Mobile-bearing insert translational and rotational kinematics in a PCL-retaining total knee arthroplasty

Rotational Soft-Tissue Balance Is Highly Correlated with Rotational Kinematics in Total Knee Arthroplasty

Recovery of normal knee kinematics is critical for improving functional outcomes and patient satisfaction after total knee arthroplasty (TKA). The kinematics pattern after TKA varies from case to case, and it remains unclear how to reproduce normal knee kinematics. The present study aimed to evaluate rotational knee kinematics and soft-tissue balance using a navigation system and to assess the influence of intraoperative soft-tissue balance on the rotational knee kinematics. We evaluated 81 osteoarthritic knees treated with TKA using a posterior stabilized (50 knees) or cruciate retaining (31 knees) prosthesis. Rotational kinematics were assessed at 0, 30, 45, 60, and 90 degrees flexion angles by using a computer-assisted navigation system. Correlation between femorotibial rotational position and measured soft tissue balance was assessed by using Spearman's rank correlation coefficient. Rotational soft-tissue balance (the median angle of rotational stress) was significantly correlated with rotational kinematics (rotational axis of the femur relative to the tibia throughout the range of motion) at all measured angles after TKA. The correlation coefficients between the median angle of rotational stress and rotational kinematics were 0.97, 0.80, 0.74, 0.71, and 0.70 at 0, 30, 45, 60, and 90 degrees of flexion, respectively (p-values <0.0001 in all measured angles). The correlation coefficient increased as the knee approached full extension. Our findings suggest that soft-tissue balance is a key factor for rotational kinematics, following both cruciate-retaining and posterior-stabilized TKA.

[Effectiveness comparison of mobile-bearing and fixed-bearing prostheses in total knee arthroplasty for ten years follow-up]

Objective

To compare the clinical results of mobile-bearing and fixed-bearing prostheses in total knee arthroplasty (TKA) during 10 years follow-up so as to provide a reference for clinical selection of TKA prosthesis.

Methods

Between January 2002 and December 2005, 113 patients with osteoarthritis of the knee joint underwent primary TKA, and the clinical data were retrospectively analyzed. Mobile-bearing prosthesis was used in 47 cases (group A) and fixed-bearing prosthesis in 66 cases (group B). There was no significant difference in age, gender, body mass index, varus and flexion deformity of the knee, range of motion (ROM) of the knee, knee society score (KSS), and Western Ontario and McMaster University Osteoarthritis Index (WOMAC) between 2 groups before operation ( P>0.05), so the data were comparable.

Results

The operation time of groups A and B was (88.1±6.5) and (90.3±7.2) minutes respectively, showing no significant difference ( t=1.666, P=0.099). The wounds healed by first intention in all patients of both groups, and no postoperative early complications of incision infection and deep venous thrombosis occurred. The follow-up time was 10.2-12.3 years (mean, 10.8 years) in group A, and was 10.2-12.6 years (mean, 11.3 years) in group B. Revision was performed in 3 cases of group A and 4 cases of group B; the survival rates of prosthesis were 93.6% and 93.9% in groups A and B respectively, showing no significant difference ( χ²=0.005, P=0.944). The postoperative knee ROM, KSS score, and WOMAC score were significantly improved when compared with preoperative ones ( P<0.05). The knee ROM and KSS score of group B were significantly better than those of group A at 6 weeks after operation ( P<0.05), but no significant difference was found between 2 groups at 1, 3, and 10 years after operation ( P>0.05). The WOMAC score of group A was significantly better than that of group B at 10 years after operation ( t=2.086, P=0.037), but no significant difference was shown at 6 weeks, 1 year, and 3 years after operation ( P>0.05). At 10 years after operation, the excellent and good rate of KSS score was 87.2% in group A and was 84.8% in group B, showing no significant difference ( χ²=0.018, P=0.893).

Conclusion

Good medium- and long-term clinical results can be achieved in TKA with both mobile-bearing and fixed-bearing prostheses. The TKA with fixed-bearing prosthesis is relatively simple with better early effectiveness of rehabilitation; and the TKA with mobile-bearing prosthesis could provide better long-term degree of satisfaction in WOMAC score, but a higher surgical skill and soft tissue balance techniques are needed.

