Is the clock face an accurate, precise, and reliable measuring tool for anterior cruciate ligament reconstruction?

(1) To assess the use and practice of the clock face among surgeons who routinely perform anterior cruciate ligament (ACL) reconstructions, and (2) to assess the accuracy, precision, and reliability of 3 commonly used clock-face schemes in ACL reconstruction.

First, 9 surgeons completed a questionnaire assessing the use and definition of the clock-face technique. Next, to assess the accuracy, precision, and reliability of the clock face, each surgeon estimated the "time" of 8 artificial femur models with a black dot located on the posterior aspect of the lateral condylar wall. The estimates were performed using 3 different clock-face schemes and were repeated 10 months later. Solutions for each specimen were obtained by use of a computer graphical interface.

More than half of the respondents (55%) use the clock face in ACL reconstructions, with the reported mean ideal "time" for a femoral tunnel in a right knee of 10:05 (SD, 31 minutes). When we accounted for the different clock definitions, this ideal position was found along the entire lateral condylar wall. In the assessment of the performance of the clock face, the mean error was 32 to 40 minutes (which translates to 3 to 4 mm) among the 3 clock schemes. The maximum error was 4 hours 0 minutes, and the range of responses was 1 hour 0 minutes to 4 hours 0 minutes depending on the specimen and clock scheme. Regardless of the clock scheme used, the intrarater and inter-rater reliabilities were similar-measuring, on average, 0.78 and 0.68, respectively.

The clock face continues to be commonly used in ACL reconstruction. Different clock-face definitions affect the position for the same "time." When the clock-face parameters were strictly defined, there was good reliability with borderline accuracy and poor precision.

Considering the borderline performance of the clock face in accuracy and poor precision, we recommend against using the clock face in ACL reconstruction.