These joints are connected by tough cartilage between the bone and can be classified as primary synchondroses or secondary symphyses. Synchondroses Synchondroses are cartilaginous joints formed of hyaline cartilage, and are mainly found in the growing skeleton as the ossification centres of growing bone that will ossify over time synostosis , such as the epiphyseal growth plate. Cartilaginous joints are usually immobile but, in a rare condition in children and adolescents, the attachment of the epiphysis loosens, allowing the femoral head to slip down the femoral neck.
This is known as a slipped upper femoral epiphysis and often presents with the child developing an unexpected limp Robson and Syndercombe Court, In the mature skeleton, an example of a synchondrosis is the first sternocostal joint between the first rib and the manubrium ; all other sternocostal joints are synovial. The intervertebral discs between the vertebral bodies of the spine are an example of bones connected by fibrocartilage.
These fibrous joints allow relatively limited movement individually but extensive movement can be achieved collectively across the whole spine. Another example of a symphysis is the symphysis pubis in the pelvis, which helps maintain pelvic stability.
In pregnancy, the symphysis pubis is softened by hormones to allow for expansion during delivery. As symphyses allow slight movement between the articulating surfaces, they are considered to be amphiarthroses.
Synovial joints are designed to allow free movement of the joint and are classified as diarthroses. Characterised by a gap between the articulating bones, they are held in close proximity by a joint capsule. Contraction of the infrastructure of muscles around the joint maintains movement, while stability is maintained through the use of soft tissue structures, such as ligaments, labra, fat pads and menisci Danning, The joint has an outer fibrous capsule that encapsulates the entire joint and is attached to the periosteum, allowing movement, maintaining tensile strength and helping to prevent dislocation.
This layer also contains the synovial membrane synovium , which is composed of synoviocytes of which there are two types:. Synovial fluid The synovial fluid helps protect the joint from mechanical injury and contains hyaluronic acid and lubricin Danning, In a healthy joint, the synovial fluid is very viscous and clear, and is either colourless or a pale straw colour.
Water is able to enter the joint very easily during inflammation but, once it mixes with hyaluronic acid, it cannot leave as quickly Robson and Syndercombe Court, — as such, although it may only take a few hours for the joint to swell, it can take a few days for that swelling to subside. The synovial fluid may become infected by a haematogenous blood-borne spread of bacteria, extension of an adjacent infection or direct inoculation following trauma or an invasive procedure.
This is known as septic arthritis and can damage the synovium or cartilage. Rheumatoid arthritis This is an autoimmune inflammatory arthropathy that affects the synovium. It occurs more often in smokers and is three times more common in women than men Ralston and McInnes, Clinical onset is characterised by the abnormal production of cytokines and inflammatory mediators such as interleukin 1, interleukin 6, interleukin 15 and tumour necrosis factor Ralston and McInnes, This causes the synovium to become inflamed and hypertrophied so the synovial villi become thickened and fuse together to form a pannus.
The pannus invades the surrounding tissue such as the cartilage, ligaments and joint capsule , which this can lead to progressive destruction of the joint Danning, Rheumatoid arthritis can also affect periarticular structures, including tendon sheaths and bursas, as well as having extra-articular manifestations.
Osteoarthritis The articulating surfaces in synovial joints are coated with approximately mm of hyaline cartilage, which provides a smooth surface and reduces friction during movement. This helps distribute the weight across the joint, reducing friction and damage to the bone surface Robson and Syndercombe Court, Osteoarthritis is a degenerative condition involving focal loss of the articular cartilage, so the cartilage becomes less efficient at protecting the ends of the bone Ralston and McInnes, Over time, this can cause bony surfaces to rub together on movement, causing pain and audible crepitus.
As the bone attempts to compensate for the loss of articular cartilage, it produces new bone to try and stabilise the joint. This results in bone thickening under the remaining cartilage sclerosis and formation of osteophytes at the joint margins, which can reduce the range of movement of the joint.
Supporting ligaments Synovial joints are designed to permit movement while, at the same time, maintaining balance, strength and stability.
They vary in structure and the type of movement they permit — Table 2 summarises the different types. The stability of the joint depends on its shape, the number and position of supporting ligaments around it, their strength and the tension they exert Tortora and Derrickson, Supporting ligaments are described according to their position in relation to the capsule extracapsular or intracapsular.
Excessive tension on ligaments, such as moving the joint beyond its functional range of movement, can cause them to stretch and may mean they sprain or tear. The muscles span the joint and connect the bones. When the muscles contract, they pull on the bones, causing them to move.
Muscles can only contract. They cannot actively extend, or lengthen. Therefore, to move bones in opposite directions, pairs of muscles must work in opposition. For example, the biceps and triceps muscles of the upper arm work in opposition to bend and extend the arm at the elbow see Figure below.
What other body movements do you think require opposing muscle pairs? In exercises such as weight lifting, skeletal muscle contracts against a resisting force see Figure below.
Using skeletal muscle in this way increases its size and strength. In exercises such as running, the cardiac muscle contracts faster and the heart pumps more blood. Using cardiac muscle in this way increases its strength and efficiency. Continued exercise is necessary to maintain bigger, stronger muscles. How do your bones move? Males are on average taller than females because male puberty tends to occur later, so male bones have more time to grow Waugh and Grant, Over-secretion of human growth hormone during childhood can produce gigantism, whereby the person is taller and heavier than usually expected, while over-secretion in adults results in a condition called acromegaly.
If there is a fracture in the epiphyseal growth plate while bones are still growing, this can subsequently inhibit bone growth, resulting in reduced bone formation and the bone being shorter. It may also cause misalignment of the joint surfaces and cause a predisposition to developing secondary arthritis later in life. A discrepancy in leg length can lead to pelvic obliquity, with subsequent scoliosis caused by trying to compensate for the difference.
