Touching reality: Bridging the user-researcher divide in upper-limb prosthetics.

Realistically improving upper-limb prostheses is only possible if we listen to users' actual technological needs.

Robotic retroperitoneal lymph node dissection for primary and post-chemotherapy testis cancer.

The role of retroperitoneal lymph node dissection (RPLND) in testicular cancer is well established in both the primary and post-chemotherapy setting. The aim of this study was to report our 2 years oncological outcomes of robotic RPLND. A retrospective review was performed of all patients undergoing robotic RPLND by a single surgeon at Princess Margaret Cancer Centre. Demographic, perioperative, and oncologic data were analyzed using descriptive statistics. Between September 2014 and June 2020, 141 patients underwent an RPLND [33 (23.4%) were primary, 108 (76.6%) were post-chemotherapy]. 27 (19.1%) patients underwent a robotic bilateral template nerve-sparing RPLND. RPLND indication was primary (i.e. pre-chemotherapy) in 18 (66.7%), and post-chemotherapy in 9 (33.3%) patients. Stage at RPLND was 2A (n = 15, 55.6%), 2B (n = 9, 33.3%), 2C (n = 1, 3.7%) and 3 (n = 2, 7.4%). Median OR time (incision to closure) was 525 min and blood loss was 200 ml. Nerve sparing was performed in all but one case. Six (22.2%) adjuvant procedures were performed including two (7.4%) vascular repairs. Median length of stay was 2 days. Viable tumor was detected in 17 (63%) and teratoma in 9 (33.3%). Median follow-up was 31.3 months. No adjuvant chemotherapy was given. Three patients (11.1%) relapsed: 2 out-of-field and 1 with both in-field and out-of-field disease. Robotic RPLND can be performed safely. Long-term follow-up of series such as ours, enriched with patients with viable disease and/or teratoma, and not treated with adjuvant chemotherapy is required to ensure oncological outcomes are comparable to the open approach.

Medical imaging call centre: a communication success story.

AIM: To evaluate utilisation of a medical imaging call centre (MICC) at a multi-site, academic radiology department, focusing on communication of critical, urgent, or significant unexpected findings. MATERIALS AND METHODS: Institutional research ethics board approval was obtained. All calls made to MICC from 1 January to 31 December 2019 were reviewed retrospectively. The total number of calls, date, and reason of each call, level of report alert, and turnaround time (TAT) were recorded. Level 1, 2, and 3 alerts were defined as "potentially life-threatening new/unexpected findings", "could result in morbidity/mortality", or "not immediately life-threatening or urgent", respectively. TAT was defined as the time from alert request received by the MICC until acknowledgement of receipt by the referring physician, with a desired TAT of 60 min, 3 h, and 3 days for each level, respectively. RESULTS: The MICC received 29,799 calls in 2019, on average 2,483 (range 1,989-3,098) calls per month. The most common indications for contacting the MICC were to request imaging reports to be expedited (14,916 calls, 50%) and issuing report alerts to communicate unexpected or urgent findings (7,060 calls, 24%). Average number and range of calls for Level 1, 2, and 3 alerts were 57 (39-80), 345 (307-388), and 187 (127-215) per month, respectively. Average TAT for Level 1, 2, and 3 report alerts were 59 min, 2 h 26 min, and 19 h 39 min, respectively. CONCLUSION: The MICC received a large volume of calls and was a successful method for timely communication of unexpected or urgent imaging findings using a three-tiered alert system.

A Low Percentage of Patients Satisfy Typical Indications for Single-stage Exchange Arthroplasty for Chronic Periprosthetic Joint Infection.

