1) INTRODUCTION. Total knee arthroplasty (TKA) is one of the most common orthopaedic procedures performed, and is projected to exponentially increase over the next 20 years. As primary TKA cases increase, so does the frequency of revisions. The primary goals for all TKA cases include alleviating pain and improving overall knee function. The objective of this study was to evaluate the change in outcomes as measured by the Knee Society Score (KSS) between primary and revision TKA systems. 2) METHODS. This data was collected as part of three prospective, post-market, multicenter studies comparing preoperative to 6-week data. Patients were stratified into two groups based on type of single radius knee device; Posteriorly Stabilized (PS) group and Total Stabilizer (TS) group. Early clinical outcomes based on the KSS and operative data were used to compare groups. 3) RESULTS. The KSS was compared to determine the amount of improvement in revision vs. primary cases. Within the KSS Pain/Motion section, the improvement in range of motion was greatest in the TS revision group (change of 8°) in comparison to the primary PS group (change of 3°), as well as a significant decrease in pain classification. The KSS Functional scores improved significantly more in the revision group compared to the primary group. 4) DISCUSSION and CONCLUSION. Studies have determined that revision TKAs have lower rates of functional outcomes, leading to a decreasing trend in KSS. This trend can be correlated to increased difficulty of the surgical technique due to increased bone loss and anatomical changes, as well as a higher constraint in revision TKA devices. The design of a single radius knee revision system addresses these issues with revision TKA and has been shown to have comparable KSS evaluations to patients receiving primary single radius TKAs

Instability is reported to account for around 20% of early TKR revisions. The concept of restoring the “Envelope of Laxity” (EoL) mandates a balanced knee through a continuous arc of functional movement. We therefore hypothesised that a single radius (SR) design should confer this stability since it has been proposed that the SR promotes normal medial collateral ligament (MCL) function with isometric stability throughout the full arc of motion. Our aim was to characterise the EoL and stability offered by a SR cruciate retaining (CR)-TKR, which maintains a SR from 10–110° flexion. This was compared with that of the native knee throughout the arc of flexion in terms of anterior, varus/valgus and internal/ external laxity to assess whether a SR CR-TKR design can mimic normal knee joint kinematics and stability. Eight fresh frozen cadaveric lower limbs were physiologically loaded on a custom jig. The operating surgeon performed anterior drawer, varus/ valgus and internal/external rotation tests to determine ‘maximum’ displacements in 1) native knee and 2) single radius CR-TKR (Stryker Triathlon) at 0°, 30°, 60°, 90° and 110° flexion. Displacements were recorded using computer navigation. Significance was determined by linear modelling (p≤0.05). The key finding of this work was that the EoL offered by the SR CR-TKR was largely equivalent to that of the native knee from 0–110°. The EoL increased significantly with flexion angle for both native and replaced knees. Overall, after TKR anterior laxity was comparable with the native knee, whilst total varus-valgus and internal-external rotational laxities reduced by only 1°. However, separated varus and valgus laxities at 110° significantly increased after TKR as did anterior laxity at 30° flexion. In conclusion, the overall EoL offered by the SR CR-TKR is comparable to that of the native knee. In the absence of soft tissue deficiency, the implant appears to offer reliable and reproducible stability throughout the functional range of movement, with exception of anterior laxity at 30° and varus and valgus laxity when the knee approaches high flexion. These shortcomings should offer scope for future work

Introduction. In this study, three-dimensional (3D) digital image correlation (DIC) was adopted to investigate the strain in the superficial medial collateral ligament (sMCL) of the human knee. To our knowledge, no reports or validation of 3D DIC measurement on human collagenous tissue exists. The first part of this research project focused on the validation of 3D DIC (1) as a highly accurate tool for non-contact full field strain analysis of human collagenous tissue. In the second part, 3D DIC was used to measure the strain patterns in the superficial medial collateral ligament (sMCL) of the native knee (2). In a third part, the strain pattern in the sMCL after total knee arthroplasty (TKA) in an ‘optimal’ (3) and with a proximalised joint line (4) was analysed. Methods. (1) Six fresh frozen human Achilles tendon specimens were mounted in a custom made rig for uni-axial loading. The accuracy and reproducibility of 3D DIC was compared to two linear variable differential transformers (LVDT's). (2) The strain pattern of the sMCL during the range of motion (ROM) was measured using 3D DIC in six fresh frozen cadaveric knees. The knees were mounted in a custom made rig, applying balanced tension to all muscle groups around the knee. The experiment was repeated after computer navigated implantation of a single radius posterior stabilised (PS) TKA in ‘optimal’ (3) and with a 4 mm proximalised joint line (4). Results. (1) Accuracy analysis revealed that the scatter was very low for all specimens (0,03%) and a spatial resolution of 0,1 mm for strain measurement was reached. When compared to the LVDT, DIC showed excellent correlation (R = 0.99). (2) Overall, the sMCL behaved isometrically between 0° and 90° of flexion showing less 1% slackening in all specimens. Further slackening was seen in deeper flexion. Significant regional inhomogeneity was observed (fig 1). The highest strains (up to 5% lengthening) were seen in the proximal part. The middle and distal part were near isometric between 0° and 90° of flexion. (3) A significant alteration of the strain pattern was seen after TKA with an increased strain in all parts of the sMCL from 90° to deeper flexion (fig 2). (4) This effect became significantly more pronounced with joint line proximalisation. Discussion. Strain in the native sMCL proved to be inhomogeneously distributed with significant differences between proximal, middle and distal part during the ROM. The higher baseline strain in the proximal part might be the explanation for the fact that most of the sMCL lesions are seen in that region. A single radius TKA failed to reproduce the native sMCL strain pattern from 90° to deeper flexion. This effect became even more pronounced with joint line proximalisation. These higher sMCL strains might compromise deeper flexion after TKA. Conclusion. The strain pattern of the sMCL in the native knee showed important regional differences during the ROM and significant alterations after TKA implantation and joint line proximalisation

