The influence of contemporary knee design on high flexion: a kinematic comparison with the normal knee

Radiographic evaluation of anterior tibial translation in the prone position after total knee arthroplasty: comparison of BCS-TKA and PS-TKA

PURPOSE

The purpose of this study was to evaluate the anterior tibial translation (ATT) in the prone position after total knee arthroplasty (TKA).

METHODS

Fifty subjects (50 knees) undergoing bi-cruciate substituting (BCS)-TKA (Journey II: Smith and Nephew) and age-gender matching 50 subjects (50 knees) undergoing posterior stabilizing (PS)-TKA, were included in this study. Approximately, six months after surgery, and when the subjects had recovered their range of knee motion, following the Mae's method, accurate lateral radiographic imaging of the knee was performed with full knee extension in both supine and prone positions. The maximal protrusion length of the femoral posterior component, posterior to the extension line parallel to the tibial shaft from the edge of the posterior tibial plateau, was measured on lateral radiographs. The difference in length between the prone and supine positions was regarded as the prone-ATT. The posterior protrusion length of the femoral component, and the prone-ATT were compared between BCS and PS-TKA.

RESULTS

The posterior protrusion length of the femoral component in the supine position was BCS-TKA 4.3 ± 1.9 mm, and PS-TKA 8.7 ± 2.3 mm. The length in the prone position was BCS-TKA 4.8 ± 2.3 mm, and PS-TKA 10.7 ± 2.2 m. Posterior protrusion length of the femoral component was significantly larger in both positions in PS-TKA when compared with BCS-TKA. In PS-TKA, posterior protrusion length of the femoral condyle was significantly larger in the prone position when compared to the supine position. No significant difference was observed in BCS-TKA. Prone-ATT was significantly larger in PS-TKA (2 ± 1.9 mm) when compared to BCS-TKA (0.7 ± 2 mm).

CONCLUSION

Even in a position corresponding to daily movement such as the prone position, ATT was significantly larger in PS-TKA, when compared to BCS-TKA.

Comparing Outcomes of Bicruciate-Stabilized and Cruciate-Retaining Total Knee Arthroplasty

Background

Bicruciate-stabilized (BCS) total knee arthroplasty (TKA) aims to restore normal kinematics by replicating the function of both cruciate ligaments. Conventional cruciate-retaining (CR) design in TKA has shown previous clinical success with lower complication rates. This study compared the patient-reported outcomes between the BCS and CR TKA designs.

Methods

This retrospective study examined patients who underwent primary TKA using a CR or a BCS implant. Patient demographics, Knee Injury and Osteoarthritis Outcome Score for Joint Replacement (KOOS, JR), and Forgotten Joint Score (FJS) were compared between two cohorts. Patient-reported outcome measures were analyzed using independent samples t-tests.

Results

There were no significant preoperative demographic differences between groups. The CR cohort (n = 756) had significantly higher average KOOS, JR Scores compared to the BCS cohort (n = 652) at 3 months (59.7 ± 3.8 vs. 53.0 ± 3.9, p < 0.001) and 2 years (62.6 ± 8.0 vs. 53.8 ± 6.7, p = 0.001) after TKA. Within the cohort, KOOS, JR delta differences were not significant for CR when comparing patient scores 3 months to 1 year after surgery. Meanwhile, the BCS patients did show significant delta improvement (4.1 ± 1.9, p = 0.030) when compared 3 months to 1 year after surgery. One year postoperatively, the BCS cohort (n = 134) showed a significantly higher average FJS score (49.5 ± 31.4, vs. 36.8 ± 28.5, p = 0.028) than the CR cohort (n = 203). Both cohorts displayed a significant difference in delta improvements within their respective cohort when measuring FJS from 3 months to 1 year, 2 years, and 3 years after surgery.

Conclusions

The CR cohort performed better on average, compared to the BCS cohort in measures of KOOS, JR scores at the 2-year follow-up. The BCS cohort performed marginally better regarding FJS only at 1-year follow-up.

Restoring Anatomical Features in Primary Total Knee Arthroplasty

Today, the number of people affected by gonarthrosis symptoms is increasing proportionally. Total knee arthroplasty (TKA) is a successful intervention that aims to reduce pain and restore knee function. However, studies have shown that active young patients still have limitations in performing activities such as skiing, golfing, surfing, and dancing. Over the last few years, total knee arthroplasty has undergone significant changes. Most of the modern TKA implants are designed to reproduce the normal biomechanics of the knee joint, mimicking the physiological pattern with greater compliance in the medial compartment between the tibial insert and femoral condyle and less congruence on the lateral side. Unfortunately, functional outcomes are compromised in approximately half of TKA patients. This loss may be caused by the abnormal kinematics and inherent instability of many contemporary implants. The proper alignment of the femoral component during TKA is a crucial step that influences postoperative results. The position of the femoral component in the axial plane is responsible for flexion stability, knee joint kinematics, flexion alignment, and patellar tracking. The main goal when choosing a type of prosthesis is to achieve an adequate recovery that leads to an improvement in mobility and an increase in the efficiency of the quadriceps.

How does asymmetric tibial insert affect tibiofemoral kinematics and contact stresses in total knee Arthroplasty?

