Obturator Neuropathy

By Bernard M. Abrams, M.D.

Obturator Neuropathy is an uncommon affliction but may cause medial thigh pain. [1] While its description as an entrapment neuropathy is historically interesting, [2] the most common causes by far are trauma and, unfortunately, iatrogenic trauma is the most common cause.

Anatomically, the Obturator nerve is formed within the psoas muscle by the ventral divisions of the ventral primary rami of the L2, L3 and L4 nerve roots. It shares fibers from the same nerve roots as the femoral nerve. After descending through the psoas muscle, it emerges from the medial border of the psoas at the pelvic brim immediately anterior to the sacroiliac joint. In the female, it is separated from the ovary by a thin layer of peritoneum. The nerve then curves downward and forward around the pelvic cavity wall to emerge through the Obturator foramen where it is in company with the Obturator vessels.

The Obturator canal is an osseofibrous canal formed by a hiatus in the Obturator membrane up against the pubic bone. Of the anatomical structures in the canal, the nerve is the closet to the bone leading to its purported involvement in osteitis pubis. [3] In the canal, it divides into anterior and posterior branches.[4] The anterior branch innervates the adductor longus, adductor brevis and gracilis muscles. The supply to the pectineus muscles is variable. The posterior branch supplies the Obturator externus and adductor magnus muscles. The adductor brevis muscle may be supplied by either branch. Articular branches are given off to the hip joint. [4] There is sensory innervation of a limited area of the upper medial thigh. Because of its position, the nerve is seldom directly traumatized.

Clinical Picture
While seldom damaged alone in extensive trauma, the hallmarks of Obturator neuropathy are pain and weakness of the adductor musculature. The patient cannot stabilize the hip joint and leg weakness is usually the predominant complaint but paresthesias, often painful, may be the main complaint. Maneuvers that stretch the nerve such as extension or lateral leg movement may increase the pain. In an Obturator hernia, if still mobile, an increase in abdominal pressure as in coughing, sneezing, or straining will increase the pain. [5]

Careful examination of the strength of the hip adductors and quadriceps muscle as well as the patella reflexes as well as the sensory deficit may serve to differentiate Obturator neuropathy from femoral neuropathy but the two nerves are often damaged together because of their shared nerve root and lumbar plexus origin and course in pelvic trauma or hip surgery. Lumbar radiculopathy of L3 and/or L4 may also account for the weakness and shifts the focus to the lumbar spine for pathology.

Etiology
Broad categories of etiology are pelvic fractures; complications of hip replacements; malignant pelvic mass or endometriosis (note its proximity to the ovary in the female); obturator hernia, complications of labor, lithotomy position, entrapment and as a complication in the newborn.

Causes of Obturator Neuropathy

• Pelvic fractures

• Direct penetrating injuries

• Malignancies of the pelvis

• Endometriosis

• Complications of hip arthroplasty including encasement by cement

• Obturator hernia

• Obturator nerve entrapment

• Lithotomy position

• Pregnancy and labor(multiple possible mechanisms)

• Pelvic hemorrhage(including as an untoward result of procedures such as cardiac catheterization

• Obturator palsy of the newborn

As previously stated, isolated Obturator nerve injuries are relatively rare and, pelvic fractures and penetrating injuries, such as gunshot wounds, much more frequently injure multiple nerves and or other neural structures such as nerve roots or the lumbar plexus. [6, 7, 8, 9] The Obturator nerve can be injured during hip or pelvic surgery as a result of stretch, retractor compression, injury due to cement (encasement or thermal injury) or electrocautery. [10, 11, 12, 13, 14]

Massive pelvic hemorrhage, either spontaneously or during gynecological surgery can cause Obturator neuropathy. [15, 16] Obturator hernias can cause pain down the medial thigh, especially with Valsalva maneuvers. [17, 18] The lithotomy position has been implicated in obturator neuropathies both in urological and gynecological surgeries[19, 20, 21, 22, 23] It has also been reported during pregnancy and delivery but here multiple factors are at play including the fetal head, forceps application, hematoma or other trauma occasioned by caesarian section or improper lithotomy position. [24, 25]

Malignant tumors can compress or invade the Obturator nerve as can endometriosis and laparoscopic pelvic lymphadenectomy making visualization of the nerve mandatory during electrocautery. [26, 27] Aneurysm of the hypogastric artery can also produce compression of the Obturator nerve. [6, 28, 29] Obturator neuropathy caused by cardiac catherization is a special case of retroperitoneal hematoma formation compressing the nerve. [30, 31]

