In vivo kinematics of high-flex mobile-bearing total knee arthroplasty, with a new post-cam design, in deep knee bending motion

Clinical usefulness and safety in the early phase after a newly designed rotating-platform total knee arthroplasty: A prospective multicentre cohort study with a 2-year follow up

BACKGROUND

This study aimed to assess the clinical results and safety of a newly designed rotating-platform posterior-stabilised total knee arthroplasty (TKA) in the early postoperative phase, within 2 years of follow up.

METHODS

This prospective, multicentre cohort study included 100 consecutive patients who underwent rotating-platform posterior-stabilised (PS) TKA (Vanguard PSRP). After excluding dropouts, 93 patients were analysed. The objective Knee Society Score (KSS)-2011, subjective KSS-2011, knee range of motion, EuroQol 5 Dimension index, complications, and survival rates were assessed before TKA and at 6 months, 1 year, and 2 years postoperatively. The scores at each time-point were compared, and the survival rate was assessed with revision as the endpoint. To demonstrate non-inferiority, the clinical outcomes of patients who underwent rotating-platform PS TKA were compared with those collected retrospectively from 50 patients who underwent fixed-PS TKA (Vanguard PS), defined as the control group.

RESULTS

All clinical outcomes at the final follow up significantly improved compared with their preoperative values (P < 0.001). The objective KSS-2011 was 90.0 ± 8.2 points, subjective KSS-2011 satisfaction was 30.7 ± 8.6 points, expectation was 10.4 ± 2.1 points, and functional activity was 74.0 ± 18.5 points at 2 years postoperatively. Complications included knee dislocation in one patient and surgical site infection in one patient. The survival rate was 99% at 2 years postoperatively. Clinical outcomes, complications, and survival rates of newly designed TKA were not statistically different compared with the control group.

CONCLUSION

The newly designed rotating-platform PS TKA showed good clinical results and suitable safety during the early postoperative phase in this prospective multicentre cohort study.

The Association between In Vivo Knee Kinematics and Patient-Reported Outcomes during Squatting in Bicruciate-Stabilized Total Knee Arthroplasty

Bicruciate-stabilized total knee arthroplasty (BCS TKA) has been developed to improve TKA kinematic performance. However, the relationship between in vivo kinematics and patient-reported outcomes (PROs) has not been well described. This study was performed to clarify the relationship between in vivo kinematics and PROs in a cohort of patients undergoing BCS TKA. Forty knees were evaluated using a two-dimensional to three-dimensional registration technique obtained from sagittal plane fluoroscopy. In vivo kinematics including anteroposterior (AP) translation and tibiofemoral rotation were evaluated. Knee Society scores (KSSs) and Knee injury and Osteoarthritis Outcome Scores (KOOSs) were assessed before and after surgery. Relationships between tibiofemoral kinematics assessed with the knee in different positions of knee flexion and PROs were evaluated using Spearman's correlation analysis. The study demonstrated a significant negative correlation (r =  - 0.33) between medial AP translation from minimum flexion to 30 degrees flexion and postoperative KOOS activities of daily living subscale. A significant positive correlation (r = 0.51) was found between the femoral external rotation from minimum flexion to 30 degrees flexion and improvement of the KOOS pain subscale. No correlation was found between the lateral AP translation and PROs. Achieving medial AP and femoral external rotation stability in early flexion may be important in optimizing postoperative PROs.

Efficacy and safety of duloxetine for postoperative pain after total knee arthroplasty in centrally sensitized patients: study protocol for a randomized controlled trial

Background

Postoperative residual knee pain after total knee arthroplasty (TKA) is a significant factor that contributes to patient dissatisfaction. Patients with preoperative central sensitization (CS) may be more susceptible to unexplained chronic pain after TKA, and duloxetine has been reported to be effective in post-TKA pain control in patients with CS. However, there remains limited evidence to support this off-label use in routine clinical practice. Hence, we designed this randomized, placebo-controlled, triple-blind clinical trial to evaluate the effects of preoperative screening and targeted duloxetine treatment of CS on postoperative residual pain compared with the care-as-usual control group.

Methods

This randomized controlled trial includes patients with knee osteoarthritis on a waiting list for primary unilateral TKA. Patients with preoperative CS will be randomly allocated to the perioperative duloxetine treatment group (duloxetine group) or the care-as-usual control group (placebo group). Patients in the duloxetine group will receive a half-dose of preemptive duloxetine (30 mg/day) for a week before surgery and a full-dose of duloxetine (60 mg/day) for six weeks after surgery. The primary outcome is the intensity of residual pain at six months after TKA, including the visual analogue scale, 11-point numeric rating scale, the sensory dimension of the brief pain inventory, and the pain subscale of the Knee injury and Osteoarthritis Outcome Score. The secondary outcome measures will include the pain and function related outcomes. All of the patients will be followed up at one, three, and six months after surgery. All adverse events will be recorded and immediately reported to the primary investigator and ethics committee to decide if the patient needs to drop out from the trial.

