A single intraarticular platelet-rich plasma improves pain and function for patients with early knee osteoarthritis: Analyses by radiographic severity and age

Abstract

BACKGROUND:

Most studies use platelet-rich plasma (PRP) requiring multiple intraarticular injections for knee osteoarthritis (OA).

OBJECTIVE:

To investigate the efficacy of a single intraarticular PRP injection for patients with early knee OA and consider subgroup analyses of radiographic severity and age, respectively.

METHODS:

Forty-one patients with knee OA (Kellgren-Lawrence grade 1–2) received a single PRP injection into the target knee and were assessed at baseline and 1, 3, and 6 months postinjection. The primary outcome was the mean change from baseline in the visual analog scale (VAS) pain (0–100 mm) at 6 months postinjection. Secondary outcomes included the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), Lequesne index, single leg stance test (SLS), use of rescue analgesics and patients’ satisfaction.

RESULTS:

Thirty-eight patients completed the study. The mean pain VAS decreased significantly from 45.6 $\pm$ 13.0 mm at baseline to 16.9 $\pm$ 13.4 mm, 14.0 $\pm$ 13.1 mm and 15.5 $\pm$ 14.0 mm at 1, 3 and 6-month follow-ups ( $p{<}$ 0.001 for all). Significant improvements in WOMAC, Lequesne index, SLS and consumption of analgesics from baseline ( $p{<}$ 0.001 for all) were noted at each follow-up. Patients’ satisfaction was high. No serious adverse events occurred. Subgroup analyses revealed that patients with grade 1 OA showed significantly greater VAS pain reduction at 3 months ( $p=$ 0.006) and 6 months ( $p=$ 0.005) than patients with grade 2 OA. The older-age group (age ${>}$ 60) showed significantly greater improvements in VAS pain, WOMAC function subscale scores and total scores at 6-month postinjection, compared with the younger age-group (age ${<}=$ 60). The younger-age group reported better satisfaction at 1 and 3-month postinjection.

CONCLUSIONS:

One injection of PRP improved pain and function for 6 months for patients with early knee OA. This study supports putting the one-injection regimen into clinical practice. Further research is needed for more definite conclusions.

Keywords

Intraarticular injection knee osteoarthritis platelet-rich plasma pain WOMAC score

1. Introduction

Knee osteoarthritis (OA) is a common condition that causes pain and disability. The treatment for knee OA aim to reduce pain, stiffness, and physical disability. Current treatment options include the use of simple analgesics or nonsteroidal anti-inflammatory drugs (NSAIDs), glucosamine and chondroitine sulphate, intra-articular injection of corticosteroid, hyaluronic acid and platelet-rich plasma (PRP), physical therapy, weight reduction, orthotics and surgical treatment ranging from arthroscopy to total knee replacement [1]. Due to the chronicity and incurable nature of knee OA, therapies targeting knee OA should be safe and effective for its long term management. In recent years, treatment options such as biological and regenerative methods have come into vogue.

PRP is an autologous blood product that mainly contains concentrated platelets and growth factors. The growth factors serve to promote local angiogenesis, modulate inflammation, inhibit catabolic enzymes and cytokines, recruit local stem cells and fibroblasts to sites of damage, and induce healthy nearby cells to manufacture greater numbers of growth factors [2]. Local use of PRP directly at the site of cartilage injury is thought to stimulate a natural healing cascade and accelerate cartilage repair [3, 4, 5, 6].

PRP had been reported to be an effective and safe orthobiologic in the treatment of knee OA [7, 8, 9, 10]. However, there is no clarity in reference to the number and frequency of PRP injections. A range of single to multiple injections with weekly to every 3- or 4-week schedule had been reported [11, 12]. To date, there were only few studies reporting the efficacy of a single PRP injection for the treatment of knee OA [12, 13, 14, 15, 16]. Patel et al. reported that a single PRP injection is as effective as two injections in early knee OA [12]. The single injection regimen may represent an attractive alternative, as it may decrease patient time expenditure and discomfort associated with the injection process and offer potential safety benefits to patients. Besides, the one injection regimen may possibly represent a cost-saving therapy compared with multiple injections.

Intraarticular PRP has been reported to have better results in younger patients, low body mass index patients and those with less degree of cartilage degeneration [8, 17]. However, the predictors of good response for one injection of PRP have seldom been reported [12, 13, 14]. It is important to determine the type of patients who will benefit from the therapy in order to guide its clinical use and avoid an indiscriminate clinical application. The purpose of this study was to investigate the efficacy and safety of a single injection of PRP for the treatment of early knee OA. Subgroup analyses would be done to determine whether radiographic severity or age would influence the treatment effects.

2. Materials and methods

2.1 Ethical approval

This study was conducted in accordance with the Declaration of Helsinki and was approved by the Institutional Review Board for Human Investigation of Kaohsiung Veterans General Hospital. The trial was registered at ClinicalTrials.gov (Registry number NCT04027738). All subjects provided written informed consent prior to enrollment in the study.

2.2 Study design and participants

This was a prospective study with a 6-month follow-up period done in the setting of an outpatient rehabilitation department in a tertiary care medical center between January 2017 and December 2017.

