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Biomedical subjects

C H Rorabeck

Publications and source records attributed to C H Rorabeck.

At least 109 records · Page 6Linked to original sources
PubMed1991

An evaluation of three loading configurations for the in vitro testing of femoral strains in total hip arthroplasty.

Despite recent advances in total hip arthroplasty, proximal femoral resorption and osteopenia remain problems. To analyze the proximal strain effects of three different loading conditions, strains produced in intact and postarthroplasty femora have been compared. Ten adult cadaveric femora of similar size, shape, and rigidity were tested. Ten strain-gauge rosettes were positioned on each femur. To simulate the "single leg support" phase of gait, fixtures were developed to load the femora under three different configuration: the VS (vertical shaft) configuration, with a vertically orientated femur having rotational freedom proximally and distally; the ITB (iliotibial band) configuration of a femur with rotational freedom positioned 11 degrees from the vertical, with a strain-gauge adjustable metallic simulation of the lateral muscles of the thigh; and the ABD (abductor) configuration of a femur with rotational freedom positioned 11 degrees from the vertical, with a strain-gauge adjustable metallic simulation of the abductor muscles. Each femur was loaded less than or equal to 600 N through the medial point, located at one sixth of the transcondylar distance. Strain patterns and magnitudes produced by the three loading configurations were quite different in both the intact and postarthroplasty femora. Both the ITB and the ABD configurations resulted in greater proximal medial compression and lateral tension than did the VS configuration. The magnitudes of the proximal strains were significantly greater in the ABD configuration (p less than 0.05). Postarthroplasty femora showed similar proximal results. It is proposed that meaningful strain data for the physiologically loaded femur can be obtained only with simulations that include the forces produced by the iliotibial band. To overcome the indeterminate nature and biological variation in these forces, the studies have to consider a range of forces.

Femur↗
PubMed1990

Source of the slippage in the universal joints of the Hoffmann external fixator.

An investigation was conducted to determine what improvements in the resistance to slippage could be obtained in selected interfaces (rod/clip torsional, cheek/bowl and cheek/clip) of the Hoffmann external fixator. The modification involved changing the standard wing-nut clamp for a bolt with a thread of 7 mm and a 1 mm pitch and placing an FAG 28-303 thrust-bearing (needle roller and cage assembly) between the bolt and the cheek. The results showed a significant improvement in the slippage values of all interfaces; increases of approximately six times were obtained at all torque values of the wing-nut clamp or fastener tested. Such improvements would markedly increase the reliability of external fixation systems and thus reduce the incidence of loss-of-reduction of fracture due to slippage of the universal joint.

Equipment Failure↗
PubMed1990

Analysis of radionuclide arthrograms, radiographic arthrograms, and sequential plain radiographs in the assessment of painful hip arthroplasty.

An analysis of sequential plain radiographs (XR), radionuclide arthrography, (RNA), and radiographic arthrography (RGA) was performed to determine the efficacy and usefulness of each study in the diagnosis of loosening of prosthetic hip components. Over a 2-year-period, 65 hip prostheses were assessed before operation using each type of study; these results were compared to the intraoperative assessment of the status of the components. Of the three studies, sequential plain radiographs were overall the most accurate, sensitive, and specific. Radionuclide arthrography was of no use on the acetabular side but quite useful on the femoral side, especially in cases with only minimal femoral component loosening. Radiographic arthrography was overall the least accurate or sensitive of the three studies performed.

Aged↗
PubMed1990

Treatment of compartment syndrome in children.

A compartment syndrome is a symptom complex caused by elevated tissue pressure in a closed osseofascial compartment of a limb. Left unrecognized, it results in permanent damage to muscle and nerve in that compartment. The diagnosis of a compartment syndrome is contingent on the recognition of pain out of proportion with the injury as the most important early symptom. The pain is increased with passive stretching of the muscles in the involved compartment or on palpation of the involved muscles. Once the diagnosis is suspected, prompt treatment by appropriate fasciotomy should result in maintenance of normal limb function.