BACKGROUND

Asymmetric tibial insert design is expected to restore normal knee kinematics better than symmetric design. A tri-condylar implant has asymmetric and symmetric tibial inserts with a ball-and-socket joint to replace the post-cam mechanism. The purpose of this study was to compare the knee kinematics of the two designs and to measure tibiofemoral contact stresses, including that of the ball-and-socket joint.

METHODS

Using a computer simulation, the anteroposterior position and axial rotation of the femoral component were simulated during a weight-bearing deep knee bend for six validated models. Contact forces were simultaneously simulated in the medial, lateral, and ball-and-socket compartments. The relative position and the magnitude and direction of each contact force were applied to aforce/displacement control knee simulator. The contact stresses were measured individually using a pressure sensor.

RESULTS

The asymmetric tibial insert demonstrated a more posterior position of the femoral component in the lateral compartment during the entire range of motion and greater external rotation of the femoral component, compared to the symmetrical tibial insert. The mean peak contact stress of the medial and lateral compartments was < 9 Mpa, with no significant differences between the two designs except at 0°. The contact stress of the ball-and-socket joint was < 5 MPa.

CONCLUSIONS

Asymmetry of the tibial insert shows significant kinematic difference and has little influence on the peak contact stress, which is considerably lower than the yield strength of polyethylene. The asymmetric tibial insert can lead to clinical benefits owing to its kinematic and kinetic properties.

Different squatting positions after total knee arthroplasty: A retrospective study

BACKGROUND

Total knee arthroplasty (TKA) has been shown to improve quality of life and reduce pain. High-flexion activities such as squatting, kneeling, and floor transfers are mainly listed as demanding tasks. Among them, squatting is an important position.

AIM

To provide a new squat position classification and evaluate the different squatting positions of a series of patients after primary TKA.

METHODS

From May 2018 to October 2019, we retrospectively reviewed 154 video recordings of the squatting-related motions of patients after TKA. Among the included patients, 119 were women and 35 were men. Their mean age at the index surgery was 61.4 years (range, 30 to 77).

RESULTS

The median follow-up was 12 mo (range, 6 to 156 mo). We classified those squatting-related motions into three major variations according to squatting depth: Half squat, parallel squat, and deep squat. The angles of hip flexion, knee flexion, and ankle dorsiflexion were measured in the screenshots captured from the videos at the moment of squatting nadir. A total of 26 patients were classified as half squats, 75 as parallel squats, and 53 as deep squats. The angles of hip flexion, knee flexion, and ankle dorsiflexion all differed significantly among the three squatting positions (P < 0.001). In the parallel squat group, the mean knee flexion angle (°) was 116.5 (SD, 8.1; range, 97 to 137). In the deep squat group, the mean knee flexion angle (°) was 132.5 (SD, 9.3; range, 116 to 158).

CONCLUSION

Among the three squatting positions, deep squat showed the highest hip, knee, and ankle flexion angles, followed by the parallel squat. With the improvement of squatting ability, the patient's postoperative satisfaction rate was also significantly enhanced. However, the different squatting abilities of the patients cannot be effectively distinguished from the scoring results (P > 0.05). Our squatting position classification offers a pragmatic approach to evaluating patients’ squatting ability after TKA.

Errors in using fixed flexion facet centers to determine tibiofemoral kinematics increase fourfold for multi-radius femoral component designs with early versus late decreases in the radius of curvature

BACKGROUND

One method to determine tibiofemoral joint kinematics following total knee arthroplasty (TKA) is to quantify movement of the anterior-posterior (AP) position of the flexion facet center (FFC) on each femoral condyle relative to the tibia during knee flexion. The primary objective was to determine how closely AP positions of fixed FFCs approximate AP positions of variable FFCs of multi-radius femoral component designs with early versus late initial transition angles (i.e. earliest flexion angle where the radius of curvature decreases markedly).

METHODS

Variable FFCs were determined for each femoral condyle as centers of best-fit circles to 20° segments of the sagittal profile from 0° to 120° of flexion in 15° increments. The fixed FFC of each condyle was the center of the best-fit circle from 0° to 120° of flexion. Errors in AP positions were differences between AP positions of fixed FFCs and variable FFCs.

RESULTS

For profiles with a late initial transition angle of 120° of flexion, the root mean square error (RMSE) was limited to 0.7 mm. For profiles with an early initial transition angle of 60° of flexion, the RMSE was 2.7 mm, nearly a fourfold increase.

CONCLUSIONS

To determine whether fixed FFCs can be used to indicate AP positions of femoral condyles with minimal RMSE < 1 mm, the initial transition angle should be found as an important first step. Condylar AP positions for designs with an early initial transition angle should not be approximated by AP positions of fixed FFCs when determining tibiofemoral kinematics.

