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AC150 | AC152 | MCQ-Complications | Finals Black Bank



AC151 [Jul06] [Apr07]

Which of the following contributes the LEAST to motor neuropathy following the lithotomy position?

A. Smoking
B. Diabetes mellitus
C. Elderly
D. BMI >25
E. Peripheral vascular disease

AC151 ANZCA Version [Jul06] Q112, [Apr07]

Which of the following contributes the LEAST to motor neuropathy following the lithotomy 

A. age
B. BMI (body mass index) >25
C. diabetes
D. peripheral vascular disease
E. smoking

Worked answer

AC151 [Jul06] [Apr07]

Which of the following contributes the LEAST to motor neuropathy following the lithotomy position?

  • A. Smoking - true, but incorrect answer: "Other patient-related univariate risk factors for motor neuropathy included increasing age, a history of smoking within 1 month of the procedure, and preexisting diabetes or vascular disease" (Warner, et al., Lower-extremity Motor Neuropathy Associated with Surgery Performed on Patients in a Lithotomy position in Anesthesiology 81:6-12, 1984)
  • B. Diabetes mellitus - true but incorrect answer: See A
  • C. Elderly - true but incorrect answer: See A
  • D. BMI >25 - correct answer: "Of the patient-related characteristics, low BMI was a powerful univariate risk factor for motor neuropathy" (Warner, et al., Lower-extremity Motor Neuropathy Associated with Surgery Performed on Patients in a Lithotomy position in Anesthesiology 81:6-12, 1984) Perhaps this is due to less self-padding?
  • E. Peripheral vascular disease - true but incorrect answer: See A

AC151 ANZCA Version [Jul06] Q112, [Apr07] Which of the following contributes the LEAST to motor neuropathy following the lithotomy position?

  • A. age - false
  • B. BMI (body mass index) >25 - correct answer
  • C. diabetes - false
  • D. peripheral vascular disease - false
  • E. smoking - false


All below is looking for the strongest risk factor. The question asks about which factor contributes LEAST!!! Answer B (ANZCA Version). Michael

From Morgan and Mikhail 4th Ed, p963[1]. Risk factors for lower extremity neuropathies, especially peroneal:

  • Surgical Factors
  • Improper lithotomy position
  • Extreme high lithotomy position
  • Prolonged maintenance of lithotomy (>2 hours)
  • Patient Factors
  • Hypotension
  • Thin body habitus
  • Old age
  • History of vascular diseasae
  • Diabetes
  • Smoking

--Anaestheasy Tiger 21:50, 25 Jun 2009 (EDT)

Question asks about a motor neuropathy following lithotomy (I'm assuming it means lower limb) otherwise it would be a silly question. Given this risk factors are slightly different.

For lower limb in lithotomy risks are: Improper lithotomy positioning, high lithotomy positioning, procedure >2hrs. Patient factors are: intraoperativel hypotension, thin, old age, PVD and smoking.

For ulna nv neuropathy (which I don't believe question applies to) risk factors are: male sex, hospital stay >14 days and extremes of body habitus. Reference is M&M Pg 895.