Introduction

Total knee arthroplasty (TKA) is an excellent treatment for end-stage osteoarthritis of the knee. In Asian countries, the number of TKA performed has rapidly increased, and is expected to continue so with its 4.4 billion population and increasing life expectancy. Asians' knees are known to be kinematically different to Caucasians after TKA. Controversy exists as to whether multi-radius (MR) or the newer single-radius (SR) TKA has superior outcome. Studies regarding this have been largely based on Caucasian data with few small sample Asian data.

Introduction:. Revision total knee arthroplasty (TKA) can be very complex in nature with difficulties/obstacles involving bone and soft tissue deficits, visualization and exposure, as well as alignment and fixation. Auxiliary devices such as augmentation and offset adapters help address these issues; however they increase the complexity of the reconstruction. The objective of this study was to show that use of a single radius revision TKA system allowing for minimal auxiliary revision devices can yield positive early clinical outcomes. Methods:. This data was collected as part of a prospective, post-market, multicenter study. One hundred and twenty-five single radius revision TKA cases were evaluated. Surgical details were reviewed and cases were grouped based on type of auxiliary devices used. Group 1 included cases that used only femoral and/or tibial augments. Group 2 used femoral and/or tibial augments in conjunction with femoral and/or tibial offset adapters. Early clinical outcomes, operative data and radiographic findings were used to compare cases. Results:. At 6 weeks and 1 year postoperatively, Knee Society Scores, pain, function and quality of life all improved more in Group 1 (augments only) than Group 2 (augments and offset adapters). There was no difference in range of motion postoperatively for either group. Preoperative demographics showed no differences between Group 1 and Group 2. Offset adapters were used in only 17.6% of the cases. Discussion/Conclusion:. Studies have discussed the increase in complexity of revision TKAs is associated with a decrease in patient outcomes. The surgical technique for revision TKAs can be more difficult due to an increase in bone loss and anatomical changes. Augment usage is the main auxiliary component utilized to supplement bone loss. By design, this single radius revision system limits the additional need for offset adapters to adjust patient alignment, while achieving excellent postoperative patient outcomes. Reducing the amount of devices needed for reconstruction decreases the intraoperative complexity and has shown improved functional outcomes with this single radius revision TKA system

Introduction. Increasingly young and active patients are concerned about revision arthroplasty forcing the manufacturers to think about revision prostheses that fit to this population while meeting the indications and fitting with bone losses and ligament deficiencies. One of those industrials claims that its system allows the surgeon to rise the constraint from a posterior stabilized (PS) prostheses to a semi-constraint total stabilized (TS) prostheses without modifying the gait pattern thanks to a similar single radius design. The aim of the study was to compare gait parameters in patients receiving either PS or TS knee prostheses. Methods. Nineteen patients in each groups were prospectively collected for this study and compared between each other. All subjects were assessed with a 3D knee kinematics analysis, performed with an optoelectronic knee assessment device (KneeKG®). Were measured for each knees range of motion (ROM) in flexion–extension, abduction–adduction, internal–external rotation and anterior–posterior displacement. Results. There were no significant kinematic differences between PS and TS groups. The ROM in flexion-extension was 44° in PS group vs 46° in TS group, the ROM in internal-external rotation was 5.5° in PS group vs 4°in TS group. Peak varus angle during loading was equal (2.5°) and higher in PS group during swing phases (5.5° vs 3.7°) without any significancy. There appeared to be less antero-posterior translation in the TS group (maximum posterior displacement of −1 mm vs −5 mm) linked to the larger central post-cam without any significancy. Conclusion. TS designed have comparable gait parameters than PS prostheses. Its use won't prejudice the patient concerning the walking pattern

