Understanding the cause of failure of total knee arthroplasties (TKA) is essential in guiding clinical decision making and adjusting treatment concepts for revision surgery. The purpose of the study was to determine current mechanisms of failure of TKA and to describe changes and trends in revision surgery over the last 10 years.

A retrospective review was done on all patients who had revision total knee arthroplasty during a 10-year period (2000–2009) at one institution. The preoperative evaluation in conjunction with the intraoperative findings was used to determine causes of failure. All procedures were categorizes as Sharkey et al. described previously. The data was analyzed regarding the cause of failure and displaying the incidence and trends over the last 10 years.

1225 surgeries were done in the time period with a steady increase of procedures per year (34 procedures in 2000 to 196 in 2009). The most common cause of revision TKA was aseptic failure in 65% and septic failure in 31% of the reviewed cases. However, we could observe a steady proportional increase of the septic classified revisions over the time. Both categories could be subdivided to specific causes of failure including aseptic loosening (24%), anterior knee pain (20%), instability (6,4%), arthrofibrosis (4,9%), PE wear (3,6%), malpositioning/malrotation (2,7%) periprosthetic fracture (2,0%) and other (4,6%), or in early (12,9%), late (15,4%) or low-grade infection (3,3%), respectively. Complementary to the classification Sharkey et al. described in 2002 we identified new subcategories of failure: malrotation (since 2003), Low-Grade-Infection (since 2006), allergic failure/loosening (since 2006), Mid-Flexion-Instability (since 2007), soft tissue impingement (since 2009). The incidence of the classic aseptic loosening due to PE wear shows a clear decrease in the last 10 years whereas we could observe an increase of the new diagnosis of instability, malrotation or low-grade-infection as determined cause of failure.

The detailed analysis of the failure mechanism in total knee arthroplasty is important to understand the clinical problem and to adjust treatment strategies. We were able to complement present classifications and give a first overview on the incidence for specific causes of failure. Our data shows changes in the indication for surgery over the time and compared to the collective of Sharkey et al. from 1997–2000. This might be due to new diagnostic methods and better implant materials as well as to a generally increased awareness of the specific mechanism of TKA failure.

Objectives: The aim of this study was to examine the influence of different prosthesis designs (Deep-Dish (DD) vs. posterior stabilized (PS)) on the patello-femoral pressure. The femoro-patellar pressure depends among other things on the AP stability of the knee joint. The use of DD has been described to be equally applicable with a resected or deficient PCL.

Methods: Fresh frozen human knee specimens (n = 8, 7 male, 1 female) underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. Knee motion was driven by a hydraulic cylinder applying sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The amount of patellofemoral contact pressure and its distribution was measured by means of a pressure sensitive film (Tekscan^®, Inc., Boston, USA). Patellar contact pressure was examined first after implantation of a cruciate retaining TKA (Genesis II, Smith& Nephew, Memphis, USA). An 11 mm polyethylene (PE) DD insert was tested before and after resection of the PCL. Finally, the femoral component of the CR TKA was removed and replaced by a posterior stabilized (PS) model repeating measurements with an 11 mm PE inlay. The patella was not resurfaced throughout the whole procedure. A paired sampled t-test was applied for comparison of means and considered significant at p ≤ 0.05.

Results: There was no statistical significant difference of patello-femoral peak and mean contact pressures of the DD inlay before and after resection of the PCL. After implantation of the PS TKA peak pressure was significantly lower (Mean: 6.12 ± 2.37 MPa, Range: 10.68 – 3.30 MPa) in comparison with the DD type (7.12 ± 2.53 MPa, 11.94 – 3.55 MPa; p < 0.01) with a preserved PCL. Also the mean contact pressure turned out to be lower with the PS design (p < 0.006; PS: 3.58 ± 1.25 MPa, 5.91 – 2.08 MPa, DD: 4.27 ± 1.34 MPa, 6.66 – 2.18 MPa). The contact area was also significantly smaller with the PS design (p < 0.03, PS: 140.84 ± 40.04 mm2, 188.47 – 65.10 sq mm, DD: 175.97 ± 24.46 sq mm, 222.56 – 142.56 sq mm).

After resection of the PCL differences in contact pressures and contact area between DD and PS failed to reach statistical significance although there was an obvious tendency towards lower pressures with the PS-design.

Conclusions: The results of this study suggest that a posterior stabilized TKA design reduces the retropatellar peak and mean pressure as well as the contact area in comparison with a deep-dish design when the PCL is preserved. The better reproducible rollback with a PS model could serve as a possible explanation. However, this difference is less pronounced when a DD inlay is applied after resection of the PCL. Nevertheless, a PS rather than a DD design is recommended in the PCL deficient knee.

