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

Asymmetrical tibial polyethylene geometry-cruciate retaining total knee arthroplasty does not fully restore in-vivo articular contact kinematics during strenuous activities

PURPOSE

A new CR TKA design with concave medial and convex lateral tibial polyethylene bearing components was introduced recently to improve functional outcomes. This study aimed to investigate in-vivo articular contact kinematics in unilateral asymmetrical tibial polyethylene geometry CR TKA patients during strenuous knee flexion activities.

METHODS

Fifteen unilateral CR TKA patients (68.4 ± 5.8 years; 6 male/9 female) were evaluated for both knees during sit-to-stand, single-leg deep lunges and step-ups using validated combined computer tomography and dual fluoroscopic imaging system. Medial and lateral condylar contact positions were quantified during weight-bearing flexion activities. The Wilcoxon signed-rank test was performed to determine if there is a significant difference in articular contact kinematics during strenuous flexion activities between CR TKA and the non-operated knees.

RESULTS

Contact excursions of the lateral condyle in CR TKAs were significantly more anteriorly located than the contralateral non-operated knee during sit-to-stand (3.7 ± 4.8 mm vs - 7.8 ± 4.3 mm) and step-ups (- 1.5 ± 3.2 mm vs - 6.3 ± 5.8 mm). Contact excursions of the lateral condyle in CR TKAs were significantly less laterally located than the contralateral non-operated knee during sit-to-stand (21.4 ± 2.8 mm vs 24.5 ± 4.7 mm) and single-leg deep lunges (22.6 ± 4.4 mm vs 26.2 ± 5.7 mm, p < 0.05). Lateral condyle posterior rollback was not fully restored in CR TKA patients during sit-to-stand (9.8 ± 6.7 mm vs 12.9 ± 8.3 mm) and step-ups (8.1 ± 4.8 mm vs 12.2 ± 6.4 mm). Lateral pivoting patterns were observed in 80%, 73% and 69% of patients during sit-to-stand, step-ups and single-leg deep lunges respectively.

CONCLUSION

Although lateral femoral rollback and lateral pivoting patterns were observed during strenuous functional daily activities, asymmetric contact kinematics still persisted in unilateral CR TKA patients. This suggests the specific investigated contemporary asymmetrical tibial polyethylene geometry CR TKA design evaluated in this study does not fully replicate healthy knee contact kinematics during strenuous functional daily activities.

LEVEL OF EVIDENCE

III.

Arthroscopic lateral retinacular release improves patello-femoral and femoro-tibial kinematics in patients with isolated lateral retinacular tightness

PURPOSE

Arthroscopic lateral retinacular release (LRR) has long been considered the gold standard for the treatment for anterior knee pain caused by lateral retinacular tightness (LRT). However, one-third of patients experience continuous pain postoperatively, which is thought to be related to persistent maltracking of the patella and altered femoro-tibial kinematics. Therefore, the aim of the present study was to simultaneously assess femoro-tibial and patello-femoral kinematics and identify the influence of arthroscopic LRR.

METHODS

Sixteen healthy volunteers and 12 patients with unilateral, isolated LRT were prospectively included. Open MRI scans with and without isometric quadriceps contraction were performed in 0°, 30° and 90° of knee flexion preoperatively and at 12 months after surgery. Patellar shift, tilt angle, patello-femoral contact area and magnitude of femoro-tibial rotation were calculated by digital image processing.

RESULTS

Postoperatively, patellar shift was significantly reduced at 90° of knee flexion compared to preoperative values. The postoperative patellar tilt angle was found to be significantly smaller at 30° of knee flexion compared to that preoperatively. Isometric muscle contractions did not considerably influence patellar shift or tilt in either group. The patello-femoral contact area increased after LRR over the full range of motion (ROM), with significant changes at 0° and 90°. Regarding femoro-tibial kinematics, significantly increased femoral internal rotation at 0° was observed in the patient group preoperatively, whereas the magnitude of rotation at 90° of knee flexion was comparable to that of healthy individuals. The pathologically increased femoral internal rotation at 30° without muscular activity could be significantly decreased by LRR. With isometric quadriceps contraction no considerable improvement of femoral internal rotation could be achieved by LRR at 30° of knee flexion.

CONCLUSIONS

Patello-femoral and femoro-tibial joint kinematics could be improved, making LRR a viable surgical option in carefully selected patients with isolated LRT. However, pathologically increased femoral internal rotation during early knee flexion remained unaffected by LRR and thus potentially accounts for persistent pain.

LEVEL OF EVIDENCE

II.

Elongation Patterns of the Posterior Cruciate Ligament after Total Knee Arthroplasty

This study aimed to understand the ability of fixed-bearing posterior cruciate ligament (PCL)-retaining implants to maintain functionality of the PCL in vivo. To achieve this, elongation of the PCL was examined in six subjects with good clinical and functional outcomes using 3D kinematics reconstructed from video-fluoroscopy, together with multibody modelling of the knee. Here, length-change patterns of the ligament bundles were tracked throughout complete cycles of level walking and stair descent. Throughout both activities, elongation of the anterolateral bundle exhibited a flexion-dependent pattern with more stretching during swing than stance phase (e.g., at 40° flexion, anterolateral bundle experienced 3.9% strain during stance and 9.1% during swing phase of stair descent). The posteromedial bundle remained shorter than its reference length (defined at heel strike of the level gait cycle) during both activities. Compared with loading patterns of the healthy ligament, postoperative elongation patterns indicate a slackening of the ligament at early flexion followed by peak ligament lengths at considerably smaller flexion angles. The reported data provide a novel insight into in vivo PCL function during activities of daily living that has not been captured previously. The findings support previous investigations reporting difficulties in achieving a balanced tension in the retained PCL.

Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration

Background

Restoration of natural knee kinematics for a designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty (TKA). In different posterior-stabilized TKAs, there are wide variations in tibiofemoral surfaces and post-cam design. However, it is not known whether these design variations preserve natural knee kinematics. The purpose of this study was to determine the most appropriate tibiofemoral surface and post-cam designs to restore natural knee kinematics of the TKA.

Methods

A subject-specific finite element knee modal was used to evaluate tibiofemoral surface and post-cam design. Three different posts in convex, straight, and concave geometries were considered with a fixed circular cam design in this study. In addition, this post-cam design was applied to three different surface conformities for conforming, medial pivot, and subject anatomy mimetic tibiofemoral surfaces. We evaluated the femoral rollback, internal-external rotation, and quadriceps muscle force under a deep-knee-bend condition.

Results

The three different tibiofemoral conformities showed that the convex post provided the most natural-knee-like femoral rollback. This was also observed in internal rotation. In surface conformity, subject anatomy mimetic tibiofemoral surfaces showed the most natural -knee-like kinematics and quadriceps force.

Conclusions

This study confirmed that convex post design and subject anatomy mimetic tibiofemoral surfaces provided the most natural-knee-like kinematics. This study suggested that post-cam design and tibiofemoral surface conformity should be considered in conventional and customized TKA.

Elongation of the collateral ligaments after cruciate retaining total knee arthroplasty and the maximum flexion of the knee

The mechanisms that affect knee flexion after total knee arthroplasty (TKA) are still debatable. This study investigated the elongation of the superficial medial (sMCL) and lateral collateral ligaments (LCL) before and after a posterior cruciate retaining (CR) TKA. We hypothesized that overstretching of the collateral ligaments in high flexion after TKA could reduce maximal flexion of the knee. Three-dimensional models of 11 osteoarthritic knees of 11 patients including the insertions of the collateral ligaments were created using MR images. Each ligament was divided into three equal portions: anterior, middle and posterior portions. The shortest 3D wrapping length of each ligament portion was determined before and after the TKA surgery along a weight-bearing, single leg flexion path. The relationship between the changes of ligament elongation and the changes of the maximal knee flexion after TKAs was quantitatively analyzed. The sMCL showed significant increases in length only at low flexion after TKA; the LCL showed decreases in length at full extension, but increases with further flexion after TKA. The amount of increases of the maximum flexion angle after TKA was negatively correlated with the increases of the elongations of the anterior portion (p=0.010, r=0.733) and middle portion (p=0.049, r=0.604) of the sMCL as well as the anterior portion (p=0.010, r=0.733) of the LCL at maximal flexion of the knee. The results indicated that the increases of the length of the collateral ligaments at maximal flexion after TKA were associated with the decreases of the maximal flexion of the knee. Our data suggest that collateral ligament management should also be evaluated at higher knee flexion angles in order to optimize maximal flexion of the knee after TKAs.

Geometric variable designs of cam/post mechanisms influence the kinematics of knee implants

PURPOSE

Reproducing the femoral rollback through specially designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty. Most contemporary implants use cam/post mechanism to replace the function of Posterior Cruciate Ligament. This study was aimed to determine the most appropriate cam and post designs to produce normal femoral rollback of the knee.

METHODS

Three different cams (triangle, ellipse, and circle) and three different posts (straight, convex, concave) geometries were considered in this study and were analysed using kinematic analyses. Femoral rollback did not occur until reaching 50° of knee flexion. Beyond this angle, two of the nine combinations demonstrate poor knee flexion and were eliminated from the study.

RESULTS

The combination of circle cam with concave post, straight post and convex post showed 15.6, 15.9 and 16.1 mm posterior translation of the femur, respectively. The use of ellipse cam with convex post and straight post demonstrated a 15.3 and 14.9 mm femoral rollback, whilst the combination of triangle cam with convex post and straight post showed 16.1 and 15.8 mm femoral rollback, respectively.

CONCLUSION

The present study demonstrates that the use of circle cam and convex post created the best femoral rollback effect which in turn produces the highest amount of knee flexion. The findings of the study suggest that if the design is applied for knee implants, superior knee flexion may be possible for future patients.

LEVEL OF EVIDENCE

IV.

Tibial internal rotation is affected by lateral laxity in cruciate-retaining total knee arthroplasty: an intraoperative kinematic study using a navigation system and offset-type tensor

PURPOSE

The purpose of this study was to test the hypothesis that intraoperative soft-tissue balance assessed by an offset-type tensor influences post-operative knee kinematics after cruciate-retaining (CR) total knee arthroplasty (TKA).

METHODS

The influence of intraoperative soft-tissue balance on knee kinematics in CR-TKA was retrospectively analysed in 30 patients. Intraoperative soft-tissue balance parameters such as varus angle (varus ligament balance), joint component gap (centre gap), and medial and lateral compartment gaps were measured in the navigation system while applying 40-lb joint distraction force at 0°, 10°, 30°, 60°, 90°, and 120° of knee flexion using an offset-type tensor with the patella reduced. Tibial internal rotation and tibial anterior translation were measured as the differences between the values at 60° and 120° of flexion using the navigation system. Correlations between the soft-tissue parameters and post-operative knee kinematics were analysed.

RESULTS

The varus ligament balance was positively correlated with tibial internal rotation at 60° and 90° of flexion (R = 0.54, P < 0.05; R = 0.60, P < 0.01, respectively). Furthermore, the joint component gap was positively correlated with tibial internal rotation at 90° of flexion (R = 0.44, P < 0.05), and the lateral compartment gap was positively correlated with tibial internal rotation at 60°, 90°, and 120° of knee flexion.

