Mid-flexion instability after total knee arthroplasty: woolly thinking or a real concern?

Mobile bearing shows larger rollback motion than fixed bearing in total knee arthroplasty using a medial stabilising technique with a navigation system

Purpose

This study aimed to investigate the intraoperative knee kinematics of cruciate-retaining total knee arthroplasty with a medial stabilising technique (MST-TKA) and compare the kinematics between mobile- and fixed-bearing MST-TKAs. We hypothesised that mobile-bearing MST-TKA would result in greater physiological kinematic motion than fixed-bearing MST-TKA.

Methods

Twenty-one and 20 knees underwent mobile- and fixed-bearing MST-TKAs using a navigation system (Orthopilot® ver. 6.0; B. Braun Aesculap), respectively. In the preoperative and postoperative kinematic analysis, the knee was moved manually from 0° to 120°, and femoral anteroposterior translations of the medial femoral condyle (MFC) and lateral femoral condyle (LFC) were recorded every 0.1 s from 0° to 120°. Data were subsequently extracted from the software every 10° of flexion and compared between the two groups, and the correlation coefficients between preoperative and postoperative kinematics were calculated.

Results

In the postoperative analysis, the MFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group (p < 0.01). Similarly, the LFC in the mobile-bearing group showed significant posterior translation at 100°, 110° and 120° compared to the fixed-bearing group (p < 0.05, p < 0.01 and p < 0.05, respectively). In the mobile-bearing group, the preoperative and postoperative anteroposterior translations of the MFC and LFC were correlated (p < 0.01), while in the fixed-bearing group, there was no correlation.

Conclusion

The femoral rollback motion in the mobile-bearing MST-TKA correlated with the preoperative kinematics and was larger than that in the fixed-bearing group.

Level of Evidence

Level II, therapeutic prospective cohort study.

Discrepancies in Sagittal Alignment of the Lower Extremity Among Different Brands of Robotic Total Knee Arthroplasty Systems

BACKGROUND

There is an increasing number of different brands of robotic total knee arthroplasty (TKA) systems. Most robotic TKA systems share the same coronal alignment, while the definitions of sagittal alignment vary. The purpose of this study was to investigate whether these discrepancies impact the sagittal alignment of the lower extremity.

METHODS

A total of 72 lower extremity computed tomography scans were included in our study, and 3-dimensional models were obtained using software. A total of 7 brands of robotic TKA systems were included in the study. The lower extremity axes were defined based on the surgical guide for each implant. We also set the intramedullary axis as a reference to evaluate the discrepancies in sagittal alignment of each brand of robotic system.

RESULTS

On the femoral side, the axis definition was the same for all 7 robotic TKA systems. The robotic TKA axes showed a 2.41° (1.58°, 3.38°) deviation from the intramedullary axis. On the tibial side, the 7 robots had different axis definitions. The tibial mechanical axis of 6 of the TKA systems was more flexed than that of the intramedullary axis, which means the posterior tibial slope was decreased while the tibial mechanical axis of the remaining system was more extended.

CONCLUSIONS

The sagittal alignment of the lower extremity for 7 different brands of robotic TKA systems differed from each other and all deviated from the intramedullary axis. Surgeons should be aware of this discrepancy when using different brands of robotic TKA systems to avoid unexpected sagittal alignment and corresponding adverse clinical outcomes.

LEVEL OF EVIDENCE

Level IV, Therapeutic Study.

Effect of posterior capsular release on intraoperative joint gap mismatch in the mid-flexion range during posterior-stabilized total knee arthroplasty

INTRODUCTION

Intraoperative mismatch between extension and mid-flexion joint gaps remains a critical issue in posterior-stabilized total knee arthroplasty (PS-TKA). Posterior capsular release has been found to increase the extension joint gap. However, there is still a lack of robust evidence for the effect of posterior capsular release on the mid-flexion joint gap. The purpose of the present study was to quantify the effect of posterior capsular release on the intraoperative joint gap from extension through 45° mid-flexion to flexion and to clarify how this procedure might affect the improvement of gap mismatch in the mid-flexion 45° range.

MATERIALS AND METHODS

In total, 38 consecutive cases of primary PS-TKA were reviewed. The center, medial, and lateral component gaps from extension to flexion were measured with a tensor device before and after posterior capsular release. The minimal detectable change for joint gap measurement was calculated using two methods, error variance and intra-observer intraclass correlation coefficients. Pre- and post-release joint gap differences were assessed using the paired t-test.

RESULTS

Minimal detectable change was found to be 0.59 mm. At 0° and 10° of flexion, the post-release center, medial, and lateral component gaps were significantly greater than at pre-release. At 45° and 90° and maximum flexion, there were no joint gap differences exceeding the minimal detectable change. The joint gap mismatches between 0° and 10°, and 45°, 90° and maximum flexion were significantly smaller at post-release than those at pre-release with the change values exceeding the minimal detectable change (P < 0.05).

CONCLUSION

Posterior capsular release significantly decreased both joint gap mismatch between extension and 45° mid-flexion, and extension and flexion, showing clinical usefulness in PS-TKA.

Robotic-arm assisted total knee arthroplasty is associated with comparable functional outcomes but improved forgotten joint scores compared with conventional manual total knee arthroplasty at five-year follow-up

PURPOSE

This study reports the five-year functional outcomes from a prospective cohort study comparing robotic-arm assisted total knee arthroplasty (RO TKA) versus conventional manual total knee arthroplasty (CO TKA).

METHODS

This prospective single-surgeon study included 120 patients with symptomatic end-stage knee arthritis undergoing primary TKA. This included 60 consecutive patients undergoing CO TKA followed by 60 consecutive patients undergoing RO TKA using a semi-automated robotic device. Study patients were reviewed at one, two, and five years after surgery and the following outcomes recorded: The University of California at Los Angeles activity-level (UCLA), Knee Society Score (KSS), Oxford Knee Score (OKS) Forgotten Joint Score (FJS), and any complications.

RESULTS

There were no statistical differences between RO TKA and CO TKA in the median UCLA score (p = N.S), median KSS (p = N.S), and median OKS (p = N.S) at five-year follow-up. RO-TKA was associated with statistically significant improvements in the FJS at one (p = 0.001), two (p = 0.003), and five (p = 0.025) years of follow-up compared with CO TKA. There was no statistical difference in the incidence of knee stiffness requiring manipulation under anesthesia between the two treatment groups (p = N.S).

CONCLUSION

Patients in both treatment groups had excellent functional outcomes with comparable patient reported outcomes at five-year follow-up. RO TKA was associated with statistically significant improvements in the FJS compared with CO TKA, but these differences did not reach the minimal clinically important difference at any follow-up interval. There was no overall difference in complications between the two treatment groups at five-year follow-up.

LEVEL OF EVIDENCE

II (Prospective cohort study).

Clinical, Radiographic, and Patient-Reported Outcomes Associated with a Handheld Image-free Robotic-Assisted Surgical System in Total Knee Arthroplasty

One of the primary aims of total knee arthroplasty (TKA) is restoration of the mechanical axis of the lower limb. Maintenance of the mechanical axis within 3° of neutral has been shown to result in improved clinical results and implant longevity. Handheld image-free robotic-assisted total knee arthroplasty (HI-TKA) is a novel way of performing TKA in the era of modern robotic-assisted TKA. The aim of this study is to assess the accuracy of achieving targeted alignment, component placement, clinical outcomes, as well as patient satisfaction after HI-TKA.

Mid-Flexion Instability After Total Knee Arthroplasty: Diagnosis, Implant Design, and Outcomes

Mid-flexion instability (MFI) in total knee arthroplasty refers to a distinct clinical entity where the knee is stable at full extension and 90° of flexion, but unstable somewhere between these 2 points. The presentation of MFI is often vague, and studies defining objective clinical or intraoperative measurements are limited. In this review, we aim to properly define the condition, describe diagnostic criteria and risk factors contributing to MFI, review current implant design, and present outcomes of revision surgery performed for MFI. [Orthopedics. 2023;46(1):e13-e19.].

