Key Takeaways
- Chronic equine lameness management has moved on from corticosteroid-only protocols, which the current evidence no longer supports as best practice in longstanding cases.
- Regenerative options (PRP, IRAP, stem cells) show clinical promise, but evidence quality varies considerably by modality and indication.
- 2.5% iPAAG (Arthramid) is a mechanistically distinct, single-treatment intra-articular option with published 24-month durability data in equine osteoarthritis.
- Current best practice is multimodal. No single modality addresses every component of chronic lameness.
Chronic lameness, most often driven by osteoarthritis (OA), remains the most common reason horses lose performance and leave work. For decades, the intra-articular options were essentially corticosteroids and hyaluronic acid. That picture has changed. Over the past decade the toolkit has widened to include regenerative biologics, biomechanical therapies and a non-degradable hydrogels, and the evidence base behind several of these has matured.
This overview maps the current treatment landscape for the equine clinician: what each modality does, how strong the evidence actually is, and where each sits within a multimodal protocol. The aim is a clear, defensible picture to support case selection, not a case for any single product.
What Is Chronic Lameness in Horses, and Why Is It Difficult to Manage?
Chronic lameness is persistent, recurrent or progressive locomotor dysfunction, in contrast to acute lameness, which is sudden in onset and usually traceable to a single event. In the longstanding horse it is most often driven by osteoarthritis, with navicular syndrome and soft tissue conditions such as proximal suspensory desmitis as further contributors.
The reason it is difficult to manage is structural. OA involves progressive degradation across the whole joint, including the synovial membrane, cartilage, subchondral bone and joint capsule, and no single intervention addresses all of these at once. OA is the most common cause of lameness and lost athletic function in horses, which is why it dominates the chronic caseload.
Two clinical realities follow. First, chronic OA is managed rather than cured: the aim is to slow progression and maintain comfortable function, not to reverse the disease. Second, repeat single-modality treatment reaches a ceiling. Repeated intra-articular corticosteroid cycles in particular carry cumulative considerations that make single-modality reliance harder to defend as cases progress. That is the case for a multimodal approach.
What Conventional Treatments Have Been the Standard, and Where Do They Fall Short?
Intra-articular corticosteroids and hyaluronic acid have defined the standard of care for decades. Both retain a role, but both have documented limitations in chronic, repeat-presentation cases.
Corticosteroids give rapid, reliable short-term relief and remain useful for controlling acute flares. The limitation is longer-term. A recent equine systematic review found that single-injection protocols produce short-term symptom-modifying effects with conflicting evidence for any disease-modifying benefit, and that repeated intra-articular injections showed no long-term benefit and some drawbacks (Tokawa et al 2024). Repeated or higher-dose use has also been associated with cartilage and subchondral concerns. There is an additional caution in metabolically compromised horses, where corticosteroids carry a recognised laminitis risk that is particularly relevant in PPID and EMS patients, covered in more detail in our PPID and EMS article.
Hyaluronic acid works by viscosupplementation, restoring some of the viscoelastic properties of synovial fluid. Its standalone duration in advanced OA is modest, and in practice it is frequently combined with a corticosteroid rather than relied on alone.
The practical problem in chronic cases is the repeat-injection cycle: diminishing returns with each round and accumulating risk over time. For a direct comparison of corticosteroids and iPAAG, see our corticosteroid versus iPAAG article.
What Regenerative Therapies Are Now Available for Chronic Equine Lameness?
Regenerative medicine in the equine joint covers three main options: platelet-rich plasma, IRAP (autologous conditioned serum), and mesenchymal stem cells. Each has a distinct mechanism, and each has a different quality of evidence behind it. None is universally superior, and none should be presented as a cure.
Platelet-Rich Plasma (PRP)
PRP is an autologous preparation that concentrates the patient’s own platelets to deliver growth factors into the joint, with the aim of reducing inflammation and supporting tissue repair. A 2025 equine systematic review reported that intra-articular PRP is generally safe, with mild and short-lived inflammation in some cases, and that both leukocyte-rich and leukocyte-poor preparations produced comparable improvements in lameness and joint function. The same review noted that the optimal platelet concentration, the need for activation, and the best dosing schedule remain undefined, and that most benefits were seen in the first few months (Carmona and Lopez 2025). In practice PRP is best viewed as an adjunctive option whose results depend heavily on preparation method.
