Facial Rejuvenation Using a Mixture of Calcium Hydroxylapatite Filler and Hyaluronic Acid Filler.

Calcium hydroxylapatite filler is a popular dermal filler, as it provides long-lasting results. However, it sometimes undergoes unexpected early volume loss, due to rapid gel absorption before neocollagenesis. To compensate for this phenomenon, hyaluronic acid filler was added to calcium hydroxylapatite filler for injection as a mixture. Twenty-five patients who scored 1 or 2 on the Merz 5-point scale for the nasolabial fold and jawline were injected with 3.0 mL of the mixture. The mixture was prepared with 1.0 mL of hyaluronic acid filler, 0.5 mL of lidocaine, and 1.5 mL of calcium hydroxylapatite filler. A visual analog scale (VAS) and the 5-point global satisfaction scale (GSS) were used for objective and subjective assessments. In a subset of patients, for histologic analysis, 0.1 mL of the mixture and 0.1 mL of only calcium hydroxylapatite filler were injected into the right and left postauricular areas, respectively. The histologic analysis was performed 6 months after implantation. The mean VAS and GSS scores for both sets of wrinkles were above "fair" at every follow-up, including at short-term and long-term periods. The skin biopsies from both postauricular areas from selected patients showed increased dermal collagen bundles without inflammation. The mixture of calcium hydroxylapatite filler and hyaluronic acid filler maintained constant volume with high satisfaction, as hyaluronic acid filler compensated for the unexpected early volume loss of calcium hydroxylapatite filler. This procedure can be applied safely, and it is also convenient, because no retouching procedure is needed.

Reconstruction of midface defects using local flaps: An algorithm for appropriate flap choice.

BACKGROUND: Local flap surgery is commonly performed to cover defects with appropriate skin color and texture match. The purpose of this study was to present an algorithm for choosing an appropriate flap when reconstructing a midface defect using a local flap. METHODS: Between February 2013 and February 2019, 38 patients with midface defects underwent local flap surgery. All defects larger than 3 cm in diameter were reconstructed with perforator-based transposition flaps. Defects smaller than 3 cm in diameter were reconstructed differently depending on their location. Defects near the nasolabial fold (NLF) were reconstructed with perforator-based transposition flaps, whereas defects just on the NLF were reconstructed with VY advancement flaps. Defects distant from the NLF were also reconstructed with VY advancement flaps. RESULTS: Perforator-based transposition flaps were used in 22 cases and VY advancement flaps were used in 16 cases according to our new algorithm. All flaps survived without any complications. The aesthetic results were superior for VY advancement flaps, with higher patient satisfaction scores. The skin color match was similar for both flaps, but the contour was more natural in advancement flaps than in transposition flaps. However, transposition flaps had the benefits of being able to cover relatively large defects and allowing the donor scar to be hidden in a wrinkle line. CONCLUSION: The most suitable local flap for coverage of a midface defect can be chosen based on the patient's condition. By following our algorithm, appropriate reconstructions can be performed, with satisfactory results.

(CONSORT) Wound closure using Dermabond after excision of hemangioma on the lip.

BACKGROUND: As the lip contains ample blood supply, hemangiomas often occur in this area. When surgical excision is performed, wound closure is important. To prevent infection from saliva and food, watertight wound closure is needed. The purpose of this study is to demonstrate the usefulness of Dermabond for wound closure after hemangioma excision on the lip. METHODS: Between December 2015 and August 2017, 11 patients with lip hemangioma underwent surgical excision. When closing the wound, Dermabond was used for skin closure after subcutaneous sutures. Demographic data and complications were recorded. Scars were evaluated with the Vancouver scar scale (VSS), and the postoperative shape of the lip was assessed on a 10-point satisfaction scale at 1 month and 6 months postoperatively. RESULTS: All cases completely healed without any complications, such as wound dehiscence or infection. There were no recurrences at postoperative 1 month during the follow-up period. The aesthetic results of the scars were also excellent. The average VSS score on postoperative 1 month was 4.2, and it decreased to 2.2 at postoperative 6 months. The average patient satisfaction score at postoperative 1 month was 7.4, and it increased to 9.5 at postoperative 6 months. CONCLUSION: Dermabond is useful for wound closure after hemangioma excision on the lip. It prevents wound contamination, and yields acceptable aesthetic results.

Flap selection for reconstruction of wide palatal defect after cancer surgery.