Mid-Flexion, Anteroposterior Stability of Total Knee Replacement Implanted with Kinematic Alignment: A Randomized, Quantitative Radiographic Laxity Study with Posterior-Stabilized and Medial-Stabilized Implants

UPDATE

This article was updated on January 4, 2023, because of a previous error, which was discovered after the preliminary version of the article was posted online. On page 16, in Figure 5, the x-axis that had read "P<0.0086" now reads "KSS Pain (p=0.02)," and the value for the MS group that had read "48.9" now reads "48.8."This article was updated on January 6, 2022, because of a previous error. On page 13, in the section entitled "Results," the sentence that had read "However, when only the subset of female subjects was considered, the MS group demonstrated significantly less anteroposterior laxity in 90° of flexion than the MS group (2.3 versus 5.4 mm; p = 0.008)." now reads "However, when only the subset of female subjects was considered, the MS group demonstrated significantly less anteroposterior laxity in 90° of flexion than the PS group (2.3 versus 5.4 mm; p = 0.008)."

BACKGROUND

Stability in mid-flexion is important for satisfactory clinical outcomes following total knee arthroplasty (TKA). The purpose of the present study was to compare the anteroposterior stability of knees that had been treated with a posterior-stabilized (PS) device or a medial-stabilized (MS) device. We hypothesized that mid-flexion laxity would be greater in the PS group and that clinical outcome scores would be better for the group with lower laxity.

METHODS

Sixty-three patients who had been randomly selected from a larger randomized, prospective, blinded clinical trial underwent primary TKA with either a PS implant (n = 30) or an MS implant (n = 33). Range of motion, the Knee Society Score (KSS), and the Forgotten Joint Score (FJS) were collected, and anteroposterior laxity with the knee in 45° and 90° of flexion was evaluated with stress radiographs.

RESULTS

In 45° of flexion, the MS group demonstrated significantly less total anteroposterior displacement than the PS group (mean, 3.6 versus 16.5 mm; p ≤ 0.0001). In 90° of flexion, the total anteroposterior displacement was not significantly different for the 2 groups when both male and female patients were included (mean, 3.9 versus 5.9; p = 0.07). However, when only the subset of female subjects was considered, the MS group demonstrated significantly less anteroposterior laxity in 90° of flexion than the PS group (2.3 versus 5.4 mm; p = 0.008). The groups did not differ significantly in terms of preoperative age, body mass index, sex distribution, FJS, KSS, or range of motion, and they also did not differ in terms of postoperative FJS or range of motion. However, all 33 patients in the MS group returned to sports as indicated in question 12 of the FJS, compared with 19 subjects in the PS group (p = 0.0001). The postoperative KSS Pain, Pain/Motion, and Function scores were all significantly higher in the MS group than the PS; specifically, the mean KSS Pain score was 48.8 in the MS group, compared with 44.8 in the PS group (p = 0.02); the mean KSS Pain/Motion score was 98.4 in the MS group, compared with 89.5 in the PS group (p < 0.0001); and the mean KSS Function score was 95.5 in the MS group, compared with 85.7 in the PS group (p = 0.003).

CONCLUSIONS

Mid-flexion laxity was greater in patients with PS implants than in those with MS implants, and laxity in 90° was greater in the subset of female patients in the PS group. The decreased laxity observed in the MS group correlated with higher KSS Pain, Pain/Motion, and Function scores as well as with a higher rate of return to sports activities.

LEVEL OF EVIDENCE

Therapeutic Level I . See Instructions for Authors for a complete description of levels of evidence.

A prospective comparison of total knee arthroplasty using ultra-congruent, condylar-stabilizing, and posterior-stabilized devices implanted with kinematic alignment: better 2-year outcomes with ultra-congruent

PURPOSE

This study compared the 5-year results of posterior cruciate ligament (PCL)-sacrificing total knee arthroplasty (TKA) with either a post and cam posterior-stabilized (PS) device, a dished, congruent condylar-stabilizing (CS) device, or a deep-dished ultra-congruent (UC) device. The hypothesis was that the clinical and radiographic outcomes would be equivalent. CS and PS participants were part of a prospective, randomized trial, and UC participants were part of a separate prospective, non-randomized protocol that was otherwise identical. A kinematic alignment surgical technique was utilized.

METHODS

Participants were assessed preoperatively, and postoperatively at 6 weeks, 6 months, and annually for 5 years by Knee Society Score (KSS), SF-36 v2, Lower Extremity Activity Scale (LEAS), and physical and radiographic evaluation. There were 116 CS/PS participants and 69 UC participants who participated in the study.

RESULTS

Tourniquet (P = .02) and operative (P = .01) times for the CS and UC groups were significantly shorter than the PS group. KSS Function scores were better for the UC group than the CS and PS groups at 6 months (P = .04) and 1 year (P = .03), and better in the UC group vs. CS at 2 years (P = .04). The KSS Pain-only score was also better in the UC compared to PS at 6 months (P = .04). There were no significant differences for the KSS Pain/Motion scores, flexion, SF-36, and LEAS scores at any time.

CONCLUSION

These data confirm the hypothesis that there are no clinically meaningful significant differences in outcomes between the three groups at a 5-year minimum follow-up, though there is a trend toward less pain and better function at earlier visits in the UC group.

LEVEL OF EVIDENCE

II.

Outcomes are Better With a Medial-Stabilized vs a Posterior-Stabilized Total Knee Implanted With Kinematic Alignment

BACKGROUND

There is no consensus whether a posterior-stabilized (PS) total knee device is superior to a more congruent, cruciate-substituting, medial-stabilized device (MS). This study compared the clinical outcomes of these devices. The primary hypothesis was that the clinical outcomes would be better in the MS group implanted with kinematic alignment.

METHODS

This prospective, randomized, single-center Level 1 study compared the outcomes of 99 patients who received a PS device and 101 patients who received an MS device implanted with kinematic alignment. Institutional Review Board approval and informed consent were obtained. Clinical and radiographic assessments were performed preoperatively, 6 weeks, 6 months, and annually.

RESULTS

All subjects reached the minimum follow-up of 2 years. There were no statistically significant differences in demographic characteristics, preoperative scores, or alignment (preoperative or postoperative). Tourniquet time was 7.24% longer for the PS group (40.28 min vs 37.56 min, P < .0086). There were significant differences between groups for the 1-year and 2-year Knee Society scores, Forgotten Joint Score, and ROM; in every case favoring the MS group. The FJS was 68.3 in the MS group at 2 years and 58.3 in the PS group (P = .02). The maximum flexion at 2 years was 132° in the MS group and 124° in the PS group (P < .0001).

CONCLUSION

The clinical outcomes of the MS group at 1 and 2 years were better. At the minimum 2-year follow-up, the results demonstrate the superiority of the medial-stabilized device in terms of multiple clinical outcomes.

LEVEL OF EVIDENCE

I.

A Mid-Level Constrained Insert Reduces Coupled Axial Rotation but Not Coronal Mid-Flexion Laxity Induced by Joint Line Elevation in Posterior-Stabilized Total Knee Arthroplasty: A Computational Study

BACKGROUND

Surgeons may resect additional distal femur during primary posterior-stabilized (PS) total knee arthroplasty (TKA) to correct a flexion contracture. However, the resultant joint line elevation (JLE) increases mid-flexion laxity. We determined whether a mid-level constraint (MLC) insert reduced mid-flexion laxity after JLE.

METHODS

Six computational knee models were developed using computed tomography scans and average soft tissue properties yielding balanced extension gaps but with a 10° flexion contracture. Distal femoral resections of +2 and +4 mm were simulated with PS and MLC inserts. Varus-valgus ±10 Nm moments were applied at 30°, 45°, and 60° of flexion. Coronal laxity (the sum of varus-valgus angulation) and coupled axial rotation (the sum of internal/external rotation) were measured and compared between insert models.

RESULTS

At 30° of flexion, coronal laxities with the PS insert at the +2 and +4 mm resections averaged 7.9° ± 0.6° and 11.3° ± 0.6°, respectively, and decreased by 0.8° (P = .06) and 1.0° (P = .07), respectively, with the MLC insert. PS rotational laxities at the +2 and +4 mm resections averaged 11.1° ± 3.9° and 12.5° ± 4.6°, respectively, and decreased by 5.6° (P = .01) and 7.1° (P = .02), respectively, with the MLC insert. Similar patterns were observed at 45° and 60° of flexion.

