Superficial Digital Flexor Tendon (SDFT) Injuries: A Practical Reference for Vet Rehab Therapists

This reference summarises current practices and teachings on superficial digital flexor tendon (SDFT) injury assessment and management as presented in Diagnosis and Management of Lameness in the Horse, 2nd ed., Chapter 69, “Superficial Digital Flexor Tendonitis,” by Ross, Genovese, Dyson, and Jorgensen.

It is a structured summary of that chapter, not a statement of my personal views, and not an exhaustive literature review. The chapter purposefully retains the term “tendonitis” for the clinical syndrome, this summary maintains that terminology to remain accurate to the source.

The SDFT is an energy storing tendon prone to injury in equine athletes, as well as in older horses. Pathology is often bilateral, and is most commonly the result of repeated microtrauma within the tendon leading to degeneration and weakening of the tendon over time. During gallops and landing from jumping, this tendon works close or at it’s functional limit, which makes it a common injury site. 

 

Fast facts

1. SDFT injuries are common performance-limiting problems in Thoroughbred (THB) racehorses (forelimb more than hindlimb), with bilateral involvement not unusual; eventers also carry increased risk. Age, conformation, footing, training load, and fitness interplay with risk.
2. Most athletic-use lesions occur at the mid-metacarpal region (zones 2B–3B); proximal/carpal canal lesions are less common but more overtly lame. In hindlimbs, plantar tarsal SDFT injury is part of curb.
3. Older, lightly used horses can suffer severe proximal SDFT lesions with marked lameness and a guarded prognosis compared with mid-metacarpal lesions.

 

SDFT presentation

Early signs of injury can be subtle with heat, local sensitivity to direct palpation with the tendon offloaded, and minimal to no swelling. Lameness often appears later, which may be a reason that injuries progress before they are diagnosed.

SDFT injuries can show swelling, pain, lameness, thickening of the tendon, heat, and an altered tendon profile.

There may be a lack of correlation between the severity of the injury or lesion, and the severity of tendonitis or inflammation in any given individual.

 

Red Flags for Referral

• Marked lameness with little palpable change (think proximal/carpal canal injury).
• Suspected rupture (fetlock hyperextension; palpable defect).
• Tenosynovitis (carpal or digital sheath) obscuring palpation: requires ultrasound to sort primary tendon vs sheath disease.

 

Key Risk Factors Across Disciplines

SDFT is most prevalent in racehorses as a result of the repetitive speed cycles over distance, coupled with a potential genetic factor. Training practices can also increase the prevalence of SDFT occurrence, as incidence of the injury varies between race yards and trainers. Additional factors that can predispose to injury include

• Surfaces such as hard ground, deep going, slippery or inconsistent footing;
• Conformation, such as long, sloping pasterns, long toes, low heels, or upright pasterns;
• shoeing and inappropriate trimming resulting in excess fetlock extension;
• sudden increases in workload intensity with insufficient recovery times;
• advancing age results in cumulative microdamage and degeneration that results in a reduction in tensile strength.

 

Complications and Comorbidities

SDFT injuries are known for their high rates of reinjury. This occurs because tendons will heal with fibrous tissue, causing an increase in stiffness of the fibrous or healed tissue that results in a decrease in elasticity. This places the surrounding tendon tissue under additional strain as it needs to compensate for the lack of elasticity, resulting in an increased risk of reinjury in areas adjacent to the original lesion. Adhesions can form during the healing process that can limit mobility.

Contralateral limb pathology is common, and it is good practice to evaluate both limbs even if symptoms are not apparent in the contralateral limb. SDFT can occur together with the failure of the suspensory apparatus, annular ligament syndrome or manica flexoria tears.

 

Imaging Led Rehabilitation

Progressions and loading decisions should be ultrasound-led. Exercise progressions are made when the tendon cross sectional area decreases, and when echogenicity and fibre alignment improve.

Additional ultrasound techniques such as Doppler imaging can be used to determine whether inflammation is trending down, and Ultrasound Tissue Characterization (UTC) allows us to monitor tissue repair more objectivity when it is available to us.

Before a return to full activity, horses should show a significant reduction in cross sectional areas, improvements in % hypoechoic volume, echogenicity score, and fibre alignment score. If improvements are not seen in all of these areas,  there is a high likelihood of reinjury.

 

Acute Phase Management

Load reduction & inflammation control:

• Stall rest and hand walking only,
• icing 20 min twice daily,
• supportive bandage or poultice if needed,
• NSAIDs short-term if needed,
• Casting if full rupture.
• Farriery aim: straight hoof–pastern axis and a supportive, fully grooved bar shoe. Avoid exaggerated heel changes.

Schedule ultrasound in the first few days and again at 3–4 weeks.

Client messaging: “Quiet tissue, quiet plan.” Early improvement in swelling is not structural healing, the baseline scan at 2–4 weeks sets the real clock.

 

Subacute Rehabilitation

Controlled exercise beats turnout. Unrestricted paddock time significantly worsens outcomes (“turnout is the antithesis of healing”). Programs of 9–12 months, customized to severity and ultrasound progress, yield higher return-to-work versus large-paddock rest. Build in serial ultrasound checkpoints every ~8 weeks and adjust workload to ultrasound stability, not just how the leg looks or feels.

