Post-Operative Lower Extremity Neuropathy With Boot Stirrups Compared With Candy Cane Stirrups

Abstract

Objective:

To determine if candy cane stirrup use is associated with an increased risk of lower extremity peripheral neuropathy compared to boot stirrups in women undergoing surgery requiring dorsal lithotomy positioning.

Methods:

This retrospective cohort study (June 2008 – August 2015) included patients who underwent benign gynecologic surgery lasting ≥60 minutes in lithotomy position. Patients with pre-existing neurologic disease were excluded. Stirrup type, demographics, medical history, surgical factors and relevant outcomes were collected from the medical record. Postoperative neuropathy was identified in clinical diagnoses or in provider documentation through the 6 weeks post-operative visit. Patient characteristics and outcomes were compared using Student’s t-test, Chi-square or Fisher’s exact. Logistic regression analysis was used to adjust for other clinical characteristics associated with the outcome at p≤0.1.

Results:

The study included 2449 patients, 1838 (75.1%) with boot and 611 (24.9%) with candy cane stirrups. Women positioned in boot stirrups were younger (mean (SD) age 45.6 (13.5) vs. 55.9 (15.7) years; p<0.001), heavier (body mass index (BMI) 31.5 (8.7) vs. 29.6 (7.0) kg/m²;p<0.001), more likely to smoke (n (%) 396 (21.5) vs. 105 (17.2); p=0.021) and had longer surgical duration (176.5 (90.0) and 145.3 (63.9) minutes; p<0.001), respectively. Diabetes (8.8%) did not differ between the groups (p>0.05). Neuropathy occurred less often in the boot cohort (n=29, 1.6%, 95% CI 1.1–2.3%) than in the candy cane cohort (n=21, 3.4%, 95% CI 2.1–5.2%) (p=0.008). After adjusting for age, BMI, smoking, anesthesia type and surgical time, only candy cane stirrup type (aOR (95% CI) 2.87 (1.59–5.19)) and surgical time (per hour) (aOR (95% CI) 1.40 (1.20–1.63)) were independently associated with postoperative neuropathy.

Conclusion:

Candy cane stirrups are associated with a significantly increased risk of lower extremity postoperative neuropathy compared to boot stirrups for women undergoing benign gynecologic surgery.

Précis:

The incidence of lower extremity peripheral neuropathy was significantly higher in patients positioned using candy cane stirrups versus boot stirrups.

Introduction

Pelvic surgery requiring dorsal lithotomy positioning is associated with the risk of postoperative neuropathies that may involve the femoral, obturator, sciatic, peroneal, and genitofemoral nerves (1). These neuropathies are typically mild and self-limited, but may occasionally be severe and associated with significant morbidity and medical expense (2). Warner et al found that severe motor disabilities associated with dorsal lithotomy positioning occur at a rate of 1 in 3,608 (3). Mild neuropathies occur much more frequently, at rates ranging between 1.3% – 1.9% (1, 2, 4). Patient risk factors previously associated with development of peripheral neuropathies include thin body habitus, current smoking status, diabetes mellitus, familial neuropathies and alcoholism (2). Operating room factors that have been associated with development of postoperative lower extremity neuropathies include improper placement of self-retaining retractors, improper positioning of patients in stirrups and radical surgical dissection (4).

Many neuropathies resulting from improper positioning are thought to be due to the extrapelvic portion of the femoral nerve that is angulated sharply around the inguinal ligament with excessive flexion of the thigh and external rotation of the hip. The pressure of the unyielding inguinal ligament on the nerve is theorized to cause compression and ischemic nerve injury (4, 5). Proper dorsal lithotomy positioning includes flexed and abducted thighs, flexed knees and minimal external rotation (4). This is achieved by utilizing stirrups (Figures 1 and 2). The two most commonly used stirrup types are boot stirrups and candy cane stirrups. Research comparing the risks of these two stirrups is limited. Irvin et al postulated that although no study has shown a difference, use of boot support stirrups allows weight from the lower extremity to be placed directly on the sole of the heel, without pressure on the lateral fibular head as with candy cane stirrups (4). Bohrer et al found that the incidence of neuropathies with candy cane stirrups was twice as high as with boot stirrups (2.6% vs 1.3%, respectively). However, that study was not powered to detect a significant difference between the groups (6). The primary aim of this study was to compare the incidence of lower extremity neuropathy between groups using boot and candy cane stirrups. We hypothesized that the incidence of lower extremity neuropathy would be significantly higher in the candy cane cohort compared to the boot stirrup cohort.

