2. SIGNALMENT
Presenting complaint: Chronic left forelimb lameness
20 years old
Percheron / Quarter horse
Mare
Current use: Retired
3. HISTORY
Chronic left forelimb lameness
First noted October of 2011, attended by DVM #1
Recommendations: Rest, NSAIDs
Lameness did not improve, slowly worsened.
Evaluated by DVM #2 in April of 2012.
Diagnosed straight sesamoidean desmitis by ultrasound.
Recommendations: Rest, NSAIDs, Stem cell therapy (offered but not
performed)
Has not responded to rest/NSAID therapy; progressively has
worsened
4. PHYSICAL & LAMENESS EXAM
Bright, alert, responsive
Vital parameters within normal limits
Passive Exam
Atrophy of left pectoral muscle
Marked left front soft tissue swelling, from fetlock distally to hoof capsule
Hoof tester = negative
Active Exam
Lame at the walk on hard surface (Grade 4/5 - left front)
7. PASTERN ANATOMY
Low motion, high load joint
Proximal phalanx bone (P1)
Wider proximal vs. distal
Distal aspect shaped with two condyles; separated by shallow axial groove
Palpable tubercles on lateral/medial sides for origin of pastern collateral
ligaments
Middle phalanx bone (P2)
Half as long as P1
Both extremities equal width
Proximal surface hollowed by axial ridge
Proximal collateral tubercles
Proximal-palmer border has smooth fibrocartilage
Enlarges articular surface; site of insertion for ligaments
8. PASTERN ANATOMY
Pastern (Proximal Inter-phalangeal) Joint
Restricted “low motion” joint
Paired axial & abaxial ligaments
Origin: Palmer-distal P1
Insertion: Palmer-proximal P2
Straight sesamoidean ligament
Origin: Base of proximal sesamoid bones
Insertion: Fibrocartilage of palmer P2
Joint Capsule
Dorsal and palmer pouch
Pouches are smaller (compared to that of fetlock)
9. PASTERN ANATOMY
Pastern (Proximal Inter-phalangeal) Joint
Common digital extensor tendon
Limited attachment on dorsal surface of P1 & P2
Superficial digital flexor tendon
Attaches to distal tubercles of P1 & fibrocartilage of
P2
Interosseus muscle / suspensory ligament
Insertion:
Abaxial surface of proximal sesamoid bones
Extensor branch: Extends dorsally to join
common digital extensor tendon
Distal digital annular ligament
Origin: medial and lateral P1
Sling for palmer pastern ligaments
Insertion: Palmer aspect of P111
11. TREATMENT OPTIONS
Non-surgical management:
Electrical stimulation
External coaptation with confinement
Monoiodoacetate
Ethyl alcohol
Laser without implants
Rarely successful – remaining cartilage within joint
Surgical management:
Trans-articular lag screws
Dorsal plate
Combination dorsal plate & trans-articular lag screws
12. PASTERN ARTHRODESIS
Plate / Lag Screw Combination
Axial plate with two abaxial lag screws
Biomechanical advantage
Compression across entire joint
Tensile forces induced at palmer aspect of joint by the plate neutralized
by two oblique trans-articular lag screws
Plate provides dorsal compression
Commonly 3-hole or 4-hole dynamic compression plate
Locking compression plate would be most novel ($)
Some reports of two plates, T-plates, Y-plate, spoon plates
Combine plate with two 5.5 screws placed in lag fashion (current
standard)
13. PASTERN ARTHRODESIS
Lag Technique Only
Two or three tran-sarticular screws
Parallel or diverging
4.5mm screws more likely to fail compared to 5.5mm screws
Two 5.5mm screws similar strength compared to three 5.5mm screws
Can be placed using a minimally-invasive (stab incision) approach
Drawback:
Minimal compression of dorsal surface
Discomfort from excessive bone formation impinging on extensor
tendon and / or coffin joint
14. SURGICAL TECHNIQUE
Inverted „T‟ incision
Distal to metacarpal(tarsal)-phalangeal joint
Ends 2cm proximal to coronary band
Horizontal incision extends 4cm on either side of midline
Dissect through subcutaneous tissue to common
digital extensor tendon
Two triangular skin incisions dissected free and
retracted back
Transect the CDE tendon with inverted „V‟ incision
Level of insertion of branches of suspensory apparatus
Remove any bony proliferation, present on dorsal AO
surface
Chisel & mallet
15. SURGICAL TECHNIQUE
Transect joint capsule lateral/medial collateral ligaments dorsally
Remove cartilage with curet, both articular surfaces
Changes the radii of two opposing bones
Reduces radius of proximal phalanx
Increases radius of middle phalanx
End result: Increased contact between opposing bones
If not performed, cyclic screw failure can occur
Can place cancellous bone between
