Influence of limb positioning and measurement method on the magnitude of the tibial plateau angle.
OBJECTIVE
To evaluate the effect of limb positioning and measurement technique on the magnitude of the radiographically determined tibial plateau angle (R-TPA).


METHODS
In vitro study, R-TPA was determined by 6 blinded observers and image measurement software.


METHODS
Five canine cadaver hind limbs.


METHODS
The legs were positioned on a custom-made positioning device simulating a radiographic tabletop technique in lateral recumbency. True lateral positioning was defined by superimposition of femoral and tibial condyles on the radiographic projection. Radiographs were taken while the specimens were relocated in a proximal, distal, caudal, and cranial direction with respect to the radiographic beam. For each specimen, 25 different radiographic views were obtained and 6 blinded observers determined the radiographic TPA using 2 different methods. The conventional method used precise anatomic landmarks to determine the tibial plateau. To simulate osteoarthritic changes complicating identification of these landmarks, the tangential method estimated the tibial plateau as the tangent to the central portion of the tibial plateau. After periarticular soft tissue dissection the anatomic tibial plateau angle (A-TPA) was determined. The A-TPA and the R-TPA were compared.


RESULTS
The R-TPA significantly decreased as limb position with respect to the X-ray beam changed from cranial proximal to caudal distal. The maximal mean radiographic R-TPA difference was 3.6 degrees with the first and 5.7 degrees with the second method. Regardless of the method used there was no significant difference between A-TPA and R-TPA in the true lateral position. In the peripheral positions, however, significant differences between anatomic and radiographic TPA were seen.


CONCLUSIONS
Limb positioning influenced the radiographic appearance of the tibial plateau and the magnitude of the measured TPA. Cranial and proximal positioning of the limb relative to the X-ray beam leads to overestimation whereas caudal and distal positioning leads to underestimation of the TPA.


CONCLUSIONS
True lateral positioning of the tibia defined by superimposition of the femoral and tibial condyles should be used for accurate TPA determination before tibial plateau leveling osteotomy.
Reif
Ullrich
U
Department for Small Animal Clinical Sciences, College of Veterinary Medicine-Michigan State University, East Lansing, MI, USA. ulli@tierklinik-reif.de
Dejardin
Loic M
LM
Probst
Curtis W
CW
DeCamp
Charlie E
CE
Flo
Gretchen L
GL
Johnson
Allen L
AL
D000818:Animals; D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging* / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D002102:Cadaver; D004285:Dogs / Q000293:injuries / Q000601:surgery; D011187:Posture; D011859:Radiography / Q000379:methods / Q000662:veterinary; D012421:Rupture / Q000000981:diagnostic imaging / Q000601:surgery / Q000662:veterinary; D013264:Stifle / Q000000981:diagnostic imaging* / Q000293:injuries / Q000601:surgery; D013977:Tibia / Q000000981:diagnostic imaging* / Q000601:surgery