The musculoskeletal system is responsible for all body movements. The skeletal component of the muscular system provides a structural framework for the body, which protects the internal organs and provides the shape for the body. It acts as the storage for calcium and phosphorus and plays a part in mineral homeostasis(Davidson, 2002)
Functions of the skeletal system(Haywood, 2008)
The role of the skeletal system can be classified into five categories: protection, structural support, movement, mineral and chemical storage and blood cell production.
- Protection: The strong material that makes up bones protect the internal tissues and organs of the body like the brain, ears, eyes, spine, heart, lungs, urinary, and reproductive organs.
- Structural support: The bones of the skeletal system give shape to the body and provide a supporting framework. This framework can bear the heavy weight of the body without stress and strain. They support vital internal organs against the strong force of gravity. The bones provide attachment for muscles of the body. The bones and muscles work together to form the musculoskeletal system, which are responsible for the various body movements. The skull and facial bones protect and determine the shape of the head and face. The bones are sized and shaped according to the functions they perform. For example, the long bone of the leg, the tibia, which carries the weight of the body and supports the body against gravity, is shaped like a pillar, and functions like a pillar.
- Movement: Bones are joined together at joints. It is at these joints, that the body movements take place. Each joint is structured and matched to the function it’s expected to perform. For example, the ball and socket joints of the shoulder have a great deal of mobility to perform a wide range of movements. Some joints offer a wide range of movement and some strongly resist movement. These others are built for stability. An example is the fine suture joints of the skull where almost no movement is possible. The amount of movement possible at a joint depends on how well the bones that form the joint fit together. It also depends on the amount of support offered by tissues like muscles, tendons, and ligaments around them. Huge muscle groups surround the major joints of the arms and legs and the movements at these various joints occur when the muscles pull on the bones that form the joint, which produce the movements. Here the bones function as mechanical levers.
- Mineral and Chemical Warehousing: Bones store most of the body’s calcium, phosphorus and other essential minerals. If at any time, the diet falls short of calcium, the body turns to its storehouse in the bones. The skeletal system maintains equilibrium between calcium and phosphorus- even a small change in this equilibrium can affect cellular functions and cause serious medical problems. Other minerals’ stored in bones are potassium, manganese, magnesium, silica, iron, zinc, selenium and boron(Haywood, 2008).
- Blood Cell production: Spongy bones with red bone marrow, produces blood cells. The production of red blood cells (RBCs), White Blood Cells (WBCs) and platelets is because mature blood stem cells differentiate into them, in the flat bones of the skull, ribs, sternum and ends of long bones.
Structures that make up the skeletal system and how these structures function(NASM Essentials of Personal Fitness Training, 2008)
The skeletal system is divided into two- the axial and the appendicular systems.
The Axial Skeleton: Axial skeleton is made up of the bones of the skull, rib cage, and vertebral column. There are around 80 bones in the axial skeleton.
The Appendicular Skeleton: The appendicular skeleton is made up of the bones of the upper and lower extremities, the shoulder and pelvic girdles. About 126 bones constitute the appendicular skeleton.
Functioning: About 177 of the 206 bones in the skeletal system is used for voluntary movements. The body has around 300 joints. For various movements, the bones provide two main functions, which are, providing leverage and support to the body. When acted upon by muscles, the bones perform as levers. The bones help the body maintain posture, which is necessary for the efficient distribution of forces acting on the body and thus provide support to the body(NASM Essentials of Personal Fitness Training, 2008).
Three diseases that are associated with the skeletal system and the types of treatment currently used for them
- Osteoarthritis: The commonest form of arthritis, osteoarthritis (OA, osteoarthrosis) is seen more among the elderly and is responsible for causing pain and disability among them. Pathologically, the synovial joints are affected by a focal loss of hyaline cartilage, which results in proliferation of new bone, producing remodeling of the joint contour. It is a consequence of the wear and tear that occurs in joints with age and the resulting dynamic repair process of synovial joints. The disease targets the knee and the hip joints, primarily. OA is more prevalent and symptomatic in women, except at that of the hip joint, where both genders are equally affected.
Clinical features: Many OA patients present with pain and functional restriction of joint movements, the pain being aggravated by movement and weight bearing, and relieved by rest. There is restricted movement in the affected joints, with palpable, sometimes audible crepitus along the joints. There may be muscle weakness around the joint.
Diagnosis: The diagnosis and assessment of OA is usually purely clinical. An x-ray of the joint may show focal narrowing of the joint space, marginal osteophytes, sub-chondral sclerosis, cysts or osteochondral loose bodies and deformity.
Treatment: The current treatment for OA involves patient education, pain control, and efforts to minimize disability and handicap, and reduce further structural progression of the disease. The treatment is largely symptomatic until the joints need replacement after they have become completely dysfunctional(Davidson, 2002). It is necessary to constantly monitor the progress of this disease when the disease is in its early stages and when therapeutic agents/biological agents are effective in controlling the disease(Eichaker, Cho et al 2014). Surgery is considered if conservative measures fail, and is mainly indicated for uncontrolled pain, progressive immobility and functional impairment(Davidson, 2002).
- Osteoporosis (OP): It is a common disease of the bones causing reduced bone mass, a breakdown of the internal architecture of the bone and an increased risk of fracture. The prevalence of osteoporosis (OP) and fractures related to this disease increases with age. The loss in bone mass is because of an imbalance between bone formation and bone resorption.
