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

“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

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

Introduction. Optimized tibial tray rotation during a total knee replacement (TKR) is critical for tibiofemoral congruency through full range of motion, as it affects soft tissue tension, stability and patellar tracking. Surgeons commonly reference the tibial tubercle, or the “floating tibial tray,” while testing the knee in flexion and extension. Utilization of embedded sensors may enable the surgeon to more accurately assess tibiofemoral contact points during surgery. Methods. The malrotation of the tibiofemoral congruency when utilizing the mid to medial 1/3 of the tibial tubercle for tibial rotation was evaluated in 50 posterior cruciate ligament-retaining TKRs performed by an experienced, high-volume surgeon. Sensors were embedded in the tibial trials; the rotation of the tibial tray was defined, and the femoral contact points in each compartment were captured. The surgical procedure was performed to size and then appropriately rotate the tibial tray. The anterior medial tray was pinned to control anterior-posterior and medio-lateral displacement, and allow internal and external rotation of the tray. With the capsule closed and patella reduced, the knee was reduced with trial implants. The femoral contact points and medial-lateral soft tissue tension were documented. Patellar tracking and changes in soft tissue tension were also documented. Results. In 60% (n = 30/50) of cases, further external rotation (average 5 degrees) was required. No further rotation was required in 10% (n = 5/50), and 30% (n = 15/50) required further internal rotation for optimized congruency. Patellar tracking and changes in soft tissue tension based on rotation showed parallel center of load in medio-lateral compartments and equalized intercompartment pressures resulting in optimized balance of the knee. Conclusions. Utilizing the tibial tubercle for optimized tibial tray rotation and femoral congruency was only adequate in 10% of cases. The use of sensors to define the femoral contact points on the tibia enabled the surgeon to adjust the tibial tray to optimize tibiofemoral congruency. Mal-rotated trays negatively affected soft tissue tension and patellar tracking

INTRODUCTION. Use of a novel ligament gap balancing instrumentation system in total knee arthroplasty resulted in femoral component external rotation values which were higher on average, compared to measured resection systems. In one hundred twenty knees in 110 patients the external rotation averaged 6.9 degrees (+/− 2.8) and ranged from 0.6 to 12.8 degrees. The external rotation values in this study were 4° and 2° larger, respectively, than the typical 3° and 5° discrete values that are common to measured resection systems. The purpose of the present study was to determine the effect of these greater external rotation values for the femoral component on patellar tracking and flexion instability. METHODS. One hundred twenty knees in 110 patients were consecutively enrolled by a single surgeon using the same implant across subjects. All patients underwent arthroplasty with tibial resection first and that set external rotation of the femoral component based upon use of a ligament gap balancing system. Following ligament tensioning/balancing, the femur was prepared. The accuracy of the ligament balancing system was assessed by reapplying equal tension to the ligaments using a tensioning bolt and torque wrench in flexion and extension after the bone resections had been made. The resulting flexion and extension gaps were then measured to determine rectangular shape and equality of the gaps. Postoperative Merchant views were obtained on all of the patients and patellar tracking was assessed and compared to 120 consecutive total knee arthroplasties previously performed by the same surgeon with the same implant using a measured resection system. RESULTS. Rectangular flexion and extension gaps were obtained within +/− 0.5mm in all cases. Equality of the flexion and extension gaps was also obtained within +/− 0.5mm in all cases. Merchant views of the total knee arthroplasties showed central patellar tracking with no tilt or subluxation in 90% of the ligament gap balanced knees and 74% of the measured resection knees. DISCUSSION AND CONCLUSION. External rotation values are higher on average, when ligament tensioning/balancing is employed with this novel system compared to measured resection systems. In this study this resulted in consistent matching of the flexion gap to the extension gap and better patellar tracking. These findings suggest that limiting the surgeon to discrete rotation values may be at odds with where the femur “desires” to be, given soft tissue considerations for each patient

