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Biomedical subjects

N S Eftekhar

Publications and source records attributed to N S Eftekhar.

At least 19 recordsLinked to original sources
PubMed1990

Design optimization of a prosthesis stem reinforcing shell in total hip arthroplasty.

The use of a perforated, titanium funicular shell to support the proximal femoral cortex in total hip arthroplasty was evaluated with the aid of both analytical and numerical techniques. The principal interactions between the femoral cortex, the metal shell, the implant stem and the acrylic bone cement were modeled using beam on elastic foundations theory and two-dimensional elasticity theory. Subsequent formulation of this model as a nonlinear design optimization problem enabled the determination of the dimensions of the implant and reinforcing shell which minimized an objective function based on a simplified material failure criterion. Two cases were examined, each with two cervico-diaphyseal angles: case A: with a rigid contact between a proximal prosthesis collar and the calcar femorale and case B: no collar contact (a collarless prosthesis or post-operative loosening). Case A achieved an optimal solution at a stem diameter 11-23 percent of the cortex inner diameter, a stem length to diameter ratio of 12-40, shell diameter 22-53 percent and thickness 0.2-7.2 percent of the cortex inner diameter and thickness, respectively. Case B achieved an optimal solution at a stem diameter 67-92 percent of the cortex inner diameter, length to diameter ratio of 4-6, and no shell. In case A the collar support makes the type of internal fixation unimportant, while in the more realistic case B, the shell is not recommended.

Elasticity↗
PubMed1989

Intrapelvic migration of total hip prostheses. Operative treatment.

We describe a safe operative approach for removal of a prosthesis that has migrated into the pelvis, and we recommend that a two-stage reconstruction be done when revising the total hip-replacement arthroplasty. The first stage consists of the removal of the femoral component and cement through a lateral transtrochanteric approach, followed by removal of the acetabular component through an abdominal-retroperitoneal approach to permit exposure of the major intrapelvic structures and to ascertain their relationship to the acetabular component and cement. After the acetabular component has been removed, bone grafts are applied to the pelvis. Postoperatively, the patient is placed in traction for a time and then is allowed to walk with non-weight-bearing. The second stage of reconstruction, consisting of hip replacement, is performed nine to twelve months after the first stage. A satisfactory result was obtained in the four patients for whom we followed this operative regimen. In one patient, the first-stage procedure yielded a satisfactory result and the second stage was not done.

Aged↗
PubMed1988

Incidence and mechanism of failure of cemented acetabular component in total hip arthroplasty.

Clinical results today seem to suggest that acrylic cement is crucial in producing immediate and reproducible results of pain-free joints following total hip replacement. Proper application by the use of contemporary techniques may be suitable in most conditions requiring hip replacement. The incidence of acetabular failure in a specific group of patients at risk may warrant experimentation by the use of a noncemented system. The mechanism of failure of low-friction arthroplasty may be multifaceted, but our experience indicates that the mechanisms of failure of the acetabulum have been due to excessive deepening and expansion of the acetabulum, once thought to be fundamental to the procedure. A rudimentary technique of cement pressurization, both in the femur and in the acetabulum, also may have played a part in late failures of this procedure. Early demarcation at the cement-bone interface was prevalent in young and active or heavy individuals. Demarcation and loosening were time-dependent phenomena. Demarcation and loosening also appeared with the aging process and increased osteopenia. A higher incidence of loosening also was observed in young and light-weight individuals, with presumably increased elasticity of the pelvic bone.

Acetabulum↗
PubMed1987

Long-term results of cemented total hip arthroplasty.

Long-term results of total hip replacement by low-friction arthroplasty show a consistent and reproducible outcome for relief of pain, increased mobility, and function in most patients followed for five to 15 years after surgery. In a review of 1009 consecutive operations, the rate of reoperation and potential failures for mechanical and infectious causes was 4.5%, which compares favorably with similar results in the literature. Seven series of operations employing the Charnley low-friction arthroplasty technique were compared. The failure rate was less than 10% in these series, provided that the operations had been performed either at a center dedicated to hip arthroplasty or by a surgeon devoting his career to hip replacement surgery.

Adult↗
PubMed1986

Failures and reoperations following low-friction arthroplasty of the hip. A five- to fifteen-year follow-up study.

One thousand nine Charnley low-friction arthroplasties performed by one surgeon were investigated for occurrence of failure from five to 15 years after operation. Six hundred ninety-six of the arthroplasties, 499 operations for primary and 197 for secondary surgery, qualified for study. Eleven hips of the 499 primary arthroplasties (2.2%) and five hips of 197 secondary surgery (2.5%) required reoperation. Six hips (of five patients) in primary and four hips in secondary surgery were identified as "pending failure," for which further surgical correction may be imminent. There were six deep infections (1%), one in primary and five in secondary surgery. Five patients (0.7%) required reoperations other than revision of arthroplasty. Combining the actual and pending failures resulting from mechanical failures and deep infection, there were 31 failures in 696 arthroplasties (4.5%).