Location of the natural knee axis for internal-external tibial rotation

BACKGROUND

Rotating hinge and mobile bearing tray knee replacement designs utilize a single fixed axis for tibial rotation, yet there is little published information regarding the natural internal-external axis (IEA) for tibial rotation. Identifying the IEA should provide an opportunity for reproducing normal knee kinematics and maintaining the balance of forces in the soft tissues that help control rotation of the tibia.

METHODS

The location and orientation of the IEA relative to the tibial plateau were calculated in 46 fresh frozen human cadaveric specimens using an instant center of rotation analysis at fixed knee flexion angles ranging from five degrees to 105°.

RESULTS

IEA location ranged from 4.0 to 4.9mm medial and 1.7 to 5.5mm posterior to the center of the tibial plateau (from 5° to 105° of knee flexion). IEA orientation was reported relative to a reference axis perpendicular to the plane of the tibial plateau. In the frontal plane, the IEA was not significantly different from the reference axis from five degrees to 45° flexion, and 2.0° to 2.7° valgus to the reference axis from 60° to 105° flexion. In the sagittal plane, the IEA was not significantly different from the reference axis from 5° to 15° flexion, and 3.0° to 7.0° extended from the reference axis from 30° to 105° flexion.

CONCLUSIONS

The IEA moves posteriorly with increasing knee flexion on the tibial plateau. Placement of the IEA relative to the tibial plateau for a rotating hinge or mobile bearing tray implant may represent a compromise between design objectives for moderate and deeper knee flexion.

CLINICAL RELEVANCE

This study has relevance for future knee implant designs.

No difference in ROM and knee function between mobile and floating platforms in TKA

PURPOSE

The purpose of this study was to determine whether the floating platforms (FP) were superior to rotating platforms (RP) in computer-navigated total knee arthroplasty (TKA) comparing the range of motion (ROM) as well as clinical and subjective function of the knee.

METHODS

This retrospective non-randomized single-centre cohort study includes 255 patients with a primary implanted computer-navigated e.motion™ (Aesculap B. Braun) TKA system, implanted because of clinical and radiological verified gonarthrosis. In 129 patients, the FP platform was implanted, and in 126 patients, the RP platform. As statistical procedures for differences between inlay type RP/FP in ROM and Knee Society Score (KSS) after 3- and 24-month follow-up, an analysis of covariance (with risk factors gender, age, BMI, preoperative ROM and preoperative KSS) was performed.

RESULTS

Although preoperative ROM and knee society function score (KSS part II) were significantly higher in the FP group before surgery, there was no significant difference between RP and FP in ROM and KSS at 3- and 24-month follow-up.

CONCLUSION

The FP platform design did not have an advantage in ROM as well as in clinical and subjective knee function compared with the RP platform in computer-navigated TKA neither in early follow-up examinations at 3 months postoperatively nor at long-time follow-up at 24 months postoperatively.

Single-radius, multidirectional total knee replacement

PURPOSE

The present study was designed to evaluate the mid-term (5- to 8-year) survival rate of a new total knee replacement (TKR) with a single-radius femoral component and a multidirectional, highly congruent tibial component, in comparison with an historical group (TKR with multi-radius design and fixed bearing).

METHODS

Four hundred and thirty patients were included, of which 369 patients (86 %) completed the 5-year follow-up with Knee Society Score evaluation and radiograph examination (study group = 387, control group = 83).

RESULTS

There was a significant improvement for all analysed items between pre-operative status and late follow-up. Mean knee score was 93 ± 9 points in the study group and 88 ± 16 points in the control group (p < 0.001). Mean flexion angle was not different (118 ± 11 vs. 114 ± 13 degrees). Mean functional score was 87 ± 16 points in the study group and 71 ± 24 points in the control group (p < 0.001). Survival rate at 5-year follow-up was 98.8 % (vs. 98.0 %) for mechanical revisions only, and 96.4 % (vs. 98.1 %) for all revisions.

CONCLUSIONS

The new TKR allowed obtaining significantly better results than the fixed-bearing TKR. These results are in line with the best series published in the current literature, but there was no evidence of any superiority of this TKR against already published standards.

