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Lateral stability of the joint

The lateral stability of the thumb metacarpophalangeal joint is particularly important in the thumb-index pinch. This articular stability is conditioned by the integrity of the lateral ligaments: the medial lateral ligament (located on the index side)
whose traumatic damage is the most frequent (9 cases out of 10) and the external lateral ligament.

The term "sprain" includes all ligamentous structure injuries, from a simple stretch to a complete rupture (severe sprain) of the lateral ligament of the thumb metacarpophalangeal joint.

Lesion mechanism

Sprains of the medial collateral ligament occur as a result of a trauma that suddenly pushes the thumb outwards. It is an extremely frequent pathology, most often occurring in the context of a sports accident, particularly in the context of a ski fall (either the thumb falls into the snow with the rest of the body, which continues to slide, or the thumb turns over and gets stuck in the ski pole strap). Ball sports can produce similar pictures.

What are the clinical signs of a severe thumb sprain?

The thumb is painful, often very painful, but often with minimal swelling.

The patient must be made aware that there is no correlation between the importance of the pain and the severity of the sprain. Indeed, a very painful thumb may correspond to a simple ligament stretching lesion, conversely, a moderate pain may be associated with a complete rupture of the medial collateral ligament. The diagnosis of severity must be a specialized diagnosis that will be made after a comparative examination of the laxity of the two metacarpophalangeal joints. Clear lateral instability on clinical testing indicates ligament rupture and requires surgical repair of the medial collateral ligament. In fact, unlike the lateral collateral ligament, which heals on its own after a traumatic rupture, the medial collateral ligament has a particular anatomical configuration that prevents it from reattaching itself to the base of the phalanx once it has been torn. This particularity is called 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, especially in hyperlax individuals, standard stress radiographs (in a forced position reproducing the initial mechanism of the trauma) are performed to confirm that lateral laxity is not increased on the traumatized side.

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

What is the treatment?

It is conditioned by the degree of 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 metacarpophalangeal joint of the thumb and leaves the wrist free, respectively for seven-ten days and three weeks. An adapted rehabilitation is associated with it.

On the other hand, in the case of a severe sprain (complete rupture of the medial collateral ligament), the treatment will systematically be surgical. This is not an absolute emergency. The ligament suture can be performed within ten days after the trauma without technical difficulty. Beyond that, the risk of ligament retraction may make surgical repair more difficult or impossible. It will be necessary to resort to a slightly more complicated procedure (ligamentoplasty).

The operation is performed under loco-regional anesthesia (only the operated limb is asleep), in ambulatory mode (the patient does not sleep in the clinic).

Post-operatively, a six-week immobilization of the thumb will be necessary. Specific re-education sessions will be necessary after this immobilization phase in order to regain flexibility and mobility of the thumb column.

Heavy sports or professional activities (manual or forceful work) will be forbidden for three months. The resumption of sports will be done with strapping at the beginning.

It can take up to six months for the pain to disappear after surgery or in some cases it can 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 initial ligament giving the thumb a swollen appearance.

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

Unfortunately, this is a very frequent occurrence. Many patients, who have had a serious undiagnosed sprain that they themselves do not necessarily remember, consult in the medium or long term because of the onset of disabling pain on a daily basis. Indeed, at first, the pain faded after the initial trauma and the patients adapted to their joint instability (linked to the non-repair of the medial collateral ligament). This instability will result 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 related to premature wear of the joint (appearance of arthrosis). This osteoarthritis occurs more rapidly in the thumb because it is the most used finger of the hand and because it is a joint that functions in areas of significant mobility.

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