In vivo knee kinematics during stair and deep flexion activities in patients with bicruciate substituting total knee arthroplasty

Comparative outcomes of kinematically aligned TKA with medial stabilized design vs. mechanically aligned TKA with bi-cruciate stabilized design: A propensity score-matched analysis

Purpose

Patient dissatisfaction after total knee arthroplasty (TKA) is often linked to altered knee kinematics and stability. This study compared the short-term clinical outcomes of kinematically aligned TKA (KA-TKA) and mechanically aligned TKA (MA-TKA) using bi-cruciate stabilized (BCS) implants.

Methods

In this propensity score-matched study, 60 patients who underwent either KA-TKA or MA-TKA (30 per group) with BCS implants were analyzed. Baseline characteristics, including age, sex, preoperative range of motion (ROM), and hip-knee-ankle alignment, were matched. ROM and clinical outcomes were evaluated preoperatively and at 1 year postoperatively using the 2011 Knee Society Score (KSS) subscales and Forgotten Joint Score-12 (FJS).

Results

At 1 year, the KA group achieved higher scores in KSS subscales for symptoms (23.2 vs. 20.0, p < 0.001), satisfaction (28.1 vs. 22.5, p < 0.001), functional activities (82.1 vs. 74.2, p = 0.011), and FJS (83.8 vs. 62.5, p < 0.001). No significant differences were observed in maximum extension, flexion, or KSS expectations.

Conclusions

KA-TKA demonstrated superior satisfaction and functional recovery than MA-TKA with BCS implants in the short term. These results suggested that KA-TKA, which reconstructs patient-specific alignment, may provide a more natural knee feel, leading to higher patient satisfaction compared to implant-driven BCS-TKA.

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.

Differences in kinematics and kinetics during gait between total knee arthroplasty implant designs

BACKGROUND

Implant design is important for achieving proper knee biomechanics during gait following knee arthroplasty. Bicruciate-stabilized total knee arthroplasty attempts to replicate anterior stability and rotational facilitation. However, its detailed gait biomechanics compared with other implant designs have not been analyzed. The purpose of this study is to compare knee kinematics and kinetics between bicruciate-stabilized total knee arthroplasty, posterior-stabilized total knee arthroplasty, unicompartmental knee arthroplasty, and normal knees.

METHODS

Ten healthy subjects, 16 who underwent posterior stabilized total knee arthroplasty, 12 who underwent bicruciate-stabilized total knee arthroplasty, and 13 who underwent unicompartmental knee arthroplasty were recruited. The mean follow-up period after arthroplasty was 11.0 months. Three-dimensional kinematics and kinetics were assessed using a motion capture system with subjects walking on a 5-m walkway. Comparisons between groups were conducted using the Kruskal-Wallis test, and post hoc analysis was performed for those parameters that differed significantly.

FINDINGS

The bicruciate-stabilized total knee arthroplasty group showed decreased internal rotation compared to the unicompartmental knee arthroplasty group. Compared to the control group, the posterior-stabilized total knee arthroplasty group exhibited reduced knee extension and internal rotation moment.

INTERPRETATION

Bicruciate-stabilized total knee arthroplasties exhibited different biomechanical characteristics compared to unicompartmental knee arthroplasties during terminal stance. Postoperative total knee arthroplasty rehabilitation should focus on relieving stiffness owing to insufficient knee flexion-extension motion observed in both bicruciate-stabilized and posterior-stabilized total knee arthroplasties compared with unicompartmental knee arthroplasty, which may be due to a lack of knee rotational motion during gait.

Association of Posterior Tibial Slope and Functional Outcome After Total Knee Arthroplasty: An Observational Study

Introduction Precise implant positioning, particularly a well-balanced posterior tibial slope (PTS), is crucial for the success of total knee arthroplasty (TKA) because it enhances sagittal plane stability and significantly influences knee motion patterns. The long-term impact of tibial slope on active and passive range of motion (ROM) still needs to be studied, despite ROM's crucial role in patient contentment. This study examined the relationship between tibial slope and active and passive ROM following TKA, with a follow-up period of at least three months. Materials and methods The study included 40 knees of 30 participants who had undergone initial TKA for knee osteoarthritis (KOA). These subjects were recruited between September 2023 and May 2024, with a minimum postoperative follow-up period of three months. Results Significant improvements in the average Kujala score and knee ROM were observed at postop day 7 and at the three-month follow-up as compared to preoperative measurements (p<0.001). Concurrently, there was a notable decrease in the mean posterior tibial slope (PTS) angle (p<0.001). While patients with a larger PTS angle exhibited higher average Kujala scores and knee ROM, the correlations between these variables and the PTS angle were not statistically significant. Conclusion Considering its limitations, this research indicates that the posterior tibial slope does not significantly affect the functional outcomes of patients after primary total knee replacement in the initial treatment phase.

Comparison of short-term clinical results between modified kinematically-aligned and guided motion bicruciate stabilized total knee arthroplasty

BACKGROUND

Both kinematically-aligned (KA) total knee arthroplasty (TKA) and bicruciate stabilized (BCS) TKA aim to reproduce the physiological knee kinematics. In this study, we compared the femoro-tibial component rotational mismatch between patients who underwent modified KA-TKA and those who received guided-motion BCS-TKA, and its influence on the clinical outcomes.

METHODS

In this retrospective study, 77 consecutive patients were included and divided into two groups: subjects who underwent modified KA-TKA with Persona (KA Group; n = 42) and those who received BCS-TKA with JOURNEY II (BCS group; n = 35). Range of motion, the 2011 Knee Society Score (KSS), the rotational alignment of the femoral and tibial components, and the correlations between the rotational mismatch and the 2011 KSS subscales were examined.

RESULTS

The postoperative objective knee indicators (P = 0.0157), patient satisfaction (P = 0.0039) and functional activity scores (P = 0.0013) in the KA group were significantly superior to those in the BCS group 1 year postoperatively. There was no significant difference between the two groups observed in the rotational mismatch. In the BCS group, significant negative correlations were identified between the rotational mismatch and objective indicators, patient satisfaction, and functional activity scores but not in the KA group.