Adolescent↗
PubMed1990

Long-term pain and disability in relation to residual deformity after displaced pelvic ring fractures.

In a retrospective review and follow-up study of 43 patients who had had high-energy pelvic fractures 5 or more years earlier, the occurrence of late pain and the functional outcome were adversely related to residual deformity of the pelvic ring. Among patients who had no residual deformity (displacement less than 1 cm), 88% had no serious pain and 82% had normal function. Of patients who had residual deformity (displacement more than 1 cm posteriorly), only 30% had no serious pain (p less than 0.01) and only 30% had normal function (p less than 0.01). Definitive reduction and stabilization is therefore recommended early after the injury whenever possible.

Activities of Daily Living↗
PubMed1989

Total knee arthroplasty following high tibial osteotomy for osteoarthritis.

The authors assessed the effect of proximal tibial osteotomy on the results of a subsequent total knee arthroplasty. A retrospective, clinical and radiographic analysis was carried out between a study group of 39 patients with 42 total knee arthroplasties following osteotomy and a control group of 39 patients with 41 primary arthroplasties. Outcome was assessed using the Hospital for Special Surgery (HSS) knee score, pain, function, range of motion, and radiographic evaluation. The follow-up period averaged 37 months (range, 24-50 months). The study group had 88% good or excellent results using the HSS score, compared to 90% in the control group. Function and pain improved equally in both groups. The control group had, on average, 14 degrees greater range of motion (115 degrees v. 101 degrees) after arthroplasty. The control group had, on average, posterior inclination of the tibial plateau of 7 degrees before operation and 3 degrees after operation; the corresponding values in the study group were 2 degrees and 1 degree. Using the HSS score and pain and function as parameters, previous osteotomy does not seem to affect the outcome of total knee arthroplasty. Conversely, range of motion following arthroplasty appears to be less in those with prior osteotomy. In addition, a high tibial osteotomy may alter the inclination of the tibial plateau.

Aged↗
PubMed1989

Stability and anchorage considerations for cementless tibial components.

The ability of several idealized tibial anchorage systems to resist distractive relative motion between the substrate and the component when subjected to eccentric loads was assessed using mechanical tests employing a urethane foam as a bone substitute and finite element models. Eccentric loads had to be placed within 30-35% of the edge of the tibial plate for separation to occur between an unanchored plate and the substrate. The finite element model predicted that a 90%/10% medial/lateral load distribution was required to maintain compressive vertical stresses beneath the unanchored plate. An anchorage system with four pegs each 10 mm in diameter and 20 mm long and an anchorage system with four cancellous bone screws each 6.5 mm in diameter were loaded eccentrically, and both systems prevented distraction of greater than 76 microns when mounted on urethane foam. Shorter pegs (10 mm) or a single central peg allowed distractions of 150 microns or greater to occur. These data are relevant to the design and testing of tibial components for total knee arthroplasty.

Biomechanical Phenomena↗
PubMed1989

In vitro analysis of proximal femoral strains using PCA femoral implants and a hip-abductor muscle simulator.

The strains produced in the proximal femur by noncemented and cemented PCA femoral implants have been compared to each other and to the strains in the same intact femur. The effect on the strain pattern of a hip-abductor muscle simulator was also tested. Nine embalmed femora were tested; two were used for development of the protocol, one was covered with a reflective photoelastic coating, and six were instrumented with eight strain gauge rosettes on each femur. For a given body weight on the photoelastically coated intact bone, the abductor-simulator increased the mean shear strains on both the medial (132%) and lateral (153%) aspects, with standard deviations of 13% and 20%, respectively; however, no strain-concentrated areas were observed. With an abductor simulator on the strain-gauged femurs, calcar shear strains were significantly reduced (P less than .01), from those on the intact bone, by both noncemented and cemented implants. These reductions were 74.2% and 91.8%, respectively, with no significant difference between the two techniques. Reductions in shear strain were noted at midstem on the medial side for the noncemented (20.5%) and cemented (35.9%) implants; however, only the cemented implants produced significantly less (P less than .05) strain than the intact bone at this location. At midstem on the medial aspect of the femur, there was a significant difference (P less than .05) between the data for the cemented and noncemented implants. Analysis of variance identified no other regions of significant change.

