27

Tibial Plateau Leveling

Osteotomy

Susan L. Schaefer

Introduction

Tibial plateau leveling osteotomy (TPLO) was
first described in 1993 by Slocum to address sti-
fle instability due to cruciate ligament rupture
(CR) (Slocum & Slocum 1993). By decreasing
the natural caudodistal orientation of the tib-
ial plateau, TPLO limits the shear force gener-
ated by compression of the stifle during weight-
bearing, thereby abating cranial tibial thrust
(Reifet al. 2002). The dynamic stability imparted
to the cranial cruciate ligament (CrCL)-deficient
stifle via TPLO is achieved by performing a
radial osteotomy of the proximal tibia and rotat-
ing the proximal segment to decrease the tibial
plateau angle (TPA) (Figure 27.1).
Preoperative determination of the patient’s
TPA allows calculation of the magnitude of
rotation necessary to achieve a desired post-
operative TPA. The minimum amount of rota-
tion required to neutralize cranial tibial thrust
results in a postoperative TPA of 6.5±0.9◦.Fur-
ther rotation increases strain on the caudal cru-
ciate ligament (CaCL); rotating from 6.5◦to 0◦
increases CaCL strain by 37.7±17.4% (Warzee
et al. 2001). While convention dictates measur-
ing and changing the TPA, more recent studies
have evaluated the patella tendon angle (PTA)
change seen in TPLO. After TPLO, the PTA

measures around 90◦in bothex vivoand clinical

situations (Drygaset al. 2010; Sathyaet al. 2014).

This finding suggests that the biomechanics of

TPLO may be similar to that of tibial tuberos-

ity advancement (TTA). It is important to note

that the TPLO procedure itself only addresses

dynamic stifle instability. Therefore, an inspec-

tion of intra-articular structures with appro-

priate treatment of meniscal injuries or other

abnormalities must accompany the procedure.

An excellent review of the proposed mecha-

nism of action for TPLO is available (Boudrieau

2009).

TPLO technique

The magnitude of rotation planned preop-

eratively generally correlates well with the

realized postoperative TPA result (Windolfet al.

2008). However, achieving an accurate TPA

measurement and executing the osteotomy and

tibial rotation in a manner to accurately achieve

the desired postoperative TPA without inad-

vertently creating angular or rotational limb

deformities involves a complex interplay of fac-

tors. Intra- and interobserver variability in TPA

assessment has the potential to influence preop-

erative planning and subsequent postoperative

Advances in the Canine Cranial Cruciate Ligament, Second Edition. Edited by Peter Muir. © 2018 ACVS Foundation.
This Work is a co-publication between the American College of Veterinary Surgeons Foundation and Wiley-Blackwell.

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