Sprained thumb, also named skier’s thumb, is the injury to the ulnar collateral ligament (UCL) of the thumb caused by excessive strain.
The ulnar collateral ligament (UCL) is located on the inner side of the metacarpo-phalangeal (MCP) joint between the metacarpal bone and the proximal phalange of the thumb, facing the index finger. Depending on the strain applied to the thumb, the injury to the UCL may involve damage to the adductor aponeurosis (thumb muscle), the accessory collateral ligament, bony structures, tendons and neurological tissues. The implications of these injuries can be detrimental as the thumb controls grasping, which comprises 50% of the functions of the hand.
A sprained thumb may be aggravated by the interposition of the aponeurosis (tendon-like tissue connecting the thumb muscle to the phalange) of the adductor pollicis muscle between the ruptured UCL and its site of insertion at the base of the proximal phalange. This is called the Stener lesion. This injury requires surgical treatment to prevent joint instability and loss of function.
A thumb sprain is classified depending on the extent of the UCL rupture:
Type I and II UCL injuries for incomplete sprains
Type III UCL injury for a complete rupture of the ligament.
Thumb sprains are typical sport injuries. They often occur when catching a ball, in downhill skiing or during other physical activities. These injuries are mostly found in active, young sportsmen. A thumb sprain results from the following mechanisms:
Thumb bending backwards under a hyperextension force
Thumb undergoes excessive forward bending with a hyperflexion force
Thumb lateral bending when the force is applied sideways.
Thumb sprains arise often with a fall, when catching a ball and during impacts in contact sports. The main risk factors are:
Contact sports such as hockey, football, rugby
Falls onto the hand
The symptoms arising from a sprained thumb are:
Increasing pain during thumb/hand activity
During the examination the patient provides medical history including previous hand injuries and mechanisms leading to the current injury to the thumb. The clinical examination is usually sufficient for the diagnosis of a sprained thumb and involves:
Palpation to the region of the ulnar collateral ligament
Monitoring changes in the range of movement of the thumb both passively and actively
The valgus ulnar test of the UCL determines the ligament stability and/or rupture of the sprained versus the normal thumb when applying a 30 degree flexion (normal). The test is positive for UCL rupture if the flexion the thumb leads to excessive laxity of greater than 30 degrees. X-rays, CT scan and MRI are only taken if other injuries are suspected such as wrist sprain/fracture, thumb metacarpal fracture and dislocation/instability of the MCP joint.
The management of a sprained thumb is normally achieved conservatively if a valgus laxity of MCP joint extension is less than 30°. Conservative treatment includes the immobilisation of the thumb for a week with a spica cast that is replaced with a spica thermoplastic splint for up to 6 weeks.
Additional treatments include:
Administration of NSAIDs
Physiotherapy for thumb exercises whilst the hand is in the cast or splint including flexion/extension and gripping/pinching after 10-12 weeks from injury
Surgery is required in case of severe or total rupture of the UCL or when a sprained thumb is concomitant to a thumb fracture. Different methods are available for repairing the ligament depending on the type of injury. The procedure aims to reconnect the torn ligament to the bone (proximal phalange) with a suture or a screw. If an avulsion fracture is associated to the sprain of the UCL, it will be repaired with fixation of the bone fragment. A reconstruction of the ligament may be necessary in case of neglected injury with the use of a tissue graft. After surgery a spica cast is applied for at least 4 weeks.
If a thumb sprain is neglected or treated too late the following complications may arise:
Stiffness of the MCP joint requiring physiotherapy
Arthritis of the MCP joint
During surgery the damage of the sensory nerves located on the posterior side of the thumb may cause local numbness. Infection is an additional complication following surgery.
A physical or occupational therapist will guide the patient to rehabilitation plan to restore flexibility and strength of the thumb with exercises such as thumb opposition, extension and flexion. The therapist will also inform the patient on how to modify activities to avoid recurrent injuries to the UCL. Standard rehabilitative therapy includes:
Return to activity plan
Preventing thumb sprains is achieved by protecting the thumb during physical activities and reducing the risk of falls. Common strategies are:
Wearing protective gear during sport training and carpentry work
Modification of physical activities
Exercise to improve muscle strength and flexibility of the thumb