IRAP (Interleukin-1 Receptor Antagonist Protein)
IRAP, also described as autologous conditioned serum, is produced by incubating the horse’s own blood to raise concentrations of interleukin-1 receptor antagonist protein, which blocks part of the inflammatory cytokine cascade within the joint. The mechanism is well characterised, and there is experimental support for reduced joint inflammation. Clinical evidence in naturally occurring OA is more limited: a systematic review of clinical autologous conditioned serum data identified only six qualifying studies, only one of which included a control group, and concluded there is not yet definitive evidence of efficacy. IRAP typically requires a multi-injection protocol and specialist processing, and there is no reliable evidence that it outperforms PRP. Like PRP, it is best positioned as an adjunctive therapy rather than a first-line intra-articular treatment.
Stem Cell Therapy
Mesenchymal stem cell (MSC) therapy uses bone marrow or adipose-derived cells to provide a regenerative and anti-inflammatory, largely paracrine, stimulus. The strongest equine evidence sits in tendon and ligament injury, where clinical and experimental results have been consistently positive. In OA specifically, intra-articular MSCs have shown promising but modest results for cartilage repair, and robust controlled clinical data in naturally occurring disease is still limited. MSC therapy requires laboratory processing and, in New Zealand practice, typically specialist involvement.
An honest read across the three: PRP has the broadest equine dataset but heterogeneous quality; stem cells have the strongest signal in soft tissue rather than joint disease; and IRAP has a sound mechanism but limited controlled clinical evidence in OA. All three are reasonably positioned as adjuncts within a wider protocol.
What Role Does Extracorporeal Shockwave Therapy Play?
Extracorporeal shockwave therapy (ESWT) delivers focused acoustic pressure waves to a target site, with analgesic, anti-inflammatory and tissue-repair effects. Its strongest and most consistent evidence is in proximal suspensory desmitis, and it is also used for navicular syndrome and tendinopathy. For OA, a 2023 review of equine shockwave concluded that clinical trials span several orthopaedic indications but that long-term efficacy comparisons are lacking and many recommendations remain largely anecdotal (Johnson 2023). The AAEP position statement recognises efficacy in certain chronic soft tissue conditions and OA, while advising clinicians to weigh the evidence per indication.
Two practical points matter. Shockwave is most useful as a component of a multimodal plan rather than a standalone OA treatment. And because it produces a transient analgesic effect, several competition and racing authorities restrict its use for a set period before competition, so timing needs to be planned around the horse’s calendar.
Where Does 2.5% Polyacrylamide Hydrogel Fit in the Current Treatment Landscape?
2.5% injectable polyacrylamide hydrogel (2.5% iPAAG, Arthramid) is mechanistically distinct from both the conventional and the regenerative options. It is not a drug and not a biological. It is a non-degradable hydrogel that integrates into the synovial membrane, where histology shows it becomes incorporated into the subintima within about two weeks of injection, accompanied by a low-level, transient tissue response rather than fibrosis or granuloma formation (Lowe et al 2024). Once integrated it restores tensile strength and elasticity to the synovial membrane, which supports normal joint homeostasis (Christensen et al 2016; Wimmer and AbuAlia 2025). In other words, it acts mechanically on the joint capsule and synovium, addressing a driver of the disease rather than masking pain. Preclinical osteochondral model work has also reported disease-modifying signals, including improved lameness and effusion scores and better structural outcomes in treated joints (Contino et al 2025).
On durability, an international multi-centre prospective study reported 82.5% of horses lame-free at 24 months after a single injection (Tnibar et al 2015). Controlled comparative data support this. An earlier controlled trial found iPAAG soundness of 55, 65 and 75% at 1, 3 and 6 months, versus 15, 40 and 35% for triamcinolone or hyaluronic acid (Tnibar et al 2014). A New Zealand double-blinded study in racing Thoroughbreds with middle carpal joint lameness reported 83.3% resolution at six weeks with iPAAG, compared with 27.3% for triamcinolone and 40% for hyaluronic acid (de Clifford and Lowe et al 2021). An earlier New Zealand pilot in the same population found 67.3% of horses lame-free at 12 weeks, with a further 16.7% improving enough to continue training (de Clifford and Lowe et al 2019).
