Gluteus Minimus Muscle

“Pseudo-Sciatica”

REFERRED PAIN

The referred pain from trigger points (TrPs) in the anterior part of the gluteus minimus muscle extends over the lower lateral buttock, down the lateral aspect of the thigh, knee, and leg to the ankle. The TrPs in the posterior fibers of this muscle have a similar but more posterior pattern that projects pain over the lower medial aspect of the buttock, and down the back of the thigh and calf. Pain referred from gluteus minimus TrPs can be intolerably persistent and excruciatingly severe. The TrP source of the pain is so deep in the gluteal musculature and much of the pain is so remote from the muscle that its true origin is easily overlooked. The TrPs in the anterior portion of the gluteus minimus project both pain and tenderness to the lower lateral part of the buttock, the lateral aspect of the thigh and knee, and to the peroneal region of the leg as far as the ankle. Ordinarily, gluteus minimus referred pain does not extend beyond the ankle. Rarely, however, it may include the dor- sum of the foot. Studies have found that in 55 of 70 patients seen for “sciatica” the pain was of ligamentous or muscular origin, commonly from the gluteal musculature.

INNERVATION

The gluteus minimus muscle is innervated by both the superior and inferior branches of the superior gluteal nerve.

FUNCTION

All fibers of the gluteus minimus muscle contribute to abduction of the thigh when the distal part of the lower limb is free to move. The fan-shaped arrangement of fibers in this muscle corresponds closely to the fiber arrangement in the overlying gluteus medius.

Both muscles attach to the same bones at adjacent locations; therefore, the actions of corresponding anterior or posterior fibers of the gluteus minimus and gluteus medius muscles are similar. The functions of the gluteus minimus are usually lumped with those of the gluteus medius. Authors generally agree that all of the gluteus minimus fibers assist the gluteus medius muscle in its stabilizing function of maintaining the pelvis level during ambulation. It thus helps prevent the pelvis from dropping excessively (tilting laterally) toward the unsupported side.

FUNCTIONAL (MYOTATIC) UNIT

Medial rotation at the hip by the anterior gluteus minimus and tensor fasciae latae muscles is assisted by the anterior fibers of the gluteus medius muscle.

This action is opposed chiefly by the gluteus maximus and piriformis muscles, together with the lateral rotator group: the quadratus femoris, the two gemelli, and the two obturator muscles.

Agonists for the hip abduction function of the gluteus minimus muscle are the gluteus medius and tensor fasciae latae.

Abduction is countered primarily by the four major adductor muscles: the adductores magnus, longus, and brevis with the pectineus muscle and, to a lesser extent, by the gracilis muscle.

SYMPTOMS

Patients complain of hip pain that may cause a limp during walking. Lying on the affected side may be so painful that rolling over onto that side during the night interrupts sleep. After sitting for a while, patients with active TrPs in the anterior gluteus minimus often have difficulty rising from the chair and standing up straight because the movement becomes painful.

The pain from TrPs in this muscle can be constant and excruciating. The patient may not be able to find a stretching movement or change of position that relieves the pain and can neither lie down comfortably nor walk normally.

DIFFERENTIAL DIAGNOSIS

Sciatica is a symptom, not a diagnosis; its cause should be identified.

Myofascial pain that is referred deep into the hip joint, the source is probably TrPs in the tensor fasciae latae muscle.
Low back pain in the sacral and sacroiliac regions is more likely to be due to TrPs in the gluteus medius than in the gluteus minimus muscle
The gluteus minimus and piriformis lie beside each other with occasional overlap, have adjacent attachments, and generate somewhat similar distributions of referred pain. The piriformis pain pattern may occasionally extend as far distally as the knee, whereas the gluteus minimus pattern usually includes the calf in addition to the thigh.
Pain referred from the gluteus medius is less likely to involve the thigh
Gluteus maximus TrPs restrict flexion at the hip
Piriformis TrPs restrict medial rotation
TrPs in the gluteus minimus are difficult to distinguish by palpation from those in the overlying gluteus medius throughout their large area of overlap
The gluteus minimus is a potent myofascial source of pseudoradicular syndromes. The symptoms produced by TrPs in the anterior fibers of the muscle may be mistaken for an L5 radiculopathy
Symptoms from the posterior fibers mimic an S1 radiculopathy.
Knee pain that suggests an L4 radiculopathy is not characteristic of gluteus minimus TrPs.

