A 20 years old man presented with right thigh pain and a hard mass in the right thigh.
A man aged 20 years presented with right thigh pain following a motor vehicle accident. Previous medical history and clinical examination were unremarkable except a hard mass in the right thigh. Emergency radiographs were performed followed by CT. Linear calcified structure was seen in the right thigh, articulating with the right ischial tuberosity and proximal part of the right femur.
Pelvic ribs and digits are regarded as congenital anomalies where bone develops in soft tissues adjacent to to normal bone (1).Therefore it is important to identify it as a developmental anomaly and differentiate them from post-traumatic causes such as avulsion fractures and myositis ossificans by its well corticated appearance and the absence of history of trauma(1). In doubtful cases CT may be useful.
Most often these are asymptomatic incidental findings(2)or present as a palpable lump as the patient in our case.
On plain X-Ray it appears like a rib with a clear cortex and medulla around the pelvis, and sometimes with a characteristic pseudo-articulation at the base(2).
There are various case reports of ectopic ribs within and superior to the pelvis in the literature.(3,4,5)
Commonly ectopic ribs are related to the ilium , rarely to sacrum and coccyx. In this case it was related to the ischium. Occasionally these can be at multiple sites.
Various postulations have been put forward to explain the origin of this rare developmental anomaly. One such postulation is that it arises in the
mesenchymal stage of bone growth, before the sixth week of fetal development (6)
These explanations, however, do not take into account the varied sites of attachment in the pelvis. As pelvic ribs are found at the coccyx, the pelvic walls, and the inferior abdominal wall, it must arise from an embryonic mesoderm with rib-forming capacity disposed to these regions(6).
- Pelvic rib simulating a thigh mass
In the anteroposterior (AP) pelvic X-ray and corresponding CT scans, a rib-like bony structure near the right ischium is observed, showing both well-defined cortical and medullary patterns. There is a “pseudo-joint” appearance locally. The structure is connected to surrounding bone tissue but presents no obvious fracture line or signs of fracture healing. The adjacent soft tissue does not show marked swelling or periosteal reaction, and there is no history of trauma. Overall, it appears as an isolated, well-marginated bony structure, suggesting the possibility of a congenital anomaly.
Based on the patient’s age, symptoms, and imaging findings, the differential diagnoses include:
Taking into account the young male patient with no evident trauma history and imaging demonstrating a well-formed bony structure in proximity to the pelvis (ischium), the most likely diagnosis is:
Congenital Pelvic Rib (Ectopic Rib).
Such congenital bony anomalies often require no specific intervention unless symptomatic or functionally impairing.
Given the patient’s primary complaint is a palpable mass with mild pain and no apparent functional deficits, consider the following options:
During postoperative care or conservative treatment, an individualized, progressive exercise program (following the FITT-VP principle) can be implemented:
Ensure movement control and avoid high-impact activities or excessive pressure on the affected site. If the patient has osteoporosis or other underlying conditions, a more cautious exercise regimen should be developed in consultation with a physician or physical therapist.
Disclaimer: This report provides medical reference information only and is not a substitute for an in-person medical consultation or professional diagnosis. Please implement any treatment or rehabilitation plan under the guidance of a qualified healthcare professional.
- Pelvic rib simulating a thigh mass
