Numerous papers present in-vivo knee kinematics data following total knee arthroplasty (TKA) from fluoroscopic testing. Comparing data is challenging given the large number of factors that potentially affect the reported kinematics. This paper aims at understanding the effect of following three different factors: implant geometry, performed activity and analysis method. A total of 30 patients who underwent TKA were included in this study. This group was subdivided in three equal groups: each group receiving a different type of posterior stabilized total knee prosthesis. During single-plane fluoroscopic analysis, each patient performed three activities: open chain flexion extension, closed chain squatting and chair-rising. The 2D fluoroscopic data were subsequently converted to 3D implant positions and used to evaluate the tibiofemoral contact points and landmark-based kinematic parameters. Significantly different anteroposterior translations and internal-external rotations were observed between the considered implants. In the lateral compartment, these differences only appeared after post-cam engagement. Comparing the activities, a significant more posterior position was observed for both the medial and lateral compartment in the closed chain activities during mid-flexion. A strong and significant correlation was found between the contact-points and landmarks-based analyses method. However, large individual variations were also observed, yielding a difference of up to 25% in anteroposterior position between both methods. In conclusion, all three evaluated factors significantly affect the obtained tibiofemoral kinematics. The individual implant design significantly affects the anteroposterior tibiofemoral position, internal-external rotation and timing of post-cam engagement. Both kinematics and post-cam engagement additionally depend on the activity investigated, with a more posterior position and associated higher patella lever arm for the closed chain activities. Attention should also be paid to the considered analysis method and associated kinematics definition: analyzing the tibiofemoral contact points potentially yields significantly different results compared to a landmark-based approach

Aims

The aim of this study was to compare a bicruciate-retaining (BCR) total knee arthroplasty (TKA) with a posterior cruciate-retaining (CR) TKA design in terms of kinematics, measured using fluoroscopy and stability as micromotion using radiostereometric analysis (RSA).

Introduction. A bicruciate retaining (BCR) TKA is thought to maintain a closer resemblance to the native knee kinematics compared to a posterior cruciate retaining (CR) TKA. With BCR TKAs retainment of the anterior cruciate ligament (ACL) facilitates proprioception and balance which is thought to lead to more natural knee kinematics and increased functional outcome. The aim of this study was to quantify and compare the kinematics of a BCR and CR TKA during functional tests. Materials and Methods. In this patient-blinded randomized controlled trial, a total of 40 patients with knee osteoarthritis were included, 18 of them received a BCR TKA (Vanguard XP, Zimmer-Biomet) and 22 received a CR TKA (Vanguard CR, Zimmer-Biomet). Fluoroscopic analysis was done 1 year post-operatively. The main outcome was posterior femoral rollback (i.e. translation of the femorotibial contact point (CP)) of the BCR and CR TKA during a step-up test. Secondary, the kinematics during a lunge test were quantified as anterior-posterior (AP) translation of the femorotibial CP. Independent student t-tests (or non-parametric equivalent) were used to analyze the effect of BCR versus CR TKA on these measures, to correct for the multiple testing problem post-hoc Bonferroni-Holm corrections were applied. Results. The mean AP CP for the BCR implant was not significantly different from the CR implant in the medial compartment (Figure 1, left). However, laterally the BCR implant shows a more posterior CP during late extension i.e. from 30° flexion to 0° extension (Figure 1, right). Figure 2 shows the AP CP during the final extension phase (30° flexion to 0° extension) of the step-up task for both implants on the tibia plateau. While the CR TKA remains mostly stable throughout this phase, the BCR TKA shows tibial internal rotation from 30° to 10° and tibial external rotation in the final extension phase: a kinematic pattern comparable to the natural knee's screw home mechanism. The lateral AP CP of the BCR TKA is more posterior compared to the CR TKA during the whole lunge task (Figure 3, right) the medial CP is more anterior in the 0–30° flexion (Figure 3, left). The main differences between the implants during the lunge task are observable in the early flexion phase, which is in line with ACL function. Conclusion. These preliminary results suggest that the kinematics of the BCR implant reproduces the natural screw-home mechanism in early flexion/late extension. The difference between the BCR and CR implants is mostly visible in the flexion phase in which the ACL is effective, which is in congruency with the absence of the ACL in CR TKAs. For any figures or tables, please contact the authors directly

