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. 2025 Nov 13;21:664. doi: 10.1186/s12917-025-04513-5

Computed tomography and magnetic resonance imaging of the normal distal limb in sheep (Ovis aries)

Mohamed Kamal Merai Abdel Maksoud 1,4,✉, Usama Hagag 2, Moustafa Salouci 3, HebatAllah Hamdy Mahmoud 1, Azza Ali Hassan Ibrahim 1
PMCID: PMC12613708  PMID: 41233783

Abstract

Background

Prevalence of lameness associated with distal limb affection is frequently reported in sheep. Lameness diagnosis requires a systemic orthopedic examination associated with a convenient imaging modality. Computed tomography (CT) and magnetic resonance imaging (MRI) are the most popular and accurate diagnostic modalities, providing high quality bone and soft tissue imaging. Consequently, this study aimed to combine CT and MR images with their correlative anatomical cross-sections for a comprehensive assessment of normal osseous and soft tissues in fore (n = 6) and hind (n = 6) distal limbs of lameness free sheep cadavers. These limbs were scanned using a multi-detector helical CT scanner and 1.5 tesla MRI magnet. The examined limbs were sectioned into sagittal, dorsal, and transverse slices. The acquired CT and MR images were identified and compared with the cross sections.

Results

The CT and MR images provided better visualization of the soft and bony structures of the distal limb in sheep. However, the CT images showed higher definition of the bony structures and a much clear demarcation of the trabecular pattern of the cancellous bone. These bony structures including the cortical, subchondral and cancellous bones. While, the MR images offered a valued delineation of the articular cartilage, which could not be evaluated using CT. The soft tissues in sheep distal limb including tendons, ligaments, interphalangeal joints, and interdigital gland were clearly visualized on CT and MR images. However, they were remarkably defined on the MR images.

Conclusion

CT and MRI, with the help of gross sections, admitted a comprehensive evaluation of normal soft and bone tissues constituting the distal limb in sheep. CT was appreciated to evaluate the osseous structures, while MRI was found to be the most effective for assessment the articular cartilages and soft tissues. The clinicians have to choose the appropriate modality, CT, MRI, or both, according to the clinical situations.

Keywords: CT, MRI, Distal limb, Anatomical cross-sections, Sheep

Background

Lameness is a common and major source of economic loss and poor welfare in sheep flocks [1, 2, 3]. Distal limb affection is one of the major and common causes of lameness in sheep [4, 5]. Therefore, it is important to develop an accurate diagnostic tool for a definite prognosis of the affected animals. Physical examination is frequently used for determination and diagnosis of common causes of lameness [6], while it is not possible to physically examine the swollen joints [7]. Traditional imaging tools such as radiography and ultrasonography could be useful for a presumptive diagnosis. Radiography is still the main musculoskeletal imaging technique due to its ready accessibility, low cost, and thorough description of the osseous structures [8, 9, 10], nevertheless, it is of restricted use for a precise diagnosis of superimposed osseous structures and soft tissues [11]. Although ultrasonography is the most cost-effective tool for assessing soft tissues, it is ineffective for evaluating deep structures [12]. High definitive diagnostic imaging techniques such as CT and MRI admit superior contrast resolution and provide discrimination of soft tissues and bone structures that can’t be defined correctly using traditional modalities [13].

Recently, there has been a great involvement of CT and MRI as diagnostic techniques in veterinary practices due to their various applications in both pet and productive animals [14, 15]. CT is characterized by high special resolution and three-dimensional reconstruction providing a detailed imaging of the bone elements [14]. MRI is a noninvasive imaging technique which widely used for visualization of soft tissue [15], due to its superior discrimination between various soft structures without using ionizing radiation [16]. Furthermore, these diagnostic tools enable clinicians to assess the degree of injury, determine the contributing cofactors of a disease’s susceptibility, and provide beneficial data in cases requiring surgical repair [17]. A brief knowledge of normal CT and MRI appearance of osseous and soft tissues is essential for effective use and precise interpretation of the data obtained by these tools during diagnosis of the pathological conditions [18, 19]. Normal CT and MRI of the distal limb have been reported in; bovine [12–18], dog [18], horse [19–21], and camel [22–26]. Normal CT and MRI appearance of fetlock joint have been previously studied [36], however, the imaging of other clinically relevant components of the distal limb and its unique structure in sheep, interdigital gland, were scarcely dealt. Accordingly, the aim of this study was to clarify the normal CT and MRI features of the distal limb in healthy sheep and correlate the obtained diagnostic images with their matched gross sections in an attempt to establish an anatomic reference guide for further clinical interpretation.

