44 year male patient visits orthopedic surgeon with pain at the left thumb base area, after injury (fall on open hand). There was swelling of the soft tissues at the medial part of the base of the thumb. After clinical examination the surgeon requested an MRI scan.
The images show the retracted UCL resulting in the yoyo on a string appearance. The yoyo represents the rolled up and retracted UCL, whilst the string of the yoyo is the adductor aponeurosis. There is abundant oedema at the soft tissue. No bony avulsion recognized at the area.
The ulnar collateral ligament (UCL) connects the ulnar aspect of the first metacarpal and the proximal phalanx of the thumb and functions as a major stabilizer of the first metacarpophalangeal joint. Ulnar collateral ligament injuries of the thumb are frequent injuries encountered by the orthopaedic surgeons 1.
The term gamekeeper's thumb was first used by Campbell in 1955 when he described a high prevalence of incompetence of the ulnar collateral ligament among Scottish gamekeepers who used twisting techniques for killing rabbits 2. This type of injury is also met in skiers, given the alternate name ‘skier’s thumb’, even though it is considered a rather acute injury for the latter and a chronic injury for the former 3.
The mechanism of the injury is abrupt radial stress to the UCL like a skier gripping a ski pole during a fall with the thumb in abduction.
At clinical examination there is inability of grasping activities between the thumb and the second digit and laxity with valgus stress.
The differentiation of non-displaced ulnar collateral ligament tear from displaced tear (or Stener lesion) is important, as surgery is required in the latter to avoid chronic instability and possible joint degeneration 4.
Imaging is therefore requested to establish the diagnosis, help the surgeon to decide whether to operate or not and as a guidance map for the probable surgery. Ultrasound and MRI scan can both be used to examine the base of the thumb with equal efficacy at diagnosis 5. The choice of the appropriate modality depends on the availability of the appropriate modules (e.g. high frequency linear transducer, hand surface coil), the experience of the ultrasonographer and the availability of the machine at a tight schedule (mostly for the MRI).
MRI demonstrates the yo-yo on a string appearance, the string represented by the adductor aponeurosis and the retracted UCL representing the yo-yo ball 6. However chronic injury of the ligament can result in a proximally retracted UCL deep to the adductor aponeuvrosis, which can be confused with a Stener lesion 3.
The outcome of the early fixation of the lesion is very good, resulting in good stability with only slight decrease in motion 7.
It is important to state out that in Stener lesion that the ulnar collateral ligament is transpositioned superficial to the adductor aponeurosis, therefore the ligament ends are no longer in contact and will not heal conservatively.
Disruption of the ulnar collateral ligament with Stener lesion
Based on the MRI of the base of the patient’s left thumb, the following observations were made:
An acute, forceful injury (e.g., falling onto an outstretched hand, forcibly abducting the thumb) can cause an acute UCL tear, commonly known as “Skier’s Thumb.” Chronic repetitive strain may be referred to as “Gamekeeper’s Thumb.” MRI showing ligament discontinuity and edema, along with clinical findings of joint instability and pain upon thumb abduction, are key indicators.
When a UCL tear occurs, the torn end may be displaced by the adductor aponeurosis, preventing the ligament from healing properly. MRI may show the ligament retracted proximally and lying either superficial or deep to the tendon or aponeurosis, exhibiting the characteristic “yo-yo on a string” sign.
These include injuries to the volar plate or joint capsule. However, their imaging characteristics and clinical presentation are usually distinct from a UCL injury, making them less likely in this case.
Considering the patient’s history (trauma to the thumb base, swelling and functional impairment after contusion), clinical signs (laxity on the ulnar aspect of the thumb joint, weakened abduction resistance), and MRI findings (UCL discontinuity, partial retraction, and abnormal relationship with the adductor aponeurosis), the most probable diagnosis is:
Acute Ulnar Collateral Ligament Tear with Stener Lesion.
Rehabilitation goals include restoring joint stability, improving thumb and hand function, and preventing re-injury. Progress can be guided by the FITT-VP principle:
Throughout the rehabilitation process, closely monitor any swelling, pain, or joint instability. If any adverse or worsening symptoms occur, seek medical advice promptly.
Disclaimer:
This report is based solely on the provided medical history and imaging data. It is intended for academic discussion and reference, not as a substitute for in-person consultation or professional medical advice. The final diagnosis and treatment decisions should be made by the attending physician, who will evaluate the patient’s specific condition.
Disruption of the ulnar collateral ligament with Stener lesion
