By Dr Jason Lowe BVSc, Equine Veterinarian and Chief Veterinary Officer, Contura Vet.
Key takeaways
- The pastern, or proximal interphalangeal (PIP) joint is a low-motion, high-load joint, and arthritis here progresses differently from the joints above and below it.
- Radiographically advanced pastern arthritis can be dramatic, but subtle disease exists long before those changes appear.
- Arthramid is a biocompatible 2.5% polyacrylamide hydrogel that integrates into the synovial membrane and joint capsule rather than acting pharmacologically, which is directly relevant in a joint where capsular stiffness dominates.
- The published interphalangeal evidence includes the PIP joint but does not report outcomes separately for it. That is stated openly below.
- Recommended dose for the proximal interphalangeal joint is 1 mL. Arthramid is for use only by a veterinarian.
Understanding distal limb lameness in horses
Lameness originating from the lower limb of the horse is one of the most common reasons veterinarians are called to examine performance horses. One of the frequently affected joints is the proximal interphalangeal (PIP) joint, known as the pastern joint. It plays a critical role in shock absorption, weight bearing and athletic performance.
Whether the horse competes in dressage, showjumping, eventing, racing, endurance, polo, western disciplines or is simply hacked and ridden for pleasure, disease affecting this joint can significantly impact comfort, performance and longevity.
Today, advances in diagnostic imaging and intra-articular therapies are allowing veterinarians to diagnose disease earlier and manage these cases more effectively than ever before. One treatment that has changed our approach to joint health is Arthramid® (2.5% polyacrylamide hydrogel).
The distal interphalangeal joint presents a different diagnostic and clinical picture and is covered in a companion article on coffin joint arthritis in horses
Why are pastern joint problems so challenging?
The pastern joint is a relatively low-motion joint that experiences enormous forces during exercise. Over time, repetitive loading can lead to progressive osteoarthritis, particularly in horses with conformational abnormalities or demanding athletic careers.
The clinical challenge is different from the coffin joint. Localisation is generally more straightforward, since the joint is palpable and accessible to diagnostic analgesia and radiography. The difficulty lies in timing. By the point at which periarticular new bone is obvious, considerable disease has already occurred, and the therapeutic window for influencing the soft tissue structures of the joint has narrowed.
For this joint, successful treatment begins with an accurate diagnosis made early.
The importance of early diagnosis
One of the biggest lessons we have learned over the past decade is that osteoarthritis begins long before radiographs show obvious changes.
Many horses develop:
- Synovitis (inflammation of the joint lining)
- Capsulitis (inflammation of the joint capsule)
- Early cartilage injury
- Subchondral bone changes
- Joint capsule thickening
well before significant bone spurs or joint narrowing become visible on standard radiographs.
Modern imaging techniques such as MRI, CT and advanced ultrasound are helping veterinarians identify these earlier stages of disease. This earlier diagnosis creates an opportunity for earlier intervention and potentially better long-term outcomes.
Osteoarthritis of the pastern joint (PIP joint)
The pastern joint behaves differently from the coffin joint.
Because it is a lower-motion joint, arthritis often results in:
- Significant bone spur formation
- Progressive new bone production
- Subchondral bone sclerosis
- Joint space narrowing
- Reduced flexibility and comfort
Radiographically, advanced pastern arthritis can be dramatic. However, subtle disease may exist long before major radiographic changes become evident.
Clinically, presenting signs are often less specific than the radiographs eventually suggest. Reduced flexibility, a shortened cranial phase of the stride, poor performance and a positive response to distal limb flexion are common, and lameness may be intermittent for a considerable period before it becomes persistent.
Historically, treatment has relied heavily on:
- Corrective shoeing
- Controlled exercise programmes
- NSAIDs
- Corticosteroid joint injections
- Hyaluronic acid
- Biologic therapies such as IRAP, PRP and stem cells
These treatments can be valuable, but many horses require repeated expensive interventions, and some eventually become less responsive over time, which makes the case for intervening earlier in the disease process all the more relevant.
How Arthramid® has changed the management of pastern joint arthritis and lameness
For many years veterinarians focused primarily on suppressing inflammation within the joint. Today, our understanding has evolved.
Research shows that the synovial membrane and joint capsule are central drivers of pain, inflammation and progressive joint dysfunction. Synovitis is often one of the earliest and most important features of osteoarthritis.
Unlike drugs that temporarily alter inflammation, Arthramid® is a biocompatible 2.5% polyacrylamide hydrogel that becomes integrated into the synovial membrane and surrounding soft tissues, acting as a durable biostable scaffold within the joint capsule. The synovial membrane is augmented and strengthened, joint capsule elasticity improves, shock absorption improves, and pain progressively reduces over the weeks following treatment. Histological work in normal equine joints has shown integration into the synovial sub-intima by day 14, with normal cell counts, a low-level transient macrophage response and no fibrosis or granuloma formation (Lowe et al, 2024). The mechanism is set out in more detail in the coffin joint article and on the how it works page.