Biomechanical Comparison of Kinematic and Mechanical Knee Alignment Techniques in a Computer Simulation Medial Pivot Total Knee Arthroplasty Model

Several concepts may be used to restore normal knee kinematics after total knee arthroplasty. One is a kinematically aligned (KA) technique, which restores the native joint line and limb alignment, and the other is the use of a medial pivot knee (MPK) design, with a ball and socket joint in the medial compartment. This study aimed to compare motions, contact forces, and contact stress between mechanically aligned (MA) and KA (medial tilt 3° [KA3] and 5° [KA5]) models in MPK. An MPK design was virtually implanted with MA, KA3, and KA5 in a validated musculoskeletal computer model of a healthy knee, and the simulation of motion and contact forces was implemented. Anteroposterior (AP) positions, mediolateral positions, external rotation angles of the femoral component relative to the tibial insert, and tibiofemoral contact forces were evaluated at different knee flexion angles. Contact stresses on the tibial insert were calculated using finite element analysis. The AP position at the medial compartment was consistent for all models. From 0° to 120°, the femoral component in KA models showed larger posterior movement at the lateral compartment (0.3, 6.8, and 17.7 mm in MA, KA3, and KA5 models, respectively) and larger external rotation (4.2°, 12.0°, and 16.8° in the MA, KA3, and KA5 models, respectively) relative to the tibial component. Concerning the mediolateral position of the femoral component, the KA5 model was positioned more medially. The contact forces at the lateral compartment of all models were larger than those at the medial compartment at >60° of knee flexion. The peak contact stresses on the tibiofemoral joint at 90° and 120° of knee flexion were higher in the KA models. However, the peak contact stresses of the KA models at every flexion angle were <20 MPa. The KA technique in MPK can successfully achieve near-normal knee kinematics; however, there may be a concern for higher contact stresses on the tibial insert.

A tensor with a flat surface overestimates midflexion laxity in total knee arthroplasty: Comparison between a tensor with a flat-shaped surface and a tensor with an insert-shaped surface

BACKGROUND

Soft tissue balance is important for the success of total knee arthroplasty (TKA). Various types of tensors have been developed for the precise measurement of a gap. We hypothesized that the surface shape of the tensor that contacted the TKA component affected the gap measurement. This study aimed to compare the gaps obtained with flat and insert-shaped surface tensors.

METHODS

Two senior surgeons performed 95 TKAs (Vanguard-PS:55 knees; Persona-PS:40 knees). The joint gap was measured in each static knee flexion status (0°, 30°, 45°, 60°, 90°, 120°, and full flexion). We compared the gaps measured with a flat surface tensor and an insert-shape surface tensor. We defined a significant change as a gap difference of >1 mm with a statistical significance.

RESULTS

In Vanguard-PS, significant changes were observed at 30° and 45°. In Persona-PS, significant changes were observed at 30°, 45°, and 60°. In both implants, gaps measured with the flat tensor were larger than those measured with the insert tensor at approximately midflexion, and the significant changes disappeared in higher flexion position over midflexion.

CONCLUSIONS

The surface shape of the tensor affected the measurement of midflexion laxity in TKA. When measuring the gap with a flat tensor, the midflexion laxity was overestimated. A tensor with an insert-shaped surface should be used to measure the gap in TKA.

Do the increment of femoral condyle curvature and the change of tibia shape improve clinical outcome in total knee arthroplasty? A propensity score matching analysis

PURPOSE

Recently, the Persona total knee arthroplasty (TKA) system with more anatomical features and a similarly high flexion to the previous version, LPS-Flex, was introduced and is widely used. This study aimed to compare the early outcomes obtained using Persona versus an LPS-Flex fixed PS implant.

METHODS

A total of 784 knees that underwent primary TKAs (162: Persona group and 622: LPS-Flex group) were included. After 1:2 propensity score matching, there were 143 and 286 knees in Persona and LPS-Flex groups, respectively. Range of motion at the 2-year follow-up was the primary variable. Secondary variables were functional score, ability to perform activities requiring deep knee flexion, patient satisfaction, and radiographic measurements, including radiolucent line (RLL).

RESULTS

The average postoperative maximal flexion measured by goniometer at 2 years after TKA was 126.1° ± 10.8° (range 95°-140°) for the Persona group and 132.7° ± 11.7° (range 103°-145°) for the LPS-Flex group (P < 0.05). This significant difference was observed from 1 year postoperatively (P < 0.05). The two groups did not show a significant difference in functional score, postoperative ability in high flexion activities, and satisfaction at the 2-year follow-up. The rate of RLL was significantly lower in the Persona group (P < 0.05).

CONCLUSION

At the 2-year follow-up, the Persona group had less maximal flexion; however, the difference in flexion did not seem to affect clinical outcomes. According to the radiological results, the Persona system shows less RLL than does the LPS-Flex system.

LEVEL OF EVIDENCE

III.