CONCLUSIONS

The short-term clinical results following KA-TKA showed superior objective knee indicators, patient satisfaction and functional activity scores. A negative correlation was observed between component rotational mismatch and the 2011 KSS subscales in the BCS group, compared to no relationship found between the two in the KA group. These findings suggested that KA-TKA has a relatively higher tolerance for rotational mismatch than BCS-TKA.

Effect of single-radius design on in vivo kinematics during stair activities after total knee arthroplasty

BACKGROUND

The single-radius design is one of the major total knee arthroplasty (TKA) designs and widely used all over the world. The objective of this study was to compare in vivo kinematics between the anteroposterior (AP) single-radius design with mediolateral (ML) single-radius (Non Restricted Geometry; NRG) and ML dual-radius (Triathlon) during stair activities.

METHODS

A total of 21 knees in 18 patients (NRG group: 10 knees in 7 patients, Triathlon group: 11 knees in 11 patients) with a clinically successful posterior stabilized TKA were examined. Under fluoroscopic surveillance, each patient performed stair ascending and descending motions. In vivo kinematics were analyzed using 2D/3D registration technique. The knee flexion angle, rotation angle, varus-valgus angle, AP translation of the femorotibial contact point for both the medial and lateral sides of the knee, and post-cam engagement were evaluated.

RESULTS

There were no significant differences between the two groups in rotation angle and AP translation at each flexion angle. Examining the varus-valgus angle, the NRG group showed varus position at an early flexion angle during both stair activities.Post-cam engagement was observed in both groups during both stair activities. The mean flexion angle of engagement in the NRG group, the post of which was located anterior to the Triathlon, was larger than that in the Triathlon group during both stair activities.

CONCLUSION

Despite the same AP single-radius TKA, ML single-radius might affect varus motion at an early flexion angle.

Bicompartmental, medial and patellofemoral knee replacement might be able to maintain unloaded knee kinematics

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are standard procedures for treating knee joint arthritis. Neither UKA nor TKA seems to be optimally suited for patients with bicompartmental osteoarthritis that affects only the medial and patellofemoral compartments. A bicompartmental knee arthroplasty (BKA) was designed for this patient group. This study aimed to compare the effectiveness of a BKA and TKA in restoring the kinematics of the knee joint.

MATERIALS AND METHODS

In this in vitro study, three types of knee arthroplasties (BKA, posterior cruciate ligament-retaining, and posterior cruciate ligament-resecting TKA) were biomechanically tested in six freshly frozen human cadaveric specimens. Complete three-dimensional kinematics was analyzed for each knee arthroplasty during both passive and loaded conditions in a validated knee kinematics rig. Infrared motion capture cameras and retroreflective markers were used for recording data.

RESULTS

No significant differences could be found between the three types of arthroplasties. However, similar kinematic changes between BKA and a native knee joint were documented under passive conditions. However, in a weight-bearing mode, a significant decrease in femoral rotation during the range of motion was found in arthroplasties compared to the native knee, probably caused by contraction of the quadriceps femoris muscle, which leads to a decrease in the anterior translation of the tibia.

CONCLUSIONS

Kinematics similar to that of the natural knee can be achieved by BKA under passive conditions. However, no functional advantage of BKA over TKA was detected, which suggests that natural knee kinematics cannot be fully imitated by an arthroplasty yet. Further prospective studies are required to determine the anatomic and design factors that might affect the physiologic kinematics.

Kinematics of bicruciate and posterior stabilized total knee arthroplasty during deep knee flexion and stair climbing

Second-generation bicruciate stabilized (BCS) total knee arthroplasty (TKA) was developed to substitute both anterior and posterior cruciate ligaments and replicate physiological kinematics. This study aimed to evaluate if the postcam mechanism and the surface geometry function effectively. Seventeen and twelve knees implanted with BCS TKA and posterior stabilized (PS) TKA, respectively, were analyzed. In vivo kinematics during deep knee flexion were estimated from single-plane fluoroscopic images using a 2-dimensional to 3-dimensional image registration technique. Flexion angle, anteroposterior translation, femoral external rotation (ER), and postcam engagement were compared between the groups. Postoperative 2011 Knee Society Score (KSS) was obtained at the last follow-up. The medial femoral condyle in BCS was positioned more anteriorly than that in PS from minimum flexion to maximum flexion. Posterior motion of the lateral femoral condyle was observed in both groups. ER of BCS was significantly larger compared to PS from minimum flexion to 100°. However, the amount of ER from minimum flexion to maximum flexion was similar: 6.2° ± 4.5° and 7.7° ± 4.1° in BCS and PS, respectively (P = .364). Anterior postcam engagement was observed in 76.5% and 25.0% in BCS and PS, respectively (P = .006). Posterior postcam engagement was observed in all cases in BCS and PS. There were no significant differences in KSS between the groups. The kinematic differences were likely a result of variations in articular surface geometry.

Influence of component design on in vivo tibiofemoral contact patterns during kneeling after total knee arthroplasty: a systematic review and meta-analysis

PURPOSE

Modern TKR prostheses are designed to restore healthy kinematics including high flexion. Kneeling is a demanding high-flexion activity. There have been many studies of kneeling kinematics using a plethora of implant designs but no comprehensive comparisons. Visualisation of contact patterns allows for quantification and comparison of knee kinematics. The aim of this systematic review was to determine whether there are any differences in the kinematics of kneeling as a function of TKR design.

METHODS

A search of the published literature identified 26 articles which were assessed for methodologic quality using the MINORS instrument. Contact patterns for different implant designs were compared at 90° and maximal flexion using quality-effects meta-analysis models.

RESULTS

Twenty-five different implants using six designs were reported. Most of the included studies had small-sample sizes, were non-consecutive, and did not have a direct comparison group. Only posterior-stabilised fixed-bearing and cruciate-retaining fixed-bearing designs had data for more than 200 participants. Meta-analyses revealed that bicruciate-stabilised fixed-bearing designs appeared to achieve more flexion and the cruciate-retaining rotating-platform design achieved the least, but both included single studies only. All designs demonstrated posterior-femoral translation and external rotation in kneeling, but posterior-stabilised designs were more posterior at maximal flexion when compared to cruciate retaining. However, the heterogeneity of the mean estimates was substantial, and therefore, firm conclusions about relative behaviour cannot be drawn.

