The Journal of Arthroplasty 30 (2015) 145–148
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The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Neurovascular Structure Proximity to Acetabular Retractors in Total Hip Arthroplasty Daniel Shubert, BA a, Samuel Madoff, MD b, Ralph Milillo, MD c, Sumon Nandi, MD a,b a b c
Tufts University School of Medicine, Boston, Massachusetts New England Baptist Hospital, Boston, Massachusetts North Shore-Long Island Jewish Health Care System, New Hyde Park New York
a r t i c l e
i n f o
Article history: Received 11 May 2014 Accepted 21 August 2014 Keywords: retractor acetabulum total hip arthroplasty neurovascular injury hip
a b s t r a c t Neurovascular injury during total hip arthroplasty (THA) may result in considerable morbidity or mortality. The most common cause of intraoperative neurovascular injury during THA is retractor compression. Our aims were to: 1) determine proximity of common acetabular retractor positions during THA to adjacent neurovascular structures; and 2) determine effect of patient gender on these measurements. Retractor to neurovascular structure distances were measured on 32 preoperative computed tomography images and 16 cadavers. Our data suggest the anterior inferior iliac spine is the safest anterior acetabular retractor position. With inferior progression along the anterior wall, the distance to the femoral neurovascular bundle decreases. Due to its proximity to the sciatic nerve, the position of the posterior retractor should be monitored during acetabular preparation, particularly in women. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) is among the most effective surgical interventions for improving health-related quality of life [1]. For this reason, and the increasing proportion of the population who are elderly, the demand for primary THA in the United States is estimated to increase dramatically over time [2]. As a result, the consequences of adverse events that occur in a systematic manner during THA are significant, and it is important to develop protocols that minimize the occurrence of these events. Neurovascular injury during THA is relatively rare, but may result in considerable morbidity or even mortality. The incidence of peripheral neurologic injury in a review of over 54,000 primary and revision THAs was 0.09% to 3.7% and 0.0% to 7.6%, respectively [3]. It is likely that the incidence of neurologic injury during THA is higher than that accounted for by clinical examination alone, and 79% of patients who suffer peripheral neurologic injury retain some degree of persistent neurologic dysfunction [3–6]. Vascular injury in THA, with a reported incidence of 0.1% to 0.2%, is less common than neurologic injury but more emergent [7]. False aneurysm or fistula formation, thromboembolism, loss of limb, or even mortality may result [8–12]. In THA, the most common identifiable cause of intraoperative nerve injury is compression by retractors [13]. In order of decreasing frequency, the sciatic, femoral, and superior gluteal nerves (SGN) are most commonly injured during THA [3,9]. There is evidence suggesting that postoperative sciatic nerve palsies occur largely due to direct trauma from instrumentation [14]. The primary etiology of femoral nerve injury has been shown to be retractor placement along the anterior acetabular rim [15–18]. Multiple studies have found subclinical electromyography-derived evidence of SGN
injury [6,19–21]. Female gender is the most well-established risk factor for neurologic injury during THA, with multiple studies reporting that at least 74% of these events occur in women [4,18,22,23]. The external iliac artery and femoral artery are the most frequently injured vascular structures in THA [9]. Acetabular retractors placed too far medially are the most frequent cause of femoral artery injury [7,24,25]. There is venographic evidence that intraoperative manipulation causes femoral vein distortion and damage resulting in thrombus formation [26]. Several studies have shown that surgical approach is not an independent cause of neurovascular injury during THA [4,5,27,28]. Consequently, appropriate retractor placement regardless of surgical approach is critical to minimizing the risk of neurovascular injury. However, safe acetabular retractor positions have not been well established in the literature. Safe acetabular retractor positions can be determined only by establishing the proximity of neurovascular structures to common sites of acetabular retractor placement during THA. The aims of our study were to: 1) determine the proximity of common acetabular retractor positions during THA to the femoral neurovascular bundle, superior gluteal neurovascular bundle, and sciatic nerve using computed tomography (CT) images as well as cadaveric specimens; and 2) ascertain if gender affects acetabular retractor proximity to neurovascular structures.
