Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee

In six unloaded cadaver knees we used MRI to determine the shapes of the articular surfaces and their relative movements. These were confirmed by dissection. Medially, the femoral condyle in sagittal section is composed of the arcs of two circles and that of the tibia of two angled flats. The anterior facets articulate in extension. At about 20 degrees the femur 'rocks' to articulate through the posterior facets. The medial femoral condyle does not move anteroposteriorly with flexion to 110 degrees. Laterally, the femoral condyle is composed entirely, or almost entirely, of a single circular facet similar in radius and arc to the posterior medial facet. The tibia is roughly flat. The femur tends to roll backwards with flexion. The combination during flexion of no anteroposterior movement medially (i.e., sliding) and backward rolling (combined with sliding) laterally equates to internal rotation of the tibia around a medial axis with flexion. About 5 degrees of this rotation may be obligatory from 0 degrees to 10 degrees flexion; thereafter little rotation occurs to at least 45 degrees. Total rotation at 110 degrees is about 20 degrees, most if not all of which can be suppressed by applying external rotation to the tibia at 90 degrees.     

How the knee moves

The arc of flexion used in almost all the activities of everyday life extends from about 20°±10° to 110°/120°. During this arc, the human knee corresponds to the quadrupedal mammalian knee. Both the femoral surfaces are circular with a similar radius and rotate around their geometrical centres as the knee flexes. The medial femoral condyle does not move antero-posteriorly with flexion, i.e. stability depends on the medial side of the knee. In contrast, the lateral femoral condyle is antero-posteriorly mobile and as it moves it carries the meniscus with it. This AP movement results in longitudinal tibial rotation which is facultative rather than obligatory: if posterior motion occurs, the femur rotates externally around a medial axis with flexion whereas if no AP motion occurs, the knee can flex as would a uniaxial hinge. Rotation first appears in arboreal quadrupeds (apes) and may be becoming vestigial in Man. The axis of longitudinal rotation during flexion, parallel to the tibia and perpendicular to the flexion axis, approximately intersects the latter in the centre of the medial femoral condylar sphere. Varus/valgus rotation, around an AP axis which also passes through the centre of the femoral sphere, permits the lateral femoral condyle to lift away from the tibia because the lateral collateral ligament (LCL) is slack at 90° in mid external/internal rotation. Thus, in the arc ‘20’–120° the medial femoral condyle resembles the femoral head: it is spherical, it does not translate during flexion and all three axes of rotation intersect at its centre. At 90°, forced longitudinal rotation does result in AP movement of the medial condyle and on the lateral side in a reciprocal translation which is almost sufficient to abolish the translation accompanying flexion. This movement occurs around a vertical axis which is slightly lateral to that representing longitudinal rotation with flexion.The arc from 10° to full extension is accompanied by the so-called ‘locking’ and ‘screw-home’. It appears to be a feature of bipedal terrestrial gait with an erect stance, i.e. human gait. Although the arc exists, it is rarely used fully in everyday life. The motion is complex and involves asymmetrical articular surfaces other than those used from 20° to 120°. On the medial side, the femur ‘rocks’ forward onto the upward-sloping anterior surface of the tibia and then rotates into extension around an anterior, larger radiused circular surface. On the lateral side, the femur rolls down onto the anterior horn. The result is ‘lift-off’ of the posterior facets used in the arc ‘20’–120° and progressive tightening of the structures attached posteriorly to the femur, in particular the ACL. This ligament, as it tightens, may move the lateral femoral condyle anteriorly so that extension is accompanied by about 5° of obligatory femoral internal rotation. Flexion and longitudinal rotation occur by rotation around, and translation along, a 20° oblique screw axis penetrating medially the epicondyle and, laterally, the region of the tibio-femoral contact surface.From 120° to full flexion, the motion is passive rather than active. Both femoral condyles move backwards and both lose contact with the tibia. Thus, the tibio-femoral joint is strictly speaking subluxed. Medially, the femoral condyle rolls up onto the posterior horn. Laterally, the femoral condyle rolls backwards and downwards, finally to lie posterior to the tibia, resting on the posterior horn.Although the motion of the knee is complex, it can be (and has been) imaged by MRI in the unloaded cadaveric knee, the unloaded living knee and the loaded living knee. The keys to its understanding are to divide flexion into three arcs and to appreciate that in the functional active arc (‘20’–120°) the medial femoral condyle, like the femoral head, is spherical, that it does not translate and that it rotates around three axes which intersect at its centre. By contrast, the lateral femoral condyle rolls and slides antero-posteriorly on the tibia to result in longitudinal rotation (a possibly vestigial movement in Man) around a medial axis.     

