A 45-year-old patient reported as a follow up for a motor vehicle accident with history of vague right flank pain. A pelvic radiographwas performed which revealed a large bony protuberance arising from the right sacral region.
A 45-year-old patient reported as a follow up for a motor vehicle accident with history of vague right flank pain. His clinical examination was unremarkable except for deep tenderness in the right flank. A radiograph of pelvis was advised (as shown in the fig) which showed a large bony protuberance arising from the right sacral region. This appearance is consistent with a pelvic rib, which is a rare normal variant and usually asymptomatic. Surgical intervention was offered to the patient. However, due to the limited nature of the patient’s complaints, he did not opt for intervention. For this reason, a histopathologic exam could not be performed.
In the spinal column, many anomalies related to formation or segmentation defects have been reported (1, 2). Anomalies that have a cortex and develop in the soft tissues around the vertebral column are very rare, and radiologically they look like ribs or digits (3). When seen within the pelvis or abdomen these anomalies are known as pelvic ribs or pelvic digits (4, 5, 6) Pelvic rib is a rare congenital anomaly in which bone develops in soft tissue adjacent to normal skeletal bone (5). On plain radiograph it typically appears as a rib- or a phalanx-like bone with a clear cortex and medulla related to the pelvis, often with a characteristic pseudoarticulation at the base (3). Clinically, cervical supernumerary ribs may cause neurovascular symptoms or thoracic outlet compression syndrome whereas pelvic ribs are usually asymptomatic, and, in most cases, found incidentally during the examinations for other problems (7, 8). In those rare cases in which sacral ribs cause symptoms, there is typically discomfort and diminished mobility during movement of the ipsilateral hip, and, possibly can cause compromise of the birth canal in female (9). Standard radiographs and computed tomography provide the best diagnostic information. Its differential diagnosis includes myositis ossificans, avulsion injuries, heterotopic bone formation, Fong’s disease, and osteochondroma. Pelvic digit can usually be radiologically differentiated from posttraumatic myositis ossificans and from heterotopic bone formation by its well corticated appearance and the absence of history of trauma (4, 10). CT of pelvic digit confirms the presence of cortical bone (11) and is useful in equivocal cases (12.). Myositis ossificans is characterized by a radiolucent core with a calcified periphery, which is clearly separated from adjacent bones (11). Avulsion injuries of the pelvis commonly occur during athletic activity, with peak incidence in adolescents and teenagers (13). Pain, diminished motion, and soft tissue haematoma correlate with a bony fragment (13). In some cases, new bone formation after surgery or ossification of the sacrotuberous ligament can resemble a pelvic digit (5). Fong’s disease is characterized by bilateral iliac horns arising posteriorly and centrally from the ilia (11). Osteochondroma is continuous with underlying bone (5) and a cartilaginous cap may be present (12). Pelvic digit is usually an asymptomatic, benign condition and is discovered incidentally (3). In the absence of symptoms, surgical excision is not required (10). Pelvic ribs are suggested as a rare cause of fetopelvic disproportion, and a case of scoliosis and hypoplasia of the ipsilateral gluteal musculature arising from pelvic rib has also been reported (7, 14). In conclusion, it is important to recognize and distinguish the pelvic rib from posttraumatic ossification and avulsion injuries and, thus, avoid unnecessary additional investigations. The radiographic entity of pelvic rib/ digit should be known by every radiologist as an incidental finding for which no further action is required.
The Pelvis Rib
1. On the pelvic anteroposterior (AP) radiograph, there is a protruding bone-like structure in the right sacral region resembling a rib or a digit, with clearly visible cortical and medullary components.
2. The shape of the bony structure is distinctly demarcated from the sacrum, with no obvious fracture lines or signs of acute injury.
3. There is no apparent soft tissue swelling or calcification suggestive of traumatic myositis ossificans or bone fragments.
4. No significant abnormal signal is seen in the soft tissues surrounding this bony process, and there is no remarkable malformation in adjacent joints or other pelvic structures.
Based on the imaging findings and the patient’s basic medical history, the following diagnoses may be considered:
Taking into account the imaging features (intact bone structure, clear delineation of cortex and medulla, a rib-like or digit-shaped appearance) and the absence of apparent traumatic signs or history of soft tissue injury, the most likely diagnosis is:
Congenital Pelvic Rib or Pelvic Digit (Pelvic rib / Pelvic digit)
This condition is a benign congenital anomaly and typically does not directly correlate with the patient’s present complaint (right-sided flank discomfort). It is often discovered incidentally during imaging.
Since pelvic ribs (pelvic digits) are generally asymptomatic and have a good prognosis, no specific treatment is required if there are no distinct symptoms or complications. If the patient’s chronic lower back or pelvic discomfort is caused by other issues, the following can be considered:
For rehabilitation exercise prescriptions, you may refer to the FITT-VP principle:
| Element | Recommendation |
|---|---|
| Frequency | Begin with 3–4 sessions per week, progressing gradually to 5 sessions, based on individual recovery |
| Intensity | Start with low-intensity exercises (e.g., walking, gentle stretching) and progressively increase as tolerated |
| Time | Initiate at 15–20 minutes per session, then gradually extend to 30 minutes or more |
| Type | Focus on safe, controlled aerobic activities and core/hip stabilization exercises, such as seated stretches, core strengthening, or low-impact aerobic workouts (e.g., swimming, elliptical) |
| Volume | Follow a gradual progression, increasing the total exercise volume by about 10% per week, balancing actual activity and physical capacity |
| Progression | If no significant discomfort is reported, gradually escalate intensity or incorporate more advanced training, transitioning from basic stretches to reinforcing core stability training |
Disclaimer: This report provides a reference-based analysis derived from the current imaging and patient history. It does not replace in-person clinical evaluations or professional medical advice. In case of any concerns or worsening symptoms, please seek advice from an appropriate specialist or hospital.
The Pelvis Rib
