Soft tissue balance in total knee arthroplasty: does stress relaxation occur perioperatively?

Ligament Tension and Balance before and after Robotic-Assisted Total Knee Arthroplasty - Dynamic Changes with Increasing Applied Force

The optimal force applied during ligament balancing in total knee arthroplasty (TKA) is not well understood. We quantified the effect of increasing distraction force on medial and lateral gaps throughout the range of knee motion, both prior to and after femoral resections in tibial-first gap-balancing TKA. Twenty-five consecutive knees in 21 patients underwent robotic-assisted TKA. The posterior cruciate ligament was resected, and the tibia was cut neutral to the mechanical axis. A digital ligament tensioning tool recorded gaps and applied equal mediolateral loads of 70 N (baseline), 90 N, and 110 N from 90 degrees to full extension. A gap-balancing algorithm planned the femoral implant position to achieve a balanced knee throughout flexion. After femoral resections, gap measurements were repeated under the same conditions. Paired t-tests identified gap differences between load levels, medial/lateral compartments, and flexion angle. Gaps increased from 0 to 20 degrees in flexion, then remain consistent through 90 degrees of flexion. Baseline medial gap was significantly smaller than lateral gap throughout flexion (p <0.05). Increasing load had a larger effect on the lateral versus medial gaps (p <0.05) and on flexion versus extension gaps. Increasing distraction force resulted in non-linear and asymmetric gap changes mediolaterally and from flexion to extension. Digital ligament tensioning devices can give better understanding of the relationship between joint distraction, ligament tension, and knee stiffness throughout the range of flexion. This can aid in informed surgical decision making and optimal soft tissue tensioning during TKA.

Functional knee apparatus for the evaluation of ligamentous tensions on contact loads

BACKGROUND

Soft tissue balancing is integral in providing stability following total knee arthroplasty (TKA). Although intraoperative contact load sensors are providing insights into the effects of soft tissue balancing, there is still a lack of understanding of the relationship between the knee's ligamentous tensions and joint surface contact loads. This study reports on the development of a multifunctional testing apparatus that can quantify the effects of ligamentous tension on joint contact loads in a controlled repeatable environment.

METHODS

The functional knee apparatus was constructed to act as an anatomical substitute for the benchtop assessment of intraoperative soft tissue balancing. The system was calibrated through reproduction of results from a cadaveric study that employed intraoperative load sensors. Experimentation was then conducted to quantify the effects of tensile pretension variation on measured contact loads throughout the full range of flexion.

RESULTS

A linear relationship between the ligamentous tensions and contact loads was observed, with ligaments contributing to 74-80% of the measured contact loads. Ligamentous tensions could be approximated from measured contact loads to within ± 23 N.

CONCLUSION

The proposed apparatus can prove to be a valuable tool in the continued exploration of currently undocumented effects (e.g. surgical alteration) in soft tissue balancing. In addition to quantifying the relationship between ligamentous tensions and joint contact loads, soft tissue loading conditions where bicondylar contact was lost (i.e. known sign of kinematic instability) were identified. As a corollary, this system may be able to provide insights on soft tissue balancing standards predictive of patient outcomes.

Systematic alignments yield balanced knees without additional releases in only 11% of knee arthroplasties: a prospective study

PURPOSE

The literature suggests that "forgotten" knees are the most stable knees postoperatively. The main objective of our study was to determine whether a systematic alignment (mechanical, anatomical or kinematic) makes it possible to stabilise the operated joint in extension and in flexion.

METHODS

This monocentric prospective cohort study was conducted between May 1st, 2021 and October 31st, 2021. A total of 132 consecutive patients undergoing primary navigated total knee arthroplasty were included, with a mean age of 72.4 years (7.9; 48.8-91.2 years), a mean body mass index (BMI) of 28.6 kg/m² (4.6; 17.6-41.6) and 71.2% (94/132) women. Mechanical, anatomical and kinematic knee alignments were simulated using Kick software for each patient. The primary outcome was the targeted rate of balanced knees for each type of alignment, based on a three-point score, aiming for a 3/3 score for each knee. Our secondary outcome was to characterise the specific implantation finally achieved by the surgeon.

RESULTS

The targeted balance was reached in 10.6% (14/132), 10.6% (14/132) and 12.9% (17/132) of knees with mechanical, anatomical and kinematic alignment simulations, respectively. None of these simulations provided a superior number of balanced knees (p = 0.87). When simulating a patient-specific implantation, the highest score was reached in 89.1% (115/132) of cases.

CONCLUSION

Systematic alignment simulations achieved knee balance in only 11% of cases. Patient-specific implantation, favouring knee balancing over alignment, allowed an 89% perfect score rate without having to perform any collateral release.

LEVEL OF EVIDENCE

Case series. Level 4.

Predictive Gap-balancing Reduces the Extent of Soft-tissue Adjustment Required After Bony Resection in Robot-assisted Total Knee Arthroplasty-A Comparison With Simulated Measured Resection

Background

To understand the extent and frequency of soft-tissue adjustment required to achieve mediolateral (ML) balance in measured resection (MR) vs gap-balancing (GB) total knee arthroplasty, this study compared ML balance and joint laxity throughout flexion between the 2 techniques. The precision of predictive GB in achieving ML balance and laxity was also assessed.

Methods

Two surgeons performed 95 robot-assisted GB total knee arthroplasties with predictive balancing, limiting tibial varus to 3° and adjusting femoral positioning to optimize balance. A robotic ligament tensioner measured joint laxity. Planned MR (pMR) was simulated by applying neutral tibial and femoral coronal resections and 3° of external femoral rotation. ML balance, laxity, component alignment, and resection depths were compared between planned GB (pGB) and pMR. ML balance and laxity were compared between pGB and final GB (fGB).

Results

The proportion of knees with >2 mm of ML imbalance in flexion or extension ranged from 3% to 18% for pGB vs 50% to 53% for pMR (P < .001). Rates of ML imbalance >3 mm ranged from 0% to 9% for pGB and 30% to 38% for MR (P < .001). The mean pMR laxity was 1.9 mm tighter medially and 1.1 mm tighter laterally than pGB throughout flexion. The mean fGB laxity was greater than the mean pGB laxity by 0.5 mm medially and 1.2 mm laterally (P < .001).

Conclusion

MR led to tighter joints than GB, with ML gap imbalances >3 mm in 30% of knees. GB planning improved ML balance throughout flexion but increased femoral posterior rotation variability and bone resection compared to MR. fGB laxity was likely not clinically significantly different than pGB.

