The immediate postoperative kinematic state after anterior cruciate ligament reconstruction with increasing peroperative tension

The last steps in anterior cruciate ligament (ACL) reconstruction are tensioning and fixation of the ligament. However, how much tension should be applied to the ligament in general or in each individual and in which position the ligament should be fixed remain unanswered questions. The purpose of this study was to investigate the effect of increasing ligament tension on the immediate postoperative kinematic state of the ACL-reconstructed knee. Nine cadaver knees were mounted in a mechanical measuring device based on a redesign of the Genucom knee testing system, so that the femur was fixed to a force plate and the moving tibia to a goniometer arm for registration of movement. The ligament was attached on the tibial side to a Kistler load cell and a turnbuckle for adjustment of ligament tension. The ligament was tensioned at 30° of flexion with 5, 33, 66, 99 and 132 N. The cadaver knees were tested with an intact ACL, after sacrifice of the ACL and after reconstruction of the ACL with an ABC ligament. Results showed that there was a significant decrease in knee motion when the tension was higher than 33 N. This resulted in an overconstrained knee with less anteroposterior translation, internal-external rotation and varus-valgus movement compared with the uninjured knee.     

An in vitro study of the Müller anterolateral femorotibial ligament tenodesis in the anterior cruciate ligament deficient knee

The biomechanical effectiveness of the Müller anterolateral femorotibial ligament (ALFTL) iliotibial band tenodesis on anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. Anterior drawer and internal rotation of the tibia were measured at 15 degrees increments from 0 degrees to 90 degrees in response to 50 N of anteriorly applied tibial force and 3 Nm of internally applied internal torque, respectively, in the intact knee, the ACL excised knee, and following the ALFTL reconstruction. A strain gage was used to measure the resting graft tension and to measure strain in the graft during the load-displacement tests. The Müller ALFTL tenodesis failed to return normal anterior stability to the ACL deficient knee (P less than 0.05). The tenodesis did, however, reduce the anterior laxity of the ACL deficient knee from 30 degrees to 90 degrees of knee flexion (P less than 0.05). The tenodesis overconstrained internal tibial rotation of the ACL excised knee from 30 degrees to 90 degrees (P less than 0.05). Measurements of strain in the tenodesis supported the load-displacement findings that the tenodesis was most effective in constraining anterior drawer and internal tibial rotation from 30 degrees to 90 degrees of knee flexion.     

Effect of knee flexion on the in situ force distribution in the human anterior cruciate ligament

This study was conducted to evaluate the effect of applied load on the magnitude, direction, and point of tibial intersection of the in situ forces of the anteromedial (AM) and posterolateral (PL) bands of the human anterior cruciate ligament (ACL) at 30° and 90° of knee flexion. An Instron was used to apply a 100 N anterior shear force to 11 human cadaver knees, 6 at 30° of knee flexion and 5 at 90° of knee flexion. A Universal Force Sensor (UFS) recorded the resultant 6 degree-of freedom (DOF) forces/moments. Each specimen then underwent serial removal of the AM and PL bands. With the knee limited to 1 DOF (anteroposterior), tests were performed before and after each structure was removed. Because the path was identical in each test, the principle of superposition was applied. Thus, the difference between the resultant forces could be attributed to the force carried by the structure just removed. The magnitudes of force in the ACL at 30° and 90° of knee flexion were 114.1±7.4 N and 90.8±8.3 N, respectively (P<0.05). At 30°, the AM and PL bundles carried 95% and 4% of the total ACL force, respectively. At 90°, the AM and PL bands carried 85% and 13%, respectively (P<0.05). The direction of the in situ force in the whole ACL as well as its two bands correlated with the anatomic orientation of the ligament. The resultant total ACL force intersected the tibial plateau at the posterolateral aspect of the AM band's insertion at 30° of knee flexion, while at 90°, the force intersection moved posteriorly to the AM/PL border. This research provides new insight into the fundamental force relationships of the ACL and its bundles. In response to an anterior tibial shear force, the AM band of the ACL was the predominant load carrier at both 30° and 90° of knee flexion. However, contrary to carlier reports, the in situ force carried in the PL band increased as knee flexion increased. Further, the tibial intersection of the resultant ACL force moved laterally with knee flexion. These findings confirm the dynamic structure of the ACL that in itself has no isometricity and may also indicate that there is no ideal location in which to position a replacement graft. The use of this methodology with more physiologically unconstrained motion should lead to more definitive clinical conclusions.     