During total knee replacement (TKR), surgical navigation systems (SNS) allow accurate prosthesis component implantation by tracking the tibio-femoral joint (TFJ) kinematics in the original articulation at the beginning of the operation, after relevant trial components implantation, and, ultimately, after final component implantation and cementation. It is known that TKR also alters normal patello-femoral joint (PFJ) kinematics resulting frequently in PFJ disorders and TKR failure. More importantly, patellar tracking in case of resurfacing is further affected by patellar bone preparation and relevant component positioning. The traditional technique used to perform patellar resurfacing, even in navigated TKR, is based only on visual inspection of the patellar articular aspect for clamping patellar cutting jig and on a simple calliper to check for patellar thickness before and after bone cut, and, thus, without any computer assistance. Even though the inclusion in in-vivo navigated TKR of a procedure for supporting also patellar resurfacing based on patient-specific bone morphology seems fundamental, this have been completely disregarded till now, whose efficacy being assessed only in-vitro. This procedure has been developed, together with relevant software and surgical instrumentation, as an extension of current SNS, i.e. TKR is navigated, at the same time measuring the effects of every surgical action on PFJ kinematics. The aim of this study was to report on the first in-vivo experiences during TKR with patellar resurfacing. Four patients affected by primary gonarthrosis were implanted with a fixed bearing posterior-stabilised prosthesis (NRG, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. All TKR were performed by means of two SNS (Stryker®-Leibinger, Freiburg, Germany) with the standard femoral/tibial trackers, the pointer, and a specially-designed patellar tracker. The novel procedure for patellar tracking was approved by the local ethical committee; the patients gave informed consent prior the surgery. This procedure implies the use of a second system, i.e. the patellar SNS (PSNS), with dedicated software for supporting patellar resurfacing and relative data processing/storing, in addition to the traditional knee SNS (KSNS). TFJ anatomical survey and kinematics data are shared between the two. Before surgery, both systems were initialised and the patellar tracker was assembled with a sterile procedure by shaping a metal grid mounted with three markers to be tracked by PSNS only. The additional patellar-resection-plane and patellar-cut-verification probes were instrumented with a standard tracker and a relevant reference frame was defined on these by digitisation with PSNS. Afterwards, the procedures for standard navigation were performed to calculate preoperative joint deformities and TFJ kinematics. The anatomical survey was performed also with PSNS, with relevant patellar anatomical reference frame definition and PFJ kinematics assessment according to a recent proposal. Standard procedures for femoral and tibial component implantation, and TFJ kinematics assessment were then performed by using relevant trial components. Afterwards, the procedure for patellar resection begun. Once the surgeon had arranged and fixed the patellar cutting jig at the desired position, the patellar-resection-plane probe was inserted into the slot for the saw blade. With this in place, the PSNS captured tracker data to calculate the planned level of patellar bone cut and the patellar cut orientation. Then the cut was executed, and the accuracy of this actual bone cut was assessed by means of the patellar-cut-verification probe. The trial patellar component was positioned, and, with all three trial components in place, TFJ and PFJ kinematics were assessed. Possible adjustments in component positioning could still be performed, until both kinematics were satisfactory. Finally, final components were implanted and cemented, and final TFJ and PFJ kinematics were acquired. A sterile calliper and pre- and post-implantation lower limb X-rays were used to check for the patellar thickness and final lower limb alignment. The novel surgical technique was performed successfully in all four cases without complication, resulting in 30 min longer TKR. The final lower limb alignment was within 0.5°, the resurfaced patella was 0.4±1.3 mm thinner than in the native, the patellar cut was 1.5°±3.0° laterally tilted. PFJ kinematics was taken within the reference normality. The patella implantation parameters were confirmed also by X-ray inspection; discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. At the present experimental phase, a second separate PSNS was utilised not to affect the standard navigated TKR. The results reported support relevance, feasibility and efficacy of patellar tracking and PFJ kinematics assessment in in-vivo navigated TKR. The encouraging in-vivo results may lay ground for the design of a future clinical patella navigation system the surgeon could use to perform a more comprehensive assessment of the original whole knee anatomy and kinematics, i.e. including also PFJ. Patellar bone preparation would be supported for suitable patellar component positioning in case of resurfacing but, conceptually, also in not resurfacing if patellar anatomy and tracking assessment by SNS reveals no abnormality. After suitable adjustment and further tests, in the future if this procedure will be routinely applied during navigated TKR, abnormalities at both TFJ and PFJ can be corrected intra-operatively by more cautious bone cut preparation on the femur, tibia and also patella, in case of resurfacing, and by correct prosthetic component positioning

