Erroneous inference of frame failure in a Lillehei-Kaster heart-valve prosthesis.
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Modular component dissociation is a potential problem of current modular total hip arthroplasty (THA) systems. We describe a case of dissociation of the modular THA at the femoral head-neck interface after loosening of the acetabular shell during closed reduction for posterior dislocation of THA. The causes of this dissociation and acetabular shell loosening are discussed. Successful treatment was provided with surgical revision of the acetabular and the femoral head components. The present case serves as a graphic reminder that the acetabular shell overhanging the acetabular bone must be avoided when implanting modular THA components.
A cementless titanium femoral stem was revised 5 years after implantation because of acute pain and progressive osteolysis. Substantial amounts of titanium and polyethylene wear debris were found in the surrounding tissues. Multiple sources of this debris were found as well as detachment of titanium fiber-mesh pads from the body of the femoral stem.
Continuous measurement of hemodynamic and gas exchange parameters during the administration of sodium nitroprusside (0.5-1 microgram/kg/min-1) in 25 patients with marked heart failure following mitral valve replacement demonstrated favorable hemodynamic and respiratory changes.
Detailed characterization of wear particles is necessary to understand better the implant wear mechanisms and the periprosthetic tissue response. The purposes of the present study were to compare particle characteristics of current with older designs of metal-on-metal (MM) total hip replacements (THRs), and to determine the effect of implantation time on wear particle characteristics. Metal wear particles isolated from periprosthetic tissues from 19 patients with MM THRs of current and older designs and at different implantation times (very short, longer, and very long) were studied using transmission electron microscopy and energy dispersive X-ray analysis. The particles from the current design implants with implantation times of not more than 15 months (very short-term) were almost exclusively round to oval chromium oxide particles. In all other cases, although the predominance was still round to oval chromium oxide particles, greater proportions of cobalt-chromium-molybdenum (Co-Cr-Mo) particles, mainly needle-shaped, were detected. Very long-term THRs implanted for more than 20 years had the highest percentage of needle-shaped Co-Cr-Mo particles. Particle lengths were not markedly different between the different designs and implantation times except for the current design implants of not more than 15 months, which had a significantly smaller mean length of 39 nm. In conclusion, the implant design did not seem to have a significant influence on particle characteristics whereas the implantation time appeared to have the most effect on the particles. It should be noted that, because of the limited number of tissue retrievals available, some uncertainty remains regarding the generality of these findings.
There has been renewed interest in reverse shoulder arthroplasty for the treatment of glenohumeral arthritis with concomitant rotator cuff deficiency. Failure of the prosthesis at the glenoid attachment site remains a concern. The purpose of this study was to examine glenoid component stability with regard to the angle of implantation. This investigation entailed a biomechanical analysis to evaluate forces and micromotion in glenoid components attached to 12 polyurethane blocks at -15 degrees, 0 degrees, and +15 degrees of superior and inferior tilt. The 15 degrees inferior tilt had the most uniform compressive forces and the least amount of tensile forces and micromotion when compared with the 0 degrees and 15 degrees superiorly tilted baseplate. Our results suggest that implantation with an inferior tilt will reduce the incidence of mechanical failure of the glenoid component in a reverse shoulder prosthesis.
The incidence of failure of knitted Dacron arterial prostheses is thought to be significantly greater than that reported in the literature. Five cases of immediate and late defects in grafts of various manufacture are reported and a sixth case is discussed. The development of increased porosity to achieve more complete graft healing is thought to play a role in both early and late graft failure. Although the precise etiologic mechanisms are yet to be determined, the Dacron fibers were noted to become separated with subsequent widening of the graft interstices with resulting hemorrhage through the "intact" prosthetic material. Related theories of explanation are reviewed, and guidelines for study of these defective prostheses are suggested. It is essential that this complication of arterial grafting be recognized and that pertinent clinical experiences be documented in the surgical literature.