Satisfactory mid- to long-term outcomes of TKA aligned using conventional instrumentation for flexion gap balancing with minimal soft tissue release

PURPOSE

To describe a technique for flexion gap management in total knee arthroplasty (TKA) using conventional instrumentation with minimal soft tissue release, by aligning the femoral component to restore close-to-native posterior condylar angle (PCA). The hypothesis was that this technique renders consistent outcomes, regardless the preoperative deformity or intraoperative parameters.

METHODS

In a consecutive series of 152 TKAs, the femoral component was rotated to restore anatomic PCA of 2° ± 2° and the flexion gap was balanced with a final lateral flexion laxity of 1-3 mm. Patients were assessed using the Knee Society Score (KSS), the Oxford Knee Score (OKS) and University of California Los Angeles (UCLA) activity score at a minimum follow-up of 4 years. Uni- and multivariable analyses were performed to determine associations between clinical scores and patient demographics, PCA, laxity, pre- and postoperative hip-knee-ankle (HKA) angle, and preoperative femoral mechanical angle (FMA) and tibial mechanical angle (TMA).

RESULTS

Intraoperative measurements indicated a target PCA of 2.9° ± 1.0° (range 0°-6°) with a final lateral flexion laxity of 1.5 ± 0.6 mm (range 0-3). The target PCA was achieved in 145 knees (95%) and the desired final lateral flexion laxity was achieved in 151 knees (99.3%). There were no significant differences in postoperative clinical outcomes between knees within the target PCA range and outliers. KSS function decreased with age and preoperative HKA angle, and was lower for women, while KSS satisfaction improved with follow-up. OKS increased with target PCA and follow-up, decreased with preoperative TMA, was lower for women and better for knees with resurfaced patellae. UCLA activity decreased with age, preoperative HKA angle and BMI, and was lower for women.

CONCLUSIONS

In this consecutive series of 152 TKAs performed with minimal ligament release, the target PCA and final lateral flexion laxity were simultaneously achieved in 95% of knees. At a minimum follow-up of 4 years, adequate clinical scores and patient satisfaction were achieved, even in knees outside the target PCA range.

LEVEL OF EVIDENCE

IV.

Kinetic Sensors for Ligament Balance and Kinematic Evaluation in Anatomic Bi-Cruciate Stabilized Total Knee Arthroplasty

Sensor technology was introduced to intraoperatively analyse the differential pressure between the medial and lateral compartments of the knee during primary TKA using a sensor to assess if further balancing procedures are needed to achieve a “balanced” knee. The prognostic role of epidemiological and radiological parameters was also analysed. A consecutive series of 21 patients with primary knee osteoarthritis were enrolled and programmed for TKA in our unit between 1 September 2020 and 31 March 2021. The VERASENSE Knee System (OrthoSensor Inc., Dania Beach, FL, USA) has been proposed as an instrument that quantifies the differential pressure between the compartments of the knee intraoperatively throughout the full range of motion during primary TKA, designed with a J-curve anatomical femoral design and a PS “medially congruent” polyethylene insert. Thirteen patients (61.90%) showed a “balanced” knee, and eight patients (38.10%) showed an intra-operative “unbalanced” knee and required additional procedures. A total of 13 additional balancing procedures were performed. At the end of surgical knee procedures, a quantitatively balanced knee was obtained in all patients. In addition, a correlation was found between the compartment pressure of phase I and phase II at 10° of flexion and higher absolute pressures were found in the medial compartment than in the lateral compartment in each ROM degree investigated. Moreover, those pressure values showed a trend to decrease with the increase in flexion degrees in both compartments. The “Kinetic Tracking” function displays the knee’s dynamic motion through the full ROM to evaluate joint kinetics. The obtained kinetic traces reproduced the knee’s medial pivot and femoral rollback, mimicking natural knee biomechanics. Moreover, we reported a statistically significant correlation between the need for soft tissue or bone resection rebalancing and severity of the initial coronal deformity (>10°) and a preoperative JLCA value >2°. The use of quantitative sensor-guided pressure evaluation during TKA leads to a more reproducible “balanced” knee. The surgeon, evaluating radiological parameters before surgery, may anticipate difficulties in knee balance and require those devices to achieve the desired result objectively.

Postoperative laxity of the lateral soft tissue is largely negligible in total knee arthroplasty for varus osteoarthritis

PURPOSE

To evaluate the integrity of lateral soft tissue in varus osteoarthritis knee by comparing the mechanical axis under varus stress during navigation-assisted total knee arthroplasty before and after compensating for a bone defect with the implant.

METHODS

Sixty-six knees that underwent total knee arthroplasty were investigated. The mechanical axis of the operated knee was evaluated under manual varus stress immediately after knee exposure and after navigation-assisted implantation. The correlation between each value of the mechanical axis and degree of preoperative varus deformity was compared by regression analysis.

RESULTS

The maximum mechanical axis under varus stress immediately after knee exposure increased in proportion to the degree of preoperative varus deformity. Moreover, the maximum mechanical axis under varus stress after implantation increased in proportion to the degree of preoperative varus deformity. Therefore, the severity of varus knee deformity leads to a progressive laxity of the lateral soft tissue. However, regression coefficients after implantation were much smaller than those measured immediately after knee exposure (0.99 vs 0.20). Based on the results of the regression formula, the postoperative laxity of the lateral soft tissue was negligible, provided that an appropriate thickness of the implant was compensated for the bone and cartilage defect in the medial compartment without changing the joint line.

CONCLUSION

The severity of varus knee deformity leads to a progressive laxity of the lateral soft tissue. However, even if the degree of preoperative varus deformity is severe, most cases may not require additional procedures to address the residual lateral laxity.

Selective medial release using multiple needle puncturing with a spacer block in situ for correcting severe varus deformity during total knee arthroplasty

INTRODUCTION

We aimed to establish a selective and sequential medial release technique using multiple needle puncturing (MNP) with a spacer block in situ in severe varus deformity during total knee arthroplasty (TKA) and to investigate its efficacy and safety.

MATERIALS AND METHODS

A total of 128 patients with a varus angle >15° were included. Patients were classified according to the tightness of extension and flexion (group 1, no tightness; group 2, extension; group 3, flexion; group 4, extension and flexion). When medial tightness was found on extension, the posterior clearing procedure, including release of the posterior capsule, posterior oblique ligament, and semimembranosus, was performed sequentially. When medial tightness was found on flexion, MNP using an 18-gauge needle with a spacer block in situ was performed at the anterior portion of the superficial MCL (aMCL). Clinical and radiological evaluations including stress radiographs were performed.

RESULTS

Among 128 knees, 110 required medial release (posterior clearing procedure only in 44 [34.3%], MNP with a spacer block in situ at aMCL only in 38 [29.7%], posterior clearing procedure and MNP in 28 [21.9%]). The mediolateral gap imbalances on extension and/or flexion were significantly improved (p < 0.001 in all). There were no significant differences in clinical radiological outcomes among groups. Over-release, iatrogenic transection, and postoperative laxity on the stress radiographs were not observed.

