Obturator Nerve Entrapment Description

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Chronic groin pain is a difficult problem to evaluate. The differential diagnosis for groin symptoms is broad and may include gynecologic, urologic, and colorectal diseases. Moreover, neuropathies of the cutaneous nerves around the hip have been highlighted as etio-logic factors for groin pain.35,37 Nonetheless, the information on this topic is sparse, partly because these injuries are rare. The literature on groin pain of neural origin has mainly focused on the genitofemoral, lateral femoral cutaneous, ilioinguinal, and iliohy-pogastric nerves.37 The obturator nerve, in contrast to the other four cutaneous nerves around the groin, lies protected deep within the pelvis and the medial thigh. The cases documenting injury to the obturator nerve have been limited to isolated case reports of neuropathy due to unusual entrapping lesions or as a consequence of surgical complications. Obturator nerve entrapment has been identified as an unusual cause of groin pain in athletes.36 The neuropathy is possibly caused by an entrapping fascial or vascular structure that is relieved with surgical decompression.

Etiology

Understanding the anatomy of the obturator nerve and its relationship with the adductor muscles is helpful for understanding the syndrome and for surgical planning. The classic description of the anatomic course of the obturator nerve comes from Gray's Anatomy.73 The obturator nerve forms from the convergence to the ventral divisions of the ventral rami of L2, L3, and L4 spinal nerves within the psoas major muscle. The nerve then descends through the psoas muscle to emerge from its medial border at the pelvic brim. The nerve then curves downward and forward around the wall of the pelvic cavity and travels through the obturator foramen, after which it divides into anterior and posterior branches. The anterior branch enters the thigh over the obturator externus muscle and the posterior branch through the fibers of that same muscle. The anterior branch innervates the adductor longus, gracilis, and adductor brevis muscles. It also gives an articular branch to the hip joint near its origin. It divides into numerous named and unnamed branches, including the cutaneous branches to the subsartorial plexus, vascular branches to the femoral artery, communicating branches to the femoral cutaneous nerves, accessory obturator nerve, and directly to the skin of the medial thigh. The posterior division continues to innervate the obturator externus, adductor magnus, the adductor bre-vis (if it has not received supply from the anterior division) and gives an articular branch to the knee joint. Its supply to the adductors is variable; therefore, care must be taken when dissecting around the obturator foramen, especially superiorly because it descends over the ramus to join the anterior division.74

Obturator neuropathy is an uncommon mononeu-ropathy usually associated with a well-defined event or an invasive procedure.75 There have been several isolated case reports of obturator nerve injury due to compressive causes and entrapment. Obturator nerve injury has been reported after retroperitoneal hemorrhage, after fractures of the pelvis, invading pelvic tumors, endometriosis, and after aneurysms of the hy-pogastric artery and obturator hernias.76-79 It has also been described after procedures such as total hip replacement, forceps vaginal delivery, urologic surgery, and prolonged positioning in the lithotomy posi-tion.80-83 The insult to the obturator nerve in these isolated cases is apparent from the clinical history and description. The etiology of obturator neuropathy without such external insults is much more uncertain. Until recently there have been no athletic or sports-related cases reported. Bradshaw and col-leagues36 reported their observations on 32 surgical cases of obturator neuropathy in athletes. In addition to making surgical observations, they also performed six cadaveric dissections. The salient points made were (a) entrapment of the obturator nerve occurs at the level of the obturator foramen and the proximal thigh rather than in the obturator tunnel; (b) definition of a unique fascial arrangement surrounding the adductor longus and the pectineus muscle that is probably central in the pathogenesis of this condition (Figure 5.8); and (c) the results of positive radionucleo-tide tests attesting to the presence of inflammatory changes along the adductors, which may also have a contributory effect. Last, the authors point out that the biomechanical differences seen in male anatomy, such as higher ilial bones, smaller pelvic inlet, and a narrower subpubic angle, alter the vector of the obturator nerve and perhaps predispose it to injury.

Harvey and Bell74 proceeded to map out the details of the fascial planes surrounding the obturator nerve. Their cadaveric study illustrated fascial and vascular anatomy and specifically looked at the fascia surrounding the vascular pedicles and its relationship to the anterior branch of the obturator nerve. The fascial thickening around the vascular pedicle derived from the medial circumflex femoral artery was thought to be most capable of impinging. Their findings seemed to correlate with the surgical findings of Harvey and Bell.74 Other authors

Femoral Nerve Thickening

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Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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