Materials and Methods Study Design
The Conflict of Interest statement associated with this article can be found at http://dx. doi.org/10.1016/j.arth.2014.08.024. Reprint requests: Sumon Nandi, MD, New England Baptist Hospital, Department of Orthopedic Surgery, 125 Parker Hill Avenue, Fogg Building, Suite 501, Boston, MA 02120. http://dx.doi.org/10.1016/j.arth.2014.08.024 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Computed Tomography Data Computed tomography (CT) scans of the hip performed preoperatively for a primary total hip arthroplasty (THA) computer-guided
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D. Shubert et al. / The Journal of Arthroplasty 30 (2015) 145–148
navigation protocol were our data source. All scans were with multiplanar 2-dimensional reformats (coronal and sagittal). CTs of 16 male and 16 female patients performed in 2012 with equal distribution of left and right hips were selected at random from our institutional electronic radiograph archive. The distance from five common acetabular retractor positions in total hip arthroplasty to the closest neurovascular structure was measured on each hip CT. The distance from three anterior acetabular retractor positions to the femoral neurovascular bundle, the distance from one superior retractor position to the superior gluteal neurovascular bundle, and the distance from one posterior retractor position to the sciatic nerve were determined. The three anterior retractor positions were: 1) the anterior inferior iliac spine (AIIS); 2) along the anterior wall at the 3 o’clock position for the right hip or 9 o’clock position for the left hip (direct anterior); and 3) along the anterior wall immediately superior to the superior pubic ramus (antero-inferior). The superior retractor position was the 12 o’clock position immediately superior to the acetabular rim. The posterior retractor position was along the posterior wall at the 9 o’clock position for the right hip or 3 o’clock position for the left hip. The distance from an inferior retractor position to the obturator neurovascular bundle was not measured, as this structure could not be reliably identified on CT. Retractor positions were demonstrated on a 3-dimensional pelvis model to the radiologists in this study, who then established corresponding points on digital hip CT images. Distances from these points to the closest neurovascular bundle were measured using a digital caliper tool on an AGFA (Greenville, SC) Impax picture archiving and communication system (PACS). Two blinded, board-certified radiologists served as raters. Each rater made all measurements independently. The measurement protocol for each retractor site was first standardized with 20 training cases by the two raters prior to evaluation of the 32 study cases. Distances from retractor positions to adjacent neurovascular structures were determined on digital CT images as follows (Fig. 1). The three anterior measurements were performed sequentially on axial images. The AIIS retractor position was determined by first identifying the origin of the direct head of the rectus femoris, and then scrolling inferiorly 0.5 cm. Then, the shortest distance from the medial cortex of the anterior column to the femoral neurovascular bundle was measured. The second anterior retractor position was identified on the same image as above at the inferior-most confluence of the AIIS and the acetabulum. The shortest distance from this point to the femoral neurovascular bundle was measured. The third anterior retractor position was identified by scrolling 1.0 cm inferiorly from the second retractor position. At this level, the distance from the most anterior point of the anterior column medial cortex to the femoral neurovascular bundle was determined. The posterior retractor position was identified on an axial image as the point on the posterior wall 0.5 cm superior to the concavity nadir at the junction of the acetabulum and ischium. From this point, the distance to the sciatic nerve was measured. The superior retractor position was defined as the 12 o’clock position of the acetabulum first on sagittal, then coronal images. Then, the shortest distance from the lateral-most point of the acetabular cortex to the fat plane between the gluteus medius and minimus containing the superior gluteal neurovascular bundle was measured.
A
B
C
D
Fig. 1. Computed tomography images demonstrating acetabular retractor positions and adjacent neurovascular structures. (A) Distances from anterior inferior iliac spine (AIIS) and direct anterior (DA) retractor positions to femoral neurovascular bundle (FNVB); (B) distance from antero-inferior (AI) retractor position to FNVB; (C) distance from posterior (P) retractor position to sciatic nerve (ScN); (D) distance from superior (Sup) retractor position to superior gluteal neurovascular bundle (SGNVB).
Distances from the superior retractor position to the superior gluteal neurovascular bundle were not measured, as this anatomic structure could not be consistently identified on the available cadavers. The cadavers were stored in a supine position, which distorted posterior anatomy. As a result, distances from the posterior retractor position to the sciatic nerve were also not measured. Statistical Analysis As two independent raters were used in obtaining the CT data, linear mixed-effects modeling was performed to account for variation across raters. Multiple comparisons with the Tukey Method were used to test the difference between any two groups. P b 0.05 with a two-sided test was considered significant. Power analysis was used to calculate sample size. With type I error set at 5%, and desired power N0.90 to detect a 5 mm difference between pairs of retractor positions in distance to the closest neurovascular structure, a sample size of 32 CT scans was required. Results
Cadaveric Data Twelve cadavers in our institution’s anatomy laboratory with an intact lower extremity were utilized for this study. Six male and 6 female cadavers, with an equal distribution of left and right lower extremities, were randomly selected from the available cadavers. The ilioinguinal approach was performed by a single surgeon on all cadavers. The anterior acetabular retractor positions were identified, confirmed by two of the co-authors, and the shortest distance to the femoral neurovascular bundle was measured. A single metal ruler was used for all measurements.
Computed Tomography Data (Tables 1a and 1b) Of all the retractor positions, the AIIS was the farthest from the adjacent neurovascular structure at a mean of 2.65 cm (P b 0.0001), followed by the direct anterior and superior retractor positions at a mean of 2.03 to 2.20 cm (P ≤ 0.0135). The antero-inferior retractor position was the closest to the adjacent neurovascular structure at a mean of 0.95 cm (P ≤ 0.0001), followed by the posterior retractor position at a mean of 1.75 cm (P ≤ 0.0135).
D. Shubert et al. / The Journal of Arthroplasty 30 (2015) 145–148 Table 1a Distance From Retractor Position to Adjacent Neurovascular Structure as Measured on Computed Tomography Images.
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Table 2a Distance From Retractor Position to Adjacent Neurovascular Structure as Measured on Cadaveric Specimens.
