The use of ultrasound-guided platelet-rich plasma injections in the treatment of hip osteoarthritis: a systematic review of the literature

Osteoarthritis (OA) is a syndrome of joint pain and dysfunction that is caused by joint degeneration⁽¹⁾. OA affects more people than any other joint disease, and has widespread economic and social consequences. The problem is likely intensified by current demographic trends, including the pandemic of obesity and higher recreational activity levels of our elderly population⁽²⁾. Currently, there is no known cure for OA. Therefore, treatment is aimed at decreasing pain, maintaining or improving joint mobility, and limiting functional impairment⁽³⁾. Inflammation has been postulated as a key driver for pain in OA⁽⁴⁾, but a recent meta-analysis concluded that disease-modifying antirheumatic drugs (DMARDs) do not provide pain relief beyond placebo in OA⁽⁵⁾.

Lately, platelet-rich plasma (PRP) has become increasingly popular among the orthopaedic community as a minimally invasive technique for enhancing tissue healing in different conditions including rotator cuff pathology⁽⁶⁾, greater trochanteric pain syndrome⁽⁶⁾, knee osteoarthritis⁽⁷⁾, lateral epicondylitis⁽⁸⁾, osteochondral lesions of the talus⁽⁹⁾ and other orthopaedic conditions. It has been postulated that PRP promotes soft tissue healing by delivering a higher than normal concentration of platelets and, therefore, an increased concentration of platelet derived growth factors to the diseased area⁽¹⁰⁾. This has been shown in various studies^(11–14).

The use of PRP in treating hip OA has become more prevalent in recent years. The purpose of this review is to summarise the existing knowledge on the role of PRP in hip OA.

A search of the National Institute for Health and Care Excellence (NICE) database has been completed using the Healthcare Databases Advanced Search (HDAS) tool. In addition, we utilised the PubMed database to search the Medical Literature Analysis and Retrieval System Online (MEDLINE), Excerpta Medica database (EMBASE), Cumulative Index of Nursing and Allied Health (CINAHL) and Allied and Complimentary Medicine (AMED) databases. The search was conducted from their year of inception to June 2018 with the keywords “hip joint” and “ultrasound guided injection”.

Broad search keywords were used rather than specific terms to ensure no articles were missed. There was no language limit and all relevant published articles and abstracts were included. The Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) methodology guidance was employed⁽¹⁵⁾.

Abstracts from the search were reviewed for relevant articles by two authors. All references listed in the relevant articles were also reviewed for any other papers not found in the initial search. Studies were included if they were randomised control trials (RCT), and reported clinical and functional outcomes of patients treated with PRP for hip OA. Due to a small number of studies, we did not set a minimum follow-up period. Case reports, reviews, conference abstracts, case series, studies on animals and technical notes were excluded.

Once relevant RCTs were identified, data was extracted using a standardised form for each of the following: author, year of publication, study design, sample size, demographics, diagnostic test, injection technique, outcome measures and follow-up frequency. Due to the heterogeneity of the included data, a meta-analysis could not be conducted and, therefore, all data was reported descriptively.

The hip joint is the second most affected joint with OA after the knee, with a high prevalence in patients older than 50 years⁽²⁰⁾. OA of the hip can be very devastating, and the significance of the disease is manifested in the persistent pain and functional impairment which undermine the patient’s quality of life. Currently, cartilage loss is not considered to be the main factor triggering OA. More accurately, the triggering factor is suggested to be a malfunction in the affected joint, including all the tissues that maintain the articular homeostasis. Subchondral bone is identified as the starting place for pathologic changes, and cartilage is the victim of this process. Subchondral bone pathology inevitably leads to the onset of OA if not properly treated⁽²¹⁾.

To date, non-operative treatments remain very limited, and none were proven to stop or slow the progressive nature of the disease. Therefore, hip arthroplasty usually comes as the only definitive solution for patients with hip OA. Since PRP-based therapies have broken into clinical practice, they have been increasingly used as a non-operative option to treat earlier stages of joint degeneration to provide symptomatic relief and delay surgical intervention⁽²²⁾. The high amount of growth factors in PRP is thought to have an inductive and protective effect on chondrocytes as well as anti-inflammatory action, eventually restoring joint homeostasis.

The evidence from this review suggests that ultrasound-guided hip PRP injections may be efficacious in delivering long-term and clinically significant pain reduction in patients with hip OA, and may also lead to an improvement in function. The treatment effect appears to be of rapid onset, with better outcomes reported in the first 8 weeks post-injection. The magnitude of pain reduction and functional improvement decreases thereafter, although two trials report clinically significant differences in both pain and function at 12 months post-injection. Although these trials did not report details of the clinicians administering the injection, the procedure itself seemed well tolerated by patients, and only one significant minor complication was reported.

The limitations of this review include a small number of high-quality studies performed, and a relatively small number of participants. Small trials are known to potentially overestimate treatment effect sizes or report a significant effect when none is present. Furthermore, participants in these trials presented with variable degrees of OA. The authors reported outcomes at different follow-up intervals, and to enable comparison, it was necessary to use ranges (4–8 weeks and 4–6 months). The heterogeneity in methodology between trials, coupled with the limited reporting of trial statistics, makes it difficult to accurately compare results. This highlights the importance of the development and use of core outcomes for clinical trials in this area. All included RCTs compared PRP with HA, and there were no trials comparing PRP with placebo, limiting our ability to draw a firm conclusion.

Hip intra-articular PRP injections, when performed under ultrasound guidance, appear to be well tolerated and may be efficacious in delivering long-term and clinically significant pain reduction in patients with hip OA, and may also lead to an improvement in function, though the quality of evidence is relatively poor. Future trials should be sufficiently large and include a placebo group. Standardised outcomes, such as those recommended by the Osteoarthritis Research Society International (OARSI), should be used, and the results should be presented in a manner which will facilitate their inclusion in future meta-analyses.