Biomechanical comparison of different graft positions for single-bundle anterior cruciate ligament reconstruction

Purpose

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.

Methods

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.

Results

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.

Conclusion

Among the techniques, AM–AM afforded the highest in situ force and the least ATT.     

前交叉韧带起止点X线下定位的研究

目的研究X线下前交叉韧带(anterior cruciate ligament,ACL)起止点印迹在股骨髁及胫骨平台上的定位,为术中重建ACL制备骨隧道时提供参考依据。方法采集12例正常国人膝关节标本,制作标本后分别在股骨髁及胫骨平台将ACL起止点边缘用金属丝标记,标记后摄标准的正侧位膝关节标本x线片,使用X-Caliper测量仪在CR片上精确测量ACL股骨髁和胫骨平台止点的几何中心与CR片骨性标记之间的距离。结果ACL股骨侧止点中心在股骨干力学轴与其平行线之间(65．3±1．1)%处,在Blumensaat线及其平行线之间(78．1±1．0)%处。胫骨侧止点中心在正位片上位于胫骨平台(47．1±2．6)%处,在侧位片位于(43．9±1．7)%处。结论股骨干力学轴和Blumensaat线及与其平行的股骨髁切线结合更方便定位ACL股骨侧标记；X线下胫骨平台定位更为准确。     

Comparison of tunnel positions in single-bundle anterior cruciate ligament reconstructions using computer navigation

Recurrent rotational instability has been identified as a potential source of failure of anterior cruciate ligament (ACL) reconstructions. The aim of the study was to assess whether knee kinematics in the horizontal configuration more closely resemble the intact knee when compared with other single-bundle configurations. Using the Praxim computer navigation system, ACL reconstructions were performed with tibialis anterior grafts in six fresh-frozen whole lower extremity cadaver specimens (12 knees). In each knee, all four reconstruction configurations: conventional (PL tibia to AM femur), anteromedial (AM), posterolateral (PL), and horizontal (AM tibia to PL femur) were performed. Standardized Lachman and pivot shift examinations were performed. For all graft positions during the pivot shift, decreases in the amount of ATT were observed compared with the ACL-deficient state. The knees with grafts placed in the anterior tibial footprint (AM and horizontal) had less ATT with the Lachman and pivot shift maneuvers than knees with grafts placed in the posterior tibial footprint (PL and conventional). A significant difference in depth of impingement was noted only between the AM position and the PL position. Single-bundle ACL reconstructions using graft placement within the anterior footprint on the tibia may reduce rotational instability when compared with more vertical configurations.     

Tibial tunnel enlargement after anterior cruciate ligament reconstruction by autogenous bone-patellar tendon-bone graft

This retrospective study was designed to evaluate changes in the diameter of the tibial tunnel over time following the reconstruction of the anterior cruciate ligament (ACL) with a bone-patellar tendon-bone autograft in 44 patients. The changes in the geometry of the bone tunnels were measured radiographically during the immediate postoperative period and at time intervals between 3 and 36 months after surgery. The dimensions at 1 year were correlated with the 1-year clinical results. The distance between the sclerotic margins of the tibial tunnel was measured at the distal tunnel exis on the medial tibial cortex, in the middle of the tunnel, and proximally at the level of the joint line. The dimensions were calculated by using a magnification factor determined by reference to the interference screw of known diameter located within the tunnel. The position of the centre of the tibial tunnel with regard to Blumensaat's line was also measured. The average tunnel diameter at the proximal tibial exit increased from 12±1.9 mm (mean ± standard deviation) postoperatively to 14±2.2 mm at 3 months. The average proximal tunnel diameter did not significantly change from 3 months to 2 years, and then decreased to 13±2.4 mm at 3 years. At 1 year, most of the patterns of osteolysis were of the cone type (57%), followed by the cavity type (40%) and line type (3%). The degree of osteolysis was not related to the tibial tunnel position with respect to Blumensaat's line. There was no correlation between the changes in tunnel diameter and either the IKDC score or the residual joint laxity measured by a KT-1000 arthrometer. The aetiology of tunnel enlargement is currently unknown. Possible factors responsible for bone resorption include micromotion of the graft relative to the tunnel wall, leading to an inflammatory response in the tunnel, or stress shielding of the tunnel wall proximal to the interference screw.     

