Anterior cruciate ligament deficiency alters the in vivo motion of the tibiofemoral cartilage contact points in both the anteroposterior and mediolateral directions

BACKGROUND: Quantifying the effects of anterior cruciate ligament deficiency on joint biomechanics is critical in order to better understand the mechanisms of joint degeneration in anterior cruciate ligament-deficient knees and to improve the surgical treatment of anterior cruciate ligament injuries. We investigated the changes in position of the in vivo tibiofemoral articular cartilage contact points in anterior cruciate ligament-deficient and intact contralateral knees with use of a newly developed dual orthogonal fluoroscopic and magnetic resonance imaging technique. METHODS: Nine patients with an anterior cruciate ligament rupture in one knee and a normal contralateral knee were recruited. Magnetic resonance images were acquired for both the intact and anterior cruciate ligament-deficient knees to construct computer knee models of the surfaces of the bone and cartilage. Each patient performed a single-leg weight-bearing lunge as images were recorded with use of a dual fluoroscopic system at full extension and at 15 degrees , 30 degrees , 60 degrees , and 90 degrees of flexion. The in vivo knee position at each flexion angle was then reproduced with use of the knee models and fluoroscopic images. The contact points were defined as the centroids of the areas of intersection of the tibial and femoral articular cartilage surfaces. RESULTS: The contact points moved not only in the anteroposterior direction but also in the mediolateral direction in both the anterior cruciate ligament-deficient and intact knees. In the anteroposterior direction, the contact points in the medial compartment of the tibia were more posterior in the anterior cruciate ligament-deficient knees than in the intact knees at full extension and 15 degrees of flexion (p < 0.05). No significant differences were observed with regard to the anteroposterior motion of the contact points in the lateral compartment of the tibia. In the mediolateral direction, there was a significant lateral shift of the contact points in the medial compartment of the tibia toward the medial tibial spine between full extension and 60 degrees of flexion (p < 0.05). The contact points in the lateral compartment of the tibia shifted laterally, away from the lateral tibial spine, at 15 degrees and 30 degrees of flexion (p < 0.05). CONCLUSIONS: In the presence of anterior cruciate ligament injury, the contact points shift both posteriorly and laterally on the surface of the tibial plateau. In the medial compartment, the contact points shift toward the medial tibial spine, a region where degeneration is observed in patients with chronic anterior cruciate ligament injuries.     

Polyethylene damage and knee kinematics after total knee arthroplasty.

This study characterizes the relationship between in vivo knee kinematics and polyethylene damage by combining fluoroscopic analysis of tibiofemoral contact during dynamic activities and implant retrieval analysis in the same patients. Six patients (eight knees) underwent posterior cruciate ligament-retaining total knee arthroplasty. All patients participated in fluoroscopic analysis during a stair-rise and descent activity and treadmill gait an average of 18 months after arthroplasty, and articular contact was measured. Subsequently, all polyethylene tibial inserts were retrieved after an average of 26 months in vivo function: three at autopsy and five at revision. There was a statistically significant correlation between the damage location on the retrieved inserts and the articular contact location measured fluoroscopically during the activities. The femoral contact and polyethylene damage occurred predominantly on the posterior half of the tibial articular surface, and the damage pattern was largest in the compartment with the greatest range of in vivo femoral contact for each patient. This study showed that in vivo fluoroscopic analysis can predict the damage location on the polyethylene articular surface.     

