by Simon Mears, M.D.
- Methods of Hip Fracture Confirmation
- Classification of Hip Fractures
Osteoporosis is characterized by a brittle skeleton resulting from decreased bone mass.
To maintain strength, cortical bone increases in diameter, but the thickness of the cortex itself decreases.
Methods of Hip Fracture Confirmation
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.
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.
CT scans reveal fractures only when they are displaced. CT scans are useful for detecting fracture nonunion in the presence of hardware.
Classification of Hip Fractures
Femoral Neck Fractures
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
Treatment of Unstable Fractures
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.
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.
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.
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.
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.
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.
Treatment of Stable Fractures
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
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.
With a long intramedullary hip screw, cross locking cannot be done with a jig and must be done freehand under fluoroscopy. Therfore, cross-locking is more difficult. The nail extends throughout the shaft, protecting the rest of the bone from future fracture.
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
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.
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