Stem surface roughness alters creep induced subsidence and 'taper-lock' in a cemented femoral hip prosthesis.

The clinical success of polished tapered stems has been widely reported in numerous long term studies. The mechanical environment that exists for polished tapered stems, however, is not fully understood. In this investigation, a collarless, tapered femoral total hip stem with an unsupported distal tip was evaluated using a 'physiological' three-dimensional (3D) finite element analysis. It was hypothesized that stem-cement interface friction, which alters the magnitude and orientation of the cement mantle stress, would subsequently influence stem 'taper-lock' and viscoelastic relaxation of bone cement stresses. The hypothesis that creep-induced subsidence would result in increases to stem-cement normal (radial) interface stresses was also examined. Utilizing a viscoelastic material model for the bone cement in the analysis, three different stem-cement interface conditions were considered: debonded stem with zero friction coefficient (mu=0) (frictionless), debonded stem with stem-cement interface friction (mu=0.22) ('smooth' or polished) and a completely bonded stem ('rough'). Stem roughness had a profound influence on cement mantle stress, stem subsidence and cement mantle stress relaxation over the 24-h test period. The frictionless and smooth tapered stems generated compressive normal stress at the stem-cement interface creating a mechanical environment indicative of 'taper-lock'. The normal stress increased with decreasing stem-cement interface friction but decreased proximally with time and stem subsidence. Stem subsidence also increased with decreasing stem-cement interface friction. We conclude that polished stems have a greater potential to develop 'taper-lock' fixation than do rough stems. However, subsidence is not an important determinant of the maintenance of 'taper-lock'. Rather subsidence is a function of stem-cement interface friction and bone cement creep.

The effect of implantation of aortic stents on compliance and blood flow. An experimental study in pigs.

Balloon dilation of coarctation of the aorta has been found to be an effective modality for treatment. Recently, in the older child and adult, implantation of endovascular stents has been considered a clinical alternative to dilation alone. Little is known, however, of the effect of implantation of stents on aortic compliance. To investigate this impact of implantation, we studied 18 piglets, divided into experimental and control groups. At median weight of 14 kg, 2 pairs of ultrasonic crystals were implanted on the aortic wall. After 1 week, all animals underwent catheterization. In the experimental group, a 3 cm long balloon expandable stent was implanted in the descending thoracic aorta between the pairs of crystals. Measurements of arterial pressure and dimensions were performed before implantation and immediately thereafter, and at follow-up catheterization. The index of stiffness, beta, and the the elastic modulus of aortic pressure-strain, were calculated as indexes of arterial compliance. The change in compliance during the period of study was not different between groups. At follow-up, no difference was observed between groups in the velocity of the aortic pulse wave, the augmentation index, or the maximum velocity of flow of blood. The stents remained patent and did not affect aortic growth or medial wall thickness. There was no difference between groups in levels of plasma renin activity and serum aldosterone. In this animal model studied over the short term, therefore, implantation of stents does not affect aortic compliance. Further studies are required to elucidate the long term effects of stents on the hemodynamics affecting the aortic wall and local flow dynamics.

Surgical treatment of aortic arch hypoplasia in infants and children with biventricular hearts.

BACKGROUND: Results of aortic arch reconstruction in the setting of biventricular physiology are well documented in the adult population, however, in children, surgical outcome of this subgroup of patients is less clear. METHODS: We studied the clinical outcomes of 37 children aged 8 days to 15 years (median 26 months), who underwent aortic arch reconstruction for arch hypoplasia from 1982 to 1997. The children were divided into three groups: Group 1 (20 patients) had isolated aortic arch lesions, Group 2 (13 patients) had associated intra-cardiac pathology yet conserving a biventricular physiology, Group 3 (4 patients) had Williams Syndrome. Previous interventions for coarctation had been performed in 30 patients (81%). Arch repair consisted of a patch aortoplasty in the majority of patients (35 of 37 children). RESULTS: Operative mortality occurred in 5 children, 4 in Group 2 (31%), 1 in Group 3 (25%) and none in Group 1. Permanent neurological complications occurred in 2 children (5 %). During the follow-up, which ranged from 1 month to 8 years, balloon angioplasty for arch obstruction was required in 1 child. There was one late death, associated with a subsequent intra-cardiac repair. CONCLUSIONS: Aortic arch surgery in children with isolated arch hypoplasia, is associated with excellent early and late survival in addition to a low reintervention rate. Alternative perfusion and operative strategies must be implemented in infants with associated intra-cardiac anomalies to improve results.

