Osteoarthritis (OA) is thought to develop and progress secondary to rotational and translational instability within the stifle joint after cranial cruciate ligament (CCL) rupture. Cranial tibial subluxation (CTS) is typically detected during physical examination with the tibial compression test. The development of a repeatable radiographic technique for assessing CTS in vivo was investigated to determine radiographic landmarks present in dogs with OA and test their repeatability for assessing CTS in a cadaver. The effects of radiopaque markers and digital radiographic magnification on the repeatability of CTS measurement were also assessed.

Radiographs of CCL rupture and degrees of OA were used to determine landmarks for CTS measurement. CTS was then induced in cadaver and mediolateral radiographs taken. Measurements were made to determine repeatable landmarks for CTS. Twenty cadaver stifles were used and 8 anatomic CTS measurements evaluated. Accounting for inter- and intraobserver variability, CTS in the normal nonosteoarthritic stifle can be quantified most reliably by measuring from the caudal aspect of the intercondylar fossa on the femur to the intercondylar eminence on the tibia. CTS is secondarily most reliable when measuring from the caudal aspect of the intercondylar fossa to the cranial tibial or caudal tibial plateau. Apparently, magnification does not affect measurement reliability.

Commentary
This experiment evaluated normal cadaver stifles to determine the most reliable landmarks for measuring the length of cranial translation or drawer after CCL transection. On radiographs, measuring the distance between the caudalmost extent of the intercondylar fossa (just distal to the fabellae on a lateral image) of the femur and the intercondylar eminence of the tibia was the most reliable. 

These results are useful for future in vitro studies evaluating the amount of drawer with varying CCL surgical repair procedures. The next logical step is determining reliability of these landmarks in stifles with OA changes for use in clinical cases.—Jonathan Miller, DVM, MS, DACVS

Source
Radiographic landmarks for measurement of cranial tibial subluxation in the canine cruciate ligament deficient stifle. Plesman R, Sharma A, Gilbert P, et al. VET COMP ORTHO TRAUMATOL 6:478-487, 2012.