Canine medial and lateral femoral condyles are equally prominent, but the articular surface of the medial femoral condyle projects more cranially than that of the lateral femoral condyle. There are three sesamoid bones in the caudal stifle joint region. Two are located in the heads of the gastrocnemius muscle caudal to the stifle joint and are called fabellae.
The sesamoid in the lateral head is the largest, is palpable, and articulates with the lateral femoral condyle, whereas the one in the medial head is smaller and may not have a distinct facet on the medial femoral condyle. The third is the smallest, is located in the proximal attachment of the popliteus muscle, and articulates with the lateral tibial condyle. The canine patella, or kneecap, is the largest sesamoid bone in the body.
It is an ossification in the quadriceps femoris muscle. The patella alters the pull, increases the moment arm, and protects the quadriceps tendon, as well as provides a greater contact surface for the tendon on the trochlea of the femur than would exist without the patella. The canine patellar articular surface is mildly convex. The canine tibia is the major bone in the crus. The triangular proximal tibia is wider than the distal cylindrical tibia. Medial and lateral tibial condyles, an intercondylar eminence, and a tibial tuberosity are on the proximal tibia.
The tibial plateau slopes distally from cranial to caudal. The extensor groove, on the cranial tibia and lateral to the tibial tuberosity, provides a pathway for the long digital extensor muscle.
There is a popliteal notch on the caudal tibia in the midline, where the popliteal vessels course. The tibia articulates with the fibula proximally, along the interosseous crest, and distally. The tibial cochlea articulate with the trochlea of the talus to form the talocrural joint. The canine fibula is a long, slender bone that articulates with the tibia and also serves as a site for muscle attachment. There is a distinctive groove in the lateral malleolus, the sulcus malleolaris lateralis, through which course the tendons of the lateral digital extensor and peroneus brevis muscles.
The tarsus, or hock, consists of the talus, calcaneus, a central tarsal bone, and tarsal bones I to IV see Figure The talus articulates with the distal tibia and has prominent ridges. At the talocrural joint, two convex ridges of the trochlea of the talus articulate with two reciprocal concave grooves of the cochlea of the tibia. The orientation of the grooves and ridges deviates laterally approximately 25 degrees from the sagittal plane.
This deviation allows the hindpaws to pass lateral to the forepaws when dogs gallop. The central tarsal bone lies between the talus and the numbered tarsal bones I to III.
Tarsal IV is large and articulates with the calcaneus and metatarsal bones, spanning this entire region. The canine hindpaw has five metatarsal bones; however, the first metatarsal can be short or absent. Dogs have many sesamoid bones that are embedded in tendons where there are significant compressive and tensile forces produced during muscle contractions. The sesamoid bones at the dorsal surface of each metatarsophalangeal joint align the extensor tendons for optimal joint action.
The sesamoid bones on the plantar surface of the hindpaw align flexor tendons. The spine consists of five areas of the vertebral column: the cervical vertebrae and its articulation with the head, thoracic vertebrae, lumbar vertebrae, sacral vertebrae, and the coccygeal vertebrae Figures through The number of vertebrae is listed in Box Carpal pad: Small pad palmar to the carpus.
Metacarpal pad: Largest pad palmar to the MCP joints; triangular in shape. Digital pads: Palmar to the DIP joints; ovoid and flat. Tarsal pad: Small pad plantar to the talocrural joint. Metatarsal pad: Largest pad plantar to the MTP joints; triangular in shape. Digital pads: Plantar to the DIP joints; ovoid and flat.
Borders: Inguinal ligament to C7-T1 disk. Caudal or coccygeal: Cd1-Cd20; some dogs have more or fewer. Sternum: 8 fused bones—manubrium or first sternebra, 6 additional sternebrae, and the xiphoid process. All vertebrae, except the sacral vertebrae, remain separate and form individual joints.
Four sites with limited motion exist within the canine spine. The nonparallel alignment of the articular surfaces markedly restricts joint accessory motions, such as glides. The restricted joint motions and areas resulting from these joint alignments include atlantoaxial motion other than rotation, the cervical C 7-thoracic T 1 junction, the caudal thoracic region, and the sacrum.