Pre-operative and post-operative kinematic analysis in total knee arthroplasty. A pilot study

Introduction: Total knee replacement is the treatment of choice in knee osteoarthritis. Despite this, there is still a percentage of unsatisfied patients. Recently, prosthetic designs have been developed to improve the kinematics of the prosthetic knee. Materials and methods: Between June 2016 and November 2016 we enrolled 26 patients underwent to total knee arthroplasty divided in two groups (A and B) treated respectively with Journey 2 implant and the Attune impltant. Each patient was evaluated with functional scores (KOOS and KSS) and with kinematic analysis using the Bioval System. Results: In the group A, compared to the pre-operative, the flexion of the operated knees is significantly increased (31.27°±3.13° → 35.02°±2.1°) as well as that of the unoperated knee (34.34°±2.8° → 35.39°±3.5°). The pre/post-operative comparison of the muscles’ activation timing showed an improvement for the unoperated side, which is closed to the physiological pattern, while the operated side showed an incorrect activation of all the investigated muscles. Conclusions: The Journey 2 prosthesis seems to reach better results in rotational flexion, rotational freedom and muscles activation during free walking. Furthermore, it seems that with this prosthesis the patient can feel his “new prosthetic knee” more similar and closer to the physiological one. More studies are needed to confirm these results. (www.actabiomedica.it)

Effect of tibial component alignment on knee kinematics and ligament tension in medial unicompartmental knee arthroplasty

Objectives

Unicompartmental knee arthroplasty (UKA) is one surgical option for treating symptomatic medial osteoarthritis. Clinical studies have shown the functional benefits of UKA; however, the optimal alignment of the tibial component is still debated. The purpose of this study was to evaluate the effects of tibial coronal and sagittal plane alignment in UKA on knee kinematics and cruciate ligament tension, using a musculoskeletal computer simulation.

Methods

The tibial component was first aligned perpendicular to the mechanical axis of the tibia, with a 7° posterior slope (basic model). Subsequently, coronal and sagittal plane alignments were changed in a simulation programme. Kinematics and cruciate ligament tensions were simulated during weight-bearing deep knee bend and gait motions. Translation was defined as the distance between the most medial and the most lateral femoral positions throughout the cycle.

Results

The femur was positioned more medially relative to the tibia, with increasing varus alignment of the tibial component. Medial/lateral (ML) translation was smallest in the 2° varus model. A greater posterior slope posteriorized the medial condyle and increased anterior cruciate ligament (ACL) tension. ML translation was increased in the > 7° posterior slope model and the 0° model.

Conclusion

The current study suggests that the preferred tibial component alignment is between neutral and 2° varus in the coronal plane, and between 3° and 7° posterior slope in the sagittal plane. Varus > 4° or valgus alignment and excessive posterior slope caused excessive ML translation, which could be related to feelings of instability and could potentially have negative effects on clinical outcomes and implant durability.

Cite this article: K. Sekiguchi, S. Nakamura, S. Kuriyama, K. Nishitani, H. Ito, Y. Tanaka, M. Watanabe, S. Matsuda. Bone Joint Res 2019;8:126–135. DOI: 10.1302/2046-3758.83.BJR-2018-0208.R2.

Bicruciate Substituting Total Knee Arthroplasty Improves Stair Climbing Ability When Compared with Cruciate-Retain or Posterior Stabilizing Total Knee Arthroplasty

PURPOSE

The purpose of this study was to compare stair climbing and descent ability following bicruciate substituting (BCS), cruciate retaining (CR), and posterior stabilizing (PS) total knee arthroplasties (TKAs).

MATERIALS AND METHODS

Sixty-three participants undergoing BCS-TKA (journey II: Smith and Nephew), 47 participants undergoing CR-TKA (FINE: Teijin Nakashima Medical), and 38 participants undergoing PS-TKA (FNK: Teijin Nakashima Medical) were included in this study. Before and 12 months after surgery, a questionnaire was administered to assess daily stair climbing and descent ability. In the questionnaire, stair climbing and descent ability were classified as (1) stair climbing and descent one step at a time, (2) stair climbing and descent two steps at a time, and (3) unable to climb or descend stairs. The necessity of a handrail was also evaluated and classified as: (1) necessary, (2) unnecessary, and (3) unable to climb or descend stairs with handrail. Statistical analysis (χ ²-test) was performed to compare these data between the types of TKA.

RESULTS

Preoperatively, no significant differences in stair climbing and descent ability or between handrail classifications were observed between the three different TKA groups. Postoperatively, the percentage of patients able to climb stairs one step at a time was significantly higher in BCS-TKA group (89%), when compared with CR (72%) or PS (58%) TKA groups. No significant differences in stair descent ability or among the handrail necessity classifications were observed between the types of TKA.

CONCLUSION

BCS-TKA resulted in significantly better stair climbing ability when compared with CR or PS-TKA. This may indicate that the design of BCS-TKA better reproduces native anterior cruciate ligament and posterior cruciate ligament function and improves knee stability during stair climbing activity.

