4.12: Diseases and Injuries of Joints

Common musculoskeletal problems such as bursitis, sprains, strains, and arthritis show how inflammation, tissue injury, and joint wear can disrupt movement, cause pain, and shape treatment approaches. 

Master this section and you'll be able to:

• Define and differentiate bursitis, sprains, and strains based on the tissues affected, causes, and common locations in the body.
• Distinguish sprains and strains.
• Explain the role of bursae in joint function and outline how inflammation affects their protective function.
• Compare and contrast osteoarthritis, rheumatoid arthritis, and gout in terms of causes, pathophysiology, symptoms and treatment strategies.
• Explain the suffix "-itis"

Bursitis

Bursitis is the inflammation of a bursa — the small, fluid-filled sac that cushions and reduces friction between bones, tendons, and muscles near joints. When a bursa gets inflamed, it can cause pain, swelling, tenderness, and sometimes joint stiffness.

Although bursae are found all over the body, bursitis most often strikes at the shoulder, hip, knee, or elbow joints:

• Shoulder – Subacromial bursitis affects the bursa between the acromion of the scapula and a shoulder tendon passing beneath it.
• Hip – Trochanteric bursitis involves the bursa over the greater trochanter of the femur, just below the hip’s outer side.
• Hip (sitting pressure) – Ischial bursitis occurs in the bursa between the skin and the ischial tuberosity, the bony part you sit on.
• Knee – Prepatellar bursitis (“housemaid’s knee”) affects the bursa between the skin and the kneecap. It is now more often seen in roofers, carpet layers, or floor installers who kneel without knee pads.
• Elbow – Olecranon bursitis (“student’s elbow”) inflames the bursa between the skin and the tip of the ulna at the back of the elbow.

Bursitis can be acute (lasting just a few days), or chronic (lingering). Repeated acute episodes of bursitis can result in a chronic condition.

Causes include overuse of a muscle, trauma, prolonged pressure, rheumatoid arthritis, gout, or infection. Repeated acute episodes can turn into a chronic problem.

Treatment depends on the cause. Treatments for the disorder include antibiotics if the bursitis is caused by an infection, or anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids if the bursitis is due to trauma or overuse. Chronic bursitis may require that fluid be drained, but additional surgery is usually not required. In summary

• Infection – antibiotics.
• Inflammation from trauma or overuse – anti-inflammatory drugs (NSAIDs) or corticosteroid injections.
• Chronic bursitis – fluid drainage, with surgery (rarely needed).

Bursitis is your body's way of saying, "Ease up! I am tired of the friction"! 

💡Note:

In medical terminology, the suffix “-itis” means inflammation. It comes from Greek and has been used in medicine for centuries to describe a body part that is red, swollen, painful, and often warm due to irritation or infection.

Examples other than bursitis are arthritis – inflammation of a joint (arthro- = joint); tonsillitis – inflammation of the tonsils; dermatitis – inflammation of the skin (derma- = skin). 

Key tip:
When you see or hear “-itis” in a medical term, your brain should think: “Something here is inflamed.”  That means there is likely pain, swelling, and often heat and redness. 

 

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Sprains

A sprain is an acute injury to a ligament — the strong, fibrous tissue that connects bone to bone — usually caused by a sudden or forceful movement that pushes a joint beyond its normal range of motion. Ligaments are tough, but they are not indestructible. Their collagen fibers have just a hint of give, stretching only about 4% of their length before reaching their limit. Go past that, and those fibers begin to tear.

Sprains can happen in any joint, but the ankle, knee, and wrist are the usual trouble spots. Many sprains are mild, producing some swelling and bruising that respond well to the classic first-aid formula RICE:

• Rest
• Ice
• Compression
• Elevation

On the other end of the spectrum are severe sprains involving complete ligament tears or ruptures, accompanied by bone fractures. These can cause significant instability, sharp pain, and limited mobility — and may require weeks of immobilization, surgical repair, and physical therapy. 

Sprains are classified by severity:

First-degree sprain (mild) – Only a small portion of the ligament’s collagen fibers are overstretched or damaged on a microscopic level. There is mild swelling or bruising, but the joint remains stable with normal range of motion. Most people recover in 4 days to 4 weeks.