Individual vertebral bone size and shape vary among breeds. For any one breed, canine cervical through lumbar vertebrae are fairly consistent in size. The consistent size in dogs reflects the relatively equivalent cranial-to-caudal compressive loading. Because dogs are quadruped, there is weight bearing on all four limbs.
The massive cervical extensor muscle activity requires relatively large and strong cervical vertebrae to support the muscle mass. Canine intervertebral disks likewise change little in size from the cervical through the lumbar vertebrae. The C5-C6 area is a site of relative hypermobility in large dogs. The spinal cord ends at lumbar L L6-L7. The canine atlas, or C1 vertebra see Figure , has a transverse foramen in each transverse process, a craniodorsal arch, and right and left lateral vertebral foramina for the passage of cervical spinal nerve 1.
The atlas has correspondingly shaped condyles for articulation with the occiput. The canine lateral wings or transverse processes are prominent and easily palpable from the skin surface. The canine axis or C2 has a large spinous process with an expanded arch, a wide body, and large transverse processes see Figure The spinous process is nonbifid. The canine axis is very large relative to the size of other canine cervical vertebrae. The axis has a dens, which projects cranially to allow pivotal motion between the atlas and axis.
The condyles are oriented near the transverse plane to allow cervical spine rotation. The C3-C6 vertebrae have nonbifid spinous processes, large and flat spinous processes, caudal and cranial articular surface facets that are narrower than the transverse processes, large transverse processes, and transverse foramina for the passage of vertebral arteries. Caudal and cranial articular surfaces are oriented between the dorsal and transverse planes to facilitate cranial and caudal glides needed for cervical spine flexion and extension.
The C7 vertebra has a similar shape, a large prominent nonbifid spinous process, and caudal and cranial articular surfaces, which are oriented nearly craniocaudally. Thoracic vertebrae see Figure have small bodies relative to the size of the entire vertebrae.
Canine spinous processes are relatively long. The spinous processes block excessive extension of the thoracic spine. At T10, the size of the body begins to increase and the length of spinous process decreases. The spinous processes are oriented close to the transverse plane. Cranial to T11, the spinous processes project caudally, but caudal to T11, they project cranially.
Caudal and cranial articular surfaces are oriented close to the dorsal plane. Lumbar vertebrae see Figure have bodies that are larger than thoracic vertebral bodies. Canine lumbar transverse processes are long and thin, and they project lateroventrocranially. In the cranial lumbar spine, cranial and caudal articular surfaces are oriented between the transverse and sagittal planes, which facilitate lumbar spine flexion and extension.
The L7-S1 joint appears to orient between the sagittal and frontal planes to allow more rotation at this intervertebral level. The canine sacrum is relatively narrow and is linked to the pelvis with sacroiliac joints see Figure Caudal Cd vertebrae see Figure have distinct bodies and transverse processes.
The cranial articular surfaces are similar to those in more cranial vertebrae in shape and location; however, the caudal articular processes are bifid and are more centrally located, whereas articular processes in more cranial vertebrae are located more laterally.
Hemal arches are separate bones that articulate with the ventral surfaces of the caudal ends of the bodies of Cd4-Cd6. The hemal arches provide protection for the median coccygeal artery, which is enclosed by the arches. In vertebrae caudal to Cd6 and in relatively the same position as the hemal arches are the paired hemal processes, which extend from Cd7-Cd17 or Cd The ribs have vertebral attachments see Figure There are nine pairs of vertebrosternal, or true, ribs and four pairs of vertebrocostal, or false, ribs.
The sternum is relatively long and has a manubrium and xiphoid process, with a prominent xiphoid cartilage. The ribs limit overall thoracic spine motion and protect internal organs. The body segments of the forelimb and hindlimb are illustrated in Figures and , respectively, with the major joints and their flexor and extensor surfaces. Body segments are listed and defined in Box Types of joints are listed in Box Tarsal joints or hock joints this joint is referred to as the hock joint in common usage.
Talocalcaneocentral and calcaneoquartal joints combined. Synovial: Proximal and distal tibiofibular. The shape of articular surfaces of bones helps define the motions available for a joint. Articular surfaces of two bones forming a joint are usually concave on one bone and convex on the other bone.