 

A simple scaffold (adapt per lesion & scans):

• Phase 1 (0–8 wks): Hand walk only; progress duration if limb stays cool/quiet and ultrasound trends are stable.
• Phase 2 (8–20 wks): Introduce straight-line in-hand/under-saddle walk with short trot sets on level, consistent footing; avoid circles/deep going; reassess by ultrasound before each increment.
• Phase 3 (5–9+ months): Gradual trot mileage, then canter; postpone lateral work/jumping/collection until ultrasound shows fiber realignment and lesion consolidation.

 

When continuing to compete or train is discussed: Only minimal injuries fared acceptably with symptomatic treatment and continued work, and reinjury rates were high once lesions exceeded mild. Ultrasound monitoring is non-negotiable if this path is chosen.

 

Treatment Options

Common medical/biologic options:

• MSCs (Mesenchymal Stem Cells): Clinical reports suggest reduced reinjury versus historical controls, but your day-to-day still hinges on controlled exercise + ultrasound-led progression.
• Hyaluronan (HA; intralesional): Mixed evidence; some ultrasound improvement reported, but long-term reinjury not consistently different to exercise alone. Generally well-tolerated.
• Corticosteroids (peri/intralesional): Repeated use may impair healing; occasionally used at low dose with HA for peripheral, mild lesions requires down-scaled training and close imaging. Avoid methylpred acetate due to mineralization risk.
• Polysulfated glycosaminoglycan (PSGAGs; systemic/intralesional): No clear long-term advantage over controlled exercise alone; some use in the acute stage for putative enzyme/cytokine modulation.
• Counter-irritation (external/internal blistering, pin firing): Tradition persists, but evidence of benefit is limited; if used, it must be paired with controlled exercise and serial ultrasound.
• Modalities (therapeutic US, low-level laser, ESWT, PEMF): Frequently used, but clinical studies showing superiority over well-run controlled exercise programs are lacking. Position them as adjuncts, not substitutes for graded loading.

 

Surgical Scenarios Rehab Therapists Will Encounter

• Superior Check Ligament Desmotomy: Aims to reduce SDFT load, improve gliding, and protect inelastic scar. Literature shows variable results versus conservative care; some series report >50% making ≥5 starts post-op with long time lines (~12 months). Others find no advantage and note possible suspensory risk. Regardless, success depends on tightly controlled, structured rehabilitation with no uncontrolled turnout.
• Palmar Annular Ligament (PAL) Desmotomy: In chronic distal metacarpal SDFT tendonitis where the PAL compresses the swollen tendon, decompression can restore glide; pairing with check desmotomy is sometimes performed. Your role: manage post-op edema control, progressive loading, and sheath mobility while protecting the repair.

 

Prognosis & Return-to-Work Guidance

Prognosis hinges on location (mid-metacarpal more favorable than proximal/carpal canal), severity, discipline demands, age, and adherence to a controlled program with imaging led progression. Even when the limb looks good at 4–5 months, collagen remodelling still lags; premature return to harder work invites recurrence. Many THBs have guarded prospects for racing; conversion to lower-demand disciplines is common for severe injuries. Standardbreds tend to cope better than THBs when work continues, but risk remains.

 

Objective readiness checklist before workload jumps

• Cooling, non-sensitive tendon with stable, normalizing profile.
• No new hypoechoic foci; Echogenicity and Fibre Alignment Score substantially decreased from baseline.
• Cross sectional area trending down toward the contralateral limb.
• The horse has tolerated the current step for ≥2–4 weeks without heat/swell after work.

 

Your rehab priorities 

1. Protect early repair: Ice/bandage in the acute phase; prevent over-stride and sharp turns; manage farriery to a neutral axis.
2. Load with discipline: Straight-line, level, repeatable surfaces; avoid deep or variable footing until ultrasound shows alignment gains.
3. Measure, don’t guess: Ultrasound checkpoints drive progressions and catch deterioration early.
4. Coach owner expectations: 9–12 months is common; “looking good” does not equal “ready.”
5. Coordinate the team: Surgeon/GP, farrier, and rehab align on the same milestones and imaging criteria.

 

Bottom line

Controlled, ultrasound-gated loading is the therapy with the strongest practical signal in SDFT rehab. Biologics, drugs, modalities, and even surgery sit around that core, not in place of it. With patience, structure, and objective checkpoints, many horses can return to useful work while keeping reinjury risk as low as possible.

 

Reference

Mike W. Ross and Sue J Dyson, Diagnosis and Management of Lameness in the Horse, Second edition. Chapter 69, Superficial Digital Flexor Tendonitis, Mike W. Ross, Ronald L. Genovese, Sue J. Dyson, and Joan S. Jorgensen.

Ovendale, T., Desfontaines, B. 2025. Organ Systems – Tendon: Equine Pathology & Surgery [Lecture to EPS226]. Equine-librium College, Plettenberg Bay, 2025.

OpenAI. (2025). ChatGPT [Large language model]. https://chat.openai.com/chat