Simon Lenschow

Importance of Femoral Tunnel Placement in Double-Bundle Posterior Cruciate Ligament Reconstruction Biomechanical Analysis Using a Robotic/Universal Force-Moment Sensor Testing System

Background Previous studies have identified the femoral attachment of the posterior cruciate ligament fibers as one of the primary determinants of fiber tension behavior. In addition, a double-bundle posterior cruciate ligament reconstruction has been shown to restore the intact knee kinematics more closely than does a single-bundle reconstruction. Hypothesis An anterior tunnel position in double-bundle posterior cruciate ligament reconstruction restores the biomechanics of the normal knee more closely than does a posterior tunnel position. Study Design Controlled laboratory study. Methods Kinematics and in situ forces of human knees after double-bundle posterior cruciate ligament reconstruction with 2 different femoral tunnel positions (anterior vs posterior) were evaluated using a robotic/universal force-moment sensor testing system. Within the same specimen, the resulting knee kinematics and in situ forces were compared. For statistical analysis, 2-way analysis of variance repeated measures were performed. Results The femoral tunnel position of the double-bundle hamstring graft had significant effect on the resulting posterior tibial displacement and in situ forces of the hamstring grafts. The anterior femoral tunnel position provided significantly less posterior tibial translation than did the posterior tunnel position. There was a tendency toward higher in situ forces of grafts fixed in the anterior tunnel when compared to the posterior position, but this difference was statistically not significant. Conclusion An anterior position of the bone tunnels in double-bundle posterior cruciate ligament reconstruction restores the normal knee kinematics more closely than does a posterior position of the tunnels. Clinical Relevance In double-bundle posterior cruciate ligament reconstruction, posterior placement of the tunnel should be avoided.

Joint kinematics and in situ forces after single bundle PCL reconstruction: a graft placed at the center of the femoral attachment does not restore normal posterior laxity

Introduction: Femoral tunnel placement has a great influence on the clinical outcome after PCL reconstruction. Materials and methods: Using a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of human knees following soft-tissue single bundle PCL reconstruction fixed at the center of the femoral attachment. Results: Posterior tibial translation significantly increased at all flexion angles after transsection of the posterior cruciate ligament (p<0.05). PCL reconstruction resulted in significantly less posterior tibial translation at all flexion angles when compared to the PCL deficient knee (p<0.05). The differences in the in situ force between the intact ligament and the reconstructed graft were statistical significant (p<0.05). Conclusion: Single bundle PCL reconstruction with a soft-tissue graft fixed at the center of the femoral attachment is able to reduce the posterior tibial translation significantly. However, it cannot restore kinematics of the intact knee and in situ forces of the intact PCL.

Medial Patellofemoral Ligament Reconstruction: Fixation Strength of 5 Different Techniques for Graft Fixation at the Patella

PURPOSE To compare the structural properties of 5 different fixation strategies for a free tendon graft at the patella in medial patellofemoral ligament (MPFL) reconstruction under cyclic loading and load to failure testing. METHODS We used porcine patella and flexor tendons. We tested the following fixation techniques: 3.5-mm titanium anchor, transosseous 1-mm braided polyester suture, interference screw fixation, medial bone bridge, and transpatellar tunnels. We preconditioned each graft between 5 and 20 Nm before cyclic loading with 100 Nm for 1,000 cycles was started, and then performed load to failure testing. We recorded maximum load, stiffness, and elongation. RESULTS In the bone bridge group, 60% of all specimens failed during cyclic testing. Fixation by transosseous sutures showed significantly less stiffness compared with all other techniques (P < .05). The bone bridge technique showed significantly lower load to failure compared with all other techniques (P < .05). Differences between the other groups were not significant. CONCLUSIONS Fixation of a free tendon graft by transosseous sutures provides similar load to failure and elongation but less stiffness compared with fixation by anchors, interference screws, or transverse tunnels. Load to failure for the bone bridge technique was significantly lower than that for all other techniques. Furthermore, this fixation technique had a lower load to failure than that of the native MPFL. CLINICAL RELEVANCE Fixation of soft tissue grafts at the patella by 1-mm braided polyester suture provides adequate fixation strength without implants in the patella, which might cause soft tissue irritation. Further studies will have to show if the lesser stiffness of this technique causes problems in the clinical setting or if this laxity might even be an advantage because it makes this reconstruction more forgiving concerning overtensioning the graft. Significantly lower load to failure of the bone bridge technique should be considered in postoperative treatment.

Soft-tissue graft fixation in posterior cruciate ligament reconstruction: evaluation of the effect of tibial insertion site on joint kinematics and in situ forces using a robotic/UFS testing system

IntroductionSurgical reconstruction of the posterior cruciate ligament (PCL) is recommended in acute injuries that result in severe tibial subluxation and instability. The surgical outcome level may be affected by the tibial fixation site. In response to a 110-N posterior tibial load, kinematics and in situ forces of anatomical soft-tissue graft fixation in single-bundle PCL reconstruction using an interference screw fixation are significantly closer to those in the intact knee than with extracortical fixation with two staples.Materials and methodsUsing a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of porcine knees following single-bundle PCL reconstruction fixed at two different tibial fixation sites: anatomical interference screw and extracortical fixation.ResultsThe site of the tibial graft fixation had significant effect on the resulting posterior displacement and in situ forces of the graft. Both PCL reconstruction techniques reduced the posterior tibial translation significantly. Proximal fixation techniques provided significantly less posterior tibial translation than extracortical fixation. Single-bundle PCL reconstruction with an interference screw showed higher in situ forces of the graft than the extracortical fixation.ConclusionsThe kinematics and in situ forces of a single-bundle PCL reconstruction using an interference screw fixation technique are superior to the primary stability of an extracortical fixation with staples.

