The fleshy pad between your thumb and index finger is mostly one muscle called the first dorsal interosseous, and when it hurts, the cause is usually some form of overuse, a trigger point (a tight knot in the muscle), nerve compression farther up the arm, or referred pain from a nearby joint. Because this small muscle works hard during virtually every gripping, pinching, and squeezing motion your hand performs, it is surprisingly vulnerable to strain. The good news is that most causes are identifiable and treatable without surgery, but the range of possible culprits is wider than most people expect.
What That Muscle Does and Why It Matters
The first dorsal interosseous sits in the web space between the thumb and index finger and is responsible for moving the index finger sideways, away from the middle finger. It also plays a major role in stabilizing the index finger when you perform a lateral pinch, the motion you use to turn a key, hold a credit card, or grip a sheet of paper between your thumb and the side of your index finger. When this muscle is weak or injured, that stabilization breaks down, and the index finger can drift toward the pinky side during pinching, making the hand feel clumsy and weak.1PubMed. Reconstruction of lateral pinch in an isolated paralysis of the first dorsal interosseous muscle – A new surgical technique
This muscle is also one of the thickest interosseous muscles in the hand, which is partly why you can feel it so easily when you squeeze your thumb against your index finger. Its prominence and constant involvement in daily hand tasks make it a common site for pain complaints, particularly in people who use their hands intensively for work, sports, or hobbies.
Repetitive Strain and Overuse
The most common reason for pain in the thumb web space, particularly in younger adults, is simply doing too much with your hands. Repetitive gripping, pinching, and fine motor tasks load this muscle over and over. Text messaging is a well-studied example: young adults with thumb pain from heavy texting show tenderness in the web space and reduced lateral and tip pinch strength compared to those without thumb pain.2PubMed Central. Clinical and Ultrasonic Evaluation of the Thumb: Comparison of Young Adults With and Without Thumb Pain With Text Messaging The pain does not always stay localized to the web space, either. Tenderness can show up at multiple joints along the thumb and at the anatomical snuff box on the wrist side.
Texting is just one example. Any activity that involves sustained or repeated pinching, gripping, or spreading of the fingers can produce the same kind of overuse pain. Writing with a pen for hours, using scissors or pruning shears, playing racket sports, and working with hand tools all fall into this category. Musicians are at particular risk: performance-related musculoskeletal disorders are common among instrumentalists and frequently affect the upper extremities, the result of intense, repetitive demands on muscles and tendons that most people rarely stress to that degree.3ScienceDirect / Journal of Hand Therapy. A musician-centered approach to management of performance-related upper musculoskeletal injuries Guitarists, pianists, and string players often describe aching in the web space after long practice sessions.
The pattern with overuse injuries is predictable: the pain builds gradually rather than appearing after a single event, tends to be worse during or immediately after the activity, and eases with rest. If you have noticed the ache mainly when you are doing a lot with your hands and it fades on days you take it easy, overuse is the likely explanation.
Myofascial Trigger Points
If you press into the web space and find a spot that is exquisitely tender and refers a deep ache into the surrounding area, you may have a myofascial trigger point. These are essentially irritable knots within a taut band of muscle that can develop when a muscle is overworked, held in a shortened position for too long, or stressed by repetitive tasks. The first dorsal interosseous is a frequent site for trigger points, and they are especially common in people who already have thumb base osteoarthritis. In one study, about 88 percent of patients with thumb carpometacarpal osteoarthritis on their dominant hand had trigger points in the first dorsal interosseous, compared with about 48 percent on the dominant hand in healthy controls.4Topics in Geriatric Rehabilitation. Prevalence of Myofascial Trigger Points in the First Dorsal Interosseous Muscle in Patients With Thumb Carpometacarpal Osteoarthritis Compared to Healthy Controls
What makes trigger points tricky is that they can hurt even when you are not actively using the muscle. People often describe a dull, deep ache that sometimes radiates into the index finger or the back of the hand, even at rest. Pressing on the knot reproduces or intensifies the pain, which distinguishes it from more generalized soreness. Trigger points can also develop as a secondary response to another problem, like arthritis at the base of the thumb or nerve compression. In those cases, treating only the knot without addressing the underlying issue usually leads to recurrence.
Thumb Base Arthritis
The carpometacarpal joint at the base of the thumb sits very close to the web space, and arthritis in that joint is one of the most common causes of hand pain in people over 50. Because the first dorsal interosseous stabilizes the index finger side of the pinch while the thumb joint absorbs the opposing force, inflammation or degeneration at the thumb base often spreads its pain into the web space. You might feel the ache most during tasks that load the joint, such as opening jars, turning doorknobs, or writing.
