Joints A union or junction between two or more bones. Articulation
Joint Classification Joints can be classified by several criteria- Simple or Compound- by the number of bones articulating with each other. Simple- articulations united by two bones. Compound- articulations united by more than two bones.
Joint Classification Structural Classification- classified by their uniting medium. Fibrous- an articulation united by fibrous tissue allowing little or no movement. Cartilagenous- an articulation united by fibrocartilage, hyline cartilage, or both as in a symphysis. Synovial- an articulation united by a synovial joint capsule, these joints are freely movable.
Joint Classification Functional Classification- indicates the degree of motion possible. Synarthrosis- the tight, fixed union allowing little or no movement and having great strength. Ex. Skull bones Amphiarthrosis- connected by CT or fibrocartilage allowing slight motion. Ex. Vertebrae Diarthrosis- united by a joint capsule and are freely moveable- synovial joints. Gomphosis- the name for fibrous implantation of teeth into the jaw.
Synovial Joints Characterized by their mobility, joint cavity, articular cartilage, synovial membrane, and fibrous capsule. This is the most common type of joint. Functionally, it is freely moveable.
Synovial Joints Joint capsule- the 2 layered structure surrounding the joint. Fibrous layer- the white & yellow elastic fibrous part of the joint capsule. It attaches to the periosteum on or near the margin of the articular cartilage. Synovial membrane- the inner lining of the fibrous layer. It is highly vascular, nerve rich, and produces synovial fluid.
Synovial Joints Synovial fluid- the viscous liquid that lubricates the joint and supplies nutrients. Articular cartilage- the translucent cartilage covering the ends of bones. It reduces the effects of friction. Ligaments- strong bands of white fibrous CT uniting bones. They function to keep joint surfaces in apposition and still allow movement.
Synovial Joints Meniscus or Disc- a plate of fibrocartilage partially or completely dividing a joint cavity. It functions to allow a greater variety of motion and alleviate friction. Bursa- a sac-like structure between different tissue that reduces friction between these tissues.
Classification of Synovial Joints By movement- the contraction of muscles crossing a joint and the shape of a joint produce its characteristic movements. Plane- arthroidal joint having flat articular surfaces allowing a gliding or sliding motion. Ball & Socket- a spheroidal joint consisting of a spheroidal head fitting into a pit or socket.
Classification of Synovial Joints By movement… Hinge- a joint allowing movement at right angles. Pivot- allows rotation around a longitudinal axis of a bone. Condylar- formed by 2 condyles of one bone fitting into the cavities of another bone.
Movement of Synovial Joints Flexion- decreasing the angle between 2 bones. Extension- increasing the angle between 2 bones. Abduction- moving a part away from the medial plane. Adduction- moving a part toward the medial plane. Circumdunction- movement circumscribing a cone shape accomplished by combining flexion, abduction, extension, & adduction. Rotation- movement around the long axis of a part. Universal- all of the above movements.
Humeroradioulnar Head of the radius- articulates with the hureral condyle & the ulna. Trochlear notch of the Ulna- articulates with the trochlea of the humeral condyle. Anconeal process of the Ulna- fits into the olecranon fossa of the humerus.
Carpal Joints A hinge joint allowing flexion and extension with some lateral movement. It consists of 3 main joints: antebrachiocarpal, middle carpal, & carpometacarpal.
Antebrachiocarpal Radiocarpal joint Between the distal radius & ulna and the proximal row of carpal bones. Lots of movement.
Middle Carpal Joint Between the 2 rows of carpal bones. It communicates with the carpometacarpal joint. Lots of movement.
Carpometacarpal Joint Between the distal row of carpal bones and the metacarpal bones. Very little movement.
Intercarpal Joints Plane joints between the individual carpal bones. Articulations between the proximal ends of the metacarpal bones.
Metacarpaophalangeal Joints The articulation between the metacarpals & the proximal phalanges including the palmar sesamoid bones. A modified hinge joint allowing flexion & extension.
Phalangeal Joints Proximal Interphalangeal joints- synovial joints between the proximal and middle phalanges. Distal Interphalangeal Joints- between the middle and distal phalanges.
Pelvic Joints relatively immovable articulation between the wings of the sacrum & the ilium. This is a combined cartilagenous and synovial joint.
Pelvic Joints Pelvic Symphysis- a slightly moveable joint between the 2 hip bones. Coxofemoral- the ball & socket type synovial joint between the head of the femur and the acetabulum of the pelvis.
