Joint line changes in cruciate-retaining versus posterior-stabilized computer-navigated total knee arthroplasty

Introduction

This study compared joint line changes and functional outcomes between cruciate-retaining (CR) and posterior-stabilized (PS) computer-navigated total knee arthroplasties (TKAs). With the increased precision offered by computer navigation, we hypothesized that there should be minimal differences in the joint line changes between the groups and thus no significant differences in the clinical outcomes.

Materials and methods

A retrospective study of 195 patients with a minimum of 2-year follow-up following primary surgery was conducted. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups.

Results

CR knees had a significantly lesser mean joint line change of 1.70 mm as compared to 2.34 mm in PS knees (p = .04) but the absolute difference was only 0.64 mm. The PS group had significantly better final range of motion of 122° (±9.9°) as compared to 114° (±15.0°) in the CR group (p < .0001). There were no significant differences in the final outcome scores.

Conclusion

Although there is a significant difference statistically in the joint line changes between the groups, this difference is less than 1 mm and probably has no significant clinical impact. This is further affirmed by the fact that there was no significant difference in the clinical outcomes. The increased range seen in PS knees is probably not related to joint line changes.

Level of evidence

III.     

Quadriceps force in relation of intrinsic anteroposterior stability of TKA design

Purpose

Decreased quadriceps strength and fatigue is suspected to be one of the contributing factors for anterior knee pain and malfunction after total knee arthroplasty (TKA). The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL).

Materials and methods

Eight fresh frozen human knee specimens underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. The quadriceps force was measured after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith&Nephew, Memphis, TN, USA) applying a conventional CR (11 mm) and a highly conforming (deep dished, DD) polyethylene (PE) inlay consecutively before and after resection of the PCL. Finally, tests were repeated with a posterior-stabilized (PS) design.

Results

Simulating a physiological knee extension, no significant differences in the average quadriceps force were detected between the cruciate preserving inlays (CR 1,146.57 ± 88.04 N, DD 1,150.19 ± 97.54 N, P = 0.86) as long as the PCL was intact. After resection of the PCL, the required quadriceps force increased significantly for both designs (CR 1,203.17 ± 91.51 N, P < 0.01 and DD 1,191.88 ± 80.07 N, P < 0.03). After implantation of the posterior stabilized femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR or DD (PS 1,130.91 ± 107.88 N, P < 0.01) inlay. With a deficient PCL there were no statistical differences for the DD design in comparison with CR in mean quad forces (CR 1,203.17 ± 91.51 N vs. DD 1,191.88 ± 80.07 N, P = 0.50) nor in peak forces (CR 1,729.44 ± 161.86 N, DD 1,688.66 ± 123.18 N, P = 0.17).

Discussion

At intact PCL peak quad forces and mean forces beyond 70° of flexion could be shown to be significantly lower with a PS TKA design in comparison with cruciate preserving designs such as CR and DD. In the PCL deficient knee quad forces with a highly conforming implant (DD) and CR were significantly higher than with a PS TKA. The use of PS implants in all PCL deficient knees seems to be advisable.     

Changes in ligamentous laxity after posterior stabilized total knee replacement and factors correlated with postoperative laxity

Instruction

Total knee arthroplasty (TKA) performed with the gap technique can achieve rectangular gaps during flexion and extension by proper bone resection and subsequent soft tissue release. Acquisition of appropriate soft tissue balance is important for successful TKA. It is unknown, however, whether the intraoperative well-balanced ligamentous laxity changes postoperatively over time. We hypothesized that even if good soft tissue balance was achieved intraoperatively the lateral ligamentous laxity would increase with time postoperatively. This phenomenon depends on preoperative background factors.

Methods

We used the angle between the component surfaces of the tibia and femur to define ligamentous laxity. Changes in ligamentous laxity after posterior stabilized minimally invasive surgery (MIS)-TKA were analyzed retrospectively in 150 knees based on radiographic measurements. At 12 months after the operation, the cases were divided into two groups in which the lateral ligamentous laxity in flexion was either ≤3° (balanced group) or >3° (unbalanced group). Factors with a potential to encourage postoperative ligamentous laxity were analyzed.

