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Fixing Hip Fractures

by Simon Mears, M.D.


Hip fractures are a common injury in the United States; approximately 280,000 occurred in 1998. The number of annual hip fractures has been projected to surpass 500,000 annually by the year 2040. The fracture of a hip can lead to morbidity, a change in living arrangements, or death. One-year mortality rates of 12% to 36% have been reported. Approximately 22% of patients require an increased level of care 1 year after hip fracture. Consequently, hip fractures are feared by the elderly.

Osteoporosis is characterized by a brittle skeleton resulting from decreased bone mass.

The predominant mechanism of hip fracture in the elderly population is a fall from a standing position People with osteoporosis often have other comorbidities that lead to an increased rate of falling. The elderly are also more likely than the general population to experience the type of fall that results in a hip fracture. People with a slower gait have less forward momentum. Thus, when these people fall, they tend to buckle and fall to the side, making a fracture is more likely. The decrease in bone mass in the elderly is caused by a number of factors, including: reduced biosynthetic and replicative potential of osteoblasts, increased osteoclast activity, reduced physical activity (a stimulus for bone remodeling), genetic predisposition, decreased calcium intake, and hormonal influences. The net result is that bone resorption outpaces bone building. Postmenopausal women are especially at risk because of estrogen deficiency. Women can lose as much as 35% of their cortical bone and 50% of their trabecular bone in the 30 to 40 years after menopause.

To maintain strength, cortical bone increases in diameter, but the thickness of the cortex itself decreases.
cortical bone
A larger diameter increases the strength of a bone but makes the bone vulnerable to rotational and bending forces. Loss of trabecular bone, which arises normally along lines of stress, also decreases the strength of the bone. Certain people are susceptible to particular patterns of injury. Of people who sustain a second, contralateral hip fracture, 90% experience the same pattern of injury. This finding indicates that the microtrabecular architecture must be important.

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Methods of Hip Fracture Confirmation
In the elderly, hip pain is usually indicative of a fracture. Pain resulting from a fracture usually presents as onset of groin or upper thigh pain. Depending on the severity of the injury, the patient may or may not be able to walk. Regardless, one must rule out a hip fracture, a pelvis fracture, a spine injury, spinal stenosis, trochanteric bursitis, muscle tears, and knee injuries. The anteroposterior (AP) pelvis view allows the affected and contralateral hips to be compared. The view of the unaffected hip can be used for preoperative planning. A cross-table lateral radiograph should also be obtained by flexing the unaffected hip and knee and pointing the x-ray beam at the groin of the affected side. This view places the beam at a right angle to the femoral neck without manipulation of the affected side and reveals any posterior comminution of the femur.

An AP radiograph should be obtained of the affected hip with the leg in internal rotation (see below). In this view, the lesser trochanter should be only partially visible. The internal rotation view will position the entire neck to best visualize fracture lines.
AP radiograph with leg in internal rotation
Because plain radiographs may appear normal or inconclusive, other imaging studies must be considered.Magnetic resonance imaging (MRI) scans are the most sensitive for the evaluation of fractures, particularly occult or nondisplaced fractures. MRI scans can be used immediately after injury and can reveal soft-tissue pathology, such as muscle strains, greater trochanteric bursitis, and pelvic fractures.

fracture lines
 Fracture lines immediately after injury.

edema in soft tissuew
 Edema in the soft tissues

Radionuclide bone scans that may be used 48 to 72 hours after the injury, are sensitive for metastatic disease. Bones scans are valuable for patients who cannot get an MRI scan.
Radionuclide bone scans

CT scans reveal fractures only when they are displaced.  CT scans are useful for detecting fracture nonunion in the presence of hardware.
CT scan of fracture

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Classification of Hip Fractures
There are three broad categories of hip fractures based on the location of the fracture: femoral neck fractures, intertrochanteric fractures, and subtrochanteric fractures.

Femoral Neck Fractures
The femoral neck is the most common location for a hip fracture, accounting for 45% to 53% of hip fractures.  Per 100,000 person years, approximately 27.7 femoral neck fractures occur in men and 63.3 occur in women.  The femoral neck is the region of the femur bounded by the femoral head proximally and the greater and lesser trochanters distally (shown below).  A femoral neck fracture is intracapsular, that is within the hip joint and beneath the fibrous joint capsule.
femoral neck fracture

Although other, more detailed classification systems exist, in general fractures are classified as stable and unstable. Each category has different operative management options.

