Page 361 - Canine Lameness

19.5 Patellar uxation 333

(A) (C) (E)

(B) (D) (F)

Figure 19.14 Examples of patients with MPL in two patients. Patient I (A–D) presented with bilateral STIFLE REGION
Grade 2 MPL. Images (A, B) show a displaced patella, minimal joint effusion, and degenerative changes
commonly seen with patellar luxation. Note that there is no radiographic evidence of MPL in images (C, D)
since the patella was located within the trochlear groove at the time of the radiographs. The patient also
had a chronic injury to the (white arrow) lateral head of the gastrocnemius muscle as indicated by
degeneration of the lateral fabella. Patient II (E, F) was diagnosed with CCLD and MPL as indicated by the
more advanced (white arrows) degenerative changes and (black arrow) moderate-severe amount of joint
effusion. These features can be used to raise the index of suspicion for concurrent CCLD but are not
diagnostic. The cranial tibial subluxation on the other hand (note the location of the femoral condyles in
relation to the intercondylar eminence) indicates disruption of the CCL.

correction. Several techniques have been described to measure the femoral varus angle (FVA)
(Dudley et al. 2006; Miles et al. 2015) and precise radiographic positioning is crucial to obtain accu-
rate measurements. Several features have been suggested to determine appropriate positioning,
namely that the patella should be centered within the trochlear groove, the fabellae should be
bisected by the femoral cortices, the lesser trochanter should be partially visible, the proximal
nutrient foramen should be visible in the center of the diaphysis, and the vertical walls of the inter-
condylar fossa should be visible as parallel lines (Jackson and Wendelburg 2012; Kowaleski et al.
2018). To accomplish a true craniocaudal view, the femur needs to be perpendicular to the radio-
graphic beam and parallel to the detector. With modern X-ray equipment, this can be accomplished
by angling the radiographic beam so that it is perpendicular to the femur or taking the radiograph
in lateral recumbency with the beam horizontally. Alternatively, the patient’s body may be elevated
(Figure 19.15). Attempting to obtain a true craniocaudal view via traditional extended femur views
will result in femoral foreshortening and inaccurate femoral varus measurements (Jackson and