Results

Our data show that the postoperative ligamentous laxity in extension did not change, whereas the lateral ligamentous laxity in flexion increased with time. This change was significantly related to the preoperative lateral ligamentous laxity, body weight, body mass index, and age.

Conclusion

The results of this study should be taken into account by surgeons performing MIS-TKA with the gap technique.     

Joint gap measurement in total knee arthroplasty using a tensor device with the same articulating surface as the prosthesis

Background

We developed a new tensor to measure the joint gap throughout knee flexion during total knee arthroplasty (TKA). This tensor has the same articular shape as that of the tibial liner, including the post structure and the curvature of femorotibial articular surface, to measure the gap intraoperatively under the same conditions as after TKA. The present study aimed to examine the precision of the new tensor for gap measurement after implantation.

Methods

We performed TKA using the modified gap technique in four cadaveric knees and measured the gaps using the new tensor. The intra-observer and inter-observer error of the tensor was analyzed using 168 measurements of the gaps as determined at least twice by two surgeons. In addition, the gaps in rotating-platform posterior-stabilized TKA were measured at seven positions with the knee bending from extension to full flexion.

Results

The inter-observer and intra-observer errors were 0.8 and 0.3 mm, respectively, indicating precise and reproducible gap measurement. The gaps before implantation in reduced patellar position were 12.1 mm at extension and 12.5 mm at 90° flexion. The gaps after implantation were 9.1, 12.9, 13.1, 13.5, 13.8, 13.3, and 10.1 mm at 0°, 30°, 45°, 60°, 90°, 120°, and full flexion, respectively.

Conclusions

The new tensor provides precise and reproducible measurements. Although the joint gap before implantation was parallel and equal at extension and 90° flexion, the joint gap after implantation was variable throughout knee flexion. This feature of the gap should be considered during the operation.     

Comparing navigation-based in vivo knee kinematics pre- and postoperatively between a cruciate-retaining and a cruciate-substituting implant

Purpose

Individual physiological knee kinematics are highly variable in normal knees and are altered following cruciate-substituting (PS) and cruciate-retaining (CR) total knee arthroplasty (TKA). We wanted to know whether knee kinematics are different choosing two different knee designs, CR and PS TKA, during surgery using computer navigation.

Methods

For this purpose, 60 consecutive TKA were randomised, receiving either CR (37 patients) or PS TKA (23 patients). All patients underwent computer navigation, and kinematics were assessed prior to making any cuts or releases and after implantation. Outcome measures were relative rotation between femur and tibia, measured medial and lateral gaps and medial and lateral condylar lift-off.

Results

We were not able to demonstrate a significant difference in femoral external rotation between either group prior to implantation (7.9° CR vs. 7.4° PS) or after implantation (9.0° CR vs. 11.3° PS), both groups showed femoral roll-back. It significantly increased pre- to postoperatively in PS TKA. In the CR group both gaps increased, the change of the medial gap was significantly attributable to medial release. In the PS group both gaps increased and the change of the medial and of the lateral gap was significant. Condylar lift-off was observed in the CR group during 20° and 60° of flexion.

Conclusion

This study did not reveal significant differences in navigation-based knee kinematics between CR and PS implants. Femoral roll-back was observed in both implant designs, but significantly increased pre- to postoperatively in PS TKA. A slight midflexion instability was observed in CR TKA. Intra-operative computer navigation can measure knee kinematics during surgery before and after TKR implantation and may assist surgeons to optimise knee kinematics or identify abnormal knee kinematics that could be corrected with ligament releases to improve the functional result of a TKR, whether it is a CR or PS design. Our intra-operative finding needs to be confirmed using fluoroscopic or radiographic 3D matching after complete recovery from surgery.     

Gap measurement in posterior-stabilized total knee arthroplasty with or without a trial femoral component

Purpose

To investigate the effects of a trial femoral component on the intraoperative joint gap and intraoperative joint gap kinematics throughout the range of knee motion in minimally invasive surgery–total knee arthroplasty (MIS–TKA) with the gap technique.