CONCLUSION

The high heterogeneity may be due to a combination of variability in the kneeling activity and variations in implant geometry within each design category. There remains a need for a high-quality prospective comparative studies to directly compare designs using a common method.

LEVEL OF EVIDENCE

Systematic review and meta-analysis Level IV.

Posterior tibial slope and anterior post-cam contact can change knee kinematics in extension in bi-cruciate stabilized total knee arthroplasty

Aims

This study aims to investigate the effects of posterior tibial slope (PTS) on knee kinematics involved in the post-cam mechanism in bi-cruciate stabilized (BCS) total knee arthroplasty (TKA) using computer simulation.

Methods

In total, 11 different PTS (0° to 10°) values were simulated to evaluate the effect of PTS on anterior post-cam contact conditions and knee kinematics in BCS TKA during weight-bearing stair climbing (from 86° to 6° of knee flexion). Knee kinematics were expressed as the lowest points of the medial and lateral femoral condyles on the surface of the tibial insert, and the anteroposterior translation of the femoral component relative to the tibial insert.

Results

Anterior post-cam contact in BCS TKA was observed with the knee near full extension if PTS was 6° or more. BCS TKA showed a bicondylar roll forward movement from 86° to mid-flexion, and two different patterns from mid-flexion to knee extension: screw home movement without anterior post-cam contact and bicondylar roll forward movement after anterior post-cam contact. Knee kinematics in the simulation showed similar trends to the clinical in vivo data and were almost within the range of inter-specimen variability.

Conclusion

Postoperative knee kinematics in BCS TKA differed according to PTS and anterior post-cam contact; in particular, anterior post-cam contact changed knee kinematics, which may affect the patient’s perception of the knee during activities.

Cite this article: Bone Joint Res 2020;9(11):761–767.

Coordinate system requirements to determine motions of the tibiofemoral joint free from kinematic crosstalk errors

The relative rigid body motions between the femur and the tibia (termed tibiofemoral kinematics) during flexion activities can provide an objective measure of knee function. Clinically meaningful tibiofemoral kinematics are defined as the six relative rigid body motions expressed in a joint coordinate system where the motions about and along the axes conform to clinical definitions and are free from kinematic crosstalk errors. To obtain clinically meaningful tibiofemoral kinematics, coordinate systems must meet certain requirements which neither have been explicitly stated nor in fact satisfied in any previous publication known to the author. Starting with the joint coordinate system of Grood and Suntay (1983) where motions conform to clinical definitions, the body-fixed axes must correspond to the functional (i.e. actual) axes in flexion-extension and internal-external axial rotation to avoid kinematic crosstalk errors in rotations and both functional axes must be body-fixed throughout knee flexion. To avoid kinematic crosstalk errors in translations, the origins of the femoral and tibial Cartesian coordinate systems, which serve as stepping stones for computing translations, must lie on the functional body-fixed axes. Neither the paper by Grood and Suntay nor the ISB recommendation (Wu et al., 2002) which adopted the joint coordinate system of Grood and Suntay explains these requirements. Indeed meeting these requirements conflicts with the ISB recommendation thus indicating the need for revision to this recommendation. Future studies where clinically meaningful tibiofemoral kinematics are of interest should be guided by the requirements described herein.

Patient-specific instrumentation improves functional kinematics of minimally-invasive total knee replacements as revealed by computerized 3D fluoroscopy

BACKGROUND AND OBJECTIVES

Minimally-invasive total knee arthroplasty (MIS-TKA) has demonstrated very good short-term success, but its mid- to long-term results remain inconclusive. The success may be related to the tradeoff between a small incision and accurate positioning of the implant components. Patient-specific instrumentation (PSI) aims to improve the accuracy in restoring the knee axis and the clinical outcomes for MIS-TKA, but the results are yet to be confirmed by accurate assessment during functional activities. The purpose of the current study was to measure and compare the in vivo three-dimensional (3D) rigid-body and surface kinematics of MIS-TKA implanted with and without PSI during isolated knee active flexion/extension and sit-to-stand using state-of-the-art 3D model-based fluoroscopy technology.

METHODS

Ten patients treated for advanced medial knee osteoarthritis by MIS-TKA without PSI (non-PSI group) and nine with PSI (PSI group) participated in the current study. Each subject performed non-weight-bearing knee flexion/extension and sit-to-stand tasks while the motion of the prosthetic knee was under bi-plane fluoroscopy surveillance. The computer models of each of the knee prosthesis components were registered to the measured fluoroscopy images for each time frame via a novel validated 3D fluoroscopy method. Non-parametric 1-tailed Mann-Whitney tests were performed to detect the differences in the joint and surface kinematic variables every 10° of knee flexion between the non-PSI and PSI groups. The 1-tailed significance level was at α = 0.05.

RESULTS

The PSI group showed clear, coupled flexion/internal rotation during activities, while the non-PSI group remained roughly at an externally rotated position with slight internal rotations. The coupled rotation in the PSI group was accompanied by an anterior displacement of the medial contact and a posterior displacement of the lateral contact, which was different from the screw-home mechanism. Neither of the two groups showed the normal roll-back phenomenon, i.e., posterior translation of the femur relative to the tibia during knee flexion.

CONCLUSIONS

With the state-of-the-art 3D fluoroscopy method, differences in both the rigid-body and surface kinematics of the prosthetic knees between MIS-TKA with and without PSI were identified. Patients with PSI demonstrated significant positive effects on the reconstructed rigid-body kinematics of the knee, showing clearer coupled flexion/internal rotations - an important kinematic characteristic in healthy knees - than those without PSI during activities with or without weight-bearing. However, none of them showed normal contact patterns. The current findings will be helpful for surgical instrument design, as well as for surgical decision-making in MIS total knee arthroplasty.

Tibiofemoral kinematics in healthy and osteoarthritic knees during twisting

Purpose

The purpose of this study was to determine the in vivo kinematics of healthy knees and those with osteoarthritis (OA), during twisting using density-based image-matching techniques.

Methods

Five healthy subjects and 26 patients with medial knee OA performed twisting under periodic X-ray imaging.