People with thumb base arthritis frequently develop secondary trigger points in the first dorsal interosseous, which can make the pain feel muscular rather than joint-related.4Topics in Geriatric Rehabilitation. Prevalence of Myofascial Trigger Points in the First Dorsal Interosseous Muscle in Patients With Thumb Carpometacarpal Osteoarthritis Compared to Healthy Controls This layering of joint pain and muscle pain can be confusing if you are trying to self-diagnose. A simple grind test, where you press the thumb straight into its base joint and rotate it, often reproduces the deeper joint pain and can help distinguish it from pure muscle soreness. In one study of young adults with thumb pain, about one in five had a positive grind test, suggesting joint involvement even in a population you would not normally associate with arthritis.2PubMed Central. Clinical and Ultrasonic Evaluation of the Thumb: Comparison of Young Adults With and Without Thumb Pain With Text Messaging
Ligament Injuries at the Thumb
A sudden forceful bending of the thumb, the kind that happens when you catch a ball awkwardly, fall on an outstretched hand, or catch your thumb on something during a contact sport, can injure the ulnar collateral ligament at the thumb’s main knuckle. This injury, sometimes called “skier’s thumb” or “gamekeeper’s thumb,” produces pain and swelling that radiates into the web space and along the inner edge of the thumb. Injury to this ligament is very common and can become disabling if missed or left untreated.5PubMed Central. Injury to the ulnar collateral ligament of the thumb
Athletes are hit especially hard because the thumb collateral ligaments are essential for precision grip and pinch, and injuries occur at a higher frequency in competitive sports.6PubMed. Thumb metacarpophalangeal joint collateral ligament injury management If your web space pain started after a specific incident involving the thumb being pulled backward or sideways, this kind of ligament injury deserves prompt evaluation. Left alone, an unstable ligament can lead to chronic weakness and progressive arthritis.
Ulnar Nerve Compression
Not all web space pain originates in the hand. The first dorsal interosseous is supplied by the ulnar nerve, the nerve that runs along the inner side of the elbow (the one responsible for the “funny bone” sensation). When the ulnar nerve is compressed, most commonly at the elbow in a condition called cubital tunnel syndrome, it can produce weakness, wasting, and pain in the muscles it controls, including the first dorsal interosseous.
What makes cubital tunnel syndrome deceptive is that it sometimes presents with prominent involvement of the first dorsal interosseous muscle, looking a lot like a problem at the wrist or even in the web space itself.7Europe PMC. Ulnar Distribution Paresthesia, Weakness and Atrophy: a Characteristic Presentation of Cubital Tunnel Syndrome You may notice tingling or numbness in the ring and pinky fingers, difficulty spreading your fingers apart, or a visible flattening of the web space as the muscle atrophies. The pain itself can feel like a deep ache in the web space even though the actual compression is happening at the elbow. If your web space discomfort comes with numbness in the last two fingers or feels worse when your elbow is bent for a long time (sleeping, holding a phone to your ear), ulnar nerve involvement is worth investigating.
When the Problem Starts in the Neck
Pain in the web space can occasionally be referred from the cervical spine. Cervical radiculopathy, where a nerve root in the neck is compressed by a herniated disc or bone spur, can produce pain, weakness, and sensory changes that travel all the way down the arm into the hand.8Europe PMC / Journal of Spine Surgery. A clinical review of hand manifestations of cervical myelopathy, cervical radiculopathy, radial, ulnar, and median nerve neuropathies The C8 and T1 nerve roots, which contribute to the ulnar nerve, are the ones most likely to send symptoms into the web space.
This type of referred pain usually comes with other clues: neck stiffness, pain that worsens with certain head positions, or symptoms that run down the inside of the arm before reaching the hand. If all you feel is web space pain with no neck or arm involvement, a cervical cause is unlikely but not impossible. Clinicians sometimes describe a “double crush” scenario, where mild nerve irritation at both the neck and the elbow combine to produce hand symptoms that neither site would cause on its own.
How to Sort Out the Cause
With so many potential origins, figuring out why your web space hurts comes down to a few key questions:
- Gradual or sudden? Gradual onset after increased hand use points toward overuse or trigger points. Sudden onset after a fall or forceful thumb bend raises concern for a ligament injury.
- Numbness or tingling? Pins-and-needles in the ring and pinky fingers suggest ulnar nerve compression. Numbness that extends up the forearm points toward the neck or brachial plexus.
- Joint grinding or catching? Pain at the base of the thumb that worsens with rotation suggests arthritis at the carpometacarpal joint.
- A tender knot? A localized spot in the muscle belly that reproduces deep, aching pain when pressed is likely a trigger point.
- Neck involvement? If the hand pain increases when you tilt or turn your head, cervical radiculopathy is worth ruling out.
Most clinicians start with a physical examination and history. If nerve compression is suspected, electrodiagnostic testing (a nerve conduction study) can pinpoint where along the nerve the problem lies. For suspected arthritis, X-rays of the thumb base are typically sufficient. Ligament injuries sometimes need an MRI to determine whether surgical repair is warranted.