Objective: Decreased quadriceps strength may contribute to anterior knee pain after total knee arthroplasty (TKA). The quadriceps force necessary to establish full extension is strongly dependent on the position and the relative length of the lever arms over the knee joint. The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL).

Methods: Eight fresh frozen human knee specimens were tested in a kinematic device that simulated an isokinetic knee extension cycle from 120° of flexion to full extension. Knee motion was driven by a hydraulic cylinder applying sufficient force to the quadriceps tendon to produce an extension moment of 31 Nm. The quadriceps force was measured using a load cell attached to the quadriceps tendon after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith& Nephew, Memphis, Tn, USA) applying a conventional and a highly conforming polyethylene (PE) inlay before and after resection of the PCL. Finally, the femoral component of the CR TKA was replaced by a posterior stabilized (PS) design and measurements were redone.

Results: No significant differences in the average quadriceps force were detected between the different PCL retaining inlays (CR, highly conforming) as long as the PCL was intact. However, after resection of the PCL, the required quadriceps force increased significantly for both designs (CR: 4.7%, p < 0.01, Highly conforming: 3.5%, p < 0.03). After implantation of the PS femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR (−6.0%, p < 0.01) or highly conforming (−5.1%, p < 0.01) inlay. With a PS design average quadriceps extension force was not significantly different from cruciate retaining TKA inlays at an intact PCL.

Conclusions: The data of this in vitro study suggest that the quadriceps extension force is significantly higher for knees after cruciate retaining TKA with PCL deficiency, independent of the use of a CR or DD inlay. Thus, the integrity of the PCL should be secured in clinical practice when using a cruciate preserving TKA design.

INTRODUCTION: The techniques to stabilize the patella can be divided into two groups: the first group seeks to change the direction of the extensor mechanism in order to medialize the extending force vector of the quadriceps muscle, e.g. by a distal medialization of the tibial tuberosity or a proximal realignment; the second seeks to reconstruct the medial patellofemoral ligament (MPFL). The goal of this study was therefore to measure changes in patellofemoral kinematics in the intact, MPFL deficient knee, after medial transfer of the tibial tuberosity, after proximal realignment as well as after reconstruction of the MPFL.

METHODS: Eight fresh frozen right knee specimens were mounted in a knee simulator in which isokinetic flexion-extension motions were simulated. Extension cycles were simulated from 120° flexion to full knee extension with an extension moment of 31 Nm. Movement of the patella relative to the femur was measured using an ultrasound based 3D motion analysis system (Zebris, Isny, Germany). During the first test cycles, patellar movement under intact knee conditions were measured, while a constant 100 N laterally oriented force was applied by means of a steel cable attached to the patella. Subsequently, patellar movement was again measured after: transecting the MPL (deficient knee), performing a medialization of the tibial tuberosity, after reconstruction of the transected MPL using a semitendinosus autograft and after proximal realignment.

RESULTS: The patella of the intact knee moved along a medial path with a maximum attained position of 8.8 mm at 25° of knee flexion. The patella of the deficient knee moved up to 4.6 mm (p=0.04) in the medial direction at maximal extension at 30° of knee flexion. After medial transfer of the tibial tuberosity patellar movement reached a maximum medial position of 12.8 mm (p=0.04) at 22° of knee flexion with the laterally oriented force. With a reconstructed MPL, the patella attained a maximum medial position 14.8 mm (p=0.04) at 24.0° of knee flexion. Following proximal realignment, the patella moved on a medial, but significant (p=0.03) different path up to 13.8 mm medially at 30° of knee flexion. In addition, following medialization of the tibial tuberosity and proximal realignment, the center of the patella was significantly (p=0.03) more internally rotated (tilted) than the physiologic patella.

DISCUSSION: The shape of the movement curves after the stabilizating procedures resulted in a medialization relative to intact and deficient conditions. With the reconstructed medial patellofemoral ligament, the patella moved along the most medially oriented path with physiologic tilting. The results suggest that a semi-tendinous autograft can provide sufficient stabilization to prevent lateral displacement or subluxation with physiologic patellar tilt.

INTRODUCTION The ability to evaluate the alignment of total knee arthroplasty using postoperative radiographs might be confounded by limb rotation. The aim of the presented study was therefore to measure the effect of limb rotation on postoperative radiographic assessment and to introduce a mathematical correction to calculate the true axial alignment in cases of a confounded radiograph.

