An in vivo biomechanical analysis of the soft-tissue envelope of osteoarthritic knees

doi:10.1016/j.arth.2003.09.008

The Journal of Arthroplasty

Volume 19, Issue 2, February 2004, Pages 217-223

https://doi.org/10.1016/j.arth.2003.09.008 Get rights and content

Abstract

Soft-tissue balancing and the amount of tension applied to the ligaments in a well-functioning total knee arthroplasty (TKA) has, thus far, not been accurately quantified. A ligament-tensioning device was used to measure displacement between the tibia and femur versus load during 86 consecutive TKAs. Measurements were made in flexion and extension following bone cuts and final soft-tissue balancing to calculate mean effective stiffness (MES) of the soft-tissue envelope and mean resting force on the implanted polyethylene component. MES was not affected by age or gender and did not differ in flexion versus extension. MES was significantly higher in posterior cruciate-retaining knees compared with posterior cruciate-sacrificing knees. There was no statistical difference between mean resting force on the polyethylene in flexion versus extension, or in posterior cruciate-retaining versus -sacrificing knees. These biomechanical data will serve as a good starting point for which to compare the expected stiffness of the ligaments and resting load on the polyethylene in well-balanced knees.

Section snippets

Materials and methods

The surgical technique and soft-tissue balancing procedure for TKA utilizing the ligament tensioning device (Fig. 1) used in this study has been previously reported in detail [11]. Since that report [11], the torque meter handle has been added to the ligament-balancer device. The calibration of the device was performed by the manufacturer (Stryker Howmedica Osteonics, Allendale, NJ).

Following the distal femoral and proximal tibial bone cuts, the knee is balanced in extension. The tensioner

Results

The generalized load versus displacement curves for both posterior cruciate-retaining and posterior cruciate-substituting knees are indicated in Fig. 2. Mean effective stiffness (MES) was not affected by age in either posterior cruciate-substituting knees (r²=.09) or posterior cruciate-retaining knees (r²=.07). For posterior cruciate-substituting knees, no significant difference in the average effective stiffness could be demonstrated between men and women in either flexion (P=.42) or

Discussion

To the best of our knowledge, this is the first time in vivo measurements of the effective stiffness of the soft-tissue envelope of osteoarthritic knees have been measured using a balancer. Attfield et al. [12] used an electronic tensioning device during 8 TKAs; however, the goal of their study was to determine soft-tissue imbalance of the medial compartment compared with the lateral compartment. They found that the medial-lateral imbalance reached a maximum before decreasing to a lower level

Conclusions

The MES of the soft-tissue envelope around osteoarthritic knees has been approximated and the load versus displacement curve has been characterized. The only factor that appears to affect this biomechanical property is retention of the PCL, which increases the effective stiffness. In addition, the mean resting force on the polyethylene implant has been estimated in this series of TKAs. These data serve as a baseline in our attempt to establish quantifiable guidelines for how “tightly” or how

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Cited by (36)

