Chapter 15: Musculoskeletal system

Human Musculoskeletal System (Locomotor System)

The organ system that gives humans the ability to move

• Skeleton (bones)

• Muscles (skeletal muscles)

• Joints (connect individual bones to form a functioning unit)

• Ligaments (fibrous tissues that connect bones to other bones)

• Tendons (fibrous tissues that connect bones to muscles)

Common Musculoskeletal Conditions: Joints

Osteoarthritis (wearing down of cartilage between bones)

Rheumatoid arthritis (autoimmune inflammatory disorder of the joints)

Psoriatic arthritis (inflammatory arthritis in people with psoriasis)

Gout (inflammatory arthritis due to crystallization of uric acid)

Common Musculoskeletal Conditions: Bone

Osteoporosis (density and quality of bone is reduced, [porous bone])

Osteopenia (bone mineral density is lower than normal)

Fractures

Common Musculoskeletal Conditions: Muscles

Sarcopenia (loss of muscle with aging and immobility)

Myopathies

Arthroscopy

Endoscopic procedure that allows examination of a joint interior with a specially designed endoscope

Highly accurate as it allows direct visualization of the anatomic site

Test results and clinical significance

• Torn cartilage

• Torn ligament

• Degenerative arthritis

• Rheumatoid arthritis

• Synovitis (inflammation of the lining of the joint)

• Cyst

Arthrocentesis with synovial fluid analysis

Used to establish the diagnosis of

• Joint infection

• Arthritis

• Gout

• Synovitis

• Neoplasms

Also done to identify the cause of joint inflammation

Sterile needle is inserted into the joint space and synovial fluid is aspirated

Synovial fluid is then examined microscopically and chemically

Synovial Fluid Analysis

Bone (Long) X-Rays

This x-ray study is performed to evaluate any bone for

• fracture

• infection

• arthritis

• tendonitis

• bone spurs

Bone age can be determined in children to evaluate growth by comparing appearance and growth plates against standard bone atlases

• Serial x-rays of wrists and arms, pelvis and skull

Healing of a fracture can be monitored

Vertebral Radiography (Spinal X-ray)

Spinal radiography is used to evaluate back or neck pain

Evaluation of any area of the spine

The type and the extent depends on the patient’s clinical
condition

Test results and clinical significance

• Degenerative arthritis changes

• Disk disorders

• Traumatic or pathologic fractures

• Scoliosis

• Spondylosis (arthritis due to wear and tear to the spine)

• Suspected spinal osteomyelitis (infection of the bone)

Myelography: Provides radiographic visualization of

The spinal canal

Nerve roots

Surrounding meninges

Myelography: Procedure

Radio-opaque dye is injected into the subarachnoid space of the spinal canal and the contents of the canal can be fluoroscopically outlined.

Take X-rays of the spine

CT scan or MRI scans can be performed for more detailed images

Myelography: Test results and clinical significance

Spinal cord tumors

Herniated disk

Arthritic bone spurs

Lumbar stenosis

Osteoporosis Diagnosis

A bone mineral density (BMD) test, also called DEXA (Dual Energy X-ray Absorptiometry) scan:

• Uses low-dose X-rays to measure bone mineral density (how much calcium and other minerals are)
  in a specific area of your bone. This test helps:

  • Diagnose osteoporosis/Osteopenia

  • Predict fracture risk.

  • Monitor patients who are receiving treatment for osteoporosis

Diagnosis of osteoporosis... cont.

The spinal bone is the best representative of cancellous (spongy) bone

The radius (forearm) is the best representative of cortical (dense bone)

The hip is suitable for analysis of mixed bone.

Diagnosis of osteoporosis: Results expressed as a T score and a Z score

T-score: The difference between your bone mineral density and 0, which is the bone mineral density of a
healthy young adult.

Z-score: The difference between your bone mineral density and the average bone mineral density for healthy
people of your age, ethnicity, and sex.

• T/Z-score of -2.5 or lower indicates osteoporosis.

• T/Z-score between -1 and -2.5 indicates osteopenia.

• T/Z-score between 0 and -1 indicates normal bone density.

  

The T-score is typically used for individuals under the age of 50 while, a Z-score is used for older people.

