Red Light Therapy for Bone Spavin in Horses: Why "It Will Fuse Eventually" Is Usually Wrong
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There is a sentence almost every owner hears within a week of a bone spavin diagnosis: keep him in light work and the hocks will fuse eventually. It is comforting, it is repeated by good horsemen, and for most horses it is not what happens. The equine veterinary literature is blunt on this point — reaching fusion naturally is the exception rather than the rule, not a default you can plan around. If you have just been handed a set of radiographs and told to keep hacking, that single correction should reshape how you think about the next eighteen months. For the wider picture of how arthritic change behaves across the whole joint, our guide to hock arthritis in horses covers ground this article deliberately does not.
The second core point decides the prognosis: "bone spavin" is not one diagnosis. Which of the three lower hock joints is involved separates a horse who comes back sound from one who does not, and the difference is not subtle. Two horses carrying the same word on the same report can have completely different futures. That is also why the wait-and-see plan needs a deadline and a fallback rather than an open horizon — and why the day-to-day comfort work you do around it, from farriery and controlled exercise to a red light therapy hock wrap, carries more weight than it would if fusion were a certainty.
The third point is where light honestly fits, and it is narrower than most marketing suggests: red light therapy cannot fuse a joint and cannot reach subchondral bone — but a genuine part of what hurts in a spavin horse sits a few millimetres under the skin. The cunean tendon and its bursa lie directly across the spavin site, and the compensation the hock creates in the back and hindquarters is superficial muscle. Those are reachable. The arthritic joint surface is not. Everything below follows from taking that distinction seriously.
What Bone Spavin Actually Is — And Why Three Joints Decide Everything
The hock is not one joint. It is a column of four, stacked, doing completely different jobs. At the top sits the tarsocrural, or tibiotarsal, joint, which supplies almost all of the hock's visible flexion — the high-motion joint. Below it sit three low-motion joints: the proximal intertarsal (PIT), the distal intertarsal (DIT), and the tarsometatarsal (TMT) at the bottom. Between them, those three contribute only a small fraction of the hock's total range of movement.
The short answer. Bone spavin is osteoarthritis of the tarsometatarsal, distal intertarsal and, less commonly, proximal intertarsal joints. It is a common cause of lameness and poor performance in horses across all disciplines. Lameness may be one-sided or bilateral, and disease can sit in one joint alone or in two or three concurrently.
Because the affected joints barely move, fusion is not the failure state in bone spavin — it is the goal. Every treatment pathway, from years of conservative management through to a drill and a general anaesthetic, points at the same destination. The disagreement in the field is never about whether fusion is desirable. It is about how likely you are to get there unaided, and how long you are willing to wait.
Why "low motion" is the most important phrase in this diagnosis
Here is the logic that makes bone spavin different from arthritis anywhere else in the horse. A joint that barely moves does not need to move. If the DIT and TMT fuse solid — bone bridging across what used to be a joint space — the horse loses very little function, because those joints were only ever contributing a few degrees. And once there is no movement, there is no grinding, and therefore no pain.
The pathogenesis is not fully understood, but compression and rotation producing uneven or excessive loading during exercise is thought to contribute. Distal tarsal osteoarthritis frequently develops in joints with entirely normal conformation. Where conformation is a factor, sickle-hocked, cow-hocked and excessively straight hocks lead the list, along with incomplete ossification of the distal tarsal bones during development.
The joint that breaks the rule
The proximal intertarsal joint is the exception, and it is the reason a diagnosis of "bone spavin" without a joint name is close to useless. The PIT communicates with the high-motion tarsocrural joint above it. Osteoarthritis there is less common but carries a distinctly more guarded prognosis for return to soundness — you cannot pursue fusion in a joint sharing a compartment with the one doing all the bending.