Randomized Controlled Trial of Sensor-Guided Knee Balancing Compared to Standard Balancing Technique in Total Knee Arthroplasty
2021, Journal of Arthroplasty
Citation Excerpt :
The leg was brought into full extension and the bone ends opposed to confirm satisfactory alignment and then distracted to confirm adequate gap to accommodate at least the minimum bearing insert of 9 mm. A tensor balancer device (Monogram Balancer; Stryker) was introduced into the knee in full extension and the tension was applied until the torque meter read 32, which has been deemed an appropriate tension based on prior study of the device [13]. The displacement or gap in millimeters was recorded and angular deformity was corrected to within 3 mm by further soft tissue release or bone resection.
Despite advances in total knee arthroplasty (TKA) technology, up to 1 in 5 patients remain dissatisfied. This study sought to evaluate if sensor-guided knee balancing improves postoperative clinical outcomes and patient satisfaction compared to a conventional gap balancing technique.
We undertook a prospective double-blind randomized controlled trial of patients presenting for elective primary TKA to determine a difference in TKA soft tissue balance between a standard gap balancing (tensiometer) approach compared to augmenting the balance using a sensor-guided device. The sensor-guided experimental group had adjustments made to achieve a balanced knee to within 15 pounds of intercompartmental pressure difference. Secondary outcomes included differences in clinical outcome scores at 6 months and 1 year postoperative, including the Oxford Knee Score and Knee Society Score and patient satisfaction.
The sample comprised of 152 patients, 76 controls and 76 experimental sensor-guided cases. Within the control group, 36% (27/76) of knees were unbalanced based on an average coronal plane intercompartmental difference >15 pounds, compared to only 5.3% (4/76) within the experimental group (P < .0001). There were no significant differences in 1-year postoperative flexion, Knee Society Score, or Oxford scores. Overall, TKA patient satisfaction at 1 year was comparable, with 81% of controls and experimental cases reporting they were very satisfied (P = .992).
Despite the use of the sensor-guided knee balancer device to provide additional quantitative feedback in the evaluation of the soft tissue envelope during TKA, we were unable to demonstrate improved clinical outcomes or patient satisfaction compared to our conventional gap balancing technique.
Different targets of mechanical alignment do not improve knee outcomes after TKA
2019, Knee
Citation Excerpt :
The aim of achieving neutral alignment has been challenged with the knowledge that a large proportion of the healthy non-arthritic population are not normally in neutral alignment [25,26], therefore achieving neutral alignment after TKA could be considered abnormal for this group. Some propose maintaining constitutional alignment [17,27,28], whereby the knee is maintained closer to the original knee alignment rather than correcting it to mechanical neutral alignment, as a way of improving TKA function as the ligamentous structures around the knee are not placed in a relatively abnormal position [22–24,29]. Even the traditional methods of measured resection or ligamentous balance have been challenged more recently by the concept of kinematic alignment [28,30,31] in which the femoral and tibial components are aligned with the natural axis of flexion and rotation of the knee of each particular individual.
Accurate alignment is a basic principle of TKA surgery, but achieving alignment within this target may not translate into superior outcomes after surgery.
To assess if neutral TKA mechanical alignment was associated with superior knee outcomes and to examine the effect of various aspects of pre-operative and post-operative alignment on knee function.
Analysis of a database of 444 TKA patients between June 2009 and October 2016. Knee outcomes (WOMAC, AKSS and knee range of motion) were collected before surgery and during follow-up at a minimum of six months.
Analysis included 444 TKA patients (62% female, mean age 66 years, mean follow-up 23 months). Deformity varied from 21° varus (mean = 7.9, SD = 2.8) to 17° valgus deformity (mean = 7.7, SD = 2.8). Pre-operatively, 101 (23%) knees were in native neutral mechanical alignment, while 278 (63%) were in varus and 65 (15%) were in valgus. Post-operatively, a group of 365 (82%) TKA were found to be in neutral mechanical alignment and a group of 79 (18%) TKA were noted to be ‘Outliers’ (17 [4%] TKA > 3° varus and 62 [14%] TKA > 3° valgus alignment). Restoration of the target of alignment of 0 ± 3° or 0 ± 1°, did not have better functional outcomes scores, range of motion or prosthesis longevity than those in the outlier range.
Neutral TKA alignment did not appear to be a significant contributing factor to the improvement in knee function in short-medium term follow-up.
Accuracy of Balancing at Total Knee Surgery Using an Instrumented Tibial Trial
2016, Journal of Arthroplasty
Balancing is an important part of a total knee procedure, and in recent years, more emphasis has been given to quantifying the process.
During 101 total knee surgeries, initial bone cuts were made using navigation. Lateral and medial contact forces were determined throughout flexion using an instrumented tibial trial. Balancing was defined as a ratio of the medial and total force, the target being 0.5 (equal lateral and medial forces). Based on the initial values, surgical corrections were selected to achieve balancing. The most common corrections were soft tissue releases (63 incidences), including MCL, posterolateral corner, posteromedial corner, and changing tibial insert thicknesses (34 incidences).
After final balancing, the mean ratio was 0.52 ± 0.14, between 0.35 and 0.65 being achieved in 80% of cases. In 84% of cases, only 0-2 corrections were required. The average total force on the condyles was 215 ± 86 N.
