SUNScholar - Browsing by Author "Van der Merwe, A."

Browsing by Author "Van der Merwe, A."

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Developing a patient-specific maxillary implant using additive manufacturing and design
(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Booysen, G. J.; Van der Merwe, A.; De Beer, D.; Van den Heever, C.; Els, J.
ENGLISH ABSTRACT: Maxillectomy is the surgical removal or resection of the maxilla or upper jaw bone. A total or partial maxillectomy can be performed depending on how far the tumour has spread. This paper will discuss a patient diagnosed with an aggressive tumour in half of the top jaw who had to undergo an operation to remove the hemi-maxilla and orbital floor. Due to the extent and complexity of the defect, it was decided to manufacture an anatomical model of the hard tissues for planning a possible laser-sintered titanium implant using Additive Manufacturing (AM). The CRPM had only two weeks to design and manufacture the titanium implant, due to the severity of the tumour. The anatomical model was sent to the surgeon to cut the nylon model where the bone resection was planned. Furthermore, the prosthodontist made a wax model of the planned titanium frame that was reverse- engineered and used as reference geometry in the design software.Materialise® design suite was used to design the patient-specific maxilla and cutting jig. The EOS M280 Direct Metal Laser Sintering (DMLS) system was instrumental in achieving the direct manufacturing of the bio-compatible titanium implant. The EOS P385 system was used to manufacture the pre-operation planning model as well as the cutting jig.The process chain followed to complete this case study will be discussed showing how this intervention improved the quality of life of a SA patient. Furthermore, the proposed paper and presentation will discuss the post-operation review of the patient showing the impact AM had in accelerating patient-specific implant manufacturing. The authors seek to claim a progressed level of maturity in the proposed manufacturing value chain. The claim is based on the successful completion of the analysis and synthesis of the problem , the validated proof-of-concept of the manufacturing process and the in-vivo implementation of the final product.
Evaluation of the visual prostate symptom score in a male population with great language diversity and limited education : a study from Namibia
(Health & Medical Publication Group, 2014-05) Heyns, C. F.; Steenkamp, B. A.; Chiswo, J.; Stellmacher, G. A.; Fortsch, H.E. A.; Van der Merwe, A.
Background. A visual prostate symptom score (VPSS) using pictograms was developed to assess the force of the urinary stream, urinary frequency, nocturia and quality of life (QoL). Objective. To compare the VPSS with the international prostate symptom score (IPSS) and maximum (Qmax) and average (Qave) urinary flow rates in men from diverse language groups with limited schooling. Methods. Men with lower urinary tract symptoms admitted to the urology ward at Windhoek Central Hospital, Namibia, were evaluated. Patients who were unable to complete the questionnaires alone were assisted by a doctor or nurse. Local ethics committee approval was obtained. Statistical analysis was performed using Student’s t-test and Spearman’s rank correlation test. Results. One hundred men (mean age 56.3 years, range 20.1 - 95.4) were evaluated over a period of one year. All the men understood one or more of 15 languages, and 30 were illiterate; 32 had <5 years of schooling, 34 had 5 - 9 years and 34 had >9 years. The VPSS took significantly less time to complete than the IPSS. There were statistically significant correlations between the total VPSS and IPSS scores, between the four VPSS questions and the corresponding IPSS questions, and between Qmax and Qave and the VPSS total and VPSS questions on the force of the urinary stream and QoL. Conclusion. The VPSS pictograms depicting the force of the urinary stream and QoL correlated significantly with Qmax and Qave, indicating that they can be used as single-item questions to rapidly assess bladder outflow obstruction in men with limited education.
Isgemiese hartsiekte as risiko vir algemene narkose en chirurgie
(Health & Medical Publishing Group, 1984) Coetzee, A.; Van der Merwe, A.
The risk of myocardial reinfarction in the patient who has suffered a pre-operative infarction is well documented. In a literature search, the cardiovascular risk implied by either asymptomatic or symptomatic ischaemic heart disease (without infarction) to the patient scheduled for anaesthesia and surgery appears to be minimal provided that hypotension, hypoxia, tachyarrhythmias and hypertension are avoided. However, a myocardial ischaemic incident prior to surgery seems to warrant the postponement of elective surgical procedures.
The learning factory : a didactic platform for knowledge transfer in South Africa
(Faculty of Engineering, Department of Industrial Engineering, Stellenbosch University, 2016) Van der Merwe, A.; Hummel, V.; Matope, S.
