To avoid the early onset of osteoarthritis after partial meniscectomy an effective replacement of injured meniscal tissue would be desirable. The present study investigates the behaviour of a new silk derived scaffold supplied by Orthox Ltd. (Abingdon, UK) in an in vivo sheep model. The scaffolds where derived from silk fibres by processing into an open porous matrix. Nine sheep (4 ± 1 years) underwent partial meniscectomy at the anterior horn of the medial meniscus followed by implantation of a scaffold. The unoperated contralateral stifle joint served as control. After six months the animals were sacrificed and the joints inspected for inflammation. The Young's modulus of the tibial cartilage, meniscus and scaffold was determined by indentation or confined compression tests. All tissues were fixed in formaldehyde for histology. The data were analysed by a Wilcoxon and Mann-Whitney-U-test.INTRODUCTION:
METHODS:
The human body is a complex and continually adapting organism. It is theorised that the morphology of the proximal femur is closely related to that of the distal femur. Patients that have abnormal anatomy in the proximal femur, such as a high femoral neck anteversion angle, may have abnormal anatomy in the distal femur to overcome proximal differences. This phenomenon is of key interest when performing Total Hip Replacement (THR) or Total Knee Replacement (TKR) surgery. The current design and placement of existing hip and knee implants does not account for any correlation between the anatomical parameters of the proximal and distal femur, where bone anatomy may have adapted to compromise for abnormalities. A preliminary study of 21 patients has been carried out to assess the relationship between the proximal and distal femur. The difficulties in defining and measuring key anatomical parameters on the femur have been widely discussed in the literature [1] due to its complex three dimensional geometry. Using CT scans of healthy octogenarians, it was possible to mark key anatomical landmarks which could be used to define various anatomical axes throughout the femur. Correlation analyses could then be carried out on these parameters to assess the relationship between proximal and distal femur morphology. Each femur was initially realigned along the mechanical axis (MA); defined by joining the centre of the femoral head (FHC) to the centre of the intercondylar notch (INC) [2]. All anatomical landmarks were then identified using the Materialise Mimics v12 software (Figure 1 and 2) and exported into Microsoft Excel for analysis. Key anatomical parameters which were derived from these landmarks included the femoral neck axis (FNA), femoral neck anteversion angle (FNAA) [1–4], condylar twist angle, clinical transepicondylar axis (TEA), trochlea sulcus angle and medial and lateral trochlea twist. A correlation analysis was carried out on SPSS Statistics v20 (IBM) to assess the relationship between proximal and distal anatomical parameters.Introduction
Methods
One common surgical treatment of even early OA is the implantation of a Total Joint Arthroplasty. In case of younger patients this procedure is questionable. The present study investigates the behaviour of a new silk derived scaffold supplied by Orthox Ltd. (Abingdon, UK) in an in vivo sheep model. This scaffold allows replacing the damaged areas with a resurfacing technique and will avoid the implantation of a total joint in cases of early OA. The scaffolds where derived from silk fibres by processing into a composite of an open porous matrix in combination with a fibres mash with the same material and covered with a smooth surface. During the process the fluid silk can be casted in any shape. Eight sheep (4 ± 1 years) underwent a surgery where a large defect (2×1 cm) was created in the weight bearing zone of the medial condylus followed by implantation of a scaffold. The unoperated contra lateral stifle joint served as control. After six months the animals were sacrificed and the joints inspected for inflammation. The Young's modulus of the cartilage and scaffold was determined by indentation or confined compression tests. All tissues were fixed in formaldehyde for histology. The data were analysed by a Wilcoxon and Mann-Whitney-U-test. The roughness of the smooth surface was measured. Synovial fluid was harvested by punction before opening the joint and analysed for particle wear debris and for any signs of inflammation.INTRODUCTION:
METHODS:
Our aim was to determine the effects of tibial component malrotation and posterior slope on knee kinematics following Scorpio cruciate retaining total knee replacement in cadaver specimens. The movements of the hip, thigh and lower leg were monitored in 3D using a validated infra-red Computer Navigation System via bone implanted trackers. Ten normal comparable cadaver specimens were mounted in a custom rig allowing 3D assessment of kinematics under various loading conditions. The specimens then underwent Navigated TKR as per normal operating surgical protocols however an augmented tibial component was implanted. This allowed the researchers to precisely modify the rotation of the tibial component around its predetermined central axis, as well as to alter the posterior slope of the component. A pneumatic cylinder was used to provide a simulated quadriceps extension force while the knee was tested with a variety of applied loads including anterior and posterior draw, abduction and adduction, internal and external rotation. TKR kinematics are significantly different from those of the native knee (p<
0.05). Increasing tibial posterior slope resulted in an incremental posterior position of the femur (p<
0.05), deviation of the neutral path of motion (p<
0.05) and alteration of the normal AP envelope of laxity (p<
0.05). Tibial component malrotations over 10 degrees resulted in increasing deviations of the neutral movement path of motion (p<
0.05) without significantly affecting the envelope of laxity. Tibial component malrotations of more than 10 degrees, when combined with a posterior slope of six degrees or more, resulted in prosthetic subluxation under certain loading conditions. This study has demonstrated significant differences in knee kinematics before and after total knee implantation. Increasing values of internal and external rotation, as well as posterior slope of the tibial tray resulted in further deviations of total knee kinematics from normal by altering the neutral path of motion and the soft tissue envelope, with combined misalignments resulting in the greatest deviations from normal with prosthetic subluxation in some cases. Deviations from normal kinematics may result in increased ligament tension and incongruence or dysfunction of the component articulations, with the generation of sheer forces in the gait cycle. These may contribute to premature wear and loosening. Surgeons should be aware of this when considering the addition of posterior slope or assessing tibial component positioning in TKR.
