Effects of eccentric exercise in patients with subacromial impingement syndrome: a systematic review and meta-analysis

摘要

BackgroundSubacromial impingement syndrome is a common healthcare problem, especially in adult populations. Prevalence is estimated to between seven and 26% of the general population [1], and almost half of all shoulder-related pain in patients seeking primary health care is related to subacromial impingement syndrome [2]. A thorough understanding of the treatment of this condition is therefore of importance for physiotherapists and other healthcare personnel.Subacromial impingement syndrome is a condition where the subacromial space, the area directly below the acromion process and above the shoulder joint, has narrowed. This can happen for several reasons, traditionally categorised as either primary or secondary causes. Primary causes are structural changes or morphological pre-conditions of the acromion process [3, 4]. Secondary causes often depend on multiple factors such as rotator cuff syndrome (strains or tears to the muscles and/or tendons of the muscles making up the rotator cuff), tendinopathy (inflammation or degeneration) in one or more of the same muscle tendons (infraspinatus, supraspinatus or subscapularis) and/or inflammation of the subacromial bursa [5, 6]. The long head/tendon of the biceps brachii can also be involved [6].Eccentric exercises are exercises performed only during the elongation phase of muscle activation (i.e. the lowering or slowing-down phase of a limb) and normally at a high intensity. A possible hypothesis for their benefits is that they could potentially reverse painful neovascularization within damaged tendons, which has been shown in a study on eccentric exercise and Achilles tendinopathy [7]. Eccentric exercises have also been shown to decrease swelling of the Achilles tendon [8].Due to their high intensity, and the fact that collagen growth in tendons tends to peak 24 to 72?h after training [9], enough time for recovery seems vital for effective rehabilitation with eccentric exercises. It could therefore be expected that in eccentric exercise regimens, not only how the exercise is performed (eccentric versus concentric phase) and its intensity, but also its frequency and duration will be of importance.It also has been proposed that injuries to tendons and other soft tissue are the most common causes of long-term shoulder pain in general. Histological examinations of tendon injuries of the supraspinatus in patients with subacromial impingement syndrome have shown changes to the tendon resembling those in patients with similar injuries of the patellar and Achilles tendon [10]. Patellar and Achilles tendinopathy are two types of tendon injuries where high intensity eccentric exercise has been shown effective, not only in decreasing pain but also in stimulating tissue regeneration and restoring function [11,12,13]. This makes it relevant to investigate whether eccentric exercises could be equally effective in treating patients with subacromial impingement syndrome.Earlier studies have shown that exercise, in general, is effective in treating subacromial impingement syndrome [14], at least as effective as corticosteroid injections for treating pain [15] and equally long-term effective as surgery [16]. Eccentric exercise in particular also has shown promising results in three uncontrolled studies [17,18,19].It is not clear at present which type of exercise/training is the most effective for subacromial impingement syndrome, and whether this differs depending on involved structures and underlying mechanisms [14, 16, 20, 21]. Previous reviews [22,23,24] on eccentric exercise and subacromial impingement syndrome have only had access to a limited set of data, up to two randomised controlled trials (RCTs) [25, 26] and one or more of the uncontrolled studies mentioned above [17,18,19]. A new review including recently published studies and incorporating a meta-analysis, not previously performed, would therefore be able to generate new knowledge, especially since this is a relatively new field of research [22]. Therefore, the aim of this systematic review was to investigate the effects of eccentric exercise on pain and function in patients with subacromial impingement syndrome compared with other exercise regimens or interventions. A secondary aim was to describe the included components of the various eccentric exercise regimens that have been studied.