Materials and methods

A total of 103 patients [15 men (15 knees) and 89 women (89 knees)] aged 50–88 years (mean 74.8 years) who received MIS–TKA with the gap technique were included. The intraoperative joint gap differences (90° flexion gap distance minus 0° extension gap distance) with and without the trial femoral component were compared. Subsequently, the intraoperative joint gap kinematics at 0°, 45°, 90°, and 120° with the trial femoral component were investigated.

Results

The intraoperative component gap difference (4.4 ± 2.7 mm) was larger than the estimated joint gap difference (1.2 ± 1.9 mm) (p < 0.01). The mean intraoperative component gap distances at 0°, 45°, 90°, and 120° of knee flexion were 14.7 ± 2.6, 19.0 ± 3.2, 19.2 ± 3.4, and 16.6 ± 3.3 mm, respectively. The intraoperative component gap distance increased significantly from 0° extension to 90° of knee flexion (p < 0.01), and then decreased significantly toward deep knee flexion at 120° (p < 0.01).

Conclusions

The trial femoral component influenced the intraoperative gap measurements, and increased the intraoperative gap difference. The joint gap kinematics with the trial femoral component were not constant throughout the range of knee motion, even if the appropriate joint gaps in extension and flexion were achieved. For acquisition of constant stability throughout the knee motion, the present results should be taken into account by surgeons performing MIS–TKA with the gap technique.     

Influence of intra-operative parameters on postoperative early recovery of active knee flexion in posterior-stabilized total knee arthroplasty

Purpose

Active knee flexion is more important for daily activities than passive knee flexion. The hypothesis is that the intra-operative parameters such as osteotomized bone thickness and soft tissue balance affect the postoperative active flexion angle in total knee arthroplasty (TKA). Therefore, we evaluate the influence of intra-operative parameters on postoperative early recovery of active flexion after posterior-stabilized (PS) TKA.

Methods

The subjects were 45 osteoarthritic knees undergoing primary PS TKA with anterior-reference technique. Intra-operative soft tissue balance was measured using an offset type tensor, and each osteotomized bone thickness was also measured. Pre- and postoperative active knee flexion angles were measured using lateral radiographs. Liner regression analysis was used to determine the influence of these intra-operative parameters on postoperative active flexion angles or recovery of active flexion angles.

Results

Pre-operative flexion angle was positively correlated with postoperative flexion angle (R?=?0.52, P?=?0.0002). Postoperative flexion angle was negatively correlated with the osteotomized bone thickness of femoral medial posterior condyle (R?=??0.37, P?=?0.012), and femoral lateral posterior condyle (R?=??0.36, P?=?0.015). Recovery of flexion angle was slightly negatively correlated with gap difference calculated by subtracting joint gap at extension from that at flexion between osteotomized surfaces (R?=??0.30, P?=?0.046).

Conclusions

The osteotomized bone thickness of the femoral posterior condyle is a significant independent factor of postoperative flexion angles. This indicates that the restoration of the posterior condyle offset may lead to larger postoperative active flexion angles in PS TKA.     

Flexion–extension gap in cruciate‐retaining versus posterior‐stabilized total knee arthroplasty: A cadaveric study

We re‐examined experimental model results using half‐body specimens with intact extensor mechanisms and navigation to evaluate cruciate‐retaining (CR) and posterior stabilized (PS) total knee arthroplasty (TKA) component gaps through an entire range of motion. Six sequential testing regimens were conducted with the knee intact, with a CR TKA in place, and with a PS TKA in place, with and without 22 N traction in place at each stage. Each of 10 knees was taken through six full ranges of motion from 0° to 120° at every stage using a navigated knee system to record component gapping. No significant difference was found between loaded and unloaded component gaps, and no significant differences were found in component gapping between CR and PS TKAs throughout a full range of motion. Flexion–extension gap measurements were significantly different from previously published data (at 90° flexion). No difference was found in kinematics when comparing CR and PS TKA component designs. Our results suggest that intact extensor mechanisms may be required to perform proper kinematic studies of TKA. Our findings provide evidence that the extensor mechanism may play a major role in the flexion–extension gaps in cadaveric knees. © 2014 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 32:627–632, 2014.     