Figure 1.

Dorsal lithotomy positioning using boot stirrups (7)

Figure 2.

Dorsal lithotomy positioning using candy cane stirrups (7)

Figures 1 and 2 reprinted from Journal of Minimally Invasive Gynecology, Volume 24, Issue 1, Abdalmageed OS. Bedaiwy MA. Falcone T. Pages 16–27, 2016 with permission from Elsevier.

Methods

This retrospective cohort study was approved by the University of Iowa Institutional Review Board and conformed to the STROBE (Strengthening the Reporting of Observational studies in Epidemiology) guidelines (8). Patients who underwent benign gynecologic surgery between June 2008 through August 2015 requiring dorsal lithotomy positioning were screened for inclusion. A waiver of consent was provided for this study by the Institutional Review Board. Patients were grouped into two cohorts (candy cane and boot) based on the stirrup type documented in the text of the operative note. Stirrup type was also confirmed based on separate operating room nursing documentation. Patient data was obtained by manual review of the electronic medical record. This review was performed by 5 (AW, EC, MS, SA, JK) of the authors and 3 (JD, AA, PH) additional research assistants. All individuals performing the chart review were trained and audited by a single author (AW) to ensure consistent and accurate data extraction. Inclusion criteria included benign gynecologic surgery requiring dorsal lithotomy position within the study collection dates, clearly documented stirrup type in the electronic medical record, and age greater than 18 years old. Additionally, due to prior reports of neuropathy occurring primarily after extended time in lithotomy (3), cases were only included if case length was greater than or equal to 60 minutes. Exclusion criteria were a history of pre-existing neuropathic symptoms, gynecologic malignancy, coagulopathy or personal history of venous thromboembolism (VTE).

Subject data were collected and managed using REDCap electronic data capture tools hosted at the University of Iowa (9). REDCap (Research Electronic Data Capture) is a secure, web-based software platform designed to support data capture for research studies, providing an intuitive interface for validated data capture, audit trails and automated export procedures to common statistical packages. Data collected from each included subject’s medical record included route of surgery, length of case, age, weight, height, body mass index (BMI), smoking status, history of diabetes, history of neurologic disease, stirrup type (boot versus candy cane), documented development of postoperative lower extremity peripheral neuropathy, presence of physical therapy consultation within 6 weeks after surgery, documented VTE within 6 weeks after surgery and type of anesthesia (regional versus general).

The primary outcome of the study was new onset postoperative lower extremity neuropathy. All notes (progress notes, discharge summary, telephone notes, nursing notes and all post-operative encounters) and recorded diagnoses in the patient record were carefully searched from the day of surgery through 6 weeks postoperatively for descriptions of neuropathy symptoms in the lower extremities, including numbness, tingling, and motor weakness. When a medical record was noted to have a documented postoperative lower extremity neuropathy, the neuropathy was recorded in detail and then reviewed by two separate physician reviewers (AW and JK) to determine if the described event was likely representative of a peripheral neuropathy. Neuropathy was defined as the description of lower extremity weakness, numbness, pain or tingling documented in the medical record and deemed by the treating provider (as documented in the record) to represent a neuropathy. Secondary outcomes included lower extremity VTE and need for postoperative physical therapy consultation within 6 weeks after surgery. Lower extremity VTE was chosen as an exploratory secondary outcome because this is a known risk of pelvic surgery, and we postulated that immobilization in differing stirrup types could potentially contribute to clot development.

Based on prior literature, the incidence of post-operative lower extremity peripheral nerve injury was conservatively estimated at 1.3% with boot stirrups and 2.6% with candy cane stirrups (odds ratio of 2.0) (6). To achieve power of 80% to show this difference we initially planned to analyze data from 3532 patients. However, an interim analysis was performed after 2449 chart abstractions were completed. This demonstrated statistically significant findings. Therefore, data collection was stopped at that time.

