If the stifle is locked in full extension and is properly positioned (the patella is superimposed in the center of the distal
femur and the fabellae are bisected by their respective femoral cortex), then the medial margin of the tuber calcis should
be superimposed on the center of the distal tibia (Figure 3B). Medial or lateral deviation of the tuber calcis from this location indicates external or internal tibial torsion, respectively.
The position of the fibular head with respect to the stifle articular surface on radiographs is correlated with palpation
to help direct placement of the most proximal jig pin and subsequent proximal screws.
Figure 3B. A caudocranial radiograph showing the proper position of the stifle. Note the corresponding position of the medial
margin of the tuber calcis on the center of the distal tibia, suggesting the absence of internal or external tibial torsion.
Training and instrumentation
Many complications reported with this technique are related directly or indirectly to surgeon error.14-16 I developed experience with the technique in more than 700 procedures performed in private specialty practice and, then,
mentored surgical residents as they gained expertise with TPLO in a university veterinary teaching hospital. The skills to
expertly perform this technique consistently cannot be developed without solid orthopedic surgical skills, procedure-specific
training, and an ongoing mentor relationship with a surgeon experienced in performing TPLOs. Aside from an extensive investment
of time into training and mentoring, TPLO requires a considerable financial investment for surgical instrumentation. Necessary
instruments include high-quality surgical lighting, suction and cautery equipment, a power drill, appropriate plating instruments
and screw inventory, an osteotome and mallet, precision calipers, an array of retractors, and TPLO-specific components including
a TPLO saw, saw blades, saw blade sharpeners, jigs, a drill guide, and implants. These combined training and instrumentation
investments, in addition to increased operative time and complexity, account for the increased cost of this procedure compared
with more traditional treatments.
The affected hindquarter is shaved from the dorsal and ventral midlines to the mid-metatarsus, and the patient is positioned
in dorsal recumbency. The foot is wrapped routinely; the wrap is kept distal to the hock so that the talocrural joint can
be fully flexed and extended. The surgeon evaluates limb alignment and correlates palpation observations to the preoperative
radiographs. Routine hanging limb preparation and surgical draping are then performed.
A craniomedial approach to the stifle and proximal tibia is used. The surgeon makes a fascial incision starting between the
sartorius muscle bellies proximally, extending distally through the tendinous insertion of the pes anserinus muscle group
(caudal belly of the sartorius, gracilis, and semitendinosus muscles) about 6 to 10 mm caudal to the cranial margin of the
tibial crest. At the distal end of the tibial crest, the fascial incision shifts to the cranial midline of the tibia to release
the medial border of the cranial tibial muscle. Starting at the distal end of the surgical field, the surgeon lifts the semitendinosus
muscle from the medial tibial surface to reveal the firm insertions of the gracilis and sartorius muscles on the medial aspect
of the tibial crest. The shiny white insertion of the medial collateral ligament is visualized. The surgeon sharply incises
the insertions of the gracilis and sartorius muscles, using care to protect the medial collateral ligament. Care is also used
to preserve the pes anserinus muscle group layer as it is sharply incised from the underlying joint capsule.
Arthrotomy and meniscal procedures
Next, a medial parapatellar arthrotomy is performed routinely, and the cranial and caudal cruciate ligaments, medial and lateral
menisci, long digital extensor tendon, synovial lining, and joint cartilage are evaluated. The cranial cruciate ligament is
débrided as appropriate. Placing a small Hohmann retractor between the caudal cruciate ligament and the tibial plateau facilitates
visualization of the menisci while protecting the caudal cruciate ligament from inadvertent laceration.