Shoulder pain is the third leading musculoskeletal complaint with subacromial impingement syndrome (SIS), accounting for 44–65% of all shoulder complaints, resulting in functional limitation and disability [1,2,3,4].

SIS is mechanical compression of the rotator cuff tendons, long head of the biceps and subacromial bursae under the coracoacromial arch. [5] It is an umbrella term including rotator cuff tendonitis, tendinosis, partial or complete tears and bursal inflammation [3,4,5,6,7]. It could be due to acromioclavicular joint arthritis, acromial spurs, rotator cuff tendinopathy and scapular muscular dyskinesia. This results in a reduction in the potential space available for rotator cuff tendons in the subacromial space and triggers the cascade associated with SIS [1, 5].

SIS is diagnosed clinically as localized anterolateral shoulder pain lasting longer than 2 weeks, exacerbated by arm elevation, above-head movement and lying on the affected side [6, 8]. The “impingement sign” manifests as pain on shoulder abduction between 70° and 120° (painful arc) and is confirmed with the “impingement test”, where pain is relieved by injection of 5–10 ml of 1% xylocaine into the subacromial space. Provocative tests such as Neer, Hawkins and empty can tests can be positive [8].

There is no consensus regarding effective treatment for SIS. This lack of consensus might be related to a proposed multifactorial pathogenesis [3, 5]. Nevertheless, conservative therapy, including exercise, analgesia, physiotherapy and subacromial injections, is the first-line treatment and yields satisfactory results [5, 9]. Alternatively, those who have not improved resort to surgery [5]. Subacromial corticosteroid injection is commonly used; however, its efficacy remains controversial [10,11,12]. On the other hand, platelet-rich plasma (PRP) injection has recently garnered significant attention in stimulating tissue healing in numerous musculotendinous pathologies, including SIS [13,14,15,16].

The regenerative and immunomodulatory properties of PRP depend on the hyperphysiological content of autologous growth factors released after platelet activation, including platelet-derived, transforming, fibroblast, endothelial, connective tissue, vascular endothelial and hepatocyte growth factors (HGFs), which stimulate epithelial cells and fibroblasts, resulting in new collagen and elastin formation [15,16,17].

Significant variability exists among different PRP preparations, whether commercially available or non-commercial double-centrifugation techniques, with variation in the number of platelets and concentration of growth factors. The lack of standardization for an ideal number of platelets has a definite influence on clinical results [15,16,17].

A new patented blood product named lyophilized growth factors (L-GF) [18], which is a refined modification of conventional PRP therapy, has been developed. It uses allogenic pathogen-free platelets with a standardized number instead of autologous platelets used in PRP as a source of growth factors [19]. It showed encouraging results in patients with primary knee osteoarthritis with regard to pain, effusion and function [19], in addition to efficacy and safety in plantar fasciitis [20]. This growing evidence supporting its safety and efficacy encourages further research to verify its utility as a treatment for a spectrum of musculoskeletal disorders, including SIS.

The aim of this study was to evaluate the efficacy of injection of platelet-derived L-GF in the treatment of subacromial impingement.

This double-blind, randomized placebo-controlled trial was conducted on all consecutive patients with SIS who did not respond to conservative treatment for more than 3 months and were recruited from the Outpatient Clinic of Physical Medicine, Rheumatology and Rehabilitation Department, Alexandria University Hospitals between October 2020 and March 2021. The trial registration number is NCT04330027, date of first registration (01/04/2020).

Diagnosis of SIS Patients were diagnosed with SIS by the following:

Clinically Anterolateral shoulder and/or lateral upper arm pain, [6] positive painful arc between 70° and 120° of active abduction, [8] positive impingement sign (Neer’s sign or Hawkins–Kennedy test). [3]

Ultrasonographically Elicitation of the transient arc of pain during shoulder abduction, coinciding with passage of the supraspinatus tendon beneath the coracoacromial arch. [21]

Exclusion criteria included patients with a history of shoulder surgery, fracture, dislocation or subluxation, full-thickness rotator cuff tear, positive “drop arm sign”, frozen shoulder or degenerative arthropathy of the glenohumeral joint, cervical spine or upper extremity disorders with a significant impact on the shoulder, diabetes mellitus, active infection or other painful, function-limiting disorders of the shoulder and significant systemic disease [2, 4, 14, 19, 20].

Approval for this prospective clinical study was granted by the local ethics committee, and informed consent was obtained from all patients.

The current study included 60 patients (40 females and 20 males, aged between 24 and 75 years) who were randomly divided into two equal groups. Group 1 received subacromial saline injection, and group 2 received L-GF injection. Both groups were injected once under US guidance.