04/13/2022
Lumbar and Sacral Plexus with Clinical Cases
http://accessphysiotherapy.mhmedical.com/data/Multimedia/grandRounds/lumbar/media/lumbar_print.html
by Annie Burke-Doe, PT, MPT, PhD. Practicing physical therapist and associate professor at the University of St. Augustine for Health Sciences in San Diego, California
Slide 1: Lumbar and Sacral Plexus with Clinical Cases
Welcome to Neuroanatomy in Physical Therapy. I am Dr. Annie Burke-Doe, a practicing physical therapist and an associate professor at the University of St. Augustine for Health Sciences in San Diego, California.
This lecture series has been developed for physical therapists embarking on the study of neurology. In this lecture we will focus on the lumbar and sacral plexus, which provides nervous innervation to the lower limb.
Slide 2: Lumbar Plexus
The lumbar plexus is a nervous plexus in the lumbar region of the body, which forms part of the lumbosacral plexus. As with the brachial plexus, the spinal nerves contributing to the lumbar plexus have both anterior and posterior divisions (anterior on this slide is shaded yellow and posterior is shaded blue). The lumbar portion of the plexus is formed by the ventral divisions of the first four lumbar nerves (L1 through L4) and from contributions of the last thoracic nerve (T12). Additionally, the ventral rami of the fourth lumbar nerve passes communicating branches to the sacral plexus. The nerves of the lumbar plexus pass in front of the hip joint and mainly support the anterior portion of the thigh. So, when you think about this ventral aspect, you should think about it supporting the anterior portion of the thigh.
The plexus is formed lateral to the intervertebral foramina (which are not pictured here) and pass through psoas major. Its smaller motor branches are distributed directly to the psoas major, while larger branches leave the muscle at various sites to run obliquely downward through the pelvic area and leave the pelvis under the inguinal ligament, with the exception of the obturator nerve, which exits the pelvis through the obturator foramen.
Slide 3: Femoral and Obturator Nerves
It is most clinically important to be familiar with the functions of the femoral, obturator, sciatic, tibial, and peroneal nerves in the lower extremity. Let’s start with the motor functions of the femoral and obturator nerves (pictured here).
I would like you to begin by tracing the largest and longest nerve in the plexus, the femoral nerve, with your finger. That way you can follow its pathway. You can see that it gives motor innervation to iliopsoas (which refers to both the psoas and iliacus at their inferior ends), pectineus, sartorius, and the quadriceps muscle group. Motor functions of the femoral nerve include hip flexion at L2-3 (lift my knee) and knee extension at L3-4 (kick the door).
Next, trace the obturator nerve with your finger as it leaves the lumbar plexus and descends behind the psoas major on its medial side, then travels into the lesser pelvis, and finally leaves the pelvic area through the obturator canal. In the thigh, it sends motor branches to obturator externus before dividing into an anterior and posterior branch, both of which will continue distally. These branches are separated by adductor brevis and supply all the thigh adductors with motor innervation, including pectineus, adductor longus, adductor brevis, adductor magnus, adductor minimus, and gracilis.
Slide 4: Femoral and Obturator Nerves
Here on the right we can see the sensory distribution of the femoral nerve, which provides sensory innervation to the anterior thigh, posterior lower leg, and hindfoot. In the thigh, it divides into numerous sensory and motor branches and the saphenous nerve, which is its long, sensory, terminal branch that continues down to the foot.
The obturator nerve (pictured in darker blue) has an anterior branch that supplies the skin on the medial, distal part of the thigh.
When testing sensation clinically, it is also important to link the dermatomes (which are pictured on the left) to provide the clinician information related to the spinal level involved.
Slide 5: The Sacral Plexus
The sacral plexus (pictured here) arises from L4 through S3 and S4 at the lumbosacral enlargement. Some authors do not differentiate between the lumbar and the sacral plexus and describe them together. The sacral plexus provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, as well as part of the pelvis. The most clinically important branches arising from the plexus are the sciatic, tibial, and peroneal nerves. Branches from the posterior division are in blue, and branches from the anterior division are in yellow.
