Lecture 8- Eq Tendon Ligament

Clinical signs of soft tissue injury

Swelling, heat, tenderness, thickening, altered posture, lameness, joint instability

Soft tissue injury differentials

Muscle strain; tendonitis; ligament sprain (desmitis); synovitis; tenosynovitis; bursitis; cellulitis; seroma; hematoma

Prevalence of tendon/ligament injuries

11-46% in performance horses; most common soft tissue injury in racing TBs

Risk of re-injury

43-93% recurrence rate

Most common tendon injury

SDFT tendonitis ("bowed tendon")

SDFT injury prevalence

93% of soft tissue injuries in National Hunt horses; 97% forelimbs; 9% bilateral

Suspensory ligament desmitis prevalence

Common in jumpers and dressage; chronic repetitive strain

Tendon function

Connects muscle to bone; transfers force; induces joint mobility

Ligament function

Connects bone to bone; provides joint stability

Microscopic tendon anatomy

Type I collagen for tensile strength; proteoglycans for viscoelasticity

Collagen fiber arrangement

Parallel bundles → linear ultrasound pattern

Endotenon function

Surrounds fiber bundles; carries vessels, nerves, lymphatics

Paratenon function

Surrounds tendon; synovial cells for gliding

Synovial sheath locations

Digital flexor sheath; carpal flexor sheath; tarsal flexor sheath

Tendon vascular supply

Musculotendinous junction; enthesis; endotenon; mesotendon

Tendon nerve supply

Golgi tendon organs (proprioception); free nerve endings (nociception)

Tendon biomechanics

Transmit force; resist load; stabilize joints; store/release elastic energy

Stiff tendons

Better for controlled movement (walking, turning)

Compliant tendons

Better for energy storage (running, jumping)

Stress-strain curve: crimp

Wavy fibers straighten with load

Stress-strain curve: microtrauma

Partial fiber injury before rupture

Digital flexor tendon strain

10-12% rupture in vitro; 12-16% strain at gallop

Suspensory ligament function

Prevents fetlock hyperextension

Etiology: overuse

Accumulated microtrauma; inadequate rest

Etiology: acute overload

Sudden high-impact injury; musculotendinous junction

Etiology: conformation

Poor hoof balance; bone/joint anomalies increase stress

Etiology: genetic

Collagen defects → increased extensibility, poor healing

Tendon injury location

Core lesion in center of tendon due to high load + poor vascularity

SDFT re-injury rate

23-80% within 2 years

Tendon healing phase 1

Acute inflammation (1-2 weeks): fibrin, blood, debris

Tendon healing phase 2

Proliferation (3-6 weeks): Type III collagen, disorganized

Early mobilization (

Detrimental to collagen orientation

Mobilization >3 weeks

Improves tensile strength and healing

Tendon healing phase 3

Remodeling (6 weeks-12 months): Type I collagen, linear alignment

Fibrosis effect

Alters strain; increases re-injury risk

Ligament injury consequences

Neuromuscular dysfunction; altered proprioception; poor coordination

Ligament pain effects

Co-contractions; flexor-extensor imbalance; chronic hypertonicity

Contracted tendons

SDFT → fetlock flexion; DDFT → elevated toe

Tendon/ligament healing challenges

High forces; poor vascularity; fibrosis; slow remodeling

Diagnosis: observation

Swelling, lameness

Diagnosis: palpation

Pain, heat, swelling, fibrosis

Diagnosis: gait

Joint stiffness; positive flexion tests

Diagnostic anesthesia caution

May interfere with ultrasound interpretation

Soft tissue palpation: edema

Fluid accumulation in subcutis

Soft tissue palpation: cellulitis

Dermal/subcutis infection

Soft tissue palpation: effusion

Joint capsule, tendon sheath, bursa

Ultrasound purpose

Identify structure, fiber disruption, lesion type, extent

Ultrasound lesion types

Diffuse disruption; core lesion

Ultrasound zones

1A-3C; each ~4 cm; used for localization

Ultrasound CSA

Increased with edema/fibrosis; measured at standard zones

Ultrasound echogenicity

Hypoechoic (fluid/disruption); hyperechoic (fibrosis/mineralization)

