This multi-center clinical trial represents the first study to evaluate local injection of LAA for treatment of equine tendonitis and desmitis, and reports that 72% of treated horses returned to or exceeded their previous level of work after at least six months following treatment. In a previous report describing the outcome of 99 horses with tendon and ligament injuries treated with local injection of a PRP preparation, 81% of the horses returned to their previous use, 12% had clinical improvement but could not perform at the previous level, and 7% were classified as failures.21 Another controlled clinical study evaluating local injection of MSCs and PRP for the treatment of tendonitis and desmitis lesions in the cannon region of 23 horses reported 13 (57%) to returning to racing within 15 months of treatment.22 Differences in the type and location of lesions as well as the breed or discipline of horses could account for the discrepancy between these success rates.
The most common lesion in the current study was categorized as suspensory branch desmitis (SBD), representing 38 of the 128 (30%) lesions reported. A prior case series described 11 horses with 18 SBD lesions treated with a single intra-lesional injection of PRP reported that five horses (45%) returned to their previous level of work within three months.23 In another study, 22 warmblood sport horses were treated for SBD using intra-lesional allogeneic umbilical cord-derived MSCs resulting in 15 (68%) had returning to at least the same level of work after six months or more.24 In the current study, 25 of 38 (66%) SBD lesions were associated with horses that either returned to or exceeded their previous level of work following local injection of LAA, a similar or more favorable rate than these prior reports.23,24
In the current study, proximal suspensory desmitis (PSD) lesions accounted for 15 (12%) of the lesions, and 73% of those were associated with horses that either returned to or exceeded their previous level of work following local injection of LAA. In a previous study, 107 of 127 (84%) horses with forelimb PSD and 108 of 144 (75%) horses with hindlimb PSD were treated with a series of three peri-ligamentous injections of ACS, entered full training by 110 days from the initial injection, and had no recurrence of lameness after a month of training.25 In the current study, five of six (83%) forelimb PSD lesions and six of nine (67%) hindlimb PSD lesions were associated with horses that either returned to or exceeded their previous level of work, similar rates for forelimbs and slightly less favorable rates for hindlimb PSD compared to the previous study.25
Superficial digital flexor (SDF) tendonitis accounted for 15 (12%) of the lesions in the current study. A case series of 22 racing Thoroughbreds with SDF tendonitis of varying severity reported that 64% of horses returned to racing following intra-lesional injection with PRP.26 In a controlled clinical trial of 20 horses with forelimb SDF tendonitis, 8 of 10 (80%) horses treated with intra-lesional injection of PRP were performing at their previous level or higher 12 months post-injury while only 6 of 10 (60%) control horses shared that success.27 A case series of 40 racing Thoroughbreds with SDF tendonitis treated with a series of four or five intra-lesional injections of insulin-like growth factor-type 1 reported that 21 of 34 (62%) horses for which race data were available raced at least once after treatment.28 Additionally, 23 warmblood sport horses treated with intra-lesional injection of allogeneic umbilical cord-derived MSCs for SDF tendonitis resulted in 20 (87%) of these horses returning to at least the same level of work at least six months following treatment.24 In the current study, 67% of the SDF tendonitis lesions treated with local injection of LAA were associated with horses that returned to or exceeded their previous level of work. The range of success rates reported in these previous reports and the current study may be explained by differences in number, breed and discipline of the horses as well as the location (fore vs hind, proximal vs. distal) and severity of the lesions.
In the current study, deep digital flexor (DDF) tendonitis lesions accounted for 25 of the 128 (20%) lesions and were categorized anatomically as either cannon region or foot/pastern region. All 10 DDF tendonitis lesions in the cannon region as well as 13 of 20 (65%) in the foot/pastern region were associated with horses returning to or exceeding their previous level of work. A study treating six warmblood sport horses with intra-lesional injection of allogeneic umbilical cord-derived MSCs for DDF tendonitis reported that four of these horses (67%) returned to their previous level of work six or more months post-treatment,24 a rate similar to the current study. A search of the current literature could find no reports evaluating the use of regenerative modalities in the treatment of DDF tendonitis of the foot/pastern region exclusively. A retrospective case study of 20 horses with 22 DDF tendonitis lesions treated with endoscopic debridement and/or navicular suspensory desmotomy reported that only nine (45%) returned to pre-treatment performance levels after six or more months.29 Thus, it would appear that local injection of LAA may be beneficial in the treatment of these lesion types.
