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PubMed2004

Challenges and recent developments in hearing aids. Part II. Feedback and occlusion effect reduction strategies, laser shell manufacturing processes, and other signal processing technologies.

This is the second part of a review on the challenges and recent developments in hearing aids. Feedback and the occlusion effect pose great challenges in hearing aid design and usage. Yet, conventional solutions to feedback and the occlusion effect often create a dilemma: the solution to one often leads to the other. This review discusses the advanced signal processing strategies to reduce feedback and some new approaches to reduce the occlusion effect. Specifically, the causes of three types of feedback (acoustic, mechanical, and electromagnetic) are discussed. The strategies currently used to reduce acoustic feedback (i.e., adaptive feedback reduction algorithms using adaptive gain reduction, notch filtering, and phase cancellation strategies) and the design of new receivers that are built to reduce mechanical and electromagnetic feedback are explained. In addition, various new strategies (i.e., redesigned sound delivery devices and receiver-in-the-ear-canal hearing aid configuration) to reduce the occlusion effect are reviewed. Many manufacturers have recently adopted laser shell-manufacturing technologies to overcome problems associated with manufacturing custom hearing aid shells. The mechanisms of selected laser sintering and stereo lithographic apparatus and the properties of custom shells produced by these two processes are reviewed. Further, various new developments in hearing aid transducers, telecoils, channel-free amplification, open-platform programming options, rechargeable hearing aids, ear-level frequency modulated (FM) receivers, wireless Bluetooth FM systems, and wireless programming options are briefly explained and discussed. Finally, the applications of advanced hearing aid technologies to enhance other devices such as cochlear implants, hearing protectors, and cellular phones are discussed.

Acoustics↗
PubMed1998

In vivo distraction forces in extendible endoprosthetic replacements--a study of 34 patients.

Using an instrumented distraction tool 34 extendible endoprosthetic replacements were lengthened to measure total resistance to extension. The study consisted of 19 distal femoral, 2 proximal femoral, 1 total femoral, 8 proximal tibial, 1 distal humeral, 2 proximal humeral and 1 total humeral replacements. Among these prostheses a total of 76 measurements were made. The initial load on the prosthesis due to soft tissues and muscles varied between 0 and 578 N with an overall mean of 128 N. There was a linear relationship between extension and load. At 6 mm extension the load varied between 42 and 1513 N with a mean of 476 N. There was very little difference between the means of femoral and tibial measurements. There was very little resistance to extension in the total humeral replacement due to the absence of glenoid and muscle attachment. In the distal humeral replacement all three measurements were comparable with the forces in proximal tibial replacements. Two cases showed very high resistance to extension, which was mainly attributed to the presence of large amounts of scar tissues observed at surgery. During one lengthening operation a 30 s pause at 1 mm increments from 0 to 9 mm showed load recovery of approximately 10 per cent for up to 3 mm, beyond which there appeared to be stiffening of tissues.

Adolescent↗
PubMed2002

In vivo RANK signaling blockade using the receptor activator of NF-kappaB:Fc effectively prevents and ameliorates wear debris-induced osteolysis via osteoclast depletion without inhibiting osteogenesis.

Prosthesis failure due to wear debris-induced osteolysis remains a major clinical problem and the greatest limitation for total joint arthroplasty. Based on our knowledge of osteoclast involvement in this process and the requirements of receptor activator of NF-kappaB (RANK) signaling in osteoclastogenesis and bone resorption, we investigated the efficacy of RANK blockade in preventing and ameliorating titanium (Ti)-induced osteolysis in a mouse calvaria model. Compared with placebo controls we found that all doses of RANK:Fc above 1 mg/kg intraperitoneally (ip) per 48 h significantly inhibited osteoclastogenesis and bone resorption in response to Ti implanted locally. Complete inhibition occurred at 10 mg/kg ip per 48 h, yielding results that were statistically equivalent to data obtained with Ti-treated RANK-/- mice. We also evaluated the effects of a single injection of RANK:Fc on day 5 on established osteolysis and found that Ti-treated were still depleted for multinucleated tartrate-resistant acid phosphatase-positive (TRAP+) cells 16 days later. More importantly, this osteoclast depletion did not affect bone formation because the bone lost from the osteolysis on day 5 was restored by day 21. An assessment of the quantity and quality of the newly formed bone in these calvariae by calcein labeling and infrared (IR) microscopy, respectively, showed no significant negative effect of RANK:Fc treatment. These studies indicate that osteoclast depletion via RANK blockade is an effective method to prevent and reverse wear debris-induced osteolysis without jeopardizing osteogenesis.

Acid Phosphatase↗
PubMed2006

Is collagen a good banding material for outlet control of vertical gastroplasty? Preliminary study in pigs.

