Biomedical subjects

J C Goh

Publications and source records attributed to J C Goh.

At least 19 recordsLinked to original sources

PubMed2001

Paired cylindrical interbody cage fit and facetectomy in posterior lumbar interbody fusion in an Asian population.

STUDY DESIGN: The intervertebral disc heights and interfacetal distances of normal lower lumbar segments were measured from MRI scans of 150 male subjects. OBJECTIVES: To investigate the probabilities of paired cylindrical interbody cage placement across the facet joints of the lower lumbar spine in an Asian population with respect to the spinal segmental level, facetectomy, and the restoration of normal intervertebral height. SUMMARY OF BACKGROUND DATA: Cylindrical interbody cage devices often require extensive facetectomy for insertion through a posterior approach in a posterior lumbar interbody fusion (PLIF) procedure. This is because the transverse dimension of a pair of cages could far exceed the interfacetal interval of the lumbar segment. METHODS: One hundred and fifty MRI scans of the lumbosacral spine of male patients between the ages of 18 and 55 years undergoing investigation for low back pain were collected for this study. The interfacetal distances and intervertebral disc heights were measured from transverse and sagittal images, respectively, at L3/L4, L4/L5 and L5/S1. Degenerated discs were not measured. The inner, mid, and outer interfacetal distances were compared with the dimensions of paired cages of 13, 15, and 17 mm in diameter to obtain the proportion of lumbar segments at a particular spinal level that would accommodate paired cages of different diameters and under conditions of varying degrees of facetectomy. RESULTS: Without facetectomy, there was no lumbar segment that could accommodate paired cages as well as restore intervertebral height. With hemi-facetectomy, very few segments at L3/L4 and L4/L5 could fit paired cages. At L5/S1, fewer than 9% of segments could fit paired cages and restore intervertebral heights. The proportion of segments that could accommodate paired cages increased with near-total facetectomy: 25% of L5/S1 segments could accommodate 15-mm cages with restoration of intervertebral heights. CONCLUSIONS: Paired cylindrical cage installation in the majority of patients is likely to require near-total or total facetectomy, with implications for potential segmental instability. Among the three lumbar segments studied, L5/S1 had the highest proportion of segments that could accommodate paired cages and at the same time restore intervertebral height.

Adolescent↗

PubMed2001

Optimization of stacked half-hitch knots for arthroscopic surgery.

PURPOSE: This study was conducted to determine the optimal configuration of stacked half-hitch knots that would give the maximum knot-holding capacity (KHC). TYPE OF STUDY: Mechanical testing study. METHODS: The 2 types of suture materials tested were No. 1 PDS II monofilament and No. 2 Ethibond braided (Ethicon, Somerville, NJ) because these are the 2 most commonly used sutures in arthroscopic surgery. Twelve configurations of stacked half-hitch knots including 2 versions of the Revo knot were tested. Knots were tied between 2 steel hooks 7 mm apart on a manual knot-testing machine. The steel hooks were spread apart to break the knot and the KHC was determined by the peak load recorded on the digital force transducer. Maximum KHC was achieved for No. 1 PDS II sutures by locking the knot with 2 RHAPs (reversing half-hitch on alternate post) and, for No. 2 Ethibond sutures, by locking the knot with 3 RHAPs. Because of the possibility of PDS II sutures unraveling, it is recommended for both No. 1 PDS II and No. 2 Ethibond sutures, that all stacked half-hitches be locked with 3 RHAPs. By adding 1 RHAP to the Revo knot, failure by slippage can be eliminated. RESULTS: The recommended knots tied with braided No. 2 Ethibond sutures were 1.5 times stronger than knots tied with No. 1 PDS II sutures. Although there was variability in the KHC of the recommended knots tied by different surgeons using different knot tiers, the greatest difference in the mean KHC was less than 10%. CONCLUSIONS: Stacked half-hitch knots locked with 3 RHAPs are unlikely to fail by slippage.

Arthroscopy↗

PubMed2001

Linear correlation between axial and lateral bone mineral density of lumbar vertebrae.

The placement of most spinal interbody devices is above the cancellous region of the vertebral bodies. Dual X-ray absorptiometry (DXA) scans of patients are usually taken from the anterior-posterior or the lateral projection. DXA scans taken in vitro from the axial direction would most closely indicate the bone mineral density (BMD) of the bone at this region. So far, in vitro studies have not been conducted to determine the correlation between axial and lateral scans. Because lateral DXA BMD scans are noninvasive and have low radiation dosage, they could be used as a predictive tool to determine the quality of cancellous bone at the centrum of the vertebral bodies, where spinal interbody devices are commonly placed.