CONCLUSION

With additional distal femoral resections to alleviate a flexion contracture, utilizing an MLC insert substantially reduced coupled axial rotation but had a minimal impact on coronal laxity compared to a PS insert. Efforts should be taken to avoid JLE in primary total knee arthroplasty as even MLC inserts may not mitigate coronal laxity.

Primary Total Knee Arthroplasty Revised for Instability: A Detailed Registry Analysis

BACKGROUND

Instability after total knee arthroplasty is a common but poorly understood complication.

METHODS

Data from a large national registry was used to study patient and prosthesis characteristics of 2605 total knee arthroplasty revisions for instability. The cumulative percent revision was calculated using Kaplan-Meier estimates, and Cox proportional models used to compare revision rates. The rate of further revision was analyzed with regard to prostheses used in the first revision.

RESULTS

Instability increased from 6% of all first revision procedures in 2003 to 13% in 2019. The revision risk was lower for minimally stabilized prostheses, males, and patients aged ≥65 years. Polyethylene insert exchange was used for 55% of revision procedures, using a thicker insert in 93% and a change in insert conformity in 24% of cruciate-retaining knees. The increase in either thickness or conformity had no effect on the rate of further revision. After a revision for instability, 24% had a second revision by 14 years. Recurrent instability accounted for 32% of further revisions. A lower second revision rate was seen after revision of both femoral and tibial components, and where constrained components were used.

CONCLUSION

Revision for instability is increasing. Revising both femoral and tibial components led to a lower rate of second revision compared to a change in insert alone. Recurrent instability was common.

Mid-flexion laxity could be identified with continuous flexion-arc gap assessment in patients with a large preoperative convergence angle

PURPOSE

To analyze the incidence of intraoperative mid-flexion laxity using continuous flexion-arc gap assessment, risk factors for mid-flexion laxity, and clinical results in navigation-assisted total knee arthroplasty (TKA).

METHODS

Ninety posterior-stabilized TKAs were performed under navigation guidance for patients with degenerative arthritis and varus deformity. Intraoperatively, the gap between the trial femoral component and insert was evaluated in the navigation system with continuous flexion-arc gap assessment. Each medial and lateral gap at flexion (90°) and extension (0°) were made to be less than 3 mm. Mid-flexion laxity was determined when the gap in the flexion range between 15° and 60° was 3 mm or more. The proportion of knees with mid-flexion laxity was investigated. The factors affecting mid-flexion laxity were identified in terms of demographics, preoperative convergence angle, and change in joint line height and posterior femoral offset. The Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index were evaluated.

RESULTS

There were 31 cases (34.4%) of lateral mid-flexion laxity (average peak mid-flexion gap = 3.7 mm). The other 59 cases did not show mid-flexion laxity. The preoperative convergence angle was the only significant factor affecting lateral mid-flexion laxity (odds ratio = 1.466, p = 0.002). There were no significant differences in the clinical results between the groups with and without mid-flexion laxity.

CONCLUSIONS

The continuous flexion-arc gap assessment was useful in evaluating mid-flexion laxity using navigation-assisted TKA. The preoperative convergence angle, reflecting soft-tissue laxity, can be a practical and simple radiographic finding for predicting lateral mid-flexion laxity.

LEVEL OF EVIDENCE

IV.

Robotic-arm assisted total knee arthroplasty is associated with improved accuracy and patient reported outcomes: a systematic review and meta-analysis

This systematic review and meta-analysis were conducted to compare the accuracy of component positioning, alignment and balancing techniques employed, patient-reported outcomes, and complications of robotic-arm assisted total knee arthroplasty (RATKA) with manual TKA (mTKA) and the associated learning curve. Searches of PubMed, Medline and Google Scholar were performed in October 2020 using PRISMA guidelines. Search terms included "robotic", "knee" and "arthroplasty". The criteria for inclusion were published clinical research articles reporting the learning curve for RATKA and those comparing the component position accuracy, alignment and balancing techniques, functional outcomes, or complications with mTKA. There were 198 articles identified, following full text screening, 16 studies satisfied the inclusion criteria and reported the learning curve of rTKA (n=5), component positioning accuracy (n=6), alignment and balancing techniques (n=7), functional outcomes (n=7), or complications (n=5). Two studies reported the learning curve using CUSUM analysis to establish an inflexion point for proficiency which ranged from 7 to 11 cases and there was no learning curve for component positioning accuracy. The meta-analysis showed a significantly lower difference between planned component position and implanted component position, and the spread was narrower for RATKA compared with the mTKA group (Femur coronal: mean 1.31, 95% confidence interval (CI) 1.08-1.55, p<0.00001; Tibia coronal: mean 1.56, 95% CI 1.32-1.81, p<0.00001). Three studies reported using different alignment and balancing techniques between mTKA and RATKA, two studies used the same for both group and two studies did not state the methods used in their RATKA groups. RATKA resulted in better Knee Society Score compared to mTKA in the short-to-mid-term follow up (95%CI [- 1.23,  - 0.51], p=0.004). There was no difference in arthrofibrosis, superficial and deep infection, wound dehiscence, or overall complication rates. RATKA demonstrated improved accuracy of component positioning and patient-reported outcomes. The learning curve of RATKA for operating time was between 7 and 11 cases. Future well-powered studies on RATKAs should report on the knee alignment and balancing techniques utilised to enable better comparisons on which techniques maximise patient outcomes.Level of evidence III.

Intraoperative Assessment of Gap Balancing in Total Knee Arthroplasty Using Navigation with Joint Stability Graphs

The purpose of this study was to assess continuous gaps in the replaced knee throughout the full range of motion (ROM) after total knee arthroplasty (TKA) using a joint stability graph, and to analyze the gap laxity in the mid-flexion range. Ninety-three TKAs were performed using imageless navigation with a joint stability graph. While positioning guides for each respective cut, the surgeon can safely preview the resection's impact for the resulting joint gaps and control the soft tissue balance at the knee flexion of 0° (extension) and 90° (flexion). The gaps between the femoral component and insert were evaluated throughout the full ROM using the joint stability graph. The mechanical axis (MA) and change of joint line height were radiographically evaluated. Posthoc power analyses using a significant α value of 0.05 were performed on the proportion of the mid-flexion instability as a primary outcome to determine whether the sample had sufficient power. The power was determined to be sufficient (100%). The flexion-extension gap differences in each medial and lateral compartment and the mediolateral gap differences in flexion and extension were all ≤3 mm. None of the knees had mid-flexion instability, which is defined by a peak mid-flexion gap that is 3 mm greater than the smaller value of flexion or extension gap. The average MA was well corrected from varus 11.4° to varus 1.0° postoperatively. The proportion of postoperative well-aligned knees (MA ≤ 3°) was 87.1%. The joint line height was well preserved (14.7 vs. 14.8 mm, p = 0.751). The joint stability graph in TKA using the navigation can effectively evaluate the continuous gap throughout the ROM, including the mid-flexion range. Mid-flexion instability was uncommon in primary TKAs with appropriate alignment and proper preservation of the joint line. The Level of evidence for the study is 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.

Evaluating the "Patella-Friendly" Concept in Total Knee Arthroplasty: A Minimum 15-Year Follow-Up Outcome Study Comparing Constant Radius, Multiradius Cruciate-Retaining, and Nonanatomical Cruciate-Retaining Implants

BACKGROUND

Patella-friendly femoral components were developed in order to reduce anterior knee pain and patellofemoral complications in total knee arthroplasty (TKA), but their effect on long-term outcome is still unclear.

METHODS

We retrospectively evaluated prospectively collected data from 3 groups consisting of 100 patients (100 knees in each). In group A, the constant radius a-MP, in group B the multiradius cruciate-retaining Genesis II, and in group C the nonanatomic, multiradius, cruciate-retaining AGC TKA was implanted. Patients of all groups were matched for age, gender, side, body mass index, and length of follow-up. Preoperative and postoperative clinical outcome data in the form of Knee Society System (KSS), Short Form-12, Western Ontario and McMaster University Osteoarthritis Index, and Oxford Knee Score were available at regular intervals for groups A and B. For patients of group C, KSS score data were available at the same time intervals. In all groups, the patellofemoral compartment was assessed using the Clinical Patella Score scale. Anterior knee pain, secondary patella resurfacing, implant failure, and radiological outcome were assessed in patients of all groups.