During the first years of their employment, the graduates are a liability to industry. The employer goes an extra mile to bridge the gap between university-exiting and profitable employment of engineering graduates. Unfortunately some cannot take this risk. Given this scenario, this paper presents a learning factory approach as a platform for the application of knowledge so as to develop the required engineering competences in South African engineering graduates before they enter the labour market. It spells out the components of a Stellenbosch University Learning Factory geared towards production of engineering graduates with the required industrial skills. It elaborates on the didactics embedded in the learning factory environment, tailor-made to produce engineers who can productively contribute to the growth of the industry upon exiting the university.
Prostate cancer among different racial groups in the Western Cape : presenting features and management
(Health and Medical Publishing Group (HMPG), 2011-04) Heyns, C. F.; Fisher, M.; Lecuona, A.; Van der Merwe, A.
Objectives. We aimed to compare the presenting features and management of prostate cancer among different racial groups. Patients and methods. We studied all patients diagnosed with prostate cancer at the Urological Oncology Clinic, Tygerberg Hospital, from January 1995 to December 2005. Most presented symptomatically as PSA screening is not readily available in the referral area of the hospital. Race was self-defined as white, coloured or black. Statistical analysis was performed using Student’s t-test or Fisher’s exact test, where appropriate. A two-tailed p-value <0.05 was accepted as statistically significant. Results. There were 901 patients: 291 (32.3%) white, 539 (59.8%) coloured and 71 (7.9%) black. Mean age at presentation was significantly higher in the white than the coloured and black groups (69.7, 67.9 and 68.9 years, respectively). Grade 1 adenocarcinoma was most common in the white (37%) and coloured groups (38%), and grade 2 was most common in the black group (39%). There was a significantly lower percentage of patients with T3-4 disease at diagnosis in the white group (47%) than the coloured (61%) and black (62%) groups. Mean serum PSA at diagnosis was significantly higher in the black than the coloured and white groups (766.1, 673.3 and 196.1 ng/ml, respectively). Potentially curative therapy (radical prostatectomy or radiotherapy) was chosen by 31% of white, 23% of coloured and only 12% of black patients. The mean duration of follow-up was significantly shorter in the black than in the white or coloured groups (24.0, 31.5 and 35.0 months, respectively). Conclusions. Black men presented with higher grade and stage disease and higher serum PSA, received potentially curative treatment less often, and had a shorter follow-up (probably owing to shorter survival) than the white and coloured groups. Greater prostate cancer awareness and education among patients and physicians and more widespread use of PSA screening of presymptomatic men at risk of prostate cancer is needed.
Prostate specific antigen : brief update on its clinical use
(AOSIS, 2008) Heyns, C. F.; Van der Merwe, A.
Prostate specific antigen (PSA) testing of asymptomatic men enables the diagnosis of localised prostate cancer which is potentially curable, but it also poses certain risks. Doctors run the risk of litigation for failure to diagnose cancer at a curable stage, while patients run the risk of being diagnosed with non-significant cancer, incurring costs and possible complications without any survival benefit. PSA reflects a 'range of risk' for prostate cancer: the higher the PSA, the greater the risk. There is no 'normal' PSA, because even with a PSA below 4 ng/ml cancer can be detected on biopsy in up to 20% of men. However, the prevalence of high-grade (life-threatening) cancer is relatively low at low PSA values. The following recommendations appear reasonable: • PSA testing should be offered to all men aged 50 years or more (45 years in those with a family history of prostate cancer and - possibly - African men); • Alternatively, PSA testing should be done at 40, 45 and 50 years and then every two to four years (the lower the baseline value, the lower the risk of ever developing prostate cancer); • PSA testing should be repeated annually if it is more than 2 ng/ml and every two years if less than 2 ng/ml; • Stop PSA testing in asymptomatic men over 75 years or with less than 10 years' life expectancy, and in those aged over 65 years with PSA less than 0.5 to 1 ng/ml. The free-to-total PSA ratio and PSA density (PSA divided by prostate volume) can be used to decide which patients need prostatic biopsy. PSA velocity (increase of PSA per year) can predict which men are likely to develop prostate cancer or to die of it (the higher the PSA velocity, the greater the risk). PSA doubling time (the period it takes for the PSA to double) correlates with the prognosis both before and after treatment (the shorter the doubling time, the worse the prognosis). An internet Prostate Cancer Risk Calculator is available which calculates a man's risk by taking into account his age, race, family history, PSA level, findings on rectal examination and prior negative biopsy. Although this is a very convenient tool, it should be used with caution, especially at low PSA values, because there is a real risk of overdiagnosis.