Discussion

This clinical trial will convey the latest evidence of the efficacy and safety of the application of duloxetine in postoperative pain control in CS patients who are scheduled for TKA. The study results will be disseminated at national and international conferences and published in peer-reviewed journals.

Trial registration

Chinese Clinical Trial Registry (http://www.chictr.org.cn) registration number: ChiCTR2000031674. Registered 07 April 2020.

In vivo kinematics of a newly updated posterior-stabilised mobile-bearing total knee arthroplasty in weight-bearing and non-weight-bearing high-flexion activities

BACKGROUND

The purpose of this study was to clarify the in vivo kinematics of a newly updated posterior-stabilised (PS) mobile-bearing total knee arthroplasty during high-flexion activities in weight-bearing (WB) and non-weight-bearing (NWB) conditions. The hypothesis was that the kinematics would differ between the WB and NWB conditions, and the kinematics would be affected by the WB condition.

METHODS

The kinematics of 19 knees were investigated under fluoroscopy during squatting (WB) and active-assisted knee flexion (NWB) with two- and three-dimensional registration technique. Accordingly, the range of motion, anteroposterior (AP) translation of the medial and lateral contact points, axial rotation of the femoral component relative to the tibial component, and kinematic pathway were evaluated.

RESULTS

There was no difference in the knee's range of motion between the WB and NWB conditions. The medial AP translation of the femur did not differ in each flexion angle between WB and NWB conditions except for flexions of 70°. There was no difference in the lateral AP translation of the femur at all tested flexion angles between the WB and NWB conditions. The external femoral rotation and the medial pivot motion were observed throughout all flexion angles in WB conditions. The clinical relevance is that this implant could produce ideal medial AP stability and medial pivot motion.

CONCLUSION

The medial AP translation of the femur was stable for AP direction when it was in both WB and NWB conditions. In WB conditions, the medial pivot motion was observed throughout all flexion angles.

LEVEL OF EVIDENCE

III.

Effect of material selection on tibial post stresses in posterior-stabilized knee prosthesis

Aims

The material and design of knee components can have a considerable effect on the contact characteristics of the tibial post. This study aimed to analyze the stress distribution on the tibial post when using different grades of polyethylene for the tibial inserts. In addition, the contact properties of fixed-bearing and mobile-bearing inserts were evaluated.

Methods

Three different grades of polyethylene were compared in this study; conventional ultra high molecular weight polyethylene (UHMWPE), highly cross-linked polyethylene (HXLPE), and vitamin E-stabilized polyethylene (VEPE). In addition, tibial baseplates with a fixed-bearing and a mobile-bearing insert were evaluated to understand differences in the contact properties. The inserts were implanted in neutral alignment and with a 10° internal malrotation. The contact stress, von Mises stress, and equivalent plastic strain (PEEQ) on the tibial posts were extracted for comparison.

Results

The stress and strain on the tibial post for the three polyethylenes greatly increased when the insert was placed in malrotation, showing a 38% to 56% increase in von Mises stress and a 335% to 434% increase in PEEQ. The VEPE insert had the lowest PEEQ among the three materials. The mobile-bearing design exhibited a lower increase in stress and strain around the tibial posts than the fixed-bearing design.

Conclusion

Using VEPE for the tibial component potentially eliminates the risk of material permanent deformation. The mobile-bearing insert can help to avoid a dramatic increase in plastic strain around the tibial post in cases of malrotation. The mobility allows the pressure to be distributed on the tibial post and demonstrated lower stresses with all three polyethylenes simulated.

Cite this article: Bone Joint Res 2020;9(11):768–777.

Joint line elevation is not associated with mid-flexion laxity in patients with varus osteoarthritis after total knee arthroplasty

PURPOSE

Previous cadaver studies showed that the additional bone cuts in the distal and posterior femur and joint line elevation resulted in laxity at mid-flexion after total knee arthroplasty (TKA). However, these results are not always applicable to TKA candidates because the related studies used cadaver knees with no osteoarthritis. It was hypothesized that the joint line elevation results in mid-flexion laxity after TKA in patients with knee osteoarthritis. The purpose of this study was to analyze the relationship between joint line elevation and mid-flexion laxity in patients with knee osteoarthritis.