It is difficult for surgeons to make the decision on which design or material to use given multiple available options for total knee arthroplasty. Due to the complex interaction of soft tissue, implant position, patient anatomy, and kinematic demands of the patient, the prosthetic design of a knee device has traditionally been more important than materials. The purpose of this study was to examine the overall influence of both implant design and materials on volumetric wear rates in an in vitro knee simulator study for two knee designs. Two different designs (single radius and J-curve) with two highly crosslinked materials (Sequentially crosslinked and annealed PE (X3®, Stryker Orthopaedics, Mahwah, NJ) (7.5 kGy moderately crosslinked UHMWPE (XLPE, Smith and Nephew, Memphis, TN)) were evaluated. The two designs tested were the Triathlon® CR knee system (single radius design)(Stryker Orthopaedics, Mahwah, NJ) and the Legion™ Oxinium® CR knee system (J-curve design) (Verilast™, Smith and Nephew, Memphis, TN). Three inserts per condition were tested in this study. This comparison incorporates the effects of both materials and designs: different femoral component materials, different tibial bearing materials, and implant geometry (J-curve vs. single radius saggital profile). All devices were tested under ISO 14243-3 normal walking using an MTS knee simulator for a total of 5 million cycles. Standard test protocols were used for cleaning, weighing and assessing the wear loss of the tibial inserts (ASTM F2025). Soak control specimens were used to correct for fluid absorption with weight loss data converted to volumetric data (by material density). Statistical analysis was performed using the Student's t-test. Total volume loss results are shown in Figure 1. Test results show a 36% reduction (p<0.05) in volume loss and a 30% reduction (p<0.05) in wear rate for the single radius design compared to the J-curve design, respectively. All comparisons are statistically significant by the t-test method (p<0.05). Visual examination of all worn inserts revealed typical wear scars and features on the condylar surfaces, including burnishing. Results indicate superior wear resistance for the single radius system. This finding indicates that a combination of implant design and prosthesis material plays a significant role in knee wear rates. The in vitro low volumetric wear observed in the single-radius prosthesis could theoretically influence long term survivorship in vivo, and supports the potential for improved durability and long term wear performance for this design when compared to a J-curved femoral component. Longer term clinical evidence such as published studies or outcomes reported in the available joint registries will be needed to establish whether any material or design can achieve a 30-year or longer outcome

INTRODUCTION. Use of a novel ligament gap balancing instrumentation system in total knee arthroplasty (TKA) resulted in femoral component external rotation values which were higher on average, compared to measured bone resection systems. In one hundred twenty knees in 110 patients the external rotation averaged 6.9 degrees (± 2.8) and ranged from 0.6 to 12.8 degrees. The external rotation values in this study were 4° and 2° larger, respectively, than the typical 3° and 5° discrete values that are common to measured resection systems. The purpose of the present study was to determine the effect of these greater external rotation values for the femoral component on patellar tracking, flexion stability and function of two different TKA implant designs. METHODS. In the first arm of the study, 120 knees in 110 patients were consecutively enrolled by a single surgeon using the same implant design (single radius femur with a medial constraint tibial liner) across subjects. All patients underwent arthroplasty with tibial resection first and that set external rotation of the femoral component based upon use of a ligament gap balancing system. Following ligament tensioning / balancing, the femur was prepared. The accuracy of the ligament balancing system was assessed by reapplying equal tension to the ligaments using a tensioning bolt and torque wrench in flexion and extension after the bone resections had been made. The resulting flexion and extension gaps were then measured to determine rectangular shape and equality of the gaps. Postoperative Merchant views were obtained on all of the patients and patellar tracking was assessed and compared to 120 consecutive total knee arthroplasties previously performed by the same surgeon with the same implant using a measured resection system. In the second arm of the study, 100 unilateral knees in 100 patients were consecutively enrolled. The same instrumentation and technique by the same surgeon was used, but with a different implant design (single radius femur without a medial constraint tibial liner). RESULTS. Rectangular flexion and extension gaps were obtained within ± 0.5mm in all cases. Equality of the flexion and extension gaps was also obtained within ± 0.5mm in all cases. Merchant views of the total knee arthroplasties showed central patellar tracking with no tilt or subluxation in 90% of the ligament gap balanced knees and 74% of the measured resection knees. Arthrofibrosis resulting in a closed manipulation under anesthesia was required in 6% of the knees with single radius femurs and medial constaint tibial liners, but only in 1% of the single radius femur knees without medial constraint liners. DISCUSSION AND CONCLUSION. External rotation values are higher on average, when ligament tensioning / balancing is employed with this novel system compared to measured resection systems. In this study this resulted in consistent matching of the flexion gap to the extension gap and better patellar tracking. These findings suggest that limiting the surgeon to discrete rotation values may be at odds with where the femur “desires” to be, given soft tissue considerations for each patient. Also, even with ideal soft tissue balancing, TKA implant design can have a significant affect on the outcome measure of development of arthrofibrosis

