Reconstrução transtúnel tibial do ligamento cruzado posterior: estudo anatômico em cadáveres para a feitura do túnel tibial

Dynamic Three-Dimensional Computed Tomography Mapping of Isometric Posterior Cruciate Ligament Attachment Sites on the Tibia and Femur: Single- Versus Double-Bundle Analysis

PURPOSE

(1) To determine the area of posterior cruciate ligament (PCL) insertion sites on the lateral wall of the medial femoral condyle (LWMFC) that demonstrates the least amount of length change through full range of motion (ROM) and (2) to identify a range of flexion that would be favorable for graft tensioning for single-bundle (SB) and double-bundle (DB) PCL reconstruction.

METHODS

Six fresh-frozen cadaveric knees were obtained. Three-dimensional computed tomography point-cloud models were obtained from 0° to 135°. A point grid was placed on the LWMFC and the tibial PCL facet. Intra-articular length was calculated for each point on the femur to the tibia at all flexion angles and grouped to represent areas for bone tunnels of SB and DB PCLR. Normalized length changes were evaluated.

RESULTS

Femoral tunnel location and angle of graft fixation were significant contributors to mean, minimum, and maximum normalized length of the PCL (all p < .001). Tibial tunnel location was not significant in any case (all p < .22). A femoral tunnel in the location of the posteromedial bundle of the PCL resulted in the least length change at all tibial positions (maximum change 13%). Fixation of the anterolateral bundle in extension or at 30° flexion resulted in significant overconstraint of the PCL graft. The femoral tunnel location for a SB PCLR resulted in significant laxity at lower ranges of flexion.

CONCLUSION

PCL length was significantly dependent on femoral tunnel position and angle of fixation, whereas tibial tunnel position did not significantly contribute to observed differences. All PCL grafts demonstrated anisometry, with the anterolateral bundle being more anisometric than the posteromedial bundle. For DB PCLR, the posteromedial bundle demonstrated the highest degree of isometry throughout ROM, although no area of the LWMFC was truly isometric. The anterolateral bundle should be fixed at 90° to avoid overconstraint, and SB PCLR demonstrated significant laxity at lower ranges of flexion.

CLINICAL RELEVANCE

Surgeons can apply the results of this investigation to surgical planning in PCLR to optimize isometry, which may ultimately reduce graft strain and the risk of graft failure. Additionally, DB PCLR demonstrated superiority compared with SB PCLR regarding graft isometry, as significant laxity was encountered at lower ranges of flexion in SB PCLRs. Fixation of the ALB at 90° flexion should be performed to avoid overconstraint in knee extension.

Nonanatomic Tibial Tunnel Placement for Single-Bundle Posterior Cruciate Ligament Reconstruction Leads to Greater Posterior Tibial Translation in a Biomechanical Model

PURPOSE

To determine the effect of varying proximal-distal tibial tunnel placement on posterior cruciate ligament (PCL) laxity.

METHODS

Nine matched pairs (18 total) of cadaveric knees (mean age 79.3 years, range 60 to 89), were studied. The specimens from each pair were randomly divided into 2 groups based on tibial tunnel placement: (1) anatomic tunnel and (2) proximal nonanatomic tunnel. A 150-N cyclic posterior tibial load was applied using a Materials Testing System machine at 0°, 30°, 60°, and 90° of knee flexion. Each specimen completed 50 cycles at a rate of 0.2 Hz at each knee flexion angle. In 10 specimens, a static 250-N posterior tibial load was applied at 90° of knee flexion. Posterior tibial translation was recorded. Load to failure for all specimens was recorded.

RESULTS

With application of a 150-N posteriorly directed cyclic force, the anatomic tunnel group had significantly less posterior tibial translation (millimeters, mean [standard deviation (SD)]) than the proximal nonanatomic tunnel group at 0°, 30°, 60°, and 90° of knee flexion: 1.1 (0.3) v 1.5 (0.4), P = .031; 1.1 (0.6) v 2.2 (0.9), P = .019; 0.9 (0.4) v 2.0 (0.6), P = .001; 0.9 (0.6) v 2.9 (0.7), P < .001, respectively. The anatomic tunnel group also demonstrated significantly less posterior tibial translation (millimeters, mean [SD]) than the nonanatomic tunnel group at 90° with a static 250-N posteriorly directed force applied (P <.05): 2.3 (1.3) v 6.1 (2.3), P = .016. Four pairs were excluded from the 250-N results because of prior load to failure testing.

CONCLUSIONS

Anatomic tibial tunnel placement re-creating the tibial origin of the PCL results in significantly less posterior tibial translation than proximal nonanatomic tibial tunnel placement. Correct placement of the tibial tunnel during PCL reconstruction is essential for avoidance of posterior laxity.

CLINICAL RELEVANCE

Anatomic tibial tunnel placement during PCL reconstruction may ensure a more stable reconstruction.