股骨单隧道内分叉双束纤维重建后交叉韧带的实验研究

目的在人膝关节标本上行股骨单隧道分叉双束纤维重建后交叉韧带(posterior cruciate ligament,PCL),探讨其术式的优缺点。方法应用力学试验机对14侧捐赠新鲜冷冻人膝关节标本进行生物力学测试,男12侧,女2侧;年龄20～31岁。标本股骨段长20cm,胫骨段长20cm。首先测量PCL完整时胫骨后移距离和交叉韧带的应变(完整组,n=14);然后切断PCL(切断组,n=14),测量胫骨受力时的后移距离后,再将标本随机分为两组:单束重建组(n=7)和分叉双束重建组(n=7),分别测量屈膝0、30、60、90和120°5个角度时胫骨后移距离和移植韧带的应变。结果胫骨受到100N后向力量,完整组在不同屈膝角度下,胫骨向后移位1.97±0.29～2.60±0.23mm,前外束和后内束纤维交替紧张松弛。切断组膝关节明显松弛,胫骨向后移位达11.27±1.06～14.94±0.67mm,与完整组比较差异有统计学意义(P<0.05);单束纤维重建组,在不同屈膝角度下胫骨向后移位1.99±0.19～2.72±0.38mm,移植韧带持续紧张。双束纤维重建组在不同屈膝角度下胫骨向后移位2.27±0.32～3.05±0.44mm,移植的双束纤维交替紧张,协同作用。组内比较:双束重建组在不同屈膝角度时胫骨向后位移差异无统计学意义(P>0.05),而单束重建组在屈膝90°时与屈膝30、60和120°时相比,胫骨后移增大,差异有统计学意义(P<0.05)。结论股骨单隧道内分叉双束纤维重建PCL术在各屈膝角度均能有效防止胫骨后移,股骨单隧道单束重建术屈膝90°时后移较其他角度时增大。分叉双束重建PCL的两束纤维束交替紧张,生物力学特征更接近于正常PCL。     

One- and two-incision anterior cruciate ligament reconstruction: a biomechanical comparison including the effect of simulated closed-chain exercise

The purpose of this study was to evaluate the effect of simulated closed-chain exercise on anterior translation in the anterior cruciate ligament (ACL) reconstructed knee comparing patellar tendon grafts secured with endoscopic and two-incision techniques. ACL reconstructions, were performed on five matched pairs of fresh frozen cadaver lower extremities. One of each pair had endoscopic (inside-out) placement of the femoral interference screw and other had outside-in femoral screw placement. A model for closed-chain exercise was developed to simulate half squat exercises using a custom apparatus on the Material Testing machine with a 356 N (80 lb) axial load and 40 N (9 lb) static hamstring force. Knee motion from near full extension to 60 degrees flexion was achieved by varying the quadricep force. One thousand squats were performed, and KT-1000 arthometry was done before and after cycling each specimen. The femur-graft-tibia constructs were then stressed to failure. Closed-chain cycling resulted in no significant change in anterior translation in either group. The mean maximum load to failure of the femur-graft-tibia construct was 340.4N in the one-incision group and 434.2 N in the two-incision group. P=.048 was considered statistically significant. Anterior translation did not increase after 1,000 simulated half knee bends in either the one- or two-incision groups. Shallow knee bends are an important part of aggressive rehabilitation programs, and our data support the position that these closed-chain exercises do not deleteriously affect the graft. Though the maximum strength to failure differed significantly between the one- and two-incision groups, both techniques offered sufficient strength to withstand an aggressive simulated rehabilitation protocol.Arthroscopy 1998 Mar;14(2):176-81     

Kinematic analysis of conventional and high-flexion cruciate-retaining total knee arthroplasties: an in vitro investigation

This study examined the kinematics of a cruciate-retaining (CR) total knee arthroplasty (TKA) component that attempts to enhance knee flexion by improving posterior tibiofemoral articular contact at high-flexion angles. Using an in vitro robotic experimental setup, medial and lateral femoral translations of this CR design were compared with that of a conventional CR TKA design and intact knee under a combined quadriceps and hamstring muscle load. Both CR TKA designs showed similar kinematics throughout the range of flexion (0 degrees -150 degrees ). The TKAs restored nearly 80% of the posterior femoral translation of the intact knee at 150 degrees . The posterior cruciate ligament (PCL) forces measured for the high-flexion CR TKA component indicate that the PCL is important in the mid-flexion range but has little effect on knee kinematics at high flexion.     