The shapes of the tibial and femoral articular surfaces in relation to tibiofemoral movement

We report a study of the shapes of the tibial and femoral articular surfaces in sagittal, frontal and coronal planes which was performed on cadaver knees using two techniques, MRI and computer interpolation of sections of the articular surfaces acquired by a three-dimensional digitiser. The findings using MRI, confirmed in a previous study by dissection, were the same as those using the digitiser. Thus both methods appear to be valid anatomical tools. The tibial and femoral articular surfaces can be divided into anterior segments, contacting from 0 degrees to 20 +/- 10 degrees of flexion, and posterior segments, contacting from 20 +/- 10 degrees to 120 degrees of flexion. The medial and lateral compartments are asymmetrical, particularly anteriorly. Posteromedially, the femur is spherical and is located in a conforming, but partly deficient, tibial socket. Posterolaterally, it is circular only in the sagittal section and the tibia is flat centrally, sloping downwards both anteriorly and posteriorly to receive the meniscal horns. Anteromedially, the femur is convex with a sagittal radius larger than that posteriorly, while the tibia is flat sloping upwards and forwards. Anterolaterally, both the femoral and tibial surfaces are largely deficient. These shapes suggest that medially the femur can rotate on the tibia through three axes intersecting in the middle of the femoral sphere, but that the sphere can only translate anteroposteriorly and even then to a limited extent. Laterally, the femur can freely translate anteroposteriorly, but can only rotate around a transverse axis for that part of the arc, i.e., near extension, during which it comes into contact with the tibia through its flattened distal/medial surface as against its spherical posterior surface.     

In vivo three-dimensional knee kinematics using a biplanar image-matching technique.

A biplanar image-matching technique was developed and applied to a study of normal knee kinematics in vivo under weightbearing conditions. Three-dimensional knee models of six volunteers were constructed using computed tomography. Projection images of the models were fitted onto anteroposterior and lateral radiographs of the knees at hyperextension and every 15 degrees from 0 degrees to 120 degrees flexion. Knee motion was reconstructed on the computer. The femur showed a medial pivoting motion relative to the tibia during knee flexion, and the average range of external rotation associated with flexion was 29.1 degrees . The center of the medial femoral condyle translated 3.8 mm anteriorly, whereas the center of the lateral femoral condyle translated 17.8 mm posteriorly. This rotational motion, with a medially offset center, could be interpreted as a screw home motion of the knee around the tibial knee axis and a posterior femoral rollback in the sagittal plane. However, the motion of the contact point differed from that of the center of the femoral condyle when the knee flexion angle was less than 30 degrees. Within this range, medial and lateral contact points translated posteriorly, and a posterior femoral rollback occurred. This biplanar image-matching technique is useful for investigating knee kinematics in vivo.     

Comparison of kinematic analysis by mapping tibiofemoral contact with movement of the femoral condylar centres in healthy and anterior cruciate ligament injured knees.

Two methods of analysis of knee kinematics from magnetic resonance images (MRI) in vivo have been developed independently: mapping the tibiofemoral contact, and tracking the femoral condylar centre. These two methods are compared for the assessment of kinematics in the healthy and the anterior cruciate ligament injured knee. Sagittal images of both knees of 20 subjects with unilateral anterior cruciate ligament injury were analysed. The subjects had performed a supine leg press against a 150 N load. Images were generated at 15 degrees intervals from 0 degrees to 90 degrees knee flexion. The tibiofemoral contact, and the centre of the femoral condyle (defined by the flexion facet centre (FFC)), were measured from the posterior tibial cortex. The pattern of contact in the healthy knee showed the femoral roll back from 0 degrees to 30 degrees, then from 30 degrees to 90 degrees the medial condyle rolled back little, while the lateral condyle continued to roll back on the tibial plateau. The contact pattern was more posterior in the injured knee (p=0.012), particularly in the lateral compartment. The medial FFC moved back very little during knee flexion, while the lateral FFC moved back throughout the flexion arc. The FFC was not significantly different in the injured knee (p=0.17). The contact and movement of the FFC both demonstrated kinematic events at the knee, such as longitudinal rotation. Both methods are relevant to design of total knee arthroplasty: movement of the FFC for consideration of axis alignment, and contact pattern for issues of interface wear and arthritic change in ligament injury.     

