Introduction. Persistent patellofemoral (PF) pain is a common postoperative complication after total knee arthroplasty (TKA). In the USA, patella resurfacing is conducted in more than 80% of primary TKAs [1], and is, therefore, an important factor during surgery. Studies have revealed that the position of the patellar component is still controversially discussed [2–4]. However, only a limited number of studies address the biomechanical impact of patellar component malalignment on PF dynamics [2]. Hence, the purpose of our present study was to analyze the effect of patellar component positioning on PF dynamics by means of musculoskeletal multibody simulation in which a detailed knee joint model resembled the loading of an unconstrained cruciate-retaining (CR) total knee replacement (TKR) with dome patella button. Material and Methods. Our musculoskeletal multibody model simulation of a dynamic squat motion bases on the SimTK data set (male, 88 years, 66.7 kg) [5] and was implemented in the multibody dynamics software SIMPACK (V9.7, Dassault Systèmes Deutschland GmbH, Gilching, Germany). The model served as a reference for our parameter analyses on the impact on the patellar surfacing, as it resembles an unconstrained CR-TKR (P.F.C. Sigma, DePuy Synthes, Warsaw, IN) while offering the opportunity for experimental validation on the basis of instrumented implant components [5]. Relevant ligaments and muscle structures were considered within the model. Muscle forces were calculated using a variant of the computed muscle control algorithm. PF and tibiofemoral (TF) joints were modeled with six degrees of freedom by implementing a polygon-contact model, enabling roll-glide kinematics. Relative to the reference model, we analyzed six patellar component alignments: superior-inferior position, mediolateral position, patella spin, patella tilt, flexion-extension and thickness. The effect of each configuration was evaluated by taking the root-mean-square error (RMSE) of the PF contact force, patellar shift and patellar tilt with respect to the reference model along knee flexion angle. Results. The analysis showed that the PF contact force was mostly affected by patellar component thickness (RMSE=440 N) as well as superior-inferior (RMSE=199 N), and mediolateral (RMSE=98 N) positioning.. PF kinematics was mostly affected by mediolateral positioning, patellar component thickness, and superior-inferior positioning. Medialization of the patellar component reduced the peak PF contact force and caused a lateral patellar shift. Discussion. Based on our findings, we conclude that malalignment in mediolateral and superior-inferior direction, tilt and thickness of patellar resurfacing are the most important intraoperative parameters to affect PF dynamics. It could be shown that the translational positioning is more critical than rotational positioning regarding PF contact force. Reported findings are in good agreement with previous experimental and clinical studies [2–4]. Our data reveal that patellar component positioning has to be aligned precisely during total knee arthroplasty to prevent postoperative complications. For any figures or tables, please contact authors directly

Introduction:. The widespread use of TKA promoted studies on kinematics after TKA, particularly of the femorotibial joint. Knee joint kinematics after TKA, including the range of motion (ROM) and the physical performance, are also influenced by the biomechanical properties of the patella. Surgeons sometimes report complications after TKA involvinganterior knee pain, patellofemoral impingement and instability. However, only few studies have focused specially on the patella. Because the patella bone is small and overlapped with the femoral component on scan images. In addition, the patellar component in TKA is made of x-ray–permeable ultra-high molecular weight polyethylene. It is impossible to radiographically determine the external contour of the patellar component precisely. No methods have been established to date to track the dynamic in vivo trajectory of the patella component. In this study, we analyzed the in vivo three-dimensional kinematics of the patellar component in TKA by applying our image matching method with image correlations. Methods:. A computed tomography (CT) and an x-ray flat panel detector system (FPD) were used. FPD-derived post-TKA x-ray images of the residual patellar bone were matched by computer simulation with the virtual simulation images created using pre-TKA CT data. For the anatomic location of the patellar component, the positions of the holes drilled for the patellar component pegs were used. This study included three patients with a mean age of 68 years (three females with right knee replacement) who had undergone TKA with the Quest Knee System and achieved a mean passive ROM of 0 to ≥ 130° after 6 or more month post-TKA. We investigated three-dimensional movements of the patellar component in six degrees of freedom (6 DOF) during squatting and kneeling. Furthermore, we simulated the three-dimensional movement of the patellar component, and we estimated and visualized the contact points between the patellar and femoral components on a three-dimensional model. Results:. Average root mean square errors of this technique with the patellar bone of a fresh-frozen pig complete knee joint have been confirmed as 0.2 mm for the translations and 0.2 degrees for the rotation. The 6 DOF analysis results showed that patellar dynamics were similar for all subjects on squatting and kneeling. For the patellar rotation during squatting, only 1 to 2 additional degrees were noted for all subjects. During kneeling, the patellar rotation noted adduction for all subjects. The patellar contact point on the femoral component gradually showed superior shift, increasing the distance with knee flexion during squatting and kneeling (Fig, 1. 2). Discussions and Conclusions:. In this study, no patellar shifts were detected in rotation or tilt during squatting, suggesting that the patellar component remained in the positions designed for early stages of flexion. And the patellar component shifted towards the lateral side during squatting. This finding suggests the idea that the patellar movement reflected the design of the Quest Knee system. This study demonstrated that the analytical method is useful for evaluating the pathologies and post-surgical conditions of the knee and other joints

