Anterior-posterior Laxity Research Articles

Analysis of three-dimensional in vivo knee kinematics using dynamic magnetic resonance imaging

Patients continue to develop premature arthritis despite good subjective and objective evaluations of anterior cruciate ligament (ACL) reconstructed knees. Current objective evaluations have been limited to muscle strength examination, radiographic imaging, and laxity measurements. Anterior-posterior laxity measurements were originally developed to diagnose ACL insufficiencies; however, their application has been broadened to evaluate the success of ACL reconstructions . Although we recognize the importance of the meniscal function in preventing osteoarthritis , we do not have any means to evaluate meniscal kinematics after ACL injuries and reconstruction. In this article, we will highlight the importance of developing new methods in evaluating in vivo tibiofemoral and meniscal kinematics under dynamic conditions. We will also present our recent work on magnetic resonance analysis of knee kinematics under simulated weight-bearing conditions. We hope that we can extend this technique in dynamic evaluation of cruciate ligament injured knees. With better quantification of three-dimensional tibiofemoral and meniscal kinematics, we hope that we can improve our ability to diagnose, treat and critically evaluate our reconstructions for the cruciate ligament injured patients.

Biomechanics of rotational instability and anatomic anterior cruciate ligament reconstruction

The anterior cruciate ligament (ACL) is the primary restraint to tibial anterior translation (anterior draw). Tibial anterior draw is normally accompanied by a “coupled” tibial internal rotation. Both internal rotation and anterior translation can be increased by rupture of the ACL, resulting in a large movement of the mobile lateral tibial plateau. Arthroscopic ACL reconstruction adequately restores the anterior draw; however, the peripheral structures that are the primary restraints to tibial rotation often are neglected. Recent work has shown that a residual or “mini” pivot shift can remain after successfully restoring the anterior-posterior laxity of the knee. The search for a better restoration of normal kinematics has reawakened interest in double-bundle reconstructions. Although biomechanical studies have demonstrated that this type of reconstruction may better restore the normal kinematics, there is as yet no clinical evidence. Draw testing should now be superseded by kinematics measures of both rotations and translations of the knee with quantified loads to provide objective measures that better assess the efficacy of new surgical techniques.

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 Blumensaat's line, at the 10:30-11:00 o'clock 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 degrees 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 degrees 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 degrees 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 degrees 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.

Initial tension and anterior load-displacement behavior of high-stiffness anterior cruciate ligament graft constructs.

Because the tension that exists in an anterior cruciate ligament graft when the knee is unloaded (the initial tension) affects the surgical outcome and because high initial tension has a number of adverse consequences, the primary purpose of this study was to determine quantitatively how much less initial tension was required for a high-stiffness construct than for a low-stiffness construct. A secondary purpose was to determine how the stiffness of the graft construct affects the anterior load-displacement behavior of the knee from 0 degrees to 90 degrees of flexion. Anterior-posterior load-displacement was measured in each of ten intact cadaveric knee specimens, the anterior cruciate ligament was excised, and the anterior cruciate ligament was reconstructed with a double-loop bovine tendon graft. Graft constructs of different stiffness were created with use of six springs, ranging in stiffness from 25 to 275 N/mm to simulate the fixation stiffness. After adjusting the initial tension of the graft so that the anterior-posterior laxity of the reconstructed knee matched that of the intact knee, the 0-N posterior limit and the 225-N anterior limit were measured at 0 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. The highest stiffness fixation (275 N/mm) required an average of 73 N of initial tension, which was more than three times less than the average of 242 N of initial tension required by the lowest stiffness fixation (25 N/mm). The 225-N anterior limit was overconstrained an average of 1.0 mm with the highest stiffness fixation (275 N/mm), which was 3.6 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm). Likewise, the posterior limit was overconstrained an average of 2.6 mm with the highest stiffness fixation (275 N/mm), which was 3.8 mm less than the overconstraint with the lowest stiffness fixation (25 N/mm). The initial tension for a high-stiffness graft construct is more than three times less than that for a low-stiffness construct. The initial tension for a high-stiffness graft construct better restores both the 225-N anterior limit and the 0-N posterior limit to normal than the initial tension for a low-stiffness graft construct over the range of flexion from 0 degrees to 90 degrees.

