ULTRASOUND ARTICLE
Ultrasound-Guided Injection of the Intrapelvic Portion of the Obturator Internus in a Cadaver Model Sang Chul Lee, MD, PhD,* Dong-wook Rha, MD, PhD,* Hee-Jin Kim, DDS, PhD,† Hun-mu Yang, DDS, PhD,‡ Sang-Hee Lee, DDS,† and DongJin Koh, MD*
Background and Objectives: Musculoskeletal dysfunction of the pelvic floor is common. One of the intrapelvic muscles, the obturator internus (OI), can be substantially stressed during its sharply angulated exit from the pelvis. However, there may be considerable overlap between symptoms and signs arising from the OI and other potential pain generators including the levator ani in the pelvic region. Accurate diagnosis for the OI might permit more efficient treatment combined with OI-specific exercise and behavior modification. Therefore, we hypothesized that ultrasound (US)-guided needle insertion in the intrapelvic portion of the OI would be accurate when a pararectal approach is used for diagnostic and therapeutic purposes. Methods: Bilateral US-guided intramuscular injections in the pelvic area were performed using 6 fresh, nonembalmed male cadavers. When the needle was positioned in the targeted muscle, 0.5 mL of green filler was injected. After the injection procedure, each specimen was dissected to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI. Results: Twelve injections were made into the targeted muscles in the 6 cadaveric specimens. All injections placed filler into the OI muscles just medial to the inferior pubic ramus. There was no case in which a needle passed through unintended structures, such as neurovascular structures. Conclusions: The newly developed US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI. This US-guided method facilitated a more precise approach to the intrapelvic portion of the OI and may help differentiate conditions or symptoms caused by other structures. (Reg Anesth Pain Med 2014;39: 347–350)
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hronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), previously termed nonbacterial prostatitis/prostatodynia, and interstitial cystitis affect nearly 3 million people in the United States. Musculoskeletal dysfunction of the pelvic floor is commonly identified in both diagnostic groups and frequently coexists with other pelvic pathologies as evidenced by its identification in approximately 80% of patients afflicted with prostatitis and interstitial cystitis.1,2 Significant symptomatic relief can often be achieved through management of the musculoskeletal
From the *Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine; †Division in Anatomy and Developmental Biology, Department of Oral Biology, BK21 PLUS Project, Human Identification Research Center, Yonsei University College of Dentistry, Seoul; and ‡Department of Anatomy, College of Medicine, Dankook University, Cheonan, Republic of Korea. Accepted for publication March 6, 2014. Address correspondence to: Sang Chul Lee, MD, PhD, Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, South Korea (e‐mail: [email protected]). The authors declare no conflict of interest. Copyright © 2014 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000093
dysfunction, but musculoskeletal problems are often overlooked in patients with pelvic floor pain because undue clinical attention is paid to the pelvic viscera.3 Anderson et al4 reported that in 72 men with CP/CPPS, the most prevalent pain site was the penis (90.3%) and that myofascial trigger points (MTrPs) in pelvic floor muscles, the levator ani or obturator internus (OI), reproduced penile pain in more than 75% of cases. The diagnostic criteria for identifying active MTrPs in each pelvic floor muscle have been described.5 However, as the authors relied on palpation to identify MTrPs, MTrPs of the levator ani cannot be differentiated from those of the OI. In a previous study, trigger point injections into the levator ani through the transvaginal approach were tried. Although the first trigger point injection resulted in a 72% rate of success (defined as a decrease in pain visual analog scale of 50% or more), transvaginal palpation could not confirm MTrPs in the levator ani muscles.6 Srinivasan et al3 introduced the injection methods to the intrapelvic portion of the OI or levator ani muscles through a transvaginal or pararectal approach. However, as the injection was not image-guided, it was impossible to reliably show that the intrapelvic portion of the OI or levator ani was targeted. The OI is commonly involved along with the levator ani in cases of musculoskeletal dysfunction involving the pelvic floor.7 It is important to determine which of these 2 muscles is most responsible for musculoskeletal dysfunction. As opposed to the levator ani, which