The imaging findings varied with the age of the patients. The following table summarizes the common pathologies in different age groups.
It was seen that apart from common pathologies like septic arthritis and osteomyelitis, several other less common pathologies were also seen on MRI imaging.
- In children < 10 years, who had hip pain, the diagnosis of developmental dysplasia of hip, Jeuvenile idiopathic arthritis and Perthes disease was not uncommon, apart from septic arthritis and osteomyelitis. Rarely a neoplastic lesion may be seen (e.g. Eosinophilic granuloma/Ewing's sarcoma/ neuroblastoma metastasis).
- In 10-17 years old, hip pain maybe due to slipped upper femoral epiphysis, post traumatic avulsion fracture or soft tissue hematoma. Occasionally Osteoid Osteoma or soft tissue neoplasm e.g. Desmoid tumor can be the cause. Malignant neoplasm (Ewings / Osteosarcoma) is rare but can occur.
- In 18-24 years old Avascular necrosis or sports injury with ligamentous tears maybe seen, A soft tissue Schwannoma or a bone neoplasm (Fibrous dysplasia / Exostosis) may occasionally be seen.
Perthes disease: It is an idiopathic avascular necrosis of proximal femoral epiphysis. It occurs most commonly in boys, typically between 5-8 years age. It can be bilateral but usually asymmetrical. MRI findings include flattening of femoral head, subchondral fracture, loss of high T1 marrow signal and a double line sign of T2 fatsat sequence. if disease progresses then fragmentation and collapse of femoral head may occur.
Secondary Avascular necrosis: Findings are similar to Perthes disease but there would be a known cause. The causes include steroid therapy, sickle cell disease SLE, or a complication of hip dysplasia treatment.
Developmental dysplasia of hip: Hip dysplasia is characterized by an abnormal ratio between acetabulum and femotral head. (4) if there is a suspicion of the condition in infants< 6 months age, ultrasound is done for detection. Findings on radiographs suggest established dysplasia. The symmetry of hips is noted along with tracing Helgenreiners, Perkins and Shentons lines and measuring acetabular angle. MRI is useful in treatment planning, monitoring and post operative evaluation. On imaging there would be asymmetry of the hip joints, loss of sphericity, flattening and superolateral subluxation of femoral head, enlargement of femoral neck and acetabular cavity, joint effusion and synovitis. If left untreated it may lead to gait abnormality, discrepancy in limb length, early osteoarthritis and avascular necrosis.
Jeuvenile idiopathic arthritis: Large joints are mainly affected, including the hips and sacroiliac joints. It maybe unilateral but is frequently bilateral. (5) Radiographs are usually normal early in the disease. MRI may show tenosynovitis, bone edema, periostitis, joint effusion and thickened synovium. Cartilage loss and erosions are not frequently seen. MRI may also assess the resulting growth disturbances.
Septic arthritis and osteomyelitis: The child would have hip pain, fever and local swelling. Biochemical markers i.e. ESR and CRP would be raised. Radiographs and Ultrasound are poorly sensitive in the early stages while MRI is effective in the early diagnosis of osteomyelitis, and in assessing the degree of bone articular cartilage and adjacent soft tissue involvement. On contrast enhanced MRI the collections i.e. subperiosteal, intraarticular and soft tissue collection would be seen to show marginal enhancement. Brodies abscess is a subacute osteomyelitis with intraosseous abscess formation. Osteonecrosis and fistulous tracts would also be evident on MRI.
Slipped capital femoral epiphysis: This is a Salter Harris type 1 fracture of upper femoral epiphysis. It occurs commonly in boys and in obese children. The epiphysis slips posteromedially. Standard radiography is the first line imaging withAP and frog leg lateral views. In early cases of slipped femoral epiphysis MRI is more sensitive than radiographs in which edema is seen in the femoral epiphysis and metaphysis alonf with epiphyseal slip. It may progress to avascular necrosis, if left untreated. Necrosis typically involves the antetrolateral femoral head. Diffusion weighted images may detect the vascularity of femoral head and any AVN. (6) Late complications include pistol grip deformity (enlargement and shortening of femoral neck and varus deformity, osteoarthritis and limb length discrepancy due to fusion of physis.
Trauma / avulsion injuries: If there is any history of trauma it would be clearly given, however in very young children with corner or bucket handle fracture and no clear history of trauma, a suspicion of non accidental injury should be raised. Traumatic bony avulsion injuries are a frequent cause of hip pain in adolescents with sports related injury.
Ligamentous or muscle tear may also be seen in cases of trauma, appearing as discontnuity in muscle fibres, hematoma formation and edema.
Neoplasms: Benign or malignant neoplasms though not commonly seen but occasionally maybe a cause of hip pain in children and young adults. These include Eosinphilic Granuloma, simple bone cyst, aneurysmal bone cyst, fibrous dysplasia, osteoid osteoma or a schwannomma in soft tissues around hip joint. Malignant neoplasms include neuroblastoma metastasis, Ewings sarcoma/ osteosarcoma, Lymphoma and Leukemia.