Does the femur roll-back with flexion?

MRI studies of the knee were performed at intervals between full extension and 120 degrees of flexion in six cadavers and also non-weight-bearing and weight-bearing in five volunteers. At each interval sagittal images were obtained through both compartments on which the position of the femoral condyle, identified by the centre of its posterior circular surface which is termed the flexion facet centre (FFC), and the point of closest approximation between the femoral and tibial subchondral plates, the contact point (CP), were identified relative to the posterior tibial cortex. The movements of the CP and FFC were essentially the same in the three groups but in all three the medial differed from the lateral compartment and the movement of the FFC differed from that of the CR Medially from 30 degrees to 120 degrees the FFC and CP coincided and did not move anteroposteriorly. From 30 degrees to 0 degrees the anteroposterior position of the FFC remained unchanged but the CP moved forwards by about 15 mm. Laterally, the FFC and the CP moved backwards together by about 15 mm from 20 degrees to 120 degrees. From 20 degrees to full extension both the FFC and CP moved forwards, but the latter moved more than the former. The differences between the movements of the FFC and the CP could be explained by the sagittal shapes of the bones, especially anteriorly. The term 'roll-back' can be applied to solid bodies, e.g. the condyles, but not to areas. The lateral femoral condyle does roll-back with flexion but the medial does not, i.e. the femur rotates externally around a medial centre. By contrast, both the medial and lateral contact points move back, roughly in parallel, from 0 degrees to 120 degrees but they cannot 'roll'. Femoral roll-back with flexion, usually imagined as backward rolling of both condyles, does not occur.     

Tibiofemoral movement 3: full flexion in the living knee studied by MRI

We studied active flexion from 90 degrees to 133 degrees and passive flexion to 162 degrees using MRI in 20 unloaded knees in Japanese subjects. Flexion over this arc is accompanied by backward movement of the medial femoral condyle of 4.0 mm and by backward movement laterally of 15 mm, i.e., by internal rotation of the tibia. At 162 degrees the lateral femoral condyle lies posterior to the tibia.     

固定平台后稳定型假体全膝关节置换术后的运动学研究

 目的 探讨固定平台后稳定型假体全膝关节置换(total knee arthroplasty,TKA)术后膝关节在负重屈膝下蹲时的运动学特征。方法 选取10名健康志愿者和10例固定平台后稳定型假体TKA术后患者。制作骨骼及膝关节假体三维模型,在持续X线透视下完成负重下蹲动作,膝关节屈曲度每增加15°截取一幅图像。通过荧光透视分析技术完成三维模型与二维图像的匹配,再现股骨与胫骨在屈膝过程中的空间位置,通过连续的图像分析比较正常与固定平台后稳定型假体TKA术后膝关节在负重下蹲时股骨内、外髁前后移动及胫骨内外旋转幅度。结果 负重下蹲时,正常膝关节平均屈曲136°,股骨内、外髁分别后移(7.3±1.2) mm和(19.3±3.1) mm,胫骨平均内旋23.8°±3.4°;TKA术后膝关节平均屈曲125°,股骨内、外髁分别后移(1.4±1.6) mm和(6.4±1.7) mm,胫骨平均内旋8.5°±3.4°。结论 固定平台后稳定型假体TKA术后膝关节运动与正常膝关节相似,均表现出股骨内、外髁后移及胫骨内旋运动,但幅度小于正常膝关节,且在屈膝过程中存在股骨矛盾性前移及胫骨外旋现象。     

Joint biomechanics and design of modern knee prostheses--time for revised thinking!