Brief report: validation of a system for automated measurement of knee laxity

Objective. To determine the accuracy and repeatability of an automated quantitative fluoroscopic imaging system for measuring knee laxity. Design. Cadaveric validation study. Background. Current methods of measuring anterior–posterior laxity lack sufficient accuracy and repeatability. A commercially developed fluoroscopic software package, capable of measuring laxity, required validation. Methods. Five human cadaveric knees were used. A constant force of 130 N was applied anteriorly and posteriorly in turn to the tibia of each knee with the femur fixed in 30° and 90° of flexion. Quantitative fluoroscopic measurements of anterior–posterior laxity were determined using image analysis software. Fluoroscopic results were compared to the true anterior–posterior displacements of the tibia, which were simultaneously recorded using linear transducers directly attached to the cadaveric specimens. Results. The quantitative fluoroscopic method underestimated laxity by an average of 0.40 mm with a root mean square error of 0.49 mm. The 95% confidence intervals for anterior and posterior laxity error were calculated to be −0.99 to 0.25 mm and −0.89 to 0.03 mm, respectively, where a negative error represents an underestimation. Conclusions. The quantitative fluoroscopic method offers a dramatic improvement in accuracy over current laxity measurement techniques and acceptable repeatability for assessing ligament damage. RelevanceThe considerably more accurate, validated measurement system of this study could improve ligament assessment and diagnosis, and the recognition of injuries otherwise undetected with current methods.

Reconstruction of knees with combined cruciate deficiencies: a biomechanical study.

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. 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. 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. 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.

Enhancement of Tendon-Bone Integration of Anterior Cruciate Ligament Grafts with Bone Morphogenetic Protein-2 Gene Transfer

The integration of tendon grafts used for replacement of the anterior cruciate ligament is still sometimes unsatisfactory and may be associated with postoperative anterior-posterior laxity. The goal of this study was to examine the capacity of bone morphogenetic protein-2 (BMP-2) gene transfer to improve the integration of semitendinosus tendon grafts at the tendon-bone interface after reconstruction of the anterior cruciate ligament in rabbits. The anterior cruciate ligaments of adult New Zealand White rabbits were replaced with autologous double-bundle semitendinosus tendon grafts. The semitendinosus tendon grafts had been infected in vitro with adenovirus-luciferase, adenovirus-LacZ (AdLacZ), or adenovirus-BMP-2 (AdBMP-2); untreated grafts served as controls. The grafts were examined histologically at two, four, six, and eight weeks after surgery. In additional experiments, the structural properties of the femur-anterior cruciate ligament graft-tibia complexes, from animals killed eight weeks postoperatively, were determined from uniaxial tests. The stiffness (N/mm) and ultimate load to failure (N) were determined from the resulting load-elongation curves. Genetically engineered semitendinosus tendon grafts expressed reporter genes as well as BMP-2 in vitro. The AdLacZ-infected grafts showed two different histological patterns of transduction. Intra-articularly, infected cells were mostly aligned along the surface, and they decreased in number between two and eight weeks after surgery. In the intra-tunnel portions of the grafts, the number of infected cells did not decrease during the observation period. Moreover, a high number of transduced cells was found in the deeper layers of the tendons. In the control group, granulation-type tissue at the tendon-bone interface showed progressive reorganization into a dense connective tissue, and a later establishment of fibers resembling Sharpey fibers. In the specimens with an AdBMP-2-infected anterior cruciate ligament graft, a broad zone of newly formed matrix resembling chondro-osteoid had formed at the tendon-bone interface at four weeks after surgery. This area was increased at six weeks, showing a transition from bone to mineralized cartilage and nonmineralized fibrocartilage. In addition, in the AdBMP-2-treated specimens, the tendon-bone interface in the osseous tunnel was similar to that of a normal anterior cruciate ligament insertion. The stiffness (29.0 +/- 7.1 N/mm compared with 16.7 +/- 8.3 N/mm) and the ultimate load to failure (108.8 +/- 50.8 N compared with 45.0 +/- 18.0 N) were significantly enhanced in the specimens with an AdBMP-2-transduced graft when compared with the control values (p < 0.05). This study demonstrates that BMP-2 gene transfer significantly improves the integration of semitendinosus tendon grafts in bone tunnels after reconstruction of the anterior cruciate ligament in rabbits. Novel technologies including gene therapy and tissue engineering, such as those described in this study, may provide useful therapeutic procedures to enhance biological healing after reconstruction of the anterior cruciate ligament.

