DOI: https://doi.org/10.52973/rcfcv-luz313.art2

Received: 26/04/2021 Accepted: 15/06/2021

Revista Cientica, FCV-LUZ / Vol. XXXI, N°3, 87 - 92, 2021

ABSTRACT

The Tibial Tuberosity Advancement (TTA) surgical technique is

used in veterinary surgery to limit cranial tibial translation during

canine gait, lengthening the lever arm of the quadriceps in

Anterior Cruciate Ligament-decient (ACL-decient) stie joints.

It is know that after TTA, the patellofemoral pressure decreases,

but the Patellar Tendon (PT) behavior has not been observed

experimentally yet. This study measures the PT force under

caudal femoral drawer at knee exion angles from 135° to 90°

in intact and pathological knee to asses the eect of TTA on the

tendon. Five fresh cadaveric adult canine stie joint were tested

in an apparatus in which muscle forces of the canine hind limb

were simulated. Each knee was tested in three dierent conditions:

intact, ACL-decient and with TTA. PT force was measured using

a electrical transducer. The greater the joint flexion angles,

the greater the PT force. The knee average force of the five

specimens in 90º exion were 28.4 ± 3.2 Newtons (N) for the

intact, 28.2 ± 3.4 N for the ACL-decient and 24.9 ± 2 N for the

TTA knee, which decreased compared to the healthy knee, so

TTA generates a loosening of the PT force. The PT force showed

a fast rate of change in the operated knee because of a shift in

the pattern of knee exion, so the biomechanics of the entire joint

could be inuenced by the TTA technique.

Key words: Tibial tuberosity advancement; patellar tendon; force;

trauma; canine stie joint

RESUMEN

La técnica quirúrgica de avance de la tuberosidad tibial (ATT)

es usada en cirugía veterinaria para limitar la translación craneal

de la tibia durante la marcha canina, alargando el brazo de

palanca del cuádriceps, en articulaciones de rodilla con ligamento

cruzado anterior (LCA) deciente. Es conocido que después a la

intervención de la ATT, la presión patelofemoral disminuye, pero el

comportamiento del Tendón Patelar (TP) aún no ha sido observado

bajo experimentación. Este estudio mide la fuerza del TP bajo una

fuerza femoral caudal a unos ángulos de exión de la rodilla de

135° a 90° en rodilla intacta y dañada para determinar el efecto

de la ATT sobre el tendón. Cinco articulaciones de rodilla canina

refrigeradas fueron ensayadas en un banco de ensayos, en el

cual se simularon las fuerzas musculares de la extremidad trasera

canina. Cada rodilla fue probada en tres condiciones: intacta, con

LCA deciente y con la ATT. La fuerza del TP se midió usando

transductores eléctricos. A mayores ángulos de exión, mayor fue

la fuerza sobre el TP. Las fuerzas medias de las rodillas en los

cinco especímenes en exión de 90º fueron, 28,4 ± 3,2 Newtons

(N) para la intacta, 28,2 ± 3,4 N para el LCA deciente y 24,9 ± 2

N para la ATT, la cual disminuye comparada con la rodilla sana,

lo que muestra que la TTA genera un aojamiento en la fuerza

del TP. La fuerza del TP tiene un porcentaje de cambio mayor en

la rodilla con la ATT, debido a cambios en el comportamiento de

exión de la rodilla, por lo que la biomecánica de la articulación al

completo podría estar inuenciada por dicha técnica.

Palabras clave: Avance de la tuberosidad tibial; tendón patelar;

fuerza; trauma; articulación canina

The eect of Tibial Tuberosity Advancement on Patellar tendon force

in Canine Stie Joint under Caudal Femoral Drawer

Efecto del Avance de la Tuberosidad Tibial (ATT) sobre la fuerza del tendon Patellar en

Articulación de Rodilla Canina bajo Fuerza Femoral Caudal

Elsa Pérez-Guindal* and Marta Musté-Rodríguez

Department of Strength of Materials and Engineering Structures, Universidad Politécnica de Cataluña (EPSEVG-UPC).