METHODS A synthetic lower left extremity (Sawbones®, Inc,Vashon Island, WA) was used to create a total knee arthroplasty of the Interax I.S.A.® knee prosthesis system (Stryker, Limerick, Ireland). Laser guided measurement of the tibia showed a femoral valgus angle of 6.5° postoperatively. The model was fixed in an upright stand which positioned the limb in varying degrees of rotation. Four series of 10 antero-posterior (AP) radiographs were taken with the knee in full extension, with femoral limb rotation ranging from 20° external rotation to 20° internal rotation in respect to the x-ray beam, in 5° increments. After digitizing each radiograph, four observer independently measured the femoral valgus angle for each series of the long leg radiographs using a digital measurement software (MEDICAD®, Hectec, Altfraunhofen, Germany). Each observer was instructed to determine the femoral valgus angle following the software’s guidelines. In addition each observer measured the geometrical distances of the femoral component figured on the radiographic film. Using a student t-test, the effect of femoral limb rotation on the measured femoral valgus angle and a correlation between femoral rotation and femoral valgus angle was established. Then for each limb rotation the distances ratio was determined to calculate the limb rotation.

RESULTS Without an application of femoral rotation the femoral valgus angle was measured radiographically to be 6.5° (SD 0.4°). With external femoral rotation the measured femoral valgus angle linearly decreased to a minimum of 4.5° (SD 0.2°) at 20° femoral rotation. The linear regression (R2=0.94) calculated a 0.09° change of radiographically measured femoral valgus angle per femoral rotation angle. With the femoral rotation the radiographically measured ratio decreased linearly (R2=0.98) with further internal rotation.

DISCUSSION The results of the presented study suggest a significant influence of femoral rotation during radiographic evaluation of limb alignment after total knee arthroplasty. With further external femoral rotation the radiographically apparent femoral valgus angle decreases. As the apparent femoral valgus angle changes linearly, a calculation of the distances of the particular femoral component could be used to determine the real femoral valgus angle in cases of femoral limb rotation.

Introduction: Recent knee prosthesis designs postulate to allow more flexion of the knee without increasing the contact stress on the polyethylene inlay. The study’s purpose was to compare the tibiofemoral contact stress of four different inlay types of a new “high flexion knee prosthesis system under dynamic, physiologic loading conditions in an in vitro test. Thereby, the cruciate retaining and posterior stabilizing designs were compared.

Material and Methods: The TriathlonTM system was implanted into 5 knees of fresh frozen human specimens. The prosthesis system is available with a mobile bearing (MCR) or fixed bearing inlay (FCR). In addition, the posterior stabilized design was although tested in the same manner (MPS=mobile bearing and FPS=fixed bearing inlay). After implantation, specimens were mounted for biomechanical testing in a knee simulator. The test mimicked both the speed and resulting moment exerted during a lower limb isokinetic extension test in a range of tibial motion from 120 degrees flexion to full knee extension. The quadriceps force cylinder was force-controlled provided a constant torque on the lower limb of 31 Nm whereby forces of up to 1500 N were recorded. Inlay motion was measured using an ultrasonic tracking system (CMS 100TM, Zebris GmbH; Isny, Germany). The tibiofemoral peak contact stress was measured using resistive ink, 0.1-mm-thin pressure sensors (Tekscan, Boston), measuring 572 points per compartment at 10 Hz.

Results: Average maximum peak contact stress was 18.8 (+/−6.6 MPa) at 11.5° flexion for the medial inlay (MCR) and 23 MPa (+/−11.7 MPa) at 119.5 deg for the lateral inlay (MCR). For the FCR we measured 23 MPa (+/−9,6 MPa, medial) at 67.5° and 19.7 MPa (+/−8.2 MPa, lateral) at 119.9° knee flexion. The average maximum contact stress on the MPS inlay was 19 MPa (+/− 12.6 MPa, medial) at 7.5° and 20 MPa (+/− 13.4 MPa) at 120°. For the FPS we measured 20.8 MPa (+/−13.1 MPa, medial) at 40.6° and 19 MPa (+/−11.6 MPa, lateral) at 120° knee flexion.

The maximal rotation recorded for the inlay centers was 1.6 ± 1.2 mm at 1.2° knee flexion and 4.3 ± 3.3 mm at 1.3° for the MPS design.

Discussion: This in vitro study characterizes the movement of the mobile bearing inlays of the TriathlonTM system on the tibial baseplate under simulated physiologic loading. With the dynamic ultrasonic tracking device the range of motion and internal/external rotation movement can be accurately determined. The results of this study correlated qualitatively to radiographic measurements. Contact pressures seem not to exceed the maximum contact stress of UHMWPE significantly even at high flexion angles up to 120°. The posterior stabilized design showed no significant lower maximum contact stresses than the cruciate retaining design.

