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Author: Dr. Terance Lee
Editor: Dr, Suneet Sood
Narrators: Thong Yi Kun, Alan Koay

Transcript

Hi! Thank you for having me. Through today’s case, we will look back at a topic in basic anatomy and its clinical relevance. This case is particularly interesting because we have a patient who had undergone a surgical procedure in one region but later presented with a problem in a different anatomical region.

Wow, let us start and learn.

We have a 55-year-old man who underwent an abdominoperineal resection for the diagnosis of rectal carcinoma. Soon after the surgery, he reported weakness in his left foot and had difficulty walking. He described that he would ‘catch his toes’ whenever he walked.

Ok, so the patient had pelvic surgery and later had a problem with his foot. That seems unfortunate and unexpected. You’ve mention his toes will get ‘caught’, mind explaining more about this presentation?

He had what we usually call a foot drop. There is weakness in the muscles responsible for dorsiflexion. Patients compensate by lifting their feet higher than usual to prevent their toes from scraping the ground when walking. We call it a high steppage gait.

Upon examination, eversion of the foot was weak. Ankle plantarflexion and foot inversion was normal.

Did the patient have a nerve injury? Are we looking at a case of inadvertent nerve injury at the hip region perhaps due to the surgery?

You get it right for the first part. We are indeed exploring a case of peripheral neuropathy. The next step is to use our clinical skills to localize the site of lesion to answer your second question. A foot drop can be caused by injury anywhere in the peripheral nervous system. The entire nerve root can be affected, such as an L5 radiculopathy.  Or the sciatic nerve can be affected. Or the common fibular nerve at the leg.

If we look back at the examination findings, plantarflexion was normal. Radiculopathy or sciatic nerve injury will cause weakness to both dorsiflexion and plantarflexion. Thus, we are looking at a fibular nerve injury in this man because only dorsiflexion and eversion were affected. The fibular nerve, of course, is a branch of the sciatic. It comes out of the sciatic just above the knee.

So the cause is a lesion at the knee when the surgery is at the pelvic region. Please explain.

Firstly, the fibular nerve travels very superficially near the fibular head. As it is superficial slightly below the knee level, at this site it is more prone to injury.

It can be injured during knee surgery or during a fracture of the knee or the fibula.

That’s understandable. But how can surgery on the pelvis cause injury to the fibular nerve at the knee?

To explore this case, we should take a few steps back. If we stop focusing on the site of surgery but other factors such as – the positioning of the procedure, we may find the answer.

Ah, then I would have to understand how abdominoperineal resection is performed.

Abdominoperineal resection is a procedure to remove the anus, rectum and sigmoid colon. For this operation, the patient has to be placed in a lithotomy-Trendelenburg position. To adopt the lithotomy position, the patients’ legs are spread apart to gain access to the anal region – hips flexed and abducted while the knees were flexed and supported by stirrups. You can see this position in gynecological procedures, labour and of course, lithotomy, which is the removal of stones from bladder, urinary tract or kidney.

Here comes the solution for the puzzle, the culprit seems to be the stirrups! Stirrups are metal devices that support the legs at the knee level. Picture this –  patient was laid supine. The table was tilted, head down, so that the intestines would fall towards the diaphragm, and away from the site of the surgery. This is the Trendelenburg position. In this position, the metal stirrups press on the side of the knee, directly over the fibular nerve. If the procedure is long, and abdominoperineal resections take several hours, the nerve damage can be irreversible. Proper padding of the stirrup can prevent the problem.

Thank you Dr!

References

Marciniak C. Fibular (Peroneal) Neuropathy – Electrodiagnostic Features and Clinical Correlates. Phys Med Rehabil Clin N Am. 2013; 24: 121–137. Available from: https://depts.washington.edu/neurolog/images/emg-resources/Fibular_Peroneal_Neuropathy.pdf

Rutkove SB. Overview of lower extremity peripheral nerve syndromes [database on the Internet]. In: Shefner JM, Dashe JF, ed. Waltham, MA: UpToDate Inc; 2017 Aug 29 [cited 2017 Sep 1]. Available from: http://www.uptodate.com