Biomechanics and wear comparison between mechanical and kinematic alignments in total knee arthroplasty

The uses of mechanical and kinematic alignments in total knee arthroplasty are under debate in recent clinical investigations. In this study, the differences in short-term biomechanics and long-term wear volume between mechanical and kinematic alignments in total knee arthroplasty were investigated, based on a subject-specific musculoskeletal multi-body dynamics model during walking gait simulation. An increase of 8.2% in the peak tibiofemoral medial contact force, a posterior contact translation by maximum 4.7 mm and a decrease of 5.5% in the wear volume after a 10-million-cycle simulation were predicted in the kinematic alignment, compared with the mechanical alignment. Nevertheless, the tibiofemoral contact mechanics, the range of motions and the long-term wear were not markedly different between mechanical and kinematic alignments. Furthermore, the mechanical alignment with a posterior tibial slope similar to that under the kinematic alignment was found to produce similar anterior-posterior translation and the range of motion, and an approximate wear volume, compared with the kinematic alignment. The ligament forces under the kinematic alignment were influenced markedly by as much as 25%, 50% and 77% for the medial collateral ligament, lateral collateral ligament and posterior cruciate ligament forces, respectively. And, a maximum increase of 40% for patellofemoral contact force was predicted under the kinematic alignment. These findings suggest that the kinematic alignment is an alternative alignment principle but no marked advantages in biomechanics and wear to the mechanical alignment. The adverse effects of the kinematic alignment on patella loading and soft tissue forces should be noticed.

ACL substitution may improve kinematics of PCL-retaining total knee arthroplasty

PURPOSE

One of the key factors responsible for altered kinematics and joint stability following contemporary total knee arthroplasty (TKA) is resection of the anterior cruciate ligament (ACL). However, ACL retention can present several technical challenges, and in some cases may not be viable due to an absent or nonfunctional ACL. Therefore, the goal of this research was to investigate whether substitution of the ACL through an anterior post mechanism could improve kinematic deficits of contemporary posterior cruciate ligament (PCL) retaining implants.

METHODS

Kinematic analysis of different implant types was done using KneeSIM, a previously established dynamic simulation tool. Walking, stair-ascent, chair-sit, and deep knee bend were simulated for an ACL-substituting (PCL-retaining) design, a bi-cruciate-retaining and ACL-sacrificing (PCL-retaining) implant, as well as the native knee. The motion of the femoral condyles relative to the tibia was recorded for kinematic comparisons.

RESULTS

The ACL-substituting and ACL-retaining implants provided similar kinematic improvements over the ACL-sacrificing implant, by reducing posterior femoral shift in extension and preventing paradoxical anterior sliding. During all simulated activities, the ACL-sacrificing implant showed between 7 and 8 mm of posterior shift in extension in contrast to the ACL-retaining implant and the ACL-substituting design, which showed overall kinematic trends similar to the native knee.

CONCLUSION

The absence of ACL function has been linked to abnormal kinematics and joint stability in patients with contemporary TKA. ACL-substituting implants could be a valuable treatment option capable of overcoming the limitations of contemporary TKA, particularly when retaining the native ACL is not feasible or is challenging.

Medial tilting of the joint line in posterior stabilized total knee arthroplasty increases contact force and stress

BACKGROUND

Kinematically aligned total knee arthroplasty is based on the concept to represent the premorbid joint alignment with cruciate-retaining implants, characterized by medial tilt and internal rotation. However, kinematic and kinetic effects of kinematically aligned total knee arthroplasty with posterior-stabilized implants is unknown. The purpose of this study was to examine the effect of medial tilting of the joint line with posterior-stabilized implants.

METHODS

A mechanical alignment model, and medial tilt 3° and 5° models were constructed. Knee kinematics and contact forces were simulated using a musculoskeletal computer simulation model. Contact stresses on the tibiofemoral joint and the post area were then calculated using finite element analysis.

FINDINGS

From 0° to 120° of knee flexion, greater external rotation of the femoral component was observed in medial tilt models (-0.6°, 1.8° and 4.2° in mechanical alignment, medial tilt 3° and medial tilt 5° models, respectively). The peak contact stresses on the tibiofemoral joint and the post area at 120° of knee flexion were higher in medial tilt models. The peak contact stresses on the post area in medial tilt 3° and 5° models were 2.2 and 3.8 times greater than that in mechanical alignment model, respectively.

INTERPRETATION

Medial tilting of the joint line causes greater axial rotation even with posterior-stabilized implants, which can represent near-normal kinematics. However, medial tilting of the joint line in total knee arthroplasty with posterior-stabilized implants may have a higher risk for polyethylene wear at the tibiofemoral joint and post area, leading to subsequent component loosening.

Analysis of in-vivo articular cartilage contact surface of the knee during a step-up motion

BACKGROUND

Numerous studies have reported on the tibiofemoral articular cartilage contact kinematics, however, no data has been reported on the articular cartilage geometry at the contact area. This study investigated the in-vivo tibiofemoral articular cartilage contact biomechanics during a dynamic step-up motion.

METHODS

Ten healthy subjects were imaged using a validated magnetic resonance and dual fluoroscopic imaging technique during a step-up motion. Three-dimensional bone and cartilage models were constructed from the magnetic resonance images. The cartilage contact along the motion path was analyzed, including cartilage contact location and the cartilage surface geometry at the contact area.

FINDINGS

The cartilage contact excursions were similar in anteroposterior and mediolateral directions in the medial and lateral compartments of the tibia plateau (P>0.05). Both medial and lateral compartments were under convex (femur) to convex (tibia) contact in the sagittal plane, and under convex (femur) to concave (tibia) contact in the coronal plane. The medial tibial articular contact radius was larger than the lateral side in the sagittal plane along the motion path (P<0.001).