Results

The osseous elements forming the sheep distal limb involved distal extremity of metacarpus/metatarsus, three pairs of phalanges (proximal, middle, and distal), and the proximal and distal sesamoid bones. These osseous structures were depicted and clearly evaluated in all planes of CT and MR images (Figs. 1, 2, 3, 4, 5, 6 and 7). The articular surfaces of these bony structures shared in formation of three pairs of joints in each limb including; metacarpo/metatarsophalangeal joint, and the proximal and distal inter-phalangeal joints. The articular cartilages of these joints were depicted in sagittal and dorsal MR images as a thin layer of intermediate signal intensity (Figs. 2 and 3). In bone window CT images, these cartilages couldn’t be distinguished from the underlying subchondral bone. Moreover, it was challenging to identify the articular cartilages covering the articular surfaces of the sesamoid bones on CT images. The subchondral bone was delineated at the extremities of the phalanges and distal extremity of metacarpus/metatarsus as a thin layer of low signal intensity on MR images and intermediate tissue density on bone kernel CT images (Figs. 2 and 3). The cortical bone displayed a homogenous hypointensity on MR images compared to surrounding homogenous intensity soft tissues. Bone Window CT images provided a definite discrimination of the cortical bone from the medulla and cancellous bone, where it exhibited a higher tissue density with homogenous and smooth periosteal and endosteal surfaces (Figs. 2, 3 and 5). The cancellous bone could be differentiated from the cortical and subchondral bones, and it possessed heterogeneous intermediate to high signal intensity on MR images with unclear trabecular branches. While on CT images, the cancellous bone appeared with intermediate tissue density and showed a slightly branched trabecular pattern (Figs. 2 and 3). The medullary cavity and fat in the bone marrow between the trabecular spaces of the cancellous bone were also identified with homogenous high signal intensity on MR images and low tissue density on CT images (Figs. 2, 3 and 5). The cortical bone of the proximal and distal sesamoid bones was easily distinguished on CT images with higher tissue density comparing to the surrounding tissue, while on MR images the cortical bone exhibited lowered signal intensity. The cancellous bone of the sesamoid bones appeared with homogenous intermediate signal intensity on MR images and low tissue density on CT images (Figs. 2, 4 and 7). In addition, the hoof capsule was clearly depicted in all planes with heterogeneous intermediate signal intensity on MR images, and high tissue density on CT images (Figs, 2, 3, 7). While, the corium of the hoof was best outlined in transverse images with intermediate intensity on MR images, and low tissue density on CT images (Fig. 7).

Fig. 1.

Fig. 1

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Three-dimensional reconstructed computed tomographic dorsal view of the right fore distal limb of sheep. The numbered lines refer to the approximate planes of each anatomical section and its representative CT and MR images: sagittal plane (1), dorsal plane (2), and transverse planes (3–6). a, metacarpus; b, proximal phalanx; c, middle phalanx; d, distal phalanx; e, metacarpophalangeal (fetlock) joint; f, proximal interphalangeal (pastern) joint; g, distal interphalangeal (coffin) joint; h, abaxial distal sesamoid bones; rd, rudimentary digit III; rd’, rudimentary digit IV

Fig. 2.

Fig. 2

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Sagittal views of the right fore distal limb of sheep (plane 1 as referred in Fig. 1): anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, distal extremity of the metacarpus III; 2, cortical bone of metacarpus; 3, medullary cavity of metacarpus; 4, proximal sesamoid bone; 5, cancellous bone; 6, subchondral bone; 7, articular cartilage; 8, suspensory ligament; 9, interdigital phalangeo-sesamoidean ligament; 10, manica flexoria; 11, dorsal synovial pouch of the fetlock joint; 12, palmar synovial pouch of the fetlock joint; 13, dewclaw; 14, proximal phalanx; 15- cortical bone of proximal phalanx; 16, medullary cavity of proximal phalanx; 17, SDFT; 18, DDFT; 19, palmar ligaments of the pastern joint; 20, common digital extensor tendon; 21, dorsal synovial pouch of the pastern joint; 22, palmar synovial pouch of the pastern joint; 23, middle phalanx; 24, distal phalanx; 25, dorsal ligament of the coffin joint; 26, inserted part of the common digital extensor tendon; 27- dorsal synovial pouch of the coffin joint, 28, palmar synovial pouch of the coffin joint; 29, distal sesamoid bone; 30, abaxial collateral navicular ligament (proximal part), 31, abaxial collateral navicular ligament (distal part); 32, inserted part of the deep digital flexor tendon; 33, navicular bursa; 34, digital cushion; 35, hoof capsule

