Background. Patellofemoral complications have dwindled with contemporary total knee designs that market anatomic trochlear grooves that intend to preserve normal patella kinematics. While most reports of patellofemoral complications address patella and its replacement approach, they do not focus on shape of trochlear grooves in different prostheses [1]. The purpose of this study was to characterize 3D geometry of trochlear grooves of contemporary total knee designs (NexGen, Genesis II, Logic, and Attune) defined in terms of sulcus angle and medial-lateral offset with respect to midline of femoral component in coronal view and to compare to those of native femurs derived from 20 osteoarthritic patient CT scans. Materials and Methods. Using 3D models of each implant and native femur, sulcus location and orientation were obtained by fitting a spline to connect sulcus points marked at 90°, 105°, 130°, and 145° of femoral flexion (Fig A). Implant reference plane orientations were established using inner facets of distal and posterior flanges. Reference planes of native femurs were defined using protocols developed by Eckhoff et al. [2] where coronal plane was defined using femoral posterior condyles and greater trochanter. In the coronal plane, a best fit line was used to measure sulcus angle and medial-lateral offset with respect to midline at the base of trochlear groove (Fig B). Results. With exception to Logic (0° sulcus angle & 0 mm offset), contemporary knee designs include high valgus angulations (4° to 18°) with laterally-biased offsets (3 to 5 mm). The native sulcus angle on average was slightly valgus, but varied significantly among the cohort (−0.2° ± 4.6°). Native trochlear groove offset was biased laterally (2.5 ± 1.7 mm). Discussion. We observed a considerable geometric deviation between native femur and implants in terms of sulcus angle while both geometries displayed comparable lateral bias at the base of trochlear groove. Similar to past studies by Iranpour et al. [4] and Feinstein et al. [5], a large variation in sulcus angle was observed among the selected native femurs with an average of small valgus angulation (Fig C). However, most contemporary trochlear grooves are biased towards higher valgus angulations. Retrieval and registry studies have shown that NexGen trochlear groove design (4° sulcus angle) has been shown to better accommodate natural patellas, which highlights that the differences among designs may be significant [5,6]. It remains unclear which features specifically translate to better patellafemoral outcomes, which is a merit for further study. Conflict of Interest: None. Figure A. Sulcus points defined at various flexion angles. Figure B. Best fit line to measure ML-offset and sulcus angle. Figure C. Sulcus angle comparison to past studies. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Total knee arthroplasty (TKA) is widely accepted as a successful surgical intervention to treat osteoarthritis and other degenerative diseases of the knee. However, present statistics on limited survivorship and patient-satisfaction emphasise the need for an optimal endoprosthetic care. Although, the implant design is directly associated with the clinical outcome comprehensive knowledge on the complex relationship between implant design (morphology) and function is still lacking. The goal of this study was to experimentally analyse the relationship between the trochlear groove design of the femoral component (iTotal CR, ConforMIS, Inc., Bedford, MA, USA) and kinematics in an in vitro test setup based on rapid prototyping of polymer-based replica knee implants. The orientation of the trochlear groove was modified in five different variations in a self-developed computational framework. On the basis of the reference design, one was medially tilted (−2°) and four were laterally tilted (+2°, +4°, +6°, +8°). For manufacturing, we used rapid prototyping to produce synthetic replicates made of Acrylnitril-Butadien-Styrol (ABS) and subsequent post-processing with acetone vapor. The morpho-functional analysis of the replicates was performed in our experimental knee simulator. Tibiofemoral and patellofemoral kinematics were recorded with an optical tracking system during a semi-active flexion/extension (∼10° to 90°) motion. Looking at the results, the patellofemoral kinematics, especially the medial/lateral translation and internal/external rotation were mainly affected. During low flexion, the patella had a more laterally position relative to the femur with increasing lateral trochlear orientation. The internal/external rotation initially differentiated and converged with flexion. Regarding the tibiofemoral kinematics, only the tibial internal/external rotation showed notable differences between the modified replica implants. We presented a workflow for an experimental morpho-functional analysis of the knee and demonstrated its feasibility on the example of the trochlear groove orientation which might be used in the future for comprehensive implant design parameter optimisation, especially in terms of image based computer assisted patient-specific implants