What Helps
Treatment depends on the cause, but several approaches overlap across conditions. For overuse and trigger points, the first line is reducing the aggravating activity and giving the muscle time to recover. Sustained gripping or pinching tasks should be broken up with rest intervals. Stretching the thumb web space gently, pressing the thumb away from the palm, can relieve tightness. Applying direct pressure to a trigger point for 30 to 60 seconds at a time, though uncomfortable, often helps release it.
For thumb base arthritis, strengthening the first dorsal interosseous and the opponens muscle can improve joint stability and reduce pain. A randomized trial found that a home exercise program focusing on stretching the adductor muscle and strengthening the first dorsal interosseous and opponens was used as part of a stabilization approach for thumb carpometacarpal osteoarthritis.9PubMed. Dynamic stabilization home exercise program for treatment of thumb carpometacarpal osteoarthritis: A prospective randomized control trial The logic is straightforward: a stronger web space muscle stabilizes the index finger, which in turn takes load off the arthritic thumb joint during pinch.
Thumb web spacer splints, which hold the thumb in a slightly open position, have been shown to improve hand function in certain populations by preventing the thumb from collapsing into the palm and overloading the web space.10PubMed Central. The effect of a thumb web spacer splint on hand function in children with hemiplegic cerebral palsy While that particular study focused on children with cerebral palsy, the same splinting principle is widely used by hand therapists for adults with thumb arthritis or web space tightness. Off-the-shelf thumb spica splints from a pharmacy serve a similar role for everyday use.
For ulnar nerve compression, the key is reducing pressure on the nerve at the elbow. Avoiding prolonged elbow flexion, using a towel or pad around the elbow at night to keep it from bending fully, and modifying workstation ergonomics can all help. When conservative measures fail, surgical release of the cubital tunnel is an option with generally good outcomes.
Ergonomic Adjustments Worth Making
Whatever the underlying cause, certain daily habits put extra stress on the web space and are worth modifying. Gripping your phone with a wide pinch for long stretches overloads both the first dorsal interosseous and the thumb base joint. A pop socket, phone ring grip, or simply resting the phone on a surface while you scroll takes most of that strain away. Similarly, if your work involves sustained gripping of tools, look for tools with wider, padded handles. A thicker grip reduces the force your web space muscles have to generate to maintain hold.
Keyboard and mouse use matter too. If your wrist is cocked to one side or your hand is bunched into a tight claw over a small mouse, the interosseous muscles work overtime to keep the fingers positioned. A vertical mouse or an ergonomic keyboard that keeps the hand in a more neutral posture can make a measurable difference over an eight-hour workday. These adjustments may sound minor, but cumulative strain from years of suboptimal positioning is exactly how many people end up with chronic web space pain in the first place.
Why This Muscle Seems to Hurt More Than Others in the Hand
One reason the first dorsal interosseous is a disproportionate source of complaints is evolutionary. The human hand’s precision grip, the ability to bring the thumb pad squarely against the index finger pad, is one of our most distinctive features. Research modeling precision grip in both modern humans and fossil hominins has found that both joint mobility and digit proportions are critical for manipulation potential, and that the precision grip pattern seen in modern humans may extend back millions of years to some of the oldest known hominin species.11Europe PMC / Royal Society Interface. Estimating thumb-index finger precision grip and manipulation potential in extant and fossil primates The first dorsal interosseous is central to this grip: it keeps the index finger stable while the thumb provides opposing force. We evolved to use this muscle intensively, and modern life, with its phones, keyboards, and tools, pushes that usage to levels and durations that even an evolved grip system was not built to sustain indefinitely.
The muscle’s anatomical position also makes it vulnerable. It sits in a confined space between two metacarpal bones, so any swelling from inflammation or overuse has limited room to expand. That compression can amplify pain signals and make even mild irritation feel disproportionately uncomfortable compared with the same level of strain in a larger, less confined muscle.
When to Get It Checked
Most web space pain resolves with rest, activity modification, and gentle stretching within a few weeks. But some presentations warrant a visit to a clinician sooner rather than later. Visible wasting of the muscle, where the web space looks noticeably flatter on one hand than the other, suggests nerve damage that needs evaluation. Persistent numbness in the ring and pinky fingers is another red flag pointing toward ulnar nerve compression. Thumb instability after a fall or impact, where the thumb feels loose when you try to pinch, could indicate a torn collateral ligament that may need surgical repair to avoid chronic problems.5PubMed Central. Injury to the ulnar collateral ligament of the thumb And pain that has persisted for more than six weeks despite rest, or that keeps returning every time you resume normal activities, is worth a professional assessment to rule out joint disease, nerve entrapment, or another structural issue that simple rest will not fix.