RESULTS

At 10-year and 15-year follow-up, patients of group A showed statistically significant (s.s.) higher (all P = .000) KSS values as compared to those of groups B and C. At 15-year follow-up, patients of group B showed s.s. higher (P = .001) KSS values as compared to those of group C. At 10-year and 15-year follow up, patients of group A showed s.s. higher (all P = .00) Western Ontario and McMaster University Osteoarthritis Index and Oxford Knee Score values as compared to those of group B. At 15-year follow-up only, patients of group A showed s.s. higher (P = .00) Short Form-12 (physical) values as compared to those of group B. In terms of Clinical Patella Score, patients in group A had s.s. higher values (P = .05) when compared to those of groups B and C. Anterior knee pain was recorded in 4.4% of TKAs in group A, 7.5% in group B, and 17.2% in group C. One (1.1%) patient in group A, 3 (3.25%) in group B, and 7 (8%) in group C underwent secondary resurfacing.

CONCLUSION

Anatomical, patella-friendly, constant radius femoral components outperform others in reducing anterior knee pain and patella complications in TKA in which the patellae are left nonresurfaced.

Revision knee surgery: the practical approach

Revision total knee arthroplasty (rTKA) is a challenging procedure with often unreproducible results. A step-by-step approach is fundamental to achieving good outcomes.

Successful surgery requires a correct diagnosis of the original cause of failure. Only with an accurate and detailed plan can surgeons overcome difficulties presented in this scenario.

Any bone loss should be prevented during prosthetic component removal. Efficient tools must be chosen to avoid time-consuming manoeuvres.

Joint reconstruction based on a ‘dual-zone’ fixation is essential to provide a long-term survivorship of the implant. The use of relatively short fully cemented stems combined with a biological metaphyseal fixation is highly recommended by authors.

Flexion and extension gaps are accurately balanced after the establishment of the tibial platform.

Varus-valgus laxity is commonly managed with a condylar constrained prosthesis. If hinged implants are required, a stronger implant fixation is needed to counteract constraints forces.

Cite this article: EFORT Open Rev 2021;6:495-500. DOI: 10.1302/2058-5241.6.210018

Loss of Knee Flexion and Femoral Rollback of the Medial-Pivot and Posterior-Stabilized Total Knee Arthroplasty During Early-Stance of Walking in Chinese Patients

Background The medial-pivot (MP) prosthesis was developed to produce more physiological postoperative knee kinematics and better patient satisfaction than traditional prostheses, but outcomes are inconsistent in different studies of Caucasian patients. This study aimed to investigate the postoperative patient satisfaction and in vivo knee kinematics of the MP and posterior-stabilized (PS) prosthesis during gait activity in Chinese patients.

Methods A retrospective analysis of 12 patients was received for this study in each MP group and PS group. Patient-reported satisfaction level and Forgotten Joint Score (FJS) were evaluated with questionnaires. A dual fluoroscopic imaging system was used to investigate in vivo knee kinematics of MP and PS total knee arthroplasty (TKA) during treadmill walking at a speed of 0.4 m/s.

Results Comparable promising patient satisfaction and overall FJS (MP 60.7 ± 15.35 vs. PS 51.3 ± 17.62, p = 0.174) were found between the MP and PS groups. Peak flexion appeared at around 70% of gait cycle with values of 52.4 ± 7.4° for MP and 50.1 ± 3.6° for PS groups (no difference). Both groups maintained a stable position at the stance phase and began to translated anteriorly at toe-off with an amount of 4.5 ± 2.3 mm in the MP and 6.6 ± 2.7 mm in the PS (p = 0.08) group until late swing. The range of this external rotation motion was 5.9 ± 4.8 and 6.2 ± 4.1° (p = 0.79) for the MP and PS, respectively.

Conclusion A similar knee kinematics pattern characterized by a loss of early-stance knee flexion and femoral rollback during walking was observed in the MP and PS TKAs. Our study confirmed similar effectiveness of MP TKA compared to PS TKA in Chinese patients, while the change of knee kinematics of both implants during slow walking should be noted.

Additional distal femoral resection increases mid-flexion coronal laxity in posterior-stabilized total knee arthroplasty with flexion contracture : a computational study

AIMS

Surgeons commonly resect additional distal femur during primary total knee arthroplasty (TKA) to correct a flexion contracture, which leads to femoral joint line elevation. There is a paucity of data describing the effect of joint line elevation on mid-flexion stability and knee kinematics. Thus, the goal of this study was to quantify the effect of joint line elevation on mid-flexion laxity.

METHODS

Six computational knee models with cadaver-specific capsular and collateral ligament properties were implanted with a posterior-stabilized (PS) TKA. A 10° flexion contracture was created in each model to simulate a capsular contracture. Distal femoral resections of + 2 mm and + 4 mm were then simulated for each knee. The knee models were then extended under a standard moment. Subsequently, varus and valgus moments of 10 Nm were applied as the knee was flexed from 0° to 90° at baseline and repeated after each of the two distal resections. Coronal laxity (the sum of varus and valgus angulation with respective maximum moments) was measured throughout flexion.

RESULTS

With + 2 mm resection at 30° and 45° of flexion, mean coronal laxity increased by a mean of 3.1° (SD 0.18°) (p < 0.001) and 2.7° (SD 0.30°) (p < 0.001), respectively. With + 4 mm resection at 30° and 45° of flexion, mean coronal laxity increased by 6.5° (SD 0.56°) (p < 0.001) and 5.5° (SD 0.72°) (p < 0.001), respectively. Maximum increased coronal laxity for a + 4 mm resection occurred at a mean 15.7° (11° to 33°) of flexion with a mean increase of 7.8° (SD 0.2°) from baseline.

CONCLUSION

With joint line elevation in primary PS TKA, coronal laxity peaks early (about 16°) with a maximum laxity of 8°. Surgeons should restore the joint line if possible; however, if joint line elevation is necessary, we recommend assessment of coronal laxity at 15° to 30° of knee flexion to assess for mid-flexion instability. Further in vivo studies are warranted to understand if this mid-flexion coronal laxity has negative clinical implications. Cite this article: Bone Joint J 2021;103-B(6 Supple A):87-93.

Anatomical evaluation of the femoral attachment of the posterior oblique ligament

INTRODUCTION

Tibiofemoral joint instability reduces patient satisfaction after total knee arthroplasty (TKA). However, surgeons sometimes encounter excessive medial joint laxity without medial over-release on the tibial side. It was hypothesized that over-resection of the posteromedial femoral condyle can injure the medial stabilizers, especially the posterior oblique ligament (POL) at its femoral attachments.

MATERIALS AND METHODS

Thirteen fixed cadaveric knees were exposed, and 3 anatomical points were identified: the posterior edge and midpoint of the POL femoral attachment, and the posterior edge of the superficial medial collateral ligament (sMCL) femoral attachment. The distance from the surface of the posteromedial femoral condyle to each point was measured. Correlations between each point and the anterior-posterior or medial-lateral dimensions of the distal femur were also calculated.

RESULTS

The average distances to the posterior edge and midpoint of the POL femoral attachment and the posterior edge of the sMCL femoral attachment were 13.7 mm (9.0-18.4), 17.9 mm (11.5-22.6), and 22.7 mm (14.7-29.4), respectively. There were moderate correlations between the distance to each point and the anterior-posterior or medial-lateral dimensions of the distal femur.

CONCLUSIONS

The minimal distance from the surface of the posteromedial condyle to the POL posterior edge was 9.0 mm. Over-resection of the posteromedial femoral condyle, even with a general TKA femoral component, might injure the POL at its femoral attachments, especially in patients with small distal femurs, while the sMCL is rarely damaged.

LEVEL OF EVIDENCE

Level IV.

Temporal Trends of Revision Etiologies in Total Knee Arthroplasty at a Single High-Volume Institution: An Epidemiological Analysis

Background

Temporal changes in revision total knee arthroplasty (rTKA) may have implications in determining the etiology for implant failure. The purpose of this study was to 1) perform an epidemiologic analysis of etiologies that required rTKA and 2) determine whether temporal changes existed for revision over the study period.

