P O R O U S T T A S u r g i c a l T e c h n i q u e

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POROUS TTA

Developed by:

poroustta@itccanarias.org

P O R O U S T T A S u r g i c a l T e c h n i q u e

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1. Introduction

One of the most common visits to a veterinary hospital is related to limb in the dog´s paws.

Controversy exists for explaining this although it is thought that first cause is stifle´s affection, even

over coxofemoral joint. Since the beginning of the 20th century Anterior Cruciate Ligament (ACL)

rupture in dogs has been widely studied including details related to its origin, how to diagnose it and

what treatment is the most efficient. Scientific discussion has not brought conclusive results. Why

do patients´ cruciate ligaments rupture? How should affection be diagnosed? And finally, if patient

suffers cruciate ligament affection ¿how should it be treated; conservative or surgical treatment?

And related to surgical treatment ¿what technique: intracapsular, extracapsular or osteotomy?

Consensus is established about what is the origin of cruciate ligament affection: most of evaluated

and treated patients with this affection did not shown a traumatic origin. Stifle is affected by

inflammatory/degenerative processes that accompanied by subsequent microtraumas generate

affection of ACL collagen ultrastructure and losing of functionality.

Diagnose of this pathology includes clinical examination following by radiographic examinations and

other current methods (Magnetic Resonance, CT scan, ultrasound scan, ….) allowing the surgeon to

view rupture of cruciate ligament and/or joint´s changes due to ACL affection.

Maybe question most repeated in last 40 years in Veterinary Science is what should be done after

diagnosing ACL pathology. Multiple techniques have emerged during these last years supported by

best achieved results. They argued better immediate results, retarding joint degenerative pathology.

These innovative techniques were fostered by several factors: emerging diagnosing methods,

development of new biomaterials and implants, news skills of surgeons, etc. But maybe main reason

is that none of these techniques provides successful results in all cases.

Tibial tuberosity advancement was first described by Dr. Maquet. This belgium surgeon argued

that advancing the tibial tuberosity would reduce femorotibial contact forces in extension

position as well as retropatellar pressures in patients with stifle arthrosis.

Montavón, Tepic et al. (2002) argued that this behavior is similar in the dog so tibial tuberosity

advancement (TTA) counteracts cranial shear femorotibial forces in stifles with defective anterior

cruciate ligament. TTA tries to achieve a patella tendon angle of 90 degrees to the tibial plateau

with the stifle in 135 degrees of extension. This was studied using a 3D finite elements model for

3D reconstruction corresponding to a human cadaver knee specimen. This study demonstrated

that TTA technique reduced non only femoropatellar contact forces but also femorotibial contact

forces in extension position.

Decreasing of retropatellar pressure in dog after TTA has been experimentally demonstrated

recently (Hoffmann et al 2009). This reduction should protect patellar and femoral articular cartilage

avoiding ulterior injures.

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2. Adventages

1. Simplify the surgical technique: partial osteotomy of crista tibiae enhances fixation stability in

such a way that fixation plate has a smaller size and lesser amount of screws is needed.

2. Shorten the convalescence: bone defect created after crista tibiae advancement is refilled by a

porous titanium cage providing an excellent fixation removing the need to place graft/bone

substitutes or similar.

3. POROUS TTA cage´s porosity fosters osteconduction accelerating bone ingrowth and

stabilization.

4. It is a minimally invasive surgical technique due to smaller size of the implant. This osteotomy

allows a shorter skin incision providing higher posterior comfort for patient (Artiles 2012).

5. Resources optimization: surgical procedure requires common used instruments in a veterinary

hospital avoiding spending money in specific instruments. It is an excellent solution and its price

is very interesting.

6. Technique is rapid, simple and reproductible. No bending of any implant.

3. Implants

The POROUS TTA procedure was developed by Instituto Tecnologico de Canarias through iterations

during clinical testing to best meet the exacting demands of the procedure.

• POROUS TTA Cages

Porous cages are made of Ti6Al4V ELI (ISO 5832-3). Several tibial tuberosity advancements are

provided (5 sizes: 12, 9, 6.5, 4.5 and 3 mm) and several widths for each advancement: 3 different

widths for advancements of 12, 9 and 6.5 mm; and 2 different widths for lesser advancements of 4.5

and 3 mm.

Multiple sizes of cages are disposable so surgeon has enough options during surgical procedure. In

order to decide which cage must be used it is important to understand nomenclature of cage´s

codification. Code includes three geometric measures of the cage: thickness (A), coinciding with

value of required tibial tuberosity advancement; width (B) and length (H).

Cage´s Code: A x B x H

• A: Advancement

• B: Width

• H: Length

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12X23X30 12X20X30 12X17X30

9X20X26 9X17X26 9X14X26

6.5X17X20 6.5X14X20 6.5X11X20

4.5X11X13 4.5X8X13

3X7X8 3X5x8

• Plates

Plates are made of Titanium (Ti CP Grade 4, ISO 5832-2) so they are able to bent. It allows best

adjustment to dog anatomy although in most cases bending is not needed.