CONCLUSIONS

The intraoperative varus ligament balance and joint component gap values were factors that predicted post-operative knee kinematics after CR-TKA. Lateral laxity at mid-to-deep knee flexion plays a significant role in tibial internal rotation.

LEVEL OF EVIDENCE

III.

A new spacer-guided, PCL balancing technique for cruciate-retaining total knee replacement

PURPOSE

The goal of this study was to investigate whether a new posterior cruciate ligament (PCL) balancing approach with a spacer technique during total knee arthroplasty (TKA) reproduced the correct tibiofemoral contact point (CP) location. It was hypothesized that it should be possible to adequately balance the PCL with this geometrical technique, obtaining correct position and stability of the medial femoral condyle, independent of insert shape.

METHODS

Nine fresh-frozen full-leg cadaver specimens were used. After native testing, prototype components of a new PCL-retaining implant were implanted using navigation and a bone-referencing technique. After finishing the bone cuts, the spacer technique was used to ascertain balancing of the PCL and the tibial cut was corrected if necessary. Passive and squat motions were performed before and after TKA using a dynamic knee simulator while tibiofemoral kinematics were recorded using six infrared cameras. CPs (native and implant) were calculated as the projections of the femoral condylar centres on the horizontal plane of the tibia.

RESULTS

The spacer technique resulted in correct PCL balancing in all specimens. The kinematic patterns of native and replaced knees showed no statistically significant differences in passive and squat motions. The medial CP after TKA was at the same position as in the native knee. No paradoxical sliding forward was seen after TKA, supporting our hypothesis.

CONCLUSIONS

The spacer technique can be applied by surgeons during PCL-retaining TKA and will lead to good PCL balancing, indicated by a correct CP, no lift-off in flexion and no posterior sag.

Clinical biomechanics of instability related to total knee arthroplasty

BACKGROUND

Tibiofemoral instability is a common reason for total knee arthroplasty failure, and may be attributed to soft tissue deficiency and incorrect ligament balancing. There are many different designs of implant with varying levels of constraint to overcome this instability; however there is little advice for surgeons to assess which is suitable for a specific patient, and soft tissue balance testing during arthroplasty is very subjective.

METHOD

The current theories on primary and secondary soft tissue restraints to anterior/posterior, varus/valgus, and internal/external rotational motion of the knee are discussed. The paper reviews biomechanics literature to evaluate instability in the intact and implanted knee.

FINDINGS

The paper highlights important intra- and extra-capsular structures in the knee and describes the techniques used by clinicians to assess instability perioperatively. In vitro cadaveric studies were found to be a very useful tool in comparing different implants and contributions of different soft tissues.

INTERPRETATION

In vitro cadaveric studies can be utilised in helping less experienced surgeons with soft tissue releases and determining the correct implant. For this to happen, more biomechanical studies must be done to show the impact of release sequences on implanted cadavers, as well as determining if increasingly constrained implants restore the stability of the knee to pre-deficient conditions.

In vivo kinematics of the extensor mechanism of the knee during deep flexion

While various factors have been assumed to affect knee joint biomechanics, few data have been reported on the function of the extensor mechanism in deep flexion of the knee. This study analyzed the patellofemoral joint contact kinematics and the ratio of the quadriceps and patellar tendon forces in living subjects when they performed a single leg lunge up to 150 deg of flexion. The data revealed that in the proximal-distal direction, the patellofemoral articular contact points were in the central one-third of the patellar cartilage. Beyond 90 deg of flexion, the contact points moved towards the medial-lateral edges of the patellar surface. At low flexion angles, the patellar tendon and quadriceps force ratio was approximately 1.0 but reduced to about 0.7 after 60 deg of knee flexion, implying that the patella tendon carries lower loads than the quadriceps. These data may be valuable for improvement of contemporary surgical treatments of diseased knees that are aimed to achieve deep knee flexion.

Differences in knee joint kinematics and forces after posterior cruciate retaining and stabilized total knee arthroplasty

BACKGROUND

Posterior cruciate ligament (PCL) retaining (CR) and -sacrificing (PS) total knee arthroplasties (TKA) are widely-used to treat osteoarthritis of the knee joint. The PS design substitutes the function of the PCL with a cam-spine mechanism which may produce adverse changes to joint kinematics and kinetics.

METHODS

CR- and PS-TKA were performed on 11 human knee specimens. Joint kinematics were measured with a dynamic knee simulator and motion tracking equipment. In-situ loads of the PCL and cam-spine were measured with a robotic force sensor system. Partial weight bearing flexions were simulated and external forces were applied.

RESULTS

The PS-TKA rotated significantly less throughout the whole flexion range compared to the CR-TKA. Femoral roll back was greater in the PS-TKA; however, this was not correlated with lower quadriceps forces. Application of external loads produced significantly different in-situ force profiles between the TKA systems.

CONCLUSIONS

Our data demonstrate that the PS-design significantly alters kinematics of the knee joint. Our data also suggest the cam-spine mechanism may have little influence on high flexion kinematics (such as femoral rollback) with most of the load burden shared by supporting implant and soft-tissue structures.

Less femorotibial rotation and AP translation in deep-dished total knee arthroplasty. An intraoperative kinematic study using navigation

PURPOSE

Hyper-congruent inserts have been proposed as another means of posterior stabilization in total knee arthroplasty. Their kinematics, partially unexplored, is reported to be possibly erratic. The objectives of the present study were to detect whether prostheses with such a constrained design would provide antero-posterior (AP) stability without interfering with high flexion.