The effect of femoral attachment location on anterior cruciate ligament reconstruction: graft tension patterns and restoration of normal anterior–posterior laxity patterns

The issue of the best place to attach an anterior cruciate ligament graft to the femur is controversial, and different anatomic or isometric points have been recommended. It was hypothesised that one attachment site could be identified that would be best for restoring normal anterior–posterior laxity throughout the range of knee flexion. It was also hypothesised that these different attachment sites would cause different graft tension patterns during knee flexion. Using six cadaver knees, an isometric point was found 3 mm distal to the posterior edge of Blumensaats line, at the 10:30–11:00 oclock position in right knees, at the antero-proximal edge of the anatomic ACL attachment. Anterior–posterior laxity was measured at ±150 N draw force at 20–120° flexion with the knee intact and after anterior cruciate ligament transection. The graft was placed at the isometric point, and AP laxity was restored to normal at 20° flexion, then measured at other angles. Graft tension was measured throughout, and also during passive flexion–extension. This was repeated for four other graft positions around the isometric point in every knee. Laxity was restored best by grafts tensioned to a mean of 9±14 N, positioned isometrically and 3 mm posterior to the isometric point. Their tension remained low until terminal extension. Grafts 3 mm anterior to the isometric point caused significant overconstraint, and had higher tension beyond 80° knee flexion. Small changes in attachment site had large effects on laxity and tension patterns. These results support an isometric/posterior anatomic femoral graft attachment, which restored knee laxity to normal from 20 to 120° flexion and did not induce high graft tension as the knee flexed. Grafts attached to the roof of the intercondylar notch caused overconstraint and higher tension in the flexed knee.     

A biomechanical analysis of two reconstructive approaches to the posterolateral corner of the knee

The objective of this study was to evaluate the effects of the biceps femoris tenodesis and popliteofibular ligament reconstruction on knee biomechanics. Ten human cadaveric knees were tested in the intact, posterolateral corner (PLC)-deficient, and PLC-reconstructed conditions using a robotic/universal force moment sensor testing system. The knees were subjected to: (1) a 134 N posterior tibial load, and (2) a 10 Nm external tibial torque applied to the tibia at full extension, 30° and 90° of flexion. External tibial rotation of the intact knee ranged from 18.3±4.6° at full extension to 27.9±4.6° at 30° under the 10 Nm external tibial torque. These values increased after sectioning the PLC by 2.8°–7.5° at 30° and 90° respectively. After the popliteofibular ligament reconstruction, external tibial rotation values were not significantly different from those for the intact knee at any angle tested, while values following the biceps tenodesis were as much as 5.7° greater than the intact knee. Under the 134 N posterior tibial load, there were minimal decreases in posterior tibial translation of up to 0.9 mm with the biceps tenodesis and up to 1.6 mm with the popliteofibular ligament reconstruction compared to the intact knee. The in situ forces in the biceps tenodesis were not significantly different than the intact PLC at full extension or 30°, while the in situ forces in the popliteofibular graft were not significantly different at any flexion angle. Our data suggests that by restoring external tibial rotation the popliteofibular ligament reconstruction more closely reproduces the primary function of the PLC as compared to the biceps tenodesis.     

Roles of ACL remnants in knee stability

Purpose

This study evaluated knee laxity in anterior tibial translation and rotation following removal of anterior cruciate ligament (ACL) remnants using a computer navigation system.

Methods

This prospective study included 50 knees undergoing primary ACL reconstruction using a navigation system. ACL remnants were classified into four morphologic types: Type 1, bridging between the roof of the intercondylar notch and tibia; Type 2, bridging between the posterior cruciate ligament and tibia; Type 3, bridging between the anatomical insertions of the ACL on the lateral wall of the femoral condyle and the tibia; and Type 4, no bridging of ACL remnants. Anterior tibial translation and rotatory laxity were measured before and after remnant resection using a navigation system at 30°, 60°, and 90° of knee flexion. The amount of change in anterior tibial translation and rotatory laxity of each type was compared among the types.