The incidence of lower extremity neuropathy was compared between the two cohorts (boot stirrups vs candy cane stirrups) using Fisher’s exact test. Additional outcomes were compared using appropriate statistical tests including chi squared and student’s t test. Dependent variables that were found to be significant at p≤ 0.1 were then placed into a logistic regression model to quantify strength of association and adjust for confounding variables.

Results

Eight-thousand five-hundred thirty-eight patient records were evaluated for inclusion over the study period. 6089 were excluded as outlined in Figure 3. Two-thousand four-hundred forty-nine patients met inclusion criteria and were included in the analysis. Boot stirrups were used in 1838 (75.1%) and candy cane stirrups in 611 (24.9%). Women who were positioned in boot vs. candy cane stirrups were younger (mean (SD) age 45.6 (13.5) vs. 55.9 (15.7) years; p<0.001), heavier (body mass index (BMI) 31.5 (8.7) vs. 29.6 (7.0) kg/m²; p<0.001), more likely to smoke (n (%) 396 (21.5) vs. 105 (17.2); p=0.021) and had longer surgical duration (176.5 (90.0) and 145.3 (63.9) minutes; p<0.001), respectively (Table 1). Presence of diabetes mellitus did not differ between the groups. The most common procedures in the boot cohort were laparoscopic adnexal surgery (n=699), laparoscopic hysterectomy (n=603) and sacral colpopexy (n=174) and in the candy cane cohort vaginal hysterectomy (n=289), posterior (n=274) and anterior (n=201) colporrhaphy.

Figure 3.

Subject flow diagram.

*Individuals assessed for eligibility may have been excluded for more than one criterion. **VTE=venous thromboembolism.

Table 1.

Patient characteristics.

	Boot (n=1838; 75.1%)	Candy cane (n= 611; 24.9%)	p
Patient Characteristics
Age (y, SD)	45.6 (13.5)	55.9 (15.7)	<.001
BMI* (kg/m2, SD)	31.5 (8.7)	29.6 (7.0)	<.001
Smoker (n, %)	396 (21.5%)	105 (17.2%)	0.021
Diabetes (n, %)	152 (8.3%)	63 (10.3%)	0.122
Surgical Characteristics
Surgical time (m, SD)	176.5 (90.9)	145.3 (63.9)	<0.001
General anesthesia (n, %)	1833 (99.7)	599 (98.0)	<0.001
Spinal anesthesia (n, %)	3 (0.2)	10 (1.6)	<0.001

^*BMI=body mass index.

Fifty (2.0%) subjects developed post-operative lower extremity neuropathies (Table 2). The mean surgical duration in neuropathy cases was 221.4 (SD 99.7) minutes. The most common nerve distribution affected was femoral (n=14, 28.0%). However, 25 cases had no specific nerve distribution mentioned in the medical record. The majority of neuropathies were sensory only (n=41, 82.0%). Thirty-five (70.0%) had resolution of the neuropathy at the time of the last follow up in the record. The remainder all had at least some improvement in reported symptoms at the time of last follow up. Six patients in the candy cane cohort had persistent symptoms at time of last follow up, while 9 patients in the boot cohort had persistent symptoms. No significant motor deficits were present at the time of last follow up for any subject.

Table 2.

Neuropathy cases.