Two-bundle posterior cruciate ligament reconstruction: how bundle tension depends on femoral placement

BACKGROUND: Clinically, one-bundle posterior cruciate ligament reconstructions frequently result in the return of abnormal posterior translation. We hypothesized that the return of posterior translation is caused by a nonuniform distribution of load among the graft fibers. The purpose of the present study was to determine how the femoral attachment location of the second bundle of a two-bundle posterior cruciate ligament reconstruction affects the anterior bundle tension and the load distribution between the graft bundles. METHODS: One and two-bundle posterior cruciate ligament reconstructions (one one-bundle type and three two-bundle types) were performed in nineteen cadaveric knees. The grafts were tensioned to restore posterior translation to within +/-1 mm of that of the intact knee at 90 degrees of flexion while a 100-N posterior force was applied to the proximal part of the tibia. For each reconstruction, the total graft tension was a minimum of 2.3 times larger than the applied posterior force. Bundle tension and knee motions were measured as the knee was cycled from 5 degrees to 120 degrees of flexion while a 100-N posterior force was applied. Analysis of variance was used to compare the four reconstructions, and post hoc testing was performed with use of Fischer's protected least significant difference method. RESULTS: Two-bundle reconstructions involving a middle-distal or middle-middle second bundle significantly reduced the tension in the anterior bundle in comparison with the tension in the one-bundle (anterior-distal) reconstruction. The peak anterior-bundle tensions with the middle-distal and middle-middle second bundles were 43% and 37% less than the peak bundle tension for the one-bundle reconstruction (p < 0.001 and p = 0.002, respectively). With the exception of the average bundle tension, the tension parameters calculated for the middle bundle decreased as the distance from the articular cartilage increased. The peak tensions for the middle-middle and middle-proximal bundles were 32% and 61% less than that for the middle-distal bundle (p = 0.028 and p = 0.001, respectively). CONCLUSIONS: The femoral position of the second bundle significantly affected the tension in the anterior bundle and the load distribution. A second bundle placed in a middle or distal position resulted in a significant reduction in anterior bundle tension and in cooperative load-sharing (with the bundles functioning together). A proximal second bundle resulted in reciprocal loading (with one bundle functioning in flexion and one in extension), but the tension in the anterior bundle was not different from the tension in the one-bundle reconstruction.     

Joint kinematics and in situ forces after single bundle PCL reconstruction: a graft placed at the center of the femoral attachment does not restore normal posterior laxity

Introduction: Femoral tunnel placement has a great influence on the clinical outcome after PCL reconstruction. Materials and methods: Using a robotic/universal force moment sensor (UFS) testing system, we examined joint kinematics and in situ forces of human knees following soft-tissue single bundle PCL reconstruction fixed at the center of the femoral attachment. Results: Posterior tibial translation significantly increased at all flexion angles after transsection of the posterior cruciate ligament (p<0.05). PCL reconstruction resulted in significantly less posterior tibial translation at all flexion angles when compared to the PCL deficient knee (p<0.05). The differences in the in situ force between the intact ligament and the reconstructed graft were statistical significant (p<0.05). Conclusion: Single bundle PCL reconstruction with a soft-tissue graft fixed at the center of the femoral attachment is able to reduce the posterior tibial translation significantly. However, it cannot restore kinematics of the intact knee and in situ forces of the intact PCL.     