METHODS

30 knees with varus osteoarthritis undergoing TKA were evaluated. Two femoral trial component models were prepared: (1) normal model with a thickness of the distal and posterior femoral components of 9 mm, and (2) 2-mm joint line elevation model with a thickness of the distal and posterior femoral components of 9 - 2 = 7 mm. This 2-mm joint line elevation model simulated an additional bone cut in the distal and posterior femur, and joint line elevation, without an additional bone cut. The femoral trial component models were set before implantation and measured the joint gap kinematics using a tensor device through the full knee range of motion.

RESULTS

The differences in joint gap change from 30° to 90° were not statistically significant between the two models. However, the joint line elevation model decreased the joint gap laxity at 120° (p = 0.02) and at 145° (p = 0.01).

CONCLUSIONS

This study showed that a 2-mm joint line elevation was not associated with mid-flexion laxity in patients with varus osteoarthritis in the knee. The results of this study differed from the results in previous cadaver studies.

LEVEL OF EVIDENCE

Therapeutic study, level II, prospective comparative study.

Mobile-bearing insert used with total knee arthroplasty does not rotate on the tibial tray during a squatting activity: a cross-sectional study

Background

Total knee arthroplasty (TKA) is commonly performed around the world. Implant designs include fixed-bearing and mobile-bearing. Mobile-bearing design was developed as a rotating platform that allows axial rotation of the insert around the longitudinal axis. This phenomenon may limit full exploitation of the characteristics of the mobile-bearing insert, which may cause wearing and reduce longevity. However, there is limited knowledge on rotational behavior of the polyethylene mobile-bearing insert under weight-bearing conditions. We aimed at determining the rotational motion of each component at full extension and flexed positions during a squatting activity after TKA.

Methods

This study was a cross-sectional study (level 4) involving patients with severe knee osteoarthritis scheduled to receive TKA. We examined 13 knees of 11 patients after mobile-bearing TKA (NexGen LPS-Flex, Zimmer Inc.) at 10 weeks and 1 year postoperatively. Four identical metallic beads were embedded into the insert. Wide-base squatting was chosen for analyses. Three-dimensional in vivo poses of the prostheses were created using a 3D-to-2D registration technique. During flexion, rotation of the femoral component relative to the insert (FEM/INS) and tibial component (FEM/TIB) as well as insert rotation relative to the tibial component (INS/TIB) were computed. Repeated measure 2-way ANOVA and post hoc test was used.

Results

In the fully extended position, FEM/INS was significantly smaller than INS/TIB both at 10 weeks (− 0.3° vs. 6.3°, p = .013) and 1 year (− 0.8° vs. 4.9°, p = .011), respectively. During the squatting activity, rotation motions of FEM/TIB, FEM/INS, INS/TIB were 5.7°, 5.9°, and 1.8° at 10 weeks and 6.3°, 5.5°, and 1.6° at 1 year, respectively. Rotation motion of FEM/INS was significantly greater than that of INS/TIB at both 10 weeks (p < .001) and 1 year (p < .001).

Conclusions

The mobile-bearing insert enhances the compatibility of FEM/INS in extension; the amount of INS/TIB rotation is significantly smaller than that of FEM/INS during a squatting activity. This information will inform surgeons to take caution to perform TKA with a fixed insert in which 6.3° of rotational offset would be added to the rotational alignment at FEM/INS at full extension.

Trial registration

UMIN-CTR, UMIN000024196. Retrospectively registered on 9 September 2016.

How prosthetic design influences knee kinematics: a narrative review of tibiofemoral kinematics of healthy and joint-replaced knees

INTRODUCTION

To improve the total knee arthroplasty (TKA) prosthesis design, it is essential to study the kinematics of the tibiofemoral joint. Many studies have been conducted in this area; however, conflicting results and incomparable testing methods make it difficult to draw definitive conclusions or compare research from studies. The goal of this article is to introduce what is known about both healthy and prosthetic tibiofemoral joint kinematics.

AREAS COVERED

Healthy tibiofemoral joint kinematics are reviewed in vivo by different activities, and the kinematics of existing knee prosthetic design features are considered separately. These features include but are not limited to cruciate retaining, posterior cruciate substituting, mobile-bearing, and high flexion.

EXPERT COMMENTARY

The type of activity that is being performed has a great influence on the kinematics of healthy knees, and the influences of different TKA prosthetic design features on the kinematics are complex and varied. Moreover, the TKA postoperative functional performance is influenced by many factors, and prosthetic design is among them, but not the only one that defines the performance.

