INTRODUCTION

The main function of the cranial cruciate ligament isto prevent cranial displacement of the tibia (tibialthrust) and hyperextension of the stifle joint. It alsoplays a role in preventing internal rotation of the tibiaand is aided in this function by the collateralligaments and the caudal cruciate ligament(Arnoczky, 1993). Rupture of the cranial cruciateligament (CRCL) is a common cause of hind limblameness in the dog, which leads to instability of thejoint (Johnson & Johnson, 1993).

The term cranial cruciate ligament-deficient stifle isused here because there is a wide variation ofpathology, which may range from a partial to acomplete tear of the ligament. Over the yearsnumerous surgical techniques have been described totreat the CRCL-deficient stifle (Moore & Read,1996). These techniques all aim to stabilise the joint,which can be done statically or dynamically.Examples of static stabilisation of the joint are the‘over the top’ technique and the tibio-fabellar suture(Lampman et al., 2003). Examples of dynamicstabilisation include the Tibial Plateau LevellingOsteotomy (TPLO) and the Tibial TuberosityAdvancement Technique (TTA) (Slocum & Devine,1983, Tepic et al., 2002).

BIOMECHANICS

Introduction

In humans most ruptures of the CRCL are traumaticwhereas in our canine patients CRCL deficiency istypically associated with a history of progressivelameness consistent with a degenerative process.There is still considerable controversy with regard tothe aetiology and pathogenesis of the condition butweakening, secondary to repetitive microtrauma, isbelieved to cause the majority of CRCL instabilitiesin dogs, especially in the larger breeds (Hayashi et al.,2003). In 1983 Slocum and Devine found that thelikely underlying cause for this repetitivemicrotrauma to the CRCL was the cranial tibialthrust and this provided the basis for the TibialPlateau Levelling Osteotomy (TPLO).

Cranial tibial thrust

Knowledge of the forces that act within the stiflejoint is important to understand the pathogenesis ofCRCL disease as well the rationale behind the TTAtechnique.

During weight bearing there is a forward translationof the tibia (tibial thrust) in relation to the femur.This is because the tibial plateau is oriented in acaudodistal direction. Most dogs have a tibial plateauangle of approximately 22-26º. In the normal patienttibial thrust is counteracted by passive and activerestraints. The passive restraints are the CRCL andthe menisci, whereas the active restraints are theflexor muscles (Fig. 1).

Rationale behind the TTA procedure

Tepic et al., (2002) found that the total joint force inthe stifle is approximately parallel to the patellarligament. They also found that if the angle betweenthe tibial plateau and patellar ligament is 90º, there isno shear component of the total joint force andtherefore no strain on the cranial cruciate ligament.This is the situation when the stifle is held in 90º offlexion. This point is called the cross-over point. Infull extension the angle between tibial plateau andpatellar ligament is approximately 105º and thecranial cruciate ligament is loaded. In full flexion theangle is 70º and the caudal cruciate ligament isloaded (Fig. 2).

SMALL ANIMAL ● SURGERY ★★UK Vet - Vol 14 No 4 May 2009 1

Joachim Proot CertSAS MRCVSCALDER VETERINARY GROUP, SAVILE ROAD, DEWSBURY, WEST YORKSHIRE. WF12 9LN

Tibial tuberosity advancement techniquefor the stabilisation of the cranial cruciateligament-deficient stifle joint

Fig. 1: Tibial plateau angle, joint forces and tibialthrust of the canine hind limb during weight bearing.

is less versatile then the TPLO technique. On theother hand the TTA technique is less prone tounintended angular limb deformities.

PRE-OPERATIVE PLANNING

The TTA technique involves an osteotomy in thenon-weight bearing portion of the tibia just behindthe tibial tuberosity. The tibial tuberosity is advancedcranially to achieve a 90º angle between the patellarligament and the tibial plateau (see above). Theadvanced tibial tuberosity is secured in place using atitanium cage and screws and a titanium bone plate.The plate is held in place with a fork and bonescrews (Fig. 4).

The plate acts as a tension band plate. The cagedefines the advancement of the tibial tuberosity andcurrently cages ranging from 3 mm to 12 mm inwidth are available. Plate sizes range from 2 hole to8 hole plates which corresponds to the size of thetibial tuberosity (Fig. 5).

The rationale behind the TTA procedure is that inthe cranial cruciate deficient stifle we can move thecross-over point to full extension and therefore wenever reach an angle that would result in loading ofthe cranial cruciate ligament. In other words, if theangle between the tibial plateau and the patellarligament can never exceed 90º then the cranialcruciate ligament will never be loaded. There are twoways of achieving this: the TTA technique moves thetibial tuberosity cranially to the point where thepatellar ligament is perpendicular to the tibialplateau and the TPLO technique rotates the tibialplateau by making a radial cut in the proximal tibia(Fig. 3).