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. Overstuffing the patellofemoral joint during total knee arthroplasty (TKA) is considered a potential cause of limited knee flexion and patellar maltracking. We investigated the effect of patellar thickness on intraoperative knee flexion and patellar tracking in navigated TKA. Methods. Twenty osteoarthritic knees (20 patients) were investigated in this study. Knees with valgus deformity were excluded. The same posterior stabilized prosthesis was employed in all the 20 cases. Preoperative patellar thickness was measured using a caliper, and patellar resection was performed to restore the native thickness by placing a standard 10-mm-thick trial patella. After placement of all trial components, maximal flexion against gravity was measured using a navigation system. The trial patella was also assessed for tracking, with and without suturing of the medial capsule (the “three-stitch” test and no-thumb test, respectively). Subsequently, 2-mm and 4-mm augmentations were applied to the standard trial patella, and the aforementioned measurements and assessments were repeated. Results. The average preoperative patellar thickness was 22.7 mm. Knee flexion with the standard trial patella was 125.3° ± 8.1°. Increasing the patellar thickness by 2 mm significantly (p < 0.0001) reduced the knee flexion by an average of 4.2°. Similarly, a 4-mm augmentation significantly (p < 0.0001) decreased the knee flexion by an average of 8.9°. Increased patellar thickness had no visible effect on patellar tracking in any of the knees. Conclusion. Patellofemoral overstuffing should be avoided to achieve optimal knee flexion in TKA. However, our findings indicate that patellar tracking is not influenced by patellar thickness

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

INTRODUCTION. Despite a large percentage of total knee arthroplasty failures occurs for disorders at the patello-femoral joint (PFJ), current navigation systems report tibio-femoral (TFJ) kinematics only, and do not track the patella. Despite this tracking is made difficult by the small bone and by its full eversion during surgery, a new such technique has been developed, which includes a new tracker, new corresponding surgical instrumentation also for patellar resurfacing, and all relevant software. The aim of this study is to report an early experience in patients of these measurements, i.e. TFJ and PFJ kinematics. METHODS. These measurements were taken in the first ten patients, affected by primary gonarthrosis and implanted with a resurfacing posterior-stabilised prosthesis in the period July 2010 – May 2011. A standard knee navigation system was enhanced by a specially-designed patellar tracker, mounted with a cluster of three light emitting diodes. Standard procedures for femoral and tibial bone preparation were performed according to the navigation system, and the patellar was resurfaced. Relevant resection planes were taken by an instrumented verification probe. Final position of the three components and lower limb alignment were also acquired. Joint kinematics was deduced from the anatomical survey, which included anatomical landmarks on the patellar posterior aspect, and according to established recommendations and original proposals. RESULTS. In addition to the standard assessment of TFJ kinematics, patellar tracking was performed successfully in all cases without complications, resulting in a maximum of 30 min longer operations. PFJ kinematics (see figure) after replacement and resurfacing showed a mean (± standard deviation, over the patients) range of flexion, tilt and medio-lateral shift respectively of 66.9° ± 8.5° (mean of minimum flexion ÷ of maximum flexion, 15.6° ÷ 82.5°), 8.0° ± 3.1° (−5.3° ÷ 2.8°), and 5.3 ± 2.0 mm (−5.5 ÷ 0.2 mm). Statistically significant correlations were found between the internal/external rotation of the femoral component and the range of PFJ tilt (p=0.05; R=0.64); in three patients, medio-lateral PFJ shift seemed to be affected by the medio-lateral position of the femoral component. DISCUSSION AND CONCLUSIONS. Data obtained from our preliminary experience support the relevance, feasibility and efficacy of patellar tracking in navigated knee arthroplasty by means of a standard knee navigation system, suitably extended to track also the patellar motion. Patellar-based measurement provides for a more comprehensive assessment of the whole knee function, not only for the resurfacing but also for a best possible positioning of the femoral and tibial components