The inclusion criteria were: patients aged 20–70 years, symptomatic knee OA with pain for at least 6 months despite conservative treatment such as analgesics, NSAIDs and/or physical therapy, average knee pain of at least 30 mm on a 100-mm visual analog (VAS) scale, grade 1 or 2 knee OA according to the Kellgren-Lawrence grading system based on standing anterior-posterior and lateral knee radiographs taken within the previous 6 months [18]. Radiological evidence of bilateral knee OA was accepted if global pain VAS in the contralateral knee was less than 30 mm.

Exclusion criteria were: previous orthopedic surgery on the spine or lower limbs; disabling OA of either hip or foot; knee instability or marked valgus/varus deformity; history of severe knee trauma; intraarticular injections into the knee in the past 6 months; infections or skin diseases around the target knee; women ascertained or suspected pregnancy or lactating; presence of malignancy, hematological disease, collagen vascular diseases, or autoimmune diseases; therapy with anticoagulants or anti-aggregating agent; or serious medical conditions that would interfere with assessments during the study.

Major protocol violations included surgery, initiation of physical therapy, and use of proscribed medications. Patients were said to be noncompliant when they missed any patient visit.

2.3 Study process

The study consisted of a screen visit, a baseline visit during which intraarticular injection was done and follow-up visits at 1, 3 and 6 months after the injection. Potential study participants returned for a baseline visit after a 1-week washout period for NSAIDs and analgesics. Before injection, demographic data and baseline assessments were collected.

2.4 Intervention

The patients received a single 3-ml injection of PRP. Approximately 10-mL of venous blood was drawn from each patient and centrifuged using an Arthrex autologous conditioned plasma (ACP) kit (a low-leukocyte ACP system), spun at a speed of 1500 rpm for 5 minutes. The platelet concentration obtained was approximately 2–3 times greater than the baseline platelet concentration.

All the injections were done by the same experienced physician using aseptic procedures. All injection procedures were carried out using 23 gauge needles based on anatomic landmarks. With the patient in a sitting position and the knee flexed to 90 ${}^{\circ}$ , the injection was given at 1 cm proximal to the joint line, lateral to the patellar tendon, through the anterolateral portal. The needle was directed towards the intercondylar notch.

None of the patients received physical therapy after the injection. No regular analgesics, glucosamine or chondroitin, NSAIDs or physical therapy for knee were permitted during the study. Acetaminophen (500 mg; maximum daily dose, 4 g) was the only rescue medication allowed for knee pain. Acetaminophen was not permitted during the 24-hour period prior to each study visit. Use of rescue medication during the study period was recorded in a patient diary.

2.5 Outcome measures

The primary outcome was the change from baseline in the VAS pain score at 6 months. The patient rated the average severity of knee pain on knee movement over the previous week on a 0–100 mm VAS (0 $=$ no pain; 100 $=$ worst possible pain) [19].

Secondary outcome measures included the following:

The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, Likert Scale) is a 24-item questionnaire with 3 subscales measuring pain, stiffness, and physical function [20]. The patient answers the questions and then receives a cumulative score in each of the 3 areas (pain, 0–20; stiffness, 0–8; physical function, 0–68). Total score is 96 and higher scores indicate worse outcomes.

Lequesne index was used to assess severity of knee symptoms during the last week [21]. It includes the measurement of pain, walking distance, and activities of daily living. Maximal score is 24 and higher scores represent worse function.

Single-leg stance test (SLS) is done by raising one foot up without touching it to the supported lower extremity with target knee and maintain balance for as long as possible. Each participant performed 3 trials, and the best result of the 3 trials was recorded [22].

These variables were measured at baseline (before intervention), 1, 3 and 6 months after injections by a physician not involved in PRP injection. Patients were asked to rate their treatment satisfaction compared to the preinjection condition, using a 100 mm VAS (0 $=$ completely dissatisfied, 100 $=$ completely satisfied) at 1, 3 and 6 months after injections.

The occurrence of adverse events was recorded, including duration, action taken and outcome.

2.6 Statistical analysis

Based on the G*Power 3.0 and the statistical method used for the study purpose, Wilcoxon signed-rank test, the required sample size was 35 participants (power $=$ 0.8; alpha $=$ 0.05; parent distribution: normal; effect size dz $=$ 0.5). Considering the dropout rate, we increase the sample size 20% to get the sample size 42.

We used the Statistical Package for the Social Sciences (version 20.0; SPSS Inc, Chicago, IL, USA) for all analyses. Changes in outcome measures among baseline, 1, 3, and 6-month postinjection were assessed using Friedman tests and Wilcoxon signed-rank tests as post hoc analyses with Bonferroni’s corrections. A $p$ value less than 0.05 was regarded as statistically significant.

2.6.1 Subgroup analysis

After data collection was complete, we divided patients by radiographic severity and age and subgroup analyses were done to compare the outcome scores at various time points to determine whether radiographic severity or age would influence the treatment response. Between-subgroup differences were assessed using Mann-Whitney U tests for satisfaction and for improvement (i.e. each follow-up comparing with baseline) of other outcome measures. Within-subgroup differences were assessed using Friedman tests and Wilcoxon signed-rank tests as post hoc analyses with Bonferroni’s corrections. A $p$ value less than 0.05 was considered as statistically significant.

