Biomechanics of the Cranial Cruciate Ligament-Deficient Stifle Treated by Tibial Osteotomies 273(A) (B)Figure 32.1 Slocum theorized that, during weight-bearing, the joint reaction force (magenta arrow) is approximately
parallel the longitudinal axis of the tibia. In the cranial cruciate ligament-deficient stifle (A), the joint reaction force can
be resolved into a cranially directed tibiofemoral shear component (parallel to tibial plateau) and a joint-compressive
force (perpendicular to tibial plateau). By leveling the tibial plateau (B), the joint reaction force is perpendicular to the
tibial plateau, and thus can only be resolved into a joint-compressive force; cranial tibial thrust is eliminated. Source:
Kimet al. 2008. Reproduced with permission from John Wiley & Sons, Inc.
presenting with early partial CR (Hulseet al.
2010).
The integrity of the CaCL must be assessed
at the time of arthrotomy or arthroscopy before
performing TPLO. In the authors’ experience,
CaCL abnormalities of varying severity can
occur concurrently with CR (see also Chap-
ter 17). The underlying cause of CaCL degener-
ation and rupture is also unknown, but it may
be secondary to osteoarthritic change, or due to
the same pathologic processes that causes CrCL
fiber damage and rupture. TPLO increases
loads on the CaCL during weight-bearing
(Warzee et al. 2001), which may accelerate
any pre-existing CaCL degeneration postopera-
tively. While rare, complete rupture of the CaCL
has been documented (Slocum & Slocum 1993).
This complication will result in severe stifle
instability. Hence, CaCLabnormalities may pre-
clude the use of TPLO in CrCL-deficient stifles.
Another biomechanical theory argues that
the tibia is not axially loaded as proposed by
Slocum. Rather, Tepic suggests that the total
femorotibial joint forcesin vivoare directed par-
allel to the patellar tendon (Tepicet al. 2002).
Cranial tibial thrust, according to this model,
is then dependent on the angle between the
tibial plateau and the patellar tendon (Fig-
ure 32.2). This model also predicts that cra-
nial tibial translation should not occur when a
CrCL-deficient stifle is flexed beyond 90◦.The
role of the flexion angle in stifle biomechanics
has been investigated inex vivostudies. As the
joint approaches 90◦of flexion, the quadriceps
mechanism becomes a stabilizer and effectively
unloads the CrCL by pulling the tibia caudally
(Pozziet al. 2008; Kimet al. 2009b). Likewise, tib-
ial tuberosity advancement aims to impart func-
tional stability by moving the patellar tendon
angle to approximately 90◦when the stifle is