Absorptiometry, Photon↗

PubMed2001

An introduction to biodegradable materials for tissue engineering applications.

Tissue generation by autogenous cell transplantation is one of the most promising treatment concepts being developed as it eliminates problems of donor site scarcity, immune rejection and pathogen transfer. Cultured cells are seeded onto a three-dimensional biocompatible scaffold that will slowly degrade and resorb as the soft and hard structures grow and assimilate in vitro and/or in vivo. The 3-D scaffold provides the necessary template for cells to proliferate and maintain their differentiated state. Ultimately, it defines the overall shape of the tissue-engineered transplant. The aim of this review is to describe and discuss the scaffold materials of natural and synthetic origin that are of specific interest to tissue engineers. This review is based on previous publications and our own experience in the use of biomaterials of natural and synthetic origin for tissue engineering applications. Biodegradable polymers which have been used for tissue engineering applications are mainly based on clinically established medical devices and implants. In the group of macromolecules of natural origin collagen, alginate, agarose, hyaluronic acid derivatives, chitosan, and fibrin glue have been used as scaffolds. Man-made polymers such as polyglycolide (PGA), polylactides (PLLA, PDLA), poly(caprolactone) (PCL), and poly(dioxanone) (PDS) have been studied as matrix material to guide the differentiation and proliferation of cells into the targeted functional premature and/or mature tissue. Appropriate selection of scaffold material with respect to the targeted tissue is essential. Today, biomaterials of choice remain to be those approved by the US Food and Drug Administration. In spite of that, novel biomaterials should be developed specifically designed for tissue engineering applications.

Absorbable Implants↗

PubMed2000

Biomechanical study on the effect of twisted human patellar tendon.

OBJECTIVE: To compare the stiffness and maximum strength between the untwisted and twisted free-tendon. DESIGN: 22 twisted and untwisted sectioned-specimens of human cadaver patellar tendons were used and pulled to failure to obtain load-deformation profiles from which stiffness, maximum load to failure and elastic elongation limit were derived. BACKGROUND: In the reconstruction of the deficient anterior cruciate ligament, the use of the central one-third of the patellar tendon is a well-established procedure in which, prior to insertion, the tendon graft may be twisted to mimic the natural orientation of the anterior cruciate ligament in the knee joint. RESULTS: The untwisted tendons had a mean stiffness of 36.5 kg/mm (SD, 16.6 kg/mm) and maximum load of 165.9 kg (SD, 86.8 kg). With a 90 degrees twist, the average stiffness of the twisted tendon was 66.5 kg/mm (SD, 25.4 kg/mm), with maximum load at 364.5 kg (SD, 109.9 kg), an increase of over 100%. The elastic elongation limit, or allowable elongation before permanent deformation or failure, was significantly larger in twisted tendons by 35%. CONCLUSION: Twisting increased the resistance to deformation of the tendon in this study. Relevance The finding supports the surgical practice of pre-twisting tendon grafts for anterior cruciate ligament reconstruction, based on the premise that a stronger and stiffer graft provides a more favourable outcome.

Adult↗

PubMed2000

Biomechanical Strength of Large Diaphyseal Deep-frozen Allografts.

The aim of this paper is to study the biomechanical strength of deep-frozen allografts as they heal. Twenty-eight adult cats were used with the tibia as the experimental model site. Deep-frozen allografts stored at -80 degrees C were used to reconstruct a large tibial defect (at least two-thirds of the diaphysis). An intra-medullary rod was used for fixation. The healing was studied by X-ray at observation periods of 4, 6, 8, 12, 16, 24 and 36 weeks. Post-transplantation biomechanical testing was performed using the Shimadzu Universal Testing Machine DCS series with a torsion test device of 50 kg force metre. Parameters studied included maximum torque, torsional stiffness and energy of absorption. The transplanted grafts were compared to the mechanical properties of the internal controls of the normal opposite tibia of each cat. The results of the mechanical tests demonstrated that deep-frozen allografts did not regain normal strength. At nine months, only about 60% of normal torque strength and about 80% of normal torsional stiffness was achieved. Clinically, it is important to employ strong and rigid internal fixation using intra-medullary nailing rather than plating to allow for immediate mobilisation and reduce the rate of graft fracture.

