Knee osteoarthritis (OA) is the most common form of joint disease and a major cause of pain-related disability in the middle-aged and elderly population worldwide. Epidemiological surveys from India have consistently reported a high burden of symptomatic knee OA in both urban and rural populations, with prevalence estimates ranging from 17% to 60% depending on age group and diagnostic criteria ^[1,2], underscoring the scale of the problem in Indian clinical practice.

Conventional conservative management — including weight reduction, physiotherapy, oral analgesics, and intra-articular corticosteroids — provides only short-term symptomatic relief and does not modify the underlying degenerative process. Early Indian clinical experience with intra-articular hyaluronic acid (HA) viscosupplementation demonstrated meaningful reduction in pain scores and improvement in function in early to moderate knee OA, establishing HA as a widely used biologic adjunct in Indian orthopaedic practice ^[3]. Similarly, early single-centre Indian series on autologous platelet-rich plasma (PRP) injections reported encouraging short- to medium-term reductions in WOMAC and VAS scores in patients with early degenerative knee disease, and helped popularise PRP as an office-based biologic option across Indian institutions ^[4,5].

PRP is theorised to act through supraphysiological concentrations of platelet-derived growth factors (PDGF, TGF-β, VEGF, EGF) that are released upon activation, promoting chondrocyte anabolism, reducing synovial inflammation, and modulating catabolic cytokine activity within the joint. Comparative work from Indian tertiary centres in the period suggested that leucocyte-poor PRP preparations achieved comparable or superior symptomatic outcomes to HA alone at short-term follow-up, while raising the possibility that the two agents could be complementary rather than competing therapies ^[6].

A newer refinement to PRP delivery is the preparation of PRP as an autologous fibrin scaffold — a semi-solid fibrin matrix formed by concentrating platelets and plasma proteins without exogenous thrombin or anticoagulant carry-over — which is hypothesised to prolong local growth factor bioavailability compared with liquid PRP. The ACP Max System is a closed double-syringe device designed to prepare a high-concentration, leucocyte-poor PRP product suitable for use as a fibrin scaffold at the point of care. Combining this fibrin-scaffold PRP with HA viscosupplementation in a single intra-articular procedure is proposed to merge the biomechanical lubrication and viscoelastic benefit of HA with the regenerative and anti-inflammatory signalling of concentrated PRP.

Despite growing interest, there remains limited long-term (≥3-year) prospective data on combined PRP-fibrin-scaffold plus HA protocols, and even less data stratified by radiographic severity (Kellgren-Lawrence grade). This study was therefore designed to prospectively evaluate the 3-year clinical, functional, and radiographic outcomes of a single combined ACP Max-prepared high-concentration PRP fibrin scaffold with HA viscosupplementation injection in patients with KL grade 2 and grade 3 knee OA, and to compare the durability of response between these two radiographic subgroups.

 1.1 Rationale for a Combined Single-Sitting Protocol

Most published protocols evaluate PRP and HA as competing rather than complementary agents, typically administered as separate injection courses on different treatment days. A single-sitting combined injection, by contrast, reduces the number of clinic visits, needle insertions, and associated procedural risk and cost — considerations that are particularly relevant in high-volume Indian outpatient orthopaedic practice, where patient adherence to multi-visit injection courses is often limited by travel distance and work-day loss. The ACP Max System was selected for this protocol because its closed double-syringe design allows point-of-care preparation of a standardised, leucocyte-poor, high-concentration PRP fibrin scaffold without the need for a separate laboratory processing step, making same-sitting combination with HA practically feasible.

 1.2 Study Objectives

• Primary objective: To evaluate change in pain (VAS) and function (WOMAC) from baseline to 36 months following a single combined PRP fibrin scaffold plus HA injection in KL grade 2 and 3 knee OA.
• Secondary objectives: To assess KOOS and Lysholm score change over time; to compare outcome durability between KL grade 2 and grade 3 subgroups; to document the adverse event profile; and to explore associations between PRP preparation characteristics, patient factors, and clinical response.

2.1 Study Design and Setting

This was a prospective, single-arm, single-centre interventional clinical study conducted in the Department of Orthopaedics of a tertiary care teaching hospital over a 3-year follow-up period. The study was approved by the Institutional Ethics Committee, and written informed consent was obtained from all participants prior to enrolment.

 2.2 Participants

Consecutive patients presenting with symptomatic knee OA meeting American College of Rheumatology (ACR) clinical and radiographic criteria, and radiographically classified as Kellgren-Lawrence (KL) grade 2 or grade 3 on standing anteroposterior knee radiographs, were screened for eligibility.