3. Results

3.1 Patient characteristics

Forty-six participants were assessed for eligibility, of whom 5 were excluded, and 41 participants were enrolled for intervention (Fig. 1). Three patients withdrew during the study period, leaving 38 patients available for the analysis at 6-month follow-up. The demographic and clinical characteristics of the study participants are shown in Table 1. Patients were predominantly female (65.8%), the mean age was approximately 57.9 years (range 31–70 years), the mean body mass index was 24.5 kg/m ${}^{2}$ (range 20.8–30.8 kg/m ${}^{2}$ ). Plain radiographs showed grade 1 and grade 2 OA in 15 and 23 patients, respectively.

Table 1
Demographic and baseline characteristics of the participants

Characteristic	Knee OA ( $n=$ 38)	Range
Age (years)	57.9 $\pm$ 9.5	31–70
$\leqslant$ 60	21 (55.3%)
$>$ 60	17 (44.7%)
Sex (F/M)	25/13
Weight (kg)	71.5 $\pm$ 11.9	50–92
Height (cm)	164.4 $\pm$ 7.6	150–176
BMI (kg/m ${}^{2}$ )	24.5 $\pm$ 2.8	20.8–30.8
Employment status (light worker/	18/20
heavy labor)
Knee injection side (left/right)	15/23
Radiographic stage (Kellgren-
Lawrence grade), $n$ (%)
Grade 1	15 (39.5%)
Grade 2	23 (60.5%)
Disease duration (years)	2.6 $\pm$ 1.1	1–5

The values are given as mean $\pm$ standard deviation or number of patients; OA $=$ osteoarthritis; BMI $=$ body mass index.

Figure 1.

Flow diagram of participants through the trial.

3.2 Primary and secondary outcomes

Patients showed significant VAS pain change among four time points from baseline to three follow-ups after a single PRP injection using a Friedman test ( $p{<}$ 0.001) (Table 2). Then a Wilcoxon signed-rank test as post-hoc analysis with a Bonferroni’s correction found significant differences at 1, 3, and 6 months after the single PRP injection as compared with baseline data. The mean VAS decreased significantly from 45.6 $\pm$ 13.0 mm at baseline to 16.9 $\pm$ 13.4 mm, 14.0 $\pm$ 13.1 mm and 15.5 $\pm$ 14.0 mm at 1, 3 and 6-month follow-ups ( $p{<}$ 0.001), corresponding to a mean improvement of 28.7 mm, 31.6 mm and 30.1 mm from baseline, respectively (all $p$ values ${<}$ 0.001) (Table 2). However, there were no statistical differences at 3 and 6 months as compared with the one at 1 month, nor was at 6 months as compared with the one at 3 months after the PRP injection for VAS pain (Table 2).

Table 2
The outcome measures before and after treatment

	Baseline		1 month		3 months		6 months		$P$ value ${}^{\dagger}$	Post hoc test ${}^{\S}$
VAS	45.6	$\pm$ 13.0	16.9	$\pm$ 13.4	14.0	$\pm$ 13.1	15.5	$\pm$ 14.0	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
WOMAC-pain subscale ${}^{\text{a}}$	7.2	$\pm$ 2.8	2.7	$\pm$ 1.8	2.9	$\pm$ 2.5	3.5	$\pm$ 2.8	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
WOMAC-stiffness subscale ${}^{\text{a}}$	2.2	$\pm$ 0.8	1.0	$\pm$ 1.1	0.9	$\pm$ 1.0	1.0	$\pm$ 0.9	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
WOMAC-function subscale ${}^{\text{a}}$	20.5	$\pm$ 10.4	9.4	$\pm$ 7.1	9.5	$\pm$ 6.8	10.5	$\pm$ 8.0	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
WOMAC-total ${}^{\text{a}}$	29.9	$\pm$ 12.9	13.2	$\pm$ 9.0	13.2	$\pm$ 8.9	14.9	$\pm$ 10.8	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
Lequesne index ${}^{\text{a}}$	7.6	$\pm$ 3.7	3.9	$\pm$ 2.6	3.7	$\pm$ 3.0	3.9	$\pm$ 2.7	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
SLS (sec)	24.4	$\pm$ 15.9	47.6	$\pm$ 23.7	44.5	$\pm$ 21.7	43.9	$\pm$ 21.5	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
Acetaminophen (tablets/week) ${}^{\text{a}}$	14.3	$\pm$ 2.4	3.4	$\pm$ 2.1	3.1	$\pm$ 2.3	3.3	$\pm$ 2.2	$<$ 0.001 ${}^{*}$	AB ${}^{}$ AC ${}^{}$ AD ${}^{*}$
Satisfaction			74.5	$\pm$ 17.4	73.2	$\pm$ 15.3	72.1	$\pm$ 15.7	0.061

The values are given as mean $\pm$ standard deviation, VAS $=$ Visual analog scale for pain, WOMAC $=$ The Western Ontario and McMaster Universities Osteoarthritis Index, SLS $=$ Single limb stance. ${}^{\dagger}$ Friedman test. ${}^{\S}$ Wilcoxon signed-rank test with a Bonferroni’s correction. ${}^{\text{a}}$ Higher scores represent worse pain or function. ${}^{*}p<$ 0.001. AB is the comparison before and 1 month after the PRP injections; AC is the comparison before and 3 month after the PRP injections; and AD is the comparison before and 6 months after the PRP injections.

