Pathophysiological Changes of the Musculoskeletal System

As the term connotes, a musculoskeletal system is associated with the muscles and the body's skeleton. The system comprises bones, skeletal muscles, chondroid tissues- the articular cartilage, meniscus, intervertebral discs, tendons, fats, ligaments, and joint capsules (Boros & Freemont, 2017). Collectively, these tissues form a skeletal structure that gives shape to the organisms, enabling movement and an endoskeleton for protecting its delicate internal organs. Also, the system is essential for homeostasis by facilitating humoral signaling and serving as a reservoir of organic and inorganic molecules such as calcium and phosphate ions. The bone marrow synthesizes blood cells crucial for various body functions, such as transportation of nutrients.  

Change in structure, that is, any alteration in shape, density, or composition of the bones, muscles, and other musculoskeletal components, interferes with the system's functioning. For example, broken bones hinder movement, distort the body's shape, and in some fatal cases, like for the spinal cord, leads to death. These alterations leading to musculoskeletal dysfunction are generally referred to as musculoskeletal disorders (MSD). According to the World Health Organization (WHO, 2019), these conditions include short-lived events, such as fractures, sprains, and strains that occur suddenly and the life-long present for an extended period characterized by continuous pain and disability among different ages. About 1.71 billion persons worldwide are suffering from MSDs, making it an important subject. MSDs are responsible for disabilities, limited mobility, and agility. Also, the MSDs derail the world's economy by sending a large workforce to early retirement and limiting their participation in society's essential activities. Understanding the pathophysiology of the MSDs resulting from structural and mass alterations is crucial to its prevention and appropriate management. On prevention, their predisposing factors need to be comprehended to form part of solving the entire puzzle. 

Significant causes of musculoskeletal alterations 

Aging 

Aging is a time-dependent aspect that progressively reduces the physiological function of organs and tissues. Declined cartilage resilience, loss of ligament elasticity, deterioration of muscle strength, and increased bone fragility are associated with old age. They interfere with the musculoskeletal system's mass and structure (Gheno, Cepparo, Rosca & Cotten, 2012). These factors are prerequisites to various MSDs. 

A fracture is a medical term for a broken bone that distorts the body's skeleton's structure and affects musculoskeletal components. Generally, a bone will break or dislocate in joints when a significant force is applied to it. When a bone breaks and damages the overlying skin causing a wound is referred to as an open fracture, while when the surrounding skin remains intact, then the fracture is closed. The bone is meant to withstand some stress; however, they fracture when the force becomes excess. The case is different in the weakened bone due to age, which is also associated with other MSDs, the fragility fractures. 

The frequency of fractures increases with age and is common among older people, mostly from falls and osteoporosis (Ambrose, Cruz & Paul, 2015). They are prevalent in childhood but less fatal due to the body's ability to heal compared to fractures in adults quickly. Difficulty in mobility and the decline of old age strength predisposes older adults to falls, leading to bone breakage. Bones become more brittle with age as they lose calcium and other minerals reducing their density. These bones become thinner and weaker, and easy to break, and unfortunately, take longer to heal (Mishra, Gajjar & Patel, 2016).  

Changes in gait and posture, especially in women in post-menopause ages, occur due to the spinal column's structural and density changes (Ibeneme et al., 2018). The vertebrae bones of the spinal column have disks which are gel-like cushions at each joint. Aging leads to the thinning and shortening of the disks and fluid loss in the spinal column. Additionally, some minerals are lost, making the bones thin and the trunk curves due to compression resulting in spurs (Saxon, Etten & Perkins, 2014). As a result, there is a slight loss in height and less pronounced foot arches. Since the brittle bones of the arms and legs don't change in length, the limbs will appear longer than the shortened abdomen. Symptoms include a change in gait and curved backbone coupled with the difficulty in movement and pain. 

Joints, for example, the knee joint, have cartilage and synovial fluid that ensures its flexibility. However, aging wears out the cartilage and causes calcium deposition-calcification, and reduces synovial fluid, resulting in the joints' stiffness (Swann, 2012). Such degeneration is common around shoulders (Bain & Clitherow, 2015). At the finger joints, aging brings about wearing out of cartilage and slight thickening of bones around the joint, causing swellings referred to as osteophytes common among women (Sabitha, 2018). Movement or activity involving these joints is much interfered with due to pain resulting from friction resulting from reduced fluid and damaged cartilage. 