UNLABELLED: We report outcome in eight cases of ankle arthrodesis after failure of a total ankle prosthesis. MATERIAL AND METHODS: This series included eight patients, mean age 57 years (range 36-76) who had initially: post-traumatic talocrural joint degeneration (n=4), rheumatoid polyarthritis (n=3), idiopathic talocrural degeneration (n=1). Three patients had a New Jersey (DePuy) cemented prosthesis, four had a Star (Link) uncemented prosthesis and one, whose implantation was performed in another institution, had a spherical cemented prosthesis. The preoperative Kitaoka score was 19.1 (0-32). Seven patients had subtalar joint degeneration; one patient had a subtalar arthrodesis. The tibial component was cemented alone in two patients, the talar piece in three (two with talar fracture). Failure resulted from loosening, talus fracture or deep infection. Bipolar loosening was observed in two patients. Time to revision was 36 months (range 4-108). Arthrodesis was associated with an iliac graft for seven patients: several tricortical grafts (vertical alignment of the corticals) and cancelous grafts for filling. The height of the graft was adjusted to the substance loss. A bone graft could not be used in one patient who had a deep infection. The arthrodesis was fixed with an anterior plate bridging the talocrural space in six patients, with an external fixator in infected patient, with a conventional centromedullary tibial nail transfixing the talocrural joint and planted in the talus and the calcaneus in one. Outcome was assessed with the Kitaoka score. Mean follow-up was 56 Months (range 10-114). RESULTS: The overall Kitaoka score improved to 54/100 (range 42-70) at last follow-up. The arthrodesis provided improvement in all patients although the final outcome was still considered poor in three patients. Radiographic healing was obtained in seven patients at a mean 3.1 months (range 2.5-6). Wound healing was slow in two patients. One patient developed a deep infection early. DISCUSSION: The rate of fusion was 87%. This is in the general range reported in the literature; use of an iliac graft allows preserving joint height but because of the poor bone quality often encountered, residual bone stock may be insufficient to achieve complete fixation with screwing. Plate fixation appears to be a better way of achieving fixation. This provides a rate of fusion comparable with earlier series where external fixation was generally employed. For us, external fixation should be reserved for infected cases. Use of a conventional anterograde nail can be another solution in the event of poor bone quality. The overall result remains relatively modest although all the patients achieved a functional gain with arthrodesis. The results obtained are less satisfactory than after first-intention ankle arthrodesis.
This paper reviews the use of the Swanson finger prosthesis, concentrating on clinical results from the metacarpophalangeal (MCP) joint and modes of prosthetic "failure". While "failure" is generally associated with fracture, it is recognised that fracture does not always necessitate replacement of the Swanson prosthesis. Fracture tends to occur at the junction of the distal stem and hinge of the prosthesis. Initial improvements in ulnar deviation and range of motion (ROM) tend to be gradually reduced over the duration of implantation, and there is little evidence to suggest any long-term improvement in hand strength. Bone erosion and silicone synovitis have been seen but at a much lesser incidence than in other joints implanted with silicone spacers. An evaluation of retrieved Swanson prostheses, tied in with patient history and hand measurements might provide additional information to improve the design of the Swanson prosthesis itself and of other finger prostheses.
A three-dimensional non-linear finite element analysis of a cemented femoral component in which the component was partially debonded from the cement mantle was used to assess the effects of debonding on stresses in the cement. Three cases of partial cement-metal debonding were modelled with debonding of the proximal portion of the implant down to a horizontal plane which was 35, 62.5, or 82.5 mm below the prosthesis collar. Each situation was studied under loads simulating both gait and stairclimbing. Also, complete debonding between the implant and the surrounding cement mantle was modeled for loads simulating gait. Under stair climbing loads with partial cement-mental debonding, hoop stresses of 13-18 MPa were observed in the cement at the cement-metal interface at the proximal postero-medial corner of the implant. Similarly, in stair climbing, the maximum principal stresses in the cement were also adjacent to the proximal postero-medial region of the implant. These stresses were compressive and increased from 15 MPa with fully bonded interfaces to 48 MPa with debonding down to 82.5 mm below the prosthesis collar. Under gait loads, complete debonding caused high compressive stresses up to 34.9 MPa in the cement distal to the prosthesis tip. Thus, cement failure subsequent to prosthesis debonding is likely in the proximal region in a partially debonded implant due to stair climbing loads and is likely below the prosthesis tip in a fully debonded implant due to gait loading.
