Elongation of simulated whipstitch post anterior cruciate ligament reconstruction tibial fixation after cyclic loading

Posterior laxity increases over time after PCL reconstruction

PURPOSE

Restoration of posterior tibial translation (PTT) after reconstruction of the posterior cruciate ligament (PCL) is deemed necessary to restore physiological knee kinematics. However, current surgical techniques have failed to show a complete reduction of posterior laxity. It was hypothesized that early postoperative PTT increases over time.

METHODS

The study comprised of 46 patients (10 female, 36 male; 30 ± 9 years), who underwent PCL reconstruction in a single-surgeon series. Patients were evaluated by bilateral stress radiographs in a prospective manner preoperatively; at 3, 6, 12 and 24 months; and at a final follow-up (FFU) of at least 5 years. Covariants included age, gender, BMI, tibial slope (TS) and the number of operated ligaments. Two blinded observers reviewed all radiographs, evaluating the TS and the posterior tibial translation.

RESULTS

All patients were evaluated at a mean final follow-up of 102 (range 65-187) months. Mean side-to-side difference of the PTT significantly improved from preoperative to 3-month postoperative values (10.9 ± 3.1 vs. 3.6 ± 3.8 mm; P < 0.0001). The PTT increased to 4.6 ± 3.7 mm at 6 months, to 4.8 ± 3.3 mm at 12 months, to 4.8 ± 3.2 mm at 24 months, to 5.4 ± 3.4 mm at FFU. Consequently, there was a significant increase of PTT between 3-month and final follow-up (3.6 ± 3.8 vs. 5.4 ± 3.4 mm; P = 0.02). Flattening of the TS resulted in a significantly higher PTT compared to subjects with a high TS at 24 months and FFU. There was no significant influence by BMI, age, gender and the number of operated ligaments.

CONCLUSIONS

Early results after PCL reconstruction seem promising as posterior tibial translation is significantly improved. However, there is a significant increase in PTT from early postoperative values to the final follow-up of at least 5 years. This is particularly notable in patients with flattening of the TS. As a consequence, surgeons and patients need to be aware that initial posterior stability should not be equated with the final outcome.

LEVEL OF EVIDENCE

Cohort study, Level III.

Biomechanical properties of femoral posterior cruciate ligament fixations

PURPOSE

The success of reconstructions of the posterior cruciate ligament (PCL) mainly depends on the fixation strength of the tendon-bone interface. Reliable data about the mechanical characteristics of PCL fixation techniques are sparse. The aim of this study was to investigate the biomechanical properties of different femoral PCL fixation techniques.

METHODS

Fresh human cadaver quadriceps (Q) and hamstring (H) tendons were harvested and fixed into porcine femora with a press-fit fixation suturing the tendon over a bone bridge (group A), a novel implant post-fixation (group B) or an interference screw fixation (group C). Each group consisted of 10 specimens. The constructs were cyclically stretched and eventually loaded until failure. Elongation during cyclic loading, stiffness, failure mode and maximum failure load was evaluated.

RESULTS

Elongation during cyclical loading was significantly larger between the 1st and the 20th cycle than between the 20th and the 500th cycle in all groups (p < 0.05). Maximum failure load was 409 ± 71 (336-517) N in group QA, 456 ± 58 (347-510) N in group QB, 548 ± 116 (400-798) N in group QC, 472 ± 114 N (316-676 N) in group HA, 494 ± 98 N (371-668 N) in group HB and 498 ± 87 N (391-687 N) in group HC (significantly higher for QB compared to QA, p < 0.05).

CONCLUSION

This is the first study investigating the biomechanical properties of femoral PCL fixations. Implant-free fixation techniques like press-fit or post-fixations are able to withstand equal biomechanical forces compared to interference screw fixation. The novel fixations described in this study can be considered as a reliable alternative for the reconstruction of PCL using either hamstring or quadriceps tendons.

Effect of suturing the femoral portion of a four-strand graft during an ACL reconstruction

PURPOSE

A suture passed along the part of the graft that will be inserted into the femoral tunnel is widely used by surgeons, because it could prevent the graft sliding on the femoral fixation device during pulling from the tibial side. The aim of this study was to evaluate the biomechanical effects of suturing the intratunnel femoral part of the graft during an anterior cruciate ligament (ACL) reconstruction.