The outlook worsens further if bony change is present in both the tarsocrural joint and the distal tarsal joints; that combination is generally regarded as poor. Conversely, once the intertarsal and tarsometatarsal joints have fused, whether by natural progression or by arthrodesis, the prognosis is a rideable horse, typically with no lameness once warmed up, though often with a lower foot flight arc that never fully returns.
| Joint | Motion | Role in bone spavin | What fusion means here |
|---|---|---|---|
| Tarsocrural | High | Not bone spavin — this is the bog spavin and OCD joint | Fusion would be catastrophic; never a target |
| Proximal intertarsal | Low, but communicates upward | Least commonly affected of the three | More guarded outlook; the fusion strategy is compromised |
| Distal intertarsal | Low | Commonly affected | Fusion generally means a sound, rideable horse |
| Tarsometatarsal | Low | Most commonly affected | Fusion generally means a sound, rideable horse |
The question to ask your vet
Not "does he have spavin?" but "which joints, and is the proximal intertarsal or the tarsocrural involved?" That single question separates a good prognosis from a guarded one, and it changes whether pursuing fusion is even the right strategy.
Bone spavin and bog spavin are near-opposite conditions
The shared word causes real confusion, and the two findings behave nothing alike. Bog spavin is distension of the high-motion tarsocrural joint with excess synovial fluid — a soft, fluctuant swelling at the front of the joint and in the medial and lateral plantar pouches. It is a physical finding rather than a specific diagnosis, it does not itself create lameness, and in horses under three it is usually caused by an osteochondritis dissecans lesion. Bone spavin is hard, bony, low, medial and painful. If you are working out which one you are looking at, our separate article on bog spavin in horses handles that condition on its own terms.
The Fusion Myth: Why "Just Keep Working Him" Fails More Horses Than It Helps
In the early stages of bone spavin it is not uncommon for vets to advise putting the horse on phenylbutazone and keeping him in work, in the hope that the joint eventually fuses naturally. In many cases that is a perfectly reasonable opening move. The problem is what owners hear: that all hocks eventually fuse, and that time alone will resolve this.
The claim that does not survive contact with the literature
The concept that all hocks eventually fuse is explicitly described in the equine veterinary literature as a falsehood. It is the exception rather than the rule which gets to that point naturally. Most horses will show lameness again as soon as the painkillers are stopped.
The specialist literature on refractory low-motion-joint osteoarthritis makes the same point from the other direction: in most horses, cartilage degeneration and bony fusion of the distal intertarsal and tarsometatarsal joints does result in soundness — but osteoarthritis progresses all the way to fusion in only a small number of cases.
What happens instead
What usually happens is partial. New bone forms around the joint margins — osteophytes that stabilise the region without ever bridging it. On a radiograph the joint space narrows and new bone appears, but the joint has failed to fuse. Those osteophytes can then interfere with neighbouring structures, which becomes a problem in its own right. The horse is left in a long middle ground: too changed to be normal, not fused enough to be pain-free.
The test that tells you the truth
There is a simple, unglamorous way to know which category your horse is in. If he has been comfortable on bute for eight months and goes lame within a fortnight of coming off it, you are not watching a joint fuse — you are watching a joint being medicated. That distinction is worth forcing into the conversation at every re-examination, because timing matters: arthrodesis performed earlier in the course of the disease generally carries a better prognosis than one performed late.
How long does fusion take when it does happen?
Faster than expected in a minority, far slower than hoped in most. Ankylosis between the central and third tarsal bones can occur within a year in some individuals, at which point the lameness resolves. Owner and clinician experience commonly cites up to two years for the process to run its course, with the standing caveat that many horses never complete it without intervention. Both hocks are frequently involved, so a horse who fuses on one side may remain visibly asymmetric for a long stretch.
Where this leaves supportive therapy. If fusion were guaranteed, comfort management would just be a way of passing the time. Because it is not guaranteed, everything you do to keep the horse moving well — farriery, controlled work, bodywork, photobiomodulation on the tissues it can actually reach — is doing double duty. It buys comfort now, and it protects the movement quality the fusion strategy needs in order to have any chance at all.
Reading a Spavin Horse Before You Read the X-ray
Bone spavin rarely announces itself. It develops slowly, and a great many horses show no clear signs until the disease is already established. The signs that do appear are easy to file under "getting older" or "not schooling well," which is precisely why they get missed for months.
The gait signature
Because tarsal flexion is painful, the horse stops flexing. That produces the most recognisable pattern in this condition: an abnormal gait with a low foot flight arc, a shortened forward movement of the hoof and decreased hock action, so the hind leg appears to drag rather than swing. The affected limb tends to land toe-first, wearing that toe down noticeably faster than the other. At rest the horse may park the toe on the ground with the heel slightly raised, and over time the heel on that foot can become elongated.
