Effect of Tunnel Position and Graft Size in Single-Bundle Anterior Cruciate Ligament Reconstruction: An Evaluation of Time-Zero Knee Stability
To determine whether (1) increased graft size with anatomic anterior cruciate ligament reconstruction (ACLR) would confer proportionally increased time-zero biomechanical stability and (2) larger grafts would compensate for the inferior time-zero biomechanical kinematics of nonanatomic, single-bundle ACLR.
Ten cadaveric knees were allocated for single-bundle ACLR in an anatomic, center-center or nonanatomic, posterolateral-to-anteromedial footprint position with hamstring autograft. Medial arthrotomy defined the native anterior cruciate ligament (ACL) tibial and femoral footprints. ACLR was performed with a 6-mm semitendinosus graft in 6-mm tunnels and repeated with a 9-mm semitendinosus and gracilis graft in 9-mm tunnels for each knee. Lachman and instrumented pivot-shift examinations assessed knee stability in the ACL-intact, ACL-deficient, and ACLR conditions. Medial and lateral meniscectomies after ACL transection created reproducible pivot shifts. Significance was defined as P < .05.
ACLR in the center-center or posterolateral-to-anteromedial position significantly reduced anterior tibial translation compared with the ACL- and meniscus-deficient conditions (P < .001). Larger graft size, however, did not significantly improve time-zero biomechanical stability compared with a smaller graft in the same position for either reconstruction (P = .41 to .74). A center-center ACLR controlled tibial translation significantly better than a nonanatomic graft position regardless of graft size (P < .001). A smaller graft in the anatomic position controlled tibial translation significantly better than a larger graft in a nonanatomic position (P < .001).
This study showed that increasing graft size did not improve the time-zero biomechanical stability of the knee after ACLR. Increased graft size did not compensate for the biomechanical instability documented with the nonanatomic tunnel position. Restoration of native footprint anatomy in ACLR is of paramount importance regardless of graft size and source.
A larger graft size does not ameliorate the inferior time-zero biomechanics associated with nonanatomic tunnel preparation during single-bundle ACLR.
Available from: Nicolas Pujol
- "Finally, Bedi et al.  published recently a cadaveric study to determine whether increased graft size (9 mm diameter) with anatomic ACL reconstruction would result in a better biomechanical stability than 6 mm diameter grafts. They found no improvement with the use of thicker grafts. "
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ABSTRACT: BACKGROUND: The aim of modern techniques for anatomic reconstruction of the ACL is to reproduce ACL footprints, in order to restore anatomy and therefore normal biomechanics. Is there an oversizing of the hamstring grafts related to ACL dimensions? METHODS: Twenty-two paired cadaver knees were dissected. ACL dimensions at mid-portion and ACL footprints were measured after removing the synovial membrane. Hamstrings were harvested and prepared in a quadruple strand graft in order to measure the mean circumference. RESULTS: The average ACL tibial and femoral insertion site areas of the ACL were 117.9mm(2) (range, 90 to 130mm) and 96.8mm(2) (range, 80 to 121mm), respectively. The average diameter and cross sectional area of the ACL tendon at mid-portion were 6.1mm (range, 5 to 7mm) and 29.2mm(2) (range, 20 to 38.9), respectively. The average diameter and cross-sectional area of the 4-stranded hamstring tendons were 6.7 (range, 5 to 8) and 35.3mm(2) (range, 20 to 50), respectively. There was a correlation between the 4-stranded hamstring grafts and ACL dimensions (footprints, ligament at mid substance, p<0.01). The cross sectional area of hamstring tendon was significantly larger than the ACL area at mid-portion (mean 20.9%, p<0.05). CONCLUSION: With current ACL reconstruction techniques, the graft is oversized at a mean of 21%, despite a good correlation between the ACL and the hamstring tendon, especially among small subjects and women. The question arises whether the anatomic reconstruction of the ACL should fill ACL footprints or mimic the ligament itself. CLINICAL RELEVANCE: Hamstrings grafts are significantly larger than native ACL.
Available from: Cesar A Q Martins
- "While the graft diameter does affect graft stiffness, it can be noted that the smaller grafts did restore the intact anterior tibial translation and in some cases the in situ force of the graft was greater than that of the intact ACL. Moreover, a recent study comparing 6- and 9-mm tunnels for a single-bundle ACL reconstruction revealed that increasing the graft size did not improve the time-zero biomechanical stability . Grafts were made from both semitendinosus and gracilis tendons and there may be a difference in these tissues. "
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Recent reports have highlighted the importance of an anatomic tunnel placement for anterior cruciate ligament (ACL) reconstruction. The purpose of this study was to compare the effect of different tunnel positions for single-bundle ACL reconstruction on knee biomechanics.
Sixteen fresh-frozen cadaver knees were used. In one group (n = 8), the following techniques were used for knee surgery: (1) anteromedial (AM) bundle reconstruction (AM–AM), (2) posterolateral (PL) bundle reconstruction (PL–PL) and (3) conventional vertical single-bundle reconstruction (PL-high AM). In the other group (n = 8), anatomic mid-position single-bundle reconstruction (MID–MID) was performed. A robotic/universal force-moment sensor system was used to test the knees. An anterior load of 89 N was applied for anterior tibial translation (ATT) at 0°, 15°, 30° and 60° of knee flexion. Subsequently, a combined rotatory load (5 Nm internal rotation and 7 Nm valgus moment) was applied at 0°, 15°, 30° and 45° of knee flexion. The ATT and in situ forces during the application of the external loads were measured.
Compared with the intact ACL, all reconstructed knees had a higher ATT under anterior load at all flexion angles and a lower in situ force during the anterior load at 60° of knee flexion. In the case of combined rotatory loading, the highest ATT was achieved with PL-high AM; the in situ force was most closely restored with MIDMID, and the in situ force was the highest AM–AM at each knee flexion angle.
Among the techniques, AM–AM afforded the highest in situ force and the least ATT.
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ABSTRACT: The aims of this study were (1) to evaluate the femoral tunnel position after anatomic double-bundle and nonanatomic single-bundle reconstruction; (2) to evaluate the influence of rotation of the femur caused by limb malalignment on measurements of the position of the femoral ACL tunnel aperture relative to Blumensaat's line.
3D CT scans were performed in 5 patients after anatomic double-bundle reconstruction and 5 patients after nonanatomic single-bundle reconstruction. Digitally reconstructed lateral radiographs were generated from the 3D CT scans to determine the tunnel position on the femur along and perpendicular to Blumensaat's line. The femur was then rotated to simulate internal/external and varus/valgus rotations from 0° to 15° in 5° increments. At each rotated bone position, tunnel position relative to Blumensaat's line was calculated and the difference from the lateral radiograph was calculated.
After double-bundle reconstruction, the AM tunnel was located at 31.5 (±5.0) % along Blumensaat's line and 29.7 (±13.6) % perpendicular to Blumensaat's line, and the PL tunnel at 36.2 (±12.9) % along Blumensaat's line and 34.2 (±7.6) % perpendicular to Blumensaat's line. Valgus greater than 10° significantly affected the assessment of tunnel position (P = 0.043). After nonanatomic single-bundle reconstruction, the tunnel position was 35.4 (±15.0) % along Blumensaat's line and -2.7 (±19.4) % perpendicular to Blumensaat's line. Internal rotation of more than 10° significantly affected the assessment of tunnel position (P = 0.043).
Tunnel position after anatomic double-bundle reconstruction and nonanatomic single-bundle reconstruction can be determined on lateral radiographs. However, valgus and internal rotation of more than 10° can introduce significant errors in tunnel position estimates.
Case series, Level IV.
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