First-Principles Study of Structural and Electronic Properties of MoS1.5Se0.5 Alloy

The effects of relative positions of Se atoms in a monomolecular layer of MoS[Formula: see text]Se[Formula: see text] have been studied. It is demonstrated that the distribution of Se atoms between top and bottom chalcogen planes is most energetically favorable. For a more probable distribution of Se atoms this monolayer alloy is a direct semiconductor with the fundamental bandgap of 2.35[Formula: see text]eV. We have also evaluated the optical band gaps of the alloy at 77[Formula: see text]K (1.86[Formula: see text]eV) and room temperature (1.80[Formula: see text]eV), which are in a good agreement with the experimentally measured bandgap of 1.79[Formula: see text]eV.

Surface plasmons in suspended graphene: launching with in-plane gold nanoantenna and propagation properties

Graphene physics and plasmonics are two fields which, once combined, promise a variety of exciting applications. One of those applications is the integration of active nano-optoelectronic devices in electronic systems, using the fact that plasmons in graphene are tunable, highly confined and weakly damped. A crucial challenge remains before achieving these active devices: finding a platform enabling a high propagation of Graphene Plasmons Polaritons (GPPs). Suspended graphene presenting ultrahigh electron mobility has given rise to increasing interest. We numerically studied the plasmonic properties of suspended graphene. We propose a hybrid configuration and a set of conditions to launch graphene plasmons via an in-plane gold nanoantenna, for micrometric propagation of surface plasmons in suspended graphene. Finally, we propose a realistic optoelectronic device based on the use of suspended graphene.

Re-ordering chaotic carbon: origins and application of textured carbon

Formation of nanocrystals with preferred orientation within the amorphous carbon matrix has attracted lots of theoretical and experimental attentions recently. Interesting properties of this films, easy fabrication methods and practical problems associated with the growth of other carbon nanomaterials such as carbon nanotubes (CNTs) and graphene gives this new class of carbon nanostructure a potential to be considered as a replacement for some applications such as thermal management at nanoscale and interconnects. In this short review paper, the fabrication techniques and associated formation mechanisms of these nanostructured films have been discussed. Besides, electrical and thermal properties of these nanostructured films have been compared with CNTs and graphene.

Growth and characterization of bamboo-shaped carbon nanotubes using nanocluster-assembled ZnO:Co thin films as catalyst

Bamboo-shaped carbon nanotubes (CNTs) had been successfully fabricated by a plasma enhanced chemical vapor deposition method, in which nanocluster-assembled ZnO:Co thin film was used as catalyst. It was found that bamboo-shaped CNTs were generally grown in a direction perpendicularly to the substrate surface with the tops of CNTs dominated by the droplet-like catalyst covered by the carbon layer. The diameter of CNTs was ranged from 20-50 nm. High resolution of TEM image showed that the typical CNT had a multi-walled structure with an inner core presented. The ordered graphite layers were inclined to an axis of CNT about 18 degrees and the interlayer space of a CNT was about 0.35 nm. Two peaks in Raman spectrum at 1586 cm(-1) and 1372 cm(-1) were identified as G-band and D-band for graphite, respectively. The results showed that catalyst based on ZnO:Co thin films could be used for the growth of CNTs with bamboo-shaped structure.

Densitometry trends in postmenopausal Asian women undergoing bisphosphonate treatment

INTRODUCTION

Bisphosphonates have been shown to be effective in reducing the risk of fragility fractures in several landmark clinical trials conducted in Western populations. However, limited studies on bone mineral densitometry (BMD) trends have been conducted in Asian women. We conducted a retrospective review of electronic records to determine the actual BMD trends in a local population of postmenopausal women on bisphosphonate treatment.

METHODS

The electronic records of all women over 50 years of age who had undergone BMD at Singapore General Hospital in 2004 were examined. Patients who were later started on bisphosphonates and continued the treatment for at least two years were selected for the study. Their subsequent BMD results were recorded, and longitudinal analysis was applied to determine the BMD trends as a cohort.

RESULTS

A total of 254 postmenopausal women were included for analysis. Their mean BMD T-score was -2.70 before treatment, and improved to -2.56 and -2.27 one and two years after treatment, respectively. However, the score deteriorated to -2.50 and -2.62 three and four years after treatment, respectively. The difference between each year's results and those of the baseline was statistically significant.

CONCLUSION

In our study, the BMD scores in our local population showed improvement in the first two years of bisphosphonate treatment but declined subsequently. Our findings contrasted with those of studies conducted in Western populations. Further prospective studies are suggested so as to elucidate the actual BMD trends and fracture risk reduction in Asian women on bisphosphonate treatment.

