Intraoperative patient positioning balances patient safety with surgical ease and access to surgical sites.1 Incorrect positioning can lead to both transient and long-term injuries that affect patient recovery, including joint dislocations, plexus injuries, pressure ulcers and nerve injuries. Up to 37% of patients complain about lower back pain after surgery in lithotomy position.1
Iatrogenic neuropathy to the ilioinguinal, iliohypogastric, obturator, femoral, genitofemoral, lateral femoral cutaneous, pudendal, sciatic and common peroneal nerves have all been reported after gynecologic surgery.2 Neurologic injuries often go unrecognized and studies report rates between 1.1 and 1.9%.2–4 Risk factors for these injuries include patient age, type of surgery, operating time, body mass index (BMI, calculated as weight in kilograms divided by height in meters squared), and inappropriate patient positioning.1–4 Of these, the most modifiable risk factor is patient positioning. Anatomical studies have attempted to identify appropriate angles of flexion and abduction at the hip using cadavers.5,6 Recommendations for lithotomy positioning include avoiding excessive hip flexion or abduction, direct pressure on the peroneal neck, leg contact with support rods, and positions that do not align the thigh, knee and heel to the contralateral shoulder.1
Common lithotomy stirrup types include strap stirrups (eg, candy cane stirrups, Sims stirrups) and boot stirrups (eg, Allen stirrups, Yellofin stirrups). Data comparing these two stirrup types are scant and conflicting.2,7 Owing to the rarity of occurrence, a sample size of 3,852 people would be needed to assess a difference in neurologic outcome between the stirrups.2 Therefore, the use of a functional patient outcome to compare stirrups is prudent. Developed by the National Institutes of Health, PROMIS (Patient-Reported Outcomes Measurement Information System) is a freely available tool for measuring comprehensive functional outcomes, and it has been validated and has demonstrated response to interventions in a diverse clinical population.8–11 Physical function is an important indicator of health, and the PROMIS physical function tool measures the respondents’ ability to perform basic and instrumental activities of daily living.9 Recent studies have demonstrated correlation between PROMIS and pelvic floor questionnaires among patients with pelvic organ prolapse who are undergoing urogynecologic management.12,13 The primary objective of this study was to compare participant positioning during vaginal surgery and its effect on the PROMIS physical function domain through STIRUPPS (Study Investigating Role of Unalike participant Positioning on PROMIS Scores).
This was a randomized, single-masked trial among women undergoing vaginal surgery with the Division of Urogynecology at University of Louisville from March 2018–October 2019. Approval for this study was obtained from the institutional review board at University of Louisville, and all participants signed an informed consent. This study was registered on clinictrials.gov (ID: NCT03446950). A review of literature and clinicaltrials.gov was performed in February 2018 and was repeated in February 2020 to confirm the novelty of this trial.
Eligible participants were approached at the preoperative visit and were enrolled after signing an informed consent. Participants were requested to complete their baseline questionnaires at this visit, which included demographic characteristics, health history, and baseline pain on a 100-point visual analogue scale (VAS) for the lower back, hips, buttocks, thighs, knees, calves, and feet. Participants also completed PROMIS physical function-20a, pain intensity-3a, pain interference-8a, and PFDI-20 (Pelvic Floor Disability Index) at baseline.14 Participants were included if they were older than age 18 years, were fluent in English, and were undergoing vaginal surgery. Participants were excluded if they were unable to provide informed consent, were unwilling or unable to follow-up in 6 weeks, were undergoing combined abdominal surgery by open, laparoscopic or robotic routes, or would require repositioning intraoperatively. Participants were also excluded if they were immobile or wheelchair bound, had a pre-existing neurologic condition limiting physical function, were undergoing surgery under local anesthesia only, anticipated or requested to be awake during positioning, or reported being unable to tolerate high lithotomy position.
Participants were randomized 1:1 to either candy cane stirrups or boot stirrups (Yellofin stirrups) using sequentially numbered opaque sealed envelopes, which were opened after administration of anesthesia. Participants remained masked to their allocation group for the duration of the study. The randomization sequence was generated by a statistician (J.G.) in permuted blocks of 6–10 participants and placed in the sequentially numbered opaque sealed envelopes before the start of study recruitment. After allocation, participants were positioned in the assigned stirrup by the attending surgeon, with assistance from the surgical team. Next, the operating surgeon measured the angle of flexion at the hip and knee joints in a standardized fashion using a goniometer (Video 1).15 To measure the angle of abduction and external rotation at the hip, the fulcrum of the goniometer was placed at the anal opening and the “angle between the femurs” was measured as demonstrated in Video 1. At the completion of surgery, the participant was returned to supine position and the stirrups were removed from the bed before participant awakening. Intraoperative findings including type of surgery, estimated blood loss, duration of surgery and intraoperative complications were recorded.