INTERPRETATIONS

These data revealed that both the medial and lateral compartments of the knee experienced convex (femur) to convex (tibia) contact in sagittal plane (or anteroposterior direction) during the dynamic step-up motion. These data could provide new insight into the in-vivo cartilage contact biomechanics research, and may provide guidelines for development of anatomical total knee arthroplasties that are aimed to reproduce normal knee joint kinematics.

The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee

OBJECTIVES

Little biomechanical information is available about kinematically aligned (KA) total knee arthroplasty (TKA). The purpose of this study was to simulate the kinematics and kinetics after KA TKA and mechanically aligned (MA) TKA with four different limb alignments.

MATERIALS AND METHODS

Bone models were constructed from one volunteer (normal) and three patients with three different knee deformities (slight, moderate and severe varus). A dynamic musculoskeletal modelling system was used to analyse the kinematics and the tibiofemoral contact force. The contact stress on the tibial insert, and the stress to the resection surface and medial tibial cortex were examined by using finite element analysis.

RESULTS

In all bone models, posterior translation on the lateral side and external rotation in the KA TKA models were greater than in the MA TKA models. The tibiofemoral force at the medial side was increased in the moderate and severe varus models with KA TKA. In the severe varus model with KA TKA, the contact stress on the tibial insert and the stress to the resection surface and to the medial tibial cortex were increased by 41.5%, 32.2% and 53.7%, respectively, compared with MA TKA, and the bone strain at the medial side was highest among all models.

CONCLUSION

Near normal kinematics was observed in KA TKA. However, KA TKA increased the contact force, stress and bone strain at the medial side for moderate and severe varus knee models. The application of KA TKA for severe varus knees may be inadequate.Cite this article: S. Nakamura, Y. Tian, Y. Tanaka, S. Kuriyama, H. Ito, M. Furu, S. Matsuda. The effects of kinematically aligned total knee arthroplasty on stress at the medial tibia: A case study for varus knee. Bone Joint Res 2017;6:43-51. DOI: 10.1302/2046-3758.61.BJR-2016-0090.R1.

Cruciate Retaining Implant With Biomimetic Articular Surface to Reproduce Activity Dependent Kinematics of the Normal Knee

Alterations in normal knee kinematics following total knee arthroplasty (TKA) arise in part from the non-anatomic articular geometry of contemporary implants. In this study, the kinematics of a novel posterior cruciate-retaining (CR) implant with anatomic (biomimetic) articular surface, were compared to that of contemporary CR implants during various simulated activities. Across different simulated activities the biomimetic-CR mimicked normal kinematic patterns more closely than contemporary CR implants. In particular, during deep knee bend and chair-sit, the biomimetic-CR showed medial pivot motion, while other CR implants showed abnormal motion including lateral pivot or no pivot, and paradoxical anterior sliding. Further in vivo and clinical studies are needed to determine whether such biomimetic implants can truly help to achieve a more normal feeling knee and improved patient satisfaction.

Regaining Native Knee Kinematics Following Joint Arthroplasty: A Novel Biomimetic Design with ACL and PCL Preservation

Lack of ACL and non-anatomic articular surfaces in contemporary total knee implants result in kinematic abnormalities. We hypothesized that such abnormalities may be addressed with a biomimetic bi-cruciate retaining (BCR) design having anatomical articular surfaces. We used dynamic computer simulations to compare kinematics among the biomimetic BCR, a contemporary BCR and cruciate-retaining implant for activities of daily living. During simulated deep knee bend, chair-sit and walking, the biomimetic BCR implant showed activity dependent kinematics similar to healthy knees in vivo. Restoring native knee geometry together with ACL preservation provided these kinematic improvements over contemporary ACL-preserving and ACL-sacrificing implants. Further clinical studies are required to determine if such biomimetic implants can result in more normal feeling knees and improve quality of life for active patients.

Ligament balancing in total knee arthroplasty-Medial stabilizing technique

Ligament balancing is one of the most important surgical techniques for successful total knee arthroplasty. It has traditionally been recommended that medial and lateral as well as flexion and extension gaps are equal. This article reviews the relevant literature and discusses the clinical importance of the aforementioned gaps. Current evidence indicates that achieving medial stability throughout the range of motion should be a high priority in ligament balancing in total knee arthroplasty. Finally, the medial stabilising surgical technique, which aims to achieve good medial stability in posterior cruciate-retaining total knee arthroplasty, is introduced.

Kinematic alignment produces near-normal knee motion but increases contact stress after total knee arthroplasty: A case study on a single implant design

BACKGROUND

Kinematically aligned total knee arthroplasty (TKA) is of increasing interest because this method might improve postoperative patient satisfaction. In kinematic alignment the femoral component is implanted in a slightly more valgus and internally rotated position, and the tibial component is implanted in a slightly more varus and internally rotated position, than in mechanical alignment. However, the biomechanics of kinematically aligned TKA remain largely unknown. The aim of this study was to compare the kinematics and contact stresses of mechanically and kinematically aligned TKAs.

METHODS

A musculoskeletal computer simulation was used to determine the effects of mechanically or kinematically aligned TKA. Knee kinematics were examined for mechanically aligned, kinematically aligned, and kinematically aligned outlier models. Patellofemoral and tibiofemoral contact forces were measured using finite element analysis.