Retractor Position
Mean Distance in cm (SD)
Retractor Position
Mean Distance in cm (SD)
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior Posterior Superior
2.65 (0.51) 2.20 (0.41) 0.95 (0.36) 1.75 (0.34) 2.03 (0.47)
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
2.81 (0.59) 1.39 (0.31) 0.94 (0.26)
As the retractor position moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreased to a minimum immediately superior to the superior pubic ramus (P b 0.0001). Cadaveric Data (Tables 2a and 2b) The AIIS was the farthest anterior retractor position from the femoral neurovascular bundle at a mean distance of 2.81 cm (P b 0.0001). Again, as the retractor position moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreased to a minimum mean of 0.94 cm immediately superior to the superior pubic ramus (P b 0.0001). Gender (Tables 3a and 3b) The distances between posterior (P = 0.0002), superior (P = 0.0002), as well as certain anterior acetabular retractor positions and adjacent neurovascular structures were shorter in women than in men. Based on computed tomography images, the direct anterior retractor position was significantly closer to the femoral neurovascular bundle in women than in men (P = 0.0030), while the AIIS trended towards being closer to the femoral neurovascular bundle in women (P = 0.0596). In cadaveric specimens, however, the AIIS was the only anterior retractor position that was closer to the femoral neurovascular bundle in women than in men (P = 0.0272). Discussion In order to achieve proper acetabular exposure during THA, retractors are placed circumferentially around the acetabulum. Retractor placement is a leading cause of intraoperative neurovascular injury during THA [3,13]. The sciatic nerve, femoral neurovascular bundle, and superior gluteal neurovascular bundle are most commonly at risk, and the majority of intraoperative neurovascular injuries occur in women [4,18,22,23]. To decrease the likelihood of neurovascular injury, safe acetabular retractor positions must be identified. There is a paucity of literature guiding acetabular retractor placement during THA. Therefore, we studied the distance from five common acetabular retractor positions to the adjacent neurovascular structure using CT scans and cadaveric specimens. We also determined if these distances vary by gender. Our data from both CT images and cadaveric specimens suggest that the anterior acetabular retractor position that is least likely to cause Table 1b P Values for Pairwise Comparisons Between Distances From Retractor Positions to Adjacent Neurovascular Structures as Measured on Computed Tomography Images. Retractor Position
Anterior Inferior Direct AnteroIliac Spine (AIIS) Anterior Inferior
Anterior inferior iliac – spine (AIIS) Direct anterior Antero-inferior Posterior Superior
Posterior Superior
b0.0001
b0.0001 b0.0001
b0.0001
–
b0.0001 b0.0001 – b0.0001 –
0.1256 0.0001 0.0135 –
Table 2b P Values for Pairwise Comparisons Between Distances From Retractor Positions to Adjacent Neurovascular Structures as Measured on Cadaveric Specimens. Retractor Position
Anterior inferior Iliac Spine (AIIS)
Direct anterior
AnteroInferior
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
–
b0.0001 –
b0.0001 b0.0001 –
injury to the femoral neurovascular bundle is the AIIS. As the retractor is moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreases and the potential risk of injury to this structure increases. In complex or revision THA with aberrant anatomy or significant acetabular bone loss, there are fewer cues for retractor placement and a reported higher incidence of neurovascular injury [4,27,29–32]. In these cases, it may be particularly important to place the anterior acetabular retractor in the AIIS, an easily identifiable bony landmark where retractor placement minimizes risk of neurovascular injury. The distance from the posterior acetabular retractor position to the sciatic nerve was less than that of most retractor positions to adjacent neurovascular bundles. This may explain the observation that sciatic nerve injury is the most common intraoperative nerve injury during THA [3,5,13,27]. Due to the proximity of the sciatic nerve to the posterior acetabular retractor, this retractor should be placed carefully, monitored closely during acetabular preparation, and adjusted as needed. We found that anterior, posterior, and superior acetabular retractors are closer to the adjacent neurovascular structures in women than in men. This may be due to variation in neurovascular anatomy, smaller stature, or reduced muscle mass in women as compared to men [3,8,22,33]. Our findings may provide a rationale for female gender as an established risk factor for nerve injury during THA, with nearly three quarters of all nerve injuries occurring in women [4,18,22,23]. Though our study may help guide acetabular retractor placement in THA, we understand that our work has limitations. First, our anatomic measurements were not made intraoperatively, but on CT images and cadaveric specimens. CT images were taken with the patient in a supine position. Many surgeons perform THA in a lateral decubitus position, and anatomic relationships may differ with positioning. Cadaveric embalming or storage may also distort anatomy. Secondly, patients scheduled for THA were not randomly selected for CT imaging of the affected hip. CT scans of patients who elected to undergo THA with computer-guided navigation were retrospectively reviewed, and there may be selection bias with this population. Thirdly, retractor positions
Table 3a Effect of Gender on Distance From Acetabular Retractor to Adjacent Neurovascular Structure as Measured on Computed Tomography Images. Retractor Position
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior Posterior Superior
Mean Distance in cm (SD) Female
Male
2.48 (0.48) 1.99 (0.39) 0.85 (0.33) 1.54 (0.24) 1.74 (0.35)
2.83 (0.50) 2.40 (0.33) 1.04 (0.38) 1.95 (0.30) 2.31 (0.40)
P Value
0.0596 0.0030 0.1440 0.0002 0.0002
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Table 3b Effect of Gender on Distance From Acetabular Retractor to Adjacent Neurovascular Structure as Measured on Cadaveric Specimens. Retractor Position
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
Mean Distance in cm (SD) Female
Male
2.45 (0.63) 1.27 (0.37) 0.87 (0.27)
3.17 (0.26) 1.52 (0.19) 1.02 (0.26)
P Value
0.0272 0.1710 0.3498
Posterior and superior retractor positions were not evaluated due to limitations in the cadaveric specimens.
