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Conditions of the Thigh Quiz

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In a femoral shaft fracture, which pattern of displacement is most likely, given the normal muscle attachments on the femur?

A The proximal fragment is internally rotated and extended, while the distal fragment is flexed
B Both proximal and distal fragments are flexed and abducted
C Both proximal and distal fragments are extended and adducted
D The proximal fragment is abducted and flexed, while the distal fragment is adducted and extended ✓
E The proximal fragment is adducted and extended, while the distal fragment is abducted and flexed

The answer is D: The proximal fragment is abducted and flexed, while the distal fragment is adducted and extended

Explanation

Why D is correct

See Femoral shaft fracture. Option D is correct. The femur is a very strong bone in young adults, so breaking the shaft needs a high-velocity injury such as a road traffic collision. Once the bone is broken, the muscles attached to each fragment pull it in their own direction. The proximal fragment (the upper part, nearer the hip) is pulled into abduction (away from the midline) and flexion by gluteus medius, gluteus minimus and iliopsoas (the muscle that flexes the hip). The distal fragment (the lower part) is pulled into adduction (towards the midline) by the adductor muscles and into extension by gastrocnemius (the calf muscle, which attaches just above the knee). This gives a varus deformity of the lower fragment, meaning it angles inwards. The thigh is often massively swollen from bleeding, and a lot of blood can be lost even without an open wound. In adults most shaft fractures are fixed surgically, commonly with an intramedullary nail.

Cause: breaking the femoral shaft needs a high-velocity injury such as a road traffic collision.
Upper fragment: pulled into abduction and flexion by gluteus medius, gluteus minimus and iliopsoas.
Lower fragment: pulled into adduction and extension by the adductors and gastrocnemius.

Why the other options are incorrect

A. The proximal fragment is internally rotated and extended, while the distal fragment is flexed: This pattern of internal rotation and extension of the upper fragment does not match the muscles attached to it. The upper fragment is pulled into abduction and flexion, not internal rotation and extension.
B. Both proximal and distal fragments are flexed and abducted: Both fragments cannot be pulled in the same direction, because the muscles attached to each are different. The lower fragment is pulled by the adductors, so it is not flexed and abducted.
C. Both proximal and distal fragments are extended and adducted: Extension and adduction of both fragments ignores the abductors and hip flexor that act on the upper fragment. The upper fragment is pulled into abduction and flexion.
E. The proximal fragment is adducted and extended, while the distal fragment is abducted and flexed: This reverses the real muscle pull, putting the abductor and flexor muscles on the wrong fragment. Gluteus medius, gluteus minimus and iliopsoas are attached above the fracture, not below it.

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1
Which nerve is compressed in meralgia paraesthetica?
2
A 78-year-old woman falls from standing height and has severe pain and swelling over the distal thigh. Examination suggests a displaced distal femoral fracture. Which associated complication must be specifically assessed for early because of its anatomical relationship to the distal femur?

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