Abstract
Variations in the pivot shift test have been proposed by many authors, though, a test comprised of rotatory and valgus tibial forces with accompanied knee range of motion is frequently utilised. Differences in applied forces between practitioners and patient guarding have been observed as potentially decreasing the reproducibility and reliability of the pivot shift test.
We hypothesise that a low-profile pivot shift test (LPPST) consisting of practitioner induced internal rotatory and anterior directed tibial forces with accompanied knee range of motion can elicit significant differences in internal tibial rotation and anterior tibial translation between the anterior cruciate ligament (ACL) deficient and ACL sufficient knee.
Fresh, frozen cadaver knees were used for this study. Four practitioners performed the LPPST on each ACL sufficient knee. The ACL of each knee was subsequently resected and each practitioner performed the LPPST on each ACL deficient knee. Our quantitative assessment utilised computer assisted navigation to sample (10Hz) the anterior translation and internal rotation of the tibia as the LPPST force vectors were applied. We subsequently pooled and averaged data from all four practitioners and analysed the entrance pivot (tibial reduction with knee range of motion from extension into flexion) and the exit pivot (tibial subluxation with knee range of motion from flexion into extension).
We observed a significant difference in anterior tibial translation and internal tibial rotation in the ACL deficient vs. ACL sufficient knees during both the entrance and exit pivot phases of the LPPST. The entrance pivot (n=140) was found to have an average maximum anterior tibial translation of 7.83 mm in the ACL deficient knee specimens compared to 1.23 mm in the ACL sufficient knee specimens (p<0.01). We found the ACL deficient knees to exhibit an average maximum internal tibial rotation of 12.38 degrees compared to 11.24 degrees in the ACL sufficient specimens during the entrance pivot (p=0.04). The exit pivot (n=120) was found to have an average maximum anterior tibial translation of 7.82 mm in the ACL deficient knee specimens compared to 1.44 mm in the ACL sufficient knee specimens (p<0.01). The ACL deficient knees exhibited an average maximum internal tibial rotation of 12.44 degrees compared to 11.13 degrees in the ACL sufficient knee specimens during the exit pivot (p=0.02).
Our results introduce a physical exam maneuver (LPPST) consisting of practitioner induced internal rotatory and anterior directed forces, with notable absence of valgus force, on the tibia while applying knee range of motion. Our results demonstrate that the LPPST can elicit significant anterior translation and internal rotary differences in an effort to differentiate between the ACL deficient and ACL sufficient knee. Our work will next seek to explore the clinical reproducibility of this physical exam maneuver.