Results

The tibiofemoral rotation at the ipsilateral/contralateral twist in healthy and OA knees were 11° ± 9.3° externally/9.5° ± 5.6° internally (p < 0.05) and 4.4° ± 7.2° externally/2.7° ± 8° internally (p < 0.05), respectively.

Conclusions

The kinematic analysis of OA knees during twisting revealed significantly smaller tibiofemoral rotation than those of healthy knees.

Total Knee Arthroplasty Kinematics

Knee kinematics is an analysis of motion pattern that is utilized to assess a comparative, biomechanical performance of healthy nonimplanted knees, injured nonimplanted knees, and various prosthetic knee designs. Unfortunately, a consensus between implanted knee kinematics and outcomes has not been reached. One might hypothesize that the kinematic variances between the nonimplanted and implanted knee might play a role in patient dissatisfaction following TKA. There is a wide range of TKA designs available today. With such variety, it is important for surgeons and engineers to understand the various geometries and kinematic profiles of available prostheses. The purpose of this review is to provide readers with the pertinent information related to TKA kinematics.

Bicruciate-stabilised total knee arthroplasty provides good functional stability during high-flexion weight-bearing activities

PURPOSE

Bicruciate-stabilised total knee arthroplasty (BCS-TKA) uses a dual-post-cam mechanism as a substitute for the anterior cruciate ligament and posterior cruciate ligament (PCL), with the surface geometry providing additional guidance for axial rotation and posterior translation. However, the effect of weight-bearing on the kinematics of BCS-TKA has not been investigated. Therefore, the aim of this study was to clarify the effect of weight-bearing on the kinematics of BCS-TKA during high-flexion activities.

METHODS

The kinematics of 11 BCS-TKAs were evaluated under fluoroscopy, with two- and three-dimensional image registration, during squatting weight-bearing and active-assisted knee flexion non-weight-bearing. The following variables were measured: knee range of motion, axis of femoral rotation relative to the tibial component, anteroposterior (AP) translation of the medial contact point, kinematic path of the joint surfaces, lateral femorotibial contact point, and anterior and post-cam engagement.

RESULTS

The weight-bearing condition did not influence the range of knee flexion, axis of femoral rotation, medial pivot pattern during early flexion, or bicondylar rollback beyond mid-flexion. With regard to AP translation, both the medial and lateral contact points had more posterior locations in weight-bearing than in non-weight-bearing at the mid-flexion angle. Anterior engagement was identified in 6/11 knees (54.5%) in weight-bearing and 4/11 knees (36.3%) in non-weight-bearing. Post-cam engagement was observed in all knees, with the angle of flexion at engagement being larger in weight-bearing than in non-weight-bearing.

CONCLUSION

Although weight-bearing resulted in a posterior location of the medial and lateral contact points of the BCS-TKA design compared with non-weight-bearing in the mid-range of knee flexion, the amount of anterior translation was small overall. Therefore, BCS-TKA provides good stability during high-flexion weight-bearing activities. However, BCS-TKA is associated with high rate of the anterior engagement during early flexion. Therefore, understanding a patient's activities is an important factor when selecting the most appropriate TKA method.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee

PURPOSE

To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion.

METHODS

Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee.

RESULTS

At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation.

CONCLUSIONS

The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs.

LEVEL OF EVIDENCE

Level IV.

Knee implant kinematics are task-dependent

Although total knee arthroplasty (TKA) has become a standard surgical procedure for relieving pain, knowledge of the in vivo knee joint kinematics throughout common functional activities of daily living is still missing. The goal of this study was to analyse knee joint motion throughout complete cycles of daily activities in TKA subjects to establish whether a significant difference in joint kinematics occurs between different activities. Using dynamic videofluoroscopy, we assessed tibio-femoral kinematics in six subjects throughout complete cycles of walking, stair descent, sit-to-stand and stand-to-sit. The mean range of condylar anterior-posterior translation exhibited clear task dependency across all subjects. A significantly larger anterior-posterior translation was observed during stair descent compared to level walking and stand-to-sit. Local minima were observed at approximately 30° flexion for different tasks, which were more prominent during loaded task phases. This characteristic is likely to correspond to the specific design of the implant. From the data presented in this study, it is clear that the flexion angle alone cannot fully explain tibio-femoral implant kinematics. As a result, it seems that the assessment of complete cycles of the most frequent functional activities is imperative when evaluating the behaviour of a TKA design in vivo.

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.

Preoperative tibial mechanical axis orientation and articular surface design influence on the coronal joint line orientation relative to the ground during gait after total knee arthroplasties

PURPOSE

Neutral lower limb alignment does not necessarily produce a horizontal joint line after total knee arthroplasty (TKA). The orientation of the pre- and postoperative tibial mechanical axes (TMAs-G), tibial component, and joint line relative to the ground were evaluated.

METHODS

The study group included 46 knees, 23 posterior-stabilized (PS) and 23 bicruciate-stabilized (BCS) TKAs. Using whole-leg standing radiographs, the static orientation of the pre- and postoperative TMAs-G and the tibial component as well as the postoperative alignment were measured. Applying image-matching techniques, the dynamic coronal orientation of the tibial component and joint line over the stance phase of gait were analysed. The correlation between static and dynamic orientation of the tibial component and differences in the joint line between the PS and BCS TKAs were evaluated.

RESULTS

In standing, the postoperative TMA-G (0.8° ± 2.8°) and tibial component (1.5° ± 2.4°) were laterally tilted with a strong correlation. The preoperative lateral tilt of the TMA-G (7.9° ± 5.1°) was a significant predictor of the postoperative TMA-G. The lateral tilt of the tibial component increased to 5.1° ± 2.4° on dynamic analysis, and was moderately correlated to static orientation. The dynamic orientation of the joint line was smaller for the BCS (1.8° ± 2.4°) compared to the PS (5.5° ± 2.7°) TKA.

CONCLUSION

Even with a mechanically well-aligned TKA, a lateral tilt of the tibial component was identified due to the lateral tilt of the postoperative TMA-G and the stance phase of gait. The BCS can better accommodate the residual lateral tilt of the joint line due to the 3° medial inclination of the joint surfaces of the implant. This study increases the awareness of surgeons regarding the possibility of the coronal joint line orientation to influence preoperative TMA-G and be accommodated by articular surface design, even in mechanically aligned TKA.