Sciatica

Sciatica is a non-specific term commonly applied to the symptom of pain radiating. downward from the buttock over the posterior or outer side of the lower limb. The pain may be either myofascial or neurological in origin. Myofascial TrPs in the posterior gluteus minimus muscle can be a common source of sciatica. This cause of sciatica is easily overlooked if the clinician does not examine the muscles.

Clinicians suggest “pseudosciatica” is a more appropriate diagnosis than “sciatica” when sensory and motor neurological findings are normal. In these cases, they suggest that bursitis and myofascial pain probably cause the symptoms. Studies have reported that in 50 of 70 cases of sciatica, the pain was caused by ligamentous and muscular lesions. Others note that many of the patients designated as having sciatica without evidence of neurological disease probably suffer pain of myofascial origin.

ACTIVATION AND PERPETUATION OF TRIGGER POINTS

Myofascial TrPs in the gluteus minimus muscle may be activated or perpetuated by sudden acute or repetitive chronic overload, SI joint dysfunction, injection of medications into the muscle, and nerve root irritation.

Perpetuating factors may include prolonged immobility, tilting the pelvis by sitting on a wallet, and unstable equilibrium when standing.

Activation of Trigger Points

Gluteus minimus TrPs may be activated by an acute overload imposed by a fall; by walking too far or too fast, especially on rough ground; or by overuse in running and sports activities, such as tennis and handball.

Distortion of the normal gait sufficient to induce gluteus minimus TrPs was caused in one case by a painful blister on the foot and, in another case, by walking extensively for 2 days while limping on a painful knee.

Referred pain in the lower limbs following SI joint displacement results most frequently from TrPs located in the gluteus minimus muscle.

The next most likely muscles to be involved with SI joint dysfunction are the erector spinae, quadratus lumborum, gluteus medius, gluteus maximus, piriformis, and, less frequently, the adductors of the thigh.

The post-lumbar laminectomy pain syndrome is frequently caused by residual myofascial TrPs that had been activated by the radiculopathy, for which a successful laminectomy had been performed. These active TrPs remain like dust on the shelf that must be wiped clean. Such residual gluteus minimus TrPs are particularly confusing when they mimic the pain for which the laminectomy was performed.

Perpetuation of Trigger Points

Prolonged immobility is a potent source of aggravation of TrPs. Since the position of the right foot is fixed on the accelerator when one drives a car, the right hip muscles are effectively immobilized unless a special effort is made to reposition the thigh and hip.

The gluteus minimus and gluteus medius muscles are relatively immobilized during prolonged standing, as when waiting in line or when standing at a cocktail party. Unless the individual frequently shifts weight from one lower limb to another, the latent TrPs may become active.

Sacroiliac joint dysfunction can both activate and perpetuate these gluteal TrPs.

Sitting on a wallet placed in a long back pocket can impinge on gluteus minimus TrPs and produce referred pain in a sciaticlike distribution.

TRIGGER POINT EXAMINATION

Anterior Trigger Points patient lies supine, with the thigh of affected limb extended to the limit of comfort. If necessary, the knee is supported by a pillow. The anterior superior iliac spine is palpated at the anterior end of the iliac crest. The tensor fasciae latae muscle is identified by asking the patient to try to rotate the thigh medially against resistance while the clinician palpates to locate the tensed muscle that lies just under the skin.

The anterior fibers of the gluteus minimus are then explored for TrP tenderness by palpating deeply, first anterior to and then posterior to the tensor fasciae latae muscle, just distal to the level of the anterior superior iliac spine.