Results

The different morphologic types of ACL remnants were as follows: Type 1, 15 knees; Type 2, 9 knees; Type 3, 6 knees; and Type 4, 20 knees. The amount of change in anterior tibial translation and rotatory laxity at 30° knee flexion in Type 3 was significantly larger than in the other types. There were no significant differences in either tibial translation or rotatory laxity at 60° and 90° knee flexion among the types.

Conclusions

In Type 3, ACL remnants contributed to anteroposterior and rotatory knee laxity evaluated at 30° knee flexion. The bridging point of the remnants is important to knee laxity. The Type 3 remnant should be preserved as much as possible when ACL reconstruction surgery is performed.

Level of evidence

Prognostic study, Level II.     

Tibiofemoral kinematics of the anterior cruciate ligament (ACL)-deficient weightbearing, living knee employing vertical access open "interventional" multiple resonance imaging

BACKGROUND: Our current understanding of tibiofemoral kinematics in the anterior cruciate ligament (ACL)-deficient knee is very limited. Using vertical open-access MRI, it is possible to accurately analyze tibiofemoral motion in patients with isolated rupture of the ACL. STUDY: Prospective cohort study. PURPOSE: To assess if ACL rupture alters normal knee weightbearing kinematics. METHODS: Tibiofemoral motion was assessed through the arc of flexion from 0 degrees to 90 degrees in 10 patients with isolated rupture of the ACL in one knee and a normal contralateral knee. Midmedial and midlateral sagittal images were analyzed in all positions of flexion in both knees to assess the tibiofemoral relationship. RESULTS: In the lateral compartment of the knee, the tibial plateau is persistently subluxed anteriorly throughout the arc of flexion from 0 degrees to 90 degrees (flexion facet center to posterior tibial cortex distance of 15.8 mm +/- 2.9 in ACL-deficient knees compared to 21.4 mm +/- 1.4 in normal knees at 0 degrees extension, P <.0001) when compared to normal knees. The medial tibiofemoral relationship is unchanged compared to normal knees. CONCLUSION: Rupture of the ACL changes tibiofemoral kinematics producing anterior subluxation of the lateral tibial plateau. CLINICAL SIGNIFICANCE: Altered kinematics may explain, at least in part, the increased incidence of secondary osteoarthritis in patients with ACL rupture.     

The biomechanical effect of posterior cruciate ligament reconstruction on knee joint function. Kinematic response to simulated muscle loads

BACKGROUND: The effectiveness of posterior cruciate ligament reconstruction in restoring normal kinematics under physiologic loading is unknown. HYPOTHESIS: Posterior cruciate ligament reconstruction does not restore normal knee kinematics under muscle loading. STUDY DESIGN: In vitro biomechanical study. METHODS: Kinematics of knees with an intact, resected, and reconstructed posterior cruciate ligament were measured by a robotic testing system under simulated muscle loads. Anteroposterior tibial translation and internal-external tibial rotation were measured at 0 degrees, 30 degrees, 60 degrees, 90 degrees, and 120 degrees of flexion under posterior drawer loading, quadriceps muscle loading, and combined quadriceps and hamstring muscle loading. RESULTS: Reconstruction reduced the additional posterior tibial translation caused by ligament deficiency at all flexion angles tested under posterior drawer loading. Ligament deficiency increased external rotation and posterior translation at angles higher than 60 degrees of flexion when simulated muscle loading was applied. Posterior cruciate ligament reconstruction reduced the posterior translation and external rotation observed in posterior cruciate ligament-deficient knees at higher flexion angles, but differences were not significant. CONCLUSION: Under physiologic loading conditions, posterior cruciate ligament reconstruction does not restore six degree of freedom knee kinematics. Clinical Relevance: Abnormal knee kinematics may lead to development of long-term knee arthrosis.     

