Joint Disorders & Injuries Caused by Homeostatic Imbalances

Instructor: Cheryl Rosenfeld

Cheryl has taught veterinary and medical student for over 20 years and has a DVM and PhD degree in reproductive biology.

Joints are susceptible to injuries; this lesson will consider joint injuries, including bursitis and arthritis, that can occur. Injuries to the knee and ankle joint, which are common in athletes, will also be explored. Updated: 01/28/2021


Joints have bursae, fluid-filled sacs, to help cushion and reduce friction in the joint. Such structures are lined with synovial cells that produce synovial fluid to help lubricate this region. Bursae are located at friction point, where muscles and/or tendons need to slide across the bone. A bursa helps to reduce friction along the gliding surface. Bursitis is inflammation of one or more bursae and can result in movement along such joints becoming more difficult and painful. The inflammation is exacerbated by the movement of tendons and muscles across an inflamed bursa, which can result in stiffening of the muscles in this area. Bursitis tends to affect more superficial bursae. Signs of bursitis include:

  • Heat and redness in the joint region.
  • Joint pain and stiffening
  • Burning pain around the joint region, specifically where the bursa for the joint resides.
  • Exercise or other excessive motion can aggravate the pain, resulting in increased stiffness of the joint up to 24 hours later.
  • Bursitis in the shoulder joint may lead to a snapping, grinding, or popping sound, called 'scapula syndrome', although it may not be painful.

Bursitis can occur due to one or more of these causes:

  • Trauma to the joint
  • Auto-immune disorders
  • Infections
  • Iatrogenic (doctor-induced)
  • Repetitive movements and excessive pressure on the joints
  • Immune-deficiencies, such as HIV and diabetes

Bursae of the shoulder, knee, and elbow joints are most likely to be affected. Secondary conditions that can occur due to bursitis include several auto-immune and other disorders:

  • Rheumatoid arthritis - an auto-immune disorder of the joints
  • Systemic lupus erythematosus (SLE) - an autoimmune attack on several tissues and cell of the body
  • Gout - inflammation of the joint that may be associated with uric acid stones
  • Scleroderma formation - an autoimmune attack on the skin, blood vessels, muscles, and internal organs


Arthritis is inflammation of the joints, and numerous causes can result in this disorder. The two most common causes are osteoarthritis, otherwise known as degenerative joint disease (DJD), which occurs with age and is common in the fingers, knee, and hips, and rheumatoid arthritis, an auto-immune disorder that generally affects hands and feet. Other commons causes of arthritis are:

  • Gout
  • Fibromyalgia - chronic widespread pain
  • Septic arthritis, also called infectious arthritis, generally bacterial in origin, such as Lyme disease due to Borrelia burgdorferi

Signs of arthritis include:

  • Redness, warmth, and swelling of the joint
  • Decreased range of motion of the affected joints
  • Lameness if the knee or hip joint region are involved
  • Radiographic evidence showing erosion of the articular cartilage on one or more bones and potential 'joint mice', where portions of the articular cartilage may actually break off the main bone and be present in the joint cavity.

Causes of arthritis vary depending on the specific type of arthritis. In osteoarthritis, past injury, such as a fracture, or chronic stress, on the joint can increase the likelihood of cartilage erosion and/or ligament tears, including the patellar ligament and anterior cruciate ligament. Such changes result in increased friction in the joint and further destabilization of the region, which increases the wearing down of the articular cartilage. As DJD progresses, it can result in bone rubbing against bone, which is painful and can increase the potential risk for even further damage. It is a vicious cycle in this sense.

Rheumatoid arthritis and other autoimmune disorders, such as SLE, involve the individual's own immune system attacking components of the joint. Therefore, the mainstay of such treatments involves immunosuppressants.

Knee and Ankle Injuries

Injuries to the knee and ankle regions are common. In this section, we will consider some of the main injuries that can occur in these two areas.

The knee joint is the articulation between four bones: femur, tibia, fibula, and patella. This joint also includes several important ligaments, such as the anterior, posterior, medial, and lateral cruciate ligaments and patellar ligament. Common injuries to the knee joint include:

  • A sprain or tear of a ligament, including the anterior cruciate ligament that prevents the tibia from moving ahead of the femur, medial cruciate, lateral cruciate, or posterior cruciate. Of these, a tear of the anterior cruciate ligament is the most common, especially in athletes.

  • Patellar luxation - where the patella (kneecap) becomes displaced.

  • Meniscus injury (medial or lateral), the meniscus is comprised of fibrocartilage that helps to cushion the joint and is slow to heal if injured. An injury generally causes it to be replaced by fibrous tissue rather than fibrocartilage.

  • Muscle strain, including the surrounding quadriceps muscles, hamstring muscles, popliteal, patellar tendon, hamstring tendon, or popliteal tendon

  • Fracture of the femur, tibia, and/or patella - depending on the type of fracture will determine how easily it heals and what methods might be needed to repair the fracture, such as a splint, intramedullary (IM) pin, or an external fixator.

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