Femoral neck fracture, a common feature

Femoral neck fractures are a common feature of particular populations of people with specific problems. Fractures of the neck of the femur are common in post-menopausal women and are secondary to a decrease in bone density. They are less common as stress fractures in people who put significantly increased forces on their hips such as runners and military personnel who are much younger and fitter.

These fractures can also occur at almost any age by a direct fall on the hip with great force or if there are pathological changes in the bone such as tumours. The circulatory anatomy of the femoral head and neck have long convinced specialists in orthopaedics that it is vital to restore the bony alignment of the fragments to avoid the risk of avascular necrosis (AVN) in the head of the femur. A fracture can cause loss of the blood supply in the femoral head, allowing it to die and collapse which causes significant problems and requires operation. Keeping patients immobilised in a hip plaster spica was used initially until Smith-Petersen developed a more predictable internal fixation in the 1930s.

The Richards Screw Plate uses compression applied to the fracture site by a sliding fixation technique. Compressive and shear stresses pass across the femoral necks when we do normal things such as walk but they can be greatly increased by involvement in sports such as jumping, high athletic performance and jogging. The bodyweight can be amplified five or six times across the hip in fairly standard activities such as stair climbing, let alone sport. The groin, the lateral hip and the anterior thigh are the typical areas of presentation of hip related pain from many pathological changes as well as stress fractures, which may worsen to complete fractures with or without displacement with its risks and complications.

Normal bones can resist normal mechanical stresses and if the stresses reach abnormal levels then the structural supports in bone can fail, presenting as a stress fracture. On the other hand, if bone is altered by hormonal insufficiency or other pathological conditions it will be unable to resist even normal stresses and so will fail. Hormonal levels of oestrogen keeps bone turnover and rebuilding at normal levels and bone can become more brittle with a drop in concentrations of the hormone. Post menopause women and highly trained women can both suffer this problem.

A specialist will consider stress fracture in the differential diagnosis of an athlete who, after an increase in training, presents with a new hip pain problem. The pain is generally worse with the sport and better with resting. Bone scanning is a more sensitive investigation than x-rays in this case. The vast majority of these fractures occur in elderly persons who fall or twist, fracturing the femoral neck. Diagnosis is established by noting an inability to stand on the leg, a laterally rotated leg, a shortened limb and pain in the side of the hip and the groin.

Displacement of transverse femoral neck fractures occurs in ten to fifteen percent of cases and avascular necrosis is a risk in these injuries. Operative management is the necessary option and the choice of the technique depends on the fracture. Fractures occur in many positions anatomically and are grouped into categories, with fractures just below the head carrying the highest risk of circulatory disturbance. These are managed either by Thompson hemi-arthroplasty or by total hip replacement. Fractures in the neck can be internally fixed.

It is common for femoral neck fractures to be undisplaced and compacted, in other words the fragments have been compressed together and are stable under load. This makes conservative rather than surgical management more appropriate. Other fractures are mechanically unstable because they are under tension of the fragments to separate and displace, needing surgical fixation with one of many devices for upper femoral fixation. Trochanteric, sub-trochanteric and lower neck fractures can come more commonly into this category.

Once the fracture is replaced or fixed the patient is allowed 24 hours to recover medically then the physiotherapist and an assistant will check the operative instructions, review the patient's observations and get the patient up weight bearing with a frame or crutches.