“The shortest distance between two points is a straight line.” This explains many cases of patellar maltracking, when the patellar track is visualised in three dimensions. The three-dimensional view means that rotation of the tibia and femur during flexion and extension, as well as rotational positioning of the tibial and femoral components are extremely important. As the extensor is loaded, the patella tends to “center” itself between the patellar tendon and the quadriceps muscle. The patella is most likely to track in the trochlear groove IF THE GROOVE is situated where the patella is driven by the extensor mechanism: along the shortest track from origin to insertion. Attempts to constrain the patella in the trochlear groove, if it lies outside that track, are usually unsuccessful. Physiologic mechanisms for tibial-femoral rotation that benefit patellar tracking (“screw home” and “asymmetric femoral roll-back”) are not generally reproduced. Practical Point. A patellofemoral radiograph that shows the tibial tubercle, illustrates how the tubercle, and with it the patellar tendon and patella itself, are all in line with the femoral trochlea. To accomplish this with a TKA, the femoral component is best rotated to the transepicondylar axis (TEA) and the tibial component to the tubercle. In this way, when the femoral component sits in its designated location on the tibial polyethylene, the trochlear groove will be ideally situated to “receive” the patella. Knee Mechanics. Six “degrees of freedom” refers to translation and rotation on three axes (x,y,z). This also describes how arthroplasty components can be positioned at surgery. The significant positions of tibial, femoral and patellar components are: 1. Internal-external rotation (around y-axis) and 2. Varus-valgus rotation (around z axis). 3. Medial-lateral translation (on x-axis). The other positional variables are less important for patella tracking. Biomechanical analyses of knee function are often broken down into: i. Extensor power analysis (y-z or sagittal plane) and ii. Tracking (x-y or frontal plane). These must be integrated to include the effects of rotation and to better understand patellar tracking. Effect of Valgus. Frontal plane alignment is important but less likely to reach pathological significance for patellar tracking than rotational malposition clinically. For example if a typical tibia is cut in 5 degrees of unintended mechanical valgus, this will displace the foot about 5 cm laterally but the tibial tubercle only 8 mm laterally. An excessively valgus tibial cut will not displace the tubercle and the patella as far as mal-rotation of the tibial component. Effect of Internal Rotation of Tibial Component. By contrast, internal rotation of the tibial component by 22 degrees, which is only 4 degrees in excess of what has been described as tolerable by Berger and Rubash, displaces the tubercle 14 mm, a distance that would place the center of most patella over the center of the lateral femoral condyle, risking dislocation. Dynamically, as the knee flexes, if the tibia is able to rotate externally this forces the tubercle into an even more lateral position, guaranteeing that the patella will align lateral to the tip of the lateral femoral condyle, and dislocate. The design of femoral components, in particular the varus-valgus angle of the trochlear groove, has an effect on patellar tracking. This effect will be accentuated by the surgical alignment technique of the femoral and tibial components. Component positions that mimic the orientation of the normal anatomy usually include more valgus alignment of the femoral component. This rotates the proximal “entrance” of the femoral trochlear groove more medially, making it more difficult for the patella to descend in the trochlear groove

BACKGROUND. Conventional TKA surgery attempts to restore patients to a neutral alignment, and devices are designed with this in mind. Neutral alignment may not be natural for many patients, and may cause dissatisfaction [1]. To solve this, kinematical alignment (KA) attempts to restore the native pre-arthritic joint-line of the knee, with the goal of improving knee kinematics and therefore patient's function and satisfaction [1]. Proper prosthetic trochlea alignment is important to prevent patella complications such as instability or loosening. However, available TKA components have been designed for mechanical implantation, and concerns remain relating the orientation of the prosthetic trochlea when implants are kinematically positioned. The goal of this study is to investigate how a currently available femoral component restores the native trochlear geometry of healthy knees when virtually placed in kinematic alignment. METHODS. The healthy knee OAI (Osteoarthritis Initiative) MRI dataset was used. 36 MRI scans of healthy knees were segmented to produce models of the bone and cartilage surfaces of the distal femur. A set of commercially available femoral components was laser scanned. Custom 3D planning software aligned these components with the anatomical models: distal and posterior condyle surfaces of implants were coincident with distal and posterior condyle surfaces of the cartilage; the anterior flange of the implant sat on the anterior cortex; the largest implant that fitted with minimal overhang was used, performing ‘virtual surgery’ on healthy subjects. Software developed in-house fitted circles to the deepest points in the trochlear grooves of the implant and the cartilage. The centre of the cartilage trochlear circle was found and planes, rotated from horizontal (0%, approximately cutting through the proximal trochlea) through to vertical (100%, cutting through the distal trochlea) rotated around this, with the axis of rotation parallel to the flexion facet axis. These planes cut through the trochlea allowing comparison of cartilage and implant surfaces at 1 degree increments - (fig.1). Trochlear groove geometry was quantified with (1) groove radial distance from centre of rotation cylinder (2) medial facet radial distance (3) lateral facet radial distance and (4) sulcus angle, along the length of the trochlea. Data were normalised to the mean trochlear radius. The orientation of the groove was measured in the coronal and axial plane relative to the flexion facet axis. Inter- and intra-observer reliability was measured. RESULTS. In the coronal plane, the implant trochlear groove was oriented a mean of 8.7° more valgus (p<0.001) than the normal trochlea. The lateral facet was understuffed most at the proximal groove between 0–60% by a mean of 5.3 mm (p<0.001). The medial facet was understuffed by a mean of 4.4 mm between 0–60% (p<0.001) - (fig.2). CONCLUSIONS. Despite attempts to design femoral components with a more anatomical trochlea, there is significant understuffing of the trochlea, which could lead to reduced extensor moment of the quadriceps and contribute to patient dissatisfaction

Abnormal patella height has been found to be one of the main reasons for abnormal contact between patella and trochlear groove leading to patellar instability in children. Many methods have been described to diagnose patellar instability but most of them are justified only in adults. The reason being incomplete ossification in the paediatric population. These methods have been divided into direct and indirect methods. We analysed the MRI scan of knee of 57 children between 12–14 years of age with no previous diagnosis of patellar instability. Patients with a diagnosis of patellar instability, previous surgery on the knee or trauma and poor MRI scan were excluded from the study. We used Insall -Salvati Index (ISI), Caton-Deschamp Index (CDI) and Patella-Trochlear Index (PTI) and compared the results. We found that 40% of measurements by CDI and 41% by ISI showed patella alta in patients with normal patella height. 10% of patients in PTI readings had value suggestive of abnormal patella height. We concluded that PTI is a more reliable index to be used in children as it uses the length of articular surface and does not rely on bony landmarks. Studies done show PTI is a more reliable and accurate method of measuring patella height