LEVEL OF EVIDENCE

IV.

Patient-specific design for articular surface conformity to preserve normal knee mechanics in posterior stabilized total knee arthroplasty

BACKGROUND

Contemporary total knee arthroplasty (TKA) provides remarkable clinical benefits. However, the normal function of the knee is not fully restored. Recent improvements in imaging and manufacturing have utilized the development of customized design to fit the unique shape of individual patients.

OBJECTIVE

The purpose of the present study is to investigate the preservation of normal knee biomechanics by using specific articular surface conformity in customized posterior stabilized (PS)-TKA.

METHODS

This includes customized PS-TKA, PS-TKA with conforming conformity (CPS-TKA), medial pivot conformity with PS-TKA (MPS-TKA), and PS-TKA with mimetic anatomy femoral and tibial articular surface (APS-TKA). In this study, kinematics, collateral ligament force and quadriceps force were evaluated using a computational simulation under a deep knee bend condition.

RESULTS

A conventional TKA did not provide the normal internal tibial rotation with flexion leading to abnormal femoral rollback. The APS-TKA exhibited normal-like femoral rollback kinematics but did not exhibit normal internal tibial rotation. However, APS-TKA exhibited the most normal-like collateral ligament and quadriceps forces.

CONCLUSIONS

Although the APS-TKA exhibited more normal-like biomechanics, it did not restore normal knee biomechanics owing to the absence of the cruciate ligament and post-cam mechanism.

Bi-cruciate substituting total knee arthroplasty provides varus-valgus stability throughout the midflexion range

BACKGROUND

Proper soft tissue balance is crucial for a successful clinical outcome after total knee arthroplasty (TKA). Bi-cruciate substituting (BCS)-TKA has been developed to more closely approximate normal knee characteristics. The purpose of the present study was to evaluate midflexion laxity before and after BCS-TKA using a navigation system, and assess the correlation between intraoperative laxity and the maximum flexion angle after surgery.

METHODS

Fifty-one knees in 46 patients with osteoarthritis replaced with BCS prosthesis were assessed. Manual mild passive internal-external rotational and varus-valgus stress was applied to the knees, and the maximum total laxity was measured automatically by a navigation system before and after TKA. The correlations with the range of motion (ROM) were evaluated using Spearman's correlation coefficients (ρ).

RESULTS

Internal-external stress assessment revealed no statistically significant difference at each flexion angle before and after BCS-TKA. In contrast, the varus-valgus stress assessment revealed that BCS-TKA had significantly decreased varus-valgus laxity from preoperative levels at 20-120° flexion angles. Furthermore, the maximum flexion angle at six months after surgery significantly correlated with the intraoperative laxity at deep flexion range.

CONCLUSION

BCS-TKA stabilized varus-valgus laxity to better than preoperative levels at midflexion range.

Laxity and contact forces of total knee designed for anatomic motion: A cadaveric study

BACKGROUND

Total knee designs that attempt to reproduce more physiological knee kinematics are gaining attention given their possible improvement in functional outcomes. This study examined if a total knee designed for anatomic motion, where the soft tissue balancing was intended to replicate anatomical tibiofemoral contact forces, can more closely reproduce the laxity of the native knee.

METHODS

In an ex-vivo setting, the laxity envelope of the knees from nine lower extremity specimens was measured using a rig that reproduced surgical conditions. The rig allowed application of a constant varus/valgus (V/V) and internal-external (I/E) torque through the range of motion. After testing the native knee, total knee arthroplasty (TKA) was performed using the Journey II bi-cruciate substituting implant. Soft tissue balancing was guided by targeting anatomical compressive forces in the lateral and medial tibiofemoral joints with an instrumented tibial trial. After TKA surgery, the laxity tests were repeated and compared to the native condition.

RESULTS

The TKA knee closely reproduced the coronal laxity of the native knee, except for a difference at 90° of flexion for valgus laxity. Looking at the rotational laxity, the implant constrained the internal rotation relative to the native knee at 45 and 60° of flexion. The forces on the tibial trial for the neutral path of motion showed higher values on the medial side as the knee flexed.

CONCLUSIONS

This study suggested that when using an anatomically-designed knee, the soft tissue balancing should also aim for anatomical contact forces, which will result in close to normal laxity patterns.

Bi-cruciate stabilized total knee arthroplasty can reduce the risk of knee instability associated with posterior tibial slope

PURPOSE

The purpose of this study was to evaluate the relationship between posterior tibial slope and knee kinematics in bi-cruciate stabilized (BCS) total knee arthroplasty (TKA), which has not been previously reported.

METHODS

This computer simulation study evaluated Journey 2 BCS components (Smith & Nephew, Inc., Memphis, TN, USA) implanted in a female patient to simulate weight-bearing stair climbing. Knee kinematics, patellofemoral contact forces, and quadriceps forces during stair climbing (from 86° to 6° of flexion) were computed in the simulation. Six different posterior tibial slope angles (0°-10°) were simulated to evaluate the effect of posterior tibial slope on knee kinematics and forces.

RESULTS

At 65° of knee flexion, no anterior sliding of the tibial component occurred if the posterior tibial slope was less than 10°. Anterior contact between the anterior aspect of the tibial post- and the femoral component was observed if the posterior tibial slope was 6° or more. An increase of 10° in posterior tibial slope (relative to 0°) led to a 4.8% decrease in maximum patellofemoral contact force and a 1.2% decrease in maximum quadriceps force.

CONCLUSION

BCS TKA has a wide acceptable range of posterior tibial slope for avoiding knee instability if the posterior tibial slope is less than 10°. Surgeons should prioritize avoiding adverse effects over trying to achieve positive effects such as decreasing patellofemoral contact force and quadriceps force by increasing posterior tibial slope. Our study helps surgeons determine the optimal posterior tibial slope during surgery with BCS TKA; posterior tibial slope should not exceed 10° in routine clinical practice.