[Spin out - an avoidable complication in total knee replacement]

Spin out of a rotating polyethylene (PE) platform after total knee replacement leads to rotation of the bearing compared to the fixed metal components of the prosthesis at the femur and tibia of approximately 90°. This complication occurs only in prosthesis designs which do not have a rotation limitation. Identification of this complication and its management are described exemplified by two cases. Strategies to avoid spin out are discussed. The most promising way is to avoid using prosthesis designs in which spin out can occur.

Comparison of fixed- and mobile-bearing total knee arthroplasty with a mean five-year follow-up: A meta-analysis

Controversy exists regarding the clinical and radiological differences in outcomes between fixed-bearing (FB) and mobile-bearing (MB) total knee arthroplasties (TKAs) at the mid- or long-term follow-up. We therefore conducted a meta-analysis and systematic review of randomized controlled trials (RCTs) that have evaluated FB and MB TKAs. We searched the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library, Medline and Embase. The data, including demographic information, methodological quality, duration of follow-up, clinical and radiographical outcomes, patient preferences and complications, were extracted. The methodological quality of the studies was assessed in accordance with the guidelines presented in the Cochrane Handbook for Systematic Reviews of Interventions. Nine trials, studying 1,821 knees, were eligible for data extraction and meta-analysis. The Knee Society score and the maximum knee flexion demonstrated no difference between the FB and MB groups (P=0.47 and P=0.72, respectively). Similarly, no difference was revealed between the groups for radiological outcomes or general health results. An increased number of high-quality RCTs with long-term follow-ups are required to validate the results.

Kinematics of a highly congruent mobile-bearing total knee prosthesis

PURPOSE

Limited or absent axial rotation of the mobile insert of total knee prostheses could lead to high contact stresses and stresses at the bone-implant interface, which in turn might lead to implant loosening. The aim of this study was to assess knee kinematics and muscle activation and their possible change over time in patients with a highly congruent, mobile-bearing total knee prosthesis.

METHODS

A prospective series of 11 rheumatoid arthritis patients was included to participate in this fluoroscopic and EMG study; only 7 patients completed the study. Kinematic evaluations took place 7 months, 1 and 2 years post-operatively. Repeated measurements ANOVA and linear mixed-effects model for longitudinal data were used to compare the differences between the follow-ups.

RESULTS

There are no significant changes in axial rotations between follow-up moments for the femoral component as well as the mobile insert. The insert remained mobile and followed the femoral component from 0° until approximately 60° of knee flexion. Diverging and reversed axial rotations and translations were seen during the dynamic motions.

CONCLUSIONS

Knee kinematics and muscle activation do not appear to change in the first 2 post-operative years. Reversed and divergent axial rotations with increasing knee flexion indicate that as soon as the congruency decreases, the femoral component is no longer forced in a certain position by the insert and moves to a self-imposed position. At lower knee flexion angles, the femoral component might be obstructed by the highly congruent insert and therefore might not be able to move freely.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

Prosthesis alignment affects axial rotation motion after total knee replacement: a prospective in vivo study combining computed tomography and fluoroscopic evaluations

Background

Clinical consequences of alignment errors in total knee replacement (TKR) have led to the rigorous evaluation of surgical alignment techniques. Rotational alignment in the transverse plane has proven particularly problematic, with errors due to component malalignment relative to bone anatomic landmarks and an overall mismatch between the femoral and tibial components’ relative positions. Ranges of nominal rotational alignment are not well defined, especially for the tibial component and for relative rotational mismatch, and some studies advocate the use of mobile-bearing TKR to accommodate the resulting small rotation errors. However, the relationships between prosthesis rotational alignment and mobile-bearing polyethylene insert motion are poorly understood. This prospective, in vivo study evaluates whether component malalignment and mismatch affect axial rotation motions during passive knee flexion after TKR.

Methods

Eighty patients were implanted with mobile-bearing TKR. Rotational alignment of the femoral and tibial components was measured from postoperative CT scans. All TKR were categorized into nominal or outlier groups based on defined norms for surgical rotational alignment relative to bone anatomic landmarks and relative rotational mismatch between the femoral and tibial components. Axial rotation motion of the femoral, tibial and polyethylene bearing components was measured from fluoroscopic images acquired during passive knee flexion.