INTRODUCTION. Over the past 40 years of knee arthroplasty, significant advances have been made in the design of knee implants, resulting in high patient satisfaction. Patellar tracking has been central to improving the patient experience, with modern designs including an optimized Q-angle, deepened trochlear groove, and thin anterior flange.[1–4] Though many of today's femoral components are specific for the left and right sides, Total Joint Orthopedics’ (TJO) Klassic® Knee System features a universal design to achieve operating room efficiencies while providing all the advancements of a modern knee. The Klassic Femur achieves this through a patented double Q-angle to provide excellent patellar tracking whether implanted in the left or the right knee (Figure 1). The present study examines a prospective cohort of 145 consecutive TKA's performed using a modern universal femur and considers patients’ pre- and post-operative Knee Society Clinical Rating System score (KSS). METHODS AND MATERIALS. 145 primary total knee arthroplasties (TKA) were performed during the study using a measured resection technique with a slope-matching tibial cut for all patients. The posterior cruciate ligament (PCL) was sacrificed to accommodate an ultra-congruent polyethylene insert. The distal femur was cut at five degrees (5°) valgus; the tibia was resected neutral (0°) alignment for valgus legs and in two degrees (2°) of varus for varus alignment. The patella was resurfaced for all patients. Patients were followed annually for up to 46 months and were evaluated using the KSS score on a 200-point scale. RESULTS. The final study group comprised 127 primary TKAs. The average age was 68 years (51–90) with 45 males and 68 females. The average weight was 110kg (range: 75–151kg) for men and 88kg (range: 50–129kg) for women. One patient deceased during the follow-up period, four required manipulation under anesthesia, and two required revision for periprosthetic joint infection. There were no failures due to patellar maltracking. No special soft tissue releases were required in any patient. Average pre-operative knee score was 107, improving to 182 at average follow-up of 41 months (36–46 months). Results are summarized in Table 1. DISCUSSION. The improvement in patient clinical experience demonstrates that a universal femoral design can achieve excellent results if it incorporates modern technologies. A double Q-angle design with a deepened trochlear groove and a thin anterior flange appears to provide excellent patellar tracking for all patients in this cohort. This study is limited to the experience of a single institution. Further study would improve the extensibility of these findings. It does show, however, that a femur using a universal design with modern patellar tracking can improve patient satisfaction with their knee following TKA. For any figures or tables, please contact the authors directly

BACKGROUND. Trochlear geometry of modern femoral implants is designed for the mechanical alignment (MA) technique for Total Knee Arthroplasty (TKA). The biomechanical goal is to create a proximalised and more valgus trochlea to better capture the patella and optimize tracking. In contrast, Kinematic alignment (KA) technique for TKA respects the integrity of the soft tissue envelope and therefore aims to restore native articular surfaces, either femoro-tibial or femoro-patellar. Consequently, it is possible that current implant designs are not suitable for restoring patient specific trochlea anatomy when they are implanted using the kinematic technique. This could cause patellar complications, either anterior knee pain, instability or accelerated wear or loosening. The aim of our study is therefore to explore the extent to which native trochlear geometry is restored when the Persona. ®. implant (Zimmer, Warsaw, USA) is kinematically aligned. METHODS. A retrospective study of a cohort of 15 patients with KA-TKA was performed with the Persona. ®. prosthesis (Zimmer, Warsaw, USA). Preoperative knee MRIs and postoperative knee CTs were segmented to create 3D femoral models. MRI and CT segmentation used Materialise Mimics® and Acrobot Modeller® software, respectively. Persona. ®. implants were laser-scanned to generate 3D implant models. Those implant models have been overlaid on the 3D femoral implant model (generated via segmentation of postoperative CTs) to replicate, in silico, the alignment of the implant on the post-operative bone and to reproduce in the computer models the features of the implant lost due to CT metal artefacts. 3D models generated from post-operative CT and pre-operative MRI were registered to the same coordinate geometry. A custom written planner was used to align the implant, as located on the CT, onto the pre-operative MRI based model (figure 1). In house software enabled a comparison of trochlea parameters between the native trochlea and the performed prosthetic trochlea (figure 2). Parameters assessed included 3D trochlear axis and anteroposterior offset from medial facet, central groove, and lateral facet. Sulcus angle at 30% and 40% flexion was also measured. Inter and intra observer measurement variabilities have been assessed. RESULTS. Varus-valgus rotation between the native and prosthetic trochleae was significantly different (p<0.001), with the prosthetic trochlear groove being on average 7.9 degrees more valgus. Medial and lateral facets and trochlear groove were significantly understuffed (3 to 6mm) postoperatively in the proximal two thirds of the trochlear, with greatest understuffing for the lateral facet (p<0.05). The mean medio-lateral translation and internal-external rotation of the groove and the sulcus angle showed no statistical differences, pre and postoperatively (figure 3). CONCLUSION. Kinematic alignment of Persona. ®. implants poorly restores native trochlear geometry. The clinical impact of this finding remains to be defined. For figures/tables, please contact authors directly.