AIM AND METHOD: This review article summarises new knowledge about knee kinematics and induces a new discussion about the design of total knee arthroplasty (TKA) components. RESULTS: According to these new observations, knee flexion is not linked to femoral rollback but to a rotational movement between tibia and femur. The axis of this rotation is situated in the medial compartment of the knee when an intact anterior craciate ligament is present and not centrally through the tibial spines. In case of ACL insufficiency, such as that following TKA, the center of rotation shifts into the lateral compartment. Furthermore, the form of the posterior femoral condyle is not elliptical but round. CONCLUSION: Rotational movements between femoral component and tibial baseplate with the polyethylene-inlay have to be possible. One needs an asymmetric surface of the polyethylene-inlay, because different movements occur in the medial compartment than in the lateral compartment. The option to construct the posterior femoral condyle with a single radius allows a high congruency with the articulating inlay. The surgeon should let the new findings influence his choice of a TKA system. A closer analysis of modern prosthetic designs with either fixed or mobile bearings reveals that a few systems have already incorporated some of the new kinematic aspects of the knee.     

Kinematics of medial osteoarthritic knees before and after posterior cruciate ligament retaining total knee arthroplasty

Total knee arthroplasty (TKA) is a widely accepted surgical procedure for the treatment of patients with end‐stage osteoarthritis (OA). However, the function of the knee is not always fully recovered after TKA. We used a dual fluoroscopic imaging system to evaluate the in vivo kinematics of the knee with medial compartment OA before and after a posterior cruciate ligament‐retaining TKA (PCR‐TKA) during weight‐bearing knee flexion, and compared the results to those of normal knees. The OA knees displayed similar internal/external tibial rotation to normal knees. However, the OA knees had less overall posterior femoral translation relative to the tibia between 0° and 105° flexion and more varus knee rotation between 0° and 45° flexion, than in the normal knees. Additionally, in the OA knees the femur was located more medially than in the normal knees, particularly between 30° and 60° flexion. After PCR‐TKA, the knee kinematics were not restored to normal. The overall internal tibial rotation and posterior femoral translation between 0° and 105° knee flexion were dramatically reduced. Additionally, PCR‐TKA introduced an abnormal anterior femoral translation during early knee flexion, and the femur was located lateral to the tibia throughout weight‐bearing flexion. The data help understand the biomechanical functions of the knee with medial compartment OA before and after contemporary PCR‐TKA. They may also be useful for improvement of future prostheses designs and surgical techniques in treatment of knees with end‐stage OA. © 2010 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 29:40–46, 2011     

Effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on tension of an anterior cruciate ligament graft: an in vitro study

BACKGROUND: High tension in an anterior cruciate ligament graft adversely affects both the graft and the knee; however, it is unknown why high graft tension in flexion occurs in association with a posterior femoral tunnel. The purpose of the present study was to determine the effect of the angle of the femoral and tibial tunnels in the coronal plane and incremental excision of the posterior cruciate ligament on the tension of an anterior cruciate ligament graft during passive flexion. METHODS: Eight cadaveric knees were tested. The angle of the tibial tunnel was varied to 60 degrees, 70 degrees, and 80 degrees in the coronal plane with use of three interchangeable, low-friction bushings. The femoral tunnel, with a 1-mm-thick posterior wall, was drilled through the tibial tunnel bushing with use of the transtibial technique. After the graft had been tested in all three tibial bushings with one femoral tunnel, the femoral tunnel was filled with bone cement and the tunnel combinations were tested. Lastly, the graft was replaced in the 80 degrees femoral and tibial tunnels, and the tests were repeated with excision of the lateral edge of the posterior cruciate ligament in 2-mm increments. Graft tension, the flexion angle, and anteroposterior laxity were recorded in a six-degrees-of-freedom load-application system that passively moved the knee from 0 degrees to 120 degrees of flexion. RESULTS: The graft tension at 120 degrees of flexion was affected by the angle of the femoral tunnel and by incremental excision of the posterior cruciate ligament. The highest graft tension at 120 degrees of flexion was 169 +/- 9 N, which was detected with the graft in the 80 degrees femoral and 80 degrees tibial tunnels. The lowest graft tension at 120 degrees of flexion was 76 +/- 8 N, which was detected with the graft in the 60 degrees femoral and 60 degrees tibial tunnels. The graft tension of 76 N at 120 degrees of flexion with the graft in the 60 degrees femoral and 60 degrees tibial tunnels was closer to the tension in the intact anterior cruciate ligament. Excision of the lateral edge of the posterior cruciate ligament in 2 and 4-mm increments significantly lowered the graft tension at 120 degrees of flexion without changing the anteroposterior position of the tibia. CONCLUSIONS: Placing the femoral tunnel at 60 degrees in the coronal plane lowers graft tension in flexion. Our results suggest that high graft tension in flexion is caused by impingement of the graft against the posterior cruciate ligament, which results from placing the femoral tunnel medially at the apex of the notch in the coronal plane.     