Tribological Properties of Tetrahedral Carbon Films Deposited by Filtered Cathodic Vacuum Arc Technique

Ta-C films have been deposited using FCVA technique. The hardness and Young's modulus of the films on both silicon and sapphire substrates are determined by an ultra low load depth sensing nanoindenter to examine their dependence on the carbon ion energy. An optimum ion energy around 80 to 90 eV has been found, which coincides with the energy at which the sp3 content and film density reach maximum values. At this ion energy, the hardness, modulus and critical load of a 60 nm film on sapphire exhibit maximum values of 60 GPa, 580 GPa and 7 mN, respectively, whilst the frictional coefficient shows a minimum of 0.16.

Dewetting of polymer films by ion implantation

We report dewetting of thermodynamically stable, thick (approximately 100 nm) polystyrene films by titanium ion implantation. The dynamic dewetting patterns in time evolution are recorded. The dewetting mechanism is determined to be heterogeneous nucleation, where the defects and Ti nanoparticles formed by ion implantation serve as the nuclei. In addition, we observe abundant rims with regular polygonal shapes in dewetting patterns. This is attributed to fingering instability, which results from the balance between the driving force arisen from thermally induced surface tension gradient and the resistive forces from the combination of friction force, Laplace pressure and long-range van der Waals interactions. Finally, a model based on mass conservation is used to qualitatively describe the transition from circular to polygonal shaped rims at a critical diameter for holes.

Abrupt stress induced transformation in amorphous carbon films with a highly conductive transition phase

We demonstrate that when, and only when, the biaxial stress is increased above a critical value of 6+/-1 GPa during the growth of a carbon film at room temperature, tetrahedral amorphous carbon is formed. This confirms that the stress present during the formation of an amorphous carbon film determines its sp;{3} bonding fraction. In the vicinity of the critical stress, a highly oriented graphitelike material is formed which exhibits low electrical resistance and provides Ohmic contacts to silicon. Atomistic simulations reveal that the structural transitions are thermodynamically driven and not the result of dynamical effects.

A novel amperometric biosensor based on ZnO:Co nanoclusters for biosensing glucose

ZnO:Co nanoclusters were synthesized by nanocluster-beam deposition with averaged particle size of 5 nm and porous structure, which were for the first time adopted to construct a novel amperometric glucose biosensor. Glucose oxidase was immobilized into the ZnO:Co nanocluster-assembled thin film through Nafion-assisted cross-linking technique. Due to the high specific active sites and high electrocatalytic activity of the ZnO:Co nanoclusters, the constructed glucose biosensor showed a high sensitivity of 13.3 microA/mA cm2. The low detection limit was estimated to be 20 microM (S/N=3) and the apparent Michaelis-Menten constant was found to be 21 mM, indicating the high affinity of the enzyme on ZnO:Co nanoclusters to glucose. The results show that the ZnO:Co nanocluster-assembled thin films with nanoporous structure and nanocrystallites have potential applications as platforms to immobilize enzyme in biosensors.

Enhanced field emission from injector-like ZnO nanostructures with minimized screening effect

Injector-like zinc oxide (ZnO) nanostructures have been synthesized on Si substrate by the vapour phase transport method. Samples with different areal densities were obtained by controlling the temperature. The field emission properties of the injector-like ZnO nanostructures showed a clear dependence on the areal density of the nanostructures, which is due to the screening effect. The samples with a needle length of 850 nm and an areal density of 1 × 10(8) cm(-2) showed the lowest field emission turn-on field of 1.85 V µm(-1) at a current density of 10 µA cm(-2), and the current density reaches 1 mA cm(-2) at an applied field of 4.7 V µm(-1).

A comparison of teriparatide and calcitonin therapy in postmenopausal Asian women with osteoporosis: a 6-month study

OBJECTIVE

The number of hip fractures is expected to double in the next 20 years, with current estimates that Asia will account for 37% of these cases. As bone mineral density (BMD) may be used as a measure of fracture risk, we sought to compare the effects of teriparatide with salmon calcitonin treatment on changes in BMD, biochemical bone markers, and safety in postmenopausal Asian women with osteoporosis.

METHODOLOGY

A total of 104 patients (n = 47 teriparatide [20 g/day subcutaneously] and n = 57 calcitonin [100 IU/day subcutaneously]) were enrolled in Hong Kong, Singapore, Philippines, Malaysia, and Thailand. Calcium (> or = 500 mg/day) and vitamin D (200-400 IU/day) supplements were taken throughout the 6-month controlled, randomized study.

RESULTS

Teriparatide was associated with a 5.03 +/- 4.77% increase in lumbar spine BMD (p < 0.0001, mean +/- SD change from baseline), whereas changes in lumbar spine BMD for patients on calcitonin were not statistically significant (mean change of 0.36 +/- 4.12%, p = 0.16). Comparison of the two groups indicated that teriparatide treatment improved lumbar spine BMD statistically significantly more than calcitonin (p < 0.0001). No statistically significant changes were observed for total hip or femoral neck BMD. Serum bone-specific alkaline phosphatase (BSAP) increased by 55.9% (median change from baseline, p < 0.0001) in the teriparatide group, and remained stable with calcitonin (5.0% change, p = 0.24); osteocalcin increased by 156.15% (median change from baseline, p < 0.0001) with teriparatide, and decreased with calcitonin (-15.25%, p = 0.03). Similar rates of adverse events were observed, with nausea and dizziness the most commonly reported for both groups (teriparatide versus calcitonin, 13.0% versus 23.2% p = 0.21, 10.9% versus 21.4% p = 0.19, respectively). There were no clinically relevant changes observed in laboratory parameters.