Background. Intraoperative balancing of total knee arthroplasty (TKA) can be accomplished by either more prevalent but less predictable soft tissue releases, implant realignment through adjustments of bone resection or a combination of both. Robotic TKA allows for quantifiable precision performing bone resections for implant realignment within acceptable final component and limb alignments. Objective. To provide a direct comparison of patient reported outcomes between implant realignment and traditional ligamentous release for soft tissue balancing in TKA. Methods. IRB approved retrospective single surgeon cohort study of prospectively collected operative and clinical data of consecutive patients that underwent TKA with a single radius design utilizing kinematic sensors to assess final balance with or without robotic assistance allowing for a minimum of 12 months clinical follow up. Operative reports were reviewed to characterize the balancing strategy. In surgical cases using robotic assistance, pre-operative plan changes that altered implant placement were included in the implant realignment group. Any patient that underwent both implant realignment and soft tissue releases was analyzed separately. Kinematic sensor data was utilized to quantify ultimate balance to assure that each cohort had equivalent balance. Patient reported outcome data consisting of Knee Society- Knee Scores (KS-KS), Knee Society- Function Scores (KS-FS), and Forgotten Joint Scores (FJS) were prospectively collected during clinical follow up. Results. 182 TKA were included in the study. 3-Month clinical follow up was available for 174/182 knees (91%), 1-Year clinical follow up was available for 167/182 knees (92%) and kinematic sensor data was available for 169/182 knees (93%). Kinetic sensor data showed that on average all of the balancing subgroups achieved clinically equivalent balance. Use of robotic-arm assistance provided the tools and confidence to decrease from ligament release only in 40.8% of non-robotic cases to 3.8% in the robotic group, and the use of component realignment alone increased from 23.7% in the non-robotic cases to 48.1% in the robotic TKA group. KS-KS, KS-FS and FJS scores showed improvements in outcomes at both the 3-month and 1-year time points in the implant realignment cohort compared to the ligamentous release cohort. KS-KS, KS-FS, and FJS at 1-year were 1.6, 7.6, and 17.2 points higher respectively. While none of the comparisons reached statistical significance, KS-FS at 1 year showed a statistically and clinically significant difference (MCID 6.1–6.4) increase of 7.7 points in the implant realignment cohort compared to the ligamentous cohort. The 1-year trend can be further explained by the outperformance (MCID increase of 6.4 points) of the implant realignment robotic cohort at 1-year compared to the non-robotic ligamentous cohort. Conclusions. Directly comparing TKA patients balanced with implant realignment alone versus ligamentous release alone versus combined technique, a trend toward clinical improvement above a minimally clinical significant difference in KS-FS scores benefiting the implant realignment technique was seen at both 3-months and 1-year post-operatively. We hypothesize that the benefit of implant realignment is achieved through decreased soft tissue trauma as well as potentially greater predictability and sustainability of soft tissue balance than with soft tissue releases alone

Object. Although single-radius designs have theoretical advantages in some aspects, there has been a paucity of evaluation studies. The purpose of this study was to compare 10-year clinical, radiological, survivorship outcomes of single radius and multi radius posterior stabilized prosthesis in total knee arthroplasty(TKA) with Rheumatoid Arthritis (RA). Method. In this retrospective observational study, we reviewed 240 patients (240 knees) with RA who underwent TKA between Oct 2005 and Dec 2007: SR group (120 patients, 120 knees, Stryker Scorpio NRG) and MR group (120 patients, 120 knees, Depuy sigma RP). A 1 : 1 matched case control study was conducted in two groups which were similar in terms of age, gender, BMI, ASA classification and operation team. Mean follow-up periods were 10.73±1.13 (range: 8–13) years and 10.82±1.09 (range: 7–13) years. Results. In SR group, the mean HSS score improved significantly from 38.63±8.76 to 87.67±6.62, the mean VAS score decreased significantly from 7.37±0.24 to 0.45±0.12. the mean range of motion improved significantly from 105.52°±7.78°to 124.32°±8.12° (p<0.001). In MR group, the mean HSS score improved significantly from 38.75±8.34 to 89.29±5.21, the mean VAS score decreased significantly from 7.62±0.26 to 0.33±0.10. the mean range of motion improved significantly from 104.18°±7.62° to 122.52°±8.03°(p<0.001). (See Figure 1) Clinical and functional improvements had no significant differences between the two groups. 6 complications were noted in SR group, including 2 cases of prosthetic loosening, 1 case of periprosthetic osteolysis, 3 cases of periprosthetic bright lines.6 complications were noted in MR group, including 2 cases of prosthetic loosening and 4 cases of periprosthetic bright lines. No case of infection was observed in two groups. Survivorship using Kaplan-Meier survival analysis was 97.5% (95% confidence interval [CI]: 96.8–98.3%) for the SR at 10 years and 98.3% (95% CI: 97.3–99.5%) for the MR group at 10 years, with no significant difference (p=0.755). (See Figure 2). Conclusion. This study suggested that both single-radius and multi-radius posterior stabilized prostheses can lead to satisfactory outcomes for clinical function, radiological evaluation and survivorship among RA patients undergoing TKA, and no significantly clinical differences was shown in two types of prostheses

Since 1997, a patented rim flared cup has been used for both primary and revision total hip arthroplasty with great success. The concept was based on a “stretched” hemispherical geometry to improve initial contact between cup and bone. This improved geometry provided a 1 mm press fit predominantly at the perimeter of the acetabulum much like the footprint of the native anatomic acetabulum. Thousands of these were implanted. A second version of this concept was introduced in August 2011. This similarly “stretched” geometry provides 1.6 mm of press fit. Building on what was learned from the original design, this updated, stretched geometry was created with a single radius for a smooth transition from the apex to the peripheral press fit. Porous coating is the key to implant durability. With this aggressive “sticky” porous coating, only 0.6 mm of press fit is required. This porous coating has 60% porosity, and 150–400 mm pore size. It has a tensile strength of 5000 psi (The FDA requires a minimum of 2900 psi) and a mean thickness of 0.8 mm. Three thousand cups have been implanted with the author contributing 400. In our own primary subgroup done in 2014–15, 142 had 2–4 year follow up with zero loosening. There was one infection and 2 dislocations. One implant was revised on a patient with psoas tendonitis from an oversized cup. At retrieval it showed excellent ingrowth into the porous coating with 38% ingrowth. This graduated rim fit concept has a proven track record spanning 2 decades and provides a stable and reproducible acetabular construct