In vivo kneeling biomechanics after posterior stabilized total knee arthroplasty

Background Kneeling is one of the activities sought by patients after total knee arthroplasty (TKA). This study investigated the six degrees of freedom (DOF) kinematics and three-dimensional (3D) contact during weight-bearing kneeling. Methods A total of 16 South Korean female patients (22 knees) after posteriorly stabilized (PS) TKA (LPS-Flex) were randomly recruited and had the same surgeon. The patients were imaged using a dual fluoroscopic technique while they kneeled from initial to maximum flexion. The acquired images and 3D models were then used to recreate the in vivo pose of the components. Contact was determined by locating the surface intersections in the tibiofemoral and cam/post (between the femoral cam and tibial post) articular compartments. Results Patients flexed, on average, from 107.3° to 128.0° during the kneeling activity. Changes in kinematics included 1.0 mm of proximal, 0.9 mm of medial, and 7.6 mm of posterior translation and 1.7° of varus rotation (P < 0.04). A difference in internal tibial rotation was not detected. Articular contact moved posteriorly by 5.9 mm and 6.4 mm in the medial and lateral compartments, respectively. Contact also moved medially by 3.2 mm and 5.8 mm in the medial and lateral compartments. A decrease in articular contact was observed in both condyles, and lateral condylar lift-off increased with flexion (P = 0.0001). More than 80% of the patients demonstrated cam/post engagement, which always occurred in the distal portion of the post. Conclusions In this patient cohort, the knee joint was constrained during the weight-bearing activity such that femoral subluxation and dislocation were not observed. Furthermore, posterior cam/post engagement occurred only in the distal portion of the tibial post, which may improve the longevity of the post. The tibiofemoral and cam/post articular contact data presented in this study further suggest that kneeling may be performed by patients after clinically successful PS TKA who feel comfortable with the activity and are free of pain.     

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.     

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.     

Effects of Posterior Tibial Slope on a Posterior Cruciate Retaining Total Knee Arthroplasty Kinematics and Kinetics

BackgroundIt has been hypothesized that increasing posterior tibial slope can influence condylar rollback and play a role in increasing knee flexion. However, the effects of tibial slope on knee kinematics are not well studied. The objective of this study is to assess the effects of tibial slope on femorotibial kinematics and kinetics for a posterior cruciate retaining total knee arthroplasty design.MethodsA validated forward solution model of the knee was implemented to predict the femorotibial biomechanics of a posterior cruciate retaining total knee arthroplasty with varied posterior slopes of 0°-8° at 2° intervals. All analyses were conducted on a weight-bearing deep knee bend activity.ResultsIncreasing the tibial slope shifted the femoral component posteriorly at full extension but decreased the overall femoral rollback throughout flexion. With no tibial slope, the lateral condyle contacted the polyethylene 6 mm posterior of the midline, but as the slope increased to 8°, the femur shifted an extra 5 mm, to 11 mm posterior of the tibial midline. Similar shifts were observed for the medial condyle, ranging from 7 mm posterior to 13 mm posterior, respectively. Increasing posterior slope decreased the posterior cruciate ligament tension and femorotibial contact force.ConclusionThe results of this study revealed that, although increasing the tibial slope shifted the femur posteriorly at full extension and maximum flexion, it reduced the amount of femoral rollback. Despite the lack of rollback, a more posterior location of condyles suggests lower chances of bearing impingement of the posterior femur and may explain why increasing slope may lead to higher knee flexion.     

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.     

Tibiofemoral kinematic analysis of kneeling after total knee arthroplasty

Some surgeons warn against kneeling after total knee arthroplasty (TKA), because limited clinical data exist. We describe the tibiofemoral contact position of TKA components during kneeling in vivo. Ten posterior-substituting (PS) and 10 cruciate-retaining (CR) designs were examined using a radiographic image-matching technique. Movement from standing to kneeling at 90 degrees produced different responses. CR knees translated anteriorly (medial, 4 +/- 4 mm; lateral, 2 +/- 6 mm). PS knees underwent little posterior translation (medial, 0.2 +/- 3 mm; lateral, 1 +/- 4 mm). Movement from 90 degrees to maximum flexion produced femoral posterior translation (CR medial, 5 +/- 4 mm; CR lateral, 5 +/- 4 mm; PS medial, 6 +/- 4 mm; PS lateral, 6 +/- 3 mm). The relationship between tibiofemoral contact position and flexion angle was more variable for CR (r2=.38) than for PS (r2=.64). Knee kinematics was similar to other deep-flexion weight-bearing activities.     

