Specific Nerve Injuries
S1 Nerve Injury
The S1 nerve innervates the calf muscles (Gastrocnemius and Soleus) along with some hamstring muscles and the gluteus maximus muscle. Injury to this nerve will cause weakness of the ability to lift up the heel. This motion is important for many activities. Walking requires a “push-off” of the foot to propel the body forward. Without calf muscle strength, the length of stride on that leg will be shorter, creating a limp. With the activity of running, the stride length will be even shorter, making the limp more noticeable. Climbing and descending stairs will be noticeably more difficult with the weak leg. All athletic endeavors will be more limiting.
Numbness, paresthesias (pins and needles) and pain usually will follow the same pattern. Initial pain will occur in the buttocks and radiate down that leg through the back of the thigh, the back of the leg and the bottom of the foot. The bottom and outside of the foot can be numb.
L5 Nerve Injury
The L5 nerve innervates the tibialis anterior, the foot and toe dorsiflexor, the peroneal muscles and the gluteus medius muscle. Weakness of any of these muscles can create a pathological gait. Compression of the L5 nerve will also cause numbness, paresthesias (pins and needles) and pain in the L5 distribution. This is buttocks pain that radiates down behind the thigh to the back of the calf and then to the top of the foot. The big toe might be numb along with the inside of the foot.
The tibialis anterior (TA) muscle is important to raise the foot up when walking. With the action of walking, one leg is in contact with the ground while the other leg swings forward. The foot on the swing leg is brought upwards by this TA muscle to prevent the toes from catching on the ground. A foot drop (weakness of the TA muscle) will cause the toes to catch the ground unless one of two pathological gaits is adopted, the circumduction gait or the steppage gait.
The circumduction gait is noted by a wide swing outwards while the leg is swinging forward. Bringing the leg out in a circle (abducting the leg) will clear the foot off the floor but requires more energy for this maneuver and slows the speed of walking. Likewise, the steppage gait is just like it sounds. The patient will adopt a maneuver that will appear like the involved leg is climbing a step to clear the foot. That is, the knee will bend and the foot will be lifted higher on that side to clear the toes.
The peroneal muscles stabilize the foot on the ground by contracting to prevent the foot from “turning in”. Weakness will feel like the ankle in in danger of becoming sprained with certain steps, especially if the surface of the ground is uneven.
The gluteus medius muscle contracts to pull the hip up on the opposite side. Weakness of this muscle will cause the patient to adopt a Trendelenberg gait (named after the physician who discovered it). This gait is characterized by a lean to the side of weakness with every swing of the opposite leg. This lean pulls the pelvis up to compensate for the drop of the hip on the opposite side.
The toe dorsiflexor muscles pull up the great toe and little toes. This action is important only for karate experts, technical rock climbers and NFL place kickers. Most patients with an L5 nerve malfunction will have weakness of these muscles and not know it. In fact, I like to think that the EHL (extensor hallicus longus- great toe dorsiflexor) is the “canary in the coal mine”. That is, weakness of this muscle absolutely confirms an L5 nerve injury and weakness is very common with injury to this nerve. If the tibialis anterior (TA) muscle is weak along with great toe weakness, this confirms that the TA is an L5 innervated muscle.
L4 Nerve Injury
Involvement of the L4 nerve can produce weakness of the tibialis anterior muscle as well as the quadriceps muscles (the anterior thigh muscles that straightens out the knee). Pain and numbness would radiate down the buttocks to the back of the upper thigh but then could radiate around to the front of the shin. Symptoms typically would stop at the ankle and not descend into the foot (with rare exceptions).
If the L4 nerve innervates the tibialis anterior muscle (about 50% of the time), weakness could ensue in that muscle. Symptoms from weakness of this muscle have been discussed in the L5 nerve section.
Weakness of the quadriceps femorus muscles (QF) would cause a feeling that the leg is not dependable and would “give way” at the knee by forced loading of the leg. Climbing and especially descending stairs would lead to a feeling that you could fall. Patients with significant weakness would ascend stairs with the “good leg” and descend with the “bad leg”. With subtle weakness, the leg would fatigue towards the end of a flight of stairs.
L3 Nerve Injury
The L3 nerve contributes to the femoral nerve. The main muscle complex innervated by the L3 nerve is quadriceps femorus group. Pain and numbness typically will radiate to the buttocks, possibly the back of the thigh, the front of the lower thigh and sometimes slightly below the front of the knee.
Like the L4 nerve, the L3 nerve also innervates the quadriceps femorus muscles. Symptoms from weakness are noted under the L4 nerve column.
L2 Nerve Injury
The L2 nerve covers the anterior thigh. Pain, numbness and paresthesias (pins and needles) from injury of this nerve would radiate to the anterior thigh but also would involve the posterior pelvis and possibly the buttocks. Weakness would involve the Iliopsoas muscle.
The Iliopsoas muscle is the main muscle that would lift up the thigh when ascending stairs. It is the same muscle that in involved with a full sit-up (not the “crunchers” that we commonly think of). This muscle also pulls the leg forward when walking. Weakness will reduce the length of the stride and cause a type of limp.
L1 Nerve Injury
This nerve also covers the anterior thigh but also involve the groin area. Pain into the groin has to be differentiated from hip disorders (arthritis). Typically, higher up buttocks pain is also associated with compression of this nerve.
The L1 nerve also supplies the psoas muscle and weakness has been covered in the section of the L2 nerve.
For additional resources on symptoms of lumbar nerve injuries, please contact the office of Dr. Donald Corenman, spine specialist and back doctor serving the communities of Vail, Aspen, Denver and Grand Junction, Colorado.