What 'failed conservative care' actually means

Most people asking this question have been trying for months — physiotherapy sessions, over-the-counter painkillers, attempts at weight loss — and are still struggling with daily activities. That persistence is a reasonable signal that conservative management has reached its limit, but the threshold is more specific than it might feel during a difficult week.

A genuine trial generally means at least three to six months of structured physiotherapy, a sustained exercise programme, weight management where relevant, and appropriate analgesia — taken consistently, not intermittently. Failure is defined by inadequate symptom control that limits daily function: difficulty walking, disturbed sleep, or an inability to manage stairs without significant pain. A single bad day, or a flare after unusual activity, does not on its own meet that threshold.

Imaging — an X-ray or MRI — can confirm the degree of joint change, but a scan showing moderate OA is not a verdict that conservative care has failed. Symptoms and their effect on day-to-day life drive the escalation decision, not the scan alone. The NHS is clear that surgery is considered only in a minority of patients for whom all other options have genuinely been exhausted, which means a meaningful middle tier of treatment options sits between physiotherapy and the operating theatre.

The injection middle tier — what sits between physio and surgery

Between failed conservative care and surgical referral sits a well-defined tier of intra-articular therapies — treatments delivered directly into the knee joint by injection, bypassing the digestive system and limiting systemic effects. Five main options populate this space: platelet-rich plasma (PRP), hyaluronic acid (viscosupplementation), polyacrylamide hydrogel (Arthrosamid®), autologous protein solution (nStride APS), and bone marrow aspiration concentrate (BMAC).

None of these options reverses structural joint damage or erases arthritis. Their role is to reduce pain and inflammation, support the joint environment, and — in carefully selected patients — create enough functional improvement to delay or avoid an operation. That distinction matters when setting expectations at the outset.

Disease stage, confirmed on imaging, determines which of these therapies is appropriate. Mild-to-moderate OA with a salvageable joint is the right territory for injectable options; end-stage bone-on-bone disease is a surgical conversation, and injections are unlikely to provide durable relief at that point.

Within the injection tier itself, PRP carries the largest published evidence base for patients who have not responded to conventional care and is typically considered first. Hyaluronic acid, Arthrosamid®, nStride APS, and BMAC each suit particular clinical profiles — different disease stages, prior treatment history, or joint characteristics — and may come into play when PRP alone has not achieved adequate relief or is not indicated. Because head-to-head trials between most of these agents are largely absent from the literature, identifying which option fits a given patient requires specialist assessment and shared decision-making rather than a fixed hierarchy.

PRP injections: the evidence after first-line failure

For patients who have exhausted conventional options, PRP's most consistent benefit is functional: reduced pain on movement, improved scores on validated measures of stiffness and daily activity, and a meaningful proportion achieving what researchers classify as a clinically important response.

The comparative evidence is reasonably robust for this specific population. A one-year RCT of 160 patients with Kellgren–Lawrence grades 1–4 who had not responded to conventional treatment found PRP superior to hyaluronic acid across all WOMAC pain and SF-36 quality-of-life parameters at 12 months (p<0.001). A 2024 real-world cohort of 431 patients who had already failed first-line therapy reinforces this: 56.2% met OMERACT OARSI responder criteria at 6 months, with treatment failure occurring in just 8.4% of cases.

The mechanism appears to be primarily anti-inflammatory rather than mechanical. Intra-articular PRP reduces synovial IL-17 — a pro-inflammatory cytokine — by approximately 75%, while raising TGF-β by around 80%, pointing to a biological effect on the joint environment rather than simple lubrication or cushioning.

One expectation needs to be set clearly: PRP is not a tissue-regeneration therapy in practice. 3D-MRI analysis at six months found cartilage thickness increased in fewer than 20% of knees at the posteromedial femoral and medial tibial regions — the sites most affected by medial OA. Symptom relief is what the evidence reliably supports; structural restoration is not. For patients hoping an injection will reverse visible joint changes on imaging, that distinction matters when deciding whether to proceed.

This profile — consistent symptomatic benefit, anti-inflammatory mechanism, limited structural repair — explains why PRP is typically the first injectable option to consider when conservative care has run its course.

Hyaluronic acid, Arthrosamid, and other injectable options

Hyaluronic acid (viscosupplementation)

Hyaluronic acid (HA) injections replenish the synovial fluid's natural lubricating properties, which become depleted in arthritic joints. The evidence base is well-established — but meta-analytic data flag an important caveat: when trials include patients with advanced, bone-on-bone disease, HA's apparent benefit contracts markedly. Its strongest signal is in early-to-moderate OA, or as a bridging treatment while the clinical picture develops. Patients with significant joint-space narrowing on imaging are less likely to achieve the same functional gains as those treated at an earlier stage.

