12/26/2023 0 Comments Diagram of nerve endings in feet![]() ![]() Titled, “Development and variation of the nerves and the musculature of the inferior extremity and of the neighboring regions of the trunk in man”, the paper delivers on its impressive title. ![]() Then we discovered Bardeen (1906), a magnificent and magisterial work 130 pages in length. We found a similar written description in Sunderland (1968). That was at least an advance on what we knew starting out. (2002), which in turn reproduced a figure from Rouvière and Delmas (1973), a French textbook, which showed the obturator nerve passing the knee and innervating part of the calf. But a little digging turned up Bouaziz et al. Virtually all introductory anatomy textbooks show the obturator nerve only going to the thigh. Our first question: was this a known variation, or had Brittany discovered something new in the annals of human anatomy? Standing on the shoulders of giants We carefully cleaned and photographed the nerve, and then we hit the books. Instead, it was coming from the anterior division of the obturator nerve, right behind the adductor longus muscle (when people do the splits, this is the muscle that makes a visible ridge from the inner thigh to the groin). But when we traced back Brittany’s nerve, it wasn’t coming from the femoral nerve. I didn’t immediately freak out, because everyone has a nerve from the thigh running down to the inner side of the ankle and foot: the saphenous branch of the femoral nerve, which comes out of the anterior thigh (also highlighted in the above image). We were skinning the thigh and leg that day, and in her assigned cadaver, Brittany had found a nerve from the medial thigh running all the way down to the inner side of the ankle and foot. ![]() I was teaching in the gross anatomy lab in the fall of 2013 when one of our podiatry students, Brittany Staples, called me over to her table. In rare cases, however, the obturator nerve doesn’t stay in the thigh. Here’s a diagram from Gray’s Anatomy, 40th edition, showing the common cutaneous distribution of the obturator nerve (Standring et al. The cutaneous branch of the obturator nerve typically innervates a variable but limited patch of skin on the inner thigh. The obturator nerve arises from the spinal levels of the 2nd-4th lumbar vertebrae (L2-L4), exits the pelvis through the obturator canal behind the superior ramus of the pubis, and innervates the adductor muscles of the medial compartment of the thigh. That said, aside from complex areas where the domains of multiple nerves intersect (like the groin), most body regions get their cutaneous innervation from just one nerve. Known boundaries between cutaneous branches of different nerves are approximate, both because they vary from person to person, and because the territories of the nerves themselves interdigitate and overlap at very fine scales. Every inch of your skin lies in the domain of one cutaneous nerve or another. Your skin is innervated by cutaneous nerves, which relay sensations of touch, pressure, vibration, temperature, and pain to your central nervous system, and carry autonomic (involuntary) fibers to your sweat and sebaceous glands and the arrector pili muscles that raise and lower your hairs (as when we get goosebumps). When the obturator nerve won’t stay in its lane I’m excited for two reasons: first, the paper reports some genuinely new human gross anatomy, which happens surprisingly often but still isn’t an everyday occurrence, and second, the first six authors are my former students. Today sees the publication of a new paper, “Cutaneous branch of the obturator nerve extending to the medial ankle and foot: a report of two cadaveric cases,” by Brittany Staples, Edward Ennedy, Tae Kim, Steven Nguyen, Andrew Shore, Thomas Vu, Jonathan Labovitz, and yours truly. The image I put together explaining the new discovery. ![]()
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