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Biomedical subjects

D Siu

Publications and source records attributed to D Siu.

14 recordsLinked to original sources
PubMed1996

Femoral articular shape and geometry. A three-dimensional computerized analysis of the knee.

An average, three-dimensional anatomic shape and geometry of the distal femur were generated from x-ray computed tomography data of five fresh asymptomatic cadaver knees using AutoCAD (AutoDesk, Sausalito, CA), a computer-aided design and drafting software. Each femur model was graphically repositioned to a standardized orientation using a series of alignment templates and scaled to a nominal size of 85 mm in mediolateral and 73 mm in anteroposterior dimensions. An average generic shape of the distal femur was synthesized by combining these pseudosolid models and reslicing the composite structure at different elevations using clipping and smoothing techniques in interactive computer graphics. The resulting distal femoral geometry was imported into a computer-aided manufacturing system, and anatomic prototypes of the distal femur were produced. Quantitative geometric analyses of the generic femur in the coronal and transverse planes revealed definite condylar camber (3 degrees-6 degrees) and toe-in (8 degrees-10 degrees) with an oblique patellofemoral groove (15 degrees) with respect to the mechanical axis of the femur. In the sagittal plane, each condyle could be approximated by three concatenated circular arcs (anterior, distal, and posterior) with slope continuity and a single arc for the patellofemoral groove. The results of this study may have important implications in future femoral prosthesis design and clinical applications.

Aged↗
PubMed1995

Dermatofibrosarcoma protuberans in a renal transplant patient.

Dermatofibrosarcoma protuberans in an unusual soft tissue tumour with a propensity for local recurrence and rarely metastatic spread. Given its indolent course it may be mistaken for atypical scarring or a keloid growth. Early diagnosis and prompt wide local resection of this entity are required in order to prevent a local recurrence. We report a patient who developed locally invasive dermatofibrosarcoma protuberans 4 years after a successful renal transplantation. Although other forms of sarcoma have been reported as a complication of organ transplantation and immunosuppression, this pathology has, so far, not been reported in a transplant recipient.

Adult↗
PubMed1991

A standardized technique for lower limb radiography. Practice, applications, and error analysis.

The normal standing radiograph, which provides a view of the knee only, is prone to errors of parallax and poor control of patient positioning. A standardized radiographic procedure was developed to control these sources of error. Anteroposterior and lateral views of the lower limb (hip and knee) are obtained without moving the patient from a standardized position; this includes control of ankle position and limb rotation. To correct for parallax error, radiopaque markers are positioned between the patient and the x-ray source. The locations of bone landmarks and reference markers on the radiographs are digitized, and a software package provides a display of key parameters. Error analysis of the method confirmed that most angles were sensitive to contrived positional variations, especially limb rotation and knee flexion. Load distribution between limbs was not critical. The greatest error was random. Most angles were reproducible within +/- 1.3 degrees or less at 95% confidence.

Aged↗
PubMed1991

A quantitative approach to radiography of the lower limb. Principles and applications.

A method is described which provides standardised reproducible radiographic images of the lower limb. Anteroposterior and lateral radiographs are digitised and processed by computer to provide graphic/numeric displays of angles and linear measurements, relating the centre points of the hip, knee, and ankle. Two cases illustrate how surgical planning is facilitated when standardised data are available. These data confirm the close relationship between postoperative limb alignment and positioning of prosthetic elements.

Aged↗
PubMed1989

Alignment of the first metatarsal-phalangeal joint: important criteria for a new joint replacement.

Joint replacement is one of many options for the treatment of the first metatarsophalangeal (MTP) joint. Studies of the geometry of that joint have shown that it consists of two distinct articulations, the metatarsophalangeal and the MT-sesamoidal. Both are important, but the MT-sesamoidal tolerates only small deviations from an ideal alignment. The aim of this study was to investigate the alignment of the first MTP joint of a potential patient population, in order to design an optimal surface replacement. One measurement, the extension angle between the MT and the proximal phalanx was found to be the most important alignment criterion for the successful design of an implant and the necessary instruments. This angle controls the delicate interplay between the metatarsal head and the sesamoids and tolerates only small deviations from the normal range before the chance of sesamoidal subluxation increases significantly. The pre-operative knowledge of this and other alignment criteria is important for the ideal placement of an anatomical implant.

Humans↗
PubMed1989

Surgical implications of varus deformity of the knee with obliquity of joint surfaces.

