Hip fracture

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"We come into the world under the brim of the pelvis and go out through the neck of the femur"

Until the middle of this century a fractured neck of femur would inevitably lead to the death of the sufferer. With the discovery of penicillin, surgery on the hip became possible and hip replacements began. Today approximately 50,000 people in the UK have hip replacement every year.

Femoral neck fracture is most common in people in their 80's where it is usually associated with osteoporosis. The fracture often results from a low impact accident such as a minor fall. In younger people femoral neck fracture is usually due to a major trauma, such as a car crash.

Case study of femoral neck fracture and hip replacement

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Terminology




Vascular Anatomy

Vascular anatomy of the head of femurThe arterial supply of the hip joint, especially that of the head and neck of femur is of particular clinical importance. The degree of damage to the blood supply, and thus fracture treatment, is greatly affected by the exact site and the severity of the fracture.

Fracture severity

Fracture healing is dependant on blood supply. In parts of the femur outside the hip capsule (extracapsular), blood is normally conveyed through both the endosteum and the periosteum. In the event of an extracapsular fracture the bone depends on the periosteum for the maintenance of blood supply and the formation of a callus.

Intracapsular blood supply is normally conveyed entirely through the endosteum, because there is essentially no periosteum. This lack of periosteum means that intracapsular fracture healing can be slow and difficult because it depends on the union of the endosteum (endosteal union) which is by definition disrupted by a fracture. A severe fracture will leave little endosteal union and this reduces the likely success of healing.

Fracture site

The major supply of blood to a long bone is by it's nutrient artery, in the case of the femur this is a perforating branch of the profunda femoris. In the case of the upper end of the femur there is an intracapsular supply:

A major disruption to either of the main sources of intracapsular blood can lead to avascular necrosis.

Common fracture sitesThe fracture site is important to the treatment of hip fracture and the success of fracture healing. Shown here are the common fracture sites.


Sub-capital fracturePetrochanteric fracture
A sub-capital fracture severely compromises the blood supply to the head of the femur resulting in a high risk of avascular necrosis. The fracture would usually result in a replacement of the femoral head (hemiarthroplasty), leaving the natural acetabulum.A petrochanteric fracture only partially compromises the blood supply and has a good chance of healing. The fracture would usually be treated by internal fixation with screws.


Subcapital fracture; Garden's classification

Garden's classification of hip fracture scheme
Type I fractures have the best outcome. The bone ends are impacted into one another, which facilitates vascular re-growth. Type II fractures are not impacted and are thus less stabl. However there is minimal displacement of the bones from the anatomically normal position, and this is beneficial.
Type III fractures are complete but there is only partial displacement. Type IV fractures are complete with total displacement. The two ends of bone are completely separated.

Methods of fixation

Traditionally hip fractures were treated using traction, but this was associated with a very high mortality. Now hip fracture is commonly treated operatively, either by open reduction and internal fixation (dynamic hip screw), or by hip replacement (hemiarthroplasty). In some cases hip fracture is still treated by traction.

X-ray of dynamic hip screw in-situ Dynamic hip screw Fractures of type I & II are usually treated by internal fixation using a Dynamic hip screw.
x-ray of femoral head prothesis Femoral head prosthesis in femur Femoral head prosthesis In type III & IV fractures the degree of disruption results in an unacceptably high level of avascular necrosis and the femoral head should be replaced (hemiarthroplasty).
Complete hip replacementIf there is damage to the acetabulum the patient may require a Complete hip replacement.

Case study of femoral neck fracture and hip replacement

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Osteology

Head of the femur showing orientation of trabeculae Lines of trabeculae in the head of the femur

Forces as much as 6x body weight are transmitted across the hip. The bone remodels according to the forces applied (Wolff's law) and this is reflected in the trabecular pattern illustrated above. This is highly relevant to fracture mechanism and fixation.

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