Aims

The complex relationship between acetabular component position and spinopelvic mobility in patients following total hip arthroplasty (THA) renders it difficult to optimize acetabular component positioning. Mobility of the normal lumbar spine during postural changes results in alterations in pelvic tilt (PT) to maintain the sagittal balance in each posture and, as a consequence, markedly changes the functional component anteversion (FCA). This study aimed to investigate the in vivo association of lumbar degenerative disc disease (DDD) with the PT angle and with FCA during postural changes in THA patients.

Objectives

The medially spherical GMK Sphere (Medacta International AG, Castel San Pietro, Switzerland) total knee arthroplasty (TKA) was previously shown to accommodate lateral rollback while pivoting around a stable medial compartment, aiming to replicate native knee kinematics in which some coronal laxity, especially laterally, is also present. We assess coronal plane kinematics of the GMK Sphere and explore the occurrence and pattern of articular separation during static and dynamic activities.

Objectives

Unicompartmental knee arthroplasty (UKA) is one surgical option for treating symptomatic medial osteoarthritis. Clinical studies have shown the functional benefits of UKA; however, the optimal alignment of the tibial component is still debated. The purpose of this study was to evaluate the effects of tibial coronal and sagittal plane alignment in UKA on knee kinematics and cruciate ligament tension, using a musculoskeletal computer simulation.

Background. The overall goal of total knee arthroplasty (TKA) is to facilitate the restoration of native function following late stage osteoarthritis and for this reason it is important to develop a thorough understanding of the mechanics of a normal healthy knee. While there are several methods for assessing TKA mechanics, these methods have limitations that make them prohibitive to both replicating physiological systems and evaluating non-implanted knees. These limitations can be circumvented through the development of mathematical models that use anatomical and physiological inputs to computationally simulate joint mechanics. This can be done in an inverse or forward manner to solve for either joint forces or motions respectively. The purpose of this study is to evaluate one such forward model and determine the accuracy of the predicted motions using fluoroscopy. Methods. In vivo kinematics were determined during flexion from full extension to 120 degrees for ten normal, healthy, subjects using fluoroscopy and a 3D-to-2D registration method. All ten subjects had previously undergone CT scans allowing for the digital reconstruction of native femur and tibia geometries. These geometries were then input into a ridged body forward model based on Kane's system of dynamics. The resulting kinematics determined through fluoroscopy and the mathematical model were compared for all of the ten subjects. Results. The three kinematic parameters evaluated for this study were the initial positioning and translation of the medial and lateral condylar contact point in addition to the axial position and rotation of the femur with respect to the tibia. The model simulations demonstrated an average of −2.16mm of medial condyle translation, −14.03mm of lateral condyle translation, and 20.09°of axial rotation. Through fluoroscopy, subjects demonstrated an average of −3.63mm of medial condyle translation, −16.02mm of lateral condyle translation, and 15.65°of axial rotation. Comparing these two methods the model predicted on average an additional 1.47mm of medial condyle translation, 1.98mm of lateral condyle translation, and 4.44° less axial rotation compared to the fluoroscopic analysis of the same ten subjects. Conclusion. In comparing the simulation kinematics to the that of the fluoroscopic assessment, the results are comparably similar demonstrating a forward model can be a viable assessment of knee kinematics in the future. By validating mathematical simulation as a feasible means of mechanical assessment, it becomes possible to evaluate mechanics using inputs to reflect extraordinary and theoretical instances such as trauma patients and congenital deformities unable to be assessed by other methods. The nature of the model also allows for a seamless transition to assess TKA mechanics, creating a more efficient means of evaluating both device design and surgical technique

Introduction

Better functional outcomes, lower pain and better stability have been reported with knee designs which restore physiological knee kinematics. Also the ability of the TKA design to properly restore the physiological femoral rollback during knee flexion, has shown to be correlated with better restoration of the flexor/extensor mechanism, which is fundamental to the function of the human knee. The purpose of the study is to compare the kinematics of three different TKA designs, by evaluating knee motion during Activities of Daily Living. The second goal is to see if there is a correlation between the TKA kinematics and the patient reported outcomes.