Treatment of Stable Fractures
Stable fractures are nondisplaced, exhibiting no deformity, or impacted in a valgus positions.  Stable fractures may not be detectable on plain radiographs, and MRI scanning may be required.
stable fracture on radiograph and mri
Because nonoperative management results in a secondary displacement rate of 40%, stable femoral neck fractures are generally best treated with surgical stabilization and immediate mobilization. Treatment is by operative pinning with three parallel cannulated screws placed adjacent to the femoral neck cortex. 
pinning using parallel cannulated screws

Treatment of Unstable Fractures
Unstable femoral neck fractures are displaced and can be seen on plain radiographs. 
Unstable femoral neck fractures
On physical examination, the leg of the affected side is externally rotated and shortened; the degree of rotation and shortening varies with the degree of displacement. Displaced fractures in young patients are usually treated with pinning. Pining is chosen because the risks of arthroplasty, including prosthetic wear and loosening, are high for young patients, and their rate of healing is high due to the absence of osteoporosis. As age and osteoporosis increase, the rate of failure (nonunion, secondary displacement, avascular necrosis) increases.

Hemi- or total joint arthroplasty is associated with a lower rate of repeat surgery than internal fixation and is often the better option for older patients. Younger patients may opt for screw fixation and hip salvage. In hemiarthroplasty, the acetabular cartilage is left intact and the implant articulates with the acetabulum.
Hemiarthroplasty requires less surgery than a total joint replacement because the acetabulum is not resurfaced. There is a smaller risk of dislocation with hemiarthoplasty because it uses a much bigger head size than total hip arthroplasty. In more active patients, hemiarthroplasty also has a risk of acetabular cartilage wear and revision to total hip arthroplasty.

Femoral implants can be cemented or cementless, and there are many designs of each type. Implant fixation can be achieved by the injection of bone cement around the prosthesis or by bony ingrowth into the prosthesis. A bipolar implant has two heads so that motion can occur between one head and the acetabular cartilage and between the two heads.
bipolar implant
In theory, this arrangement helps to reduce acetabular wear and provide increased motion. A unipolar implant has only one large head that articulates with the acetabular cartilage.

There appears to be no clinical difference between the outcomes of patients with bipolar or unipolar implants in terms of acetabular wear and hip motion. Compared with unipolar implants, bipolar implants are more expensive and have an additional interface for prosthetic wear. Thus, there appears to be no compelling reason to recommend the more expensive bipolar implant over the unipolar for the elderly patient with a hip fracture. If the stem is not well fixed in the proximal femur, either type will fail quickly.

Total joint replacement typically is performed on an active patient or one with preexisting arthritis. During a total joint replacement, the acetabulum is resurfaced and a metal cup with a polyethylene liner is fixed inside. Articulation at the hip takes place between the implant’s head and the polyethylene liner.
metal cup with polyethylene liner
The decision to treat femoral neck fractures with pinning or with arthroplasty is controversial. The advantages of pinning include less invasive surgery, less blood loss, and less postoperative morbidity. However, treatment by pinning carries a higher risk of more surgery in the future. As implied, arthroplasty results in more acute postoperative morbidity, but it offers fewer reoperations for nonunion, hardware failure, and osteonecrosis.

My protocol divides patients into three categories: patients with nondisplaced fractures, “low” activity patients with displaced fractures, and “high” activity patients with displaced fractures. Nondisplaced fractures are treated with pinning. Displaced fractures in inactive patients are treated with unipolar hemiarthroplasty. Displaced fractures in highly active patients are treated with total hip replacement.

Treatment Failures
The failures of screw treatment are nonunion and late avascular necrosis. Nonunion results primarily from a failure to achieve adequate mechanical stabilization of the fracture. If the bone does not heal, the screws will slide and backout as the fracture collapses.
avascular necrosis
Nonunion typically presents with worsening groin or buttock pain. Late avascular necrosis results from insult to the blood vessels that supply the femoral neck and head. Radiographic monitoring up to 3 years should detect most cases of avascular necrosis. The treatment for avascular necrosis or nonunion is hip replacement.

Failure of a hemiarthroplasty results in pain and acetabular erosion. Other complications include dislocation, fracture, and infection. The treatment for a failed hemiarthroplasty is conversion to a total hip replacement.

The failures of a total hip replacement are similar to those of a hemiarthroplasty: loosening, implant wear, infection, fracture, and dislocation. Treatment for a failed total hip replacement is a revision arthroplasty.
revision arthroplasty

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Intertrochanteric Fractures
Intertrochanteric fractures are breaks of the femur between the greater and the lesser trochanters.  They are extracapsular fractures that is, outside the hip joint’s fibrous capsule.
intertrochanteric fracture

The epidemiology of intertrochanteric fractures is similar to that of femoral neck fractures.  Per 100,000 person years, intertrochanteric breaks occur in 34 men and 63 women.  Intertrochanteric fractures account for approximately 38% to 50% of all hip fractures.