Introduction. Patellar crepitus and clunk are tendofemoral-related complications predominantly associated with posterior-stabilizing (PS) total knee arthroplasty (TKA) designs [1]. Contact between the quadriceps tendon and the femoral component can cause irritation, pain, and catching of soft-tissue within the intercondylar notch (ICN). While the incidence of tendofemoral-related pathologies has been documented for some primary TKA designs, literature describing revision TKA is sparse. Revision components require a larger boss resection to accommodate a constrained post-cam and stem/sleeve attachments, which elevates the entrance to the ICN, potentially increasing the risk of crepitus. The objective of this study was to evaluate tendofemoral contact in primary and revision TKA designs, including designs susceptible to crepitus, and newer designs which aim to address design features associated with crepitus. Methods. Six PS TKA designs were evaluated during deep knee bend using a computational model of the Kansas knee simulator (Figure 1). Prior work has demonstrated that tendofemoral contact predictions from this model can differentiate between TKA patients with patellar crepitus and matched controls [2]. Incidence of crepitus of up to 14% has been reported in Insall-Burstein® II and PFC® Sigma® designs [3]. These designs, in addition to PFC® Sigma® TC3 (revision component), were included in the analyses. Primary and revision components of newer generation designs (NexGen®, Attune® and Attune® Revision) were also included. Designs were evaluated in a patient model with normal Insall-Salvati ratio and a modified model with patellar tendon length reduced by two standard deviations (13mm) to assess worst-case patient anatomy. Results. During simulations with normal patellar tendon length, only PFC® Sigma® and PFC® Sigma® TC3 showed tendofemoral contact within the trochlea, and no design showed contact at the transition to the ICN (Figure 2). In simulations with patella baja, Insall-Burstein® II, PFC® Sigma®, and PFC® Sigma® TC3, demonstrated tendofemoral contact across the trochlea at the transition into the notch. In contrast, NexGen®, Attune® and Attune® Revision showed tendon contact for approximately half the width of the transition to the notch (Figure 3). PFC® Sigma® and Attune® demonstrated very similar tendofemoral contact to their equivalent revision components, although the shorter trochlear groove of Attune® Revision marginally increased contact at the transition. Discussion. Insall-Burstein® II, PFC® Sigma®, and PFC® Sigma® TC3 designs showed full contact with the quadriceps tendon at the anterior border of the ICN when combined with a short patellar tendon. NexGen®, Attune® and Attune® Revision had a more gradual transition between the trochlea and the notch, which resulted in less exposure to tendon contact. Even with the shorter trochlear groove required for revision components, Attune® Revision showed minimal difference in tendofemoral contact when compared with Attune®. There appears to be distinct benefit in a femoral design which reduces tendofemoral contact at the transition to the ICN; this may be of particular importance for patients with patella baja

Patella resurfacing is becoming more routine in total knee replacements with recent reports indicating improved long term outcomes. Despite this, patella osteotomy relies heavily on how the cutting jig is applied rather than on fixed anatomical landmarks. Recognised complications of asymmetric patella resection are patella fractures, patella maltracking, bony impingement and pain. Accurate instruments have been developed for other aspects of total knee replacements. However cutting guides for the patella tend to be cumbersome with poor reproducibility. Patella tilt is defined as the angle subtended by a line joining the medial and lateral edges of the patella and the horizontal. Keeping this angle to a minimum results in congruent alignment of the patella button within the trochlear groove. Current patella cutting jigs do not take this angle into consideration as they require full eversion of the patella laterally, not only making accurate placement of the jig difficult but also putting excessive strain on the surrounding soft tissue. This study describes a new cutting technique for the patella osteotomy which is referenced off the distal femoral condyles ensuring a more accurate and reproducible cut without having to evert the patella. With the femoral component trial in situ and the patella in its normal anatomical lie, the knee is flexed to 30°. The patella cutting jig is then applied in the usual manner making sure that adequate thickness of patella remains but it is placed parallel to a line joining the two condyles of the femoral component. By cutting the patella in this position parallel to the distal femoral condyles, patella tilt is minimised and the patella button will be aligned evenly within the trochlear groove. Currently all patients requiring patella resurfacing at our institution are undergoing this technique and the short term results have been very promising. This study presents a novel patella cutting technique that utilises a fixed landmark to ensure a more accurate and reproducible osteotomy. We are planning a large scale trial comparing pre- and post-operative knee scores and radiological assessment of patients having this new technique compared to standard cutting techniques. This will allow us to report on the longer term effects and pave the way for better patella resurfacing instrumentation

Introduction. Mechanical integrity of patella can be weakened by the technique of removing the articulating surface. The senior author developed the technique of maintaining subchondral bone of the lateral patellar facet in early 1980s. Though laboratory studies have demonstrated deleterious effect of excessive resection of patella on the strains in the remaining bone under load; clinical studies have not shown the importance of strong subchondral bone of lateral facet to have an effect on patellar fracture prevalence. We present the results of our patellar resection technique preserving the subchondral bone of lateral facet. Methods. 393 TKRs were performed between 1989 and 1996 using cruciate substituting modular knee with recessed femoral trochlear groove and congruent patello-femoral articulation. 45 patients with 48 knees died and 37 patients with 41 knees were lost to follow-up. Three hundred and four knees were followed for an average 10 years (range 5 -16 years). Patellar surface was resected with an oscillating saw without the use of cutting guide. The medial facet and most of the articular cartilage of the lateral facet was resected, while preserving the subchondral bone of lateral facet. An all-polyethylene implant with single peg was used in most cases. Results. There have been two fractures in the cohort with prevalence of 0.66%. Eight TKRs were revised for synovitis and osteolysis. Patellar osteolysis was found in 4 of these cases, with loosening of 3 of these patellae, and 1 patellar fracture. Two patellar implants had global radiolucencies and were considered loose. The average knee score in unrevised knees improved from 48.6 to 92.2, while functional scores improved from 50 to 81.1. Conclusion. We believe that maintaining this anatomic landmark allows for preserved patellar strength, and in association with a femoral component with a recessed trochlear groove, has resulted in our low patellar fracture rate in primary TKR and revision cases for patellar osteolysis