WOMAC (including 3 subscale scores and total scores) changed significantly among four time points from baseline to 1, 3, and 6 months after injections ( $p{<}$ 0.001) (Table 2). In pain, stiffness, function subscale scores and total scores, the post-hoc analyses found significant improvements at 1, 3, and 6 months after PRP injection as compared with baseline data (all $p$ values ${<}$ 0.001). However, there were no statistical differences at 3 and 6 months as compared with the one at 1 month, nor was at 6 months as compared with the one at 3 months after the PRP injection (Table 2).

Patients improved significantly in Lequesne index and SLS scores from baseline to each follow-up visit, respectively (all $p$ values ${<}$ 0.001) (Table 2). Acetaminophen consumption reduced significantly during the study period ( $p{<}$ 0.001) (Table 2). Patients’ satisfaction rates were high, with no significant differences among three follow-up visits ( $p{>}$ 0.05) (Table 2).

3.3 Results of subgroup analyses

In this study, there were 15 patients with Kellgren-Lawrence grade 1 OA and 23 patients with grade 2 OA. At baseline, the grade 2 group showed greater WOMAC function subscale scores and total scores, and Lequesne index scores ( $p{<}$ 0.05) (Table 3). Significant improvements in the outcome measures (including VAS, WOMAC subtotal and total scores, Lequesne index and SLS) among four time points from baseline to 1, 3, and 6 months postinjections were noted in patients with grade 1 and grade 2 OA ( $p{<}$ 0.05 for all) (Table 3). Patients in the grade 2 group showed significant difference in their satisfaction among three follow-ups ( $p=$ 0.047) (Table 3). Subgroup analyses comparing patients with different x-ray grades revealed that patients with grade 1 OA showed significantly greater improvement in VAS pain at 3 months ( $p=$ 0.006) and 6 months ( $p=$ 0.005) than patients with grade 2 OA (Table 3). No significant between-subgroup differences in WOMAC (including subscale scores and total scores), Lequesne index, SLS, and patients’ satisfaction were noted at any follow-up time point, except for significant differences in improvement of WOMAC function subscale scores and total scores at 1 month postinjection ( $p=$ 0.008 and $p=$ 0.018, respectively).

Table 3
Comparison between different OA Kellgren-Lawrence grade

	Grade 1 ( $n=$ 15)		Grade 2 ( $n=$ 23)		$P$ value ${}^{\dagger}$
VAS baseline	42.7	$\pm$ 9.6	47.5	$\pm$ 14.6
VAS 1 month	11.4	$\pm$ 12.5	20.3	$\pm$ 13.2	0.267
VAS 3 month	4.0	$\pm$ 7.1	20.6	$\pm$ 12.0	0.006 ${}^{*}$
VAS 6 month	6.3	$\pm$ 9.9	21.5	$\pm$ 13.1	0.005 ${}^{*}$
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-pain baseline	6.3	$\pm$ 2.8	7.7	$\pm$ 2.8
WOMAC-pain 1 month	2.3	$\pm$ 1.6	3.0	$\pm$ 1.9	0.299
WOMAC-pain 3 month	1.8	$\pm$ 1.9	3.7	$\pm$ 2.6	0.395
WOMAC-pain 6 month	2.5	$\pm$ 1.9	4.1	$\pm$ 3.1	0.682
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-stiffness baseline	1.9	$\pm$ 1.0	2.4	$\pm$ 0.7
WOMAC-stiffness 1 month	0.9	$\pm$ 0.3	1.2	$\pm$ 0.2	0.547
WOMAC-stiffness 3 month	0.5	$\pm$ 0.6	1.1	$\pm$ 1.2	0.466
WOMAC-stiffness 6 month	0.6	$\pm$ 0.5	1.2	$\pm$ 1.0	0.745
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-function baseline	15.7	$\pm$ 8.5	23.6	$\pm$ 10.5
WOMAC-function 1 month	9.3	$\pm$ 6.7	9.5	$\pm$ 7.4	0.008 ${}^{*}$
WOMAC-function 3 month	6.4	$\pm$ 5.9	11.4	$\pm$ 6.8	0.138
WOMAC-function 6 month	7.0	$\pm$ 6.5	12.8	$\pm$ 8.3	0.419
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-total baseline	23.9	$\pm$ 11.0	33.8	$\pm$ 12.7
WOMAC-total 1 month	12.5	$\pm$ 8.4	13.7	$\pm$ 9.5	0.018 ${}^{*}$
WOMAC-total 3 month	8.7	$\pm$ 6.9	16.2	$\pm$ 8.9	0.411
WOMAC-total 6 month	10.1	$\pm$ 8.3	18.1	$\pm$ 11.1	0.632
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
Lequesne index baseline	5.9	$\pm$ 3.6	8.7	$\pm$ 3.4
Lequesne index 1 month	2.5	$\pm$ 1.6	4.7	$\pm$ 2.8	0.399
Lequesne index 3 month	3.3	$\pm$ 3.6	4.0	$\pm$ 2.6	0.207
Lequesne index 6 month	3.0	$\pm$ 2.5	4.5	$\pm$ 2.7	0.190
$P$ value ${}^{\S}$	$<$ 0.005 ${}^{*}$		$<$ 0.001 ${}^{*}$
SLS baseline (sec)	26.5	$\pm$ 14.4	23.0	$\pm$ 17.1
SLS 1 month (sec)	53.3	$\pm$ 18.3	43.9	$\pm$ 26.4	0.244
SLS 3 month (sec)	48.6	$\pm$ 13.9	41.8	$\pm$ 25.4	0.256
SLS 6 month (sec)	52.1	$\pm$ 13.4	38.5	$\pm$ 24.1	0.060
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
Satisfaction 1 month	70.3	$\pm$ 22.6	77.2	$\pm$ 12.8	0.506 ${}^{\text{a}}$
Satisfaction 3 month	73.0	$\pm$ 20.3	73.3	$\pm$ 11.4	0.638 ${}^{\text{a}}$
Satisfaction 6 month	75.0	$\pm$ 14.4	70.2	$\pm$ 16.5	0.366 ${}^{\text{a}}$
$P$ value ${}^{\S}$	0.758		0.047 ${}^{*}$

