The Posterior Condylar Offset Ratio.
BACKGROUND
Posterior Condylar Offset is an area of interest in knee arthroplasty research and clinical outcome. The aim of the study is to define a quantifiable Posterior Condylar Offset Ratio, a normal value for this ratio and to confirm its reproducibility on pre-operative radiographs.


METHODS
We propose a new Posterior Condylar Offset Ratio which is defined as the maximal thickness of the posterior condyle projecting posteriorly to a straight line drawn as the extension of the posterior femoral shaft cortex, divided by the maximal thickness of the posterior condyle projecting posterior to a straight line drawn as the extension of the anterior femoral shaft cortex on a true lateral radiograph of the distal quarter of the femur. We have measured this on 100 true lateral radiographs (50 females, 50 males, and mean age 65 years).


RESULTS
The mean ratio was 0.44 (SD 0.02) and was shown to have good reproducibility (intra-observer error 0.899 and inter-observer error 0.882. The ratio was also very consistent between male and female patients (0.44 (SD 0.02) for the males and 0.45 (SD 0.02) for the females). Adjusting the ratio for reported posterior condyle articular cartilage thickness increased the ratio to 0.47 (SD 0.02).


CONCLUSIONS
We suggest our Posterior Condylar Offset Ratio is a useful tool to aid further research in this area of knee arthroplasty and propose a normal value of 0.44 on radiographs and 0.47 on post-operative knee arthroplasty radiographs.
Avon Orthopaedic Centre, Southmead Hospital, Westbury-on-Trym, Bristol, BS10 5NB, United Kingdom.
Parm
P
Johal
Mohammed A
MA
Hassaballa
Jonathan D
JD
Eldridge
Andrew J
AJ
Porteous
D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001837:Body Weights and Measures; D015331:Cohort Studies; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging*; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000502:physiology; D008297:Male; D008875:Middle Aged; D011859:Radiography; D016059:Range of Motion, Articular; D012016:Reference Values; D015203:Reproducibility of Results; D012737:Sex Factors