Reconstructive interventions of the posterior cruciate ligament--experimental studies of isometric aspects. Part II: Studies of the posterior cruciate ligament replacement model]

Isometric positioning of the posterior cruciate ligament (PCL) graft is important for successful reconstruction of the PCL-deficient knee. This study documents the relationship between graft placement and changes in intra-articular graft length during passive range of motion of the knee. In eight cadaveric knees the PCL was identified and cut. The specimens were mounted in a stabilizing rig. PCL reconstruction was performed using a 9-mm-thick synthetic cord that was passed through tunnels 10 mm in diameter. Three different femoral graft placement sites were evaluated: (1) in four specimens the tunnel was located around the femoral isometric point, (2) in two specimens the tunnel was positioned over the guide wire 5 mm anterior to the femoral isometric point, (3) in two specimens the tunnel was positioned over the guide wire 5 mm posterior to the isometric femoral point. In all knees only one tibial tunnel was created around the isometric tibial point. The location of the isometric points was described in part I of the study. The proximal end of the cord was fixed to the lateral aspect of the femur. Distally the cord was attached to a measuring unit. The knees were flexed from 0 degree to 110 degrees, and the changes in the graft distance between the femoral attachment sites were measured in 10 degrees steps. Over the entire range of motion measured the femoral tunnels positioned around the isometric point produced femorotibial distance changes of within 2 mm. The anteriorly placed tunnels produced considerable increases in femorotibial distance with knee flexion, e.g. about 8 mm at 110 degrees of flexion.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of isometric graft posterior cruciate ligament reconstruction on anterior tibial translation

Eight fresh-frozen cadaver knees were studied to evaluate whether an isometrically placed posterior cruciate ligament (PCL) graft restores normal posterior tibial translation without overconstraining anterior tibial translation. Each knee was tested with a three-axis load cell in the intact state, after PCL sectioning, and after PCL reconstruction. After PCL reconstruction, posterior tibial displacement was restored to values observed in the intact state for all flexion angles except 60 degrees and 90 degrees. Anterior tibial translation was not significantly changed for any of the three states. These results indicate isometric reconstruction of the PCL significantly reduces posterior tibial translation without overconstraining anterior tibial translation.     

Knee Kinematics in Anterior Cruciate Ligament-Substituting Arthroplasty With or Without the Posterior Cruciate Ligament

Few studies have compared functional kinematics in knees using identical prostheses with or without the posterior cruciate ligament (PCL). This study contrasted in vivo knee kinematics with an anterior cruciate ligament-substituting arthroplasty with and without PCL retention. We hypothesized that knees without PCLs would exhibit less femoral posterior translation, and consequently less maximum knee flexion. Fifty-six knees were studied using dynamic radiography at least one year post-surgery, with twenty-seven knees retaining the PCL and twenty-nine knees having the PCL sacrificed. Consistent with our hypothesis, PCL-sacrificing knees showed more anterior femoral condylar positions. Contrary to our hypothesis, PCL-sacrificing knees demonstrated greater knee flexion during kneeling (122° versus 115°). Contracted PCLs in severely deformed knees likely were the cause of limited flexion in some retaining knees.     

The biomechanical characteristics of arthroscopic tibial inlay techniques for posterior cruciate ligament reconstruction: in vitro comparison of tibial graft tunnel placement

Purpose

The hypothesis of the present study was that the biomechanical properties of arthroscopic tibial inlay procedures depend on tibial graft bone block position.

Methods

Five paired fresh-frozen human cadaveric knee specimens were randomized to a reconstruction with quadriceps tendon placing the replicated footprint either to the more proximal margin of the remnants of the anatomical PCL fibrous attachments (group A) or to the distal margin of the anatomical PCL fibrous attachments at the edge of the posterior tibial facet to the posterior tibial cortex in level with the previous physis line (group B). The relative graft-tibia motions, post cycling pull-out failure load and failure properties of the tibia-graft fixation were measured. Cyclic displacement at 5, 500 and 1,000 cycles, stiffness and yield strength were calculated.

