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Study of the anatomical position of the femoral nerve by magnetic resonance imaging in patients with fractured neck of femur: relevance to femoral nerve block

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Study of the anatomical position of the femoral nerve by magnetic resonance imaging in patients with fractured neck of femur: relevance to femoral nerve block
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  Original contribution Study of the anatomical position of the femoral nerve bymagnetic resonance imaging in patients with fractured neckof femur: relevance to femoral nerve block Shehzad Mehmood MB, FCARCSI, DIBICM (Resident in Anesthesiology) a, ⁎ ,Margaret Coleman MB, FFARCSI (Staff Anesthesiologist) a ,Mary Egan BSc (Senior Radiographer) b , Jim Crotty MB, FFR RCSI (Staff Radiologist) b ,Dominic Harmon MB, FCARCSI, MD (Professor of Anaesthesia) a a   Department of Anaesthesia & Intensive Care Medicine, Mid-Western Regional Hospital, Dooradoyle, Limerick, Ireland   b  Department of Radiology, Mid-Western Regional Hospital, Dooradoyle, Limerick, Ireland  Received 20 November 2007; revised 30 April 2009; accepted 18 May 2009 Keywords: Anesthesia: Regional;Femoral nerve block; Neck of femur fracture AbstractStudy Objective:  To determine the anatomical location of the femoral nerve in patients who havesustained fracture of the neck of femur, and its relevance to femoral nerve block technique. Design:  Prospective, observational clinical study. Setting:  Orthopedic and Radiology departments of a regional hospital. Subjects:  10 consecutive adult ASA physical status II and III patients (mean age, 78.5 yrs) and 4 adult healthy volunteers. Interventions:  A T1 magnetic resonance imaging scan was performed of both upper thighs in patientsand healthy volunteers successfully. Measurements:  The distance (mm) between the midpoint of the femoral artery and the midpoint of thefemoral nerve, and the distance of the femoral nerve from the skin was measured at the mid-inguinalligament, the pubic tubercle, and at the mid-inguinal crease. Data are shown as means (SD). Differences between both sides were compared using paired Student's t-tests.  P   b  0.05 was significant. Main Results:  In patients the mean distance (mm) between the midpoint of the femoral nerve from themidpoint of femoral artery at the mid-inguinal crease on the fractured and non-fractured sides was 10.7and 11.0, respectively (  P   = 0.87). The mean distance (mm) between the midpoint of the femoral nervefrom the midpoint of the femoral artery at the mid-inguinal ligament on the fractured and non-fracturedsides was 9.64 and 12.5, respectively (  P   = 0.03). The mean distance (mm) between the midpoint of thefemoral nerve from the midpoint of the femoral artery at the pubic tubercle on the fractured and non-fractured sides was 8.74 and 10.49, respectively (  P   = 0.18). Conclusions:  Blockade of the femoral nerve may be easier to perform at the mid-inguinal crease in patients with fractured neck of femur.© 2010 Elsevier Inc. All rights reserved. ⁎ Corresponding author. Tel.: +353 86 609 8209; fax: +353 1 621 6915.  E-mail address:  drsmehmood@hotmail.com (S. Mehmood).0952-8180/$  –  see front matter © 2010 Elsevier Inc. All rights reserved.doi:10.1016/j.jclinane.2009.05.007Journal of Clinical Anesthesia (2010)  22 , 122 – 125  1. Introduction Femoral nerve block is used for postoperative analgesiafollowing surgery for hip fracture. Femoral nerve block significantly decreases opioid requirements in the first 24 hours postoperatively [1,2]. Peripheral nerve blocks arealso useful in providing anesthesia and postoperativeanalgesia for non-hip fracture surgery [3].A consistent relationship of the femoral nerve to thefemoral artery is important for a successful femoral nerve block technique [4]. Anatomical distortion due to fracture of the neck of femur may change this relationship. Magneticresonance imaging (MRI) studies have been used to defineanatomy relevant to peripheral nerve block  [5,6], to suggest technique modifications [7,8], and to show spread of localanesthetic [9-11].The aim of this imaging study was to determine theanatomical location of the femoral nerve in patients whosustained fracture of the neck of femur. With intracapsular fractures of the neck of femur, the femur moves proximallyand rotates externally. The femur also moves posteriorly andmedially. The head of the femur after initial movement returns to its normal position. With extracapsular fractures,displacement of the femur is typically much greater. Therelationship between the femoral nerve and artery isimportant in the femoral nerve block technique [4]. Our study hypothesis was that these anatomical changes withfractured neck offemur may distort relationships between thefemoral nerve and artery, and have implications for thefemoral nerve block technique in these patients. 