Introduction. Better functional outcomes, lower pain and better stability have been reported with knee designs which restore physiological knee kinematics. Also the ability of the TKA design to properly restore the physiological femoral rollback during knee flexion, has shown to be correlated with better restoration of the flexor/extensor mechanism (appropriate flexor/extensor muscle lever arm, sufficient quadriceps force to extend the knee under load and limited patello-femoral force), which is fundamental to the function of the human knee. The purpose of the study is to compare the kinematics of three different TKA designs, by evaluating knee motion during Activities of Daily Living. The second goal is to see if there is a correlation between the TKA kinematics and the patient reported outcomes. Methods. Ten patients who are at least 6 months after their Total Knee Replacement are included in this study. Seven satisfied and 3 dissatisfied patients are selected for this design. In this study 5 different movements are being analysed: flexion/extension; Sitting on and rising from a chair, Stair climbing, descending stairs, Flexion and extension open chain and squatting. These movements will be captured with a fluoroscope. The 2D images that are obtained, are matched with the 3D implants. (see figure 1 and 2.) This 3D image is processed with custom-made software to be able to analyse the movement (figure 3.). Tibio-femoral contactpoints of the medial and lateral condyles, tibio-femoral axial rotation, determination of the pivot-point are analysed and described. After this analysis, a correlation between the kinematics and the KOOS and KSS is investigated. Results. Currently 6 patients underwent the fluoroscopic analysis and completed the questionnaires. At this moment the movements are being analysed and a correlation between the TKA kinematics and the patient reported outcomes will be investigated. Conclusion. Patient satisfaction is determined by several variables. In this study we hope to be able to conclude that the kinematics of a TKA are also an important variable. The results of this first group will be ready in july 2015

Objectives

Because posterior cruciate ligament (PCL) resection makes flexion gaps wider in total knee replacement (TKR), preserving or sacrificing a PCL affects the gap equivalence; however, there are no criteria for the PCL resection that consider gap situations of each knee. This study aims to investigate gap characteristics of knees and to consider the criteria for PCL resection.

Orthopaedic surgeons and their patients continue to seek better functional outcomes after total knee replacement, but TKA designs claim characteristic kinematic performance that is rarely assessed in patients. The objectives of this investigation is to determine the in vivo kinematics in knees with Cruciate Retaining TKA using Patient Specific Technology during activities of daily living and to compare the findings with previous studies of kinematics of other CR TKA designs. Four knees were operated by Triathlon CR TKA using Patient Specific Technology and a fluoroscopic measurement technique has been used to provide detailed three-dimensional kinematic assessment of knee arthroplasty function during three motor tasks. 3D fluoroscopic analysis was performed at 4-month follow-up. The range of flexion was 90°(range 5°–95°) during chair-rising, 80°(range 0°–80°) during step up and 100° (range 0°–100°) during leg extension. The corresponding average external rotation of the femur on the tibial base-plate was 7.6° (range +4.3°; +11.9°), 9.5° (+4.0°; 13.5°) and 11.6° (+4.5°; +16.1°). The mean antero-posterior translations between femoral and tibial components during the three motor tasks were +4.7 (−3.7; +1.0), +6.4 (−3.8; +2.6) and +8,4 (−4.9; +3.5) mm on the medial compartment, and −2.5 (−7.1; −9.6), −3.6 (−6.1; −9.7), −2.6 (−7.7; −10.3) mm on the lateral compartment, respectively, with the medial condyle moving progressively anterior with flexion, and the medial condyle moving progressively posterior with flexion. We compared Triathlon CR PSI TKA results from this study with Genesis II CR TKA, with Duracon CR TKA, with Triathlon CR TKA and with the healthy knee kinematics. The results of this study showed no screw home mechanism. The internal rotation of the tibia with knee flexion is close to normal, better than Genesis II, Duracon and Triathlon CR TKA operated with standard surgery. The medial condyle is characterized by the same pattern of the other implants, with a paradoxical anterior translation of 5 mm. The lateral condyle shows a posterior rollback better than Triathlon CR operated with standard surgery. For the first time is demonstrated that the surgical technique can modify the tibio-femoral kinematics