Rotational malalignment in total knee arthroplasty (TKA) may lead to several complications. Transepicondylar axis has been accepted for a reference of femoral rotation. In contrast, standard reference of tibial rotation remains controversial. Currently, two techniques are widely used, the anatomical landmarks technique and the range-of-movement (ROM) technique. Fifty-one patients underwent posterior-stabilized TKA with center-post self-align ROM technique for tibial component placement. Laurin view radiograph and computer tomography (CT) were used to assess the prosthetic position. The rotational mismatch between tibial and femoral components was 2.00° ± 0.34° (range, 0.1°-5.8°). All TKA showed a tibiofemoral mismatch within 10° (range, 0.1° −5.8°). Intraoperative evaluation of patellar tracking by no-thumb test and the Laurin view showed normal range in 90%. We concluded that tibial component placement with center-post self-align technique in PS-TKA can produce good patellar tracking with acceptable range of tibiofemoral mismatch

Maltracking of the patella associated with TKA is usually the result of several factors coming together in the same patient. Causes of maltracking include residual valgus limb alignment, valgus placement of the femoral component, patella alta, poor prosthetic geometry, internal rotation of the femoral or tibial component, excessive patellar thickness, asymmetric patellar preparation, failure to perform a lateral release when indicated, capsular dehiscence, and dynamic instability. Prior to wound closure after implantation of total knee arthroplasty, patellar tracking should be evaluated to assess the potential need for lateral release. The incidence of lateral release in the past was quite high in some series. Most experienced surgeons will report a lateral release rate less than 5% for varus knees. It is usually higher for valgus knees because they are often associated with patella alta and preoperative subluxation. The classic intraoperative test for patellar tracking has been referred to as the “rule of no thumb” In this test, first suggested by Fred Ewald, the patella is returned to the trochlear groove in extension with the capsule unclosed. The knee is then passively flexed and one assesses whether or not the patella tracks congruently without capsular closure. If it does and the medial facet of the patellar component contacts the medial aspect of the trochlea no lateral release need be considered. If the patella dislocates or tilts, lateral release may be necessary. The test should be repeated with 1 suture closing the capsule at the level of the superior pole. If tracking then becomes congruent without excessive tension on the suture, no release is necessary. If tilting still persists, some surgeons like to assess tracking with the tourniquet deflated so that any binding effect on the quadriceps can be eliminated from the test. A tight PCL can also impart apparent patellar tilt as the femoral component is drawn posteriorly while the tibia (with its tubercle) moves anteriorly

For as long as surgeons have been performing total and partial knee arthroplasty, surgeons have debated the efficacy, safety, and requirement of a pneumatic tourniquet. Advocates claim that blood loss is less, visualization is improved, and the cement technique is better with the use of a tourniquet. Others would argue that the use of the tourniquet or limited tourniquet use is safer, does not increase blood loss, and does not compromise visualization and cementing technique. Multiple meta-analyses have been performed that provide very little true evidence of superiority. One such study from Yi et al, concludes that the use of the tourniquet reduces surgical time, intraoperative and total blood loss, but increases postoperative total blood loss. They also conclude that DVT and SSI are “relatively augmented” with use. There may be issues with the timing of tourniquet release in these pooled studies, with others stating that releasing the tourniquet prior to wound closure, supposedly for hemostasis, significantly increases the total and calculated blood loss. Huang et al report that with proper control in the amount of pressure, a debatable topic in and of itself, and shorter duration of inflation, release after closure can reduce blood loss without increased complications. One additional issue is patellar tracking, and the need to lateral release. The tourniquet significantly affects assessment of tracking and the need for lateral release, potentially causing the surgeon to unnecessarily perform a lateral release with the tourniquet inflated. Lastly, research has suggested that using a tourniquet may affect recovery of lower extremity strength and function. Dennis et al compared quadriceps strength and found that use of the tourniquet resulted in “slightly” lower strength postoperatively out to 3 months. The fatal flaw in this study and others is that there is no accepted minimal clinically important difference for quad function, and thus they powered their study to detect a difference of 12 Nm, and the actual difference, while statistically significant, did not even meet their arbitrary power set point. Thus, while strength may be slightly impaired by the use of a tourniquet, it was not different enough to meet their criteria. Additionally, in their study, 64% of the “no-tourniquet” knees actually had a tourniquet used for cementation to “minimise blood at the bone-cement interface and maximise fixation”. Clearly, even these authors are concerned with the results of not using a tourniquet. These authors utilise a pneumatic tourniquet in all cases of primary TKA and release the tourniquet prior to closure to ensure hemostasis and accurately assess patellar tracking. In doing so, we use the methodology of limb occlusion pressure to minimise the pressure to that necessary for ensuring a clear field. Additionally, these authors emphasise the ultimate in surgical efficiency allowing for extremely short tourniquet times, even in the most difficult cases. As an example, in 1300 consecutive obese patients with BMI equal or greater than 35, the average tourniquet time for primary TKA was 49 minutes. These short times, with the minimum pressure allow for the best of both worlds and little to no downside