2. Materials and methods Following Mid-Western Regional Hospital Ethics Com-mittee approval and written, informed consent, 10 consec-utive ASA physical status II and III adults, with a mean age78.4 years and fracture of the neck of femur, were studied between October and December 2005. The male-to-female patient ratio was 1:9. Four healthy, adult volunteers (meanage 76.2 yrs) without fracture of the neck of femur also werestudied. All patients and volunteers were screened for anycontraindications to MRI scanning.A T1 MRI scan of both upper thighs was performed preoperatively in patients and healthy volunteers. Limb position was not controlled, as would be the case duringfemoral nerve block technique. The distance (mm) betweenthe midpoint of the femoral artery and midpoint of thefemoral nerve was measured. The distance between the skinand femoral nerve also was measured. Measurements wereobtained on the fractured and nonfractured sides in all patients. Measurements were taken at three anatomicallevels: I. mid-inguinal ligament, II. pubic tubercle, and III.mid-inguinal crease. Data are shown as means (ranges).Data sets were tested for normality. Data are means (SD).Two-tailed student-t tests were performed. A  P  -value b  0.05 was significant. 3. Results Four healthy adult volunteers without, and 10 patientswith fractured neck of femur were included in this imagingstudy. Their data are shown in Table 1.These anatomical surface landmarks were identified bytwo attending anesthesiologists, then labelled using MRIcontrast markers (ie, Vitamin E capsules). Fast-spin echo proton density transverse axial sequences were obtained at these levels. Distances to the targets were measured by anindependent, study-blinded interpreter. A line simulating theneedle insertion path (simulated or virtual needle) was placedthrough the labelled insertion sites on the image andextended posteriorly in a sagittal plane (perpendicular tothe horizontal plane) to the targets. Measurements betweenthe midpoint of the femoral artery and nerve were defined ina direction at right angles to the wall of the femoral artery.In normal age and gender-matched healthy volunteers(n = 4), mean distance between the midpoint of the femoralartery and midpoint of the femoral nerve at the mid-inguinalcrease was 9 mm (7-12) on the left and 9.75 mm (8-12) onthe right lower limb (Fig. 1). Mean distance of the femoralnerve from skin at the mid-inguinal crease was 33.25 mm Table 1  Demographic characteristics of healthy volunteersand patients with fractured neck of femur Healthy VolunteersAge (yrs) Gender (M/F) Weight (kg) Height (cm)69.0 (SD:7.7) M:F 1:3 70.0 (SD:6.2) 180.7 (SD:2.5)Patients with fractured neck of femur 78.4 (SD:5.9) M:F 1:9 70.9 (SD:5.6) 178.5 (SD:2.8) Data are means (SD). Fig. 1  Mean distance of femoral nerve from artery at inguinalcrease level in 4 healthy volunteers without fractured neck of femur. 123Femoral nerve position  (19-44) on the right and 31.25 mm (18-44) on the left lower limb. Mean distance between the midpoint of the femoralartery and midpoint of the femoral nerve at the mid-inguinalligament was 7.5 mm (5-9) on the right and 8.5 mm (5-12) onthe left lower limb. Mean distance of the femoral nerve fromskin at the mid-inguinal ligament was 43.5 mm (26-69) onthe right and 42.75 mm (29-60) on the left lower limb. Meandistance between the midpoint of the femoral artery andmidpoint of the femoral nerve at the pubic tubercle was9.5 mm (8-12) on the right and 9.5 mm (8-12) on the left lower limb. Mean distance of the femoral nerve from the skinat the pubic tubercle was 34 mm (16-44) on the right and31.75 mm (18-47) on the left lower limb.In the study patients (n = 10), mean distance between themidpoint of the femoral nerve from