Introduction. We have been re-evaluating patellofemoral alignment after total knee arthroplasty (TKA) by using a weight- bearing axial radiographic view after detecting patellar maltracking (lateral tilt > 5° or lateral subluxation > 5 mm) on standard non-weight-bearing axial radiographs. However, it is unclear whether the patellar component shape affects this evaluation method. Therefore, we compared 2 differently shaped components on weight-bearing axial radiographs. Methods. From 2004 to 2013, 408 TKAs were performed with the same type of posterior-stabilized total knee implant at our hospital. All patellae were resurfaced with an all-polyethylene, three-pegged component to restore original thickness. Regarding patellar component type, an 8-mm domed component was used when the patella was so thin that a 10-mm bone cut could not be performed. Otherwise, a 10-mm medialized patellar component was selected. Twenty-five knees of 25 patients, in whom patellar maltracking was noted on standard axial radiographs at the latest follow-up, were included in this study. Knees were divided into 2 groups: 15 knees received a medialized patella (group M) while 10 received a domed patella (group D). Weight-bearing axial radiographs with patients in the semi-squatting position were recorded with the method of Baldini et al. Patellar alignment (tilt and subluxation) was measured according to the method described by Gomes et al. using both standard and weight-bearing axial views. Results. Patients’ demographic data, such as age at surgery, sex, and disease were similar for both groups. The average follow-up period was significantly longer in group D than group M (5.4 years vs. 2.5 years, respectively; p = 0.0045, Mann- Whitney U-test). The lateral tilt angle decreased significantly (p < 0.0001, paired t-test) from 6.5° ± 2.8° to 1.0° ± 1.2° with weight bearing in group M. However, this parameter in group D changed from 6.7° ± 2.7° to 4.7° ± 3.0° with weight bearing; the difference was not significant. Lateral subluxation also decreased significantly (p < 0.0001, paired t-test) from 5.1 mm ± 2.4 mm to 2.5 mm ± 1.4 mm with weight bearing in group M. However, that in group D changed from 2.8 mm ± 2.7 mm to 2.4 mm ± 2.8 mm with weight bearing, and the difference was not significant. On weight-bearing views, patellar maltracking was noted in 4 knees in group D but no knees in group M. The difference was significant (p = 0.017, Fisher's exact test). One of the 21 patients with adequate patellar tracking (4.8%) and 1 of 4 patients with maltracking (25%) complained of mild anterior knee pain. Discussion. Patellar tracking on axial radiographic views improved better in group M than in group D with weight bearing. The patellofemoral contact area was maintained with a domed patella despite tilting, but not with a medialized patella. Our results indicate that the shape difference affected the degree of radiographic improvement. Thus, the weight-bearing axial radiographic view devised by Baldini et al. is useful for evaluating patellofemoral alignment after TKA, but the shape of the patellar component should be considered for result interpretation

Complications of the patellofemoral (PF) joint remain a common cause for revision of total knee replacements. PF complications, such as patellar maltracking, subluxation, dislocation and implant failure, have been linked to femoral and patellar component alignment. Computational analyses represent an efficient method for investigating the effects of patellar and femoral component alignment and loading on output measures related to long term clinical success (i.e. kinematics, contact mechanics) and can be utilized to make direct comparisons between common patellar component design types. Prior PF alignment studies have generally involved perturbing a single alignment parameter independently, without accounting for interaction effects between multiple parameters. The objective of the current study was to determine critical alignment parameters, and combinations of parameters, in three patellar component designs, and assess whether the critical parameters were design specific. A dynamic finite element (FE) model of an implanted PF joint was applied in conjunction with a 100-trial Monte Carlo probabilistic simulation to establish relationships between alignment and loading parameters and PF kinematics, contact mechanics and internal stresses (Figure 1). Seven parameters, including femoral internal-external (I-E) alignment, patellar I-E, flexion-extension (F∗∗∗∗∗E) and adduction-abduction (A-A) rotational alignment, and patellar medial-lateral (M-L) and superior-inferior (S-I) translational alignment, as well as percentage of the quadriceps load on the vastus medialis obliquus (VMO) tendon, were perturbed in the probabilistic analysis. Ten output parameters, including 6-DOF PF kinematics, peak PF contact pressure, contact area, peak von Mises stress and M-L force due to contact, were evaluated at 80 intervals during a simulated deep knee bend. Three types of patellar component designs were assessed; a dome-compatible patellar component (dome), a medialized dome-compatible patellar component (modified dome), and an anatomic component (anatomic). Model-predicted bounds at 5 and 95% confidence levels were determined for each output parameter throughout the range of femoral flexion (Figure 2). Traditional sensitivity analysis, in addition to a previously described coupled probabilistic and principal component analysis (probabilistic-PCA) approach, were applied to determine the relative importance of alignment and loading parameters to knee mechanics in each of the three designs. The dome component demonstrated the least amount of variation in contact mechanics and internal stresses, particularly in the 30–100° flexion range, with respect to alignment and loading variability. The modified dome had substantially reduced M-L contact force when compared with the dome. The anatomic design, while wide bounds of variability were predicted, had consistently greater contact area and lowered contact pressure than the dome and modified dome designs. The anatomic design also reproduced more natural sagittal plane patellar tilt than the other components. All three designs were most sensitivity to femoral I-E alignment. Thereafter, sensitivity to component alignment was design specific; for the anatomic component, the main alignment parameter was F-E, while for the domed components it was a combination of F-E and translation (M-L and S-I) (Figure 3). Understanding the relationships and design-specific dependencies between alignment parameters can add value to surgical pre-operative planning, and may help focus instrumentation design on those alignment parameters of primary concern

