Volume 6, Case 15
Soledad S. U. Raroque, MD
Children's Medical Center of Dallas
University of Texas Southwestern School of Medicine
A four year old female is brought to the emergency department with a complaint of right hip and knee pain. About two hours prior to presentation, the child had been running when she slipped and refused to bear weight or move her right lower extremity. There is no other history of significant medical or surgical problems.
Exam: VS: T 36.7, P120, RR 24, BP 120/77. She is awake and alert in no acute distress. Her right lower extremity is held in flexion at the hip and knee, adducted and internally rotated. A bony prominence at her right gluteal region is appreciated. She resists attempts at passive range of motion about the hip because of pain. Pulses are full. Motor and sensory functions are all intact. The rest of her physical examination is normal. Radiographs of the pelvis and hips are obtained.
View Pelvis and Hip Radiographs.
AP view.
Oblique view.
The AP view shows a dislocation of the right hip. The oblique view is difficult to interpret. Clinically, this is a posterior dislocation. There is no evidence of fracture. The patient was sedated in the emergency department. Closed reduction of the right hip was done by applying traction in line with the deformity and gently flexing the hip to 90 degrees. Concentric reduction was obtained. Repeat radiographs showed complete reduction with no evidence of fracture or epiphyseal injury.
View Post-Reduction Pelvis and Hips.
AP view.
Frog view.
The child was hospitalized and underwent 48 hours of skin traction. Upon discharge, she had continued full range of motion, no pain and no evidence of redislocation. She was followed-up by the orthopedic service for several months.
Teaching Points:
1. Traumatic hip dislocation (THD) is an uncommon injury in children and adolescents. Falls are the single most common cause followed by high velocity injuries such as motor vehicle accidents and sports-related incidents. Boys are more frequently affected than girls. It may also be seen in relatively minor trauma in young children less than 5 years of age due perhaps to joint laxity and a shallow acetabular fossa.
2. Posterior dislocations are more common than anterior dislocations. These injuries often occur after a blow to the knee with the hip and knee in flexion, as in a motor vehicle crash with an unrestrained child striking one knee against the dashboard. The leg would be adducted, flexed and internally rotated at the hip, as in this case. There is a relative shortening of the extremity and protrusion of the greater trochanter into the gluteal region. Anterior dislocations, on the other hand, are usually caused by an excessive external rotation or a direct blow to the greater trochanter with the hip externally rotated. The leg would typically be held in abduction, extension and external rotation.
3. The occurrence of an obvious traumatic episode followed by limb dysfunction and local evidence of injury of the affected body part narrows the differential considerably. A plain radiograph may confirm a fracture, avulsion, dislocation or soft-tissue injury. In cases of THD, other views of the hip joint (e.g. oblique and lateral views) may be difficult to obtain because of the limited range of motion in some patients. Additional radiographs of the ipsilateral extremity may be indicated to rule out other fractures or injuries. Approximately 25% of hip dislocations are associated with knee injuries.
4. Early recognition is essential in the management of THD. Immediate closed reduction (within 6 hours after the injury) under general anesthesia or intravenous sedation has been shown to have a better prognosis. A hip dislocation is reduced by flexing the hip and knee to 90 degrees and applying axial traction of the thigh. Repeat pelvic radiographs which show a widened medial joint space indicate an incomplete reduction. Late diagnosis and failure to achieve a concentric reduction invariably requires an open reduction. After a successful reduction, immobilization either with traction or spica cast, may be done to maintain stability. There is no consensus in the orthopedic literature about the type of post-reduction care or the duration of non-weight bearing significantly affecting the prognosis of THD.
5. Computed tomography (CT) has been used after reduction attempts to identify fractures or intraarticular loose bodies not apparent on standard radiographs. Magnetic resonance imaging (MRI) has also been found to improve the diagnostic accuracy of hip dislocation. Studies to compare the two modalities have yet to be done.
6. The major complications of THD are frequent and include avascular necrosis, recurrent dislocation, sciatic nerve injury or traction injuries and traumatic arthritis. The severity of the trauma and the period until reduction are considered to be important prognostic factors.
References