CONCLUSION

The selective and sequential technique using posterior clearing and/or MNP with a spacer block in situ can be a reliable option for managing medial tightness in severe varus deformity during primary TKA.

Residual medial tightness in extension is corrected spontaneously after total knee arthroplasty in varus knees

PURPOSE

Although soft tissue balancing is considered important for successful total knee arthroplasty (TKA), it is unclear whether the laxity and balance achieved intraoperatively change postoperatively. A recent study demonstrated anaesthesia significantly influenced knee joint laxity after TKA; however, there has been no comparison of the varus-valgus laxity immediately after TKA and in the postoperative period under the same anesthetic conditions. Therefore, quantitative stress arthrometric studies were conducted under identical conditions to identify changes in coronal ligament laxity after TKA spontaneously.

METHODS

A consecutive series of 28 knees with varus of more than 5° in 28 patients undergoing staged bilateral TKAs was prospectively evaluated. Postoperative varus-valgus laxity was measured immediately after surgery, with the patient still under spinal anaesthesia; and again at the time of the contralateral TKA, again under anaesthesia. The mean time between the first and second operations was 9.7 ± 7.3 months.

RESULTS

Mean medial laxity significantly changed from 2.4° ± 1.6° just after the first operation under anaesthesia to 3.8° ± 1.4° just after contralateral TKA under anaesthesia (p < 0.001), but no significant change occurred in lateral laxity (5.6° ± 2.4° just after the first operation and 5.7° ± 2.1° after contralateral TKA, n.s.). Significant negative correlations were identified between laxity immediately after surgery and the amount of laxity change on both the medial (R = - 0.63, p < 0.001) and lateral sides (R = - 0.53, p < 0.001).

CONCLUSION

Spontaneous soft tissue correction occurs after TKA. The findings from this study provides a rationale that it is not necessary for surgeons to perform the medial soft tissue release until the soft tissue tension is equalized on both the medial and lateral sides which has the risk of excessive release leading to instability. In situations where the surgeon is confronted with a knee that becomes too tight or too loose depending on the insert thickness, it is recommended to choose the thicker insert with the understanding that the knee will initially have a slightly tighter medial compartment that will loosen over time. The results of this study provide technical considerations that can help a surgeon achieve adequate postoperative stability.

LEVEL OF EVIDENCE

IV.

Relationship between outcome scores and knee laxity following total knee arthroplasty: a systematic review

Background and purpose - Instability following primary total knee arthroplasty (TKA) is, according to all national registries, one of the major failure mechanisms leading to revision surgery. However, the range of soft-tissue laxity that favors both pain relief and optimal knee function following TKA remains unclear. We reviewed current evidence on the relationship between instrumented knee laxity measured postoperatively and outcome scores following primary TKA. Patients and methods - We conducted a systematic search of PubMed, Embase, and Cochrane databases to identify relevant studies, which were cross-referenced using Web of Science. Results - 14 eligible studies were identified; all were methodologically similar. Both sagittal and coronal laxity measurement were reported; 6 studies reported on measurement in both extension and flexion. In knee extension from 0° to 30° none of 11 studies could establish statistically significant association between laxity and outcome scores. In flexion from 60° to 90° 6 of 9 studies found statistically significant association. Favorable results were reported for posterior cruciate retaining (CR) knees with sagittal laxity between 5 and 10 mm at 75-80° and for knees with medial coronal laxity below 4° in 80-90° of flexion. Interpretation - In order to improve outcome following TKA careful measuring and adjusting of ligament laxity intraoperatively seems important. Future studies using newer outcome scores supplemented by performance-based scores may complement current evidence.

The impact of residual varus alignment following total knee arthroplasty on patient outcome scores in a constitutional varus population

BACKGROUND

Following a total knee arthroplasty (TKA), restoration of the mechanical axis of the lower limb to a neutral position of 0° ± 3° is generally considered the standard of care. Little is known, however, regarding the impact of realignment defined according to the patient's physiologic anatomy on clinical outcome scores.

METHODS

The study included 67 knees with a mean age of 65.9 ± 8.3 years with unilateral osteoarthritis (OA) who underwent a primary unilateral TKA for medial end-stage OA. Patients were categorized based on post-operative limb alignment in one of two ways, either based on alignment relative to their contralateral, physiologic side (physiologic), or alignment relative to a neutral axis (neutral). Knee Society Score (KSS), Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC), and the 12-Item Short Form Survey (SF-12) were compared between the two groups.

RESULTS

WOMAC Total and subscale scores improved for both groups between the pre- and post-operative time points. SF-12 scores were comparable post-operatively between the groups. WOMAC and KSS total and subscale scores were slightly greater post-operatively in the group not aligned according to their physiologic anatomy (neutral). However, none of these differences reached a level of significance.

CONCLUSION

Post-operatively, residual varus and neutral limb alignment lead to comparable clinical outcome scores. In a constitutional varus population with medial end-stage OA, aligning the lower limb during a TKA to a neutral position rather than the patient's native anatomy does not negatively impact self-reported patient outcome scores at the one and two-year time points.

Assessment of the midflexion rotational laxity in posterior-stabilized total knee arthroplasty

PURPOSE

To evaluate changes in midflexion rotational laxity before and after posterior-stabilized (PS)-total knee arthroplasty (TKA).

METHODS

Twenty-nine knees that underwent PS-TKA were evaluated. Manual mild passive rotational stress was applied to the knees, and the internal-external rotational angle was measured automatically by a navigation system at 30°, 45°, 60°, and 90° of knee flexion.

RESULTS

The post-operative internal rotational laxity was statistically significantly increased compared to the preoperative level at 30°, 45°, 60°, and 90° of flexion. The post-operative external rotational laxity was statistically significantly decreased compared to the preoperative level at 45° and 60° of flexion. The post-operative internal-external rotational laxity was statistically significantly increased compared to the preoperative level only at 30° of flexion. The preoperative and post-operative rotational laxity showed a significant correlation at 30°, 45°, 60°, and 90° of flexion.

CONCLUSION

Internal-external rotational laxity increases at the initial flexion range due to resection of both the anterior or posterior cruciate ligaments and retention of the collateral ligaments in PS-TKA. Preoperative and post-operative rotational laxity indicated a significant correlation at the midflexion range. This study showed that a large preoperative rotational laxity increased the risk of a large post-operative laxity, especially at the initial flexion range in PS-TKA.

LEVEL OF EVIDENCE

III.

Patient-related factors influence stiffness of the soft tissue complex during intraoperative gap balancing in cruciate-retaining total knee arthroplasty

PURPOSE

How much force is needed to pre-tension the ligaments during total knee arthroplasty? The goal of this study was to determine this force for extension and flexion, and for both compartments, and to identify predicting patient-related factors.