INTRODUCTION. Wear and fracture of patellar components has been frequently reported as a failure mode for cemented and press-fit patellar components. Malalignment of the patellar components may cause higher contact stresses, which may lead to excessive wear, delamination, and/or component fracture. In vitro testing of the patella in a clinically relevant malaligned condition is necessary to demonstrate adequate performance of the patellar component and assess the endurance of its fixation features under severe loading conditions. The purpose of this study was to test in vitro the patellar components under malaligned conditions using a knee joint simulator. MATERIALS AND METHODS. A 6 station MTS (Eden Prairie, MN) knee joint wear simulator and Alpha Calf Fraction serum (Hyclone Labs, Logan, UT) diluted to 50% with a pH-balanced 20-mMole solution of deionized water and EDTA was used (protein level = 20 g/l) for testing. Asymmetric, all-polyethylene, patellar components with an overall construct thickness of 11 mm (Duracon®, Stryker Orthopaedics, Mahwah, NJ) were used. Appropriately sized cobalt-chrome femoral components articulated against the patellae. The patellae were cemented (Simplex, Stryker Orthopaedics, Mahwah, NJ) to delrin fixtures, which placed the patella in 10° of lateral tilt (Figure 1). This angle was chosen based off the work of Huang et al, which was one of the larger average tilt angles reported in vivo. Replicating this scenario in vitro allows for observation of the potential scenario that may occur as the femoral component maintains contact strictly on the thinner lateral edge of the patella, concentrating both the axial and shear loads on a small area of polyethylene. The loading and kinematic profiles used for testing were published previously (maximum axial load: 2450N and maximum patellofemoral angle: 54°. Variations of the loading profile were studied by evaluating the effects of heavier patients, which increased the maximum axial load to 3100N(250lb patient) and 3750N(300lb patient) (Figure 2). Lateral offset was tested to evaluate the effect of malalignment. Increments of 1mm were analyzed starting from the neutral position, eventually reaching a maximum lateral offset of 5mm. A 6-dof load cell was placed beneath the patella fixturing to capture dynamic loads (ATI, Apex, NC). The axial and medial/lateral shear loads where used to calculate the resultant medial/lateral shear force being applied to the patellar pegs. RESULTS. The results of using a heavier loading profile and increasing lateral offset are shown in Figure 3. At neutral alignment, the effect of increasing the axial load caused an increase of 10% in resultant shear force. At 5 mm of lateral offset, the increase in loading caused the shear force to increase by 16%. With each loading profile, increasing the lateral offset from 0 to 5 mm caused the resultant shear force to increase two-fold. DISCUSSION. This test model allows for an aggressive method of testing patellar implants and it includes variables to adjust for severity (lateral offset and joint reaction force). Although increasing the amount of lateral patellar offset increases the resultant shear forces, the patellar wear rates remained minimal and constant. Hence, a femoral component that has a forgiving patellar tracking may demonstrate minimal wear, even when evaluated in extremely aggressive test conditions. Note: These results are specific to the device used since the results will be dependant on the function and design of the patellar implant and patella/femur track

Introduction. A large number of total knee arthroplasty (TKA) patients, particularly in Japan, India and the Middle East, exhibit anatomy with substantial proximal tibial torsion. Alignment of the tibial components with the standard anterior-posterior (A-P) axis of the tibia can result in excessive external rotation of the tibial components with respect to femoral component alignment. This in turn influences patellofemoral (PF) mechanics and forces required by the extensor mechanism. The purpose of the current study was to determine if a rotating-platform (RP) TKA design with an anatomic patellar component reduced compromise to the patellar tendon, quadriceps muscles and PF mechanics when compared to a fixed-bearing (FB) design with a standard dome-shaped patellar component. Methods. A dynamic three-dimensional finite element model of the knee joint was developed and used to simulate a deep knee bend in a patient with excessive external tibial torsion (Figure 1). Detailed description of the model has been previously published [1]. The model included femur, tibia and patellar bones, TKA components, patellar ligament, quadriceps muscles, PF ligaments, and nine primary ligaments spanning the TF joint. The model was virtually implanted with two contemporary TKA designs; a FB design with domed patella, and a RP design with anatomic patella. The FB design was implanted in two different alignment conditions; alignment to the tibial A-P axis, and optimal alignment for bone coverage. Four different loading conditions (varying internal-external (I-E) torque and A-P force) were applied to the model to simulate physiological loads during a deep knee bend. Quadriceps muscle force, patellar tendon force, and PF and TF joint forces were compared between designs. Results. The RP design demonstrated consistently lower medial-lateral (M-L) force at the PF joint than the FB design, with greater differences between designs in later flexion once the patella was engaged in the sulcus groove; root-mean-square (RMS) differences in M-L force averaged 50 N less in the RP design throughout the flexion cycle, and 70 N less after 45° flexion (Figure 2). The FB design aligned for optimal bone coverage demonstrated 15% higher M-L forces than the FB design aligned with the tibial A-P axis. RMS load required by the quadriceps muscle was 60 N lower with the RP design than the FB design throughout the cycle (Figure 2). Discussion. Comparing a RP design with an anatomic patellar component and a FB design with a domed patellar component, the RP design demonstrated lower M-L PF joint and soft-tissue extensor mechanism forces. Differences were more pronounced under conditions of high I-E torque where the RP design accommodated large relative TF rotation. Differences in FB alignment resulted in substantially different PF M-L forces; when the FB component was mal-aligned with respect to the tibial A-P axis (and the line-of-action of the patellar tendon) the resulting M-L PF force was increased. The RP design reduced the demands on the extensor mechanism and loads on the PF joint and facilitated better coverage of the resected tibial bone surface