Fracture of the insert cone of a polyethylene liner in a failed posterior-stabilized, rotating-platform total knee arthroplasty

Failures unique to posterior cruciate-substituting total knee prostheses rarely include polyethylene post fractures but have been described. We report a case involving a fracture of the distal insert cone of a rotating-platform (RP) polyethylene liner in a primary total knee arthroplasty. This case highlights a 67-year-old male presenting with new-onset knee pain and recurrent effusions with osteolysis 11 years following placement of a posterior-stabilized, RP total knee arthroplasty. At the time of revision surgery, the polyethylene insert cone was found to be fractured just below the junction between cone and the body of the insert. Liner exchange, synovectomy, and osteolytic-defect curettage and cement packing were performed. One year following revision surgery, the patient is without pain and has returned to function without limitations. Clinicians must be aware of this possible failure with RP prostheses in the setting of pain with a stable knee, recurrent aseptic effusions, and osteolysis.

Joint Gap in Mid-Flexion Is Not a Predictor of Postoperative Flexion Angle After Total Knee Arthroplasty

BACKGROUND

Postoperative knee flexion angle is one of the most important outcomes of total knee arthroplasty (TKA). Intraoperative ligament balancing may affect the postoperative range of motion of the knee. However, the relationship between intraoperative ligament balancing and postoperative flexion angle was still controversial. The purpose of this study was to determine whether intraoperative joint gap affects postoperative knee flexion angle or not.

METHODS

Prospective multicenter study of 246 knees with varus osteoarthritis undergoing a posterior-stabilized, mobile-bearing TKA was performed. The joint gap before implantation and after implantation was measured. The joint gap after implantation was measured using a specially designed tensor device with the same shape of a total knee prosthesis at 0°, 30°, 60°, 90°, 120°, and 145° of flexion with the reduction of the patellofemoral joint. Stepwise multiple regression analysis was conducted to determine the predictors of the flexion angle of the knee after the operation.

RESULTS

Predictors were identified in the following 3 categories: (1) preoperative flexion angle, (2) intraoperative flexion angle, and (3) joint gap looseness at 120° of flexion (joint gap after implantation at 120° of flexion - joint gap after implantation at 0° of flexion) (R = 0.472, P < .01).

CONCLUSION

Flexion angle after TKA was not affected by the flexion joint gap looseness before implantation and the joint gap looseness after implantation from 30° to 90° of flexion. Surgeons should notice that joint gap looseness in mid-flexion range did not increase the postoperative knee flexion angle.

Comparison of in vivo polyethylene wear particles between mobile- and fixed-bearing TKA in the same patients

PURPOSE

Polyethylene wear particle generation is one of the most important factors that affects the mid- to long-term results of total knee arthroplasties (TKA). Mobile-bearing total knee prostheses were developed to reduce polyethylene wear generation. However, whether mobile-bearing prostheses actually generate fewer polyethylene wear particles than fixed-bearing prostheses remains controversial. The aim of this study was to compare, within individual patients, the in vivo polyethylene wear particles created by a newly introduced mobile-bearing prosthesis in one knee and a conventional fixed-bearing prosthesis in other knee.

METHODS

Eighteen patients receiving bilateral TKAs to treat osteoarthritis were included. The synovial fluid was obtained from 36 knees at an average of 3.5 years after the operation. The in vivo polyethylene wear particles were isolated from the synovial fluid using a previously validated method and examined using a scanning electron microscope and an image analyser.

RESULTS

The size and shape of the polyethylene wear particles from the mobile-bearing prostheses were similar to those from the conventional fixed-bearing prostheses. Although the number of wear particles from the mobile-bearing prosthesis (1.63 × 10⁷ counts/knee) appeared smaller than that from the fixed-bearing prosthesis (2.16 × 10⁷ counts/knee), the difference was not statistically significant.

CONCLUSIONS

The current in vivo study shows that no statistically significant differences were found between the polyethylene wear particles generated by a newly introduced mobile-bearing PS prosthesis and a conventional fixed-bearing PS prosthesis during the early clinical stage after implantation.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

No difference in terms of radiostereometric analysis between fixed- and mobile-bearing total knee arthroplasty: a randomized, single-blind, controlled trial

PURPOSE

A concern that arises with any new prosthesis is whether it will achieve satisfactory long-term implant stability. The gold standard of assessing the quality of fixation in a new or relatively new implant is to undertake a randomized controlled trial using radiostereometric analysis. It was hypothesized that both mobile-bearing total knee arthroplasty and fixed-bearing total knee arthroplasty have comparable migration patterns at 2-year follow-up. This study investigated two types of cemented total knee arthroplasty, the mobile- or fixed-bearing variant from the same family with use of radiostereometric analysis.