We investigated the characteristics of patients who achieved Japanese-style deep flexion (seiza-sitting) after total knee replacement (TKR) and measured three-dimensional positioning and the contact positions of the femoral and tibial components. Seiza-sitting was achieved after surgery by 23 patients (29 knees) of a series of 463 TKRs in 341 patients. Pre-operatively most of these patients were capable of seiza-sitting, had a lower body mass index and a favourable attitude towards the Japanese lifestyle (27 of 29 knees). According to two-/three-dimensional image registration analysis in the seiza-sitting position, flexion, varus and internal rotation angles of the tibial component relative to the femoral component had means of 148° (sd 8.0), 1.9° (sd 3.2) and 13.4° (sd 5.9), respectively. Femoral surface contact positions tended to be close to the posterior edge of the tibial polyethylene insert, particularly in the lateral compartment, but only 8.3% (two of 24) of knees showed femoral subluxation over the posterior edge. The mean contact positions of the femoral cam on the tibial post were located 7.8 mm (sd 1.5) proximal to the lowest point of the polyethylene surface and 5.5 mm (sd 0.9) medial to the centre of the post, indicating that the post-cam contact position translated medially during seiza-sitting, but not proximally. Collectively, the seiza-sitting position seems safe against component dislocation, but the risks of posterior edge loading and breakage of the tibial polyethylene post remain.

Cite this article: Bone Joint J 2013;95-B:782–7.

Introduction. Previous fluoroscopy studies have been conducted on numerous primary-type TKA, but minimal in vivo data has been documented for subjects implanted with revision TKA. If a subject requires a revision TKA, most often the ligament structures at the knee are compromised and stability of the joint is of great concern. In this present study, subjects implanted with a fixed or mobile bearing TC3 TKA are analyzed to determine if either provides the patient with a significant kinematic advantage. Methods. Ten subjects are analyzed implanted with fixed bearing PFC TC3 TKA and 10 subjects with a mobile bearing PFC TC3 TKA. Each subject underwent a fluoroscopic analysis during four weight bearing activities: deep knee bend (DKB), chair rise, gait, and stair descent. Fluoroscopic images were taken in the sagittal plane at 10 degree increments for the DKB, 30 degree increments for chair rise, and at heel strike, toe off, 33% and 66% cycle gait and stair descent. Results. The average weight bearing maximum flexion for the fixed bearing TKA group was 104 degrees (SD = 18.2 degrees). The average medial and lateral anterior-posterior (AP) translation for these subjects from full extension to maximum weight-bearing flexion was −6.74 mm and −8.0 mm in the posterior direction, respectively. The average femorotibial axial rotation was 1.27 degrees from full extension to maximum flexion. The average medial and lateral AP translations respectively from full extension to maximum flexion are shown in Figures 1 and 2 and the corresponding average femorotibial axial rotation pattern is shown in Figure 3. Subjects implanted with a mobile bearing device are presently being analyzed. Discussion. The fixed bearing device, on average, does not allow for much axial rotation when compared to less constrained or mobile bearing TKA designs. Previous studies have mobile bearing rotating platform primary posterior stabilized devices have documented that the bearing does rotate with the femur. Therefore, it is assumed subjects having a mobile bearing TC3 TKA may achieve greater axial rotation. Subjects having the fixed bearing TC3 TKA did achieve posterior femoral rollback of both condyles, revealing that a fixed bearing revision TKA may act more like a hinged device

