Twisting and gripping load the little-finger sideEmerging evidence
Turning your palm up and down happens at the joints between the two forearm bones, and at the wrist the TFCC holds the ulna in place as the radius turns around it. An NHS hand clinic calls the TFCC "one of the main stabilisers of the wrist, particularly on twisting movements". Gripping with the palm down makes the ulna sit relatively longer: in 120 healthy volunteers, by about 1.3 mm on average, and in 66 wrists a hard grip added about 2 mm, pressing it towards the wrist bones. In 9 forearms from donors, more load went through the little-finger side with the wrist bent that way and the palm turned fully down.
The ECU tendon on the back of that side is under most tension when you turn the palm up with the wrist bent towards the little finger. These are imaging and laboratory studies of people without pain, so they explain why turning hurts there; they don't prove that ordinary turning causes damage.
Sources 4, 5, 6, 7, 8, 9
Several causes sit on the little-finger side, and they're hard to tell apartEmerging evidence
Reviews name TFCC tears, from a fall with a twist or from wear, as the commonest cause. In one specialist clinic of 110 patients with little-finger-side wrist pain, there were 17 different diagnoses; most were TFCC injuries, the ulna pressing on the wrist bones (ulnar impaction), arthritis of small joints on that side, an old break of a wrist bone, or the ECU tendon, and specialists needed MRI or CT to tell four of them apart. No study gives how common each is in the general public.
A clinician presses the soft spot beside the bony knob of the ulna: in 272 people having keyhole surgery, tenderness there picked up 95% of the ligament injuries it looks for, but in the 110 clinic patients it was positive in several different diagnoses. A tendon that snaps painfully as the palm turns up points to the ECU. Ulnar impaction comes on gradually and hurts most gripping palm down; a guideline says it shouldn't be diagnosed without X-ray and MRI findings that fit. The joint between the forearm bones (the distal radioulnar joint) hurts with loading and turning, and after an injury it can clunk or lock.
Sources 10, 11, 12, 13, 8, 9
The thumb side: tendons and the base of the thumbStrong evidence
De Quervain's affected about 1 in 100 women and 1 in 200 men of working age in a UK population survey. UK hand surgeons say its pain is "aggravated especially by lifting the thumb, as in the hitchhiker position or when using scissors", that mothers of small babies seem prone to it, and that some mild cases recover over a few weeks. The usual thumb-in-fist test can also hurt in wrists without the condition: in 72 wrists without symptoms it gave 8 false alarms.
Arthritis at the base of the thumb usually appears after 45 and makes opening jars and turning keys hard. It shows on X-ray in about a quarter of women over 55, but "many people with arthritis of this joint have no significant pain", UK hand surgeons say.
Sources 14, 15, 16, 17
Racquets, clubs and the gymEmerging evidence
In 370 club tennis players, 50 (13%) had had a wrist injury, 30 of them ECU tendon problems, and little-finger-side injuries went with Western and semi-Western forehand grips. In professional players, wrist-driven topspin, the two-handed backhand and high string tension were blamed, and it was the hand nearer the racquet head that was hurt. In 128 European Tour golfers, 30% had had wrist problems; 87% of little-finger-side problems were in the leading wrist, and players blamed hard ground and practice mats.
These are surveys and case series of players, mostly elite, so they show patterns, not causes. A hard jar to the heel of the hand from a club, bat or racquet handle can break the hook of the hamate, an uncommon injury that needs a special X-ray view.
Sources 18, 19, 20, 9, 11
Sprains, arthritis and a hot wristEmerging evidence
"After 2 weeks, most sprains and strains will feel better", the NHS says, and UK hand surgeons say an injury that seems to be a sprain but "doesn't get better ... may indicate a more significant injury". In later life, arthritis of the joint between the forearm bones showed on X-ray in 21% of 676 wrists of people aged 50 to 89 in a Japanese town, though changes on an X-ray aren't the same as pain.
Calcium crystals often settle in the TFCC: they showed there in 74% of 316 wrists of people with calcium crystal disease, though in the general population aged 60 or over crystal deposits are common and usually cause no symptoms. A sudden hot, swollen wrist can be crystals, gout or an infection, and needs help the same day. In rheumatoid arthritis, the sheath of the ECU tendon is one of the most often involved.
Sources 21, 22, 23, 24, 25, 26, 3
What a scan shows, and what it doesn'tStrong evidence
After an injury, an X-ray comes first, for a fracture and the position of the joints; it also shows how long the ulna is. A magnetic resonance imaging (MRI) scan shows the TFCC: across studies it picked up roughly 75% to 90% of full-thickness tears, and an MRI with dye in the joint (an MR arthrogram) did a little better. Keyhole surgery is the most reliable test. Ultrasound shows the ECU tendon moving as the forearm turns.
Scans also find things that don't hurt. TFCC changes showed on MRI in 39 of 103 volunteers' wrists, including 23 complete tears, and in all 3 people over 60; holes in the disc were found in 53% of wrists over 60 after death; and the ECU tendon looked abnormal or slipped in many tennis players without pain. So a scan matters when it changes the plan (a fracture, a long ulna, an unstable joint or surgery), not to put a name to every ache.
Sources 7, 8, 27, 28, 29, 30, 31, 32, 33
How it usually goesEmerging evidence
"The vast majority of TFCC tears heal with time", an NHS hand clinic says: healing takes about 3 months, "it is often 6-12 months before normal function is regained", and tears from wear can take up to 2 years to settle. In one US clinic, 57% of 84 people with a TFCC injury who wore a splint or cast for at least 4 weeks didn't need surgery; in an Australian group of 124, 41% had an excellent result about 6 years on. Different groups, different measures, so no single figure fits everyone.
ECU tendon pain in professional tennis players settled in 2 to 24 weeks. Mild de Quervain's can recover in a few weeks. NHS inform expects a new wrist problem to start settling within 6 weeks. No one can promise a date.
Sources 7, 34, 35, 19, 15, 36