Oliver Kessler

Navigation improves accuracy of rotational alignment in total knee arthroplasty

Successful total knee arthroplasty 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 total knee arthroplasty achieved greater implantation precision than a nonnavigated technique. The primary variable was rotation of the femoral component in the transverse plane, measured from postoperative radiographs and computed tomography 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 had conventional total knee arthroplasty without navigation; Group N patients had total knee arthroplasty using a computer-assisted knee navigation system. Analysis showed 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 postoperative 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, and can help to avoid femoral malrotation and errors in axial alignment.

Reduced variability of acetabular cup positioning with use of an imageless navigation system.

Positioning the acetabular component is one of the most important steps in total hip arthroplasty; malpositioned components can result in dislocations, impingement, limited range of motion, and increased polyethylene wear. Conventional surgery makes use of specialized alignment guides provided by the manufacturers of the implants. The use of mechanical guides has been shown to result in large variations of cup inclination and version. We investigated acetabular cup alignment with the nonimage-based hip navigation system compared with a conventional mechanically guided procedure in 12 human cadavers. Postoperative cup position relative to the pelvic reference plane was assessed in both groups with the use of a three-dimensional digitizing arm. In the navigated group, a median inclination of 45.5° and a median anteversion of 21.9° (goals, 45° and 20°) were reached. In the control group, the median inclination was 41.8° and the median anteversion was 24.6°. The ninetieth percentile showed a much wider range for the control group (36.1°–51.8° inclination, 15°–33.5° anteversion) than for the navigated group (43.9°–48.2° inclination, 18.3°–25.4° anteversion). This cadaver study shows that computer-assisted cup positioning using a nonimage-based hip navigation system allowed for more consistent placement of the acetabular component.

Changes in knee kinematics reflect the articular geometry after arthroplasty.

We hypothesized changes in rotations and translations after TKA with a fixed-bearing anterior cruciate ligament (ACL)-sacrificing but posterior cruciate ligament (PCL)-retaining design with equal-sized, circular femoral condyles would reflect the changes of articular geometry. Using 8 cadaveric knees, we compared the kinematics of normal knees and TKA in a standardized navigated position with defined loads. The quadriceps was tensed and moments and drawer forces applied during knee flexion-extension while recording the kinematics with the navigation system. TKA caused loss of the screw-home; the flexed tibia remained at the externally rotated position of normal full knee extension with considerably increased external rotation from 63° to 11° extension. The range of internal-external rotation was shifted externally from 30° to 20° extension. There was a small tibial posterior translation from 40° to 90° flexion. The varus-valgus alignment and laxity did not change after TKA. Thus, navigated TKA provided good coronal plane alignment but still lost some aspects of physiologic motion. The loss of tibial screw-home was related to the symmetric femoral condyles, but the posterior translation in flexion was opposite the expected change after TKA with the PCL intact and the ACL excised. Thus, the data confirmed our hypothesis for rotations but not for translations. It is not known whether the standard navigated position provides the best match to physiologic kinematics.

A mobile-bearing knee prosthesis can reduce strain at the proximal tibia.

Mobile and fixed-bearing knee prostheses are likely to generate distinct strain gradients in the proximal tibia. The resulting strain distribution in the proximal tibia governs bone remodeling and affects implant integration and stability. We determined the effects of fixed and mobile-bearing total knee prostheses on strain distribution at the proximal tibia. This mobile-bearing prosthesis was evaluated in cadaveric specimens under axial and torsional loading. Strain on the proximal tibial cortex was measured with rosette strain gages and an optical full-field strain acquisition system. Tibial torsion in response to combined axial and torsional loading was documented. There was no difference in cortex strain between the fixed and the mobile-bearing prostheses under 1.5 kN axial loading. Superimposing 10° tibial internal rotation induced 22% less compressive strain in the mobile-bearing prosthesis compared with the fixed-bearing prosthes1s. Under 10° tibial external rotation, the mobile-bearing prosthesis induced 33% less compressive strain than the fixed-bearing prosthesis. Optically acquired strain fields showed peak compressive strain at the anteromedial aspect 30 mm below the joint line. The mobile-bearing prosthesis reduced torque in the proximal tibia during knee rotation by 68-73% compared with the fixed-bearing prosthesis. Our data suggest that the particular mobile-bearing prosthesis tested potentially reduces elevated strain levels in the proximal tibia.

Avoidance of medial cortical fracture in high tibial osteotomy: improved technique.

A new technique in oblique incomplete high tibial osteotomy that permits an increase of valgus correction while preventing fracture of the medial cortex was investigated. Closing wedge or opening wedge osteotomy was done on 23 tibias from cadavers before loading in an Instron testing machine. In seven specimens (Group 1), lateral oblique wedge osteotomy was done. In seven other specimens (Group 2), one medial oblique cut was made. In both groups, the osteotomy terminated 10 mm from the cortex and approximately 2 cm below the plateau. In nine specimens (Group 3), the osteotomy terminated in a 5-mm diameter hole, drilled in an anteroposterior direction, with its center positioned 10 mm from the medial cortex and 2 cm below the articular surface. The maximum angle of opening or closing before fracture of the cortex took place was recorded. In Groups 1 and 2, similar maximum correction angles were observed, 6.7° versus 6.5°, respectively. In Group 3, the stress relieving hole allowed the correction angle to be increased to 10°. An oblique high tibial valgus closing wedge osteotomy with an apical drill hole allows a significant increase of the correction angle compared with the same osteotomy without a drill hole. Medial open wedge osteotomy offers no advantage over lateral closed wedge osteotomy in the maximum obtainable correction angle without failure of the cortex.