CONCLUSIONS

Both treatments were similarly tolerated, however teriparatide was associated with greater increases in lumbar spine BMD and bone formation markers, demonstrating the unique mechanism of action and safety of this treatment for osteoporosis in these Asian women.

Comparing 2-year outcomes of anterior cruciate ligament reconstruction using either patella-tendon or semitendinosus-tendon autografts: a non-randomised prospective study

PURPOSE

To compare the results of anterior cruciate ligament (ACL) reconstructions using either a patella-tendon autograft or a semitendinosus-tendon autograft.

METHODS

Based on surgeon experience and preference, 68 patients underwent ACL reconstruction using either a quadruple-strand semitendinosus autograft (n = 34) or a central one-third bone-patella tendon-bone autograft (n = 34). Each patient was assessed preoperatively and postoperatively at 3, 6, and 24 months using the International Knee Documentation Committee (IKDC) knee score, Biodex muscle strength and endurance testing, and the KT1000 instrumented arthrometer test of knee laxity to anterior translation. All assessments at the 2-year follow-up were performed by the same physician and physiotherapist.

RESULTS

While ACL reconstruction improved knee stability and IKDC knee scores significantly, there was no statistically significant difference between semitendinosus- and patella-tendon autograft reconstructions in terms of long-term knee score or laxity to anterior translation. Semitendinosus graft reconstruction was associated with less donor-site morbidity and hamstring weakness. Meniscectomy was associated with poorer long-term knee scores.

CONCLUSION

ACL reconstruction is associated with a significantly better IKDC knee score and laxity measurement at 2-year follow-up. However, we were unable to demonstrate a significantly better long-term outcome in knee score or laxity to anterior translation with either a patella-tendon autograft or a semitendinosus-tendon autograft.

Assessment of blood-induced cartilage damage in rabbit knees using scanning electron microscopy

PURPOSE

To investigate the harmful effects of a single episode of intra-articular bleeding on articular cartilage of rabbit knees using scanning electron microscopy.

METHODS

Autologous blood was injected into the right knee joints of 18 New Zealand white rabbits. Surface and cellular damages were examined by the scanning electron microscope (n=9) and light microscope (n=34), respectively. The injected right knees were then compared with the corresponding control left knees at one, 3, and 6 weeks after the blood injection.

RESULTS

The articular surface of the injected knees turned uniformly rough with multiple pits after one week. Maximal changes with elevations and depressions were observed at 3 weeks. These changes reversed at 6 weeks with the irregularities smoothing out. A similar pattern of transient cartilage damage was noted histologically.

CONCLUSION

Both scanning electron microscopic and light microscopic findings suggest that a single episode of intra-articular bleeding leads to articular cartilage damage but this appears to be reversible. Our findings of transient damage to the articular cartilage suggest that there is no need for intra-articular evacuation and washout following an acute episode of haemarthrosis.

Piriformis pyomyositis: a rare cause of sciatica

A 30-year-old Thai woman with piriformis pyomyositis presented with sciatica. Computed tomography showed swelling and enhancement of the right gluteus medius and piriformis muscles. She made a complete recovery after a course of intravenous antibiotics. This condition has only been reported three other times and is often diagnosed with difficulty. It could be erroneously dismissed as a lumbar disc prolapse. If untreated, it could lead to prolonged hospital stay and death. A high index of suspicion, early diagnosis and appropriate antibiotic or surgical treatment leads to full recovery.

Morbidity following anterior cruciate ligament reconstruction using hamstring autograft

INTRODUCTION

As anterior cruciate ligament (ACL) reconstruction becomes more frequently performed, the expectation of earlier return to activities becomes higher; hence graft selection becomes more important. The use of hamstring tendon autograft is perceived to have less postoperative morbidities. We evaluate the early postoperative complications in this prospective study.

MATERIALS AND METHODS

Seventy-six patients operated by the same surgeon were assessed preoperatively, and 3 and 6 months after surgery. The hamstring and quadriceps strength were measured with Biodex machine and the side-to-side laxity measured using KT-1000 instrument. The patients were also assessed for their subjective complaints using IKDC (International Knee Documentation Committee) Knee Scoring System.

