Equine Foot/Pastern Flashcards
describe the anatomy of the pastern bone (3)
- a saddle joint formed from the distal aspect of the proximal phalanx (P1) and the proximal aspect of the middle phalanx (P2)
- bound dorsally by common or long digital extensor tendon; pretty limited range of motion
- palmar/plantar support structures:
-distal sesamoidean ligaments: back of P1 and P2
-SDFT and DDFT
-proximal and distal digital annular ligaments: like a sleeve to hold flexor tendons in place
-medial and lateral collateral ligaments: provide stabilization
describe physical exam of the pastern (5)
- pastern region should be symmetric and free of swelling or bony enlargement
- pastern injuries are rarely bilateral (but OA may be), so always compare with contralateral limb
- abnormalities (swelling or bony enlargement) usually obvious because of minimal soft tissue in the area
- lameness associated with pastern region can be subtle to severe depending on injury
-generally, injuries involving the PIPJ or DFTs cause obvious lameness
-lameness due to early strains of distal sesamoidean ligaments may be mild - pain often exacerbated by distal limb flexion or lunging with affected limb on inside of circle
what are 5 differential diagnoses for disorders of the pastern region?
- osteoarthritis (OA)
- osteochondrosis (OC)
- fractures
- infection
- tendon/ligament injuries
describe diagnostic procedures for the pastern region
- regional nerve blocks (some complications)
-PIPJ not always completely anesthetized by abaxial sesamoid block, so a low 4 point block may also be necessary; beware of anesthetic migration!
-AVOID nerve block if fracture suspected - intra-articular anesthesia: pastern is one of the harder joints to block/inject bc crappy landmarks
- diagnostic imaging:
-rads/US for initial characterization of injury
-nuclear scintigraphy/bone scan: isotope binds in higher rates of bone turnover; good for pelvis!
-CT; helpful for pre-op plan of fracture repair
-MRI
describe tendon/ligament injury
- most frequently occurring (in order) in forelimb are:
-superficial digital flexor tendon
-oblique sesamoidean ligament
-deep digital flexor tendon
-straight distal sesamoidean ligament - tendon/ligament injuries are less common in pastern region of hindlimb
describe orthopedic injuries in pastern region
- P1 fractures most often in racing breeds
- P2 fractures most common in western-type activity horses
- treated with internal fixation if orientation of fracture allows
describe osteoarthritis of the proximal interphalangeal joint
- also called high ringbone
(low ringbone = OA of coffin joint) - predispositions: jumping, dressage, western-type activities
- treatment:
-mild OA: NSAIDs and IA anti-inflams
-advanced: surgical arthrodesis: better outcome with hindlimb than forelimb (less weight on hind end); can get away with this because PIPJ is a relatively low motion joint so can do and still have an athletic career
describe osteochondrosis of proximal interphalangeal joint
- less common than in other joints in horses
- osteochondral fragments associated with OC tend to occur dorsally on palmar/plantar eminence of P2
- arthroscopic removal possible, but low mobility in joint = hard to get in to operate
describe subluxation of the PIP joint
- uncommon!
- medial/lateral subluxation is due to severe injury to the collateral ligaments
- palmar/plantar subluxation usually follows a severe traumatic soft tissue innury
-complete tear of distal sesamoidean ligaments
-SDFT branch injury - treatment of med/lateral palmar/plantar:
-conservative management with external coaptation or surgical arthrodesis - dorsal subluxation:
-can occur without any identifiable structural abnormalities or soft tissue structures
-occurs primarily in hindlimbs of young horses
-lameness usually absent or mild
-treatment similar to other sublux types
-subsequent damage to stabilizing soft tissue structures more likely with more chronic subluxation
describe distal limb flexor anatomy
- SDFT inserts on distal P1 and proximal P2, NOT on P3, so fetlock contracture = SDFT
- DDFT insert on flexor cortex of P3 (only flexor insert on P3); if fetlock normal but heel off ground = DDFT
what is the etiology of distal limb flexural deformity (2)?
- congenital: usually neonates
-uterine malposition (big foal little mare)
-teratogenic insults: toxin ingestion in utero
-genetic defects - acquired: any age, chronic pain
-physitis
-OC
-degenerative joint disease
-soft tissue injury
-infection
pain = reflexive muscle contraction = tendon restructuring and loss of elastic capability
describe clinical presentation of congenital versus acquired distal limb flexural deformity
congenital: foal born unable to stand and knuckling over
acquired:
-abnormal fetlock angle
-heel of foot not toching ground
-abnormal hoof growth
describe diagnostics and treatment of congenital versus acquired distal limb flexural deformity and general prognosis
congenital:
-physical exam: unable to manually extend distal limb to normal position
-treatment:
–bandage/splint
–high dose oxytetracycline (diluted in saline) IV once daily for up to 3 days to prevent influx of calcium ions into muscle fibers to allow some relaxation of tendon
acquired:
-physical exam: distal limb does not fully extend when weight bearing, heel not touching ground, abnormal hoof growth rate (heel > toe)
-treatment:
–early (<1 week from onset): nutritional correction, farriery (if DDFT), pain management
–advanced: surgery and farriery (accessory ligament (of SDFT or DDFT) desmotomy)
prognosis:
-dependent upon duration
-generally better for congenital than acquired
know which accessory ligaments associated with SDFT and DDFt
SDFT: accessory ligament/radial check ligament is more proximal; comes off back of radius
DDFT: accessory ligament/inferior check ligament is more distal and comes off back of MC 3
cut the accessory ligament attached to the contracted ligament to treat flexural deformity!!
describe navicular apparatus
- collateral sesamoidean ligaments hold navicular bone in place/suspensory ligaments of navicular bone
- distal sesamoidean/impar ligaments: hold navicular bone in pace distally
- DDFT forms navicular bursa as it passes by to attach to P3
- also called the podotrochlear apparatus, nav bone = distal sesamoid bone
