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Hip injuries


Essentials

  • 1

    Fracture of the hip is a major cause of morbidity and mortality in the elderly, with a large impact on health care and resources.

  • 2

    Hip injuries are frequently a pathological disease of the elderly. However, hip fractures and dislocations also occur in young people who sustain high-energy trauma.

  • 3

    Extracapsular hip fractures are associated with significant haemorrhage.

  • 4

    Avascular necrosis (AVN) of the femoral head is a complication of intracapsular femoral neck fractures as well as hip dislocation.

  • 5

    The hip joint is least stable when flexed and adducted and thus prone to dislocation. Posterior hip dislocations are an orthopaedic emergency, as they are associated with sciatic nerve injury and AVN.

  • 6

    Anterior hip dislocations are associated with femoral neurovascular injury and occult hip joint fractures.

Anatomy

The hip joint is a large ball-and-socket articulation encompassing the acetabulum and proximal femur. The hip joint provides a high degree of stability and mobility.

Blood supply

The head and intracapsular portion of the femoral neck receive the majority of their blood supply from the extracapsular trochanteric anastomosis arterial ring, with a minor supply arising from the foveal branch of the obturator artery via the ligamentum teres to the femoral head.

Retinacular arteries from the extracapsular ring pass under the reflection of the hip capsule to supply the femoral neck and head in a retrograde manner. Intracapsular fractures disrupt this ‘distal-to-proximal flow’ and so may result in avascular necrosis of the femoral head.

Avascular necrosis

Avascular necrosis (AVN) following hip injury refers to ischaemic bone death within the femoral head due to compromise of its blood supply. Increased bone density of the femoral head is the radiographic feature of AVN, but this may take up to 6 months to become manifest.

AVN results primarily from the disruption of the trochanteric anastomosis in femoral neck fractures and is the commonest early complication of these fractures. Traumatic haemarthrosis with or without a fracture may also result in intracapsular tamponade. AVN occurs when the intracapsular pressure exceeds the diastolic blood pressure.

AVN is also seen following posterior dislocation and is related to the degree of trauma and the length of time the femoral head is out of the joint. Early management is thus an orthopaedic emergency, as reduction within 6 hours results in an AVN rate of less than 10%.

In addition, chronic pancreatitis, alcohol abuse, sickle cell anaemia, vasculitis, irradiation, decompression illness (DCI) and the prolonged use of corticosteroids may all result in AVN.

Classification of hip fractures

Hip fractures are either intracapsular or extracapsular. Intracapsular fractures involve the femoral neck or head. Extracapsular fractures include intertrochanteric, trochanteric and subtrochanteric types and are four times more common than intracapsular fractures.

The incidence of hip fractures increases exponentially with age, with the fracture rate doubling for every decade over 50 years. Hip fractures occur most frequently in white postmenopausal women, as 50% of 65-year-old women and 100% of women over the age of 85 have a bone mineral density below fracture threshold level (osteoporosis).

Intracapsular fractures

Femoral head

Femoral head fractures are uncommon and are usually associated with dislocations of the hip. They often occur in young patients, 75% of cases being associated with motor vehicle accidents (MVAs).

Classification

Fractures of the superior aspect of the femoral head are usually associated with anterior dislocation, whereas inferior femoral head fractures occur with posterior dislocation. Fractures may involve a single fragment (type 1) or comminution (type 2).

Clinical evaluation

Symptoms and signs of femoral head injuries are usually those of the associated dislocation rather than the fracture itself. Femoral head fractures are not always picked up on initial x-rays. In the absence of abnormality on plain radiography and the presence of persistent pain following reduction of a hip dislocation, further imaging with a computed tomography (CT) scan should be performed.

Management

Immediate orthopaedic referral is essential, as prompt reduction of the dislocation and appropriate stabilization of the fracture reduce the risk of AVN, increasing the chances of a return to full mobility. The prognosis is related to the severity of the initial trauma, time to definitive reduction and the number of failed closed relocation attempts.

Complications

AVN occurs in 15% to 20% of cases, post-traumatic arthritis in 40% and myositis ossificans in 2%.

Femoral neck fractures

Intracapsular fractures are four times more common in females than males. There are four main causes of this type of injury:

  • Elderly, with minimal trauma following a fall onto the greater trochanter (pathological fracture)

  • Elderly, with torsion or twisting injury prior to fall (pathological fracture)

  • Young person involved in high-energy trauma (excessive loading)

  • Repetitive stress or cyclical loading injuries (stress fracture).

Classification

The Garden classification system is commonly used to describe intracapsular neck of femur fractures.

Garden I:

Incomplete, impacted or stress fractures that are stable. Trabeculae of the inferior neck are still intact and, although they may be angulated, they are still congruous.

Garden II:

Undisplaced fracture across the entire femoral neck. The weight-bearing trabeculae are interrupted, without displacement. These fractures are inherently unstable and must be fixed.

Garden III:

Complete femoral neck fracture with partial displacement. There is associated rotation of the femoral head, with non-congruity of the head and acetabular trabeculae.

Garden IV:

Complete subcapital fracture with total displacement of fracture fragments. There is no congruity between proximal and distal fragments, but the femoral head maintains a normal relationship with the acetabulum.

These fractures may be further simplified into non-displaced (Garden I and II) and displaced (Garden III and IV).

Clinical assessment and management

Non-displaced fractures

Non-displaced fractures include stress fractures, Garden I and Garden II fractures. Stress fractures are usually the result of repetitive abnormal forces on normal bone in fit, active young people, such as military recruits or marathon runners, but they may occur with repetitive normal stresses on abnormal bones, as in rheumatoid arthritis or patients taking long-term steroids.

These fractures present with pain that is gradual in onset and worse after activity, radiating from the groin to the medial aspect of the knee. Patients walk with a limp and often present late. Physical examination reveals no obvious deformity, although there is mild discomfort on passive movement at the extremes of motion and percussion tenderness over the greater trochanter.

Additional radiological examination with a bone scan and/or magnetic resonance imaging (MRI) is indicated when initial x-rays are normal but there is persistent pain. MRI is the investigation of choice, being more sensitive than bone scans in the first 24 hours. It is of similar accuracy to bone scans in fracture assessment at 72 hours.

Stress fractures and Garden I impacted fractures are considered stable and may be treated conservatively under close orthopaedic supervision. Garden II fractures, although non-displaced, are inherently unstable and must be fixed internally.

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