Introduction. Previous fluoroscopic studies compared total knee arthroplasty (TKA) kinematics to normal knees. It was our hypothesis that comparing TKA directly to its non-replaced controlateral knee may provide more realistic kinematics information. Using fluoroscopic analysis, we aimed to compare knee flexion angles, femoral roll-back, patellar tracking and internal and external rotation of the tibia. Material and methods. 15 patients (12 women and 3 men) with a mean age of 71.8 years (SD=7.4) operated by the same surgeon were included in this fluoroscopic study. For each patient at a minimum one year after mobile-bearing TKA, kinematics of the TKA was compared to the controlateral knee during three standardized activities: weight-bearing deep-knee bend, stair climbing and walking. A history of trauma, pain, instability or infection on the non-replaced knee was an exclusion criteria. A CT-scan of the non-replaced knee was performed for each patient to obtain a 3-D model of the knee. The Knee Osteoarthitis Outcome Score (KOOS) was also recorded. Results. Active flexion was significantly higher in the TKA group with a weight-bearing flexion averaging 103.4° and a passive flexion 133°, and respectively 96.4° and 135° for the contro-lateral knee. Twelve TKA patients out of 15 showed a higher flexion than their contro-lateral knee. The extension was also singificantly higher in the TKA group than in their contro-lateral knee (−4.8° versus −1.8) (p=0.0095). The axial rotation was significantly higher in the non-replaced knees than in the TKA group with respectively 18.7 ° versus 8.9° (p=0.0005). The position of the femorotibial contact point during the arc of flexion was significantly more posterior for the non-replaced knees compared to the TKA. The tracking of the patella showed significantly less lateral tilt for the TKA. KOOS scores were comprised between 70 and 100 but none of the patient did consider the replaced knee as a forgotten knee. Discussion and conclusion. The results of our study demonstrated that TKA may restore the arc of flexion with a better patellar tracking even if kinematics parameters of TKA are not directly comparable to the contro-lateral knees. This kinematics differences may explain why despite very good specific quality of life and functional score, none of the patient considered his/her replaced knee as a forgotten knee

Knee mechanics - Knee forces during ADL and sports activities in TKA patients. Background. Tibiofemoral forces are important in the design and clinical outcomes of TKA. Knee forces and kinematics have been estimated using computer models or traditionally have been measured under laboratory conditions. Although this approach is useful for quantitative measurements and experimental studies, the extrapolation of results to clinical conditions may not always be valid. We therefore developed a tibial tray combining force transducers and a telemetry system to directly measure tibiofemoral compressive forces in vivo. Methods. Tibial forces were measured for activities of daily living, athletic and recreational activities, and with orthotics and braces, for 4 years postoperatively. Additional measurements included video motion analysis, EMG, fluoroscopic kinematic analysis, and ground reaction force measurement. A third-generation system was developed for continuous monitoring of knee forces and kinematics and for classifying and identifying unsupervised activities outside the laboratory using a wearable data acquisition hardware. Results. Peak forces measured for the following activities were: walking (2.6±0.2xBW); jogging (4.2±0.2)xBW; stationary bicycling (1.3±0.15)xBW; golfing (4.4±0.1)xBW; tennis (4.3±0.4)xBW; skiing (4.3±0.1)xBW; hiking(3.2±0.3)xBW; StairMaster exercise (3.3±0.3)xBW; Elliptical machine exercise (2.3±0.2)xBW; leg press machine (2.8±0.1)xBW; knee extension machine (1.5±0.03)xBW, rowing machine (0.9±0.1)xBW. Conclusions. In vivo measured knee forces can be used to enhance existing in vitro models and wear simulators and to improve prosthetic designs and biomaterials as well as guide physicians in their recommendations to patients of “safe” activities following TKA

