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M de Waal Malefijt

Publications and source records attributed to M de Waal Malefijt.

7 recordsLinked to original sources
PubMed2005

A three-dimensional dynamic finite element model of the prosthetic knee joint: simulation of joint laxity and kinematics.

For testing purposes of prostheses at a preclinical stage, it is very valuable to have a generic modelling tool, which can be used to optimize implant features and to avoid poor designs being launched on to the market. The modelling tool should be fast, efficient, and multi-purpose in nature; a finite element model is well suited to the purpose. The question posed in this study was whether it was possible to develop a mathematically fast and stable dynamic finite element model of a knee joint after total knee arthroplasty that would predict data comparable with published data in terms of (a) laxities and ligament behaviour, and (b) joint kinematics. The soft tissue structures were modelled using a relatively simple, but very stable, composite model consisting of a band reinforced with fibres. Ligament recruitment and balancing was tested with laxity simulations. The tibial and patellar kinematics were simulated during flexion-extension. An implicit mathematical formulation was used. Joint kinematics, joint laxities, and ligament recruitment patterns were predicted realistically. The kinematics were very reproducible and stable during consecutive flexion-extension cycles. Hence, the model is suitable for the evaluation of prosthesis design, prosthesis alignment, ligament behaviour, and surgical parameters with respect to the biomechanical behaviour of the knee.

Arthroplasty, Replacement, Knee↗
PubMed2005

Mechanical testing of impaction bone grafting in the tibia: initial stability and design of the stem.

Clinical experience of impaction bone grafting for revision knee arthroplasty is limited, with initial stability of the tibial tray emerging as a major concern. The length of the stem and its diameter have been altered to improve stability. Our aim was to investigate the effect of the type of stem, support of the rim and graft impaction on early stability of the tray. We developed a system for impaction grafting of trays which we used with morsellised bone in artificial tibiae. Trays with short, long thick or long thin stems were implanted, with or without support of the rim. They were cyclically loaded while measuring relative movement. Long-stemmed trays migrated 4.5 times less than short-stemmed trays, regardless of diameter. Those with support migrated 2.8 times less than those without. The migration of short-stemmed trays correlated inversely with the density of the impacted groups. That of impaction-grafted tibial trays was in the range reported for uncemented primary trays. Movements of short-stemmed trays without cortical support were largest and sensitive to the degree of compaction of the graft. If support of the rim was sufficient or a long stem was used, impacted morsellised bone graft achieved adequate initial stability.

Arthroplasty, Replacement, Knee↗
PubMed2004

Increased expression of CCL18, CCL19, and CCL17 by dendritic cells from patients with rheumatoid arthritis, and regulation by Fc gamma receptors.

BACKGROUND: Dendritic cells (DC) have a role in the regulation of immunity and tolerance, attracting inflammatory cells by the production of various chemokines (CK). Fc gamma receptors (Fc gamma R) may be involved in regulation of the DC function. OBJECTIVE: To assess the expression of CK by immature (iDC) and mature DC (mDC) and its regulation by Fc gamma R in patients with RA and healthy donors (HC). METHODS: Expression of CK by DC from patients with RA and from HC was determined by real time quantitative PCR and ELISA. DC were derived from monocytes following standardised protocols. To study the potential regulation by Fc gamma R, iDC were stimulated with immune complexes (IC) during lipopolysaccharide (LPS) induced maturation. The presence of CK was studied in synovial tissue from patients with RA, osteoarthritis, and healthy subjects by RT-PCR and immunohistochemistry. RESULTS: iDC from patients with RA had markedly increased mRNA levels of the CK CCL18 and CXCL8. Upon maturation with LPS, expression of CCL18, CCL19, CXCL8, CCL3, and CCL17 increased dramatically, reaching significantly higher levels in patients with RA. Monocytes failed to express these CK, except for CXCL8 and CCL3. IC-mediated triggering of the Fc gamma R on DC from patients with highly active RA down regulated all CK, whereas the reverse was seen when DC from patients with low disease activity and healthy donors were stimulated. CCL18 was significantly increased in RA synovial tissue. CONCLUSION: Increased CK expression by DC was found in patients with RA. This expression is partly regulated by Fc gamma R triggering and results in an inhibitory DC subtype in RA upon Fc gamma R-mediated triggering.

Arthritis, Rheumatoid↗
PubMed2003

The trochlea is bilinear and oriented medially.

Malfunctioning of total knee replacements often is related to patellofemoral problems. Because the trochlea guides the patella during flexion and extension, its geometry has a major influence in patellofemoral problems. There is controversy in the literature: relative to the mechanical axis, some authors have found a laterally oriented trochlea and others have found a medially oriented trochlea. The groove of implanted prosthetic femoral components always has lateral or neutral orientations. The objectives of the current study were to clarify the controversy found in the literature, to determine whether the trochlear orientation is truly linear, and to determine whether the orientation depends on the size of the femur. The trochleae of 100 human femurs were measured using a three-dimensional measurement system. Detailed analysis of the results indicated that the trochlea is best described as bilinear, with the distal half oriented 0.2 degrees +/- 2.8 degrees laterally and the proximal half oriented 4.2 degrees +/- 3.2 degrees medially. Trochlear orientation was not dependent on bone size.

Cadaver↗
PubMed2003

A different fixation of the femoral component in total knee arthroplasty may lead to preservation of femoral bone stock.

Good femoral bone stock is important for the stability of the femoral component in revision knee arthroplasty. However, the primary total knee replacement (TKR) may cause significant loss of bone stock in the distal anterior femur. Earlier stress-induced bone remodelling simulations have suggested that a completely debonded component may save bone stock in the distal anterior region. However, these simulations did not consider the fixation of a debonded implant and possible secondary effects of micromotions and osteolysis at the interface. The current study tries to combine the preservation of bone stock with adequate component fixation. Different bone remodelling simulations were performed around femoral knee components with different sizes of bonding area and different friction characteristics of the debonded area. The fixation of the femoral component with different bonding characteristics is quantified with calculated implant-bone interface stresses. The results show that a bonded femoral component with a debonded inner side of the anterior flange may significantly reduce bone resorption in the endangered distal anterior femur, without jeopardizing the fixation of the femoral implant. This effect may be obtained in vivo by using a femoral component with a highly polished inner side of the anterior flange.

Arthroplasty, Replacement, Knee↗
PubMed2000

Evaluating hand surgery in patients with rheumatoid arthritis: short-term effect on dexterity and pain and its relationship with patient satisfaction.

Short-term effect of hand surgery on hand function in activities of daily life (dexterity) and pain were studied in 70 patients with rheumatoid arthritis. Only surgical interventions aimed at improvement of function and/or pain relief were included in the study. Patients were assessed before surgery and 6 and 12 months after surgery. Clinical change in the surgical group was observed in the number of painful and swollen joints, observed dexterity, and pain in the hand. Six months after surgery 74% of the patients showed positive clinical change in hand functioning and/or hand pain. Clinical effects remained stable between 6 and 12 months after surgical assessments. Both change in observed dexterity and pain had an independent impact on the patient's satisfaction with the results of the surgery.

Arthritis, Rheumatoid↗