RESULTS

The strength and endurance index of the quadriceps and hamstrings recovered and improved by the sixth month after surgery. The recovery by the quadriceps muscle is more marked and by the sixth month, it has recovered to more than the preoperative level. As for laxity, the average side-to-side difference at 30 pounds was 2.75 mm by 6 months. Of these patients, the side-to-side difference was less than 5 mm in 66 patients (5 mm as taken to be acceptable for graft success). As for IKDC rating, at the sixth month, 71 patients had normal or near normal knee by their own assessment. No patients had anterior knee pain at rest. Sensory deficits were only present in 3 patients with complaints of numbness over the distribution of the saphenous nerve or its infrapatellar branch.

CONCLUSION

Most morbidities are temporal in nature and do not significantly affect the patient's activities.

Patellar allografts in anterior cervical fusion - a two-year clinical and radiographic study

Donor site morbidity, which occurs in 15% to 20% with the use of autografts for anterior cervical fusion, is eliminated with the use of allografts. While allografts from the iliac crest, ribs, fibula, femoral head and skull have been used in anterior cervical fusion, the use of patellar allografts has not been previously reported. Twenty-two patients underwent Cloward anterior cervical decompression and fusion using bicortical patellar allografts from 1993 to 1997. Fifteen patients, with a follow-up period of at least two years, were reviewed. Eleven patients (73.4%) had good or excellent results at an average of 42.8 months after surgery. Fourteen patients (93.4%) achieved union. Two patients (13.3%) developed collapse of the graft with extrusion, one of whom still achieved union. These results are comparable to those reported of anterior cervical fusion using autografts or other types of allografts.

Prospective trial of resurfaced patellaversus non-resurfaced patella in simultaneous bilateral total knee replacement

INTRODUCTION

A prospective trial was carried out in simultaneous bilateral total knee replacement to compare the outcome of resurfaced versus non-surfaced patella.

METHODS

Thirty-five patients between 1997 and 2002 had simultaneous bilateral total knee replacement with resurfaced patella on the left and non-resurfaced patella on the right knee using the same implant in both.

RESULTS

There were 29 females and six males with a mean age of 65.3 years. Mean follow-up was 3.18 years. There was no significant difference between the resurfaced and non-resurfaced knees with respect to the overall Knee Society clinical score (p = 0.093 preoperative, 0.310 postoperative) or the pain (p = 0.715 preoperative, 0.395 postoperative) or function subscores (p = 0.126 preoperative, 0.317 postoperative). The postoperative range of motion was 109 and 110 degrees for the resurfaced patella and non-resurfaced patella respectively (p = 0.894). The post-operative knee scores between patients with or without pre-operative anterior knee pain (p = 0.238) and between those who were obese and non-obese (p = 0.387) were not significantly different. 82.9% of patients felt that the resurfaced knee and 80% felt that the non-resurfaced knee were much better than before. There was no major preference for either knee for climbing stairs and getting out of chair.

CONCLUSION

The functional and symptomatic outcome of total knee replacement with or without patella resurfacing is the same in the local population. Also, the present study demonstrated no evidence that the weight of the patient or the presence of preoperative anterior knee pain should be considered as factors in the decision to resurface the patella.

The posterior cruciate ligament: an anthropometric study in Asians and evaluation of safe limits for bony tunnel creation during reconstruction

INTRODUCTION

Quantitative data regarding the dimensions of the posterior cruciate ligament (PCL) and its insertions have not been studied in Asians, and concerns have been raised regarding the danger of vascular injury when the bony tunnels are created during arthroscopically-assisted reconstruction.

MATERIALS AND METHODS

Ten male cadavers were used in this study, incorporating dissection and procedural arms. In the procedural arm, the path of the drill bit was tracked fluoroscopically as the tibial and femoral tunnels were created during simulated reconstructive surgery, and the effect of varying knee flexion angles was studied. Fluoroscopic images were analysed using specialised image processing software.

RESULTS

The mean length of the PCL at full extension was 37.7 +/- 1.9 mm, and the mean mid-substance width was 13.7 +/- 1.7 mm. The mean sagittal distance between the exit point of the tibial tunnel and the anterior surface of the popliteal artery, across all knee flexion positions, was merely 6.0 mm (range, 2.8 to 10.2 mm). This distance tended to increase with increasing knee flexion, but this was not statistically significant. The mean distance between the exit point of the femoral tunnel and the femoral artery was 51.1 mm (range, 42.1 to 59.0 mm).

CONCLUSIONS

The dimensions of the PCL and its insertions in Asians do not vary greatly from those reported for Western subjects. The distance from the exit point of the tibial tunnel to the popliteal artery is very small and, although this distance increases with increasing knee flexion, the improvement in the safety margin may neither be clinically nor statistically significant. The margin of safety for drilling of the femoral tunnel is much greater.