METHODS

The kinematics of 10 knees replaced with hyper-congruent inserts was tested intra-operatively with a specially designed navigation system (Praxim, La Tronche, Isère, France), to measure AP displacements of femoro-tibial contact points at knee flexion.

RESULTS

Femoro-tibial contact points in full extension were in a posterior position compared to their initial position before implantation (8 ± 6 mm medially, 15 ± 10 mm laterally, P < 0.004). AP displacements were different from pre-operative displacements (3 ± 4 mm vs -5 ± 2 mm for the medial condyle, P < 0.01 and -2 ± 6 mm vs -22 ± 8 mm for the lateral condyle, P < 0.001). Forward rolling persisted in four cases, with the medial condyle being involved in three of them (9, 9, and 6 mm, respectively). Post-operative flexion of 122° on average was not correlated with AP displacements.

CONCLUSIONS

Hyper-congruent prostheses partially stabilized femoral condyles at knee flexion. Posterior displacements were reduced with no consequence on range of flexion. Posterior stabilization was imperfect, and paradoxical displacements were detected by navigation, which could therefore help optimize knee balance.

LEVEL OF EVIDENCE

Diagnostic study, Level II.

In vivo function of posterior cruciate ligament before and after posterior cruciate ligament-retaining total knee arthroplasty

PURPOSE

The object of this study was to investigate the in vivo function of the posterior cruciate ligament (PCL) in patients before and after a PCL-retaining total knee arthroplasty (TKA).

METHODS

Eleven patients with advanced osteoarthritis (OA) of the knee were recruited. Magnetic resonance scans of each OA knee were obtained, and 3D computer models, including the femoral and tibial insertion areas of the anterolateral and posteromedial bundles of the PCL, were created. Before and after PCL-retaining TKA, dual fluoroscopic images of each knee were acquired during weight-bearing knee flexion. The images and computer models were used to reproduce the in vivo motion of the knee. The function of the PCL bundles was described in terms of elongation, elevation and deviation. Twenty-two healthy controls were also included as normal references.

RESULTS

PCL bundles of the OA knees were overstretched during late knee flexion and orientated more medially throughout flexion compared with normal knees. After PCL-retaining TKA, PCL bundles were further overstretched during late flexion and changed from medially directed in normal and OA knees to almost sagittally directed, which may compromise function in controlling knee rotation.

CONCLUSIONS

The current PCL-retaining TKA systems and surgical techniques may not adequately re-establish normal biomechanics of PCL bundles after PCL-retaining TKA.

Comparisons of kinematics and range of motion in high-flexion total knee arthroplasty: cruciate retaining vs. substituting designs

PURPOSE

The purpose of this study was to compare in vivo kinematics, range of motion, and functional outcomes in patients that received either a high-flexion cruciate retaining or a high-flexion cruciate substituting knee.

METHODS

Forty-eight high-flexion cruciate retaining (CR) and 47 high-flexion cruciate substituting (PS) knees were included in this study and followed for an average of 27 months (24-33). Weight-bearing and non-weight-bearing maximal flexions and functional scores were compared between two groups. For kinematics evaluations, amount of posterior femoral roll-back and internal tibial rotation from 0° to maximal flexion using lateral radiographs under weight-bearing conditions were also compared.

RESULTS

Average weight-bearing maximal flexion was 126.3° in the PS group, which was significantly higher than the 115.0° in the CR group. Average functional scores showed no significant difference between the two groups. In terms of kinematics, the average amount of posterior femoral roll-back during full flexion was 9.6 mm in the PS group and 6.1 mm in the CR group, which was a significant difference. However, internal tibial rotation during full flexion was not significantly different in the two groups.

CONCLUSION

PS high-flexion TKA provided greater weight-bearing maximal flexion and posterior femoral roll-back than CR high-flexion TKA, although no difference in clinical outcomes was observed between the two prosthesis designs.

In vivo knee kinematics in patients with bilateral total knee arthroplasty of 2 designs

Many younger and highly active patients desire to achieve high flexion after total knee arthroplasty. This study's purpose was to determine if a contemporary total knee arthroplasty design improved functional knee flexion compared with a traditional total knee arthroplasty in patients living a Western lifestyle. Ten patients with bilateral total knee arthroplasty of 2 types were studied during weight-bearing lunge, kneeling, and stair activities using fluoroscopic imaging. There were no differences in maximum knee flexion during lunging or kneeling. Statistically significant differences in tibial rotation and condylar translation were observed during the 3 activities. Although several joint kinematic differences were observed, no important functional differences were observed in clinically excellent, high performing subjects with bilateral total knee arthroplasty of 2 types.

Does greater knee flexion increase patient function and satisfaction after total knee arthroplasty?

The purpose of this study was to determine whether high flexion leads to improved benefits in patient satisfaction, perception, and function after total knee arthroplasty (TKA). Data were collected on 122 primary TKAs. Patients completed a Total Knee Function Questionnaire. Knees were classified as low (≤ 110°), mid (111°-130°), or high flexion (>130°). Correlation between knee flexion and satisfaction was not statistically significant. Increased knee flexion had a significant positive association with achievement of expectations, restoration of a "normal" knee, and functional improvement. In conclusion, although the degree of postoperative knee flexion did not affect patient satisfaction, it did influence fulfillment of expectations, functional ability, and knee perception. This suggests that increased knee flexion, particularly more than 130°, may lead to improved outcomes after TKA.

Influence of bi- and tri-compartmental knee arthroplasty on the kinematics of the knee joint

Background

The cruciate ligaments are important stabilizers of the knee joint and determine joint kinematics in the natural knee and after cruciate retaining arthroplasty.