METHODS

This prospective, patient-blinded, randomized, controlled trial was designed to investigate early migration of the tibia component after two years of follow-up with use of radiostereometric analysis. A total of 50 patients were randomized to receive a mobile- or fixed-bearing TKA from the same family. Patients were evaluated during 2-year follow-up, including radiostereometric analysis, physical and clinical examination and patient reported outcome measures (PROMs).

RESULTS

At two-year follow-up, the mean (±SD) maximum total point motion (MTPM) in the fixed-bearing group was 0.82 (±1.16) versus 0.92 mm (±0.64) in the mobile-bearing group (p = n.s) with the largest migration seen during the first 6 weeks (0.45 ± 0.32 vs. 0.54 ± 0.30). The clinical outcome and PROMs significantly improved within each group, not between both groups.

CONCLUSIONS

Measuring early micromotion is useful for predicting clinical loosening that can lead to revision. The results of this study demonstrate that early migration of the mobile-bearing is similar to that of the fixed-bearing component at two years and was mainly seen in the first weeks after implantation.

LEVEL OF EVIDENCE

Randomized, single-blind, controlled trial, Level I.

In vivo kinematics of knee replacement during daily living activities: Condylar and post-cam contact assessment by three-dimensional fluoroscopy and finite element analyses

In total knee replacement, the investigation on the exact contact patterns at the post-cam in implanted patients from real in vivo data during daily living activities is fundamental for validating implant design concepts and assessing relevant performances. This study is aimed at verifying the restoration of natural tibio-femoral condylar kinematics by investigating the post-cam engagement at different motor tasks. An innovative validated technique, combining three-dimensional fluoroscopic and finite element analyses, was applied to measure joint kinematics during daily living activities in 15 patients implanted with guided motion posterior-stabilized total knee replacement. Motion results showed physiological antero-posterior translations of the tibio-femoral condyles for every motor task. However, high variability was observed in the position of the calculated pivot point among different patients and different motor tasks, as well as in the range of post-cam engagement. Physiological tibio-femoral joint rotations and contacts at the condyles were found restored in the present knee replacement. Articular contact patterns experienced at the post-cam were found compatible with this original prosthesis design. The present study reports replaced knee kinematics also in terms of articular surface contacts, both at the condyles and, for the first time, at the post-cam. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1396-1403, 2017.

Bi-cruciate substituting total knee arthroplasty improved medio-lateral instability in mid-flexion range

PURPOSE

Appropriate medio-lateral (ML) stability is an important factor of good clinical outcome following total knee arthroplasty (TKA). We hypothesized that a newly introduced Bi-Cruciate Stabilized substituting (BCS) prosthesis reduces the medio-lateral instability in mid-flexion range. The purpose of this study was to measure the ML stability (varus ligament balance) using a new tensor device after implantation of BCS TKA and to analysis the association between varus ligament balance and clinical results after TKA.

MATERIALS AND METHODS

We evaluated 33 patients who underwent 39 Journey. 2. BCS TKA using the measured resection technique. We measured the gaps after implantation from extension to full flexion with reduced patella by constant distraction force with 120N. The varus ligament balance gap was defined as the gap calculated by subtracting from Lateral to medial component gap. The clinical results at 2years after operation was compared with intraoperative varus ligament balance.

RESULTS

Varus ligament balance showed its maximum gap at full knee extension and 120° flexion. Varus ligament balance at 30°, 60° and 90° of flexion were significant differences in the varus ligament balance at full extension. (* p < 0.05). The varus ligament balance gap was negatively corrected with postoperative 2011 Knee society score (patient's satisfaction) (r = 0.661, p = 0.001).

CONCLUSIONS

The most important findings of the present study are that BCS TKA can reduces the ML instability in mid-flexion range, and improve simultaneously the patient's satisfaction.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Intraoperative Manipulation for Flexion Contracture During Total Knee Arthroplasty