Measurement of in-vivo force response of intra-abdominal soft tissues for surgical simulation

The lack of data on in-vivo material properties of soft tissues has been a significant impediment in the development of virtual reality based surgical simulators that can provide the user with realistic visual and haptic feedback. As a first step towards characterizing the mechanical behavior of organs, this work presents in-vivo force response of the liver and lower esophagus of pigs when subjected to ramp and hold, and sinusoidal indentations delivered using a haptic feedback device, Phantom, employed as a mechanical stimulator. The results show that pulse significantly affects the reaction forces and that the lower esophagus is 2 to 2.5 times stiffer than the liver.

Clinical applications of bone graft substitutes in spine surgery: consideration of mineralized and demineralized preparations and growth factor supplementation

Bone graft substitutes may be broadly classified as mineralized and demineralized preparations. This article reviews the basic science and biology underlying each preparation. A review of the clinical and experimental applications of each preparation follows. The text concludes with a review of growth factors as biological supplements.

Autogenous osteochondral morselised grafts for full thickness osteochondral defects in the knee joints of pigs

The aim of this study is to firstly ascertain the survival of autogenously grafted morselised cartilage for full thickness osteochondral defects in knee joints of pigs. Secondly, it is to determine the quality of the grafted cartilage that survives and to score to it based on a recognised and tested system of indices and thirdly, to recognise, if any, the potential for reconstitution of the osteochondral junction. Two groups of five pigs were followed up for six and 12 weeks. Similar osteochondral defects were created in the medial condyles of both knees with the right medial femoral condyle defect filled with graft and the left used as control and filled with gel foam. At the end of the study period, an independent pathologist assessed the defects macroscopically and microscopically with an accepted and comparable histological scoring system. Macroscopically, there was better filling of the defect and restoration of bony contour in the grafted group compared to the control. Microscopically, at six weeks, filling of the defect, nature of predominant tissue, matrix staining and nature of cells all showed significantly better histological score than the control using the Mann-Whitney U test at the level of significance of p<0.05. At 12 weeks, in addition to the above, the reconstitution of osteochondral junction also showed a significantly better score. Comparing the test groups at six and 12 weeks, the reconstitution of the osteochondral junction was significantly better at 12 weeks. In conclusion, the autogenous osteochondral morselised graft persisted as mature hyaline cartilage with good histological score at six weeks with significantly better reconstitution of osteochondral junction occurring at 12 weeks. The use of morselised graft allows for the inclusion of bone graft which possibly allows for larger amounts of donor tissue and thus the possibility of treating larger defects. In the human model the donor site would be the non-weight bearing surfaces of the knee such as the intercondylar notch as described by Walgenbach A and Stone KR at the 1997 Annual Meeting of the American Academy of Orthopaedic Surgeons in San Francisco.

The effect of surgically implanted bullet fragments on the spinal cord in a rabbit model

BACKGROUND

Whether or not to remove bullets or bullet fragments from the spinal column of a neurologically intact patient has been a subject of continual debate. The controversy is due in part to a lack of information about the long-term effects of bullet fragments on spinal cord tissue. Although many studies have demonstrated the toxic effects of metal fragments on brain tissue, to our knowledge no one has evaluated the effects of the metals contained in commercially available bullets on spinal cord tissue.

METHODS

Copper, aluminum, and lead fragments from three commercially available bullet cartridges were implanted in intradural and extradural locations in seventeen New Zealand White rabbits. At an average of 9.8 months, the metal content of specimens of blood, cerebrospinal fluid, and liver were determined. The spinal cords were harvested and examined histologically.

RESULTS

There was a significant increase in the copper level of blood from the rabbits with an implanted copper fragment compared with that of the control animals (p = 0.007). Concentrations of copper and lead were not elevated, compared with the control values, in the serum or liver. Histological examination of the spinal cords revealed major destruction of both the axons and the myelin of the dorsal column adjacent to the intradural copper fragments. Intradural fragments of lead caused similar destruction of myelin and axons in the dorsal column, but to a lesser degree. Minimal spinal cord or meningeal histological changes were noted around the aluminum intradural fragments, and no pathological changes were found near any fragments placed in an extradural location.

CONCLUSIONS

The results of this study show that certain metals contained in commercially available bullets can cause varying degrees of neural destruction independent of the initial mechanical injury caused by implantation. Of the three metals tested, copper fragments consistently caused a substantial localized area of neural injury within the spinal cord.

CLINICAL RELEVANCE

In our study, copper fragments caused local neural toxicity involving as much as 10% of the spinal cord area, suggesting that there may be a scientific basis for removal of copper fragments lodged in the spinal cord, even in the absence of a neurological deficit.

Results of cervical laminoplasty and a comparison between single and double trap-door techniques

Thirty-seven patients were studied for an average of 32.1 months after canal-expansive laminoplasty for the treatment of multiple-level cervical stenosis caused by spondylosis, ossification of posterior longitudinal ligament, prolapsed intervertebral disc, and other conditions. Short-term and medium-term results were recorded clinically, using the scoring system proposed by the Japanese Orthopedic Association. The canal expansion was also recorded with radiological studies. The improvement rate was good to excellent in 58.3% of the patients. Postoperative neurological deterioration occurred in only four patients. Poorer results were observed in female patients and in those in whom surgery was delayed. Surgery within 12 months of onset of symptoms gave good results. Serious complications occurred in only two patients. There were 12 patients who were treated with the single trap-door (unilateral) laminoplasty and 25 patients treated with the double trap-door (sagittal splitting of the spinous processes) laminoplasty; their results were compared. There was no significant difference in neurological outcome between the two methods.