Aging causes atrophy, which is the decline of lean body mass due to partial loss of muscular tissues, called sarcopenia (Wilkinson, Piasecki & Atherton, 2018). For men, these changes are evident at about the age of 20 years, while in women, it occurs in the 40s. The rate and amount of muscular alteration are influenced by genes (Amarya, Singh & Sabharwal, 2018). Additionally, the deposition of a fat age-associated pigment called lipofuscin alters muscle functioning (Moreno-Garcia et al., 2018). During this phase, muscle fibers shrink while the lost ones are substituted with tough fibrous tissues affecting the muscles' normal contraction and relaxation. Noticeably, this is frequent in the arms, which becomes thin and bony limiting activity due to the weak muscles' reduced strength. 

As a result of the musculoskeletal system's age-related alterations, weak, brittle bones are risk factors of breaking and predispose an individual to osteoporosis. Stiff joints lead to osteoarthritis, while vertebrae compression causes gait changes, loss of balance, and instability, significant causes of injury inflicting by falls. On the other hand, muscle loss manifests as fatigue, weakness, and reduced reflexes among older people. All these symptoms are manifestations of structural and density changes disrupting normal musculoskeletal functioning.  

Regarding the management of these conditions, moderate exercise programs are recommended for they are essential in maintaining healthy muscles, joints, bones and speeding up the recovery course of some MSDs (Abou Elmagd, 2016). Exercises strengthen bones, maintains the joints' flexibility, and reduces calcification and lipofuscin deposition, which are cause MSDs. Additionally, a balanced diet for enough calcium minerals to sustain a healthy musculoskeletal system to prevent conditions is required.  

Musculoskeletal infections 

Arkun (2019) notes three fundamental infections of the skeletal system: osteomyelitis, septic arthritis, and mycetoma. These infections are caused by various microorganisms, bacteria, fungi, parasites, and viruses. These pathogenic microorganisms may gain entry into the musculoskeletal system through direct inoculation using penetrative trauma or infection spread from adjacent soft-tissues or circulating blood from a localized tissue. The attack of these microorganisms of musculoskeletal components prompts some responses such as edema, consequently altering the system's structure and physiology. 

Osteomyelitis is mainly caused by bacteria such as Staphylococcus aureus in spinal and long bones. The suppurating inflammatory infection osteomyelitis develops through hematogenous processes. In adults, most of the infections spread from adjacent cellulitis resulting from direct trauma. On the other hand, it results from the hematogenous process (Lee eta l., 2016). The bacteria's presence within the metaphysis elicits increased vascular permeability allowing the influx of leukocytes resulting in edema. Pressure builds inside the rigid bone as pus collects in this confinement. The pressure causes pus exudation through open channels as it limits blood supply to the area. As a result, necrosis of the affected bone occurs, creating a sequestrum that makes bacterial eradication impossible unless the bone is removed. During suppuration, the connective tissues' membrane may become elevated, and after some time, a new bone called involucrum may be deposited. Overly, the functioning and structure of the musculoskeletal system are altered. In advanced stages, the inflammation around the infected area causes the soft tissues and bones to become painful, leading to restricted movement and pseudoparalysis. The infection is treated using antibiotics when at the acute phase. However, besides antibiotic administration, surgical procedures are recommended to remove the dead bones and necrotic tissues in chronic cases. 

Septic arthritis is the infection of the joints and, in particular, the synovial membrane by bacteria.  Neisseria gonorrhoeae  is the primary microorganism for septic arthritis, which causes genital lesions among young adults. Simultaneously, in other ages, Staphylococcus aureus is the typical agent that spreads from a cutaneous lesion (Raukar & Zink, 2014). Septicemia extends infections from a site outside the joint into or on the synovial membrane. These microorganisms then proliferate either on the synovial membrane or an adjacent bone. The proliferation induces inflammation of the affected tissues prompting leukocytes in the synovial fluid. Untreated septic arthritis in its acute phase, pyogenic arthritis, the cartilage gets dissolved beginning at the part in contact with adjacent bones. The dissolving of the cartilage exposes the underlying bone accompanied by other destructive alterations in the synovial fluid. As a result, affected joints become swollen and acutely painful, causing difficulties in movement. Treatment includes draining the synovial fluid and systemic antibiotic therapy.  