Barcelona, Spain. *Email: elsa.perez@upc.edu

The eect of Tibial Tuberosity Advancement (TTA) / Pérez-Guindal and Musté-Rodríguez .____________________________________

INTRODUCTION

Tibial tuberosity advancement (TTA) surgical technique is used

successfully to repair the anterior cruciate ligament (ACL)-decient

stie, one of the most common problem in orthopedics [3, 7]. Anterior

displacement of the tibial tubercle was recommended in humans

by Maquet to reduce pressure and pain in the patellofemoral (PF)

joint in patients with osteoarthritis [10]. In veterinary surgery, the

TTA is used to limit cranial tibial translation (CTT) during canine

gait, lengthening the lever arm of the quadriceps in ACL-decient

stie joints [12, 18]. There are several studies that support the

theoretical foundations of TTA [1, 5, 9, 11], using in vitro models

that measure the CTT.

A decrease in retropatellar pressure after TTA has recently been

demonstrated experimentally in the dog (canis lupus familiaris) [4].

Another recent study evaluated the eects of TTA on the entire

knee joint biomechanics by a nite element model [17]. It found

that PF contact force increased with exion and these contact

force values were smaller with an advance of 2.5 centimetres (cm).

The study also found that not only PF joint, but biomechanics of

the femorotibial (FT) joint were signicantly inuenced by tibial

tubercle elevation. Previous investigations focused on the eect

of TTA on contact pressure at the PF and FT joint [8], but direct

measurements on patellar tendon (PT) force have not been

obtained experimentally in dogs.

The aim of this investigation was to measure the PT force

under caudal femoral drawer at exion angles from 135° to 90°,

and determine the eect of TTA on PT structure and the possible

eects on TF joint biomechanics. An unconstrained canine stie

joint was tested in vitro in three dierent conditions: intact knee,

ACL-decient knee and knee with TTA. PT force was measured

using electrical extensometry. Based on previous literature, PF

forces increase with the knee in exion and the values decrease

with TTA, so it was hypothesized that PT force behaves similarly. It

was expected that the PT force increases with exion and that the

TTA repair technique for ACL-decient knees reduces the PT force.

MATERIALS AND METHODS

Specimen preparation

Five fresh cadaveric right canine knees from adult dogs between

25 to 35 kilograms (kg) body weight were used for this study.

The posterior extremity specimens were extracted preserving the

femoral head, while the tibia was sectioned at its distal third. All

muscular structures were excluded, and the extremities were deep-

frozen at -30 °C immediately afterwards. Initial position of the knee

was at an extension angle of 135°, when CTT occurs during canine

gait [2, 6, 15]. Muscle forces of the canine hind limb in this position

were simulated in accordance with a mathematical model [16].

Since the trials were performed on specimens free of muscles and

tissues, a reduction factor was applied.

A variable force spring attached to the proximal end of the femur

and the top of the patella was used to play the role of the extensor

muscles (FIGS. 1 and 2). The spring was pre-stressed with a force

corresponding to 48 % of the dog’s weight. To recreate the exor

muscles, mostly attached to the Achilles calcaneus tendon, it was

used a constant weight provided by thin plastic cords that were

anchored to the supracondylar tuberosities of the femur with two

3.5 milimeters (mm) threaded screws. The cords ran parallel to

the tibia towards the heel and passed through a pulley system.

The recreated muscle was the Gastrocnemius, the bulkier muscle

with its lateral and medial heads, contributing 29.09 % of the

specimen’s weight (FIG. 1).

FIGURE 1. Testing bench with specimen and musculature

simulators subjected to the caudal femoral force system

at a exion angle

Material-testing machine measurements

The knee specimens were xed to an apparatus designed and

constructed in the laboratory. The distal end of the tibia-bula

of each specimen was introduced in a container with a high

mechanical strength composite to ensure their embedding. The

tibia was bent 30 degrees forward to simulate its position during

canine gait. The container with the tibia was placed on the testing

bench mounting plate with four M6 screws (FIG. 2). In order to

produce the caudal femoral drawer, the distal end of the femur

was perforated using an M5 threaded rod at the top height of the

condyles, and a metal bar was inserted through the holes. A 3-mm

steel sheet adaptor was xed on the metal bar to which the force

sensor was connected. The sensor, in turn, was connected to a

horizontal force applicator metal wire through a pulley (FIG. 1).

The spring force simulating the extensor muscles held the limb

in extension. The upper stop limited the angle of the limb to 135

degrees. The joint was left free for the rest of the knee movements,

so when the shear force was applied the knee exed from the

135° to 90°.