Results of revision total knee arthroplasty

BACKGROUND/AIM OF STUDY

The results of primary total knee arthroplasties have improved over the years but some still fail, requiring revision. Revision total knee arthroplasty is technically more difficult and has not enjoyed the same success rates as the index operation. The aim of this retrospective study was to review the results of revision total knee arthroplasties carried out at our centre. This is the first study in Singapore on revision total knee arthroplasty.

METHODS

A retrospective study where 17 patients (18 knees) had been followed up since their revision operations were clinically assessed. Based on the Knee Society Clinical Scoring System, they were assigned separate knee and function scores (each having a maximum possible 100).

RESULTS

The mean knee score was 76 (range 35-93), which rates as good. Of the 18 knees, 67% had excellent or good knee scores. By comparison, the mean function score was 56 (range 0-90) which rates as poor and 33% had excellent or good function scores.

CONCLUSION

Revision total knee arthroplasty achieves good and excellent results in spite of technical difficulties often associated with the revision operation. The difference in mean knee and function scores emphasises that many other factors such as physical strength and stamina affect function. Nevertheless, 15 patients were able to walk out of their house and around their neighbourhood for varying distances. This satisfied their expectations and the poor mean function score may reflect different expectations of patients overseas from whence this scoring system originated.

Calcium sulfate- and calcium phosphate-based bone substitutes. Mimicry of the mineral phase of bone

Calcium sulfate and calcium phosphate have provided the orthopedic surgeon a viable alternative to autogenous bone grafting as either an osteoconductive bone void filler or a bone graft extender. These materials mimic the mineral phase of bone and are resorbed at a rate similar to the rate of bone formation. Thus, they are able to provide some structural support and prevent ingrowth of fibrous tissue while facilitating creeping substitution by the host bone.

The results of autogenous tibial periosteal transplants for full thickness cartilage defects in the knee joints of pigs

An experimental study was conducted to demonstrate macroscopic and microscopic healing of full thickness cartilage defects with mature stable hyaline cartilage after autogenous tibial periosteal transplants in the knee joints of pigs. Similar full thickness osteochondral defects were created in the medial femoral condyles of both knees in 10 healthy young adult pigs. Periosteal transplants were performed on the left knees and the right knees used as controls. The pigs were sacrified in two groups at 6 weeks and 3 months. The knees were inspected for healing and stability of the graft. Microscopic sections were taken and evaluated using a histological score developed by O'Driscoll. Macroscopically, almost all defects with periosteal grafts healed with a translucent bluish-white colour indicating articular cartilage formation. There was good restoration of the bony contour and filling of the defects were superior to controls. Histologically, we were able to demonstrate immature hyaline cartilage which matured at 3 months. The newly formed tissue was stable and well-incorporated. It had almost complete bonding to the adjacent articular margin, good reconstitution of the osteochondral junction and a well maintained structural integrity. We concluded that periosteal transplants in the knee of a pig model healed with mature stable hyaline cartilage.

The Mitchell distal metatarsal osteotomy for hallux valgus--the Singapore General Hospital experience

BACKGROUND

Fifty-five Mitchell distal metatarsal osteotomies for hallux valgus performed over a period of four years have been retrospectively reviewed. The 38 patients were followed for an average of 30 months (range 12 to 60 months).

RESULTS

The preoperative hallux valgus angle averaged 30.9 degrees +/- 8.2 degrees SD (range 18 degrees to 60 degrees) and the postoperative angle averaged 12.2 degrees +/- 4.6 degrees (range 5 degrees to 20 degrees).

CONCLUSION

Ninety-two percent of the patients were satisfied with the result of the procedure. They stated that, given the identical situation, they would undergo the operation again.

Use of a collagen-hydroxyapatite matrix in spinal fusion. A rabbit model

STUDY DESIGN

The efficacy of a specially designed mineralized bovine collagen matrix as a carrier for bone marrow stem cells was studied in a rabbit posterolateral spinal fusion model.

OBJECTIVES

To determine if bone marrow cells added to Healos matrix will lead to fusion rates, biomechanical properties, and histologic properties comparable with those of fusions using autologous iliac crest bone graft; and to determine if the addition of preservative-free heparin to anticoagulate the bone marrow during harvest will adversely affect the fusion rate.