Trace your finger beginning at L4-5 to see that the posterior division leads to the superior gluteal nerve, which innervates the gluteus medius, minimus, and tensor fasciae latae, whose actions are abducting and medial rotation of your thigh. As you continue to travel down with your finger, you will find the inferior gluteal nerve, which innervates the gluteus maximus, and whose actions are to extend and laterally rotate the thigh, as well as to extend the lower trunk. You will now descend down to the sciatic and common peroneal nerve. Now follow the anterior division of the tibial nerve that innervates the lower extremity, which will be discussed further as we go forward.
Slide 6: The Sciatic Nerve
Here on slide 6, we are looking at the sciatic nerve. The sciatic nerve is the largest peripheral nerve in the body. It is comprised of the tibial and common peroneal nerve and exits the pelvis inferior to the piriformis muscle, between the ischial tuberosity and the greater trochanter of the femur. Motor functions include thigh adduction, medial rotation, and hip extension, as well as knee flexion.
Clinically, in sciatic neuropathy, there is weakness of all foot and ankle muscles, of knee flexion, loss of Achilles tendon reflexes, and sensory loss in the foot and lateral leg below the knee. The term “sciatica” is a vague term and refers to all disorders causing painful paresthesias in a sciatic distribution.
Slide 7: The Tibial Nerve
The tibial nerve (pictured here) is the larger, medial and terminal branch of the sciatic nerve. Trace the tibial nerve with your finger as it continues the line of the sciatic nerve through the popliteal fossa and into the leg. In the popliteal fossa, the nerve gives off branches to gastrocnemius, popliteus, plantaris, and soleus muscles. The tibial nerve also provides an articular branch to the knee joint and a cutaneous branch that will become the sural nerve. The sural nerve will supply the lateral side of the foot.
Below the soleus muscle, the nerve lies close to the tibia and supplies tibialis posterior, the flexor digitorum longus, and flexor hallucis longus. The nerve passes into the foot running posterior to the medial malleolus. Here it is bound down by the flexor retinaculum in company with the posterior tibial artery.
In the foot, the nerve divides into medial and lateral plantar branches. Motor functions of the tibial nerve include foot plantar flexion and inversion and toe flexion.
Slide 8: The Tibial Nerve
In the foot, the tibial nerve divides into medial and lateral plantar branches. Cutaneous distribution of the medial plantar nerve is to the medial sole and the medial three-and-a-half toes, including the nail beds on the dorsum, like the median nerve in the hand.
The lateral plantar nerve cutaneous innervation is to the lateral sole and lateral one-and-a-half toes, like the ulnar nerve.
Slide 9: The Common Peroneal Nerve
Now, let’s trace the common peroneal nerve in its pathway as it descends obliquely along the lateral side of the popliteal fossa to the head of the fibula. Where the nerve winds around the head of the fibula, it is palpable.
The common peroneal nerve divides into the superficial peroneal nerve and the deep peroneal nerve.
The superficial peroneal nerve supplies the muscles of the lateral compartment of the leg, including peroneus longus and peroneus brevis. These two muscles help in eversion and plantar flexion of the foot. The deep peroneal nerve innervates the muscles of the anterior compartment of the leg, which are tibialis anterior, extensor hallucis longus, extensor digitorum longus, and peroneus tertius. Together these muscles are responsible for dorsiflexion of the foot and extension of the toes.
Clinically, peroneal nerve palsy can cause drop foot with weakness of foot dorsiflexion and eversion and sensory loss over the dorsolateral foot and shin. An ankle foot orthotic may improve function if the foot drop is significant.
Slide 10: The Common Peroneal Nerve with Superficial and Deep Peroneal Sensory Distribution
Depicted here on slide 10, the common peroneal nerve supplies sensation to the lateral and anterior surfaces of the upper part of the leg. The superficial peroneal nerve supplies sensation to the distal third of the leg and the dorsum of the foot, while the deep peroneal nerve supplies contiguous sides of the first and second toes.
Slide 11: Regions of Sensory Innervation Supplied by Cutaneous Nerve Branches
Here on slide 11, we see regions of sensory innervation supplied by the lateral cutaneous nerve of the thigh and the obturator nerve (both depicted in gray).
