed in the sire and grandsire; therefore OC latens could not be ruled out in those individuals.
To our knowledge, OC manifesta has not previously been reported in free-ranging gray wolves. Other differentials, such as delayed ossification of the humeral head as a normal variation in these wolves, were excluded because of the typical morphologic features of the lesion on radiographs and histopathology. Similarly to domestic dogs, OC was diagnosed bilaterally and affected the caudal aspect of the humeral head, where the articular cartilage is usually thicker (Johnston 1998). In domestic dogs, males are more susceptible than females (Ytrehus et al. 2007); we confirmed lesions also in the female wolf, albeit showing a less severe form or earlier stage of the disease compared with her male siblings. However, the female individual (5- to 6-mo old) had been killed nearly 4 wk before her sibling M1 and nearly 6.5 wk before her sibling M2. This is in line with the typical age of 5–9 mo for clinical disease in the GHJ in dogs (Pollard and Phillips 2018; Schebitz and Wilkens 1977), and thus it remains unclear if the different disease severity is due to age or gender.
Osteochondrosis is a complex disease with multiple contributing factors, such as nutritional elements, heavy physical activity, or trauma. It is difficult to assess such factors in free-ranging animals. Two of the three wolves examined showed evidence of a previous trauma, representing a potential predisposing factor for OC. Furthermore, M1 had a very good nutritional status, which may be a potential risk factor for OC. However, M2 and F1 had a moderate and poor nutritional status, respectively (Mech 2008). Another possible predisposing factor in dogs is genetics, with conflicting heritability reported (Everts et al. 2000; Ytrehus et al. 2007; Ohlerth et al. 2016). Manifestation of the disease in all three siblings highlights the possible presence of a genetic predisposition, revealing a susceptibility inherited through their lineage. Therefore, it is necessary to monitor all individuals related to the original pack for OC lesions when they are to be necropsied in the future. No other wolves examined at our institution in previous years have shown evidence of OC lesions on radiographs, but the presence of OC in other individuals in previous years cannot be totally ruled out, as joints are not routinely opened, for reasons of carcass preservation for taxidermy.
Compared with large-breed dogs, it is unlikely that the lesions observed in the wolves had a clinical impact, as the cartilage was still intact. In dogs, lesions at this stage may either repair or progress to OCD, leading to potential lameness and later joint arthrosis. As no OC manifesta or OCD lesions have been reported previously in this population, it may be argued that such lesions potentially heal in wolves. Nevertheless, the previous reports describing subchondral defects resembling OCD in extinct dire wolves Aenocyon dirus (Schmökel et al. 2023), as well as in one dingo (Lawier et al. 2015) and the mandibles of four gray wolves (Döring et al. 2018), suggest that free-ranging canids can be affected by this disease.
Given our finding of OC manifesta in gray wolves, the possibility of this disease should be considered in free-ranging or captive-bred lame wolves. Additionally, our findings highlight the importance of a systematic examination of all organ systems and the advantages of radiographic examination preceding necropsy.
The authors express their gratitude to the Swiss Federal Office for the Environment, the Carnivore Ecology and Wildlife Management group KORA, the Laboratoire de Biologie de la Conservation at the University of Lausanne, and the hunting authorities of the canton of Grisons for their valuable support.