Extensor carpi ulnaris (ECU) tendinopathy is a load-related tendon disorder that causes pain along the tendon on the little-finger side of the back of the wrist. ECU subluxation, or instability, is a containment problem: the tendon shifts partly or fully out of its groove, often with a painful snap during forearm rotation.
Both cause ulnar-sided wrist pain, and they can coexist, but they are not the same problem and they are not managed the same way.
What the ECU tendon does
The extensor carpi ulnaris runs along the ulnar side of the forearm and passes through the sixth dorsal compartment, a groove at the end of the ulna, before attaching at the base of the fifth metacarpal. A 2024 review of ECU instability described its primary actions as wrist extension and ulnar deviation, and noted that pathology tends to follow repetitive loading of, or acute trauma to, a wrist positioned in flexion, supination and ulnar deviation (Thirumavalavan, 2024).
Inside the groove, a fibro-osseous subsheath holds the tendon against the ulna. Above it, the extensor retinaculum adds a second layer. When the forearm turns palm-up, the tendon angle changes and the subsheath carries more of the job of keeping it in place.
ECU tendinopathy
ECU tendinopathy produces pain along the dorsal-ulnar wrist and distal forearm with loading. A narrative review described it as common in stick and racquet sports, attributed to repetitive motion and axial loading, and listed conservative care that included rest, anti-inflammatory medication, injections and therapy such as exercise, splinting, activity modification, manual therapy and modalities (Zarro, 2024).
Typical features include:
- Pain along the tendon just beyond the end of the ulna, sometimes extending toward the fifth metacarpal
- Pain with resisted wrist extension and ulnar deviation
- Pain with gripping, pushing up from a chair, backhands, golf, hockey or repetitive tool use
- Tenderness along the tendon, sometimes with mild local swelling
- No sensation of the tendon moving out of place
ECU subluxation and instability
ECU instability describes a tendon that does not stay seated in its groove. It may follow a single forceful supination-flexion injury, such as a mishit golf shot or a twisting fall, or develop more gradually in sports that load the rotated wrist.
Common features include:
- A palpable or visible snap on the dorsal-ulnar wrist during forearm rotation, especially when turning the palm up with the wrist bent toward the little finger
- A sense that the tendon slips over the bone
- Pain with the snapping, sometimes with weakness or apprehension in that position
- Symptoms that track with rotation more than with pure wrist extension
A snapping tendon is not automatically painful or abnormal, which is one reason the history matters as much as the movement.
What the 2025 cadaver study adds
A 2025 study used ultrasound to examine ECU position in eight cadaveric upper extremities. In wrists with an intact subsheath and a shallow ulnar groove, the tendon subluxated significantly in supination, wrist flexion and ulnar deviation, and groove depth correlated with the change in subluxation. Cutting the subsheath alone did not significantly increase subluxation; adding a cut to its distal extension did, particularly in pronation (Inoue, 2025).
These findings come from a small cadaveric study and cannot by themselves predict symptoms or treatment outcomes in living patients. They help explain why bone shape and positioning may matter, and why the subsheath is not the only structure involved.
Why dynamic ultrasound matters
A static image shows the tendon in one position. Instability is about what happens during motion, so dynamic ultrasound, scanning while the patient rotates the forearm and moves the wrist, can show whether the tendon stays in the groove, subluxates or dislocates.
Ultrasound also shows tendon thickening, splits, fluid in the sheath and the shape of the groove. Those findings still need to be matched to the patient's pain, as the research below shows.
Why imaging has to match the symptoms
Static changes
75%
of wrists (39 of 52) in asymptomatic tennis players showed ECU abnormalities
Dynamic instability
42%
of wrists (22 of 52), most of it subluxation, in players without symptoms
PMID 25217825 · 26 players aged 26 to 61
Structural findings can occur without pain. Imaging is evidence about anatomy, not automatic proof of the pain generator.
Abnormal ultrasound is not the same as the pain source
In a 2015 ultrasound study of 26 asymptomatic recreational and competitive tennis players, most wrists had static ECU abnormalities, most often a partial tear just past the groove, and 24 of 26 players had tendinosis or tearing in at least one wrist. Dynamic instability appeared in 22 of 52 wrists, and 19 players had instability in at least one wrist. The study found no relationship between the static and dynamic findings (Sole, 2015).
None of these players had wrist pain. A thickened tendon, a partial tear or a tendon that shifts during rotation can be an adaptation to sport rather than the cause of a patient's symptoms. Findings matter when they match where it hurts, what provokes it and how the tendon behaves when symptoms are reproduced.
For this reason, we interpret ECU imaging in light of the history and exam. A finding gains weight when it sits exactly where the patient is tender, when loading or rotation reproduces the familiar pain, and when it fits how symptoms behave over time. Without that match, an abnormal scan is a finding to note, not a diagnosis.
Other causes of ulnar-sided wrist pain
- TFCC injury: the triangular fibrocartilage complex sits between the end of the ulna and the carpal bones. Pain deeper in the joint, clicking, pain with weight-bearing on the hand and pain after a fall or twisting injury point toward the TFCC rather than the tendon.
- Distal radioulnar joint (DRUJ) instability: a loose or painful joint during forearm rotation, sometimes after a fracture, is a joint problem.
