Authors: de Clifford, L., Vallance, S. A., Wood, E., Gieseg, M., Lowe, J.N.
Contact author: Leigh de Clifford | Leigh@matavet.co.nz
INTRODUCTION:
To evaluate the long-term safety and efficacy of 2.5% injectable polyacrylamide hydrogel (2.5% iPAAG) in Thoroughbred racehorses through retrospective analysis of clinical records.
METHODS:
Medical records from a single Australian veterinary practice (2017-2023) were analysed for Thoroughbred racehorses treated with 2.5% iPAAG. Safety assessment included 701 horses receiving 1,156 injections across 15,050 race starts. Efficacy analysis focused on 214 horses receiving multiple treatments. Performance was evaluated using Timeform ratings, and safety was assessed through catastrophic musculoskeletal injury (CMI) rates and adverse events.
RESULTS:
The most common injection volume used was 2ml. The most frequently treated joints were middle carpal (135/39%), front fetlock (113/33%), hind fetlock (45/9.5%) and tarsometatarsal (41/9.5%).
The average treatment interval was 234 days.
Performance data was overwhelmingly positive showing horses maintained or improved Timeform ratings post-treatment for the joint treated, regardless of how many treatments were given.
Interestingly win% and % 1st-3rd did not improve, indicating that treatment is not performance enhancing but allows the horse to achieve its athletic potential. The study documented a CMI rate of 0.0003 per 1000 starts, significantly lower than the Australian industry standard of 0.52/1000.
Only two adverse events were recorded (0.17% of injections). At study conclusion, 38.8% of horses remained in active training, with retirement reasons primarily non-lameness related.
Table 1: Number of horses by number of joints treated
Table 2: Number of horses by number of treatments for each horse
DISCUSSION:
This comprehensive analysis represents the largest safety study of 2.5% iPAAG in racing Thoroughbreds to date. The remarkably low CMI rate (0.0003 per 1000 starts) suggests that 2.5% iPAAG treatment does not increase injury risk, even with repeated administration. This finding is particularly significant given the high- stress environment of racing and training.
The adverse event rate of 0.17% is superior to published rates for other intra-articular treatments (~2%)5. The distribution of treated joints aligns with typical injury patterns in racing Thoroughbreds, with middle carpal and metacarpophalangeal joints predominating.
Performance data indicates that 2.5% iPAAG maintains athletic function across multiple joint types. The average treatment interval of 234 days suggests sustained therapeutic benefit, though intervals tended to decrease with subsequent treatments. Career longevity data, showing an average of 28 races regardless of treatment frequency, supports the safety of repeated administration, unlike that of other intra-articular treatments.
The high percentage of horses remaining in active training (38.8%) or retiring for non-joint related reasons (39.8%) further supports the long-term safety profile of 2.5% iPAAG. The low rate of joint-related retirement (1.9%) is particularly noteworthy in this high-risk population.
Despite the inherent limitations of retrospective analysis, the substantial dataset of safety data, performance outcomes, and career longevity metrics suggests that 2.5% iPAAG offers a valuable treatment option for managing joint-related conditions in high-performance equine athletes.
PUTTING IT INTO PRACTICE:
Arthramid® is indicated for use in any synovial joint exhibiting clinical signs of osteoarthritis, including but not limited to joint pain, synovitis, effusion, pain on flexion, and lameness responsive to intra-articular analgesia. It is also appropriate where diagnostic imaging (such as radiography, ultrasonography, scintigraphy, CT, or MRI) reveals abnormal joint pathology consistent with OA.
Early intervention is recommended, particularly in cases presenting with synovitis and capsular thickening, although Arthramid® remains effective in chronic and severe presentations of osteoarthritis.
Prior to administration, a thorough review of the patient’s history is essential to rule out soft tissue pathology, active infection, or suspected fracture in order to minimise the risk of complications and ensure appropriate use.
The dose of 2.5% iPAAG may vary depending on the severity of disease, the size of the joint and duration of clinical signs. The following recommendations have been made based on observed clinical responses to treatment as seen in this and other studies.
Table 3: Dose recommendations by joint