The signal intensity was highest in the proximal region and lowest in the distal region of the reconstructed graft at 6 months postoperatively. A steep GBA was significantly correlated with high signal intensities of the proximal graft in this early period. A steep GBA may negatively affect proximal graft healing after ACL reconstruction.

Purpose To determine in vivo dynamic graft bending angle (GBA) in anterior cruciate ligament (ACL) reconstructed knees, correlate the angle to tunnel positions and tunnel widening, and evaluate the effects of two femoral tunnel drilling techniques on GBA. Methods Patients with an isolated ACL injury undergoing reconstruction were included from 2011 to 2012. Trans-portal techniques were used to create femoral tunnels. Tunnel locations were determined using 3D-CT. Tibio-femoral kinematics during treadmill walking and running were assessed using dynamic stereo X-ray analysis 6 months and 2 years postoperatively. The GBA was calculated from the 3D angle between the graft and femoral tunnel vectors at each motion frame. Cross-sectional area of femoral tunnels were measured at 6 months and compared to initial size to assess tunnel widening. Results A total of 54 patients were included. Use of flexible drills resulted in significantly higher GBA during walking (80.6° ± 7.8°; p<0.001) and running (80.5° ± 9.0°; p=0.025) than rigid drills (walking: 67.5° ± 9.3°, running: 74.1° ± 9.6°). It led to greater tunnel widening of 113.9±17.6 %, compared with rigid drills of 97.7±17.5 % (p=0.003). Femoral and tibial apertures were located in similar anatomic positions in both groups, but femoral tunnel exits were located more anteriorly (p<0.001) in the flexible drill group. Higher GBA was highly correlated with anterior location of femoral exits (r=0.63, p<0.001) and moderately correlated with greater tunnel widening (r=0.48, p<0.001). Conclusions High GBA was identified during dynamic activities after anatomic ACL reconstruction using a trans-portal femoral tunnel drilling technique. The GBA was greater when flexible drills were used. The high bending angle resulted from more anterior location of femoral tunnel exits, and correlated with early bone tunnel widening at 6 months. These results suggest that high GBA may increase stress on the bone-graft interface and contribute to greater tunnel widening after anatomic ACL reconstruction, although clinical impact should be further investigated. Level of Evidence Level III, retrospective comparative study

III.

Background:Anterior cruciate ligament (ACL) injury increases the risk of meniscus and articular cartilage damage, but the causes are not well understood. Previous in vitro studies were static, required extensive knee dissection, and likely altered meniscal and cartilage contact due to the insertion of pressure sensing devices.Hypothesis:ACL deficiency will lead to increased translation of the lateral meniscus and increased deformation of the medial meniscus as well as alter cartilage contact location, strain, and area.Study Design:Descriptive laboratory study.Methods:With minimally invasive techniques, six 1.0-mm tantalum beads were implanted into the medial and lateral menisci of 6 fresh-frozen cadaveric knees. Dynamic stereo x-rays (DSXs) were obtained during dynamic knee flexion (from 15° to 60°, simulating a standing squat) with a 46-kg load in intact and ACL-deficient states. Knee kinematics, meniscal movement and deformation, and cartilage contact were compared by novel imaging coregistration.Results:During dynamic knee flexion from 15° to 60°, the tibia translated 2.6 mm (P = .05) more anteriorly, with 2.3° more internal rotation (P = .04) with ACL deficiency. The medial and lateral menisci, respectively, translated posteriorly an additional 0.7 mm (P = .05) and 1.0 mm (P = .03). Medial and lateral compartment cartilage contact location moved posteriorly (2.0 mm [P = .05] and 2.0 mm [P = .04], respectively).Conclusion:The lateral meniscus showed greater translation with ACL deficiency compared with the medial meniscus, which may explain the greater incidences of acute lateral meniscus tears and chronic medial meniscus tears. Furthermore, cartilage contact location moved further posteriorly than that of the meniscus in both compartments, possibly imparting more meniscal stresses that may lead to early degeneration. This new, minimally invasive, dynamic in vitro model allows the study of meniscus function and cartilage contact and can be applied to evaluate different pathologies and surgical techniques.Clinical Relevance:This novel model illustrates that ACL injury may lead to significant meniscus and cartilage abnormalities acutely, and these parameters are dynamically measurable while maintaining native anatomy.

III.