Today the use of pneumatic tourniquet is commonly accepted in total knee arthroplasty (TKA) to reduce perioperative blood loss. There are a few prospective randomised and nonrandomised studies that compare the effect of tourniquet release timing in cementless or cemented unilateral TKA. However, many of these studies show an inadequate reporting and methodology. This randomized prospective study was designed to investigate the efficiency of tourniquet release timing in preventing perioperative blood loss in a simultaneous bilateral TKA study design. To our knowledge, this is the first study of its kind, in which the effect of tourniquet release timing on perioperative blood loss was investigated in simultaneous bilateral cemented TKA.

In 20 patients (40 knees) one knee was operated with tourniquet release and hemostasis before wound closure, and the other knee with tourniquet release after wound closure and pressure dressing. To determine the order of tourniquet release technique for simultaneous bilateral TKA, patients were randomized in two groups: ‘Group A’ first knee with tourniquet release and hemostasis before wound closure, and ‘Group B’ second knee with tourniquet release and hemostasis before wound closure. The blood loss was recorded 48 hours postoperative for each technique.

We found no significant difference in total blood loss between both techniques (p =.930), but a significant difference in operating time (p =.035). There were no postoperative complications at a follow-up of 6 month. Other studies report an increase the blood loss in early tourniquet release and an increase the risk of early postoperative complications in deflation of tourniquet after wound closure. In this study we found no significant difference in perioperative blood loss and no increase of postoperative complications. Therefore, we recommend a tourniquet release after wound closure to reduce the duration of TKA procedure and to avoid possible risks of extended anaesthesia.

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: Besides other techniques to reduce blood loss, the use of pneumatic tourniquet is commonly accepted in total knee arthroplasty (TKA). Furthermore it is used to maintain a clean and dry operative field to improve visualization, to use a better cementing technique, and to reduce operating time. The time of tourniquet release is discussed controversially in literature. However, there are only a few prospective randomised studies that compared the effect of timing of tourniquet release in cementless or cemented TKA. To our knowledge, this is the first study that investigated the influence of tourniquet release on blood loss in a randomized prospective study in simultaneous bilateral cemented TKA.

Methods: 20 patients (40 knees) underwent simultaneous bilateral cemented TKA with the cemented Triathlon Knee System (Stryker) between February and May 2006. The mean age of the patients was 67 years (67+/−11 years). 7 males and 13 females were treated with TKA (mean tourniquet pressure: 282.5+/−33.5 mm Hg). In 20 patients one knee was operated with tourniquet release and hemostasis before wound closure (“Technique A”), and the other knee with tourniquet release after wound closure and pressure dressing (“Technique B”). To determine the order of tourniquet release technique in simultaneous bilateral TKA, the patients were randomized in two groups: “Group A” (20 knees) first knee with tourniquet release and hemostasis before wound closure, and “Group B” (20 knees) second knee with tourniquet release and hemostasis before wound closure. The patients were given low molecular weight heparin and a leg dressing to prevent deep vein thrombosis. The blood loss was monitored two days after surgery till removal of the wound drains.

Results: We found no significant difference in total blood loss between “Technique A” (753+/−390 ml) and “Technique B” (760+/−343 ml) (p=.930). Furthermore there was no significant difference in total blood loss between both techniques after randomizing in “Group A” (“Technique A” 653+/−398 ml; “Technique B” 686+/−267 ml; p=.751) and “Group B” (“Technique A” 854+/−374 ml; “Technique B” 834+/−406 ml; p=.861). However, the operating time showed a significant difference between “Technique A” (58+/−18 minutes) and “Technique B” (51+/−17 minutes) (p=.035).

Discussion: In this study we compared the effect of timing of tourniquet release on perioperative blood loss in a randomized prospective study in simultaneous bilateral cemented TKA. Our results showed no significant difference of blood loss but a significant difference of operation time. Therefore, we recommend a tourniquet release after wound closure to reduce operating time and to minimize the risk of peri- and postoperative complications at approximately similarly blood loss between both techniques.

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.

Purpose: The study was designed to evaluate the biomechanical and neurohistological properties of the infrapatellar fat especially concerning its potential role in the anterior knee pain syndrome.

Methods: Isokinetic knee extension from 120 of flexion to full extension was simulated on 10 human knee cadaver specimens (6 male, 4 female, average age at death 44 years). Joint kinematics was evaluated by ultrasound sensors (CMS 100TM, Zebris, Isny, Germany), and retro-patellar contact pressure was measured using a thin-film resistive ink pressure system (K-ScanTM 4000, Tekscan, Boston). The infrapatellar tissue pressure was analyzed using a closed sensor cell. The patellar contact pressure was measured before and after resection of the infrapatellar fat pad. The distribution of nerve fibres in the infrapatellar fat pad was assed immunohistologically in a second part of the study.

Results: Infrapatellar tissue pressure significantly increased during knee extension < 20 and flexion > 100 ranging from 343 (223) mbar at O- to 60 (64) mbar at 60 of flexion. Total resection of the infrapatellar fat pad resulted in a significant decrease in tibial external rotation of 3° in full knee extension (p=0.011), combined with a significant medial translation of the patella between 29 and 69° knee flexion (p=0.017 to 0.028). Retropatellar contact pressure was significantly (p< 0.05) reduced at all flexion angles, at 120° knee flexion more than in full knee extension. Studying all the detectable nerves present in 50 fields (x200 objective) we found an average of 6.4 substance-P- (25%) of a total of 24.7 nerve fibres in the infrapatellar fat pad. There was a significantly (p< 0.01) higher number of substance-P-fibers (24.4 (28%) of 105.7) in the superficial synovial tissue. The number of S-100-fibers was significantly (p< 0.05) higher in the central and lateral part of the fat pad.

Conclusions: Based on these results, we conclude that resection of the infrapatellar fat pad could potentially reduce clinical symptoms in the anterior knee pain syndrome, and that, contrary to commonly believed, the infrapatellar fat pad may have a biomechanical function and play a role in the anterior knee pain syndrome.