Effects of femoral tunnel placement on knee laxity and forces in an anterior cruciate ligament graft

The purpose of this study was to measure the effects of variation in placement of the femoral tunnel upon knee laxity, graft pretension required to restore normal anterior–posterior (AP) laxity and graft forces following anterior cruciate ligament (ACL) reconstruction. Two variants in tunnel position were studied: (1) AP position along the medial border of the lateral femoral condyle (at a standard 11 o'clock notch orientation) and (2) orientation along the arc of the femoral notch (o'clock position) at a fixed distance of 6–7 mm anterior to the posterior wall. AP laxity and forces in the native ACL were measured in fresh frozen cadaveric knee specimens during passive knee flexion-extension under the following modes of tibial loading: no external tibial force, anterior tibial force, varus–valgus moment, and internal–external tibial torque. One group (15 specimens) was used to determine effects of AP tunnel placement, while a second group (14 specimens) was used to study variations in o'clock position of the femoral tunnel within the femoral notch. A bone-patellar tendon-bone graft was placed into a femoral tunnel centered at a point 6–7 mm anterior to the posterior wall at the 11 o'clock position in the femoral notch. A graft pretension was determined such that AP laxity of the knee at 30 deg of flexion was restored to within 1 mm of normal; this was termed the laxity match pretension. All tests were repeated with a graft in the standard 11 o'clock tunnel, and then with a graft in tunnels placed at other selected positions. Varying placement of the femoral tunnel 1 h clockwise or counterclockwise from the 11 o'clock position did not significantly affect any biomechanical parameter measured in this study, nor did placing the graft 2.5 mm posteriorly within the standard 11 o'clock femoral tunnel. Placing the graft in a tunnel 5.0 mm anterior to the standard 11 o'clock tunnel increased the mean laxity match pretension by 16.8 N (62%) and produced a knee which was on average 1.7 mm more lax than normal at 10 deg of flexion and 4.2 mm less lax at 90 deg. During passive knee flexion-extension testing, mean graft forces with the 5.0 mm anterior tunnel were significantly higher than corresponding means with the standard 11 o'clock tunnel between 40 and 90 deg of flexion for all modes of constant tibial loading. These results indicate that AP positioning of the femoral tunnel at the 11 o'clock position is more critical than o'clock positioning in terms of restoring normal levels of graft force and knee laxity profiles at the time of ACL reconstruction.

Biomechanical effects of femoral notchplasty in anterior cruciate ligament reconstruction.

Notchplasty is frequently performed in conjunction with anterior cruciate ligament reconstruction. Bench loading tests were performed on 26 fresh-frozen knee specimens to measure excursion of a bone-patellar tendon-bone graft, anterior-posterior laxity of the knee, and graft forces before and after performing a 2-mm and a 4-mm notchplasty. The mean intraarticular pretension required to restore normal anterior-posterior laxity at 30 degrees of flexion (laxity-matched pretension level) was 27 N before notchplasty, 48 N after 2-mm notchplasty, and 65 N after 4-mm notchplasty. The mean graft pretension decreased 53% and 58%, respectively, on completion of a loading test series involving anterior-posterior and constant tibial loading forces. Mean laxity increased 1.4 mm at full extension and decreased 1.8 mm at 90 degrees of flexion after a 2-mm notchplasty. Mean graft forces increased markedly between 30 degrees and 90 degrees of passive flexion after notchplasty. Our results show that after a notchplasty, a higher level of graft pretension will be necessary to restore normal laxity at 30 degrees of flexion. This increased level of pretension, combined with changes in graft excursion, produced dramatic increases in graft force when the knee was flexed to 90 degrees. These relatively high forces would be detrimental to a remodeling graft and could lead to subsequent failure of the reconstruction.