The "works out of it" pattern
Classic bone spavin lameness is worse cold and better warm — it often disappears with exercise and returns after rest. Owners describe a horse who comes out of the stable stiff and looks fine twenty minutes later. This is one of the most misleading features of the disease, because it reads as "just stiff" rather than "arthritic," and it lets the condition run unaddressed. Where the articular surfaces have been affected, the lameness can become continuous.
Upper limb flexion makes the lameness worse, which is why the hind limb flexion test is central to the workup: the leg is lifted and flexed at the hock, held for around a minute, then the horse is trotted off. Diagnosis rests on history, physical examination and radiographs looking for joint degeneration and abnormal bony growth — and critically on diagnostic analgesia, since relief of pain after anaesthetic injection of the distal intertarsal joints or the cunean bursa is what actually localises the problem.
The signs that appear nowhere near the hock
This is the part that matters most for supportive care, and it is badly under-discussed. Horses with bone spavin are frequently sore along the muscles on one or both sides of the spine. Racing, jumping and other sport horses may develop soreness in the gluteal muscles — trochanteric bursitis — as a direct result of the spavin. Owners describe the pattern repeatedly: the hocks are the diagnosis, but the back is what became unmanageable, and back soreness was often what prompted the vet call in the first place.
- Stiff out of the stable, then apparently normal after twenty minutes of work
- Stumbling behind, or difficulty coming underneath themselves in dressage work
- Trouble going downhill on trails and hacks
- Refusing jumps they previously took willingly
- Loss of extension — a medium trot that used to be there and is not any more
- Western horses: difficulty with sliding stops and spinning off the hind legs
- Back and gluteal soreness that keeps returning after bodywork
None of these points at a hock on its own. Together, in a horse who is stiff out of the box and lands toe-first behind, they should.
Why the Radiographs and the Lameness Often Disagree
One of the most useful pieces of epidemiology in this field comes from Icelandic horses, a breed that appears predisposed to osteoarthritis of the distal hock joints. An epidemiological study found that 23% of Icelandic horses in Sweden had radiological signs of bone spavin. A causal relationship was established between hind limb lameness, radiological evidence of bone spavin, the horses' ages and their hock angles — but no relationship was found with environmental factors such as training and showing.
The finding that should change how you read a report
In that population, the lameness is often mild despite moderate-to-severe radiological changes. Radiographic severity and clinical lameness are not the same axis, and treating them as interchangeable leads to both over-treatment and under-treatment.
Modern CT imaging has reinforced the point from the other direction: multiple pathologies can be present in different tarsal joints at the same time as the osteoarthritis visible on plain radiographs. What you see on a film is a partial picture of what is happening inside the hock.
The practical consequence is straightforward. You are treating a horse, not a radiograph. A frightening set of films on a comfortable horse does not mandate aggressive intervention, and a mild-looking set on a horse who cannot hold a canter lead does not let anyone off the hook. Age and hock conformation carry real weight; how much the horse has been shown does not.
Where Red Light Therapy Actually Fits — And Where It Does Not
This is the section most articles on red light therapy for bone spavin get wrong, usually by implying that the light reaches the arthritic joint surface. Take the limitations first, because they define the useful part.
What light cannot do
It cannot fuse a joint. Nothing about photobiomodulation drives bone bridging across a joint space — that is what monoiodoacetate, ethyl alcohol, surgical drilling and laser-facilitated arthrodesis are for.
It cannot reverse osteoarthritis. Bone spavin is irreversible; treatments aim to slow progression, manage pain and reduce lameness.
It cannot substitute for intra-articular medication, and it will not do the job of a bisphosphonate acting on bone remodelling.
The penetration question, answered honestly
Device marketing routinely claims near-infrared light reaches five to ten centimetres. The peer-reviewed picture is considerably more conservative: one review of photobiomodulation parameters places red wavelengths at roughly 0.5 to 1 mm and near-infrared at around 2 mm before losing 37% of intensity, and skin-optics modelling puts 850 nm at approximately 2.4 mm. Reviewers examining the mechanism have gone further, suggesting the critical light–tissue interaction happens in the skin at capillary level, with effects on deeper structures being secondary, chemically-mediated events.