The effect of anterior cruciate ligament graft rotation on knee biomechanics

Purpose

The purpose of this study was to evaluate the effects on knee biomechanics of rotating the distal end of the bone-patellar tendon graft 90° in anatomic single-bundle (SB) anterior cruciate ligament (ACL) reconstruction with a porcine model.

Methods

Twenty (n = 20) porcine knees were evaluated using a robotic testing system. Two groups and three knee states were compared: (1) intact ACL, (2) deficient ACL and (3) anatomic SB ACL reconstruction with (a) non-rotated graft or (b) rotated graft (anatomic external fibre rotation). Anterior tibial translation (ATT), internal (IR) and external rotation (ER) and the in situ tissue force were measured under an 89-N anterior tibial (AT) load and 4-N m internal and external tibial torques.

Results

A significant difference from the intact ACL was found in ATT at 60° and 90° of knee flexion for rotated and non-rotated graft reconstructions (p < 0.05). There was a significant difference in the in situ force from the intact ACL with AT loading for rotated and non-rotated graft reconstructions at 60° and 90° of knee flexion (p < 0.05). Under IR loading, the in situ force was significantly different from the intact ACL at 30° and 60° of knee flexion for rotated and non-rotated graft reconstructions (p < 0.05). There were no significant differences in ATT, IR, ER and the in situ force between rotated and non-rotated reconstructions.

Conclusion

Graft rotation can be used with anatomic SB ACL reconstruction and not have a deleterious effect on knee anterior and rotational biomechanics. This study has clinical relevance in regard to the use of graft rotation to better reproduce the native ACL fibre orientation in ACL reconstruction.

     

Biomechanics of intratunnel anterior cruciate ligament graft fixation

Interference screw fixation of bone-patellar tendon-bone grafts now is considered the standard against which all ACL graft-fixation techniques are compared, but mechanical fixation of the ACL graft in the bone tunnels is the weak link in the early postoperative period. This article discusses some of the limitations of in vitro biomechanical studies and reviews variables that influence the tensile properties of intratunnel fixation methods for bone-tendon-bone and soft tissue grafts.     

MR imaging of anterior cruciate ligament reconstruction graft

OBJECTIVE. The objective was to determine the MR imaging findings that differentiate intact anterior cruciate ligament reconstruction graft, partial-thickness tear, and full-thickness tear, using arthroscopy as the gold standard. MATERIALS AND METHODS. Sixteen consecutive MR imaging examinations were retrospectively and independently evaluated by two musculoskeletal radiologists for primary signs (graft signal, orientation, fiber continuity, complete discontinuity, and thickness) and secondary signs (anterior tibial translation, uncovered posterior horn lateral meniscus, posterior cruciate ligament hyperbuckling, and abnormal posterior cruciate ligament line) of anterior cruciate ligament reconstruction graft tear in 15 patients with follow-up arthroscopy. Results were compared with arthroscopy, and both receiver operating characteristic curves and kappa values for interobserver variability were calculated. RESULTS. Arthroscopy revealed four full-thickness graft tears, seven partial-thickness tears, and five intact grafts. Of the primary signs, graft fiber continuity in the coronal plane and 100% graft thickness in the sagittal or coronal plane were most valuable in excluding full-thickness tear. Complete discontinuous graft in the coronal plane also was valuable in diagnosis of full-thickness tear. Of the secondary signs, anterior tibial translation and uncovered posterior horn lateral meniscus assisted in differentiating graft tear (partial or full thickness) from intact graft. The other primary and secondary signs were less valuable. Kappa values were highest for graft fiber continuity and graft discontinuity in the coronal plane. CONCLUSION. Full-thickness anterior cruciate ligament graft tear can be differentiated from partial-thickness tear or intact graft by evaluating for graft fiber continuity (coronal plane), complete graft discontinuity (coronal plane), and graft thickness (coronal or sagittal plane).     