METHODS

Bovine digital extensor tendons and tibias were harvested from 20 fresh-frozen mature bovine knees ranging in age from 18 to 24 months. Quadruple-strand bovine tendons were passed through the tibial tunnel and secured distally with a bioabsorbable interference screw. In one half of all grafts (N = 10), the looped-over part of the graft was sutured in a whipstitch technique over a distance of 30 mm (Group 1). In one half of all grafts (N = 10), the looped-over part was left free from any suture (Group 2). The grafts were preconditioned at 50 N for 10 min, followed by cyclic loading at 1 Hz between 50 N and 250 N for 1,000 cycles. Load-to-failure test was then carried out at a rate of 1 mm/s.

RESULTS

There was no statistically significant difference between mean stiffness at pullout and yield load between the two groups. In all specimens on Group 1, failure occurred following to partial breaking and then slipping of the tendons between the screw and the tunnel. Concerning Group 2, in six cases failure occurred as described for Group 1 specimens. In the remaining four cases, failure occurred entirely through the ligament mid-substance.

CONCLUSIONS

Suturing in a whipstitch fashion the femoral portion of the graft doesn't affect the mechanical proprieties of the ACL graft. When suspension fixation device is used, suturing the looped-over part of the graft could be helpful in order to provide equal tension in all of the strands of the graft at time of tibial fixation.

[Implant-free tibial fixations of the posterior cruciate ligament. Development and biomechanical testing]

BACKGROUND

A secure tibial press fit technique in posterior cruciate ligament reconstructions may be a relevant alternative to common techniques because no hardware is necessary. Up to the present point in time no biomechanical data exist for a tibial press fit posterior cruciate ligament (PCL) reconstruction. This study compares the biomechanical properties of hamstring and quadriceps tendon grafts using a press fit technique with those of an interference screw fixation.

METHODS

Quadriceps and hamstring tendons of 20 human cadavers (age 49.2±18.5 years) were used. A press fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 27 porcine tibiae. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness and elongation during failure testing and cyclical loading were investigated.

RESULTS

The maximum load to failure was 518±157 N (387-650 N) for the K group, 558±119 N (466-650 N) for the I group and 620±102 N (541-699 N) for the Q group. The stiffness was 55±27 N/mm (18-89 N/mm) for the K group, 117±62 N/mm (69-165 N/mm) for the I group and 65±21 N/mm (49-82 N/mm) for the Q group. The stiffness of the I group was significantly larger (ANOVA on ranks, P=0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th and the 20th cycle (P<0.03).

CONCLUSION

All techniques exhibited larger elongation during initial loading. Load to failure and stiffness were significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. The results of group K were inferior. All three investigated fixation techniques exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Future randomized, clinical trials have to investigate the biological effectiveness of these fixation techniques.

The fixation strength of tibial PCL press-fit reconstructions

PURPOSE

A secure tibial press-fit technique in posterior cruciate ligament reconstructions is an interesting technique because no hardware is necessary. For anterior cruciate ligament (ACL) reconstruction, a few press-fit procedures have been published. Up to the present point, no biomechanical data exist for a tibial press-fit posterior cruciate ligament (PCL) reconstruction. The purpose of this study was to characterize a press-fit procedure for PCL reconstruction that is biomechanically equivalent to an interference screw fixation.

METHODS

Quadriceps and hamstring tendons of 20 human cadavers (age: 49.2 ± 18.5 years) were used. A press-fit fixation with a knot in the semitendinosus tendon (K) and a quadriceps tendon bone block graft (Q) were compared to an interference screw fixation (I) in 30 porcine femora. In each group, nine constructs were cyclically stretched and then loaded until failure. Maximum load to failure, stiffness, and elongation during failure testing and cyclical loading were investigated.

RESULTS

The maximum load to failure was 518 ± 157 N (387-650 N) for the (K) group, 558 ± 119 N (466-650 N) for the (I) group, and 620 ± 102 N (541-699 N) for the (Q) group. The stiffness was 55 ± 27 N/mm (18-89 N/mm) for the (K) group, 117 ± 62 N/mm (69-165 N/mm) for the (I) group, and 65 ± 21 N/mm (49-82 N/mm) for the (Q) group. The stiffness of the (I) group was significantly larger (P = 0.01). The elongation during cyclical loading was significantly larger for all groups from the 1st to the 5th cycle compared to the elongation in between the 5th to the 20th cycle (P < 0.03).

CONCLUSION

All techniques exhibited larger elongation during initial loading. Load to failure and stiffness was significantly different between the fixations. The Q fixation showed equal biomechanical properties compared to a pure tendon fixation (I) with an interference screw. All three fixation techniques that were investigated exhibit comparable biomechanical properties. Preconditioning of the constructs is critical. Clinical trials have to investigate the biological effectiveness of these fixation techniques.