The frontal pelvic plane provides a valid reference system for implantation of the acetabular cup: Spatial orientation of the pelvis in different positions

Background The frontal pelvic plane has traditionally served as the reference plane for implantation of the acetabular cup during total hip arthroplasty, with referencing performed with the patient supine on the operating table. During daily activities in an upright position, the frontal pelvic plane changes from a horizontal to a vertical orientation. If this change in orientation is accompanied by a substantial change in pelvic inclination angle, it would mean that the use of the frontal pelvic plane as a reference plane for implantation of the acetabular cup would not be valid for proper alignment of the cup. To evaluate this possibility, we measured the change of inclination of the pelvis from the supine to the standing position. Subjects and methods We evaluated 120 patients, first positioned in a standing position and then supine on a table. Three pelvic landmarks were digitized percutaneously, and the spatial coordinates were calculated with regard to pelvic orientation in the horizontal and the vertical plane. Results We found a mean inclination of 6.7° in the standing position and 5.6° in the supine position. Patients who were more than 60 years of age who did not have coxarthrosis had a greater inclination angle (8.7°) while standing. Pelvic orientation was stable with regard to the supine and standing positions. These results were independent of sex, level of arthrosis, or status after implantation of a total hip replacement. Interpretation The frontal pelvic plane is a valid reference plane for implantation of the acetabular cup.   ▪

A method to quantify alteration of knee kinematics caused by changes of TKR positioning.

Few in-vitro studies have investigated changes in kinematics caused by total knee replacement (TKR) implantation. The advent of surgical navigation systems allows implant position to be measured accurately and the effects of alteration of TKR position and alignment investigated. A test rig and protocol were developed to compare the kinematics of TKR-implanted knees for different femoral component positions. The TKR was implanted and the component positions documented using a navigation system. The quadriceps was tensed and the knees were flexed and extended manually. Torques and drawer forces were applied to the tibia during knee flexion-extension, while recording the kinematics with the navigation system. The implant was removed and replaced on an intramedullary fixation that allowed proximal-distal, and internal-external rotation of the femoral component without conducting a repeated arthrotomy on the knee. The implant was repositioned using the navigation system to reproduce the previously achieved normally navigated position and the kinematics were recorded again. The recorded kinematics of the knee were not significantly different between both normal implantation and intramedullary remounting for tibial internal-external rotation, varus-valgus angulation, or posterior drawer, at any angle of knee flexion examined. Anterior drawer was increased approximately 2.5mm across the range 20-35 degrees knee flexion (p<0.05), but was otherwise not significantly different. This method of navigating implant components and of moving them within the closed knee (thus avoiding artefactual effects of repeated soft tissue manipulations) can now be used to quantify the effect on kinematics of alteration of the position of the femoral component.

Higher strains in the inner region of the meniscus indicate a potential source for degeneration.

Complex structural properties of menisci can be characterized in part by their inhomogeneous strain response under compression. This pilot study explored the feasibility to quantify characteristic strain distributions on meniscus cross-sections subjected to static compression using electronic speckle pattern interferometry (ESPI). Cross-sectional specimens of 5-mm thickness were harvested from eight human menisci. After application of 20% pre-strain, strain maps in response to 10μm compression were captured with ESPI. The 10μm compression induced an aggregate strain of nominally 0.14% and resulted in highly non-uniform strain distributions. Local compressive strain captured by ESPI ranged from 0.03% to 0.7%. The highest strain was in the central region of meniscus cross-sections, and the lowest magnitude of strain was at the femoral surface of the meniscus. After stratifying for age, peak compressive strain in older menisci (71±6 years, n=4) was 0.33%±0.09, compared to 0.25%±0.06 in younger menisci (34±9 years, n=4). In conclusion, this study captured for the first time continuous strain distribution maps over entire meniscus cross-sections. The non-uniform strain distributions demonstrated inhomogeneous structural properties. Age-related differences in characteristic strain distributions likely represent degenerative changes. As such, ESPI provides a novel strategy of further characterize meniscal function and degeneration.

Friction properties of a new silk fibroin scaffold for meniscal replacement

The menisci protect the articular cartilage by reducing contact pressure in the knee. To restore their function after injury, a new silk fibroin replacement scaffold was developed. To elucidate its tribological properties, friction of the implant was tested against cartilage and glass, where the latter is typically used in tribological cartilage studies. The silk scaffold exhibited a friction coefficient against cartilage of 0.056, which is higher than meniscus against cartilage but in range of the requirements for meniscal replacements. Further, meniscus friction against glass was lower than cartilage against glass, which correlated with the surface lubricin content. Concluding, the tribological properties of the new material suggest a possible long-term chondroprotective function. In contrast, glass always produced high, non-physiological friction coefficients.

Correction to: In vivo performance of a novel silk fibroin scaffold for partial meniscal replacement in a sheep model

The author would like to correct the errors in the publication of the original article. The corrected details are given below for your reading.