The relationship between graft tensioning and the anterior–posterior laxity in the anterior cruciate ligament reconstructed goat knee

The tension applied to the anterior cruciate ligament (ACL) graft at time of fixation is thought to influence graft healing, knee kinematics, and joint contact forces; however, the optimal tensioning procedure remains unclear. An animal model provides a means by which the effect of graft tensioning on healing can be studied. Prior to using the model, the relationship between graft tensioning and knee kinematics at time of surgery should be established. Our objective was to explore the relationship between graft tensioning and anterior–posterior (A–P) laxity of the reconstructed goat knee. Eight cadaver knees were tested. The A–P laxity values of the intact knee were measured with the knee at 30°, 60°, and 90° flexion. The ACL was then severed and the laxity measurements were repeated. The ACL was reconstructed using a bone-patellar tendon–bone autograft. The laxity measurements were repeated for nine different tensioning conditions; three tension magnitudes (30, 60, and 90 N), each applied with the knee at three angles (30°, 60° and 90°). Both graft tension and the knee angle at which it was applied produced significant changes on A–P laxity values. An increase in tension reduced laxity values. A tension level of 60 N applied with the knee flexed to 30° was the best combination for restoring normal A–P laxity values at all knee angles tested.

The elongation behavior of the anterior cruciate ligament graft in vivo. A long-term follow-up study.

The relationship between the elongation values of an autogenous bone-patellar tendon-bone graft immediately after fixation and the anterior-posterior laxity of the knee 5 years later was studied in vivo. Immediately after fixation, the change in the graft midsubstance length during passive knee flexion-extension was measured using a Hall-effect transducer, and anterior-posterior knee laxity was measured with the KT-1000 arthrometer. Subjects were divided into group 1 (N = 6), with graft elongation values bounded by the 95% confidence intervals of the normal anterior cruciate ligament elongation values, and group 2 (N = 7), subjects with values outside these intervals. Immediately after reconstruction, the side-to-side difference in anterior-posterior laxity between the reconstructed and uninjured knees was not different between group 1 (-2.6 +/- 0.7 mm, mean +/- SEM) and group 2 (-1.7 +/- 1.0 mm) (P = 0.49). At 5-year follow-up, the difference was 1.2 +/- 0.7 mm for group 1, while for group 2 it was significantly greater at 4.7 +/- 0.6 mm (P = 0.004). At surgery, graft elongation values produced by flexion of the knee that are outside the limits of the anterior cruciate ligament result in significant increases in anterior knee laxity at long-term follow-up, while grafts with elongation values similar to the normal anterior cruciate ligament do not. Not only is restoration of anterior-posterior laxity values to within normal limits important, but the biomechanical behavior of the graft produced by flexion-extension of the knee should be appreciated.

The effect of cyclic displacement on the biomechanical characteristics of anterior cruciate ligament reconstructions.

This study was conducted to clarify the influence of cyclic displacement on the structural properties of four types of femur-graft-tibia complexes used to reconstruct the anterior cruciate ligament. Forty hindlimbs from pigs were used. In two groups, bone-patellar tendon-bone grafts were secured with interference screws (group A) or the suture-post technique (group B). In two groups, multistrand flexor tendons were fixed using the tape-staple technique (group C) or the sutures-tied-over-a-button technique (group D). In each group, five femur-graft-tibia complexes underwent tensile failure tests without cyclic displacement. The other five complexes underwent 5000 cycles of cyclic elongation for 2 mm, and then underwent the tensile failure tests. The initial stiffness significantly decreased after cyclic displacement in each group, although there were no significant differences in the linear stiffness and the ultimate failure load between the tests with and without cyclic displacement. These findings suggest that 5000 cycles of repetitive elongation of the femur-graft-tibia complex by 2 mm does not jeopardize the graft fixed with the procedures used in this study, despite a slight but significant increase of an anterior-posterior laxity of the knee.

Three-dimensional knee kinematics and stability in patients with a posterior cruciate ligament tear.

