Instrumentation of the patellar osteotomy in total knee arthroplasty. The relationship of patellar thickness and lateral retinacular release.

This study investigates the influence of patellar thickness in total knee arthroplasty (TKA) with routine patellar resurfacing on the rate of lateral retinacular release. A study group comprised of 121 TKAs using surgical instrumentation allowing a measured resection of the patella was compared with a control group comprised of 100 TKAs using an "eye-ball" technique for patellar resurfacing without particular attention to patellar thickness. A composite without patellar thickness equal to or slightly less than the original patella was attempted in the study group. The average thickness difference of the patella in the study group was -1.58 mm. Lateral retinacular release for patellar maltracking was performed in 12.4% of knees in the study group compared with 55% of knees in the control group. The variation in patellar thickness in this series often led to a residual bone thickness < 15 mm. No clinical problems have been observed to date.

Current status of physical measurements of the skeleton.

An overview is presented of some of the major methods of measuring the skeleton in the past 30 years. These include single photon absorptiometry (SPA), dual photon absorptiometry (DPA), quantitative computed tomography (QCT), and recently dual energy radiographic absorptiometry (DRA), also called DEXA (dual energy x-ray absorptiometry). In addition to these methods, all attempting to measure bone mineral density, regional and total body calcium have been determined by in vivo neutron activation analysis (IVNAA). An attempt to determine bone quality as contrasted with bone quantity has been made using ultrasound, with measurements of speed of sound and of attenuation as useful parameters to characterize bone tissue. While the various methods for measuring bone density have been most useful, no one method includes all the features required to be entirely satisfactory: excellent precision and accuracy and the ability to measure volumetric density in gm/cm3. Least successful has been the ability to predict fracture risk, an essential goal in helping the patient.

Arthroscopic evaluation and treatment of the patellofemoral joint.

Patellofemoral pain is a multifactorial problem. No single successful solution for problems related to the patellofemoral joint has been identified. One needs to consider the interaction of all of the factors affecting the extensor mechanism. Evaluation begins with a careful history, physical examination, and appropriate radiographic studies. Arthroscopy can provide additional information regarding the condition of the articular cartilage, patellar tracking, and the presence of other intra-articular lesions. Conservative treatment is the cornerstone of management and is effective in more than two-thirds of patients, making surgical treatment necessary in only a minority of instances. ALRR, although not an innocuous procedure, has an acceptably low complication rate and provides predictably good results when used in properly selected patients.

A study of the homogeneity of the trabecular bone mineral density in the calcaneus.

In the past our laboratory has reported a method of measuring trabecular bone mineral density (TBMD) in the calcaneus in vivo by using the coherent-to-Compton scattering ratio. In the present work the distribution of TBMD in the calcaneus has been studied, and the reproducibility of this technique in vivo has been determined. It is found that although the TBMD may vary within the calcaneus, a region exists over which the variation in density is not large. This region coincides with the midportion of the heel and is the site chosen for the measurement of TBMD by the coherent-to-Compton scattering ratio technique. The reproducibility of this technique in vivo has been determined to be 3.4%.

Trabecular bone mineral density measurement in vivo: use of the ratio of coherent to Compton-scattered photons in the calcaneus.

Trabecular bone mineral density (TBMD) was measured in vivo in the calcaneus by a new method that uses the ratio of coherent to Compton-scattered photons arising from irradiation of a small volume of trabecular bone by a gamma ray source with highly collimated geometry. TBMD values for healthy men (22-77 years) were in the range of 180-357 mg/ml, and values for healthy women (18-73 years) were in the range of 160-321 mg/ml. In contrast, values in a small group of paraplegics were in the range of 90-199 mg/ml.

Quantitative assessment of bone mineral by photon scattering: accuracy and precision considerations.

A method to determine the bone mineral density of the calcaneum has been reported earlier by our laboratory. In this method, the calcaneum is irradiated by a 60-keV photon beam from 241Am source and both the coherent and Compton scattered photons are detected by a high-purity Ge detector. The bone mineral density is determined by measuring the ratio of coherent-to-Compton scattered photons. The accuracy and the precision (in vitro) of the method are reported in this paper. The accuracy was determined to be 5%. This was obtained by comparing the bone mineral density values of cadaver calcanea measured directly by Archimedes' volume displacement method with the values measured by the scattering method. The precision was determined to be 3% by measuring the bone mineral density of a calibration phantom intermittently over a ten-month period by the scattering method.

Quantitative assessment of bone mineral by photon scattering: calibration considerations.