Effects of twisting of the graft in anterior cruciate ligament reconstruction

In an in vitro study on six knees from cadavers, the effect of bone-patellar tendon-bone graft twist on anterior knee laxity was measured at different knee flexion angles. A motion and loading rig was used to prescribe the flexion angle, to restrain axial rotation, and to apply 100 N anterior force to the tibia. Roentgen stereophotogrammetric analysis was used to measure the relative anteroposterior position of the tibia and femur. The tibial bone block was cemented in a cylinder that allowed rotation in the bone tunnel. The anterior cruciate ligament was transected and reconstructed with neutral, 90 degrees, and 150 degrees internal twists and 90 degrees and 150 degrees external twists. External and internal graft twists in the reconstruction resulted in significant reductions of anterior laxity, however, at the cost of a more posterior position of the unloaded tibia relative to the femur (anteroposterior-error). The results are explained by the anterior relocation of the graft insertion by twisting the tibial bone block. The inclination angle of the graft in the anteroposterior direction flattens, which could improve the anterior laxity. A consequent side effect is the increase of posterior shift of the tibia relative to the femur.     

Motion of the femoral condyles in flexion and extension during a continuous lunge

Numerous studies have reported on in‐vivo posterior femoral condyle translations during various activities of the knee. However, no data has been reported on the knee motion during a continuous flexion‐extension cycle. Further, few studies have investigated the gender variations on the knee kinematics. This study quantitatively determined femoral condylar motion of 10 male and 10 female knees during a continuous weightbearing flexion‐extension cycle using two‐dimensional to three‐dimensional fluoroscopic tracking technique. The knees were CT‐scanned to create three‐dimensional models of the tibia and femur. Continuous images of each subject were taken using a single‐fluoroscopic imaging system. The knee kinematics were measured along the motion path using geometric center axis of the femur. The results indicated that statistical differences between the flexion and extension motions were only found in internal‐external tibial rotation and lateral femoral condylar motion at the middle range of flexion angles. At low flexion angles, male knees have greater external tibial rotation and more posteriorly positioned medial femoral condyle than females. The knee did not show a specific pivoting type of rotation with flexion. Axial rotation center varied from lateral to medial compartments of the knee. These data could provide useful information for understanding physiological motion of normal knees. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 33:591–597, 2015.     

Factors affecting the impingement angle of fixed- and mobile-bearing total knee replacements: a laboratory study

Maximum flexion-or impingement angle-is defined as the angle of flexion when the posterior femoral cortex impacts the posterior edge of the tibial insert. We examined the effects of femoral component placement on the femur, the slope angle of the tibial component, the location of the femoral-tibial contact point, and the amount of internal or external rotation. Posterior and proximal femoral placement, a more posterior femoral-tibial contact point, and a more tibial slope all increased maximum flexion, whereas rotation reduced it. A mobile-bearing knee gave results similar to those of the fixed-bearing knee, but there was no loss of flexion in internal or external rotation if the mobile bearing moved with the femur. In the absence of negative factors, a flexion angle of 150 degrees can be reached before impingement.     