were represented by a point in space in our study, which did not account for the dimensions of the retractor. Despite these limitations, our data suggest that the safest anterior acetabular retractor position during THA that minimizes risk to the femoral neurovascular bundle is the AIIS. Care should be taken in placing retractors inferiorly along the anterior wall as the distance to the femoral neurovascular bundle decreases in this position. During acetabular preparation, the position of the posterior acetabular retractor should be checked periodically to ensure that migration has not occurred given the close proximity of the sciatic nerve. These considerations are particularly important in women and in patients who lack the usual anatomic cues for retractor placement, such as those undergoing revision surgery for significant acetabular bone loss. Future work may examine intraoperative distances from retractors to adjacent neurovascular bundles during acetabular and femoral preparation. References 1. Ethgen O, Bruyère O, Richy F, et al. Health-related quality of life in total hip and total knee arthroplasty. A qualitative and systematic review of the literature. J Bone Joint Surg Am 2004;86-A(5):963. 2. Kurtz S, Mowat F, Ong K, et al. Prevalence of primary and revision total hip and knee arthroplasty in the United States from 1990 through 2002. J Bone Joint Surg Am 2005; 87(7):1487. 3. Brown GD, Swanson EA, Nercessian OA. Neurologic injuries after total hip arthroplasty. Am J Orthop (Belle Mead NJ) 2008;37(4):191. 4. Johanson NA, Pellicci PM, Tsairis P, et al. Nerve injury in total hip arthroplasty. Clin Orthop Relat Res 1983;179:214. 5. Weale AE, Newman P, Ferguson IT, et al. Nerve injury after posterior and direct lateral approaches for hip replacement. A clinical and electrophysiological study. J Bone Joint Surg (Br) 1996;78(6):899. 6.. Picado CH, Garcia FL, Marques Jr W. Damage to the superior gluteal nerve after direct lateral approach to the hip. Clin Orthop Relat Res 2007;455:209. 7. Nachbur B, Meyer RP, Verkkala K, et al. The mechanisms of severe arterial injury in surgery of the hip joint. Clin Orthop Relat Res 1979;141:122.
8. Lewallen DG. Neurovascular injury associated with hip arthroplasty. Instr Course Lect 1998;47:275. 9. Shoenfeld NA, Stuchin SA, Pearl R, et al. The management of vascular injuries associated with total hip arthroplasty. J Vasc Surg 1990;11(4):549. 10. Heyes FL, Aukland A. Occlusion of the common femoral artery complicating total hip arthroplasty. J Bone Joint Surg (Br) 1985;67(4):533. 11. Hopkins NF, Vanhegan JA, Jamieson CW. Iliac aneurysm after total hip arthroplasty. Surgical management. J Bone Joint Surg (Br) 1983;65(3):359. 12. Scullin JP, Nelson CL, Beven EG. False aneurysm of the left external iliac artery following total hip arthroplasty. Clin Orthop Relat Res 1975(113):145. 13. Schmalzried TP, Noordin S, Amstutz HC. Update on nerve palsy associated with total hip replacement. Clin Orthop Relat Res 1997;344:188. 14. DeHart MM, Riley Jr LH. Nerve injuries in total hip arthroplasty. J Am Acad Orthop Surg 1999;7(2):101. 15. Wasielewski RC, Crossett LS, Rubash HE. Neural and vascular injury in total hip arthroplasty. Orthop Clin North Am 1992;23(2):219. 16. Simmons Jr C, Izant TH, Rothman RH, et al. Femoral neuropathy following total hip arthroplasty. Anatomic study, case reports, and literature review. J Arthroplasty 1991;6:S57 [Suppl.]. 17. Slater N, Singh R, Senasinghe N, et al. Pressure monitoring of the femoral nerve during total hip replacement: an explanation for iatropathic palsy. J R Coll Surg Edinb 2000; 45(4):231. 18. Solheim LF, Hagen R. Femoral and sciatic neuropathies after total hip arthroplasty. Acta Orthop Scand 1980;51(3):531. 19. Ramesh M, O'Byrne JM, McCarthy N, et al. Damage to the superior gluteal nerve after the Hardinge approach to the hip. J Bone Joint Surg (Br) 1996;78(6):903. 20. Abitbol JJ, Gendron D, Laurin CA, et al. Gluteal nerve damage following total hip arthroplasty. A prospective analysis. J Arthroplasty 1990;5(4):319. 21. Kenny P, O'Brien CP, Synnott K, et al. Damage to the superior gluteal nerve after two different approaches to the hip. J Bone Joint Surg (Br) 1999;81(6):979. 22. Weber ER, Daube JR, Coventry MB. Peripheral neuropathies associated with total hip arthroplasty. J Bone Joint Surg Am 1976;58(1):66. 23. Edwards BN, Tullos HS, Noble PC. Contributory factors and etiology of sciatic nerve palsy in total hip arthroplasty. Clin Orthop Relat Res 1987;218:136. 24. Aust JC, Bredenberg CE, Murray DG. Mechanisms of arterial injuries associated with total hip replacement. Arch Surg 1981;116(3):345. 25. Salama R, Stavorovsky MM, Iellin A, et al. Femoral artery injury complicating total hip replacement. Clin Orthop Relat Res 1972;89:143. 26. Stamatakis JD, Kakkar VV, Sagar S, et al. Femoral vein thrombosis and total hip replacement. Br Med J 1977;2(6081):223. 27. Navarro RA, Schmalzried TP, Amstutz HC, et al. Surgical approach and nerve palsy in total hip arthroplasty. J Arthroplasty 1995;10(1):1. 28. Jolles BM, Bogoch ER. Surgical approach for total hip arthroplasty: direct lateral or posterior? J Rheumatol 2004;31(9):1790. 29. Farrell CM, Springer BD, Haidukewych GJ, et al. Motor nerve palsy following primary total hip arthroplasty. J Bone Joint Surg Am 2005;87(12):2619. 30. Schmalzried TP, Amstutz HC, Dorey FJ. Nerve palsy associated with total hip replacement. Risk factors and prognosis. J Bone Joint Surg Am 1991;73(7):1074. 31. Nercessian OA, Macaulay W, Stinchfield FE. Peripheral neuropathies following total hip arthroplasty. J Arthroplasty 1994;9(6):645. 32. Sunderland S. Nerves and nerve injuries. 2nd ed. London: Churchill Livingstone; 1978 154. 33. Nuwer MF, Schmalzried TP. Nerve palsy: etiology, prognosis, and prevention. In: Amstutz HC, editor. Hip arthroplasty. New York, NY: Churchill Livingstone; 1991. p. 415.