BACKGROUND: Periprosthetic joint infection (PJI) is a leading cause of revision arthroplasty. Considerable controversy still exists whether single- or two-stage exchange is the better approach for patients with chronic PJI. Historically, single-stage exchange arthroplasty was thought to have an unacceptably high risk of reinfection compared with two-stage exchange but recent studies have demonstrated that this may not be the case. To be considered for single-stage exchange, patients should meet certain criteria including a preoperatively identified nonvirulent pathogen in an immunocompetent host with an uncompromised soft tissue envelope. It is unclear what proportion of patients with chronic PJI actually meet these criteria. Additionally, patients who meet the criteria for single-stage exchange are selected because, in principle, they may be more likely to be able to overcome the infection, but it is unknown what the reinfection risk is in patients undergoing two-stage exchange who might have met selection criteria for single-stage exchange. QUESTIONS/PURPOSES: (1) What percentage of patients with chronic PJI treated at our institution met the International Consensus Meeting criteria for single-stage exchange arthroplasty? (2) Is the risk of persistent or recurrent infection lower for patients treated with two-stage exchange who met International Consensus Meeting criteria for single-stage exchange than it is among those who did not meet those inclusion criteria? METHODS: Between 2012 and 2016, one referral center treated 120 patients with chronic PJI as determined by Musculoskeletal Infection Society (MSIS) criteria. During this time, we used single-stage exchange only rarely in patients with chronic PJI (3%; four of 120), and only in oncologic patients with mega-prosthesis implants; 7% (eight of 120) underwent other procedures (resection arthroplasty or arthrodesis). Of the remaining 108, 16% (17) were lost to follow-up; the remaining 91 were evaluated in this retrospective study. To answer our first question, we applied the International Consensus Meeting indications for single-stage exchange, which were a known nonvirulent preoperative organism, an immunocompetent host, and a healthy soft-tissue envelope without a sinus tract; we then calculated the percentage of patients who would have met those criteria. To answer our second question, we compared those who would and would not have met those criteria in terms of the proportion who were determined to be infection-free at 2 years using the MSIS criteria. RESULTS: Only 19% (20 of 108) of patients met the International Consensus Meeting criteria for single-stage exchange. With the numbers available, there was no difference between those who met and did not meet those criteria in terms of the proportion of patients who had persistent or recurrent infection 2 years after treatment (three of 15 versus 32% [24 of 76]; p = 0.38). CONCLUSIONS: We found that only a small proportion of patients who presented with chronic PJI to a referral center would have been suitable for single-stage direct exchange; with the numbers available, we found no difference in the reinfection risk after two-stage revision in those patients compared with those who would not have met those criteria. Consequently, it is possible that a small proportion of patients may benefit from single-stage exchange, but our small sample size may have missed important differences in reinfection risk, and so our findings on that question must be considered preliminary. Larger studies randomizing patients who meet single-stage criteria to either single- or two-stage exchange will better elucidate the true reinfection risk in this patient population. LEVEL OF EVIDENCE: Level III, therapeutic study.

Partial orchiectomy: The Princess Margaret cancer centre experience.

INTRODUCTION: Radical orchiectomy (RO) is the standard treatment for a testis cancer. Organ sparing surgery can be considered in the setting of a solitary functioning testis or bilateral tumors. It has also been suggested as an alternative to RO for small lesions. In this study we report our partial orchiectomy (PO) experience. METHODS: We performed a retrospective review using our prospectively maintained database analyzing PO. RESULTS: Between 1983 and 2018, 77 patients underwent PO. Mean age was 31.3 years (range 17-56). A lesion was palpable in 70 (90.9%) and median lesion size 14.1 mm (range 3-35 mm). Reasons for PO included ``small lesion" in 39 (50.6%); solitary functioning testis in 30 (39%); bilateral lesions in 6 (7.8%); or assumed benign lesion in 1 (1.3%). Median follow-up was 43.5 months (range 1-258). Lesion histology was benign in 25 (32.5%). A positive surgical margin was noted in 6 (7.8%) with none developing local or distant recurrence. Sixteen (20.8%) patients underwent salvage ipsilateral RO at a median of 3 months (range 0-46). Reasons for salvage RO included a radiologically detected lesion in 7, palpable lesion in 4, positive surgical margin in 3 and adverse pathology in 2 patients. Malignant histology was present in 12 (75%) of the salvage RO specimens. There were no reported Clavien-Dindo Grade 3 to 5 complications. CONCLUSION: Organ sparing surgery is a safe and feasible approach to small testis lesions. For the third with benign disease, and even those with malignant histology, a RO can be avoided in carefully selected patients.

Development of a new patient-reported outcome measure to evaluate treatments for acne and acne scarring: the ACNE-Q.