Results

The cyclic displacement at 5, 500 and 1,000 cycles measured consistently more in group A without statistically significant difference (4.11?±?1.37, 7.73?±?2.73 and 8.18?±?2.75 mm versus 2.81?±?1.33, 6.01?±?2.37 and 6.46?±?2.37 mm). Mean ultimate load to failure (564.6?±?212.3) and yield strength (500.2?±?185.9 N) were significantly higher in group B (p?Conclusion Replicating the anatomical PCL footprint at the posterior edge of the posterior tibial facet yields higher pull-out strength and less cycling loading displacement compared to a tunnel position at the centre of the posterior tibial facet.     

Biomechanical effects of medial-lateral tibial tunnel placement in posterior cruciate ligament reconstruction.

With most posterior cruciate (PCL) reconstruction techniques, the distal end of the graft is fixed within a tibial bone tunnel. Although a surgical goal is to locate this tunnel at the center of the PCL's tibial footprint, errors in medial-lateral tunnel placement of the tibial drill guide are possible because the position of the tip of the guide relative to the PCL's tibial footprint can be difficult to visualize from the standard arthroscopy portals. This study was designed to measure changes in knee laxity and graft forces resulting from mal-position of the tibial tunnel medial and lateral to the center of the PCL's tibial insertion. Bone-patellar tendon-bone allografts were inserted into three separate tibial tunnels drilled into each of 10 fresh-frozen knee specimens. Drilling the tibial tunnel 5 mm medial or lateral to the center of the PCL's tibial footprint had no significant effect on knee laxities; the graft pretension necessary to restore normal laxity at 90 degrees of knee flexion (laxity match pretension) with the medial tunnel was 13.8 N (29%) greater than with the central tunnel. During passive knee flexion-extension, graft forces with the medial tibial tunnel were significantly higher than those with the central tunnel for flexion angles greater than 65 degrees while graft forces with the central tibial tunnel were not significantly different than those with the lateral tibial tunnel. Graft forces with medial and lateral tunnels were not significantly different from those with a central tunnel for 100 N applied posterior tibial force, 5 Nm applied varus and valgus moment, and 5 Nm applied internal and external tibial torque. With the exception of slightly higher graft forces recorded with the medial tunnel beyond 65 degrees of passive knee flexion, errors in medial-lateral placement of the tibial tunnel would not appear to have important effects on the biomechanical characteristics of the reconstructed knee.     

Biomechanics of posterior-substituting total knee arthroplasty: an in vitro study

The cam-spine system in posterior-substituting total knee arthroplasty was designed to improve posterior stability and to increase posterior femoral translation (rollback). Little is known on its effectiveness in the restoration of femoral rollback under functional loads. In the current study, the effect of cam-spine engagement on knee motion under simulated muscle loads was investigated using knees from cadavers. The translations of the lateral and medial femoral condyles of the knee before and after total knee arthroplasty were compared from 0 degrees to 120 degrees flexion. Cam-spine contact forces were measured under the same muscle loads. The posterior translations of both femoral condyles in the total knee arthroplasty were significantly lower than that of the native knee beyond full extension. Cam-spine engagement occurred between 60 degrees and 90 degrees flexion followed by an increase in posterior translation of both femoral condyles. However, the resultant femoral translation of the total knee arthroplasty was still lower than that of the native knee from 90 degrees to 120 degrees flexion. Knee motion after cam-spine engagement was independent of muscle loads, indicating the importance of the cam-spine mechanism at high flexion angles. Decreased posterior translation of both femoral condyles after total knee arthroplasty may be a limiting factor at high flexion.     

Study of the posterior cruciate ligament using a 3D computer model: ligament biometry during flexion, application to surgical replacement of the ligament