Results

Axial rotation motion was generally accomplished in two phases, dominated by polyethylene bearing rotation on the tibial component in early to mid-flexion and then femoral component rotation on the polyethylene articular surface in later flexion. Opposite rotations of the femur-bearing and bearing-baseplate articulations were evident at flexion greater than 80°. Knees with outlier alignment had lower magnitudes of axial rotation and distinct transitions from external to internal rotation during mid-flexion. Knees with femoral-tibial rotational mismatch had significantly lower total axial rotation compared to knees with nominal alignment.

Conclusions

Maintaining relative rotational mismatch within ±5° during TKR provided for controlled knee axial rotation during flexion. TKR with rotational alignment outside of defined surgical norms, with either positive or negative mismatch, experienced measurable kinematic differences and presented different patterns of axial rotation motions during passive knee flexion compared to TKR with nominal mismatch. These findings support previous studies linking prosthesis rotational alignment with inferior clinical and functional outcomes.

Trial Registration

Clinical Trials NCT01022099

Reproducibility of an optical measurement system for the clinical evaluation of active knee rotation in weight-bearing, healthy subjects

INTRODUCTION

A knee is typically evaluated passively by a clinician during an office visit, without using dedicated measurement tools. When the knee is evaluated with the patient standing and actively participating in the movement, the results will differ than when the knee is passively moved through its range-of-motion by the surgeon. If a precise measurement system was available, it could provide additional information to the clinician during this evaluation.

HYPOTHESIS

The goal of this study was to verify the reproducibility of a fast, flexible optical measurement system to measure rotational knee laxity during weight-bearing.

MATERIAL AND METHODS

Two passive reflective targets were placed on the legs of 11 subjects to monitor femur and tibia displacements in three dimensions. Subjects performed internal and external rotation movements with the knee extended or flexed 30°. During each movement, seven variables were measured: internal rotation, external rotation and overall laxity in extension and 30° flexion, along with neutral rotation value in 30° flexion. Measurement accuracy was also assessed and the right and left knees were compared. Reproducibility was assessed over two measurements sessions.

RESULTS

The calculated intra-class correlation coefficient (ICC) for reproducibility was above 0.9 for five of the seven variables measured. The calculated ICC for the right/left comparison was above 0.75 for five of the seven variables measured.

DISCUSSION

These results confirmed that the proposed system provides reproducible measurements. Our right/left comparison results were consistent with the published literature. This system is fast, reproducible and flexible, which makes it suitable for assessing various weight-bearing movements during clinical evaluations.

LEVEL OF EVIDENCE

Level III, experimental study.

Wear damage in mobile-bearing TKA is as severe as that in fixed-bearing TKA

BACKGROUND

Mobile-bearing TKAs reportedly have no clinical superiority over fixed-bearing TKAs, but a potential benefit is improved polyethylene wear behavior.

QUESTIONS/PURPOSES

We asked whether extent of damage and wear patterns would be less severe on retrieved mobile-bearing TKAs than on fixed-bearing TKAs and if correlations with patient demographics could explain differences in extent or locations of damage.

METHODS

We performed damage grading and mapping of 48 mobile-bearing TKAs retrieved due to osteolysis/loosening, infection, stiffness, instability or malpositioning. Visual grading used stereomicroscopy to identify damage, and a grade was assigned based on extent and severity. Each damage mode was then mapped onto a photograph of the implant surface, and the area affected was calculated.

RESULTS

Marked wear damage occurred on both surfaces, with burnishing, scratching, and pitting the dominant modes. Damage occurred over a large portion of both surfaces, exceeding the available articular borders in nearly 30% of implants. Wear of mobile-bearing surfaces included marked third-body debris. Damage on tibiofemoral and mobile-bearing surfaces was not correlated with patient BMI or component alignment. Damage on mobile-bearing surfaces was positively correlated with length of implantation and was greater in implants removed for osteolysis or instability than in those removed for stiffness or infection.

CONCLUSIONS

Each bearing surface in mobile-bearing implants was damaged to an extent similar to that in fixed-bearing implants, making the combined damage score higher than that for fixed-bearing implants. Mobile-bearing TKAs did not improve wear damage, providing another argument against the superiority of these implants over fixed-bearing implants.