Planning for TTA Surgery

Robert Botte, DVM, Diplomate ACVS
Veterinary Surgical Service
San Diego, California
Kyon Symposium 2010
Zurich
!  Special
Considerations
"  Anatomic
variation
"  Precise implant placement
"  Factors affecting amount of advancement
"  Use of oversized plates
!  Complications
!  Dogs
vary in size
!  Variation in proximal tibia
!  Potential complications
"  Poor
osteotomy location
"  Poor plate placement
"  Poor cage placement
Proximal Tibia Variation
! Tibial Tuberosity Length
! Insertion Point of Patellar Tendon
! Cranial Border (Tibial Crest)
! Area proximal to the insertion
11
Cranial border variation
37 kg Labrador
P7 + C9
45 kg rottweiler
P5 + C12
Tibial Tuberosity Length
25 kg Staffordshire terrier
33 kg Labrador retriever
Need more advancement with short TT length
25 kg Staffordshire terrier
33 kg Labrador retriever
Preoperative planning, non-digital radiographs
Preoperative planning, digital radiographs
Patellar tendon origin
Femoral
condyle
center
Tibial
condyle
center
10 cm K-wire
Tracing on clear transparency
Standard Use of TTA Drill Guide
Measuring Osteotomy Location
TTA Plate Used as a Drilling Template
Drill most distal fork hole first
Visualize all 4 landmarks simultaneously
Osteotomy
Patellar
tendon
insertion
Distal
cranial
Border
Cranial
cortex of
tibia
Mark location for most proximal fork prong
Align drill guide with mark
Inspect plate position
!  Small
dogs
!  Unusual anatomy
!  Open physis
!  Oversized plate
Unusual Anatomy
• Low PT insertion point
• Short TT length
• Indistinct cranial border
11
25 kg German
Shepherd Mix
Unusual anatomy
25 kg German
Shepherd Mix
Indistinct vs. Distinct Cranial Border
31 kg Staffordshire terrier
42 kg German shepherd
Indistinct vs Distinct Cranial Border
Poor plate position
Good plate position
Indistinct vs Distinct Cranial Border
Dealing with Indistinct Cranial Border
Adjust plate position
or
Use new long TTA plate
Indistinct Cranial Border
Left leg - 5 hole standard plate
31 kg Staffordshire terrier
Right leg – 5 hole long plate
31 kg Staffordshire terrier
Common tangent method to
measure amount of advancement
90º
Common
tangent
12
!  Cage
taper
!  Patellar tendon insertion height
!  Anatomy proximal to patellar tendon insertion
!  Patellar tendon insertion direction of movement
!  Proximal displacement of cut segment
!  Cage location proximodistal
Cage Taper
5 mm
7 mm
9 mm
Adapted from Lafaver et al. Veterinary Surgery 2007;36:573-586
Effect of cage taper and anatomy on advancement
+
+
Anatomic variation proximal to patellar tendon
insertion can affect advancement
+
A
A
Anatomic variation proximal to patellar tendon
insertion can affect advancement
+
Direction of
movement of
patellar tendon
insertion
Patellar tendon
insertion moves in a
different direction
than that measured
by the common
tangent method
Proximal
displacement of the
cut segment affects
advancement
Less advancement
with no proximal
displacement
More advancement
with proximal
displacement
!  Limb
not fully extended when radiographed
!  Cage taper and anatomic variation
!  Direction of patellar tendon insertion
movement
!  Saw kerf
Computer simulation
to determine the
amount of
advancement to
achieve 90 degrees
to common tangent
Draw line
representing
patellar tendon at
90 degrees to
common tangent
Simulate osteotomy
and rotate tibial
tuberosity segment
Measure X to
determine the
advancement
required to move the
patellar tendon 90
degrees to the
common tangent
!  To
increase osteotomy length and cage size
!  Repair of patellar luxation after TTA
!  Following broken plate screw
Plate and cage combinations
Commonly Used
Combinations
Plate size Cage size
3, 4 hole
5, 6
6, 7, 8
7, 8
6 mm
9 mm
12 mm
15 mm
Questionable
Combinations
Plate size Cage size
4 hole
5
9 mm
12 mm
Potential problem with cage too wide and
plate too short (osteotomy too short)
Potential
fracture at
lower edge
of cage
Adapted from Lafaver et
al. Veterinary Surgery
2007;36:573-586
Complication resulting from P4 + C9 ?
Post TTA
30 kg English bulldog
7 week post TTA
Oversized 5 hole plate to accommodate 9 mm
cage, fork cut to 4 prongs to avoid P4 + C9.
Distal cranial
border
25 kg English
bulldog
Distal cranial
border
5 hole plate with 4 prong fork
Is a longer osteotomy with an
oversized plate warranted?
!  6
cases
" 3 English bulldog
" 1 tibial tuberosity fracture
!  Needs further study
" Is it beneficial?
# Should P4 + C9 and P5 + C12 be avoided?
" Is it safe? Stress riser/tibia fracture at distal
osteotomy?
!  Alternative – new long TTA plate in select cases
Less concern about
P4 + C9 and
P5+C12 with low
patellar tendon
insertions because
of extra osteotomy
length proximal to
the insertion
P5 + C12
42 kg Labrador ret
Oversized plate for patellar luxation after TTA healed
33 kg Labrador retriever
Patellar luxation after TTA healed
osteotomy
Tibial tuberosity transposition and oversized plate
6 hole plate replaced with 7 hole plate, fork cut to 6
prongs to avoid original plate screw holes
Oversized plate after screw head sheared off
31 kg pit
bull terrier
Major Complications 25 (5.2%)
!  5 (1.0%) Septic arthritis
!  4 (0.8%) Tibial tuberosity fracture
!  4 (0.8%) Subcutaneous infection
!  4 (0.8%) Medial patellar luxation
!  3 (0.6%) Screw insertion errors
!  2 (0.4%) Pivot shift, 1 dog bilateral
!  1 (0.2%) Fixation failure
!  1 (0.2%) Periosteal reaction proximal tibia
!  1 (0.2%) Draining tract
Minor Complications 23 (4.7%)
!  10 (2.1%) Partial wound dehiscence
!  6 (1.2%) Trauma to LDE tendon
!  4 (0.8%) Lick granuloma
!  3 (0.6%) Minor wound drainage
!  8
(1.6%) Partial wound dehiscence
!  5 (1.0%) Septic arthritis
!  3 (0.6%) Subcutaneous infection
!  3 (0.6)% Lick granuloma
!  1 (0.2%) Tibial tuberosity fracture
!  1 (0.2%) Fixation failure
!  1 (0.2%) Plate removal for draining tract
!  1 (0.2 %) Pivot shift
!  1 (0.2%) Patellar luxation
Key factors to reduce TTA complications include:
!  Accurate implant placement
!  Accurate osteotomy location
!  Sufficient tibial tuberosity advancement
QUESTIONS??