Over the past decade, there has been an increase in the number of total knee arthropalsty (TKA). Demand of TKA for the young patients who often have high physical demands is also increasing. However, the revision rate in such young patients is much higher due to polyethylene (PE) wear and instability (Julin J, Acta Orthop 2010). Therefore, next generation total knee prostheses are expected to decrease PE wear and to provide stability. Although in vitro study such as wear simulator test provides important information about PE wear, we have often encountered the discrepancy between the in vitro results and in vivo results. Thus we have performed in vivo PE wear particle analysis, and showed that in vivo PE wear was affected by the design of articulating surface and the materials of femoral component and PE insert (Minoda Y, JBJS Am 2009). Medial pivot design, ceramic femoral component, and highly cross-linked PE decreased in vivo PE wear particle generation. Patients who underwent bilateral staged TKAs were more likely to prefer medial pivot prosthesis or ACL-PCL retaining prosthesis than the other types of prostheses, because they feels “more stable overall” (Pritchett JW, J Arthroplasty 2011). In vivo fluoroscopic 3D analysis showed that medical pivot and bi-cruciate substituting designs restored physiological knee motion and provided higher reproducibility (Mueller J. Komistek RD, Trans ORS 2009, Iwakiri K, Trans ORS 2007). The excellent mid-term clinical results of those newly introduced total knee prosthesis, such as alumina medial pivot TKA (Iida T, ORS 2008), medial pivot TKA (Mannan K, JBJS Br 2009, Kakachalions T, Knee 2009), ACL-PCL retaining TKA (Clouter JM, JBJS Am 1999), and highly cross-linked PE (Hodrick JT, CORR 2008), have been reported. From the point of view of in vivo PE wear, in vivo stability, and the mid-term clinical results, we suspect that medial pivot prosthesis is one of the prostheses which meet the demand in future especially for young active patients

In general TKA can be divided into two distinct groups: cruciate retaining and cruciate substituting. The cam and post of the latter system is in fact a mechanical substitution of the intricate posterior cruciate ligament. In our previous work we and many other investigators have focused on the movement of the femoral component relative to the tibial tray. Little information is available about the relative movement between the cam part of the femoral component and the post of the tibial insert. In this study we determine the distance and the changes in distance between the cam of the femoral component and the tibial post during extension, flexion at 90° and full flexion. The secondary purpose is to analyse possible differences between FBPS and MBPS TKA. Methods. 12 subjects' knees were imaged using fluoroscopy from extension over 90° to maximum kneeling flexion. The images were digitized. The 3-dimensional (3D) position and orientation of the implant components were determined using model-based shape-matching techniques, manual matching, and image-space optimization routines. The implant surface model was projected onto the geometry-corrected image, and its 3D pose was iteratively adjusted to match its silhouette with the silhouette of the subject's TKA components. The results of this shapematching process have standard errors of approximately 0.5° to 1.0° for rotations and 0.5 mm to 1.0 mm for translations in the sagittal plane. Joint kinematics were determined from the 3D pose of each TKA component using the 3-1-2 Cardan angle convention. This process resulted in a distance map of the femoral and tibial surfaces, from which the minimum separations were determined for the purpose of this study between cam and post (fig1.). Separation distances between the tibial polyethylene (PE) insert's post and the femoral prosthesis component have been calculated in three steps. First, the surface models of all three components as well as their position and orientation were extracted from the data files produced by the fluoroscopic kinematic analysis. Next, a set of 12 points were located on the post of each tibial insert (fig2.). Finally, for each point, the distance to the femoral component was quantified. For each step in this process, custom MATLAB. (r). (The MathWorks(tm) Inc., Natick, MA, USA) programs were used. For each of the 12 points on the post, a line was constructed through the point and parallel to the outward-facing local surface normal of the post. The resulting set of lines was then intersected with the femoral component model. Intersection points where lines ran “out of” the femoral component, detected by a positive dot product of the femoral component surface normal with the post surface normal (used to define the line), were discarded. Finally, the distances between the 12 points on the post and the intersection points on each line were calculated. For each line, the smallest distance was retained as a measure of the separation between insert and femoral component. Where a line did not intersect the femoral component, the corresponding separation distance was set to infinity. In each position, distances are measured at 6 pairs of points. Two indices of asymmetry are analysed: . The absolute difference between both measurements within a pair. Perfect symmetry is present when this absolute difference equals zero. The proportion of pairs where one of both measurements equals infinity. Indeed, this situation refers to the presence of ‘extreme’ asymmetry. A linear model for repeated measures is used to analyse the absolute differences as a function of the between-subjects factor condition (mobile bearing or fixed bearing) and the within-subject factors position (4 levels) and pair (6 levels). More specifically, a direct likelihood approach is adopted using a compound symmetric covariance matrix. Results. There is a significant difference in absolute difference between the fixed and mobile bearing condition (p=0.046). On average, the absolute difference is higher in the fixed bearing condition, 1.75 (95%CI: 1.39;2.11) vs 1.20 (95%CI:0.78;1.62). (fig2.). Conclusion. The separation distances between post and cam show less asymmetry in the Rotating platform TKA, meaning less or no contact between the post and cam surfaces which are possible sources of wear