Osteostixis of both subchondral bone plates
2.5mm drill bit, 0.5cm apart
16. SURGICAL TECHNIQUE
Extend foot - close pastern joint to normal
anatomic position
Place plate on dorsal surface
Contour plate to bone, increase contact
Two holes overlying distal proximal phalanx
One hole overlying proximal middle phalanx
Avoid extensor process, distal sesamoid bone
Place two plate screws
Proximal & distal
Drill 4.0 mm thread hole perpendicular to phalanx
Neutral & loading
17. SURGICAL TECHNIQUE
Drill 5.5 mm glide hole for trans-articular
screw
Middle phalanx wider than proximal; diverge screw
Dorso-axial to palmaro(plantaro)-abaxial
Enter joint halfway between dorsal & palmer(plantar)
cortices
Countersink used to create depression for
screw head
Thread hole for trans-articular lag screw
drilled, tapped, and screwed
Lag Technique 4.5 Cortex Screw 5.5 Cortex Screw
Gliding Hole 4.5 mm 5.5 mm
Thread Hole 3.2 mm 4.0 mm
Screw Tap 4.5 mm 5.5 mm
18. SURGICAL TECHNIQUE
Tighten trans-articular screws, followed by tightening two bone plate
screws
Place final proximal bone plate screw in routine fashion
Closure of CDE tendon, simple continuous, absorbable suture
Skin closed using non-absorbable suture or staples
19. CAST PLACEMENT
Objectives:
Placed to protect fixation in recovery
Support healing of soft tissue structures
Provide addition fixation / stabilization of the joint
Placement:
Foam cast padding
Stockinet
Synthetic cast material
Sets in 5 minutes, allows weight bearing in 30 minutes
Permeable, yet still resistant to water
3-4 rolls circumferentially with 50% overlap
1-2 rolls in dorsal-palmer direction
Methyl-methacrylate on solar surface
20. POST OPERATIVE CARE
¼ tube omeprazole, SID, PO
Phenylbutazone
Varies depending on comfort level
Mostly - 1 gram phenylbutazone, BID, PO
Occasionally – 2 grams phenylbutazone in AM, 1 gram in PM, PO
Twice daily physical examinations
Check cast / check bandage splint Q6hr
Monitor weight bearing, up/down Q1hr
21. POST OPERATIVE CARE
Recheck radiographs taken on August 8th, 2012
7 days post-op
Noted bending of trans-articular lag screws
Recovery
Largest force applied
22. POST OPERATIVE CARE
First cast change on August 28th, 2012
Under general anesthesia
Sutures removed from incision
Appeared healthy
Cast sores
Moderate cast sore noted on the palmer fetlock
Mild, superficial sore on the dorsal proximal cannon bone
Silver sulfadiazine applied prior to second cast placement
Recovery from anesthesia unremarkable
Recheck radiographs – no change in screw bending
23. CAST MANAGEMENT
Cast Sores
Dorsal-Proximal aspect of metacarpus / metatarsus III
Compression at breakover or cast loosening
Palmer / plantar aspect of fetlock; abaxial sesamoid
Pressure applied during stance / load phase
Signs
Decreased weight bearing
Suppuration through cast (flies)
Swelling above cast
Increased heat on palpation
May necessitate early cast removal
Other cast complications
Breakage, osteopenia, joint stiffness, tendon laxity
24. POST OPERATIVE CARE
September 7th, 2012
36 days post op
Cast removal
Cleaned wounds
Bandaged leg
Placed PCV splint
Dorsal aspect
Hoof wall to carpus
25. POST OPERATIVE CARE
Recheck radiographs on
September 9, 2012
38 days post-op
Noted mild to moderate
hyperextension of the coffin joint
Bending of screws static
Intact
No indication of infection
Evidence of bony proliferation
Joint fusion
26. OUTCOME
Tuesday, September 25th
8 weeks out from surgery (54 days)
Recheck radiographs revealed no further changes in implants
Noted negative coffin bone angle
EDSS shoes placed by farrier + trim
Currently doing bandage with splint q12hr and bandage without splint q12hr
27. REHABILITATION
Confine horse to stall rest
Minimum 3 months
Hand-walking is sometimes considered at 6 weeks post-op
Small paddock turn-out following stall rest
Additional 3 months
Return to exercise / intended use
Considered at 6 months post-op, in most cases
Time from surgery to return to use ranges from 6 to 12 months
29. LITERATURE
“Proximal interphalangeal joint arthrodesis using a combination
plate-screw technique in 53 horses.” Knox et al. 2006
47% osteoarthritis
21% joint luxation
13% subchondral bone cysts
11% fractures
60% had 3 hole DCP, 32% had 4 hole DCP
93% wore cast for 14 days or less, only one cast applied
11% experienced cast sores on dorsal MC3/MT3 & back of fetlock
Median hospitalization duration 25 days
30. LITERATURE
Knox et al, continued.