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Neurovascular Structure Proximity to Acetabular Retractors in Total Hip Arthroplasty Daniel Shubert, BA a, Samuel Madoff, MD b, Ralph Milillo, MD c, Sumon Nandi, MD a,b a b c
Tufts University School of Medicine, Boston, Massachusetts New England Baptist Hospital, Boston, Massachusetts North Shore-Long Island Jewish Health Care System, New Hyde Park New York
a r t i c l e
i n f o
Article history: Received 11 May 2014 Accepted 21 August 2014 Keywords: retractor acetabulum total hip arthroplasty neurovascular injury hip
a b s t r a c t Neurovascular injury during total hip arthroplasty (THA) may result in considerable morbidity or mortality. The most common cause of intraoperative neurovascular injury during THA is retractor compression. Our aims were to: 1) determine proximity of common acetabular retractor positions during THA to adjacent neurovascular structures; and 2) determine effect of patient gender on these measurements. Retractor to neurovascular structure distances were measured on 32 preoperative computed tomography images and 16 cadavers. Our data suggest the anterior inferior iliac spine is the safest anterior acetabular retractor position. With inferior progression along the anterior wall, the distance to the femoral neurovascular bundle decreases. Due to its proximity to the sciatic nerve, the position of the posterior retractor should be monitored during acetabular preparation, particularly in women. © 2014 Elsevier Inc. All rights reserved.
Total hip arthroplasty (THA) is among the most effective surgical interventions for improving health-related quality of life [1]. For this reason, and the increasing proportion of the population who are elderly, the demand for primary THA in the United States is estimated to increase dramatically over time [2]. As a result, the consequences of adverse events that occur in a systematic manner during THA are significant, and it is important to develop protocols that minimize the occurrence of these events. Neurovascular injury during THA is relatively rare, but may result in considerable morbidity or even mortality. The incidence of peripheral neurologic injury in a review of over 54,000 primary and revision THAs was 0.09% to 3.7% and 0.0% to 7.6%, respectively [3]. It is likely that the incidence of neurologic injury during THA is higher than that accounted for by clinical examination alone, and 79% of patients who suffer peripheral neurologic injury retain some degree of persistent neurologic dysfunction [3–6]. Vascular injury in THA, with a reported incidence of 0.1% to 0.2%, is less common than neurologic injury but more emergent [7]. False aneurysm or fistula formation, thromboembolism, loss of limb, or even mortality may result [8–12]. In THA, the most common identifiable cause of intraoperative nerve injury is compression by retractors [13]. In order of decreasing frequency, the sciatic, femoral, and superior gluteal nerves (SGN) are most commonly injured during THA [3,9]. There is evidence suggesting that postoperative sciatic nerve palsies occur largely due to direct trauma from instrumentation [14]. The primary etiology of femoral nerve injury has been shown to be retractor placement along the anterior acetabular rim [15–18]. Multiple studies have found subclinical electromyography-derived evidence of SGN
injury [6,19–21]. Female gender is the most well-established risk factor for neurologic injury during THA, with multiple studies reporting that at least 74% of these events occur in women [4,18,22,23]. The external iliac artery and femoral artery are the most frequently injured vascular structures in THA [9]. Acetabular retractors placed too far medially are the most frequent cause of femoral artery injury [7,24,25]. There is venographic evidence that intraoperative manipulation causes femoral vein distortion and damage resulting in thrombus formation [26]. Several studies have shown that surgical approach is not an independent cause of neurovascular injury during THA [4,5,27,28]. Consequently, appropriate retractor placement regardless of surgical approach is critical to minimizing the risk of neurovascular injury. However, safe acetabular retractor positions have not been well established in the literature. Safe acetabular retractor positions can be determined only by establishing the proximity of neurovascular structures to common sites of acetabular retractor placement during THA. The aims of our study were to: 1) determine the proximity of common acetabular retractor positions during THA to the femoral neurovascular bundle, superior gluteal neurovascular bundle, and sciatic nerve using computed tomography (CT) images as well as cadaveric specimens; and 2) ascertain if gender affects acetabular retractor proximity to neurovascular structures.