No in vitro data is available to biomechanically evaluate the ability of the anterior cruciate ligament (ACL) to maintain knee joint kinematics after bicruciate-retaining bi-compartmental knee arthroplasty (BKA).

Therefore, the objective of the current study was to investigate the kinematics of the natural knee joint, before and after installing bicruciate-retaining BKA and posterior cruciate retaining total knee arthroplasty. Specifically, we incorporated a dynamic knee simulator to simulate weight-bearing flexions on cadaveric knee specimen before and after surgical manipulations.

Methods

In this cadaveric study we investigated rotational and translational tibiofemoral kinematics during simulated weight-bearing flexions of the intact knee, after bi-compartmental knee arthroplasty (BKA+), after resecting the ACL in BKA (BKA-), and after posterior cruciate retaining total knee arthroplasty (TKA).

Results

Rotation of BKA+ is closest to the intact knee joint, whereas TKA shows significant differences from 30 to 90 degree of flexion. Within the tested flexion range (15 to 90 degree of flexion), there was no significant difference in the anterior-posterior translation among intact, BKA+, and TKA knees. Resecting the ACL in BKA leads to a significant anterior tibial translation.

Conclusions

BKA with intact cruciate ligaments resembles rotation and translation of the natural knee during a simulated weight-bearing flexion. It is a suitable treatment option for medial and patellofemoral osteoarthritis with advantages in rotational characteristics compared to TKA.

In vivo comparison of knee kinematics before and after high-flexion posterior cruciate-retaining total knee arthroplasty

The objectives of this study were to compare preoperative and postoperative knee kinematics for subjects implanted with flexion-enhanced posterior cruciate-retaining total knee arthroplasty during deep flexion and to examine flexion performance of the prosthesis design. Three-dimensional kinematics was analyzed by fluoroscopic examinations of subjects using a single-plane model-image registration technique. Preoperatively, knee kinematics demonstrated small posterior femoral translation and limited axial rotation. These motions differed significantly from patterns previously reported for normal knees. Postoperatively, flexion performance was maintained, averaging 130 degrees , and kinematic patterns were similar to preoperative patterns. Although total knee arthroplasty can reduce pain and maintain functional performance, it appears that the characteristics of varus arthritic knee mechanics persist after arthroplasty.

Anatomic double-bundle anterior cruciate ligament reconstruction: kinematics and knee flexion angle-graft tension relation

PURPOSE

The purpose of this study was to compare the bundle tension curves and resultant knee kinematics between 2 tensioning protocols in anatomic double-bundle anterior cruciate ligament (ACL) reconstruction.

METHODS

Anatomic double-bundle ACL reconstruction was performed in 7 male cadaveric knees. Each graft was tensioned to 22 N under 2 conditions: (1) both bundles tensioned at 20 degrees of knee flexion (20/20 protocol) or (2) posterolateral (PL) bundle tensioned at 15 degrees and anteromedial (AM) bundle at 45 degrees (45/15 protocol). Knee kinematics were recorded in response to anterior and combined rotatory loads in the intact, ACL-deficient, and reconstructed states. Bundle tension was recorded dynamically with knee motion and during each loading test.

RESULTS

Tensioning both bundles at 20 degrees of knee flexion resulted in a reciprocal bundle tension pattern that was not statistically different; the PL bundle tension was greater than the AM bundle tension in full extension, and the AM bundle tension was greater than the PL bundle tension from 25 degrees to 120 degrees. In the second tensioning protocol, the AM bundle tension was significantly greater than the PL bundle tension at all flexion angles. Both tensioning protocols restored normal knee kinematics.

CONCLUSIONS

Bundle-tensioning protocol is a variable that has a significant effect on the bundle-loading patterns in double-bundle ACL reconstruction. The 20/20 protocol resulted in AM and PL bundle-loading patterns that were equivalent during dynamic testing, whereas the 45/15 protocol led to excessive tension in the AM bundle in full extension. We recommend equal tensioning of both bundles with the knee at 20 degrees of flexion to restore relatively normal tension curves in each bundle and to avoid excessive stress on the AM bundle.

CLINICAL RELEVANCE

In double-bundle ACL reconstruction, there is no consensus regarding bundle-tensioning protocols. This study provides data on the individual bundle tension curves that result from 2 commonly used tensioning protocols. These data will assist clinicians as the technique and application of double-bundle ACL reconstruction move forward.

Biomechanical analysis of posterior cruciate ligament retaining high-flexion total knee arthroplasty

BACKGROUND

High-flexion knee replacements have been developed to accommodate a large range of flexion (>120 degrees ) after total knee arthroplasty. Both posterior cruciate ligament retaining and sacrificing high-flexion knee designs have been marketed. The main objective of this study was to evaluate the biomechanical performance of a cruciate-retaining high-flexion knee replacement. Furthermore, the mechanical behaviour of this high-flexion knee replacement was compared to both a cruciate-retaining conventional and a posterior-stabilized high-flexion knee replacement.

METHODS

A finite element prosthetic knee model was developed to analyze the mechanical performance of the knee designs evaluated in this study. Polyethylene stresses and the amount of femoral rollback were studied during a squatting movement (flexion <or=150 degrees).

FINDINGS

During deep knee flexion, the cruciate-retaining high-flexion design demonstrated a lower peak tibio-femoral contact stress (74.7 MPa) than the cruciate-retaining conventional design (96.5 MPa). The posterior-stabilized high-flexion design showed the lowest peak tibio-femoral contact stress at the condylar articulation (54.2 MPa), although the post was loaded higher (77.4 MPa). The knee designs analyzed in this study produced a similar amount of femoral rollback during normal knee flexion (flexion > 120 degrees), whereas the cruciate-retaining designs showed a paradoxical anterior movement of the femoral condyles during high-flexion (flexion>120 degrees).