the midpoint of thefemoral artery at the mid-inguinal crease on the fractured andnonfractured sides was 10.7 mm (4.5) and 11.0 mm (3.7),respectively (  P   = 0.87; Fig. 2). Mean distance of the femoralnerve from the skin at the mid-inguinal crease on thefractured and non-fractured sides was 32.2 mm (8.9) and33.1 mm (8.5), respectively (  P   = 4.31).Mean distance between the midpoint of the femoralnerve from the midpoint of the femoral artery at the mid-inguinal ligament on the fractured and non-fractured sideswas 9.64 mm (4.2) and 12.5 mm (5.3), respectively (  P   =0.03; Fig. 3). Mean distance of the femoral nerve from theskin at the mid-inguinal ligament on the fractured and non-fractured sides was 49.03 mm (12.3) and 47.91 mm (14.5),respectively (  P   = 0.67).Mean distance between the midpoint of the femoralnerve from the midpoint of the femoral artery at the pubictubercle on the fractured and non-fractured sides was8.74 mm (1.7) and 10.49 mm (3.3), respectively (  P   = 0.18;Fig. 4). Mean distance of the femoral nerve from the skinat the pubic tubercle on the fractured and non-fracturedsides was 29.75 mm (11.3) and 34.94 mm (12.5),respectively (  P   = 0.18).When the volunteers were added to the study group andcombined t-test analysis was performed, the only significant difference was found at the mean distance between themidpoint of the femoral nerve from the midpoint of thefemoral artery at the mid-inguinal ligament (  P   = 0.031). 4. Discussion Femoral nerve block is used for preoperative and postoperative analgesia following hip fracture. The aim of this imaging study was to determine the anatomical locationof the femoral nerve in patients who have sustained fractureof the neck of femur.With intracapsular fracture of the neck of femur, thefemur moves proximally and rotates externally. The femur also moves posteriorly and medially [12]. The head of thefemur after the initial movement returns to its normal position. In extracapsular fracture, displacement of the femur typically is much greater  [12]. Peripheral nerve block is anexercise in which applied anatomy with anatomical changesmay have clinical significance [13]. It was the studyhypothesis that anatomical changes associated with fracture Fig. 2  Mean distance between femoral nerve and artery at theinguinal crease level in patients with fractured neck of femur. Fig. 3  Mean distance between femoral nerve and artery at themid-inguinal point in patients with fractured neck of femur. Fig. 4  Mean distance between femoral nerve and artery at the pubic tubercle level in patients with fractured neck of femur. 124 S. Mehmood et al.  of the neck of femur may change anatomy relevant tofemoral nerve block.In our study, at the midpoint of the inguinal ligament thedistance of the femoral nerve from the femoral artery on thefractured side was different from that of the nonfracturedside. This difference was small (mean, two mm). Thisdifference was not found at the mid-inguinal crease or the public tubercle levels, a finding that may be relevant to thefemoral nerve block technique in these patients.Study limitations include absence of power analysis andsmall sample size. Successful ultrasound guidance has beenreported in the femoral nerve block technique [9]. It allowsone to visualize real-time anatomical relationships for femoral nerve block, and it may obviate any anatomicalchanges associated with hip fractures.Our study shows that there is no significant anatomicalvariation of the femoral nerve and artery relationship between the left and right sides in healthy adult volunteers.An important and clinically significant relationship betweenthe femoral artery and femoral nerve at the mid-inguinalcrease as compared with the mid-inguinal ligament wasnoted in our study, consistent with the findings of Vloka et al[4]. Femoral nerve anatomy in patients with fracture of theneck of femur as it relates to the femoral nerve block technique has not been studied previously.In our study, at the mid-inguinal ligament the distance of the femoral nerve from the femoral artery on the fracturedside was different from the non-fractured side. Thisdifference, as a result of hip fracture, was not found at themid-inguinal crease or the public tubercle levels. Thisinformation is relevant to the femoral nerve block techniquein these patients. Femoral nerve