case 29 subtrochanteric femur fractures

An 84-year-old female presents to her family practice physician with thigh pain for the past 3 months. On further discussion with her in clinic, she states that she has had pain in her thigh for approximately 3 months. She attributes this to beginning a new walking regimen in order to lose weight. Her medical history includes: significant osteoporosis (treated with alendronate for the past 8 years), hypertension, hyperlipidemia, and diabetes. She denies any history of trauma and only an upper respiratory infection approximately 2 weeks prior. Her last T score was −1.8. Radiographs reveal subtrochanteric sclerosis or cortical thickening as shown in Figure 6–39.

 

 

 

 

Figure 6–39

 

What is her most likely diagnosis?

1. Osteomyelitis

2. Insufficiency fracture

3. Osteomyelitis

4. Renal osteodystrophy

5. Stress reaction

 

Discussion

The correct answer is (E). This patient’s clinical history and radiographs are consistent with a bisphosphonate-related fracture of her subtrochanteric region. This a relatively uncommon side effect of prolonged bisphosphonate use. The typical history consists of prolonged bisphosphonate use greater than 5 years, insidious onset of pain, and no trauma. Radiographs often display lateral cortical thickening progressing to a transverse fracture line with medial spike.

What is the mechanism of action of alendronate?

1. Farnesyl pyrophosphate inhibition

2. Formation of inappropriate ATP analogue

3. RANK ligand inhibition

4. Adenyl cyclase activation

5. Increased renal absorption of vitamin D

 

Discussion

The correct answer is (A). Nitrogen-containing bisphosphonates, such as alendronate, risedronate, zolendranate, and ibandronate, decrease osteoclast function via inhibition of the cholesterol pathway via farnesyl pyrophosphate synthase and GTPase prenylation. Formation of a toxic ATP analogue is the mechanism of action of non–nitrogen-containing bisphosphonates such as clodronate and etidronate. RANK ligand inhibitors, such as denosumab, inhibit RANKL binding to RANK via monoclonal Ig2. Parathyroid hormone analogues, such as teriparatide injections, given daily, increase bone density by increasing coupled bone remodeling.

The patient discontinues bisphosphonate use; however, 1 week later the patient presents to the emergency department with severe pain in her left thigh and inability to bear weight. Radiographs display a transverse fracture line with a medial cortical spike (Fig. 6–40).

 

 

 

Figure 6–40

 

What is the appropriate treatment for this fracture?

1. Short intramedullary nail

2. Long intramedullary nail

3. Dynamic hip screw

4. External fixator application

5. Tension band

 

Discussion

The correct answer is (B). The use of a long intramedullary nail would be most appropriate for this fracture type. Subtrochanteric fractures are defined as fractures occurring within 5 cm of the lesser trochanter. The use of a short intramedullary nail in this region would be inappropriate due to the location of the distal interlocking screw. The use of a dynamic hip screw in this fracture would be inappropriate due to the high rate of nonunion and fixation failure. Use of a fixed-angle blade plate is possible, however, this can be associated with increased

morbidity as weight bearing commonly must be restricted in the postoperative period.

How should the proximal fragment be manipulated to assist in reducing this fracture?

1. Adduction, internal rotation, and extension

2. Abduction, internal rotation, and extension

3. Adduction, external rotation, and flexion

4. Abduction, external rotation, and extension

5. Adduction, internal rotation, and flexion

 

Discussion

The correct answer is (A). The typical deformity associated with subtrochanteric femur fractures is flexion, abduction, and external rotation due to the pull of the iliopsoas, gluteus, and short external rotators. Consequently, internal rotation, extension, and adduction of the proximal fragment will help obtain the appropriate reduction. Lateral positioning can aid in fracture reduction by making it easier to bring the distal segment to the flexed proximal segment.

 

Objectives: Did you learn...?

 

 

Mechanism and complications of common osteoporosis treatments? Treatment of subtrochanteric femur fractures?

 

Common reduction technique for subtrochanteric femur fractures?