Midterm clinical and radiographic results of the medial pivot total knee system

Purpose

The ADVANCE® Medial Pivot Knee System was designed with a highly congruent medial compartment and a less conforming lateral compartment to more closely mimic the kinematics of the normal knee. The purpose of this study was to evaluate the midterm clinical and radiographic outcomes of this total knee arthroplasty (TKA) system.

Methods

Between January 1998 and December 2006, 421 primary TKAs were performed in 373 subjects using this system and a surgical technique that resects the posterior cruciate ligament. Of these, 365 TKAs in 320 subjects were available for a follow-up visit occurring at a mean of 5.3 years. Subjects were evaluated using Knee Society Scores, range of motion, and radiographic review.

Results

The average Knee Society clinical score was 95.5 at final follow-up, with 358 (98 %) TKAs having excellent or good results. Range of motion increased from a preoperative mean of 115 to 119° at final follow-up. Component survivorship, excluding revisions for infection or trauma, was 96.6 % at five years.

Conclusions

This study demonstrates subjects implanted with the ADVANCE® Medial Pivot Knee System achieved satisfactory clinical and radiographic midterm outcomes.     

Total knee arthroplasty of the stiff knee: three hundred and four cases

Purpose

The purpose of this study was to analyse the results of total knee arthroplasty (TKA) in stiff knees (flexion ≤90° and/or flexion contracture ≥20°). Our hypothesis was that despite having poorer results than those obtained in a “standard” population and a high rate of complications, TKA was a satisfactory treatment in patients with osteoarthritis of the knee associated with significant stiffness.

Methods

Three hundred and four consecutive primary HLS TKAs (Tornier), whose data were prospectively collected between October 1987 and October 2012, were retrospectively analysed at a mean of 60 months (range, 12–239) postoperatively. Two groups, those with a “flexion contracture” and those with a “flexion deficit”, were assessed for postoperative range of motion (as integrated to the Knee Society score [KSS]), physical activity level and patient satisfaction.

Results

At the latest follow-up, range of motion was significantly improved, as was the KSS. Ninety-four percent of patients were satisfied or very satisfied, and activity levels were increased after surgery. The complication rate, however, was high in patients with a preoperative flexion deficit (17 %). Pain and residual stiffness were the most common complications.

Conclusion

TKA provides satisfactory results in patients with knee osteoarthritis associated with significant pre-operative stiffness. The surgical plan should be adapted to anticipate complications, which are particularly frequent in the presence of a flexion deficit.     

Design and kinematics in total knee arthroplasty

Purpose

Posterior stabilised (PS) total knee arthroplasty (TKA) design development that focused on restoring normal knee kinematics was followed by the introduction of reason-guided motion designs. Although all PS fixed-bearing knee designs were thought to have similar kinematics, reports show they have differing incidences and magnitudes of posterior femoral rollback and axial rotation. In this retrospective comparative study between two guided-motion total knee systems, we hypothesised that kinematic pattern has an influence on clinical and functional outcomes.

Methods

This study represents the continuation of a previously reported clinical and kinematics analysis. We retrospectively reviewed 347 patients treated with two different TKA designs: Scorpio NRG (Stryker Orthopedics) and Journey Bi-Cruciate Stabilised (BCS) knee system (Smith & Nephew). Two hundred and eighty-one patients were assessed clinically. Patients were divided into groups according to implanted TKA. Clinical evaluation with the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire was performed. Fifteen Scorpio NRG and 16 Journey BCS patients underwent video fluoroscopy during stair climbing, chair rising/sitting and step up/down at six months of follow-up.

Results

At an average 29 months of clinical follow-up, patients with Journey BCS TKAs reported better clinical results. Stiffness was more frequently reported in the Journey group (5.2 % vs 1.2 %), whereas anterior knee pain was observed in the Scorpio NRG group (1.9 %) only. Both prosthetic models reported different posterior translation of the medial and lateral contact points (CP) in all analysed motor tasks during knee flexion (BCS 10–18 mm; NRG Scorpio 2–3 mm). Both designs produced progressive external rotation of the femoral component relative to the tibia during flexion.