The effect of anterior cruciate ligament graft orientation on rotational knee kinematics

Purpose

To determine whether coronal graft orientation and tunnel placement for single-bundle anterior cruciate ligament (ACL) reconstruction is associated with tibial rotation excursion during functional activities.

Methods

Eighty-four patients who had undergone ACL reconstruction over a ten-year time span had tibial rotation measured during level walking, using a three-dimensional motion analysis system. Fifty-two patients also had measures taken during the more dynamic task of single-limb landing. During the 10-year period, the position of the graft was deliberately changed from a vertical to more horizontal orientation in the coronal plane. Post-operative radiographs were analysed for the coronal graft orientation and femoral and tibial tunnel positions. Radiographic measurements of graft orientation and tunnel position were then correlated with the amount of tibial rotational excursion recorded during the walking and landing tasks.

Results

For the single-limb landing task, a significant positive correlation was observed between the coronal graft angle and rotational excursion (R = 0.35, R ²  = 0.12, p = 0.01). This indicated greater rotational excursion was associated with vertical graft orientation, but only explained 12 % of the variance. No correlations were found between coronal graft angle and tibial rotation during level walking.

Conclusions

These findings support the notion that ACL graft orientation may play a role in rotational kinematics of the ACL-reconstructed knee, particularly during higher impact activities.

Level of evidence

IV.     

Effects of graft pretensioning in anterior cruciate ligament reconstruction

Purpose

Graft pretensioning is used in anterior cruciate ligament (ACL) reconstruction to prevent secondary slackening. Its effects on collagen fibrillar ultrastructure are not known. In this study, we hypothesized that graft pretensioning in ACL reconstruction creates ultrastructural changes detectable in scanning electron microscopy (SEM).

Methods

A prospective comparative study was carried out on 38 ACL reconstructions using a 4-strand semitendinosus graft. Samples were harvested intra-operatively before and after pretensioning for 30?s, 2 or 5?min. The images produced in SEM were analyzed using an original semi-quantitative ?CIP? score taking into account collagen cohesion, integrity, and parallelism. Intra- and inter-tester reliability for the CIP score were tested.

Results

The CIP scores decreased by 3.5 (1.6) points after pretensioning (P?P?Conclusion Pretensioning ACL grafts resulted in alteration of the collagen fibrillar ultrastructure, detectable using SEM. These results confirm the existence of collagen ultrastructural changes after pretensioning that may be related to its duration.

Level of evidence

Prospective comparative study, Level II.     

前交叉韧带重建术后假体功能不全的影像评价

目的 探讨前交叉韧带重建术后假体功能不全的影像特点.方法 同顾性分析24例韧带重建术后因功能不全而接受二次关节镜的患者,包括16例假体断裂,8例假体松弛.影像评价包括骨道关节内口的位置、韧带假体的MRI表现、骨关节病程度及相关并发症.假体断裂组和松弛组的骨道内口位置、MRI表现为断裂的比例及骨关节病等的比较,采用Fisher精确概率法比较.结果 断裂组中,2例股骨骨道关节内口位置异常,3例胫骨骨道关节内口位置异常;松弛组中,3例股骨骨道关节内口位置异常,4例胫骨骨道关节内口位置异常.两组间比较,股骨骨道关节内口位置异常(P=0.289)和胫骨骨道关节内口位置异常的比例(P=0.167)差异均无统计学意义.断裂组中,MRI正确诊断15例完全断裂,1例部分断裂表现为正常;松弛组中,4例表现为正常,其余4例在MRI上被诊断为假体断裂.两组在MRI上表现为断裂的比例差异存在统计学意义(P =0.028).断裂组中,14例可见骨关节病;松弛组中,5例可见骨关节病.两组骨关节病的比例差异无统计学意义(P=0.289).结论 假体断裂和假体松弛骨道关节内口位置异常和骨关节病的比例差异无统计学意义;MRI可以正确诊断绝大多数假体断裂,而部分假体松弛则容易被误诊为假体断裂.     