BACKGROUND: The resection of head and neck cancer can result in postoperative defect. Many patients have difficulty swallowing and masticating, and some have difficulty speaking. Various types of flaps are used for palatal reconstruction, but flap selection remains controversial. Therefore, our study will suggest which flap to choose during palatal reconstruction. METHODS: Thirteen patients who underwent palatal reconstruction from 30 January, 1989 to 4 October, 2016 at our institution. Size was classified as small when the width was < 4 cm², medium when it was 4-6 cm², and large when it was ≥ 6 cm². Based on speech evaluation, the subjects were divided into a normal group and an easily understood group. After surgery, we assessed whether flap selection was appropriate through the evaluation of flap success, complications, and speech evaluation. RESULTS: Defect size ranged from 1.5× 2.0 cm to 5.0× 6.0 cm. In four cases, the defect was in the anterior third of the palate, in eight cases it was in the middle, and there was one case of whole palatal defect. There were three small defects, two medium-sized defects, and eight large defects. Latissimus dorsi free flaps were used in six of the eight large defects in the study. CONCLUSION: The key to successful reconstructive surgery is appropriate selection of the flap with reference to the characteristics of the defect. Depending on the size and location of the defect, the profiles of different flaps should be matched with the recipient from the outset.

Multiplane Forehead Shortening: Sparing the Frontalis Muscle and Supraorbital Nerve.

BACKGROUND: An appropriate forehead-to-face ratio is an important factor contributing to a balanced and attractive face. Conventional methods have been used to correct long forehead, but these methods have drawbacks. The primary objective of this study was to introduce a modified technique with better results. METHODS: Between March of 2015 and March of 2017, 525 patients with long forehead underwent multiplane forehead shortening with sparing of the frontalis muscle and supraorbital nerve. The operation began with a design indicating the area of skin excision. The sensory nerves were preserved during the skin excision, and the frontalis muscle was not cut. Subgaleal dissection was performed through a small window on the galea. The postoperative assessments included the change in forehead length, sensory changes on the scalp, the presence of a scar, alopecia, and synchronous movement of the flap. RESULTS: A mean forehead shortening of 2.0 cm (range, 1.1 to 2.8 cm) was observed. Sensory deficits were observed only in the anteromedian scalp, which the supratrochlear nerve innervates. However, sensation recovered to the normal level within 6 months. Scars were barely visible or not visible at all in 85.5 percent of the patients. Postoperative alopecia occurred in only two cases. The synchronous movement of the forehead and scalp was natural in all cases. CONCLUSION: This modified technique of multiplane forehead shortening with sparing the frontalis muscle and supraorbital nerve provided both cosmetic and functional benefits. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, IV.

Treatment of deep cavities using a perforator-based island flap with partial de-epithelization.

BACKGROUND: The perforator-based island flap is a popular option for defect coverage. In cases with deep cavities, however, the classical island flap may not be a suitable option. By de-epithelization of the peripheral portion of a perforator-based island flap, the distal part of the flap can be used to fill deep spaces, as the flap can be folded and inserted into the spaces. METHODS: From June 2015 to April 2017, 21 cases of deep internal defects were reconstructed with perforator-based island flaps with peripheral de-epithelization. A fasciocutaneous flap was elevated and rotated with the pivot point on the perforator. After performing de-epithelization on the periphery of the flap, the de-epithelized portion of the flap was inserted and anchored into the internal defect. Demographic information about the patients, the size of the defects, the perforators that were used, and complications were recorded. RESULTS: During the follow-up period (mean, 14.2 months) of total 21 cases, no major complications such as flap loss occurred. In 2 cases, a minor complication was observed. Temporary flap congestion was seen in 1 case, and was treated with a short period of leech therapy, and the other case was partial necrosis on the flap margin, which was cured with minimal debridement and conservative treatment. No major problems have occurred, especially on the de-epithelized part of the flap and in the occupied space. CONCLUSIONS: With performing careful procedure, a perforator-based island flap with partial de-epithelization can be a useful option for the surgical treatment of deep cavities. TRIAL REGISTRATION: This study was retrospectively registered in the institutional review board on human subjects research and the ethics committee, Hanyang University Guri Hospital (Institutional Review Board File No. 2018-01-003-002 https://www.e-irb.com:3443/devlpg/nlpgS200.jsp ).

Modified C-H flap for simultaneous nipple reconstruction during autologous breast reconstruction: Surgical tips for safety and cosmesis.