SUMMARY OF BACKGROUND DATA

Although the development of new preparations of osteoinductive agents has advanced rapidly in recent years, the carrier systems that have been used in their application have received less attention. The composition and structure of the matrix used are key components affecting the ability of the matrix to function as a scaffold on which cells can migrate, adhere, proliferate, and form bone. The composition and design of matrix components also determine the ability of osteoinductive agents to influence local and hematogenously derived osteogenic precursor cells, which migrate to or are brought into the fusion site. Thus, the properties of the carrier can affect the behavior and efficacy of the osteoinductive agent that is used. The authors studied the properties of a new mineralized collagen matrix called Healos, which has been engineered specifically for spinal fusion application.

METHODS

Forty-four adult female New Zealand white rabbits were divided into five groups. Groups 1-4 underwent bilateral intertransverse fusion between L5 and L6. The fusions were augmented with either autologous iliac crest bone graft, Healos matrix alone, Healos matrix mixed with autologous bone marrow, or Healos matrix combined with heparinized autologous bone marrow. At 8 weeks after surgery, the fusions were characterized radiographically, histologically, and biomechanically. The rate of fusion was determined by radiographic analysis. The fifth group consisted of two animals whose bone marrow was aspirated from their tibias and femurs and then sent for determination of total nucleated cell count.

RESULTS

At 8 weeks, the radiographically determined fusion rate for autologous bone graft was 75% (9/12 animals), compared with 100% (10/10 and 9/9 animals) for groups in which fusions were done by using Healos matrix augmented with bone marrow (P < or = 0.1). Matrix used alone yielded a fusion rate of 18% (2/11 animals, P < or = 0.006). Histologically, the most mature bone was seen in the group augmented with autologous iliac crest graft, followed in decreasing order by the groups augmented with Healos with heparinized bone marrow, Healos with unheparinized bone marrow, and Healos alone. Biomechanically, the group augmented with autologous graft had the highest mean stiffness, followed by the groups augmented with Healos with heparinized bone marrow, Healos with untreated bone marrow, and finally Healos matrix alone. However, the differences in stiffness between groups were not statistically significant with the number of spines tested.

CONCLUSIONS

These results show that Healos is an osteoconductive matrix that can be a useful carrier in the biologic and mechanical environment of a posterolateral intertransverse fusion site. In combination with bone marrow, it produces fusion rates that are comparable with those of autologous bone graft. However, it must be combined with an osteoinductive or osteogenic agent to ensure reliable fusion rates and alone cannot produce reliable osteogenesis. The Healos matrix was not compared with other commercially available matrices currently in use. Therefore, the efficacy of Healos relative to these other materials could not be determined.

Anthropometry of anterior cruciate ligament in Singaporean Chinese

Accurate reproduction of the anatomy of the anterior cruciate ligament during reconstructive surgery is paramount for obtaining good functional results. Graft size and length are important components of the reconstruction and the references we have used are Western figures. We feel that these Western figures do not apply to our local population. We performed an anthropometric study to test the hypothesis that the anterior cruciate ligament in the Singaporean Chinese is smaller than that quoted in Western literature. The study revealed that the anterior cruciate ligament in Singaporean Chinese is shorter and narrower. More importantly, the anterior cruciate ligament orientation in our study population is more vertical. This suggests that placement of the femoral tunnel in anterior cruciate ligament reconstruction has to be in a more vertical position to reproduce the physiometry of the anterior cruciate ligament.

Histochemical and molecular analyses of distraction osteogenesis in a mouse model

A tibial lengthening scheme in the mouse was used to study the molecular and cellular events regulating tissue regeneration during distraction osteogenesis. Here, we report on the surgical technique and frame design and describe the histochemical and molecular aspects of distraction during different phases of treatment. A total of 26 mice were used in this study. The treatment protocol was divided into a latency period of 7 days, a phase of active distraction that lasted 10 days with a distraction rate of 0.42 mm/day, and a maturation phase of 9 days. During latency, the distraction site resembled a stabilized fracture callus on both a histochemical and a molecular level. During active distraction, the gap was characterized by a central fibrous interzone bordered by primary matrix fronts, regenerate bone aligned with the distraction force, parallel columns of vascular sinusoids, and a medullary cavity. Alkaline phosphatase activity was detected in the endosteal and periosteal surfaces of the bone ends. Tartrate resistant acid phosphatase staining revealed that osteoclasts remodeled the bone regenerate as it formed. Collagen type I was expressed in the periosteum and the primary matrix front during distraction, whereas collagen type-II transcripts were localized to discrete regions on the periosteal surfaces, immediately adjacent to the osteotomy ends. Collagen type-II transcripts were not detected in the fibrous interzone. During the maturation phase, cells within the fibrous interzone expressed collagen type I and exhibited abundant alkaline phosphatase activity, suggesting that they had begun to terminally differentiate. Collectively, these data demonstrate the utility of a mouse model to study the molecular and cellular bases for the regeneration and remodeling of tissue.