We have developed a 3D computed model of the knee joint, constructed from MRI acquisitions in a living individual. We have used this model to perform an anatomic and biometric study of the posterior cruciate ligament (PCL) during flexion, and an assessment of the optimal location for an intraarticular graft. The method used a 3D computed model constructed from MRI acquisitions during knee flexion (0 to 75 degrees). The range of motion was limited by a positioning device. We took 13 acquisitions from 0 to 75 degrees of flexion. Each acquisition consisted of 21 sagittal cross sections of 3 mm slice thickness. We used the Delaunay reconstruction to obtain a 3D geometric model. A matching process to fix one part of the articulation during the movement, allows for the kinematic analysis of the tibia relative to the fixed femur. This model allows to follow the displacement of a bone point during knee flexion. Knowing the relative displacement of the bone insertions of the ligament, it may be possible to determine the length of the PCL and its bands, to evaluate the length variation during movement, and to determine the optimal location for the insertion of an intraarticular graft, that would lead to the least stretch during flexion. It was found that the mean length of the PCL was 30.2 mm, with the posterior band being 30% longer than the anterior band. During flexion the posterior band increases its length by 10% at 50 degrees flexion, and by 20% at 75 degrees flexion. The anterior band stretches more, to reach 40% elongation at 75 degrees flexion. The best position for insertion of a graft seems to be in the posterolateral portion of the anatomic tibial insertion, and posterior to the anatomic femoral insertion. This method confirms the data in the literature, states precisely the length of the different bands of the PCL, and specifies the points of insertion for a graft, which lead to the least variation in length during flexion.     

Posterior Cruciate Ligament

Improved understanding of the anatomy and biomechanics of the posterior cruciate ligament (PCL) has led to the evolution and improvement of anatomic-based reconstructions. The PCL is composed of the larger anterolateral bundle (ALB) and the smaller posteromedial bundle (PMB). On the femoral side, the ALB spans from the trochlear point to the medial arch point on the roof of the notch, while the PMB occupies the medial wall from the medial arch point to the most posterior aspect of the articular cartilage. Because of these broad and distinct attachments, the bundles have a load-sharing, synergistic and codominant relationship. Both restrict posterior translation; however, the ALB has a proportionally larger role in restricting translation throughout flexion, whereas the PMB has a role comparable to that of the ALB in full extension. In addition, the PMB resists internal rotational at greater flexion angles (> 90°). Consequently, it is difficult to restore native kinematics with a single graft. Biomechanical analysis of single- versus double-bundle PCL reconstructions (SB PCLR vs DB PCLR) demonstrates improved restoration of native kinematics with a DB PCLR, including resistance to posterior translation throughout flexion (15°-120°) and internal rotation in deeper flexion (90°-120°). Similarly, clinical research demonstrates excellent outcomes following DB PCLR, including functional outcomes comparable to those of anterior cruciate ligament reconstructions, with no significant differences between isolated and multiligament PCL injuries. Compared to SB PCLR, systematic review has demonstrated the superiority of DB PCLR based on objective postoperative stress radiography and International Knee Documentation Committee scores in randomized trials. In addition to reconstruction techniques, recent research has identified other factors that impact kinematics and PCL forces, including decreased tibial slope, which leads to increased graft stresses, and incidence of native PCL injuries. As the understanding of these other contributing factors evolves, so will surgical and treatment algorithms that will further improve patients’ outcomes.     

Reducing the “killer turn” in posterior cruciate ligament reconstruction

Purpose: Graft abrasion caused by sharp graft angulation at the graft-tunnel margin of the proximal tibia (the “killer turn”) may cause graft failure after posterior cruciate ligament (PCL) reconstruction using the traditional anteromedial route tibial tunnel. One method to reduce the graft angulation is to use the anterolateral route tibial tunnel. However, less acute graft angulation may increase joint translation because of a decrease in graft compressive force. The purpose of this study was to compare the graft angulation and joint translation between anteromedial and anterolateral route tibial tunnels. Type of Study: Biomechanical study. Methods: Twelve above-the-knee amputation specimens were used in this study. Anteromedial and anterolateral tibial tunnels were made at the desired locations, and the same femoral tunnel was used. Graft angulation was measured by inserting a malleable pin into the tibial and femoral tunnels. Measurements of graft angulation were performed with the knee in extension and in 90° of flexion. The joint translation was measured by the posterior translation of the tibia on the femur at 90° of flexion with a 15-lb posterior force applied to the anterior proximal tibia after PCL reconstruction through the respective tunnels. Results: The difference in graft angulation between anterolateral and anteromedial route tibial tunnels was statistically significant (P < .001); however, the difference in joint translation showed no statistical significance between the 2 tunnel routes. Conclusions: The anterolateral route tibial tunnel significantly reduced the sharp graft angulation (“killer turn”) at the graft tunnel margin of the proximal tibia, but it did not increase the joint translation as compared with the traditional anteromedial route tibial tunnel. The anterolateral route tibial tunnel is thought to be a better choice when arthroscopic PCL reconstruction is performed with the tunnel technique.     