Prior implant designs have relied on a four-bar link theory and featured J-curve femoral components intended to recreate femoral rollback of the native knee, but this design could lead to anterior femoral sliding or paradoxical motion. Recent kinematic analyses of the native human knee have shown the medial compartment to be more stable to anteroposterior translation than the lateral, resulting in a “medial pivot” motion as the knee flexes. “Medial pivot” designs in total knee arthroplasty were introduced in the 1990s to attempt to re-create this motion. They consist of an asymmetric tibial insert with a highly congruent medial compartment and less conforming lateral compartment. The femoral component has a single radius of curvature and a high degree of conformity. In vivo fluoroscopic studies have shown medial pivot designs to be successful in achieving its intended motion, while other cruciate-retaining designs had a higher incidence of paradoxical anterior translation and lateral condylar lift-off. Furthermore, numerous investigations have shown medial pivot designs to have excellent outcomes and survivorship at up to 10 years post-operatively. However, the contention in this debate that medial pivot designs avoid the need for ligament balancing is incorrect. Appropriate ligament balancing remains a crucial aspect of any successful total knee arthroplasty and is no less important based on the implant design utilised. In the Methods section of all prior reports using a medial pivot design, the authors have noted that appropriate ligament balancing was obtained both in flexion and extension consistent with the recommended technique with other primary TKA implant designs. From a kinematic standpoint, this makes absolute sense. If a patient has a valgus imbalance with loose medial structures, then as the knee is brought into flexion the femur will not maintain congruency and contact with the conforming tibial surface – thus the medial pivot motion will be lost. Thus, balancing remains critical. Lastly, although not the focal point of this debate, whether re-creation of a medial pivot motion in total knee arthroplasty actually improves patient outcomes remains an area of debate. A recent investigation by Warth and Meneghini, et al. demonstrated that re-creation of a medial-pivot pattern intra-operatively did not correlate with patient-reported outcomes at 1-year post-operatively. Thus, although the concept of a medial pivot design has merit, whether this will consistently improve outcomes and patient satisfaction remains to be seen

Introduction. Anterior knee pain (AKP) is a recognized cause of patient's dissatisfaction after total knee arthroplasty. Potential implant/technique related contributors to AKP are patellofemoral maltracking, trochlear geometry, femoral malrotation, patellar tilt and overstuffing. The primary aim of this prospective, matched pair study was to assess the safety, efficacy and performance of an anatomic patella and its effect on AKP in in a matched pair analysis. Material and Methods. Between July 2012 and May 2013, 55 consecutive posterior stabilized cemented Attune TKAs (Depuy) were matched to the PFC Sigma group based on age, gender, and body mass index (BMI). All surgeries were performed via medial parapatellar approach with patellar resurfacing. Clinical and radiographic analysis was performed prospectively with minimum 6 month follow-up. Radiographic measurements included overall limb alignment, anterior offset, posterior offset, joint line, patellar thickness, patellar tilt and patellar displacement by two independent observers. Results. The mean functional outcomes were similar in both groups. AKP incidence between Attune and PFC was statistically insignificant (3.6% and 3.8%). Radiographic analysis revealed no mal-alignment, or osteolysis. No complications such as infection, patellar fracture, subluxation or dislocations were observed. Discussion. Attune knee design demonstrates excellent short-term safety and efficacy. At minimum 6-month follow-up, anatomical patella with shows less AKP than single radius patella design. Longer follow-up is required to assess functional outcome this design

Total knee arthroplasty aims at restoring the function of the native knee. An important aspect at this point are the knee kinematics, as it can be assumed that following TKA surgery these should resemble the native conditions. The use of cadaveric testing is since long an important step in the development and validation of implant designs and surgical techniques. However, this cadaveric testing has primarily focused on squatting under load bearing conditions. The main research question of this paper is therefore to evaluate the impact of TKA surgery on the knee kinematics under a range of boundary conditions. A set of five cadaveric knees have been tested in a newly developed and validated knee simulator at Ghent University. In contrast to other simulators, this simulator allows simulating a wide range of conditions as it facilitates a controlled movement of the ankle in the sagittal plane under continuously variable hamstring and quadriceps loading. In the framework of this study, two different motion patterns have been studied. First, the knees were subjected to a traditional squatting motion maintaining constant quadriceps loading. Second, the knees were tested while performing a cycling movement with a highly variable quadriceps load during the extension phase. For both cases, the studied motion patterns have been repeated five times. Following the evaluation of the native knee kinematics, TKA surgery was performed using a single radius implant. During surgery, the implant alignment has been controlled using computer navigation. Subsequently, the same boundary conditions have been applied and the kinematics again recorded. Focusing on the native knee, the measured kinematic patterns for the squatting motion significantly differ from the ones observed for the cycling movement for similar flexion angles. This is attributed to a difference in quadriceps loading. However, following TKA surgery, the kinematic patterns are remarkably comparable between the squatting and cycling experiments. These observations suggest that the TKA design considered in this study displays a highly constrained behavior. More specifically, the design appears to favor the squatting behavior. Further study is however required to thoroughly evaluate this observation for other implant designs and a wider range of motion patterns