Fig. 3.

Fig. 3

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Dorsal views of the left hind distal limb of sheep (plane 2 as referred in Fig. 1); anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, distal extremity of the metacarpus; 2, cancellous bone; 3, subcondral bone; 4, articular cartilage; 5, sagittal ridge; 6, abaxial collateral ligament of the fetlock joint; 7, axial collateral ligament of the fetlock joint; 8, synovial pouch of the fetlock joint; 9, proximal interdigital ligament; 10, proximal phalanx; 11, cortical bone of the proximal phalanx; 12, medullary cavity of the proximal phalanx; 13, middle phalanx; 14, abaxial collateral ligament of the pastern joint; 15, axial collateral ligament of the pastern joint; 16, synovial pouch of the pastern joint; 17, neck of the interdigital gland; 18, distal phalanx; 19, hoof capsule

Fig. 4.

Fig. 4

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Transverse views of the right fore distal limb of sheep at the level of proximal sesamoid bones (plane 3 as referred in Fig. 1): anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, lateral digital extensor tendon; 2, lateral branch of the lateral tendon of common digital extensor muscle; 3, medial branch of the lateral tendon of common digital extensor muscle; 4, medial limb of common digital extensor tendon; 5, distal extremity of metacarpus; 6, sagittal ridge; 7, dorsal synovial pouch of fetlock joint; 8, palmar synovial pouch of fetlock joint; 9, abaxial collateral ligaments of fetlock joint; 10, axial collateral ligaments of fetlock joint; 11, axial proximal sesamoid bones; 12- abaxial proximal sesamoid bones, 13, interdigital interseamoidean ligament; 14, collateral sesamoidean ligament, 15, palmar ligaments of fetlock joint; 16, DDFT; 17, SDFT; 18, manica flexoria; 19, pl, palmar annular ligament

Fig. 5.

Fig. 5

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Transverse images of the left hind distal limb of sheep (plane 4 as referred in Fig. 1): anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, lateral digital extensor tendon; 2, lateral branch of the lateral tendon of the long digital extensor muscle; 3, medial branch of the lateral tendon of the long digital extensor muscle; 4, medial tendon of the long digital extensor muscle; 5, cortical bone of proximal phalanx; 6, medullary cavity of proximal phalanx; 7, DDFT; 8, SDFT; 9, manica flexoria; 10- proximal annular ligament; 11, adipose tissue

Fig. 6.

Fig. 6

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Transverse images of the right fore distal limb of sheep at level of proximal interphalangeal joint (plane 5 as referred in Fig. 1); anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, lateral digital extensor tendon; 2, lateral branch of the lateral limb of common digital extensor tendon; 3, medial branch of the lateral limb of common digital extensor tendon; 4, medial limb of common digital extensor tendon; 5, proximal phalanx; 6, middle phalanx; 7, abaxial collateral ligament of pastern joint; 8, axial collateral ligament of pastern joint; 9, plantar ligaments of pastern joint; 10, dorsal synovial pouch of pastern joint; 11, plantar synovial pouch of pastern joint; 12- neck of interdigital gland; 13, body of interdigital gland; 14, inserted part of SDFT; 15, DDFT; 16, distal annular ligament

Fig. 7.

