Myofascial Pain Syndrome Affecting the Piriformis and the Obturator

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gated surgical release to a few select cases.4 There are 6 external rotator muscles ... piriformis muscle causes the piriformis syndrome with a well-known clinical ...
Blackwell Science, LtdOxford, UKPPRPain Practice1530-70852005 World Institute of Pain54361363Case ReportMyofascial Pain SyndromeDALMAU-CAROLÀ

CLINICAL REPORT

Myofascial Pain Syndrome Affecting the Piriformis and the Obturator Internus Muscle Joan Dalmau-Carolà, MD, FIPP Clinica Girona, Rheumatology Service, Girona, Catalonia, Spain

 Abstract: The obturator internus muscle is an external rotator of the hip. Obturator internus injury may occur and be hidden by the piriformis syndrome. Clinical symptoms may offer some clues to the clinician. The selective injection technique described here facilitates precise diagnosis.  Key Words: syndrome

obturator

internus

injection,

piriformis

INTRODUCTION The term “piriformis syndrome” was coined by the Belgian anatomist Adrian Spigelius 4 centuries ago. Caillet, Pace, and Steiner introduced local injection of the piriformis.1 Botulinum toxin injection2,3 has relegated surgical release to a few select cases.4 There are 6 external rotator muscles of the hip: piriformis, superior gemellus, obturator internus, inferior gemellus, obturator externus, and quadratus femoris. They are in close anatomic proximity to one another, and they work as a functional unit. The piriformis originates from the anterior surface of the sacrum and inserts into the upper part of the greater trochanter, passing out of the pelvis through the greater sciatic notch. Lying inferior to the piriformis, the obturator internus muscle also arises within the pelvis. It originates at the medial surface of the pubis, covers the obturator foramen, and passes by Address correspondence and reprint requests to: Joan Dalmau-Carolà, Clinica Girona, Rheumatology Service, 17002 T. de Lorenzana Street, 39, 3-3, Girona, Catalonia, Spain. E-mail: [email protected].

© 2005 World Institute of Pain, 1530-7085/05/$15.00 Pain Practice, Volume 5, Issue 4, 2005 361–363

the lesser sciatic notch to insert onto the greater trochanter laterally. As the obturator internus passes through the lesser sciatic notch, leaving the pelvic cavity, it is joined by the superior gemellus, which originates at the ischium just above the foramen, and the inferior gemellus, which also originates at the ischium, but below the foramen. The quadratus femoris and obturator externus, which are more anterior, lie inferior to the gemelli muscles. They arise from the lateral aspect of the ischial tuberosity and insert onto the posterior aspect of the greater trochanter.5 Contracture of the piriformis muscle causes the piriformis syndrome with a well-known clinical picture and its accompanying vascular and neural symptoms.6,7 Obturator internus muscle injury may be obscured by the piriformis syndrome. The selective muscle injection can help to recognize the offending muscle.

CASE REPORT At presentation, the patient was a 76-year-old white man with a 2-year history of focal complaints of pain in the right trochanteric-gluteal region. The deep aching pain was aggravated in the right lateral decubitus position and interfered with sleep. The pain, which worsened over time, was accompanied by a cold sensation in the right foot. The patient reported having fallen onto the gluteal region on 2 occasions some years previously. The pain was unresponsive to physical therapy and 2 trochanteric injections. On examination, the patient exhibited full lumbar range of motion and experienced no pain. The flexion-

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adduction-internal rotation (FAIR test) of the right hip reproduced the trochanteric-gluteal pain. On palpation there was localized tenderness of the right piriformis muscle. There was no leg length discrepancy. Dorsalis pedis pulses were palpable and symmetric bilaterally. An injection of piriformis muscle was performed to confirm the diagnosis (Figure 1). The muscle was localized using fluoroscopy; 1 mL of Iohexol-240 contrast was injected to confirm correct intramuscular placement. A solution containing triamcinolone (40 mg) in 5 cc of 0.25 % bupivacaine was then injected. A home program of stretching and strengthening exercises was given to the patient. Two weeks later, there was a 50% pain reduction measured on a visual analog scale. On examination a trigger point was found at the level of the right internal obturator muscle, located several centimeters caudal to the piriformis muscle. After obtaining informed consent from the patient, we performed a selective obturator internus muscle injection. The patient was placed prone with the fluoroscope C-arm directed to the right buttock. We localized the target point on the right ramus ossis ischii (ischial ramus forming part of the obturator foramen), where a portion of the obturator internus originates. After the skin was anesthetized, in a tunnel view fashion, bone was gently contacted with a 22-G spinal needle. The needle was then withdrawn 2 to 3 mm, and 1 mL of Iohexol-240 was injected (Figure 2). Finally, triamcinolone (40 mg) in 5 mL 0.25% bupivacaine was injected. A fortnight later and at 3 months follow-up, the patient was pain-free and the cold feeling in the foot had disappeared.

There are 6 external rotator muscles of the hip: piriformis, superior gemellus, obturator internus, inferior gemellus, obturator externus, and quadratus femoris. The “piriformis syndrome” is a well-known and common clinical condition that often has accompanying vascular and neural symptoms.8 The piriformis muscle injection technique has been precisely described. However, the pain patterns of the other 5 muscles have not been completely separated from the former syndrome.9 The trigger point in our patient was more caudal than the commonly observed piriformis trigger points (Figure 3). Anatomically, the piriformis muscle often merges with the common tendon of the obturator internus and gemelli muscles in its lateral insertion on the greater trochanter. Medially, the muscles separate in a fan-like manner: the piriformis muscle is anchored rostrally on the anterior surface of the sacrum; the obturator internus is located caudally, surrounding the ramus ossis ischii at a 90-degree angle, where it presents an ideal target point for injection, and arises from around the foramen obturatum (obturator foramen) and its membrane. The case reported presented as piriformis syndrome with its characteristic trigger point and vascular symptoms. Typically, the piriformis syndrome symptoms are aggravated by sitting. In the case presented, the symptoms were aggravated in lateral recumbency, suggesting a possibly different anatomical abnormality. In addition, the selective piriformis muscle injection gave only 50% relief. Furthermore, examination after the pirifor-

Figure 1. Iohexol contrast medium into right piriformis muscle.

Figure 2. Iohexol contrast medium into right obturator internus muscle.

DISCUSSION

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lowing the described anatomical landmarks, with the aid of fluoroscopy and contrast medium, we successfully located the target point and the patient found lasting relief.

REFERENCES

Figure 3. Piriformis trigger points, A and B; Obturator internus trigger point, C.

mis injection elicited a presumably previously overlooked trigger point in the obturator muscle. The hip external rotators form a functional unit, and the muscular components can be injured by similar mechanisms. Selective muscle injection provides the opportunity to make accurate diagnosis. Precise injection techniques allow for the use of botulinum toxin for prolonged effect.10 An alternative obturator internus injection technique with botulinum toxin has been described.11 In this approach, the target point is the lateral border of the obturator foramen. In our technique, the target point is in the center of the ramus ossis ischii. Touching bone with the tip of the needle assures accurate depth assessment. In this procedure, care must be taken to avoid damage to the sciatic nerve, which runs laterally.12 Fol-

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