Adult↗
PubMed1985

Prosthetic synovitis.

The term "prosthetic synovitis" is applied to reactive changes resulting from a synovial-like membrane formed between a failed prosthesis (noninfected) and the bone interface. This report is the result of light-microscopic and clinical examination of more than 100 specimens obtained at surgery of failed previous hip replacements. The morphology and cell distribution of those tissues removed at surgery in 51 noninfected cemented total hip operations allowed a quantitative estimate of surface cell population by a "touch imprint" technique; qualitative and quantitative estimate (scale, 1 to 4+) of cell population and foreign body materials by light microscopy; and electron microscopy and biochemical analysis of selected samples. Histologic examination included the following cell population, in decreasing order of frequency: acidophilic histiocytes (95%); giant cells (80%); fibronoid material (80%); lymphocyte and plasma cells (26%); and neutrophils (8%). Microscopic examination showed that the largest particles of acrylic cement and shards of high-density polyethylene appeared to be walled off by connective tissue capsules. The majority of smaller particles were incorporated into the histiocyte/macrophage or giant cell population. Histochemistry indicated that these particles elicited "foci" of cellular activity within the synovial-like membrane. This increased activity included the appearance of increased endogenous peroxidase activity in those macrophages within the "foci"; increased betagalactosidae activity among these histiocytes; and a localization of acid phosphates activity within giant cells along the borders of inclusions within the cell cytoplasm. We conclude that wear products resulting from total hip arthroplasty, including the bone cement, can induce increased lysosomal and proteolytic activity within the histiocyte and giant cell populations. It may be important to emphasize that there were "reactive foci" within the membrane and that the entire membrane, even though infiltrated with macrophages, did not respond uniformly to the presence of prosthetic debris. We advance a theory that the first step toward a distractive phenomenon at the interface is micromotion between the cement and bone. Micromotion may be caused by removal of subchondral plate during total hip replacement, leading to fatigue and loss of trabeculae and resultant increase motion, thus bone loss. Bone loss may be the direct result of mechanical injury, increased osteoclasis, or direct lysis of bone by various enzymes released by the interface membrane.

Acetabulum↗
PubMed1983

Osteonecrosis of the femoral head treated by pulsed electromagnetic fields (PEMFs): a preliminary report.

This has been a preliminary report with a short-term follow-up of a small number of observations (28 hips of 24 patients). The follow-ups ranged from 6 to 36 months, with an average of 17.8 months. Only eleven hips (in eleven patients) were followed an average of 8 months after cessation of the treatment. It should be emphasized that this was a "pilot" study, in which no control series was used to determine the natural course of the disease in a comparable clinical setting. Of note was the pain relief, in 19 of 23 patients with moderate to severe pretreatment pain. Also there was an improved function, which suggests that at least in approximately two thirds of the patients there was some clinical benefit from this mode of treatment. In eight hips, clinical conditions did not change; and in two they worsened, requiring further treatment. Eighteen remaining hips were thought to have been benefited by the treatment. Six femoral heads that had already developed varying degrees of collapse (Ficat Type III) collapsed further (1 to 2 mm), and two round heads (Ficat II) progressed to off-round (Ficat III). This preliminary study suggests that further exploration of pulsed electromagnetic fields (PEMFs) is warranted in the treatment of osteonecrosis of the femoral head.

Adolescent↗
PubMed1976

Systemic and local complications following low-friction arthroplasty of the hip joint. A study of 800 consecutive operations.

At the New York Orthopaedic Hospital, a study was made of postoperative complications in 800 consecutive total hip replacements of the Charnley low-friction arthroplasty type. Specially designed records made it possible to document and include all systemic and local complications of this procedure. While the rate of postoperative infection was low (less than 1%), thromboembolism and deep-vein thrombosis incidence was high despite the introduction of a prophylactic anticoagulation regimen. There were no deaths during or immediately after surgery, but six occurred within the first six weeks postoperatively. Two were due to a massive pulmonary embolus (proved at autopsy), two to myocardial infarction (clinical diagnosis), and one to a perforated cecum (proved at autopsy). The incidence of mechanical and technical failures in our series was relatively low and quite comparable with results reported by others.

Aged↗
PubMed1975

Fixation of the femoral head prosthesis with methylmethacrylate.

The techniques used in fixation of the femoral prosthesis in total hip replacement are often based on empiricism and raise questions about: venting the medullary canal with a catheter during the insertion of cement; the inclusion of blood into cement during insertion with possible deleterious effects; recementing a prosthesis; increased strength imparted to an endoprosthesis by cement itself. Biological variables are minimized by the use of paired wet formalin preserved femurs; one acting as control. A single static load was applied until failure. The results show trends and gross differences and are not statistically evaluated. The methylmethacrylate-bone-metal system consistently produces good results with reasonable but not careless variations in technique. A hemiprosthesis is presented which can easily be converted to a standard Charnley prosthesis by using a small amount of fresh cement.

Evaluation Studies as Topic↗