Some articular surfaces are flat. Occasionally adjacent bones are convex on both joint surfaces. Intraarticular structures, such as the medial and lateral menisci in the stifle joint, may modify adjacent surfaces.
Understanding the concave-convex relationships as a guiding principle in determining joint motion allows prediction of possible joint motions based on articular surface shape. Ligamentous and other soft tissue around the joint guide and restrict the motion that would be possible based on articular surface shape alone.
Joint motions are named, most commonly, by movement of the distal bone relative to the proximal bone. For example, cranial movement of the tibia on a stable femur is named stifle joint extension. The major direction of motion, such as flexion of the stifle, is physiologic or osteokinematic motion. Accessory, or arthrokinematic, motion is smaller in magnitude and less observable. Examples of accessory motions are glide or slide, rotary motion, distraction or traction, and compression or approximation.
A normal amount of glide occurs in normal functioning joints. Glides are shear type or sliding motions of opposing articular surfaces. Rolls involve one bone rolling on another. Gliding motion in combination with rolling is needed for normal physiologic joint motion. Spins are joint surface motions that result in continual contact of articular cartilage areas on opposite sides of a joint. Distraction or traction accessory motions are tensile or pulling-apart movements between bones. Compressive or approximation accessory motions are compressive or pushing-together movements between bones.
Normal joint motion involves both physiologic motion and accessory motion. Physiologic motion in joints with opposing concave and convex articular surfaces involves both roll and glide. Roll occurs in the same direction as the movement of the moving segment of the bone, but glide directions differ based on whether the moving articular surface is concave or convex.
A glide is described by identifying the joint motion, the direction of the glide, and which bone is moving. For example, stifle flexion involving the tibia and femur is termed caudal glide of the tibia on the femur. Joint motions are named by one body segment approaching or moving away from another body segment or movement of some referenced body landmark. Joint motions are named in the following sections and described see Figures and as they refer to the limbs, starting from normal stance.
Limb motion is usually described by motion of the joint rather than a body segment. For example, elbow flexion is recommended rather than forearm flexion. Occasionally, body segment motion is used to describe limb motion when motion does not involve axial motion with a joint as a pivot point. The anatomy of the feline musculoskeletal system usually reflects its size, mobility and diet Conzemius et al.
In particular, the feline musculoskeletal system is more flexible, skeletal muscles are strip-shaped and the intermediate connective tissue is looser. Cats are relatively smaller in size and have a bigger body surface to body weight ratio, resulting in a lighter skeleton. Feline long bones have a wider medullary canal and thinner cortex and the flat bones have a width of barely a few millimetres, resulting in higher risk for greenstick or complete fractures during surgical manipulations for internal or external fixation Ness et al.
Furthermore, in contrast with dogs the feline long bones are relatively straighter and tubular, and the medullary canal has the same diameter in all length, a fact which ensures the effectiveness of intramedullary fixation Scott and placement of stainlesssteel ring fixation sutures in their metaphyses. If we compare the epiphyseal growth plates between the two species, feline epiphyseal plates are plainer and more horizontal in general.
As in dogs, the epiphyseal growth plate closure time is individualised and there is no particular order for growth plate fusion, however epiphyseal growth plates can be categorised in three types relative to the time of closure as it is summarised in Table 3 Smith Epiphyseal growth plates which close late are mostly affected by delayed closure and in certain cases cartilage remnants can persist in animals older than two years.
Nevertheless, in contrast to dogs, angular limb deformities are less frequent in cats, mostly due to smaller size and reduced development potential. Veterinary surgeons should be aware of these processes during the surgical approach of the peripheral scapula, during retraction of the infraspinatus muscle from the scapular spine, as well as in order to avoid fractures of the coracoid process Johnson a. Figure 1. The clavicle bone can be observed cranial to the feline shoulder joint in radiographs, which is without clinical significance, but it should not be mistaken for a scapular fracture Figure 2.
Figure 2. These anatomical structures are worthy of note during surgical approach and internal fixation of the distal end of the humeral bone Johnson b.