The values are given as mean $\pm$ standard deviation. ${}^{\dagger}$ Between-group difference of change from baseline to each follow-up determined using the Mann-Whitney U test. ${}^{\S}$ Within-group difference determined using Friedman test. ${}^{*}p<$ 0.05. ${}^{\text{a}}$ Mann-Whitney U test.

Table 4

Comparison between different age populations

	Age $\leqslant$ 60 ( $n=$ 21)		Age $>$ 60 ( $n=$ 17)		$p$ value ${}^{\dagger}$
VAS baseline	39.1	$\pm$ 8.9	53.5	$\pm$ 13.0
VAS 1 month	8.2	$\pm$ 9.5	27.7	$\pm$ 9.0		0.194
VAS 3 month	11.3	$\pm$ 10.0	17.4	$\pm$ 15.9		0.054
VAS 6 month	14.4	$\pm$ 10.6	16.8	$\pm$ 17.5		0.023 ${}^{*}$
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-pain baseline	6.8	$\pm$ 3.0	7.6	$\pm$ 2.7
WOMAC-pain 1 month	1.9	$\pm$ 1.5	3.8	$\pm$ 1.6		0.183
WOMAC-pain 3 month	2.4	$\pm$ 2.3	3.5	$\pm$ 2.6		0.988
WOMAC-pain 6 month	3.5	$\pm$ 2.5	3.4	$\pm$ 3.2		0.140
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-stiffness baseline	2.2	$\pm$ 0.6	2.2	$\pm$ 1.1
WOMAC-stiffness 1 month	0.6	$\pm$ 0.8	1.7	$\pm$ 1.1		0.011 ${}^{*}$
WOMAC-stiffness 3 month	0.6	$\pm$ 0.9	1.2	$\pm$ 1.1		0.152
WOMAC-stiffness 6 month	1.0	$\pm$ 0.7	0.9	$\pm$ 1.1		0.819
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		0.004 ${}^{*}$
WOMAC-function baseline	17.7	$\pm$ 8.3	23.9	$\pm$ 11.9
WOMAC-function 1 month	6.6	$\pm$ 5.8	12.9	$\pm$ 7.1		0.918
WOMAC-function 3 month	8.3	$\pm$ 6.2	10.8	$\pm$ 7.5		0.115
WOMAC-function 6 month	9.8	$\pm$ 7.0	11.4	$\pm$ 9.3		0.018 ${}^{*}$
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
WOMAC-total baseline	26.7	$\pm$ 10.5	33.8	$\pm$ 14.7
WOMAC-total 1 month	9.0	$\pm$ 7.1	18.4	$\pm$ 8.5		0.659
WOMAC-total 3 month	11.3	$\pm$ 7.5	15.6	$\pm$ 10.1		0.176
WOMAC-total 6 month	14.3	$\pm$ 8.9	15.8	$\pm$ 13.0		0.013 ${}^{*}$
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
Lequesne index baseline	7.2	$\pm$ 3.6	8.0	$\pm$ 3.7
Lequesne index 1 month	3.5	$\pm$ 2.3	4.4	$\pm$ 2.9		0.801
Lequesne index 3 month	2.8	$\pm$ 2.0	4.9	$\pm$ 3.6		0.425
Lequesne index 6 month	3.8	$\pm$ 1.9	4.2	$\pm$ 3.5		0.813
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
SLS baseline (sec)	26.5	$\pm$ 18.9	21.8	$\pm$ 11.3
SLS 1 month (sec)	48.7	$\pm$ 24.0	46.4	$\pm$ 24.0		0.872
SLS 3 month (sec)	45.0	$\pm$ 23.3	43.9	$\pm$ 20.2		0.297
SLS 6 month (sec)	45.0	$\pm$ 21.1	42.6	$\pm$ 22.5		0.814
$P$ value ${}^{\S}$	$<$ 0.001 ${}^{*}$		$<$ 0.001 ${}^{*}$
Satisfaction 1 month	83.1	$\pm$ 12.3	63.8	$\pm$ 17.1	$<$	0.001 ${}^{*\text{a}}$
Satisfaction 3 month	80.5	$\pm$ 12.9	64.1	$\pm$ 13.3	$<$	0.001 ${}^{*\text{a}}$
Satisfaction 6 month	75.0	$\pm$ 17.1	68.5	$\pm$ 13.3		0.134 ${}^{\text{a}}$
$P$ value ${}^{\S}$	0.004 ${}^{*}$		0.982