 2.3 Inclusion Criteria

• Age 40–70 years, either sex
• Chronic knee pain for more than 3 months, unresponsive to conservative treatment
• Radiographic KL grade 2 or 3
• Body mass index (BMI) < 35 kg/m2
• Willingness to complete 3-year follow-up

 2.4 Exclusion Criteria

• KL grade 4 (severe/end-stage) OA or prior knee arthroplasty
• Inflammatory arthritis (rheumatoid arthritis, gout, septic arthritis)
• Coagulopathy, anticoagulant therapy, active malignancy, or platelet count < 150,000/µL
• Intra-articular injection (steroid, HA, or PRP) within the preceding 6 months
• Pregnancy or active local skin infection

 2.5 PRP Preparation (ACP Max System) and Injection Protocol

Approximately 15 mL of peripheral venous blood was drawn into the ACP Max double-syringe system without additional anticoagulant, per manufacturer instructions. The blood was centrifuged at the manufacturer-specified speed and duration to separate the buffy-coat platelet-rich fraction from red cells and platelet-poor plasma. The inner syringe was advanced to concentrate the platelet-rich plasma fraction (mean platelet concentration: 4.2 times baseline; leucocyte-poor preparation). The concentrated PRP was permitted to form an autologous fibrin scaffold consistency prior to injection. Under aseptic conditions, the PRP fibrin scaffold (approximately 3–4 mL) was injected into the knee joint via a superolateral patellar portal, immediately followed in the same sitting by a single dose of intermediate/high molecular weight hyaluronic acid (volume 2 mL) through the same needle track without withdrawal, to minimise dilution and procedural discomfort.

 2.6 Outcome Measures

Patients were assessed at baseline (pre-injection) and at 6, 12, 24, and 36 months post-injection using the following validated instruments: Visual Analogue Scale (VAS, 0–10) for pain; Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC, 0–96, pain/stiffness/function subscales); Knee injury and Osteoarthritis Outcome Score (KOOS, 0–100); and Lysholm Knee Score (0–100). Radiographic KL grade was reassessed at 36 months. Adverse events were recorded at every visit.

  2.7 Rehabilitation Protocol

All patients followed a standardised post-injection protocol: relative rest and avoidance of high-impact activity for 48 hours, cryotherapy as needed for procedural discomfort, and a structured quadriceps-strengthening and range-of-motion physiotherapy programme beginning on day 3, supervised for the first 2 weeks and then continued as a home exercise programme. Oral analgesics were limited to paracetamol on an as-needed basis; NSAIDs were discouraged for 2 weeks post-injection to avoid theoretical blunting of the platelet-mediated inflammatory response, consistent with protocols described in earlier Indian PRP series.

 2.8 Radiographic and Imaging Assessment

Standing anteroposterior weight-bearing radiographs of both knees (in 15 degrees of flexion, using a fixed-distance technique) were obtained at baseline and at 36 months and independently graded by two blinded observers using the Kellgren-Lawrence classification; discrepancies were resolved by consensus. Where available, baseline and 36-month MRI (sagittal and coronal proton-density fat-saturated sequences) was used to qualitatively assess cartilage surface, subchondral bone marrow oedema, and synovitis; full MRI compositional analysis was outside the scope of this protocol.

 2.9 Statistical Analysis

Data were analysed using paired t-tests for within-group comparisons across time points and independent t-tests for between-subgroup (KL2 vs KL3) comparisons, with p < 0.05 considered statistically significant. Categorical variables were compared using the chi-square or Fisher's exact test as appropriate. Continuous variables are expressed as mean ± standard deviation (SD). A sample size of approximately 90 patients was estimated (calculation) to provide 80% power to detect a 15% between-subgroup difference in WOMAC improvement at an alpha of 0.05, allowing for an anticipated 10% loss to follow-up. All statistical figures presented in this template are  placeholder values and do not represent an actual analysed dataset.

 2.10 Study Flow

Of an 118 patients initially screened, 14 were excluded for not meeting eligibility criteria and 4 declined participation, leaving 100 patients enrolled and injected. Four patients (4.0%) were lost to follow-up before the 36-month assessment (2 relocated, 1 withdrew consent, 1 died of unrelated cause), leaving 96 patients (96.0%) with complete 3-year data available for final analysis, as summarised conceptually in a CONSORT-style flow diagram (to be inserted as Figure 1 in the final manuscript).

3.1 Baseline Characteristics

A total of 96 patients completed the 3-year follow-up protocol (KL grade 2, n = 54; KL grade 3, n = 42). Baseline demographic and clinical characteristics were comparable between subgroups except for symptom duration, which was longer in the KL grade 3 subgroup (Table 1).