BACKGROUND: To maintain the long-term effects of a gastric bariatric operation, bands are often placed to control the restriction. Erosion into the gastric wall by these devices remains a problem. A soft resiliant prosthesis of animal origin, constituted by a network of non-absorbable collagen fibres, may be a solution to this problem. This study assessed, in a porcine model, the histological reaction of the gastric wall following apposition of a band of porcine collagen (Pelvicol, Bard). METHODS: 15 female pigs weighing on average 21 kg underwent vertical banded gastroplasty (VBG). Stoma control was achieved with a band of porcine collagen (2 cm wide, 7 cm long and 2 mm thick). The pigs were sacrificed 1 month after VBG, and histological analysis was performed at a macroscopic and microscopic level. RESULTS: There was no peri-operative death, although 2 pigs died in the postoperative period (the first case developed a bowel fistula and sepsis, and the second pig died of unrelated causes). There were 2 additional morbidities (gastric fistula on the linear staple-line away from the Pelvicol band) that led to an early euthanasia of 2 pigs. Post-mortem macroscopic analyses in the remaining 11 pigs did not reveal migration of the device, and there was no tissue reaction on postoperative microscopic analyses. 10 of the pigs had lost weight at 1 month, averaging 3.42 kg. CONCLUSION: Porcine collagen appears to be an effective and safe alternative to the current methods of control of pouch outlet. The flexibility and homogeneity of this prosthesis may be useful to limit the risk of erosion of the gastric wall. Although these properties have been assessed in pelvic operations in humans, this work needs to be studied in a prospective long-term study in humans.

Animals↗
PubMed1997

[Effect of integrated distance studs on cement thickness of implanted PE-acetabulum cups--experimental in vitro studies for improved cementing technique].

Variations in cement thickness between PE cups and acetabular bone are biomechanically unfavourable, and may contribute to prosthetic loosening. Integrated distance studs should in the first instance, prevent local thinning of the cement. In an experimental study we compared the thickness of the cement mantel of implanted PE cups without such studs. In the case of cups with studs, significantly fewer areas of thin cement (0-1 mm) were found in comparison with cups with no studs. "Bald" areas of cement (0-0.2 mm) were virtually prevented by the studs. We are of the opinion that PE cups with integrated studs on the surface ensure a uniform cement thickness around the cup, as well as decreasing the risk of "bald" areas in the cement, thus reducing loosening.

Acetabulum↗
PubMed1994

The relationship between the design, position, and articular wear of acetabular components inserted without cement and the development of pelvic osteolysis.

Between 1983 and 1987, an acetabular component with a unique chamfered-cylinder design was inserted without cement in 134 hips. With use of this design, initial stability is achieved through a cylindrical interference fit with the peripheral rim of the acetabulum, without the need for pegs, spikes, or screws. At an average of sixty-four months (range, forty to ninety-six months) after implantation, follow-up data were available for 113 hips (ninety-three patients). No component had been revised for loosening or was radiographically loose. However, the prevalence of balloon-like osteolysis of the pelvis was 17 per cent (nineteen hips). This bone loss was generally not associated with pain or other symptoms. Ten of the nineteen hips that were associated with pelvic osteolysis (including six of the nine that were associated with osteolysis of the ilium) had been reconstructed with use of an acetabular component that had no holes in the shell (that is, the shell was completely solid). This finding indicates that, while elimination of holes through the acetabular shell may have advantages, it will not prevent pelvic osteolysis. The osteolysis of the ilium was associated with a lateral opening of the acetabular component of more than 50 degrees (p < 0.0001). All of the hips in this series had insertion of a porous-ingrowth femoral resurfacing component made of titanium alloy. These components are no longer used. Revision of the femoral side due to osteolysis provided a unique opportunity to inspect directly forty-two clinically well functioning acetabular components. All of the polyethylene liners and acetabular shells were found to be rigidly fixed. Inflammatory tissue at the periphery of the implant-bone interface resulted in circumferential resorption of periacetabular bone despite rigid fixation of the component. This is direct evidence that a process of bone resorption similar to that reported at the cement-bone interface of cemented acetabular components can occur at the implant-bone interface of components inserted without cement. At the reoperation, a communication that had led to the pelvic osteolysis was found through areas of bone resorption at the periphery of the implant-bone interface. These areas were essentially cystic and were filled with a mixture of fluid and friable, yellow-tan tissue. It appeared that the osteolytic process had expanded into the soft cancellous bone and marrow while being contained by the denser cortical shell of the pelvic bones.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetabulum↗
PubMed1999

Revision of the acetabular component without cement after a previous acetabular reconstruction with use of a bulk femoral head graft in patients who had congenital dislocation or dysplasia. A follow-up note.