87% used for intended use
81% forelimb
95% hindlimb
18% developed implant infections
Enterbacter, Streptococcus, Staphylococcus, Pseudomonas
7% had implants removed
PIP joint degeneration pre-op not predictive of post-op success
Early cast removal: shorter hospitalization, improved comfort; but
increased cyclic load on implants
31. LITERATURE
“A Technique for Laser-Facilitated Equine Pastern Arthrodesis
Using Parallel Screws Inserted in Lag Fashion.” Watts et al,
2010.
Sample size = 7 joints
Diode laser, 2000 J of energy to joint
3 parallel 5.5mm lag screws
Lag screws placed using stab incisions (minimally invasive)
Bandage or bandage casts for 3 weeks
Turn-out by 3 months
Results: at 6 months
5 horses sound
4 horses with radiographic evidence of joint fusion
5 horses returned to intended use
2 horses with lameness / did not return to previous use
32. LITERATURE
Watts et al, continued.
Laser – vaporization of synovial fluid, chondrocyte death
Heating – collagen contraction, joint capsule shrinking
Decrease nerve innervation
Decreased cost, decreased post-operative pain
1 horse had soft tissue necrosis at site of needle-laser insertion
More dorsal peri-articular bone formation
Further investigations:
Histopathology of cartilage / ankylosis after laser
Determine optimal laser dose
33. LITERATURE
“Minimally invasive plate fixation of lower limb injury in horses: 32
cases” James et. al, 2006
Articular cartilage removed using 5.5mm drill bit
Stab incision to place tran-sarticular lag screws
Small incision made over mid-P1, 3 cm length, proximal aspect of
site
„Plate passing device‟
Subtendinous tunnel created
Plate (4 hole DCP) placed and aligned using fluoroscopic
guidance
Bone plate screws placed through stab incisions
34. LITERATURE
James et al., continued.
5 joints treated for PIP arthrodesis
All hindlimbs treated
All 5 returned to previous function
Decreases post-op pain, decreases post-operative hospitalization
Maintaining soft tissue envelope decreases risk of infection
Decreased exposure to OR air, surgical field contamination
Increased tissue handling & tissue dehydration decreases tissue immunity
Doubling of infection rate with each hour of surgery
Less complete cartilage destruction?
35. LITERATURE
“Arthrodesis of the Equine Proximal Interphalangeal Joint: A
biomechanical comparison of two parallel headless, tapered,
variable-pitched, titanium compression screws and two parallel
5.5 mm stainless-steel cortical screws” Wolker et al., 2009.
Cadaver limbs, 10 each group
3-point bending materials-testing machine
Force applied in dorsal-palmer direction
Measured maximal bending moment at time of failure & composite stiffness
No biomechanical difference between two screw types
1 horse in tapered group had failure at screws
Rest in study failed at bone, not screw
36. LITERATURE
Wolker et al., continued.
Suggestion that tapered, headless screws:
Are more biocompatible
Decrease soft tissue irritation
Increased bone-screw interface = increased fatigue resistance
Titanium screws may be less inflammatory than stainless steel
Tapered screws have continuous variable thread pitch along
length
Provides only 2mm compression
Thought is that tapered screws would decrease dorsal
proliferation seen with lag screw fixation (by itself)
Need clinical study
37. LITERATURE
“Ethyl alcohol for chemical arthrodesis of the proximal
interphalangeal joint.” Caston. 2010 AAEP.
