1 Case presentation

A 41-year-old right-handed female amateur athlete presented with a traumatic injury to her right thumb sustained during a recreational newcomb ball match. While attempting to catch a high-speed serve, she experienced a hyperextension injury, resulting in immediate sharp pain, swelling, and bruising in the first metacarpophalangeal (MCP) and interphalangeal (IP) joints of her thumb.

Patient reported a “snapping” sensation at the time of impact, followed by severe tenderness and visible deformity in the thumb, accompanied by a restricted range of motion. Upon arrival to the emergency department, physical examination revealed notable swelling and discoloration of the thumb. Initial radiographic imaging demonstrated a small free-floating bone fragment near the IP joint, leading to an initial diagnosis of an avulsion fracture (see Fig. 1). The patient was immobilized in a thumb spica cast with a recommended immobilization period of six weeks and prescribed non-steroidal anti-inflammatory drugs for pain management.

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Fig. 1 (A) Lateral and (B) PA view X-ray films of the patient's right hand as seen in the ER.

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At the two-week follow-up, the patient reported persistent discomfort, ongoing tenderness, and limited function in her thumb despite adherence to the treatment plan. Given her ongoing symptoms and atypical pain distribution, a more comprehensive assessment was pursued. Bilateral anteroposterior (AP) and lateral (LAT) radiographs were obtained to compare both hands. Surprisingly, an identical free-floating bone fragment was observed in the contralateral thumb's IP joint, suggesting that the fragment might represent a normal anatomical sesamoid bone rather than an avulsion fracture.

A subsequent ultrasound examination confirmed ligamentous injury consistent with a partial tear in the ulnar collateral ligament (UCL), revealing soft tissue swelling and partial disruption of the ligament fibers. Consequently, the diagnosis was revised, and the patient's cast was removed. She was fitted with a removable thumb splint and prescribed a structured rehabilitation program.

The patient's rehabilitation consisted of a six-week thumb splint regimen, followed by progressive physiotherapy, focusing on strengthening exercises and range-of-motion improvements. At her eight-week review, she demonstrated significant improvements in pain and function, regaining nearly full range of motion. By the tenth week, she could resume light recreational activities, and by twelve weeks post-injury, she returned to her newcomb ball league, ultimately achieving full recovery.

2 Discussion

Injury patterns in sports that are not widely studied, such as newcomb ball, can present unique challenges for clinicians, particularly when anatomical variations complicate diagnostic imaging. Newcomb ball, akin to volleyball but with catching, involves high-impact hand contact. In sports like volleyball, hand injuries are common, with finger sprains, dislocations, and fractures frequently observed¹. While there is limited documentation on the injury profile for newcomb ball, given the similarities in hand engagement, clinicians can reasonably expect parallel injury types.

3 Avulsion fractures of the Thumb's IP joint

Avulsion fractures of the thumb's interphalangeal joint are relatively uncommon but can occur in sports or activities involving forced hyperextension or direct trauma to the thumb. These fractures often arise when a tendon or ligament forcefully pulls a small bone fragment away from the main bone, typically at the attachment site of the distal phalanx¹. In the thumb, avulsion fractures may involve the insertion of the flexor pollicis longus or the extensor pollicis longus tendons, disrupting the thumb's functional mechanics². Clinically, avulsion fractures of the thumb IP joint often present with acute pain, localized swelling, and limited active range of motion³. Patients frequently report an inability to grip or pinch without significant discomfort. On examination, tenderness is usually evident at the site of the fracture, and in cases where ligamentous or tendon attachment is compromised, instability or abnormal alignment may be noted³. Radiographic imaging is critical for diagnosing avulsion fractures, typically showing a small, displaced bone fragment near the IP joint⁴. However, distinguishing avulsion fractures from anatomical sesamoid bones can be challenging. Anatomical sesamoids at the IP joint of the thumb are less common and may resemble avulsion fragments on radiographs, particularly in trauma cases⁵. Misinterpretation, as seen in this case, can lead to inappropriate management. Management of thumb IP joint avulsion fractures depends on the extent of fragment displacement and the joint's stability. Small, non-displaced fractures are typically treated with immobilization, such as a thumb spica splint or cast, to allow for proper healing^2,3. More complex or displaced fractures may necessitate surgical intervention to restore joint integrity and prevent chronic instability or functional impairment. Rehabilitation focuses on restoring range of motion, strengthening exercises, and gradual return to activities, with careful monitoring to prevent reinjury^1,2. In this case, the initial radiographic findings suggested an avulsion fracture, prompting immobilization and conservative management. However, bilateral imaging and subsequent assessment clarified that the bone fragment was an anatomical sesamoid, not an avulsion fracture. The revised diagnosis allowed for appropriate adjustment in management, enabling a faster recovery and avoiding unnecessary prolonged immobilization.

