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Tibial Valgus in an 18 month old Romanian Shepherd Dog
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Davies Aidan P61671 TIBIA Tibia Caudo cranial 19 02 2021 14 10 06 490

The patient is a neutered male Romanian Shepherd dog who was rescued from Romania by the owner six months prior to presentation. The owner was informed the patient had suffered a fracture following an RTA prior to arrival in the UK which is strongly believed to be the cause of the angular limb deformity. The patient had been managing with the deformity well, however he had deteriorated rapidly prompting the requirement for assessment.

Proximal tibial physis closure times are around 9-10 months in dogs. Significant trauma to the physis prior to this age can result in premature arrest of the endochondral ossification process resulting in either a shortened limb or, where physis damage is incomplete, an angular deformity arising from asymmetrical growth as is assumed to be the case in this patient.

The referring veterinary surgeon carried out orthogonal radiography of both tibia. The frontal plane view (caudo-cranial projection) revealed a valgus deformity of the proximal tibia, the hock deviating laterally relative to the stifle.

These changes are consistent with the presumed early closure to the lateral aspect of proximal tibial physis prior to growth arrest.

Optimal evaluation of these three-dimensional deformities is through computed tomography (CT) and there is the option of making 3D printed custom built saw guides to facilitate treatment of these cases. CT was not a feasible option with this case and planning was performed based on radiography and using VPOPPro planning software.

Planning:

The deformity was evaluated by measuring the mechanical medial proximal tibial axis (mMPTA) (117 degrees). The location and magnitude of the wedge of bone to remove from the medial aspect of the proximal tibia was calculated to correct the mMPTA to the reference angle of 93 degree. The optimal site of bone removal (the CORA) to achieve correction without any translation was very close to the patella tendon insertion. Practically removing bone this proximally would have increased risk of a post operative fracture due to limited bone stock for plate insertion. As a result the osteotomy was moved distally, wedge magnitude increased slightly to account for this move and the minor translation accounted for by lateralising the proximal fragment slightly during reduction following wedge ostectomy.

Definitions:

Mechanical axis: The axis between the centre of the joints at either end of the bone. For the tibia this is between the intercondylar eminence proximally and centre of the talar ridges distally.

mMPTA: The mechanical medial proximal tibial angle. The reference for this can be obtained from a normal contralateral image or from the literature the mean angle in normal Labradors is 93 degrees (Dismukes et al, 2007)

CORA: Centre of rotation and angulation. The point at which it is optimal to correct the angulation deformity and is derived from the human surgeon Paley’s work on defining terms and laws to facilitate planning of angular deformities.

Treatment:

A routine general anaesthetic was administered. Local regional anaesthesia and systemic multimodal analgesia were administer along with intravenous antibiosis 30 minutes prior to incision and every 90 minutes thereafter until completion of surgery.

A medial approach to the proximal tibia was performed with exposure of the tibia facilitated by elevation of the pes anserinus and the cranial tibial muscle. The location of osteotomy was measured from anatomical markers of the patella tendon insertion and the proximal joint surface, this ostectomy location was marked using diathermy and a bone scribe. A wedge gauge was also used to confirm the angle and magnitude of the bone being removed. A TPLO jig was pre-placed above and below the osteotomy using 2.5mm pins placed in a cranial to caudal orientation.

An oscillating saw was then used to cut the wedge of bone with the assistant guiding the cut and rechecking magnitude and orientation based on the pre-measured values. On completion the wedge was removed and the bone fragments reduced and aligned using the TPLO jig and point to point forceps across the jig pins.

A medial 3.5mm locking TPLO plate and a caudo-medial 2.7mm dynamic locking plate were placed to stabilise the osteotomy.

Radiography confirmed adequate bone apposition and resolution of tibial vagus.

Outcome

After six weeks of controlled, restricted exercise radiography confirmed progression of healing at the osteotomy site. The patient then underwent a period of gradually increasing exercise over the following six weeks.

Lameness and limb function improved significantly and the owner reports now, 12 months following surgery, that the patient is using the leg normally with no indication of discomfort.


References:

Dismukes DI, Tomlinson JL, Fox DB, Cook JL, Song KJ. Radiographic measurement of the proximal and distal mechanical joint angles in the canine tibia. Vet Surg. 2007 Oct;36(7):699-704. doi: 10.1111/j.1532-950X.2007.00323.x. PMID: 17894597.