Once bone has formed and matured, it undergoes constant remodelling by osteoclasts and osteoblasts, whereby old bone tissue is replaced by new bone tissue Fig 4. Bone remodelling has several functions, including mobilisation of calcium and other minerals from the skeletal tissue to maintain serum homoeostasis, replacing old tissue and repairing damaged bone, as well as helping the body adapt to different forces, loads and stress applied to the skeleton.
Calcium plays a significant role in the body and is required for muscle contraction, nerve conduction, cell division and blood coagulation. Serum calcium levels are tightly regulated by two hormones, which work antagonistically to maintain homoeostasis.
Calcitonin facilitates the deposition of calcium to bone, lowering the serum levels, whereas the parathyroid hormone stimulates the release of calcium from bone, raising the serum calcium levels. Osteoclasts are large multinucleated cells typically found at sites where there is active bone growth, repair or remodelling, such as around the periosteum, within the endosteum and in the removal of calluses formed during fracture healing Waugh and Grant, The osteoclast cell membrane has numerous folds that face the surface of the bone and osteoclasts break down bone tissue by secreting lysosomal enzymes and acids into the space between the ruffled membrane Robson and Syndercombe Court, These enzymes dissolve the minerals and some of the bone matrix.
The minerals are released from the bone matrix into the extracellular space and the rest of the matrix is phagocytosed and metabolised in the cytoplasm of the osteoclasts Bartl and Bartl, Once the area of bone has been resorbed, the osteoclasts move on, while the osteoblasts move in to rebuild the bone matrix.
Osteoblasts synthesise collagen fibres and other organic components that make up the bone matrix. They also secrete alkaline phosphatase, which initiates calcification through the deposit of calcium and other minerals around the matrix Robson and Syndercombe Court, As the osteoblasts deposit new bone tissue around themselves, they become trapped in pockets of bone called lacunae. Once this happens, the cells differentiate into osteocytes, which are mature bone cells that no longer secrete bone matrix.
The remodelling process is achieved through the balanced activity of osteoclasts and osteoblasts. If bone is built without the appropriate balance of osteocytes, it results in abnormally thick bone or bony spurs. Conversely, too much tissue loss or calcium depletion can lead to fragile bone that is more susceptible to fracture.
Typical features on X-ray include focal patches of lysis or sclerosis, cortical thickening, disorganised trabeculae and trabecular thickening.
As the body ages, bone may lose some of its strength and elasticity, making it more susceptible to fracture. This is due to the loss of mineral in the matrix and a reduction in the flexibility of the collagen.
Adequate intake of vitamins and minerals is essential for optimum bone formation and ongoing bone health. Two of the most important are calcium and vitamin D, but many others are needed to keep bones strong and healthy Box 2.
Key nutritional requirements for bone health include minerals such as calcium and phosphorus, as well as smaller qualities of fluoride, manganese, and iron Robson and Syndercombe Court, Calcium, phosphorus and vitamin D are essential for effective bone mineralisation. Vitamin D promotes calcium absorption in the intestines, and deficiency in calcium or vitamin D can predispose an individual to ineffective mineralisation and increased risk of developing conditions such as osteoporosis and osteomalacia.
Other key vitamins for healthy bones include vitamin A for osteoblast function and vitamin C for collagen synthesis Waugh and Grant, Physical exercise, in particular weight-bearing exercise, is important in maintaining or increasing bone mineral density and the overall quality and strength of the bone.
This is because osteoblasts are stimulated by load-bearing exercise and so bones subjected to mechanical stresses undergo a higher rate of bone remodelling. Reduced skeletal loading is associated with an increased risk of developing osteoporosis Robson and Syndercombe Court, Bone is a dynamic structure, which is continually remodelled in response to stresses placed on the body.
Changes to this remodelling process, or inadequate intake of nutrients, can result in changes to bone structure that may predispose the body to increased risk of fracture. Part 2 of this series will review the structure and function of the skeletal system. Tagged with: Newly qualified nurses: systems of life. Sign in or Register a new account to join the discussion. You are here: Orthopaedics.
Skeletal system 1: the anatomy and physiology of bones. Abstract The skeletal system is formed of bones and cartilage, which are connected by ligaments to form a framework for the remainder of the body tissues.
This article has been double-blind peer reviewed Scroll down to read the article or download a print-friendly PDF here if the PDF fails to fully download please try again using a different browser Read part 2 of this series here. Box 1. Types of bones Long bones — typically longer than they are wide such as humerus, radius, tibia, femur , they comprise a diaphysis shaft and epiphyses at the distal and proximal ends, joining at the metaphysis.
Most long bones are located in the appendicular skeleton and function as levers to produce movement Short bones — small and roughly cube-shaped, these contain mainly cancellous bone, with a thin outer layer of cortical bone such as the bones in the hands and tarsal bones in the feet Flat bones — thin and usually slightly curved, typically containing a thin layer of cancellous bone surrounded by cortical bone examples include the skull, ribs and scapula.
Most are located in the axial skeleton and offer protection to underlying structures Irregular bones — bones that do not fit in other categories because they have a range of different characteristics. They are formed of cancellous bone, with an outer layer of cortical bone for example, the vertebrae and the pelvis Sesamoid bones — round or oval bones such as the patella , which develop in tendons.
Box 2. Vitamins and minerals needed for bone health Key nutritional requirements for bone health include minerals such as calcium and phosphorus, as well as smaller qualities of fluoride, manganese, and iron Robson and Syndercombe Court,
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