Predictive mathematical modeling of knee static laxity after ACL reconstruction: in vivo analysis

Previous studies did not take into consideration such large variety of surgery variables which describe the performed anterior cruciate ligament (ACL) reconstruction and the interaction among them in the definition of postoperative outcome. Seventeen patients who underwent navigated Single Bundle plus Lateral Plasty ACL reconstruction were enrolled in the study. Static laxity was evaluated as the value of anterior/posterior displacement at 30° and at 90° of flexion, internal/external rotation at 30° and 90° of knee flexion, varus/valgus test at 0° and 30° of flexion. The evaluated surgical variables were analyzed through a multivariate analysis defining the following models: AP30estimate, AP90estimate, IE30estimate, IE90estimate, VV0estimate, VV30estimate. Surgical variables has been defined as the angles between the tibial tunnel and the three planes, the lengths of the tunnel and the relationship between native footprints and tunnels. An analogous characterization was performed for the femoral side. Performance and significance of the defined models have been quantified by the correlation ratio (η(2)) and the corresponding p-value (*p < 0.050). The analyzed models resulted to be statistically significant (p < 0.05) for prediction of postoperative static laxity values. The only exception was the AP90estimate model. The η(2) ranged from 0.568 (IE90estimate) to 0.995 (IE30estimate). The orientation of the tibial tunnel resulted to be the most important surgical variable for the performed laxity estimation. Mathematical models for postoperative knee laxity is a useful tool to evaluate the effects of different surgical variables on the postoperative outcome.

A biomechanical analysis of controllable intraoperative variables affecting the strength of rotator cuff repairs at the suture-tendon interface

BACKGROUND

The tissue-suture interface remains the weakest aspect of a rotator cuff repair, highlighting the importance of identifying techniques to improve stitch strength. Choice of suture-passing devices, size of the tissue bite, and stitch configuration are variables that may influence stitch strength and therefore repair stability.

PURPOSE

To evaluate the effect that size of the tissue penetrator device and tissue bite size have upon the holding strength of commonly used stitches.

STUDY DESIGN

Controlled laboratory study.

METHODS

Three different-sized tissue-penetrating devices, small circular, midsized circular, and large rectangular, were used to place sutures in 192 infraspinatus tendon grafts of sheep. Tissue bite sizes of either 0.5 cm or 1.0 cm for 4 different stitches, a simple, mattress, modified Mason-Allen (MMA), and massive cuff (MAC) stitch, were tested. Grafts were cyclically loaded and then loaded to failure. Mixed multivariate regression analysis was used to test the effect of instrument, bite size, and stitch configuration on peak-to-peak displacement, cyclic elongation, and load to failure.

RESULTS

The average ultimate load to failure with the smallest penetrating device was 112 N, significantly higher than with both the midsized (95 N) and large devices (91 N) (P < .001). The average load to failure was 31 N higher for a 1.0-cm bite size when compared with a 0.5-cm bite size (P < .001). The largest load-to-failure differences were found with the type of stitch placed: simple, 48 N; mattress, 69 N; MMA, 130 N; and MAC, 152 N (all P < .02). For simple and mattress stitches, each additional pass of the suture increased the load to failure by 21 N. In MMA and MAC stitches, an additional pass resulted in an increase in the load to failure by 50 N. Cyclic elongation did not differ by instrument type (all P > .5). The elongation of stitches with a 1.0-cm bite size was 0.14 mm higher than stitches with a 0.5-cm bite size (P < .001). No meaningful difference in peak-to-peak displacement was seen for bite size, instrument type, or stitch construct.

CONCLUSION

The strength of rotator cuff stitches was significantly affected by the different-sized tissue-penetrating instruments and size of the bite. However, the greatest predictor of time-zero stitch strength is the type of stitch placed.

CLINICAL RELEVANCE

This study highlights the importance of stitch configuration in the repair of rotator cuff tears.