CASE        35   Predictors of fixation failure

 

A 65-year-old male was struck by a car at low speed while crossing the street. Upon evaluation in the trauma bay he was found to have pain in his left hip with painful range of motion about his hip. He had strong, symmetric, palpable dorsalis pedis and posterior tibialis pulses and had full sensation in all dermatomal distributions in his bilateral lower extremities. His AP and lateral radiographs of his hip are shown in Figure 6–36A and B.

 

 

Figure 6–36 A–B

 

What is the most indicative sign of stability of this fracture nondisplaced intertrochanteric femur fracture seen in Figure 6–36A and B?

1. Intact posteriomedial cortex

2. Degree of metadiaphyseal comminution

3. No subtrochanteric extension of fracture

4. Displacement of greater trochanter less than 5 mm

5. Reverse obliquity fracture pattern

 

Discussion

The correct answer is (B). This patient sustained an intertrochanteric femur fracture. When evaluating these fractures it is paramount that the posterior medial cortex be examined in order to determine fracture stability as this impacts implant choice and fixation options, as does the presence of an intact lateral wall. An intact posterior medial cortex allows for resistance of compressive loads and resistance of varus collapse postoperatively. Unstable patterns include those fractures with reverse obliquity, comminuted posterior medial cortex, comminuted lateral wall, subtrochanteric extension, and displacement of the lesser trochanter. Stable fracture patterns allow the use of a sliding hip screw or cephalomedullary nail. However, unstable fractures preclude the use of a sliding hip screw due to high failure rates and collapse into varus and retroversion.

What fracture pattern presents an increased risk of intraoperative malreduction due to flexion of the proximal fragment when using a dynamic hip screw?

1. Right-sided reverse oblique fracture

2. Left-sided unstable intertrochanteric femur fracture

3. Right-sided subtrochanteric femur fracture

4. Left-sided basicervical femoral neck fracture

5. All intertrochanteric fractures

 

Discussion

The correct answer is (B). Left-sided, unstable intertrochanteric femur fractures are at increased risk of malreduction interoperatively while placing the dynamic hip screw due to the rotational torque imparted on the fracture when positioning the implant. This causes clockwise rotation and proximal segment flexion due to the overall decrease in fracture stability. Right-sided fractures do not exhibit this phenomenon because this rotational torque is converted into a compressive force. A second antirotational screw can be placed prior to the compressive dynamic screw in order to assist with decreasing the incidence of malreduction when placing the dynamic hip screw.

When placing a dynamic hip screw, what is predictive of screw pullout postoperatively?

1. Degree of peri-implant stability

2. Associated femoral head fracture

3. Age greater than 65

4. Tip-apex distance

5. Use of an additional (antirotation) screw

 

Discussion

The correct answer is (D). The tip-apex distance (TAD) is the summation of the distance between the femoral head and the tip of the screw (Fig. 6–37). It has been shown to be predictive of screw cutout. The other factors listed above likely contribute to screw cutout but have not yet been proven. A TAD >25 mm is indicative of increased screw pullout.

 

 

 

Figure 6–37 (Illustrated by David Beavers.)

 

Objectives: Did you learn...?

 

 

Radiographic indicators of stability? Predictors of fixation failure?

 

Risks for malreduction?