block is performed moresuccessfully at the level of the mid-inguinal crease [14]. Themain factors include greater width of the femoral nerve and amore predictable femoral artery-nerve relationship at themid-inguinal crease versus the mid-inguinal ligament  [4].The femoral nerve block technique may be performed inemergency departments to treat acute pain in patients withfemoral neck fractures. Patients report a reduction in painfollowing the procedure [15,16]. Its landmarks are veryimportant for successful block as it is also performed by non-anesthesiologists in this group of patients [17].During the femoral nerve block technique, the hip ismaintained in the neutral position [18]. This is true for non hip-fracture surgery; however, it was not the case inthis study. In this study, limb position was not altered soas to avoid patient discomfort. Our study did not look at the anatomical relationship with the lower limb in theneutral position.In conclusion, the femoral nerve block technique is usedfor postoperative analgesia following hip fracture surgery.This study supports the finding that femoral nerve block may be easier to perform at the mid-inguinal crease level in patients with fracture of the neck of femur. At this level, theanatomical relationship between the femoral nerve and thefemoral artery remains consistent. References [1] Haddad FS, William RL. Femoral nerve block in extracapsular femoralneck fractures. J Bone Joint Surg Br 1995;77:922-3.[2] Coad NR. Post-operative analgesia following femoral neck surgery – comparison between 3 in 1 femoral nerve block and lateral cutaneousnerve block. Eur J Anaesthesiol 1991;8:287-90.[3] Horlocker TT.Peripheral nerve blocks – regional anesthesia for the newmillennium. Reg Anesth Pain Med 1998;23:237-40.[4] Vloka JD, Hadzi ć  A, Drobnik L, Ernest A, Reiss W, Thys DM.Anatomical landmarks for femoral nerve block: comparison of four needle insertion sites. Anesth Analg 1999;89:1467-70.[5] Crighton IM, Barry BP, Hobbs GJ. A study of the anatomy of caudalspace using magnetic resonance imaging. Br J Anaesth 1997;78:391-5.[6] Klaastad O, Smedby O, Kielstrup T, Smith HJ. The verticalinfraclavicular brachial plexus block: a simulation study usingmagnetic resonance imaging. Anesth Analg 2005;101:273-8.[7] Klaastad O, Lilleås FG, Røtnes JS, Breivik H, Fosse E. Magneticresonance imaging demonstrates lack of precision in needle placement  by the infraclavicular brachial plexus block described by Raj et al.Anesth Analg 1999;88:593-8.[8] Niemi-Murola L, Krootila K, Kivisaari R, Kangasmäki A, Kivisaari L,Maunuksela EL. Localization of local anesthetic solution by magneticresonance imaging. Ophthalmology 2004;111:342-7.[9] Marhofer P, Nasel C, Sitzwohl C, Kapral S. Magnetic resonanceimaging of the distribution of local anesthetic during the three-in-one block. Anesth Analg 2000;90:119-24.[10] Mannion S, Barrett J, Kelly D, Murphy DB, Shorten GD. Adescription of the spread of injectate after psoas compartment block using magnetic resonance imaging. Reg Anesth Pain Med 2005;30:567-76.[11] Klaastad O, Smedby O, Thompson GE, et al. Distribution of localanesthetic in axillary brachial plexus block: a clinical and magneticresonance imaging study. Anesthesiology 2002;96:1315-24.[12] Delee JC. Fractures and dislocations in adults. In: Bucholz RW,Heckman JD, Court-Brown CM, Tornetta P, Koval KJ, editors.Rockwood and Green's Fractures in Adults, Vol 2. Philadelphia:Lippincott Raven Publishers; 2005. p. 1668-70.[13] Lew K, Townsen G. Failure to obtain adequate anaesthesia associatedwith a bifid mandibular canal: a case report. Aust Dent J 2006;51:86-90.[14] Schulz-Stübner S, Henszel A, Hata JS. A new rule for femoral nerve blocks. Reg Anesth Pain Med 2005;30:473-7.[15] Finlayson BJ, Underhill TJ. Femoral nerve block for analgesia infractures of the femoral neck. Arch Emerg Med 1988;5:173-6.[16] Fletcher AK, Rigby AS, Heyes FL. Three-in-one femoral nerve block as analgesia for fractured neck of femur in the emergency department:a randomized, controlled trial. Ann Emerg Med 2003;41:227-33.[17] Cole A. Nurse-administered femoral nerve block after hip fracture. Nurs Times 2005;101:34-6.[18] Lang SA, Yip RW, Chang PC, Gerard MA. The femoral 3-in-1 block revisited. J Clin Anesth 1993;5:292-6. 125Femoral nerve position
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