Introduction. Recently, tibial insert design of cruciate-substituting (CS) polyethylene insert is employed and widely used. However, in vivo kinematics of using CS polyethylene insert is still unclear. In this study, it is hypothesized that CS polyethylene insert leads to stability of femoro-tibial joint as well as posterior-stabilized (PS) polyethylene insert, even if PCL is sacrificed after TKA. The purpose of this study is an investigation of in vivo kinematics of femoro-tibial joint with use of CS polyethylene insert before and after PCL resction using computer assisted navigation system and tensor device intra-operatively in TKA. Materials and Methods. Sixty-one consecutive patients who had knees of osteoarthritis with varus deformity were investigated in this study. All TKAs (Triathlon, Stryker) were performed using computer assisted navigation system. During surgery, using a tensor device, after bony cut of femur and tibia, joint gaps were assessed in 0 and 90 degrees in flexion. Then, CS polyethylene tibial trial insert were inserted after trial implantation of femoral and tibial components, before and after resection of PCL, respectively. The kinematic parameters of the soft-tissue balance, and amount of coronal and sagittal relative movement between femur and tibia were obtained by interpreting kinematics, which display tables throughout the range of motion (ROM) in the navigation system. In each ROM (30, 45, 60, 90, max degrees), the data were analyzed with a ANOVA test, and mean values were compared by the multiple comparison test (Turkey HSD test) (p< 0.05). Results. Joint gap assessment revealed significant enlargement in both of extension and 90 degrees in flexion after PCL resection compared with before resection. In kinematic analyses in navigation system, regarding to amount of sagittal movement of tibia, there were significances between before and after PCL resection in 60 and 90 degrees in flexion, 1.2mm difference in 60 degrees, and 2.3mm difference in 90 degrees in flexion. There were no significance between before and after PCL resection in the other degrees in flexion. Regarding to the other analyses, varus/ valgus and rotation, there were no differences between before and after resection of PCL. In addition, concerning ROM, maximum extension angle is significantly lower, and maximum flexion angle is significantly higher after than before PCL resection. Discussion. These results demonstrated that CS polyethylene insert might have a stability of femoro-tibial joint nearly after PCL resection as well as before PCL resection. The main design feature of Triathlon CS insert is single radius and rotary arc, in addition, the posterior lip is same as that of Triathlon CR, which can be the factor to avoid paradoxical anterior movement and to permit internal and external rotation between femoral and tibial component. Due to the design features and benefits, there is a high possibility that use of CS insert without PCL can lead same stability as PCL remained, and improvement of ROM. Based on these backgrounds, it is suggested that CS insert may have an additional choice of PCL resection in case of tight gap of flexion in TKA

Introduction. Contemporary total knee systems accommodate for differential sizing between femoral and tibial components to allow surgeons to control soft tissue balancing and optimize rotation. One method some manufacturers use to allow differential sizing involves maintaining coronal articular congruency with a single radius of curvature throughout sizes while clipping the medial-lateral width, called a single coronal geometry system. Registry data show a 20% higher revision rate when the tibial component is smaller than the femur (downsizing) in the DePuy PFC system, a single coronal system, possibly from increased stresses from edge loading or varying articular congruency. We examined a different single coronal geometry knee system, Smith & Nephew Genesis II, to determine if edge loading is present in downsized tibial components by measuring area and location of deviation of the polyethylene articular surface damage. Methods. 45 Genesis II posterior-stabilized polyethylene inserts (12 matched and 33 downsized tibial components) were CT scanned. 3D reconstructions were registered to corresponding pristine component reconstructions, and 3D deviation maps of the retrieved articular surfaces relative to the pristine surfaces were created. Each map was exported as a point cloud to a custom MATLAB code to calculate the area and weighted center of deviation of the articular surfaces. An iterative k-means clustering algorithm was used to isolate regions of deviation, and a shrink-wrap algorithm was applied to calculate their areas. The area of deviation was calculated as the sum of all regions of deviation and was normalized to the area of the articular surface. The location of deviation was described using the weighted center of deviation and the location of maximum deviation on the articular surfaces relative to the center of the post (Fig. 1). Pearson product moment correlations were conducted to examine the correlation between length of implantation (LOI) and the medial and lateral areas of deviation for all specimens, matched components, and downsized components. Results. The mean LOIs for downsized and matched tibial components were not different (36±28 months vs 46±26 months, p=0.24). Areas of deviation for the medial and lateral sides for both downsized and matched components increased with LOI (p<0.001). Medial and lateral sides of matched retrievals were not different in location of maximum deviation, maximum deviation, and weighted center of deviation (p>0.4). The matched and downsized retrievals did not have different centers of deviation in the medial-lateral direction, maximum deviations, or locations of maximum deviations (p>0.1). Discussion. Our results suggest that downsizing the tibial component in the Genesis II system, a single coronal geometry system, did not affect the area or location of deviation on the articular surface. Overall, the weighted center of deviation remained close to the dwell point and did not change as a function of tibial downsizing. However, we saw deviation patterns biased peripherally for inserts with low LOI in both matched and downsized cohorts. With increasing LOI, the deviation expanded to cover the majority of the available articular surface. Our results suggest the need to further examine this and other systems determine the effects of differential sizing. For figures/tables, please contact authors directly.