BACKGROUND: Psychosocial concerns represent important outcomes in studies of treatments for acne and acne scarring. Also important, but largely overlooked, is the concept of appearance. OBJECTIVES: To design an acne-specific patient-reported outcome measure for acne and acne scarring. METHODS: We used a mixed-methods approach. Phase I involved 21 patient interviews that were audio-recorded, transcribed and coded. Concepts were identified and developed into scales that were refined through 10 cognitive interviews and input from 16 clinical experts. Phase II involved data collection at hospital and community-based dermatology clinics in Canada and the U.S.A. Eligible participants were aged 12 years and older with acne and/or acne scars on the face, chest and/or back. Rasch Measurement Theory (RMT) analyses were performed to examine psychometric properties. RESULTS: Phase I led to the development of seven scales that measure appearance of facial skin, acne (face, chest and back) and acne scars, acne-specific symptoms and appearance-related distress. In phase II, 256 patients completed the ACNE-Q. RMT analysis provided evidence that the items of each scale worked together conceptually and statistically. Most participants scored within the range of measurement for each scale (81·9-93·1%). Reliability was high, with person separation index values and Cronbach alpha values > 0·90 for the appearance scales, ≥ 0·87 for appearance-related distress and ≥ 0·75 for symptoms. Worse scores on appearance scales correlated with worse symptom scores and more appearance-related distress. CONCLUSIONS: The ACNE-Q is a rigorously developed instrument that can be used to measure appearance and other patient-centred concerns. What's already known about this topic? Acne is a common dermatological condition that can have an important impact on psychosocial function. Current patient-reported outcome measures specific to acne focus mostly on measuring psychological and social impact. What does this study add? The ACNE-Q provides a set of independently functioning scales that measure appearance of facial, back and chest acne, acne scarring and facial skin. Additional scales measure appearance-related distress and acne symptoms. What are the clinical implications of this work? ACNE-Q provides the dermatology community with a rigorously developed patient-reported measure for acne that can be applied in clinical trials, research and patient care. The measurement of appearance by ACNE-Q scales is more comprehensive than in other instruments providing important information on appearance of their acne and/or acne scars from the patient perspective.

Clinical Characteristics and Outcomes of Late Relapse in Stage I Testicular Seminoma.

AIMS: To identify the characteristics and outcomes associated with late relapse in stage I seminoma. MATERIALS AND METHODS: A retrospective review was carried out of all patients with stage I seminoma managed at our institution between 1981 and 2011. Data were obtained from a prospectively maintained database. Late relapse was defined as tumour recurrence > 2 years after orchiectomy. RESULTS: Overall, 1060 stage I seminoma patients were managed with active surveillance (n=766) or adjuvant radiotherapy (n=294). At a median follow-up of 10.6 years (range 1.2-30), 142 patients relapsed at a median (range) of 14 (3-129) months; 128 on active surveillance and 14 after adjuvant radiotherapy. The late relapse rate for the active surveillance and adjuvant radiotherapy groups was 4% and 1%, respectively. There was no specific clinicopathological factor associated with late relapse. Isolated para-aortic node(s) was the most common relapse site in active surveillance patients either in late (88%) or early relapse (82%). Among the active surveillance group, no patients with late relapse subsequently developed a second relapse after either salvage radiotherapy (n=25) or chemotherapy (n=6), whereas in early relapse patients a second relapse was reported in seven (10%) of 72 patients treated with salvage radiotherapy and one (4%) of 23 patients who received chemotherapy; all second relapses were subsequently salvaged with chemotherapy. No patient in the adjuvant radiotherapy group developed a second relapse after salvage chemotherapy (n=10) or inguinal radiotherapy/surgery (n=4). Of seven deaths, only one was related to seminoma. Among active surveillance patients, the 10 year overall survival for late and early relapse groups were 100% and 96% (P = 0.2), whereas the 10 year cancer-specific survival rates were 100% and 99% (P = 0.3), respectively. CONCLUSIONS: In stage I seminoma, the extent and pattern of late relapse is similar to that for early relapse. For active surveillance patients, selective use of salvage radiotherapy/chemotherapy for relapse results in excellent outcomes regardless of the timing of relapse, whereas salvage radiotherapy for late relapse seems to be associated with a minimal risk of second relapse.

Endovascular Aneurysm Repair Increases Aortic Arterial Stiffness When Compared to Open Repair of Abdominal Aortic Aneurysms.