Reconstruction of knees with combined cruciate deficiencies: a biomechanical study

BACKGROUND: Clinical results of dual cruciate-ligament reconstructions are often poor, with a failure to restore normal anterior-posterior laxity. This could be the result of improper graft tensioning at the time of surgery and stretch-out of one or both grafts from excessive tissue forces. The purpose of this study was to measure anterior-posterior laxities and graft forces in knees before and after reconstructions of both cruciate ligaments performed with a specific graft-tensioning protocol. METHODS: Eleven fresh-frozen cadaveric knee specimens underwent anterior-posterior laxity testing and installation of load cells to record forces in the native cruciate ligaments as the knees were passively extended from 120 degrees to -5 degrees with no applied tibial force, with 100 N of applied anterior and posterior tibial force, and with 5 N-m of applied internal and external tibial torque. Both cruciate ligaments were reconstructed with a bone-patellar tendon-bone allograft. Only isolated cruciate deficiencies were studied. We determined the nominal levels of anterior and posterior cruciate graft tension that restored anterior-posterior laxities to within 2 mm of those of the intact knee and restored anterior cruciate graft forces to within 20 N of those of the native anterior cruciate ligament during passive knee extension. Both grafts were tensioned at 30 degrees of knee flexion, with the posterior cruciate ligament tensioned first. Measurements of anterior-posterior knee laxity and graft forces were repeated with both grafts at their nominal tension levels and with one graft fixed at its nominal tension level and the opposing graft tensioned to 40 N above its nominal level. RESULTS: The anterior and posterior cruciate graft tensions were found to be interrelated; applying tension to one graft changed the tension of the other (fixed) graft and displaced the tibia relative to the femur. The posterior cruciate graft had to be tensioned first to consistently achieve the nominal combination of mean graft forces at 30 degrees of flexion. At these levels, mean forces in the anterior cruciate graft were restored to those of the intact anterior cruciate ligament under nearly all test conditions. However, the mean posterior cruciate graft forces were significantly higher than the intact posterior cruciate ligament forces at full extension under all test conditions. Anterior-posterior laxity was restored between 0 degrees and 90 degrees of flexion with both grafts at their nominal force levels. Overtensioning of the anterior cruciate graft by 40 N significantly increased its mean force levels during passive knee extension between 110 degrees and -5 degrees of flexion, but it did not significantly change anterior-posterior laxity between 0 degrees and 90 degrees of flexion. In contrast, overtensioning of the posterior cruciate graft by 40 N significantly increased posterior cruciate graft forces during passive knee extension at flexion angles of <5 degrees and >95 degrees and significantly decreased anterior-posterior laxities at all flexion angles except full extension. CONCLUSIONS: It was not possible to find levels of graft tension that restored anterior-posterior laxities at all flexion positions and restored forces in both grafts to those of their native cruciate counterparts during passive motion. Our graft-tensioning protocol represented a compromise between these competing objectives. This protocol aimed to restore anterior-posterior laxities and anterior cruciate graft forces to normal levels. The major shortcoming of this tensioning protocol was the dramatically higher posterior cruciate graft forces produced near full extension under all test conditions.     

Anterior cruciate ligament reconstruction stability with continuous passive motion. The role of isometric graft placement.