Kinematics were different after TKR. Increasing posterior slope resulted in increasing posterior position of the femur, particularly at maximum flexion. Posterior slope also resulted in a deviation of the neutral path of motion and alteration of the normal envelope of laxity. Tibial component malrotations over 5 degrees resulted in deviations of the neutral path of motion without affecting the envelope of laxity. Combined malrotations over 10 degrees with posterior slopes over 6 degrees resulting in prosthetic subluxation under certain loading conditions.
This study investigated the difference in proximal tibial cortical strain distribution using a fixed or mobile bearing design for TKA. Eight fresh frozen human cadaver tibias were used. The strain magnitude and distribution on the anterior cortex of the proximal tibia during axial and rotational loading of the knee were measured with a quantitative full-field strain measurement technique (Electronic Speckle Pattern Interferometry). First, strain distributions of the intact knee were acquired. Subsequently, strain distributions after implantation of conventional and mobile bearing PCL retaining total knee implants (Scorpio®) were measured Under each loading condition, the minimum principal strain was greater in magnitude as compared to the maximum principal strain. Under 1,500 N axial loading, the resulting minimum principal strain magnitude and orientation was nearly identical between the mobile bearing configuration(500 ± 287m;e;), and the fixed bearing configuration (500 ± 286m;e;). In response to 10° internal rotation, this strain increased to 782 ± 371m;e; and 1000± 389m;e; for the mobile and fixed tibial component, respectively. In 10° external rotation, minimal principal strain decreased to 421 ± 233m;e; for the mobile bearing, but increased to 632 ± 293m;e; for the fixed bearing. These differences between mobile and fixed bearing scenarios were highly statistically significant. For this in-vitro study under exact controlled loading conditions the mobile bearing design induced less strain in the proximal tibia than the fixed bearing tibial component. The difference in strain levels may be of importance for bone remodeling and osseointegration.
Menisci contribute to load distribution, damping and stabilization of the knee. Meniscal tears are a common injury in the young and active population during combined axial loading and twisting of the knee. The in situ effect of combined axial loading and knee rotation on hoop strain in the medial meniscus of human cadaveric specimens was examined. Four fresh-frozen human cadaver knees were rigidly potted in base fixtures. Muscle tissue was removed, and the joint capsule and ligamentous structures were preserved. Through two arthrotomies, strain sensors (DVRTs) were placed in the peripheral border into the mid-substance of the medial meniscus. These DVRTs captured circumferential hoop strains e;AM, e;PM in the anteromedial and posteromedial medial meniscus. Each specimen was mounted in a knee loading simulator, driven by a biaxialmaterial test system and were axial loaded with 1,4 kN. While maintaining axial load, ± 10° tibial rotation (IR, ER) was subsequently applied at 1°/s. Tests were conducted for knees flexion between 10° and 60° in 10° intervals. Strain reports e;AM and e;PM were highly similar for any given test. Therefore, they were averaged to express meniscal hoopstrain as e;AVG. At 30° flexion, 1.4 kN axial load yielded e;AVG =0.9%±0.4%. ER resulted in a significant strain increase (2.1%±0.8%) (p=0.003). IR caused a decrease (0.2%±0.7). At 60° knee flexion, 10° ER induced significantly less strain (1.3%±0.9%) as compared to the 10° flexed knee(2.8%±1.3). For knee flexion from 10° to 50°, combined ER and axial loading-caused significantly higher strain as compared to axial loading alone. This study documents for the first time strain in the medial meniscus under combined axial and torsional loading. The finding that meniscal strain can increase over two-fold during 10°external rotation has implications for injury biomechanics and meniscal repair strategies.