Second-degree sprain (moderate) – The ligament is partially torn, causing more noticeable swelling, tenderness, bruising, and some joint instability. Weight-bearing may be painful, and range of motion is often limited. Recovery can take 4 weeks to 4 months, depending on the extent of damage.

Third-degree sprain (severe) – The ligament is completely torn or ruptured, and in some cases, it pulls away a small piece of bone (avulsion fracture). These injuries often cause major swelling, bruising, instability, and an inability to bear weight. Interestingly, some patients feel no pain at all if the injury also severs nearby nerve endings. Recovery may take 3 to 6 months, and surgery is sometimes required.

   

Figure \(\PageIndex{1}\): Third Degree Sprains.  Excessive twisting of the knee joint can cause two different types of third degree sprains: the anterior cruciate ligament may tear completely or it may pull out of its attachment site on the tibia causing an avulsion. (Image credit: "ACL Tear and ACL Avulsion Illustrations" are based on original case courtesy of Dr. Matt Skalski, Radiopaedia.org. From the case rID: 21443) 

Strains

A strain is an acute injury to a muscle or its tendon (the strong cord that connects muscle to bone). Strains are sometimes called “pulled muscles” — and for good reason. They are often caused by sudden, forceful contractions or overstretching that push the muscle-tendon unit past its limits.

Muscle fibers, like ligaments, can only stretch so far before they start to tear. These injuries are common in the lower back, hamstrings, and calf muscles, especially during sports or heavy lifting. Mild strains can cause discomfort but heal quickly with RICE (Rest, Ice, Compression, Elevation) and gentle stretching, while severe strains can sideline someone for months and may even require surgery.

Strains are classified by severity:

First-degree strain (mild) – A small number of muscle or tendon fibers are overstretched or slightly torn. There may be mild pain, tenderness, and stiffness, but no significant loss of strength or range of motion. Recovery typically takes a few days to 3 weeks.

Second-degree strain (moderate) – There is a partial tear in the muscle or tendon. Symptoms include moderate pain, swelling, bruising, and noticeable loss of strength or flexibility. Everyday activities and sports are often painful. Recovery can take 3 to 12 weeks depending on the location and severity.

Third-degree strain (severe) – The muscle or tendon is completely ruptured, sometimes with a visible gap or deformity where the tear occurred. There is usually sudden, sharp pain (sometimes accompanied by a “popping” sound), severe swelling, bruising, and total loss of function in the affected area. Recovery can take 3 to 6 months and often requires surgical repair followed by physical therapy.

Figure \(\PageIndex{2}\): Achilles Tendon Injuries.  Acute rupture is a complete or partial tear of the tendon that happens when it is overstretched, often feeling like a sudden kick to the back of the ankle and making it hard to walk.  Achilles tendinopathy is a chronic condition in which repeated small tears (tendinosis) weaken and degenerate the tendon, often from increasing activity too quickly without proper preparation. Partial tears can mimic its symptoms, while complete ruptures cause sudden, more severe impairment.
 

Comparing Sprains and Strains

Feature	Sprain	Strain
Tissue Affected	Ligament (connects bone to bone)	Muscle or tendon (connects muscle to bone)
Common Causes	Sudden twist, fall, or force pushing a joint beyond its normal range of motion	Sudden, forceful muscle contraction or overstretching
Common Locations	Ankle, knee, wrist	Lower back, hamstrings, calf muscles
Key Symptoms	Swelling, bruising, pain, possible joint instability	Pain, muscle spasm, weakness, swelling, bruising
First-degree (Mild)	Minor stretching or microscopic tears; mild swelling/bruising; joint stable; recovery in 4 days–4 weeks	Few fibers overstretched; mild pain/stiffness; recovery in few days–3 weeks
Second-degree (Moderate)	Partial tear; moderate swelling/bruising; some instability; pain with weight-bearing; recovery in 4 weeks–4 months	Partial tear; moderate pain/swelling/bruising; loss of strength/flexibility; recovery in 3–12 weeks
Third-degree (Severe)	Complete tear or rupture (sometimes with avulsion fracture); severe instability; may have no pain if nerves damaged; recovery in 3–6 months, often with surgery	Complete rupture; severe pain, swelling, bruising, loss of function; recovery in 3–6 months, often with surgery
Treatment	RICE, immobilization, possible surgery/physical therapy	RICE, gradual stretching/strengthening, possible surgery/physical therapy

 

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Arthritis

Arthritis is a common problem that affects synovial joints, causing inflammation inside the joint. This inflammation can lead to pain, swelling, stiffness, and reduced movement. There are over 100 different types of arthritis. It can be triggered by aging, damage to the articular cartilage, autoimmune disorders, infections, or even genetic factors.

