A comprehensive glossary of medical terms related to rhizarthrosis (thumb base arthritis). Written in plain language for patients.
A
Arthrodesis
Surgical fusion of a joint. In thumb arthritis, the CMC joint is permanently fixed in a functional position. Eliminates pain but also eliminates joint motion.
Arthroplasty
Joint replacement surgery. In rhizarthrosis, the damaged CMC joint surfaces are replaced with an artificial prosthesis (implant).
Arthroscopy
Minimally invasive surgery using a tiny camera and instruments inserted through small incisions. Used for early-stage rhizarthrosis (debridement, synovectomy).
B
Basal Joint
Another name for the first carpometacarpal (CMC) joint at the base of the thumb. ‘Basal joint arthritis’ is the same as rhizarthrosis.
Beak Ligament (AOL)
The anterior oblique ligament — the most important stabiliser of the CMC joint. When it weakens, the joint becomes unstable and prone to arthritis.
Bone Spur (Osteophyte)
A bony projection that forms along joint margins as arthritis progresses. Visible on X-rays and can cause pain when they impinge on surrounding tissues.
C
Carpometacarpal Joint (CMC)
The joint where the first metacarpal bone of the thumb meets the trapezium bone of the wrist. This ‘saddle joint’ allows the thumb’s unique range of motion.
CE Marking
European conformity marking indicating a medical device meets EU safety and performance requirements. Required for implants sold in Europe.
Cortisone Injection
An injection of corticosteroid medication directly into the CMC joint to reduce inflammation and pain. Typically provides 3-6 months of relief.
D
DASH Score
Disabilities of the Arm, Shoulder and Hand questionnaire. A 30-item survey that measures upper extremity disability. Scale 0-100 (lower = better function).
Dual-Mobility
A prosthesis design with two articulating surfaces (an inner bearing that moves within an outer cup). Reduces dislocation risk. Used in the Touch CMC 1.
E
E-E-A-T
Experience, Expertise, Authoritativeness, Trustworthiness. Google’s framework for evaluating health content quality. Critical for medical websites.
Eaton-Littler Classification
The standard 4-stage system for grading rhizarthrosis severity on X-rays. Stage I (early) through Stage IV (severe, with pantrapezial arthritis).
F
FDA (Food and Drug Administration)
The US regulatory agency that approves medical devices and drugs. Implants need either 510(k) clearance or PMA approval to be sold in the US.
G
Grind Test
The most common clinical test for rhizarthrosis. The examiner pushes and rotates the thumb metacarpal into the trapezium. Pain and grinding = positive test.
Grip Strength
The force generated when gripping an object, measured with a dynamometer. Rhizarthrosis typically reduces grip strength by 30-50%.
H
Hyaluronic Acid
A naturally occurring joint lubricant. Injected into the CMC joint as a treatment (viscosupplementation). Some studies show benefit similar to cortisone with fewer side effects.
L
LRTI
Ligament Reconstruction Tendon Interposition. A surgical technique where the trapezium is removed and a rolled-up tendon is placed in the space. Often combined with trapeziectomy.
M
Metacarpal
The long bones of the hand. The first metacarpal connects the thumb to the wrist via the CMC joint.
O
Opposition
The ability to touch the thumb tip to each fingertip. This uniquely human movement is made possible by the saddle-shaped CMC joint.
Osteoarthritis (OA)
Degenerative joint disease caused by cartilage breakdown. Rhizarthrosis is osteoarthritis specifically of the thumb CMC joint.
Osteotomy
A surgical procedure that cuts and realigns bone. Occasionally used for early-stage rhizarthrosis to redistribute joint forces.
P
Pantrapezial Arthritis
Arthritis that extends beyond the CMC joint to involve the scaphotrapezial (ST) joint. Corresponds to Eaton Stage IV and affects surgical options.
Pinch Strength
The force generated when pinching between thumb and fingers. Key pinch (lateral), tip pinch, and palmar pinch are measured separately.
PRP (Platelet-Rich Plasma)
A treatment using concentrated platelets from your own blood, injected into the joint. Contains growth factors that may promote healing. Emerging evidence for thumb arthritis.
Pyrocarbon
A form of carbon with elastic properties similar to bone. Used in some interposition implants (e.g., ELiS) to reduce stress shielding.
R
Rhizarthrosis
Osteoarthritis of the trapeziometacarpal (TMC/CMC) joint at the base of the thumb. From Greek ‘rhiza’ (root) + ‘arthron’ (joint) + ‘osis’ (condition).
Robert View
A specialised X-ray projection that shows the CMC joint in true anteroposterior view. Essential for accurate Eaton staging.
S
Saddle Joint
A joint where the two bone surfaces are shaped like saddles sitting at 90 degrees to each other. The CMC joint is the body’s best example. Allows motion in multiple planes.
Splint (Orthosis)
A custom-made or prefabricated brace that stabilises the CMC joint. Reduces pain during activities by limiting excessive joint motion. A first-line treatment.
Subluxation
Partial dislocation of a joint. In rhizarthrosis, the metacarpal bone slides off the trapezium as ligaments weaken, creating a visible bump at the thumb base.
T
Thenar Muscles
The group of muscles forming the fleshy pad at the base of the thumb. Thenar atrophy (muscle wasting) is a sign of advanced rhizarthrosis.
Trapeziectomy
Surgical removal of the trapezium bone. The gold standard operation for advanced rhizarthrosis (Eaton Stage III-IV). Can be done with or without LRTI.
Trapezium
A small, irregularly shaped carpal (wrist) bone that forms the base of the CMC joint. Latin name: ‘os trapezium’. The bone removed in a trapeziectomy.
V
VAS (Visual Analogue Scale)
A pain measurement tool where patients mark their pain on a 0-10 line. 0 = no pain, 10 = worst pain imaginable. Used in almost all clinical studies.
W
WALANT
Wide Awake Local Anaesthesia No Tourniquet. A surgical technique where patients are awake (under local anaesthetic) during hand surgery. Increasingly popular for thumb procedures.
Z
Z-Deformity
A characteristic thumb deformity in advanced rhizarthrosis: the CMC joint adducts, the MCP joint hyperextends, and the IP joint flexes, creating a zigzag shape.
Medical Disclaimer: These definitions are simplified for patient understanding. For precise medical definitions, consult a medical textbook or your healthcare provider.