By Dr Jason Lowe BVSc, Equine Veterinarian and Chief Veterinary Officer, Contura Vet.
Key takeaways
- The distal interphalangeal (DIP) joint is one of the most frequently implicated structures in distal limb lameness, and its position within the hoof capsule makes localisation difficult.
- Osteoarthritis begins in the synovial membrane and joint capsule well before radiographic change becomes evident.
- Arthramid is a biocompatible 2.5% polyacrylamide hydrogel that integrates into the synovial membrane rather than acting pharmacologically.
- In a case series of 12 horses with coffin joint osteoarthritis that had failed at least two previous intra-articular treatments, eight were lame free at six months (Janssen et al, 2012).
- Recommended dose for the distal 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 most frequently affected joints is the distal interphalangeal (DIP) joint, commonly known as the coffin joint. This joint 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 proximal interphalangeal joint behaves differently and is covered in a companion article on pastern joint arthritis in horses.
Why are coffin joint problems so challenging?
The coffin joint sits deep within the hoof capsule, making diagnosis particularly difficult. Pain arising from this area may be confused with disease involving the navicular apparatus, collateral ligaments, hoof structures or other adjacent tissues. Even diagnostic nerve blocks can sometimes desensitise multiple structures, making interpretation complex.
For this joint, successful treatment begins with an accurate diagnosis.
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. MRI can identify cartilage defects and subtle soft tissue and subchondral bone lesions that may not be visible on radiographs despite significant lameness.
This earlier diagnosis creates an opportunity for earlier intervention and potentially better long-term outcomes.
Osteoarthritis of the coffin joint (DIP joint)
Coffin joint arthritis is a common cause of chronic foot pain and reduced performance.
Typical signs include:
- Shortened stride length
- Poor performance
- Reluctance to turn
- Intermittent or persistent lameness
- Reduced willingness to work
- Bilateral forelimb lameness
As disease progresses, cartilage loss, inflammation and subchondral bone changes can significantly limit a horse’s athletic future.
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.
How Arthramid® has changed the management of coffin 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.
This is where Arthramid® works differently.
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. It acts as a durable biostable scaffold within the joint capsule.
Following treatment:
- Blood vessels and collagen fibres move around the hydrogel
- The synovial membrane becomes augmented and strengthened
- Joint capsule elasticity improves
- Shock absorption improves
- Synovial cell function is supported by a better functioning synovium
- 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).
This mechanism helps explain why many veterinarians are seeing longer-lasting results than are traditionally achieved with corticosteroids or other therapies alone.
Clinical results in horses with coffin joint arthritis
The published evidence specific to the coffin joint comes from a case series in which every horse had already failed conventional intra-articular treatment.
Janssen, Koene and Lischer (2012) treated 12 horses with osteoarthritis of the distal interphalangeal joint at the Tierärztliche Klinik für Pferde Lüsche between 2008 and 2011. Mean age was 10 years, with a range of 4 to 14. The population was made up of showjumpers, all warmbloods with the exception of one pony. Every horse had shown chronic recurrent forelimb lameness for at least three months and had already been medicated intra-articularly at least twice, without success, using hyaluronic acid, glucocorticoids and/or autologous conditioned serum.
The diagnostic workup was thorough. Lameness improved by at least 50% following a palmar digital nerve block, and again following intra-articular anaesthesia of the coffin joint assessed at one minute. Radiography and standing low-field MRI of both forefeet were performed in every case, with at least two positive MRI findings required for enrolment. Horses with collateral ligament desmitis, deep digital flexor tendinopathy, osteoarthritis secondary to joint infection or previous coffin joint arthroscopy were excluded.
Each affected coffin joint received 1 mL of 2.5% polyacrylamide hydrogel under aseptic conditions. Orthopaedic shoeing was applied at the time of the first treatment to shorten the toe, improve break-over and correct mediolateral imbalance. Aftercare was five days of box rest, then two weeks of hand walking for 20 minutes twice daily, then one week of walking under saddle before walk and trot ridden work, with workload adjusted to the individual horse after the one-month examination.
At baseline, mean lameness grade was 1.8 on a 5-point scale and mean joint effusion 1.75 on a 4-point scale. In one month, four horses were lame free, three had improved, four were unchanged and one had deteriorated. At six months, eight of 12 horses were lame free and back in showjumping, two had improved and two remained lame, one of which was subsequently neurectomised. Mean lameness grade at six months was 0.3.
No adverse reactions were observed in any of the 12 horses. Repeat imaging in two horses at three and six months showed no change in subchondral bone or joint capsule compared with the initial examination.
Two points belong with that result. Every horse received corrective shoeing at the time of treatment, so the outcome reflects a combined intervention rather than the hydrogel in isolation. And the authors were explicit that unchanged imaging findings pointed to a palliative rather than curative effect, and called for controlled double-blinded studies to establish duration of effect and mechanism. Follow-up ended at six months, and there was no control group.
One observation in the paper is worth carrying into case selection. Three horses had an osseous cyst-like lesion in the distal second phalanx communicating with the coffin joint, a finding that ordinarily carries a guarded prognosis. All three were lame free at final follow-up, and two of them had presented with the highest lameness grade and the most marked joint effusion in the study. That is an observation in three horses rather than evidence, but it is a useful prompt not to write these cases off on imaging alone.
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?”
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
Coffin 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 where lameness has been localised to the DIP joint and where synovitis and capsulitis are prominent features, including horses that have become less responsive to repeated corticosteroid use. The published coffin joint work was conducted specifically in horses that had failed at least two previous intra-articular treatments.
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 distal interphalangeal joint is 1 mL, varying with severity of disease, joint size and duration of clinical signs.
Aftercare. The protocol used by Janssen et al was five days of box rest, two weeks of controlled hand walking, then a graduated return to ridden work.
Setting client expectations. Response is progressive over the weeks following treatment rather than immediate. In the published series, a third of horses were lame free at one month and two thirds at six months. Saying so at the time of injection avoids the mid-course assumption that treatment has failed.
Concurrent management. Farriery, weight management, exercise modification and rehabilitation remain part of the programme, and the outcome usually depends on all of them.
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.