Fixed‐bearing medial unicompartmental knee arthroplasty restores neither the medial pivoting behavior nor the ligament forces of the intact knee in passive flexion

Medial unicompartmental knee arthroplasty (UKA) is an accepted treatment for isolated medial osteoarthritis. However, using an improper thickness for the tibial component may contribute to early failure of the prosthesis or disease progression in the unreplaced lateral compartment. Little is known of the effect of insert thickness on both knee kinematics and ligament forces. Therefore, a computational model of the tibiofemoral joint was used to determine how non‐conforming, fixed bearing medial UKA affects tibiofemoral kinematics, and tension in the medial collateral ligament (MCL) and the anterior cruciate ligament (ACL) during passive knee flexion. Fixed bearing medial UKA could not maintain the medial pivoting that occurred in the intact knee from 0° to 30° of passive flexion. Abnormal anterior–posterior (AP) translations of the femoral condyles relative to the tibia delayed coupled internal tibial rotation, which occurred in the intact knee from 0° to 30° of flexion, but occurred from 30° to 90° of flexion following UKA. Increasing or decreasing tibial insert thickness following medial UKA also failed to restore the medial pivoting behavior of the intact knee despite modulating MCL and ACL forces. Reduced AP constraint in non‐conforming medial UKA relative to the intact knee leads to abnormal condylar translations regardless of insert thickness even with intact cruciate and collateral ligaments. This finding suggests that the conformity of the medial compartment as driven by the medial meniscus and articular morphology plays an important role in controlling AP condylar translations in the intact tibiofemoral joint during passive flexion. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1868–1875, 2018.

     

Magnetic resonance image analysis of meniscal translation and tibio‐menisco‐femoral contact in deep knee flexion

The purpose of this study was to clarify meniscal displacement and cartilage–meniscus contact behavior in a full extension position and a deep knee flexion position. We also studied whether the meniscal translation pattern correlated with the tibiofemoral cartilage contact kinematics. Magnetic resonance (MR) images were acquired at both positions for 10 subjects using a conventional MR scanner. Subjects achieved a flexion angle averaging 139° ± 3°. Both medial and lateral menisci translated posteriorly on the tibial plateau during deep knee flexion. The posterior translation of the lateral meniscus (8.2 ± 3.2 mm) was greater than the medial (3.3 ± 1.5 mm). This difference was correlated with the difference in tibiofemoral contact kinematics between medial and lateral compartments. Contact areas in deep flexion were approximately 75% those at full extension. In addition, the percentage of area in contact with menisci increased significantly due to deep flexion. Our results related to meniscal translation and tibio‐menisco‐femoral contact in deep knee flexion, in combination with information about force and pressure in the knee, may lead to a better understanding of the mechanism of meniscal degeneration and osteoarthritis associated with prolonged kneeling and squatting. © 2008 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:673–684, 2008     

Polyethylene contact stresses, articular congruity, and knee alignment.

Increased conformity at the tibiofemoral articulation increases contact area and reduces contact stresses in total knee arthroplasty. Malalignment, however, can increase polyethylene contact stresses. The effect of knee alignment and articular conformity on contact stresses was evaluated in a finite element model. The polyethylene insert and femoral component were modeled in high- and low-conformity conditions. An axial tibial load of 3000 N was applied across the tibiofemoral articulation at different knee positions ranging from 0 degrees, to 90 degrees, flexion, 0 to 10 mm anteroposterior translation, 0 degrees to 10 degrees axial rotation, and coronal plane angulation (liftoff). Increased conformity significantly reduced contact stresses in neutral alignment (by 44% at 0 degrees flexion and 36% at 60 degrees and 90 degrees flexion). Liftoff significantly increased contact stresses in low- and high-conformity conditions, but to a lesser degree in the high-conformity condition. Malalignment in rotation was most detrimental especially with the high-conformity insert design. Overall, increasing articular conformity reduced stresses when the knee was well-aligned. However, malalignment in axial rotation was detrimental. Mobile-bearing knee designs with increased articular congruity may result in lower contact stresses, especially the rotating-bearing designs that theoretically minimize rotational malalignment.     

Three-dimensional tibiofemoral kinematics during deep flexion kneeling in a mobile-bearing total knee arthroplasty

Achieving very deep flexion after total knee arthroplasty is an important goal of most patients in Japan, Asia, and the Middle East because of floor-sitting lifestyles. Numerous knee arthroplasty designs have been introduced to permit high flexion. We performed an in vivo radiographic analysis of tibiofemoral motions during weight-bearing kneeling in one high-flexion knee arthroplasty design. Twenty knees implanted with a posterior-stabilized rotating-platform knee arthroplasty flexed an average of 126°. The femoral condyles translated posteriorly from extension to maximum flexion. Total posterior condylar translations averaged 11.6 and 4.7 mm for the lateral and medial condyles, respectively. Tibial internal rotation in 19 knees averaged 9° from extension to maximum flexion. Knees implanted with a posterior-stabilized, rotating-platform knee arthroplasty show deep flexion knee kinematics consistent with the implant design intent.     