No	Stirrup type	Time (min)	Procedure	Approach	Distribution	Laterality	Motor loss	Sensory loss	Pain or paresthesia	Complete resolution
1	Boot	444	TVH, RA-LSC, PR with biologic graft, cysto	Vaginal	Common peroneal	R	N	Y	N	Persistent at 4 months
2	Boot	406	RA-TLH, RA-LSC, cysto	Robotic	Femoral	L	N	Y	N	Y
3	CC	195	Colpocleisis, MUS, perineorrhaphy, cysto	Vaginal	Unspecified	L	Y	Y	Y	Persistent at 3 months
4	CC	190	USLS, AR, PR, perineorrhaphy, cysto	Vaginal	Femoral	R	N	Y	Y	Y
5	CC	244	TVH, USLS, AR, PR, MUS, cysto	Vaginal	Common peroneal	L	Y	Y	N	Y
6	Boot	95	RA-BSO	Robotic	Lateral femoral cutaneous	R	N	Y	N	Persistent at 2 months
7	Boot	434	LAVH, primary repair of rectal injury, cysto	Vaginal and laparoscopic	Sciatic	L	Y	Y	Y	Persistent at 4 months
8	CC	253	TVH, RSO, USLS, AR, MUS, PR, cysto	Vaginal	Femoral	R	N	Y	N	Persistent at 3 months
9	Boot	496	TAH, BSO, MUS, cysto, colovaginal fistula repair, sigmoid colon resection, loop ileostomy	Laparotomy	Unspecified	B	N	Y	Y	Y
10	Boot	164	RA-laparoscopy, ex lap, left ovarian cystectomy	Robotic and laparotomy	Femoral	R	N	Y	N	Persistent at 2 months
11	Boot	231	LAVH, BSO	Vaginal and laparoscopic	Femoral	B	N	Y	Y	Y
12	Boot	70	LA-LSO	Vaginal	Ilioinguinal/Iliohypogastric	R	N	Y	Y	Persistent at 1 month
13	Boot	286	RA-LSC, MUS, cysto	Vaginal and robotic	Unspecified	B	N	Y	Y	Y
14	Boot	343	RA-TLH, RA-LSC, MUS, cysto	Vaginal and robotic	Femoral	L	N	Y	Y	Y
15	CC	231	MUS, cysto	Vaginal	Unspecified	L	N	Y	N	Y
16	Boot	204	RA-TLH, BS	Robotic	Femoral	R	N	Y	N	Persistent at 2 months
17	Boot	185	RA-TLH, BSO	Robotic	Unspecified	B	N	Y	Y	Y
18	CC	165	TVH, USLS, PR, cysto	Vaginal	Sciatic	L	N	Y	Y	Persistent at 1 month
19	Boot	238	RA-TLH, BSO	Robotic	Femoral	L	N	Y	Y	Persistent at 2 months
20	Boot	271	RA-TLH, culdoplasty, PR, cysto	Vaginal and robotic	Sciatic	L	N	N	Y	Y
21	CC	227	TVH, BSO, culdoplasty, cysto	Vaginal	Unspecified	L	N	Y	N	Y
22	Boot	159	LAVH, BS	Vaginal and laparoscopic	Femoral	B	N	Y	N	Y
23	CC	213	TVH, USLS, AR, PR, MUS, cysto	Vaginal	Lateral femoral cutaneous	R	N	Y	Y	Y
24	Boot	209	LAVH, BS, MUS, cysto	Vaginal and laparoscopic	Unspecified	B	N	Y	N	Y
25	Boot	71	LA-BSO	Laparoscopic	Femoral	L	N	Y	N	Y
26	CC	250	TVH, USLS, MUS, PR, cysto	Vaginal	Unspecified	R	N	Y	N	Y
27	Boot	120	TLH	Laparoscopic	Femoral	B	N	N	Y	Y
28	CC	208	TVH, cysto	Vaginal	Sciatic	R	Y	Y	Y	Persistent at 5 months
29	Boot	178	TLH/BS, cysto	Laparoscopic	Unspecified	R	Y	Y	Y	Y
30	Boot	114	SILS TLH, BS, cysto	Laparoscopic	Ilioinguinal/Iliohypogastric	R	N	Y	Y	Y
31	Boot	154	SILS TLH, BSO, vaginal laser	Laparoscopic and vaginal	Unspecified	L	N	Y	N	Y
32	CC	143	Colpocleisis, MUS, PR, cysto	Vaginal	Unspecified	B	Y	Y	N	Y
33	CC	60	AR, MUS, cysto	Vaginal	Femoral	L	Y	N	N	Y
34	CC	154	SSLF, PR	Vaginal	Femoral	R	N	Y	N	Y
35	CC	160	TVH, cysto	Vaginal	Femoral	B	N	Y	Y	Y
36	Boot	341	RA-TLH, BSO, RA-LSC, MUS, cysto	Robotic and vaginal	Unspecified	B	N	N	Y	Persistent at 1 month
37	CC	284	TVH, BSO, USLS, culdoplasty, PR, cysto	Vaginal	Unspecified	B	Y	Y	Y	Y
38	Boot	250	Diagnostic laparoscopy, ex lap, TAH, BS, cysto	Laparoscopic and laparotomy	Unspecified	B	N	Y	N	Y
39	CC	230	TVH, BSO, USLS, AR, PR, MUS, cysto	Vaginal	Unspecified	L	N	Y	N	Y
40	Boot	157	LA-BSO	Laparoscopic	Unspecified	R	N	Y	N	Y
41	Boot	357	TVH, cysto, LA-cystotomy repair and ureteral stent placement	Vaginal and laparoscopic	Unspecified	L	N	Y	N	Y
42	Boot	358	RA-TLH, BS, RA-LSC, partial trachelectomy, cysto	Vaginal and robotic	Unspecified	L	N	N	Y	Y
43	CC	265	TVH, cysto	Vaginal	Unspecified	R	N	Y	Y	Y
44	CC	133	TVH, cysto	Vaginal	Unspecified	R	N	Y	N	Persistent at 1 month
45	Boot	117	SILS-TLH, BSO	Laparoscopic	Unspecified	B	N	N	Y	Y
46	Boot	269	RA-myomectomy	Robotic	Unspecified	R	N	N	Y	Y
47	CC	106	Vaginal mesh removal, cysto	Vaginal	Unspecified	B	N	Y	N	Y
48	Boot	109	Abdominal myomectomy	Laparotomy	Unspecified	R	N	Y	N	Persistent at 1 month
49	CC	288	TVH, USLS, AR, PR, cysto	Vaginal	Lateral femoral cutaneous	R	N	Y	Y	Persistent as 12 months
50	CC	240	TVH, BS, USLS, PR, MUS, cysto	Vaginal	Unspecified	L	Y	Y	Y	Y