When patients were divided by age, some interesting findings emerged. Using 60 years of age as the cutting point, patients were classified into the younger age-group (age $<$ 60 years, $n=$ 21) and the older age-group (age ${>}$ 60 years, $n=$ 17). At baseline, the older age-group showed greater VAS pain ( $p{<}$ 0.001) (Table 4). Both groups showed significant improvements in the outcome measures (including VAS, WOMAC subscale scores and total scores, Lequesne index and SLS) among four time points from baseline to 1, 3, and 6 months postinjections ( $p{<}$ 0.05 for all) (Table 4). The younger-age group demonstrated significant differences in their satisfaction among three follow-ups ( $p=$ 0.004) (Table 4). The improvement of treatment outcomes at each follow-up comparing with baseline data were compared between the 2 age groups. The older-age group demonstrated significantly greater reduction in VAS pain, WOMAC function subscale scores and total scores at 6-month postinjection compared with the younger age-group. However, the younger-age group showed significantly greater reduction in WOMAC stiffness subscale scores at 1-month postinjection. The younger-age group also demonstrated significantly greater satisfaction at 1 and 3-month follow-ups, compared with the older age-group.

3.4 Adverse events

No infections, allergic reactions, or other serious adverse events occurred during the study. Five (13.2%) patients developed minor adverse events after PRP injections. These adverse events were mild and transient, and self-resolved in 2 days without any therapeutic intervention. No patients withdrew from the study because of any adverse event.

4. Discussion

This study demonstrated that one injection of PRP was safe and effective for 6 months in the treatment of Kellgren-Lawrence grade 1 or 2 knee OA. The one injection regimen of PRP reduced pain, improved function and resulted in high patient satisfaction. Patients with grade 1 OA showed significantly greater improvement in VAS pain at 3 and 6 months than patients with grade 2 OA. Patients aged over 60 years showed significantly greater reduction in VAS pain, WOMAC function subscale and total scores at 6 month postinjection compared with patients aged 60 years or younger. Patients aged 60 years or younger reported greater satisfaction at 1 and 3 months than patients aged over 60 years.

Pain reduction is the primary indication for the use of intra-articular knee injection. In clinical trials of chronic pain treatments, reduction in chronic pain intensity of at least 30% appeared to reflect at least moderate clinically important differences [23]. In our study, the mean VAS pain score reduced by 28.7 mm (62.9%), 31.6 mm (69.3%), and 30.1 mm (66.0%) at 1, 3, and 6-months postinjection, respectively. It appeared that pain reduction was documented in our study and the magnitude of pain reductions were far beyond clinical meaningful significance. Li et al. investigated the efficacy of single injection of PRP for Kellgren-Lawrence grade 1 or 2 knee OA. The median VAS score improved from 64.2 mm at baseline to 42.8 mm at 6-months follow-up, corresponding to a median reduction of 33.3% from baseline [13]. Interestingly, greater VAS pain reduction (66.0%) at 6-months postinjection was noted in our study population.

The patients experienced significant improvements in all WOMAC subscale and total scores through the 6-month follow-up, supporting the efficacy of PRP injections in relieving pain and stiffness for patients with knee OA. The minimum clinically important differences (MCID) for changes in WOMAC pain and function scores was set at 20% [24]. Patients in our study experienced a 51.4% improvement in WOMAC-pain and a 48.8% improvement in WOMAC-function from baseline at 6-month postinjection, much exceeded the MCID. Patel et al. reported a mean WOMAC-pain reduction of 50.9% from baseline at 6 months after a single injection of PRP in grade 1 or 2 knee OA, which was very similar to our results [12]. Sánchez et al. compared PRP and hyaluronic acid in patients with knee OA, and they also reported that treatment with PRP reduced the WOMAC index by 50% [25].

Lequesne defined effective treatment forms as those leading to a score improvement of 30–40% at the time of follow-up [26]. In our study, the mean Lequesne index scores improved by 3.7 points from baseline at 6-month post PRP injection, representing an improvement of 48.7%, which was beyond the values used to define treatment effectiveness.

There is limited evidence supporting the use of a single PRP injection for the treatment of early stage knee OA [12, 13, 14, 15, 16]. Patel et al. reported that a single intraarticular PRP in concentrations of 10 times the normal amount is as effective as 2 injections to alleviate symptoms in early knee OA [12]. Similar to our results, they reported that patients with grade 1 OA showed better results than those with grade 2 [12]. Different from their study, the PRP concentration in our present study was approximately 2–3 times greater than baseline platelet concentration. Interestingly, we found that patients aged over 60 years showed significantly greater reduction in VAS pain at 6-month postinjection compared with those aged 60 years or younger, as at baseline patients in the older-age group were more painful than those in the younger-age group. Li et al. reported a case series with 21 patients and they concluded that one injection of PRP seems to be effective in patients with low-grade knee OA [13]. Compared with their case series, we had larger sample size and we used more subjective and objective outcome measures. Buendía-López et al. reported that a single intraarticular PRP resulted in pain reduction and function improvement in patients with early knee OA at the 52-week follow-up, superior to a single injection of hyaluronic acid and the use of oral NSAID [14]. Kesiktas et al. recently reported that a single intraarticular PRP, hyaluronic acid, or peptide injection provided satisfactory results in terms of pain and function in knee OA at 3 months [27]. Although various studies reported the efficacy of one injection of PRP for knee OA, direct comparison among these studies was not possible because of different study population, different PRP preparation method and different outcome measures.

