Joint Health Glossary
Clear, easy-to-understand definitions of medical terms related to joint pain, arthritis treatments, and healthcare coverage.
Acetabulum
The cup-shaped socket of the pelvis that holds the head of the femur (thigh bone) in the hip joint.
Appeal
A formal request to have your insurance company reconsider a denied claim or coverage decision. You have the right to appeal most insurance denials, including Medicare decisions.
Arthroplasty
Surgical reconstruction or replacement of a joint, commonly called joint replacement surgery. The damaged joint surfaces are removed and replaced with artificial components made of metal, plastic, or ceramic.
Arthroscopy
A minimally invasive surgical procedure where a surgeon inserts a small camera (arthroscope) into a joint through tiny incisions to diagnose and sometimes treat joint problems.
Articular Cartilage
The smooth, white tissue covering the ends of bones in joints. Its breakdown is the primary feature of osteoarthritis.
Bilateral Arthritis
Arthritis affecting the same joint on both sides of the body, such as both knees or both hips. Common in osteoarthritis due to similar wear patterns.
Bone Spur
A smooth, bony growth that develops along the edges of bones, especially in joints affected by osteoarthritis. Also called an osteophyte.
Bone-on-Bone
A colloquial term describing advanced osteoarthritis where cartilage has worn away completely, allowing direct contact between bone surfaces. Often painful and may require surgery.
Bursa
Small, fluid-filled sacs that cushion bones, tendons, and muscles near joints. Bursitis (inflammation of a bursa) can cause joint pain similar to arthritis.
Bursae
Small, fluid-filled sacs that act as cushions between bones, tendons, and muscles near joints, reducing friction during movement. Singular form is 'bursa.'
Cartilage
A smooth, rubbery connective tissue that covers and protects the ends of bones where they meet to form joints, allowing them to glide smoothly during movement.
Chondromalacia
Softening and deterioration of cartilage, most commonly affecting the underside of the kneecap. Often considered an early stage of patellofemoral arthritis.
Coinsurance
Your share of the costs of a covered service, calculated as a percentage. With Medicare Part B, you pay 20% coinsurance after meeting your deductible.
Corticosteroid
A powerful anti-inflammatory medication similar to cortisol (a hormone naturally produced by the body) that can be injected into joints to quickly reduce swelling and pain.
Covered Service
A healthcare service that your insurance plan includes in your benefits and will help pay for, assuming you meet all requirements like deductibles and prior authorization.
CPT Code
Current Procedural Terminology codes used by healthcare providers to identify specific medical services for billing. Each joint injection, office visit, or therapy session has a specific CPT code.
Crepitus
A crackling, popping, or grinding sensation or sound that occurs during joint movement, often felt or heard when bones with damaged cartilage rub together.
Deductible
The amount you must pay out-of-pocket for healthcare services before your insurance starts paying. Medicare Part B has an annual deductible of $240 (2024).
Degenerative Joint Disease
Another name for osteoarthritis, emphasizing the progressive wear-and-tear nature of the condition. Often abbreviated as DJD.
DME (Durable Medical Equipment)
Medical equipment prescribed for home use that can withstand repeated use, serves a medical purpose, and is appropriate for home settings. Includes knee braces, walkers, TENS units, and other devices for joint pain.
Effusion
Excess fluid buildup inside a joint, causing visible swelling. Also called 'water on the knee' when it occurs in the knee joint.
EOB (Explanation of Benefits)
A statement from your insurance company explaining what was billed, what they paid, and what you owe. Not a bill, but shows how your claim was processed.
Femur
The thigh bone - the longest and strongest bone in the body. The lower end of the femur forms the upper part of the knee joint.
Flare-Up
A temporary worsening of arthritis symptoms, often triggered by overactivity, weather changes, or stress. Flare-ups can increase pain, swelling, and stiffness for days or weeks.
Fluoroscopy
A real-time X-ray imaging technique that allows doctors to see moving images of internal structures on a monitor, often used to guide needle placement during joint injections.
Humeral Head
The ball-shaped top of the upper arm bone (humerus) that fits into the shoulder socket. Arthritis here causes shoulder pain and limited range of motion.
Hyaluronic Acid
A naturally occurring substance found in synovial fluid that gives it its thick, gel-like consistency and lubricating properties. Also used as an injection treatment for joint pain.
ICD-10
International Classification of Diseases codes used to identify diagnoses. Your ICD-10 code for osteoarthritis determines what treatments insurance will cover.
Inflammation
The body's natural protective response to injury or irritation, characterized by redness, warmth, swelling, and pain in the affected area.
Joint Capsule
A tough, fibrous envelope that surrounds a joint, enclosing the joint space and containing synovial fluid. Its inner lining produces the fluid that lubricates the joint.
Joint Space
The gap between bones in a joint, visible on X-rays. Narrowing of joint space indicates cartilage loss and is a key diagnostic sign of osteoarthritis.
Joint Stiffness
Difficulty moving a joint through its full range of motion, often worst after rest. A hallmark symptom of osteoarthritis, typically improving with gentle movement.
Labrum
A ring of fibrocartilage that deepens and stabilizes the hip and shoulder sockets. Labral tears can cause pain and may contribute to arthritis development.
Ligament
Strong bands of fibrous connective tissue that connect bones to other bones, providing joint stability. Ligament injuries can accelerate arthritis development.