requires internal manipulation by a therapist through the rectum or vagina for rehabilitation, the intrapelvic portion of the OI may be treated by patient through external stretching and strengthening. Although not formally documented, we have experienced patients with tender perineal muscles who are reluctant to use conventional α-blockers, analgesics, and antibiotics. These patients found short-term relief after ultrasound (US)-guided injection with a modified method of Srinivasan et al3 (blind pararectal approach). Ultrasound-guided injection allows real-time scanning of the targeted muscle and adjacent structures, and facilitates accurate depth control of needle placement.8 Furthermore, US-guided trigger point injections of deep muscles, such as the iliopsoas, hip adductor, and low back muscles, are reported to be accurate, safe, and efficient.9,10 To maintain the effect of US-guided intramuscular injection over a long period, especially in the case of myofascial pain syndrome, stretching exercises and behavioral corrections are essential to avoid early recurrence of pain after trigger point injection. Stretching exercises and behavioral corrections can be prescribed more appropriately when the target muscle for intramuscular injection is identified. On the basis of the OI anatomy, we hypothesized that USguided needle insertion into the intrapelvic portion of the OI would be accurately accomplished when a pararectal approach is used. Therefore, the purpose of the present study was to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI in a fresh cadaver model.
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
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Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
Lee et al
METHODS Bilateral intramuscular injections of the intrapelvic portion of the OI were performed using 6 fresh unembalmed male cadavers. The average age (SD) at death was 71.7 (5.8) years (range, 65–79 years). There was no evidence of previous injury or surgical procedure around the pelvis. None of the recorded causes of death were deemed to have affected the results of this study with regard to needle placement or dissection. We performed B-mode, real-time ultrasonography using the ACCUVIX A30 system (Samsung, Seoul, South Korea) interfaced with a linear array transducer (5–12 MHz). An investigator (S.C.L.) with more than 7 years of experience in musculoskeletal ultrasonography carried out these procedures. Cadavers were positioned lying on the lateral side with the examination side down. The contralateral hip was placed in a position of flexion and the examined side of the hip was placed in the neutral position so the US probe was able to access the perineum. Manual palpation of the inferior pubic ramus was done followed by that of underlying muscles. The probe was then moved to the inner side of the inferior pubic ramus so that the targeted muscle was identified on the US image (Fig. 1A). As necessary, the conspicuity of the targeted muscle could be increased by angling the probe medially as far as possible. Injections were performed with an 8.7-cm, 22-gauge needle after estimation of target depth by sonography. Using a realtime technique, the probe was placed in close proximity to the puncture site and the needle was advanced under direct US control (Fig. 1B). The needle was in-plane with the probe. When the needle was positioned in the targeted muscle, 0.5 mL of green filler (dye) was injected (Fig. 1C). For each specimen, the same technique was completed on both sides. After the injection procedure, an expert anatomist (H.J.K.) dissected each specimen to identify whether the targeted muscle was the OI and to evaluate the accuracy of the injections and any complications (defined as a needle passage through unintended structures, such as significant neurovascular structures). The OI was confirmed by passively rotating the hip internally and externally, which moved the OI but not the levator ani. Descriptive statistics were used to report the location of the US-guided OI injections.
RESULTS Twelve injections were made into the targeted muscles in 6 fresh cadaveric specimens. All injections placed green filler into the OI muscles just medial to the inferior pubic ramus (Fig. 2). However, in all 12 cases, injection of 0.5-mL filler did not cover the entire intrapelvic portion of the OI, but remained mostly limited to the medial side of the inferior pubic ramus. No muscles other than the OI were injected during the
procedure. There were no cases where the injection targeted the levator ani. In all 12 cases, the levator ani was considerably remote from the injected area (Fig. 3). There were no cases in which the needle passed through unintended neurovascular structures.