Some arthritic knees with varus deformity show excessive valgus angulation of the femoral joint surface with proximal tibia vara. This causes a downward and medial inclination of the articular surfaces in the coronal plane. The patients we studied had a medial shift of the standing load-bearing axis, and arthritic changes mainly in the medial compartment. Some also had lateral tibial subluxation with twisting of the distal femur and proximal tibia in opposite directions. We assessed the articular geometry by precise radiographic analysis, and compared the results with those in normal volunteers and a group of osteoarthritic patients. The prevalence of this type of deformity in our osteoarthritic patients was 11.5%; its recognition allows the use of specific operative correction that may include double osteotomy or the precise orientation of prosthetic components.

Adolescent↗
PubMed1987

The anatomy and functional axes of the femur.

Linear and angular measurements were made on thirty-two cadaveric femora with respect to the mechanical (functional) axes of the bone. The long axis was defined as a line from the center of the femoral head to the anterolateral attachment of the posterior cruciate ligament. The transverse axis was defined as a line through the posterior cruciate ligament parallel to the line connecting each epicondyle. The condylar width, the length of each interepicondylar line, correlated well with depth, but the projections of the condyles from the transverse plane revealed significant variations from specimen to specimen. Considerable variation also was found between femora in terms of angular dimensions (that is, the angle of anteversion and the neck-shaft angle proximally, and the valgus angle of the femoral shaft distally). Considerable interspecimen variation in the angles between the transcondylar plane and the femoral center, in accord with the valgus angle of the femoral shaft distally, was also noted. The mean transcondylar valgus angle (described as the tangent of the condyles to the perpendicular of the long axis) was 3.8 degrees. In contrast, little variation among specimens was noted for the angle made by the shaft and the long axis.

Aged↗
PubMed1986

The clinical significance of proteinuria in patients with nonparasitic chyluria.

Five patients with heavy proteinuria and nonparasitic chyluria due to congenital abnormalities of the lymphatic system are described. Renal biopsies confirmed the clinical suspicion of an underlying glomerulonephritis. The coexistence of glomerulonephritis and chyluria in these patients was thought coincidental. Tests of value in detecting a concomitant glomerulonephritis in these patients with chyluria include urinary RBC morphology, quantitation of 24-hour urinary protein, and immunoelectrophoresis of serum and urinary proteins. Contrary to previous reports, the present study suggests that chyluria does not produce proteinuria of enough severity to cause hypoproteinemia.

Adult↗
PubMed1986

A three-dimensional finite element analysis of the upper tibia.

A three-dimensional finite element model of the proximal tibia has been developed to provide a base line for further modeling of prosthetic resurfaced tibiae. The geometry for the model was developed by digitizing coronal and transverse sections made with the milling machine, from one fresh tibia of average size. The load is equally distributed between the medial and lateral compartments over contact areas that were reported in the literature. An indentation test has been used to measure the stiffness and the ultimate strength of cancellous bone in four cadaver tibiae. These values provided the statistical basis for characterising the inhomogeneous distribution of the cancellous bone properties in the proximal tibia. All materials in the model were assumed to be linearly elastic and isotropic. Mechanical properties for the cortical bone and cartilage have been taken from the literature. Results have been compared with strain gage tests and with a two-dimensional axisymmetric finite element model both from the literature. Qualitative comparison between trabecular alignment, and the direction of the principal compressive stresses in the cancellous bone, showed a good relationship. Maximum stresses in the cancellous bone and cortical bone, under a load which occurs near stance phase during normal gait, show safety factors of approximately eight and twelve, respectively. The load sharing between the cancellous bone and the cortical bone has been plotted for the first 40 mm distally from the tibial eminence.

Aged↗
PubMed1986

The development of a surface arthroplasty for the elbow.

Complex kinematics, anatomical features, and load distribution have contributed to the poor function of constrained and semiconstrained cemented arthroplasties of the elbow. Resurfacing by porous-coated components has the potential, by reproduction of normal joint geometry and restoration of ligament balance, to re-create relatively normal kinematics and load-bearing and provide relief of pain. A method was developed to provide information on the geometry of the lower humeral joint surface and olecranon fossa. The information gained was used to design components to resurface the trochlea, capitellum, and olecranon fossa. A technique was also developed to remove a minimal amount of subchondral bone from the ulna and humerus in a precisely directed fashion for exact fit of the porous-coated components.

Elbow Joint↗
PubMed1985

Universal bone cutting device for precision knee replacement arthroplasty and osteotomy.

Since malplacement contributes most to loosening of total knee replacements (TKR), a jig was devised, aligned to and mounted on the tibia, with a 3 degrees of freedom sliding saw. A central distractor, attached to the jig, positions and aligns the knee at 0 degrees or 90 degrees. The femur is then rigidly linked to the jig for bone cutting. Resurfacing designs (Cloutier and Townley) have been regularly implanted, aligned +/- 1 degree. This precision should minimize loosening and improve function.

Aged↗