Posterior Trigger Points

To locate strongly active TrPs in the posterior portion of the gluteus minimus, the patient lies on the uninvolved side with the uppermost thigh adducted and slightly flexed to about 30°

ASSOCIATED TRIGGER POINTS

Active myofascial TrPs in the gluteus minimus muscle rarely present as a single muscle syndrome. The TrPs in this muscle are most often observed in association with TrPs in the piriformis, gluteus medius, vastus lateralis, peroneus longus, quadratus lumborum, and, sometimes, the gluteus maximus muscle.

The two muscles that are most closely associated functionally with the gluteus minimus (the gluteus medius and the piriformis) are also the most likely to develop secondary TrPs.

The posterior fibers of the gluteus minimus and the piriformis muscle frequently develop associated TrPs.

Similarly, the anterior fibers of the gluteus minimus and the tensor fasciae latae are closely related functionally and may develop associated TrPs.

The vastus lateralis may develop TrPs that are satellites to those in the anterior part of the gluteus minimus muscle.

Myofascial TrPs commonly develop in the posterior portion of the gluteus minimus muscle, and less frequently in the anterior portion, as satellites to quadratus lumborum TrPs.

This coupling can be so strong that pressure exerted on the quadratus lumborum TrPs induces not only the expected referred pain in the buttock but also unexpected pain referred down the back of the lower limb.

This additional pain results from activation of satellite TrPs in the posterior part of the gluteus minimus; pressure applied to these gluteal TrPs elicits the same lower limb pain.

Sometimes elimination of the quadratus lumborum TrPs inactivates the satellite gluteal TrPs. In other patients, TrPs in the two muscles must be inactivated separately.

Similarly, the peroneus longus, which lies in the pain reference zone of the anterior part of the gluteus minimus, has been seen to develop satellite TrPs from that part of this gluteal muscle.

NEEDLING POSTION

Injection of TrPs (Xs) in the anterior and posterior parts of the right gluteus minimus muscle.

The solid line follows the crest of the ilium to the anterior superior iliac spine (solid circle).

The dotted line marks the borders of the gluteus minimus muscle and indicates its attachment to the greater trochanter (open circle).

Pic A, probing close to the posterior border of the tensor fasciae latae muscle to locate anterior gluteus minimus TrPs (anterior large X).

Pic B, probing under the anterior border of the tensor fasciae latae muscle to inject the trigger-point location shown in A by the large anterior X.

Pic C, injection of the most common posterior gluteus minimus TrPs (in the area marked by the posterior large X in A and B).

Home Therapeutic Program

A self-stretch that is effective for inactivating anterior gluteus minimus TrPs is illustrated.

This should be coordinated with respiration so that the patient inhales during the isometric contraction phase and exhales during the relaxation phase.

The position illustrated also can be employed with this contraction-relaxation technique.

In this case, the contraction during inhalation should support the weight of the lower extremity without lifting it.

During exhalation, the patient relaxes and allows gravity to lengthen the muscle.

Corrective Posture and Activities

For patients with active gluteus minimus TrPs, standing is more painful than sitting.

They should be encouraged to sit whenever possible, especially in situations where one usually stands, as when working in the kitchen.

If standing is unavoidable, weight should be shifted regularly from one foot to the other.

Even when sitting, it is helpful to change positions every 15 or 20 minutes by standing up, moving around the room, and sitting down again. An interval timer placed across the room is a helpful reminder to change positions when a person is preoccupied with a task.

When an individual sleeps on the side with the thighs flexed, a pillow between the knees and legs helps maintain the uppermost thigh horizontal and the involved gluteus minimus muscle in a neutral position

Patients with symptoms from posterior gluteus minimus TrPs should carry the wallet elsewhere than in the back pocket. The wallet can cause “back-pocket sciatica” when sitting on it compresses a gluteus minimus TrP, and it can also tilt the pelvis