The effects of tibial rotation on posterior translation in knees in which the posterior cruciate ligament has been cut

BACKGROUND: One of the most useful clinical tests for diagnosing an isolated injury of the posterior cruciate ligament is the posterior drawer maneuver performed with the knee in 90 degrees of flexion. Previously, it was thought that internally rotating the tibia during posterior drawer testing would decrease posterior laxity in a knee with an isolated posterior cruciate ligament injury. In this study, we evaluated the effects of internal and external tibial rotation on posterior laxity with the knee held in varying degrees of flexion after the posterior cruciate and meniscofemoral ligaments had been cut. MATERIALS AND METHODS: Twenty cadaveric knees were used. Each knee was mounted in a fixture with six degrees of freedom, and anterior and posterior forces of 150 N were applied. The testing was conducted with the knee in 90 degrees, 60 degrees, 30 degrees, and 0 degrees of flexion with the tibia in neutral, internal, and external rotation. All knees were tested with the posterior cruciate and meniscofemoral ligaments intact and transected. Repeated-measures analysis of variance was used for statistical analysis. RESULTS: At 30 degrees, 60 degrees, and 90 degrees of flexion, there was a significant increase in posterior laxity following transection of the posterior cruciate and meniscofemoral ligaments. At 60 degrees and 90 degrees of flexion, there was significantly less posterior laxity when the tibia was held in internal compared with external rotation. At 0 degrees and 30 degrees of flexion, there was no significant difference in posterior laxity when the tibia was held in internal compared with external rotation. CONCLUSIONS: After the posterior cruciate and meniscofemoral ligaments had been cut, posterior laxity was significantly decreased by both internal and external rotation of the tibia. Internal tibial rotation resulted in significantly less laxity than external tibial rotation did at 60 degrees and 90 degrees of knee flexion.     

Three-dimensional knee joint movements during a step-up: Evaluation after anterior cruciate ligament rupture

The three-dimensional motions of the knee were analysed during closed kinetic chain knee extension in 13 patients with unilateral chronic injury of the anterior cruciate ligament. The patients ascended a platform, and serial stereophotogrammetric roentgenograms were exposed from about 100° of flexion to full extension. From a position of about 100° of knee flexion and 20° of internal rotation, the tibia rotated externally during the extension. Almost no tibial adduction or abduction was observed. The tibial intercondylar eminence translated laterally, distally, and anteriorly relative to the femur. In knees with absence of the anterior cruciate ligament, the intercondylar eminence had a more posterior position compared with the contralateral normal knees. The proximal tibia was used as a fixed reference segment to evaluate the anteroposterior translations of a central point in the femoral condyles. The femoral point was more anteriorly displaced in the injured than in the contralateral knees. This difference might reflect increased activity of the hamstrings in the injured knees, because it was most pronounced at 80° of flexion and decreased with increasing extension. In the sagittal plane, the mean helical axis was positioned close to the femoral insertion of the ligament at 80° of flexion and was displaced distally and anteriorly during extension. In the frontal plane, the axis had a transverse direction at 80° of flexion. At close to full extension, the axis was positioned distally in the lateral condyle and proximally in the medial condyle. In the horizontal plane, the helical axes ran slightly more anteriorly in the medial than in the lateral femoral condyle but changed inclination at close to full extension and became almost parallel to the transverse axis.     

A correlative study of the geometry and anatomy of the distal femur

Sixteen knees were examined roentgenographically in the lateral plane. Ten knees were examined from autopsy subjects. The distal articular femur may be represented by three circular surfaces: (1) the floor of the patellar groove (articulating with the patella from 10 degrees to 100 degrees), (2) the posterior femoral condyles (articulating with the tibia from 10 degrees to 150 degrees), and (3) the distal condyles (articulating with the tibia from 0 degrees to 10 degrees). The radii of these surfaces, their angular arcs, and the distances between their centers varied with the size of the femur but fell within a narrow range. The radii of the patellar groove and the posterior femoral condyles averaged 24 mm and 21 mm, and the average angle subtended by these arcs was 90 degrees and 140 degrees, respectively. The average distance between the centers of these two circles was 20 mm. The femoral attachment of the synovial and patellar retinacular reflections was found in the area of the center of the patellar groove circle. The femoral attachments of the medial collateral and posterior cruciate ligaments and of the lateral collateral and anterior cruciate ligaments were found to be in the area of the center of the circle of the medial and lateral posterior femoral condylar circles, respectively.     