Journal Article↗

PubMed2000

Principal structural testing of trans-tibial prosthetic assemblies: specimen preparation.

A simple alignment apparatus and the method of transferring the offset test load to the prosthetic assembly through an aligned mandrel for the principal structural tests in accordance with ISO 10328 is presented. The new alignment apparatus was used to prepare test specimens consisting of traditional laminated prosthetic sockets, adaptors, shanks and foot blocks. The alignment apparatus proved useful in ensuring proper orientation and positioning of the components relative to one another as well as to the loading coordinate axes. The sockets and the other components achieved the maximum load specifications during the static failure tests and no failure of components was observed in the cyclic tests.

Artificial Limbs↗

PubMed2000

Influence of PLIF cage size on lumbar spine stability.

STUDY DESIGN: In vitro biomechanical testing on functional spine units with posterior lumbar interbody fusion cage implants of progressively larger sizes. OBJECTIVES: To determine the influence of increasing cage size on the restoration of spine stability after total facetectomy. SUMMARY OF BACKGROUND DATA: Bilateral insertion of cages in posterior lumbar interbody fusion commonly involves facetectomy. To restore stability with no additional instrumentation, the cages must provide sufficient distraction of the vertebrae and adequate tension in the anulus. The size of cages is therefore an important consideration in posterior lumbar interbody fusion. METHODS: Eight human lumbar functional spine units were obtained and divided into two equal groups; one group underwent bending tests and the other twisting. The functional spinal units were tested intact, after total bilateral facetectomy and with three sets of cages that were progressively larger in size. RESULTS: After facetectomy, the functional spine unit's stiffness reduced significantly from that of the intact spine in extension (48% of intact), lateral bending (25%), and torsion (39%). With the posterior insertion of small cages into the facetectomized functional spine units, only extension stiffness was restored to the intact level, whereas flexion stiffness reduced significantly (41% of intact). The medium cages restored the lateral bending stiffness of the facetectomized functional spine units; only the large cages managed to restore the torsional stiffness. Flexion stiffness of the facetectomized functional spine units with cages remained significantly less than that of the intact spine, regardless of cage size. CONCLUSION: In the facetectomized lumbar spine unit, cage size influences lateral bending and torsional stability.

Biomechanical Phenomena↗

PubMed1999

Postoperative vomiting (POV) in the paediatric outpatient general surgical population.

AIM: To determine the incidence of postoperative vomiting (POV) in the paediatric outpatient general surgical population, the factors affecting POV and the incidence of unplanned admissions contributed by POV. METHOD: One hundred and ninety-nine children below 13 yeas of age undergoing elective outpatient general surgical procedures were enrolled into this prospective study. Anaesthesia was induced either intravenously or via the inhalational route. It was then maintained with nitrous oxide, oxygen and isoflurane or halothane. The age, sex, body weight, duration of fasting, administration of trimeprazine, type of general surgical procedure, maintenance technique for general anaesthesia, duration of general anaesthesia, the administration of opiods or local anaesthetics and the incidence of POV were noted. The results were analysed initially with chi-squared test and subsequently subjected to multivariate logistic regression analysis and stepwise variable selection method. RESULTS: The incidence of POV was 8.5%. Duration of general anaesthesia greater than one hour was associated with a significantly higher incidence of POV. Postoperative emesis did not contribute to unplanned admissions in these day surgical patients.

Adolescent↗

PubMed1998

Biomechanical study of tibialis anterior tendon transfer.

The tibialis anterior tendon transfer has been used in the treatment of recurrent congenital clubfoot and paralytic equinovarus foot deformities in cerebral palsy. This study attempts to determine the optimal site of tibialis anterior tendon insertion for ankle and foot motion and to compare the split and whole tendon transfer. Ten fresh normal anatomic leg specimens were used. The lateral half of the tibialis anterior tendon was detached from its insertion, passed beneath the extensor retinaculum, and anchored to the appropriate tarsal bone by a barbed staple. Tension was applied, and ankle and foot motions were measured. The experiment was done by anchoring the tendon to the tarsal bones along the axis of the second metatarsal and serially through to the axis of the fifth' metatarsal. The entire experiment was repeated using the whole tibialis anterior tendon. For split tendon transfer, insertion onto the fourth metatarsal axis was the most effective route; it produced maximal dorsiflexion with minimal supination and pronation. For whole tendon transfer, the ideal site of insertion was along the third metatarsal axis. However, the difference between the average maximum dorsiflexion achieved by the split tendon transfer and that of total tendon transfer is not statistically significant.