Many recent knee prostheses are designed aiming to the physiological knee kinematics on tibiofemoral joint, which means the femoral rollback and medial pivot motion. However, there have been few studies how to design a patellar component. Since patella and tibia are connected by a patellar tendon, tibiofemoral and patellofemoral motion or contact forces might affect each other. In this study, we aimed to discuss the optimal design of patellar component and simulated the knee flexion using four types of patellar shape during deep knee flexion. Our simulation model calculates the position/orientation, contact points and contact forces by inputting knee flexion angle, muscle forces and external forces. It can be separated into patellofemoral and tibiofemoral joints. On each joint, calculations are performed using the condition of point contact and force/moment equilibrium. First, patellofemoral was calculated and output patellar tendon force, and tibiofemoral was calculated with patellar tendon force as external force. Then patellofemoral was calculated again, and the calculation was repeated until the position/orientation of tibia converged. We tried four types of patellar shape, circular dome, cylinder, plate and anatomical. Femoral and tibial surfaces are created from Scorpio NRG PS (Stryker Co.). Condition of knee flexion was passive, with constant muscle forces and varying external force acting on tibia. Knee flexion angle was from 80 to 150 degrees. As a result, the internal rotation of tibia varied much by using anatomical or plate patella than dome or cylinder shape. Although patellar contact force did not change much, tibial contact balances were better on dome and cylinder patella and the medial contact forces were larger than lateral on anatomical and plate patella. Thus, the results could be divided into two types, dome/cylinder and plate/anatomical. It might be caused by the variations of patellar rotation angle were large on anatomical and plate patella, though patellar tilt angles were similar in all the cases. We have already reported that the anatomical shape of patella would contact in good medial-lateral balance when tibia moved physiologically, therefore we have predicted the anatomical patella might facilitate the physiological tibiofemoral motion. However, the results were not as we predicted. Actually our previous and this study are not in the same condition; we used a posterior-stabilized type of prosthesis, and the post and cam mechanism could not make the femur roll back during deep knee flexion. It might be better to choose dome or cylinder patella to obtain the stability of tibiofemoral joint, and to choose anatomical or plate to the mobility

Purpose. Measurements of patellar kinematics are essential to investigate the link between anterior knee pain following knee arthroplasty and patellar maltracking. A major challenge in studying the patellofemoral (PF) joint postoperatively is that the patellar component is only partially visible in the sagittal and close-to-sagittal radiographs. The narrow angular distance between these radiographs makes the application of conventional bi-planar fluoroscopy impossible. In this study a methodology has been introduced and validated for accurate estimation of the 3D kinematics of the PF joint post-arthroplasty using a novel multi-planar fluoroscopy approach. Method. An optoelectronic camera (Optotrak Certus) was used to track the motion of an ISO-C fluoroscopy C-arm (Siemens Siremobil) using two sets of markers attached to the X-ray source and detector housings. The C-arm was used in the Digital Radiography (DR) mode, which resembles an ordinary X-ray fluoroscopy image. A previously-developed technique (Cho et al., 2005; Daly et al., 2008) was adapted to find the geometric parameters of the imaging system. Thirty-eight DRs of the calibration phantom were obtained for the 190 of rotation of the C-arm at 5 rotational increments while data from motion markers were recorded continuously at a frequency of 100 Hz. A total knee replacement prosthesis was implanted on an artificial bone model of the knee, and the implant components and bones were rigidly fixed in place using a urethane rigid foam. For the purpose of validation, positions of the implant components were determined using a coordinate measuring machine (CMM). Sagittal and obliquely sagittal radiographs of the model were taken where the patellar component was most visible. For each DR the geometric parameters of the system were interpolated based on the location of the motion markers. The exact location of the projection was then determined in 3D space. JointTrack Bi-plane software (Dr. Scott Banks, University of Florida, Gainesville) was used to conduct 2D-3D registration between the radiographs and the reverse-engineered models of the implant components. Results of the registration were directly compared to the ground-truth obtained from the CMM to calculate the accuracies. Results. The accuracies for the PF were found to be 0.48 mm and 1.32 for position and orientation of the components. For the tibiofemoral joint these values were found to be 0.89 mm and 1.43, respectively. Conclusion. The multi-planar method can be used to assess the sequential kinematics of the patellofemoral and tibiofemoral joints including the mediolateral translation and tilt of the patellar component, which are obscured in standard 2D sagittal measurements and are not possible using the traditional bi-planar setup. A limitation is that it can only be used for static imaging of the joint. It has the advantage of a relatively low radiation dose. This methodology can be used to investigate the relationship between maltracking of the patella and anterior knee pain as well as other postoperative complications