Osteoarthritis

The most common form is osteoarthritis — often called the “wear-and-tear” arthritis — which becomes more likely as we age.
Risk factors include:

• Previous joint injuries
• Jobs with heavy physical labor
• Sports with repeated running, twisting, or throwing
• Carrying excess body weight

All of these put extra stress on the articular cartilage that normally cushions the ends of bones in synovial joints. Over time, this cartilage becomes thinner and less able to protect the bone.

When cartilage wears down:

1. More stress is placed on the underlying bone.
2. The joint produces extra synovial fluid in an attempt to protect itself, which can cause swelling and stretch the articular capsule, leading to stiffness and pain.
3. The bone beneath the damaged cartilage may thicken and develop rough or bumpy surfaces, making movement painful and promoting more inflammation.

Figure \(\PageIndex{3}\): Osteoarthritis. Osteoarthritis of a synovial joint results from aging or prolonged joint wear and tear. These cause erosion and loss of the articular cartilage covering the surfaces of the bones, resulting in inflammation that causes joint stiffness and pain.  In more advanced stages of osteoarthritis bone spurs (small sharp nodules) develop on the bones, which then accelerates further cartilage damage.  (Image credits: "Healthy Knee Joint" and "Advanced Osteoarthritis" by Injury Map are licensed under CC BY 4.0.)

Progression and Treatment of Osteoarthritis

In the early stages of osteoarthritis, symptoms can sometimes improve with gentle activity that “warms up” the joint. However, symptoms may return — and even worsen — after exercise.

In advanced osteoarthritis, the affected joints often become so painful that movement is limited, leading to reduced mobility and more stiffness.

There is no cure for osteoarthritis, but several treatments can reduce pain and help maintain mobility:

• Lifestyle changes such as weight loss and low-impact exercises (like swimming or cycling)
• Medications, both over-the-counter and prescription, to reduce pain and inflammation

For severe cases, doctors may recommend joint replacement surgery (arthroplasty). This is a major procedure, so other options are always tried first. When performed, arthroplasty can significantly reduce chronic pain and restore mobility within months.

Examples (see the image below):

Total hip arthroplasty:

1. Damaged parts of the hip — including the head and neck of the femur and the acetabulum (hip socket) — are removed.
2. A prosthetic femoral head (a rounded ball on a shaft) is inserted into the femur’s shaft.
3. The acetabulum is reshaped, and a replacement socket is fitted in.
    

Total knee arthroplasty:

1. Damaged parts of the knee — including the ends of the femur and tibia  — are removed, along with any degraded cartilage and sometimes the underside of the patella.
2. The exposed surfaces of the femur and tibia are precisely shaped and resurfaced.
3. Metal components are fitted over the ends of the femur and tibia to create new joint surfaces. A plastic (polyethylene) liner is inserted between these components to serve as the new cartilage.
4. The underside of the patella may also be resurfaced and fitted with a plastic button, depending on the patient's needs and the surgeon's approach.

The prosthetic parts are pre-made (and occasionally custom-designed) for optimal fit and function.

Figure \(\PageIndex{4}\): Shoulder, Hip, and Knee Arthroplasty. Illustration of prosthetic implants for shoulder, hip, and knee joint replacements. 

Here is what this looks like in real life:

Figure \(\PageIndex{5}\):  Hip (left) and Knee Replacements (right). Damaged cartilage and bone have been replaced with metal and plastic components. Left: AP X-ray of the pelvis after hip arthroplasty. Right: Lateral and AP X-rays of the knee three months after arthroplasty.  

