hind limb lameness

Correction of hind limb deformities and patellar luxation in a Chihuahua

// Published May 19, 2016 by Admin

A 1.8kg 10 month old female entire Chihuahua was presented for hind limb lameness of several months’ duration. Examination revealed grade III medial patellar luxation on the right and grade IV medial patellar luxation on the left. Radiographs confirmed bilateral medial patellar luxation and showed relatively severe distal femoral varus and compensatory proximal tibial valgus affecting the left hind limb (see figure 1).


Bilateral surgery was performed to address patellar luxation in a single session.

Right stifle:

  • Deepening of the trochlear groove by rectangular block recession trochleoplasty.
  • Realignment of the quadriceps mechanism by tibial tuberosity elevation and lateralisation (fixation with two K-wires and a tension band wire).

Left stifle:

veterinary orthopaedic bone plate

Figure 3. 1.0mm bone plates used in this procedure. The plates were removed following healing of the ostectomies 12 weeks postoperatively.

  • Pre-operative planning using centre of rotational angulation (CORA) technique to measure deformities.
  • Laterally-based closing wedge ostectomy of the distal femur, fixation with a 15-hole 1.0mm cuttable malleable plate and eight 1.0mm screws.
  • Medially-based closing wedge ostectomy of the proximal tibia, fixation with a 7-hole 1.0mm T-plate and seven 1.0mm screws.
  • Deepening of the trochlear groove by rectangular block recession trochleoplasty.


How do we grade patellar luxation?

Patellar luxation is graded according to the position of the patella and its spontaneous reduction or luxation following manipulation (see table below).

  • Grade 1 = patella is usually in the groove, can be luxated with manipulation and will reduce again spontaneously.
  • Grade 2 = patella is usually in the groove, can be luxated and will remain luxated until actively reduced into the groove.
  • Grade 3 = patella is usually luxated, can be reduced but will luxate again spontaneously.
  • Grade 4 = patella is permanently luxated and cannot be reduced.
Patellar luxation grade Usual patellar position Patellar position after manipulation
1 In In
2 In Out
3 Out In
4 Out Out


How do femoral and tibial angular limb deformities affect patellar stability?

The patella functions within the quadriceps mechanism, which may be considered a bowstring with its origin at the level of the proximal femoral diaphysis and its insertion at the tibial tuberosity (see figure 4). If the femoral trochlear groove does not lie along a straight line between these two points, then tension in the quadriceps muscles will act to luxate the patella.

Orthopaedic surgery in Chihuahua

Figure 4. Full limb caudocranial projections showing: (left) distal femoral varus and proximal tibial valgus pre-op and (right) straightened limb post-op. Red line= location of quadriceps mechanism, green circle= location of patella.

Author: Phil Witte BVSc, BSc, CertAVP, MRCVS

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