Improving the Quality of Life of Patients With Medical Devices by a Timely Analysis of Adverse Events.

Implanted and non-implanted medical devices, including artificial joints, are widely accepted to improve the quality of life of patients. While implant survival rates of over 80% can be accepted for artificial joints, there is still a large need to achieve higher survival rates at 15 years or longer to reduce the need for revisions due to implant failure before the end of the patient's life. Therefore, artificial joints are constantly improved with design changes and new designs, including modified or new materials. Most of these improvements perform as expected, but there are still cases where previously unknown failures occur, requiring premature revisions. A few examples of such unsuccessful improvements in the last 20 years are mentioned in this technical case report. The main focus of this paper is on an acetabular cup that was recalled due to unexpected revisions after a few weeks to a few months in vivo. The main reason for the revisions were small amounts of an oily residue containing endotoxins trapped inside the porous coating applied to the cup to facilitate bone ingrowth. The cup was recalled within 4 months after the company become aware of the problem, and prior to knowing exactly why the cups were failing early. The root cause analysis took several more months to complete. The lessons learned during the analysis are discussed so that similar events in other implantable medical devices can be avoided. The acetabular cup case aims to highlight that a timely root cause analysis, triggered by very few unexplained revisions, will benefit patients and improve the quality of life.

Customized surface-guided knee implant: Contact analysis and experimental test.

Contact pressure and stresses on the articulating surface of the tibial component of a total knee replacement are directly related to the joint contact forces and the contact area. These stresses can result in wear and fatigue damage of the ultra-high-molecular-weight polyethylene. Therefore, conducting stress analysis on a newly designed surface-guided knee implant is necessary to evaluate the design with respect to the polyethylene wear. Finite element modeling is used to analyze the design's performance in level walking, stair ascending and squatting. Two different constitutive material models have been used for the tibia component to evaluate the effect of material properties on the stress distribution. The contact pressure results of the finite element analysis are compared with the results of contact pressure using pressure-sensitive film tests. In both analyses, the average contact pressure remains below the material limits of ultra-high-molecular-weight polyethylene insert. The peak von Mises stresses in 90° of flexion and 120° of flexion (squatting) are 16.28 and 29.55 MPa, respectively. All the peak stresses are less than the fatigue failure limit of ultra-high-molecular-weight polyethylene which is 32 MPa. The average contact pressure during 90° and 120° of flexion in squatting are 5.51 and 5.46 MPa according to finite element analysis and 5.67 and 8.14 MPa according to pressure-sensitive film experiment. Surface-guided knee implants are aimed to resolve the limitations in activities of daily living after total knee replacement by providing close to normal kinematics. The proposed knee implant model provides patterns of motion much closer to the natural target, especially as the knee flexes to higher degrees during squatting.

Corrosion on the acetabular liner taper from retrieved modular metal-on-metal total hip replacements.

Eight retrieved metal-on-metal total hip replacements displayed corrosion damage along the cobalt-chromium alloy liner taper junction with the Ti alloy acetabular shell. Scanning electron microscopy indicated the primary mechanism of corrosion to be grain boundary and associated crevice corrosion, which was likely accelerated through mechanical micromotion and galvanic corrosion resulting from dissimilar alloys. Coordinate measurements revealed up to 4.3mm(3) of the cobalt-chromium alloy taper surface was removed due to corrosion, which is comparable to previous reports of corrosion damage on head-neck tapers. The acetabular liner-shell taper appears to be an additional source of metal corrosion products in modular total hip replacements. Patients with these prostheses should be closely monitored for signs of adverse reaction towards corrosion by-products.

An energy dissipation and cross shear time dependent computational wear model for the analysis of polyethylene wear in total knee replacements.

The cost and time efficiency of computational polyethylene wear simulations may enable the optimization of total knee replacements for the reduction of polyethylene wear. The present study proposes an energy dissipation wear model for polyethylene which considers the time dependent molecular behavior of polyethylene, aspects of tractive rolling and contact pressure. This time dependent - energy dissipation wear model was evaluated, along with several other wear models, by comparison to pin-on-disk results, knee simulator wear test results under various kinematic conditions and knee simulator wear test results that were performed following the ISO 14243-3 standard. The proposed time dependent - energy dissipation wear model resulted in improved accuracy for the prediction of pin-on-disk and knee simulator wear test results compared with several previously published wear models.

