Piriformis syndrome
Encyclopedia
Piriformis syndrome is a neuromuscular disorder that occurs when the sciatic nerve
is compressed or otherwise irritated by the piriformis muscle
causing pain
, tingling and numbness in the buttocks
and along the path of the sciatic nerve
descending down the lower thigh and into the leg. Diagnosis is often difficult due to few validated and standardized diagnostic tests, but one of the most important criteria is to exclude sciatica
resulting from compression/irriation of spinal nerve roots, as by a herniated disk.
The syndrome may be due to anatomical variations in the muscle-nerve relationship, or from overuse or strain.
Uncontrolled studies have suggested theories about the disorder, however a large scale formal prospective outcome trial found that the weight of the evidence-based medicine is that piriformis syndrome should be considered as a possible diagnosis
when sciatica
occurs without a clear spinal cause. The need for controlled studies is supported by studies of spinal disk disease that show a high frequency of abnormal disks in asymptomatic patients.
Inactive gluteal muscles also facilitate development of the syndrome. These are important in both hip extension and in aiding the piriformis in external rotation
of the femur
. A major cause for inactive gluteals is unwanted reciprocal inhibition
from overactive hip flexors
(psoas major, iliacus, and rectus femoris). This imbalance usually occurs where the hip flexors have been trained to be too short and tight, such as when someone sits with hips flexed, as in sitting all day at work. This deprives the gluteals of activation, and the synergist
s to the gluteals (hamstrings, adductor magnus, and piriformis) then have to perform extra roles they were not designed to do. Resulting hypertrophy of the piriformis then produces the typical symptoms.
Sciatic nerve
The sciatic nerve is a large nerve fiber in humans and other animals. It begins in the lower back and runs through the buttock and down the lower limb...
is compressed or otherwise irritated by the piriformis muscle
Piriformis muscle
The piriformis is a muscle in the gluteal region of the lower limb. It was first named by Spigelius, a professor from the University of Padua in the 16th century.- Origin and insertion :...
causing pain
Pain
Pain is an unpleasant sensation often caused by intense or damaging stimuli such as stubbing a toe, burning a finger, putting iodine on a cut, and bumping the "funny bone."...
, tingling and numbness in the buttocks
Buttocks
The buttocks are two rounded portions of the anatomy, located on the posterior of the pelvic region of apes and humans, and many other bipeds or quadrupeds, and comprise a layer of fat superimposed on the gluteus maximus and gluteus medius muscles. Physiologically, the buttocks enable weight to...
and along the path of the sciatic nerve
Sciatic nerve
The sciatic nerve is a large nerve fiber in humans and other animals. It begins in the lower back and runs through the buttock and down the lower limb...
descending down the lower thigh and into the leg. Diagnosis is often difficult due to few validated and standardized diagnostic tests, but one of the most important criteria is to exclude sciatica
Sciatica
Sciatica is a set of symptoms including pain that may be caused by general compression or irritation of one of five spinal nerve roots that give rise to each sciatic nerve, or by compression or irritation of the left or right or both sciatic nerves. The pain is felt in the lower back, buttock, or...
resulting from compression/irriation of spinal nerve roots, as by a herniated disk.
The syndrome may be due to anatomical variations in the muscle-nerve relationship, or from overuse or strain.
Uncontrolled studies have suggested theories about the disorder, however a large scale formal prospective outcome trial found that the weight of the evidence-based medicine is that piriformis syndrome should be considered as a possible diagnosis
Medical diagnosis
Medical diagnosis refers both to the process of attempting to determine or identify a possible disease or disorder , and to the opinion reached by this process...
when sciatica
Sciatica
Sciatica is a set of symptoms including pain that may be caused by general compression or irritation of one of five spinal nerve roots that give rise to each sciatic nerve, or by compression or irritation of the left or right or both sciatic nerves. The pain is felt in the lower back, buttock, or...
occurs without a clear spinal cause. The need for controlled studies is supported by studies of spinal disk disease that show a high frequency of abnormal disks in asymptomatic patients.
Pathophysiology
When the piriformis muscle shortens or spasms due to trauma or overuse, it can compress or strangle the sciatic nerve beneath the muscle. Generally, conditions of this type are referred to as nerve entrapment or as entrapment neuropathies; the particular condition known as piriformis syndrome refers to sciatica symptoms not originating from spinal roots and/or spinal disk compression, but involving the overlying piriformis muscle. In 17% of an assumed normal population the sciatic nerve passes through the piriformis muscle, rather than underneath it, and in 16.2% of patients undergoing surgery for a suspected piriformis syndrome such an anomaly was found leading to doubt about the importance of the anomaly as a factor in piriformis syndrome. Some researchers discount the importance of this relationship in the etiology of the syndrome.Inactive gluteal muscles also facilitate development of the syndrome. These are important in both hip extension and in aiding the piriformis in external rotation
External rotation
External rotation is rotation away from the center of the body.The muscles of external rotation include:* of arm/humerus at shoulder** Deltoid muscle** Infraspinatus** Teres minor* of thigh/femur at hip ** Gluteus maximus...
of the femur
Femur
The femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
. A major cause for inactive gluteals is unwanted reciprocal inhibition
Reciprocal inhibition
“ When the central nervous system sends a message to the agonist to contract, the tension in the antagonist is inhibited by impulses from motor neurons, and thus must simultaneously relax. This neural phenomenon is called reciprocal inhibition. This information can be used to ease the pain of an...
from overactive hip flexors
Hip flexors
In human anatomy, the hip flexors are a group of skeletal muscles that act to flex the femur onto the lumbo-pelvic complex, i.e., pull the knee upward....
(psoas major, iliacus, and rectus femoris). This imbalance usually occurs where the hip flexors have been trained to be too short and tight, such as when someone sits with hips flexed, as in sitting all day at work. This deprives the gluteals of activation, and the synergist
Synergist
A Synergist is a kind of muscle that performs, or helps perform, the same set of joint motion as the agonists. Synergists muscles act on movable joints. Synergists are sometimes called as "neutralizers" because they help cancel out, or neutralize, extra motion from the agonists to make sure that...
s to the gluteals (hamstrings, adductor magnus, and piriformis) then have to perform extra roles they were not designed to do. Resulting hypertrophy of the piriformis then produces the typical symptoms.