On postoperative day 1, participants were requested to complete a 100-point VAS questionnaire for pain in lower back, hips, buttocks, thighs, knees, calves and feet. Participants who were discharged home on the same day as surgery received a phone call on postoperative day 1 from a masked investigator to record pain scores. At 6 weeks postoperatively, participants were asked to complete their follow-up questionnaires in person or over the telephone, because the PROMIS questionnaire has been validated for both methods.16 Questionnaires at 6 weeks included the PROMIS physical function, pain intensity and pain interference short forms, as well as the PFDI-20 and the Patient Global Impression of Improvement (after treatment only).17 Any participant-reported complaints of limb paresthesia or neurologic injury were recorded. Adverse events during surgery and up to 6 weeks after surgery were recorded and classified using the modified Clavien-Dindo classification system.18,19 All data were entered and stored in REDCap (research electronic data capture).20
The primary outcome of this study was a change in the score of the PROMIS physical function short form-20a from baseline to 6 weeks after surgery. This is a 20-question short form that is scored using a T-score, with interpretation method built into the scoring algorithm. A score of 50 is considered mean for the general U.S. population, with 10=1 SD.8,13 An increase in score to greater than 50 is interpreted to have more of the domain factor being measured than the general population. For instance, a score higher than 50 for physical function indicates that the respondent has physical function that is better than the general U.S. population, whereas a score higher than 50 for pain intensity indicates that the respondent has greater pain intensity than the general population. The minimally important difference for this questionnaire has been found to be 2.9 To achieve 80% power using a moderate Cohen effect (d=0.5) for the primary outcome, we required a sample size of 64 participants in each group (128 participants total) to demonstrate a difference between the two types of stirrups. We estimated a 20% loss to follow-up and planned to recruit 153 women.
We planned an interim analysis after 50% of the enrolled participants had completed follow-up, with stop measures of greater than 10% neurologic injury in either group or a difference of more than 2 SDs in the primary outcome between the groups. Categorical variables were compared between groups using χ2 and Fisher exact tests, and continuous variables were analyzed using two-sample t tests; within-group comparisons of continuous variables were performed using paired t tests. For nonparametric data, the Mann-Whitney test was conducted for between-group comparisons. Significance level was set at 0.05 for all tests. Both intention to treat and per protocol analyses were performed, but only intention to treat analysis is reported. A linear regression model was built to predict the change in the PROMIS score using the stirrup groups and correcting for the preselected variables of age, BMI, Charlson comorbidity index and duration of surgery. For all calculations, we include only the participants with responses. To calculate PFDI-20 scores, we include only participants who answered at least one question on each subscale. Missing items were reconciled by using the mean from answered items only.14 Data were analyzed using R 3.5.1. and are reported using CONSORT (Consolidated Standards of Reporting Trials) guidelines.21,22
From March 2018–October 2019, 464 women were screened for participation, and 155 (33%) were enrolled (Fig. 1). We subsequently excluded 14 participants, leaving 141 to be randomized, 74 to candy cane stirrups and 67 to boot stirrups. Of those randomized, three participants were lost to follow-up at 6 weeks (two in the candy cane stirrups group and one in the boot stirrups group) and, therefore, excluded from the intention to treat analysis, which included 138 participants (72 in the candy cane stirrups group and 66 in the boot stirrups group). There were six protocol deviations, four in the candy cane stirrups group and two in the boot stirrups group. In the candy cane stirrups group, one person was randomized postoperatively instead of intraoperatively, one person did not receive the assigned allocation per surgeon’s preference, and two were unexpectedly repositioned intraoperatively. The per protocol analysis included 132 participants (68 in the candy cane stirrups group and 64 in the boot stirrups group).