Conclusions

Journey BCS showed statistically significant better KOOS results. The higher posterior femoral rollback observed in the kinematic assessment of this design, associated with a better patellofemoral design, may be the reason for better clinical outcome. The reported cases of stiffness and anterolateral joint pain could be attributed to excessive medial and lateral tibiofemoral posterior translation. The NRG group demonstrated good axial rotation, but this was not coupled with physiological kinematic patterns. Patellofemoral pain can be explained by a less friendly femoral-groove design. TKA clinical–functional outcome and complications were highly influenced by the bearing geometry and kinematic pattern of prosthetic designs.     

Comparison of Intraoperative Soft Tissue Balance Between Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty Performed by a Newly Developed Medial Preserving Gap Technique

Background

Medial stability of the knee is considered to be associated with good clinical results after total knee arthroplasty (TKA). This study aimed to compare intraoperative soft tissue balance between cruciate-retaining (CR) and posterior-stabilized (PS) TKA performed by a newly developed medial preserving gap technique, which aimed at preserving medial stability throughout the range of motion.

Influence of tibial slope on extension and flexion gaps in total knee arthroplasty: increasing the tibial slope affects both gaps

Purpose

Increasing the tibial slope is often performed if the flexion gap is narrower than the extension gap. The main hypothesis of this study is that increasing the tibial slope coincidentally enlarges the extension gap.

Methods

Twenty formalin-fixed cadaveric knees were obtained for study. After CT in full extension and 90° flexion, the data of each specimen were entered into a standardized coordinate system and virtual bone cuts were performed with incrementally increasing the posterior slope. Gaps were measured at tibiofemoral contact points in 90°-flexion and full extension in the medial and lateral compartment.

Results

Increasing the tibial slope did significantly widen both the extension and the flexion gaps (p?p?Conclusions Increasing the tibial slope beyond the pre-operative planning in order to widen a tight flexion gap intra-operatively is not recommended as doing so will increase the extension gap simultaneously and will make the medial and lateral flexion gaps unequal.     

Posterior condylar offset influences the intraoperative soft tissue balance during posterior-stabilized total knee arthroplasty

Purpose

This study aimed to clarify the influence of the posterior condylar offset (PCO) on intraoperative soft tissue balance including the joint component gap and varus ligament balance measured by an offset-type tensor during posterior-stabilized (PS) total knee arthroplasty (TKA).

The influence of patella height on soft tissue balance in cruciate-retaining and posterior-stabilised total knee arthroplasty

Purpose

Although the patella reduced or everted position has recently been recognised as an important factor influencing soft tissue balance during assessment in total knee arthroplasty (TKA), the influence of patella height on soft tissue balance has not been well addressed. Therefore, the relationship between soft tissue balance and patella height was investigated and differences between cruciate-retaining (CR) and posterior-stabilised (PS) TKA were compared.

Methods

Forty consecutive patients blinded to the type of implant received, were randomised prospectively. Using lateral radiographs, pre-operative patella height was measured. Using an offset-type tensor designed to measure the soft tissue balance with a reduced patellofemoral (PF) joint and femoral component in place, soft tissue balance was intra-operatively assessed in CR TKA (n = 20) and PS TKA (n = 20) in osteoarthritic patients. The joint component gap and varus ligament balance at zero, ten, 45, 90 and 135° of knee flexion with the patella reduced were measured.

Results

In PS TKA, the joint component gap positively correlated with patella height at 90 and 135° of knee flexion. However, there was no correlation between joint component gap and patella height at other flexion angles in PS TKA and any flexion angle in CR TKA. Varus ligament balance showed no significant correlation with patella height in either CR or PS TKA.

Conclusion

Analysis of soft tissue balance and patella height only showed a positive correlation in joint component gap at a high flexion angle (90 and 135°) in PS TKA but not in other parameters examined. Pre-operative measurement of patella height may be an important factor for predicting an intra-operative flexion gap in PS TKA.