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Lateral joint stability

Lateral stability of the thumb's metacarpophalangeal joint is particularly important in the thumb-index pinch. This joint stability depends on the integrity of the lateral ligaments: the medial collateral ligament (located on the index finger side)
which is most frequently affected by trauma (9 out of 10 cases), and the lateral collateral ligament.

The term "sprain" covers all damage to ligamentous structures, from simple stretching to complete rupture (severe sprain) of the lateral ligament of the thumb's metacarpophalangeal joint.

Mechanism of injury

Sprains of the medial collateral ligament occur as a result of trauma, which causes the thumb to suddenly move outwards. This is an extremely frequent pathology, most often the result of a sporting accident, notably a ski fall (either the thumb falls into the snow with the rest of the body, which continues to slide, or the thumb flips over and gets stuck in the ski pole strap). Similar pictures can be found in ball sports.

What are the clinical signs of a severe thumb sprain?

The thumb is sore, often very sore, but often only slightly swollen.

The patient must be made aware that there is no correlation between the degree of pain and the severity of the sprain. In fact, a very painful thumb may correspond to a simple ligament stretching injury, while moderate pain may be associated with a complete rupture of the medial collateral ligament. The diagnosis of severity must be a specialized one, made after a comparative examination of the laxity of the two metacarpophalangeal joints. Clear lateral instability on clinical testing indicates ligament rupture, and necessitates surgical repair of the medial collateral ligament. Unlike the lateral collateral ligament, which heals on its own after a traumatic rupture, the medial collateral ligament has a particular anatomical configuration, preventing it from reattaching to the base of the phalanx on its own once torn. This is known as the Stenner effect.

What additional tests are useful for diagnosis?

Standard radiography is essential to rule out an associated fracture-arachment.

In case of diagnostic hesitation, particularly in hyperlax patients, standard stress radiographs (in a forced position reproducing the initial mechanism of the trauma) are taken to confirm that lateral laxity is not increased on the traumatized side.

Ultrasound is not routinely performed. It will only be performed in cases of diagnostic doubt.

What is the treatment?

It depends on the severity of the sprain.

Mild sprains (simple ligament stretching) and moderate sprains (partial rupture of the medial collateral ligament) are treated with a custom-made thermoformed orthosis that immobilizes the thumb's metacarpophalangeal joint, leaving the wrist free for seven to ten days and three weeks respectively. Appropriate rehabilitation is also provided.

In the case of a severe sprain (complete rupture of the medial collateral ligament), however, treatment is systematically surgical. This is not an absolute emergency. Ligament suturing can be performed within ten days of the trauma, without technical difficulty. Beyond that, the risk of ligament retraction may make surgical repair more difficult, if not impossible. A slightly more complicated procedure (ligamentoplasty) will be required.

The procedure is performed under locoregional anesthesia (only the operated limb is put to sleep), on an outpatient basis (the patient does not sleep in the clinic).

Post-operatively, the thumb must be immobilized for six weeks. After this immobilization phase, specific rehabilitation sessions are required to restore flexibility and mobility to the thumb column.

No heavy sports or professional activities (manual or heavy-duty work) for three months. Resumption of sport will be with strapping at first.

It can take up to six months for the pain to disappear after surgery, or in some cases it may persist as rheumatic pain (discomfort in wet weather).

It should be noted that the injured joint remains permanently swollen: in fact, the ligament scar is thicker than the original ligament, giving the thumb a swollen appearance.

What are the risks of not recognizing a severe thumb metacarpophalangeal joint sprain?

Unfortunately, this is a very common occurrence. Many patients who have had a serious sprain that went undiagnosed and which they themselves no longer necessarily remember, consult us in the medium or long term because of the onset of disabling pain in their daily lives. Initially, the pain subsides after the initial trauma, and patients adapt to their joint instability (due to non-repair of the medial collateral ligament). This instability will be reflected in a loss of strength, and often the sensation that their thumb tends to "leak" when gripping with the thumb-index clamp. Progressively, the patient will experience pain linked to premature wear of the joint (osteoarthritis). This osteoarthritis occurs more rapidly in the thumb, as it is the most frequently used finger on the hand, and a joint that operates in areas of high mobility.