The strongest evidence base for this question is currently Table 1 of Warner's 2000 article (PMID 11020742) (please amend this statement if you find a stronger source)
  • Miller:
  • US Closed Claims Database:1)Among all nerve damages --> F=M 2)Ulnar --> M: 75% 3) Brachial --> M=F 4)Lumbosacral --> F: 71% ==> so female is one of the risk factors
  • Three risk factors were strongly associated with increased risk of developing a neuropathy in the lithotomy position: 1)prolonged surgery (>3 hours) 2)very thin body habitus 3)recent cigarette smoking. (anon)
  • surely, women spend a lot more time in lithotomy than blokes, so wouldn't that explain the difference? (I'm thinking elderly )Erich 12:56, 31 Jan 2007 (EST)
  • dunno Erich, there seems to be a lot of lithotomy in urology Gasmama
  • Still struggling The main issue that I have with these questions is that the only factor that has been consistently associated with motor neuropathy in the lithotomy position is duration of surgery (eg time in an abnormal position. I really have no evidence based method of listing the other factors. At this stage I'm going with PVD but that's only because age, BMI, smoking and DM have been associated with foot drop (although PVD has been too. Thoughts? Kara 15:51, 17 Feb 2007 (EST)
  • Some say high BMI is protective because of more padding and BMI<25 is a risk. Duncan 18:17, 17 Feb 2007 (EST)
  • Duncan, who's some ? Erich 20:58, 17 Feb 2007 (EST)
  • The 1994 study by Warner is also important (Anesthesiology. 1994 Jul;81(1):6-12). This showed low BMI is a risk. I looked at the study in the college library and it does not clarify whether age or obesity was more dangerous. I am going for obesity based on the explanation given in one of these studies that low BMI caused direct nerve trauma through lack of padding. But I haven't been able to find a good reference and have spent approx 6-8 hours on this question, but am over it now.--Mark 06:42, 18 Feb 2007 (EST)
  • nuh Mark, I'm still going age, based on Table 1 as above. (not up to 6 hours yet but also rapidly getting over it!) Erich 12:33, 18 Feb 2007 (EST)
  • Not really keeping track of time-maybe I should. E, I'm not following you on age here. Can you highlight for me why PVD is a better risk factor for causing neuropathy? I'm also inclined towards obesity-the Warner 2000 study is patient who had a purely sensory neuropathy, whereas the 1994 study only came up with 3 risk factors-prolonged surgery (>3 hrs), very thin body habitus and recent cigarette smoking. Just. About. Over. It.....Kara 21:21, 19 Feb 2007 (EST)
  • ooooh... you think E.. oh.. let me have another look Erich 22:15, 19 Feb 2007 (EST) had another look at table 1... (can you get it by the way?) age seems protective (!) which is why I like it... I guess I'm also guessing that PVD, with its association with DM and smoking is probably a risk factor as well... this whole question seems based on such a weak evidence-base I feel like I'm just staring at tea-leaves!! so I'm thinking age because it had a trend to being protective Erich 22:30, 19 Feb 2007 (EST)
  • I know, but there is sort of a peak if you are middle aged (maybe they were a big podgier as well). PVD was a zero sum gain, and DM was protective in the 2000 study (!) and not mentioned as an RF in the 1994 paper. I agree, they sort of go hand in hand. Maybe I should go age. It's sort of the odd one out. Kara 22:52, 19 Feb 2007 (EST)
  • Above struggles noted. Remember seeing that obesity is protective but I'm unsure if this was referring to all or just upper limb (somewhere, can't remember where). Not significant in Warner's study. That's probably good enough for me (DavidB). Certainly, age, smoking, PVD, and DM have been suggested as risk factors in the literature. Obesity has been suggested as a risk factor but it just doesn't crop up that much.
Morgan and Mikhail, 3rd Ed p 892 'lower extremity neuropathies, especially involving the 
peroneal nerve, have been associated with impropr lithotomy positioning, extreme (high) 
lithotomy position, and especially long duration (greater than 2 hours). Patient risk factors 
for this complication include hypotension, thin body habitus, old age, and history of vascular, 
diabetes or smoking.' - I'm going for BMI>25 - Liz 31/3/07

The same comments are made in Morgan and Mikhail 4th Edition p963[2] - I'm going for BMI >25 too--Anaestheasy Tiger 21:50, 25 Jun 2009 (EDT)

1994 Anesthesiology article (reference below) has a table giving relative risk for all options listed - increased risk with smoking, diabetes and PVD, no difference with age, and increased risk with BMI < 20 (so elevated BMI kind of protective). ix 12/7/07

hooray! being fat is good for something! Gasmama I'm truly over this

minkel777 - i vote bmi>25 too


  • Warner MA, Martin JT, Schroeder DR, Offord KP, Chute CG (1994) Lower-extremity motor neuropathy associated with surgery performed on patients in a lithotomy position. Anesthesiology. 1994 Jul;81(1):6-12. PMID 8042811 (seems to be the only evidence that directly relates to this question, but not available online)
  • Warner MA, Warner DO, Harper CM, Schroeder DR, Maxson PM (2000) Lower extremity neuropathies associated with lithotomy positions. Anesthesiology. 2000 Oct;93(4):938-42. PMID 11020742
  • Sawyer RJ, Richmond MN, Hickey JD, Jarrratt JA (2000) Peripheral nerve injuries associated with anaesthesia. Anaesthesia. 2000 Oct;55(10):980-91 PMID 11012494
  • Winfree CJ (2005) Iatrogenic peripheral nerve injuries. Curr Surg. 2005 May-Jun;62(3):283-8. No abstract available. PMID 15890209
  • Anesthesiology April 2000, 92(4) Practice advisory for the prevention of perioperative peripheral neuropathies" [3]
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