RESULTS

Greater femoral rollback and more external rotation of the femoral component were observed with kinematically aligned TKA than mechanically aligned TKA. However, patellofemoral and tibiofemoral contact stresses were increased in kinematically aligned TKA.

CONCLUSIONS

These findings suggest that kinematically aligned TKA produces near-normal knee kinematics, but that concerns for long-term outcome might arise because of high contact stresses.

Knee arthroplasty with a medial rotating total knee replacement. Midterm clinical findings: a district general experience of 38 cases

BACKGROUND

The Medial Rotating Knee replacement (MRK) was first used in 1994, reporting high rates of satisfaction. It is designed to replicate natural knee kinematics and improve stability and function. There are limited studies on the mid-term clinical outcomes, in particular in a district general hospital (DGH) environment. This is the first study that we are aware of that evaluates the learning curve of the implementation of this knee system in this environment.

PATIENTS/METHOD

Between 2007 and 2009 we performed 38 consecutive MRK replacements (MAT ORTHO, UK) in 36 patients. The mean follow-up was four years. Patients were evaluated clinically, using OKS and patient questionnaire and radiographically (good/acceptable/poor) to assess outcome.

RESULTS

Mean age was 73.0 years. Mean pre-operative OKS was 17.7 (range 8-29), which rose to 38.1 (range 23-48) at latest follow up (p<0.005). Overall 71% of the patients were either satisfied (29%) or very satisfied (42%). 81% felt an improvement of the ability to go up or down stairs and 92% felt stable. All poor radiographic and the majority of acceptable outcomes were experienced in the first 50% of cases.

CONCLUSION

The MRK can be successfully implanted in a DGH environment. It improves pain and function comparably to standard TKRs, however, subjective improvement may be higher. Radiographic evaluation shows an acceptable learning curve.

LEVEL OF EVIDENCE

Level IV case series.

Development of a scale to assess performance following primary total knee arthroplasty

BACKGROUND

Quantitative assessment of postsurgical knee motion provides sensitive measurements, but results are technical and may not be meaningful to patients. Although several knee-specific instruments exist, no patient-reported outcome (PRO) measure correlates function with improved stability, motion, satisfaction, and confidence.

OBJECTIVE

To address both the above limitations by developing a PRO measure to assess the phenomenon of a "normal" knee after primary total knee arthroplasty (TKA).

METHODS

A draft conceptual model linking the impact of clinical mechanics to hypothesized functional outcomes was generated after a literature review of available assessment tools. Participants aged 18 to 80 years having undergone TKA within the past 10 to 18 months were identified and screened by clinical sites to participate in phase 1 focus groups or phase 2 in-depth interviews. Participants were asked to describe their TKA experiences, including how their knee feels now, followed by cognitive debriefing of Patient's Knee Implant Performance (PKIP) draft items.

RESULTS

Phase 1 results indicated that concepts of confidence, stability, and satisfaction in patients' replacement knee when performing certain activities were distinct and important in the patients' assessment of their TKA. Phase 2 efforts yielded a final version of the PKIP measure containing nine items assessing the broader concepts of stability, confidence, and satisfaction in association with activities. Presurgical and postsurgical versions of the measure were created.

CONCLUSIONS

Results of this qualitative study support use of the PKIP as a complementary PRO measure to assess performance after primary TKA. Psychometric evaluation of the PKIP is planned.

Comparison of the clinical outcomes after total knee arthroplasty with the LCS rotating platform mobile bearing knee system and the PFC Sigma RP-F mobile bearing knee system

Background

We compared clinical outcomes after total knee arthroplasty with the Low Contact Stress (LCS) rotating platform mobile bearing knee system and the Press Fit Condylar Sigma rotating platform high flexion (PFC Sigma RP-F) mobile bearing knee system.

Methods

Fifty cases of total knee arthroplasty were performed with the PFC Sigma RP-F mobile bearing knee system and sixty-one cases were performed with the LCS mobile bearing total knee arthroplasty. The average duration of follow-up was 2.9 years.

Results

The mean Hospital for Special Surgery (HSS) knee score was 62.1 (range, 52 to 75) in the LCS group and 61.9 (range, 50 to 74) in the Sigma RP-F group preoperatively, and 90.1 (range, 84 to 100) in the LCS group and 89.8 (range, 83 to 100) in the Sigma RP-F group at the final follow-up. The mean preoperative flexion contracture was 6.7° (range, 0° to 10°) in the LCS group and 9.3° (range, 0° to 15°) in the Sigma RP-F group preoperatively. The mean range of motion was 124.6° (range, 105° to 150°) in the LCS group and 126.1° (range, 104° to 145°) in the Sigma RP-F group at the final follow-up.

Conclusions

After a minimum duration of follow-up of two years, we found no significant differences between the two groups with regard to the range of knee motion or the clinical or radiographic results.