Tibial tunnel area changes following arthroscopic anterior cruciate ligament reconstructions with autogenous patellar tendon graft

We investigated radiographic changes in tibial tunnel area after ACL reconstructions with autogenous patellar tendon grafts on anteroposterior and lateral radiographs over 3 years. Fifty patients followed up for at least 1 year were included in the study. Radiographs were taken on the day of surgery and 3, 6, 9, 12, 24, and 36 months postoperatively. Tibial tunnels on both radiographs were divided into proximal, middle, and distal one-third. The area of each one-third and the greatest diameter of the tibial tunnel on both radiographs was measured using an image-processing software. According to the tunnel area changes, the shape of tibial tunnel was classified into one of four shapes; cylinder, mallet, reverse bottle, and reverse triangle. The correlations between area, diameter and shape of the tunnel, and clinical variables including arthrometer measurement and clinical score were determined. The areas of each one-third of the tibial tunnels on lateral radiographs was always greater than that on anteroposterior radiographs, although the diameters on the two radiographs did not differ significantly. The area of proximal one-third largest and that of distal one-third smallest on both radiographs at any time point. The enlargement and reduction occurred within 3 months and tended to continue for 9 months. Thereafter the tunnel change stabilized on both radiographs. The most common shape of the enlarged tunnels was cylindrical on anteroposterior radiographs reverse triangle on lateral radiographs. No negative effects of enlarged area, diameter, or tunnel shape on clinical results were found in our study.     

Native anterior cruciate ligament obliquity versus anterior cruciate ligament graft obliquity: an observational study using navigated measurements

BACKGROUND: The goal of anterior cruciate ligament reconstruction is to attain a graft that closely resembles the native anterior cruciate ligament anatomy. By reconstructing the original anatomy, one hopes to eliminate issues related to graft elongation, impingement, and excessive tension while achieving ideal knee kinematics. HYPOTHESIS: Clinical grafts placed using the transtibial technique will differ in the sagittal and coronal planes when compared with obliquity of the anatomic anterior cruciate ligament. STUDY DESIGN: Controlled laboratory study/case series; Level of evidence, 4. METHODS: With the assistance of computer navigation, our study compared the anterior cruciate ligament orientation of 5 cadaver knees with 12 clinical anterior cruciate ligament-reconstructed knees using the transtibial technique. Results: Clinical graft obliquity differed from the anatomic anterior cruciate ligament in all flexion angles: 0 degrees, 30 degrees, 60 degrees, and 90 degrees. In the sagittal plane, the clinical graft obliquity differed from the anatomic anterior cruciate ligament by 13.6 degrees, 12.7 degrees, 16.7 degrees, and 17 degrees, respectively. In the coronal plane, the clinical graft obliquity differed from the anatomic anterior cruciate ligament by 4.9 degrees, 7.6 degrees, 8.9 degrees, and 12.7 degrees, respectively. Paired t tests demonstrated that the difference between the clinical and anatomic anterior cruciate ligament was significant (P <.05), except in the coronal plane at 0 degrees of flexion. In spite of this, all patients demonstrated a negative pivot shift and Lachman at the conclusion of their reconstructions and at 6-month follow-up. CONCLUSION: The sagittal and coronal plane obliquity of well-functioning grafts placed using the transtibial technique were more vertical than anatomic fibers. CLINICAL RELEVANCE: Graft obliquity, in both the coronal and sagittal plane, may be an important means to target appropriate anterior cruciate ligament graft position and can be monitored using surgical navigation systems.     