Biomechanical Phenomena↗
PubMed1989

Randomized trials in orthopaedics: why, how, and when?

There is increasing recognition that major new medical therapies should be rigorously evaluated before they are put into general clinical use. Randomized controlled trials provide the most unbiased assessment of the risks and benefits of such therapies. In this article, the most important aspects of the design and execution of a randomized clinical trial in orthopaedics are discussed. These include the reasons for and mechanisms of randomization, appropriate selection of patients and therapy, reasons for the blinding of therapy, types of measures of outcome that can be used, aspects of sample-size calculation and analysis of data, and ethics of randomized controlled trials.

Cementation↗
PubMed1989

Stiffness of bone underlying the tibial plateaus of osteoarthritic and normal knees.

The mechanical properties of normal cancellous bone in the proximal tibia have been reported extensively in previous studies in terms of support of a total knee arthroplasty (TKA); yet, little is known about these mechanical properties in the osteoarthritic (OA) state. Fifteen normal and 28 OA tibial plateaus, obtained from autopsy or TKA, were mechanically tested using an indentor technique to assess the variation of stiffness patterns. The medial:lateral stiffness ratio calculated for the normal plateaus was significantly different from the ratios computed for specimens with medial compartment OA and lateral compartment OA; however, the ratio was unchanged in tricompartment OA. These data should receive greater consideration in the design of TKA, which has traditionally been designed on the mechanical properties of normal tibiae.

Adult↗
PubMed1989

Analysis of the pull-out strength of screws and pegs used to secure tibial components following total knee arthroplasty.

The purpose of this study was to compare the pull-out forces of 3.8-mm and 6.5-mm diameter cancellous screws and a round peg 10 mm in diameter, implanted in bovine vertebral cancellous bone and two different grades of polyurethane. The relationships between the pull-out forces and the properties of the material into which they were inserted were also examined. For the same depth of insertion, the pull-out force of a 6.5-mm diameter screw was two times larger than that of a 3.8-mm diameter screw. Despite its smaller diameter, a 6.5-mm diameter screw demonstrated a pull-out force 13.6% greater than that of an optimally press-fitted 10-mm diameter round peg when both were inserted to the same depth; however, optimal compression for the peg was strongly dependent upon the size of predrilling and the modulus of elasticity of the material into which the peg was inserted. The pull-out force of a cancellous screw has a linear relationship with the shear strength of the material into which it is inserted. The pull-out force of a peg exhibits a linear relationship with the modulus of elasticity of the material into which it is inserted.

Animals↗
PubMed1989

Compartment syndromes of the lower leg.

Increased lower-leg intracompartmental pressure compromising neuromuscular function within that compartment is termed compartment syndrome. This condition may be acute (often trauma induced) or chronic (usually exercise related). In a conscious, alert patient, acute compartment syndromes usually are easy to diagnose clinically; however, in the unconscious patient, a diagnostic aid such as the intracompartmental pressure monitor is useful. Using the slit catheter device, compartmental pressures in excess of 30-35 mmHg in a normally perfused patient suggest the need for open compartment fasciotomy. Chronic compartment syndromes require dynamic pressure measurements for an accurate diagnosis. The most important parameters are elevated postexercise pressures and delayed restoration of normal compartmental pressures. Subcutaneous fasciotomy may be sufficient in accurately diagnosed cases of chronic compartment syndrome.

Acute Disease↗
PubMed1988

The long-term results of ankle arthrodesis.