Purpose. Femoral component malrotation is a common cause for persisting symptoms and revision following total knee arthroplasty (TKA). There is ongoing debate about the most appropriate use of femoral landmarks to determine rotation. The Sulcus Line (SL, See Figure 1) is a three-dimensional curve produced from multiple points along the trochlear groove. Whiteside's Line, also known as the anteroposterior axis (APA), is derived from single anterior and posterior points. The purposes of the three studies presented are to i) assess the SL in a large clinical series, ii) demonstrate the effect of parallax error on rotational landmarks, and iii) assess the accuracy of a device which transfers a geometrically corrected SL onto the distal cut surface of the femur. Methods. The first study assessed the SL using a large, single surgeon series of consecutive patients (n=200) undergoing primary TKA. The postoperative CT scans of patients were examined to determine the final rotational alignment of the femoral component. In the second study measurements were taken in a series of 3DCT reconstructions of osteoarthritic knees (n=44) comparing the rotational landmarks measured along either the mechanical axis or the coronal axis of the trochlear groove. The third study assessed the accuracy of a novel trochlear alignment guide (TAG) using cadavers (n=10). Results. The mean position of the femoral component in the clinical series was 0.6° externally rotated to the surgical epicondylar axis, with a standard deviation of 2.9° (range −7.2° to 6.7°). On the 3DCT reconstructions the APA (88.2°±4.2°) had significantly higher variance when compared with the SL (90.3°±2.7°) (F=5.82, p=0.017). An axis derived by averaging the SL and the PCA+3° produced a significant decrease in both the number of outliers (p=0.03 vs PCA, p=0.007 vs SL) and the variance (F=6.15, p=0.015 vs SL). The coronal alignment of the SL varied widely relative to the mechanical axis (0.4°±3.8°) and the distal condylar surface (2.6°±4.3°). The results of the cadaver study found that using the TAG and the SL produced less variability than the APA (SD 2.0° compared to 3.7°). In addition, this level of accuracy was maintained when using the TAG to transfer the SL onto both the distal femoral condyles and the distal cut surface of the femur. Conclusions. The multiple points used to determine the SL confer anatomical and geometrical advantages and therefore it should be considered a separate rotational landmark to the APA. These findings suggest that much of the variability in the measurement of the APA, documented in the literature, is caused by parallax error. A new device, the TAG, is able to accurately transfer a geometrically correct SL on to the distal cut surface of the femur. This allows accurate comparison between the SL and other landmarks, including the PCA, which is likely to decrease the risk of femoral component malrotation

When dealing with the patella in total knee arthroplasty (TKA) there are three philosophies. Some advocate resurfacing in all cases, others do not resurface, and a third group selectively resurfaces the patella. The literature does not offer one clear and consistent message on the topic. Treatment of the patella and the ultimate result is multifactorial. Factors include the patient, surgical technique, and implant design. With respect to the patient, inflammatory versus non-inflammatory arthritis, pre-operative presence or absence of anterior knee pain, age, sex, height, weight, and BMI affect results of TKA. Surgical technique steps to enhance the patellofemoral articulation include: 1) Restore the mechanical axis to facilitate patellofemoral tracking. 2) Select the appropriate femoral component size with respect to the AP dimension of the femur. 3) When performing anterior chamfer resection, measure the amount of bone removed in the center of the resection and compare to the prosthesis. Do not overstuff the patellofemoral articulation by taking an inadequate amount of bone. 4) Rotationally align the femur appropriately using a combination of the AP axis, the transepicondylar axis, the posterior condylar axis, and the tibial shaft axis. 5) If faced with whether to medialise or lateralise the femoral component, always lateralise. This will enhance patellofemoral tracking. 6) When resurfacing the patella, only evert the patella after all other bony resections have been performed. Remove peripheral osteophytes and measure the thickness of the patella prior to resection. Make every effort to leave at least 15 mm of bone and never leave less than 13 mm. 7) Resect the patella. The presenter prefers a freehand technique using the insertions of the patellar tendon and quadriceps tendon as a guide, sawing from inferior to superior, then from medial to lateral to ensure a smooth, flat, symmetrical resection. Medialise the patellar component and measure the thickness of reconstruction. 8) When not resurfacing the patella, surgeons generally remove all the peripheral osteophytes, and some perform denervation using electrocautery around the perimeter. 9) Determine appropriate patellofemoral tracking only after the tourniquet is released. 10) Close the knee in flexion so as not to tether the soft tissues about the patella and the extensor. With or without patellar resurfacing, implant design plays in important role in minimizing patellofemoral complications. Newer designs feature a so-called “swept back” femur in which the chamfer resection is deepened, and patellofemoral overstuffing is minimised. Lateralizing the trochlear groove on the anterior flange, orienting it in valgus alignment, and gradually transitioning to midline have improved patellofemoral tracking. Extending the trochlear groove as far as possible into the tibiofemoral articulation has decreased patellofemoral crepitation and patellar clunk in posterior stabilised designs. With respect to the tibial component, providing patellar relief anteriorly in the tibial polyethylene has facilitated range of motion and reduced patellar impingement in deep flexion. On the patella side, the all-polyethylene patella remains the gold standard. While data exist to support all three viewpoints in the treatment of the patella in TKA, it is the presenter's opinion that the overwhelming data support patella resurfacing at the time of primary TKA. It is clear from the literature that the status of the patellofemoral articulation following TKA is multifactorial. Surgical technique and implant design are key to a well-functioning patellofemoral articulation. Pain is the primary reason patients seek to undergo TKA. Since our primary goal is to relieve pain, and there has been a higher incidence of anterior knee pain reported without patellar resurfacing, why not resurface the patella?