Kneeling is one of important motion in Asians culture, also there were teachers of tea or flower ceremony who sit seiza routinely. But also, people in the Middle East need deep flexion keeling when they pray. At the symposium with the title of “A Challenge of deep flexion after TKA”, held at the 33rd Annual Meeting of Japanese Society of Reconstructive Arthroplasty in 2003, it was agreed that the definition of post-operative deep flexion to be more than 130 degrees of flexion. Four hundred and seventy two patients treated with a total of 598 consecutive primary total knee arthroplasties were performed and 480 knees were followed for 4.1 to 10.6 years(mean, 7.2 years). Preoperatively, the mean Hospital for Special Surgery knee score was 45.8 points. At the time of latest follow-up, the mean knee score was 88.5 points. The mean preoperative and postoperative ranges of flexion were 116 and 134 degrees, respectively. No knee developed osteolysis, aseptic loosening. A revision operation was performed in 3 knees because of infection. Achieving deep flexion is multi-factorial, such as preoperative planning, surgical procedure, prosthesis design, and postoperative rehabilitation. About surgical tips for deep flexion, posterior positioning of femoral component will increase the femoral posterior offset and decrease the anterior patello-femoral pressure. Through osteophyte removal will increase the posterior clearance and avoid the bone-polyethylene impingement. The flexion gap should be balanced after creating a balanced extension gap, since preparation of the flexion gap affects the extension gap in TKA. Based upon studies of the healthy knee in deep flexion, it was hypothesized that deep flexion would require tibial internal rotation greater than 20 degrees, greater posterior translation of the lateral femoral condyle than the medial condyle, and subluxation of the articular surfaces in terminal flexion. However, as the results of our fluoroscopic analysis of kinematics during deep flexion kneeling after fixed bearing PS TKA, tibial internal rotation increased with greater knee flexion, but there was high variability about the trend line. Patients with deeply flexing fixed bearing PS knee arthroplasty showed two phases of condylar translation with deep flexion. Interestingly, these two-phase translations are dictated by the design of the cam/post mechanism and serve to maintain the condyles within the posterior articular surfaces of the tibia plateau. Surface separation of both medial and lateral condyles was observed in terminal flexion. At least direct edge wear by the femoral condyle in maximum flexion is denied from this phenomenon. However, potential problems of TKA that allows for deep flexion are considerable such as dislocation, polyethylene wear, and anterior knee pain. In TKA using PS type of implant, the risk of insert damage also exists in factors other than deep flexion motion, such as cam/post or notch/post. Surgeons must confirm carefully not to set implants loose, or not to leave remnants of osteophytes during surgery and to pay attention not to raise the activity level of patients too high after surgery