Methods

All rTKA procedures performed at a single institution from 2009 to 2019 were analyzed. Revision procedures were stratified into 2 time periods, 2009-2013 and 2014-2019, to assess for changes over time. Patients' electronic medical record, operative report, and radiographs were reviewed to ensure diagnosis information was accurately documented in relation to the predominate etiology necessitating the revision procedure.

Results

Three thousand and nine patients undergoing rTKA between 2009 and 2019 were identified with a mean age of 64.6 years. A total of 1,666 (55.4%) patients were female, and the majority of patients were Caucasian (2,306, 76.6%). The 3 most frequent rTKA etiologies were aseptic loosening (35.1%), periprosthetic infection (33.2%), and instability (16.0%). A higher proportion of patients underwent rTKA for arthrofibrosis (5.1% vs 3.4%, P = .023) and periprosthetic joint infection (38.9% vs 28.6%, P < .001) between 2009 and 2013, while a significantly higher proportion of patients underwent rTKA for instability (12.6% vs 18.8%, P < .001) between 2014 and 2019.

Conclusion

Aseptic loosening was the most common cause for rTKA over the last decade. rTKA for arthrofibrosis and periprosthetic joint infection was more frequent between 2009 and 2013, while a significantly higher proportion of patients underwent rTKA for instability in 2014-2019. Future studies will need to focus on identifying and reducing risk factors for the trending causes of rTKA.

[Kinematic alignment-management of deformities and flexion contractures]

BACKGROUND

Kinematic alignment (KA) total knee arthroplasty (TKA) has proven to be a viable alternative to mechanical alignment (MA) TKA. Like any technique, its validity has to encounter challenges. Two of these are flexion contracture and large deformities of the knee.

FLEXION CONTRACTURE

Flexion contracture is commonly treated with posterior capsular release. Often, however, this technique is not sufficient. Many surgeons accustomed to MA techniques and guided by traditional femoral instruments manage the problem by proximalizing the distal femoral cut. However, this has proven to be a surgical mistake that often leads to mid-flex knee instability. KA rules limit this mistake but leave the problem of flexion contracture. In these cases, the surgeon acts on the tibia distalizing the cut and, so as not to create instability in flexion, decreasing the slope. The technique is effective to obtain full extension but often leaves instability at 90° of knee flexion. To avoid this, it is useful to use the so-called "virtuous mistake" strategy, which strictly follows the KA guidelines but undercuts the posterior femoral condyles by 2 mm.

DEFORMITIES

Another problem that often limits the use of KA is large deformities. It is necessary to distinguish whether they are intra or extra-articular. In the first case, it is possible to decide whether to use the pure KA technique or to restrict the indication at the level of the tibial cut. In the latter, extraarticular osteotomies or combined procedures (osteotomy plus KA) have to be performed.

Midflexion instability in total knee arthroplasty: a systematic review

PURPOSE

The aim of this systematic review was to evaluate the evidence on the existence of midflexion instability in primary total knee arthroplasty and which factors might contribute to this condition.

METHODS

A comprehensive search of PubMed, Medline, Cochrane, CINAHL, and Embase databases was conducted since the inception of the database to July 2019. All relevant articles were retrieved, and their bibliographies were hand searched for further references on midflexion instability in primary total knee arthroplasty. The search strategy yielded 28 articles. After duplicate removal titles, abstracts and full text were reviewed. Fifteen studies were assessed for eligibility, 8 studies were excluded because they did not fully comply with the inclusion criteria. Seven articles were finally included in this systematic review. Anteroposterior translation, total knee arthroplasty design such as posterior-stabilized or posterior-cruciate-retaining total knee arthroplasty, joint line position with posterior condylar offset and joint gaps were considered to significantly influence midflexion stability.

RESULTS

Based on this systematic review anteroposterior translation of ≥ 7 mm was an independent risk factor for midflexion instability at 30° knee flexion. Joint line position can be altered by up to 5 mm without measurable changes in joint stability and both an increase and a decrease in posterior condylar offset led to 30° midflexion instability.

CONCLUSION

Midflexion instability in primary total knee arthroplasty remains to be not entirely understood. Due to the low quality of available evidence, it is difficult to make any definitive conclusions. The factors which can lead to this condition were analyzed in this review, furthermore, we did not find exhaustive evidence on midflexion instability existence as an isolated entity. Nonetheless, this review will form a baseline for future research and creates awareness for the routine assessment of midflexion instability in primary total knee arthroplasty.

LEVEL OF EVIDENCE

IV.

Risk Factors for Mid-Flexion Instability After Total Knee Arthroplasty: A Systematic Review

BACKGROUND

Mid-flexion instability after total knee arthroplasty (TKA) is a clinical entity that is not well studied and one that has been associated with patient dissatisfaction and inferior outcomes. We sought to provide a comprehensive review of risk factors associated with mid-flexion instability.

METHODS

A comprehensive literature search of PUBMED, EMBASE, Google Scholar, and Cochrane Library was performed using keywords "mid flexion," "instability," and "knee arthroplasty" in all possible combinations. All studies published from 2010 to 2020 in English were considered for inclusion. Research design, question studied, and outcomes were recorded for each study. Quantitative and qualitative analysis was performed.

RESULTS

Eighteen articles meeting inclusion criteria were identified and reviewed. There were 5 computational studies, 5 cadaveric studies, and 8 clinical studies. There were 14 different risk factors investigated in relation to mid-flexion instability after TKA: 6 implant-related, 6 technique-related, and 2 patient-related factors. Of these risk factors, 5 had contradictory results published to date, resulting in an inconclusive association with mid-flexion instability. The results of this review suggest that the effects of joint line elevation and radius-of-curvature of the femoral component on mid-flexion instability are inconclusive while articular surface conformity and preoperative joint laxity may play a bigger role than previously thought.

CONCLUSION

Mid-flexion instability after TKA is a clinical entity distinct from other established forms of instability. There are patient-related, implant-related, and technique-related factors associated with mid-flexion instability. The majority of the evidence on this topic is derived from computational and cadaveric studies, underscoring the need for further clinical studies.

Improvements in Isokinetic Quadriceps and Hamstring Strength Testing After Focused Therapy in Patients With Flexion Instability

BACKGROUND

There is a paucity of literature to guide non-operative treatment for patients with problems after total knee arthroplasty (TKA). We sought to quantify how quadriceps and hamstring strength could improve with focused physical therapy (PT) and whether improving leg strength may prevent revision surgery for patients with flexion instability (FI) after TKA.

METHODS

This retrospective study included patients diagnosed with FI by one of the 4 fellowship-trained arthroplasty surgeons at a single academic institution. Patients with FI were referred for strength measurements and a focused PT program. In total, 166 patients completed isokinetic testing to quantify their relative quadriceps and hamstring power, torque, and work measures compared to their contralateral leg. Fifty-five (33.5%) patients subsequently completed post-PT isokinetic testing. Statistical analysis was conducted to evaluate strength deficits in the knee with FI.

RESULTS

Patients with FI were found to be 20.5%-38.4% weaker in all strength domains compared to the contralateral leg (P < .001). Patients who completed PT and pre-isokinetic and post-isokinetic testing demonstrated statistically significant gains in all extension metrics by a net range of 24.7%-34.2% (P = .011-.029) and their flexion strength metrics improved by 32.5%-40.2% (P = .002-.005). About 81.9% of patients in this subgroup did not undergo revision TKA. Those subjects who went on to revision did not statistically improve in any strength domain (P = .063-.121).

CONCLUSION

Patients with FI after TKA have significantly weaker quadriceps and hamstrings in the operative compared to contralateral leg. Patients who did not undergo revision knee arthroplasty and completed a formal PT program improved quadriceps and hamstring strength by 30%.

LEVEL OF EVIDENCE

IV (Case series).

