Neuroma formation after above- or below-knee amputation is a common source of post-amputation pain, which has been successfully treated with surgical interventions and ultrasound-guided percutaneous injections of local anesthetic and steroids. Performing ultrasound-guided injections or cryoneurolysis of the sciatic nerve after above knee amputations can be challenging because the normal anatomic relationships may change once the distal insertions of muscles and nerves are severed.

We report here an additional potential challenge to understanding the anatomic relationships after above knee amputations that was observed while performing cryoneurolysis of the sciatic nerve for persistent post-amputation pain. Written consent for publication was obtained from the patient.

In this patient, the sciatic nerve was significantly retracted, presumably because a neuroma had formed. The nerve could not be identified for the first 10 cm proximal to the stump (Figure A). Scanning distally from the subgluteal view of the sciatic nerve confirmed that a neuroma had formed approximately 13 cm proximal to the stump (Figure B) resulting in retraction of the nerve and an empty nerve sheath distally. Anesthesiologists should be aware of this phenomenon when performing ultrasound-guided nerve blocks or other therapies on above-knee amputees. In such patients, nerve stimulation or scanning from a more proximal point where the anatomy can be clearly visualized should be considered (Figure C).

FIGURE
figure 1

A) Empty nerve sheath due to retraction of the sciatic nerve; B) Neuroma at the distal tip of the sciatic nerve; C) Subgluteal view of the sciatic nerve

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