There were no statistically significant differences between the two groups at baseline or perioperative characteristics (Table 1). Participants underwent vaginal surgeries that included any combination of vaginal hysterectomy, vaginal vault suspension (uterosacral or sacrospinous ligament fixation), vaginectomy (partial or total), mid-urethral slings, or other surgeries such as urethral diverticulectomy, fistula repair, or mesh excision. There were no between-group differences in duration of surgery, estimated blood loss, and adverse events at 6 weeks postoperation. The angles of flexion at the hips and knees were similar between groups, as well (Fig. 2). A significant difference was noted in the angle between the femurs (mean±SD, 88.7±13.4 candy cane vs 77.2±13.3 boot, P<.01). When asked about pain using the VAS on postoperative day 1, there was no difference in median pain in the lower back, buttocks, hips, thighs, knees, calves, or feet between the two groups (Fig. 3).
Adverse events at up to 6 weeks after surgery, recorded using the modified Clavien-Dindo classification score, were similar between the two groups (Table 1).18,19 There were two participants, one in each group, who reported neurologic injury in the postoperative period (2/138, 1.4%). The participant in the candy cane stirrups group reported sensory femoral neuropathy, which resolved spontaneously. The participant in the boot stirrups group reported unilateral foot numbness along the peroneal nerve distribution, which was persistent at 6 weeks after surgery.
The primary outcome, change in physical function based on the PROMIS physical function short form-20a, was significantly different between the two groups (change in physical function: −3.8, 95% CI −6.4 to −1.3, P<.01) (Table 2). This difference of 3.8 between the groups was greater than the minimum clinically important difference of 2, and Cohen’s effect size value was d=0.51. There were also significant within-group differences, with participants randomized to candy cane stirrups demonstrating worsening physical function (change in physical function: −1.9, 95% CI −3.9 to 0.0, P=.05) and participants randomized to boot stirrups reporting improved physical function (change in physical function: 1.9, 95% CI 0.2–3.6, P=.03) at 6 weeks after surgery. Although pain intensity improved in the boot stirrups group, there were no other differences in pain intensity or interference between the groups. The PFDI-20 improved significantly in both groups after surgery, but this improvement was similar between groups. There was also no significant difference between groups on the Patient Global Impression of Improvement, with 75% (52/69) of participants in the candy cane stirrups group reporting that they were much better or very much better compared with 85% (55/65) in the boot stirrups group. These results did not change significantly on per-protocol analysis (unpublished data).
For the linear regression model, fit to predict PROMIS scores using stirrup group, and controlling for confounders (age, BMI, Charlson comorbidity index score, and duration of surgery), the change in PROMIS physical score between groups was −4.0 (95% CI −6.7 to −1.4, P<.01) favoring boot stirrups. In this same model, pain intensity and pain interference did not change significantly between the groups (change in pain intensity score: 1.8, 95% CI −5.0 to 1.3, P=.26; change in pain interference: 0.8, 95% CI −2.6 to 4.3, P=.64).
Our study demonstrates that women randomized to boot stirrup positioning in vaginal surgeries had better physical function outcomes at 6 weeks after vaginal surgery when compared with women who were positioned in candy cane stirrups. Previous studies have raised concerns about the role of patient positioning in neurologic injuries after gynecologic surgery, specifically the role of candy cane stirrups compared with boot stirrups, but this is the first randomized controlled trial comparing these two positioning methods.2,23
Neurologic injuries are uncommon after gynecologic surgery.24,25 Prospective studies have found that neuropathies usually present within 7 days postoperatively, and, although motor deficits are reported, most positioning injuries are purely sensory with 90% of them resolving spontaneously.2,3,26 We observed 1.4% new neuropathies, consistent with existing literature. Both cases reported sensory loss only and involved the femoral nerve and the superficial branch of peroneal nerve with spontaneous resolution of symptoms by 6 weeks in one of the cases. Despite previous studies suggesting that neuropathies are more common in candy cane stirrups as compared with boot stirrups, we did not have sufficient power from our sample size to draw conclusions.2
Patient-reported outcomes increasingly have been used to monitor patient disease state,10 because these directly reflect patient experience of well-being, rather than inferring it from other outcomes. Their use in pelvic reconstructive surgery has seen a recent increase with the constantly evolving definition of surgical success. The freely available, multidimensional PROMIS profile provides additional functional data for patients with pelvic floor dysfunction. Studies have found that women who undergo surgery for pelvic organ prolapse can see a 5–8 point improvement in their physical function scores at 3–12 months after surgery with similar improvements noted in pain intensity and pain interference.12,13 Interestingly, we found that, although participants who underwent surgery positioned in boot stirrups reported similar improvements in physical function at 6 weeks, women positioned in candy cane stirrups worsened in their physical function scores. Similar trends were seen in pain intensity, but this outcome was not significant between the two groups.