Background. Although early TKA designs were symmetrical, during the past two decades TKA have been designed to include asymmetry, pertaining to either the trochlear groove, femoral condylar shapes or the tibial component. More recently, a new TKA was designed to include symmetry in all areas of the design, in the hopes of reducing design and inventory costs. Objective. The objective of this study was to determine the in vivo kinematics for subjects implanted with this symmetrical TKA during a weight-bearing deep knee bend activity. Methods. In vivo deep knee bend (DKB) kinematics for 21 subjects implanted with symmetrical posterior cruciate sacrificing (PCS) fixed bearing TKA were obtained using fluoroscopy. A 3D-to-2D registration technique was used to determine each subjects anteroposterior translation of lateral (LAP) and medial (MAP) femoral condyles and tibiofemoral axial rotation and their weight-bearing knee flexion. Results. During the DKB, the average maximum weight-bearing flexion was 111.7° ± 13.3°. On average, from full extension to maximum knee flexion, subjects experienced 2.5 mm ± 2.0 mm femoral rollback on lateral condyle −2.5 mm ± 2.2 mm of medial condyle motion in the anterior direction (Figure 1). This medial condyle motion was consistent for the majority of the subjects with the lateral condyle exhibiting rollback from 0° to 60° of flexion and then an average anterior slide of 0.3 mm from 60° to 90° of flexion. On average, the subjects in this study experienced 6.6° ± 3.3° of axial rotation, with most of rotation occurring in early flexion, averaging 4.9° (Figure 2). Discussion. Although subjects in this study were implanted with a symmetrical TKA, they did experience femoral rollback of the lateral condyle and positive axial rotation. Both of these kinematic parameters were normal-like in pattern, compared to the normal knee in early flexion, but in deeper flexion the pattern of motion varied from the normal knee. Also, the magnitude of posterior femoral rollback and axial rotation revealed similarities to previous fluoroscopy studies on subjects implanted with an asymmetrical TKA design. This was only a single surgeon study, so it is unclear if the results are TKA or surgeon influenced. Therefore, it is proposed that more patients be analyzed having this TKA implanted by other surgeons. For any figures or tables, please contact the authors directly

Background. The goal of patellofemoral arthroplasty (PFA) is to replace damaged cartilage, and to correct underlying deformities, to reduce pain and prevent maltracking. We aimed to determine how PFA modifies patellar height, tilt, and tibial tuberosity to trochlear groove (TT-TG) distance. The hypothesis was that PFA would correct trochlear dysplasia or extensor mechanism malalignment. Methods. The authors prospectively studied a series of 16 patients (13 women and 3 men) aged 64.9 ± 16.3 years (range, 41 to 86) that received PFA. All knees were assessed pre-operatively and six months post-operatively using frontal, lateral, and ‘skyline’ x-rays, and CT scans to calculate patellar tilt, patellar height and tibial tuberosity–trochlear groove (TT-TG) distance. Results. The inter-observer agreement was excellent for all parameters. (ICC > 0.95). Pre-operatively, the median patellar tilt without quadriceps contraction (QC) was 17.5° (range, 5.3°–33.4°) and with QC was 19.8° (range, 0°–52.0°). The median Caton- Deschamps Index (CDI) was 0.91 (range, 0.80–1.22) and TT-TG distance was 14.5mm (range, 4.0–22.0). Post-operatively, the median patellar tilt without QC was 0.3° (range, −15.3°–9.5°) and with QC was 6.1° (range, −11.5°–13.3°). The median CDI was 1.11 (range, 0.81–1.20) and TT-TG distance was 10.1mm (range, 1.8–13.8mm). Conclusion. The present study demonstrates that, beyond replacing arthritic cartilage, trochlear-cutting PFA improves patellofemoral congruence by correcting trochlear dysplasia and standardizing radiological measurements as patellar tilt and TT-TG. The association of lateral patellar facetectomy diminishes local effects of OA and improves patellar tracking by reducing the patellar tilt

Patellofemoral complaints are the common and nagging problem after total knee arthroplasty. Crepitus occurs in 5% to over 20% of knee arthroplasty procedures depending on the type of implant chosen. It is caused by periarticular scar formation with microscopic and gross findings indicating inflammatory fibrous hyperplasia. Crepitus if often asymptomatic and not painful, but in some cases can cause pain. Patella “Clunk Syndrome” is less common and represents when the peripatella scarring is abundant and forms a nodule which impinges and “catches” on the implant's intercondylar notch. Patella Clunk was more common with early PS designs due to short trochlear grooves with sharp transition into the intercondylar notch. Clunks are very infrequent with modern PS implants. This syndrome has been reported in CR implants as well. Thorough debridement of the synovium and scarring at the time of arthroplasty is thought to reduce the occurrence of crepitus and clunks. Larger patella with better coverage of the cut bone may also be helpful. The diagnosis can be made on history and physical exam. X-rays are also helpful to assess patella tracking. MRI or ultrasound can be used to identify and confirm the diagnosis, but this is not mandatory. Painful crepitus and clunk syndrome that fail conservative management of NSAIDS and physical therapy may require surgery. Both crepitus and clunk can be treated with arthroscopic removal of the peripatella scar. Patella maltracking should also be assessed and treated. While recurrence may occur, it is uncommon