Clinical Features :OP can affect any bone but the most common sites are forearm bones, spine, and femur, resulting in Colles’ fracture, vertebral fractures and hip fractures. This disease often evades diagnosis because low bone density does not cause symptoms; patients with advanced osteoporosis may be completely asymptomatic until a fracture occurs.
Diagnosis: People with suspected OP should undergo bone densitometry of the spine and hip joints. If this shows a Bone Mass Densitometry (BMD) score of -2.5 or less at either site, the diagnosis is confirmed. Other than aging, secondary causes of OP should be looked for like, thyrotoxicosis, myeloma and primary hyperparathyroidism. Hypogonadism should be excluded by measurement of sex hormones and gonadotropins when osteoporosis occurs in men and pre- menopausal women(Mulder, Moreira Kulak, & Shane, 2006).
Treatment: People with normal BMD scores are reassured and monitored. Those with mild osteopenia are advised about making lifestyle changes like increasing exercise, stopping smoking and alcohol, increasing dietary calcium intake, and about reassessment after 3-5 years’. Patients with severe osteopenia are treated with medicines like bisphosphonates, which adsorb on to bone surfaces and become incorporated into the bone matrix beneath resorbing osteoclasts, thus inhibiting bone resorption. Hormone replacement therapy is effective in pre-menopausal women and older women with established osteoporosis. Calcium supplements slow post menopausal bone loss and so also does calcitonin. Calcium can be given with vitamin D supplementation for the primary prevention of fractures in elderly people. Raloxinfene, which is a selective estrogen receptor agonist in some tissues and antagonist in others, is used to increase bone mass and reduces the risk of vertebral fractures in post-menopausal women with OP. The response to treatment of patients is measured by repeating BMD measurements’ within 1-2 years of starting treatment(Davidson, 2002; Sambrook & Cooper, 2006).
- Cancer- associated bone disease: Many malignancies have bone diseases related to them. This can manifest in many ways. Hypercalcemia is a common metabolic complication of malignancy, caused by excessive release of parathyroid hormone related protein by solid tumors of the lung, breast, and genitourinary system. Osteomalacia occurs less frequently as a complication of mesenchymal tumors, because of the release of fibroblast growth factor ectopically by tumors. This growth factor acts on the kidney to promote phosphaturia(Hannan et al., 2008).
Bone metastases occur as a complication of tumors of the bronchus, breast, prostate, and multiple myeloma. Metastatic bone disease presents with bone pain, pathological fractures or neurological/spinal compression due to nerve root or spinal cord compression. Clinical history gives a clue to the diagnosis and x-rays show local osteolytic lesions or osteosclerotic lesions (prostate cancers). The treatment of cancer associated bone disease is multi-disciplinary and involves treating the primary tumor with chemotherapy, surgery, radiotherapy, or hormone therapy. Non-Steroidal anti-inflammatory drugs are given to control tumor pain, and nerve blockade or local radiotherapy may be required for nerve root compression. Surgery of the bones may be required if the metastases have caused pathological fractures. Surgical decompression may be required as a palliative measure in the treatment of spinal metastases encroaching the spinal cord. For osteolytic lesions, bisphosphonates might be used so the bone surrounding tumor deposits are protected from resorption(Davidson, 2002; Pockett et al., 2010).
Since the skeletal system provides the framework around which the body muscles, tissues, skin, internal organs, blood vessels and every other part of the body is built, it is one of the most important systems of the body.
References
Davidson, S. (2002). Davidson’s Principles and Practice of Medicine. (Christopher Haslett; Edwin R.chilvers; Nicholas A. Boon; Nicki R. Colledge, Ed.) (19th ed., p. 1392). Elsevier - Health Sciences Division. Retrieved from http://books.google.com/books?id=sTwGnwEACAAJ&pgis=1
Eichaker, L. R., Cho, H., Duvall, C. L., Werfel, T. A., & Hasty, K. A. (2014). Future nanomedicine for the diagnosis and treatment of osteoarthritis. Nanomedicine (London, England), 9(14), 2203–15. doi:10.2217/nnm.14.138
Hannan, F. M., Athanasou, N. A., Teh, J., Gibbons, C. L. M. H., Shine, B., & Thakker, R. V. (2008). Oncogenic hypophosphataemic osteomalacia: biomarker roles of fibroblast growth factor 23, 1,25-dihydroxyvitamin D3 and lymphatic vessel endothelial hyaluronan receptor 1. European Journal of Endocrinology / European Federation of Endocrine Societies, 158(2), 265–71. doi:10.1530/EJE-07-0485
Haywood, K. (2008). Skeletal System (p. 80). Marshall Cavendish. Retrieved from http://books.google.com/books?id=7xmvvOrbor0C&pgis=1
Mulder, J. E., Moreira Kulak, C. A., & Shane, E. (2006). Secondary Osteoporosis. In Dynamics of Bone and Cartilage Metabolism (pp. 717–737). doi:10.1016/B978-012088562-6/50044-3
NASM Essentials of Personal Fitness Training. (2008) (p. 552). Lippincott Williams & Wilkins. Retrieved from http://books.google.com/books?id=-qW8oV-SXo4C&pgis=1
Pockett, R. D., Castellano, D., McEwan, P., Oglesby, A., Barber, B. L., & Chung, K. (2010). The hospital burden of disease associated with bone metastases and skeletal-related events in patients with breast cancer, lung cancer, or prostate cancer in Spain. European Journal of Cancer Care, 19(6), 755–60. doi:10.1111/j.1365-2354.2009.01135.x
Sambrook, P., & Cooper, C. (2006). Osteoporosis. Lancet. doi:10.1016/S0140-6736(06)68891-0