Fig. 7

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Transverse images of the left fore distal limb of sheep at level of distal interphalangal joint (plane 6 as referred in Fig. 1): anatomical cross-section (A), MR image (B), bone window CT image (C), and soft tissue window CT image (D). 1, middle phalanx; 2, distal phalanx; 3, distal sesamoid bones; 4, joint cavity of coffin joint; 5, abaxial collateral ligaments of coffin joint; 6, axial collateral ligaments of coffin joint; 7, abaxial collateral navicular ligament (distal limb); 8, axial collateral sesamoidean ligaments, 9, insertion of DDFT; 10, digital cushion; 11, corium of hoof; 12, hoof capsule

The most clinically correlated soft tissues of the sheep distal limb were visualized and clearly identified in both CT and MR images. On the palmar/plantar aspect of the distal limb, SDFT and DDFT were clearly depicted with hypointensity on MR images, and hyperdensity in soft tissue CT images (Figs. 2, 4, 5, 6 and 7). The annular ligaments surrounding the digital flexor tendons could be seen with low signal intensity on MR images, and heterogeneous intermediate tissue density in CT images (Figs. 4, 5 and 6). Furthermore, the sleeve of SDFT, manica flexoria, could be delineated as a thin line of homogenous low signal intensity on MR images, and intermediate tissue density on CT images (Figs. 2, 4 and 5). In addition, the navicular bursa could be depicted with low signal intensity on MR images and hypodensity on CT images (Fig. 2). In addition, the digital extensor tendons could be depicted as two narrow strips on the dorsal aspect of each digit. In forelimb, lateral digital extensor tendon, lateral and medial branches of the lateral tendon of the common digital extensor muscle, and medial tendon of the common digital extensor muscle. In hind limb, lateral digital extensor tendon, lateral and medial branches of the lateral tendon of the long digital extensor muscle, and medial tendon of the long digital extensor muscle. These tendons displayed low signal intensity on MR images and intermediate tissue density on CT images (Figs. 4, 5 and 6).

The soft structural components of the joints in the distal limb were clearly defined and smoothly differentiated in CT and MR images. The synovial fluid within the joint cavities and their pouches exhibited homogenous intermediate signal intensity on MR images and hypodensity on CT images (Figs. 2, 3, 4, 6 and 7). The ligaments of each joint forming the distal limb were clearly outlined in several planes with low signal intensity on MR images, and heterogeneous intermediate tissue density on CT images. The transverse images provided a good depiction of most ligaments of the fetlock joint, including the collateral, palmar/plantar, interdigital intersesamoidean, and collateral sesamoidean ligaments (Fig. 4). While, the interdigital phalangeosesamoidean ligament was best outlined in the sagittal image (Fig. 2), and the proximal interdigital ligament was depicted in the dorsal image (Fig. 3). However, the short and cruciate ligaments couldn’t be identified using CT and MR images. The ligaments of the pastern joint; the collateral ligaments could be defined in dorsal and transverse images, and the palmar/plantar ligaments could be assessed in sagittal and transverse images (Figs. 2 and 6). In addition, the dorsal ligament of the coffin joint was visualized in the sagittal image (Fig. 2), and the collateral ligaments of this joint were outlined in the transverse image (Fig. 7). Furthermore, the abaxial collateral navicular ligament was delineated in the sagittal images (Fig. 2), while the axial one could be seen in the transverse image (Fig. 7).

Moreover, the two parts of the interdigital gland, body and neck, were clearly outlined in dorsal and transverse planes with low signal intensity on MR images, and intermediate tissue density on CT images (Figs. 3 and 6).

Discussion

To the author’s knowledge, the current study is the first report to correlate CT, MRI, and cross-sectional anatomy for assessment of the anatomical architecture of the sheep distal limb. This combination of normal CT, MRI, and gross sections provided a detailed description of the bony and soft tissue components and permitted a systemic characterization of the normal signal intensity and tissue density for each individual structure constituting the sheep distal limb.

In the current study, using CT and MRI allowed for a comprehensive visualization of thin sections in sheep distal limb into several customizable planes, which would enable the veterinary clinicians to interpret the distal limb in various perspectives and appropriately identify the lesion. However, the protocol used in this study to obtain these images in these planes and to maximize visualization of the various structures in the distal limb was longer than that expected in the practical situations. This prolonged protocol was designed to provide comprehensive and standard reference images of the normal structures in the sheep distal limb, which could help in accurate interpretation of CT and MR images in the clinical cases. Shorter protocols are recommended in clinical settings to reduce the acquisition time, and thus the cost, and risks of general anesthesia [37].