DISCUSSION In the present study, we intended to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI in fresh cadavers for the treatment of pelvic floor pain. All OI muscles were injected successfully without neurovascular injury or inappropriate injection of other muscles. The evaluation and management of patients presenting with pelvic floor pain is challenging because of the complex anatomy, broad differential diagnoses, and lack of specific physical examination findings. Clinicians should not only consider a variety of potential pain generators intrinsic to the pelvic region but also recognize the potential for the lumbar spine and hip joint to refer pain into the pelvic area. Pain arising from the OI has been recently reported.11 The OI possesses unique anatomy among the hip short external rotators.12 It originates from within the pelvis along the obturator foramen and membrane, exits through the lesser sciatic foramen by curving around the posterior ischium, and courses laterally deep to the sciatic nerve toward its common insertion with the gemelli on the medial side of the greater trochanter.13 Similar to the piriformis, the OI functions primarily as a hip external rotator and may assist in abducting the flexed hip.14 The OI might be substantially stressed during its sharply angulated exit from the pelvis, as evidenced by the presence of a saddle-shaped cartilaginous region on the posterior ischium over which the OI tendon glides (Fig. 4).15 Also, pain associated with prolonged sitting can also be attributed to the OI.11 However, there may be considerable overlap between symptoms and signs arising from the OI and other potential pain generators including the levator ani in pelvic region. The results of the current study only provide information that this US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI in adult cadavers. However, as the intrapelvic portion of the OI is located in close proximity to the levator ani, the condition could be misdiagnosed or underestimated as a problem confined to levator ani only. As the current US-guided method allowed proper injection to the OI, US-guided injection could be used as a diagnostic method, instead of palpation or symptom evaluation, to confirm the muscle responsible for the problem between the OI and levator ani. Consequently, when the OI is the pain generator, it is easier to apply conventional muscle-specific stretching exercise or behavioral corrections than for the levator ani. With the injection method introduced in this study, the injected green filler spread into less than half of intrapelvic part of the OI. The purpose
FIGURE 1. A, US image of the OI. The probe of US was placed to the inner side of the inferior pubic ramus. B, Injection under direct US control. C, Corresponding US image of (B). A indicates anterior; P, posterior.
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Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
FIGURE 2. Left intrapelvic portion of the OI. All injections placed green filler into the OI just medial to the inferior pubic ramus. However, in all 12 cases, injection of 0.5-mL filler did not cover the entire intrapelvic portion of the OI, but was mostly limited to the medial side of the inferior pubic ramus. L indicates left; P, posterior.
of this study was to confirm proper injection to target muscle, thus 0.5-mL low-diffusion filter was used. Injection agents or solutions that have higher diffusability, such as local anesthetics or steroids, may cause injection into the higher portion of the muscle. A study introducing a different route of US-guided injection to the OI used a 5.2-MHz curvilinear array probe in patients positioned prone.11 The posterior ischium was used as a landmark to inject the extrapelvic portion of the OI located inferior to the gluteus maximus. We focused on the intrapelvic portion of the OI, whereas Smith et al11 focused on the extrapelvic portion of the OI. The latter study considered the extrapelvic portion of the OI as the origin of gluteal pain and we hypothesized that the intrapelvic portion of the OI was the responsible muscle for pelvic floor pain, commonly regarded as CP in men. In our experience, when the injection was done using the approach of Smith et al,11 pelvic floor pain was not relieved. Furthermore, the tenderness was found in the intrapelvic portion of the OI but not in the extrapelvic portion of the OI on physical examination in many cases with pelvic floor pain. Due to the sharply angulated exit
US-Guided Injection of OI
FIGURE 4. Illustration of the OI. The OI are composed of the intrapelvic and extrapelvic portion. The OI can be substantially stressed during its sharply angulated exit from the pelvis, as evidenced by the presence of a saddle-shaped cartilaginous region on the posterior ischium over which the OI tendon glides. Gem indicates superior and inferior gemelli; GMa, gluteus maximus; GMe, gluteus medius; GMi, gluteus minimus; Pir, piriformis; Pn, pudendal nerve; QF, quadratus femoris; Sn, sciatic nerve.
