The Femoral Nerve Tension Test, also known as the Femoral Nerve Stretch Test (FNST) is a test used to screen for sensitivity to stretch soft tissue at the dorsal aspect of the leg, possibly related to nerve root impingements. It was first described by Wasserman in 1919.
Literature suggests that this test is not used as commonly as the Straight Leg Raise (SLR) test because of less frequent upper lumbar radioculopathies as compared to lower lumbar radiculopathies.
It is considered as an anterior corollary of SLR and assesses the mobility of upper lumbar nerve segments.
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| Femoral Nerve Tension Test |
Purpose
The prone knee bending test is a neural tension test used to stress the femoral nerve and the mid lumbar (L2-L4) nerve roots.The femoral nerve tension test is used to screen for sensitivity to stretch soft tissue at the dorsal aspect of the leg, possibly related to root impingements.
Clinically Relevant Anatomy
The Femoral Nerve comes from the Plexus Lumbosacralis (more specific the Plexus Lumbalis) and branches out into the N. Saphenus, the Rr. Musculares and the Rr. Cutanei Femoris Anteriores. This ramification happens usually about 2.5 cm under the inguinal ligament.The femoral nerve lies within Scarpa’s triangle (or the ‘Trigonum Femorale Mediale’) which is bounded by the inguinal ligament (superiorly), the medial border of the Sartorius muscle and the lateral border of the Adductor Longus muscle (The muscles Pectineus and Iliacus and Psoas lie within this triangle as well).
The femoral nerve lies (most laterally) next to the femoral artery and femoral vein (medially).
Technique
The patient lies prone, and the therapist stands on the affected side and stabilizes the pelvis to prevent anterior rotation with one hand. With the other hand, the therapist then maximally flexes the knee to end range.If no positive signs are noted in this position, the therapist proceeds to extend the hip while maintaining knee flexion. The therapist can add a few alterations to the test position to identify the nerve involved.
The Lateral Femoral Cutaneous Nerve bias test includes prone lying with passive hip extension adduction and knee flexion whereas the Sapheneous Nerve bias test includes prone-lying hip extension, abduction and external rotation with knee flexion, ankle dorsiflexion, and eversion
Normal response: Knee flexion allowing the heel to touch the buttocks. A pull or a stretch is felt in the quadriceps.
If unilateral pain is produced in the lumbar region, buttocks, posterior thigh, between the ranges of 80-100 degrees of knee flexion in a combination of these regions, the test is considered positive.
The dura is tensioned between 80 and 100 degrees and positive findings in this range could be indicative of a disk herniation affecting the L2, L3 or L4 nerve root. Positive findings secondary to a disc herniation can be differentiated from quadriceps problems based upon the range in which pain is reproduced.
If pain is produced before 80 degrees of knee flexion, quadricep tightness and/or injury may be the cause. Also, if tightness exists, the pelvis rises on that side as hip flexes in response to passive knee flexion.
As tight rectus femoris can also produce pain in the anterior thigh, thus it is important to perform the test on both sides and compare the symptoms.
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