Previous studies examined normal CT and MRI appearance of the equine distal limbs in a standing position in an attempt to produce high-contrast diagnostic images and more detailed anatomic structures in a limited time with minimum acquisitions [28, 29]. Using CT and MRI in ruminants is still under progress and was restricted to the cadaveric research. Cadaveric limbs are frequently used to investigate normal MRI anatomy with similar signal intensity observed in live animals [38], and the results could be feasible to be applied in live animals [39]. The current investigation is a first attempt to describe normal CT and MRI anatomy using the cadaveric distal limbs of sheep. Understanding of normal tissue density and signal intensity based on cadaveric distal limbs of sheep could facilitate interpretation and overall assessment of tissue changes in the affected animals. Consequently, the annotated data provided standard anatomic reference for further clinical CT and MRI studies in sheep distal limbs.

Using CT and MRI in animal practices was hindered by high-cost, limited equipment, and the risks of general anesthesia, especially in large animals. Recently, medical imaging tools are progressively developed to be used as a part of the clinical diagnosis in animal clinics [40]. Moreover, CT and MRI scanners are readily available and widely used in pet clinics [15]. This rapid evolution in imaging modalities would encourage the veterinarians to introduce these tools in diagnosis protocols, especially in extensive sheep flocks. The obtained data in our study admitted an investigational overview using CT and MR images in correlation to anatomical cross-sections for future evaluation of several ovine arthopedic problems.

Diagnostic images play a crucial role in the evaluation of several limb injuries and help the physicians to early identify the main factors associated with the beginning and progression of the disease. Traditional radiography is commonly used for examination of the musculoskeletal disorders due to its low cost and feasibility, but it is less sensitive for imaging of the soft tissue, and comminuted fractures [41]. Ultrasonography is a relatively inexpensive tool that enables imaging of tendons, ligaments, synovial fluid, bone surface, and articular cartilage changes, however, its capacity to evaluate deeper structures is limited by attenuation of sound beams, operator dependence, and bone restrictions [12, 42]. Moreover, arthroscopy is an essential method for diagnosis of the intararticular pathologies as it provides a magnified view of the intararticular joint surfaces, however, it is an invasive tool depending on visual evaluation and manual palpation, and the deeper articular structures are unreachable because of anatomic limitations [43]. CT and MRI are valued alternatives that increased the diagnostic efficiency of the musculoskeletal diseases through reducing the superimposition of the soft tissues and improving visualization of tissue detail. Using CT and MRI in the current study provided a clear identification and assessment of entire soft and osseous structures in the sheep distal limb. CT admitted a comprehensive visualization of the osseous structures, including cortical and cancellous bones, with a clear demarcation of the trabecular pattern of the cancellous bone. In addition, CT images could be obtained in very small sections with excellent spatial resolution, facilitating a thorough investigation of bone lesions, therefore, CT has proved to be an efficient tool in the diagnosis of lameness related to distal limb disorders in horse [44]. However, the articular cartilages at the extremities forming the sheep distal limb could not be visualized on CT images. On MR images, the cartilaginous structures were easily delineated. Furthermore, MRI afforded higher soft tissue resolution than CT, displaying the extent of the pathological alterations in both soft and osseous tissues. Consequently, MRI is the best tool for assessment of soft tissue disorders, and CT is considered the technique of choice for examination bone damages [45]. In addition, using variable MRI sequences provides marked distinction and high definition of the relevant anatomic structures, which support precise identification and prognosis of several lesions [35, 39]. The current investigation is considered the first report to assess the sheep distal limb using a single sequence MRI (T1), so, further MRI studies on the sheep distal limb using different MRI sequences are recommended.