of the OI from the pelvis, we believe that the effective injection on the intrapelvic portion of the OI could be done using our approach. Injection into the intrapelvic portion of the OI was regarded as a treatment method for CP/CPPS or interstitial cystitis-related muscle problem with the study subjects (male cadavers). However, women are affected more commonly than men with pelvic floor pain (nearly 4:1 female preponderance).1 Hence, we think US-guided injection could also be used for diagnostic and therapeutic purposes in OI-originated pain in women who have been misdiagnosed with diseases such as pelvic inflammatory disease. There are some limitations to our study. Despite successful injection of the OI, this study did not verify the usefulness of this technique in clinical practice. Further studies are needed to evaluate the therapeutic efficacy of injection into the intrapelvic portion of the OI using this US-guided pararectal approach in managing muscle-originated pelvic floor pain. This study is also limited because the cadavers had normative body mass index. It is unclear whether ultrasonographic real-time scanning is able to gain an adequate image in obese patients. We have defined complications of the injection as needle passage through unintended neurovascular structures. Although we reported that there were no complications, our failure to identify the obturator and pudendal nerves during dissection is another limitation.
CONCLUSIONS FIGURE 3. Overall perineal area seen from the bottom. There was no case where the injection was done in levator ani. The levator ani was remote from the injected area. P indicates posterior; R, right. © 2014 American Society of Regional Anesthesia and Pain Medicine
The newly developed US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI in adult cadavers. This US-guided method facilitates a more precise approach to the intrapelvic portion of the OI and differentiates conditions or symptoms caused by other structures. Accurate diagnosis for the OI might provide a more
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Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
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efficient treatment combined with OI-specific exercise and behavior modification.
7. Weiss JM. Pelvic floor myofascial trigger points: manual therapy for interstitial cystitis and the urgency-frequency syndrome. J Urol. 2001;166:2226–2231.
ACKNOWLEDGMENTS The authors thank Mr Dong-Su Jang, research assistant, Department of Anatomy, Yonsei University College of Medicine, Seoul, Korea, for the help with the figures.
8. Berweck S, Feldkamp A, Francke A, Nehles J, Schwerin A, Heinen F. Sonography-guided injection of botulinum toxin A in children with cerebral palsy. Neuropediatrics. 2002;33:221–223.
REFERENCES 1. Sinaki M, Merritt JL, Stillwell GK. Tension myalgia of the pelvic floor. Mayo Clin Proc. 1977;52:717–722. 2. Hetrick DC, Ciol MA, Rothman I, Turner JA, Frest M, Berger RE. Musculoskeletal dysfunction in men with chronic pelvic pain syndrome type III: a case control study. J Urol. 2003;170:828–831. 3. Srinivasan AK, Kaye JD, Moldwin R. Myofascial dysfunction associated with chronic pelvic floor pain: management strategies. Curr Pain Headache Rep. 2007;11:359–364. 4. Anderson RU, Sawyer T, Wise D, Morey A, Nathanson BH. Painful myofascial trigger points and pain sites in men with chronic prostatitis/ chronic pelvic pain syndrome. J Urol. 2009;182:2753–2758. 5. Travell JG, Simons DG. Myofascial Pain and Dysfunction: The Trigger Point Manual. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 1998. The Lower Extremities, vol. 2 6. Langford CF, Udvari Nagy S, Ghoniem GM. Levator ani trigger point injections: an underutilized treatment for chronic pelvic pain. Neurourol Urodyn. 2007;26:59–62.