This study utilized the low-leukocyte ACP system (Arthre, Germany) based on increasing evidence that it is the ratio of platelets to leukocytes and not only the number of platelets that determines the biological activity of a PRP-type product [28].

Evaluation of the efficacy for one-injection regimen of PRP in the Asian population was also a major concern of this study, as most previous studies with a single injection regimen were conducted with Caucasian or mixed populations [12, 13, 14, 15, 16]. The findings are not necessarily applicable to the Asia population, as recent studies have claimed that platelet function differs with ethnicity [29, 30]. We choose to use a single injection regimen because there is evidence of no significant differences between a single dose and multiple doses, suggesting the possibility to avoid multiple injections protocols, and consequently reducing the health expenses in terms of cost-efficacy.

Patient satisfaction is a fundamental goal in the treatment of OA patients and it reflects the summation of all factors relating to successful clinical treatment. Results of patients’ global satisfaction showed that most patients were satisfied with the treatment. Interestingly, we found that patients aged 60 years or younger reported greater satisfaction at 1 and 3 months postinjection than patients aged over 60 years. No patients reported dissatisfaction or aggravations of the symptoms throughout the study period.

In this study, all adverse events were mild and self-limiting. The absence of serious adverse events, noted in previous studies and in the present trial, suggests that PRP represents a safe treatment option for patients with knee OA.

There were several limitations in this study. First, this was a single center study and we recruited patients with Kellgren-Lawrence grade 1 and 2 tibiofemoral OA only. The result can not be generalized to all the OA populations with different radiographic severity. Second, the sample size was small and the follow-up time was short. Additional studies with larger sample size and longer follow-up period would be needed to confirm the long-term efficacy. Third, because of budget limit, we did not have a control group. There is a strong placebo effect from joint injections, which may cause a nearly 30% pain reduction during the first few weeks [31]. Thus, we may possibly miss the placebo effects and overestimate the real effects of PRP. However, because the placebo effect would mostly be seen in the early periods, the late findings of this study at 3 and 6 months may reflect reliable results for PRP injections. Further research including a sham control, corticosteroid injection, or hyaluronic acid injection is of great interest. The optimal number and frequency of injections, the potential use in joints other than the knees, as well as the role for repeated series of injections must be clarified in the future.

5. Conclusions

This study showed that a single injection of PRP was effective and safe for patients with Kellgren-Lawrence grade 1 or 2 knee OA. Subgroup analyses revealed that patients with grade 1 OA showed significantly greater VAS pain reduction at 3 and 6 months than patients with grade 2 OA. The older-age group (age ${>}$ 60) showed significantly greater improvements in VAS pain, WOMAC function subscale scores and total scores at 6-month postinjection, compared with the younger age-group (age ${<}=$ 60). The younger-age group reported better satisfaction at 1 and 3-month postinjection. The findings of this study support putting the one injection regimen of PRP into clinical practice for patients with early knee OA. The exact mechanisms of PRP, the racial differences in the efficacy of PRP, and the cost-effective values compared with other injection regimens should be explored in the future.

Author contributions

SFS was the principal investigator of the study and responsible for the trial operation, study design, knee injections and completion of the manuscript. IHL was responsible for the study design, evaluations, and writing-up the manuscript. YCC, SYW and HYH contributed to the conception and study design, project administration, data interpretation and writing up the manuscript. CWH and HSL were responsible for sample size calculation, statistical analysis and data interpretation. All authors have read and agreed to the published version of the manuscript.

Funding

SFS received an academic research fund for Kaohsiung Veterans General Hospital (no. VGHKS106-131).

Footnotes

Acknowledgments

We wish to express our sincere gratitude to all the investigators and patients who participated in the trial.

Conflict of interest

The authors report no conflicts of interest.

References

Adams

. An analysis of clinical studies of the use of crosslinked hyaluronan, in the treatment of osteoarthritis. J Rheumatol Suppl. 1993; 39: 16-8.

Cugat

Cusco

Seijas

Álvarez

Steinbacher

Ares

, et al. Biologic enhancement of cartilage repair: the role of platelet-rich plasma and other commercially available growth factors. Arthroscopy. 2015; 31: 777-83.

Kabiri

Esfandiari

Esmaeili

Hashemibeni

Pourazar

Mardani

. Platelet-rich plasma application in chondrogenesis. Adv Biomed Res. 2014; 3: 138.

Sundman

Cole

Karas

Della Valle

Tetreault

Mohammed

Fortier

. The anti-inflammatory and matrix restorative mechanisms of platelet-rich plasma in osteoarthritis. Am J Sports Med. 2014; 42: 35-41.

Spreafico

Chellini

Frediani

Bernardini

Niccolini

Serchi

, et al. Biochemical investigation of the effects of human platelet releasates on human articular chondrocytes. J Cell Biochem. 2009; 108: 1153-65.

van Buul

Koevoet

Kops

Bos

Verhaar

Weinans

, et al. Platelet-rich plasma releasate inhibits inflammatory processes in osteoarthritic chondrocytes. Am J Sports Med. 2011; 39: 2362-70.