CC= candy cane. L=left. R=right. B=bilateral. Y=yes. N=no.

AR= anterior repair

BS= bilateral salpingectomy

BSO= bilateral salpingo-oophorectomy

Cysto= cystoscopy

Ex lap= exploratory laparotomy

LA= laparoscopic assisted

LAVH= laparoscopic assisted vaginal hysterectomy

LSC= laparoscopic sacral colpopexy

LSO= left salpingo-oophorectomy

MUS= mid urethral sling

PR= posterior repair

RSO= right salpingo-oophorectomy

SILS= single incisión laparoscopic surgery

SSLF= sacrospinous ligament fixation

TAH= total abdominal hysterectomy

TLH= total laparoscopic hysterectomy

TVH: total vaginal hysterectomy

RA= robotic assisted

USLS= uterosacral ligament suspension

Lower extremity peripheral neuropathy occurred less often in the boot cohort (n=29, 1.6%, 95% CI 1.1–2.3%) than in the candy cane cohort (n=21, 3.4%, 95% CI 2.1–5.2%) (p=0.008) (Table 3). After adjusting for age, BMI, smoking, anesthesia type and surgical time, only candy cane stirrup type (vs. boot) (aOR 2.87 [1.59–5.19]) and surgical time (per hour) (aOR 1.40 [1.20–1.63]) were independently associated with postoperative lower extremity neuropathy. The frequency of neuropathy by quartile of surgical time is presented in Table 4. The incidence of post-operative physical therapy consultation was not significantly different between groups but was more common in the candy cane cohort. The incidence of VTE was very low, and there is insufficient power to generalize the comparison between the groups.

Table 3.

Unadjusted and adjusted odds of development of lower extremity neuropathy between cohorts.

	Boot	Candy cane	p
Primary outcome (n, %, 95% CI)
Lower extremity neuropathy	29 (1.6) [1.1–2.3]	21 (3.4) [2.1–5.2]	0.008
Adjusted analysis*
Stirrup type		aOR 2.87, 95% CI [1.59–5.19]
Surgical time (per hour)		aOR 1.40, 95% CI [1.20–1.63]
Secondary outcomes (n, %)
Physical therapy consultation	40 (2.2)	21 (3.4)	0.098
VTE within 6 weeks	4 (0.2)	0 (0.0)	0.578

^*A logistic regression model including lithotomy type, age, BMI, smoking status, anesthesia type and surgical time as covariates determined that only lithotomy type and surgical time were significantly associated with neuropathy.

Table 4.

Frequency of neuropathy by surgical time quartile.