Introduction/Aim. Outcomes for guided motion primary total knee arthroplasty (TKA) in obese patients are unknown. Materials and Methods. 1,684 consecutive patients underwent 2,059 primary TKAs with a second-generation guided motion implant (Journey II Bi-Cruciate Stabilized Knee System, Smith & Nephew, Inc., Memphis) between 2011–2017 at three European and seven US sites. Results. Of 2,003 (97.3%) TKAs in 1,644 patients with BMI data: average age 64.5 years; 58.4% females; average BMI 32.5 kg/m. 2. ;13.4% had BMI ≥ 40 kg/m. 2. Subjects with BMI ≥ 40 kg/m. 2. had longest length of hospital stay (LOS) at European sites; LOS similar at US sites. Subjects with BMI ≥ 40 kg/m. 2. (P=0.0349) had longest surgery duration. BMI ≥ 40 kg/m. 2. had more re-hospitalizations or post-TKA reoperations than BMI < 40 kg/m. 2. (12.7% and 9.2% at five-year post-TKA, P<.0495). 62 TKAs were revised (3.39/100 TKA at five years) with no differences in revision risk between groups. 17 (27.4%) revisions involved femoral or tibial component removal; 45 (72.6%) involved tibial insert or patellar component removal only with revision risk similar between groups. Discussion. Our results corroborate literature-reported revision outcomes of standard TKAs in obese patients. Conclusion. Surgery duration and long-term complication rates are higher in patients with BMI ≥ 40 kg/m. 2. , but device revision risk is not elevated

Total knee arthroplasty (TKA) is a successful operation associated with a high rate of clinical success and long-term durability. Cementless technology for TKA was first explored 30 years ago with the hope of simplifying the performance of the procedure and reducing an interface for potential failure by eliminating the use of cement. Poor implant design and the use of first generation biomaterials have been implicated in many early failures of these prostheses due to aseptic loosening and reflected the failure of either the tibial or patellar component. Despite this, many excellent intermediate and long-term series have clearly demonstrated the ability of cementless TKA to perform well with good to excellent survival, comparable to that of cemented designs. Lessons learned from the initial experiences with cementless technology in TKA have led to improvements in prosthetic design and materials development. One of the most innovative biomaterials introduced into orthopaedics for cementless fixation is porous tantalum. Compared to other commonly used materials for cementless fixation, porous tantalum has the highest surface friction against bone, optimizing initial stability at the implant-bone interface as a prerequisite for long-term stability of the reconstruction. At the 2013 AAOS Annual Meeting, Abdel presented the 5-year Mayo Clinic experience with cementless TKA utilizing a highly porous monoblock tibial component in 117 knees and found NO difference in survivorship compared to cemented fixation with a re-operation rate of 3.5% in both groups. They had no revisions for aseptic loosening. These early to intermediate results reflect our own experience with all cementless TKA utilizing a cobalt-chromium fibermesh femoral component, as well as monoblock porous tantalum tibial and patellar components with up to 11-year follow up. In that series of 115 patients, there was a 95.7% survival of implants, with no revisions of any components for aseptic loosening. Further advantages to using cementless fixation include the elimination of concerns with regard to monomer-induced hypotension, thermal necrosis from PMMA polymerization, and third body wear secondary to retained or fragmented cement. Savings are also realised from elimination of the costs of cement, a PMMA mixing system, cement gun, pulse lavage system, and irrigation solution. Perhaps the greatest cost savings is derived from the reduction in operating room time. At our institution–a Level 1 county trauma center with an orthopaedic residency training program–we typically spend an average of 19 minutes of operating room time for the cementing of a total knee arthroplasty. Our average time expended for insertion of all three cementless implants is 47 seconds–representing a significant savings in the hospital operating room time charge. From the standpoint of the patient, the shorter operating time reduces the time under anesthesia, the blood loss, the risk of venous thromboembolism, as well as the infection risk–optimizing the conditions for a reduction in post-operative complications, directly impacting a potential reduction in morbidity and mortality. Overall, the performance of all cementless TKA at our facility is cost-saving, is easily performed and reproduced by orthopaedic residents, and brings potential advantages to the patient in the form of a reduction in complications and an improvement in outcomes. Cementless fixation is the wave of the future, and the future is now

