Doctors perform thumb arthritis tests, such as the grind test, to assess the joint at the base of this digit. A positive test reproduces pain on the joint, confirming that a person has thumb arthritis.

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The thumb base joint is one of the most common areas of osteoarthritis (OA) in the hand. Thumb arthritis is more common in adults aged 50 years and above.

Doctors use several tests to diagnose thumb arthritis. These tests aim to reproduce the pain of arthritis. They include:

  • grind test
  • traction-shift test
  • lever test
  • pinch test
  • pinch strength

This article explores thumb arthritis, the tests to evaluate it, the steps involved, and the expected results.

Thumb arthritis, also called basal thumb arthritis or basal joint arthritis refers to the breakdown and degeneration of the cartilage in the joint at the base of the thumb, which is called the carpometacarpal (CMC) joint or the trapeziometacarpal joint.

This saddle-shaped joint is responsible for the unique ability of the thumb to contact all the other four digits — the fingers — contributing to 40% of the overall function of the hand.

Thumb arthritis is usually a type of OA that results from gradual wear in the joint.

Thumb arthritis is a progressive disease that causes a gradual deterioration of the CMC joint of the thumb. According to the Eaton-Litter classification, the disease has four stages:

  • Stage 1: In this stage, only slight joint space widening is present. The joint surfaces are normal, and there are no bone spurs, or osteophytes, present.
  • Stage 2: There is a slight narrowing of the joint. The bone may be thicker and have fluid-filled lesions that bone surrounds. These effects are known as sclerosis and cystic changes, respectively. The joint may also have osteophytes and loose bodies that are smaller than 2 millimeters (mm).
  • Stage 3: Similar to stage 2, sclerosis and cystic changes are present in the joint. There is already a marked joint space narrowing and the presence of osteophytes or loose bodies that are larger than 2 mm.
  • Stage 4: In addition to all the changes that occur in stage 3, this stage includes arthritis of the scaphotrapezial joint in the wrist.

Doctors can perform several physical tests to see whether a person has thumb arthritis.

CMC thumb grind test

The grind test is the diagnostic tool that doctors most commonly use to evaluate and confirm OA.

To perform the grind test, the doctor will apply pressure to the thumb metacarpal and simultaneously rotate the thumb metacarpal base.

The test is positive if it causes pain in the joint.

Traction-shift test

The traction-shift test is a newer diagnostic technique that doctors can use.

This test is similar to the grind test, as it uses the occurrence of pain to determine whether a person has thumb arthritis.

A doctor grasps the joint’s two ends, pulls them apart, and then relocates them. Pain can indicate subluxation, or partial dislocation, and the presence of thumb arthritis.

Pinch test

This simple test involves asking a person to make a letter O with the tip of the thumb touching the tip of the index finger.

A person has arthritis if they cannot assume the position, and the shape of their hand looks more like a letter D. Trying to pinch may also produce pain.

People who get a positive result on this test will likely also experience pain if they try to pinch or grip an object.

Lever test

In the lever test, the doctor places their thumb and index finger at the base of the first metacarpal, just after the CMC joint, and rocks the thumb back and forth to apply pressure over the anterior oblique ligament.

The test is positive if it reproduces the pain at the base of the thumb. A 2016 study comparing three physical examinations for thumb arthritis found that the lever test was the most sensitive and, therefore, the least likely to produce a false-negative result.

This test is also called the pressure-shear test. A similar 2019 study stated that the test is superior over the grind test and other maneuvers in diagnosing thumb CMC arthritis.

Metacarpal flexion and extension tests

In a metacarpal extension test, a person extends the thumb while the doctor tries to resist the motion by placing a finger on the interphalangeal joint. The test is positive if the person experiences pain.

Doctors perform the metacarpal flexion test in the same way, except that the person tries to flex their thumb instead of extending it.

Pinch strength test

A 2016 study found that people with early thumb CMC arthritis have poor pinch strength. Doctors may sometimes assess the pinch strength of the affected hand and compare it with that of the unaffected hand.

This test uses a device called a pinch dynamometer. The device measures a person’s strength in doing three pinches: lateral pinch, three-point pinch, and two-point pinch.

Symptoms that may indicate thumb arthritis include pain when performing activities that require gripping, grasping, and pinching. The condition may also cause the following symptoms:

  • tenderness or discomfort at the thumb base
  • limited range of motion
  • weak grip and pinch strength
  • swelling or stiffness at the thumb base

Doctors will start the diagnosis of thumb arthritis by examining the thumb to check for symptoms such as swelling, tenderness, pain, and the presence of lumps.

They may also wish to rule out carpal tunnel syndrome, which can produce some similar symptoms.

In some cases, the doctor may order an X-ray of the thumb. An X-ray can reveal signs of thumb arthritis, including:

  • joint space narrowing
  • presence of osteophytes and loose bodies
  • bone and cartilage changes

Certain people have an increased risk of developing thumb arthritis, including individuals who work on a computer for extended periods and those who have other conditions that affect the cartilage, such as rheumatoid arthritis.

Learn more about the causes and risk factors for thumb arthritis.

Thumb arthritis may get worse over time, as no treatment can stop its progression. Instead, treatment aims to reduce pain and improve and maintain function.

The stage of the person’s condition and the severity of their symptoms will inform their treatment.

Treatments for thumb arthritis include:

Thumb arthritis is a condition that can cause severe pain and significantly affect a person’s use of their hands.

Anyone who feels discomfort and pain at the base of the thumb should contact a doctor for a diagnosis so that they can start any necessary treatment as early as possible.

By modifying their activities and receiving suitable treatment, many people with thumb arthritis can manage their symptoms.