4 Ulnar collateral ligament tears in the thumb

The ulnar collateral ligament of the thumb is essential for stabilizing the MCP joint during pinching or grasping activities⁶. UCL injuries in the thumb, often termed "skier's thumb” due to their association with falls on an outstretched hand while gripping, are common in sports with high thumb stress, such as newcomb ball, volleyball, and skiing⁷. UCL tears are classified as partial or complete and typically involve a sudden valgus force on the thumb, causing ligamentous disruption that leads to pain, swelling, and instability⁸. The clinical presentation of UCL tears includes tenderness at the ulnar side of the thumb's MCP joint, decreased grip strength, and joint laxity on stress testing⁹. Diagnosing UCL tears can be challenging; clinical exams often reveal instability on valgus stress tests, and imaging especially ultrasound or MRI may show partial or complete disruption of the ligament fibers, as seen in this case¹⁰. Missed or misdiagnosed UCL injuries can result in chronic instability, pain, and loss of pinch strength, potentially impacting hand function significantly^7,9,10.

5 Conclusion

The implications of misdiagnosis in this case highlight the critical importance of diagnostic accuracy in sports injuries. Mistaking a partial tear of the ulnar collateral ligament for an avulsion fracture can lead to a series of negative outcomes. Firstly, inappropriate treatment, such as prolonged immobilization, may delay the healing process and cause unnecessary joint stiffness. Secondly, the lack of proper treatment for the ligament tear could result in chronic joint instability, potentially compromising long-term hand function. Additionally, misdiagnosis can cause undue anxiety for the patient and delay their return to sports activities. This case emphasizes the need for a comprehensive diagnostic approach, including bilateral imaging and thorough clinical assessment, especially when dealing with less common sports or anatomical variants. Improving diagnostic accuracy can prevent unnecessary treatments, shorten recovery times, and enhance clinical outcomes for both amateur and professional athletes. Furthermore, it underscores the importance of considering anatomical variations and the value of comparative imaging in challenging cases, ultimately leading to more precise and effective patient care and avoid unnecessary treatments. By understanding the prevalence of sesamoid bones and adopting a comprehensive diagnostic protocol, clinicians can improve diagnostic accuracy and optimize patient outcomes.

CRediT authorship contribution statement

Eden Amiel: MD, MPH (Candidate), Supervision, Conceptualization, data collection, manuscript drafting, critical review, and approval of the final manuscript. Shir Cohen: MD, Clinical interpretation, manuscript editing, and approval of the final manuscript. Elad Epshtein: MD, MPH (Candidate), Clinical interpretation, manuscript editing, and approval of the final manuscript, All authors confirm that they have contributed significantly to the work and agree to be accountable for all aspects of the research to ensure the accuracy and integrity of the publication.

Guardian/patient's consent

The patient provided written informed consent for the publication of this case report, including the use of anonymized medical data and images. The patient was informed that no identifying information would be disclosed and that all data presented in the case would maintain strict confidentiality.

For further assurance, all ethical guidelines for publishing patient information have been adhered to.

Ethical statement

This study was conducted in accordance with the principles outlined in the Declaration of Helsinki and all applicable ethical guidelines. Patient data were anonymized to maintain confidentiality, and no identifying information is presented.

Written informed consent was obtained from the patient for the publication of this case report and accompanying images. The authors ensured that the research and reporting process adhered to institutional and ethical standards for the protection of patient rights and privacy.

Funding statement

The authors declare that no funding was received from any public, commercial, or not-for-profit agencies for the research, authorship, or publication of this case report.