Ankle↗

PubMed1998

Difficult pulmonary artery catheterization in a patient with persistent left superior vena cava.

A persistent left superior vena cava is an uncommon congenital abnormality. It arises when the left anterior cardinal vein fails to regress during the embryonic period. Although such patients are usually asymptomatic, they may have associated cardiovascular abnormalities. The anaesthetist may encounter difficulty in the insertion of pulmonary artery catheters. Other implications in the management of these patients in the operating theatre or intensive care unit are discussed.

Aged↗

PubMed1997

Periprosthetic bone remodelling after cementless total hip replacement. A prospective comparison of two different implant designs.

In a prospective study of 14 patients undergoing total hip replacement we have used dual-energy X-ray absorptiometry (DEXA) to investigate remodelling of the bone around two different designs of cementless femoral prosthesis. The bone mineral density (BMD) was measured at 12-weekly intervals for a year. Eight patients (group A) had a stiff, collarless implant and six (group B) a flexible isoelastic implant. Patients in group A showed a decrease in BMD from 14 weeks after operation. By 12 months, the mean loss in BMD was 27%, both medially and laterally to the proximal part of the implant. Those in group B showed an overall increase in BMD which reached a mean of 12.6% on the lateral side of the distal portion of the implant. Our results support the current concepts of the effects of stem stiffness and flexibility on periprosthetic remodelling.

Bone Density↗

PubMed1996

Pattern of fall and bone mineral density measurement in hip fractures.

The objectives of this study were to determine the pattern of fall and the bone mineral density distribution in hip fracture patients. The study was carried out on 260 patients (204 females and 56 males) with hip fractures over a period of three years (i.e. 1991 to 1993). The patients were all above 50 years old and the average age was 77.7 years for women and 76.8 years for men. Information relating to their falls and subsequent hip fractures were collected. Bone mineral density of the contralateral intact femoral neck was measured using dual energy X-ray absorptiometry (Model XR26, Norland Corporation, USA). Bone mineral density in the patients with hip fracture (mean value 0.55 g/cm2) was significantly lower than the fracture threshold value of 0.64 g/cm2. Falls which would result in direct impact on the hip such as sideways, backwards and straight down formed 95.6% of the cohort. Forty-six (17.7%) of the patients fell from a seated or lying position and their bone mineral density were significantly lower (i.e. 0.45 g/cm2). Two hundred and twenty-three (85.7%) of the patients fell on hard surfaces such as ceramic, marble and concrete. Two hundred and twelve (81.5%) of the falls occurred indoors and 153 (58.8%) while walking. Low bone mineral density and falls are important risk factors in hip fracture in the elderly population. Patients with low bone mineral density can sustain a hip fracture from mild trauma such as falling from a seated or lying position. It is therefore necessary to monitor bone mineral density values as well as to prevent or minimise the risk of falling.

Absorptiometry, Photon↗

PubMed1995

Effect of decalcification on bone mineral content and bending strength of feline femur.

The relationships between bone mineral content (BMC), bone calcium, and bone strength were studied in fractionally demineralized feline femurs. In 44 pairs of cat femurs, the right bones were decalcified in ethylene diaminetetra acetic acid (EDTA) to 20%, 40%, 60%, 80%, and 100% of the mineral content of the intact left bone (= control). The bones were then loaded to failure, and maximum strength values were recorded. The data were then used to calculate the percentage strength of the right relative to the left femurs. A correlation coefficient (r) of 0.970 was found between the percentage decalcification and percentage bending strength. A direct relationship (r = 0.876) was also observed between the total calcium extracted and total loss in BMC. The EDTA solutions were spot checked for protein content to determine if the organic matrices had been altered by demineralization. Protein was never detected. Nor did the demineralized tissues display histologic evidence of gross microscopic damage. This study has shown that in cat femurs, 20% decalcification led to about 35% loss in bending strength, and 60% decalcification caused 75% loss in strength. These values are significant as they highlight the importance of calcium to the strength of osteopenic bone.

Animals↗

PubMed1995

Effect of femoral rotation on bone mineral density measurements with dual energy X-ray absorptiometry.