OBJECTIVES: The initial survival advantage seen with endovascular aneurysm repair (EVAR) over open repair does not persist in the long term. Pulse wave velocity (PWV) is a measure of arterial stiffness, and increased PWV is an independent risk factor for increased cardiovascular morbidity and mortality. This prospective comparative pilot study examined the effect of implantation of an aortic graft on PWV in patients undergoing open or endovascular aortic aneurysm repair. PATIENTS AND METHODS: Thirty-four patients (15 open and 19 EVAR) were recruited. Patient demographics were similar in both the groups. Pulse wave velocity was calculated for all patients preoperatively and postoperatively using a standardized technique on a Philips IU22 Vascular Ultrasound machine and the results compared. RESULTS: An increase in mean PWV following EVAR was demonstrated. The mean postprocedure PWV of 9.7 (± 4.5) cm/sec detected in the open group was significantly lower than the elevated 12.2 (± 4.5) cm/sec detected in the EVAR group. The surgical group also demonstrated a mean decrease of 0.2 (± 4.9) cm/sec in PWV following open repair compared to a mean increase of 3.3 (± 3.7) cm/sec in the EVAR group. CONCLUSION: EVAR patients have a significantly higher postoperative PWV measurement than those undergoing open abdominal aortic aneurysm repair. Patients who have undergone EVAR may be at a higher risk of cardiovascular morbidity in the long term. A larger scale study with a longer prospective follow-up is required.

Wedge effect following intramedullary hip screw fixation of intertrochanteric proximal femur fracture.

INTRODUCTION: The aim of the current study was to determine whether application of an intramedullary hip screw for definitive management of intertrochanteric fracture was associated with post-operative deformity. Specifically this study investigated whether nail insertion would cause a "wedge effect" of the intertrochanteric fracture manifesting as lateralization of the femoral shaft and varus malalignment. MATERIALS AND METHODS: The trauma database at the University of Pittsburgh Medical Center was investigated to identify all intertrochanteric fractures (AO/OTA 31A) over the past 3 years treated with an IMHS. Fractures eligible for inclusion were performed under the supervision of a fellowship trained orthopedic trauma surgeon. All fractures were reduced in optimal alignment using percutaneous or mini-open strategies during the reaming process and nail insertion. The entry portal was over-reamed by at least 1.5 mm. Cases selected for review of the "wedge effect" had optimal post-operative imaging allowing for assessment of discrepancy between the operative and normal hip. RESULTS: Forty six patients with an average age of 77 years were included for study. Fifty percent were classified as unstable patterns. Shaft lateralization following IMHS fixation of the fractured hip was found to be an average of 7 mm greater than the contralateral intact hip (p < 0.001) (range 0-30 mm). The neck-shaft angle of the operative hips was 129° as compared to 133° on the intact side (p = 0.009). The stability of the fracture pattern was not predictive for post-operative lateralization of the femoral shaft or varus angulation (p > 0.05) (Table 2). There was no difference in post-operative deformity among techniques used for maintenance of reduction during reaming and nail insertion (p > 0.05). Despite deformity, all cases demonstrated radiographic radiographic fracture union. CONCLUSION: Despite attention to detail, the application of an intramedullary hip screw for intertrochanteric fracture has the tendency to lateralize the shaft relative to the head/neck segment (The "wedge effect").

Genotype-defined cancer risk in juvenile polyposis syndrome.

BACKGROUND: Germline mutations in SMAD4 and BMPR1A disrupt the transforming growth factor ß signal transduction pathway, and are associated with juvenile polyposis syndrome. The effect of genotype on the pattern of disease in this syndrome is unknown. This study evaluated the differential impact of SMAD4 and BMPR1A gene mutations on cancer risk and oncological phenotype in patients with juvenile polyposis syndrome. METHODS: Patients with juvenile polyposis syndrome and germline SMAD4 or BMPR1A mutations were identified from a prospectively maintained institutional registry. Medical records were reviewed and the clinical patterns of disease were analysed. RESULTS: Thirty-five patients had germline mutations in either BMPR1A (8 patients) or SMAD4 (27). Median follow-up was 11 years. Colonic phenotype was similar between patients with SMAD4 and BMPR1A mutations, whereas SMAD4 mutations were associated with larger polyp numbers (number of patients with 50 or more gastric polyps: 14 versus 0 respectively). The numbers of patients with rectal polyps was comparable between BMPR1A and SMAD4 mutation carriers (5 versus 17). No patient was diagnosed with cancer in the BMPR1A group, whereas four men with a SMAD4 mutation developed gastrointestinal (3) or extraintestinal (1) cancer. The gastrointestinal cancer risk in patients with juvenile polyposis syndrome and a SMAD4 mutation was 11 per cent (3 of 27). CONCLUSION: The SMAD4 genotype is associated with a more aggressive upper gastrointestinal malignancy risk in juvenile polyposis syndrome.

Comparison of colour duplex ultrasound with computed tomography to measure the maximum abdominal aortic aneurysmal diameter.