Abstract only
Clinical cases of diagnosed pastern osteoarthritis
Results:
19 out of 21 horses returned to intended use
Not all cases had radiographic examination confirming joint fusion
Average time till return to work was 8 months
Each horse had multiple injections (minimum of 3 per horse)
3 horses had mild, transient complications – what type not defined in abstract
Suggestion that if surgical fusion is not an option, this may be an
alternative, more affordable technique
38. LITERATURE
“A limited surgical approach for pastern arthrodesis in horses with
severe osteoarthritis” Jones et al., 2009.
Retrospective of 12 pastern joints fused
Joint was not dis-articulated
Cartilage was not debrided
Applied bone plate and trans-articular screws in standard fashion
Results:
Identified shorter hospitalization time & shorter surgical time
Determined that 92% of cases decreased one grade of lameness
73% of owners would elect to do procedure again
Poor retrospective
39. LITERATURE
“Distal limb cast sores in horses: Risk factors and early detection
using thermography” Levet et al., 2009.
Prospective analysis: 70 horses
Superficial dermal sore / deep dermal sore / full thickness sore
Thermography prior to cast removal at coolest site, dorsal cannon bone, and
palmer/plantar fetlock
Results:
80% had superficial dermal sore
34% had deep dermal sore
1% had full thickness sore
No influence of type of injury, clipped skin,
Incidence increased with duration of cast and age of horse
40. LITERATURE
Levet et al., continued.
Cosmetic blemish
5% - alopecia, leukotrichia, or scar
Thermography
Detects surface temperature via measuring infra-red radiation
Performed in 35 cases
Severity of sores associated with increasing temperature
Measuring difference between location and coolest part of cast
Cut off values for probable superficial dermal sore = 2.3 C difference
Cut off value for probable deep dermal sore = 4.3 C difference
41. REFERENCES
Auer JA: Arthrodesis techniques, in Auer JA, Stick JA (eds): Equine Surgery (ed 4).
Philadelphia, PA, WB Saunders, 2006, pp 1073–1086
Johnson JE: Ringbone: treatment by ankylosis. Proc Am Assoc Equine Pract 20:67–80, 1974
Knox, P.M. and Watkins, J.P. (2006) Proximal interphalangeal joint arthrodesis using a
combination plate-screw technique in 53 horses (1994-2003). Equine vet. J. 38, 538-542.
MacLellan, K., Crawford, W.H. and MacDonald, D.G. (2001) Proximal interphalangeal joint
arthrodesis in 34 horses using two parallel 5.5-mm cortical bone screws. Vet. Surg. 30, 454-
459.
Read EK, Chandler D, Wilson DG: Arthrodesis of the equine proximal interphalangeal joint: a
mechanical comparison of 2 parallel 5.5 mm cortical screws and 3 parallel 5.5 mm cortical
screws. Vet Surg 34:142–147, 2005
Schaer, T.P., Bramlage, L.R., Embertson, R.M. and Hance, S. (2001) Proximal interphalangeal
arthrodesis in 22 horses. Equine vet. J. 33, 360-365.
Stashak TS: The Pastern, in Stashak TS (ed): Adams‟ Lame- ness in Horses (ed 5).
Philadelphia, PA, Lippincott, Wil- liams & Wilkins, 2002, pp 733–741
Watt BC, Edwards RB, Markel MD, et al: Arthrodesis of the equine proximal interphalangeal
joint: a biomechanical comparison of three 4.5mm and two 5.5mm cortical screws. Vet Surg
30:287–294, 2001
Notes de l'éditeur
Digital radiographs of the left front pastern/foot region revealed a palmar subluxation of the proximal interphalangeal joint with osteophyte formation on the dorso-proximal aspect of P2. Osteophyte formation was also present on the distal aspect of P1, with significant osteoarthritis. Slight loss of boney definition of P3 likely due to disuse atrophy and significant soft tissue opacity at the level of P1 and P2 on the left front foot.
PIP: Hyper extended and subluxated
Former days, horses at pasture were hobbled and hobbles were called “pasterns”. The narrowest part of limb above the hoof was easiest to attach the pastern hobble – and eventually the area became called ‘the pastern’.
Change to conservative, chemical and surgical
Check drill to screw sizes
Strong cast material
980nm diode laserNeedle in dorsal and palmer/plantar pouch – confirmed using thru-thru lavageFluroscopic guidance1cm stab incisionsIntended use – pleasure riding, pasture, low level hunter