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Ankle foot orthoses (AFO) are often used for patients who cannot generate a strong enough extension moment at the knee to allow functional gait. Orthotists often cut out portions of the AFO around the malleoli in order to improve comfort. There has been some question as to how this affects the stress distribution around the orthosis, the fatigue performance of the device, and the AFOs stiffness. To examine this, three orthoses were constructed with differing curvatures cut out of the malleolar regions. Photoelastic coatings were placed on the most stiff and least stiff orthoses, and the stress distributions while wearing the device were examined. A fixture was created to test the orthosis, and the stress distribution while loaded in the fixture closely matched the distribution with actual wear. These orthoses were then tested in fatigue for 500,000 cycles at 5 Hz in displacement control. Initial displacements were set to provide maximum loads of 45 lbs. The displacement settings for the stiffest orthosis were 0.4 to 0.6 inches of deflection; the load decreased from 44 lbs to 28 lbs after the final cycle. The least stiff displacement varied from 1.3 to 1.5 inches, and the load value changed from 46 lbs to 35 lbs. The data will be useful in guiding orthotists in building AFOs, particularly when shaving portions of the AFO for comfort. Excessive shaving may seriously degrade the performance of the device, especially after longer life cycles.
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A 40-year-old man with Björk-Shiley valves implanted in the aortic and mitral positions nine months previously presented with central chest pain. Shortly after admission he developed clinical features consistent with left ventricular failure. Fracture of the mitral prosthesis was diagnosed by echocardiography. At emergency operation the outlet strut of the mitral valve was found to be fractured and the disc was in the left ventricle. The patient survived valve re-placement and is in good health four years later.
Revision stapedectomy operations performed over a 13-year period (1977 to 1990) for a conductive hearing loss are reviewed in terms of intraoperative findings and hearing results. All operations were performed in a conventional manner without use of laser techniques. A management algorithm based on intraoperative findings is described. Results are compared with previously reported series. The 66 cases include 20 males and 46 females, ranging in age from 8 to 73 years. Mean time between original and revision stapedectomy was 12.5 years. Prostheses encountered at time of revision included wireloop (29), Robinson (18), polyethylene (14), other (3), and two were not found. The most common cause of failure was displacement of the prosthesis. Incus erosion was found in 48% of wireloops, 35% of polyethylene, and only 11% of the Robinson prostheses. Revision resulted in closure of the pure-tone average (PTA) air-bone gap to within 10 dB in 46% and to within 15 dB in 76%. Sensorineural hearing loss (> 10 dB) occurred in 5 cases (7.6%), and a decline in speech discrimination (> 10%) occurred in 17%. Three of four cases requiring drillout had gap closure to within 10 dB. Findings suggest that our management technique produces results comparable to other large reported series. Drillout at the time of revision can be recommended.
Acetabular revision rates after cemented total hip arthroplasty vary from series to series in the literature. Little attention has been paid to the type of primary osteoarthritis in these previous series. We studied 782 cemented total hips in 671 patients with an average follow up of 7.5 years. Acetabular revision rates were analyzed in medial, lateral, and global primary osteoarthritis using survivorship analysis. Medial osteoarthritis was associated with a higher acetabular revision rate when compared to lateral osteoarthritis (P = .015). No differences were noted in acetabular revision rates when the preoperative diagnosis was medial vs global or lateral vs global primary osteoarthritis (P = .18 and P = .45, respectively). According to this study, a preoperative diagnosis of medial primary osteoarthritis should be added to a list of several factors associated with increased cemented acetabular failure, especially in the Charnley prosthesis.
Careful attention to axial alignment, soft tissue balance, and stability will minimize prosthetic failure. In revision arthroplasty a prosthesis designed to replace bone loss with the least constraint possible should be used. In the current series revision of the noninfected failed total knee arthroplasty has provided satisfactory results in 50% to 60% of the patients. We believe that use of the newer implants and instrumentation will improve results markedly.