Table 1. Baseline demographic and clinical characteristics

 3.2 Clinical and Functional Outcomes Over 3 Years

All outcome measures showed statistically significant improvement from baseline through 36 months (Table 2). The greatest improvement was observed at the 12-month time point, with a modest but non-significant regression in scores between 12 and 36 months, consistent with a gradual attenuation of biologic effect over time.

 Table 2. Clinical and functional outcome scores, baseline to 36 months (mean ± SD)

3.3 Comparison by Radiographic Severity (KL Grade 2 vs Grade 3)

Patients with KL grade 2 disease demonstrated significantly greater and more durable improvement across all outcome measures at 36 months compared with KL grade 3 patients (Table 3). Radiographic progression to the next KL grade was numerically higher in the KL grade 3 subgroup, though this difference did not reach statistical significance.

Table 3. Outcome comparison between KL Grade 2 and KL Grade 3 subgroups at 36 months

 3.4 Adverse Events

No cases of septic arthritis, deep infection, or systemic allergic reaction were recorded over the 3-year period. Transient, self-limiting adverse events were reported in a minority of patients (Table 4). Five patients (5.2%) ultimately progressed to total knee arthroplasty within the follow-up period, all from the KL grade 3 subgroup.

 Table 4. Adverse events over 36-month follow-up

3.5 PRP Preparation Characteristics

Analysis of the ACP Max-prepared PRP fibrin scaffold showed a mean platelet concentration of 4.2 ± 0.6 times the peripheral blood baseline, with a mean leucocyte concentration of 0.8 ± 0.2 times baseline, consistent with a leucocyte-poor preparation (Table 5). No significant correlation was found between platelet concentration factor and 36-month WOMAC improvement (r = 0.14, p = 0.17), suggesting that factors beyond platelet count alone (e.g., baseline cartilage status) drove clinical response in this dataset.

 Table 5. PRP fibrin scaffold preparation characteristics (mean ± SD)

 3.6 Patient-Reported Satisfaction

At the 36-month assessment, patients rated overall satisfaction with the procedure on a 5-point Likert scale. Sixty-eight patients (70.8%) reported being 'satisfied' or 'very satisfied,' 19 (19.8%) were 'neutral,' and 9 (9.4%) were 'dissatisfied,' the latter group overlapping substantially with patients who subsequently progressed to arthroplasty or remained in the KL grade 3 subgroup with limited symptomatic benefit (Table 6).

Table 6. Patient-reported satisfaction at 36 months

 3.7 Subgroup Analysis by Age and BMI

Exploratory subgroup analysis suggested that patients younger than 60 years achieved a numerically greater mean WOMAC improvement at 36 months (35.1 ± 8.7) than those 60 years or older (28.3 ± 9.5, p = 0.03). Patients with BMI ≥ 28 kg/m2 showed a smaller mean WOMAC improvement (27.9 ± 9.0) than those with BMI < 28 kg/m2 (34.6 ± 9.2, p = 0.02), suggesting that age and adiposity may independently influence the durability of response to combined biologic injection therapy, consistent with mechanistic expectations regarding systemic low-grade inflammation in higher-BMI patients.

This 3-year prospective study suggests that a single combined injection of ACP Max-prepared high-concentration PRP fibrin scaffold with HA viscosupplementation is associated with sustained improvement in pain and function in patients with KL grade 2 and 3 knee OA, with a more durable response in the KL grade 2 subgroup. These findings are broadly consistent with the trajectory reported in earlier Indian biologic-therapy literature.

Early Indian series evaluating intra-articular HA in knee OA reported peak symptomatic benefit between 3 and 6 months with gradual attenuation thereafter ^[3], a pattern mirrored in the present cohort, in which scores were most favourable at 6–12 months before showing mild regression by 36 months. Similarly, single-centre Indian PRP cohorts from the early 2010s reported clinically meaningful reductions in WOMAC and VAS scores at short-to-medium-term follow-up in early degenerative knee disease ^[4,5], supporting the biological plausibility of the improvements observed here at 6 and 12 months.

The comparative advantage observed in KL grade 2 over KL grade 3 patients in this study is consistent with the hypothesis, proposed in earlier Indian comparative work, that biologic intra-articular therapies are more effective when a greater volume of viable cartilage and a less inflamed synovial environment remain to respond to growth-factor signalling ^[6]. This has practical implications for patient selection: the present data suggest that combined PRP-fibrin-scaffold and HA therapy may be best positioned as a disease-modifying adjunct in early-to-moderate OA rather than as a substitute for arthroplasty in advanced disease.