Moreover, the above anatomical structures can be trapped between bone fragments in supracondylar fractures of the humeral bone, and in this case the resection of the inner wall of the foramen is required.
Finally, intramedullary fixation of the humerus can be problematic due to the presence of the supracondylar foramen, due to the fact that while advancing the pin toward the distal end of the humerus, the tip can exit through the foramen and injure the median nerve and brachial artery. Figure 3. Lateral and craniocaudal depiction of the elbow joint of a cat. Figure 4. A short, large diameter intramedullary pin is advanced up to a few millimetres medially to the supracondylar foramen in the distal diaphysis of the humerus of a cat.
A longer, smaller in diameter intramedullary pin is advanced up to the median epicondyle of the humerus of the cat running through the surpracondylar foramen modified from Langley-Hobbs []. The feline ulnar nerve is located beneath the short part of the medial head of the triceps brachii muscle Figure 5. This muscle is located caudal to the medial epicondyle of the humerus, where it inserts in the medial aspect of the olecranon. Care should be given in avoiding injury to the ulnar nerve during retraction of the muscle in order to visualise the fracture site Johnson b.
Figure 5. It is visible in mediolateral radiographs of the elbow joint, in the craniolateral aspect of the radial head Figure 6 and it should not be mistaken for osteophytes or chip fractures Wood et al.
Figure 6. Lateral radiograph of the elbow joint of a cat where the sesamoid bone in the tendon of origin of the supinator muscle of a cat can be visualised arrow modified from Thrall []. Because there is greater mobility between the two antebrachium bones in comparison with dogs, fracture management by fixation of only one of them may lead to insufficient stabilisation of the other Schrader Figure 7.
The ligamentum teres provides a significant portion of the feline femoral head perfusion, as opposed to dogs Culvenor et al. This might explain the fact that avascular necrosis of the femoral head has not been observed in cats.
The muscles surrounding the hip joint present certain differences between dogs and cats, which should be taken into consideration during hip joint surgical approach. The tensor fasciae latae muscle and the vastus lateralis muscle are wider in cats.
Furthermore, in cats the gluteal muscles are larger, rendering the surgical approach of the hip joint more challenging Johnson c. The sartorius muscle, which is encountered during lateral surgical approach of the femur Johnson c , is singular in cats, whereas in dogs it has a cranial and caudal head. The main stress points of the acetabulum in cats are the central and caudal third, in contrast to dogs where the stress points are in the cranial third.
It is worthy of note that in cats the cranial cruciate ligament is broader than the caudal, a fact that is considered to be one of the factors contributing to relatively low frequency of rupture Scavelli , Umphlet Finally, each of the two lateral ligaments of the tibiotarsal joint is comprised by two short ligaments, meaning that there is no long segment as in dogs.
The veterinary surgeon needs to be aware of this fact when performing a dorsal approach to the cervical spine. Furthermore, the absence of supporting ligaments is the reason why the cervical spine tends to flex in feline neuromuscular disorders. In cats there is relatively inaccurate correspondence between neurotomes and vertebrae as opposed to dogs, therefore a localized lesion tends to affect a smaller number of neurotomes.
There is a historical tendency to use medical treatment for several feline orthopaedic disorders, whereas the same problems in dogs are managed surgically Ness at al. Even though there are times when medical treatment can be appropriate, treatment should be individualised in each case.
It is of key importance to realise that even though cats and dogs have several conditions in common, the two species differ greatly and cats should not be managed as small dogs, a fact which is one of the most common misconceptions in a clinical setting, not just in orthopaedics but in other disciplines as well.
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Saunders Elsevier, Philadelphia, pp. Johnson KA a The Scapula and shoulder joint. Elsevier Saunders, St. Johnson KA b The Forelimb. Johnson KA c The Hindlimb. Progr Vet Neurol 5, — Langley-Hobbs SJ Fractures of the humerus. In: S. Johnston, K. Veterinary Surgery Small Animal. Martin SL The domesticated cat. In: R. The Cat. Diseases and Clinical Management. Churchill Livingstone, New York, pp. McCarthy PH, Wood AK Anatomical and radiological observations of the sesamoid bone of the popliteus muscle in the adult dog and cat.
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