Our study provides data to surgeons on the results to expect when balancing a knee, which can enhance both accuracy and consistency of the procedure.
Are ligament-tensioning devices interchangeable? A study of femoral rotation
2016, Revue de Chirurgie Orthopedique et Traumatologique
Le réglage de la rotation fémorale peut être obtenu par mise en tension du cadre ligamentaire le genou fléchi à 90° ou à l’aide de repères osseux. Le but principal de ce travail était de comparer la rotation fémorale déterminée à l’aide de différents systèmes de tension ligamentaire (STL) et son but secondaire de comparer cette rotation à celle indiquée par l’axe transépicondylien (ATE).
Nous avons pratiqué 13 PTG postéro-stabilisées Hifit (Ceraver^®) sur des genoux cadavériques. Avant réalisation de la coupe condylienne postérieure (CCP), nous avons mesuré, par une méthode originale, la rotation fémorale induite par 5 STL différents (2 à crémaillère, un à vis, un à force mesurée et un à cales) ainsi que la hauteur de l’espace fémoro-tibial central (DFTC).
Les deux STL à crémaillère procuraient une rotation externe significativement plus élevée (p = 0,002) de 4,94°C et 4,46° en moyenne que les STL à force mesurée et à cales (3,25° et 4,07° respectivement). Les DFTC engendrées par les différents STL étaient significativement différentes (p < 0,005), avec une différence moyenne de l’ordre de 2 mm entre les STL à crémaillère ou vis et ceux force mesurée et à cales. Les moyennes des différences entre les rotations déterminées avec les STL et l’ATE étaient proches de 0° mais avec des écarts-types supérieurs à 4°.
La rotation fémorale dépendait de la force de distraction exercée. Les STL à force de distraction non mesurée majoraient les forces de distraction et la rotation externe. Le repère de l’ATE ne correspondait pas toujours à une tension ligamentaire équilibrée.
Étude expérimentale.
Are ligament-tensioning devices interchangeable? A study of femoral rotation
2016, Orthopaedics and Traumatology: Surgery and Research
Citation Excerpt :
Several ligament-tensioning devices (LTDs) based on different mechanisms are available. The tibio-femoral distraction force produced by the device may involve the knee joint compartments individually [11] or simultaneously [13,14] or may be positioned using an intramedullary rod [15]. The primary objective of our study was to compare the rotations obtained using various LTDs.
During total knee arthroplasty (TKA), femoral rotation can be adjusted either in relation to bony landmarks or by tensioning the ligaments with the knee in 90° of flexion. The primary objective of this study was to compare femoral rotations achieved using various ligament-tensioning devices. The secondary objective was to compare these femoral rotations to that indicated by the transepicondylar axis (TEA).
We performed 13 posterior-stabilised TKA procedures using HiFit (Ceraver^®) on cadaver knees. Before performing the posterior condyle cut, we used an original method to measure the femoral rotation induced by five different ligament-tensioning devices (2 with a ratchet mechanism, 1 with screws, 1 force-sensing device, and 1 with spacer blocks) and the central tibio-femoral distance (CTFD).
Both ratchet tensioners provided significantly greater mean external rotation values (P = 0.002), of 4.94° and 4.46°, respectively, compared to the force-sensing and spacer tensioners. Significant differences were found across devices for CTFD, with a mean difference of about 2 mm between the ratchet and screw tensioners versus the force-sensing and spacer tensioners. The mean differences in rotations obtained using the tensioners versus the TEA were close to 0° but with standard deviations greater than 4°.
Femoral rotation was dependent on the distraction force applied to the joint. Tensioners that did not measure the distraction force were associated with greater distraction force and external rotation values. The TEA criterion did not reliably indicate good ligament balance.
Experimental study.
Robotic and Sensor-Assisted Technologies in Knee Arthroplasty
2015, Operative Techniques in Orthopaedics
Citation Excerpt :
Through technological advancements in intraoperative instrumentation, improved implant placement and optimized knee stability,5 coupled with appropriate limb alignment and minimal bone resection, have led to improved outcomes and knee function.6,7 The ability now to quantify the soft tissue knee envelope,8 with embedded sensors, allows surgeons to use data to define imbalance, instability, or an overtensioned ligament complex (Fig. 6). Using intraoperative sensors, the surgeon may dynamically adjust the implant rotation, limb alignment,9 and soft tissue tension (Fig. 7) to improve knee replacement balance.
The advancements in knee arthroplasty over the past several decades have focused on implant material and design. Recently, the focus on improved surgical techniques to maximize patient outcomes, and implant longevity, have become integrated into the surgeons’ workflow. Robotics, and advanced sensor technologies enable precise surgical techniques with reproducible surgical outcomes. The ability to provide surgeons with dynamic intraoperative feedback, coupled with a defined algorithmic approach in their operative execution, enables surgeons of all expertise and experience to achieve their surgical plan in an efficient manner. In this current economy-focused health care environment, these technologies must continue to address short and long-term patient satisfaction, implant function, and a reduction in the overall revision burden.

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^☆: No benefits or funds were received in support of this study.

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An in vivo biomechanical analysis of the soft-tissue envelope of osteoarthritic knees☆

Abstract

Section snippets

Materials and methods

Results

Discussion

Conclusions

J Arthroplasty

J Arthroplasty

J Orthop Res

Clin Biomech (Bristol, Avon)

J Biomech

J Biomech

J Arthroplasty

Med Eng Phys

J Biomech