Knee kinematics in bi-cruciate stabilized total knee arthroplasty during squatting and stair-climbing activities

This study aimed to evaluate clinical outcomes and in vivo kinematics of bi-cruciate stabilized (BCS) total knee arthroplasty (TKA), using image-matching techniques. We analyzed tibiofemoral anteroposterior translation, axial rotation, and anterior/posterior cam-post contact for 22 BCS TKAs during squatting and stair-climbing. The functional activities on the 2011 Knee Society Score were significantly improved from 36 to 71. The tibiofemoral translation and axial rotation during squatting/stair-climbing were 16.1 mm/7.1 mm and 2.5° external/1.1° internal, respectively. Anterior/posterior cam-post contacts were observed during squatting (14%/96%) and stair-climbing (27%/96%). In conclusion, BCS TKA produced physiological sagittal plane kinematics during activities with favorable clinical outcomes.

Changes in total knee arthroplasty design affect in-vivo kinematics in a redesigned total knee system: A fluoroscopy study

BACKGROUND

Journey II Bi-Cruciate-Stabilized knee system was designed to overcome the complications of Journey Bi-Cruciate-Stabilized, including ilio-tibial band inflammation and episodes of dislocation. The purpose of this study was to assess differences in knee kinematics between the first and second-generation design by means of video-fluoroscopy. Re-designed prosthesis in-vivo kinematics was analyzed during activities of daily living and results were eventually compared with those of the previous system, as reported in a previously published study. It was hypothesized that changes in components' design influences replaced knee's kinematic patterns.

METHODS

Sixteen patients (3 males, 13 females) implanted with the redesigned prosthesis were assessed by video-fluoroscopy during stair-climbing, chair-rising and leg-extension at 8 months of follow-up. Patterns of axial rotation and antero-posterior motion of the medial and lateral femoral condyles were obtained. Range of Motion and International Knee Society Score were recorded pre- and post-operatively. Student t-tests were applied to compare the mean of each interesting variables.

FINDINGS

The comparison of the kinematics of the two designs revealed similar patterns of axial rotation, with progressive femoral external rotation in flexion and reduced absolute values of displacement for the new system. Reduced posterior displacements of the medial and lateral condyles were observed in Journey II patients. In terms of absolute location, the lateral condyle in the redesigned prosthesis showed a more anterior position on the tibial-baseplate embedded coordinate system at maximal flexion.

INTERPRETATION

Design changes in the recently-introduced total knee system contributed to modify its in-vivo knee kinematics as demonstrated by video-fluoroscopy.

In Vivo Kinematic Comparison of a Bicruciate Stabilized Total Knee Arthroplasty and the Normal Knee Using Fluoroscopy

BACKGROUND

The bicruciate stabilized (BCS) total knee arthroplasty (TKA) features asymmetrical bearing geometry and dual substitution for the anterior cruciate ligament and posterior cruciate ligament (PCL). Previous TKA designs have not fully replicated normal knee motion, and they are characterized by lower magnitudes of overall rollback and axial rotation than the normal knee.

METHODS

In vivo kinematics were derived for 10 normal knees and 40-second generation BCS TKAs all implanted by a single surgeon. Mobile fluoroscopy and three-dimensional-to-two-dimensional registration was used to analyze anterior-posterior motion of the femoral condyles and femorotibial axial rotation during weight-bearing flexion. Statistical analysis was conducted at the 95% confidence level.

RESULTS

From 0° to 30° of knee flexion, the BCS subjects exhibited similar patterns of femoral rollback and axial rotation compared to normal knee subjects. From 30° to 60° of knee flexion, BCS subjects experienced negligible anterior-posterior motions and axial rotation while normal knees continued to rollback and externally rotate. Between 60° and 90° the BCS resumed posterior motion and, after 90°, axial rotation increased in a normal-like fashion.

CONCLUSION

Similarities in early flexion kinematics suggest that the anterior cam-post is supporting normal-like anterior-posterior motion in the BCS subjects. Likewise, lateral femoral rollback and external rotation of the femur in later flexion provides evidence for appropriate substitution of the PCL via the posterior cam-post. Being discrete in nature, the dual cam-post mechanism does not lend itself to adequate substitution of the cruciate ligaments in mid-flexion during which anterior cruciate ligament tension is decreasing and PCL tension is increasing in the normal knee.

Second-generation bi-cruciate stabilized total knee system has a lower reoperation and revision rate than its predecessor

INTRODUCTION

Total knee arthroplasty (TKA) can provide pain relief and good long-term results. However, nearly 30% of post-surgical patients are unsatisfied due to persistent pain and functional deficits. A second-generation bi-cruciate stabilized TKA device has a post-cam mechanism with an asymmetric femoral component, a polyethylene insert, and a medially concave and laterally convex shape. The device is designed to provide guided motion, and thus improve knee kinematics by more closely approximating a normal knee. The aim of this study was to evaluate early complication and revision rates of the second-generation device and to compare its clinical performance to the first-generation device.

MATERIALS AND METHODS

In this retrospective, longitudinal, non-concurrent cohort study, 140 TKAs were performed using the second-generation device on 131 patients from 2012 to 2016, and 155 TKAs were performed using the first-generation device on 138 patients from 2009 to 2012. Primary outcomes were occurrence of revisions and reoperations.

RESULTS

There were 31 reoperations [3.21 per 100 observed component years (OCY)] in 22 (2.28 per 100 OCY) TKAs in the first-generation device cohort compared to five reoperations (1.92 per 100 OCY) in four TKAs (1.54 per 100 OCY) in the second-generation device cohort. The adjusted hazard ratio (HR) was 3.50 (P = 0.0254). There were 21 revisions (2.17 per 100 OCY) in 16 (1.66 per 100 OCY) TKAs in the first-generation device cohort, compared to only three revisions (1.15 per 100 OCY) in two TKAs (0.77 per 100 OCY) in the second-generation device cohort. The adjusted HR was 4.16 (P = 0.0693).

CONCLUSION

The improved design of the second-generation device appears to be associated with a lower risk of reoperation and revision compared to that of the first-generation device.

LEVEL OF EVIDENCE

III.