Introduction. Historically, knee implants have been designed using average patient anatomy and despite excellent implant survivorship, patient satisfaction is not consistently achieved. One possibility for this dissatisfaction relates to the individual patient anatomic variability. To reduce this inter-patient variability, recent advances in imaging and manufacturing have allowed for the implementation of patient specific posterior cruciate retaining (PCR) total knee arthroplasty (TKA). These implants are individually made based on a patient's femoral and tibial anatomy determined from a pre-operative CT scan. Although in-vitro studies have demonstrated promising results, there are few studies evaluating these implants in vivo. The objective of this study was to determine the in vivo kinematics for subjects having a customized, individually made(CIM) knee implant or one of several traditional, off-the-shelf (OTS) TKA designs. Methods. In vivo kinematics were assessed for 108 subjects, 44 having a CIM-PCR-TKA and 64 having one of three standard designs, OTS-PCR-TKA which included symmetric TKA(I), single radius TKA(II) and asymmetric TKA(III) designs. A mobile fluoroscopic system was used to observe subjects during a weight-bearing deep knee bend (DKB), a Chair Rise and Normal Gait. All the subjects were implanted by one of two surgeons and were clinically successful (HSS Score>90). The kinematic comparison between the three designs involved range of motion, femoral translation, axial rotation, and condylar lift-off. Results. During the DKB, subjects having a CIM-TKA experienced 5.72 (σ=3.03) mm of lateral condyle posterior femoral rollback (PFR) compared to 3.81 (σ=3.08) mm, 1.12 (σ=3.15) mm, and 0.19 (σ=3.53) mm for subjects having the three OTS-TKA designs respectively (Figure 1). For the CIM-TKA 87.5% of subjects demonstrated overall PFR compared to 81%, 72% and 64% of the traditional designs respectively. With Respect to axial rotation, the CIM-TKA demonstrated 4.44° (σ=5.4) of axial rotation compared to 4.59° (σ=3.19), 5.8° (σ=5.58), and 4.41° (σ=5.84) for subjects having the three OTS-TKA designs respectively (Figure 2) and 87.5%, 92%, 76% and 71.4% of the subjects respectively showing normal rotation. These trends were similar with respect to the chair rise activity. During DKB, subjects having a CIM-TKA achieved 107° of weight-bearing knee flexion, while subjects having an OTS-TKA achieved 100°, 97° and 102°, respectively. Discussion. Subjects with a CIM-TKA experienced posterior motion of their lateral condyle during flexion and an anterior motion during extension, while 19–28% of patients having an OTS-TKA experienced lateral condyle moving in the anterior direction during flexion, paradoxical to the normal knee pattern. In general, the CIM-TKA experienced translation and rotation patterns more similar to the normal knee pattern than the OTS-TKA designs (figure 3). Additionally subjects having an OTS-TKA experienced a higher incidence of anterior sliding and reverse axial rotation. The DKB range of motion was slightly larger for the CIM-TKA and the standard deviation of the lateral condyle motion was smaller for the subjects having a CIM-TKA demonstrating less variability between patients. Significance. This study found that CIM-CR-TKA Implants demonstrate kinematic patterns more similar to the normal knee, but less in magnitude while experiencing less variability between subjects compared to the OTS-CR-TKA designs. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

The purpose of this study was to compare intraoperative varus-valgus laxities in total knee arthroplasty [TKA] using either a single-radius femoral design or multi-radius femoral design. 56 TKAs were performed by using a single radius femoral design (Scorpio NRG, SR group) and 59 TKAs were performed by using a multi-radius femoral design (Zimmer NexGen, MR group), both with a minimum of 1-year follow-up. We compared intra-operative varus-valgus laxities at 0°, 30°, 60°, 90° of flexion using the navigation system (Orthopilot, Aesculap, Tuttlingen, Germany). A series of clinical outcomes were evaluated at the time of the latest follow-up including HSS, WOMAC, VAS score during stair climbing. At 30°, 60° of flexion, the mean total varus-valgus laxities in SR group (6.2 ± 3.5° at 30° of flexion and 6.8 ± 1.5° at 60° of flexion) were significant less than those in MR group (9.2 ± 4.3° at 30° of flexion and 8.3 ± 3.8° at 60° of flexion) (p=0.027 and p=0.042, respectively). In the clinical results, there was not significant difference. The single-radius femoral designs for TKA showed evidently less intra-operative mid-flexion stability compared with the multi-radius femoral design. However clinical outcomes revealed no other significant dissimilarity on HSS, WOMAC and VAS scores during stair climbing