Joint line elevation and tibial slope are associated with increased polyethylene wear in cruciate-retaining total knee replacement

The purpose of this retrieval study was to determine the effect of implant positioning on wear, taking patient-related factors into account. Therefore, the volumetric material loss of 59 retrieved tibial liners was quantitatively determined using a coordinate measuring-machine. All retrievals were made of the same polyethylene and design by a single manufacturer. Using time in-situ and linear regression, a wear rate for each liner was determined and corrected for bedding-in. Backside damage was qualitatively scored. The following implant positioning parameters were obtained from radiographs: anatomical lateral-distal femoral angle, anatomical medial-proximal tibial angle, femoral tilt angle, and posterior tibial slope. The patella position was assessed by the Blackburne-Peel index and the Insall-Salvati ratio. Unlike the Insall-Salvati ratio, the Blackburne-Peel index is known to detect surgical joint line elevation. Using general linear modeling the most impactful factors on wear rate and backside damage was determined, thereby taking patient demographic factors into account. The mean volumetric wear rate was 11.6 mm³ /y. Wear decreased with older age (P = .021) and female sex (P = .001). The wear rate increased with joint line elevation as indicated from a decreased Blackburne-Peel index (P = .019), and increased with increased posterior tibial slope (P = .026). The backside damage score also increased with joint line elevation (P = .036). A Blackburne-Peel index decrease of 0.1, signifying joint line elevation, was found to increase the wear rate by 1.8 mm³ /y and increase back-sided wear. A high tibial slope (>7°) led to a 9.3 mm³ /y increase in wear rate compared with a low tibial slope (<3°). The results of this study demonstrate that tibial liner positioning has a significant impact on polyethylene wear with potential implications on osteolysis over time.

Does Knee Prosthesis Survivorship Improve When Implant Designs Change? Findings from the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

TKA generally has excellent long-term survivorship. When a new knee system supersedes a previous model, increased survivorship, improved functional performance, or both may be expected, because key areas of design modification are often targeted to address wear, stability, and the patellofemoral articulation. However, not all design changes are beneficial, and to our knowledge, knee arthroplasty has not been systematically evaluated in the context of design changes that occur during the development of new knee arthroplasty systems.

QUESTIONS/PURPOSES

Using the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) we performed multiple old-to-new comparisons of frequently used contemporary knee implants to ask: (1) does overall prosthesis survivorship free from revision increase when a new knee prosthesis system is introduced to replace a prior prosthesis system? (2) Has survivorship free from revision improved for the revision indications of wear, instability, and patellofemoral articulation issues, where development efforts have been concentrated?

METHODS

Data from the AOANJRR from September 1999 to December 2017 were used to compare the survivorship of prostheses free from revision at a maximum of 17 years in procedures where a new design model was introduced to replace a prior knee system from the same manufacturer. Only prosthesis systems used in a minimum of 2000 primary TKA procedures for osteoarthritis that had a minimum of 5 years of follow-up were included. Varus-valgus constrained and hinge TKA designs were excluded. Cruciate-retaining, posterior-stabilized, and medial pivot-design knees were considered separately. The new and old prosthesis systems were paired for analysis. Survivorship was calculated with Kaplan Meier estimates and comparisons were performed using the Cox proportional hazards method. Subanalyses according to the three main revision indications were performed, and where possible, analyses were performed based on polyethylene types (highly cross-linked polyethylene and ultra-high-molecular-weight polyethylene), combined and separated. Revision was defined as a reoperation of a previous knee arthroplasty in which one or more of the components was removed, replaced, or added. There were 323,955 TKA procedures and 11 new prosthesis system designs that were introduced to replace an earlier knee system from the same manufacturer. Of these prosthesis system pairs, six were cruciate-retaining prostheses, four were posterior-stabilized designs, and one was a medial pivot design.

RESULTS

Six of the 11 knee system pairs showed improved survivorship with the new design, three were no different, and in two, the newer prosthesis systems had a higher rate of revision than the old one did. When revision for wear was analyzed, five prosthesis systems showed improvement, five were no different, and one had a higher rate of revision than the previous system did. There was no improvement in the rate of revision for instability; seven new prosthesis systems showed no difference from the previous system and four new prosthesis systems had a higher rate of revision than the previous system did. A subanalysis of revision for patellofemoral complications showed improvement in two comparisons, no difference in six, and a higher revision rate in two; one could not be calculated because of an insufficient number of revisions for this reason.

CONCLUSIONS

It is difficult to predict whether a new system will demonstrate better survival than a previous one, and widespread uptake of a new design before a benefit is shown in robust clinical studies is unwise. Similarly, adoption of a new system for which there is no difference in survivorship from a previous model may be premature because a new device may have associated unknown and unintended consequences. Healthcare policy makers and therapeutic device regulators should similarly be guided by results and seek out peer-reviewed evidence before accepting change to established practice. Surgeons must be aware that implant changes may not translate into better survivorship and must seek compelling evidence of improvement in survival and/or function before changing systems.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Shear wave speeds track axial stress in porcine collateral ligaments

Ligament tension is an important factor that can affect the success of total knee arthroplasty (TKA) procedures. However, surgeons currently lack objective approaches for assessing tension in a particular ligament intraoperatively. The purpose of this study was to investigate the use of noninvasive shear wave tensiometry to characterize stress in medial and lateral collateral ligaments (MCLs and LCLs) ex vivo and evaluate the capacity of shear wave speed to predict axial load. Nine porcine MCL and LCL specimens were subjected to cyclic axial loading while shear wave speeds were measured using laser vibrometry. We found that squared shear wave speed increased linearly with stress in both the MCL (r²_avg = 0.94) and LCL (r²_avg = 0.98). Shear wave speeds were slightly lower in the MCL than the LCL when subjected to a comparable axial stress (p < 0.001). Specimen-specific calibrations predicted tension within 13.0 N, or 5.2% of the maximum load. A leave-one-out analysis was also performed and showed that calibrated relationships based on ligament type could predict axial tension within 15% of the maximum load. These observations suggest it may be feasible to use noninvasive shear wave speed measures as a proxy of ligament loading, which in the future might enhance decision making during orthopedic procedures such as TKA.

A Single Surgeon Series Comparing the Outcomes of a Cruciate Retaining and Medially Stabilized Total Knee Arthroplasty Using Kinematic Alignment Principles

BACKGROUND

Total knee arthroplasty (TKA) designs are developed to optimize kinematics and improve patient satisfaction. The cruciate retaining (CR) and medially stabilized (MS) TKA designs have reported good mid-term follow-up outcomes. However, reasons for consistently high rates of patient dissatisfaction following a TKA remain poorly understood. To further investigate this, we compared the short-term functional outcomes and quality of life, using patient-reported outcome measures (PROMs) and range of motion (ROM), between a CR and MS TKA.

METHODS

A prospective comparison was made between 2 groups (44 CR-TKAs vs 46 MS-TKAs). The Knee Injury and Osteoarthritis Outcome Score (KOOS), KOOS-12, KOOS-Short form, KOOS-Joint Replacement, Oxford Knee Score, Western Ontario and McMaster Universities Osteoarthritis Index, UCLA Activity Scale, and EuroQuality of life - 5 Dimension were completed preoperatively and 1 year postoperatively. The Forgotten Joint Score (FJS) and Visual Analogue Scale-Satisfaction were completed at 1 year postoperatively. ROM was collected preoperatively and 1 year postoperatively.

RESULTS

Patients who underwent an MS-TKA scored significantly better than the CR-TKA on the FJS (MS = 79.87, CR = 63.8, P = .005), the KOOS-12 Quality of Life subscale (MS = 82.8, CR = 74.4, P = .43), and the KOOS Quality of Life subscale (MS = 82.8, CR = 74.6, P = .44). There was no difference between the groups in all assessed PROMs or ROM, preoperatively and 1 year postoperatively.

CONCLUSION

Patients who underwent the MS-TKA scored significantly better on the FJS and the quality of life subscale of the KOOS and KOOS-12 than those who underwent a CR-TKA. All other assessed PROMs and ROM were comparable between the 2 groups and demonstrated that both implants facilitated symptom relief and improved daily function at 1 year postoperatively. These findings suggest that at short-term follow-up, the MS device is more likely to allow a patient to "forget" that a joint has been replaced and restore their quality of life. Long-term assessment of MS-TKA design outcomes in larger cohorts is recommended.