There are 6 sizes of plates distinguishing two groups according to their width: 7 mm or 4 mm. Wider

plates will be used in biggest dogs so they provide greater holes for using screws with greater

diameter.

Plates are non-straight excluding smaller one (4R). This fact provides polyvalence and best

adjustment to crista tibiae.

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Plates dispose of two holes for cortex screws in crista tibiae (color code shown in the following

image: holes with diameter of 2.9 mm, red; holes with diameter of 2.2 mm, green) excluding smaller

one with has only one hole.

They have only one greater hole for tibial screw (color code shown in the following image: holes

with diameter of 3.7 mm, blue; holes with diameter of 2.9 mm, red; and holes with diameter of 2.2

mm, green)

Related to plate code, width (not confuse with thickness which is 1 mm in all plates) is linked with

the number on its name. The following letter is linked to its size: large (L), medium (M) and small (S).

The letter R is an exception for the only one straight plate.

• Self-tapping Cortex screws

Screws are made of Titanium alloy (Ti6Al4V, ISO 5832-3). Screws are self-tapping and Hex Head. Set

has four different measures of diameter (3.5, 2.7, 2 and 1.5 mm). Each diameter offers several

lengths showed in the following table:

Ø 1.5 mm Ø 2 mm Ø 2.7 mm Ø 3.5 mm

Ø 1.5 x 6 mm Ø 2 x 6 mm Ø 2,7 x 14 mm Ø 3,5 x 16 mm

Ø 1.5 x 8 mm Ø 2 x 8 mm Ø 2,7 x 16 mm Ø 3,5 x 18 mm

Ø 1.5 x 10 mm Ø 2 x 10 mm Ø 2,7 x 18 mm Ø 3,5 x 20 mm

Ø 1.5 x 12 mm Ø 2 x 12 mm Ø 2,7 x 20 mm Ø 3,5 x 22 mm

Ø 1.5 x 14 mm Ø 2 x 14 mm Ø 2,7 x 22 mm Ø 3,5 x 24 mm

Ø 2 x 16 mm Ø 2,7 x 24 mm Ø 3,5 x 26 mm

Ø 2,7 x 26 mm Ø 3,5 x 28 mm

Ø 3,5 x 30 mm

Width: 7 mm Width: 4 mm

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4. Surgical procedure

Surgical procedure is explained step by step:

Patient´s placement: patient is placed in dorsal

recumbency over side of the limb to be

surgically treated. The other limb is tied to a

stand in the opposite side. Surgical approach is

located on medial aspect of tibia positioned

such that lateral side is in contact with the

tabletop. If patient presents bilateral ruptures

of both ACL, it is possible to accomplish

surgical procedure of both stifles by

positioning dog in supine recumbent position.

Modified Maquet Procedure is going to be

carried out so crista tibiae osteotomy is partial

in distal direction. A skin incision is made on

the medial aspect separated 1 cm to cranial

edge and starting from 1 cm proximal to

insertion of ACL to 1 cm distal to end of crista

tibiae. If patellar dislocation must be treated

too, then approach will be enlarged.

Incision is developed at the crural fascia,

proper retracting of the tibia. Vascular damage

must be minimized. Musculature of the lateral

aspect must not be unaltered. Incision must

be deeper in the caudal zone to patellar

ligament because spreader will be inserted in

this zone.

Location of the hole at the distal end of the

osteotomy for controlling crack propagation

(Maquet hole). This point must be in the distal

zone of the crista tibiae, nearly to 4 m of

cranial border on average (in a large dog the

cortex is approximately 5mm thick and in a

small dog approximately 3mm). Location is

shown in the image (hole accomplished).

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After location, Maquet hole will be drilled by

using a drill with diameter of 2, 2.5 or 2.9 mm

depending on patient. Avoiding bone and

surrounding tissues damage by using enough

irrigation.

Spreaders must be used in order to achieve a

wide surgical vision. A specific one spreader

(provided by POROUS TTA technique) has to

protect the patellar tendon allowing saw guide

will be inserted through it at the same time.

Most dorsal zone of the patellar tendon must

be located in order to protect the tendon.

Spreader will be used with this purpose.

The saw guide is provided for ensuring

osteotomy standardization. The saw is slotted

in order to insert saw blade presenting a hole

that must coincide with Maquet Point in its

proper location. For location, guide must be

placed inside the spreader. Afterwards, drill

used previously for drilling Maquet hole must

be placed new again in the distal hole of the

saw guide such guide maintains optimal

positioning during bone sawing. Guide must

be placed guaranteeing proper osteotomy´s

angle by turning around Maquet hole. In the

case of medium- big patients, saw guide must

be positioned just caudal to patellar ligament.

