Innervation of Gluteus Medius Muscle and its Relationship with Myofascial Pain.

Myofascial pain syndrome (MPS) is the most frequent cause of chronic musculoskeletal pain. According to the International Association for the Study of Pain, diagnosis of chronic pain due to MPS is based mostly on demonstration of trigger points and reproduction of pain by maneuvers which place stress upon proximal structures or nerve roots. The lack of a formal, widely accepted, criterion-based diagnostic guideline hampers adequate management of this disorder. The gluteus medius muscle is a primary stabilizer of the pelvis during gait and myofascial disorders result in increased sensitivity, spontaneous pain, and weakness in the leg abduction. Also, MTPs of the gluteus medius muscle are common features of patellofemoral and low back pain. Three trigger points are described for the gluteus medius muscle: anterior, middle and posterior, but anatomical correlation is still lacking.

METHODS: Gluteus medius muscles from ten adult cadavers were dissected to determine the point where the superior gluteal nerve branches enter the muscle belly. We divided the muscle in four areas (I to IV) obtained by two perpendicular lines; a longitudinal line was determined by the highest muscle attachment in the iliac crest and the great trochanter of the femur, and the transversal line was traced at the midpoint of the longitudinal line. To compare the number of points among quadrants, we employed generalized estimation equations with correlation matrix exchangeable between pairs of quadrants, with marginal Poisson distribution and identity link function. To compare quadrants, we used 2 to 2 multiple Bonferroni comparisons. Clinically, we examined 24 patients presenting with and without pain at the gluteal region and obtained the level of painful sensitivity with the digital pressure pain meter (Force Ten FDX Digital Force Cage-Wagner Instruments, Greenwich- EUA). Twenty measurements were obtained for each muscle totaling 960 measurements in the patients group. Measurements were taken in five distinct points in all areas corresponding to the estimated quadrants defined by the same landmarks used during anatomical dissections. The algometer measures the lowest pressure to produce pain, thus the lowest numbers represent the highest pain sensitivity.

RESULTS: . The total number of superior gluteal nerve entry points was 3±2; 2±2; 1±2 and 3±2 for quadrants I, II, III, and IV respectively. Algometer values were 5.10±2.7; 5.14±2.56; 5.29±2.8 and 5.50±2.79 for quadrants I, II, III and IV respectively. In quadrant I the patients showed greater sensitivity with the algometer and it is a quadrant that presented the largest number of nerves penetrating the muscle, the same occurring for quadrant 2. Quadrant 3 that presented the smallest number of nerves penetrating the muscle obtained a higher value for the algometer.

CONCLUSION: Anatomical correlation of the MTP may be useful for a better understanding of the physiopathology of these disorders and provide basis for their treatment.