Renal artery embolisation : indications and utilisation at Tygerberg Hospital
(Health and Medical Publishing Group, 2019) Pretorius, R.; Vlok, S.; Van der Merwe, A.; Zarrabi, A. D.; Du Toit, K.
ENGLISH ABSTRACT: To evaluate the indications, efficacy and outcomes of endovascular renal artery embolisation (RAE) in the management of renal haemorrhage, specifically in cases of non-iatrogenic origin. METHODS: This is a retrospective case note review of 92 patients who underwent RAE in the period from August 1999 to August 2014 at Tygerberg Hospital. RESULTS: Renal artery embolisation was performed in a total of 92 patients. The indication was traumatic renal injury in 60 patients (65.2%), with mean age 28.2 years. The mechanism of injury was stabbing (55.4%), blunt trauma (7.6%) and gunshot (2.2%). Digital subtraction angiography (DSA) showed pseudo-aneurysm in 32.6%, arteriovenous fistula in 19.6% and segmental artery injury in 13%. : 85% after one, 88.9% after a second attempt, with an overall success rate of 98.3% after two attempts. In 20 of the 92 patients (mean age 50.2 years) the indication was malignancy (21.7%). Other cases included iatrogenic haematuria (4.3%) and angiomyolipoma (3.3%). Embolisation was repeated in 16.3%, with eventual success rate of 93.8%. Post-embolisation syndrome was the most common complication, seen in 9.8% of all cases. Of the 9 patients who returned for follow-up with renogram imaging, 4 had a differential function of > 20% of the embolised kidney. CONCLUSION: Renal artery embolisation remains a very successful method of managing renal haemorrhage at this hospital, whether this results from trauma, malignancy, iatrogenic or other causes.
Retroperitoneoscopic live donor nephrectomy : review of the first 50 cases at Tygerberg Hospital, Cape Town, South Africa
(Health & Medical Publishing Group, 2014-06) Van der Merwe, A.; Heyns, C. F.
Background. Changing from an open to a laparoscopic live renal donor programme poses challenges and may affect donor and graft outcomes. Objectives. To evaluate donor safety and graft outcomes for the first 50 retroperitoneoscopic live donor nephrectomies performed at Tygerberg Hospital, Cape Town, South Africa. Methods. The procedures were performed by a single surgeon from 8 April 2008 to 3 April 2012. Operative and anatomical data were prospectively collected. A flank approach with lateral and posterior placements was used. Vascular control was achieved with Hem-o-lok clips in the majority of cases. Results. The mean age of the donors was 31.5 years (range 18 - 50), 28 (56.0%) were male, and the left kidney was harvested in 28 (56.0%) of cases. The mean operating time was 149.8 minutes (range 75 - 250), mean warm ischaemic time (WIT) 181.3 seconds (107 - 630), mean blood loss 139.7 ml (5 - 700) and mean hospital stay 3.2 days (2 - 5). Mean WIT was significantly longer for right-sided than left-sided nephrectomy (213 v. 162 seconds). In two right-sided cases the renal vein was too short and vena profunda femoris was used to create length. No donor received a blood transfusion. Comparing the last 25 with the first 25 cases showed a significant decrease in mean WIT (158 v. 204 seconds, respectively) and operating time (128 v. 172 minutes, respectively). No major complications occurred. Conclusion. Our initial 50 retroperitoneoscopic live donor nephrectomies were performed without major complications. Donor safety was maintained during the early learning curve of the transition to minimal-access donor nephrectomy.
The role and value of water in natural capital restoration on the Agulhas Plain
(University of Pretoria, 2013) Fourie, Helanya; De Wit, Martin P.; Van der Merwe, A.
The Agulhas Plain is a low-lying coastal area within the Cape Floristic Region. It is heavily invaded by alien vegetation that infringes upon the sustainable supply of ecosystem goods and services provided by the native fynbos vegetation. Alien clearing and natural capital restoration is expected to recover these ecosystem goods and services and in particular to increase water availability. The study conducts cost-benefit analyses to assess whether alien clearing and natural capital restoration would add value to the Agulhas Plain through sufficiently increasing the supply of marketable ecosystem goods and services. The results indicate that the costs of alien clearing and restoration cannot be justified in the absence of water as a valued commodity. Other ecosystem goods and services included have a negligible impact on justifying costs.
Should baseline PSA testing be performed in men aged 40 to detect those aged 50 or less who are at risk of aggressive prostate cancer?
(Health and Medical Publishing Group (HMPG), 2011-09) Heyns, C. F.; Fisher, M.; Lecuona, A.; Van der Merwe, A.