PROMIS physical function has also been correlated with currently used PFDI-20 and patient global impression of severity questionnaires.12 Specifically, worsening pelvic floor symptoms are associated with worsening physical function scores. However, in our study, despite significant improvements in pelvic floor symptoms in both groups, only the participants in the boot stirrups group reported an improvement in physical function. We also noted that more participants in the boot group reported that they were much or very much better after surgery, but these numbers did not achieve statistical significance. These are novel data, because this is the first study, to our knowledge, on intraoperative positioning in vaginal surgery to report on all of these patient-centered outcomes.
The angles of the hips and knee joints can play a role in patient positioning during the time of surgery. Guidelines for dorsal lithotomy positioning recommend preventing overflexion at hip and knee and recommend limiting abduction at the hip.1 Other studies have found ways to modify existing equipment to prevent patient positioning injuries.23 In this study, specific to participants in high lithotomy, we recorded angles of flexion at the hip and knee joints and found no difference between the candy cane and boot stirrups groups. To identify abduction and external rotation, we recorded the angle between the femurs and found that participants positioned in candy cane stirrups had greater hip abduction than those positioned in boot stirrups, which could provide a rationale for our findings.
The strengths of this study lie in its appropriately powered, randomized, single-masked design comparing two commonly used positioning tools. Owing to the low number of neurologic injuries in gynecologic populations, we used a validated, patient-reported outcome as our primary outcome to directly measure participant experience. Additionally, to add objective data to our study and investigate the relationship between positioning and patient outcomes, all positioned participants had the angles at hip and knees recorded to assess differences in positioning. We also corrected for other factors that have been identified in neuropathies, such as BMI and duration of surgery, and found that our conclusion was unchanged.
This study is not without limitations. The follow-up of this population was limited to 6 weeks after surgery. Previous studies have found continuously improving physical function scores at 3 months and 12 months after surgery and it is possible that our participants would have noted improving function if we had followed them in the long term. However, it is our practice to allow patients to return to work a maximum of 6 weeks after surgery, and we wanted to assess their ability to perform activities of daily living at the end of their convalescence period. Additionally, we were unable to mask the operating surgeon to the participant positioning device but attempted to mitigate this by using standardized goniometers and self-completed participant questionnaires. Because hip abduction can be difficult to measure in the high lithotomy position, we were limited to measuring a surrogate marker of hip abduction and external rotation. Lastly, physical function is a general measure of physical well-being and has not been directly correlated to neurologic injury in this population. We would have liked to power this study to neurologic injuries, but, owing to the low incidence, this was not feasible.
Patient positioning is an important part of gynecologic surgeries and can affect postoperative patient outcomes. In women who are undergoing vaginal surgery for pelvic floor disorders, our results suggest that participants positioned in boot stirrups have better physical function outcomes at 6 weeks after surgery when compared with those positioned in candy cane stirrups. Further investigation is warranted to assess whether these outcomes are maintained in the long term.
Authors' Data Sharing Statement
- Will individual participant data be available (including data dictionaries)? Individual requests will be considered.
- What data in particular will be shared? To be determined.
- What other documents will be available? To be determined.
- When will data be available (start and end dates)? To be determined.
- By what access criteria will data be shared (including with whom, for what types of analyses, and by what mechanism)? Please contact the corresponding author.
1. Fleisch MC, Bremerich D, Schulte-Mattler W, Tannen A, Teichmann AT, Bader W, et al. The prevention of positioning injuries during gynecologic operations. Guideline of DGGG (S1-level, AWMF registry No. 015/077, February 2015). Geburtshilfe Frauenheilkd 2015;75:792–807.
2. Bohrer JC, Walters MD, Park A, Polston D, Barber MD. Pelvic nerve injury following gynecologic surgery: a prospective cohort study. Am J Obstet Gynecol 2009;201:531.e1–7.
3. Cardosi RJ, Cox CS, Hoffman MS. Postoperative neuropathies after major pelvic surgery. Obstet Gynecol 2002;100:240–4.
4. Gumus E, Kendirci M, Horasanli K, Tanriverdi O, Gidemez G, Miroglu C. Neurapraxic complications in operations performed in the lithotomy position. World J Urol 2002;20:68–71.