Biomechanical analysis of tibial torque and knee flexion angle: implications for understanding knee injury

Knee injuries are common in sports activities. Understanding the mechanisms of injury allows for better treatment of these injuries and for the development of effective prevention programmes. Tibial torque and knee flexion angle have been associated with several mechanisms of injury in the knee. This article focuses on the injury to the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL) and the meniscus of the knee as they relate to knee flexion angle and tibial torque. Hyperflexion and hyperextension with the application of tibial torque have both been implicated in the mechanism of ACL injury. A combination of anterior tibial force and internal tibial torque near full extension puts the ACL at high risk for injury. Hyperflexion also increases ACL force; however, in this position, internal and external tibial torque only minimally increase ACL force. Several successful prevention programmes have been based on these biomechanical factors. Injury to the PCL typically occurs in a flexed or hyperflexed knee position. The effects of application of a tibial torque, both internally and externally, remains controversial. Biomechanical studies have shown an increase in PCL force with knee flexion and the application of internal tibial torque, while others have shown that PCL-deficient knees have greater external tibial rotation. The meniscus must endure greater compressive loads at higher flexion angles of the knee and, as a result, are more prone to injury in these positions. In addition, ACL deficiency puts the meniscus at greater risk for injury. Reducing the forces on the ACL, PCL and meniscus during athletic activity through training, the use of appropriate equipment and safe surfaces will help to reduce injury to these structures.     

The effect of anterior cruciate ligament reconstruction on knee joint kinematics under simulated muscle loads

BACKGROUND: Numerous studies have investigated anterior stability of the knee during the anterior drawer test after anterior cruciate ligament reconstruction. Few studies have evaluated anterior cruciate ligament reconstruction under physiological loads. PURPOSE: To determine whether anterior cruciate ligament reconstruction reproduced knee motion under simulated muscle loads. STUDY DESIGN: Controlled laboratory study. METHODS: Eight human cadaveric knees were tested with the anterior cruciate ligament intact, transected, and reconstructed (using a bone-patellar tendon-bone graft) on a robotic testing system. Tibial translation and rotation were measured at 0 degrees, 15 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion under anterior drawer loading (130 N), quadriceps muscle loading (400 N), and combined quadriceps and hamstring muscle loading (400 N and 200 N, respectively). Repeated-measures analysis of variance and the Student-Newman-Keuls test were used to detect statistically significant differences between knee states. RESULTS: Anterior cruciate ligament reconstruction resulted in a clinically satisfactory anterior tibial translation. The anterior tibial translation of the reconstructed knee was 1.93 mm larger than the intact knee at 30 degrees of flexion under anterior load. Anterior cruciate ligament reconstruction overconstrained tibial rotation, causing significantly less internal tibial rotation in the reconstructed knee at low flexion angles (0 degrees-30 degrees) under muscle loads (P < .05). At 30 degrees of flexion, under muscle loads, the tibia of the reconstructed knee was 1.9 degrees externally rotated compared to the intact knee. CONCLUSIONS: Anterior cruciate ligament reconstruction may not restore the rotational kinematics of the intact knee under muscle loads, even though anterior tibial translation was restored to a clinically satisfactory level under anterior drawer loads. These data suggest that reproducing anterior stability under anterior tibial loads may not ensure that knee joint kinematics is restored under physiological loading conditions. CLINICAL RELEVANCE: Decreased internal rotation of the knee after anterior cruciate ligament reconstruction may lead to increased patellofemoral joint contact pressures. Future anterior cruciate ligament reconstruction techniques should aim at restoring 3-dimensional knee kinematics under physiological loads.     

慢性膝关节前交叉韧带损伤患者步态的运动学分析

目的:探讨慢性膝关节前交叉韧带(ACL)损伤患者下肢关节运动学变化特点。方法:30名慢性ACL损伤患者为损伤组,30名健康人为对照组,利用三维运动分析系统对实验对象进行步态分析,比较两组的时间距离指标;比较两组在预承重期髋、膝关节最大屈曲角度和踝关节最大跖屈角度,以及膝关节最大外旋角度。结果:同对照组比较,损伤组步频、步速显著减小,步态周期时间显著增加(P<0.05)。在预承重期,损伤组最大屈髋角度同对照组相比无明显差异,最大屈膝角度显著小于对照组(P<0.05),最大跖屈角度显著小于对照组(P<0.05),最大胫骨外旋角度显著大于对照组(P<0.05)。结论:慢性ACL损伤患者行走时步态出现膝关节屈曲、踝关节跖屈角度的改变,同时,膝关节旋转角度也发生改变。     

