A 3-year-old girl was referred with leg pain and a radiograph showing a lesion, suspicious of malignancy, in the distal femur. Further imaging revealed the true nature of the lesion.
We present the case of a 3-year-old girl who presented with a 6 month history of intermittent pain in the right distal femur. Further history and examination were unremarkable. The general practitioner arranged plain of the pelvis and femur. Pelvic radiographs were normal. Radiographs of the femur revealed a lytic lesion in the medial femoral metaphysis. The likely diagnosis was thought to be a Brodies abscess but clearly a neoplastic lesion needed to be excluded. CT imaging was undertaken which revealed a bilateral medial cortical defect of the distal femur at the insertion of the medial head of gastrocnemius muscle.
Cortical disruption occurring at the origin of major muscles has been reported on numerous occasions in the literature. The most accurate term to used to describe such a lesion is an avulsive cortical irregularity (8) however terms such as metaphyseal fibrous defects, tug lesions and cortical or periosteal desmoids have been used. These lesions are frequently reported to occur in the distal femur at the origin of medial head of gastrocnemius (1,2,3,4,6). Other sites of such a phenomenon include the distal femur at the adductor magnus tendon insertion (4,5). The typical radiological appearance is a radiolucent cortical defect in a typical location associated with adjacent sclerosis (5). Differential diagnosis includes surface osteosarcoma and a non-ossifying fibroma. They are thought to arise from repetitive stress placed by the inserting muscle with subsequent microavulsions (6). They are usually incidental radiological findings but may cause occasional aches. The only reported complications are misdiagnosis and subsequent invasive investigations or surgical intervention – which has even resulted in unnecessary amputation (7). Resolution is thought to occur in adulthood but there are certainly cases of persisting irregularities in young adults (6).
Femoral avulsive cortical irregularity / Tug Lesion.
1. Based on the provided anterior-posterior and lateral X-ray images of the distal femur and corresponding CT scans, a localized cortical defect is observed in the posteromedial cortex of the distal femur.
2. The defect is nearly circular or oval in shape, with mild cortical depression visible locally and slightly sclerotic margins noted.
3. There is no apparent periosteal reaction or significant soft tissue swelling; the trabecular structure appears relatively coordinated with the surrounding bone.
4. The soft tissue around the lesion does not show obvious swelling or signs of invasion, and no significant abnormalities are noted in the adjacent joint structures (knee joint).
Based on the imaging findings, the patient’s age of 3 years, presentation with leg pain, and the absence of clear signs of malignancy, the following diagnoses or differentials can be considered:
1. Avulsive cortical irregularity (also known as cortical/periosteal desmoid or tug lesion): Commonly seen in children or adolescents, often near the distal femur at sites of tendon or ligament attachment. Repeated pulling by muscles or ligaments can lead to tiny avulsions in the cortex. Radiographically, this often appears as small cortical depressions with local sclerosis. Patients usually have little to no functional impairment or signs of malignancy.
2. Non-ossifying fibroma: Common in children and adolescents, appearing as a radiolucent lesion within the bone, often with a well-defined margin and sometimes sclerotic border. However, its typical location and appearance differ from avulsive cortical changes. Given the patient’s younger age and the lesion’s characteristics, it remains a secondary consideration.
3. Surface osteosarcoma: Although rare, tumor should be excluded. If the lesion were malignant, there would typically be periosteal reaction, soft tissue swelling, and progressive bone destruction. Clinically, there would also be progressively worsening pain and functional impairment. Current imaging does not support this.
Considering the child’s age, clinical history, and imaging characteristics, the most likely diagnosis is avulsive cortical irregularity. This lesion results from repetitive traction by tendons or ligaments on the femoral cortex. It generally has no malignant potential and carries a good prognosis. If clinical symptoms are mild and there is no progressive change, observation and follow-up are adequate without urgent intervention or treatment.
Treatment Approach:
1. Conservative observation: Since avulsive cortical irregularity is typically a benign lesion, regular follow-up imaging to monitor changes is appropriate. If there is no obvious pain or worsening of symptoms, special intervention is usually unnecessary.
2. Symptomatic management: If mild soreness occurs after activity, temporarily reduce high-intensity exercise. Local heat application or physical therapy can help relieve discomfort.
3. Surgical indications: If the lesion shows progressive enlargement, is accompanied by pathological fracture, or presents suspicious malignant changes, further examinations (e.g., MRI, biopsy) should be undertaken to determine whether surgical intervention is required.
Rehabilitation and Exercise Prescription (FITT-VP Principle):
1. Frequency: 3–4 times per week of regular, mild lower-limb strength and flexibility training, such as simple single-leg balance exercises or ankle flexibility exercises under professional guidance.
2. Intensity: Keep it light; avoid excessive traction on the affected tendons and bony attachments. When possible, opt for non-weight-bearing exercises (e.g., swimming or riding a small bike) or only short-term walking sessions.
3. Time: Begin each training session at 10–15 minutes, gradually increasing to around 20 minutes as the child’s tolerance and development allow.
4. Type: Choose low-impact activities that protect joints and bones, such as mild lower-limb strength training (simple squats, lunges) and flexibility exercises. Stop or reduce intensity if pain occurs.
5. Progression: Gradually increase exercise volume and difficulty according to the child’s age and physical development, paying attention to protecting the knee joint and distal femur. Avoid high-impact or heavy-load training too early.
6. Notes: If marked pain, swelling, or functional impairment occurs during training, seek medical advice promptly to rule out further avulsion or bone damage.
Femoral avulsive cortical irregularity / Tug Lesion.