Materials and Methods Study Design
The Conflict of Interest statement associated with this article can be found at http://dx. doi.org/10.1016/j.arth.2014.08.024. Reprint requests: Sumon Nandi, MD, New England Baptist Hospital, Department of Orthopedic Surgery, 125 Parker Hill Avenue, Fogg Building, Suite 501, Boston, MA 02120. http://dx.doi.org/10.1016/j.arth.2014.08.024 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Computed Tomography Data Computed tomography (CT) scans of the hip performed preoperatively for a primary total hip arthroplasty (THA) computer-guided
146
D. Shubert et al. / The Journal of Arthroplasty 30 (2015) 145–148
navigation protocol were our data source. All scans were with multiplanar 2-dimensional reformats (coronal and sagittal). CTs of 16 male and 16 female patients performed in 2012 with equal distribution of left and right hips were selected at random from our institutional electronic radiograph archive. The distance from five common acetabular retractor positions in total hip arthroplasty to the closest neurovascular structure was measured on each hip CT. The distance from three anterior acetabular retractor positions to the femoral neurovascular bundle, the distance from one superior retractor position to the superior gluteal neurovascular bundle, and the distance from one posterior retractor position to the sciatic nerve were determined. The three anterior retractor positions were: 1) the anterior inferior iliac spine (AIIS); 2) along the anterior wall at the 3 o’clock position for the right hip or 9 o’clock position for the left hip (direct anterior); and 3) along the anterior wall immediately superior to the superior pubic ramus (antero-inferior). The superior retractor position was the 12 o’clock position immediately superior to the acetabular rim. The posterior retractor position was along the posterior wall at the 9 o’clock position for the right hip or 3 o’clock position for the left hip. The distance from an inferior retractor position to the obturator neurovascular bundle was not measured, as this structure could not be reliably identified on CT. Retractor positions were demonstrated on a 3-dimensional pelvis model to the radiologists in this study, who then established corresponding points on digital hip CT images. Distances from these points to the closest neurovascular bundle were measured using a digital caliper tool on an AGFA (Greenville, SC) Impax picture archiving and communication system (PACS). Two blinded, board-certified radiologists served as raters. Each rater made all measurements independently. The measurement protocol for each retractor site was first standardized with 20 training cases by the two raters prior to evaluation of the 32 study cases. Distances from retractor positions to adjacent neurovascular structures were determined on digital CT images as follows (Fig. 1). The three anterior measurements were performed sequentially on axial images. The AIIS retractor position was determined by first identifying the origin of the direct head of the rectus femoris, and then scrolling inferiorly 0.5 cm. Then, the shortest distance from the medial cortex of the anterior column to the femoral neurovascular bundle was measured. The second anterior retractor position was identified on the same image as above at the inferior-most confluence of the AIIS and the acetabulum. The shortest distance from this point to the femoral neurovascular bundle was measured. The third anterior retractor position was identified by scrolling 1.0 cm inferiorly from the second retractor position. At this level, the distance from the most anterior point of the anterior column medial cortex to the femoral neurovascular bundle was determined. The posterior retractor position was identified on an axial image as the point on the posterior wall 0.5 cm superior to the concavity nadir at the junction of the acetabulum and ischium. From this point, the distance to the sciatic nerve was measured. The superior retractor position was defined as the 12 o’clock position of the acetabulum first on sagittal, then coronal images. Then, the shortest distance from the lateral-most point of the acetabular cortex to the fat plane between the gluteus medius and minimus containing the superior gluteal neurovascular bundle was measured.
A
B
C
D
Fig. 1. Computed tomography images demonstrating acetabular retractor positions and adjacent neurovascular structures. (A) Distances from anterior inferior iliac spine (AIIS) and direct anterior (DA) retractor positions to femoral neurovascular bundle (FNVB); (B) distance from antero-inferior (AI) retractor position to FNVB; (C) distance from posterior (P) retractor position to sciatic nerve (ScN); (D) distance from superior (Sup) retractor position to superior gluteal neurovascular bundle (SGNVB).