Arthrosamid® (polyacrylamide hydrogel)

Arthrosamid® operates on a different principle from any other option in this tier. A single injection of non-absorbed polyacrylamide hydrogel integrates permanently into the synovial membrane, providing long-term mechanical cushioning. It does not regenerate cartilage, does not alter the joint surface, and does not slow disease progression — but in mild-to-moderate OA it may reduce pain and create enough functional improvement to delay surgical referral. The boundary here is more defined than for most injectables: in advanced bone-on-bone disease, joint replacement carries a stronger evidence base, and Arthrosamid® is not the appropriate pathway at that stage.

nStride APS and BMAC

nStride APS (autologous protein solution) takes a conceptually distinct biological angle from PRP. Rather than targeting synovial inflammation, APS concentrates anti-catabolic proteins from the patient's own blood — molecules aimed at slowing cartilage breakdown rather than reducing inflammatory activity. This positions it as a different biological strategy, not simply a substitute for PRP or HA. That said, direct head-to-head trial data comparing APS with either option remain limited, which means clinical experience and individual patient profile carry more weight in the selection process than comparative evidence currently allows.

BMAC (bone marrow aspiration concentrate) introduces progenitor cells alongside concentrated growth factors, and represents a more investigational tier within orthobiologics. A Phase I dose-escalation study found that increasing the cellular dose did not produce proportionally greater clinical benefit — a finding that highlights the complexity of optimising this approach. For patients interested in BMAC, specialist assessment is not optional: it is where current evidence boundaries, dosing considerations, and individual joint characteristics can be properly weighed before a decision is made.

When surgery enters the conversation

Surgery becomes relevant when injections — including orthobiologics — have not provided adequate relief, or when the structural state of the joint rules out injection-based management from the outset. Two routes exist, and they suit materially different patient profiles.

Osteotomy: preserving the joint by redistributing load

For younger, active patients whose OA is confined to one compartment and accompanied by malalignment, osteotomy offers a middle ground between injections and replacement. A high tibial or distal femoral osteotomy reshapes the bone to shift load away from the damaged compartment — giving the affected area less to bear with every step. It is a joint-preservation procedure; the original knee remains in place, and the aim is to delay replacement rather than avoid it permanently.

The procedure has defined limits. It is contraindicated in rheumatoid arthritis, significant knee instability, fixed valgus deformity greater than 20°, active smoking, and osteoporosis. Patient selection — based on age, activity level, compartment involvement, and alignment — is established at specialist assessment with imaging, not from symptoms alone.

Total knee replacement

Where the joint is beyond preservation — with severe cartilage loss across multiple compartments, or where osteotomy criteria are not met — total knee replacement (TKR) is the established option. Metal and polyethylene implants resurface the joint, eliminate bone-on-bone contact, and correct alignment. It is among the highest-volume elective orthopaedic procedures performed, with well-documented long-term outcomes for pain relief and functional recovery.

The choice between these two routes is made at specialist assessment. Age, activity demands, disease distribution across compartments, and imaging findings each play a role — the decision is more nuanced than pain severity alone would suggest.

How to think about the next step — a framework for patients

Three questions help most patients locate themselves in this pathway before a specialist appointment.

Has conservative care genuinely run its course? Weeks of inconsistent exercise or a single physiotherapy referral do not constitute an adequate trial. If that phase was not structured and sustained, it may be worth revisiting before moving on — because whether injections are the right next step depends partly on what conservative management actually delivered.

Is there recent imaging, and what does it show? Pain severity alone does not determine which treatments are appropriate. Current X-ray or MRI findings are what a specialist needs to establish whether the joint is mild-to-moderate or end-stage — that structural question must be answered before any treatment decision can be made with confidence.

Which of the newer options is actually right for you? This is where general reading reaches its limit. Head-to-head trial data comparing nStride APS, BMAC, and Arthrosamid® against one another — or against PRP — do not yet exist at scale. Individual assessment, drawing on specific imaging, symptom pattern, and activity demands, is the only framework that can resolve the choice between them.

If you have worked through the options covered in this article and remain uncertain about the next step, a structured MSK assessment is the appropriate starting point. [Find out whether your joint may be suitable →]

1. [1] Increased Cellular Dosage of Bone Marrow Aspiration Concentrate Does Not Translate to Increased Clinical Effectiveness in Knee Osteoarthritis. (2024). https://doi.org/10.1007/s43465-024-01197-1 https://doi.org/10.1007/s43465-024-01197-1
2. [2] Assessment of synovial repair in primary knee osteoarthritis after platelet rich plasma (PRP) intra-articular injection. (2024). https://doi.org/10.55133/eji.310406 https://doi.org/10.55133/eji.310406
3. [3] Knee Osteoarthritis Injection Choices: Platelet-Rich Plasma (PRP) Versus Hyaluronic Acid (A one-year randomized clinical trial). (2015). https://doi.org/10.4137/CMAMD.S17894 https://doi.org/10.4137/CMAMD.S17894
4. [4] Long term improvement of knee osteoarthritis after injection of single high/very high volume of very pure PRP. (2024). https://doi.org/10.1016/j.reth.2023.12.006 https://doi.org/10.1016/j.reth.2023.12.006
5. [5] 3D-MRI analysis of cartilage thickness changes after PRP injection in medial knee osteoarthritis. (2025). https://doi.org/10.1371/journal.pone.0321067 https://doi.org/10.1371/journal.pone.0321067