	Boot (n)	Candy cane (n)
Surgical time quartile (m)
1st quartile (60–105)	3	1
2nd quartile (106–149)	4	3
3rd quartile (150–211)	8	6
4th quartile (212–1362)	14	11

Discussion

This study demonstrates that the use of candy cane stirrups (compared to boot stirrups) and increasing surgical time are significantly associated with the development of post-operative lower extremity neuropathy in benign gynecologic surgery. The overall incidence of post-operative neuropathy in this study (2.0%) is low and similar to prior studies. Bohrer et al evaluated 616 patients undergoing elective gynecologic surgery and determined the overall incidence of lower extremity neuropathy to be 1.8% (6). The incidence of neuropathy was 1.3% in cases with boot stirrups and 2.6% with candy cane stirrups in that cohort. However, they were not powered to show a significant difference between stirrup types. A recent randomized controlled trial evaluated post-operative physical function in patients undergoing vaginal surgery with candy cane stirrups compared to boot stirrups (10). Based on a validated questionnaire, they found that women in the candy cane group demonstrated worse physical function 6 weeks after surgery. They were not able to evaluate post-operative neuropathy due to their small sample size. Although the outcome of interest is different than our study, the fact that physical function is impaired in the same group that we showed has a higher incidence of peripheral neuropathy seems logical and consistent.

Warner et al found that the mean duration of anesthesia and time spent in dorsal lithotomy were longer in patients who developed lower extremity neuropathies (2). However, their small sample size precluded multivariate analysis. The same group has also published a case-control study with a large sample size that showed surgical time over 4 hours, thin body habitus and smoking were associated with post-operative neuropathy (3). However, they were not able to determine the impact of lithotomy type because that information was not available.

While our study demonstrates an association between candy cane stirrup use and development of postoperative lower extremity neuropathy, certain clinical situations may necessitate candy cane stirrup use for adequate surgical exposure. Similarly, certain patient characteristics make boot stirrups a more feasible option for many patients, which likely led to some of the differences between the two cohorts. Knowledge of the neuroanatomy of the pelvis is important to avoid neurological injury associated with patient positioning. Confirmation of proper positioning and padding of any obvious compression (especially overlying the lateral fibular head) and frequent position checks throughout the surgical case is vital to prevent injuries before they occur (7, 11, 12). The surgeons and surgical assistants should avoid leaning against stirrups or patient extremities (7, 11, 12). Despite these measures, postoperative neuropathy may occur in patients who will undergo a surgery in dorsal lithotomy position, especially if the surgery requires longer operative time or candy cane stirrups, and this risk should be discussed with the patient during the surgical consent process.

The primary strength of our study is a large cohort, which allowed us to perform multivariate analysis and detect a significant difference between stirrup types despite the low incidence of neuropathy. Our cohort also captured a variety of surgical routes and multiple surgeons at our institution, improving the generalizability of our findings. Additionally, we did not rely on billing codes to find neuropathy cases as we felt this would potentially underestimate the true incidence of neuropathy. The electronic chart of every included subject was manually reviewed to determine the presence or absence of neuropathy. Further, every case included as a neuropathy was reviewed by at least two physicians (JK and AW) who commonly care for these patients. An additional strength is that stirrup type was documented for every case both in the text of the operative note as well as in a separate nursing flowsheet.

The retrospective nature of the study is a limitation. Researchers were forced to assume lack of documentation regarding neuropathies equated to a lack of neuropathy symptoms, as the vast majority of time the absence of neuropathy was not clearly stated in the patient record. Neuropathies may have been missed if they were not clearly documented or if there was no follow up. However, assuming accurate charting, any neuropathy that was not documented is probably less likely to be of clinical relevance, as it did not require any description or further evaluation and treatment. Conversely, cases may have been included as neuropathies that would not have been deemed to be neuropathies in a prospectively evaluated cohort. An additional limitation lies in the fundamental differences (age, BMI, surgical time, etc.) between the cohorts. This is an inherent limitation of a retrospective design. The differences are most likely attributable to the tendency to choose boot stirrups in cases with longer operating times and heavier patients in an attempt to avoid injury and partly due to the different types of surgery (i.e. laparoscopic versus vaginal). Finally, this study is limited to a single institution. While our results are supported by prior research, care must be taken in generalizing our findings to other populations.

In conclusion, we found that the overall incidence of post-operative lower extremity neuropathy following benign pelvic surgery is low. However, candy cane stirrup use and increasing surgical time are independently associated with the risk of neuropathy.