METHODS

Eighty patients [55 females, mean age 71 (SD 9.7)] were recruited and had a navigated cruciate-retaining total knee arthroplasty. Distraction of the medial and lateral compartments of the extension and flexion gap (90°) with an instrumented bi-compartmental double-spring tensioner took place after finishing the bone cuts. Applied forces and resulting gap distances were recorded by the navigation system, resulting in a force-elongation curve. Lines were fitted with the intersection defined as the stiffness transition point. The slopes (N/mm) represented the stiffness of the ligamentous complex. Linear multiple regression analysis was performed to identify predicting factors.

RESULTS

The amount of force at the stiffness transition point was on average 52.3 (CI₉₅ 50.7-53.9), 54.5 (CI₉₅ 52.7-56.3), 48.3 (CI₉₅ 46.2-50.2), and 59.3 (CI₉₅ 57.0-61.6) N for the medial and lateral extension and flexion gap, respectively, and varied considerably between patients. The force at the stiffness transition point was significantly different between extension and flexion and both compartments (P < 0.05). Stiffness of the ligaments statistically significantly helped to predict the amount of force at the stiffness transition point, as well as body mass index, gender, and varus-valgus alignment.

CONCLUSION

The amount of force at the stiffness transition point varies between 48 and 59 N, depending on flexion/extension and compartment. Patient-related factors influence the stiffness transition point and can help predict the stiffness transition point. When forces higher than 60 N are used for gap distraction, the ligamentous sleeve of the knee might be over-tensioned.

LEVEL OF EVIDENCE

Prognostic study, Level I-high-quality prospective cohort study with >80 % follow-up, and all patients enrolled at same time point in disease.

Effects of Cementing on Ligament Balance During Total Knee Arthroplasty

Complications related to joint imbalance may contribute to some of the most predominant modes of failure in total knee arthroplasty (TKA). These complications include instability, aseptic loosening, asymmetric component wear, and idiopathic pain. Fixation may represent a step that introduces unchecked variability into the procedure and may contribute to the incidence of joint imbalance-related complications. The ability to quantify in vivo loading in the medial and lateral compartments would allow for the ability to confirm balance after fixation and prior to wound closure. This retrospective study sought to capture any variability and imbalance associated with cementing technique. A total of 93 patients underwent sensor-assisted TKA. All patients were confirmed to have quantifiably balanced joints prior to cementation. After cementing and final component placement, the sensor was reinserted into the joint to capture any cementation-induced changes in loading. Imbalance was observed in 44% of patients after cementation. There was no difference in the proportion of imbalance due to surgeon experience (P=.456), cement type (P=.429), or knee system (P=.792). A majority of knees exhibited loading increase in the medial compartment. It was concluded that cementation technique contributes to a significant amount of balance-related variability at the fixation stage of the procedure. The use of the sensor in this study allowed for the correction of all instances of imbalance prior to closure. More objective methods of balance verification may be important for ensuring optimal surgical outcomes. [Orthopedics. 2017; 40(3):e455-e459.].

Accuracy of Balancing at Total Knee Surgery Using an Instrumented Tibial Trial

BACKGROUND

Balancing is an important part of a total knee procedure, and in recent years, more emphasis has been given to quantifying the process.

METHODS

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).

RESULTS

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.

CONCLUSION

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.

Preoperative varus-valgus kinematic pattern throughout flexion persists more strongly after cruciate-retaining than after posterior-stabilized total knee arthroplasty

BACKGROUND

Restoration of normal knee kinematics is key to improving patient satisfaction and functional outcomes after total knee arthroplasty (TKA). However, the effect of preoperative varus-valgus kinematics due to knee osteoarthritis on the postoperative kinematics is unclear. The function of the knee ligament contributes to both knee stability and kinematics. The aim of this study was to evaluate changes in varus-valgus kinematics before and after TKA using a navigation system, in addition to comparing the pre- and postoperative changes in kinematic patterns between cruciate-retaining (CR)- and posterior-stabilized (PS)-TKAs.

METHODS

Forty knees treated with TKA were evaluated (CR-TKA 20; PS-TKA 20). Manual mild passive knee flexion was applied while moving the leg from full extension to flexion. The varus-valgus angle was automatically measured by a navigation system at every 10° of the flexion angle, and the kinematics were evaluated.

RESULTS

Kinematic patterns throughout flexion can be classified into five types. The pre- and postoperative kinematic patterns were similar in 60% of patients who underwent CR-TKA, whereas they were similar in only 25% of those who underwent PS-TKA. The mean change in the size of the varus-valgus angle throughout flexion did not differ between CR-TKA and PS-TKA. However, the distribution of changes in the size of the varus-valgus angle differed between CR-TKA and PS-TKA.

CONCLUSIONS

We obtained the following results: 1) some patterns of varus-valgus kinematics are noted under unloading conditions despite recovery of neutral alignment in extension and 2) the preoperative varus-valgus kinematic pattern persisted more strongly after CR-TKA than after PS-TKA.

An Algorithmic, Pie-Crusting Medial Soft Tissue Release Reduces the Need for Constrained Inserts Patients With Severe Varus Deformity Undergoing Total Knee Arthroplasty

BACKGROUND

We studied the need to use a constrained insert for residual intraoperative instability and the 1-year result of patients undergoing total knee arthroplasty (TKA) for a varus deformity. In a control group, a "classic" subperiosteal release of the medial soft tissue sleeve was performed as popularized by pioneers of TKA. In the study group, an algorithmic approach that selectively releases and pie-crusts posteromedial structures in extension and anteromedial structures in flexion was used.

METHODS

All surgeries were performed by a single surgeon using measured resection technique, and posterior-stabilized, cemented implants. There were 228 TKAs in the control group and 188 in the study group. Outcome variables included the use of a constrained insert, and the Knee Society Score at 6 weeks, 4 months, and 1 year postoperatively. The effect of the release technique on use of constrained inserts and clinical outcomes were analyzed in a multivariate model controlling for age, sex, body mass index, and severity of deformity.

RESULTS

The use of constrained inserts was significantly lower in study than in control patients (8% vs 18%; P = .002). There was no difference in the Knee Society Score and range of motion between the groups at last follow-up. No patient developed postoperative medial instability.

CONCLUSION

This algorithmic, pie-crusting release technique resulted in a significant reduction in the use of constrained inserts with no detrimental effects in clinical results, joint function, and stability. As constrained TKA implants are more costly than nonconstrained ones, if the adopted technique proves to be safe in the long term, it may cause a positive shift in value for hospitals and cost savings in the health care system.