Precision in femoral neck scans with dual energy X-ray absorptiometry (DXA) is affected by variability in positioning and subsequent repositioning of the femur for repeated scans. To study the in vitro effect of femoral rotation on the bone mineral density (BMD), four fresh-frozen cadaveric femurs were fixed in a specially designed jig which allows for rotation of the femurs. BMD measurements of the femurs were done in neutral position (0 degrees) i.e., with the femoral neck axis parallel to the surface of the couch and at 15 degrees, 30 degrees, and 45 degrees of internal and external rotation. In vivo precision of the femoral neck scan was determined in five normal male subjects. The scans were first done with the legs positioned using the manufacturer's foot block. Five scans were performed, with repositioning, on the left hip of each subject. The procedure was then repeated with the legs positioned using a custom-designed positioning jig to minimize the rotation of the hips during a scan. In the in vitro study, the femoral neck BMD value was minimum at neutral position (0 degrees) and increased when the femur was rotated internally or externally. In vivo precision error of the femoral neck scan was reduced by almost 50% with the use of the positioning jig when compared with the manufacturer's foot block. Femoral rotation was shown to have a significant effect on BMD measurements, and proper positioning of the femur during a scan can improve precision significantly.

Absorptiometry, Photon↗

PubMed1995

Cold extrusion deformation of UHMWPE in total knee replacement prostheses.

The use of metal-backed tibial plates in total knee replacement prostheses can result in the flow of ultra-high molecular weight polyethylene (UHMWPE) from the tibial insert into a cavity on the metal tray surface. A study of the relationship between the thickness of UHMWPE inserts and the amount of cold extrusion is reported here. An attempt was made to correlate the occurrence of cold extrusion with computer-aided analysis. UHMWPE samples of varying thickness, from 3 mm to 10 mm, were placed over cobalt-chrome (Co-Cr) discs. The Co-Cr discs had a 5 mm diameter hole placed centrally to simulate a tibial tray cavity. A cyclic load was applied at 20 Hz through a Co-Cr spherical indentor for a million cycles. The application of cyclic loading on UHMWPE samples resulted in cold-extrusion values comparable to those reported for retrieval analysis studies. Results after fatigue loading show that the samples do not suffer any gross surface damage. A shiny depression was visible at the load application site and the surface roughness value was decreased. The amount of cold extrusion increased with decreasing UHMWPE sample thickness. From the results, a minimum UHMWPE thickness of 12 mm is required if cold extrusion of UHMWPE is to be eliminated.

Biocompatible Materials↗

PubMed1995

A biomechanical model to determine lumbosacral loads during single stance phase in normal gait.

A dynamic biomechanical model to determine loads (joint forces) attained at the lumbosacral joint-centre during the stance phase of normal level walking was developed. The biomechanical model was based on rigid free body-segments; namely, the foot, shank, thigh, pelvis and head, arms and trunk (HAT) segments. In this biomechanical model, the forces and moments acting on the lumbar spine are derived from body-segment mass and movements of the trunk. These external forces and their moments must be equilibrated by internal forces, that is, contributions from the erector spinae or rectus abdominus muscle group, and abdominal pressures from within the trunk together with spine forces. Three-dimensional co-ordinate and ground-reaction force data were captured from five healthy young male subjects performing normal level walking in the motion analysis laboratory of the Department of Orthopaedic Surgery, National University of Singapore. These data were captured using the VICON motion analysis system. Both of these data sets were pre-processed, and together with relevant anthropometric parameters and physical measurements of the subject, were passed into the biomechanical model to compute the resultant loads at the lumbosacral joint-centre. The results of this study showed that the peak resultant loads at the lumbosacral joint-centre were between 1.45 and 2.07 times body-weight.

Adult↗

PubMed1995

Biomechanical study on tibialis posterior tendon transfers.

Two methods are used to route the tibialis posterior tendon anteriorly to achieve dorsiflexion: (1) around the medial side of the tibia, or the subcutaneous route; and (2) through the interosseous membrane, or the interosseous route. This study determined the effect of site of tendon insertion on ankle and foot motions and compared the efficacy of both routes. Eleven fresh normal cadaveric legs were used. The detached tibialis posterior tendon was transferred anteriorly through the interosseous membrane and anchored to the first cuneiform along the first metatarsal axis by a barbed staple. The specimen was mounted on a mechanical testing machine. Tension was applied to the tendon and ankle and foot motions were measured. The experimental procedure was repeated with tendon insertion along the second metatarsal axis and serially through to the fifth metatarsal axis. The entire experiment was repeated using the subcutaneous route. The interosseous route was more effective in achieving maximum dorsiflexion with minimal pronation. Shifting the insertion medially caused supination, whereas a more lateral insertion caused pronation.

Ankle Joint↗