The current study also describes treatment of collateral (15), distal sesamoidean (11), SDF accessory (2), and patellar (2) desmitis lesions with local injection of LAA. A search of the current literature found very few reports describing long term outcomes of horses diagnosed with these desmopathies with none evaluating the use of regenerative modalities for treatment. A study of the long-term outcome of 20 horses diagnosed with collateral desmitis of the distal interphalangeal joint and treated with a variety of modalities reports 12 (60%) horses returning to and maintaining their previous level of exercise for at least three months while eight (40%) were described to have a poor outcome.30 One horse in that report was treated with intra-lesional injection of a urinary bladder matrix powder but the outcome of that specific horses was not described.30 The current report includes 10 horses diagnosed with collateral desmitis of the distal interphalangeal joint with 9 of these (90%) returning to or exceeding their previous level of work. A previous study described 27 horses diagnosed with desmitis of the oblique (18), straight (3), or both (6) sesamoidean ligaments (10 forelimb, 17 hindlimb) treated with various non-regenerative modalities in addition to rest and rehabilitation. Of the 21 available for follow-up, 16 (76%) were competing at the same or better level of performance.31 Another study reported nine cases of straight sesamoidean desmitis (5 forelimb, 4 hindlimb) with six (67%) able to return to their intended use following primarily rest and rehabilitation for six months although four were treated surgically.32 In the current report, six of seven (86%) horses diagnosed with straight sesamoidean desmitis and all four horses diagnosed with oblique sesamoidean desmitis returned to or exceeded their previous level of work following local injection of LAA, rates more favorable than previously reported. In a prior report, six of eight (75%) horses suffering from SDF accessory desmitis returned to their previous level of performance within six months following anti-inflammatory injection of the carpal sheath and rest.33 Both of the horses diagnosed with SDF accessory desmitis in the current study returned to or exceeded their previous level of work following local injection of with LAA. In a study of nine clinical cases of patellar desmitis, five were treated with rest and rehabilitation, three were treated surgically, and one was euthanized.34 Of the nine, just one was able to return to its former level of competition. Both cases of patellar desmitis in the current report returned to or exceeded their previous level of work following local injection of with LAA. It is the authors’ opinion that the results presented in the current study support the use of local injection of LAA for these desmopathies.
In the current study, the attending veterinarians reported local adverse reactions in 13% of horses following injection of LAA. Although most of the events were transient swelling and redness, there were four reports of increase in lameness. In all four cases, the increase in lameness was reported to have resolved within 72 hours with non-steroidal anti-inflammatory treatment. In a prior report, a local injection site reaction rate of 4.35% was reported for local injection of allogenic MSCs in 164 horses with 230 lesions, which included 208 tendon or ligament lesions.35 The disparity in local adverse reaction rate between this report35 and the current study could relate to the difference in study design or the regenerative product used. Additionally, transient local adverse reaction rates as high as 12% are reported following injection of sodium hyaluronate.36
The attending veterinarian reported satisfaction with the LAA product in 92 of 100 horses, indicating an overall positive experience. Interestingly, the attending veterinarian reported satisfaction in 10 horses that failed to show improvement following local injection of LAA. Reasons for this may be that improvement was not expected due to the severity of the lesion or satisfaction referred to the LAA product’s availability and ease of administration.
Limitations of the current study include the non-blinded design and the lack of a control group. Also, the number of attending veterinarians likely introduced variability in patient selection and exact treatment methodologies (volume of LAA injected per lesion, LAA administration technique, etc.). Additionally, some of the specific lesion categories were low in numbers and may not represent an appropriate sample size, thus making interpretation difficult.