Mapping of contributions from collateral ligaments to overall knee joint constraint: an experimental cadaveric study

Understanding the contribution of the soft-tissues to total joint constraint (TJC) is important for predicting joint kinematics, developing surgical procedures, and increasing accuracy of computational models. Previous studies on the collateral ligaments have focused on quantifying strain and tension properties under discrete loads or kinematic paths; however, there has been little work to quantify collateral ligament contribution over a broad range of applied loads and range of motion (ROM) in passive constraint. To accomplish this, passive envelopes were collected from nine cadaveric knees instrumented with implantable pressure transducers (IPT) in the collateral ligaments. The contributions from medial and lateral collateral ligaments (LCL) were quantified by the relative contribution of each structure at various flexion angles (0-120 deg) and compound external loads (±10 N m valgus, ±8 N m external, and ±40 N anterior). Average medial collateral ligament (MCL) contributions were highest under external and valgus torques from 60 deg to 120 deg flexion. The MCL showed significant contributions to TJC under external torques throughout the flexion range. Average LCL contributions were highest from 0 deg to 60 deg flexion under external and varus torques, as well as internal torques from 60 deg to 110 deg flexion. Similarly, these regions were found to have statistically significant LCL contributions. Anterior and posterior loads generally reduced collateral contribution to TJC; however, posterior loads further reduced MCL contribution, while anterior loads further reduced LCL contribution. These results provide insight to the functional role of the collaterals over a broad range of passive constraint. Developing a map of collateral ligament contribution to TJC may be used to identify the effects of injury or surgical intervention on soft-tissue, and how collateral ligament contributions to constraint correlate with activities of daily living.

Comparison of cruciate retaining and PCL sacrificing TKA with respect to medial and lateral gap differences in varus knees after medial release

We aimed to clarify whether the increase in medial gap after medial release is influenced by the retention or sacrifice of posterior cruciate ligament (PCL) during navigation-assisted total knee arthroplasty. After matched pairs were done according to the equality of preoperative varus deformity and medial collateral laxity, 54 knees of each type were available for this study. In the PCL sacrificing group, the mediolateral gap difference significantly increased in both flexion and extension as the preoperative mechanical axis angle increased whereas in the cruciate retaining group, the mediolateral gap difference did not show this tendency. When preoperative mechanical axis angles were over 10.4° in extension and over 7.7° in flexion, the medial gap showed greater increases in PCL sacrificing groups than in cruciate retaining groups.

How precise is computer-navigated gap assessment in TKA?

BACKGROUND

Methods to improve gap balancing in total knee arthroplasty (TKA) include the development of calibrated distractors and various devices to determine the distances of the gaps. However, few studies have validated the accuracy or precision of computer navigation to determine these measurements, especially gaps created after bone cuts have been made; doing so would be important, because optimal surgical technique relies on appropriate gap spacing.

QUESTIONS/PURPOSES

We investigated the ability of a new image-free computer navigation surface registration protocol to measure gap distances in TKA.

METHODS

Eight embalmed cadaveric specimens of the lower extremity were used. A surface registration software protocol defined the most distal and posterior surface points of the femoral condyles and the navigation system measured the distance of the most distal femoral condyle point to the surface of the tibia after tibial resection. The tibial resection was perpendicular to the mechanical axis and was cut with a 7° posterior slope. The navigation system measured gaps spaced by modular spacing blocks at 5° intervals from full extension to 120° of flexion. Repeatability assessed repeated measures by one surgeon. Reproducibility was assessed by performing the same measurements after complete reregistration of the computer protocol to the cadaver bones.

RESULTS

The gaps measured by the computer were statistically the same as those assessed with the use of blocks with a maximum measurement error of 1 mm. Reregistration did introduce error into the measurement. The gaps changed with position of knee flexion, and there was gradual and significant stretching of the gaps with repeated measurements.

CONCLUSIONS

Preliminary testing shows that computer navigation can reproduce static measurements reliably and with equal accuracy as spacer blocks. We have not demonstrated that this could be applied in a dynamic setting.

CLINICAL RELEVANCE

This computer navigation system has sufficient precision to warrant investigation in the clinical setting for measuring gaps created during the surgical procedure.

Extension and flexion gap balancing and its correlation with alignment in navigated total knee arthroplasty

Computer-assisted surgery was developed to improve the results of conventional total knee arthroplasty (TKA). The authors investigated the preoperative varus/valgus deformity influence on the production of balanced extension and flexion gaps using computer-assisted surgery. This study evaluated data from a prospective case series. A total of 132 patients (107 women and 25 men) underwent navigated TKA. Patients were divided into the following 3 groups according to the degree of the initial varus/valgus deformity: group 1, 0° to 3°; group 2, 3° to 9°; and group 3, greater than 9°. The final lower limb mechanical axis (LLMA) and the final flexion and extension gaps were measured. Knees exhibiting up to 3° of deviation on the frontal plane and a difference of up to 3 mm between the lateral and medial gaps were considered to be aligned and balanced, respectively. Average LLMA deviation decreased from 5.58° (± 4.80°) to 1.87° (± 1.66°). For knees with varus deviation, the percentage of balancing relative to the flexion gaps was 97.8% and that relative to the extension gap was 100% (P>.05). For knees with valgus deviation, the percentage of balancing relative to the flexion gaps was 95.1% and that relative to the extension gap was 97.6% (P>.05). Approximately 92% of the LLMA alignment was achieved in the group with varus deformity, whereas 71.4% was observed in the group with valgus deformity (P<.05). Computer-assisted TKA could attain proper flexion and extension balance regardless of coronal plane malalignment magnitude. Severe valgus and varus knees are more difficult to align using navigation. No difference was found in the balance of flexion or extension gaps in valgus or varus knees, independent of the severity.

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.

Physiologic bone remodeling in medial aspect of proximal tibia after under-release of medial soft tissue during total knee arthroplasty

INTRODUCTION

This study was undertaken to investigate the incidence and to identify predictors of physiologic remodeling in the medial aspect of the proximal tibia in varus knees after total knee arthroplasty (TKA).

MATERIALS AND METHODS

One hundred and sixty-six consecutive patients (221 knees) who underwent navigation-assisted TKA and were followed for a minimum of 2 years were included. Changes in bone radiolucency in the medial aspect of the proximal tibia on the radiographs were investigated at each follow-up. All information on potential factors affecting medial tibial remodeling were retrieved and classified as being patient-, radiography-, or surgery-related.

RESULTS

Radiographic change of bone stock in the medial aspect of the proximal tibia was observed in 18 % of knees (39/221). In all of these cases, this was first detected within 3 months after surgery. During the initial phase to 3 months after surgery, bone stock radiolucency typically increased, but then gradually decreased and after 1 year postoperatively, radiolucency no longer changes with time. Of the 15 variables analyzed, the difference between medial extension gap after bone cutting and prostheses thickness was found to be significantly associated with occurrence of radiographic change of bone stock.