The three-dimensional kinematics of the knee were studied from 5 months to 15 years after unilateral posterior cruciate ligament tears occurred in eight patients. All but two patients had signs of additional ligament injuries. Repeated radiostereometric examinations were conducted when the patients ascended a platform (step-up test) and during an instrumented anterior-posterior drawer test with the knee at 30 degrees of flexion. No changes in knee kinematics were observed during the step-up test, whereas increased anterior-posterior laxity (3.8-11.3 mm) was recorded for all patients. Four of the patients had an increased side-to-side difference (more than 2 mm) in anterior as well as posterior laxity. A rupture of the posterior cruciate ligament can be diagnosed at 30 degrees of knee flexion, but an increase in anterior laxity can erroneously be interpreted as an injury of the anterior cruciate ligament. The unaffected kinematics of the knee suggest that factors such as joint load and congruity and muscle activity can compensate for the absent posterior cruciate ligament during static examinations.

Anterior-posterior knee laxity increased by exercise. Quantitative evaluation of physiologic changes.

To quantify physiologic changes in anterior-posterior laxity of the normal knee caused acutely by exercise, we evaluated the exercise level and the duration of exercise needed to cause changes in laxity, the magnitude of changes in laxity, and the time needed for laxity to return to the level before exercise, by continuously applying a fixed exercise load. After a 20-minute run at 7 km/hr, anterior laxity with a displacement force of 133 N increased by about one third, and the compliance increased by one half with anterior drawer between 0 and 67 N. These changes were maintained at a similar level during exercise. The levels before exercise were restored gradually over 1 hour after exercise. As the muscle strength showed no changes during exercise, we consider these changes in laxity are not associated with a decrease in muscle strength. Furthermore, since the changes in knee laxity after triathlon (in which the knee is subjected to prolonged excessive exercise) are similar to those after running at 7 km/hr, we believe that the magnitude of changes in laxity after exercise is fixed, regardless of the level of the exercise load. Moreover, the threshold of exercise that causes the maximum change is low.

Biomechanical response of the passive human knee joint under anterior-posterior forces

Objective. To investigate the detailed biomechanics of the passive tibiofemoral knee joints in full extension under anterior/ posterior drawer forces of up to 400 N. Design. A nonlinear three-dimensional finite element model of the entire human tibiofemoral joint consisting of bony structures, their articular cartilage layers, menisci, and four principal ligaments was utilized. Background. The mechanics of the knee joint, specially under drawer forces, have extensively been investigated. Despite all these works, the detailed joint biomechanics, specially the role of boundary conditions, load transmission through menisci/ articular cartilage layers, and coupling between menisci and cruciate ligaments are not yet quantified. Method. Nonlinear elastostatic analyses were carried out considering the tibiofemoral joint at full extension under anterior and posterior loads of up to 400 N applied either to the tibial or the femoral shaft. Cases with various boundary conditions, cruciate ligament deficiency (anterior or posterior), and total unilateral meniscectomy (medial or lateral) were analysed. Results. In addition to the total primary anterior-posterior motion of about 9 mm at ± 400 N, significant coupled external tibial rotations of about 9 ° and 10 ° were computed under 400 N femoral posterior and anterior forces, respectively. The response was influenced by the manner of loading and boundary conditions. The anterior cruciate ligament and posterior cruciate ligament were the primary restraints to femoral posterior and anterior drawer forces, respectively. Section of either of these ligaments drastically increased the joint anterior-posterior motion. In the absence of cruciates, the collaterals became the primary restraints in both anterior-posterior forces. In this case, the tibial plateaus, specially the medial one in the anterior cruciate ligament-deficient joint, experienced much larger compressive forces. In addition to causing an increase in joint primary anterior-posterior laxity and anterior cruciate ligament forces, medial meniscectomy substantially increased coupled tibial external rotation, forces on the lateral plateau, and stresses in the articular cartilage of the lateral plateau.

