Nerve Entrapment in the Lower Extremity

Nerve entrapment

This article will cover the minutiae of the sites of nerve compression in the hip and is probably of more interest to physical therapists or those who enjoy anatomy. For those that find medical jargon mind boggling, there is one point I want to get across. The cause of nerve entrapment and “sciatica” is difficult to diagnose, and is probably commonly misdiagnosed. With the reliance on MRI and CT scans, when you see a physician and tell him/her that you have radiating pain, the first thought is that it is likely coming from your lumbar spine. An image is ordered and low and behold you have a bulging disc. The problem with this is that there is a difference from findings on an MRI and clinical findings. In fact, in a study of 1211 people between the ages of 20-70, 87% had bulging discs, however were completely asymptomatic (Nakashima et al., 2015). So in other words, most people have disc bulges. When you become symptomatic, it is easy to blame it on a bulge. However, it is often the case that the compression is really occurring in the hip. If the pain starts in the buttock and not the lower back, it is probably more of a hip issue than a back issue. 

The complex anatomy of the hip creates an environment conducive to nerve entrapment. Nerves have to be able to glide within the tunnels that they occupy. They can be compressed by bony anatomy, muscles, and ligaments. Nerve compression can lead to numbness, tingling, burning pain, and weakness. The nerves that exit the lumbar spine and sacrum form what is called the lumbar plexus. The sciatic nerve is the most commonly entrapped but there are several branches of the lumbar plexus that can be compressed that are often missed in diagnosis, including pudendal, obturator, femoral, and lateral femoral cutaneous. 

Ruling out lumbar spine pathology, the sciatic nerve is most commonly compressed under the piriformis muscle. 

Piriformis

A lesser known site of compression is the ischiofemoral space, and the ischial tunnel (where the hamstring attaches to the ischial tuberosity). The pudendal nerve can be trapped in a number of locations including Alcock’s canal (between the sacrotuberous ligament and the obturator fascia), obturator internus muscle, or the space between the sacrospinous and sacrotuberous ligaments (Martin et. al, 2017).

Note the narrowed space between the ischium and the femur

Note the narrowed space between the ischium and the femur

Anteriorly, the obturator, femoral, and lateral femoral cutaneous nerves can be entrapped causing various symptoms in the hip and leg. The fascia overlying the adductors can entrap the obturator nerve. Additionally, it can be entrapped as it exits the obturator canal. The inguinal ligament can entrap the femoral nerve in the femoral triangle, or in the iliacus or adductor canal (which involves the saphenous branch). The inguinal ligament can also entrap the lateral femoral cutaneous nerve just medial to the anterior superior iliac spine (Martin et. al, 2017). 

Anterior impingement

How do we assess for entrapment? It starts by taking a thorough subjective history. There are typical complaints for many of these entrapments. Objectively, palpation, reflex and motor testing, and neural tension testing can help determine the location. Below is a summary of entrapment sites and subjective complaints to assist in differential diagnosis. 

Posterior nerve entrapments: 

Sciatic:

Site of entrapment: The piriformis, obturator internus/gemelli complex, the proximal hamstring, or the ischiofemoral space. 

Signs/symptoms: This usually includes pain in the buttock and difficulty sitting for prolonged periods. If the sciatic nerve is compressed in the ischiofemoral space, pain is reported during walking as the femur and pelvis come closer together in stance phase. If the entrapment is at the proximal hamstring and ischial tunnel, patients will complain of pain down the posterior thigh and into the popliteal space, aggravated by running at heel strike.

Pudendal:

Site of entrapment: The ischial spine, sacrospinous ligament, sciatic notch, Alcock’s canal, or obturator muscle. 

Signs/symptoms: Pain will be reported near the groin, including the penis, scrotum, labia or perineum. Symptoms are provoked with sitting except on a toilet. Cycling can also provoke pain due to repetitive compression of the nerve and the seat.

Anterior nerve entrapments:

Obturator: 

Site of entrapment: the obturator canal by the fascia of the short adductors of the hip. 

Signs/symptoms: medial thigh pain that is provoked by exercise, starting at the adductors and radiating into medial thigh. Pain in medial thigh when abducting the leg. 

Femoral: 

Site of entrapment: at the level of the inguinal ligament at the femoral triangle, or it can occur in the iliacus compartment. The saphenous branch can be compressed at the adductor canal. 

Signs/symptoms: pain or numbness into the anterior thigh and may radiate into anteromedial knee and down to the foot if the saphenous nerve is involved. Pain with modified thomas position and quadricep weakness/atrophy. 

Lateral Femoral Cutaneous:

Site of entrapment: at the perforation of the inguinal ligament medial to the anterior superior iliac spine.

Signs/symptoms: Positive pelvic compression test (pain relief due to slackening of the inguinal ligament). The lateral femoral cutaneous nerve is strictly a sensory nerve, so the symptoms are only sensory. This is associated with hypersensitivity to the touch. Gymnasts injure this nerve from repetitive uneven bar trauma. Scuba divers can experience this from the weight belt they wear. This is also known as Meralgia Paresthetica (MP) or Bernhardt-Roth syndrome. It has been associated with laparoscopic appendectomy, wearing tight clothing, pregnancy, and weight gain (Pearce, 2006).


References:

Nakashima, H., Yukawa, Y., Suda, K., Yamagata, M., Ueta, T., & Kato, F. (2015, March 15). Abnormal findings on magnetic resonance images of the cervical spines in 1211 asymptomatic subjects. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25584950

Martin, R., Martin, H. D., & Kivlan, B. R. (2017, December). NERVE ENTRAPMENT IN THE HIP REGION: CURRENT CONCEPTS REVIEW. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/29234567

Pearce. (2006, January 01). Meralgia paraesthetica (Bernhardt-Roth syndrome). Retrieved from https://jnnp.bmj.com/content/77/1/84

Christopher EllisComment