CONCLUSION

In some varus knees showing physiologic bone remodeling in the medial aspect of the proximal tibia after TKA, prostheses thickness showed a strong tendency to be larger than the medial extension gap after bone cutting.

Unified quantification of variation in passive knee joint constraint

The interrelationship that exists between multiple degrees of freedom to produce a net constraint across the range of passive motion of the knee is not fully understood. Manual joint laxity assessments were performed on 28 cadaveric specimens and used to develop a unified description of the passive laxity envelope that incorporated multiple degrees of freedom into a single analysis using radial basis functions. The unified envelopes were then included in a principal component analysis to identify the primary modes of variation. The first three modes of variation constituted 82% of the variation. The first principal component (36.5% explained variation) correlated with changes to the relationship between varus-valgus and internal-external rotation and had the largest impact on internal-external laxity. The second principal component (27.2% explained variation) correlated with a shift in the internal-external envelope. The third principal component (18.3% explained variation) correlated with a shift in the varus-valgus envelope and a change in varus-valgus laxity. This research presents a novel methodology for quantifying complex changes to passive knee constraint, which may be used as a means for objectively scoring joint laxity and evaluating complex relationships between degrees of freedom in a single analysis.

Design and cadaveric validation of a novel device to quantify knee stability during total knee arthroplasty

The success of total knee arthroplasty depends, in part, on the ability of the surgeon to properly manage the soft tissues surrounding the joint, but an objective definition as to what constitutes acceptable postoperative joint stability does not exist. Such a definition may not exist due to lack of suitable instrumentation, as joint stability is currently assessed by visual inspection while the surgeon manipulates the joint. Having the ability to accurately and precisely measure knee stability at the time of surgery represents a key requirement in the process of objectively defining acceptable joint stability. Therefore, we created a novel sterilizable device to allow surgeons to measure varus-valgus, internal-external, or anterior-posterior stability of the knee during a total knee arthroplasty. The device can be quickly adjusted between 0 deg and 90 deg of knee flexion. The device interfaces with a custom surgical navigation system, which records the resultant rotations or translations of the knee while the surgeon applies known loads to a patient's limb with a handle instrumented with a load cell. We validated the performance of the device by having volunteers use it to apply loads to a mechanical linkage that simulated a knee joint; we then compared the joint moments calculated by our stability device against those recorded by a load cell in the simulated knee joint. Validation of the device showed low mean errors (less than 0.21 ± 1.38 Nm and 0.98 ± 3.93 N) and low RMS errors (less than 1.5 Nm and 5 N). Preliminary studies from total knee arthroplasties performed on ten cadaveric specimens also demonstrate the utility of our new device. Eventually, the use of this device may help determine how intra-operative knee stability relates to postoperative function and could lead to an objective definition of knee stability and more efficacious surgical techniques.

Surgical technique: Computer-assisted sliding medial condylar osteotomy to achieve gap balance in varus knees during TKA

BACKGROUND

Extensive posteromedial release to correct severe varus deformity during TKA may result in mediolateral or flexion instability and may require a constrained implant. We describe a technique combining computer navigation and medial condylar osteotomy in severe varus deformity to achieve a primary goal of ligament balance during TKA.

DESCRIPTION OF TECHNIQUE

The goal of this procedure was to achieve mediolateral gap balance in varus knees with rigid, recalcitrant medial contracture, with or without excessive lateral laxity, not amenable to extensive medial soft tissue releases. A sliding medial condylar osteotomy (SMCO) was performed under navigation guidance and the condylar block internally fixed using cancellous screws.

METHODS

We prospectively evaluated mediolateral laxity, Knee Society scores, and knee ROM after SMCO in 12 varus arthritic knees in 11 patients (five men, six women) undergoing TKA with a minimum followup of 2 years (mean, 2 years; range, 2-2.5 years).

RESULTS

The degree of mediolateral knee laxity improved from Grade 2 (in four knees) and Grade 3 (in eight knees) preoperatively to Grade 1 (< 5 mm) in all knees at last followup. Mean Knee Society score improved from 30 (range, 10-54) to 92 (range, 86-100). Mean knee flexion improved from 106° (range, 90°-120°) to 112° (range, 100°-124°), and no knee had any extensor lag or residual flexion deformity (> 5°). Three knees had asymptomatic fibrous union at the osteotomy site.

CONCLUSIONS

Computer-assisted SMCO in varus knees with recalcitrant medial contracture achieves improved mediolateral stability and knee function after TKA. Our technique uses navigation to accurately reposition the medial condylar block to equalize medial and lateral gaps, thereby ensuring a stable well-aligned knee without deploying constrained implants.

Which factors increase risk of malalignment of the hip-knee-ankle axis in TKA?

BACKGROUND

Computer navigation has improved accuracy and reduced the percentage of alignment outliers in TKA. However, the characteristics of outliers and the risk factors for limb malalignment after TKA are still unclear.

QUESTIONS/PURPOSES

We therefore addressed the following questions: (1) What is the incidence and characteristics of outliers for postoperative limb mechanical axis (hip-knee-ankle [HKA] angle outside the conventional 180° ± 3° range) and component alignment in TKA? And (2) what are the preoperative clinical or radiographic risk factors for limb mechanical axis malalignment in TKA?

METHODS

We retrospectively reviewed the clinical and radiographic records of 1500 computer-assisted TKAs to identify outliers for postoperative HKA axis and component alignment and determined risk factors for malalignment. Full-length hip-to-ankle and knee radiographs were used to measure preoperative HKA angle, femoral coronal bowing, joint divergence angle, tibial subluxation, and tibial bone loss and postoperative HKA angle and femoral and tibial component angle.

RESULTS

The incidence of outliers for postoperative limb mechanical axis, femoral component alignment, and tibial component alignment was 7% (112 of 1500 TKAs), 7%, and 8%, respectively, with 70% of limbs placed in excessive varus and 30% in excessive valgus. Preoperative varus deformity of more than 20° and femoral bowing of more than 5° were associated with increased risk of placing the limb mechanical axis outside the acceptable ± 3° range after computer-assisted TKA.

CONCLUSIONS

The presence of preoperative radiographic risk factors should alert the surgeon to increased chance of malalignment and every measure should be undertaken in such at-risk knees to ensure proper limb and component alignment and soft tissue balance.

No difference between tibia-first and femur-first techniques in TKA using computer-assisted surgery

PURPOSE

The measured resection technique and the gap-balancing technique are two philosophies used in total knee surgery. It is still unknown whether one or the other technique provides superior results when computer-assisted surgery is performed. We hypothesized that the gap-balancing technique improves joint stability because the technique relies primarily on the soft tissue.