After guide´s positioning, osteotomy must be

executed by using an oscillating saw. A saw

blade with a thickness of approximately

0.7mm should be used. Osteotomy must be

distally extended ending in the Maquet hole,

protected by the drill. Abundant irrigation

must be used during bone sawing.

Saw guide is removed and surgeon must check

if small bony bridge persists. In this case,

osteotomy must be gently completed

removing the small bony bridge using the

same oscillating saw. Spreader must be

located in the same position in order to

preserve patellar ligament. Copious irrigation

should be used.

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On completion of the osteotomy, crista tibiae

advancement will start. Spreader has been

simply used for patellar ligament protection

but now it will be used for spreading and

holding open the osteotomy. In the

preoperative planning, the advancement was

calculated (using whatever of several existing

methods). It is suggested to open the

advancement (value of selected cage)

increased in one additional millimeter.

This process must be carried out carefully and

slowly, allowing the bone time to adjust,

taking advantage of it elasticity. The spreader

should be used with great caution in order to

avoid crista tibiae´s fracture. Provided

spreader could be blocked so opening could

be controlled. If surgeon is not in possession

of this adjustable spreader, it is possible to use

spreaders with well-known common

measures.

Cage selection. Multiple sizes of cages are

disposable so surgeon has enough options

during surgical procedure: five tibial tuberosity

advancements (12, 9, 6.5, 4.5 and 3 mm) and

several widths for each advancement (more

details in this document, in 3. Implants). The

depth of the osteotomy should be measured

with a drill depth gauge for selecting proper

cage size.

After proper osteotomy opening, cage should

be inserted into space generated by the

spreader. Whole cage must be inserted into

the bone.

Medial side of the cage must be fully or

partially in contact with medial bone cortex.

The proximal end of the cage will lie below the

proximal extremity of the tibial tuberosity.

Ensure that there is no tendency for soft tissue

to be “dragged” in between the cage and the

bone.

Other important detail is location of proximal

tip of the cage. This RX picture shows a correct

implantation. It is possible to modify the tibial

tuberosity advancement by controlling this

location. Spreader should be removed once

cage is inserted.

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Selection of the plate. There are 6 sizes of

plates distinguishing two groups according to

their width: 7 mm or 4 mm. There are 3

models of each width with several lengths:

large (L), medium (M) and small (S). Plates are

non-straight excluding smaller one (4R). This

fact provides polyvalence and best adjustment

to crista tibiae. Plate should be selected

according to dog size.

Plates dispose of two holes for cortex screws

in crista tibiae and one greater hole for tibial

screw. It is possible to use cortex screws with

diameters of 3.5, 2.7, 2 and 1.5 mm.

Plates with 7 mm of width have one tibial hole

of diameter 3.7 mm and two holes of 2.9 mm

in crista tibiae. For plates with 4 mm of width,

crista holes are 2.2 mm whereas tibial hole is

2.9 mm in non-straight plates and 2.2 mm in

the straight one (4R).

Plate fixation for osteotomy stabilization. Plate

location influences on load transmission. It

must be first fixed tibial screw. Its location

must stay always at least 1 cm (in the direction

of axial axis) below distal tip of the osteotomy

(Maquet hole). Screw must not be fully

tightened (only until be in contact with the

plate).

Second screw to be inserted will be crista

tibiae proximal screw. A gentle compression

between cage and crista tibiae fragment

should be performed before proximal screw

implantation in order to enhance porous

cage´s stability.

Its location depends on crista tibiae´s

anatomy. Plate should be oriented such angle

between tibial axis and crista tibiae fragment

would be 40 degrees. Hole for screw must be

previously drilled by using the proper drill

according to screw´s diameter to be

implanted. Cortex self-tapping screws are

provided with diameters of 3.5, 2.7, 2 and 1.5

mm, with several lengths. So it is

recommended measuring for selection the

proper screw´s length.

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A different drill to previously used for tibial

hole should be used because plates have

greater holes for crista tibiae screws

(excepting 4R where holes have same

diameter). Proximal screw must be fully

tightened and later on tibial screw too

previously implanted. Only in very energetic

dogs should be necessary to implant crista

tibiae distal screw. Anyway it could be

implanted if surgeon desires to prevent

loosening of proximal screw.

Finally surgical skin must be closed. It is

minimally invasive procedure so scar is very

short.

5. Postoperative cares

It is required a period of controlled activity so it is essential that running, jumping, and general

“rough and tumble” with other pets is avoided for the first 6 weeks. It is advisable your pet be

encouraged to take frequent short leash walks.

For proper following of surgical procedure carried out, it is required radiograph exams almost taking

lateral views four and eight weeks after implantation.

6. Support

Do not hesitate to contact with this mail if you have any question related to this surgical procedure:

poroustta@itccanarias.org (phone: 928189613)

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