Design

The design is a single-center randomized patient and assessor-blinded controlled trial. Figure 1 shows a flowchart of the study (Fig. 1), and details are listed in the SPIRIT figure (Fig. 2). The SPIRIT checklist is available as a supplement (S1). The study is conducted at the Department of Hand Surgery, Södersjukhuset, a hand trauma unit in Stockholm, with a catchment area of 2.8 million people.

Fig. 1Fig. 2Randomization

Randomization through sealed envelopes, in batches of 10, is performed by a research nurse. Stratification is used according to radiological Eaton-Littler class (1, 2, and 3). All patients are included by the authors JvK and MW or by three informed colleagues: doctors JS, MM, and KE.

Interventions 1.

High-concentration PRP injection PRP injection (0.6–1 ml). Arthrex ACPmax system

2.

Saline injection (0.6–1 ml)

All injections are administered under sterile conditions and radiological guidance on the day of randomization. Injections are performed from the dorsal, just radial, or ulnar of APL and EPB. To mimic the PRP procedure, a blood sample is taken from patients allocated to saline injection, and they must wait in the waiting area for the injection just as long as patients allocated to PRP. Patients wear a blindfold during injection. After the injections, patients do not receive any specific conservative treatment (orthoses, joint protection education). In bilateral thumb base osteoarthritis cases, the more symptomatic joint is injected and assessed.

Inclusion criteria

The following are the inclusion criteria: osteoarthritis in the thumb base, radiological Eaton-Littler class 1–3 [22], clinical signs of thumb base osteoarthritis (pain at palpation of the CMC-1 joint and pain during the provocation test).

Exclusion criteria

The following are the exclusion criteria: rheumatoid arthritis diagnosis, ongoing infection in the hand or wrist, history of gout or pseudogout in the hand, inability to co-operate with the follow-up protocol (language difficulties, severe psychiatric disorder, cognitive impairment, drug addiction), chronic pain syndrome/centralized pain, intra-articular injection in the affected joint within 6 months prior to inclusion, Eaton-Littler class 4 (defined as symptomatic STT joint osteoarthritis).

Outcome

The primary outcome is as follows: change of pain on load (numerical rating scale (NRS) 0–100) in the thumb from before the first injection to 6 months after.

The secondary outcomes are as follows:

Change in PROMs (Patient-Reported Outcome Measures) from pre-injection to 3, 6, and 12 months, including Patient-Rated Wrist/Hand Evaluation (PRWHE) score [23], Nelson score [24], and HQ-8 score [25]

Objective physical variables: key pinch and three-finger pinch strength measured by using the Saehan Medical® mechanical pinch gauges SH5010 (the mean value of three consecutive measurements is used), radial and palmar abduction of the first metacarpal [26], thumb opposition [27] (Kapandji score). All measurements are performed according to the manual for measuring motion and strength in the Swedish national quality registry HAKIR [26]

Time for the patient to experience the need for an intervention in the form of renewed injection, steroid injection, or surgery within 1 year after injection. Any adverse events, complications, and failures (defined as lack of improvement or deterioration of pain) during the study period will be recorded

Sample size

To show a difference of 20 points (out of 100), representing the minimal clinical difference [28], in pain on load NRS score between PRP and saline injection (SD 30) (3) after 6 months, 37 patients are required in each treatment arm. The power will be 80% (p < 0.05). To account for non-parametric outcomes and loss to follow-up, we aim to include 90 patients in total, 45 in each treatment arm.

Recruitment

Patients diagnosed with painful osteoarthritis in the thumb base at the Department of Hand Surgery at Södersjukhuset, Stockholm, are asked to participate in the study.

Assessment

The Patient-Reported Outcome Measure (PROM) questionnaires at baseline, 3, 6, and 12 months after the first injection and Pain Catastrophizing Scale Questionnaire (PCS [29]) at baseline (to be included as a covariate in the analysis)

Objective physical variables (key and pinch grip, MC-1 radial and palmar abduction, opposition): at baseline 3, 6, and 12 months after injection

One doctor performs the preoperative assessment and injection. A second doctor, blinded to the injection type, performs the assessments at 3 and 6 months. Adverse events are reported. At 6 months, treatment is revealed, and blinding is tested by asking the patients and assessor what treatment they believe the patient has received before disclosure. The assessment at 12 months is not blinded. If patients have persisting pain and significant problems at this point, they can proceed with another line of treatment.

Statistical analyses

For comparing PRP versus placebo, the Wilcoxon signed rank and rank sum tests and chi-square tests will be used for non-parametric data (change in PROMS and non-normally distributed outcomes at different times). The T-test will be used for changes in continuous data (objective physical variables) with a normal distribution. Shapiro–Wilk test will be used for establishing data normality. Generalized estimating equations (GEE) will be used to analyze the effect of injection, adjusting for pain catastrophizing, gender, and Eaton class. A Kaplan Meier analysis of the need for another intervention within 1 year will be formed and continuously recorded.

Ethics and data management

The study has been approved by the Swedish Ethical Review Authority, and in accordance with this permit, patients are allowed to withdraw their participation in the study without any reason and without consequence for future care. All participants will fill in an informed consent and have contact information to the research nurse and responsible surgeons should any questions or complications occur. All data are stored according to the ethical permit and is regulated under the GDPR. Data are handled in a pseudonymized form and will be presented on group level. The key to the pseudonyms is stored in a secure location at Södersjukhuset and Karolinska Institutet, only available to the authors. Patients’ insurance is covered by the Swedish Patientförsäkringen.

If patients are unable to attend any follow-up visits, they will be asked to fill out the PROMS online.

Results from the study will be published in a scientific journal and presented at hand surgery meetings.