Advances in the Canine Cranial Cruciate Ligament, 2nd edition

194 Surgical Treatment

Isometry

Isometry refers to maintaining the same dis-
tance between the attachment sites of the sta-
bilizing suture over a range of motion, and is
a critical concept for ES as well as other types
of CrCL repair. The femoral and tibial suture
attachment sites should be as isometric as pos-
sible in order to minimize the impact on sti-
fle range of flexion–extension motion and min-
imize stress on the suture and soft tissue or
bone attachments (Figure 25.5). Suture attach-
ment sites at the lateral caudodistal femur and
the lateral cranioproximal tibia should create
a suture trajectory that roughly mimics that of
the CrCL in the sagittal plane. Theoretically, the
use of isometric points should maximize the

Figure 25.5 Anatomic illustration showing points that
are most isometric on the lateral aspect of the canine
stifle, according to Hulseet al.(2010). Copyright©
Samantha J. Elmhurst at http://www.livingart.org.uk.

functional life span of the implant. However,

due to the complex shapes and motions of

the dog’s stifle joint, perfect isometry is not

achievable with extra-articular attachment sites

(Arnoczkyet al. 1977; Fischeret al. 2010; Hulse

et al. 2010).

Numerous studies have attempted to deter-

mine the optimal tibial and femoral ES attach-

ment points based on isometry, but resultant

recommendations vary widely (Roeet al. 2008;

Fischeret al. 2010; Hulseet al. 2010; Witte

2015). In two studies, measures of isometry

were based on the distance between the pro-

posed suture attachment sites on radiographs

as the limb was moved through a range of

flexion–extension motion (Roeet al. 2008; Witte

2015). Unsurprisingly, isometry was not achiev-

able, but the most isometric points were deter-

mined to be: (i) caudolaterally on the femur

at the level of the distal aspect of the lateral

fabella; and (ii) cranial and proximal on the

tibia between the tibial tuberosity and the exten-

sor groove (Roeet al. 2008; Witte 2015). Small

changes in the femoral attachment site had a

greater effect on distance between attachment

points than small changes in the tibial attach-

ment site (Roeet al. 2008). Twoex vivostud-

ies have been performed where suture tension

was tested throughout a range of flexion–

extension motion, where smaller changes in

suture tension were interpreted as a higher

degree of isometry. In one study, a circumfabel-

lar suture was recommended that then passed

through two bone tunnels just caudal to the tib-

ial tuberosity (Fischeret al. 2010), while a sec-

ondex vivostudy recommended anchoring the

suture in the femoral condyle at the level of

the distal aspect of the lateral fabella and in the

bony prominence of the tibia just caudal to the

extensor groove at the level of the tibial plateau

(Hulseet al. 2010). Due to variations of con-

formation, the most isometric points are likely

variable between breeds and individuals within

a breed (Witte 2015).

Methods of securing the suture to the

femur and tibia

The suture can be secured at the femoral and tib-

ial attachment sites in various ways. At either

site, the suture can be anchored to the bone