Errors in Calculating Anterior–Posterior Tibial Contact Locations in Total Knee Arthroplasty Using Three-Dimensional Model to Two-Dimensional Image Registration in Radiographs: An In Vitro Study of Two Methods

Knowledge of anterior–posterior (A-P) tibial contact locations provides an objective assessment of the relative motion of the tibia on the femur following total knee arthroplasty (TKA), which can be used to compare the effects of different components, surgical techniques, and alignment goals on knee function in vivo. Both the lowest point method and the penetration method have been used to calculate A-P tibial contact locations using three-dimensional (3D) model to two-dimensional (2D) image registration. The primary objective of this study was to quantify errors in calculating the A-P tibial contact location using the lowest point and penetration methods because the errors in calculating the A-P tibial contact locations using these two methods are unknown. The A-P tibial contact locations were calculated with the two methods and simultaneously measured with a tibial force sensor in ten fresh-frozen cadaveric knee specimens with a TKA. Single-plane radiographs of the knee specimens were acquired at 0 deg, 30 deg, 60 deg, and 90 deg of flexion in neutrally, internally, and externally rotated orientations. While the radiographs were exposed, reference A-P tibial contact locations were simultaneously collected using the tibial force sensor to be compared to the calculated A-P tibial contact locations. The overall root-mean-squared-errors (RMSEs) in the A-P tibial contact location calculated with the lowest point method, the penetration method with penetration, and penetration method without penetration were 5.5 mm, 3.6 mm, and 8.9 mm, respectively. The overall RMSE was lowest for the penetration method with penetration, making it the superior method for calculating A-P tibial contact locations.

Design and virtual evaluation of a customized surface-guided knee implant

Although total knee arthroplasty is generally a successful operation, many studies have shown that it results in significant alterations in the kinematics of the joint, which cause limitations in performing the activities of daily living. This study aimed to define the design features for a customized surface-guided total knee replacement and to evaluate the kinematic outcomes. Magnetic resonance imaging data of the knee joint are used to generate the design features as they relate to the functionality of the implant. The motion is guided by considering a partial ball and socket configuration on the medial condyle and varying radii of curvature on the lateral articulating surface. A virtual simulation of the behavior of the surface-guided total knee replacement was performed to investigate the motion patterns of this total knee replacement under gait and squatting loading conditions. Results of the virtual simulation show that flexion and extension of the knee make the center of the lateral condyle move more naturally in the posterior and anterior directions, in comparison to the center of the medial condyle. Such guidance is achieved as a result of the novel customized designed contact between the articulating surfaces. The proposed customized surface-guided total knee replacement provides patterns of motion close to the expected more natural target, not only during a gait cycle but also as the knee flexes to higher degrees during squatting. Major design features include location and orientation of the flexion and pivoting axes, the trace of the contact points on the tibia, and the radii of the guiding arcs on the lateral condyle.

Histopathological Evaluation of the Anterior Cruciate Ligament in Patients Undergoing Primary Total Knee Arthroplasty

This study assessed gross and histopathological ACL changes in arthritic knees (n=174) undergoing total knee arthroplasty. Histopathological changes were assessed and graded as absent (0), mild (1), moderate (2), or marked (3). These were correlated to demographic and clinical factors, and radiographic evaluations. The ACL was intact in 43, frayed in 85, torn in 15, and absent in 31 knees. Eighty-five percent had histological changes. Overall, there were significant associations between greater age and BMI, and histological changes. Grade IV knees had significantly greater calcium pyrophosphate deposits, microcyst formation, and number of pathologic changes. These correlations may aid decision-making when determining suitability for unicompartmental or bicruciate-retaining arthroplasties, though further studies should correlate these histological findings to mechanical and functional knee status.

Fluoroscopic motion study confirming the stability of a medial pivot design total knee arthroplasty

BACKGROUND

The ideal total knee arthroplasty should provide maximum range of motion and functional stability for all desired daily activities. The SAIPH™ (MatOrtho; UK) knee has a medial pivot knee kinematic pattern designed to achieve medial stability and an asymmetric posterior translation of the lateral femoral condyle during knee flexion and in this way attempts to mimic the natural knee motion. This study aims to analyze knee kinematics of the SAIPH™ total knee arthroplasty (TKA) by videofluoroscopy during four different weightbearing activities.

METHODS

Fourteen consecutive patients operated on by a single surgeon, with a minimum follow-up of 24 months were included in this IRB-approved study. There were no exclusions based on patient's functional level. A medially conforming knee was implanted in all cases. Participants in the study were asked to perform the clinically relevant functional activities of pivoting, kneeling, lungeing and step-up/down activities while their knee motion was recorded by videofluoroscopy.

RESULTS

Maximum knee flexion during the kneeling activity mean 127° (100°-155°). An asymmetric posterior translation of the lateral femoral condyle (LFC) was observed during pivoting, kneeling, lungeing and stepping. No paradoxical anterior translation of the femoral condyles was observed in any activity.

CONCLUSION

The kinematics observed in this implant are similar in pattern, although smaller in magnitude, to normal functional knees, showing a posterior translation of the lateral femoral condyle during knee flexion, with internal rotation of the tibia, and no paradoxical anterior motion in any of the four weight bearing activities.

Continuous sagittal radiological evaluation of stair-climbing in cruciate-retaining and posterior-stabilized total knee arthroplasties using image-matching techniques

In this study, we evaluated the in vivo kinematics of stair-climbing after posterior stabilized (PS) and cruciate retaining (CR) total knee arthroplasty (TKA) using radiographic-based image-matching techniques. Mid-flexion anteroposterior stability was demonstrated in all knees after CR TKA. However, paradoxical femoral translation at low flexion angles was seen in both designs. The post-cam mechanism did not function after PS TKA. Larger posterior tibial slope in PS TKA was linked to forward sliding of the femur at mid-flexion and unintended anterior tibial post impingement at knee extension. CR TKA is more sagittally stable in mid-flexion during stair climbing and attention must be given to minimize posterior tibial slope when using late cam-post engaging PS TKA designs.

Patellofemoral kinematics during deep knee flexion after total knee replacement: a computational simulation

PURPOSE

Actions requiring deep knee flexion, such as kneeling and squatting, are challenging to perform after total knee replacement (TKR), though many manufactures emphasize that their knee prostheses could safely achieve high flexion. Little is known about the patellofemoral kinematics during deep flexion. This study aimed to track the movement of the patella during kneeling and squatting through dynamic computational simulation.