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9. Rha DW, Shin JC, Kim YK, Jung JH, Kim YU, Lee SC. Detecting local twitch responses of myofascial trigger points in the lower-back muscles using ultrasonography. Arch Phys Med Rehabil. 2011;92: 1576–1580. 10. Kim DS, Jeong TY, Kim YK, Chang WH, Yoon JG, Lee SC. Usefulness of a myofascial trigger point injection for groin pain in patients with chronic prostatitis/chronic pelvic pain syndrome: a pilot study. Arch Phys Med Rehabil. 2013;94:930–936. 11. Smith J, Wisniewski SJ, Wempe MK, Landry BW, Sellon JL. Sonographically guided obturator internus injections: techniques and validation. J Ultrasound Med. 2012;31:1597–1608. 12. Aung HH, Sakamoto H, Akita K, Sato T. Anatomical study of the obturator internus, gemelli and quadratus femoris muscles with special reference to their innervation. Anat Rec. 2001;263:41–52. 13. Cox JM, Bakkum BW. Possible generators of retrotrochanteric gluteal and thigh pain: the gemelli-obturator internus complex. J Manipulative Physiol Ther. 2005;28:534–538. 14. Meknas K, Christensen A, Johansen O. The internal obturator muscle may cause sciatic pain. Pain. 2003;104:375–380. 15. Shinohara H. Gemelli and obturator internus muscles: different heads of one muscle? Anat Rec. 1995;243:145–150.
© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Ultrasound-Guided Injection of the Intrapelvic Portion of the Obturator Internus in a Cadaver Model Sang Chul Lee, MD, PhD,* Dong-wook Rha, MD, PhD,* Hee-Jin Kim, DDS, PhD,† Hun-mu Yang, DDS, PhD,‡ Sang-Hee Lee, DDS,† and DongJin Koh, MD*
Background and Objectives: Musculoskeletal dysfunction of the pelvic floor is common. One of the intrapelvic muscles, the obturator internus (OI), can be substantially stressed during its sharply angulated exit from the pelvis. However, there may be considerable overlap between symptoms and signs arising from the OI and other potential pain generators including the levator ani in the pelvic region. Accurate diagnosis for the OI might permit more efficient treatment combined with OI-specific exercise and behavior modification. Therefore, we hypothesized that ultrasound (US)-guided needle insertion in the intrapelvic portion of the OI would be accurate when a pararectal approach is used for diagnostic and therapeutic purposes. Methods: Bilateral US-guided intramuscular injections in the pelvic area were performed using 6 fresh, nonembalmed male cadavers. When the needle was positioned in the targeted muscle, 0.5 mL of green filler was injected. After the injection procedure, each specimen was dissected to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI. Results: Twelve injections were made into the targeted muscles in the 6 cadaveric specimens. All injections placed filler into the OI muscles just medial to the inferior pubic ramus. There was no case in which a needle passed through unintended structures, such as neurovascular structures. Conclusions: The newly developed US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI. This US-guided method facilitated a more precise approach to the intrapelvic portion of the OI and may help differentiate conditions or symptoms caused by other structures. (Reg Anesth Pain Med 2014;39: 347–350)
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hronic prostatitis/chronic pelvic pain syndrome (CP/CPPS), previously termed nonbacterial prostatitis/prostatodynia, and interstitial cystitis affect nearly 3 million people in the United States. Musculoskeletal dysfunction of the pelvic floor is commonly identified in both diagnostic groups and frequently coexists with other pelvic pathologies as evidenced by its identification in approximately 80% of patients afflicted with prostatitis and interstitial cystitis.1,2 Significant symptomatic relief can often be achieved through management of the musculoskeletal
From the *Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine; †Division in Anatomy and Developmental Biology, Department of Oral Biology, BK21 PLUS Project, Human Identification Research Center, Yonsei University College of Dentistry, Seoul; and ‡Department of Anatomy, College of Medicine, Dankook University, Cheonan, Republic of Korea. Accepted for publication March 6, 2014. Address correspondence to: Sang Chul Lee, MD, PhD, Department and Research Institute of Rehabilitation Medicine, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul 120-752, South Korea (e‐mail: [email protected]). The authors declare no conflict of interest. Copyright © 2014 by American Society of Regional Anesthesia and Pain Medicine ISSN: 1098-7339 DOI: 10.1097/AAP.0000000000000093