Relative contribution of the ACL, MCL, and bony contact to the anterior stability of the knee

Ligaments and other soft tissues, as well as bony contact, all contribute to anterior stability of the knee joint. This study was designed to measure the in situ force in the medial collateral ligament (MCL), anterior cruciate ligament (ACL), posterolateral structures (PLS), and posterior cruciate ligament (PCL) in response to 110 N anterior tibial loading. The changes in knee kinematics associated with ACL deficiency and combined MCL+ACL deficiency were also evaluated. Utilizing a robotic/universal force-moment sensor system, ten human cadaveric knee joints were tested between 0° and 90° of knee flexion. This unique testing system is designed to determine the in situ forces in structures of interest without making mechanical contact with the tissue. More importantly, data for individual structures can be obtained from the same knee specimen since the robotic manipulator can reproduce the motion of the intact knee. The in situ forces in the ACL under anterior tibial loading to 110 N were highest at 15° flexion, 103 ± 14 N (mean ± SD), decreasing to 59.2 ± 30 N at 90° flexion. For the MCL, these forces were 8.0 ± 3.5 N and 38.1 ± 25 N, respectively. Forces due to bony contact were as high as 34.1 ± 23 N at 30° flexion, while those in the PLS were relatively small at all flexion angles. Combined MCL+ACL deficiency was found to significantly increase anterior tibial translation relative to the ACL-deficient knee only above 60° of knee flexion. These findings confirm the hypothesis that there is significant load sharing between various ligaments and bony contact during anterior tibial loading of the knee. For this reason, the MCL and osteochondral surfaces may also be at significant risk during ACL injury. Received: 29 December 1997 Accepted: 16 July 1998     

3D kinematic in-vitro comparison of posterolateral corner reconstruction techniques in a combined injury model

With the variable injury pattern to the posterolateral structures (PLS) of the knee, a number of reconstructive procedures have been introduced. It was the aim of the present study to evaluate the resulting 3D kinematics following three different surgical techniques of reconstruction in a combined posterior cruciate ligament (PCL)/PLS injury model. In nine human cadaveric knees, 3D kinematics were recorded during the path of flexion–extension using a computer based custom made 6-degree-of-freedom (DOF) testing apparatus. Additional laxity tests were conducted at 30 and 90° of flexion. Testing was performed before and after cutting the PLS and PCL, followed by PCL reconstruction alone. Reconstructing the posterolateral corner, three surgical techniques were compared: (a) the posterolateral corner sling procedure (PLCS), (b) the biceps tenodesis (BT), and (c) a bone patellar-tendon bone (BTB) allograft reconstruction . Posterior as well as rotational laxity were significantly increased after PCL/PLS transection at 30 and 90° of flexion. Isolated PCL reconstruction resulted in a remaining external rotational deficiency for both tested flexion angles. Additional PLS reconstruction closely restored external rotation as well as posterior translation to intact values by all tested procedures. Compared to the intact knee, dynamic testing revealed a significant internal tibial rotation for (b) BT (mean=3.9°, p=0.043) and for (c) BTB allograft (mean=4.3°, p=0.012). (a) The PLCS demonstrated a tendency to internal tibial rotation between 0 and 60° of flexion (mean=2.2°, p=0.079). Varus/valgus rotation as well as anterior/posterior translation did not show significant differences for any of the tested techniques. The present study shows that despite satisfying results in static laxity testing, pathological 3D knee kinematics were not restored to normal, demonstrated by a nonphysiological internal tibial rotation during the path of flexion-extension.     