Distances from the superior retractor position to the superior gluteal neurovascular bundle were not measured, as this anatomic structure could not be consistently identified on the available cadavers. The cadavers were stored in a supine position, which distorted posterior anatomy. As a result, distances from the posterior retractor position to the sciatic nerve were also not measured. Statistical Analysis As two independent raters were used in obtaining the CT data, linear mixed-effects modeling was performed to account for variation across raters. Multiple comparisons with the Tukey Method were used to test the difference between any two groups. P b 0.05 with a two-sided test was considered significant. Power analysis was used to calculate sample size. With type I error set at 5%, and desired power N0.90 to detect a 5 mm difference between pairs of retractor positions in distance to the closest neurovascular structure, a sample size of 32 CT scans was required. Results
Cadaveric Data Twelve cadavers in our institution’s anatomy laboratory with an intact lower extremity were utilized for this study. Six male and 6 female cadavers, with an equal distribution of left and right lower extremities, were randomly selected from the available cadavers. The ilioinguinal approach was performed by a single surgeon on all cadavers. The anterior acetabular retractor positions were identified, confirmed by two of the co-authors, and the shortest distance to the femoral neurovascular bundle was measured. A single metal ruler was used for all measurements.
Computed Tomography Data (Tables 1a and 1b) Of all the retractor positions, the AIIS was the farthest from the adjacent neurovascular structure at a mean of 2.65 cm (P b 0.0001), followed by the direct anterior and superior retractor positions at a mean of 2.03 to 2.20 cm (P ≤ 0.0135). The antero-inferior retractor position was the closest to the adjacent neurovascular structure at a mean of 0.95 cm (P ≤ 0.0001), followed by the posterior retractor position at a mean of 1.75 cm (P ≤ 0.0135).
D. Shubert et al. / The Journal of Arthroplasty 30 (2015) 145–148 Table 1a Distance From Retractor Position to Adjacent Neurovascular Structure as Measured on Computed Tomography Images.
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Table 2a Distance From Retractor Position to Adjacent Neurovascular Structure as Measured on Cadaveric Specimens.
Retractor Position
Mean Distance in cm (SD)
Retractor Position
Mean Distance in cm (SD)
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior Posterior Superior
2.65 (0.51) 2.20 (0.41) 0.95 (0.36) 1.75 (0.34) 2.03 (0.47)
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
2.81 (0.59) 1.39 (0.31) 0.94 (0.26)
As the retractor position moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreased to a minimum immediately superior to the superior pubic ramus (P b 0.0001). Cadaveric Data (Tables 2a and 2b) The AIIS was the farthest anterior retractor position from the femoral neurovascular bundle at a mean distance of 2.81 cm (P b 0.0001). Again, as the retractor position moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreased to a minimum mean of 0.94 cm immediately superior to the superior pubic ramus (P b 0.0001). Gender (Tables 3a and 3b) The distances between posterior (P = 0.0002), superior (P = 0.0002), as well as certain anterior acetabular retractor positions and adjacent neurovascular structures were shorter in women than in men. Based on computed tomography images, the direct anterior retractor position was significantly closer to the femoral neurovascular bundle in women than in men (P = 0.0030), while the AIIS trended towards being closer to the femoral neurovascular bundle in women (P = 0.0596). In cadaveric specimens, however, the AIIS was the only anterior retractor position that was closer to the femoral neurovascular bundle in women than in men (P = 0.0272). Discussion In order to achieve proper acetabular exposure during THA, retractors are placed circumferentially around the acetabulum. Retractor placement is a leading cause of intraoperative neurovascular injury during THA [3,13]. The sciatic nerve, femoral neurovascular bundle, and superior gluteal neurovascular bundle are most commonly at risk, and the majority of intraoperative neurovascular injuries occur in women [4,18,22,23]. To decrease the likelihood of neurovascular injury, safe acetabular retractor positions must be identified. There is a paucity of literature guiding acetabular retractor placement during THA. Therefore, we studied the distance from five common acetabular retractor positions to the adjacent neurovascular structure using CT scans and cadaveric specimens. We also determined if these distances vary by gender. Our data from both CT images and cadaveric specimens suggest that the anterior acetabular retractor position that is least likely to cause Table 1b P Values for Pairwise Comparisons Between Distances From Retractor Positions to Adjacent Neurovascular Structures as Measured on Computed Tomography Images. Retractor Position
Anterior Inferior Direct AnteroIliac Spine (AIIS) Anterior Inferior
Anterior inferior iliac – spine (AIIS) Direct anterior Antero-inferior Posterior Superior
Posterior Superior
b0.0001
b0.0001 b0.0001
b0.0001
–
b0.0001 b0.0001 – b0.0001 –
0.1256 0.0001 0.0135 –
Table 2b P Values for Pairwise Comparisons Between Distances From Retractor Positions to Adjacent Neurovascular Structures as Measured on Cadaveric Specimens. Retractor Position
Anterior inferior Iliac Spine (AIIS)
Direct anterior
AnteroInferior
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