BACKGROUND: Revision of an acetabular component that has failed after a total hip arthroplasty in which a bulk femoral head autogenous graft or allograft was used as a structural graft for acetabular reconstruction is an uncommon but complex and challenging procedure. We previously reported the results for seventy hips at an average of 16.5 years after a total hip arthroplasty in which an acetabular reconstruction had been performed with a femoral head graft. In the present study, we evaluated a subset of nine hips from that series that had a subsequent revision of the acetabular component without cement. The purpose of the current study was to assess the usefulness of the bone graft in this revision. METHODS: The nine patients (nine hips) were followed clinically and radiographically for an average of seventy-six months (range, sixty-one to 114 months) after the index revision. In six hips the autogenous femoral head graft previously had been bolted to the lateral side of the ilium, and in one hip the femoral head allograft had been affixed in this manner. In the two remaining hips, the allograft had been placed within the acetabulum. The hips were classified according to the extent of acetabular bone loss, with use of criteria described previously. Three hips had stage-I bone loss; four, stage-II; and two, stage-IIB. A porous-coated hemispherical acetabular component was inserted without cement and fixed with screws in each hip. At least 70 percent of the porous coating was in contact with viable bone. RESULTS: At the time of the latest follow-up after the index revision, all nine acetabular components were functioning well without loosening or osteolysis and none had been revised. The average Harris hip score was 77 points (range, 61 to 98 points) compared with 49 points (range, 27 to 96 points) preoperatively. One hip had had revision of the femoral stem, and another had had exchange of the acetabular liner because of recurrent dislocations. There was no additional resorption of the residual bulk graft that was in contact with the metal shell in any hip. CONCLUSIONS: In this small series of complex acetabular revisions, the healed bulk graft provided valuable additional bone stock for the support of an acetabular component that was inserted without cement. Insertion of the acetabular component into the available bone, which consisted in major part of host bone and in minor part of united revascularized bulk graft, resulted in a well functioning hip after an intermediate duration of follow-up. In all except two hips, the enlarged bone stock allowed insertion of a larger acetabular component than had been used previously.

Acetabulum↗
PubMed2003

Extracortical bone bridging in tumor endoprostheses. Radiographic and histologic analysis.

BACKGROUND: Aseptic loosening remains a major problem following prosthetic replacement after resection of periarticular tumors. Attempts to decrease the rate of loosening led to the introduction of a composite segmental prosthesis in which the shoulder of the intramedullary stem is porous-coated to allow extracortical bone bridging and bone ingrowth. The purposes of this study were to determine the extent of extracortical bone bridging around, and the amount of bone growth into, the porous-coated shoulder of endoprostheses implanted following the resection of periarticular bone tumors and to correlate the radiographic and histologic findings. METHODS: Twenty tumor endoprostheses implanted with use of the extracortical bone-bridging technique were evaluated radiographically to determine the extent of extracortical bone and the amount of bone ingrowth. Five of these endoprostheses were retrieved and subjected to histologic analysis with backscattered electron microscopy and transmitted light microscopy to determine the extent of bone ingrowth. RESULTS: At a mean of twenty-eight months postoperatively, varying amounts of extracortical bone formation were seen radiographically in all patients. Radiographs also appeared to show bone growth into the porous-coated segment of all implants. However, histologic analysis of the five retrieved prostheses revealed that none of the extracortical bone had actually grown into the porous-coated segment of the implant. CONCLUSIONS: This study confirmed that autogenous bone-grafting of the bone-implant junction of a tumor endoprosthesis consistently results in the formation of extracortical bone. Although radiographs seemed to indicate that this bone grows into the porous coating, this was not confirmed histologically. Growth of extracortical bone into the extramedullary, porous-coated portion of tumor endoprostheses in humans may not be attainable with the current prosthetic design and surgical technique.

Adolescent↗
PubMed2006

Prosthetic management of children with unilateral congenital below-elbow deficiency.

BACKGROUND: There is substantial controversy concerning the prosthetic management of children with unilateral congenital below-elbow deficiency. The optimal age at the time of the initial fitting, the value of intensive prosthetic training, and the preferred prosthetic design for these children have not been established. METHODS: The outcomes of prosthetic management for 260 children with unilateral congenital below-elbow deficiency, treated between 1954 and 2004, were analyzed with respect to ongoing clinic attendance and self-reported prosthetic use. A successful prosthetic outcome was defined as a child and parents who continued to attend the limb-deficiency clinic and claimed at the time of the most recent follow-up that the prosthesis had been worn for any period of time. An unsuccessful prosthetic outcome was defined as a child and parents who were lost to follow-up or who claimed at the time of the most recent follow-up that the child never wore the prosthesis. Survival analysis was performed. RESULTS: An unsuccessful prosthetic outcome was noted for 127 children (49%). Initial fitting prior to the age of three years was associated with improved prosthetic outcome (p < 0.001). With the numbers studied, there was no additional benefit noted for fitting before one year of age (p = 0.60). Improved prosthetic outcomes were noted in children who had received intensive training at the time of fitting with an active terminal device (p = 0.005). Provision of a variety of prosthetic designs over the growing years was also associated with improved prosthetic outcome (p < 0.001). CONCLUSIONS: This study supports the initial prosthetic fitting for a child with unilateral congenital below-elbow deficiency prior to the age of three years, the provision of intensive training under the direction of an occupational therapist when an active terminal device is applied, and utilization of a variety of prosthetic designs over the child's years of growth. Further analysis of outcomes for the prosthetic management of these children will require more precise definitions of outcome in multiple domains and the development and validation of specific outcome instruments.