Khoshbin

Leroux

Wasserstein

Marks

Theodoropoulos

Ogilvie-Harris

, et al. The efficacy of platelet-rich plasma in the treatment of symptomatic knee osteoarthritis: a systematic review with quantitative synthesis. Arthroscopy. 2013; 29: 2037-48.

Chang

Hung

Aliwarga

Wang

Han

Chen

. Comparative effectiveness of platelet-rich plasma injections for treating knee joint cartilage degenerative pathology: a systematic review and meta-analysis. Arch Phys Med Rehabil. 2014; 95: 562-75.

Laudy

Bakker

Rekers

Moen

. Efficacy of platelet-rich plasma injections in osteoarthritis of the knee: a systematic review and metaanalysis. Br J Sports Med. 2015; 49: 657-72.

10.

Meheux

McCulloch

Lintner

Varner

Harris

. Efficacy of platelet-rich plasma injections in knee osteoarthritis: a systematic review. Arthroscopy. 2016; 32: 495-505.

11.

Görmeli

Ataoglu

Çolak

Aslantürk

, Ertem Ket. Multiple PRP injections are more effective than single injections and hyaluronic acid in knees with early osteoarthritis: a randomized, double-blind, placebo-controlled trial. Knee Surg Sport Traumatol Arthrosc. 2017; 25: 958-65.

12.

Patel

Dhillon

Aggarwal

Marwaha

Jain

. Treatment with platelet-rich plasma is more effective than placebo for knee osteoarthritis: a prospective, double-blind, randomized trial. Am J Sports Med. 2013; 41: 356-64.

13.

Martini

Via

Fossati

Randelli

Cucchi

. Single platelet-rich plasma injection for early stage of osteoarthritis of the knee. Joints. 2017; 5: 2-6.

14.

Buendía-López

Medina-Quirós

Fernández-Villacañas Marín

MÁ

. Clinical and radiographic comparison of a single LP-PRP injection, a single hyaluronic acidinjection and daily NSAID administration with a 52-week follow-up: a randomized controlled trial. J Orthop Traumatol. 2018; 19: 3.

15.

Elksniņš-Finogejevs

Vidal

Peredistijs

. Itra-articular platelet-rich plasma vs corticosteroids in the treatment of moderate knee osteoarthritis: a single center prospective randomized controlled study with a 1-year follow up. J Orthop Surg Res. 2020; 15: 257.

16.

Ghai

Gupta

Jain

Goel

Chouhan

Batra

. Effectiveness of platelet rich plasma in pain management of osteoarthritis knee: double blind, randomized comparative study. Rev Bras Anestesiol. 2019; 69: 439-47.

17.

Kon

Mandelbaum

Buda

Filardo

Delcogliano

Timoncini

, et al. Platelet-rich plasma intra-articular injection versus hyaluronic acid viscosupplementation as treatments for cartilage pathology: from early degeneration to osteoarthritis. Arthroscopy. 2011; 27: 1490-501.

18.

Kellgren

Lawrence

. Radiological assessment of osteoarthrosis. Ann Rheum Dis. 1957; 16: 494-502.

19.

Huskisson

. Measurement of pain. Lancet. 1974; 2: 1127-31.

20.

McConnell

Kolopack

Davis

. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC): a review of its utility and measurement properties. Arthritis Care Res. 2001; 45(5): 453-61.

21.

Lequesne

Mery

Samson

Gerard

. Indexes of severity for osteoarthritis of the hip and knee: validation-value in comparison with other assessment tests. Scand J Rheumatol Suppl. 1987; 65: 85-9.

22.

Bohannon

Larkin

Cook

Gear

Singer

. Decrease in timed balance scores with aging. Phys Ther. 1984; 64: 1067-70.

23.

Dworkin

Turk

Wyrwich

Beaton

Cleeland

Farrar

, et al. Consensus statement: interpreting the clinical importance of treatment outcomes in chronic pain clinical trials: IMMPACT recommendations. J Pain. 2008; 9: 105-21.

24.

Hmamouchi

Allali

Tahiri

Khazzani

Mansouri

Ali Ou Alla

, et al. Clinically important improvement in the WOMAC and predictor factors for response to non-specific non-steroidal anti-inflammatory drugs in osteoarthritic patients: a prospective study. BMC Res Notes. 2012; 5: 58.

25.

Sánchez

Fiz

Azofra

Usabiaga

Aduriz Recalde

Garcia Gutierrez

, et al. A randomized clinical trial evaluating plasma rich in growth factors (PRGF-endoret) versus hyaluronic acid in the short-term treatment of symptomatic knee osteoarthritis. Arthroscopy. 2012; 28: 1070-8.

26.

Lequesne

. The algofunctional indices for hip and knee osteoarthritis. J Rheumatol. 1997; 24: 779-81.

27.

Kesiktas

Dernek

Sen

Albayrak

Aydin

Yildiz

. Comparison of the short-term results of single-dose intra-articular peptide with hyaluronic acid and platelet-rich plasma injections in knee osteoarthritis: a randomized study. Clin Rheumatol. 2020. doi: 10.1007/s10067-020-05121-4.

28.

Boswell

Cole

Sundman

. Platelet-rich plasma: a milieu of bioactive factors. Arthroscopy. 2012; 28(3): 429-39.

29.

Edelstein

Simon

Montoya

Holinstat