Diagnostic Laboratory Tests of the Musculoskeletal System

Rheumatoid Factor (for the diagnosis of rheumatoid arthritis)

Bone Turnover Markers (to monitor treatment for osteoporosis)

Uric acid (in blood and urine)

• Used for the diagnosis of gout and the identification of persons at risk of stone formation

Vitamin D (to evaluate ability for calcium absorption)

Alkaline phosphatase (useful for the detection of bone disorders)

Aldolase (used to aid in the diagnosis and surveillance of skeletal muscle diseases)

Rheumatoid Factor (RF)

Rheumatoid factor test is the most useful immunologic test for confirming rheumatoid arthritis

• ~80% of patients with RA show positive result for RF test

RFs are IgG antibodies produced by lymphocytes in the synovial membranes in the joints which react with other IgG or IgM antibodies to form immune complexes, complement activation and tissue destruction

The RF test is directed towards identification of the IgM antibodies that react with RF

RF test method: latex agglutination test

Diagnostic Criteria for Rheumatoid Arthritis (RA)

American College of Rheumatology Criteria for RA

• Morning stiffness for at least 6 weeks

• Pain in at least one joint for the preceding 6 weeks

• Swelling in at least one joint for the preceding 6 weeks

• Symmetric bilateral joint swelling

• Presence of subcutaneous nodules

• Radiographic changes compatible with RA

Bone Turnover Markers (BTM)

Bone is continuously being turned over

• Bone resorption (breakdown by osteoclasts)

• Bone formation (by osteoblasts)

Osteoporosis is associated with increased bone resorption

• Common disease in postmenopausal women

BTMs

• “N” and “C-” telopeptides: Short, non-helical amino acid sequences at the ends of collagen molecules (released into blood and excreted in the urine following bone breakdown).

  • Good indicator of bone breakdown

• Osteocalcin: Non-collagenous protein that is primarily found in bone

  • Good indicator of bone metabolism.

• Bone-specific alkaline phosphatase (found in osteoblasts)

  • Good indicator of bone formation

Bone Turnover Markers (BTM): Increased levels

Osteoporosis

Osteodystrophy

Hyperthyroidism

Hyperparathyroidism

Rapid Bone Growth

Bone tumors

Paget’s disease

Bone Turnover Markers (BTM): Decreased levels

Hypoparathyroidism

Hypothyroidism

Effective antiresorptive therapy

Vit D Deficiency

Uric Acid Testing

Levels can be measured in both blood and urine

Helpful in evaluating uric acid metabolism in gout

• Uric acid crystal formation in the synovial fluid is the gold standard test for the diagnosis of gout

Uric acid is a nitrogenous breakdown product of purines like
adenine and guanine. (a DNA building block)

• Produced in the liver

Excreted by the kidney (75%) and the intestines (25%)

Elevated levels in the blood (hyperuricemia) may indicate Gout

• A form of arthritis caused by deposition of uric acid crystals in weight bearing joints.

Uric acid can become supersaturated in the urine and form kidney stones

Uric Acid: Test results and clinical significance - Increased Levels (hyperuricemia)

Gout

Multiple myeloma

Cancer chemotherapy

High purine diet

Chronic alcohol ingestion

• Decreases kidney tubular secretion of uric acid

Uric Acid: Test results and clinical significance - Decreased Levels (hypouricemia)

Renal disorders

• e.g., renal hypouricemia

Excessive fluid intake

Fanconi syndrome

• kidney is unable to reabsorb filtrate

Uricosuric drugs

• Drugs that increase uric acid excretion in the urine (e.g., steroids)

Vitamin D Test (Blood)

Vitamin D is a fat-soluble vitamin

• Vitamin D2 is provided by dietary sources

• Vitamin D3 is produced by the skin exposed to sunlight (UVB radiation)

Vitamin D is converted into its physiologically active form in the liver and the kidneys (becomes a hormonally active form)

• Binds to vitamin D receptors in target organs

• Vitamin D encourages calcium absorption by the intestine

• Also acts on bone, kidney and parathyroid gland cells leading to the maintenance and regulation of calcium levels in the blood

Clinical Features and Associated Vitamin D Levels

Vitamin D Tests

25(OH)D Test:

• Measures the level of 25-hydroxyvitamin D in the blood, which is the main form of vitamin D that circulates in the body. It reflects both:

  • Vitamin D prostatus bute skin from sunlight exposure.

  • Vitamin D obtained from food or supplements.

1,25(OH)2D Test (Calcitriol):

• Measures the active form of vitamin D, which is produced in the kidneys.

  • It's not usually used to check for overall vitamin D status but may be used to monitor kidney problems or to help find the cause of abnormal calcium levels in the blood.

Vit D test: Test results and clinical significance: Increased Levels

Increased dietary intake

Increased Calcium intake

Hyperparathyroidism

Vit D test: Test results and clinical significance: Decreased Levels

Rickets

Osteomalacia (softening of bones)

Osteoporosis

Gastrointestinal malabsorption syndrome

Renal & Liver disease

Inadequate dietary intake

Inadequate exposure to sunlight