Bradshaw [32]et al reported 32 athletes who had entrapment of the obturator nerve by fascial entrapment of the nerve entering the thigh with distal pain radiating along the medial thigh induced by exercise with surgical relief by excising the thickened fascia over the short adductor muscle. [32] All of the afflicted athletes participated in sports with a “leg predominance” such as soccer and rugby. Idiopathic obturator neuropathy has also been described. [33] Finally, infants are not immune to obturator neuropathy and one case possibly related to intrauterine prolonged abnormal leg position has been reported. [34]

Diagnosis
The clinical examination and the setting in which the neuropathy arose generally suggest its etiology. Electromyography is essential for confirmation of anatomical location and the differential diagnosis of much more common multiple neuropathies, lumbar plexopathies, and L3-4 nerve root lesions. For possible retroperitoneal hemorrhage or tumor, CT scan, MRI, and ultrasound are helpful. [35, 36] Angiography may be necessary in suspected hypogastric artery aneurysm.

The question of the possible relationship to diabetes mellitus arises in the same context as for femoral neuropathy. Muscles innervated by the obturator nerve are almost invariably affected by so-called diabetic amyotrophy. Two reports in the literature [37, 38] invoke diabetes as a cause of obturator neuropathy but this, as in the case of femoral neuropathy remains, problematical. A summary article evaluates the causes and outcomes. [39]

Management
Obvious inciting lesions should be treated with such curative measures as are available, i.e. surgery for management of tumors, hemorrhage, or entrapment is indicated. In particular, where hip arthroplasty has been carried out, after a period of observation, re-exploration may be indicated because of the possibility of the nerve being encased in cement. Persistent pain requires pharmacological treatment such as gabapentin, pregablin, other membrane stabilizers (newer anticonvulsants), tricyclic antidepressants, or other medications useful in neuropathic pain. One report in the Japanese literature seems to carry some promise in intractable pain but remains to be evaluated. [40]

References

1. Waldman, Steven D. The Obturator Nerve,197-199, Saunders, Philadelphia 2003. Atlas of Uncommon Pain Syndromes, Saunders, Philadelphia 2003).

2. Kopell, H.P.and Thompson, W.A.L. Obturator Nerve Entrapment N.Eng J Med, 262: 56-60, 1960.

3. Kopell, HP & Thompson, WAL,”Obturator Nerve” 610-63 in Kopell, HP & Thompson, WAL,Peripheral Entrapment Neuropathies,The Williams & Wilkins Company Baltimore 1963.

4. Stewart, John D. “The Obturator Nerve”, 407-410 in Focal Peripheral Neuropathies, Second Edition, Raven Press, New York 1993.

5. Mondelli M, Gianni F, Guazzi G, Corbelli P. Obturator neuropathy due to Obturator hernia Muscle Nerve 26:291-2, 2002.

6. Dawson DM, Hallett M, Wilbourn AJ: “Miscellaneous uncommon syndromes of the lower extremity” 369-379 in Entrapment Neuropathies Third Edition Lippincott-Raven, Philadelphia, 1998.

7. Patterson FP, Morton KS: Neurological complications of fractures and dislocations of the pelvis. J Trauma 12:1013, 1972.

8. Stoehr, M: traumatic and postoperative lesions of the Lumbosacral plexus. Arch Neurol 35:757, 1978.

9. Busis NA Femoral and Obturator Neuropathies Neurol Clin 17:633-653(review)

10. Grant P, Roise O, Ovre S. Obturator neuropathy due to intrapelvic extrusion of cement during total hip replacement-report of patients. Acta Orthop Scand 72:537-540, 2001.

11. Siliski JM, Scott RD. Obturator-nerve palsy resulting from intrapelvic extrusion of cement during hip replacement. Report of four cases. J Bone Joint Surg Am 67:1225-1228, 1985.

12. Melamed NB, Satya-Murti S. Obturator neuropathy after total hip replacement. Ann Neurol 13:578-579, 1983.

13. Bischoff C, Schonle PW. Obturator nerve injuries during intra-abdominal surgery. Clin Neurol Neurosurg 93:73, 1991.

14. Schmalzreid TP, Amstutz HC, Dorey FJ Nerve palsy associated with total hip replacement: Risk factors and prognosis. J Bone Joint Surg 73A:1074, 1991.