The effect of cyclic loading on rotated bone-tendon-bone anterior cruciate ligament graft constructs

BACKGROUND: Single-incision anterior cruciate ligament reconstruction with a bone-patellar tendon-bone construct is commonly performed with 180 degrees rotation of the graft. It has been hypothesized that further rotation of the graft to 540 degrees can effectively shorten the graft to address graft length-tunnel mismatch. Initial biomechanical failure characteristics of rotated constructs have been reported, but cyclic loading of tendons has not been performed. HYPOTHESIS: Graft rotation affects the biomechanical properties of the construct. STUDY DESIGN: Controlled laboratory study. METHODS: Thirty-five bone-patellar tendon-bone composite porcine right knee specimens were randomized into 3 groups and were externally rotated to 0 degrees , 180 degrees , or 540 degrees . Each group was then cyclically loaded in an artificial synovial fluid medium between 50 and 250 N for 5,000 cycles, loaded between 50 and 500 N for an additional 5,000 cycles, and finally subjected to load-to-failure testing. RESULTS: Graft rotation shortened constructs by 1.7 +/- 0.8 mm at 180 degrees of rotation and 7.6 +/- 2.0 mm at 540 degrees of rotation (P < .01). There was a statistically significant increase in strain during cyclic loading at 540 degrees . No significant differences in maximum load, yield stress, yield strain, or modulus of elasticity were detected in single-cycle load-to-failure testing after cyclic loading. CONCLUSION: Rotation of bone-patellar tendon-bone constructs to 540 degrees predictably shortens the effective graft length at the expense of increased strain with cyclic loading at stresses equivalent to walking and running. CLINICAL RELEVANCE: Although rotation to 540 degrees potentially addresses graft length-tunnel mismatch, further clinical evaluation is required to evaluate the impact of increased strain on knee laxity and to determine the effects of physiologic loading of rotated bone-patellar tendon-bone constructs in vivo.     

The remains of anterior cruciate ligament graft tension after cyclic knee motion

BACKGROUND: There is sometimes a return of excess knee laxity after anterior cruciate ligament reconstruction. One of the contributing factors might be a loss in graft tension. It is unknown whether the tension imposed on an anterior cruciate ligament graft degrades with time and, if so, the effect of that loss of tension on knee laxity. HYPOTHESES: The pretension in the anterior cruciate ligament graft reduces significantly within the first 500 motion cycles, and this decrease in graft tension causes an increase in knee laxity. STUDY DESIGN: Controlled laboratory study. METHODS: This study measured the remains of bone-patellar tendon-bone graft pretension after cyclical flexion-extension and the effect of any tension loss on knee laxity, using 8 cadaveric knees. A tension transducer was inserted into the graft and calibrated in situ. The reconstruction tension was 40 N at 20 degrees of flexion. In test 1, the graft tension was measured under cyclical flexion-extension in a motorized rig up to 1500 cycles. Test 2, with a new graft, also included anteroposterior and internal-external rotational knee laxity measurements at 0, 500, and 1500 cycles. RESULTS: The graft tension at 0 degrees of flexion dropped from 208 N, by 25% after 50 cycles, 41% by 500, and 46% by 1500 cycles. Anterior laxity increased from +1.4 to +2.8 mm by 500 cycles, and performing these laxity tests also caused significant tension losses. CLINICAL RELEVANCE: These results provide one possible explanation for early slackening of anterior cruciate ligament reconstructions.     

“Biological failure” of the anterior cruciate ligament graft

Anterior cruciate ligament (ACL) reconstruction has the best chance for success when the graft undergoes extensive biologic remodeling and incorporation after implantation. There are many factors that can lead to graft failure and possible revision surgery. These include patient selection; surgical technique such as graft placement and tensioning; the use of allograft versus autograft; mechanical factors such as secondary restraint laxity; lack of a correct, carefully controlled post-operative rehabilitation program; and biological factors. When a patient presents with knee instability following ligament reconstruction and there is no history of a new trauma or identifiable technical error, biological failure should be considered. However, the biologic response of the grafted tissue is closely linked to the mechanical and biochemical environment into which the graft is placed. Thus, the “biological failure” of the ACL graft is a complex pathological entity whose cause is not fully understood. Failure may be initiated by early extensive graft necrosis, disturbances in revascularization, problems in cell repopulation and proliferation, and as well difficulties in the ligamentization process. However, further study of the biological characterization of a failed graft placed in a correct mechanical environment is warranted.