OTA 1999 Posters

The Measurement of Tibial Malrotation Using CT Scanning following IM Tibial Nailing: A Cadaver Study

Emmanuel Tolessa; Hans J. Kreder, MD; David Stephens; Joel Rubenstein, Sunnybrook & Women's College Health Sciences Ctr., Toronto, ON, CANADA

Objective: To identify tibial landmarks that will allow the measurement of tibial malrotation following fracture fixation, including IM tibial nailing.

Design: Human cadaver experiment.

Methods: 10 embalmed human cadaver tibiae were obtained and subjected to intact CT scanning. A series of 5 contiguous axial CT images (3 mm in thickness) were obtained through the proximal and distal tibia. Based on these intact scans, landmarks that could be consistently identified by the two radiologists were noted proximally and distally.

Following this initial investigation, the tibial specimens were then assigned to a random amount of rotational deformity between 90 degrees of internal and 90 degrees of external rotation. An osteotomy over an IM nail was used to impose the assigned rotational deformity. Intra-cortical fixation with K- wires prevented displacement of the osteotomy during CT scanning (only proximal and distal). A second rotational deformity was then randomly assigned such that all previously internally rotated specimens underwent external rotation, and vice versa. An independent technician who was not associated with the study performed the CT scans. The CT scans were evaluated separately by two radiologists without knowledge of the imposed direction or magnitude of rotational deformity. Repeat measurements were performed by one of the radiologists (in blinded fashion).

Statistical Analysis: The imposed rotational deformity was considered the gold standard. Inverse regression analysis according to the method of Draper and Smith was used to quantify the magnitude of discrepancy between the gold standard and the CT measurement by each rater. The intraclass correlation coefficient was used to quantify inter- and intra-rater consistency.

Results: In the preliminary study it was possible to identify a proximal landmark at the level of the groove for the insertion of the posterior cruciate ligament such that a tangential line could be drawn across the posterior margin of the tibia at this level. Distally a line could be drawn across the straight portion of the posterior margin of the tibia at the level of the groove for the tibialis posterior tendon. By erecting perpendiculars to the proximal and distal lines, an angle could be generated to describe the relationship between the proximal and distal tibia. The distal landmark was externally rotated compared to the proximal landmark for all intact specimens by an average of 31.7 degrees (range 23 to 46 degrees).

The CT measurements differed from the actual rotational deformity by a mean of ­1.6 degrees (95% CI ­5.4 to +2.2 degrees). Inter-rater agreement regarding the rotational deformity was high as measured using the intraclass correlation coefficient (0.97), as was intra-rater agreement (0.98).

Conclusions: A tool has been developed to enable the quantification of rotational malalignment following tibial fracture fixation using CT landmarks at the proximal and distal tibia. The method would only be applicable to fractures not extending into the regions of the landmarks (within 1cm. of either joint). Since there is a range of "normal" values for the relationship between the two landmark lines, the opposite side should be used as a control if possible when quantifying rotational malalignment. It is not known at this time whether differences between sides exist with respect to the landmarks identified in this study.