dysfunction, but musculoskeletal problems are often overlooked in patients with pelvic floor pain because undue clinical attention is paid to the pelvic viscera.3 Anderson et al4 reported that in 72 men with CP/CPPS, the most prevalent pain site was the penis (90.3%) and that myofascial trigger points (MTrPs) in pelvic floor muscles, the levator ani or obturator internus (OI), reproduced penile pain in more than 75% of cases. The diagnostic criteria for identifying active MTrPs in each pelvic floor muscle have been described.5 However, as the authors relied on palpation to identify MTrPs, MTrPs of the levator ani cannot be differentiated from those of the OI. In a previous study, trigger point injections into the levator ani through the transvaginal approach were tried. Although the first trigger point injection resulted in a 72% rate of success (defined as a decrease in pain visual analog scale of 50% or more), transvaginal palpation could not confirm MTrPs in the levator ani muscles.6 Srinivasan et al3 introduced the injection methods to the intrapelvic portion of the OI or levator ani muscles through a transvaginal or pararectal approach. However, as the injection was not image-guided, it was impossible to reliably show that the intrapelvic portion of the OI or levator ani was targeted. The OI is commonly involved along with the levator ani in cases of musculoskeletal dysfunction involving the pelvic floor.7 It is important to determine which of these 2 muscles is most responsible for musculoskeletal dysfunction. As opposed to the levator ani, which requires internal manipulation by a therapist through the rectum or vagina for rehabilitation, the intrapelvic portion of the OI may be treated by patient through external stretching and strengthening. Although not formally documented, we have experienced patients with tender perineal muscles who are reluctant to use conventional α-blockers, analgesics, and antibiotics. These patients found short-term relief after ultrasound (US)-guided injection with a modified method of Srinivasan et al3 (blind pararectal approach). Ultrasound-guided injection allows real-time scanning of the targeted muscle and adjacent structures, and facilitates accurate depth control of needle placement.8 Furthermore, US-guided trigger point injections of deep muscles, such as the iliopsoas, hip adductor, and low back muscles, are reported to be accurate, safe, and efficient.9,10 To maintain the effect of US-guided intramuscular injection over a long period, especially in the case of myofascial pain syndrome, stretching exercises and behavioral corrections are essential to avoid early recurrence of pain after trigger point injection. Stretching exercises and behavioral corrections can be prescribed more appropriately when the target muscle for intramuscular injection is identified. On the basis of the OI anatomy, we hypothesized that USguided needle insertion into the intrapelvic portion of the OI would be accurately accomplished when a pararectal approach is used. Therefore, the purpose of the present study was to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI in a fresh cadaver model.
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
347
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
Lee et al
METHODS Bilateral intramuscular injections of the intrapelvic portion of the OI were performed using 6 fresh unembalmed male cadavers. The average age (SD) at death was 71.7 (5.8) years (range, 65–79 years). There was no evidence of previous injury or surgical procedure around the pelvis. None of the recorded causes of death were deemed to have affected the results of this study with regard to needle placement or dissection. We performed B-mode, real-time ultrasonography using the ACCUVIX A30 system (Samsung, Seoul, South Korea) interfaced with a linear array transducer (5–12 MHz). An investigator (S.C.L.) with more than 7 years of experience in musculoskeletal ultrasonography carried out these procedures. Cadavers were positioned lying on the lateral side with the examination side down. The contralateral hip was placed in a position of flexion and the examined side of the hip was placed in the neutral position so the US probe was able to access the perineum. Manual palpation of the inferior pubic ramus was done followed by that of underlying muscles. The probe was then moved to the inner side of the inferior pubic ramus so that the targeted muscle was identified on the US image (Fig. 1A). As necessary, the conspicuity of the targeted muscle could be increased by angling the probe medially as far as possible. Injections were performed with an 8.7-cm, 22-gauge needle after estimation of target depth by sonography. Using a realtime technique, the probe was placed in close proximity to the puncture site and the needle was advanced under direct US control (Fig. 1B). The needle was in-plane with the probe. When the needle was positioned in the targeted muscle, 0.5 mL of green filler (dye) was injected (Fig. 1C). For each specimen, the same technique was completed on both sides. After the injection procedure, an expert anatomist (H.J.K.) dissected each specimen to identify whether the targeted muscle was the OI and to evaluate the accuracy of the injections and any complications (defined as a needle passage through unintended structures, such as significant neurovascular structures). The OI was confirmed by passively rotating the hip internally and externally, which moved the OI but not the levator ani. Descriptive statistics were used to report the location of the US-guided OI injections.