BACKGROUND: Reconstruction of the nipple-areolar complex is the final stage of breast reconstruction. Nipple reconstruction is usually performed several months after breast reconstruction, because simultaneous reconstruction is thought to be risky. Here, we introduce our experiences of 1-stage procedures with immediate reconstruction of the nipple-areolar complex during autologous breast reconstruction. METHODS: Between 2008 and 2015, 51 mastectomy patients underwent 1-stage breast and nipple reconstruction. All cases were reconstructed immediately with autologous tissue for the breast mound. The patients were divided into 2 groups according to the method of nipple-areolar complex reconstruction. In group A, 23 cases were reconstructed with a classical C-H flap, also known as the Hammond flap. In group B, 28 cases were reconstructed with a modified C-H flap, which is the evolved form of the classical Hammond flap. The nipple-areolar complex was evaluated preoperatively, immediately postoperatively, and 1 year postoperatively. Postoperative complications were also evaluated. RESULTS: The mean projection of the reconstructed nipple decreased by approximately 50% in group A and 38% in group B during the postoperative 1 year. However, the reconstructed nipple width and areolar diameter did not show a significant change in either group. Group A showed 26% of complication rate and 17% of revision rate, whereas group B showed 11% of complication rate and 4% of revision rate. However, no major complications such as complete necrosis of the reconstructed nipple, were observed in any patients. CONCLUSION: The modified technique group showed superior results in terms of safety and cosmesis. With our modified C-H flap method, simultaneous breast and nipple reconstruction is safe and has satisfactory results.

The appropriate management algorithm for diabetic foot: A single-center retrospective study over 12 years.

BACKGROUND: Diabetic foot management is a challenge for reconstructive surgeons because it combines dramatically decreased circulation and chronic infection. The goal of managing this condition is to maximize viable tissue; however, unsatisfactory results, such as extremity amputation, are unavoidable in some cases. For appropriate management, thorough understanding of diabetic foot and the phased approach to its management is needed. The purpose of this study is to introduce an optimal algorithm for diabetic foot management by analyzing cases >12 years. METHODS: A total of 274 patients with diabetic foot at Hanyang University Guri Hospital from 2005 to 2017 were reviewed. The management process was divided into 5 steps: patient evaluation, wound preparation, improving vascularity, surgery and dressing, and rehabilitation. Patient evaluation included a microbial culture, evaluation of vascularity, and an osteomyelitis assessment. During wound preparation, debridement and negative-pressure wound therapy were performed. Vascularity was improved by radiological intervention or surgical method. Surgery and dressing were performed depending on the indications. Rehabilitation was started after complete wound healing. RESULTS: An infection was confirmed in 213 of 263 patients (81.0%). Of 74 cases in which a vascular study was performed, 83.8% showed arterial occlusion. When surgery was performed with complete eradication of the infection in 155 patients, the rate of revision surgery was 20.6%. The revision rate after surgery with a remnant infection of 66 patients was 40.9% (P = .0003). When surgery was performed after successful revascularization for improving blood flow of 47 patients, the rate of revision surgery was 21.3%. In contrast, the revision rate after surgery with unsuccessful or no revascularization of 174 patients was 28.2% (P = .359). CONCLUSION: Diabetic foot is a debilitating disease arising from multifactorial process. As its management is complex, a comprehensive but accessible treatment algorithm is needed for successful results. For this reason, the appropriate algorithm for diabetic foot management introduced in this study is significant.

Umbilical Quilting Suture Technique during Single-Port Laparoscopic Surgery.

BACKGROUND AND OBJECTIVES: Single-port laparoscopic surgery (SPLS) is popular in the gynecological field, because it is less invasive and leaves a smaller scar. However, the postoperative shape of the umbilicus is often distorted due to the intensive procedures performed through the small opening. In this report, we describe a technique for forming a satisfactory umbilicus in SPLS. METHODS: From March 2016 through April 2017, 32 patients were treated with SPLS by a single gynecologic surgeon. Group A (14 cases) underwent conventional umbilicus closure, and group B (18 cases) underwent a quilting suture technique. The umbilical shapes of each group were assessed by a plastic surgeon as was the patients' satisfaction. Evaluations were performed immediately after surgery and every month for 6 months thereafter. RESULTS: The postoperative umbilical shape in group A showed features, such as loss of depression, disappearance of the central vertical line, and irregularly bulging tissue, whereas group B had a shape similar to that of the natural umbilicus and maintained its depression and vertical line. The average scores of the plastic surgeons' evaluations immediately after the operation were 10.4 for group A and 15.1 for group B. The final scores obtained 6 months after surgery were 15.2 and 17.8, respectively. The patients' satisfaction scores immediately after the operation were 4.9 for group A and 7.3 for group B. The scores increased gradually, to 8.1 and 9.2, respectively, at 6 months after surgery. CONCLUSION: Performing quilting sutures during wound closure in SPLS is effective for making an ideal umbilicus and ensuring patients' satisfaction.