Reasonable people disagree about the exact figures. What nobody credible claims is that a wearable LED array delivers a therapeutic dose to the articular surface of the tarsometatarsal joint, buried under skin, heavy collateral ligaments and bone. If that is what you were sold, you were sold something untrue. Our detailed breakdown of red light therapy penetration depth by wavelength goes through the evidence in full.
The structure light can genuinely reach: the cunean tendon and bursa
Here the anatomy turns in your favour. Bone spavin starts to develop on the dorsomedial — inner and frontal — aspect of the hock joints. Lying directly across that region is the cunean tendon, with the cunean bursa beneath it. Veterinary teaching is explicit that the joint area underlying the cunean bursa and tendon is a common site for arthritis to develop, and cunean bursitis is recognised as a pain source in its own right, whether primary or in association with strain and bone spavin.
It is superficial enough that a clinician identifies it by palpation: with the hoof in toe-touch position and the limb unloaded, the crossing tendon becomes easier to feel, and you check for fullness above and below its course. That structure sits millimetres under the skin — and the clinical history says it matters.
The cunean tenectomy signal
Cunean tenectomy — surgically removing a section of the cunean tendon where it crosses the hock — was assessed in an owner survey covering 216 owners and 285 performance horses, in which 83% believed lameness and performance improved afterwards and said they would have the procedure done again.
Read that in both directions. The same source notes that the efficacy of cunean tenectomy has been debated, that no controlled clinical studies or experimental evidence exist to either support or refute it, and that it is rarely performed as a sole procedure today. Owner-reported outcomes are not controlled evidence. But the survey does establish something relevant: in a large group of spavin horses, altering a superficial soft-tissue structure changed how the horse went. That is the layer photobiomodulation can plausibly interact with — not the joint itself.
The secondary target: compensation
The back and gluteal soreness described earlier is not a side note. For many spavin horses it is the majority of the discomfort you can actually see and palpate. Those are large, superficial muscle groups, well within reach of near-infrared light, and muscular pain is where the photobiomodulation evidence base is strongest. Treating the topline and hindquarters of a spavin horse with an equine red light therapy back pad is not treating the hocks — it is treating what the hocks did to the rest of the horse, which is a legitimate and frequently more productive target.
What the human osteoarthritis evidence supports
Systematic review and meta-analysis of randomised placebo-controlled trials in knee osteoarthritis has found statistically significant reductions in pain for photobiomodulation compared with sham treatment. A systematic review cited within that literature reported that low-level laser photobiomodulation at 4 to 8 J per treatment spot at wavelengths between 785–860 nm, and at 1 to 3 J at 904 nm, significantly reduced pain and disability against placebo by the end of the treatment period and in the short term. Trial work in knee osteoarthritis has identified 808 nm as an optimal wavelength, with no adverse effects observed at that setting.
Two caveats belong with that. These are human knee trials, and a human knee is not a horse's tarsometatarsal joint — it is far more superficial relative to the target. And the demonstrated effect is on pain and function, not on structural disease progression. Which is precisely the claim this article is making: in bone spavin, light is a comfort tool, not a disease-modifying one.
A Practical Protocol for a Spavin Horse
The framing that makes red light therapy for bone spavin work is simple: you are not lighting up a joint. You are treating the superficial soft tissue over the spavin site and the compensation pattern it created, so the horse keeps moving well enough to do the controlled work his fusion plan depends on.
Where to place the device
The primary site is the dorsomedial aspect of the hock — inner and slightly forward, low down, over the course of the cunean tendon. This is not the point of the hock, and it is not the front of the tibiotarsal joint where a bog spavin would bulge. It is the flat, hard, medial surface where a spavin becomes palpable. A contoured wrap that holds the array flush against that surface does more useful work than a larger pad bridging air.
The secondary sites are the ones that usually deliver the visible change: the lumbar and sacroiliac region, and the gluteal mass. In a horse whose spavin has been running for months, that is where the recruitable soreness lives.
Timing it around work, not instead of work
Because this lameness is classically worse cold and better warm, the highest-value slot is before exercise, as part of the warm-up rather than as a recovery ritual afterwards. A horse who takes twenty minutes to loosen is a horse whose first twenty minutes are being ridden on a stiff, painful hock — and that is exactly the work the fusion strategy needs to be good quality. A second session on the back and hindquarters after hard work is a reasonable addition.
