Ulnar collateral ligament of the thumb

Key points

The ulnar (little-finger side) collateral ligament of the thumb has two parts, a proper collateral ligament and an accessory one^1,2.
It is the primary restraint to valgus stress, a sideways load, at the thumb’s metacarpophalangeal joint^3,4.
Loads directed into valgus or toward the radial side produce hyperabduction (the thumb forced outward past its limit) at the joint, which is how the ligament is injured^3,5.
In a Stener lesion the ligament is torn completely from the proximal phalanx, the thumb bone nearest the hand, and displaced⁶. Reported prevalence among complete ruptures runs from 11% to 87%⁷.
Two cadaver (donated body) studies give different mean failure loads for the intact ligament^8,9. One found 294 newtons in 16 thumbs from male cadavers, and the other 379 newtons in nine paired hands^8,9.

Function

Two parts across one joint

The ulnar collateral ligament of the thumb has two parts, a proper collateral ligament and an accessory one^1,2. A ligament is a tough band of tissue that holds bones together at a joint. This page calls it the ligament. One paper describes it as a thick band 4 to 8 mm wide and 12 to 14 mm long⁵. On MRI scans of 34 volunteers without symptoms, it was typically less than 3 mm thick¹⁰.

The proper part runs from the back of the head of the thumb metacarpal to the palm side of the base of the proximal phalanx^2,5. A metacarpal is one of the long bones of the hand. The proximal phalanx is the thumb bone nearest the hand. The accessory part starts on the palm side of the proper part and runs on continuously with it^2,5. It attaches to the volar (palm-side) plate^2,5.

The joint these parts cross is the thumb’s metacarpophalangeal joint, called the joint on this page^3,4. The plate below is from Gray’s Anatomy of 1918. It shows the collateral ligaments of a finger, not of the thumb.

Engraving of one finger and its metacarpal bone seen from the ulnar side. A fan-shaped collateral ligament crosses the side of the metacarpophalangeal joint from the head of the metacarpal to the base of the first phalanx, and smaller collateral ligaments cross the two joints between the phalanges. The plate shows a finger with three phalanges, not the thumb. — Collateral ligaments of a finger, from the ulnar sideHenry Vandyke Carter, in Henry Gray, Anatomy of the Human Body (1918), Fig. 338. Public domain, via Wikimedia Commons. (source, Public domain)

What the ligament holds

The joint has variably flattened condyles and moves mainly in flexion (bending) and extension (straightening)⁵. Its radial and ulnar collateral ligaments are the primary stabilisers against varus and valgus stress². Varus and valgus stress are sideways loads in opposite directions. The ulnar one is the primary restraint to valgus stress^3,4.

One paper describes the loads that injure it as valgus or radially directed^3,5. The ligament resists forces that push the thumb radially during forceful grasping².

A laboratory study simulated pinch and grip in 16 fresh-frozen thumbs from male cadavers⁸. Strain in the ligament correlated significantly with pinch force, but not with low grip force⁸. Strain here is how far something stretches as a share of its resting length.

The proper part is taut when the joint is flexed, and the accessory part is taut when it is straight^1,2. Two cadaver studies cut the parts in turn:

Half of the proper part. In 11 cadaver thumbs, this cut produced no significant increase in laxity (looseness in a joint) in any direction⁴.
The whole proper part. In autopsy specimens, this cut significantly increased valgus instability of the flexed joint¹¹. Laxity was significantly less when the joint was tested straight¹¹.
The accessory part and palmar plate as well. In those autopsy specimens, valgus instability of the straight joint then rose¹¹. It no longer differed significantly from the instability at 30 degrees of flexion¹¹.

How loose a normal thumb is

Side-to-side laxity of the joint varies among normal thumbs and across the arc of flexion and extension³. In 750 normal thumbs examined in three positions, full flexion was the most stable¹².

A person’s two thumbs can differ. Among 100 normal individuals examined with the thumb joint straight, the two thumbs differed by 10 degrees or more in 34%¹³. In 12% they differed by at least 15 degrees¹³. Another study tested 100 participants without symptoms with the joint straight. Their maximum passive radial deviation differed between left and right by a mean of 4.5 degrees¹⁴.

Breakdown

How the ligament is injured

Loads directed into valgus or toward the radial side produce hyperabduction at the joint, which is how the ligament is injured^3,5. The injury can be a partial or a complete rupture⁵. It can also extend into the dorsal (back) capsule and the volar plate⁵. A 2013 paper defines skier’s thumb as a partial or complete rupture of this ligament¹. That page covers the condition’s definition, its course and the trials.

A 1995 paper states that the usual setting is a skier whose pole forces the thumb to deviate radially¹⁵. A 1982 study suggests that a falling skier holds the pole until the hand hits the ground¹⁶. The handle then stays in the hand and acts as a fulcrum, levering the thumb into extension and abduction¹⁶.

One paper says the injury is now commonly seen in falls onto an abducted thumb⁵. It also follows a racquet or ball hitting the thumb’s ulnar side⁵. Another paper says it occurs in rugby, soccer, handball, basketball and volleyball, and even after a handshake³.

How often it happens, and to whom

The incidence of injuries to this ligament is estimated at 50 for each 100,000 emergency room visitors⁷. One paper states that they are about 10 times more common than injuries of the radial collateral ligament⁵.

The share of cases that come from skiing differs between three reports^1,18,19.

Share injured while skiing (%). Bars start at zero; the table below gives each value with its source.