Ultrasound fiber alignment

Linear vs heterogeneous

Ultrasound margins

Smooth vs irregular

Ultrasound depth

Must identify lesion relative to bone

Enthesis definition

Bone attachment site of tendon/ligament

Re-exam interval

Every 4-6 weeks

CSA changes

Decrease = remodeling; increase = chronic thickening

Adjunct imaging: radiographs

Identify fractures; enthesopathy; bony lesions

Adjunct imaging: contrast

Visualize tendon sheath, bursa, joint communication

Adjunct imaging: MRI

Best for subtle/deep tendon/ligament lesions

Common disorders list

SDFT tendonitis; suspensory desmitis; DDFT tendonitis; check ligament desmitis; collateral desmitis; interosseous desmitis; patellar ligament desmitis

SDFT tendonitis signs

Lameness; swelling; pain on palpation; ultrasound diagnosis

SDFT treatment

Minimum 6 months off; periodic ultrasound

DDFT tendonitis etiology

High-speed injury; acute trauma; distal wear-and-tear

DDFT tendonitis signs

Lameness; subtle swelling; pain; MRI definitive

DDFT association

Navicular syndrome

Digital flexor tendon sheath tenosynovitis

Palmar annular ligament constriction; synovial fluid impedes healing

Tenosynovitis treatment

Transect palmar annular ligament

Tenosynovitis prognosis

Worse with chronicity

Suspensory ligament desmitis sites

Proximal; mid-body; branches; distal

Suspensory desmitis causes

Repetitive strain; high-speed work; poor conformation

Suspensory desmitis impact

Chronic lameness; prolonged recovery

Proximal suspensory desmitis forelimb

Common in performance horses; worse on soft ground; worse on outside of circle

Forelimb suspensory desmitis association

Splint bone exostosis

Forelimb suspensory prognosis

Recurrence common; often does not return to prior level

Forelimb suspensory diagnosis

Pain on deep palpation; ultrasound; radiographs; scintigraphy; MRI

Forelimb suspensory block

Lateral palmar nerve at accessory carpal bone

Hindlimb proximal suspensory desmitis

Common in dressage/jumpers/reiners; straight hocks; hyperextended fetlocks

Hindlimb suspensory signs

Chronic lameness; shortened cranial phase; worse on soft ground

Hindlimb suspensory block

Deep branch of lateral plantar nerve

Mid-body suspensory desmitis

Similar to digital flexor tendinitis; forelimb most common

Suspensory branch desmitis cause

Hyperextension; fetlock injury

Suspensory branch desmitis signs

Moderate lameness; thickening; positive lower limb flexion

Suspensory branch ultrasound

Insertional lesions; core lesions

Suspensory branch radiographs

Proximal sesamoid bone irregularity (sesamoiditis)

Suspensory branch prognosis

Fair; ~40% return to full use; re-injury possible

Degenerative suspensory ligament desmitis

Progressive; fetlock may touch ground

DSLD signalment

Aged broodmares; Andalusian, Peruvian Paso, Paso Fino

DSLD signs

Straight hocks; fetlock hyperextension; stand with heels elevated

DSLD treatment

Corrective shoeing; fetlock arthrodesis

DSLD prognosis

Guarded

Rehabilitation: acute tendonitis

Compression wrap; confinement; cryotherapy; NSAIDs; passive ROM; controlled walking

Rehabilitation modalities

Laser; tissue heating; orthobiologics; lunge; cavelletti; ridden work

Surgical diagnostics

Arthroscopy (intra-articular ligaments); tenoscopy (flexor sheath)

Surgical treatments

Tendon repair; ligament repair; tendon sheath debridement; tendon splitting; tenotomy; check ligament desmotomy

Extensor tendon laceration

Common; heals well; 6-8 weeks rest; good prognosis (72-80%)

Flexor tendon laceration

Uncommon; severe; may mimic fracture; requires coaptation

Flexor tendon surgical repair

Appose ends; >50% damage requires repair; cast/splint

Flexor tendon prognosis

Fair-good survival; guarded athletic use; poor if sheath involved

Collateral ligament rupture

Treat like fracture; coaptation 4-6 weeks