Posterior cruciate ligament rupture alters in vitro knee kinematics

Isolated posterior cruciate ligament injuries usually are treated nonoperatively, although some patients remain symptomatic, and degenerative changes within the patellofemoral joint and the medial compartment of the tibiofemoral joint have been seen in followup studies. In vitro simulation of knee squatting was done to quantify the influence of the posterior cruciate ligament on tibiofemoral and patellofemoral kinematics. For five knee specimens, knee kinematics were measured before and after sectioning the posterior cruciate ligament, and compared using a Wilcoxon signed rank test. The only kinematic parameters that changed significantly after sectioning the posterior cruciate ligament were the tibial posterior translation and patellar flexion. The posterior translation of the tibia increased significantly between 25 degrees and 90 degrees flexion. The average increase in the posterior translation exceeded 10 mm at 90 degrees flexion. The patellar flexion increased significantly from 30 degrees to 90 degrees flexion. The average patellar flexion increase peaked at 4.4 degrees at 45 degrees flexion. Increased tibial translation could adversely influence joint stability. Increased patellar flexion could increase the patellofemoral joint pressure, especially at the inferior pole, leading to degenerative changes within the patellofemoral joint.     

Does anterior cruciate ligament reconstruction restore normal knee kinematics?: A prospective MRI analysis over two years

This prospective study used magnetic resonance imaging to record sagittal plane tibiofemoral kinematics before and after anterior cruciate ligament reconstruction using autologous hamstring graft. Twenty patients with anterior cruciate ligament injuries, performed a closed-chain leg-press while relaxed and against a 150 N load. The tibiofemoral contact patterns between 0 degrees to 90 degrees of knee flexion were recorded by magnetic resonance scans. All measurements were performed pre-operatively and repeated at 12 weeks and two years. Following reconstruction there was a mean passive anterior laxity of 2.1 mm (sd 2.3), as measured using a KT 1000 arthrometer, and the mean Cincinnati score was 90 (sd 11) of 100. Pre-operatively, the medial and lateral contact patterns of the injured knees were located posteriorly on the tibial plateau compared with the healthy contralateral knees (p=0.014), but were no longer different at 12 weeks (p=0.117) or two years postoperatively (p=0.909). However, both reconstructed and healthy contralateral knees showed altered kinematics over time. At two years, the contact pattern showed less posterior translation of the lateral femoral condyle during flexion (p<0.01).     

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.     

Lack of posteromedial tibiofemoral congruence at full flexion as a causative factor in isolated medial meniscal tears

The aim of the current study was to investigate posteromedial tibiofemoral congruence at full flexion of the knee in control knee joints and those affected by an isolated medial meniscal tear, to examine whether lack of such congruence was a causative factor in isolated medial meniscal tears. In this study, 1677 knee joints in 875 subjects were evaluated. The joints were classified as a control group (1345 joints), an isolated medial meniscal tear group (224 joints), and a contralateral isolated medial meniscal tear group (108 joints). Posteromedial tibiofemoral congruence was examined on a lateral radiograph of the knee joint at full flexion. The tangent touching the anterior and posterior parts of the articular surface of the medial tibial condyle was assumed to be the X-axis. To evaluate posteromedial tibiofemoral congruence, we measured the angle formed by the tangent that maximized the gradient of the tangent on the articular surface of the medial femoral condyle, and the tangent that maximized the gradient of the tangent on the articular surface of the medial tibial condyle. The mean angle differed significantly between the control and the isolated medial meniscal tear groups, regardless of sex. Isolated medial meniscal tears were found to be strongly related to an abnormally decreased angle, and, therefore, incongruence of the posteromedial tibiofemoral articulation at full flexion was considered to be one of the causes of isolated medial meniscal tears. Received: May 22, 2001/ Accepted: October 24, 2001     

Rotational kinematics of a modern fixed-bearing posterior stabilized total knee arthroplasty

The purpose of this study was to evaluate the rotational kinematics of a fixed-bearing posteriorly stabilized total knee design in moderate and deep flexion. Three-dimensional kinematics analyses were conducted on 20 knees in 4 weight-bearing positions using 3-dimensional shape-matching techniques. Average maximum skeletal flexion was 138 degrees . Internal tibial rotation was demonstrated in 19 of 20 knees. The average internal tibial rotation in midflexed lunge was 5.5 degrees (-3.8 degrees to 14.1 degrees ) and in maximum flexion kneeling was 4.0 degrees (-3.1 degrees to 10.6 degrees ). Separation of articular surfaces was not identified. In this study, patients with this device demonstrated patterns of rotation similar to those previously reported for both the normal knee and rotating platform designs.     