METHODS

A validated knee model was used to analyse the patellar kinematics after TKR, including shifting, tilting and rotation. The data were captured from full extension to 135° of knee flexion. For kneeling, an anterior force of 500 N was applied perpendicularly on the tibial tubercle as the knee flexed from 90° to 135°. For squatting, a ground reaction force was applied through the tibia from full extension to 135° of flexion.

RESULTS

This study found that patellar shifting and rotation in kneeling were similar to those while squatting. However, during kneeling, the patella had a greater medial tilt and showed signs of abrupt patellar tilt owning to an external force being concentrated on the tibial tubercle.

CONCLUSIONS

In terms of squatting and kneeling movements, the latter is a more strenuous action for the patellofemoral joint after TKR due to the high forces acting on the tibial tubercle. It is suggested that overweight patients or those requiring high flexion should try to avoid kneeling to reduce the risk of the polyethylene wear. Further modification of trochlear geometry may be required to accommodate abrupt changes in patellar tilting.

LEVEL OF EVIDENCE

II.

The effect of posterior tibial slope on knee flexion in posterior-stabilized total knee arthroplasty

PURPOSE

To evaluate and quantify the effect of the tibial slope on the postoperative maximal knee flexion and stability in the posterior-stabilized total knee arthroplasty (TKA).

METHODS

Fifty-six patients (65 knees) who had undergone TKA with the posterior-stabilized prostheses were divided into the following 3 groups according to the measured tibial slopes: Group 1: ≤4°, Group 2: 4°-7° and Group 3: >7°. The preoperative range of the motion, the change in the posterior condylar offset, the elevation of the joint line, the postoperative tibiofemoral angle and the preoperative and postoperative Hospital for Special Surgery (HSS) scores were recorded. The tibial anteroposterior translation was measured using the Kneelax 3 Arthrometer at both the 30° and the 90° flexion angles.

RESULTS

The mean values of the postoperative maximal knee flexion were 101° (SD 5), 106° (SD 5) and 113° (SD 9) in Groups 1, 2 and 3, respectively. A significant difference was found in the postoperative maximal flexion between the 3 groups (P < 0.001). However, no significant differences were found between the 3 groups in the postoperative HSS scores, the changes in the posterior condylar offset, the elevation of the joint line or the tibial anteroposterior translation at either the 30° or the 90° flexion angles. A 1° increase in the tibial slope resulted in a 1.8° flexion increment (r = 1.8, R (2) = 0.463, P < 0.001).

CONCLUSION

An increase in the posterior tibial slope can significantly increase the postoperative maximal knee flexion. The tibial slope with an appropriate flexion and extension gap balance during the operation does not affect the joint stability.

Posterior sliding of the femur during stair ascending and descending in a high-flex posterior stabilized total knee arthroplasty

This study investigated the anteroposterior stability of the femur during stair motions. We examined 18 knees with a clinically successful high-flexion posterior stabilized total knee arthroplasty to evaluate the in vivo kinematics of stair ascending and descending using two- to three-dimensional registration. Posterior sliding of the femur was observed while shifting weight to the leg during stair ascending and descending in almost all knees. Anterior tibial post impingement was observed in 10 knees when the knee was extended in stair ascending, whereas in stair descending, the impingement was observed in 14 knees when posterior sliding of the femur occurred. The impingement contributed to the stabilization of the knee during stair motion; however, impingement may result in additional polyethylene wear and tibial post failure.

Three-dimensional motion analysis of the human knee joint: comparison between intra- and post-operative measurements

PURPOSE

To compare intra-operative knee joint kinematic measurements immediately after total knee replacement with those of the same patients post-operatively at 6-month follow-up.

METHODS

Fifteen patients who underwent total knee arthroplasty were analysed retrospectively. Eight were implanted with one prosthesis design and seven with another. The intra-operative measurements were performed by using a standard knee navigation system. This provided accurate three-dimensional positions and orientations for the femur and tibia by corresponding trackers pinned into the bones. At 6-month follow-up, the patients were analysed by standard three-dimensional video-fluoroscopy of the replaced knee during stair climbing, chair rising and step-up. Relevant three-dimensional positions and orientations were obtained by an iterative shape-matching procedure between the silhouette contours and the CAD-model projections. A number of traditional kinematic parameters were calculated from both measurements to represent the joint motion.

RESULTS

Good post-operative replication of the intra-operative measurements was observed for most of the variables analysed. The statistical analysis also supported the good consistency between the intra- and post-operative measurements.

CONCLUSIONS

Intra-operative kinematic measurements, accessible by a surgical navigation system, are predictive of the following motion performance of the replaced knees as experienced in typical activities of daily living.

LEVEL OF EVIDENCE

Prognostic studies--investigating natural history and evaluating the effect of a patient characteristic, Level II.

In vivo kinematics of the knee during weight bearing high flexion

Achieving high flexion is an objective of contemporary total knee arthoplasty; however little is known on the knee biomechanics at high flexion under weight-bearing conditions. This study investigates the 6DOF kinematics and tibiofemoral cartilage contact biomechanics of the knee during weight-bearing flexion from full extension to maximal flexion. Eight knees from seven healthy subjects with no history of injuries or chronic pain were recruited. The knees were MRI scanned to create 3D models of the tibia and femur, including their articular cartilage surfaces. The subjects were then imaged using a dual fluoroscopic image system while performing a weight-bearing quasi-static single-legged lunge from full extension to maximal flexion. The 6DOF kinematics and the articular cartilage contact locations were measured along the flexion path of the knee. The result indicated that the internal tibial rotation increased sharply at low flexion angles (full extension to 30°), maintained a small variation in the middle range of flexion (30-120°, and then sharply increased again at high flexion angles (120° to maximal flexion). The contact point moved similarly in the medial and lateral compartments before 120° of flexion, but less on the medial compartment at high flexion angles. The results indicated that the knee motion could not be described using one character in the entire range of flexion, especially in high flexion. The knee kinematic data in the entire range of flexion of the knee could be instrumental for designing new knee prostheses to achieve physical high flexion and improving rehabilitation protocols after knee injuries.