Introduction: The amount of loading on the cruciate ligaments depends on the tension of the external muscular structures. In vivo studies using EMG have observed a proprioreceptive eccentric co-contraction of the hamstrings during isokinetic knee extension motion. This antagonistic co-contraction increases the quadriceps force necessary to produce the same extension moment on the knee, whereas the loading on the anterior cruciate ligament was measured to be reduced, with the loading on the posterior cruciate ligament to be increased. The objective of this study was thus to investigate the effect of simulated proprioreceptive co-contraction of the hamstrings muscles on quadriceps force, as well as on the relative loading on the cruciate ligament structures during knee extension under dynamic conditions and physiologic loads.

Methods: Five fresh frozen knee specimen were tested in isokinetic extension. Bow shaped loading transducers were fixed in the medial fibres of the anterior (ACL) and posterior cruciate ligament (PCL). The test cycle simulated an isokinetic extension cycle from 120 degrees of flexion to full extension, a hydraulic cylinder thereby applied sufficient force to the quadriceps tendon in a closed-loop control cycle to produce a constant extension moment of 31 Nm about the knee. A second hydraulic cylinder simulated a 200 N co-contraction force of the hamstrings tendons. The loading on the ACL and PCL was first measured in the absence of hamstrings force, and subsequently under constant co-contractive flexion force.

Results: In the absence of hamstring tension, the maximum quadriceps force was 1190 N ( SD 204 N) at 105 degrees of knee flexion. The loading on the ACL was reduced at larger flexion angles, the loading pattern of the PCL showed an inverse relationship with less loading at full extension. The maximum loading in the ACL was 161 N (SD138 N) and maximum tension in the PCL was 38.2 N (SD 34.9). With hamstring co-contraction, maximum quadriceps force increased 19.9 % ( SD 21.0% p= 0.33), maximum tension in the ACL decreased 71.9% (SD 74.3%, p=0.03), and maximum tension in the PCL increased 73.0% (SD 40.9%, p=0.03).

Discussion: This experimental setup enabled direct in vitro measurement of ACL and PCL loading during simulated isokinetic extension motions. The loading on the ACL was dependent on the knee flexion angle. We observed that co-contraction of the hamstrings reduces loading on the anterior cruciate ligament without a significant concomitant increasing the quadriceps muscle force. Our results support the hypothesis that antagonistic co-contraction of the hamstrings during extension of the knee provides an important protective function. In contrast, loading in the posterior cruciate ligament increased during hamstring activation at higher knee flexion angles.

Introduction High precision of axis alignement in Total Knee Arthroplasty by usage of navigation tools is a known fact. However, a common disadvantage of navigation tools is the additional time needed for calibration. Especially in time/cost-sensitive hospital environments this can lead to a neglection of navigation tools usage. In this study we address work-economics during navigation assisted total knee arthroplasty. Specifically, we introduce the concept of a well-trained navigator assistant who performs navigation related work steps during surgery while the primary surgeon concentrates on the remaining work-steps.

In a prospective study of primary TKA we compared environmental parameters of surgeries performed with and without the Navigator Concept.

Materials and Methods 60 Total Knee Arthroplasties were performed using an active navigation system (Stryker Navigation System) (40) or a conventional internal/external alignement jig for implantation of the Interax Knee endoprostheses. Half of the navigated knee arthroplasties were performed using a conventional set-up with a primary surgeon and two assistants serving the navigation system and performing the relevant surgical steps. The other half was done by surgeon teams of a primary surgeon, a navigator assistant and a second assistant. The surgical steps were broken down to a complex work-sharing system. The teams were intensively trained in their work-share by simulating an artificial TKA in a specially designed TKA-Navigation lab. During surgery, the timing of individual steps was recorded. Pre- and postoperative x-rays of the limbs were taken and digitized to an computerized axis-measurement system. Data of both groups were compared using ANOVA and Tuckey post-hoc tests.

Results Results showed a significant difference in surgery time between the three groups (p=0,01) with equivalent surgery times of the conventional and navigator concept group, while the remaining navigated group showed longer surgery times. Axis alignments were statistically not influenced, however demonstrated a tendency to higher precision in the navigator concept group.

Discussion This study is the first to address work-economics in navigated TKA. With the introduction of a specifically trained navigator assistant, a precise work-sharing plan and an intensive training lab, high precision in TKA can be achieved by navigation usage even in a highly cost-sensitive environment. The basis for success, however, is support and investment in training of team surgeons. This concept may provide the basis for other musculoskeletal surgeries demanding both high-tech for precision and time-effectiveness for cost reduction.