METHODS

A prospective controlled study was performed in 116 patients using the tibia-first or femur-first technique. The Columbus(TM) total knee system and the Orthopilot(®) (Aesculap(®) AG, Tuttlingen, Germany) navigation system were used in all cases. Sixty-three patients were allocated to the femur-first technique (group F) and 53 patients to the tibial first technique (group T). The mean follow-up time was 11.4 ± 1.1 months. The KSS, KOOS and SF-36 were taken prior to surgery and at the time of follow-up for clinical assessment. Long-leg weight-bearing radiographs were performed to assess ligament alignment. Radiographs in varus and valgus stress were performed using the Telos(®)-Instrument (Telos(®) GmbH, Greisheim, Germany) under a force of 15 N at the time of follow-up for the assessment of medial-lateral stability. The nonparametric t test (Mann-Whitney U-test) was used in order to compare the ligament stability and the scores between group F and group T.

RESULTS

The lateral joint space opening for groups F and T was 3.4° ± 1.4° and 3.9° ± 1.7°, respectively (n.s.), and the medial joint space opening for groups F and T was 4° ± 1.4° and 4.1° ± 1.7°, respectively (n.s.). The femorotibial mechanical axis for groups F and T revealed 1.4° ± 1.2° and 0.7° ± 2.0° of varus, respectively (p = 0.138). The clinical assessment showed significant improvement according to KSS, KOOS and SF-36 in all subscales. Neither of the sores showed significant differences between the two groups.

CONCLUSION

The surgeon should use his/her preferred surgical technique providing the implantation is performed with computer assistance. It remains unclear whether the same findings will occur after conventional surgery.

LEVEL OF EVIDENCE

II.

Standardising the clinical assessment of coronal knee laxity

Clinical laxity tests are used for assessing knee ligament injuries and for soft tissue balancing in total knee arthroplasty. This study reports the development and validation of a quantitative technique of assessing collateral knee laxity through accurate measurement of potential variables during routine clinical examination. The hypothesis was that standardisation of a clinical stress test would result in a repeatable range of laxity measurements.

Non-invasive infrared tracking technology with kinematic registration of joint centres gave real-time measurement of both coronal and sagittal mechanical tibiofemoral alignment. Knee flexion, moment arm and magnitude of the applied force were all measured and standardised. Three clinicians then performed six knee laxity examinations on a single volunteer using a target moment of 18 Nm.

Standardised laxity measurements had small standard deviations (within 1.1°) for each clinician and similar mean values between clinicians, with the valgus laxity assessment (mean of 3°) being slightly more consistent than varus (means of 4° or 5°).

The manual technique of coronal knee laxity assessment was successfully quantified and standardised, leading to a narrow range of measurements (within the accuracy of the measurement system). Minimising the subjective variables of clinical examination could improve current knowledge of soft tissue knee behaviour.

Multiple needle puncturing: balancing the varus knee

The so-called "pie crusting" technique using multiple stab incisions is a well-established procedure for correcting tightness of the iliotibial band in the valgus knee. It is, however, not applicable for balancing the medial side in varus knees because of the risk for iatrogenic transsection of the medial collateral ligament (MCL). This article presents our experience with a safer alternative and minimally invasive technique for medial soft tissue balancing, where we make multiple punctures in the MCL using a 19-gauge needle to progressively stretch the MCL until a correct ligament balance is achieved. Our technique requires minimal to no additional soft tissue dissection and can even be performed percutaneously when necessary. This technique, therefore, does not impact the length of the skin or soft tissue incisions. We analyzed 61 cases with varus deformity that were intraoperatively treated using this technique. In 4 other cases, the technique was used as a percutaneous procedure to correct postoperative medial tightness that caused persistent pain on the medial side. The procedure was considered successful when a 2- to 4-mm mediolateral joint line opening was obtained in extension and 2 to 6 mm in flexion. In 62 cases (95%), a progressive correction of medial tightness was achieved according to the above-described criteria. Three cases were overreleased and required compensatory release of the lateral structures and use of a thicker insert. Based on these results, we consider needle puncturing an effective and safe technique for progressive correction of MCL tightness during minimally invasive total knee arthroplasty.

A new surgical technique for medial collateral ligament balancing: multiple needle puncturing

In this article, we present our experience with a new technique for medial soft tissue balancing, where we make multiple punctures in the medial collateral ligament (MCL) using a 19-gauge needle, to progressively stretch the MCL until a correct ligament balance is achieved. Ligament status was evaluated both before and after the procedure using computer navigation and mediolateral stress testing. The procedure was considered successful when 2 to 4-mm mediolateral joint line opening was obtained in extension and 2 to 6 mm in flexion. In 34 of 35 cases, a progressive correction of medial tightness was achieved according to the above described criteria. One case was considered overreleased in extension. Needle puncturing is a new, effective, and safe technique for progressive correction of MCL tightness in the varus knee.

The influence of coronal plane deformity on mediolateral ligament status: an observational study in varus knees

Most surgeons believe that varus deformity leads to progressive tightness of the medial soft tissue envelope and laxity on the lateral side. It is, however, unclear at what stage of the deformity such ligament alterations occur, and whether these are the consequence of intrinsic alterations in the ligaments themselves, or rather due to extrinsic factors such as osteophytes, adhesions to the underlying bone, or other factors which may cause a tightening effect. Thirty-five varus knees that were scheduled for TKA were investigated. Ligament status was evaluated after temporary correction of alignment and removal of osteophytes, using varus/valgus testing with computer navigation technology. Knees with <10 degrees varus deformity were easily correctable to neutral after correction of the extrinsic factors that could cause medial tightness, and these knees maintained normal mediolateral laxity during varus/valgus stress testing. When coronal plane deformity exceeded 10 degrees, progressive shortening of the medial collateral ligament was noted, as well as progressive stretching of the lateral structures (P < 0.001). This study, therefore, demonstrates that the medial collateral structures become intrinsically shortened when preoperative varus deformity exceeds 10 degrees. Likewise, the lateral soft tissues become stretched. None of these occur when the preoperative deformity is <10 degrees.

Ligament releases do not lead to increased postoperative varus-valgus laxity in flexion and extension: a prospective clinical study in 49 TKR patients

This prospective study investigated whether ligament releases necessary during total knee replacement (TKR) led to a higher varus-valgus laxity during intraoperative examination after implantation of the prosthesis and after 6 months. The laxity values of TKR patients were also compared to healthy controls. Varus-valgus laxity was assessed intra- and postoperatively in extension and 70 degrees flexion in 49 patients undergoing TKR, implanted using a balanced gap technique. Knees were catalogued according to ligament releases performed during surgery. Postoperative varus-valgus laxity and laxity after 6 months had not increased following release of the posteromedial capsule, iliotibial tract, and the superficial medial collateral ligament. The obtained postoperative laxity compares well with a healthy equally aged control group. It can be concluded that the balanced gap technique results in stable knees and that releases can safely be performed to achieve neutral leg alignment without causing postoperative laxity.