There is no question that at some point many TKAs will be cementless-the question is when. The advantages of cementless TKA include a shorter operative time, no need for a tourniquet, more suitability for MIS, no concern for cement extrusion, and the history of THA. The concerns for cementless TKA include the history to date with cementless TKA (tibia and metal-backed patella), variable bony substrate, surgical cut precision, cost, revision concerns, and the patella (for patella component resurfacers). Cemented total knee arthroplasty remains the gold standard and has proven to provide durable results in most patients. The early experience with cementless tibial fixation was problematic due to tibial micromotion leading to pain and loosening. Screw fixed tibial components had additional problems as portals for polyethylene debris leading to tibial osteolysis. Moreover, metal-backed patellar components were associated with a high failure rate and most surgeons began to cement all three components. Renewed interest in cementless tibial fixation is driven in part by newer materials felt to be more suitable for ingrowth and by the perceived benefit of minimally invasive surgery. One of the concerns in limited exposure total knee arthroplasty is the difficulty in preventing the extravasation of cement posteriorly. If there is evidence-based data that quad sparing non-patella everting and limited incision length facilitates rehabilitation and does not jeopardise outcome, cementless tibial fixation will be a more attractive option in some patients. An additional concern is that the tibial surface is frequently quite variable in terms of the strength of the cancellous bone. Bone cement stabilises those differences and provides a homogeneous platform for load bearing through the tibial component

General Principles. All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion. Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex mesh can provide additional support. Acute Patella Tendon Rupture. End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture. These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture. Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions. While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

Introduction. Patellar resurfacing during Total Knee Arthroplasty (TKA) is controversial. Problems unique to patellar resurfacing may be influenced by available patellar component design. These issues include; over-stuffing (the creation of a composite patellar-prosthesis thickness greater than the native patella) that may contribute to reduced range of motion; and over-resection of the native patellar bone that may contribute to post-operative fracture. Prosthesis design may play a role in contributing to these problems. Component diameter and thickness are quite variable from one manufacturer to another and little information has been previously published about optimal component dimensions. This anatomic study was performed to define the native patellar anatomy of patients undergoing TKA, in order to guide future component design. Methods. This retrospective, IRB approved study reviewed 797 Caucasian knees that underwent primary TKA by a single surgeon. Data recorded for each patient included: gender; patellar thickness before and after resurfacing, and the size of the component that provided the greatest patellar coverage without any overhang. The residual patellar bone thickness after resection was also calculated. Results. Mean (SD) native patellar thickness was 25.24 mm (2.11) in males, versus 22.13 mm (1.89) in females (P = <0.001). 84 of 483 females (17 %) had a native patellar thickness less than or equal to 20 mm. Only 3 male patients had a native patellar thickness less than or equal to 20 mm (1%). 374 females (78%) could only accommodate a round patellar button less than or equal to 32 mm. Conclusions. These findings suggest that patellar component design can be improved for Caucasian female patients. Round components between 26 and 32 mm that measure no more than 7 mm thick would be required to avoid systematic over-stuffing or over-resection of the native patellar in female patients. Most contemporary knee systems do not meet these needs

Background. Multiple retrospective studies have compared UC with traditional bearings and shown comparable results and outcomes when looking at clinical and radiologic variables, complications rates, and implant survivorship; however, debate still exists regarding the optimum bearing surface. The present study seeks to determine whether there are any preoperative patient demographic or medical factors or anatomic variables including femoral condylar offset and tibial slope that may predict use of a UC bearing when compared to a standard CR group. Methods. The study cohort consisted of 117 patients (41 males, 76 females) who underwent primary TKA with the senior author. The implants utilized were either the CR or UC polyethylene components of the Zimmer Persona Total Knee System. Insert selection was based on intraoperative assessment of PCL integrity and soft tissue balancing. Patient demographics (age, gender, BMI) and co-morbidities (hypertension, diabetes, depression, cardiac disease, and lung disease) were recorded. Intraoperative variables of interest included extension and flexion range of motion, estimated blood loss (EBL), tourniquet time, and polyethylene and femoral component sizes. We calculated change in tibial slope and femoral condylar offset from pre- to post-surgery and computed the percentage of patients for whom an increase in tibial slope or femoral condylar offset was determined. Postoperative variables, including length of stay, complication rates and reoperation rates, were recorded. All dependent variables were compared between patients who received the UC component and patients who received the CR component. Continuous variables were assessed using independent samples t-tests, while categorical variables were compared using the chi-square test of independence. Results. There were 39 patients who received a UC insert and 78 patients who received CR insert. Patient age (p = 0.58), BMI (p = 0.34), or sex distribution (p = 0.84) did not differ between the UC and CR groups. Mean LOS (3.59 vs. 3.08; p = 0.017), EBL (54.5 vs. 46.7; p=0.021), and tourniquet time (61.2 vs. 57.4; p=0.032) were greater for the UC group. Intraoperative implant variables, including polyethylene component (p = 0.49), femoral component (p = 0.56), use of a narrow femoral component (p = 0.85), and patellar component size (p = 0,83), were similar between groups. Additionally, preoperative (p = 0.46) and postoperative (p = 0.19) condylar offset and preoperative (p = 0.66) and postoperative (p = 0.23) tibial slope were not different between the groups. However, the proportion of patients for whom tibial slope increased postoperatively was greater for the UC group compared to the CR group (43.6 vs. 21.8% respectively, p=0.018). Conclusions. Our results showed that no preoperative medical co-morbidities or demographic factors predicted use of the UC bearing; however, postoperative tibial slope was increased for a greater number of patients who received the UC implant. Patients who have an increase in their slope from their native anatomy during tibial preparation may require additional balancing of the flexion gap, and use of a UC component may be beneficial in this particular group of patients