Introduction. Studies have shown that dissatisfaction following TKA may stem from poor component placement and iatrogenic factors related to variability in surgical execution. A CT-based robotic assisted system (RA) allows surgeons to dynamically balance the joint prior to bone resection. This study aimed to determine if this system could improve TKA planning, reduce soft tissue releases, minimize bone resection, and accurately predict component size in varus knee. Method. Four hundred and seventy four cases with varus deformity undergoing primary RATKA were enrolled in this prospective, single center and surgeon study. Patient demographics and intraoperative surgical details were collected. Initial and final 3-dimensional alignment, component position, bone resection depths, use of soft tissue releases, knee balancing gaps, and component size were collected intraoperatively. WOMAC and KOOS Jr. scores were collected 6 months, and 1 year postoperatively. Descriptive statistics were applied to determine the changes in these parameters between initial and final values. Results. Native deformity ranged from 1 to 19 degrees of varus. 86% of patients in this study did not require a soft tissue release regardless of their level of coronal or sagittal deformity. Complex deformities who required a soft tissue release were corrected on average to 3 degrees varus while cases without releases were corrected to 2 degrees varus on average with the overall goal as traditional mechanical alignment. All surgeons achieved their planned sizes on the tibia and femur more than 98% of the time within one size, and 100% of the time within two sizes. Flexion and extension gaps during knee balancing were within 2mm (mean 1mm) for all knees. At latest follow-up, radiographic evidence suggested well-seated and well-fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation were reported. Mean WOMAC total score was improved from 23.8±8.0 pre-op to 8.9±7.9 1-year post-op (p<0.01). Mean KOOS Jr. score was improved from 46.8±11.6 pre-op to 77.9±14.8 1-year post-op (p<0.01). Discussion and Conclusions. New tools may allow for enhanced execution and predictable balance for TKA, which may improve patient outcomes. In this study, preoperative planning via CT scan allowed surgeons to assess bony deformities and subtly adjust component position to reduce soft tissue trauma. While this study has several limitations, RATKA for varus knees should continue to be investigated. For any figures or tables, please contact authors directly

Each of the seven cuts required for a total knee arthroplasty has its own science, and can affect the outcome of surgery. Distal Femur. Sets the axial alignment (along with the tibial cut), and too little or too much depth affects ligament tension in extension. Anterior Femur. Sets the rotation of the femoral component, which affects patellar tracking. Internal rotation results in patellar maltracking. External rotation will either notch the femur, or cause too large a femoral component to be selected. Anterior and posterior femoral cuts also determine femoral component size selection. Too small a femoral component causes notching, flexion instability, and mismatch to the tibial component. Too big a femoral component causes overstuffing, periarticular pain, and patellar maltracking. Posterior Femur. Posterior referencing usually works, and the typical knee requires 3 degrees of external rotation to align with the transepicondylar axis. In valgus knees, there may be significant hypoplasia of the lateral femoral condyle, and posterior referencing has to be adjusted to avoid internal rotation. Posterior chamfer. A 4-in-one block saves time. Anterior chamfer. Deeper anterior chamfer allows a deeper trochlear groove, for patellar tracking. Tibia. Sets axial alignment with distal femoral cut. Posterior slope loosens flexion gap. Oversizing results in painful medial overhang. Lateral overhang usually not a problem. Undersizing results in inadequate bone support and subsidence. Patella. Inset or onset. Central peg associated with fracture. Err to medial and superior to assist tracking and avoid impingement on the tibial insert

Introduction. Valgus deformity in an end stage osteoarthritic knee can be difficult to correct with no clear consensus on case management. Dependent on if the joint can be reduced and the degree of medial laxity or distension, a surgeon must use their discretion on the correct method for adequate lateral releases. Robotic assisted (RA) technology has been shown to have three dimensional (3D) cut accuracy which could assist with addressing these complex cases. The purpose of this work was to determine the number of soft tissue releases and component orientation of valgus cases performed with RA total knee arthroplasty (TKA). Methods. This study was a retrospective chart review of 72 RATKA cases with valgus deformity pre-operatively performed by a single surgeon from July 2016 to December 2017. Initial and final 3D component alignment, knee balancing gaps, component size, and full or partial releases were collected intraoperatively. Post-operatively, radiographs, adverse events, WOMAC total and KOOS Jr scores were collected at 6 months, 1 year and 2 year post-operatively. Results. Pre-operatively, knee deformities ranged from reducible knees with less than 5mm of medial laxity to up to 12° with fixed flexion contracture. All knees were corrected within 2.5 degrees of mechanical neutral. Average femoral component position was 0.26. o. valgus, and 4.07. o. flexion. Average tibial component position was 0.37. o. valgus, and 2.96. o. slope, where all tibial components were placed in a neutral or valgus orientation. Flexion and extension gaps were within 2mm (mean 1mm) for all knees. Medial and lateral gaps were balanced 100% in extension and 93% in flexion. The average flexion gap was 18.3mm and the average extension gap was 18.7mm. For component size prediction, the surgeon achieved their planned within one size on the femur 93.8% and tibia 100% of the time. The surgeon upsized the femur in 6.2% of cases. Soft tissue releases were reported in one of the cases. At latest follow-up, radiographic evidence suggested well seated and well fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation is reported. Mean WOMAC total scores were improved from 24±8.3 pre-op to 6.6±4.4 2-year post-op (p<0.01). Mean KOOS scores were improved from 46.8±9.7 pre-op to 88.4±13.5 2-year post-op (p<0.01). Discussion. In this retrospective case review, the surgeon was able to balance the knee with bone resections and avoid disturbing the soft tissue envelope in valgus knees with 1–12° of deformity. To achieve this balance, the femoral component was often adjusted in axial and valgus rotations. This allowed the surgeon to open lateral flexion and extension gaps. While this study has several limitations, RATKA for valgus knees should continue to be investigated. For any figures or tables, please contact authors directly