Joint gap balancing during total knee arthroplasty (TKA) is important for ensuring postoperative joint stability and range of motion. Although the joint gap should be balanced to ensure joint stability, it is not easy to achieve perfect balancing during TKA. In particular, relative extension gap shortening can induce flexion contracture. Intraoperative manipulation is often empirically performed. This study evaluated the tension required for this manipulation and investigated the influence of intraoperative manipulation on the joint gap in cadaveric knees. Total knee arthroplasty was performed in 6 cadaveric knees from whole body cadavers. Flexion contracture was induced using an insert that was 4 mm thicker than the extension gap, and intraoperative manipulation was performed. Study measurements included the changes in the joint gap after manipulation at 6 positions, with the knee bending from extension to 120° flexion, and the manipulation tension that was required to create a 4-mm increase in the gap. The manipulation tension needed to create a 4-mm increase in the extension gap was 303±17 N. The changes in the joint gap after manipulation were 0.4 mm, 0.6 mm, 0.2 mm, -0.2 mm, -0.4 mm, and -0.6 mm at 0°, 30°, 45°, 60°, 90°, and 120° flexion, respectively. Therefore, the joint gap was not significantly changed by the manipulation. Intraoperative manipulation does not resolve flexion contracture. Therefore, if flexion contracture occurs during TKA, treatment with additional bone cutting and soft tissue release is likely more appropriate than manipulation. [Orthopedics. 2016; 39(6):e1070-e1074.].

Mobile-bearing TKA improved the anteroposterior joint stability in mid-flexion range comparing to fixed-bearing TKA

INTRODUCTION

Proper anteroposterior (AP) joint displacement is an important indicator of good clinical outcome following total knee arthroplasty (TKA). We hypothesized that a newly introduced mobile-bearing posterior stabilized (PS) prosthesis reduces the AP joint displacement. The aim of this study is to compare the AP joint displacement between a newly introduced mobile-bearing PS TKA in one knee and a conventional fixed-bearing PS TKA in other knee.

MATERIALS AND METHODS

82 knees in 41 patients who had bilateral TKAs were investigated. All the patients received a conventional fixed-bearing PS prosthesis in one knee and a highly congruent mobile-bearing PS prosthesis in the other knee. AP joint displacement was measured using the KT-2000 arthrometer, at 30° and 75° in flexion, at average of 3.3 years after the operation.

RESULTS

AP joint displacements at 30° in flexion were 6 ± 3 mm in the knees with the mobile-bearing PS prosthesis and 9 ± 4 mm in the knee with fixed-bearing PS prosthesis (p < 0.001). AP joint displacements at 75° in flexion were 4 ± 2 mm in the knees with the mobile-bearing PS prosthesis and 6 ± 3 mm in the knee with fixed-bearing PS prosthesis (p < 0.001).

CONCLUSIONS

This study suggested that the design of the prosthesis can improve the AP joint stability in mid-flexion range.

Nontraumatic tibial polyethylene insert cone fracture in mobile-bearing posterior-stabilized total knee arthroplasty

A 72-year-old male patient underwent mobile-bearing posterior-stabilized total knee arthroplasty for osteoarthritis. He experienced a nontraumatic polyethylene tibial insert cone fracture 27 months after surgery. Scanning electron microscopy of the fracture surface of the tibial insert cone suggested progress of ductile breaking from the posterior toward the anterior of the cone due to repeated longitudinal bending stress, leading to fatigue breaking at the anterior side of the cone, followed by the tibial insert cone fracture at the anterior side of the cone, resulting in fracture at the base of the cone. This analysis shows the risk of tibial insert cone fracture due to longitudinal stress in mobile-bearing posterior-stabilized total knee arthroplasty in which an insert is designed to highly conform to the femoral component.

Peak activation of lower limb musculature during high flexion kneeling and transitional movements

Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions. Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.

Intra-operative gaps affect outcome and postoperative kinematics in vivo following cruciate-retaining total knee arthroplasty

PURPOSE

The following investigation evaluates the effect of intra-operative gaps after posterior cruciate ligament-retaining total knee arthroplasty using two-dimensional/three-dimensional registration and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC).

METHODS

Patients were divided into two groups according to their 90°-0° component gap changes using a device designed by our laboratory. The wide gap group was defined as more than 3 mm (4.3 ± 0.7 mm), and the narrow gap group was defined as less than 3 mm (1.3 ± 1.3 mm).

RESULTS

Under non-WB (weight bearing) conditions, the wide flexion gap group (N = 10) showed a significant anterior displacement of the medial femoral condyle as compared with the narrow flexion gap group (N = 20). Despite no significant differences observed under WB conditions, both femoral condyle positions during flexion were significantly more posterior than during extension. WOMAC of the tight gap group showed worse scores for two functional items demanding knee flexion (bending to floor and getting on/off toilet).

CONCLUSION

The large flexion gap could influence the late rollback under non-WB conditions and better WOMAC functional scores in the flexion items. Three to four millimetre laxity at 90°-0° component gaps may be adequate and might be necessary to carry out daily life activities.