The ratio of the coherent-to-Compton photons scattered from bone can be used to measure its mineral density. Conversion of this ratio (R) to bone mineral density (BMD) requires calibration using bone simulating phantoms. The widely used aqueous solution of K2HPO4 proved unsatisfactory for calibration purposes when using the coherent-to-Compton technique. These solutions differ markedly in their scatter spectra and composition from trabecular bone. In this study a new and more realistic series of phantoms is proposed which simulates well the trabecular bone of the calcaneum. These phantoms are made of bone ash suspended in white petrolatum in varying concentrations. A calibration curve has been established using these phantoms with a range of BMD values of 0 to 347 mg/cm3. The scatter spectra, and range of R values and BMD of these phantoms are in very good agreement with those of real trabecular bone. A measuring device has been built for the determination of the BMD of the calcaneum by using the established calibration curve.

Absolute radioassay of extended sources: an equivalent point-source coincidence-counting approach with application to the thyroid.

A general methodology is provided for the absolute assay of radioisotopes decaying with coincident photons in an extended source. In the determination of the source activity, the method requires neither the detailed consideration of the geometric and self-attenuation processes taking place between the source component points nor a knowledge of the distribution of activity across the source. It derives from the concept of the "equivalent point source," that is a fictitious point source whose activity would equal that measured for the actual extended source. It has been developed for an arbitrary number of coincident photon types displaying an arbitrary degree of mutual correlation, and for arbitrary detection geometry. A unifying formalism is developed for both point and extended sources and for single and dual detecting systems. It is found that in all cases the various instrumental and spectroscopic uncertainties appear within a composite parameter (herein called F factor) that can be determined by standard calibration procedures; this factor is in turn only weakly dependent on its own component parameters. New expressions and relationships are obtained that provide a greater physical insight into coincidence-counting methods.

Quantitative differences between the thyroid uptake of 123I and 99mTc.

Unlike 123I, sodium pertechnetate Tc99m is known to be trapped by the thyroid gland without being further processed. Whether this property alone explains the total difference between the early thyroid uptake of these two isotopes was studied in a group of goitrous patients. The absolute activities of 99mTc were measured by a conjugate-view counting method and those of 123I by a coincidence counting method. The uptake was continuously registered to give uptake curves which were analyzed according to a three-compartment model of the thyroid. Both isotopes are postulated to bind to some carriers and then to be transported into the thyroid gland before they are further metabolized. Although the differences observed between the two uptakes were somewhat model dependent, the application of compartmental analysis provides a more detailed description of the differences between the two uptakes which occur even before the organification step.

The effect of the momentum transfer on the sensitivity of a photon scattering method for the characterization of tissues.

The ratio of coherent to Compton photon scattered by a tissue-like material depends on its effective atomic number. This ratio can, therefore, be used for the in vivo characterization of tissues. The intrinsic sensitivity of this measurement is defined as the change in the coherent-to-Compton ratio for a given change in the atomic number. The effect of the scatter angle on the sensitivity has already been described by us in a paper recently submitted to this journal. In this study, the dependence of the sensitivity on the energy of the incident photons is investigated in two ways. The first approach is quasitheoretical and is based on computations of the cross sections of the coherent and Compton scattering for various energies. The second approach is experimental and it involves the measurement of the scatter ratio from a series of K2HPO4 solutions for three primary photon energies: 60, 81, and 140 keV. The combined effect of both the photon energy and the scatter angle on the sensitivity can be described by a single parameter which is the momentum transfer. It is concluded that for the limited range of the atomic numbers which apply to trabecular bone (8 less than or equal to Z less than or equal to 11) the momentum transfer reflects completely the effect of the scatter angle and photon energy on the sensitivity.

Characterization of tissue via coherent-to-Compton scattering ratio: sensitivity considerations.

It is known that the ratio (R) of the detected coherent and Compton scattered photons from bone can be used in order to determine its mineral density. This technique utilizes the dependence of the coherent scattering on the effective atomic number (Z) of the scattering medium. It is generally accepted that a small scatter angle is preferred in order to ensure adequate counting statistics by favoring the detection of more coherent photons. Moreover, it has been assumed that a change in the scatter angle does not affect the sensitivity of the measurement. Our theoretical calculations for 60-keV photons and for the range of Z that corresponds to trabecular bone, indicate that increasing the scatter angle results in a stronger power dependence of the measured ratio on Z. This implies that by increasing the scatter angle, smaller changes in the mineral density can be detected, thus improving the sensitivity of the measurement. This effect was investigated experimentally by using a collimated beam of 59.54-keV photons from Am-241 (44.4 GBq) and a collimated intrinsic germanium detector. Solutions of K2HPO4 with different concentrations were used in order to simulate trabecular bone. The scatter spectra were recorded for all solutions at six scatter angles between 37 degrees and 98 degrees and the value of R was computed for each spectrum. The sensitivity of the measurement, evaluated from these experiments increased, with the increase of the scatter angle.