Persistent patellofemoral symptoms can cause patient dissatisfaction after Total Knee Arthroplasty (TKA). The aim of this retrospective study was to evaluate patellar tracking and patient outcomes utilizing two implant designs in TKA. Medical records and radiographs of two groups of 100 consecutive patients each were reviewed. All patients underwent posterior stabilized TKA by a single surgeon; using the same operative technique but two different implant designs (Group 1: Asymmetric femoral component with deep congruent trochlear groove and Group 2: Asymmetric femoral component with shallow trochlear groove). Data was collected on demographic characteristics, patellar tilt, displacement, prosthesis-bone angle, HSS Patella Score, Knee Society Knee and Function Score. Patellar tilt more than 5° was considered significant. Statistical analysis was done using the SPSS v.16.0.3 software (SPSS, Inc., Chicago, IL). Patients' age and sex were equivalent in the two groups (p>0.57). Median follow up was 2.2 years. Pre-operative incidence of patellar tilt was similar in both groups (18% vs. 17%). After surgery, these values changed to 30% and 77% respectively. This was statistically significant (p<0.001). The Knee Society Knee and Function Score improved significantly in both groups, however the improvement in the function score was significantly greater in the first group (p=0.001). The improvement in Knee Society Knee Score (50.24 and 48.08; p= 0.18) and post-operative HSS Score (93 vs. 91; p=0.19) were not statistically significant. Our findings suggest that despite using the same operative technique, patellar tracking was significantly different between the two groups, a finding most likely attributable to the design of the femoral component. Whether the difference in patellar maltracking will affect long-term survival of the patellar component remains to be seen

With the success of the medial parapatellar approach (MPA) to total knee arthroplasty (TKA), current research is aimed at reducing iatrogenic microneurovascular and soft tissues damage to the knee. In an effort to avoid disruption to the medial structures of the knee, we propose a novel quadriceps-sparing, subvastus lateralis approach (SLA) to TKA. The aim of the present study is to compare if a SLA can provide adequate exposure of the internal compartment of the knee while reducing soft tissue damage, compared to the MPA. Less disruption of these tissues could translate to better patient outcomes, such as reduced post-operative pain, increased range of motion, reduced instances of patellar maltracking or necrosis, and a shorter recovery time. To determine if adequate exposure could be achieved, the length of the skin incision and perimeter of surgical exposure was compared amongst 22 paired fresh-frozen cadaveric lower limbs (five females/six males) which underwent TKA using the SLA or MPA approach. Additionally, subjective observations which included the percent of visibility of the femoral condyles and tibial plateau, as well as the patellar tracking, were noted in order to qualify adequate exposure. All procedures were conducted by the same surgeon. Subsequently, to determine the extent of soft tissue damage associated with the approaches, an observational assessment of the dynamic and static structures of the knee was performed, in addition to an examination of the microneurovascular structures involved. Dynamic and static structures were assessed by measuring the extent of muscular and ligamentus damage during gross dissection of the internal compartment of the knee. Microneurovascular involvement was evaluated through a microscopic histological examination of the tissue harvested adjacent to the capsular incision. Comparison of the mean exposure perimeter and length of incision was not significantly different between the SLA and the MPA (p>0.05). In fact, on average, the SLA facilitated a 5 mm larger exposure perimeter to the internal compartment, with an 8 mm smaller incision, compared to the MPA, additional investigation is required to assert the clinical implications of these findings. Preliminary analysis of the total visibility of the femoral condyles were comparable between the SLA and MPA, though the tibial plateau visibility appears slightly reduced in the SLA. Analyses of differences in soft tissue damage are in progress. Adequate exposure to the internal compartment of the knee can be achieved using an incision of similar length when the SLA to TKA is performed, compared to the standard MPA. Future studies should evaluate the versatility of the SLA through an examination of specimens with a known degree of knee deformity (valgus or varus)