Robotic technology in total knee arthroplasty: a systematic review

Robotic total knee arthroplasty (TKA) improves the accuracy of implant positioning and reduces outliers in achieving the planned limb alignment compared to conventional jig-based TKA.Robotic TKA does not have a learning curve effect for achieving the planned implant positioning. The learning curve for achieving operative times comparable to conventional jig-based TKA is 7-20 robotic TKA cases.Cadaveric studies have shown robotic TKA is associated with reduced iatrogenic injury to the periarticular soft tissue envelope compared to conventional jig-based TKA.Robotic TKA is associated with decreased postoperative pain, enhanced early functional rehabilitation, and decreased time to hospital discharge compared to conventional jig-based TKA. However, there are no differences in medium- to long-term functional outcomes between conventional jig-based TKA and robotic TKA.Limitations of robotic TKA include high installation costs, additional radiation exposure, learning curves for gaining surgical proficiency, and compatibility of the robotic technology with a limited number of implant designs.Further higher quality studies are required to compare differences in conventional TKA versus robotic TKA in relation to long-term functional outcomes, implant survivorship, time to revision surgery, and cost-effectiveness. Cite this article: EFORT Open Rev 2019;4:611-617. DOI: 10.1302/2058-5241.4.190022.

Flexion Instability After Total Knee Arthroplasty

Flexion instability after total knee arthroplasty (TKA) is caused by an increased flexion gap compared with extension gap. Patients present with recurrent effusions, subjective instability (especially going downstairs), quadriceps weakness, and diffuse periretinacular pain. Manual testing for laxity in flexion is commonly done to confirm a diagnosis, although testing positions and laxity grades are inconsistent. Nonsurgical treatment includes quadriceps strengthening and bracing treatment. The mainstays to surgical management of femoral instability involve increasing the posterior condylar offset, decreasing the tibial slope, raising the joint line in combination with a thicker polyethylene insert, and ensuring appropriate rotation of implants. Patient outcomes after revision TKA for flexion instability show the least amount of improvement when compared with revisions for other TKA failure etiologies. Future work is needed to unify reproducible diagnostic criteria. Advancements in biomechanical analysis with motion detection, isokinetic quadriceps strength testing, and computational modeling are needed to advance the collective understanding of this underappreciated failure mechanism.

Sagittal radius of curvature, trochlea design and ultracongruent insert in total knee arthroplasty

Multi radius (MR) total knee arthroplasty (TKA) has been associated with mid-flexion instability.

Single radius (SR) TKA may provide better anteroposterior stability through single flexion axis and biomechanical advantage for quadriceps function.

Medial pivot (MP) TKA and gradually reducing (GR) radius TKA produce better knee kinematics.

Clinical outcomes are equivalent for SR, MR and MP TKA.

Short-term studies have shown better clinical outcomes and kinematics for GR TKA.

Thinner and narrow anterior flange, deeper trochlea groove and more anatomical trochlea design reduces patellofemoral complications in TKA

Ultracongruent inserts provide comparable clinical outcomes to posterior-stabilized TKA and cruciate retaining TKA.

Cite this article: EFORT Open Rev 2019;4:519-524. DOI: 10.1302/2058-5241.4.180083

Dynamic sensor-balanced knee arthroplasty: can the sensor "train" the surgeon?

Background

Dynamic tibial tray sensors are playing an increasing role in total knee arthroplasty (TKA) coronal balancing. Sensor balance is proposed to lead to improved patient outcomes compared with sensor-unbalanced TKA, and traditional manual-balanced TKA. However, the "learning curve" of this technology is not known, and also whether sensor use can improve manual TKA balance skills once the sensor is taken away, effectively "training" the surgeon.

Methods

We conducted a single-surgeon prospective study on 104 consecutive TKAs. In Nonblinded Phase I (n = 49), sensor-directed releases were performed during trialing and final intercompartmental load was recorded. In Blinded Phase II (n = 55), manual-balanced TKA was performed and final sensor readings were recorded by a blinded observer after cementation. We used cumulative summation analysis and sequential probability ratio testing to analyze the surgeon learning curve in both phases.

Results

In Nonblinded Phase I, sensor balance proficiency was attained most easily at 10°, followed by 90°, and most difficult to attain at 45° of flexion. In Blinded Phase II, manual balance was lost most quickly at 45°, followed by 90°, and preserved for longest at 10° of flexion. The number of cases in the steady state periods (early phase periods where there is a mix of sensor balance and sensor imbalance) for both phases is similar.

Conclusions

A surgeon who consistently uses the dynamic sensor demonstrates a learning curve with its use, and an "attrition" curve once it is removed. Consistent sensor balance is more predictable with constant sensor use.

The assessment of instability in the osteoarthritic knee

Patient-reported instability is a common complaint amongst those with knee arthritis.

Much research has examined the assessment of self-reported instability in the knee; however, no definitive quantitative measure of instability has been developed.

This review focuses on the current literature investigating the nature of self-reported instability in the arthritic knee and discusses the possibilities of further investigation.

Cite this article: EFORT Open Rev 2019;4:70-76. DOI: 10.1302/2058-5241.4.170079

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.

A Computer Model of Mid-Flexion Instability in a Balanced Total Knee Arthroplasty

BACKGROUND

Some patients have mid-flexion instability despite stability at 0° and 90° of flexion. This study aims to determine the effects of total knee arthroplasty (TKA) stability while changing femur implant size and position.

METHODS

A computational analysis was performed simulating knee flexion of posterior stabilized (PS) and cruciate retaining (CR) TKA designs. Deviations from the ideal TKA implant position were simulated by adjusting tibiofemoral proximal-distal position and femur anterior-posterior position as well as implant size. Forces in ligaments connecting the femur and tibia were collected. Total tibiofemoral ligament load for mid-knee flexion of 15°-75° was analyzed vs proximal-distal implant position, implant size, implant design, and knee flexion for PS and CR knees. Posterior cruciate ligament load was also analyzed for CR knees.

RESULTS

Total tibiofemoral ligament load was significantly reduced by a more proximal tibiofemoral and anterior femur position (P < .001). Implant size did not have a significant effect on tibiofemoral ligament load (P > .1). Implant design and knee flexion significantly influenced total tibiofemoral ligament load (P < .001), but the interactions with implant proximal-distal position were not significant (P > .2), indicating that implant proximal-distal position had a similar effect across the 15°-75° knee flexion range for both studied PS and CR implant designs.

CONCLUSION

PS and CR TKA can be well-balanced at 0° and 90° knee flexion and have instability in mid-flexion. Elevating the joint line and shifting the femur anteriorly can cause the knee to be too loose in mid-flexion.

Validity of the intra-operative measurement of stem anteversion and factors for the erroneous estimation in cementless total hip arthroplasty using postero-lateral approach

BACKGROUND

Intra-operative estimation of stem anteversion in total hip arthroplasty (THA) using postero-lateral approach is made by the surgeon's visual assessment, using the tibia as a guide, with the assumption that tibial axis is vertical to the trans-epicondylar axis. However, the accuracy of the intra-operative estimation has rarely been verified with postoperative CT-scans, with controversies regarding these measurements particularly in case of knee osteoarthritis. Therefore we performed a prospective study to: (1) determine the accuracy of the intra-operative measurement and (2) investigate factors affecting the discrepancy between the surgeon's estimation and the real stem anteversion.

HYPOTHESIS

Intra-operative estimation of stem anteversion correlated with the real stem anteversion on CT-scan.

PATIENTS AND METHODS

Sixty-seven THAs using cementless straight stems (65 patients) without ipsilateral total knee arthroplasty were prospectively evaluated to compare the intra-operative measurement of stem anteversion with the real stem anteversion on computed tomography (CT) scans. There were 33 men and 34 women with a mean age of 59.7years (range, 27-84years) at the time of surgery. Age, tibia plateau angle, native femoral anteversion, femoro-tibial angle, body mass index, operative site, gender, coronal and sagittal tilt of the stem, stem type, ipsilateral knee osteoarthritis, and preoperative diagnosis were analyzed to evaluate the factors affecting the discrepancy between the intra-operative and CT measurements.

RESULTS

The intra-operative estimation (mean, 21.5°±8.5°; range, 5.0°-39.0°) was greater than the CT measurement (mean, 19.5°±8.7°; range, 4.5°-38.5°) by 2.0°. The mean absolute value of discrepancy was 4.5°. The correlation coefficient between intra-operative and CT measurements was 0.837. The femoro-tibial angle was associated with the discrepancy between the two measurements. In the presence of genu varum deformity, the intra-operative measurement underestimated the stem anteversion.