Implant selection in TKA remains highly variable. Surgeons consider pre-operative deformity, patient factors such as BMI and bone quality, surgical experience, retention or substitution for the PCL, type of articulation and polyethylene, cost, and fixation with or without cement. We have most frequently implanted the same implant for the majority of patients. This is based on the fact that multiple large series of TKAs have demonstrated that the most durable TKAs have been non-modular metal-backed tibial components, retention of the PCL, with a cemented all-polyethylene patellar component. Polymer wear must be addressed for long-term durability. One method for reducing polyethylene wear is eliminating modularity between a metal-backed tray and the articular bearing surface. This can be done with a metal-backed implant as with the IB-1, AGC, Vanguard Mono-lock, or with elimination of the metal backing via a one piece all-polyethylene tibial component. The all-polyethylene implants appear design and patient sensitive. We observed higher clinical failure rates in a flat-on-flat design. Other authors have observed improved survivorship with coronal dishing of the articular surfaces which centralises osseous stresses. All-polyethylene implants have promise in the future but require proven design and fixation design features

Success in knee revision begins in the office. The initial evaluations determine the implant design and pre-operative diagnosis. The physical examination identifies the presence of instability, stiffness, extensor mechanism malfunction and previous incisions all of which influence the planned procedure. Prior to surgery arrangements are made to have all manner of revision implants, removal tools, and allograft material available. Removal of implants must be done with a focus on preserving bone stock and the extensor mechanism. Initial exposure involves release of the gutters, lateral subluxation of the patella and removal of the polyethylene insert. These maneuvers combined with a quadriceps snip provide exposure for implant removal in 80–90% of cases. More extensive exposure options include quadriceps turndown, tibial tubercle osteotomy, medial epicondylar osteotomy and a femoral peel. Tools needed for implant removal include thin osteotomes, offset osteotomes, thin saws and a high-speed bur. After polyethylene removal the femur followed by the tibia are removed. In many cases the existing well-fixed patellar component can remain. The implant cement or implant bone interface is approached for cemented and cementless implants, respectively. Tools are always directed parallel to the fixation surface. Offset osteotomes are helpful gaining access to the femoral notch when femoral pegs prevent access from the sides. Central keels or peripheral pegs can complicate tibial removal. Working completely around the keel from medial and lateral disrupts the peripheral tibial interface leaving just the central posterior metaphysis. Stacked osteotomes or a slap hammer can be used to lift the baseplate from the tibia

General Principles: All repairs should be repaired in full extension. Repairs should be immobilised in full extension for 6–12 weeks. Gradual resumption of motion in a hinged brace over an additional 6–8 weeks almost always yields flexion to at least 90 degrees. Marlex Mesh has been shown to be an excellent replacement as well as an augment for deficient soft tissue. Acute tibial tuberosity avulsion: Open repair is best accomplished with a non-absorbable heavy Krackow suture, secured distally around a screw and washer followed by 6 to 8 weeks of immobilization. Augmentation with a semitendinosus graft or Marlex can provide additional support. Acute Patella Tendon Rupture: End-to-end repair is standard, but re-rupture is not uncommon, so supplemental semitendinosus reconstruction is recommended. The tendon is harvested proximally, left attached distally and passed through a transverse hole in the inferior patella. The gracilis tendon can be harvested and sutured to semitendinosus for additional length, if needed. Acute Quadriceps Tendon Rupture: These can be repaired end-to-end with a non-absorbable heavy Krackow suture. A superficial quadriceps fascial turndown or mesh may be a useful adjunct. Patella Fracture: Treatment depends on the status of the patellar component and the loss of active extension. If the component remains well fixed and the patient has less than a 20-degree lag, non-operative treatment in extension. A loose component and/or > 20-degree extensor lag requires ORIF +/− component revision. Chronic Disruptions: While standard repair techniques are possible, tissue retraction usually prevents a “tension-free” repair. If the patella remains viable and has not retracted proximally an Achilles tendon graft is appropriate. In chronic disruptions with loss of the patella, allograft extensor mechanism reconstruction may be considered. Marlex mesh repair has also been shown to be effective in reconstruction of chronic patellar and quadriceps tendon defects