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

Introduction. Post-operative clinical outcomes of TKA are dependent on a multitude of surgical and patient-specific factors. Malrotation of the femoral and/or tibial component is associated with pain, accelerated wear of the tibial insert, joint instability, and unfavorable patellar tracking and dislocation. Using the transepicondylar axis to guide implantation of the femoral component is considered to be an accurate anatomical reference and is widely used. However, no gold standard currently exists with respect to ensuring optimal rotation of the tibial tray. Literature has suggested that implantation methods, which reference the tibial tubercle, reduce positioning outliers with more consistency than other anatomical landmarks. Therefore, the purpose of this evaluation is to use data collected from intraoperative sensors to assess the true rotational accuracy of using the mid-medial third of the tibial tubercle in 98 TKAs. Methods. The data for this evaluation was retrieved from 98 consecutive patients who underwent primary TKA from the same highly experienced surgeon. Femoral component rotation was verified in every case via the use of the Whiteside line, referencing the transepicondylar axis, and confirming appropriate patellar tracking. Tibial tray rotation was initially established by location of the mid-medial third of the tibial tubercle. Rotational adjustments of the tibial tray were evaluated in real-time, as the surgeon corrected any tibiofemoral incongruency and tray malpositioning. The initial and final angles of tibial tray rotation were captured with intraoperative video feed, and recorded. A z-test of differences between pre- and post-rotational correction was performed to assess the statistical significance of malrotation present in this cohort. Results. All patients in this study received a primary TKA, using the mid-medial third of the tibial tubercle to dictate tibial tray rotation. After the sensor-equipped tibial insert was implanted, it was shown that 63.1% of patients exhibited unfavorable rotation. Of those patients, 70% were shown to have internal rotation; 30% were shown to have external rotation. The average malrotation of the tibial tray deviated from a neutral position by 6.3° ± 4.3°, ranging from 0.5° to 19.2°. The z-test of differences yielded a p-value <0.0001, indicating that the proportion of malrotation was statistically significant. The 95% confidence interval of this cohort was calculated to be between 44.8% and 71.8% of malrotation. Discussion. Malrotation in TKA isassociated with poor clinical outcomes. While no gold standard anatomic landmark currently exists for positioning the tibial tray, the mid-medial third of the tibial tubercle is widely used as a reference. However, the data from this evaluation demonstrates that, not only is this landmark insufficient for establishing optimal rotation (p < 0.0001), but that it had guided the surgeon to an average of 6.3° outside of the optimized implant congruency zone. The large confidence interval indicates that the rotational alignment of the tibial tray—based on the location of the mid-medial third of the tibial tubercle—is not only inaccurate, but also highly variable. Based on this intraoperative sensor data, we suggest that care should be taken when utilizing the tibial tubercle as the sole rotational landmark for the tibial tray

Introduction. Despite improvement in implants and surgical techniques up to 20% of Total Knee Arthroplasty TKA patients continue to report dissatisfaction. The ATTUNE Knee System was designed to provide better patellar tracking and stability through the mid-range of flexion and therefore improve patient outcomes and satisfaction. Aims. The aims of this study were to assess patient outcomes in a consecutive series of ATTUNE TKA and ensure early results were comparable to other TKA systems in Australia. Methods. Between September 2014 and December 2015, 332 ATTUNE TKR's were implanted locally. All patients in our learning curve from case 1 were included. Mean follow-up was 2.6 years (range: 2.0–3.2). Revision, complications and postoperative ROM was collected. Patient reported outcome was measured using the Multi-Attribute Arthritis Prioritization Tool (MAPT) questionnaire. Revision rates were cross checked with an AOANJRR Ad Hoc report. Results. Revision rate of the ATTUNE TKR was lower than national rates, however not statistically different (1.6% vs. 2.1%) (p=0.508). Postoperative MAPT scores were significantly lower after TKR (median 63.4 vs. 0.0) (p<0.001). A total of 86.7% patients had a good outcome postoperative TKR (MAPT≤ 20). Conclusion. Our findings suggest the ATTUNE TKR has comparable revision rates to other TKRs currently available in Australia. Furthermore, patient reported outcome was high 2.8 years postoperatively, with 85% patient satisfaction