Instructional Course Lectures, The American Academy of Orthopaedic Surgeons - Factors Contributing to Function of the Knee Joint after Injury or Reconstruction of the Anterior Cruciate Ligament*†

Restoration of musculoskeletal function is a fundamental goal of orthopaedic treatment. Until now, clinical orthopaedic concepts of injury, repair, and restoration of function of musculoskeletal systems have been described and understood primarily in structural and biomechanical terms. This perception probably evolved because the structural characteristics are the most readily visualized factors, both in the clinical setting (for example, pathological laxity due to a ruptured ligament or a fracture) and through the preponderance of structural and pathoanatomical data offered by most current imaging modalities. Structural characteristics are also the factors most directly altered by operative intervention, such as stability following repair or reconstruction of a ligament or fixation of a fracture. It is a common belief that the restoration of measurable structural and biomechanical parameters to an injured joint, such as the knee, indicates the restoration of function to that system. We do not share this view. In the past few years, emerging clinical and basic-science findings have indicated a much greater degree of underlying biological complexity. Evidence suggests that the correction of identifiable structural abnormalities is often not sufficient to restore a joint to its full preinjury level of physiological function. For example, replacement of a ruptured anterior cruciate ligament with a graft does not necessarily prevent pain, swelling, or degenerative changes in the knee, even if the increased anterior-posterior laxity that had been present before the procedure is restored to normal. This observation indicates that factors other than anatomical and structural ones probably contribute to the restoration of joint function after injury. We believe that, although these other factors are less easily visualized, they play an important role in the ultimate functional status of an injured musculoskeletal system, such as the knee. The purpose of this Instructional Course Lecture is to discuss the concept of musculoskeletal function and to …

Sagittal plane translations of the knee in anterior cruciate deficient subjects and controls.

Static anterior-posterior (AP) laxity is one of the commonly used criteria in selecting patients for cruciate ligament reconstructions, but in reality dynamic AP laxity plays a more important role. The aim of this in vivo study was to compare the sagittal translation of the knee during active and passive motion, signifying dynamic AP laxity, with static AP laxity in healthy subjects (controls) and patients with anterior cruciate ligament deficiency. The sagittal plane knee translations were recorded and compared in both knees of nine healthy subjects (Controls) and seven patients with confirmed unilateral ACL deficiency during dynamic and static situations with an electrogoniometer system. In all groups during the ascents the tibia moved anteriorly in relation to the femur, whereas during the descents it moved posteriorly. The static anterior-posterior translation was significantly smaller in the control knee than in both healthy and injured knees of the ACL deficient group (P < 0.05). The injured knee showed the same laxity (92%) as the uninjured knee during dynamic activities, but it was 46% of static laxity. Also in the injured knees, the dynamic active laxity was larger during descents than ascents (P < 0.05). The results indicate that there is also a change in mechanics of the noninjured knee following injury to the contralateral knee and that this population of patients with ACL deficiency had good control over their abnormal anterior-posterior laxity.

A biomechanical study of replacement of the posterior cruciate ligament with a graft. Part 1: Isometry, pre-tension of the graft, and anterior-posterior laxity.

Twelve fresh-frozen knee specimens from cadavera were subjected to anterior-posterior laxity testing with 200 newtons of force applied to the tibia; testing was performed before and after a femoral load-cell was connected to a mechanically isolated cylindrical cap of subchondral femoral bone containing the femoral origin of the posterior cruciate ligament. The posterior cruciate ligament then was removed, the proximal end of a thin trial isometer wire was attached to one of four points designated on the femur, and displacement of the distal end of the wire relative to the tibia was measured over a 120-degree range of motion. The potted end of a ten-millimeter-wide bone-patellar ligament-bone graft was centered over the femoral origin of the ligament and attached to the femoral load-cell. Isometry measurements were repeated with the wire attached to the bone block of the free end of the graft in the tibial tunnel. Force was recorded at the load-cell (representing force in the intra-articular portion of the graft) as pre-tension was applied, with use of a calibrated spring-scale, to the tibial end of the graft. A laxity-matched pre-tension of the graft was determined such that the anterior-posterior laxity of the reconstructed knee at 90 degrees of flexion was within one millimeter of the laxity that was measured after installation of the load-cell. Anterior-posterior testing was repeated after insertion of the graft at the laxity-matched pre-tension. The least amount of change in the relative displacement of the trial wire over the 120-degree range of flexion occurred when the wire was attached to the proximal point on the femur (a point on the proximal margin of the femoral origin of the posterior cruciate ligament, midway between the anterior and posterior borders of the ligament). The greatest change in the relative displacement was associated with the anterior point (a point on the anterior margin of the femoral origin of the ligament, midway between the proximal and distal borders). The mean relative displacements of the trial wire when it was attached to a point at the center of the femoral origin of the ligament were not significantly different from the corresponding mean displacements of the distal end of the graft when the proximal end of the graft was centered at this point. At 90 degrees of flexion, the force recorded by the load-cell averaged 64 to 74 per cent of the force applied to the tibial end of the graft. The laxity-matched pre-tension of the graft at 90 degrees of flexion (as recorded by the load-cell) ranged from six to 100 newtons (mean and standard deviation, 43.0 +/- 33.4 newtons). With the numbers available, the mean laxities after insertion of the graft were not significantly different, at any angle of flexion, from the corresponding mean values after installation of the load-cell. Isometer readings from a trial wire attached to a point on the femur provided an accurate indication of the change in the length of a graft subsequently centered at that point. Anteriorly placed femoral tunnels should be avoided, as the isometer readings indicated increased tension, with flexion of the knee, in a graft placed in this region. The force in the intra-articular portion of the graft was always less than the force applied to the bone block in the tibial tunnel. Therefore, the femoral end of the graft should be tensioned to avoid frictional losses from the severe bend in the graft as it passes over the posterior tibial plateau. With correct pre-tensioning of a graft, normal anterior-posterior laxity at 0 to 90 degrees of flexion can be restored. However, because of the considerable range in the laxity-matched pre-tensions, we recommend that the pre-tension be greater than forty-three newtons for all patients to ensure that normal laxity is restored.