Interaction between intrinsic knee mechanics and the knee extensor mechanism

The ability of the quadriceps muscles to extend the knee was studied relative to the intrinsic mechanical features of the knee joint. The quadriceps mechanical efficiency changed by nearly 50% between 0 and 90 degrees of knee flexion. The peak efficiency occurred at approximately 20 degrees of knee flexion. The mechanical efficiency of the quadriceps was dependent on the movement of the net anteroposterior (AP) tibiofemoral contact center of pressure, the change in patellar ligament angle, and the change in the quadriceps-to-ligament force transfer ratio. The average net AP tibiofemoral contact center of pressure moved posteriorly on the tibial plateau as the knee flexed from 0 to 90 degrees. The excision of both cruciate ligaments reversed the posteriorly directed movement of the net AP tibiofemoral contact center of pressure at flexion angles from 60 to 90 degrees, resulting in a reduction in extension moment.     

In vivo kinematic analysis of cruciate-retaining total knee arthroplasty during weight-bearing and non-weight-bearing deep knee bending

The purpose of the present study was to evaluate the in vivo kinematics of the posterior cruciate ligament-retaining total knee arthroplasty during weight-bearing and non-weight-bearing deep knee bending and compare these 2 different conditions. We evaluated the in vivo kinematics of the knee using fluoroscopy and femorotibial translation relative to the tibia tray by 2-dimensional/3-dimensional registration. In the weight-bearing state, the femoral component showed central pivot and bicondylar posterior rollback pattern. During non-weight-bearing, the movement anteriorly occurred on both the medial and lateral side during early flexion, whereas bicondylar femoral component rollback occurred after that. During non-weight-bearing, both the medial and lateral condyle significantly moved anteriorly compared with the weight-bearing state during early flexion. However, bicondylar femoral rollback occurred under both these conditions.     

Effect of articular step-off and meniscectomy on joint alignment and contact pressures for fractures of the lateral tibial plateau

OBJECTIVES: To determine the effects of intraarticular step-off and lateral meniscectomy on the alignment of the articular axis, contact area, and pressures for lateral tibial plateau fractures. DESIGN: Biomechanical cadaver study. INTERVENTION: Six fresh cadaveric knees were used. A simulated split fracture of the lateral tibial plateau was reproducibly created by osteotomies, and articular step-offs of zero, one, two, four, and six millimeters were achieved by using support shims. The knee was loaded with 500 newtons in 0 degrees and 350 newtons in 30 degrees of flexion. A digital camera determined changes in the alignment of the articular axis, and F-Scan sensors were inserted into the medial and lateral joint compartments to determine the pressures and pressure distributions. MAIN OUTCOME MEASUREMENT: Each specimen was tested at step-offs of zero, one, two, four, and six millimeters, with the presence or absence of the lateral meniscus. The changes in alignment of the articular axis, the contact area, and the average and maximum contact pressures for each condyle were obtained. RESULTS: Increased articular step-off heights progressively increased valgus angulation and average and maximum contact pressures and progressively decreased contact areas in lateral compartment. At a six-millimeter step-off with 0 degrees of flexion, the valgus angle increased an average of 7.6 degrees, and average contact pressures and maximum contact pressures increased an average of 208 percent and 97 percent, respectively, and contact area decreased an average of 33 percent (p < 0.05). Meniscectomy increased valgus angles by an average of 38 percent and contact pressures by an average of 45 percent and decreased contact areas by 26 percent in the lateral compartment at the same articular step-off heights (p < 0.05). CONCLUSION: The results of this study show the importance of decreasing articular step-off heights in treating lateral tibial plateau split fractures, particularly if a meniscectomy is performed.