The importance of bony impingement in restricting flexion after total knee arthroplasty: computer simulation model with clinical correlation

We constructed patient-specific models from computed tomography data after total knee arthroplasty to predict knee flexion based on implant-bone impingement. The maximum flexion before impingement between the femur and the tibial insert was computed using a musculoskeletal modeling program (KneeSIM; LifeModeler, Inc, San Clemente, California) during a weight-bearing deep knee bend. Postoperative flexion was measured in a clinical cohort of 21 knees (low-flex group: 6 knees with <100° of flexion and high-flex group: 15 size-matched knees with >125° of flexion at 2 years). Average predicted flexion angles were within 2° of clinical measurements for the high-flex group. In the low-flex group, 4 cases had impingement involving the bone cut at the posterior condyle, and the average predicted knee flexion was 102° compared with 93° measured clinically. These results indicate that the level of the distal femoral resection should be carefully planned and that exposed bone proximal to the tips of the posterior condyles of the femoral component should be removed if there is risk of impingement.

Posterior dislocation in total knee replacement: a price for deep flexion?

INTRODUCTION

Post-cam dislocation in TKA is a rare complication after posterior stabilized TKA.

PURPOSE

Four cases of posterior dislocation of the tibia relative to the femur are described in one current posterior stabilized design.

CONCLUSION

Specific design features in one contemporary high flexion TKA design contribute to high dislocation rates.

Total knee arthroplasty three-dimensional kinematic estimation prevision. From a two-dimensional fluoroscopy acquired dynamic model

INTRODUCTION

To determine six-degree of freedom of total knee arthroplasty kinematics (TKA), optimized matching algorithms for single fluoroscopic image system may be used. Theoretical accuracy of these systems was reported. Nevertheless, all reports were done under idealized laboratory experimental conditions. The aim of this study was to evaluate the "true" accuracy of a flat panel single plane video-fluoroscopy system based on computed-assisted design (CAD) model matching and compare it to TKA kinematics obtained from optoelectronic measurements as gold standard.

HYPOTHESIS

The estimation of the error produced by 2D/3D fluoroscopic registration in daily practice is misjudged in most available laboratory reports.

MATERIAL AND METHODS

The experimental set-up used a TKA implanted into femoral and tibial cadaver bones. Thirty flexions were simultaneously registered using single plane fluoroscopy and an active optical tracking system. Kinematics registered were compared using the root mean square error (RMS), the concordance correlation coefficient and Bland & Altman plot analysis.

RESULTS

The mean range of motion of flexion during the experiment was 106°. The respective RMS for flexion, varus-valgus and internal-external rotation were 0.68, 0.67 and 1.02°. The respective RMS for antero-posterior, medio-lateral and proximo-distal displacement were 1.3, 2.4 and 1.06 mm. Extreme values of the measured error concerning medio-lateral displacement were -5.4 and 22,1mm.

DISCUSSIONS

Analysis found some outliners in all degree of freedom with a systematic error and larger standard deviation than already published data. One should make sure that during the experiment the motion of interest is in the in-plane direction. Moreover, this study brings out the true threshold detection of this type of analysis.

Contact forces in several TKA designs during squatting: A numerical sensitivity analysis

Total knee arthroplasty (TKA) is a very successful procedure, but pain or difficulties during activities still persist in patients. Patient outcomes in TKA surgery can be affected by implant design, alignment or patient-related anatomical factors. This paper presents a numerical sensitivity analysis of several TKA types: a fixed bearing, posterior stabilized prosthesis, a high flexion fixed bearing guided motion prosthesis, a mobile bearing prosthesis and a hinge prosthesis. Each prosthesis was virtually implanted on the same cadaver leg model and it underwent a loaded squat, in 10s, between 0° and 120°, similar to several previous experimental tests performed on knee kinematics simulators. The aim of this examination was to investigate the sensitivity of the patello-femoral (PF) and tibio-femoral (TF) contact forces to patient-related anatomical factors, and component position in the different implant types. The following parameters were used for the sensitivity study: the proximo-distal patellar position, the patellar component tilting, the tibial component position and orientation, the locations of the medial and lateral collateral ligaments with respect to femur and tibia and the patellar tendon length. The sensitivity analysis showed that PF contact forces are mostly affected by patella height (increases up to 67% for one TKA type in patella-alta configuration), by an anterior tibial component translation (increases up to 30%), and by patellar component tilting (increases up to 29%); TF contact forces are mostly affected by the anterior displacement of the insertion points of the medial collateral ligament with respect to the reference position (increases up to 48%).

Assessment of the antero-posterior and rotational stability of the anterior cruciate ligament analogue in a guided motion bi-cruciate stabilized total knee arthroplasty

Abnormal knee kinematics and sagittal instability after most knee replacements are due in part to deficient anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) function. The guided motion bi-cruciate stabilized knee replacement aspires to stabilize the knee posteriorly and anteriorly by means of a cam-post mechanism. This investigation studies the ACL-stabilizing function of that mechanism in early flexion, and 25 knees that had undergone replacement with this implant were studied. Antero-posterior laxity at 15 degrees flexion was adequately restored for 76% (16/21) of the knees (side-to-side difference <3 mm on KT assessment), and 72% (18/25) knees exhibited a positive pivot shift test. The findings of this study suggest excellent early clinical outcomes for this implant, but the goal of replicating ACL function has only been partially achieved.