- Ulnar impaction: a relatively long ulna can load the ulnar carpus and cause pain with grip and ulnar deviation.
- Flexor carpi ulnaris: pain on the palm side of the ulnar wrist, near the pisiform, involves a different tendon.
- Ganglion or joint pathology: a lump, joint swelling or restricted motion suggests a structure other than the ECU.
- Ulnar nerve or cervical referral: tingling in the ring and little fingers, weakness of the hand muscles or pain that changes with neck position needs a nerve and neck screen. Neck-related arm symptoms are discussed on our neck pain and headaches page.
- Fracture: pain after a fall with bone tenderness, including a hook of hamate fracture in club and racquet sports, needs imaging.
How the two are distinguished in the exam
The examination asks three questions. Where exactly is the pain? Does resisted loading of the ECU reproduce it? Does the tendon move out of position, and does that movement reproduce the patient's symptom?
We palpate along the tendon from the forearm to the fifth metacarpal, test resisted wrist extension and ulnar deviation, and take the forearm through supination with wrist flexion and ulnar deviation while watching and feeling for a snap. We also screen the TFCC, DRUJ, nerve and bone. Dynamic ultrasound is used when snapping is reported or the structure involved is unclear.
| Feature | ECU tendinopathy | ECU subluxation or instability |
|---|---|---|
| Core problem | Load-related tendon pain | Tendon does not stay in its groove |
| Main symptom | Ache along the tendon with loading | Painful snap with forearm rotation |
| Provoking position | Resisted extension and ulnar deviation | Supination with wrist flexion and ulnar deviation |
| Onset | Often gradual, after a training or work change | Often after a forceful twisting injury, sometimes gradual |
| Key imaging | Tendon thickening, sheath fluid | Dynamic ultrasound showing displacement |
| Initial care | Load management and progressive loading | Protecting the provoking position; surgical opinion if persistent |
Rehabilitation depends on stability
When the tendon is stable and the problem is tendinopathy, rehabilitation usually starts with reducing the most provocative loads, then progresses wrist extension and ulnar deviation strength, grip, forearm rotation and sport- or work-specific tasks. The goal is to restore load tolerance rather than to rest the tendon indefinitely.
When the tendon is unstable, the priority shifts. Initial care often protects the forearm from the supinated, flexed and ulnarly deviated position that displaces the tendon. That may involve a splint chosen for this purpose, a period of activity modification and a gradual return to rotation-based tasks. Persistent painful instability may need a hand surgeon's opinion. The 2024 review noted that subsheath reconstruction remains debated, and that a nonanatomical technique using the extensor retinaculum is commonly used (Thirumavalavan, 2024).
Splinting is diagnosis-specific. A brace intended to calm tendinopathy is not the same as protection aimed at keeping an unstable tendon seated.
Where manual therapy fits
Manual soft-tissue treatment of the forearm muscles can be used as an adjunct when the exam finds restricted or tender muscle around a stable tendon. It does not hold a tendon in its groove, and it does not replace loading or appropriate protection.
Where shockwave fits
Shockwave therapy is not used to treat ECU instability. A mechanically displacing tendon is a containment problem, and shockwave is not designed to treat mechanical tendon displacement.
For stable ECU tendinopathy, direct ESWT trial evidence is limited. Most wrist shockwave research involves De Quervain tenosynovitis, summarized in shockwave therapy for De Quervain's and wrist tendinopathy, and those results should not be transferred to the ECU. When shockwave is considered for stable ECU tendinopathy, it is a clinical judgment based on broader tendinopathy principles, discussed openly with the patient, not a claim of proven benefit.
When to seek prompt assessment
A wrist that snaps painfully after a twisting injury, pain after a fall with bone tenderness, swelling with a hot, red joint, sudden weakness or progressive numbness should be assessed promptly rather than treated as ordinary tendon pain.
How Novo approaches ulnar-sided wrist pain
We separate tendon pain, tendon instability, TFCC and joint problems, nerve symptoms and bone injury before selecting treatment. See how we approach wrist and forearm tendon pain, and for thumb-side symptoms, De Quervain's vs intersection syndrome.
References
- Thirumavalavan J, Ibrahim Z, Byrne RA, Arant KR, Gil JA. Extensor carpi ulnaris instability: a comprehensive review of pathology and operative techniques. Hand (N Y). 2024;19(7):1090-1096. PMID 37226412. (link)
- Zarro M, Goel R, Bickhart N, May CC, Abzug JM. Extensor carpi ulnaris tendinopathy in athletes: a review of the conservative and rehabilitative options. Hand (N Y). 2024;19(3):407-413. PMID 36250572. (link)
- Inoue T, Iida A, Omokawa S, Kawamura K, Mahakkanukrauh P, Tanaka Y. Ultrasonographic evaluation of extensor carpi ulnaris tendon subluxation at the ulnar groove. Journal of Hand Surgery (American Volume). 2025;50(12):1476-1482. PMID 41071141. (link)
- Sole JS, Wisniewski SJ, Newcomer KL, Maida E, Smith J. Sonographic evaluation of the extensor carpi ulnaris in asymptomatic tennis players. PM&R. 2015;7(3):255-263. PMID 25217825. (link)
- Patrick NC, Hammert WC. Hand and wrist tendinopathies. Clinics in Sports Medicine. 2020;39(2):247-258. PMID 32115083. (link)