Mobile-bearing prosthesis and intraoperative gap balancing are not predictors of superior knee flexion: a prospective randomized study

PURPOSE

Range of motion is a crucial measure of the outcome of total knee arthroplasty. Gap balancing technique and mobile-bearing prosthesis can improve postoperative range of motion. The purpose of this study was to determine the factors that are predictive of the postoperative range of motion.

METHODS

A total of 94 knees with varus osteoarthritis were prospectively randomized to receive either a posterior-stabilized mobile-bearing or a posterior-stabilized fixed-bearing prosthesis. All preoperative and postoperative protocols and operative techniques were identical in the two groups. Extension and flexion joint gaps were measured using a tensor device during the operation. Multiple regression analysis was conducted to determine the best predictors of the knee flexion angle 2 years after the operation. The independent variables were type of prosthesis (mobile-bearing or fixed-bearing), difference between flexion and extension joint gaps (mm), age, gender, body mass index (BMI), preoperative and intraoperative knee flexion angles, change in posterior condylar offset, and posterior tilt of the tibial plateau.

RESULTS

The mean difference between flexion and extension joint gaps was 0.8 ± 1.3 (mean ± SD) mm for mobile-bearing and 0.8 ± 1.9 mm for fixed-bearing prosthesis. The mean flexion angle for mobile-bearing and fixed-bearing groups was 120 ± 16° and 116 ± 20° preoperatively (n.s.), 142 ± 9° and 141 ± 12° intraoperatively (n.s.), and 129 ± 10° and 128 ± 13° at 2 years postoperatively (p = 0.773), respectively. Predictors were identified in the following three categories: (1) preoperative flexion angle, (2) intraoperative radiographic flexion angle, and (3) BMI (R = 0.603, p < 0.001).

CONCLUSIONS

Mobile-bearing prosthesis and optimal gap balancing did not result in superior postoperative flexion angle. Better preoperative and intraoperative flexion angles and lower BMI were the significant predictors for better postoperative flexion angle.

LEVEL OF EVIDENCE

Therapeutic study, Level I.

In vivo kinematic effects of ball and socket third condyle as a post-cam mechanism in tri-condylar knee implants

BACKGROUND

Tri-condylar implants containing a ball and socket third condyle as a post-cam mechanism were developed to accommodate a lifestyle requiring frequent deep flexion activities. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during a deep knee bend activity, and to confirm the contact status of the ball and socket joint.

METHODS

Seventeen knees implanted with tri-condylar implants were analyzed using a 3D to 2D registration approach. A distance of less than 1mm denoted ball and socket contact. Medial and lateral contact positions and axial rotation were compared before and after contact. Moreover, the contact position at the third condyle and the center of the ball joint were analyzed.

RESULTS

After the third condyle contact, posterior translation of the medial and lateral contact positions increased considerably. Meanwhile, the angular rotation remained still. The center of the third condyle did not move after contact, and the contact position at the third condyle remained low.

CONCLUSIONS

The third condyle induced intensive posterior translation of both condyles, and did not prevent axial rotation, which was proved to work properly as a posterior stabilizing post-cam mechanism.

Midflexion Laxity After Implantation Was Influenced by the Joint Gap Balance Before Implantation in TKA

The relationship between the joint gap before and after implantation in 259 knees during the total knee arthroplasty was investigated using a tensor device which can attach the polyethylene insert trial. Patients were divided into following 3 groups according to the joint gap balance before implantation (flexion joint gap--extension joint gap); group 1: >1mm; group 2: -1 to 1mm, and group 3: <-1mm. Joint gap after implantation was loose at 30°, 60°, 90°, and 120° of flexion in group 1 and 2, but loose only at 30° of flexion in group 3 (p<0.01). This study showed that loose flexion joint gap before implantation increased the risk of joint gap laxity after implantation especially at midflexion ranges.

In vivo movement of femoral flexion axis of a single-radius total knee arthroplasty

The objective of this study was to investigate in vivo femoro-tibial motion using the movement of femoral flexion axis of a single-radius TKA. We examined 20 clinically successful knees with a single-radius posterior stabilized TKA to evaluate the kinematics of deep knee flexion using 2-3-dimensional registration techniques. The mean knee flexion range of motion was 117.8°. The mean rotation of the femoral component was 7.6° external rotation. The mean knee flexion angle at initial post-cam engagement was 55.2°. No paradoxical movement of femoral component was shown until 70° flexion, afterward the femoral component rolled back with flexion. The data showed that the design of this prosthesis might contribute to reduce the paradoxical anterior femoral movement and provide stability in mid-flexion ranges.