RESULTS Twelve injections were made into the targeted muscles in 6 fresh cadaveric specimens. All injections placed green filler into the OI muscles just medial to the inferior pubic ramus (Fig. 2). However, in all 12 cases, injection of 0.5-mL filler did not cover the entire intrapelvic portion of the OI, but remained mostly limited to the medial side of the inferior pubic ramus. No muscles other than the OI were injected during the
procedure. There were no cases where the injection targeted the levator ani. In all 12 cases, the levator ani was considerably remote from the injected area (Fig. 3). There were no cases in which the needle passed through unintended neurovascular structures.
DISCUSSION In the present study, we intended to evaluate the accuracy of US-guided injection into the intrapelvic portion of the OI in fresh cadavers for the treatment of pelvic floor pain. All OI muscles were injected successfully without neurovascular injury or inappropriate injection of other muscles. The evaluation and management of patients presenting with pelvic floor pain is challenging because of the complex anatomy, broad differential diagnoses, and lack of specific physical examination findings. Clinicians should not only consider a variety of potential pain generators intrinsic to the pelvic region but also recognize the potential for the lumbar spine and hip joint to refer pain into the pelvic area. Pain arising from the OI has been recently reported.11 The OI possesses unique anatomy among the hip short external rotators.12 It originates from within the pelvis along the obturator foramen and membrane, exits through the lesser sciatic foramen by curving around the posterior ischium, and courses laterally deep to the sciatic nerve toward its common insertion with the gemelli on the medial side of the greater trochanter.13 Similar to the piriformis, the OI functions primarily as a hip external rotator and may assist in abducting the flexed hip.14 The OI might be substantially stressed during its sharply angulated exit from the pelvis, as evidenced by the presence of a saddle-shaped cartilaginous region on the posterior ischium over which the OI tendon glides (Fig. 4).15 Also, pain associated with prolonged sitting can also be attributed to the OI.11 However, there may be considerable overlap between symptoms and signs arising from the OI and other potential pain generators including the levator ani in pelvic region. The results of the current study only provide information that this US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI in adult cadavers. However, as the intrapelvic portion of the OI is located in close proximity to the levator ani, the condition could be misdiagnosed or underestimated as a problem confined to levator ani only. As the current US-guided method allowed proper injection to the OI, US-guided injection could be used as a diagnostic method, instead of palpation or symptom evaluation, to confirm the muscle responsible for the problem between the OI and levator ani. Consequently, when the OI is the pain generator, it is easier to apply conventional muscle-specific stretching exercise or behavioral corrections than for the levator ani. With the injection method introduced in this study, the injected green filler spread into less than half of intrapelvic part of the OI. The purpose
FIGURE 1. A, US image of the OI. The probe of US was placed to the inner side of the inferior pubic ramus. B, Injection under direct US control. C, Corresponding US image of (B). A indicates anterior; P, posterior.
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© 2014 American Society of Regional Anesthesia and Pain Medicine
Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
FIGURE 2. Left intrapelvic portion of the OI. All injections placed green filler into the OI just medial to the inferior pubic ramus. However, in all 12 cases, injection of 0.5-mL filler did not cover the entire intrapelvic portion of the OI, but was mostly limited to the medial side of the inferior pubic ramus. L indicates left; P, posterior.