In vivo evaluation in intrathyroidal iodide metabolism.

A new coincidence counting method is used to measure absolute thyroid 125I activity with accurate correction of extrathyroidal neck activity. Data collected are analyzed according to a three-compartment model, giving parameters both dependent and independent of plasma iodide concentration. Iodide is postulated to form a complex with the iodide trap before it is transported and organified. The initial carrier-iodide complex, the intrathyroidal free iodide, and the thyroidal organic iodide pool can be determined as percentages of the injected activity. The trapping rate, the leakage rate, and the organification rate for iodide are determined as fractional turnover rates of the compartments independent of the plasma iodide concentration. The analysis is applied to the study of intrathyroidal iodide metabolism in a group of goitrous patients and a group of treated hyperthyroid patients. In the euthyroid goitrous patients, the trapping rate is slow, ranging from 0.051-0.085 min-1, and the intrathyroidal iodide pool is characteristically small, being 0.017-0.118%. The organification rate is 0.628-1.19 min-1. The leakage of iodide is virtually zero. In the treated hyperthyroid group, organification is not detectable, due to suppressive treatment by thionamides. The trapping rate is elevated (0.199-0.592 min-1), and the leakage rate is estimated to be in the range of 0.057-0.157 min-1. Because of the organification block, the intrathyroidal iodide pool is larger than that of our euthyroid group, being 1.50-7.59%. The compartment sizes and fractional turnover rates are in good agreement with previously reported values.

The measurement of trabecular bone mineral density using coherent and Compton scattered photons in vitro.

A photon scattering method for measuring the trabecular bone mineral density (TBMD) in vitro is described. This method involves the measurement of the ratio of coherent to Compton 90 degrees scattered photons from Am-241 by using a narrow beam geometry with an intrinsic germanium detector. The feasibility of using smaller scattering angles for better counting efficiency and the associated problems in their application for in-vivo measurements were investigated. Calibration of the system with fresh trabecular bone samples showed a linear relationship between the coherent to Compton ratio R of the detected counts and the TBMD (r = 0.94). The effect of the overlying soft tissue on the R ratio was significant while the effect of self-attenuation by the trabecular bone itself and the cortical layer was negligible. It was found that the marrow fat content could alter the value of the R ratio. Our results show that for a 10% increase in the fat content in the interstices of the trabecular bone there is a 2.5% decrease in the R ratio. This technique together with soft tissue corrections will enable us to measure the TBMD of the calcaneum in vivo, assuming a small variation in the trabecular fat content. The estimated absorbed dose to the bone marrow is about 139 mrad.

A dose table describing fractions of peripheral volume for 125I volume implants.

A dose table that provides the dose as a function of fractions of peripheral volume for 125I implants is presented. The table is based on seed distributions from 50 actual patient implants. Computer dosimetry was used to determine peripheral doses and dose ranges within implant volumes. The effects of seed distribution were also examined. The patient data and a study of computer-generated randomized seed coordinates within a given volume suggest that matched doses do not depend strongly on the exact position of each seed. The table provides the means for planning an implant to obtain a desired peripheral dose that can be directly compared with the postimplant computer dose calculation.

Measurement of the velocity of ultrasound in human cortical bone in vivo. Estimation of its potential value in the diagnosis of osteoporosis and metabolic bone disease.

Using a method combining the velocity of ultrasound and photon absorptiometry in the human radius in vivo, the authors measured the speed of sound in bone (U) and bone mineral content (BMC). From these measurements and a "simple" bone model, they then computed the bone mineral density, compact bone density, and modulus of elasticity. The accuracy of these parameters and of the bone model is assessed, and normal values for each parameter are given and compared with published values. The authors feel that a combination of U and BMC permits better discrimination between normal and abnormal in patients with osteoporosis or metabolic bone disease than either parameter alone.

Simultaneous determination of free thyroxine and capacity of thyroxine-binding globulin.

A simple method is described for the simultaneous determination of capacity thyroxine-binding of globulin (TBG) and free thyroxine concentration (FT4). The ratio of bound to free T4 (B/F) is first determined for two total-T4 concentrations using a Sephadex G-25 competitive-binding technique. TBG capacity and FT4 can both the calculated assuming a known value of affinity constant of TBG. The method is linear over a twenty-fold serum dilution. FT4 calculated is identical to that calculated using the method of Irvine. TBG capacity is shown to be linearly correlated to TBG concentration as determined by radioimmunoassay and is consistent with a molecular weight of 69,000 Daltons and one T4 binding site per molecule. FT4 is found to correlate with the free thyroxine index in a complicated way, depending on the degree of TBG saturation.