An in vitro study of an intraarticular and extraarticular reconstruction in the anterior cruciate ligament deficient knee

The biomechanical effectiveness of an extraarticular ACL reconstruction, an intraarticular ACL reconstruction, and the combination of these on both anterior stability and internal rotational stability of the ACL deficient knee was investigated in six cadaver knees. The extraarticular reconstruction consisted of the Müller anterolateral femorotibial ligament iliotibial band tenodesis, and the intraarticular reconstruction used the middle third of the patellar tendon in the manner of Clancy. The extraarticular reconstruction was found to overconstrain internal tibial rotation of the ACL excised knee between 30 degrees and 90 degrees (P less than 0.05). While the isolated extraarticular reconstruction did not return normal anterior stability to the ACL deficient knee (P less than 0.05), it did significantly reduce the anterior laxity of the ACL deficient knee between 30 degrees and 90 degrees of knee flexion (P less than 0.05). For the combined reconstruction, the intraarticular procedure was performed and then only enough tension was applied to the extraarticular reconstruction to take up slack in the tenodesis without shifting the rotatory position of the tibia from that produced by the intraarticular procedure alone. Neither the intraarticular reconstruction nor the combined procedure resulted in any significant shifts from normal (P less than 0.05) in the rotatory position of the unloaded tibia; during loading neither resulted in rotational displacements significantly different from normal; and both of these procedures reduced the increased anterior laxity of the ACL deficient knee to a level not statistically different from normal. Because the extraarticular reconstruction shared the load when performed with the intraarticular reconstruction as part of a combined procedure, we concluded that it would be useful as an adjunctive procedure in appropriate clinical situations.     

ACL mismatch reconstructions: influence of different tunnel placement strategies in single-bundle ACL reconstructions on the knee kinematics

To evaluate the influence of tibial and femoral tunnel position in ACL reconstruction on knee kinematics, we compared ACL reconstruction with a tibial and femoral tunnel in anteromedial (AM-AM reconstruction) and in posterolateral footprint (PL-PL reconstruction) with a reconstruction technique with tibial posterolateral and femoral anteromedial tunnel placement (PL-AM reconstruction). In 9 fresh-frozen human cadaveric knees, the knee kinematics under simulated Lachman (134 N anterior tibial load) and a simulated pivot shift test (10 N/m valgus and 4 N/m internal tibial torque) were determined at 0°, 30°, 60°, and 90° of flexion. Kinematics were recorded for intact, ACL-deficient, and single-bundle ACL reconstructed knees using three different reconstruction strategies in randomized order: (1) PL-AM, (2) AM-AM and (3) PL-PL reconstructions. Under simulated Lachman test, single-bundle PL-AM reconstruction and PL-PL reconstructions both showed significantly increased anterior tibial translation (ATT) at 60° and 90° when compared to the intact knee. At all flexion angles, AM-AM reconstruction did not show any statistical significant differences in ATT compared to the intact knee. Under simulated pivot shift, PL-AM reconstruction resulted in significantly higher ATT at 0°, 30°, and 60° knee flexion and AM-AM reconstructions showed significantly higher ATT at 30° compared to the intact knee. PL-PL reconstructions did not show any significant differences to the intact knee. AM-AM reconstructions restore the intact knee kinematics more closely when compared to a PL-AM technique resembling a transtibial approach. PL-PL reconstructions showed increased ATT at higher flexion angles, however, secured the rotational stability at all flexion angles. Due to the independent tibial and femoral tunnel location, a medial portal technique may be superior to a transtibial approach.     

Effects of sectioning the posterolateral structures on knee kinematics and in situ forces in the posterior cruciate ligament

The objective of this study was to determine the effects of sectioning the posterolateral structures (PLS) on knee kinematics and in situ forces in the posterior cruciate ligament (PCL) in response to external and simulated muscle loads. Ten human cadaveric knees were tested using a robotic/universal force-moment sensor testing system. The knees were subjected to three loading conditions: (a) 134-N posterior tibial load, (b) 5-Nm external tibial torque, and (c) isolated hamstring load (40 N biceps/40 N semimembranosus). The knee kinematics and in situ forces in the PCL for the intact and PLS-deficient knee conditions were determined at full extension, 30°, 60°, 90°, and 120° of knee flexion. Under posterior tibial loading posterior tibial translation with PLS deficiency increased significantly at all flexion angles by 5.5 ± 1.5 mm to 0.8 ± 1.2 mm at full extension and 90°, respectively. The corresponding in situ forces in the PCL increased by 17–¶19 N at full extension and 30° of knee flexion. Under the external tibial torque, external tibial rotation increased significantly with PLS deficiency by 15.1 ± 1.6° at 30° of flexion to 7.7 ± 3.5° at 90°, with the in situ forces in the PCL increasing by 15–90 N. The largest increase occurred at 60° to 120° of knee flexion, representing forces two to six times of those in the intact knee. Under the simulated hamstring load, posterior tibial translation and external tibial and varus rotations also increased significantly at all knee flexion angles with PLS deficiency, but this was not so for the in situ forces in the PCL. Our data suggest that injuries to the PLS put the PCL and other soft tissue structures at increased risk of injury due to increased knee motion and the elevated in situ forces in the PCL.     

