Relationship Between Lumbopelvic Muscles Activity and Ultrasonographic Measurement of Contralateral Anterior Humeral Translation in Chronic Unilateral Low Back Pain

Demographic data will be collected from all subjects regarding age, weight, height, and body mass index. After patient selection according to the inclusion and exclusion criteria, measuring the amplitude of gluteus maximus (GM) and contralateral latissmus dorsi (LD) muscles during prone hip extension (PHE) for the ipsilateral leg to the symptoms in unilateral CLBP patients and for the selected leg in matched controls will be carried out using surface electromyography (EMG) unit. Then ultrasonography unit will be used to assess the amount of anterior translation of humeral head (ATHH) of contralateral glenohumeral joint for both groups.

Before placement of the EMG electrodes, the skin at the anatomic landmarks will be shaved (if required), rubbed, and cleaned with isopropyl alcohol 70% to remove excess oils and debris.

The electrodes will be sterilized and placed on the muscle belly oriented parallel to the muscle fiber away from the tendon and muscle edges with the inter-electrodes distance of two centimeters. The electrodes will be secured by adhesive tape. Before recording, skin impedance will be checked to be less than 5 KΩ.

The electrodes for LD will be placed 4 cm below the inferior tip of the scapula and half the distance between the spine and the lateral edge of the torso. For GM, electrodes will be placed at half the distance between the greater trochanter and second sacral vertebra and at an oblique angle at, or slightly above, the level of the trochanter.

The two normalization procedures will be the typical maximal voluntary isometric contraction (MVIC) performed as per SENIAM Guidelines (www.seniam.org), and submaximal voluntary contraction (sub-MVC) task will be performed using the prone double leg raise. It is recommended to avoid maximal contractions of the GM muscle, because reproduction of pain on testing would have possibly invalidated the use of the root mean square (RMS) values for normalization.