Stifle A condylar joint which acts like a hinge joint with a little rotation.
Stifle **Patellar Ligament- the part of the tendon insertion of the quadriceps muscle between the patella and tibial tuberosity.
Stifle Medial & Lateral Menisci- the crescent, fibrocartilagenous discs between the tibial & femoral articulating condyles.
Stifle Cranial & Caudal Cruciate Ligaments- intra-articular ligaments named for their tibial attachments. **Cranial CL- inserts cranially on the tibia. **Caudal CL- inserts caudally on the tibia.
Tarsus “Hock” A compound hinge joint allowing for flexion & extension.
Skull Joints Mandibular Symphysis- cartilagenous joint joining the left & right mandibular bodies.
Vertebral Column Intervertebral articulations consist of 2 types of joints: Cartilagenous- are formed by interveterbral disks joining adjacent vertebral bodies. Synovial- are formed by caudal and cranial articular processes of adjacent vertebrae.
Vertebral Column Costovertebral Joints- the 2 distinct articulations between most ribs and the vertebral column. The head of each rib forms a ball & socket joint with the vertebrae. The tubercle of each rib forms a joint with the transverse process of the vertebrae. Each has a joint capsule.
Vertebral Column Atlanto-occipital Joint- the “yes” joint. Atlanto-axial Joint- the “no” joint. A pivot joint between the axis & atlas. Intervertebral Disks- The layers of fibrocartilage between bodies of adjacent vertebrae each consisting of an outer fibrous ring and an inner pulpy nucleus.
Vertebral ColumnCostochondral Junction or Joints- the fibrous joints between the ribs and costal cartilages.
Osteochondrosis Dessicans A failure of cartilage maturation. Pressure on such defective cartilage may cause a piece (joint mouse) to be separated and float free in the synovial space.
Pathology… Arthritis- Inflammation of a joint Bursa- Small, fluid-filled sac in places where friction might occur Bursitis- Inflammation of the bursa
Pathology… False Joints- a joint formed in an unreduced (unhealed) fracture, having all the structures of a synovial joint. Luxation or Dislocation- an articular separation usually due to injury or degenerative changes.
Hip Dysplasia A malformed hip joint resulting in a progressive degenerative disease having a high incidence in some breeds.
Cranial Cruciate Ligament Ruptureand Repair When the cruciate ligament is torn or stretched, instead of moving like a hinge, the knee joint will actually make a sliding motion. This abnormal motion and instability creates trauma within the joint that leads to wearing of cartilage, increased synovial fluid production and inflammation.
CCLR A torn cruciate ligament can occur in any dog if just the right (or wrong!) forces impact the knee joint. Most commonly seen in larger breeds of dogs and in dogs that are overweight The ACL surgical procedure does not actually repair the torn ligament but rather replaces the ligament with artificial material that takes over the function of the Cruciate Ligament.
Patellar Luxation Patellar luxation is usually a congenital condition in which the kneecap, or patella, dislocates outside of its normal trochlear groove. Dislocation, clinically referred to as luxation, can occur on either the medial, or inside surface, or the lateral, or outside surface, of the knee. There are varying degrees of patellar luxation that are graded depending on whether the patella is intermittently or constantly luxated. This abnormal displacement of the kneecap results in pain, cartilage damage, and arthritis. There are varying degrees of severity of this disease, and surgery may be needed.
Indications Helps determine the cause of pain or swelling in a joint Synovial fluid is collected for cytological, bacterial or biochemical analysis
Normal synovial fluid has a low cellularity, with virtually no red blood cells & only small numbers of leukocytes. The main functions of synovial fluid are nutritive support, lubrication, and “cushioning” of the articular cartilage.
In addition to cytologic evaluation, the fluid should be assessed for: Volume obtained Turbidity Mucin quality/concentration Protein concentration Color Viscosity
Sample Handling & Test Priorities Normal synovial fluid does not clot. However, with hemorrhage or blood contamination, samples may clot unless processed immediately or placed in an anticoagulant tube. EDTA is preferred for cytologic examination, while heparin is recommended for the mucin clot test.
Color & Turbidity Normal synovial fluid is clear to straw yellow and non-turbid. Turbidity, when present, is caused by cells, protein (or fibrin), or cartilage.
Viscosity Viscosity is frequently decreased in joints with bacterial inflammation.