Many systems of classification, such as the Evans system, have been used to describe intertrochanteric hip fractures. However, most systems lack reliability and, in general, intertrochanteric fractures can be divided into two categories: stable and unstable. Stable fractures are those in which the femur is broken into two or three parts. Unstable fractures are those in which the femur is broken into four parts or the fracture is of the reverse oblique pattern. Reverse oblique fractures are unstable because of the femur’s tendency to displace medially. This classification method aids in determining what method will be used for fixation.

Two-part fractures have one fracture line through the intertrochanteric area.
iwo-part fracture
While assessing the stability of a fracture, the most important points to consider are the bone of the lateral buttress and greater trochanter and the bone on the medial side of the proximal femur called the calcar.

Treatment of Stable Fractures
If the fracture is stable, treatment is with a sliding hip screw coupled to a side plate that is screwed onto the femoral shaft. (shown below)  The screw provides proximal fragment fixation.  It is set inside a telescoping barrel that allows impaction of the bone, which promotes fracture union.  The lateral buttress must be intact so that the screw will not stop sliding.
sliding hip screw

A four-part fracture has several fracture lines. The fractured bone pieces include: 1) the femoral head, 2) the lesser trochanter, 3) the greater trochanter, and 4) the remaining femur. Fractures with multiple pieces and fracture lines are termed ”comminuted”. The more pieces, the less stable is the fracture pattern. Comminution may make fixation with a sliding hip screw and side plate more likely to fail.

Treatment of Unstable Fractures
Approximately 5% of fractures are extremely unstable, and the direction of the fracture is parallel to the femoral neck. This fracture type is called the reverse oblique pattern. A high rate of failure occurs if the fracture is treated with a sliding hip screw and a side plate. Because of the angle of the fracture, there is no bone laterally to stop the screw from sliding.
sliding hip screw and side plate

For unstable intertrochanteric fractures, including those of the reverse oblique pattern and those with subtrochanteric extension, an intramedullary hip screw is indicated. This device combines a sliding hip screw with an intramedullary nail. There are many proprietary varieties, including the Gamma Nail (Stryker, Mahwah, NJ), the Trigen Trochanteric Entry Nail, (TAN nail, Smith and Nephew, Memphis TN) , and the Proximal Femoral Nail (Synthes, West Chester, PA). Intramedullary hip screws can be placed through small incisions, and blood loss may be less than with a hip screw and side plate. The nail acts as a metal buttress to prevent sliding and provides better fixation in unstable fracture patterns. No differences have been found between the two devices in stable fractures.

With a short intramedullary hip screw, the nail does not extend down the full shaft of the femur. Cross-locking of the nail is through a jig, which prevents rotation of the nail within the femur. Short intramedullary hip screws can create a stress riser in the bone at the distal screw.
short intramedullalry hip screw

With a long intramedullary hip screw, cross locking cannot be done with a jig and must be done freehand under fluoroscopy.  Therefore, cross-locking is more difficult. The nail extends throughout the shaft, protecting the rest of the bone from future fracture.
long intramedullary hip screw

The hip screw should be placed centrally within the femoral head in the strong subcortical bone. Evaluation of hip screw placement is made by determining the tip-apex distance under fluoroscopy. The tip-apex distance is the sum of the distances from the tip of the hip screw to the apex of the femoral head as measured on AP and lateral radiographs
screw placement
Baumgaertner et al. showed that no fracture had loss of fixation secondary to screw cut-out when the tip-apex distance was less than 24 mm.  When the tip-apex distance was greater than 45 mm, the screw cut-out rate increased to 60%.

Failure mechanisms of a hip screw include nonunion, screw cut-out, nail breakage, malunion, and limp.  Although sliding of the hip screw allows for bone compression and hopeful healing, it makes the limb shorten and causes abduction weakness.  Most complications are treated with total hip arthroplasty.

Subtrochanteric Fractures
Subtrochanteric fractures are located between the lesser trochanter and the femoral isthmus that is, in the proximal part of the femoral shaft.
subtrochanteric fracture
They are less common than femoral neck and intertrochanteric fractures, accounting for approximately 5% to 15 % of hip fractures.  Subtrochanteric fractures are less stable than the other two types of hip fractures and, consequently, more difficult to fix.

A subtrochanteric fracture is treated with an intramedullary hip screw.
intramedullary hip screw
No lateral buttress exists in a subtrochanteric fracture and, therefore, sliding hip screws with side plates provide poor fixation. After surgery for a hip fracture, weightbearing should be allowed as tolerated. It has been shown that patients with less stable fracture patterns protect themselves by self-restricting weightbearing and movement.

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In summary, the type of fracture determines the type of surgery. Patients with femoral neck fractures are treated with pinning or hip arthoplasty, depending on the age of the patient and the presence and degree of displacement. Patients with intertrochanteric fractures are treated with a sliding hip screw or an intramedullary hip screw, depending on the stability and location of the fracture.

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