–
b0.0001 –
b0.0001 b0.0001 –
injury to the femoral neurovascular bundle is the AIIS. As the retractor is moved inferiorly along the anterior wall, the distance to the femoral neurovascular bundle decreases and the potential risk of injury to this structure increases. In complex or revision THA with aberrant anatomy or significant acetabular bone loss, there are fewer cues for retractor placement and a reported higher incidence of neurovascular injury [4,27,29–32]. In these cases, it may be particularly important to place the anterior acetabular retractor in the AIIS, an easily identifiable bony landmark where retractor placement minimizes risk of neurovascular injury. The distance from the posterior acetabular retractor position to the sciatic nerve was less than that of most retractor positions to adjacent neurovascular bundles. This may explain the observation that sciatic nerve injury is the most common intraoperative nerve injury during THA [3,5,13,27]. Due to the proximity of the sciatic nerve to the posterior acetabular retractor, this retractor should be placed carefully, monitored closely during acetabular preparation, and adjusted as needed. We found that anterior, posterior, and superior acetabular retractors are closer to the adjacent neurovascular structures in women than in men. This may be due to variation in neurovascular anatomy, smaller stature, or reduced muscle mass in women as compared to men [3,8,22,33]. Our findings may provide a rationale for female gender as an established risk factor for nerve injury during THA, with nearly three quarters of all nerve injuries occurring in women [4,18,22,23]. Though our study may help guide acetabular retractor placement in THA, we understand that our work has limitations. First, our anatomic measurements were not made intraoperatively, but on CT images and cadaveric specimens. CT images were taken with the patient in a supine position. Many surgeons perform THA in a lateral decubitus position, and anatomic relationships may differ with positioning. Cadaveric embalming or storage may also distort anatomy. Secondly, patients scheduled for THA were not randomly selected for CT imaging of the affected hip. CT scans of patients who elected to undergo THA with computer-guided navigation were retrospectively reviewed, and there may be selection bias with this population. Thirdly, retractor positions
Table 3a Effect of Gender on Distance From Acetabular Retractor to Adjacent Neurovascular Structure as Measured on Computed Tomography Images. Retractor Position
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior Posterior Superior
Mean Distance in cm (SD) Female
Male
2.48 (0.48) 1.99 (0.39) 0.85 (0.33) 1.54 (0.24) 1.74 (0.35)
2.83 (0.50) 2.40 (0.33) 1.04 (0.38) 1.95 (0.30) 2.31 (0.40)
P Value
0.0596 0.0030 0.1440 0.0002 0.0002
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D. Shubert et al. / The Journal of Arthroplasty 30 (2015) 145–148
Table 3b Effect of Gender on Distance From Acetabular Retractor to Adjacent Neurovascular Structure as Measured on Cadaveric Specimens. Retractor Position
Anterior inferior iliac spine (AIIS) Direct anterior Antero-inferior
Mean Distance in cm (SD) Female
Male
2.45 (0.63) 1.27 (0.37) 0.87 (0.27)
3.17 (0.26) 1.52 (0.19) 1.02 (0.26)
P Value
0.0272 0.1710 0.3498
Posterior and superior retractor positions were not evaluated due to limitations in the cadaveric specimens.
were represented by a point in space in our study, which did not account for the dimensions of the retractor. Despite these limitations, our data suggest that the safest anterior acetabular retractor position during THA that minimizes risk to the femoral neurovascular bundle is the AIIS. Care should be taken in placing retractors inferiorly along the anterior wall as the distance to the femoral neurovascular bundle decreases in this position. During acetabular preparation, the position of the posterior acetabular retractor should be checked periodically to ensure that migration has not occurred given the close proximity of the sciatic nerve. These considerations are particularly important in women and in patients who lack the usual anatomic cues for retractor placement, such as those undergoing revision surgery for significant acetabular bone loss. Future work may examine intraoperative distances from retractors to adjacent neurovascular bundles during acetabular and femoral preparation. References 1. Ethgen O, Bruyère O, Richy F, et al. Health-related quality of life in total hip and total knee arthroplasty. A qualitative and systematic review of the literature. J Bone Joint Surg Am 2004;86-A(5):963. 2. Kurtz S, Mowat F, Ong K, et al. Prevalence of primary and revision total hip and knee arthroplasty in the United States from 1990 through 2002. J Bone Joint Surg Am 2005; 87(7):1487. 3. Brown GD, Swanson EA, Nercessian OA. Neurologic injuries after total hip arthroplasty. Am J Orthop (Belle Mead NJ) 2008;37(4):191. 4. Johanson NA, Pellicci PM, Tsairis P, et al. Nerve injury in total hip arthroplasty. Clin Orthop Relat Res 1983;179:214. 5. Weale AE, Newman P, Ferguson IT, et al. Nerve injury after posterior and direct lateral approaches for hip replacement. A clinical and electrophysiological study. J Bone Joint Surg (Br) 1996;78(6):899. 6.. Picado CH, Garcia FL, Marques Jr W. Damage to the superior gluteal nerve after direct lateral approach to the hip. Clin Orthop Relat Res 2007;455:209. 7. Nachbur B, Meyer RP, Verkkala K, et al. The mechanisms of severe arterial injury in surgery of the hip joint. Clin Orthop Relat Res 1979;141:122.
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