A comparison was made of the stability of isometric versus nonisometric anterior cruciate ligament (ACL) reconstructions when subjected to immediate postoperative continuous passive motion (CPM). Anterior cruciate ligament reconstructions were performed on 13 anatomic specimen knees using bone/patellar tendon/bone grafts. Nine ACL substitutions were considered isometric with maximum graft length changes of less than 1 mm. Four ACL substitutions were nonisometric with graft length changes of 3 mm or greater resulting from tightening in flexion. The specimens were subjected to CPM through 0 degrees-95 degrees knee flexion. Knee stability was remeasured with a knee arthrometer at three and 14 days after beginning CPM. All four nonisometric specimens had failed within three days, with increased anterior laxity of 2-9 mm in both the Lachman (20 degrees) and anterior drawer (90 degrees) positions. All nine isometric reconstructions successfully retained pre-CPM anterior stability within 1 mm after 14 days of CPM. This investigation illustrates the importance of isometric graft placement for ACL reconstruction success. Continuous passive motion does not appear to adversely affect immediate ACL-substitute integrity or fixation if graft placement is isometric (less than 1 mm of graft excursion through 0 degrees-110 degrees of knee motion). Continuous passive motion may cause graft deformation, fixation failure, or both, with resultant loss of knee stability if the graft is not isometrically positioned (greater than 3 mm of graft excursion resulting from tightening in flexion).     

Posterior cruciate ligament and coupled posterolateral instability of the knee

We wanted to investigate the role of the posterior cruciate ligament (PCL) in the knee's posterolateral stability and the magnitude of the coupled posterolateral instability with the knee examined at 90 degrees of flexion. The coupled posterolateral instability of the knee was studied by selective ligament cutting in cadaver knees set at 90 degrees. The coupled posterolateral displacement after cutting the PCL was 173% of the intact knee. With an intact PCL, the coupled posterolateral displacement after cutting the popliteus tendon and lateral collateral ligament with the knee at 90 degrees of flexion was 299% of the intact knee. When the PCL was cut together with the popliteus tendon and lateral collateral ligament, the coupled posterolateral displacement was 367%. The PCL plays an important role in the posterolateral stability of the knee, and its injury may cause mild (< 5 mm) to moderate (5-10 mm) posterolateral instability. Thus, in a knee with posterolateral instability, injury of the PCL must be considered. With an intact PCL, the posterolateral instability was very recognizable with the knee at 90 degrees of flexion, and injury to the PCL further increased the posterolateral instability and caused posterior translation of the knee. Therefore, examination for posterolateral instability of the knee should also be performed with the knee at 90 degrees of flexion, which is much easier to perform in a clinical setting. A positive posterior translation rather than posterolateral instability at different knee positions differentiates knees with combined PCL and posterolateral instability from knees with isolated posterolateral instability.     

增加胫骨平台后倾角度、后交叉韧带部分松解对全膝关节置换术后膝关节运动影响的实验研究

目的通过增加胫骨平台后倾角度或后交叉韧带（PCL）部分松解对全膝关节置换术（TKA）中屈曲间隙过紧进行处理,分析这两种方法对TKA术后膝关节运动学的影响。方法测量6例新鲜尸体膝关节标本在完整状态下、正常TKA、屈曲间隙过紧、增加胫骨平台后倾角以及PCL部分松解TKA术后膝关节屈曲0°、30°、60°、90°、120°时的前后松弛度、内外翻松弛度、旋转松弛度及最大屈曲度。结果屈曲过紧TKA与正常TKA相比,在屈曲30°、60°、90°和120°时前后松弛度、内外翻松弛度及旋转松弛度均显著较小（P〈0．05）。与屈曲过紧TKA相比,增加胫骨后倾角后,在屈曲30°、60°、90°和120°时前后松弛度、内外翻松弛度和旋转松弛度均明显增大（P〈0．05）。PCL部分松解与屈曲过紧TKA相比,在屈曲30°、60°、90°和120°时前后松弛度明显增加（P〈0．05）;旋转松弛度在屈曲30°、60°、90°时明显增加（P〈0．05）。与PCL部分松解相比,增加胫骨后倾角的内外翻松弛度在屈曲30°、60°、90°时明显较大（P〈0．05）;旋转松弛度在屈曲0°、30°、60°和90°时明显较大（P〈0．05）。屈曲过紧TKA的最大屈曲度（120．4°）与正常TKA（130．3°）及增加胫骨后倾角（131．1°）相比明显较小（P〈0．05）。增加后倾角与PCL部分松解（124．0°）相比,最大屈曲度较大,但差异无统计学意义（P=0．0816）。结论屈曲间隙过紧TKA术后膝关节的前后松弛度、内外翻松弛度、旋转松弛度和最大屈曲度均减小;增加胫骨平台后倾角后,前后松弛度、内外翻松弛度、旋转松弛度和最大屈曲度均明显增大;PCL部分松解仅能明显增大前后松弛度。因此对于TKA术中屈曲紧张的膝关节,增加胫骨平台后倾角比PCL部分松解能更好地改善膝关节的运动学。     