The results of 62 ankle arthrodeses, mostly performed for osteoarthritis, have been reviewed; of these, 39 were examined clinically and radiographically after an average follow-up period of seven years. Compression arthrodesis was associated with the highest incidence of complications, and an anterior sliding graft gave the most satisfactory results. Very few patients required modification of their footwear; most could walk independently with a slight limp and were able to return to their pre-operative work. However, after operation, the ability to run and to participate in vigorous sporting activities was limited. Complications included wound infection, non-union, and some change in midtarsal mobility, but excellent pain relief was reported by all patients.

Activities of Daily Living↗
PubMed1988

External skeletal fixation: choosing a system based on biomechanical stability.

Due to the increased popularity of external fixators for treating long-bone fractures, many devices are being introduced to the market. The choice of a particular fixation device depends on the anticipated loading conditions or the demands the fixator might encounter during the healing process. This study compares the biomechanical stability (rigidity, yield-load, failure-load) and load to produce 1 mm of fracture-gap displacement of various half-frames of five systems tested in axial compression, torsion, and both anterior-posterior and medial-lateral bending; the slippage tolerances of various interfaces of the universal joints or clamps were also analyzed. The frames were mounted on acrylic rods, with a midshaft transverse saw-cut, displaced by 10 mm, and set to standardized dimensions and tightened at set torques. In terms of stability, the Brooker and Hoffman systems are, in general, less stable than the RxFx, AO, and Orthofix fixators. The single half-frames of all systems, except the Orthofix, were particularly weak, and the double and stacked half-frames of each system were more stable.

Biomechanical Phenomena↗
PubMed1988

Deep-vein thrombosis and continuous passive motion after total knee arthroplasty.

Seventy-five of 150 consecutive patients who underwent total knee arthroplasty had routine physiotherapy and seventy-five had continuous passive motion of the lower limb that had been operated on as well as routine physiotherapy. A pulmonary embolus did not develop in any patient, but about 40 per cent had thrombosis in the veins of the calf, whether passive motion had been administered or not. Radiographically, the deep-vein thrombosis was seen to extend into or proximal to the popliteal vessel in 5 per cent of the patients in each group. Sex, age, obesity, or a history of hypertension or diabetes did not influence the incidence of venous thrombosis, but there was a higher incidence in patients in whom cement was used for fixation of the total knee components, irrespective of the use of continuous passive motion of the limb.

Adult↗
PubMed1988

The cemented kinematic-II and the non-cemented porous-coated anatomic prostheses for total knee replacement. A prospective evaluation.

One hundred and sixty consecutive total knee arthroplasties were performed in 143 patients: 110 procedures, with a cemented kinematic-II prosthesis and fifty procedures, with a non-cemented porous-coated anatomic prosthesis. Each patient was evaluated before the operation and six weeks and three, six, twelve, and twenty-four months postoperatively. At a minimum twenty-four-month follow-up, the average Hospital for Special Surgery knee-rating score for the patients who had a cemented kinematic-II prosthesis was 9 points higher than the average score for the patients who had a non-cemented anatomic implant (88 points and 79 points). At the same follow-up period, the maximum flexion of the knees that had a cemented kinematic-II prosthesis was greater than that of the knees that had a non-cemented anatomic prosthesis (106 degrees and 97 degrees). In addition, the rate of reoperation for the patients who had a cemented kinematic-II replacement was 4 per cent, compared with 12 per cent for the patients who had a non-cemented anatomic prosthesis. On the basis of this prospective, non-randomized clinical review of unselected patients, we concluded that the results with the cemented kinematic-II prosthesis were superior to those with the non-cemented anatomic prosthesis at a minimum twenty-four month follow-up; however, these superior results may be related to the use of cement or to differences in the designs of the prostheses, the ages of the patients, or the postoperative management of the two groups of patients.

Arthritis, Rheumatoid↗