Mycetoma is a localized chronic and progressive infection affecting the skin, the subcutaneous tissues, and bones (El Shamy, Fahal, Shakir & Homeida, 2012). Nocardia spp and Madurella mycetomi commonly cause them. The infection sets in through injury inflicted on the skin. Then the microorganisms begin to proliferate on the subcutaneous tissues spreading into the bones. The rapid growth results in hyperplasia of the adjacent tissues and pus formation with granules. The granules grow more prominent over time, developing into oozing sores deforming the affected bone. Failure to manage mycetoma will continue spreading to other body parts, and it finally destroying the underlying muscles and bone. The alteration of these musculoskeletal elements interferes with normal musculoskeletal functioning. This MSD is controlled using sulfonamides or Amphotericin depending on the causative agent. Failure to respond to these pharmacological therapies, amputation is recommended. 

Musculoskeletal diseases 

The WHO (2019) approximates that more than 150 conditions impair persons' locomotor systems worldwide. Fundamentally, characterized by persistent pain and difficulty in movement, the MSDs are the leading contributor to the global rehabilitation burden. In general, these conditions directly or indirectly affect the normal functioning of the musculoskeletal system. They involve specific parts of the system, but their effects overly hinder movement and activity. At the joints, common conditions include osteoarthritis, rheumatoid arthritis, psoriatic arthritis, ankylosing spondylitis, and gout. Conditions affecting bones are osteoporosis, osteopenia, and related fragility, and traumatic fractures. Sarcopenia affects the lean body reducing muscular mass and functionality. A unique disease is systemic lupus erythematosus, an autoimmune condition that attacks multiple sites or systems, including the musculoskeletal system. Despite different and specific pathophysiology of these conditions, they generally have similar or related symptoms and effects. However, Sozen, Ozisik, and Basaran (2017) highlight that among the MSDs, osteoporosis stands out as the most common bone condition of humans, outlining it as an essential public health issue. The condition is also a crucial risk factor for other medical conditions (Kling, Clarke & Sandhu, 2014). Besides, the disease is of economic and psychosocial importance. In explaining mechanisms of morphological and physiological disruptions of the musculoskeletal system, osteoporosis is a good example, for it provides an opportunity to elucidate on general management of MSDs. Besides the condition 

Osteoporosis 

Osteoporosis may clinically be evident until the concurrence of a fracture. The disease is uniquely associated with improved bone fragility due to structural deterioration of bones and decreased bone density (Eastell et al., 2016). the condition is chronic and progressive and prevalent among postmenopausal women and older adults of both sexes.  

Pathophysiology 

The pathogenesis of osteoporosis is a multifactorial condition created through hereditary, intrinsic, extrinsic, and lifestyle factors. Imbalances of bone resorption in the process of bone formation are the hallmark for the development of osteoporosis (Sozen, Ozisik & Basaran, 2017). Bone tissues lost during resorption are replaced during the remolding process. However, there might be a deficit in the molding process, leading to bone loss, which affects the musculoskeletal system's anatomical and physiological aspects. Molding of bone mass begins at birth and attains its peak at adulthood, after which bone mass loss begins. Beyond puberty, which is the peak of bone mass building, replacing older bones with new ones occurs. The process facilitates the removal of micro-fractures, preventing them from developing into macro fractures. Such a course is crucial in maintaining a physiologically fit skeleton.  

However, some factors such as menopause and aging create an imbalance between remolding and bone resorption by increasing the latter's rate than the former (Sozen, Ozisik & Basaran, 2017). Therefore, some bone mass is lost, leaving a structurally weak bone with reduced density predisposing the skeleton to fractures aggravated by increased fragility, which corresponds to aging. Apart from aging, sex steroid deficiencies interfere with the quality of bones disrupting the skeleton's micro-architectural integrity and, consequently, it's functioning. 

Etiology 

Osteoporosis can be categorized into two classes: primary and secondary osteoporosis in consideration of the aspects influencing bone metabolism. Primary osteoporosis is the most frequent, and it is separated into juvenile and idiopathic. Juvenile primary osteoporosis usually presents in children of both sexes from the age of 8-14 years. Sudden pains and fractures characterize this type as a result of stress. Idiopathic osteoporosis is further divided into type I (postmenopausal) and type II (age-related or senile). Type I results from estrogen deficiency in women, which causes increased trabecular bone loss. Postmenopausal osteoporosis is also marked with vertebral and distal forearm bone breakages. On the other hand, type II is caused by calcium deficiency which is typical for an aging skeleton. This type occurs both in men and women as bone mineral density decreases with aging. Frequent fractures in cortical and trabecular bones arise due to this form of osteoporosis. Often wrist, hip, and vertebral column breakages are noted with type II osteoporosis.  