Knee kinematics with a high-flexion posterior stabilized total knee prosthesis: an in vitro robotic experimental investigation

BACKGROUND: An analysis of contemporary total knee arthroplasty reveals that, on the average, patients rarely flex the knee beyond 120 degrees. The biomechanical mechanisms that inhibit further flexion after total knee arthroplasty are unknown. The objective of the present study was to investigate the capability of a single design of a fixed-bearing, high-flexion posterior stabilized total knee arthroplasty system (LPS-Flex) to restore the range of flexion to that of the intact knee. METHODS: Thirteen cadaveric human knees were tested, with use of a robotic testing system, before and after total knee arthroplasty with the LPS-Flex prosthesis. The passive path and the kinematics under an isolated quadriceps force of 400 N, under an isolated hamstring force of 200 N, and with these forces combined were determined. Posterior femoral translation of the lateral and medial femoral condyles and tibial rotation were recorded from 0 degrees to 150 degrees of flexion. RESULTS: The medial and lateral condyles of the intact knee translated posteriorly from full extension to 150 degrees, reaching a mean peak (and standard deviation) of 22.9 +/- 11.3 mm and 31.9 +/- 12.5 mm, respectively, under the combined muscle forces. Following total knee arthroplasty, the amount of posterior femoral translation was lower than that observed in the intact knee. At 150 degrees, approximately 90% of the intact posterior femoral translation was recovered by the total knee replacement. Internal tibial rotation was observed for all knees throughout the range of motion. The cam-spine mechanism engaged at approximately 80 degrees and disengaged at 135 degrees. Despite the absence of cam-spine engagement, further posterior femoral translation occurred from 135 degrees to 150 degrees. CONCLUSIONS: The tibiofemoral articular geometry of the intact knee and the knee after total knee arthroplasty with use of the LPS-Flex design demonstrated similar kinematics at high flexion angles. The cam-spine mechanism enhanced posterior femoral translation only at the mid-range of flexion. The femoral component geometry of the LPS-Flex total knee prosthesis may improve posterior tibiofemoral articulation contact in high flexion angles.     

Loss of knee extension after anterior cruciate ligament reconstruction: effects of knee position and graft tensioning

BACKGROUND: Loss of knee extension has been reported by many authors to be the most common complication following anterior cruciate ligament reconstruction. The objective of this in vitro study was to determine the effect, on loss of knee extension, of the knee flexion angle and the tension of the bone-patellar tendon-bone graft during graft fixation in a reconstruction of an anterior cruciate ligament. METHODS: The anterior cruciate ligament was reconstructed with use of tibial and femoral bone tunnels placed in the footprint of the native anterior cruciate ligament in ten cadavers. The graft was secured with an initial tension of either 44 N (10 lb) or 89 N (20 lb) applied with the knee at 0 degrees or 30 degrees of flexion. The knee flexion angle was measured with use of digital images following graft fixation. RESULTS: Tensioning of the graft at 30 degrees of knee flexion was associated with loss of knee extension in this cadaver model. Graft tension did not affect knee extension under the conditions tested. CONCLUSIONS: The results suggest that one of the common causes of the loss of full knee extension may be diminished if the graft is secured in full knee extension when the tibial and femoral tunnels are placed in the footprint of the native anterior cruciate ligament. More importantly, even when the femoral and tibial tunnels are placed in the femoral and tibial footprints of the native anterior cruciate ligament, fixing a graft in knee flexion can result in the loss of knee extension.