Choosing hardware
| Target | Sensible format | Why |
|---|---|---|
| Cunean region / medial hock | Contoured hock wrap | Only format that holds LEDs flat against an irregular, angular surface |
| Compensatory back & SI | Back pad | Large superficial muscle groups; strongest evidence base |
| Gluteals / hindquarters | Hip and shoulder wrap, or blanket | Covers the trochanteric region implicated in spavin compensation |
| Specific tender points | Handheld torch | Useful for a palpation finding; impractical for daily whole-horse work |
On wavelength: red at around 660 nm is a surface wavelength, and near-infrared in the 810–850 nm band is the one with any claim on tissue below the skin, which is why dual-wavelength arrays are standard. Do not buy on penetration claims. Buy on fit, on coverage of the specific region you have identified, and on whether the horse will stand still for the session length.
What "working" looks like — and when to stop
Set your success criteria before you start, because this condition punishes vague assessment. Reasonable markers over four to six weeks: a shorter warm-up before the stiffness clears; less reactivity on palpation over the back and gluteals; a farrier reporting the toe wearing more evenly. Unreasonable markers: change on a radiograph, a negative flexion test, or the disappearance of lameness.
Stop and escalate if: lameness worsens, the horse becomes lame at walk, heat or fresh swelling appears, the toe-first landing becomes more pronounced, or comfort collapses within days of stopping medication. Any of those is a veterinary conversation about the next tier of treatment — not a reason to add more light.
What This Should Never Replace
Bone spavin has an established treatment ladder, and red light therapy is not on it. The rungs, broadly:
- Intra-articular corticosteroid medication of the affected joints — the most common initial approach
- Long-term low-dose NSAIDs such as phenylbutazone, suxibuzone or meloxicam for horses not in competition
- Bisphosphonates — tiludronate or clodronate given intravenously to alleviate bone pain, with evidence of a greater effect in horses with periarticular osteophytes and subchondral bone change
- Hyaluronic acid, which is anti-inflammatory and helps re-establish normal joint fluid
- Corrective farriery — shortening the medial hoof wall, improving breakover by bringing the toe back, and lateral extensions to unload the medial aspect of the tarsus
- Extracorporeal shockwave therapy
- Facilitated ankylosis when medical management stops working — chemical (monoiodoacetate or ethyl alcohol), surgical drilling, or laser, which produces smaller spots of fusion than the other two
Two practical notes. Proper conditioning has been shown to have a protective effect against bone spavin, which is a further argument against long unstructured rest. And NSAIDs are prohibited in competition, as are several other treatments — if you compete, the medication plan has to be built around your discipline's rules from the outset. That is one of the few genuine advantages of a drug-free supportive modality: no withdrawal period to manage.
The Bottom Line
Bone spavin is one of the few orthopaedic conditions in the horse where the destination is a joint that no longer moves — and where arriving there usually means a rideable horse. The problem is that the road is neither automatic nor short, and the most widely repeated piece of advice about it overstates how often nature finishes the job.
Get the joints named. Find out whether the proximal intertarsal or tarsocrural joints are involved, because that is the line between a good prognosis and a guarded one. Treat the horse rather than the radiograph. Put a review date on any wait-and-see plan, and use the response to withdrawing medication as your honest read on whether fusion is actually progressing.
And place red light therapy for bone spavin where it belongs. Not on the joint — it will not get there. On the cunean region, where a genuinely superficial pain generator sits, and on the back and hindquarters, where months of altered movement have left their mark. Comfort is not a cure for bone spavin. But in a condition managed over years, where the entire strategy rests on a horse continuing to move well, comfort is not a small thing either.
Frequently Asked Questions
Will my horse's hocks fuse on their own if I just keep him in light work?
Possibly, but it is not something to plan around. The idea that all hocks eventually fuse is described in the equine veterinary literature as a falsehood — reaching that point naturally is the exception rather than the rule. Some horses do get there, and ankylosis between the central and third tarsal bones can occur inside a year in certain individuals. Most do not, and most show lameness again as soon as painkillers are stopped. Give any wait-and-see plan a defined review date rather than an open-ended one.
How long does hock fusion take?