Introduction. For the evaluation of new orthopaedic implants, cadaveric testing remains an attractive solution. However, prior to cadaveric testing, the performance of an implant can be evaluated using numerical simulations. These simulations can provide insight in the kinematics and contact forces associated with a specific implant design and/or positioning. Methods. Both a two and three dimensional simulation model have been created using the AnyBody Modelling System (AMS). In the two dimensional model, the knee joint is represented by a hinge. Similarly, the ankle and hip joint are represented by a hinge joint and a variable amplitude quadriceps force is applied to a rigid bar connected to the tibia (Figure 1a). In line with this simulation model, a hinge model was created that could be mounted in the UGent knee simulator to evaluate the performance of the simulated model. The hinge model thereby performs a cyclic motion under varying quadriceps load while recording the ankle reaction forces. In addition to the two dimensional model, a three dimensional model has been developed (Figure 1b). More specifically, a model is built of a sawbone leg holding a posterior stabilized single radius total knee implant. The physical sawbone model contains simplified medial and lateral collateral ligaments. In line with the boundary conditions of the UGent knee simulator, the simulated hip contains a single rotational degree of freedom and the ankle holds four degrees of freedom (three rotations, single translation). In the simulations, the knee is modelled using the force-dependent kinematics (FDK) method built in the AMS. This leaves the knee with six degrees of freedom that are controlled by the ligament tension in combination with the applied quadriceps load and shape of the implant. The physical sawbone model goes through five cycles in the UGent simulator using while recording the kinematics of the femur and tibia using a set of markers rigidly attached to the femur and tibia bone. The position of the implant with respect to the markers was evaluated by CT-scanning the sawbone model. Results and Discussion. In a first step, the reaction forces at the ankle in the 2D model were evaluated. The difference between the simulated and measured reaction force is limited and can be explained from a slight variation of the attachment point of the quadriceps load. For the 3D model, the kinematic patterns have been evaluated for both the simulation and physical model using Grood & Suntay definitions. The kinematic parameters display realistic trends, however, no exact match has been obtained for all parameters so far. The latter might be attributed to a number of simplifications in the simulation model as well as elastic deformation of the physical sawbone model. Conclusion. A three dimensional model of a knee implant in the UGent Knee Simulator has been developed. The simulated kinematic patterns appear realistic though no exact match with the measured patterns has been obtained. Future research will therefore focus on the development of a more realistic experimental and numerical model

Introduction. Mechanically aligned total knee arthroplasty(TKA) relies on restoring the hip-knee-ankle angle of the limb to neutral or as close to a straight line as possible. This principle is based on studies that suggest limb and knee alignment is related long term survival and wear. For that cause, there has been recent attention concerning computer-assisted TKA and robot is also one of the most helpful instruments for restoring neutral alignment as known. But many reported data have shown that 20% to 25% of patients with mechanically aligned TKA are dissatisfied. Accordingly, kinematically aligned TKA was implemented as an alternative alignment strategy with the goal of reducing prevalence of unexplained pain, stiffness, and instability and improving the rate of recovery, kinematics, and contact forces. So, we want to report our extremely early experience of robot-assisted TKA planned by kinematic method. Materials and Methods. This study evaluated the very short term results (6 weeks follow up) after robot-assisted TKA aligned kinematically. 50 knees in 36 patients, who could be followed up more than 6 weeks after surgery from December 2014 to January 2015, were evaluated prospectively. The diagnosis was primary osteoarthritis in all cases. The operation was performed with ROBODOC (ISS Inc., CA, USA) along with the ORTHODOC (ISS Inc., CA, USA) planning computer. The cutting plan was made by single radius femoral component concept, each femoral condyles shape-matched method along the transverse axis using multi-channel CT and MRI to place the implant along the patient's premorbid joint line. Radiographic measurements were made from long bone scanograms. Clinical outcomes and motion were measured preoperatively and 6 weeks postoperatively. Results. The range of motion increased from preoperative mean 113.4 (±5.4, 85 to 130) to postoperative mean 127.3 (±7.4, 90 to 140) at last follow up. The mean knee score and functional score improved from 35.4 (±10.3, 10 to 55) and 30.1 (±7.7, 10 to 60) before surgery to 88.6 (±5.8, 60 to 100) and 90.7 (±9.6, 60 to 100) at last follow up. The WOMAC score was improved from 52(±15.5) to 20(±14.8) at last follow up. The postoperative Hip-knee-ankle alignment was −1.3±2.8. The femoral component was 2.1 valgus and tibial component was 2.8 varus along the mechanical axis in coronal plane. There were no complications and failures. Conclusion. On the basis of our results, we are cautiously optimistic about robot-assisted TKA by kinematically alignment. More anatomic alignment of the implant can be associated with better flexion and better clinical outcomes scores in the kinematically aligned method in our thinking. But, at this starting point, more comparative studies with mechanical aligned group are needed and we must explore about implant survivalship issues and implant loading issues in dynamic and static condition that someone is worrying about. If the problem can be solved, there is no use worrying about it in our thinking. And what is more, the robot-assisted surgery will be very useful especially in those cases of severely deformed knees and distorted anatomy to be aligned kinematically