Introduction

Subtrochanteric fractures are fractures that occur in a zone extending from the lesser trochanter to 5cm distal to the lesser trochanter, however extension into the intertrochanteric region is common. These fractures are more difficult to treat as compared to intertrochanteric fractures due to the powerful muscle forces acting on the fragments as well as the tremendous stress that is normally placed through this region. The proximal fragment is typically flexed, abducted, and externally rotated while the distal fragment is typically adducted. When seen in young patients, they are due to high energy trauma or pathologic fracture with 10% of high energy fractures due to gun shot wounds.. In the elderly, they are often related to osteoporosis. Fracture may also occur at the site of screw placement for a femoral neck fracture if the inferior screw is placed too low as this creates a cortical defect and stress riser.

Anatomy

Subtrochanteric fractures are fractures that occur in a zone extending from the lesser trochanter to 5cm distal to the lesser trochanter. The medial and posteriomedial cortices of the subtrochanteric femur experience the highest compressive stresses in the body. The lateral cortex is under a high degree of tensile stress. These fractures occur at the cortico-cancellous junction. The high composition of cortical bone and subsequently the decreased vascularity impairs the capacity for healing of these fractures when compared to the abundant cancellous bone of the intertrochanteric region of the hip.

The proximal fragment is usually flexed and externally rotated by the pull of the iliopsoas and short external rotators, and abducted by the pull of the gluteus medius and minimus. The distal fragment is adducted and shortened by the pull of the adductors leading to a varus and procurvatum fracture alignment. These factors should be considered when attempting reduction.

Classification

Fielding Classification - This is an anatomic classification based on location of the fracture and is rarely used
Type I - at level of lesser trochanter
Type II - <2.5 cm below lesser trochanter
Type III - 2.5-5cm below lesser trochanter

Seinsheimer Classification - This system incorporates factors affecting stability and offers management guidelines.
Type I - nondisplaced
Type II - two part fractures
Subtypes based on fracture pattern and displacement
Type III - three part spiral fracture
Subtypes based on type of fracture fragments
Type IV - comminuted
Type V - intertrochanteric extension

Russell- Taylor Classification - This classification is based on integrity of the piriformis fossa. It was designed to guide treatment of intramedullary nails using a piriformis fossa starting point.
Type I - intact piriformis fossa
A - lesser trochanter attached to proximal fragment
B - lesser trochanter detached from proximal fragment
Type II - fracture extends into piriformis fossa
A - stable posterior-medial buttress
B - comminution of lesser trochanter
Orthopaedic Trauma Association Classification - Based on degree of comminution and mainly used for research purposes.

Presentation

Patients typically present in significant pain unable to ambulate with deformity of the proximal thigh. High energy mechanisms should receive a full trauma evaluation and careful inspection for open fracture. A detailed neurovascular exam of the extremity should be performed. Due to the size of the thigh compartment, hypovolemic shock is possible secondary to this fracture.

Diagnosis

For all hip fractures, an AP pelvis, internal rotation AP and cross-table lateral of the affected hip should be obtained. An MRI may also be required for pathologic fractures to evaluate the proximal femur for soft tissue extension of an underlying bone tumor.

Treatment

Initially, the limb should be stabilized with Hare traction, Buck's traction or skeletal traction. If there will likely be a delay in surgical stabilization, femoral or tibial skeletal traction should likely be employed.

Nonoperative treatment in 90-90 skeletal traction followed by hip spica casting should only be employed in those whom surgery is deemed very high risk. 90-90 traction attempts to counteract the deforming muscular forces. Traction usually is required for 12-16 weeks.

Surgical stabilization is the standard of care. The treatment option include:

Intramedullary Nail
Intramedullay fixation is the preferred treatment. First generation interlocking nails (centromedullary) are indicated when both trochanters are intact as the oblique locking screw is able to obtain adequate purchase. Second generation interlocking nails with a locking screw that extends into the femoral neck (cephalomedullary) offer more stable fixation and are indicated when the lesser trochanter is displaced or comminuted. Advantages of intramedullary fixation include 1) Potential for closed treatment with preservation of fracture hematoma and blood supply to fracture fragments, 2) Decreased the moment arm on the implant compared to a lateral plate and thus decreases the tensile stress on the implant, 3) Reaming the canal in preparation of the implant provides internal bone graft, 4) intramedullary inmplants have been found to be twice as strong as traditional extramedullary implants. Disadvantages include 1) the implant cannot be used to help facilitate reduction and the fracture site may need to be opened to affect a reduction and guide pin insertion, thus lessening benefits of closed intramedullary fixation.  It is nonetheless critical to achieve reduction and to maintain this reduction (using instruments, an incision or both as needed) while the nail is being placed.  Failure to do so will result in varus displacement during implantation.  Obtainment of proper nail starting point can be eased by lateral/lazy lateral patient positioning or the use of a trochanteric starting nail.  If a trochanteric nail is chosen, it is imperative that a very medial starting point is chosen, again to avoid varus deformity.

Ninety-Five degree Fixed angled devices
Historically this was the most common device used for operative fixation. This is a fixed angle construct which provides rigid fixation. Advantages include 1) Offers a treatment option for fractures with comminution of the trochanters that may make intramedullary implant insertion difficult, 2) Provides for multiple points of proximal fixation. Disadvantages include 1) Technically very demanding, 2) Extensive soft-tissue dissection, 3) High risk of implant failure due to tremendous stress applied to the plate laterally.

Sliding hip Screw
This device is indicated only for very proximal fractures. The sliding of the screw allows medialization of the distal fragment which reduces bending moment on fracture and implant. The sliding mechanism must cross the fracture site to lessen the risk of implant failure and the posteromedial cortex must be reconstructed to decrease the stress on the device.

Complications

Nonunion. Usually located in the cortical portion of the fracture and presents with continued inability to bear weight and continued pain.  An important predictor of nonunion accompanied by implant failure is  a varus malreduction.

Malunion, especially varus and rotational maluion after inadequate reduction and placement of an intramedullary device.

Leg length discrepancy is a concern in comminuted or segmental fracture. Radiographs of the ipsilateral leg made aide in planning and reduction.

Fixation failure

Red Flags and controversies

Plate vs. intramedullary fixation.

Role of locked plating and navigation.

Fracture may also occur at the site of screw placement for a femoral neck fracture if the inferior screw is placed too low as this creates a cortical defect and stress riser.

Outcomes

Currently, most subtrochanteric fractures in which the piroformis fossa or greater trochanter are intact can be successfully treated with an cephalomedullary device. Care must be taken to avoid varus during placement of the device. Comminuted subtrochanteric fractures may be treated with an long intramedullary device or a fixed angled plate. Sliding hip screws should generally be avoided as they have higher failure rates.

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