  

Rheumatoid Arthritis (RA)

Rheumatoid arthritis is a troublemaker that prefers freely movable joints, especially in the wrists, hands, ankles, and feet — though it can also affect the shoulders, elbows, and knees. Like osteoarthritis, RA causes pain and stiffness, but it does not stop there. It often brings along extra baggage: weakness, fatigue, and even damage to organs like the heart, blood vessels, lungs, nerves, skin, and eyes. This is because RA can attack connective tissues throughout the body. Interestingly, RA sometimes goes into periods of temporary remission, where symptoms improve.

The exact cause is still a mystery, but scientists know the how. RA is an autoimmune disease, meaning the immune system — our body’s defense team — mistakes healthy connective tissues for dangerous invaders. In a misguided attempt to “help,” it attacks normal connective tissue, treating it as if it were harmful.

In joints, this immune attack destroys cartilage, which is replaced by an unusual scar tissue called a pannus. The pannus releases enzymes that damage even more cartilage, bone, and the synovial membrane. As the pannus spreads, it replaces normal joint structures. This leads to pain, swelling, and eventually loss of joint function.

Figure \(\PageIndex{6}\): Effects of Rheumatoid Arthritis on Joint Structure. As the joint weakens, the bones shift out of position. Sometimes, the pannus becomes calcified and stiff. Progressive calcification sometimes results in fusion of the bones. In addition, the ordinary scar tissue produced at the joint shrinks as time passes, pulling the bones farther out of alignment and locking them into abnormal positions. Thus, the joint becomes distorted and immovable — often producing crippling deformities most noticeable in the hands and feet.
(Copyright 2020: Augustine G. DiGiovanna, Ph.D., Salisbury University, Maryland. Used with permission.)

There is no way to prevent or cure RA. The goals of treatment are the same as those for osteoarthritis: slowing the progress of the disease and minimizing pain and disability. Various medications may be prescribed to inhibit the immune system and relieve pain. Mild exercise helps maintain joint mobility. A variety of other treatment modalities may be initiated. Unfortunately, not all individuals respond well to these treatments.
 

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Gout

Gout (pronounced gowt) is a form of inflammatory arthritis that is often very painful. It usually affects one joint at a time—most often the big toe joint. Like other forms of arthritis, it causes pain and swelling in the affected joint(s). Gout is a chronic condition with alternating periods of flares (when symptoms worsen) and remission (when there are no symptoms).

Gout flares tend to start suddenly and can last for days or weeks. They are often followed by long symptom-free periods—sometimes lasting weeks, months, or even years—before another flare begins. While the big toe is the most common site, gout can also affect other toe joints, the ankle, or the knee.

Typical signs and symptoms of a gout flare include:

• Intense pain
• Swelling
• Redness
• Warmth (heat) in the joint

Repeated flares can lead to gouty arthritis, a more persistent form of arthritis that can last for one to two weeks before improving. Severe cases may be complicated by tophi — firm, often visible lumps under the skin caused by uric acid crystal deposits. Tophi usually develop after years of repeated gout attacks and can appear around joints, along tendons, or in other tissues. If the skin over a tophus (singular) breaks, a whitish, paste-like material made of uric acid crystals may ooze out.

Where does the uric acid come from?

Uric acid forms when the body breaks down purines, natural substances found in our cells and in many foods. Normally, excess uric acid is filtered by the kidneys and removed in urine. However, if uric acid levels become too high, they can build up in the blood (hyperuricemia) and form needle-shaped crystals in and around joints. These crystals trigger inflammation, causing the sudden pain, swelling, and redness of a gout flare.

Foods especially high in purines—such as organ meats (liver, kidney), certain seafood (sardines, anchovies), some red meats, and beer—can raise uric acid levels and increase the risk of gout attacks. People with gout are often advised to limit these foods to help prevent flares.

Diagnosis and treatment

Gout is usually diagnosed with a blood test measuring uric acid levels. Treatment often includes medications such as nonsteroidal anti-inflammatory drugs (NSAIDs) or colchicine to relieve pain and inflammation. While there is no cure for gout, it can be effectively managed with medication, lifestyle changes, and self-care strategies.

Interestingly, hyperuricemia does not always cause gout, and people with high uric acid levels but no symptoms generally do not need treatment.

Risk factors for hyperuricemia (and gout)

• Being male
• Being overweight or obese
• Having certain health conditions, such as:
  • High blood pressure (hypertension)
  • Insulin resistance or diabetes
  • Poor kidney function