Purpose: The following hypothesis was tested: the location of the tibial and femoral anterior cruciate ligament (ACL) attachments will differ according to the measurement technique (plain radiographs or CT-scan) in relation to the anatomic frame of reference.
Methods: 10 gross specimens were studied. The location of metallic reference pins implanted around the tibial and femoral ACL attachments was recorded with reference to the bone contours with a caliper on the anatomic preparation, with standard plain AP and lateral radiographs and with a CT-scan. Results were compared with appropriate statistical tests at a 0.05 level of significance.
Results: The mean ratio between the antero-posterior tibia measurement and the center of the ACL tibial attachment varied from 50 to 52%. The mean ratio between the medio-lateral tibia measurement and the center of the ACL tibial attachment varied from 49 to 51%. The mean ratio between the antero-posterior femur measurement and the center of the ACL femoral attachment varied from 74 to 80%. The results were significantly different between the three techniques (respectively P = 0.003, P = 0.02 and P = 0.045).
Discussion: The paired differences were small (3% at the tibia, 6% at the femur). There was a strong correlation and a good agreement between the three techniques. It is likely that the small differences on the tibia have few, if any, clinical relevance.
Conclusion: Both radiographic and CT-scan measurement techniques used during the present study have the potential to be used as quality control after ACL replacement.
Level of evidence: Diagnostic study-investigating a diagnostic test. Development of diagnostic criteria in a consecutive series of patients and a universally applied "gold" standard, Level II.