The dislocation of the hip occurs when the femoral head forcefully exits the pelvic socket or acetabulum. It can be a congenital condition or a result of trauma with the first being described in the pathology hip dysplasia.
A traumatic dislocation of the hip is a serious condition needing emergency care as it may occur in concomitance with fractures or injuries elsewhere in the body. The dislodgement of the femoral head from the acetabulum requires high impact forces and provokes sharp pain. It differs from the dislocation of hip prostheses and those dislocations observed in patients with congenital hip dysplasia.
A hip dislocation is divided into three types according to the positioning of the femoral head relative to the hip joint:
Anterior hip dislocation occurs with hip abduction and external rotation. It is associated with femoral head impaction, pubic dislocation and obturator dislocation. Anterior hip dislocation is associated with fracture of acetabulum, femoral head, knee injury and sciatic nerve damage.
Posterior hip dislocation (circa 90% of all dislocations) is typical when impacting to the car dashboard with a flexed hip and knee.
Central hip dislocation is caused by a lateral impact and mostly linked to acetabular fracture.
A hip dislocation can be simple if isolated or complex when involving the fracture of the acetabulum or proximal femur. This pathology may lead to long-term morbidity such as chronic pain, reduced mobility and post-traumatic osteoarthritis.
Thompson-Epstein classification of hip dislocations when associated with:
Type 1 - without minor fracture
Type 2 - single fracture of posterior acetabular rim
Type 3 - comminution of acetabular rim, with/without fragments
Type 4 - fracture of acetabular floor
Type 5 - fracture of femoral head
Steward and Milford classification of hip dislocation relies on functional changes:
Type 1 - No fracture or small fracture
Type 2 - single or comminuted posterior wall fragment although hip stability is not affected with movement
Type 3 - severe instability of the hip following loss of structural integrity
Type 4 - fracture of femoral head
Traumatic events involving high energy are the main cause of a hip dislocation. The impact is usually applied directly to the hip as it occurs with a fall from a significant height, high velocity motor vehicle accidents or falls during contact sports.
In children a hip dislocation does not require a high force but can affect the integrity of the growth plates (epiphysis) of the femur. In the young population this pathology is rare but is frequently observed in risk-taking individuals. The main causes are:
High-speed motor vehicle accidents (2/3 of all dislocations; 70%)
Falls from significant height / high velocity onto the hip
The risk factors for a hip dislocation differ in population groups:
Young age: car driving, sports
Older age: falls
Male gender: risk taking behaviours
High speed car accidents
Working at height (carpenters, electricians, builders, painters)
Sport injuries (football, rugby, water skiing, alpine skiing/snowboarding, gymnastics, running, basketball, race car driving, horse riding)
The symptoms of a dislocated hip may vary in relation to associated injuries. Soon after occurring, a hip dislocation triggers ;severe pain on the hip and pelvis radiating to the lower back and limbs. The patient is unable to move the hip and may suffer from numbness around the hip area and even paralysis of the lower limb (nerve damage).
Deformities may also appear following a hip dislocation including partial rotation, shortening, abduction/adduction of the affected limb.
Damage to the sciatic nerve manifests via lack of sensation on the back of the leg and foot, inability to dorsiflex and plantar flexion, loss of ankle reflexes. Injury to the femoral nerve causes lost sensation on the thigh, quadriceps weakness, and loss of reflexes at the knee. Vascular injury comprises the appearance of haematomas and absence of pulse. Arterial damage may compromise blood perfusion to the leg of the dislocated hip.
A hip dislocation is considered an orthopaedic emergency and first care is executed at the hospital. The eventuality of life-threatening injuries must be prioritised over the dislocation and the patient's cardiovascular condition stabilised. Following admittance, the patient is firstly immobilised and treated with painkillers (analgesics) and fluid replacement, prior to radiologic evaluation with X-rays. Often a CT scan or an MRI is performed to classify the type of dislocation and detect potential fractures, abdominal injuries and nerve damage.
A simple, displaced hip when isolated requires a closed reduction, a procedure usually undertaken within 6 hours from the accident at the emergency department or operating theatre. The patient is firstly anaesthetised or sedated. Subsequently a control X-ray is taken to confirm the correct positioning of the femoral head into the acetabulum. A closed reduction is not conducted with a femoral neck fracture. The patient is advised to follow these recommendations:
Use crutches to avoid full weight bearing
Administration of NSAIDs for pain relief and reduce inflammation
Surgical treatment for a dislocated hip is necessary when patient presentation to hospital is delayed beyond 6 hours, or with failed closed reduction and continued instability of the hip joint. Prior to surgery the limb of the affected hip may be placed into traction to reduce pressure on the joint.
Arthroscopic surgery is suitable for minor procedures, such as removal of bone and cartilage fragments from the joint space and assessment of soft tissue injuries to the cartilage, capsule, labrum. Open reduction and internal fixation (ORIF) is required to repair fractures to the femoral head, neck and acetabulum.
Most common complications following a hip dislocation are:
Recurrent dislocations due to ligament laxity and damage
Necrosis of the femoral head (avascular necrosis) due to damage of the vessels around the bone
Post-surgical infection treated with antibiotics
Hip osteoarthritis arising from injury to the cartilage tissue, requiring prosthetic replacement
Neurological deficits due to long-lasting or permanent nerve injury
Medical issues: DVT, pneumonia, pulmonary embolism
It is critical that after a period of rest following a hip dislocation the patient begins rehabilitative care with gradual and assisted walking to prevent medical complications. In the elderly, this phase may require admission to a cared facility or regular in-home visits by an occupational therapist to restore independent daily living activities. A wheelchair, crutches, walking stick, or walker may be necessary to support the patient during the first weeks while recovering from a hip dislocation. Physiotherapy care includes:
Traction for 2 weeks with abducted legs to prevent secondary dislocation
Antiinflammatory therapy (NSAIDs)
Analgesics for pain control
No weight or partial weight bearing for up to 3 months
Exercise to strengthen quadriceps, hamstrings and gluteal muscles
Stretching of hip and leg muscles
Guided return to activity and sport
A hip dislocation cannot be easily prevented and presents a certain risk for a second dislocation. Prevention is mostly based on guidelines to reduce falls and improve safety in road traffic and workplace. Some preventive measures include:
Keeping floor surfacing in sport halls well maintained
Exercise to maintain muscular strength and flexibility
Use of supporting walking devices in the elderly
Adherence to occupational health and safety procedures (harness, balustrades)
Use of road traffic safety equipment (seatbelt)
Removal of carpets or other items facilitating falls
Modify habits (use laced shoes, house illumination at night, staircase railings, non-skid tiles in bathroom)