Comparison Between CT and MR Images as More Favorable Reference Data Sets for Fusion Imaging-Guided Radiofrequency Ablation or Biopsy of Hepatic Lesions: A Prospective Study with Focus on Patient's Respiration.

PURPOSE: To identify the more accurate reference data sets for fusion imaging-guided radiofrequency ablation or biopsy of hepatic lesions between computed tomography (CT) and magnetic resonance (MR) images. MATERIALS AND METHODS: This study was approved by the institutional review board, and written informed consent was received from all patients. Twelve consecutive patients who were referred to assess the feasibility of radiofrequency ablation or biopsy were enrolled. Automatic registration using CT and MR images was performed in each patient. Registration errors during optimal and opposite respiratory phases, time required for image fusion and number of point locks used were compared using the Wilcoxon signed-rank test. RESULTS: The registration errors during optimal respiratory phase were not significantly different between image fusion using CT and MR images as reference data sets (p = 0.969). During opposite respiratory phase, the registration error was smaller with MR images than CT (p = 0.028). The time and the number of points locks needed for complete image fusion were not significantly different between CT and MR images (p = 0.328 and p = 0.317, respectively). CONCLUSION: MR images would be more suitable as the reference data set for fusion imaging-guided procedures of focal hepatic lesions than CT images.

Modified Functional Superficial Parotidectomy With Ligation of the Major Branch of the Parotid Duct Extending to the Superficial Lobe.

A functional superficial parotidectomy can maintain salivary function by preserving the Stensen duct. However, this technique still brings the possibility of salivary leakage, because major branches of the parotid duct from the resected site do not get ligated. To reduce this complication, this study introduces a modified technique with major branch ligation. From December 2008 to February 2015, 14 patients who underwent superficial parotidectomy were divided into 2 groups. Group A was treated with the modified functional superficial parotidectomy involving the major branch between the superficial lobe and parotid duct. Group B was treated with the conventional superficial parotidectomy without involving the major branch of the parotid duct. The clinical complications, period of Hemovac usage, and surgical duration were noted in each group. Two of 8 patients in group A had a major branch from Stensen duct that was ligated, and there was no evidence of salivary leakage or sialocele in any of the patients of group A, whereas group B contained 2 cases of salivary leakage, one of which became sialocele. Group A had a significantly longer Hemovac maintenance period than group B (P < 0.05), and the duration of surgery was also significantly different between the 2 groups (P < 0.05). Because a solitary major branch of the main parotid duct occasionally extends toward the superficial lobe, our modified technique-functional superficial parotidectomy with ligation of the major branch toward the superficial lobe-is a useful option for treatment of a benign parotid mass in such cases.

Automatic image fusion of real-time ultrasound with computed tomography images: a prospective comparison between two auto-registration methods.

Background A major drawback of conventional manual image fusion is that the process may be complex, especially for less-experienced operators. Recently, two automatic image fusion techniques called Positioning and Sweeping auto-registration have been developed. Purpose To compare the accuracy and required time for image fusion of real-time ultrasonography (US) and computed tomography (CT) images between Positioning and Sweeping auto-registration. Material and Methods Eighteen consecutive patients referred for planning US for radiofrequency ablation or biopsy for focal hepatic lesions were enrolled. Image fusion using both auto-registration methods was performed for each patient. Registration error, time required for image fusion, and number of point locks used were compared using the Wilcoxon signed rank test. Results Image fusion was successful in all patients. Positioning auto-registration was significantly faster than Sweeping auto-registration for both initial (median, 11 s [range, 3-16 s] vs. 32 s [range, 21-38 s]; P < 0.001] and complete (median, 34.0 s [range, 26-66 s] vs. 47.5 s [range, 32-90]; P = 0.001] image fusion. Registration error of Positioning auto-registration was significantly higher for initial image fusion (median, 38.8 mm [range, 16.0-84.6 mm] vs. 18.2 mm [6.7-73.4 mm]; P = 0.029), but not for complete image fusion (median, 4.75 mm [range, 1.7-9.9 mm] vs. 5.8 mm [range, 2.0-13.0 mm]; P = 0.338]. Number of point locks required to refine the initially fused images was significantly higher with Positioning auto-registration (median, 2 [range, 2-3] vs. 1 [range, 1-2]; P = 0.012]. Conclusion Positioning auto-registration offers faster image fusion between real-time US and pre-procedural CT images than Sweeping auto-registration. The final registration error is similar between the two methods.