5. Litwiller JP, Wells RE Jr, Halliwill JR, Carmichael SW, Warner MA. Effect of lithotomy positions on strain of the obturator and lateral femoral cutaneous nerves. Clin Anat 2004;17:45–9.
6. Deveneau NE, Forbis C, Lipetskaia L, Kinman CL, Agrawal A, Herring NR, et al. The effect of lithotomy position on nerve stretch: a cadaveric study. Female Pelvic Med Reconstr Surg 2017;23:457–61.
7. Power H. Patient positioning outcomes for women undergoing gynaecological surgeries. Can Oper Room Nurs J 2002;20:7–10, 27–30.
8. HealthMeasures.PROMIS (Patient-Reported Outcomes Measurement Information System). Available at: http://www.healthmeasures.net/explore-measurement-systems/promis
. Retrieved March 26, 2020.
9. Hays RD, Spritzer KL, Fries JF, Krishnan E. Responsiveness and minimally important difference for the patient-reported outcomes measurement information system (PROMIS) 20-item physical functioning short form in a prospective observational study of rheumatoid arthritis. Ann Rheum Dis 2015;74:104–7.
10. Lee AC, Driban JB, Price LL, Harvey WF, Rodday AM, Wang C. Responsiveness and minimally important differences for 4 patient-reported outcomes measurement information system short forms: physical function, pain interference, depression, and anxiety in knee osteoarthritis. J Pain 2017;18:1096–110.
11. Schalet BD, Hays RD, Jensen SE, Beaumont JL, Fries JF, Cella D. Validity of PROMIS physical function measured in diverse clinical samples. J Clin Epidemiol 2016;73:112–8.
12. Bochenska K, Hall E, Griffith JW, Kenton K, Alverdy A, Lewicky-Gaupp C, et al. The promise of PROMIS in pelvic organ prolapse. Female Pelvic Med Reconstr Surg 2019;25:426–9.
13. Sung VW, Wohlrab KJ, Madsen A, Raker C. Patient-reported goal attainment and comprehensive functioning outcomes after surgery compared with pessary for pelvic organ prolapse. Am J Obstet Gynecol 2016;215:659.e1–7.
14. Barber MD, Walters MD, Bump RC. Short forms of two condition-specific quality-of-life questionnaires for women with pelvic floor disorders (PFDI-20 and PFIQ-7). Am J Obstet Gynecol 2005;193:103–13.
15. Norkin CC, White DJ. Measurement of joint motion: a guide to goniometry. 5th ed. Philadelphia, PA: FA Davis; 2016.
16. Quach CW, Langer MM, Chen RC, Thissen D, Usinger DS, Emerson MA, et al. Reliability and validity of PROMIS measures administered by telephone interview in a longitudinal localized prostate cancer study. Qual Life Res 2016;25:2811–23.
17. Yalcin I, Bump RC. Validation of two global impression questionnaires for incontinence. Am J Obstet Gynecol 2003;189:98–101.
18. Gutman RE, Nygaard IE, Ye W, Rahn DD, Barber MD, Zyczynski HM, et al. The pelvic floor complication scale: a new instrument for reconstructive pelvic surgery. Am J Obstet Gynecol 2013;208:81.e1–9.
19. Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg 2004;240:205–13.
20. Harris PA, Taylor R, Thielke R, Payne J, Gonzalez N, Conde JG. Research electronic data capture (REDCap)—a metadata-driven methodology and workflow process for providing translational research informatics support. J Biomed Inform 2009;42:377–81.
21. R Core Team.R: a language and environment for statistical computing. Available at: http://www.R-project.org/
. Retrieved March 26, 2020.
22. Schulz KF, Altman DG, Moher D, Group C. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ 2010;340:c332.
23. Sze EHM. An alternate approach to using candy cane stirrups in vaginal surgery. Obstet Gynecol 2019;133:666–8.
24. Abdalmageed OS, Bedaiwy MA, Falcone T. Nerve injuries in gynecologic laparoscopy. J Minim Invasive Gynecol 2017;24:16–27.
25. Irvin W, Andersen W, Taylor P, Rice L. Minimizing the risk of neurologic injury in gynecologic surgery. Obstet Gynecol 2004;103:374–82.
26. Warner MA, Warner DO, Harper CM, Schroeder DR, Maxson PM. Lower extremity neuropathies associated with lithotomy positions. Anesthesiology 2000;93:938–42.