Limited Range of Motion
Reduced ability to move a joint through its full, normal arc of movement. A common consequence of osteoarthritis caused by pain, swelling, bone spurs, or cartilage loss.
Medical Necessity
The standard used by insurance to determine if a treatment is appropriate and needed for your condition. Services must be medically necessary for insurance to cover them.
Medicare Advantage
Private insurance plans (Part C) that provide Medicare benefits through insurance companies instead of the federal government. Often includes extra benefits but requires using network providers.
Medicare Part B
The portion of Medicare that covers outpatient medical services, including doctor visits, joint injections, and physical therapy. Requires monthly premium and 20% coinsurance for most services.
Meniscus
A C-shaped piece of rubbery cartilage in the knee joint that acts as a cushion and stabilizer between the thighbone and shinbone. Each knee has two menisci.
Molecular Weight
The size of a molecule measured in daltons. In hyaluronic acid products, molecular weight affects how thick and long-lasting the injection is, with higher molecular weight typically providing longer relief.
Nerve Block
An injection of anesthetic near specific nerves to temporarily block pain signals. Used for diagnosis, pain relief, or before surgery. Effects last hours to months depending on medication used.
NSAID
Non-Steroidal Anti-Inflammatory Drug - a type of medication that reduces pain, inflammation, and fever by blocking enzymes that produce inflammatory chemicals in the body.
Orthotic
A custom or prefabricated device worn to support, align, or correct joint and limb function. For knee arthritis, includes braces, shoe inserts, and wedged insoles that reduce joint stress.
Osteoarthritis
A degenerative joint disease where the protective cartilage that cushions the ends of bones wears down over time, causing pain, stiffness, and reduced mobility.
Osteophyte
A bony projection that forms along joint margins in response to cartilage damage. Also called bone spurs, osteophytes are a radiographic hallmark of osteoarthritis.
Out-of-Pocket Maximum
The most you have to pay for covered services in a plan year. After reaching this limit, insurance pays 100% of covered costs. Traditional Medicare has no out-of-pocket maximum, but Medicare Advantage plans do.
Partial Knee Replacement
Surgery to replace only the damaged compartment of the knee, preserving healthy bone and ligaments. Also called unicompartmental knee arthroplasty (UKA). Best for arthritis limited to one area of the knee.
Patella
The kneecap - a small, triangular bone at the front of the knee that protects the joint and improves the mechanical advantage of the quadriceps muscle.
Patellofemoral Syndrome
Pain around or behind the kneecap, often from maltracking or cartilage wear. Can occur alone or alongside knee osteoarthritis.
Physical Therapy
A healthcare specialty focused on restoring movement and function through exercise, manual therapy, and education. Often the first-line treatment for joint pain and arthritis.
Prior Authorization
Approval from your insurance company required before receiving certain treatments. If not obtained, the treatment may not be covered even if it's normally a covered benefit.
PRP
Platelet-Rich Plasma - a treatment that uses concentrated platelets from your own blood, injected into a joint to potentially promote healing and reduce inflammation.
Radiofrequency Ablation
A procedure using heat generated by radio waves to disable nerves that transmit pain signals. Provides longer-lasting relief than nerve blocks for chronic joint pain. Also called RFA or radiofrequency neurotomy.
Range of Motion
The full movement potential of a joint, usually measured in degrees of a circle. Limited range of motion means a joint cannot move through its normal arc of movement.
Rheumatoid Arthritis
An autoimmune disease where the immune system attacks joint linings, causing inflammation and damage. Different from osteoarthritis in cause and treatment.
Rotator Cuff
A group of four muscles and tendons that stabilize the shoulder joint and enable arm rotation. Rotator cuff problems are common sources of shoulder pain.
Stem Cell Therapy
An experimental treatment that uses stem cells to attempt to regenerate damaged joint tissue. Currently not FDA-approved for arthritis and not covered by Medicare.
Step Therapy
An insurance requirement to try less expensive or more conservative treatments before approving coverage for other options. Also called 'fail first' protocols.
Subchondral Bone
The layer of bone located directly beneath the cartilage in joints. Changes to subchondral bone, including sclerosis and cyst formation, are hallmarks of osteoarthritis progression.
Synovial Fluid
A thick, slippery liquid that fills the space inside joints, lubricating the joint surfaces and providing nutrients to cartilage.
Synovium
The thin membrane lining the inside of joint capsules that produces synovial fluid. Inflammation of the synovium (synovitis) is a key feature of many arthritic conditions.
Tendon
Tough fibrous tissue that connects muscles to bones, enabling movement. Tendon problems around joints can cause pain that mimics arthritis.
TENS Unit
Transcutaneous Electrical Nerve Stimulation device that delivers mild electrical pulses through the skin to relieve pain. A non-drug option for managing chronic joint pain at home.
Tibia
The shinbone - the larger of two lower leg bones. The upper surface of the tibia forms the lower part of the knee joint.
Total Knee Replacement
Surgery to replace all weight-bearing surfaces of the knee joint with metal and plastic components. Also called total knee arthroplasty (TKA). Typically reserved for severe arthritis that hasn't responded to conservative treatment.
Tricompartmental OA
Osteoarthritis affecting all three compartments of the knee: medial (inner), lateral (outer), and patellofemoral (kneecap). Often indicates more advanced disease.
Related Resources
Explore more educational content about joint health