The signal intensity and tissue density of each individual structure in the sheep distal limb were recorded in this study to be a standard reference for further accurate interpretation of the CT and MR images obtained from the lame animal. At the articular surface of each joint, the articular cartilage displayed intermediate signal intensity adjacent to the suchondral bone, which had low signal intensity on T1-weighted MRI. Similar results were observed in camel [39] and horse [46]. However, on the same MRI sequence, the articular cartilage is visualized with high signal intensity in buffalo [25, 26] and camel [35], and an intermediate signal intensity in sheep [36]. On MR images, it was difficult to outline a definite demarcation between subchondral and cortical bones due to their low signal intensity. While bone window CT offered a clear limit between these osseous structures, where the cortical bone had higher tissue density than the subchondral bone. In addition, CT images provided a clear visualization of the trabecular pattern of the cancellous bone inside the medullary cavity. These findings supported the superiority of CT for assessment of bone disorders [45]. The cancellous bone in this study exhibited intermediate to high signal intensity on MR images and low tissue density on CT images similar to those observed in camel [35]. The fat of bone marrow in the medullary cavity between the trabecular spaces of the cancellous bone had high signal intensity on MR images and low tissue density on CT images. These findings came in line with those in sheep [36], and buffalo [26]. Foot affections are one of the most significant causes of lameness in dairy sheep [47]. The current study provided a clear delineation of the hoof to be a guide for further interpretation of clinical foot imaging in sheep. In agreement with the findings reported in bovine (25), the hoof capsule was visualized with intermediate signal intensity on MR images, and hyperdensense on CT images. While this capsule was depicted with low signal intensity on MR images and can’t be distinguished from the surrounding black background in bovine (24). Furthermore, the corium of hoof could be outlined in the current study with intermediate signal intensity on MR images, and intermediate tissue density on CT images. However, this corium was visualized on MR images with two patterns in bovine, either with low signal intensity [21] or high signal intensity [25]. Similar to the results reported in camel [35] and sheep [36], the synovial fluids appeared with intermediate signal intensity on MR images and low tissue density on CT images. While, this synovial fluid appeared with high signal intensity in buffalo [26], and low signal intensity in horse [27]. Moreover, the tendons appeared hypointense on MR images and hyperdense on CT images, while the ligaments had low signal intensity on MR images and intermediate tissue density on CT images. However, both tendons and ligaments exhibited low signal intensity on MR images and high tissue density on CT images in bovine [48]. Such variation in tissue intensity and density could be attributed to the variable acquisition settings, different magnetic field, or apparatus used [25]. Regarding the interdigital gland, the previous studies revealed the morphological [49, 50] and radiographic [51] characteristics of this gland. However, our study provided a novel visualization of the interdigital gland in sheep using CT and MR images, where it appeared with low signal intensity on MR images and intermediate tissue density on CT images.

Conclusion

The current investigation provided a comprehensive description of the osseous and soft tissue components of the distal extremities in sheep using CT and MRI. Bone window CT admitted a precise identification of the osseous structures, also, soft tissues could be evaluated on soft tissue windows with less identification than obtained by MRI. MRI was found to be more effective for assessing the articular cartilages and soft tissues. Due to the relative complex structure of the distal limb, interpretation of CT and MR images requires prior thorough understanding of the normal anatomy. The anatomical cross-sections in this study established basic anatomic data of the distal limb in sheep, which could be helpful for research and clinical use. The obtained data in this study could be used as a standard anatomic reference for further interpretation of CT and MR images of sheep distal limb in clinical practices.

Materials and methods

Animals

The current study was designed using twelve cadaveric distal limbs (6 fore and 6 hind) of adult healthy Egyptian sheep with mean age of 2.36 ± 0.77 years, and mean weight of 20.16 ± 2.02 kg. These limbs were collected from the local slaughterhouse in Beni-Suef province, Egypt. These limbs were disarticulated at the carpometacarpal/tarsometatarsal joints and scanned fresh within two hours to avoid imaging artifacts. The limbs were inspected, thoroughly palpated to confirm that the limbs were free from any musculoskeletal abnormalities.

MRI protocol

The limbs were positioned with the palmar/plantar aspect contacting the examination table. T1-weighted spin echo MR images were captured using a human knee coil and a 1.5 Tesla magnet MRI scanner (Philips Intera; Philips GmbH, Hamburg, Germany) in successive three planes: sagittal, dorsal, and transverse. The transverse images were obtained perpendicular to the metacarpus/metatarsus, the sagittal planes were parallel to the DDFT, and the dorsal planes were perpendicular to both transverse and sagittal planes. The MRI acquisition settings were; a repetition time (RT) of 500 milliseconds, echo time (TE) of 24 milliseconds, slice thickness of 4 mm, gap width of 1 mm, matrix size of 128, flip angle of 90, filed of view (FOV) of 150 mm, and total scan time 2 h; 22 m. The acquired images were inspected and grossly identified, and the signal intensity of each individual structure was recorded.