A prospective comparison between auto-registration and manual registration of real-time ultrasound with MR images for percutaneous ablation or biopsy of hepatic lesions.

PURPOSE: To compare the accuracy and required time for image fusion of real-time ultrasound (US) with pre-procedural magnetic resonance (MR) images between positioning auto-registration and manual registration for percutaneous radiofrequency ablation or biopsy of hepatic lesions. METHODS: This prospective study was approved by the institutional review board, and all patients gave written informed consent. Twenty-two patients (male/female, n = 18/n = 4; age, 61.0 ± 7.7 years) who were referred for planning US to assess the feasibility of radiofrequency ablation (n = 21) or biopsy (n = 1) for focal hepatic lesions were included. One experienced radiologist performed the two types of image fusion methods in each patient. The performance of auto-registration and manual registration was evaluated. The accuracy of the two methods, based on measuring registration error, and the time required for image fusion for both methods were recorded using in-house software and respectively compared using the Wilcoxon signed rank test. RESULTS: Image fusion was successful in all patients. The registration error was not significantly different between the two methods (auto-registration: median, 3.75 mm; range, 1.0-15.8 mm vs. manual registration: median, 2.95 mm; range, 1.2-12.5 mm, p = 0.242). The time required for image fusion was significantly shorter with auto-registration than with manual registration (median, 28.5 s; range, 18-47 s, vs. median, 36.5 s; range, 14-105 s, p = 0.026). CONCLUSION: Positioning auto-registration showed promising results compared with manual registration, with similar accuracy and even shorter registration time.

The Appropriate Surgical Approach to Frontotemporal Dermoid Cysts in Adult Patients.

Because frontotemporal dermoid cysts are superficial masses on the zygomaticofrontal suture, they are usually removed by simple direct excision in pediatric patients. Adult patients, however, require a more involved treatment approach because these cysts may be large and extend deeply into the surrounding tissue. From 2008 to 2015, 33 adult patients with frontotemporal dermoid cysts were treated in our clinic under a new treatment algorithm. Patients with a cyst smaller than 2 cm in diameter were treated using a direct excisional approach without a preoperative computed tomography (CT) evaluation. Patients with a cyst larger than 2 cm in diameter underwent a preoperative CT evaluation to determine the exact location of the cyst. If the cyst invaded the temporal fossa, a hemicoronal approach was used for excision. Cysts that did not cross the lateral orbital rim were removed using a direct excisional approach. Among the 33 patients in the study, 6 patients had cysts smaller than 2 cm in diameter, and 27 patients had cysts larger than 2 cm in diameter. Of the 27 patients with large dermoid cysts, 17 cysts showed temporal fossa invasion and 10 showed no signs of temporal fossa invasion. In all cases, the cyst was completely excised without rupture, and no instances of complications or recurrence were observed. In adults with frontotemporal dermoid cysts larger than 2 cm in diameter, preoperative CT evaluations should be performed. If the evidence suggests that a cyst has invaded the temporal fossa, a hemicoronal approach is required for complete excision.

Perforator-based island flap with a peripheral muscle patch for coverage of sacral sores.

Despite numerous therapeutic advances, the treatment of pressure sores remains a challenge. The increased use of perforator flaps enables surgeons to minimize donor-site morbidity by sparing the underlying muscle. In the presence of focal deep spaces, however, the inclusion of muscle would be beneficial. The goal of this study was to introduce a method for including a muscle patch at the periphery of a perforator-based island flap for coverage of sacral pressure sores. Between March 2010 and February 2015, 26 patients with stage IV sacral sores underwent perforator-based island flap reconstruction with a peripheral muscle patch. Patient characteristics, including sex, age, defect size, and postoperative complications, were recorded. All flaps survived without major complications. No flap necrosis was noted. The present study shows that a muscle patch incorporated into the periphery of a perforator-based flap can be transferred safely. This can be a good surgical option in cases where infection control or more volume is needed.