Where the patients were seen	Share injured while skiing (%)
127 patients with an acute rupture repaired at one unit over 10 years	2.4¹⁸
One paper’s own inner-city hospital	10¹
1,582 patients operated on at two trauma centres from 1992 to 2015	35¹⁹

In the 127 patients, the most common cause was a fall, at 49%¹⁸. In the inner-city hospital it was falling on the hand, most often off a bicycle or motorcycle, in about 40%¹. In the 1,582 patients, sporting accidents were the most common cause, at 51%¹⁹.

Studies of skiers and of college and professional athletes report these figures^17,20:

One ski area. In a six-year study of 1,711 ski injuries, 40% of upper limb injuries involved the thumb, and 85% of those included this ligament¹⁷.
College sport. Across all 25 NCAA sports from 2004-2005 to 2013-2014, tears of this ligament were 8.7% of the hand and wrist injuries classed as severe²⁰.
One college football team. A sprain of this ligament was the most common of 168 hand and wrist injuries reviewed from 2003 to 2020, at 19.6%²¹.
One professional football team. From 1991 to 2014, 36 thumbs in 32 players had a collateral ligament injury at this joint²².

Where it tears

Most tears occur at the ligament’s far attachment on the proximal phalanx³. Among 1,582 surgically managed ruptures, 84% were at the distal end, 11% in the midsubstance and 5% at the proximal end¹⁹. Distal means farther from the centre of the body, and the midsubstance is the middle of the ligament. One paper reports that a bony avulsion fracture accompanies 20% to 30% of ruptures³. An avulsion is a tear in which a ligament pulls away from the bone it attaches to.

Tears are commonly graded in three tiers by stability⁵:

Grade 1 is painful without instability⁵.
Grade 2 is a partial tear, with more laxity than the other side but a firm endpoint⁵.
Grade 3 is a complete tear, with laxity and no endpoint⁵.

The Stener lesion

The adductor pollicis, a muscle in the hand, attaches to the proximal phalanx and lies superficial to the ligament^2,3. In a Stener lesion the ligament is torn completely from the proximal phalanx⁶. It is displaced to lie superficial to the aponeurosis of the adductor pollicis⁶. An aponeurosis is a broad, flat sheet of tendon. The aponeurosis then sits between the ligament and the joint⁶.

Reports of how common the lesion is differ^1,7:

A paper on the lesion’s history notes that Stener’s original paper reported it in 64% of cases²³. It adds that a later study found it in as few as 20% of operated ruptures²³.
One paper states that between 64% and 87% of complete ruptures have one¹.
Another source gives a range across studies of 11% to 87% of complete ruptures⁷.

What load breaks it

Two laboratory studies loaded intact ligaments from cadavers until they failed, and their figures differ^8,9. A newton is a unit of force.

Mean load at failure (newtons). Bars start at zero; the table below gives each value with its source.

Specimens	Mean load at failure (newtons)
16 fresh-frozen thumbs from male cadavers	294⁸
Nine paired fresh-frozen hands, pulled in tension	379⁹

In the nine-hand study, the ligament tore in its midsubstance in 7 specimens⁹.

Recovery

Whether a displaced ligament can heal

Sources do not agree on whether the ligament can heal once a Stener lesion has moved it^1,24:

A paper on the lesion’s history reports that Stener argued the ligament could not undergo natural repair without an operation²³. His reason was that the aponeurosis blocked its insertion point²³.
A 1997 paper states that with a Stener lesion present, primary healing of the ligament cannot occur without an operation²⁴.
A 2019 paper states that the aponeurosis lying between the ligament and the joint impedes healing⁶.
Authors who searched PubMed in November 2012 report finding no evidence for the general idea¹. That idea is that the ligament cannot heal when it is out of contact with its insertion¹.

A 2018 systematic review found no study comparing operation with no operation for complete ruptures²⁵. A 2023 guideline from Britain’s Society for Surgery of the Hand calls the natural history (the course without surgery) of complete ruptures uncertain²⁶. Its reason is that how often management without surgery fails varies widely²⁶. The skier’s thumb page reports the trials and follow-up studies.

What laboratory tests of repairs found

Cadaver studies have compared repaired or reconstructed ligaments with intact ones^9,27:

In nine paired fresh-frozen hands, ligaments repaired with two suture anchors failed at a mean of 84 newtons, against 379 newtons for the intact ligaments⁹.
In 11 cadavers with loads applied to thumb muscles, cutting the ligament, its accessory part, the dorsal capsule and the volar plate increased joint laxity²⁷. Reconstructing the ligament restored normal laxity²⁷.

A 2023 paper states that no repair or reconstruction using native tissues provides strength equal to the ligament’s before injury²⁸. The authors of the nine-hand study state in their introduction that adequate healing of a repaired ligament occurs at about 10 to 12 weeks⁹.

Connections

The ligament joins the thumb metacarpal to the proximal phalanx and, through its accessory part, to the volar plate^2,5. The volar plate, the dorsal capsule and the collateral ligaments hold the joint statically⁵. The muscles crossing the joint hold it dynamically⁵.

One paper names the muscles that act as dynamic restraints to valgus stress at the joint³. Three come from the forearm:

Flexor pollicis longus, in the deep group of the forearm flexors^3,29.
Extensor pollicis longus, in the deep group of the forearm extensors^3,30.
Extensor pollicis brevis, whose tendon passes through the wrist’s first dorsal compartment^3,31,32.

Three are in the hand: adductor pollicis, abductor pollicis brevis and flexor pollicis brevis³.

The elbow has a ligament that is also called the ulnar collateral ligament³³. It has its own page, the ulnar collateral ligament of the elbow. The condition page for the thumb’s ligament is skier’s thumb¹.