Introduction. Patella implant research is often overlooked despite its importance as the third compartment in a total knee replacement. Wear and fracture of resurfaced patellae can lead to implant failure and revision surgeries. New simulation techniques have been developed to analyze the performance of patella designs as they interact with the trochlear groove in total knee components, and clinical validation is sought to ensure that these simulations are appropriate. The objective of this work was to subject several patellar designs to patient-derived deep knee bend (DKB) inputs on a 6 degree of freedom (DOF) simulator and compare the resultant wear scars to clinical retrievals. Materials and Methods. Previously reported DKB profiles were developed based on in vivo patellofemoral data and include a wide range of patient variability. The profiles chosen for this body of work were based on the stress in the patellar lateral facet; maximizing this stress whilst maintaining the ability to run the profile stably on the simulator. Load/kinematic profiles were run on three patellar designs (n=3 per group) for 220,000 cycles at 0.8Hz on an AMTI VIVO joint simulator. A comparison cohort of clinically retrieved devices of the same design was identified in an IRB-approved database. Exclusion criteria included gross delamination, cracking secondary to oxidation, and surgeon-reported evidence of malalignment leading to mal-tracking. 29 Patellae were included for analysis: PFC. ®. All Poly (n=14), ATTUNE. ®. Anatomic (n=6), and ATTUNE. ®. Medialized Dome (n=9). Mean in vivo duration was 70.1 months. Patellae were analyzed under optical microscope in large-depth-of-field mode to map the surface damage profile. Burnishing ‘heat-maps’ were generated for retrievals and simulated patellae by normalizing the patellar size and overlaying silhouettes from each component of the same type using a custom-developed MatLAB code. Results. Burnishing heat-map comparisons between retrievals and simulator specimens for each of the three designs were compared. Retrievals show more variation than simulator devices, however the general loci and relative area of burnished regions is closely aligned for each of the three designs. The retrieved and simulated burnishing scar heat-maps on all-poly PFC. ®. patellae are centered medio-laterally with a wider profile on the lateral aspect. The burnishing marks are continuous. A similar observation may be made of the ATTUNE. ®. medialized dome, retrievals and simulator specimens, though the contact areas appear to be more concentrated away from the apex. The anatomic patellae show two primary regions of contact, and minimal burnishing at the apex. The simulator specimens likewise show two principal regions of contact. Discussion. Wear scar analysis shows that joint simulation on AMTI VIVO yields clinically relevant wear patterns across a variety of device types. Clinically relevant damage provides insight that load and motion inputs to the simulator deliver results that may be used to interpret in vivo performance or analyze future designs and/or materials. This qualitative surface contact analysis will help to inform future quantitative mass loss and fatigue failure studies. For any figures or tables, please contact authors directly

Osteochondral (OC) defects of the knee are associated with pain and significant limitation of activity. Studies have demonstrated the therapeutic efficacy of mesenchymal stem cell (MSC) therapies in treating osteochondral defects. There is increasing evidence that the efficacy of MSC therapies may be a result of the paracrine secretion, particularly exosomes. Here, we examine the effects of MSC exosomes in combination with Hyaluronic Acid (HA) as an injectable therapy on functional osteochondral regeneration in a rabbit osteochondral defect model. Exosomes were purified from human MSC conditioned medium by size fractionation. A circular osteochondral defect of 4.5 mm diameter and 2.5 mm depth was surgically created in the trochlear grooves of 16 rabbit knees. Thereafter, eight knees received three weekly injections of 200 µg of exosomes in one ml of 3% HA, and the remaining eight knees received three weekly injections of one ml of 3% HA only. The rabbits were sacrificed at six weeks. Analyses were performed by macroscopic and histological assessments, and functional competence was analysed via Young Modulus calculation at five different points (central, superior, inferior, medial and lateral) of the repaired osteochondral defect site. MSC exosomes displayed a modal size of 100 nm and expressed exosome markers (CD81, TSG101 and ALIX). When compared to HA alone, MSC exosomes in combination with HA showed significantly better repair histologically and biomechanically. The Young Modulus was higher in 4 out of the 5 points. In the central region, the Young Modulus of MSC exosome and HA combination therapy was significantly higher: 5.42 MPa [SD=1.19, 95% CI: 3.93–6.90] when compared to HA alone: 2.87 MPa [SD=2.10, 95% CI: 0.26–5.49], p < 0 .05. The overall mean peripheral region was also significantly higher in the MSC exosome and HA combination therapy group: 5.87 MPa [SD=1.19, 95% CI: 4.40–7.35] when compared to HA alone: 2.70 MPa [SD=1.62, 95% CI: 0.79–4.71], p < 0 .05. The inferior region showed a significantly higher Young Modulus in the combination therapy: 7.34 MPa [SD=2.14, 95% CI: 4.68–10] compared to HA alone: 2.92 MPa [SD=0.98, 95% CI: 0.21–5.63], p < 0.05. The superior region showed a significantly higher Young Modulus in the combination therapy: 7.31 MPa [SD=3.29, 95% CI: 3.22–11.39] compared to HA alone: 3.59 MPa [SD=2.55, 95% CI: 0.42–6.76], p < 0.05. The lateral region showed a significantly higher Young Modulus in the combination therapy: 8.05 MPa [SD=2.06, 95% CI: 5.49–10.61] compared to HA alone: 3.56 MPa [SD=2.01, 95% CI: 1.06–6.06], p < 0.05. The medial region showed a higher Young Modulus in the combination therapy: 6.68 MPa [SD=1.48, 95% CI: 4.85–8.51] compared to HA alone: 3.45 MPa [SD=3.01, 95% CI: −0.29–7.19], but was not statistically significant. No adverse tissue reaction was observed in all the immunocompetent animals treated with MSC exosomes. Three weekly injections of MSC exosomes in combination with HA therapy results in a more functional osteochondral regeneration as compared to HA alone