Introduction. Maximum diameter of an abdominal aortic aneurysm (AAA) is the main indication for surgery. This study compared colour duplex ultrasound (CDU) and computed tomography (CT) in assessing AAA diameter. Patients and Methods. Patients were included if they had both scans performed within 90 days. Pearson's correlation coefficient, paired t-test, and limits of agreement (LOA) were calculated for the whole group. Subgroup analysis of small (<5.0 cm), medium (5.0-6.5 cm), and large (>6.5 cm) aneurysms was performed. A P value of <0.05 was considered statistically significant. Results. 389 patients were included, giving 130 pairs of tests for comparison. Excellent correlation was in the whole group (r = 0.95) and in the subgroups (r = 0.94; 0.69; 0.96, resp.). Small LOA between the two imaging modalities was found in all subgroups. Conclusion. Small aneurysms can be accurately measured using CDU. CDU is preferable for small AAAs, but cannot supplant CT for planning aortic intervention.

Statins promote residual aneurysm sac regression following endovascular aortic aneurysm repair.

BACKGROUND: Regression of the residual sac is indicative of successful endovascular aortic aneurysm (EVAR) repair. Using color duplex ultrasound (CDU), we monitored the residual aneurysm sac following EVAR and correlated sac behavior with perioperative risk factors. METHODS: Of 145 patients with EVAR, 106 (73.1%) patients between January 01, 2003, and July 01, 2010, had at least 2 consecutive postoperative scans and thus were eligible for inclusion. Mean (± standard deviation [SD]) CDU scans per person was 4.6 (± 1.4). All were conducted by the same technologist using a standard protocol on the same machine. Aneurysm sac change in centimeters and percentage terms was calculated. The presence or absence of an endoleak was also recorded. Change in aneurysm sac size was correlated with preoperative risk factors. FINDINGS: Mean sac size change at 1 month was a decrease of 0.24 cm, equating to a percentage change of 4.3%. At 7 months, the decrease was 0.59 cm (9.8%), at 12 months, 0.73 cm (12.4%), at 18 months 0.92 cm (15.8%), and at 36 months 1.0 cm (16.6%). Both univariate and multivariate analyses demonstrated that statin therapy (P = .002) was the only risk factor variable positively associated with aneurysm regression while the presence of an endoleak was inversely related to sac reduction (P = .01). INTERPRETATION: Maximum aneurysmal sac reduction seems to occur in the first year following endograft implantation. Statin therapy appears to be associated with an increased likelihood of sac regression following EVAR. Further investigation of the role of statins in the biology of abdominal aortic aneurysmal disease is warranted.

Inhibitors of C5 complement enhance vaccinia virus oncolysis.

Genetically engineered tumor-selective vaccinia virus (VV) has been demonstrated to be a highly effective oncolytic agent, but immune clearance may limit its therapeutic potential. As previously demonstrated, immunosuppression can lead to significant enhancement of viral recovery and therapeutic effect, but the magnitude of complement-mediated viral inactivation has not been fully elucidated and warrants further investigation. Using fluorescent microscopy and quantitative plaque assays, we have determined complement's key role in viral clearance and its multi-faceted means to pathogen destruction. Complement can lead to direct viral destruction and inhibition of viral uptake into cells, even in the absence of anti-vaccinia antibodies. Our data demonstrate C5 to be integral to the clearance pathway, and its inhibition by Staphylococcal superantigen-like protein leads to a 90-fold and 150-fold enhancement of VV infectivity in both the presence and absence of anti-VV antibodies, respectively. This study suggests that complement inhibition may reduce vaccinia viral neutralization and may be critical to future in vivo work.

Importance of strict patient selection criteria for combined carotid endarterectomy and coronary artery bypass grafting.

BACKGROUND: Management of patients with severe concomitant carotid and coronary disease remains controversial. We report our experience of combined carotid endarterectomy (CEA) and coronary artery bypass surgery (CABG) over a fifteen year period using strict patient selection criteria. METHODS: From 1st January 1995 to December 31st 2009 165 patients underwent combined CABG/CEA procedures at the Mater Hospital. Mean age was 68.2 years (range 43-88) and 127 (77%) were male. Fifty-three (32%) had symptomatic carotid disease. Indications for combined procedures were the presence of symptomatic >70% or asymptomatic >80% internal carotid artery stenosis in a patient requiring urgent CABG because of either unstable angina, recent MI, severe triple vessel disease or severe Left Anterior Descending or Left Main Stem stenosis. RESULTS: Thirty-day stroke and death rate was 3%. All neurological events were in the hemisphere contralateral to the carotid surgery and symptoms had completely resolved prior to discharge from hospital. One patient required evacuation of a cervical haematoma and there were two transient XII nerve palsies. CONCLUSION: Combined CEA/CABG can be performed safely with acceptable morbidity and mortality in patients selected in accordance with strict criteria in a centre with a large experience of both cardiac and carotid surgery.