That mechanism is worth pausing on in the context of the pastern joint specifically. This is a joint where capsular stiffness and load transfer, rather than range of motion, dominate the clinical picture. Work presented on the shear stiffness of the equine synovial membrane reported normal synovial membrane elasticity in joints treated with 2.5% iPAAG compared with controls in an equine osteoarthritis model (Wimmer and AbuAlia, 2025). A treatment that acts on capsular and synovial mechanics is mechanistically well matched to a low-motion, high-load joint, and this reasoning sits alongside the clinical evidence below rather than substituting for it.
Clinical results in horses with interphalangeal joint arthritis
There is no published case series reporting outcomes for the proximal interphalangeal joint in isolation. The most directly applicable evidence includes the PIP joint within a broader interphalangeal population.
Bathe et al (2016) presented a prospective study of 20 adult sport horses with non-responsive osteoarthritis of the interphalangeal joints to the Veterinary Orthopaedic Society 43rd Annual Conference. Lameness was localised to the proximal or distal interphalangeal joint by diagnostic analgesia, with radiography or standing MRI consistent with osteoarthritis. All horses had persistent lameness after previous corticosteroid treatment. Average lameness duration was 15 months and average lameness score was 3/10. Each horse received 1 mL of 2.5% polyacrylamide hydrogel, followed by four weeks of exercise restriction before a progressive return to ridden exercise. Long-term follow-up was available for 18 cases at a median of 12 months. Twelve of 18 returned to full function, three returned to work at a lower level and three failed to improve. One horse was treated twice and had a transient adverse reaction.
Three qualifications belong with that result. It is a conference proceedings abstract rather than a peer-reviewed full paper. It did not report outcomes separately for the proximal and distal interphalangeal joints, so it cannot be read as a PIP-specific success rate. And the authors noted that a control group would have been preferable, while arguing that each case acted as its own control because conventional treatment had already failed.
Broader evidence in horses with osteoarthritis, not specific to any one joint, provides supporting context:
- Tnibar et al (2015). International multicentre prospective study, 43 horses, 24 month follow-up. 82.5% were lame free at 24 months after a single injection, with no adverse events reported.
- Tnibar et al (2014). Controlled clinical trial comparing 2.5% polyacrylamide hydrogel with triamcinolone acetonide and sodium hyaluronate. Soundness was reported in 55%, 65% and 75% of hydrogel-treated horses at one, three and six months respectively, compared with 15%, 40% and 35% in the corticosteroid and hyaluronic acid group (p=0.001).
Neither of these studies is joint-specific, and outcomes in a low-motion joint should not be assumed to match a mixed population. They are included as context for the treatment rather than as evidence for the pastern joint.
A shift toward long-term joint health
One of the most important changes in modern equine sports medicine is the move from simply managing pain to managing joint health.
For years, the conversation around osteoarthritis focused on whether a horse could compete next weekend. Increasingly, owners and veterinarians are asking a different question:
“What can we do now to help preserve joint function for the next several years?”
In the pastern joint that question has particular weight, because the natural history of untreated disease is progressive new bone formation, and the options narrow as it advances.
This shift is particularly relevant for:
- Young performance horses with early synovitis
- Horses returning from orthopaedic surgery
- Dressage horses requiring long-term soundness
- Jumpers and eventers exposed to repetitive concussion
- Racehorses moving into second careers
- Older horses still competing successfully
By targeting synovial membrane health and supporting the soft tissue structures of the joint capsule, Arthramid® has become an important option within a broader, evidence-based arthritis management programme that also includes corrective farriery, weight management, exercise modification and appropriate rehabilitation.
Putting it into practice
Pastern joint arthritis rarely responds to a single intervention, and Arthramid sits inside a management plan rather than replacing one.
Case selection. The strongest rationale is in cases identified before extensive periarticular new bone has formed, where synovitis and capsulitis are prominent features, and in horses that have become less responsive to repeated corticosteroid use. The published interphalangeal work was conducted specifically in corticosteroid-refractory cases.
Dose and administration. Arthramid is supplied in prefilled sterile 1 mL syringes for intra-articular injection only, administered via a sterile 19 to 23G needle using aseptic technique. The recommended dose for the proximal interphalangeal joint is 1 mL, varying with severity of disease, joint size and duration of clinical signs.
Aftercare. The protocol used in the published interphalangeal study was four weeks of exercise restriction before a progressive return to ridden exercise.
Setting client expectations. Response is progressive over the weeks following treatment rather than immediate. Saying so at the time of injection avoids the mid-course assumption that treatment has failed.
Concurrent management. Farriery has a substantial role in this joint given the influence of foot balance and conformation on loading, alongside weight management, exercise modification and rehabilitation.
Arthramid® is for use only by a veterinarian. Registered in New Zealand pursuant to the ACVM Act 1997, No. A011596. See www.mpi.govt.nz for registration conditions.