Isolated metal-backed patellar component revision following total knee arthroplasty

BACKGROUND

Twenty-two consecutive revisions for failed metal-backed patellar components following total knee arthroplasty in 17 patients were retrospectively reviewed. All had similar total condylar knee prosthesis inserted with retention of the posterior cruciate ligament and resurfacing of the patella with a metal-backed component. There were 3 male and 14 female patients.

RESULTS

The mean time to failure of the patellar component was 60 months (range 26 to 93 months). The majority of patients presented with metallic crepitus (86.4%) and knee pain (72.7%). At surgery, full thickness polyethylene wear exposing the metal-backing was present in 81.8% with surface damage of the femoral components present in 40.9%. All 22 cases underwent successful isolated patellar component revision with all polyethylene patellar components.

CONCLUSION

Resurfacing of the patella in total knee arthroplasty with metal-backed patellar components carries a significant risk of early failure and the use of these components is no longer practised at our institution.

Chevron osteotomy for hallux valgus--SGH experience

Thirty-one chevron osteotomies for hallux valgus performed over a period of four years were reviewed. Their follow-up period ranged from one to five years. All the patients had pain over the bunion prior to operation. After operation, there was marked decrease of pain over the first matatarsophalangeal joint. The preoperative hallux valgus angle average 27 degrees and the postoperative angle averaged 12 degrees. The preoperative intermetatarsal angle averaged 13 degrees and the postoperative angle, 8 degrees. Ninety-one per cent of the patients were satisfied with the result of the procedure.

Anterior cruciate ligament reconstruction using patellar tendon autografts--a review of results

AIM

The aim of this retrospective study was to review the results of anterior cruciate ligament reconstruction using patellar tendon autografts.

METHODS

Forty-one knees were available for evaluation at a minimum of 24 months follow-up. Objective, subjective, functional and KT-1000 arthrometric tests were performed.

RESULTS

92.7% had a negative or trace pivot shift at follow-up. None of the patients had rupture of the autografts at review. The mean post-operative single-legged hop was 81%. The KT-1000 arthrometric evaluation post-operatively revealed a mean maximum manual difference of 0.5 mm; 90.2% of these patients had a maximum manual difference of less than 4 mm. Five patients (12.2%) had a "tighter" reconstructed knee (a negative mean maximum manual difference). More than 70% of the patients in this series had good to excellent results on functional, subjective and objective evaluation scores.

CONCLUSION

Excellent motion recovery, reliable stabilisation rates, good arthrometric results and encouraging post-operative functional, subjective and objective evaluation scores can be expected in patients undergoing anterior cruciate ligament reconstruction with patellar tendon autografts.

Anterior knee pain in the military population

Anterior knee pain in our military population consititutes a diagnostic and therapeutic problem that is not always easily solved. In recent years, a better understanding of the biomechanics of the patello-femoral joint has contributed to the successful classification and treatment of many patients. However, the cause of pain remains elusive in a significant subset of patients who show no clinical or radiographic evidence of patellar malalignment and continue to have persistent pain despite adequate physiotherapy. In this article, the classification and approach to anterior knee pain are reviewed. Emphasis is placed on dividing patients into four subsets namely; normal tracking, patellar tilt, patellar subluxation and extra-articular causes of anterior knee pain. A more rational approach to the problem can then be employed and successful rehabilitation and/or surgery can be expected.

Arthroscopic treatment of osteochondral lesion of the talus

A retrospective study of the arthroscopic treatment of osteochondral lesions of the talus in 25 patients was conducted. The follow-up period ranged from 1 to 4 years with an average of 2 years. Of the 25 patients, 20 could recall a history of injury. The diagnosis could be made by standard anteroposterior and lateral X-rays in 22 out of 25 patients. The standard anteromedial and anterolateral portals were usually sufficient. Patients with stage I and II lesions did well uniformly. In the 16 patients with stage III and IV lesions, good results were obtained in 12 and fair in 4. Morbidity was minimal.

Autologous marrow injection in the treatment of delayed and non-union in long bones

A retrospective study of the use of autologous bone marrow injection for the treatment of delayed and non-union of long bones in an Orthopaedic Department, Singapore General Hospital from 1990-1991 is presented. There were 10 patients with 11 fractures (8 tibia and one each of humerus, femur and radius-ulna) available for study. Percutaneous injection of autologous marrow alone was used to stimulate healing of delayed and non-unions treated initially by plating, external fixation and in one case, by plaster cast. Marrow injection stimulated a callus formation sufficient to unite 9 of the fractures. The median time to clinical union was 10 weeks (range 4-23 weeks) and radiological union 17 weeks (range 9-29 weeks). Most patients had discomfort at the donor and injected sites for one to two days. There was one case of infection but none of the significant donor site morbidity was associated with standard open autologous grafting. Bone marrow injection was effective in stimulating bony union, with numerous advantages and considerably lower morbidity compared with standard open autologous grafting. Shorter inpatient stay was a significant feature.