Use of colour duplex ultrasound as a first line surveillance tool following EVAR is associated with a reduction in cost without compromising accuracy.

INTRODUCTION: CT scanning remains the postoperative surveillance imaging modality of choice following EVAR. Concerns regarding cost, exposure to ionising radiation and intravenous contrast have led to a search for a less expensive, equally efficacious and safer method of monitoring EVAR patients after endograft deployment. This study evaluated the cost saving obtained if CDUS was employed as a first line surveillance tool following EVAR, as well as comparing the two entities in terms of efficacy. PATIENTS & METHODS: Postoperative surveillance CTs and CDUS scans in the 145 patients who have undergone EVAR from 1st June 2003 to 1st July 2010 were compared for the detection of endoleak and determination of residual sac size. RESULTS: Adopting a protocol where CDUS was employed as the first line surveillance tool following EVAR would result in a reduction in the number of postoperative CTs required in 2010 from 235 to 36. Based on 2010 costings, this would equate to an estimated reduction in expenditure from €117,500 to €34,915 a saving of €82,585. CDUS had a sensitivity of 100% and a specificity of 85% in the detection of endoleaks compared to CT. The positive predictive value was 28% and negative predictive value 100%. The Pearson Coefficient correlation of 0.96 indicates a large degree of correlation between CDUS and CT when measuring residual aneurysm size following EVAR. CONCLUSION: CDUS can replace CT as the first line surveillance tool following EVAR. This is associated with a significant reduction in the cost of surveillance without any loss of imaging accuracy.

Oncolytic poxvirus armed with Fas ligand leads to induction of cellular Fas receptor and selective viral replication in FasR-negative cancer.

Tumor necrosis factor superfamily members, including Fas ligand and TRAIL, have been studied extensively for cancer therapy, including as components of gene therapy. We examined the use of FasL expression to achieve tumor-selective replication of an oncolytic poxvirus (vFasL), and explored its biology and therapeutic efficacy for FasR- and FasR+ cancers. Infection of FasR+ normal and MC38 cancer cells by vFasL led to abortive viral replication owing to acute apoptosis and subsequently showed both reduced pathogenicity in non-tumor-bearing mice and reduced efficacy in FasR+ tumor-bearing mice. Infection of FasR- B16 cancer cells by vFasL led to efficient viral replication, followed by late induction of FasR and subsequent apoptosis. Treatment with vFasL as compared with its parental virus (vJS6) led to increased tumor regression and prolonged survival of mice with FasR- cancer (B16) but not with FasR+ cancer (MC38). The delayed induction of FasR by viral infection in FasR- cells provides for potential increased efficacy beyond the limit of the direct oncolytic effect. FasR induction provides one mechanism for tumor-selective replication of oncolytic poxviruses in FasR- cancers with enhanced safety. The overall result is both a safer and more effective oncolytic virus for FasR- cancer.

The Task-Dependent Efficacy of Shared-Control Haptic Guidance Paradigms.

Shared-control haptic guidance is a common form of robot-mediated training used to teach novice subjects to perform dynamic tasks. Shared-control guidance is distinct from more traditional guidance controllers, such as virtual fixtures, in that it provides novices with real-time visual and haptic feedback from a real or virtual expert. Previous studies have shown varying levels of training efficacy using shared-control guidance paradigms; it is hypothesized that these mixed results are due to interactions between specific guidance implementations ("paradigms") and tasks. This work proposes a novel guidance paradigm taxonomy intended to help classify and compare the multitude of implementations in the literature, as well as a revised proxy rendering model to allow for the implementation of more complex guidance paradigms. The efficacies of four common paradigms are compared in a controlled study with 50 healthy subjects and two dynamic tasks. The results show that guidance paradigms must be matched to a task's dynamic characteristics to elicit effective training and low workload. Based on these results, we provide suggestions for the future development of improved haptic guidance paradigms.