CT scanning

The limbs used for MRI are scanned using a multi-detector helical CT scanner (Alexion Toshiba; Philips Siemens, Japan). The limbs were adjusted on the CT table as in MRI examination. CT settings included: 120 KV, 150 mA, 1 ml slice thickness, 1 mm gapping, 0.75s rotation time, 250 matrix size, and 200 mm field of view. The limbs were scanned in a proximal to distal direction from the middle level of the metacarpus/metatarsus to the end of the distal phalanx. The images were acquired in sagittal, dorsal, and transverse planes, and then reconstructed into bone window (window level 350 HUs and window width 2700 HUs) and tissue window (window level 40 HUs and widow width 120 HUs). The obtained images were inspected and grossly identified, and the density of each individual structure was recorded.

Preparation of the anatomic slices

The synovial structures of the scanned limbs were injected with red latex. For the fetlock, pastern, and coffin joints, the needle was inserted into the dorsal pouch of each joint abaxial to the extensor tendons. The palmar/plantar pouches of fetlock joints of the two digits are communicated, so one puncture is sufficient for injection of both joints. The synovial fluid was withdrawn and replaced by the red latex. The limbs were cooled at -4 °C for 24 h until the latex became solid, and then frozen at -18 °C for one week. The frozen limbs were sectioned in 2 cm thickness into sagittal, dorsal, and transverse slices from the middle of the metacarpus/metatarsus to the end of the distal phalanx using an electric band saw. A total number of 35 transverse, 8 sagittal, and 8 dorsal sections were achieved in this study. The cut surface of each slice was cleansed and photographed. The gross slices were inspected, and the relevant gross anatomical structures were identified.

Matching of the MRI and CT images with the anatomic cross-sections

For a comprehensive assessment of the most clinically relevant anatomic structures in sheep distal limb, six MRI and CT images in three planes were selected and correlated with their matched cross sections according to the reference lines in Fig. 1: one in sagittal plane (Fig. 2), one in dorsal plane (Fig. 3), and four in transverse planes (Figs. 4, 5, 6 and 7). After identification of the osseous and soft structures in each anatomic slice, the most relevant structures were labeled on the corresponding CT and MRI images. In each figure, MR images were displayed in T1-weighted spin echo sequence, and CT images were presented in bone and soft tissue windows.

Acknowledgements

The authors would like thank the Science, Technology, and Innovation Funding Authority (STDF) in cooperation with the Egyptian Knowledge Bank (EKB) for their support in publishing this article.

Abbreviations

CT

Computed Tomography

DDFT

Deep Digital Flexor Tendon

MRI

Magnetic Resonance Imaging

SDFT

Superficial Digital Flexor Tendon

T1

T1-weighted turbo-spin echo

Author contributions

MKM Abdel Maksoud, and U Hagag designed the study, optimized and obtained CT and MRI settings. MKM Abdel Maksoud, and ALH Ibrahim participated in preparation of the anatomical sections and writing the manuscript. HH Mahmoud and M Salouci contributed in data analysis and manuscript editing. All authors revised and approved the manuscript. MKM Abdel Maksoud, and U Hagag designed the study, optimized and obtained CT and MRI settings. MKM Abdel Maksoud, and ALH Ibrahim participated in preparation of the anatomical sections and writing the manuscript. HH Mahmoud and M Salouci contributed in data analysis and manuscript editing. All authors revised and approved the manuscript.

Funding

Open access funding is provided by The Science, Technology & Innovation Funding Authority (STDF) in cooperation with The Egyptian Knowledge Bank (EKB). The presented study has not received any funds from any institutions or organizations.

Data availability

The datasets used and/or analyzed during the present study are available from the corresponding authors on reasonable request.

Declarations

Ethical approval and consent to participate

The current investigation is a prospective cadaveric study approved by the Institutional Animal Care and Use Committee of Beni-Suef University, Egypt (BSU-IACUC, Permit Number: 024–044). All procedures were achieved in accordance with relevant guidelines and regulations by the Basel Declaration and the International Council for Laboratory Animal Science (ICLAS).

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Change history

2/9/2026

A Correction to this paper has been published: 10.1186/s12917-025-05265-y

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets used and/or analyzed during the present study are available from the corresponding authors on reasonable request.

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