Age Factors↗
PubMed1999

Analyses of prosthetic episodes in trans-tibial amputees.

The prosthetic episodes, i.e. actual processes of provision, identifying number of prostheses, their maintenance, repairs and replacements were analysed for 104 trans-tibial amputees aged 16 and over, over a 10 year period. The purpose of this investigation was to identify how frequently a new prosthesis is actually required for this group of amputees and what are their maintenance requirements. Variations of requirement between the amputee groups of aged 16-60 and over 60 years are also addressed. In the 10 years period of the study the amputees needed an average of 5.04 new prostheses, 6.25 refits, 2.28 major repairs and 17.04 day repairs. The younger amputees, i.e. below the age of 60 years, required significantly more new prostheses (p=0.003), more refit of sockets (p=0.0012) and more day repairs (p=0.01). Traumatic amputees below the age of 60 years needed significantly more day repairs compared to the non-traumatic amputees in the older age group (p=0.003).

Adolescent↗
PubMed2006

Effectiveness of cemented rescue screws for anterior cervical plate fixation.

OBJECT: Among the various ways to optimize the fixation of bone implants is to use bone cement, for example, in a total hip prosthesis. No data exist, however, concerning the effectiveness of cemented rescue screws for anterior cervical plate fixation. The aim of this study was to investigate whether cemented rescue screws increase fixation strength in comparison with uncemented standard screws. METHODS: Six cervical spine segments (C4-7) were explanted during routine autopsy studies from fresh human cadavers. Bone mineral density (BMD) was measured for each vertebral body (VB) using quantitative computerized tomography scanning, and 24 VBs were dissected from the segments. Two initial pilot holes were drilled into each VB parallel to the sagittal plane. Based on their BMD, the specimens were assigned to one of two groups in which torque and pullout force were tested. The test was begun with standard screws and was repeated with cannulated slotted rescue screws into which bone cement was injected. The mean values of peak torque and pullout forces resulting from the left and right measurements were used for statistical analysis. A t-test was performed to determine the effect of screw type on peak torque and pullout force. Moment correlation coefficients were calculated to determine the effect of BMD on peak torque and pullout force for each type of screw. The mean insertional peak torque was 67.1 N/cm for the standard screw and 102.6 N/cm for the cemented screw (p < 0.05). The mean pullout force was 526.9 N for standard osteoporosis screws and 531.5 N for cemented screws (p > 0.05). The effect of increased holding strength as measured by peak torque and pullout force was more pronounced in the presence of low bone density. CONCLUSIONS: Cemented rescue screws that have been inserted into a fatigued pilot hole in the cervical VB strengthen the screw-bone interface compared with the strength initially conferred by a standard screw.

Autopsy↗
PubMed2006

A silastic sheet found during endoscopic transnasal dacryocystorhinostomy for acute dacryocystitis.

PURPOSE: To report the case of a silastic sheet that was found during an endoscopic transnasal dacryocystorhinostomy for treatment of acute dacryocystitis with necrosis of the lacrimal sac. METHODS: A thirty-two year old male presented with painful swelling on the nasal side of his left lower lid two weeks prior to visiting this clinic. Fourteen years ago, the patient was involved in a traffic accident and underwent surgery to reconstruct the ethmoidal sinus. Lacrimal sac massage showed a regurgitation of a purulent discharge from the left lower punctum. Therefore, the patient was diagnosed with acute dacryocystitis and an endoscopic transnasal dacryocystostomy was performed the next day. RESULTS: The surgical finding showed severe necrosis around the lacrimal sac and a 20 x 15-mm sized silastic sheet was found crumpled within the purulent discharge. The sheet was removed, the lacrimal sac was irrigated with an antibiotic solution, and a silicone tube was intubated into the lacrimal pathway. After surgery, the painful swelling on the nasal side of left lower lid resolved gradually, and there were no symptomatic complications three months later. CONCLUSIONS: We report the first case where a silastic sheet applied during a facial reconstruction had migrated adjacent to the lacrimal sac resulting in severe inflammation.

Adult↗