We aimed to evaluate the presenting features and treatment outcome of prostate cancer in men aged <50 years, in a region where prostate specific antigen (PSA) screening is not readily available and most men present with symptoms. Methods. We analysed the data of 1 571 men with prostatic adenocarcinoma treated between January 1997 and December 2008 at our institution, a tertiary level public sector hospital serving a largely indigent population. Statistical analysis was performed using Student’s, the Mann-Whitney and Fisher’s exact tests where appropriate (p<0.05 accepted as statistically significant). Results. Of 1 571 men, 47 (3%) were aged <50 years. The group aged <50 years, compared with that aged >50 years, had a significantly greater proportion with poorly differentiated adenocarcinoma (53%), locally advanced (stage T3 - 4) tumours (56%), haematogenous metastases (75%), significantly higher serum PSA at diagnosis (mean 621, median 74 ng/ml) and shorter survival. Conclusions. Men aged <50 years presenting with symptoms owing to prostate cancer had significantly higher-risk disease, higher mean PSA, and poorer prognosis than men aged >50 years. To diagnose prostate cancer at a potentially curable stage in men aged <50 years, it is necessary to initiate baseline PSA testing at age 40 and 45 years, and to select high-risk men for PSA surveillance in order to diagnose potentially curable cancer in those with a life expectancy >20 - 25 years.
Successful en bloc transplantation of a horseshoe kidney without division of the isthmus : first case reported in South Africa
(Health and Medical Publishing Group, 2018) Zarrabi, A. D.; Wessels, S. G.; Vlok, L.; Van der Merwe, A.
This case is the first report of an en bloc transplantation of a horseshoe kidney in South Africa. The graft anatomy included complete fusion of the lower poles of the two kidney units with a single artery and vein associated with each unit. The thick isthmus of the graft kidney was supplied by a single, large caliber anomalous artery. Bench work (total duration 160 minutes) included the preparation of a short segment of donor aorta and IVC (containing the renal vessels) which were anastomosed to the recipient common iliac artery and common iliac vein respectively. The artery of the isthmus was anastomosed to the recipient right internal iliac artery. The graft was placed intraperitoneally. Cold ischaemia time was 15 hours, warm ischaemia time 144 minutes, total procedure time 450 minutes and estimated blood loss 1100 ml. Renogram (99mTc MAG-3) on days 1, 3 and 14 postoperatively revealed ATN. Hospital stay was 17 days and nadir creatinine at 6 weeks was 77 μmol/l.
Treatment of male urethral strictures - possible reasons for the use of repeated dilatation or internal urethrotomy rather than urethroplasty
(Centre of African Studies, University of Cape Town, 2012-08) Heyns, C. F.; Van der Merwe, J.; Basson, J.; Van der Merwe, A.
Objective. To investigate the possible reasons for repeated urethral dilatation or optical internal urethrotomy rather than urethroplasty in the treatment of male urethral strictures. Patients and methods. Men referred to the stricture clinic of our institution during the period April 2007 - March 2008 were reviewed and the operative urological procedures performed in the same period were analysed. Statistical analysis was performed using Student’s t-test and Fisher’s exact test (p<0.05 statistically significant). Results. The mean age of the 125 men was 49.9 years (range 12.8 - 93.4 years). Previous stricture treatment had been given 1 - 2, 3 - 4 and 5 - 6 times in 52%, 32% and 12% of patients, respectively (4% had not undergone treatment). In these groups, previous treatment was dilatation in 70%, 76% and 72%, urethrotomy in 26%, 15% and 28%, and urethroplasty in 4%, 9% and 0, respectively. The group with 5 - 6 compared with 1 - 2 previous treatments was significantly older (mean age 60.2 v. 46.6 years) and had a significantly greater proportion with underlying co-morbidities (80% v. 52%). The group that had undergone urethroplasty compared with 5 - 6 repeated dilatations or urethrotomies was significantly younger (mean age 48.2 v. 60.2 years) with a lower prevalence of co-morbidities (47% v. 80%). During the study period urethroplasty was performed in 16 (2%) of 821 inpatients, whereas 55 men were seen who had undergone ≥3 previous procedures, indicating that urethroplasty was performed in less than one-third of cases in which it would have been the optimal treatment. Owing to limited theatre time, procedures indicated for malignancy, urolithiasis, renal failure and congenital anomalies were performed more often than urethroplasty. Conclusions. Factors that possibly influenced the decision to perform repeated urethrotomy or dilatation instead of urethroplasty were limited theatre time, increased patient age and the presence of underlying co-morbidities.

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