Where it happens naturally, anywhere from under a year to around two years is the commonly cited range. Both hocks are frequently involved, so the two sides may not progress together and the horse can remain visibly asymmetric for a long stretch. Where fusion is induced by injection or surgery, most horses return to work with good improvement in lameness — though no technique is 100% successful at achieving fusion.
Should I rest him or keep him working?
This is the most common regret owners report — extended rest, followed by the realisation that the problem was arthritis all along and that rest was not helping it. Bone spavin management generally favours controlled, consistent movement over lay-up, and proper conditioning appears to be protective. The exceptions are an acute flare or a concurrent soft tissue injury. Your vet sets the level; the honest question to ask alongside it is whether the horse is comfortable enough to do that level well.
Can a horse with bone spavin still compete?
Many do, but outcomes vary widely. Owner-reported experience ranges from horses back over fences within months of diagnosis, to horses sound and competing after injections plus rest, to horses who never came right — including one hock fusing while the other did not, leaving the animal permanently uneven. Which joints are involved, whether the tarsocrural joint is also affected, and how early treatment started all move that outcome. Ask for a joint-specific prognosis rather than a general one.
Is bone spavin always in both hocks?
Not always, but it is commonly bilateral, and lameness is usually worse in one limb even when both are affected. Disease can sit in one joint only, or in two or three concurrently. Symmetric bilateral hind lameness is a known diagnostic trap: it can look like general stiffness or laziness rather than lameness, because there is no sound limb available for comparison.
My horse's back has become really sore — is that coming from the hocks?
It very plausibly is. Muscle soreness along one or both sides of the spine is a recognised feature of bone spavin, and gluteal soreness — trochanteric bursitis — is documented as a consequence of spavin in sport horses. Owners frequently describe the back becoming a bigger day-to-day problem than the hock itself. Treating the back without addressing the hock tends to produce short-lived results, because the compensation pattern regenerates as soon as the horse goes back to work.
Can red light therapy replace hock injections?
No. Intra-articular medication is delivered inside a joint capsule that light does not reach. Photobiomodulation and joint injections are not competing for the same job — one addresses superficial soft tissue and compensatory muscle pain, the other addresses inflammation inside the joint. If injections have stopped controlling the lameness, the next conversation is about bisphosphonates or facilitated ankylosis, not about adding a wrap.
Does red light therapy make the hocks fuse faster?
There is no evidence that it does, and no proposed mechanism by which it would. Fusion is driven by destruction of the remaining cartilage and bone bridging across the joint space — which is exactly why the interventions that reliably produce it are chemical or surgical. Any claim that a light device accelerates ankylosis is not supported by the literature.
Can I use it on a horse who is on bute?
Red light therapy has no drug interactions and no withdrawal period, which is part of its appeal in a condition managed over years. The caution is interpretive rather than safety-related: on NSAIDs you cannot reliably judge whether the light is contributing anything, because the drug is masking the signal you would be measuring. If you want to assess it honestly, agree a stable medication window with your vet and evaluate within it.
References
- Merck Veterinary Manual — Osteoarthritis of the Distal Tarsal Joints in Horses; Disorders of the Tarsus in Horses.
- Horse & Hound (veterinary feature) — Hock fusion: diagnosis, treatment and prognosis.
- University of Illinois College of Veterinary Medicine — Current Treatment Options for Refractory Osteoarthritis of Low-Motion Joints.
- University of Minnesota, Large Animal Surgery (open textbook) — Hock joint problems and osteoarthritis.
- Eastman et al., AAEP Proceedings — Owner Survey on Cunean Tenectomy as a Treatment for Bone Spavin (216 owners, 285 performance horses).
- ScienceDirect topic reviews — Bone Spavin, including Icelandic horse epidemiology and management of distal tarsal osteoarthritis.
- Physical Therapy (Oxford Academic) — Effectiveness of Photobiomodulation in Reducing Pain and Disability in Patients With Knee Osteoarthritis: A Systematic Review With Meta-Analysis.
- Review of light parameters and photobiomodulation efficacy (PMC) — penetration depth and dosing parameters.
Disclaimer: This article is educational and is not veterinary advice. Bone spavin requires diagnosis and management by a qualified veterinarian, including radiographs and diagnostic analgesia to establish which joints are involved. Red light therapy is a supportive comfort modality and is not a treatment for osteoarthritis. Always consult your vet before adding any therapy to a lame horse's programme.
