Hip osteoarthritis (OA) is one of the most frequent degenerative conditions, affecting all the structures around the hip joint, including the soft tissues [1,2]. The age-standardized prevalence has been estimated at 4.2% [3]. Patients with hip OA suffer from local and referred pain, stiffness, muscle weakness and restricted range of motion [1]. Recently, several authors have described a relationship between the presence of myofascial trigger points (MTrPs) and the main symptoms of hip OA [[4], [5], [6]].

MTrPs are defined as nodules in a palpable taut band of the skeletal muscle. The taut band of the MTrP is a group of contracted muscle fibres produced by the excessive release of acetylcholine in the neuromuscular junction at the motor endplates [7]. MTrPs are classified as active when they produce spontaneous local and referred pain and motor dysfunctions such as stiffness, muscle weakness and limited muscle extensibility [8]. These clinical characteristics are similar to those described in patients with hip OA.

Hip extension range of motion is the most restricted movement in patients with hip OA [9]. MTrPs in hip flexor muscles could reduce muscle extensibility and limit hip extension [8,10]. Neumann et al. [11] suggested that limitations in hip muscles extensibility could significantly disrupt the fluidity, comfort, and efficiency of many routine movements involving functional activities. It is known that muscle weakness plays an important role in the progression of OA [[12], [13], [14], [15]], but there is a lack of evidence about muscle extensibility in patients with this condition.

Several treatment techniques have been described for the management of MTrPs and are commonly classified as non-invasive and invasive. Among the non-invasive techniques, self-stretching is one of the most common non-invasive techniques used to treat MTrPs [8,16]. This technique has proved to be effective in decreasing pain and muscle weakness in patients with OA [17,18]. Concerning invasive techniques, dry needling (DN) has been widely investigated for the treatment of MTrPs [19,20]. Recent studies have shown its effectiveness to decrease pain intensity and to increase physical function in patients with knee OA [[21], [22], [23]] and its effectiveness to decrease pain intensity and muscle weakness and to increase hip range of motion and physical function in patients with hip OA [[24], [25], [26]]. However, to the best of our knowledge, muscle extensibility has never been considered in patients with hip OA. Therefore, no studies have compared DN therapy with a self-stretching protocol on muscle extensibility, pain, stiffness, and physical function in patients with hip OA. Thus, the aim of the study was to compare the effects of a DN intervention to a self-stretching protocol on muscle extensibility, pain, stiffness, and physical function in patients with hip OA.