INTERPRETATION

The current study demonstrates a cruciate-retaining high-flexion knee replacement produces a lower prosthetic load than a conventional cruciate-retaining replacement during deep knee flexion. Compared to a posterior-stabilized high-flexion design, the cruciate-retaining high-flexion design demonstrated an equivalent prosthetic loading along with an inferior amount of femoral rollback in the high-flexion range. Posterior cruciate ligament balancing is an important surgical aim for high-flexion knee arthroplasty.

Range of motion of standard and high-flexion cruciate retaining total knee prostheses

Recently, use of high-flexion design was introduced in cruciate-retaining (CR) total knee prostheses. The purpose of this study was to prospectively compare the ranges of motion (ROMs) of 89 knees with standard and 87 knees with high-flexion CR total knee prostheses. Differences in age, gender, diagnosis, preoperative ROM of the knee, and Knee Society Score between the 2 groups were not statistically significant. At 12-month follow-up, average ROM was 112.0 degrees +/- 12.6 degrees for standard, and 115.3 degrees +/- 13.4 degrees for high-flexion CR prosthesis (P = .101). To our knowledge, this is the first report on the ROM with the high-flexion CR total knee prosthesis. Using the technique of anterior referencing for femoral component sizing and using a fixed 7 degrees slope for the tibial component, we found no significant differences between groups with regard to ROM, clinical, or radiographic parameters.

Kinematics of a cementless mobile bearing posterior cruciate ligament-retaining total knee arthroplasty

Mobile bearing (MB) total knee arthroplasty (TKA) was developed to provide low contact stress and unconstrained joint motion. We studied a consecutive series of 41 knees with mobile-bearing, posterior cruciate-retaining (CR) TKAs to determine if kinematics resembled normal knees or if kinematics changed over time. Patients were studied at 3 and 21 months average follow-up with weight-bearing radiographs at full extension, 30 degrees flexion and maximum flexion. Shape-matching techniques were used to measure TKA kinematics. Implant hyperextension, maximum flexion and total ROM increased with follow-up. Tibial rotation and condylar translations did not change with time. The medial condyle did not translate from extension to 30 degrees, but translated 5 mm anteriorly from 30 degrees to maximum flexion. Lateral condylar translation was 3 mm posterior from extension to 30 degrees, with no translation from 30 degrees to maximum flexion. Tibiofemoral kinematics in CR-MB-TKAs were stable over time, but did not replicate motions observed in healthy knees. The mobile tibial insert showed rotation and translation at both follow-up examinations, but the patterns of translation were not predictable.

Design features of total knees for achieving normal knee motion characteristics

The goal of the study was to achieve a normal neutral anatomical path of motion with a total knee arthroplasty (TKA) using specific motion-guiding design features. Two reference TKA models were used, consisting of a partially conforming double-dished geometry and the same with a central cam-post for femoral rollback. Four experimental TKA models included features to produce femoral rollback with and without guidance for tibial rotation, and a feature to prevent paradoxical anterior femoral sliding. The femur was loaded down the tibial axis, and the femoral-tibial positions were recorded at a sequence of flexion angles. Subsequently, the positions were recorded with an anterior shear force superimposed. Software was used to reconstruct the paths of the transverse femoral axis on the tibia, during a full flexion range. The reference knees did not reproduce a normal neutral path of motion. However, this was achieved with an experimental design incorporating all of the motion-guiding features.

Knee stability before and after total and unicondylar knee replacement: in vivo kinematic evaluation utilizing navigation

Surgical navigation systems are currently used to guide the surgeon in the correct alignment of the implant. The aim of this study was to expand the use of navigation systems by proposing a surgical protocol for intraoperative kinematics evaluations during knee arthroplasty. The protocol was evaluated on 20 patients, half undergoing unicondylar knee arthroplasty (UKA) and half undergoing posterior-substituting, rotating-platform total knee arthroplasty (TKA). The protocol includes a simple acquisition procedure and an original elaboration methodology. Kinematic tests were performed before and after surgery and included varus/valgus stress at 0 and 30 degrees and passive range of motion. Both UKA and TKA improved varus/valgus stability in extension and preserved the total magnitude of screw-home motion during flexion. Moreover, compared to preoperative conditions, values assumed by tibial axial rotation during flexion in TKA knees were more similar to the rotating patterns of UKA knees. The analysis of the anteroposterior displacement of the knee compartments confirmed that the two prostheses did not produce medial pivoting, but achieved a postoperative normal behavior. These results demonstrated that proposed intraoperative kinematics evaluations by a navigation system provided new information on the functional outcome of the reconstruction useful to restore knee kinematics during surgery.

Kinematics of the stiff total knee arthroplasty

The kinematics of 10 total knee replacements with poor flexion (<90 degrees ) were compared with 11 replacements with good flexion (>110 degrees ) at a mean of 3 years from surgery using optical calibration with implant shape-matching techniques from radiographs taken in standing, early-lunge, and late-lunge positions. There were no significant differences between groups in anteroposterior translation of the medial and lateral femoral condyles or tibial rotation during standing and early lunge. Groups differed in amount of posterior translation of the femoral condyles during late lunge because of the poor-flexion group's inability to achieve the same amount of flexion as the good-flexion group. Poor flexion after total knee arthroplasty, we conclude, is not associated with abnormal kinematics in the setting of well-aligned, well-fixed implants.