Secondary osteoporosis indirectly results from underlying deficiencies, conditions, and use of some drugs. Renal hypercalciuria is an example of the most common predisposing condition for secondary osteoporosis. Approximately a third of premenopausal and postmenopausal women who develop this type of osteoporosis have underlying diseases of bone loss, such as malabsorption syndromes (Sozen, Ozisik & Basaran, 2017).  

Clinical manifestation 

Unless a fragility fracture occurs, osteoporosis cannot manifest since it is a silent condition (Sozen, Ozisik & Basaran, 2017). However, fragility fracture of the hips or the vertebra without major trauma hints at fractures resulting from osteoporosis. Patient history as well is used in identifying individuals likely to suffer from osteoporosis. Vertebral fractures from osteoporosis are associated with increased morbidity, back pain, height loss, deformity, and disability. Postmenopausal women are likely to experience another vertebral fracture a year later after the first one. When thoracic fractures occur, they cause restrictive lung conditions, advancing backache, and disabling kyphosis.  

Generally, osteoporotic fracture presents with abdominal pains, poor appetite, weight loss, premature food satisfaction, and constipation. The fracture may lead to changes in lifestyle, appearance while its pain limits physical activities. In the long run, other psychological impacts may be evident through depression, lowered self-esteem, fear, anxiety, among others that ultimately bring about social detraction and physical deterioration. Screening of at-risk people with other underlying conditions is necessary to check for fractures resulting from osteoporosis for proper management. 

Management of osteoporosis 

Osteoporosis can be prevented and treated, but due to its silent symptom it is difficult to manage. Healthcare professionals can achieve correct diagnosis using patient history, detailed physical examination, measurement of bone mineral density, and imaging techniques for vertebral assessment.  

Management approaches, in this case, will include enough calcium and vitamin D intake. Also, a muscle strengthening program, quitting alcohol, and smoking will help prevent osteoporosis. For calcium supplements, the Institute of Medicine (IOM) recommends 1000mg daily for men between 50-70 years and 1200mg for women over 50 and men over 70 (Moyer, 2013).  

Pharmacological management is required for the management of secondary osteoporosis. This therapy aims to prevent fractures by strengthening the bones to reduce the risk of falls or injuries, manage symptoms of bone destruction and fractures, and ensure normal physical functioning of the musculoskeletal system. By administering antiresorptive agents, these pharmacological therapies reduce bone resorption, preventing osteoporosis and fractures (Sozen, Ozisik & Basaran, 2017). The antiresorptive agents help increase bone density, and others such as zoledronic acid function in reducing vertebral and hip fractures. However, the doctor should assess the patient for contraindication, such as in patients with upper gastrointestinal disease who, if they use bisphosphonates, fail to maintain an upright posture for 30-60 minutes, hindering tablet transit.  

In summary, abnormal changes altering the morphology and physiology of the musculoskeletal system constitute an MSD. Aging, infections, diseases, and trauma are the major factors causing MSDs. These conditions are responsible for the loss of quality of life, limited movement, and socioeconomic impacts on the affected people. In fatal cases, MSDs have claimed many individuals' lives calling for attention on MSD as a health issue. Various conditions affect various ages; however, older people suffer most of the MSDs due to the body's reduced ability to remodel destroyed musculoskeletal tissues. Some of these diseases, such as osteoporosis, are silent and may not be noticed for early management. Crucial to the management of the MSDs is correct diagnosis using standardized assessment techniques. Therapeutic approaches should aim at strengthening the musculoskeletal tissues for normal functioning in movement, among other roles. However, the doctor should assess the patient for any possibility of adverse reactions, especially for pharmacological therapy. In general, prevention of these conditions is easy and less costly than treating them. The significance of MSDs as a threat to public healthcare demands collective effort and responsibility to prevent and manage the diseases.  

References 

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World Health Organization (WHO). (2019, November 26). Musculoskeletal conditions. Retrieved March 7, 2021 from https://www.who.int/news-room/fact-sheets/detail/musculoskeletal-conditions