Concerning lateral pivot shift however, a strong positive correlation was noticed between a higher grade and the difference between medial and lateral tibial translation of ACL-deficient knees (cutpoint 3.5 mm) which presents as a possibility to easily assess rotational instability applying PKTD® in MRI study of injured knee alone. Considering side-to-side differences, similar correlations were achieved for the difference in lateral translation and differential between lateral and medial translations. Somewhat surprisingly a negative correlation near statistical significance was noticed for side-to-side difference of medial compartment anterior displacement. This might reflect that some restriction in freedom of motion in medial compartment increases the pivot-shift phenomenon and should be addressed in future investigation.
For KT-1000 side-to-side difference a strong positive correlation was registered for either side-to-side difference of the amount of translation in medial or in lateral compartment. However, if considering the difference of translation in lateral and medial compartments (which somewhat reflects rotation) the results are far from statistical significance. This is also in line with the thought that KT-1000 is a valuable tool to assess anteroposterior laxity but not rotation.
Combining these results one might conclude that PKTD® proved, at least, to be as reliable in assessment of antero-posterior translation as KT-1000 and as feasible as lateral pivot shift under anaesthesia for quantification of rotation.
Neither gender nor meniscus injury demonstrated influence in results of clinical maneuvers, KT-100 or PKTD® but sample size and study design do not permit any further conclusion within this subject.
The inverse correlation of BMI and weight with side-to-side comparison of rotation (Dif. LPT-MPT) calls attention for the fact that higher weight and BMI index might increase difficulties in assessment of lateral pivot-shift either manually or using mechanized method. And in the later this subject requires reflection for subsequent improvement of devices considering the need to not only standardize load transmission but also understanding eventual need to adapt it accordingly.
Partial ACL ruptures38,39, which are difficult to recognize by preoperative MRI40, have been meriting growing interest. Despite being considered out of the scope of this study, the five cases in our initial group identified with isolated anteromedial or posterolateral bundle were correctly identified (concordance with arthroscopic findings) using MRI with PKTD®(fig 5).
By its unique feature of combining anatomical and dynamic evaluation, PKTD® might increase the capacity of radiologists to detect partial lesions in MRI. Putting ACL in tension during MRI might enable to appreciate the mechanical behaviour of partial ruptures41,42 and allow better appreciation of “biologic”/signal characteristics of the remaining bundle. This subject requires future investigation.
PKTD® might also play a future role in prevention (detecting risk factors) and/or identifying those patients which present higher rotational instability requiring an ACL reconstruction technique which provides higher rotational constraint (eg double-bundle)16.
These data provide one further step in understanding knee kinematics but their functional implication and the way in which they might affect ACL reconstruction is not completely determined. ACL research requires perseverance and patience43 although being an exciting and rewarding item.
We believe that this is a useful, reliable device to quantify anteroposterior, posteroanterior and rotational instability of the knee. This method proved to be reliable in assessment of anteroposterior translation (comparing to KT-1000) and rotatory instability (compared to lateral pivot shift under anaesthesia) of the ACL-deficient knee.
It might play a future role in prevention (detecting risk factors) or identifying partial ruptures due to its unique feature of combining anatomical and dynamic “clinical” evaluation amplified through the “eyes” of MRI.
It can be useful in surgical indication (surgery or conservative treatment) and the surgical technique choice (single or double bundle).
PCL evaluation is a difficult task specially to decide on surgery or conservative treatment. Postero-lateral and postero-medial instability are often associated with PCL lesions.PKTD® allows testing PCL lesions putting stress on the front of the tibia and measuring posterior translation on MRI and CT-Scan.