A mechanical comparison of high-flexion and conventional total knee arthroplasty

The question addressed in this study was whether high-flexion total knee arthroplasty (TKA) designs improve the mechanical behaviour of TKAs in high flexion and whether they maintain the mechanical performance of conventional TKAs at normal flexion angles.

A finite element study was performed in which the mechanical behaviour of the conventional Sigma RP and the new high-flexion Sigma RP-F were compared, during a dynamic simulation of a high-flexion squatting activity. Forces, stresses, and contact positions were calculated during different stages of the simulations.

In general, higher stresses were found with larger flexion angles for both designs. Mechanical parameters were similar in normal flexion. In high flexion, lower stress and deformation values were found for the high-flexion Sigma RP-F, except for the contact stress at the post of the insert.

This study confirms that a high-flexion design can improve mechanical behaviour at high-flexion without changing the performance in normal flexion. Hence, although a high-flexion TKA may show a similar or better performance in comparison with a conventional TKA, high-flexion activities still cause an increase in the implant stress levels. Therefore, the patient's demand for large flexion angles may reduce the longevity of TKA implants.

High incidence of loosening of the femoral component in legacy posterior stabilised-flex total knee replacement

We have examined the results obtained with 72 NexGen legacy posterior stabilised-flex fixed total knee replacements in 47 patients implanted by a single surgeon between March 2003 and September 2004. Aseptic loosening of the femoral component was found in 27 (38%) of the replacements at a mean follow-up of 32 months (30 to 48) and 15 knees (21%) required revision at a mean of 23 months (11 to 45). We compared the radiologically-loose and revised knees with those which had remained well-fixed to identify the factors which had contributed to this high rate of aseptic loosening. Post-operatively, the mean maximum flexion was 136 degrees (110 degrees to 140 degrees) in the loosened group and 125 degrees (95 degrees to 140 degrees) in the well-fixed group (independent t-test, p = 0.022). Squatting, kneeling, or sitting cross-legged could be achieved by 23 (85%) of the loosened knees, but only 22 (49%) of the well-fixed knees (chi-squared test, p = 0.001). The loosened femoral components were found to migrate into a more flexed position, but no migration was detected in the well-fixed group. These implants allowed a high degree of flexion, but showed a marked rate of early loosening of the femoral component, which was associated with weight-bearing in maximum flexion.

High-flexion TKA designs: what are their in vivo contact mechanics?

To accommodate for high flexion, new total knee arthroplasties (TKAs) have been designed. Unlike older designs which have been found to exhibit decreasing contact area with increasing flexion, we hypothesized the new designs would be associated with improved contact mechanics. We compared in vivo contact mechanics for 10 subjects having a fixed-bearing high-flexion posterior-stabilized (LPS-Flex) TKA and 10 subjects having a fixed-bearing high-flexion posterior cruciate-retaining (CR-Flex) TKA. All subjects performed deep knee bends to maximum flexion while under fluoroscopic surveillance. In vivo kinematics obtained using a three-dimensional to two-dimensional registration technique, were input into a three-dimensional inverse dynamic mathematical model to determine the contact forces. The contact areas and contact stresses were determined using a deformable contact model. The contact forces, contact areas, and contact stresses in both these implants increased with increasing flexion. The medial contact area in the LPS-Flex was higher than the CR-Flex for most of the flexion cycle. The lateral contact area was higher in the CR-Flex than the LPS-Flex in early and midflexion ranges. Although the lateral contact stresses were similar in both implants, the CR-Flex experienced higher medial contact stress than the LPS-Flex throughout flexion. However, both these implants were able to maintain sufficient contact area so the contact stress values were well below the yield strength of crosslinked polyethylene.

Tibiofemoral force following total knee arthroplasty: comparison of four prosthesis designs in vitro

Despite ongoing evolution in total knee arthroplasty (TKA) prosthesis design, restricted flexion continues to be common postoperatively. Compressive tibiofemoral force during flexion is generated through the interaction between soft tissues and prosthesis geometry. In this study, we compared the compressive tibiofemoral force in vitro of four commonly used prostheses: fixed-bearing PCL (posterior cruciate ligament)-retaining (PFC), mobile-bearing posterior-stabilized (PS), posterior-stabilized with a High Flex femoral component (HF), and mobile-bearing PCL-sacrificing (LCS). Fourteen fresh-frozen cadaver knee joints were tested in a passive motion rig, and tibiofemoral force measured using a modified tibial baseplate instrumented with six load cells. The implants without posterior stabilization displayed an exponential increase in force after 90 degrees of flexion, while PS implants maintained low force throughout the range of motion. The fixed-bearing PFC prosthesis displayed the highest peak force (214 +/- 68 N at 150 degrees flexion). Sacrifice of the PCL decreased the peak force to a level comparable with the LCS implant. The use of a PCL-substituting post and cam system reduced the peak force up to 78%, irrespective of whether it was a high-flex or a standard PS knee. However, other factors such as preoperative range of motion, knee joint kinematics, soft tissue impingement, and implantation technique play a role in postoperative knee function. The present study suggests that a posterior-stabilized TKA design might be advantageous in reducing soft tissue tension in deep flexion. Further research is necessary to fully understand all factors affecting knee flexion after TKA.

Is there a functional benefit to obtaining high flexion after total knee arthroplasty?