Safety has been documented in large retrospective cohorts, including more than 700 Thoroughbred racehorses and around 1,000 sport horses, with the treatment well tolerated and a low adverse event rate. In Australia and New Zealand there is no competition withholding time associated with Arthramid. Because it is a single treatment with a mechanical mode of action, it may also be considered in older horses, in repeat-injection cases, and where metabolic status limits corticosteroid use, subject to clinical judgement. For a direct comparison with corticosteroids, see our corticosteroid versus iPAAG article, and for the mechanism in detail see how it works.
What Does a Current Best-Practice Multimodal Protocol Look Like?
Current best practice in chronic equine lameness is not a single injection. It combines intra-articular treatment selection with systemic and supportive management. A typical protocol includes:
- Intra-articular treatment matched to the case (corticosteroid, iPAAG, or a regenerative option as indicated)
- Systemic analgesia, usually NSAIDs, for flare control and comfort
- A structured rehabilitation and controlled exercise programme
- Farriery and biomechanical support appropriate to the limb and discipline
- Weight and metabolic management, particularly in endocrine-compromised horses
On sequencing, corticosteroids remain reasonable for rapid control of an acute flare, while a longer-acting, single-treatment option such as iPAAG suits chronic, repeat-presentation joints where the aim is durable function. Regenerative options are generally layered in as adjuncts. Because a mechanically active treatment such as iPAAG works over weeks rather than immediately, it is sensible to consider treating during periods of reduced work or earlier in the training programme.
Monitoring matters as much as selection. Objective lameness grading, clear owner and trainer communication, and defined re-assessment intervals allow the protocol to be adjusted rather than simply repeated. Availability of individual modalities varies between practices in New Zealand, so local access will shape what is realistic for a given case.
How Do the Main Treatment Options Compare?
No single modality outperforms all others across every chronic lameness presentation. The evidence supports a hierarchical, case-specific approach rather than a default choice. The table below summarises where each option currently sits. Evidence levels reflect the current published equine literature and vary by indication.
| Modality | Mechanism | Evidence level (equine OA) | Duration of effect | Re-treatment | Best-suited case | NZ availability | Notable limitations |
| Corticosteroids | Anti-inflammatory glucocorticoid | Strong short-term; limited and conflicting for disease modification | Short (weeks) | Often repeated; diminishing returns | Acute flares, short-term control | Widely available | Cartilage and subchondral concerns with repeated or high-dose use; laminitis caution in metabolic horses |
| Hyaluronic acid | Viscosupplementation | Moderate; modest standalone effect | Short | Frequently repeated; often combined with corticosteroid | Mild synovitis, adjunct | Widely available | Limited standalone durability in advanced OA |
| PRP | Autologous platelet growth factors | Emerging to moderate; preparation-dependent | Short to medium (months) | Variable | Adjunct in early or mild OA | Widely available | No standardised protocol; mostly short-term data |
| IRAP (ACS) | Interleukin-1 receptor antagonist, anti-cytokine | Emerging; sound mechanism, limited controlled clinical data | Medium | Multi-injection protocol | Inflammatory-driven OA, adjunct | Practice-dependent | Specialist processing; efficacy not established versus PRP |
| Stem cell (MSC) | Regenerative and anti-inflammatory paracrine stimulus | Strong in tendon and ligament; emerging in OA | Medium to long (variable) | Case-dependent | Soft tissue injury, selected OA cases | Specialist or practice-dependent | Laboratory processing; limited controlled OA data |
| Shockwave (ESWT) | Focused acoustic pressure waves | Strong for proximal suspensory desmitis; emerging and variable for OA | Short to medium | Repeated sessions typical | Suspensory desmitis, navicular, OA adjunct | Widely available | Transient analgesia; competition-timing restrictions apply |
| 2.5% iPAAG (Arthramid) | Non-degradable hydrogel that integrates into the synovial membrane | Moderate to strong; controlled and prospective data including 24-month follow-up | Long (single treatment) | Usually single treatment per joint | Chronic OA, repeat-injection and metabolic cases | Available in NZ | Works over weeks not immediately; intra-articular use only |
Next Steps
For clinical resources, case selection guidance and New Zealand product information, visit the Arthramid equine vet page. If you are weighing iPAAG against corticosteroids for a specific joint, our corticosteroid versus iPAAG comparison sets out the evidence side by side.