Automatic Registration between Real-Time Ultrasonography and Pre-Procedural Magnetic Resonance Images: A Prospective Comparison between Two Registration Methods by Liver Surface and Vessel and by Liver Surface Only.

The aim of this study was to compare the accuracy of and the time required for image fusion between real-time ultrasonography (US) and pre-procedural magnetic resonance (MR) images using automatic registration by a liver surface only method and automatic registration by a liver surface and vessel method. This study consisted of 20 patients referred for planning US to assess the feasibility of percutaneous radiofrequency ablation or biopsy for focal hepatic lesions. The first 10 consecutive patients were evaluated by an experienced radiologist using the automatic registration by liver surface and vessel method, whereas the remaining 10 patients were evaluated using the automatic registration by liver surface only method. For all 20 patients, image fusion was automatically executed after following the protocols and fused real-time US and MR images moved synchronously. The accuracy of each method was evaluated by measuring the registration error, and the time required for image fusion was assessed by evaluating the recorded data using in-house software. The results obtained using the two automatic registration methods were compared using the Mann-Whitney U-test. Image fusion was successful in all 20 patients, and the time required for image fusion was significantly shorter with the automatic registration by liver surface only method than with the automatic registration by liver surface and vessel method (median: 43.0 s, range: 29-74 s vs. median: 83.0 s, range: 46-101 s; p = 0.002). The registration error did not significantly differ between the two methods (median: 4.0 mm, range: 2.1-9.9 mm vs. median: 3.7 mm, range: 1.8-5.2 mm; p = 0.496). The automatic registration by liver surface only method offers faster image fusion between real-time US and pre-procedural MR images than does the automatic registration by liver surface and vessel method. However, the degree of accuracy was similar for the two methods.

Wire or Hook Traction for Reducing Zygomatic Fracture.

BACKGROUND: Variable methods have been introduced for reduction of the zygomatic fractures. The Dingman elevator is used widely to reduce these fractures but is inappropriate in certain types of fractures which require atypical traction vectors. We introduce and examine an alternate method of reducing zygomatic fractures using wire and hook traction. METHODS: A retrospective study was performed for all zygomatic fracture patients admitted between 2008 and 2014. Medially rotated fractures were reduced by using a wire looped through an intermaxillary screw secured on the medial side of the zygoma. Laterally rotated fractures were reduced using a hook introduced through an infrazygomatic skin incision. RESULTS: No accidental bleeding or incomplete reduction was observed in any of the cases. Postoperative imaging demonstrated proper reduction immediately after the operation. Follow-up computed tomography study at 1 month after operation also demonstrated proper reduction and healthy union across the previous site of fracture. CONCLUSION: The hook and wire method allowed precise application of traction forces across zygomatic fractures. The fractured bone fragment could be pulled in the direction precisely opposite to the vector of impact at the time of trauma. Soft tissue damage due to dissection was minimized. In particular, this method was effective in reducing rotated bone fragments and can be an alternative option to using the zygoma elevator.

Delayed infection after a zygoma fracture fixation with absorbable plates.

A 48-year-old man who had received a bioresorbable plate fixation for a zygomatic bone fracture 13 months earlier visited our clinic complaining of sudden facial swelling. The facial computed tomographic scan showed the soft tissue swelling without any bony abnormality, and the symptoms did not improve after 1 week of antibacterial therapy. The patient had a diagnosis of a late infection caused by unresorbed plates, and exploratory surgery was performed. Partially resorbed plates and screws were seen, and we removed the remnants of such completely. The symptoms were relieved after the operation, and there was no recurrence during 8 months of follow-up.

Continuous collision detection for ellipsoids.

We present an accurate and efficient algorithm for continuous collision detection between two moving ellipsoids under rational Euclidean or affine motion. We start with a highly optimized implementation of interference testing between two stationary ellipsoids based on an algebraic condition described in terms of the signs of roots of the characteristic equation of two ellipsoids. Then we derive a time-dependent characteristic equation for two moving ellipsoids, which enables us to develop an efficient algorithm for computing the time intervals in which two moving ellipsoids collide. The effectiveness of our approach is demonstrated with several practical examples.