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.     

Anteroposterior stability of the knee during the stance phase of gait after anterior cruciate ligament deficiency

Quadriceps avoidance and higher flexion strategies have been assumed as effects of ACL deficiency on knee joint function during gait. However, the effect of ACL deficiency on anteroposterior stability of the knee during gait is not well defined. In this study, 10 patients with unilateral acute ACL ruptures and the contralateral side intact performed gait on a treadmill. Flexion angles and anteroposterior translation of the ACL injured and the intact controlateral knees were measured at every 10% of the stance phase of the gait (from heel strike to toe-off) using a combined MRI and dual fluoroscopic imaging system (DFIS). The data indicated that during the stance phase of the gait, the ACL-deficient knees showed higher flexion angles compared to the intact contralateral side, consistent with the assumption of a higher flexion gait strategy. However, the data also revealed that the ACL-deficient knees had higher anterior tibial translation compared to the intact contralateral side during the stance phase of the gait. The higher flexion gait strategy was not shown to correlate to a reduction of the anterior tibial translation in ACL deficient knees. These data may provide indications for conservative treatment or surgical reconstruction of the ACL injured knees in restoration of the knee kinematics during daily walking activities.     

Principal component analysis of knee kinematics and kinetics after anterior cruciate ligament reconstruction

This study compared the gait of 10 subjects with unilateral anterior cruciate ligament (ACL) reconstruction to a group of 12 height- and weight-matched control subjects. The analysis was based on knee flexion, adduction, and internal rotation angles and moments. The objective was to use principal component analysis (PCA) to identify knees of the ACL reconstructed subjects that fell outside normal ranges as determined by control subjects. Gait data were collected on all subjects in a motion analysis laboratory. Principal component (PC) models were developed for each gait measure based on the control subjects' data and used to assess gait waveforms of ACL reconstructed subjects. PCA allows analysis of entire gait waveforms for comparisons. In a sample of 10 ACL reconstructed subjects (7 years after surgery, on average), six of the ACL reconstructed knees had not returned to normal following surgery and eight of the contralateral knees functioned differently from controls. A majority of the differences were noted to occur in the abduction-adduction knee moment with corresponding infrequency in the differences seen in abduction-adduction rotation. PCA enabled us to identify subjects with abnormal gait waveforms as outliers relative to the normal control group.     

External stabilization of the anterior cruciate ligament deficient knee during rehabilitation

Using cadaveric specimens, we studied the effect of ACL deficiency upon anterior tibial translation during extension of the knee joint. Five knees were loaded via the quadriceps mechanism until flexion angles of 10 degrees, 25 degrees, 40 degrees, and 60 degrees were attained. At each angle, the anterior-posterior position of the tibia was documented with biplane radiography, both before and after division of the ACL. In every specimen, anterior tibial translation increased with loss of the ACL and was greatest at 25 degrees of flexion, where an average displacement of 3.3 mm was observed. Subluxation was not significant at flexion angles exceeding 60 degrees, regardless of ACL deficiency. We also examined the effect of an external restraining force on tibial subluxation in the ACL deficient knee. Posteriorly directed forces of 0 N, 45 N (10 pounds), 90 N (20 pounds), 135 N (30 pounds), and 225 N (50 pounds) were applied to the tibia at the level of the tibial tubercle. Anterior subluxation was eliminated through application of forces ranging from a maximum of 106 N (23.6 pounds) at 10 degrees to only 13 N (2.9 pounds) at 60 degrees.