Biochemical analyses of human osteoarthritic and periprosthetic synovial fluid.

Biochemical analyses were performed on osteoarthritic and periprosthetic synovial fluid in order to propose changes to lubricant specifications currently outlined in orthopaedic wear testing standards. Osteoarthritic and periprosthetic synovial fluid samples were obtained from the hip and knee joints of 40 patients. The samples in each group were analysed and compared in order to identify differences between the protein concentration, constituent fractions, osmolality, thermal stability and the hyaluronic acid concentration and molecular weight distribution of osteoarthritic and periprosthetic synovial fluid. The average total protein concentration was approximately 30 g/L, which was much higher than the 20 g/L currently specified in the knee wear testing standard; however, the 30 g/L protein concentration matched the recently revised standard for hip simulator wear testing. No significant difference was found between the protein concentration, osmolality, thermal stability, and hyaluronic acid concentration of osteoarthritic and periprosthetic synovial fluid. The clinical data provided should be used to better define the composition of a more clinically relevant lubricant for orthopaedic wear testing.

The influence of head size on corrosion and fretting behaviour at the head-neck interface of artificial hip joints.

The primary goal of this study was to determine if head size affects corrosion and fretting behaviour at the head-neck taper interface of modular hip prostheses. Seventy-four implants were retrieved that featured either a 28 mm or a 36 mm head with a metal-on-polyethylene articulation. The bore of the heads and the neck of the stems were divided into eight regions each and graded by three observers for corrosion and fretting damage separately using modified criteria as reported in the literature. The 36 mm head size featured a significant difference in the corrosion head scores (p=0.022) in comparison to the 28 mm heads. This may be attributed to a greater torque acting along the taper interface due to activities of daily living.

Knee kinematics of high-flexion activities of daily living performed by male Muslims in the Middle East.

Full flexion is critical for total knee arthroplasty (TKA) patients in the Middle East, where daily activities require a high range of motion in the lower limb. This study aimed to increase understanding of the knee kinematics of normal Muslim subjects during high-flexion activities of daily living, such as kneeling, Muslim prayer, sitting cross-legged, and squatting. The early postoperative kinematics for a select group of Muslim, high-flexion TKA patients are also reported. Mean curves were compared between the normal group and the TKA group. During kneeling, the average maximum flexion was 141.6° for the normal group and 140.2° for the TKA group. The normal group's maximum and minimum knee angles (flexion, abduction, external rotation) were reported and, with the exception of maximum extension, were not significantly different from the TKA group, despite short postoperative times.

A multiple-bundle model to characterize the mechanical behavior of the cruciate ligaments.

Measurements of elongations of the cruciate ligaments have been used to study the behaviors of these ligaments in-vitro and in-vivo, mostly based on simplified two-bundle models of the cruciates. The complex fiber anatomy of the cruciates may suggest a complex deformation behavior across the continuum of their substance that cannot be captured by only two measurement points. In this study, a new methodology was introduced to include more detailed fiber anatomy and to take into consideration the wrapping of the PCL around the intercondylar notch of the femur in deep flexion. The method was used in comparison to the conventional two-bundle models on three sample cadaver knees that underwent a passive flexion up to 150°. The elongation ratios of the bundles were measured as the ratio of change in the length of the bundles over their lengths at 0° flexion. The multiple-bundle models showed ranges of variations across the attachment sites of the cruciates which at all flexion angles were significantly larger than those observed from the conventional two-bundle models. When expressed in percentages, at 150° flexion the ranges of variations in the elongation ratio of the bundles were 32.7%±31.9% and 34%±8.6% for the ACL and PCL, respectively. Results of this study showed that important variations of elongation across the body of the cruciates can be obscured to the conventional two-bundle model of the cruciates, and therefore a more detailed bundle configuration is suggested for the purpose of studying elongation behaviors of these ligaments.

