The CrCL is an integral stabilizing structure of the stifle joint in dogs.1,2 Complete CrCL rupture, a common orthopedic condition affecting dogs, results in marked craniocaudal instability of the stifle joint. Cranial subluxation of the tibia relative to the femur occurs consistently during weight bearing.1,2 This femorotibial shearing motion results in progressive osteoarthritis, impingement and damage of the menisci, and subsequent lameness associated with CrCL insufficiency2,3
Obtaining accurate measurements of the degree of subluxation aids with detection of CrCL rupture.4 Definitive diagnosis of CrCL insufficiency, however, typically relies on the ability to elicit craniocaudal instability on direct palpation.5 Several specialized stress radiographic techniques that produce cranial translation of the tibia have been described for objective documentation of joint laxity.4,6,7 These techniques involve the use of external compressive translational devices or performing the tibial compression test during radiography.4,6,7 Quantification of the magnitude of cranial tibial translation is performed by calculating the relative displacement of osseous landmarks on lateral radiographic views of the stifle joint before and after inducing subluxation. For example, translation has been described according to the displacement of the caudal femoral condyles, or long digital extensor fossa, along a plane parallel to the tibial plateau.6,7 Quantification of cranial tibial translation can be performed by use of radiopaque markers placed in each bone, but this requires invasive, surgical implantation when used in vivo.
The femorotibial joint is not a simple hinge joint; rather, the femoral condyles have an elliptic contour and sagittal plane femorotibial motion adopts a complex roll-and-glide pattern.8 As such, the stifle joint does not have a single instant center of rotation and it is not known whether all of the reported means of obtaining static radiographic measurements of sub-luxation would be valid at various stifle joint flexion angles. Unless the stifle joint flexion angle remains consistent, these previously reported methods may not accurately measure normal or abnormal cranial tibial translation. Further, tibial osteotomies for the treatment of CrCL insufficiency impart functional stability by altering the geometry of the proximal aspect of the tibia.9 Procedures such as TPLO cause a relative shift of certain osseous landmarks, which may preclude accurate comparisons of femorotibial alignment before and after surgery.
The location of the origin and insertion of the CrCL are considered isometric; that is, the distance between these points does not change substantially throughout a range of motion.10–12 Increases in the CrCLd, regardless of stifle joint flexion angle, may therefore indicate either femorotibial joint distraction or, more likely, cranial tibial translation. We were interested in developing a clinically applicable method to evaluate the efficacy of surgical procedures in resolving cranial tibial sub-luxation in dogs with CrCL insufficiency by assessing CrCLd. The objectives of this study were to determine whether the origin and insertion of the CrCL could be repeatedly and accurately identified on mediolateral projection stifle joint radiographs and to determine the influence of stifle joint flexion angle, CrCL integrity, cranial tibial subluxation, and TPLO on CrCLd. We hypothesized that the femoral and tibial attachment sites of the CrCL could be easily and precisely identified on mediolateral projection radiographs throughout a wide range of stifle joint motion. We also hypothesized that stifle joint flexion angle, transection of the CrCL (with the stifle joint maintained in reduction), and treatment with TPLO would not alter the CrCLd, whereas induced cranial tibial subluxation would significantly increase the CrCLd.
Cranial cruciate ligament
Distance between the origin and insertion of the cranial cruciate ligament
Tibial plateau leveling osteotomy
3.5 mm cortical bone screw, Synthes USA, Paoli, Pa.
PDS, Ethicon Inc, Somerville, NJ.
Tension spring, Hillman, Cincinnati, Ohio.
Medium SCAT pin, Imex Veterinary Inc, Longview, Tex.
DICOM, NEMA, Rosslyn, Va.
Kodak Directview 5.2, Carestream Health, Rochester, NY.
2-mm stainless steel ball bearings, McMaster-Carr Supply Co, Cleveland, Ohio.
Sigmastat, SPSS Inc, Chicago, Ill.
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