Combined anterior cruciate-ligament reconstruction using semitendinosus tendon and iliotibial tract

We are reporting the results of a reconstructive procedure designed to decrease anterior tibial subluxation due to disruption of the anterior cruciate ligament. The operation combines both intra-articular and extra-articular methods. The semitendinosus tendon and the iliotibial tract are both routed from opposite directions over the top of the lateral femoral condyle and through the same oblique drill-hole in the proximal part of the tibia: the semitendinosus tendon is passed up through the tibial drill-hole, across the knee joint, over the top of the lateral femoral condyle, and deep to the fibular collateral ligament, and the iliotibial tract is passed deep to the fibular collateral ligament, over the top of the lateral femoral condyle, across the knee joint, and down through the drill-hole. Both grafts are simultaneously pulled tight while the semitendinosus tendon is sutured to the iliotibial tract laterally and the iliotibial tract is sutured to the semitendinosus tendon medially below the drill-hole. The posteromedial and lateral parts of the capsule are advanced to tighten the secondary restraints. One hundred of the first 106 consecutive patients with chronic instability who had this procedure were evaluated using subjective and objective criteria at three to seven and one-half years after surgery. The positive anterior-drawer sign tested at 25 degrees of flexion was eliminated or reduced to 1+ in eighty knees, and the positive pivot shift was reduced to zero or 1+ in ninety-one knees. The objective assessment of isokinetic muscle performance and passive tibial rotation showed significant improvements in strength and normalization of tibial rotation.     

Femoro-tibial and menisco-tibial translation patterns in patients with unilateral anterior cruciate ligament deficiency--a potential cause of secondary meniscal tears.

OBJECTIVE: To analyze menisco-tibial and femoro-tibial translation patterns in healthy and ACL-deficient knees in different knee flexion angles under muscle activity. METHODS: The ACL-deficient and contralateral healthy knees of 10 patients were examined with an open MRI system at 30 degrees and 90 degrees of knee flexion, under isometric contraction of the extensors or flexor muscle groups. Translations between the tibia, the femoral condyles and the menisci were analyzed by three-dimensional image postprocessing. RESULTS: Posterior translation of the femur and menisci relative to the tibia occurred during knee flexion (30-90 degrees) in all knees. In ACL-deficient knees, posterior translation of the medial femoral condyle (+1.3 +/- 3.8 mm) was significantly larger than in healthy knee (-0.9 +/- 2.9 mm; p<0.05), while the translation pattern of the menisci was similar (med. meniscus 0.6 +/- 2.3 mm vs. 0.6 +/- 2.7 mm). Under isometric contraction of the extensors (relative to the flexor muscle group), an increased posterior position of the femur and menisci was observed at 30 degrees knee flexion, but not at 90 degrees. This applied to ACL-deficient and healthy knees. CONCLUSIONS: This study shows a significant increase of translation of the medial femoral condyle in ACL-deficient knees, whereas menisco-tibial translation remains almost unchanged. This difference in translation patterns indicates that the posterior horn of the medial meniscus might encounter shear, potentially explaining the high rate of secondary medial meniscal tears in patients with ACL-deficiency.     

Femoral rollback after cruciate-retaining and stabilizing total knee arthroplasty

Limited data comparing the kinematics of posterior cruciate ligament-retaining or substituting total knee arthroplasty with its own intact knee under identical loadings is available. In the current study, posterior femoral translation of the lateral and medial femoral condyles under unloaded conditions was examined for intact, cruciate-retaining, cruciate ligament-deficient cruciate-retaining and posterior-substituting knee arthroplasties. Cruciate-retaining and substituting total knee arthroplasties behaved similarly to the cruciate-deficient cruciate-retaining total knee arthroplasty between 0 degrees and 30 degrees flexion. Beyond 30 degrees, the posterior cruciate-retaining arthroplasty showed a significant increase in posterior translation of both femoral condyles. The posterior cruciate-substituting arthroplasty only showed a significant increase in posterior femoral translation after 90 degrees. At 120 degrees, both arthroplasties restored approximately 80% of that of the native knee. Posterior translation of the lateral femoral condyle was greater than that observed in the medial condyle for all knees, indicating the presence of internal tibial rotation during knee flexion. The data showed that the posterior cruciate ligament is an important structure in posterior cruciate-retaining total knee arthroplasty and proper balancing is imperative to the success of the implant. The cam-spine engagement is valuable in restoring posterior femoral translation in posterior cruciate-substituting total knee arthroplasty.