Tibiofemoral joint contact forces and knee kinematics during squatting.

Axial tibiofemoral joint contact forces were non-invasively determined for two high range of motion (high flexion) squatting activities. An electromagnetic motion tracking system and a non-conductive force platform were used to collect kinematic and kinetic data. An innovative scaling method was used to model subject-specific muscle group moment arms. One subject attained a peak axial tibiofemoral joint contact force of 49.7 N/kg during squatting at 149.9 degrees knee flexion. Average joint angles and average axial joint contact forces were calculated for each of the activities in order to facilitate a comparison with stair climbing data. Compared to stair climbing, the maximum average joint contact forces during the squatting activities occurred at significantly higher flexion angles (p<0.05.) The relative simplicity of the method makes it useful for application to large subject groups from diverse regions. The results of this study can be applied to the diagnosis and treatment of pathologies, and to the development of high range of motion (ROM) knee replacements.

Three-dimensional analysis of the movement of lumbar spinal nerve roots in nonsimulated and simulated adhesive conditions.

STUDY DESIGN: Biomechanical analysis of the movement of the lumbar spinal nerve roots (NRs). OBJECTIVES: The characteristics of the movement of lumbar spinal NRs corresponding to the change of posture were three-dimensionally analyzed in nonsimulated and simulated adhesion conditions using a porcine model. SUMMARY OF BACKGROUND DATA: There is a paucity of data on the movement of NRs. MATERIALS AND METHODS: Thirty two NRs of four pig cadavers were investigated. (study 1) Two tantalum beads were sutured on respective NRs from L3 to L6. Five beads were put into each bony structure as reference points. The porcine body was put on the cage designed for three-dimensional radiostereometric analysis. Two oblique radiographs were simultaneously taken at flexion, neutral, and extension. (study 2) After study 1, either L4 NR was ligated onto the adjacent bone to mimic monoradicular adhesion. Radiographs were taken in the same manner. The movements of the beads on NRs relative to immobile standard points in each vertebra were analyzed. RESULTS: The movement of NRs was characterized as a combination of stretching/slackening and pendulum motion. The distance that NRs were stretched/slackened, the excursion, and the angles that NRs moved were: 0.39 +/- 0.29 mm, 1.81 +/- 0.63 mm, and 10.46 +/- 5.93 degrees (in nonadhesion), and 0.30 +/- 0.20 mm, 1.02 +/- 0.50 mm, and 7.13 +/- 3.79 degrees (in simulated adhesion), respectively. CONCLUSION: Adhesion might play a part in the pathogenesis of lumbar spinal disorders because mechanical irritation secondary to stretching/slackening and pendulum motion might be concentrated at the distal part of NRs, adjacent to adhesion site, which has less cerebrospinal fluid and is close to dorsal root ganglion.

Knee and hip kinetics during normal stair climbing.

Understanding joint kinetics during activities of daily living furthers our understanding of the factors involved in joint pathology and the effects of treatment. In this study, we examined hip and knee joint kinetics during stair climbing in 35 young healthy subjects using a subject-specific knee model to estimate bone-on-bone tibiofemoral and patello-femoral joint contact forces. The net knee forces were below one body weight while the peak posterior-anterior contact force was close to one body weight. The peak distal-proximal contact force was on average 3 times body weight and could be as high as 6 times body weight. These contact forces occurred at a high degree of knee flexion where there is a smaller joint contact area resulting in high contact stresses. The peak knee adduction moment was 0.42 (0.15) Nm/kg while the flexion moment was 1.16 (0.24) Nm/kg. Similar peak moment values, but different curve profiles, were found for the hip. The hip and knee posterior-anterior shear forces and the knee flexion moment were higher during stair climbing than during level walking. The most striking difference between stair ascent and level walking was that the peak patello-femoral contact force was 8 times higher during stair ascent. These data can be used as baseline measures in pathology studies, as input to theoretical joint models, and as input to mechanical joint simulators.