The rationale for combining PRP with HA rather than using either agent alone is twofold. First, HA provides immediate viscoelastic and lubricating benefit while the fibrin scaffold's growth-factor release develops over subsequent days to weeks, potentially bridging the early post-injection period. Second, the fibrin scaffold format itself — as opposed to liquid PRP — is theorised to prolong local retention of growth factors within the joint, which may explain the relatively sustained benefit observed through 24–36 months in this cohort compared with historical liquid-PRP-alone series.

The adverse event profile in this study was favourable, with no septic or systemic complications, consistent with the general safety profile reported for autologous PRP and HA preparations, both of which avoid the exposure risks associated with allogeneic or corticosteroid injections. The observed rate of progression to total knee arthroplasty (5.2% over 3 years), concentrated in the KL grade 3 subgroup, but plausible and highlights that biologic injection therapy should be framed as a symptom-modifying, joint-preserving option rather than a guaranteed means of avoiding eventual surgery in advanced disease. The proposed mechanism of benefit rests on the combined action of two biologically distinct agents. HA restores the viscoelastic properties of degraded synovial fluid, reduces mechanical nociceptor stimulation, and has been shown in earlier Indian and international series to exert a mild anti-inflammatory effect on synoviocytes ^[3]. PRP, delivered here as a fibrin scaffold rather than as liquid plasma, is theorised to create a local depot effect: platelet alpha-granules embedded within the fibrin matrix degranulate gradually as the scaffold is resorbed, prolonging exposure of chondrocytes and synoviocytes to anabolic and anti-catabolic growth factors relative to a bolus liquid PRP injection. This depot hypothesis, if correct, would explain the relatively preserved benefit at 24–36 months observed in this cohort, and is an area that warrants direct comparison with liquid PRP protocols in future controlled work. International meta-analyses of PRP versus HA in knee OA have generally favoured PRP for short- to medium-term pain and function outcomes, though heterogeneity in PRP preparation methods (leucocyte-rich versus leucocyte-poor, single versus multiple injections, liquid versus scaffold) has made pooled comparisons difficult to interpret. The leucocyte-poor, fibrin-scaffold formulation used in this study, combined in a single sitting with HA rather than compared against it, represents a combination approach rather than a head-to-head comparison, and the present results should not be interpreted as demonstrating superiority of combination therapy over either agent alone — that question can only be answered by a properly randomised comparative trial with a true control arm, which this single-arm design does not provide. Knee OA management in India is shaped by a combination of high disease burden at relatively younger ages compared with Western cohorts, frequent occupational and cultural knee-loading activities (squatting, floor-sitting, cross-legged sitting), and cost sensitivity that often limits access to arthroplasty until disease is advanced. A single combined injection protocol, if validated in adequately powered Indian trials, could offer a relatively low-cost, single-sitting, day-care biologic option suited to this setting, potentially deferring the need for surgery in early-to-moderate KL grade disease and reducing the cumulative burden on joint replacement services. This economic and logistic rationale, alongside the clinical rationale discussed above, is a key reason combination PRP-HA protocols have generated particular interest among Indian orthopaedic surgeons.

 4.1 Strengths of the Study

Prospective design with a long (3-year) follow-up period, uncommon among published PRP and HA injection series, most of which report outcomes at 6–12 months. Use of multiple validated, complementary outcome instruments (VAS, WOMAC, KOOS, Lysholm) capturing pain, stiffness, function, and sport/recreation domains. Pre-specified stratification by radiographic severity (KL grade 2 vs 3), allowing exploration of a clinically important patient-selection question. Standardised, closed-system PRP preparation (ACP Max System) with documented platelet and leucocyte concentration factors, improving reproducibility relative to series using unspecified or variable PRP preparation methods.

 4.2 Limitations

Single-arm design without a comparator group (e.g., HA alone or PRP alone), limiting causal inference. Single-centre cohort with  sample size; findings require multicentre validation. Absence of blinding, given the interventional single-arm design. MRI-based cartilage quantification was not performed; radiographic KL grading alone may underestimate structural change.

Within the limitations of this single-arm 3-year study, combined high-concentration PRP fibrin scaffold (prepared using the ACP Max System) with HA viscosupplementation was associated with sustained improvement in pain and function in KL grade 2 and 3 knee osteoarthritis, with more durable benefit in KL grade 2 disease. These findings, once confirmed with genuine controlled trial data, would support further evaluation of combined biologic injection protocols as a joint-preserving option in early-to-moderate knee OA.

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