膝十字靭帯損傷患者における装具の膝関節制動効果について

Functional knee-braces are widely used to protect injured or reconstructed anterior cruciate ligaments, despite the fact that few scientific data support their efficacy. We studied the effect of the tibial strap of the Don-Joy brace used for 17 knees with cruciate ligament insufficiency. Injuries included the following: 12 knees, PCL 5 knees. The F-scan force distribution measuring system was used for the evaluation, and involved inserting a sensor-sheet between the strap and the tibia. We then testod for the transition of forces in the gait cycle compared with normal gait. The strap forces increased in the stance phase during normal gait, although the transitional forces were small. We found that the functional knee-brace acted as a braking device for anterior posterior laxity of the tibia, but it did not go far enough. There is a current trend toward early postoperative mobilization and intensive rehabilitation after reconstruction of the cruciate ligament with a bone-patellar tendon-bone graft. In this situation the usefulness of braces must not be over inflated.

A global verification study of a quasi-static knee model with multi-bundle ligaments

The ligaments of the knee consist of fiber bundles with variable orientations, lengths and mechanical properties. In concept, however, these structures were too often seen as homogeneous structures, which are either stretched or slack during knee motions. In previous studies, we proposed a new structural concept of the ligaments of the knee. In this concept, the ligaments were considered as multi-bundle structures, with nonuniform mechanical properties and zero force lengths. The purpose of the present study was to verify this new concept. For this purpose, laxity characteristics of a human knee joint were compared as measured in an experiment and predicted in a model simulation study. In the experiment, the varus-valgus and anterior-posterior laxities of a knee-joint specimen containing the ligaments and the articular surfaces only, were determined. From this knee-joint, geometric and mechanical parameters were derived to supply the parameters for a three-dimensional quasi-static knee-joint model. These parameters included (i) the three-dimensional insertion points of bundles, defined in the four major knee ligaments, (ii) the mechanical properties of these ligament, as functions of their relative insertion orientations and (iii) three-dimensional representations of the articular surfaces. With this model the experiments were simulated. If knee-model predictions and experimental results agree, then the multi-bundle ligament models are validated, at least with respect to their functional role in anterior-posterior and varus-valgus loading of the joint. The model described the laxity characteristics in AP-translation and VV-rotation of the cadaveric knee-joint specimen reasonably well. Both display the same patterns of laxity changes during knee flexion. Only if a varus moment of 8 N m was applied and if the tibia was posteriorly loaded, did the model predict a slightly higher laxity than that measured experimentally. From the model-experiment comparisons it was concluded that the proposed structural representations of the ligaments and their mechanical property distributions seem to be valid for studying the anterior-posterior and varus-valgus laxity characteristics of the human knee-joint.