15. Cardosi RJ, Cox CS, Hoffman MS Postoperative neuropathies after major pelvic surgery. Obstet Gynecol100:240-244,2002.

16.Finan MA, Fiorica JV, Hoffman MS et. Al., Massive pelvic hemorrhage during gynecologic cancer surgery: “pack and go back” Gynec Oncol:62390-395, 1996.

17. Mondelli M, Gianni F, Guazzi G, Corbelli P. Obturator neuropathy due to Obturator hernia Muscle Nerve 26:291-2, 2002.

18. Mumenthaler M. Some clinical aspects of peripheral nerve lesions Eur Neurol 2:257, 1969.

19. Litwiller JP, Wells RE Jr, Halliwill JR, Carmichael SW, Warner MA. Effect of Lithotomy position on strain of the Obturator and lateral femoral Cutaneous nerves. Clin Anat 17:45-49, 2004.

20. Warner MA, Warner DO, Harper CM, Schroeder DR, Maxson PM Lower extremity neuropathies associated with lithotomy positions. Anesthesiology. 93:938-942, 2000.

21. Crews DA, Dohlman LE. Obturator neuropathy after multiple genitourinary procedures. Urology 29:504-505, 1987.

22. Dimachkie MM, Ohanian S, Groves MD, Vriesendorp FJ. Peripheral nerve injury after brief lithotomy for transurethral collagen injection. Urology 56:669, 2000.

23. Pellegrino MJ, Johson EW. Bilateral Obturator nerve injuries during urologic surgery. Arch Phys Med Rehabil 69:46, 1988.

24. Lindner A, Schulte-Mattler W, Zierz S. Postpartum Obturator syndrome: case report and review of the nerve compression syndrome during pregnancy and delivery. ZentrLBL Gynakol 119:93, 1997.

25. Warfield CA Obturator neuropathy after forceps delivery. Obstet Gynecol 64:47S, 1984.

26. Redwine DB, Sharpe DR: Endometriosis of the Obturator nerve: a case report. J. Reprod Med 35:434, 1990.

27. Fishman JR, Moran ME, Carey RW., Obturator neuropathy after laparoscopic pelvic lymphadenectomy Urology 42:198-200, 1993.

28. Kleiner JB, Thorne RP., Obturator neuropathy caused by an aneurysm of the hypogastric artery.J Bone Joint Surg AM 71:1408-1409, 1989.

29. Krupski WC, Bass A, Rosenberg GD, Dilley RB, Stoney RJ,. The elusive isolated hypogastric artery aneurysm: novel presentations. J Vasc Surg 10:557-562, 1989.

30. Kent KC, Moscucci M, DiMattia ST, Skillman JJ., Neuropathy after cardiac catheterization: incidence, clinical patterns and outcome. J Vasc Surg 19:1008-1013, 1013-1014(discussion) ,1994.

31. Dingeman RD, Mutz SB., Hemorrhagic neuropathy of the sciatic, femoral and obturator nerves: case report and review of the literature. Clin Orthop 27:133-136, 1977.

32. Bradshaw C, McCrory P Bell S, Brukner P., Obturator nerve entrapment: a cause of groin pain in athletes. Am J Sports Med 25:402-408, 1997.

33. Saurenmann P, Brand S., Obturator neuralgia (Howship-Romberg phenomenon) Schweiz Med Wochenschir 114: 1462-1464, 1984[German]

34. Craig WS, Clark JMP: Obturator palsy in the newborn. Arch Dis Child 37:661, 1962.

35. Rivaasseau T, Vandermarcq P, Boissonnot L, Drouineau J, Gil R., Hematoma of the psoas. Comparative diagnostic contributions of untrasound and x-ray computed tomography. J Radio 66:731-734, 1985[French]

36. Lazaro RP, Brinker RA, Weiss JJ, Olejniczak S., Femoral and obturator neuropathy secondary to retroperitoneal hemorrhage: value of the CT scan Comput Tomogr 5: 221-224, 1981.

37. Hogenhuis LAH, Rose FC., The classification of diabetic neuropathy. Neuroepidemiology 3:169-181, 1984.

38. Spritz N Nerve disease in diabetes mellitus. Med Clin North Am 62:787-798, 1

39. Sorenson EJ, Chen JJ, Daube JR., Obturator neuropathy: causes and outcomes. Muscle Nerve 25:605-607, 2002.

40. Mukubo Y, Sato K, Kawamata M., Effective radiofrequency lesioning for obturator neuropathy. Masui 52:990-992, 2003[Japanese]