Comparison of Knee Kinematics After Single-Bundle Anterior Cruciate Ligament Reconstruction via the Medial Portal Technique With a Central Femoral Tunnel and an Eccentric Femoral Tunnel and After Anatomic Double-Bundle Reconstruction: A Human Cadaveric Study

Background: Anatomic femoral tunnel placement in anterior cruciate ligament (ACL) reconstruction is considered to be a key to good primary stability of the knee. There is still no consensus on whether a centrally placed single bundle in the anatomical femoral footprint can compare with anatomic double-bundle (DB) reconstruction. Purpose/Hypothesis: The purpose of this study was to determine knee kinematics after single-bundle ACL reconstruction via the medial portal technique using 2 different femoral tunnel positions and to compare results with those of the anatomic DB technique. The hypotheses were that (1) single-bundle reconstruction using the medial portal technique with a centrally placed femoral tunnel relative to the native footprint (SB-central technique) would more closely restore intact knee kinematics compared with the same reconstruction technique with an eccentric femoral tunnel drilled in the anteromedial bundle footprint (SB-AM technique) and (2) DB reconstruction would result in superior kinematics compared with the SB-central technique. Study Design: Controlled laboratory study. Methods: Knee kinematics was examined in 10 fresh-frozen human cadaveric knees using a robotic/universal force-moment sensor system. Kinematics in simulated pivot-shift and 134-N anterior tibial loading tests were determined in different conditions within the same specimen: (1) intact ACL, (2) deficient ACL, (3) SB-AM, (4) SB-central, and (5) DB. Results: All reconstruction techniques significantly reduced anterior tibial translation (ATT) compared with a deficient ACL at 0°, 15°, 30°, 60°, and 90° in the anterior tibial loading test (P < .01, repeated-measures analysis of variance) and at 0°, 15°, and 30° in the simulated pivot-shift test (P < .001). There were no significant differences in the SB-central group and the DB group compared with the intact ACL. Reconstruction in the SB-AM group resulted in significantly increased ATT compared with the intact ACL in near-to-extension angles in both tests (0°, 15°, and 30°; P < .01). SB-central and DB reconstructions both resulted in significantly reduced ATT, in some tests at ≤30°, compared with SB-AM reconstruction (P < .05). No significant differences between the SB-central and DB groups were found (P > .05). Conclusion: The SB-central technique restored intact knee kinematics more closely than did SB-AM reconstruction at time zero. There were no differences in knee kinematics between the DB and SB-central techniques. Clinical Relevance: Anatomic single-bundle ACL reconstruction provides similar knee kinematics as anatomic double-bundle reconstruction.

Strategies for Repair of Radial Tears Close to the Meniscal Rim—Biomechanical Analysis with a Cyclic Loading Protocol

Background Lateral meniscectomy contributes to early-onset osteoarthritis. Biomechanical properties of sutures repairs for complete radial meniscal tears remain unknown. Hypothesis Double horizontal suture techniques for repair of radial meniscal tears with a shorter distance from the meniscal rim provide significantly higher structural properties than do comparable single-suture techniques with a wider distance from the meniscal rim. Study Design Controlled laboratory study. Methods In 55 fresh-frozen porcine menisci, standardized complete radial meniscal tears were repaired with different distances from the meniscal rim and tear edges and with different numbers of sutures. In group A, the suture was 4 mm from the tear and 8 mm from the meniscal rim; group B, 2 mm from tear; group C, 2 mm from tear, 12 mm from rim; group D, double-loop technique, 2 mm from tear, 5 mm and 10 mm from rim; group E, longitudinal tear sutured with 1 loop, 8 mm from rim, and 4 mm between stitches. The specimens were cyclically loaded 1000 times between 5 and 20 N and loaded to failure. Results All repaired constructs survived the cyclic loading protocol. Compared with the single-loop techniques, the double-loop technique (group D) showed a significantly higher maximum load and yield load and significantly lower displacement after 1000 cycles. Compared with group B, group C had a higher displacement after 1000 cycles (P < .05), and its stiffness showed a descriptive negative trend (P = .09). Displacement after cycling testing in group C was higher than in groups B and D (P < .05). Conclusion Repair of radial meniscal tears with a second suture and shorter distance from the meniscal rim has a positive influence on primary stability. Different distances from tear edges apparently have no influence on structural properties. Clinical Relevance Horizontal sutures for repair of radial meniscal tears provide high stability and can be enhanced with a second horizontal suture and shorter distance from the meniscal rim.