of this study was to confirm proper injection to target muscle, thus 0.5-mL low-diffusion filter was used. Injection agents or solutions that have higher diffusability, such as local anesthetics or steroids, may cause injection into the higher portion of the muscle. A study introducing a different route of US-guided injection to the OI used a 5.2-MHz curvilinear array probe in patients positioned prone.11 The posterior ischium was used as a landmark to inject the extrapelvic portion of the OI located inferior to the gluteus maximus. We focused on the intrapelvic portion of the OI, whereas Smith et al11 focused on the extrapelvic portion of the OI. The latter study considered the extrapelvic portion of the OI as the origin of gluteal pain and we hypothesized that the intrapelvic portion of the OI was the responsible muscle for pelvic floor pain, commonly regarded as CP in men. In our experience, when the injection was done using the approach of Smith et al,11 pelvic floor pain was not relieved. Furthermore, the tenderness was found in the intrapelvic portion of the OI but not in the extrapelvic portion of the OI on physical examination in many cases with pelvic floor pain. Due to the sharply angulated exit
US-Guided Injection of OI
FIGURE 4. Illustration of the OI. The OI are composed of the intrapelvic and extrapelvic portion. The OI can be substantially stressed during its sharply angulated exit from the pelvis, as evidenced by the presence of a saddle-shaped cartilaginous region on the posterior ischium over which the OI tendon glides. Gem indicates superior and inferior gemelli; GMa, gluteus maximus; GMe, gluteus medius; GMi, gluteus minimus; Pir, piriformis; Pn, pudendal nerve; QF, quadratus femoris; Sn, sciatic nerve.
of the OI from the pelvis, we believe that the effective injection on the intrapelvic portion of the OI could be done using our approach. Injection into the intrapelvic portion of the OI was regarded as a treatment method for CP/CPPS or interstitial cystitis-related muscle problem with the study subjects (male cadavers). However, women are affected more commonly than men with pelvic floor pain (nearly 4:1 female preponderance).1 Hence, we think US-guided injection could also be used for diagnostic and therapeutic purposes in OI-originated pain in women who have been misdiagnosed with diseases such as pelvic inflammatory disease. There are some limitations to our study. Despite successful injection of the OI, this study did not verify the usefulness of this technique in clinical practice. Further studies are needed to evaluate the therapeutic efficacy of injection into the intrapelvic portion of the OI using this US-guided pararectal approach in managing muscle-originated pelvic floor pain. This study is also limited because the cadavers had normative body mass index. It is unclear whether ultrasonographic real-time scanning is able to gain an adequate image in obese patients. We have defined complications of the injection as needle passage through unintended neurovascular structures. Although we reported that there were no complications, our failure to identify the obturator and pudendal nerves during dissection is another limitation.
CONCLUSIONS FIGURE 3. Overall perineal area seen from the bottom. There was no case where the injection was done in levator ani. The levator ani was remote from the injected area. P indicates posterior; R, right. © 2014 American Society of Regional Anesthesia and Pain Medicine
The newly developed US-guided pararectal approach allowed accurate insertion of a needle into the intrapelvic portion of the OI in adult cadavers. This US-guided method facilitates a more precise approach to the intrapelvic portion of the OI and differentiates conditions or symptoms caused by other structures. Accurate diagnosis for the OI might provide a more
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Regional Anesthesia and Pain Medicine • Volume 39, Number 4, July-August 2014
Lee et al
efficient treatment combined with OI-specific exercise and behavior modification.
7. Weiss JM. Pelvic floor myofascial trigger points: manual therapy for interstitial cystitis and the urgency-frequency syndrome. J Urol. 2001;166:2226–2231.
ACKNOWLEDGMENTS The authors thank Mr Dong-Su Jang, research assistant, Department of Anatomy, Yonsei University College of Medicine, Seoul, Korea, for the help with the figures.
8. Berweck S, Feldkamp A, Francke A, Nehles J, Schwerin A, Heinen F. Sonography-guided injection of botulinum toxin A in children with cerebral palsy. Neuropediatrics. 2002;33:221–223.
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Copyright © 2014 American Society of Regional Anesthesia and Pain Medicine. Unauthorized reproduction of this article is prohibited.