Surgery for coarctation of the aorta in infants younger than 3 months: end-to-end repair versus subclavian flap angioplasty: is either operation better?

OBJECTIVE: Recurrent coarctation is a complication which is seen at a consistent rate following all types of repair for coarctation of the aorta. Particularly disappointing late results are reported in younger infants, under 3 months of age. This retrospective analysis was undertaken to compare the outcomes on late follow-up between subclavian flap angioplasty and resection and end-to-end repair, in this age group. METHODS: Over a 12-year period, between 1982 and 1994, 86 infants under 3 months of age underwent surgical repair of coarctation (39 resections and end-to-end repair, and 47 subclavian flap angioplasty procedures). Operative mortality was not significantly different (P = 0.6) between resection and end-to-end repair (5.1%) and subclavian flap angioplasty (8.5%). All operative deaths (six patients) were in infants with associated ventricular septal defects. The mean follow-up for all patients was 7.95 years +/- 4.10 (range 0-14.5 years). The 5-year survival for resection and end-to-end repair was 87 +/- 5%, compared to 75 +/- 7% for subclavian flap angioplasty (P = 0.2). RESULTS: Recurrent coarctation occurred in nine patients who needed reoperation. The reoperation-free rates at both 5 and 10 years for resection and end-to-end anastomosis, and subclavian flap repair were 86 +/- 6% and 90 +/- 5%, respectively. The recurrence in the resection and end-to-end anastomosis group were due to constrictive scarring at the anastomosis, whereas periductal tissue and growth of posterior aortic ridge caused recurrence in the subclavian flap angioplasty group. There were no deaths during reoperation for recurrence. CONCLUSIONS: Both procedures are extremely effective for coarctation repair in young infants and run a similar risk of recurrence, which are due to completely different mechanisms. The surgeon's expertise is the major determinant of outcome.

FK506-induced fulminant leukoencephalopathy after single-lung transplantation.

FK506 is being used increasingly to prevent rejection after organ transplantation. Its use is associated with a wide spectrum of neurotoxicity, which has been described after most solid organ transplantations, but reports after lung transplantation are extremely rare. This is a report of the pathologic correlation of the clinical and radiologic features of delayed FK506-induced fulminant leukoencephalopathy after single-lung transplantation. The patient presented with neurologic symptoms that progressed to seizure activity. Neuroimaging showed diffuse changes in the brain, and results of a brain biopsy were consistent with leukoencephalopathy with microglial and astrocytic activation. The patient had a remarkable improvement in clinical status after discontinuation of FK506 administration, with resolution of the changes seen on neuroimaging.

Temporary stenting of the sternum after difficult cardiac operations.

Stenting the sternum may be essential to keep the sternal edges apart and optimize the hemodynamics in some patients, after cardiac operations. We have devised an effective stent that can be prepared very quickly from the equipment available in the operating room.

Konno-aortoventriculoplasty with mechanical prosthesis in dealing with small aortic root: a good surgical option.

OBJECTIVE: This study was undertaken to evaluate the effectiveness and the results with the Konno-aortoventriculoplasty. METHODS: Over a 10-year period, 21 Konno-aortoventriculoplasties were performed in 20 patients utilizing mechanical cardiac valvular prostheses, in 14 male and 6 female patients for complex left ventricular outflow tract stenosis. The mean age was 9.2 years (range 1.7-25.7 years). The pre-enlargement mean aortic annular size was 11.5 mm (6-16 mm). The mean size of the prostheses implanted was 20.4 mm (19-23 mm). In a typical case, the aortic annulus was enlarged to twice its original size. RESULTS: The only operative death was in a 8 kg, 20-month old child with previous commissurotomy, due to intractable bleeding and low output state. The mean hospital stay was 9.4 days (1-15 days), and the mean ICU stay was 3.3 days (1-7 days). The only late death was in a patient who went on to have cardiac transplantation for progressive left ventricular dysfunction. The 10-year acturial survival was 90 +/- 7%, and the reoperation free survival was 89 +/- 7%. All of the 18 surviving patients are asymptomatic at the time of last clinic visit (mean follow-up of 61.1 +/- 31.7 months, range 0-139 months). All patients had resolutions of their left ventricular hypertrophy with insignificant gradient across the repair by echocardiography. CONCLUSIONS: Konno-aortoventriculoplasty is extremely effective in the treatment of small aortic annuli and complex left ventricular outflow tract obstruction. In the present era of increasing popularity of autograft and homograft operations, the Konno procedure should remain in the technical armamentarium of the cardiac surgeon.