Mid-term results with a highly congruous mobile-bearing knee prosthesis

Two hundred and six consecutive total knee arthroplasties were performed in 180 patients with a highly congruous mobile-bearing knee prosthesis. At mean follow-up of 78 months (range: 60-102 months), the outcomes of 181 knees in 158 patients were evaluated using the American Knee Society's Knee and Functional scoring system and Radiological scoring system. Mean values for Knee and Function scores were 92.6 and 81.1, respectively versus 51.8 and 43.4 preoperatively; mean flexion range was 113.6 degrees versus 110.8 degrees preoperatively. There were no cases of bearing dislocation and no radiological signs of loosening or osteolysis. Secondary patella resurfacing was done in 7 of 52 knees in which the patella was not primarily resurfaced. Arthroplasty survival with revision for aseptic loosening as the endpoint was 100% (95% CI: 97.7-100) at 5 years and at 8 years (95% CI: 87.2-100); with revision of the arthroplasty for any reason including one revision for infection as the endpoint, survival was 99.5% (95% CI: 96.9-100) at 5 years and at 8 years (95% CI: 86.9-100). The overall results were satisfactory and compared with those of other mobile-bearing knee prostheses featuring full or partial congruence. No significant differences were noted for range of motion, knee scores and function scores between two subsets of knees that received a bearing allowing only rotation or rotation and 5 mm anteroposterior translation. Longer follow-up is needed to evaluate possible benefits of high congruence and of specific modes of bearing mobility with respect to wear and bony fixation.

Navigational predictors in determining the necessity for collateral ligament release in total knee replacement

The requirement for release of collateral ligaments to achieve a stable, balanced total knee replacement has been reported to arise in about 50% to 100% of procedures. This wide range reflects a lack of standardised quantitative indicators to determine the necessity for a release. Using recent advances in computerised navigation, we describe two navigational predictors which provide quantitative measures that can be used to identify the need for release. The first was the ability to restore the mechanical axis before any bone resection was performed and the second was the discrepancy in the measured medial and lateral joint spaces after the tibial osteotomy, but before any femoral resection.

These predictors showed a significant association with the need for collateral ligament release (p < 0.001). The first predictor using the knee stress test in extension showed a sensitivity of 100% and a specificity of 98% and the second, the difference between medial and lateral gaps in millimetres, a sensitivity of 83% and a specificity of 95%. The use of the two navigational predictors meant that only ten of the 93 patients required collateral ligament release to achieve a stable, neutral knee.

ESB Clinical Biomechanics Award 2008: Complete data of total knee replacement loading for level walking and stair climbing measured in vivo with a follow-up of 6-10 months

BACKGROUND

Detailed information about the loading of the knee joint is required for various investigations in total knee replacement. Up to now, gait analysis plus analytical musculo-skeletal models were used to calculate the forces and moments acting in the knee joint. Currently, all experimental and numerical pre-clinical tests rely on these indirect measurements which have limitations. The validation of these methods requires in vivo data; therefore, the purpose of this study was to provide in vivo loading data of the knee joint.

METHODS

A custom-made telemetric tibial tray was used to measure the three forces and three moments acting in the implant. This prosthesis was implanted into two subjects and measurements were obtained for a follow-up of 6 and 10 months, respectively. Subjects performed level walking and going up and down stairs using a self-selected comfortable speed. The subjects' activities were captured simultaneously with the load data on a digital video tape. Customized software enabled the display of all information in one video sequence.

FINDINGS

The highest mean values of the peak load components from the two subjects were as follows: during level walking the forces were 276%BW (percent body weight) in axial direction, 21%BW (medio-lateral), and 29%BW (antero-posterior). The moments were 1.8%BW*m in the sagittal plane, 4.3%BW*m (frontal plane) and 1.0%BW*m (transversal plane). During stair climbing the axial force increased to 306%BW, while the shear forces changed only slightly. The sagittal plane moment increased to 2.4%BW*m, while the frontal and transversal plane moments decreased slightly. Stair descending produced the highest forces of 352%BW (axial), 35%BW (medio-lateral), and 36%BW (antero-posterior). The sagittal and frontal plane moments increased to 2.8%BW*m and 4.6%BW*m, respectively, while the transversal plane moment changed only slightly.

INTERPRETATION

Using the data obtained, mechanical simulators can be programmed according to realistic load profiles. Furthermore, musculo-skeletal models can be validated, which until now often lacked the ability to predict properly the non-sagittal load values, e.g. varus-valgus and internal-external moments.

Soft tissue tension in extension in total knee arthroplasty affects postoperative knee extension and stability

The purpose of this study was to assess correlation of soft tissue tension in extension with postoperative extension deficit and valgus/varus instability. Sixty-four osteoarthritic knees that underwent primary total knee arthroplasty were investigated. Soft tissue tension in extension was measured during operation with a balancer/tensor device. Extension deficit was measured, and valgus/varus laxity was assessed by stress radiographs in extension and 30 degrees -flexion 1 year after operation. The extension deficit became larger with an increase of soft tissue tension a year after operation. (P < 0.05) The varus laxity in extension and 30 degrees -flexion and valgus laxity in 30 degrees -flexion became smaller with an increase of soft tissue tension (P < 0.05). Our results demonstrated that soft tissue tension during operation affects postoperative knee extension and stability.

Coronal plane stability before and after total knee arthroplasty

The success of total knee arthroplasty depends in part on proper soft tissue management to achieve a stable joint. It is unknown to what degree total knee arthroplasty changes joint stability. We used a surgical navigation system to intraoperatively measure joint stability in 24 patients under going primary total knee arthroplasty to address two questions: (1) Is the total arc of varus-valgus motion after total knee arthroplasty different from the arc of varus-valgus motion in an osteoarthritic knee? (2) Does total knee arthroplasty produce equal amounts of varus/valgus motion (ie, is the knee "balanced")? We observed no difference between the total arc of varus-valgus motion before and after total knee arthroplasty; the total amount of motion was unchanged. On average, osteoarthritic knees were "unbalanced" but were "balanced" after prosthesis implantation. We found a negative correlation between the relative amount of varus/valgus motion in extension before and after prosthesis implantation in extension and a positive correlation between how well the knees were balanced after prosthesis implantation in extension and in flexion. Our data suggest immediately after implantation knees retain a greater than normal amount of varus-valgus motion, but this motion is more evenly distributed.