Tibial Plateau Angle—How to Measure It & Why You Need to on Your Cruciate Ligament Patients
Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA
I recommend measuring tibial plateau angles (TPA—Fig 1) on all patients prior to surgery regardless of the stabilizing procedure being performed. Unpublished data have shown that the strain on the CrCL increases as the TPA increases (Hulse DA 2009). It is logical then that extracapsular sutures (“ExCap”) would be under progressively higher strain as the TPA increases. High strain upon the ExCap suture could increase the risk of premature suture stretching or breakage. While one study showed that TPA did not affect the outcome of ExCap stabilization treatment, that study did not look at dogs with TPA >34°. I currently recommend that ExCap suture stabilization be avoided in dogs when the TPA exceeds 30°.
In order to properly position a patient for radiographic measurement of TPA, I advise heavy sedation or general anesthesia. The patient is the placed in lateral recumbency with the limb of interest in the ‘down position’. The radiographic objective is to obtain a perfect medio-lateral radiograph of the entire tibia, but with the radiographic beam centered upon the stifle. It is important that the hip, stifle and tarsus each be resting upon the same surface (or at least resting at the same level) in order to avoid rotating the tibial out of the perfect medio-lateral orientation, Next, the “up” leg is pulled forward via hip flexion—the movement of this limb in the sagittal plane will help preserve the perfect mediolateral position of the ‘down’ tibia. In contrast, abduction of the upper limb tends to pull the ‘down’ limb out of the perfect medio-lateral position. Finally, remember to center the radiographic beam upon the stifle, but collimate it to include the talus (Fig 1). When properly positioned, the radiograph should show the intercondylar tubercles of the proximal tibial (collectively referred to as the “tibial eminence”) arising from a “horizon” created by the superimposed medial and lateral tibial plateau surfaces.
(VIN editor: Figure not available)