ADVANTAGES AND DISADVANTAGES

OF THE TTA TECHNIQUE

Both the TTA and the TPLO technique haveadvantages and disadvantages. The main advantage ofthe TTA technique is that it is technically easier toperform. The technique is also less invasive then theTPLO technique as the osteotomy is made in a non-weight bearing part of the tibia. The maindisadvantage of the TTA technique is that angularlimb deformities cannot be corrected and therefore

SMALL ANIMAL ● SURGERY ★★ UK Vet - Vol 14 No 4 May 20092

Fig. 2: In full extension the angle between tibialplateau and patellar ligament is 105º and the cranialcruciate ligament is loaded. In full flexion the anglebetween the tibial plateau and patellar ligament is 70ºand the caudal cruciate ligament is loaded.(Photograph courtesy of S. Tepic, Kyon®).

Fig. 5: TTA implants. (Photograph courtesy of S.Tepic, Kyon®).

Fig. 3: In essence the TTA technique and the TPLOtechnique have the same end result. This is thesituation where the angle between the patellarligament and the tibial plateau is 90º. The TTAtechnique achieves this by moving the tibial tuberositycranially and the TPLO technique by making a radialcut in the proximal tibia and rotating the tibia.(Photograph courtesy of S. Tepic, Kyon®).

Fig. 4: With a frontal plane osteotomy the tibialtuberosity is advanced cranially and secured with acage and tension band plate. The plate is attached tothe tibial tuberosity with a titanium fork. The plate issecured to the diaphyseal tibia with two titaniumbone screws.

To perform the procedure, standardised TTAinstruments are necessary. The use of theseinstruments will be described in the next articlecovering the surgical technique (Fig. 6).

Standard craniocaudal and lateral radiographs of theaffected stifle are obtained with a stifle joint angle ofapproximately 135º. The joint is positioned so thatthere is no cranial tibial translation. Pre-operativelythree measures need to determined: (a) the size ofthe cage, (b) the size of the plate and (c) the positionof the osteotomy relative to the tibial tuberosity. Forthis the TTA transparency is used (Fig.7).

a. The size of the cage

The advancement guide of the standardized TTAtransparency (Kyon®) is used to determine thesize of the cage (Fig. 8). The horizontal line ofthe advancement guide goes through the cranialand caudal margins of the tibial plate andrepresents the orientation of the tibial plateau.The vertical line of the guide represents thepatellar ligament and is drawn through thecranial border of the patella. The vertical parallellines on the bottom of the guide nowcorrespond to the amount of tibial tuberosityadvancement required (Fig. 8) and thus thewidth of the cage.

b. Choosing the size of the plate

The same TTA transparency is used to determinethe size of the tension band plate by overlyingthe template over the lateral radiograph. Theproximal plate is positioned just caudal to thetibial tuberosity. It is important to remember thatthen when the tibial tuberosity is advancedcranially the distal plate will rotate caudally. Thelocation of the distal plate should be centred overthe tibial shaft (Fig. 9).

SMALL ANIMAL ● SURGERY ★★UK Vet - Vol 14 No 4 May 2009 3

Fig. 6: Standardised TTA instruments (Kyon).(Photograph courtesy of S. Tepic, Kyon®).

Fig. 7: Standard TTA transparency. (Kyon®).

Fig. 8: The advancement guide of the transparency isplace on the lateral radiograph of the stifle todetermine the width of the cage. In this case a 6 mmcage was selected.

Fig. 9: The transparency is used to determine the sizeof the cage. In this case a 5 hole plate was chosen.

c. The position of the osteotomy

The osteotomy of the tibial tuberosity is performedfrom a point just cranial to the medial meniscusand cranial to the long digital extensor tendon tothe distal extent of the tibial crest (Fig. 10).

In a future article the surgical technique will bedescribed as well as the postoperative care andcomplications.

REFERENCES

ARNOCZKY, S. P. 1993. Pathomechanics of cruciate and meniscal

injuries. In: Disease Mechanisms in Small Animal Surgery. Ed M.J.

Bojrab. pp. 764-777. Lea and Febiger, Philadelphia, PA, USA.

HAYASHI K., FRANK J. D., DUBINSKY C. (2003) Histologic changes

in ruptured canine cranial cruciate ligament. Veterinary Surgery 32,

269-277.

JOHNSON, K. A. and JOHNSON, A. L. (1993) Cranial cruciate

ligament rupture. Pathogenesis, diagnosis, and post-operative

rehabilitation. Veterinary Clinics of North America: Small Animal

Practice 23, 717-733.

LAMPMAN, T. J., LUND, E. M. and LIPOWITZ, A. J. (2003) Cranial

cruciate disease: current status of diagnosis, surgery and risk of

disease. Veterinary and Comparative Orthopaedics and Traumatology

16, 122-1263.

MOORE, K. W. and READ, R. A. (1996) Rupture of the cranial cruciate

ligament in dogs-part II. Diagnosis and management. Compendium of

Continuing Education for the Small Animal Practitioner 18, 181-191.

SLOCUM B. and DEVINE T. D. (1983) Cranial tibial thrust: a primary

force in the canine stifle. Journal of the American Veterinary Medical

Association 183, 456-459.

TEPIC, S., DAMUR, D. M. and MONTAVON, P. M. (2002) Biomechanics

of the stifle joint. In: Proceedings of the 1st World Orthopaedic

Veterinary Congress. Munich, Germany. September 5 to 8, pp. 189-

190.

SMALL ANIMAL ● SURGERY ★★ UK Vet - Vol 14 No 4 May 20094

Fig. 10: The position of the frontal osteotomy.