On this page
Radial Collateral Ligament (RCL) Injury of the 1st MCP Joint (Thumb)
Understanding injuries to the radial collateral ligament of the thumb’s main knuckle joint, and how they are treated.
What is a Radial Collateral Ligament (RCL) Injury of the 1st Metacarpophalangeal Joint?
The radial collateral ligament (RCL) stabilises the thumb’s main knuckle joint (the 1st metacarpophalangeal joint, or MCPJ) against sideways force directed toward the palm during pinch and grip. This ligament is torn less often than its counterpart on the other side of the joint, the ulnar collateral ligament, and is usually injured by a direct blow to the radial side of the thumb or a fall that forces the thumb inward, toward the palm.
The ligament commonly tears off the bone at one of its ends, but can also be avulsed with a small bone fragment. Unlike the ulnar collateral ligament, the radial collateral ligament has no adjacent structure known to trap a torn end out of place, so this injury has no equivalent to the Stener lesion seen with ulnar-sided tears.
1st MCPJ RCL Injury at a glance
What is it?
A tear of the radial collateral ligament that stabilises the thumb's main knuckle joint on its outer side
Common symptoms
Pain, swelling and bruising over the outer (radial) side of the thumb's base, with a weak or unstable pinch grip
Who it affects
People who sustain a direct blow to the thumb or a fall that forces the thumb inward, often during ball sports or a workplace injury
Is it serious?
A complete tear usually needs surgical repair to avoid lasting instability and early arthritis
Treatment options
Splinting for partial tears, or surgical repair for complete tears
First step
An examination and imaging to determine how severe the tear is
Symptoms and how 1st MCPJ RCL Injury presents
The main symptoms are pain, swelling and bruising over the outer side of the thumb’s base, with tenderness over the radial collateral ligament. Pinch grip is often weak and painful, and some people notice a feeling that the thumb is unstable or giving way.
Causes and risk factors for 1st MCP Joint RCL Injury
- A direct blow to the radial (outer) side of the thumb
- A fall onto the hand with the thumb forced inward, toward the palm
- Ball sports injuries
- Forceful sideways bending of the thumb toward the palm
- Workplace or crush-type injuries to the thumb
How is 1st MCP Joint RCL Injury diagnosed?
Diagnosis involves examination, including gently stress testing the joint to check for sideways movement, along with an x-ray to check for an associated small bone fragment. Ultrasound, or occasionally MRI, is often performed prior to your appointment with a hand specialist to assess whether the ligament is fully or partially torn.
Unlike ulnar-sided injuries at this joint, there is no equivalent to a Stener lesion in a radial collateral ligament tear, since there is no adjacent structure known to trap the torn ligament end out of place. The diagnosis also considers whether the ligament itself has ruptured, which generally involves the ligament pulling off its insertion to the bone, or whether the bone that the ligament inserts into has broken. The latter injury is technically a fracture, because the part that needs to heal is a broken bone. The mechanics of the thumb instability is the same, but the treatment and rehabilitation varies according to the specific nature of the injury.
Treatment options for 1st MCP Joint RCL Injury
Partial tears without instability are routinely treated successfully with a thermoplastic splint under the guidance of a hand therapist to allow the ligament to heal in position. The duration of splinting and time to return to full activity varies according to the severity of the initial injury, and your response to treatment.
Complete tears generally need surgical repair, since a fully torn ligament cannot reliably heal back to length on its own and leaves the joint unstable.
When to see a hand surgeon about 1st MCP Joint RCL Injury
Any thumb injury with pain, swelling and difficulty pinching after a fall or direct blow should be assessed, ideally promptly, since a complete tear is treated more successfully soon after the injury occurs.
What to expect at your 1st MCP Joint RCL Injury appointment
At your appointment, Dr Tomlinson will examine your thumb, including stress testing the joint, and arrange imaging as indicated. Together you will discuss whether splinting or surgery is the right treatment for your injury. If you have not already been seen by a hand therapist you will be provided with a referral to one.
Frequently Asked Questions
What is an RCL injury of the thumb?
The radial collateral ligament (RCL) stabilises the thumb’s main knuckle joint (the 1st metacarpophalangeal joint, or MCPJ) against sideways force directed toward the palm during pinch and grip. It is torn less often than the ulnar collateral ligament on the other side of the same joint, usually by a direct blow to the radial side of the thumb or a fall that forces the thumb inward.
What causes it?
This injury is most often caused by a direct blow to the outer side of the thumb, a fall onto the hand with the thumb forced inward toward the palm, ball sports, or a workplace injury.
What can I do myself?
Any thumb injury with pain, swelling and difficulty pinching after a fall or direct blow should be assessed, ideally promptly, since a complete tear is treated more successfully soon after the injury occurs.
What can a hand therapist do?
Partial tears without instability are routinely treated successfully with a thermoplastic splint under the guidance of a hand therapist, allowing the ligament to heal in position. The duration of splinting and time to return to full activity varies according to the severity of the initial injury and your response to treatment.
What can a hand surgeon do?
Dr Tomlinson will examine your thumb, including stress testing the joint, and arrange imaging as indicated. Complete tears generally need surgical repair, since a fully torn ligament cannot reliably heal back to length on its own and leaves the joint unstable. Unlike the ulnar collateral ligament, there is no equivalent to a Stener lesion with this injury.
What can I expect from treatment?
At your appointment, Dr Tomlinson will examine your thumb and arrange imaging as indicated. Together you will discuss whether splinting or surgery is the right treatment for your injury. If you have not already been seen by a hand therapist, you will be provided with a referral to one.
What happens if it's left untreated?
A complete tear usually needs surgical repair to avoid lasting instability. Diagnosis and treatment soon after the injury gives the best chance of a good outcome, which is why any thumb injury with pain, swelling and difficulty pinching after a fall or direct blow should be assessed promptly.
Related conditions and treatments
This ligament injury affects the outer (radial) side of the thumb’s main knuckle joint. For the more common injury to the opposite side of the same joint, see ulnar collateral ligament rupture of the thumb. For a similar ligament injury affecting the finger joints, see collateral ligament injury of the finger MCP joints. A broken bone at the base of the thumb can occur alongside this injury, see hand fractures.