Clinical evidence is lacking to support the functional benefit of high flexion after total knee arthroplasty (TKA). A retrospective review of 511 TKAs in 370 patients was performed. The mean follow-up was 3.7 years (range, 2-8 years). Regression analysis determined the effect of obtaining high flexion (>125 degrees ) on Knee Society, stair, function, and pain scores. Of 511 TKAs, 340 (66.5%) obtained range of motion greater than 115 degrees , and 63 (12.3%) TKAs obtained high flexion greater than 125 degrees . There was no difference between the patients who obtained flexion greater than 115 degrees and those who obtained high flexion greater than 125 degrees in Knee Society scores (P = .34) and function scores (P = .57). Patients with greater than 125 degrees of flexion are 1.56 times more likely to demonstrate optimal stair function (P = .02). Obtaining flexion greater than 125 degrees after TKA does not offer a benefit in overall knee function. However, obtaining a high degree of flexion appears to optimize stair climbing.

Posterior cruciate ligament balancing in total knee replacement

We have examined the relationship between the size of the flexion gap and the anterior translation of the tibia in flexion during implantation of a posterior cruciate ligament (PCL)-retaining BalanSys total knee replacement (TKR). In 91 knees, the flexion gap and anterior tibial translation were measured intra-operatively using a custom-made, flexible tensor-spacer device.

The results showed that for each increase of 1 mm in the flexion gap in the tensed knee a mean anterior tibial translation of 1.25 mm (SD 0.79, 95% confidence interval 1.13 to 1.37) was produced.

When implanting a PCL-retaining TKR the surgeon should be aware that the tibiofemoral contact point is related to the choice of thickness of the polyethylene insert. An additional thickness of polyethylene insert of 2 mm results in an approximate increase in tibial anterior translation of 2.5 mm while the flexed knee is distracted with a force of between 100 N and 200 N.

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.

Knieprothesenkinematik

Until now it remains less clear to what extent the different types of endoprostheses can simulate the physiological motion pattern of the knee joint. The aim of this study was to present fluoroscopy and functional MRI as well as the results of these in vivo imaging techniques for TKA kinematics. Videofluoroscopy is a dynamic investigation, analyzing the subjects under fluoroscopic surveillance during different activities. Three-dimensional (3D) kinematics were recovered from the two-dimensional fluoroscopic images using a model-fitting technique. Kinematic analysis with functional MRI was performed in an open MR system at different flexion angles with external loads being applied during imaging. Femoropatellar and femorotibial 3D kinematics were analyzed by image postprocessing. The findings in healthy knees obtained with functional MRI under static conditions are in good agreement with the fluoroscopic outcome under dynamic conditions. In all investigated TKA in the mean an increased external rotated position of the femur relative to the tibia was observed at full extension, while the amount of external rotation during knee flexion was decreased. Although there was great variability among the individuals, differences were observed between the TKA-groups (e.g. posterior stabilized vs PCL retaining). Significant changes of femorotibial and femoropatellar kinematics were found in TKA compared to healthy knees, which may lead to early aseptic loosening or increased polyethylene wear The presented techniques and results allow for advanced in vivo diagnostics and may help to improve the design of TKA and to enhance the long-term performance.

A new in vivo technique for determination of femoro-tibial and femoro-patellar 3D kinematics in total knee arthroplasty

Aim was to develop an in vivo technique which allows determination of femoro-tibial and of femoro-patellar 3D-kinematics in TKA simultaneously. The knees of 20 healthy volunteers and of eight patients with TKA (PCR, rotating platform) were investigated. Kinematics analysis was performed in an open MR-system at different flexion angles with external loads being applied. The TKA components were identified using a 3D-fitting technique, which allows an automated 3D-3D-registration of the TKA. Femoro-patellar and femoro-tibial 3D-kinematics were analyzed by image postprocessing. The validity of the postprocessing technique demonstrated a coefficient of determination of 0.98 for translation and of 0.97 for rotation. The reproducibility yielded a coefficient of variation (CV%) for patella kinematics between 0.17% (patello-femoral angle) and 6.8% (patella tilt). The femoro-tibial displacement also showed a high reproducibility with CV% of 4.0% for translation and of 7.1% for rotation. While in the healthy knees the typical screw-home mechanism was observed, a paradoxical anterior translation of the femur relative to the tibia combined with an external rotation occurred after TKA. Fifty percent of the TKA's experienced a condylar lift-off of >1mm predominately on the medial side. Regarding patellar kinematics significant changes were found in both planes in TKA with an increased patella height in the sagittal plane and patella tilt and shift in the transversal plane. The results demonstrate that the presented 3D MR-open based method is highly reproducible and valid for image acquisition and postprocessing and provides--for the first time--in vivo data of 3D-kinematics of the tibio-femoral and simultaneously of the patello-femoral joint during knee flexion.

Tibiofemoral contact behavior is improved in high-flexion cruciate retaining TKA

Recently, total knee arthroplasty (TKA) designs have been modified to prevent edge loading on the posterior tibial articular surface and increase the tibiofemoral contact area at high degrees of flexion. The expected improvement in contact behavior of high-flexion TKA over conventional design is not well documented. We ascertained peak contact locations and contact areas of a conventional and a high-flexion cruciate-retaining TKA design. Both TKAs showed similar kinematics throughout the range of flexion although their contact behaviors differed: the peak contact point for the high-flexion TKA was located more anteriorly than the conventional TKA for flexion angles greater than 90 degrees. The tibiofemoral contact of both TKAs reached the polyethylene posterior edge at 150 degrees. The contact on conventional TKA reached the polyethylene posterior edge approximately 15 degrees to 30 degrees before the high-flexion TKA. The high flexion TKA exhibited similar contact areas to conventional TKA. While the clinical relevance is unclear, these data suggest high flexion TKA might improve tibiofemoral contact biomechanics if high flexion is achievable.