The battle of revision TKA is won or lost with safe, effective, and minimally bony-destructive implant removal, protecting all ligamentous stabilisers of the knee and, most importantly, the extensor mechanism. For exposure, incisions should be long and generous to allow adequate access. A standard medial parapatellar capsular arthrotomy is preferred. A synovectomy is performed followed by debridement of all scar tissue, especially in the medial and lateral gutters. All peripatellar scar tissue is excised followed by release of scar tissue within the patellar tendon, allowing for displacement or everting of the patella. As patellar tendon avulsion at any time of knee surgery yields disastrous results, the surgeon should be continuously evaluating the patellar tendon integrity, especially while displacing/everting the patella and bringing the knee into flexion. If displacement/eversion is difficult, consider rectis-snip, V-Y quadricepsplasty, or tibial tubercle osteotomy. The long-held requisite for patellar eversion prior to component removal is inaccurate. In most cases simple lateral patellar subluxation will provide adequate exposure. If a modular tibial system is involved, removal of the tibial polyethylene will decompress the knee, allowing for easier access to patellar, femoral, and tibial components. For patellar component removal, first identify the border of the patella, then carefully clean and debride the interface, preferably with electrocautery. If the tibial component is cemented all-polyethylene, remove using an oscillating saw at the prosthetic-bone interface. Debride the remaining cement with hand tools, ultrasonic tools, or burrs. Remove the remaining peg using a low-speed burr. If the tibial component is metal-backed, then utilise a thin saw blade or reciprocating saw to negotiate the undersurface of the component between the pegs. If pegs are peripherally located, cut with a diamond disc circular cutting tool. Use a trephine to remove the pegs. For femoral component removal, identify the prosthetic-bone/prosthetic-cement interface then remove soft tissue from the interface, preferably with electrocautery. Disrupt the interface around all aspects of the component, using any of following: Gigli saw for cementless components only, micro saw, standard oscillating saw, reciprocating saw, a series of thin osteotomes, or ultrasonic equipment. If the femoral component is stemmed, remove the component in two segments using an appropriate screwdriver to remove the screw locking the stem to the component. Remove the femoral component with a retrodriver or femoral component extractor. Debride cement with hand tools or burr, using care to avoid bone fracture. If a stem is present, then remove with the appropriate extraction device. If “mismatch” exists, where femoral (or likewise, tibial) boss is smaller in diameter than the stem, creating a cement block prohibiting stem removal, remove the cement with hand tools or burr. If the stem is cemented, use hand tools, ultrasonic tools, or a burr to debride the cement. Curette and clean the canals. For tibial component removal, disrupt the prosthetic-cement/prosthetic-bone interface using an oscillating or reciprocating saw. Gently remove the tibial component with a retrodriver or tibial extractor. If stem extensions are utilised, disengage and debride all proximal cement prior to removing the stem. If stem is present, then remove stem with appropriate extraction device. If stem is grit-blasted and well-fixed, create 8mm burr holes 1.5 to 2.5cm distal to tibial tray on medial aspect and a small divot using burr, then drive implant proximally with Anspach punch. Alternatively, a tibial tubercle osteotomy may be performed. If the stem is cemented, use hand tools, ultrasonic tools or burr to debride cement

Extensor mechanism complications after or during total knee arthroplasty are problematic. The prevalence ranges from 1–12% in TKR patients. Treatment results for these problems are inferior to the results of similar problems in non-TKR patients. Furthermore, the treatment algorithm is fundamentally different from that of non-TKR patients. The surgeon's first question does not focus on primary fixation; rather the surgeon must ask if the patient needs surgery and if so am I prepared to augment the repair? Quadriceps tendon rupture, periprosthetic patellar fracture, and patellar tendon rupture have similar treatment algorithms. Patients who are able to perform a straight leg raise and have less than a 20-degree extensor lag are generally treated non-operatively with extension bracing. The remaining patients will need surgical reconstruction of the extensor mechanism. Loose patellar components are removed. Primary repair alone is associated with poor results. Whole extensor mechanism allograft, Achilles tendon allograft, and synthetic mesh reconstruction are the current techniques for augmentation. In the acute setting if these are not available hamstring tendon harvest and augmentation is an option. Achilles tendons and synthetic mesh are easier to obtain than and entire extensor mechanism but are limited to patients that have an intact patella and the patella that can be mobilised to within 2–3 cm of the joint line. No matter which technique is used the principles are: rigid distal/tubercle fixation, coverage of allograft/mesh with host tissue to decrease infection, tensioning the augment material in extension, no flexion testing of reconstruction and post-operative extension bracing

Implant selection in TKA remains highly variable. Surgeons consider preoperative deformity, surgical experience, retention or substitution for the PCL, type of articulation and polyethylene, and fixation with or without cement. We have most frequently implanted the same implant for the majority of patients. This is based on the fact that multiple large series of TKA's have demonstrated that the most durable TKA's have been non-modular metal backed tibial components, retention of the PCL, with a cemented all poly patellar component. The debate of how to handle the PCL continues. In most studies at 10 years there is little reported difference. Second decade concerns usually result from polyethylene issues related to polymer wear. Sagittal “dishing” or ultracongruent implants may be a middle road that allow PCL release or resection and controlled kinematics offering improved short term results. Long term function remains the goal and it appears a CR knee offers that capacity. Newer implants such as “high flex” and “gender” specific designs have not demonstrated significant functional improvements in controlled series. Uncemented knees in many series have performed well for many surgeons from a fixation standpoint. Polymer wear must be addressed for long term durability