Can post-cam function be replaced by addition of a third condyle in PS TKA?

The purpose of the study was to analyze the effectiveness of an additional ball and socket articulation in implanted knees and whether it can replicate post-cam function. Fifteen knees implanted with a cruciate substituting (CS) polyethylene without a post and ten knees implanted with a posterior stabilized (PS) polyethylene with a post were analyzed using 3D model fitting approach. Two types of designs showed similar posterior translation and similar axial rotation. Most of the contact points at the ball and socket joint stayed within the socket height for the PS group. This study indicates that the ball and socket joint is able to function as a replacement of the post-cam mechanism, which might serve as a new way to achieve posterior stability.

Intraoperative assessment of midflexion laxity in total knee prosthesis

BACKGROUND

Soft-tissue balancing of the knee is fundamental to the success of a total knee arthroplasty (TKA). In posterior-stabilized TKA, there is no stabilizer of the anterior-posterior translation in the midflexion range in which the cam-post mechanism does not engage yet. Therefore, instability in the midflexion range is suspected to occur in posterior-stabilized TKA. The purpose of this study was to measure the joint gap throughout a full range of motion and to analyze the joint gap laxity in the midflexion range after implantation of a mobile-bearing posterior-stabilized total knee prosthesis.

METHODS

Joint gap kinematics in 259 knees with varus osteoarthritis were measured during TKAs using a tensor device with the same shape of a total knee prosthesis of the same design was used. After the implantation of a mobile-bearing posterior-stabilized prosthesis and the reduction of the patellofemoral joint, the joint gap was measured at 0°, 30°, 60°, 90°, 120°, and 145° of flexion.

RESULTS

The center size of the joint gap was tight in extension and deep flexion and loose at midflexion ranges, especially at 30° of flexion (p<0.001). The symmetry of the joint gap was varus at 0° and 145° of flexion (p<0.001).

CONCLUSIONS

Our results showed the joint gap laxity in the midflexion range after the implantation of a mobile-bearing posterior-stabilized prosthesis. Our new tensor device, which can attach the polyethylene insert trial, will provide the important information about the joint gap kinematics after implantation of total knee prostheses.

LEVEL OF EVIDENCE

IV.

In vivo femoro-tibial kinematic analysis of a tri-condylar total knee prosthesis

BACKGROUND

An alternative tri-condylar implant has been designed to incorporate necessary posterior stability without a post, but has not been evaluated. The purpose of the current study was to determine the in vivo three dimensional femoro-tibial kinematics of a tri-condylar implant during a weight bearing deep knee bend activity.

METHODS

Fluoroscopy based in vivo femoro-tibial kinematics of the tri-condylar implant was assessed for 66 knees during a deep knee bend activity, using a three dimensional to two dimensional model fitting approach.

FINDINGS

Average range of motion was 125.5° (standard deviation (SD)=20.5°) in sagittal plane, and 42 knees (63.6%) experienced at least 120° of weight-bearing knee flexion. The average amount of posterior femoral movement (PFM) was 8.7mm (SD=4.3mm) for the medial condyle and 11.2mm (SD=5.4mm) for the lateral condyle. PFM of the medial condyle was significantly smaller than that of the lateral condyle. The average amount of femoro-tibial axial rotation was 5.7° (SD=6.4°), and 56 knees (84.8%) experienced a normal axial rotation pattern. Condylar lift-off, mostly occurring in deep flexion range, was experienced in 16 knees (24.2%).

INTERPRETATION

Knees in the current study did achieve high weight-bearing flexion, more normal-like greater posterior femoral movement of lateral condyle than the medial condyle and a normal axial rotation pattern, albeit, less in magnitude than the normal knee.

Are the long term results of a high-flex total knee replacement affected by the range of flexion?

PURPOSE

The purpose of this study was to examine the effect of deep flexion on the long-term durability of a high-flex ceramic implant in total knee arthroplasty.

METHODS

Five hundred and five consecutive knees replaced with a Bi-Surface knee system (Kyocera Medical, Osaka, Japan) were divided into two groups according to the range of flexion by 135° postoperatively. Comparison of implant durability was made between the high- and low-flexion groups after a minimum ten year follow-up.

RESULTS

With revision for any surgery as the end point, the survival rates at ten years were 95.5% and 96.2% in the high- and low-flexion group, respectively (p = 0.63). With revision for mechanical failure as the end point, survival rates were 98.7% and 98.5%, respectively (p = 0.94).

CONCLUSION

Implant survival rate was similar for both groups. Deep flexion seemed not to affect long-term durability.