Purpose of the study: Comprehension of total knee arthroplasty (TKA) kinematics is primordial for improving the functional outcome and longevity of these prostheses. Several methods are available for evaluating knee kinematics. The purpose of this study was to determine the accuracy of the 2D fluoroscopic method in vitro, taking optoelectronic analysis as the gold standard. Material and methods: In order to compare these two techniques, a posterior stabilised prosthesis was implanted on dry bones. The lateral ligaments were modellised with two elastic bands. Thirty flexion movements were imposed consecutively. The kinematics of this prosthetic model were recorded simultaneously using the fluoroscope and a computer-assisted surgery system. The technique used for the fluoroscopic analysis was based on the detection of the contours and projective geometry algorithms. The statistical analysis measured differences and correlations between the two systems using the root mean square (RMS) method and interclass coefficients of correlation (ICC) in addition to Bland and Altman analyses. Results: Three hundred thirty six relative implant positions were analysed for 30 flexions from −8 to 132 degrees. The objective RMS were to the order of one degree for flexion, varus and tibia rotation. Conversely, there was a difference of 2.43±3.17 mm for the mediolateral distance (ML). Similarly the ICC were to the order of 0.9 for the six degrees of freedom of the model with the exception of ML displacement where the ICC was 0.106. These analyses were confirmed by the Bland and Altman analysis which revealed an underestimation of the ML distance by the fluoroscopic method in greatest internal rotation. Discussion: This study is the first using a realistic model to evaluate the kinematic data provided by 2D fluoroscopy in comparison with conventional navigation data. The results show a good agreement between the two techniques and a small difference in measures excepting for the ML plane. The results are less satisfactory than those reported in the literature where data were obtained from computer simulations. Conclusion: 2D fluoroscopy of the TKA kinematics provides precise data. Nevertheless, the limits and inaccuracies of this technique should be recognized. This study is a prerequisite for in vivo 2D fluoroscopy

Introduction: Mobile bearing total knee arthroplasty (TKA) has been developed to theoretically provide a better, more physiological function of the knee and produce less polyethylene (PE) wear. The theoretical superiority of mobile bearing TKA’s over fixed bearing devices has not yet been proven in clinical studies. The objective of the present study was to analyze in vivo the knee joint kinematics in the sagittal plane in a patient population that had received either a fixed or a mobile TKA in a prospective, randomized, patient- and observer-blinded, clinical study. Methods: 31 patients were evaluated by means of fluoroscopy during unloaded flexion and extension against gravity, as well as during step-up and step-down with full weight bearing. In these 31 patients, 22 fixed bearing TKAs, 16 mobile-bearing TKAs and 19 natural knee joints were included. All patients had been operated in a prospective, randomized, patient- and observer-blinded, clinical study, and had received either fixed or a mobile bearing, cruciate retaining Genesis II TKA for primary osteoarthritis. Fluoroscopic radiographs were evaluated by measuring the „patella tendon angle” as a measure of antero-posterior translation as well as the “kinematic index” as a measure of reproducibility. Results: During unloaded movement, fluoroscopic analysis did not show a significant difference between both types of prosthesis designs and the natural knee. In the weight-bearing movement, both types of TKA designs did not show the typically arched but a more linear patellar tendon angle curve, with a greater angle in extension and in flexion than the natural knees. This means that the femur glides anteriorly under load near extension and does not show the natural roll-back in flexion. In the mobile-bearing group, inter-individual deviations from the mean during weight-bearing movements were significantly less than in the fixed-bearing group. Conclusions: In the present study, no functional advantage of mobile bearing TKA over fixed bearing devices could be found. Both TKA designs showed the typical kinematics of an anterior instability. Long-term follow-ups are necessary to elucidate the possible influence of lower PE wear on the incidence of aseptic loosenings