Kinematic evaluation of the knee after total joint arthroplasty plays an important role to analyze and understand the post operative outcome of the surgical procedure. The objective of the study was to quantify in vivo kinematics of two different knee designs (dual radius, single radius) by combining video fluoroscopy and helical axis of motion analysis. 3D position of the finite helical axis (FHA) of the displacement of the tibial component of the prosthesis relative the femoral component during a knee extension from 55° to 20° flexion underweight bearing conditions was computed. The motion data were extracted from in vivo fluoroscopy measurement. Angular deviations as angles between each FHA and the mediolateral axis of the femoral component of the prosthesis, and the localization deviation as the distance between each FHA and the center of the femoral component of the prosthesis were calculated. The median and the interquartile range (IQR) of the angular deviation and the localization deviation were computed. Non-parametric Wilcoxon test compared the values of the two designs. The angular and localization deviations of the dual radius design were bigger than of the single radius design. Median localization deviation, IQR Angle deviation, IQR localization deviation showed highly significant differences between the two designs (p<
0.01). Compared to the dual radius design the single radius design modified the knee kinematics in vivo. Since it is asingle axis design FHA is therefore concentrated near this unique single axis. On the contrary the dual radius design has two axes, and the FHA floated between these two axes.
Although total knee replacement (TKR) has good long term reliability, some patients remain unhappy; this may relate to abnormal motion causing pain or instability. This study measured the effect of TKR femoral component internal-external rotation position upon knee kinematics. The kinematics of eight fresh-frozen cadaveric legs were measured, with a range of loading and states of preparation. The stages of preparation included intact; TKR in standard navigated position aligned to mechanical and epicondylar axes, TKR with three and six degree internal and then external rotation of femoral component. The loads applied were 70N anterior and posterior draw; Five Nm internal and external rotation; Five Nm valgus and varus. All these were applied in every state of preparation with the knee moved passively in 0–120deg flexion-extension, then repeated with the quadriceps tensed to 400N by a pneumatic cylinder and cable. The TKR used was a Stryker Scorpio posterior cruciate retaining. The implant positions and tibio-femoral kinematics were measured continuously using a modified software Stryker knee navigation system, leading to ′envelopes of laxity′ for each degree of freedom across the range of flexion-extension. In order to vary the implant rotation, the ‘standard’ TKR was removed and then remounted on an adjustable intra-medullary rod-intube mechanism that was also linked to the navigation system. Adjustments in 6 degrees of freedom allowed the datum position to be regained within 1mm and 1deg, using a custom software module and a sensor located on the implant. Internal rotation of the femoral component caused increasing tibial valgus with knee flexion, with the increase in valgus at 90deg matching the changed rotation. Similarly, external component rotation caused matching tibial varus with knee flexion. Varus and valgus laxities were not altered significantly from those in the datum condition by femoral component internal rotation, across the whole range of flexion. However, external rotation caused increased valgus laxity in flexion. Tibial rotational effects were complex. In the extended knee, femoral component rotation caused a matching tibial rotation. Thus, an externally rotated femoral implant magnified tibial external rotation (the screw-home) with terminal knee extension. The tibial internal rotation with knee flexion was then increased above normal, so that the tibia was internally rotated at 90deg flexion. Internal rotation of the component caused increased internal rotation laxity and decreased external rotation laxity; the opposite occurred after femoral component external rotation. Changes in femoral component position had complex effects on the movement and posture of the tibia across the range of knee flexion. Some have easily-understood consequences, such as component internal rotation caused tibial valgus in flexion, thus increasing the lateral force vector acting on the patella. The changes in rotational laxity patterns are related to the differing structures of the medial and lateral collateral ligament complexes, the lateral collateral ligament allowing greater freedom of movement in response to the altered height of the ligament attachment above the joint line at that side of the knee, whereas the medial collateral ligament maintained greater control of rotational laxity. These effects explain loss of stability in flexion and the tendency of the knee to pivot about a medial axis.
Successful total knee arthroplasty (TKA) is dependent on the correct alignment of implanted prostheses. Major clinical problems can be related to poor femoral component positioning, including sagittal plane and rotational malalignment. A prospective randomized study was designed to test whether an optical navigation system for TKA achieved greater implantation precision than a non navigated technique. The primary variable was rotation of the femoral component in the transverse plane measured from post operative radiographs and CT images. Sixty-four patients were included in the study. All patients received the Duracon total knee prosthesis. The patients were randomly divided into two groups; Group C patients underwent conventional TKR without navigation, Group N patients underwent TKR using a computer assisted Knee Navigation System. Analysis revealed that patients in Group N had significantly better rotational alignment and flexion angle of the femoral component than patients in Group C. In addition, superior post operative alignment of the mechanical axis, posterior tibial slope, and rotational alignment was achieved for patients in Group N. The use of a navigation system provides improved alignment accuracy. Specifically, it can help to avoid femoral malrotation and errors in axial alignment.