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

INTRODUCTION. In computer-aided total knee arthroplasty (TKA), surgical navigation systems (SNS) allow accurate tibio-femoral joint (TFJ) prosthesis implantation only. Unfortunately, TKA alters also normal patello-femoral joint (PFJ) functioning. Particularly, without patellar resurfacing, PFJ kinematics is influenced by TFJ implantation; with resurfacing, this is further affected by patellar implantation. Patellar resurfacing is performed only by visual inspections and a simple calliper, i.e. without computer assistance. Patellar resurfacing and motion via patient-specific bone morphology had been assessed successfully in-vitro and in-vivo in pilot studies aimed at including these evaluations in traditional navigated TKA. The aim of this study was to report the current experiences in-vivo in two patient cohorts during TKA with patellar resurfacing. MATERIALS AND METHODS. Twenty patients with knee gonarthrosis were divided in two cohorts of ten subjects each and implanted with as many fixed-bearing posterior-stabilised prostheses (NRG® and Triathlon®, Stryker®-Orthopaedics, Mahwah, NJ-USA) with patellar resurfacing. Fifteen patients were implanted; five patients of the Triathlon cohort are awaiting hospital admission. TKAs were performed using two SNS (Stryker®-Leibinger, Freiburg-Germany). In addition to the traditional knee SNS (KSNS), the novel procedure implies the use of the patellar SNS (PSNS) equipped with a specially-designed patellar tracker. Standard navigated procedures for intact TFJ survey were performed using KSNS. These were performed also with PSNS together intact PFJ survey. Standard navigated procedures for TFJ implantation were performed using KSNS. During patellar resurfacing, the patellar cutting jig was fixed at the desired position with a plane probe into the saw-blade slot; PSNS captured tracker data to calculate bone cut level/orientation. After sawing, resection accuracy was assessed using a plane probe. TFJ/PFJ kinematics were captured with all three trial components in place for possible adjustments, and after final component cementing. A calliper and pre/post-TKA X-rays were used to check for patellar thickness/alignment. RESULTS. This protocol was performed successfully in TKAs, resulting in 30 min longer TKA. Final lower limb misalignment was within 0.5°, resurfaced patella was 0.4±1.2 mm thinner than the native, and patellar cut was 0.4°±4.1° laterally tilted. Final PFJ kinematics was taken within the reference normality in both series. PFJ flexion, tilt and medio-lateral shift range were 66.9°±8.5° (minimum÷maximum, 15.6°÷82.5°), 8.0°±3.1° (−5.3°÷2.8°), and 5.3±2.0 mm (−5.5÷0.2 mm), respectively. Significant (p<0.005) correlations were found between the internal/external rotation of the femoral component and PFJ tilt (R. 2. =0.41), and between the mechanical axis on the sagittal plane and PFJ flexion (R. 2. =0.44) and antero-posterior shift (R. 2. =0.45). Patellar implantation parameters were confirmed by X-ray inspections. Discrepancies in thickness up to 5 mm were observed between SNS- and calliper-based measurements. CONCLUSIONS. These results support relevance/efficacy of patellar tracking in in-vivo navigated TKA and may contribute to a more comprehensive assessment of the original whole knee, i.e. including also PFJ. Patellar preparation would be supported for suitable component positioning in case of resurfacing, but, conceptually, also in not-resurfacing if SNS does not reveal PFJ abnormalities., Using this procedure in the future, TFJ/PFJ abnormalities can be corrected intra-operatively by more cautious bone cut preparation and prosthetic positioning on the femur, tibia and patella