Measuring systems

The devices measuring tibiofemoral shear force and PT force

were force sensors based on electromechanical transducers,

formed by a tension load cell. The device which measure PT was

xed between the spring and the patella (FIG. 2), so it measured

the quadriceps tendon (QT) force. Using a correlation factor, the QT

_____________________________________________________________Revista Cientica, FCV-LUZ / Vol. XXXI, N°3, 87 - 92, 2021

force was transformed into PT force. Nisell [14] observed that the

behavior of both tendons was similar, and that the patellar tendon

was 25 - 30 % thinner and narrower than the quadriceps tendon.

The forces in these tendons at knee angles from 120º to 60º exion

had a relation (PT/QT) of about 0.70 - 0.80 [14]. For canine knees a

relation force of QT/PT = 1.2 was applied, considering that the cross

section area between both tendons is less dierent than in humans.

Transducer

The electrical data were captured and processed by the hardware,

which included a multiplexer and a data acquisition card. The

multiplexer captured the analogue inputs from all the measuring

devices in reading channels. The data acquisition card, converted

the analogue data into digital data in the PC. Finally, the data were

managed by a software designed using the Laboratory Virtual

Instrument Engineering Workbench (LabView) Management

Program. This program was responsible for the reading management

of all channels on the acquisition card, and for displaying and saving

all the generated data in les.

Testing protocol

The rst experiment was performed with the intact stie joint. The

specimen was placed on the testing bench and xed at an angle

of 135º. A tangential force was applied of up to 200 Newtons (N).

The knee exed up to a 90º position, which was measured with a

goniometer. The shear and PT force were registered during exion.

Later, the ACL was sectioned and the trial was repeated with the

same knee. The third experiment was performed after applying

the TTA technique with surgical instruments in the laboratory. An

advance of 9.0 mm was applied to all specimens, as described in

the TTA technique by Montavon and his colleagues [13]. A device

for advancing the tibial tuberosity made of a 316LVM alloy of

stainless steel plate of 1 mm thick was used.

Variable issues

When the caudal femoral force was applied, the knee exed from

135º to 90º exion angles. Since the trial was aimed to assess the

PT behavior under CTT during exion, the knee was left free for this

movement. But only the rst and the last angle positions, which could

be matched with the PT force value, were measured. The rest of the

angles within the range didn’t have a force exact value assigned.

Statistics

A one way analysis of variance ANOVA with ve specimens was

used to compare changes in PT force between intact, ACL-decient

knee and TTA surgery. The condence limits were 95 per cent. A P

value of 0.15 was obtained, so no statistical signicant dierence

between the three groups was observed. This happened because

there were no dierences between intact and ACL-decient knees.

Thus, another analysis between intact and TTA knees was carried

out. A P value of 0.07 was obtained and, therefore, the conclusion

was that the values depended more on whether the knee was

intact or repaired with TTA.

RESULTS AND DISCUSSION

Patellar tendon forces were measured using a tension load

cell. A transducer that measured the spring force which simulated

the quadriceps muscle. Because of the high sensitivity of the

electromechanical transducers, large amounts of data per second

were gathered and highly accurate curves were developed. One

of the disadvantages of strain gauges was their sensitivity to

temperature and moisture, so the trials were performed under

controlled environmental conditions.

Figures from 3 to 7 show the relationship between shear and

PT force in each specimen. TABLE I shows the PT force values

at 90 degrees angle exion, when the values were maximum and

stabilized. The TABLE I also shows the deviation of ACL-decient

and TTA over the intact knee.

PT behavior tests under cranial shear force showed the same

behavior. PT force increased with joint exion angles from 135º

to 90º. The first value in all the specimens of 12.3 N was the

pre-tension in the muscle simulator spring.

The average PT forces of the ve specimens in 90º exion were

28.4 ± 3.2 N for the intact, 28.2 ± 3.4 N for the ACL-decient knee

and 24.9 ± 2 N for the TTA knee (TABLE 1).

The PT force values at 90º in the intact and ACL-decient knee

were very similar. ACL-decient knee was slightly lower than the

intact knee, except knee number 5, which only increased by 7.2 %.

But the values for the TTA knee decreased by approximately 20 %

compared to the healthy knee for specimens 1, 2 and 3. Only knee

No. 4 was slightly higher than the intact knee by 6.2 %. So TTA

tend to diminish the patellar tendon strain. It was also observed

FIGURE 2. Quadriceps tendon force measuring transducer

The eect of Tibial Tuberosity Advancement (TTA) / Pérez-Guindal and Musté-Rodríguez .____________________________________

FIGURE 3. Patellar tendon vs. Femoral force (Newtons)