DISCUSSION

Although intra-operative estimation of stem anteversion was slightly greater than the real stem anteversion, there was an excellent correlation between the two. The femoro-tibial angle should be considered to optimize the stem anteversion during cementless THA using postero-lateral approach.

LEVEL OF EVIDENCE

Level III, prospective case control study.

Medial Pivot in Total Knee Arthroplasty: Literature Review and Our First Experience

Background:

Traditional total knee implants designs, usually, are not able to reproduce the physiological kinematics of the knee, leaving almost 20% of the patients, those who underwent a total knee arthroplasty (TKA), not fully satisfied. Modern inserts are nowadays designed with a fully congruent medial compartment to reproduce the normal medial pivoting biomechanics of the knee. The aim of this article was to evaluate preliminary clinical improvement using the Medial Congruent (MC) insert as specific level of constraint.

Materials and methods:

A total of 10 consecutive patients have been enrolled in this study and treated using an MC tibial polyethylene insert. The Oxford Knee Score (OKS) and the Knee Society Score (KSS) have been assessed preoperatively and at 3-month, 6-month, and 1-year follow-up (FU) and used as validated measurements to evaluate early clinical improvements. Postoperative radiological examination was reviewed looking for radiolucent lines or loosening of the components.

Results:

Average improvement in OKS was from 19.5 to 41.2, whereas KSS improved with an average score from 64.7 preoperatively to 167.5 at the final FU showing good to excellent results in 95% of the treated knees. Evaluating the range of motion, the average maximum active movement was 124° and none of the patients needing for a revision surgery or manipulation under anesthesia. No complications were observed at the final FU as septic or aseptic loosening or vascular or neurologic injury.

Discussion and conclusions:

Medial Congruent insert showed good to excellent clinical results at 1-year FU. Range of motion and subjective outcomes were satisfying and comparable with results obtained in literature using traditional TKA design.

Internal femoral component rotation adversely influences load transfer in total knee arthroplasty: a cadaveric navigated study using the Verasense device

PURPOSE AND HYPOTHESIS

Correct femoral component rotation at knee arthroplasty influences patellar tracking and may determine function at extremes of movement. Additionally, such malrotation may deleteriously influence flexion/extension gap geometry and soft tissue balancing kinematics. Little is known about the effect of subtle rotational change upon load transfer across the tibiofemoral articulation. Our null hypothesis was that femoral component rotation would not influence load across this joint in predictable manner.

METHODS

A cadaveric study was performed to examine load transfer using the orthosensor device, respecting laxity patterns in 6° of motion, to examine load across the medial and lateral compartments across a full arc of motion. Mixed-effect modelling allowed for quantification of the effect upon load with internal and external femoral component rotation in relation to a datum in a modern single-radius cruciate-retaining primary knee design.

RESULTS

No significant change in maximal laxity was found between different femoral rotational states. Internal rotation of the femoral component resulted in significant increase in medial compartment load transfer for knee flexion including and beyond 60°. External rotation of the femoral component within the limits studied did not influence tibiofemoral load transfer.

CONCLUSIONS

Internal rotation of the femoral component will adversely influence medial compartment load transfer and could lead to premature polyethylene wear on the medial side.

Association between anteroposterior laxity in mid-range flexion and subjective healing of instability after total knee arthroplasty

PURPOSE

Flexion instability following total knee arthroplasty (TKA) is a common indication of early revision. The association between the objective anteroposterior (AP) laxity direction in mid-range flexion and the subjective healing of instability remains unclear; thus, this study aimed to clarify this association.

METHODS

In this study, 110 knees (74 females, 92 knees; 16 males, 18 knees) with medial pivot implants were examined with a median age of 79 (range 60-92) years for a median follow-up duration of 22 (range 6-125) months. AP laxity was measured using a KT-1000 arthrometer. Self-reported knee instability score was used for the subjective healing of instability.

RESULTS

Eighty-seven knees did not feel unstable (Group 0), whereas 23 knees felt unstable (Group 1). There was a significant difference in AP displacement [Group 0: median 6 mm; range 2-15 mm and Group 1: median 8 mm; range 4-14; p < 0.0001]. The threshold value of 7 mm was determined using the area under receiver operating characteristic curve of 0.79 [95% confidence interval (CI) 0.69-0.88, p < 0.0001]. In multivariate analysis, AP displacement of ≥7 mm was an independent risk factor for feelings of instability (odds ratio 7.695; 95% CI 2.306-25.674; p = 0.001).

CONCLUSIONS

AP laxity of ≥7 mm represents a known cause of feelings of instability. By controlling AP laxity in TKAs, without stiffness in the knee, it is possible to prevent feelings of instability. The clinical relevance is that AP laxity of <7 mm is one of the target areas in TKA.

LEVEL OF EVIDENCE

IV.

Intraoperative load-sensing drives the level of constraint in primary total knee arthroplasty: Surgical technique and review of the literature

Total knee arthroplasty is a traditional surgical procedure aimed to restore function and relief pain in patients with severe knee osteoarthritis. Recently, many medial pivot knee systems were deigned to replicate the normal knee kinematic: a highly congruent medial compartment and a less conforming lateral tibial plateau characterize these devices. A slightly asymmetric soft tissue balancing is mandatory using medial pivot designs to obtain a correct and physiological knee biomechanics leading good outcomes and long survival rates. This article describes a new surgical technique using a modern third generation TKA design combined with wireless load-sensor tibial trials to improve the correct knee load balancing with a minimal conformity of the polyethylene insert. The use of wireless load-sensing tibial trials has several benefits: it is an intraoperative, objective and dynamic tool allowing surgeons to optimize in real time soft tissue balancing. The meaning of a "truly balanced knee" is still a controversial issue in the current literature.

Varus-valgus constrained implants in total knee arthroplasty: indications and technique

Total knee arthroplasty is a successful operation that significantly improves patient's quality of life. However, studies demonstrated as only 82% to 89% of patients are satisfied with their surgery, being the other disappointed with regard to their expectations. Two to 5.7% of total knee arthroplasties (TKAs) require revision within 5 years. Both complex primary cases and revision TKA often necessitate for a higher degree of constrain than cruciate retaining or postero-stabilized implant design. In the 1970s varus-valgus constrained (VVC) or semi-constrained implants have been developed by Insall and associates from the PS design, which provide varus-valgus stability preserving a fair amount of host bone. VVC TKAs allows for a small amount of movement in the coronal, antero-posterior and axial planes. In this paper, the authors give an overview of the indications, outcomes and technique for varus-valgus constrained implants, both in the setting of primary and revision knee arthroplasty.

A soft-tissue preserving method for evaluating the impact of posterior tibial slope on kinematics during cruciate-retaining total knee arthroplasty: A validation study

BACKGROUND

The reconstructed posterior tibial slope (PTS) plays a significant role in restoring knee kinematics in cruciate-retaining total knee arthroplasty. However, conventional methods for the investigation of PTS can be limited by sample size or prone to errors due to damages to the bone and/or soft tissues. The purpose of this study was to validate a novel method for the evaluation of the effects of PTS on knee kinematics.

METHODS

Seven computer-assisted cruciate-retaining TKAs were performed by two surgeons on healthy cadaveric knees. The implanted tibial baseplates allowed precise and easy modification of the PTS in situ. Knee kinematics were evaluated during passive full range of motion test. The evaluation was performed three times at each of the five PTSs in the order of 10°, seven degrees, four degrees, one degree, and back to ten degrees. The variability of the repeated measurements, inter-surgeon variation of the data, and test reproducibility were investigated.

RESULTS

The test method was shown to be highly repeatable (low root-mean-squared errors) and has low sensitivity to surgeon variability (ANOVA). No statistical difference was found in the knee kinematics between the first and last measurements at 10° PTS (paired t-test).

CONCLUSION

The results suggested that the developed method can be used to investigate the impact of PTS on knee kinematics without disrupting the soft-tissue environment of the knee. The use of the novel tibial baseplate allowed for adjusting the PTS without re-cutting the tibia and removing the components. The method may be applied to improve the future investigation of PTS.