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A microscopic investigation of the initial part of the incubation period is performed of flow-induced cavitation erosion on austenitic stainless steel. Slip lines are readily seen all over the exposed area and up to three different slip systems are observed to operate simultaneously in a single grain. The amount of work hardening (as measured by microhardness tests) due to a single collapse is found to be negligible, although a change of surface topography as well as an increase in the surface layer disorder is found. It is argued that the energy of a single indentation can be calculated from 'static' material properties and a method of calculation is presented. The energy absorbed in a single indentation is found to be comparable to the energy of a cavity which initially has a diameter of 300 mu m. It is found that the number of indentations is proportional approximately to the 3.5th power of the hydrostatic collapse pressure.

The aim of this investigation was to study the effect of superposition of a high power ultrasonic and a ‘static’ strain on the microstructure of commercial aluminium containing 1% Si and 0.6% Mg (the static strain resulting from a constant strain-rate tensile test). A special specimen design for resonance (20 kHz) is described and the results of macroscopic measurements on the specimen are given. The internal structure was studied by transmission electron microscopy and the results obtained are supported by scanning electron microscopy of the resulting fracture surfaces. The observed internal structure is explained on the basis of the developed structure due only to the ultrasonic stress fields.

The hip-fracture incidence in persons aged 50 years and older in the two northernmost counties of Sweden was studied during three periods between 1973 and 1984. The mean age rose from 75 to 78 years, and the annual number of fractures increased from 511 to 754. Half of this increase could be attributed to demographic aging. For persons 80 years and older, the fracture incidence in 1983/84 was higher (P less than 0.01) than the fracture incidence in 1973/74. The women/men ratio was approximately 2:1 during the survey, while the ratio cervical/trochanteric fracture type changed from 1.7:1 to 1.8:1. The crude fracture incidence rate rose from 4.4 to 5.8 fractures per 1,000 women 50 years and older; the corresponding figures for men were 2.3 and 3.4. Comparison of a rural mountain population with an urban population revealed a lower age-adjusted hip-fracture incidence rate in the rural area during the final part of the study (P less than 0.001). In the rural population, there was no change in age-specific incidence during the survey, while in the urban area the age-specific incidence in person 75 years and older was higher in 1983/84 compared with 1973/74.

In a prospective study of ankle fractures in children, the growth rate was registered with a roentgen stereophotogrammetric method. The injuries were classified traumatologically according to Gerner-Smidt and anatomically according to Salter and Harris. Twenty-six ankle fractures were classified as supination--eversion injuries. Of these, eight had intraarticular injuries, 16 had extraarticular injuries of the distal tibia, and two had a zigzag fracture through the growth plate of the distal fibula. Information about growth was obtained within 3 months after fracture, and the growth pattern was found stationary about 6 months after fracture. Five types of growth pattern were observed: Normal growth (1 case), initial growth stimulation of varying length (8), initial and temporary growth retardation (1), initial and permanent growth retardation (4), and initial and permanent growth arrest (7). The other 5 had very low growth rates bilaterally. Roentgen stereophotogrammetry was found useful in extraarticular supination--eversion injuries in girls up to 12 years of age and in boys up to 13 years of age. Intraarticular supination--eversion injuries always appear when there is low remaining growth; because of growth disturbance, no follow-up is indicated. The traumatological classification was found of value in recognizing the different fracture types. Combined with an anatomical classification, high precision in predicting growth disturbance was obtained. However, factors such as trauma, displacement, skeletal maturity, and treatment must be considered. The roentgen stereophotogrammetric method permits early determination of the growth pattern with high accuracy. The growth disturbance can be registered months before this is evident from conventional radiographic examinations.

The effect of L-thyroxine and bovine growth hormone (NIH-GH-B16) on the growth in length from the proximal growth plate of the tibia in hypophysectomized female Sprague-Dawley rats was studied by the tetracycline method. The width of the growth plate was also determined, and the weight of the body and heart was registered. Completeness of the hypophysectomy was determined microscopically. Daily sc injections of 5, 10, 20 or 40 μg/kg L-thyroxine alone, or in combination with 25 or 100 μg NIH-GH-B16, were given for 20 days, starting 15 days after hypophysectomy which was performed when the rats were 60 days of age. Thyroxine alone resulted in stimulation of the longitudinal bone growth with an optimum effect at 10–20 μg/kg. Further increase of the thyroxine dose did not increase the bone growth. Thyroxine given in association with growth hormone had a higher growing promoting effect than thyroxine or growth hormone alone. The growth stimulation of the two hormones was also significantly higher than the expected additive effect, indicating a potentiating synergism. When thyroxine and growth hormone were given in combination, the longitudinal bone growth reached an optimum for almost the same dose (20 μg/kg) of thyroxine as when it was given alone. At this optimum dose of thyroxine, the dose of growth hormone determined the longitudinal bone growth. The width of the growth plate was not influenced by thyroxine administration. The body weight decreased somewhat when thyroxine was given alone, and the combination with growth hormone seemed to compensate for this weight loss. The heart weight was found to increase with increasing doses of thyroxine both when given alone and in association with growth hormone.

The cell production in the growth plate of the proximal tibia was calculated in hypophysectomized rats given growth hormone and/or thyroxine from values of longitudinal bone growth determined with oxytetracycline and the size of degenerative cells in the growth plate. The changes in longitudinal bone growth induced by thyroxine and growth hormone in hypophysectomized rats were found to be predominantly caused by changes in the cell production, whereas the changes in the size of the degenerative cells were minor. The stimulation of cell production by growth hormone was dependent on the dose and the administration period. Thyroxine was found to stimulate the cell production up to an optimum dose of thyroxine.

A prospective study of the development of necrosis of the femoral head was performed in 34 patients with fractures of the femoral neck. Technetium-99m MDP images of the hip regions were obtained immediately after nailing of the hip and at four, eight and 12 months. There was a good correlation between qualitative and numeric evaluation of isotope uptake in the femoral heads. Comparison of the activity level in the femoral head on the fracture side with that in the contralateral control site showed activity ratios to vary between1.0 for those heads showing a general reduction in activity on conventional images to1.4 with a mean of 2.0 for those showing increased activity. The initial postoperative images in 2/7 undislocated fractures showed a marked depression in femoral head activity on the fracture side; 13/21 dislocated fractures showed a similar defect suggesting a significant loss of bone remodeling. Normal Tc-99m activity in the femoral head (category 2) was observed in two fracture cases imaged within 24 hours of fracture, just prior to nailing. Repeat studies within one week of fracture and nailing demonstrated a marked depression in activity (category 0). Radiographic evidence of collapse later developed in both patients. The perfusion and blood pool images were useful for identifying femoral heads with deficient circulation. This investigation has demonstrated that the nailing procedure may threaten the vascular condition of the femoral head in hip fracture, that a dead head may be radiographically normal and clinically asymptomatic, and that the metabolic condition of the femoral head may be expressed in numeric terms suitable for statistical analysis.

The effect of the administration frequency of growth hormone on longitudinal bone growth was investigated with tetracycline as intravital marker of the bone growth of the proximal tibia in hypophysectomized rats. The total dose of growth hormone (NIH-GH-B16) and the administration period were the same in all compared experiments. It was possible to achieve an optimum growth response for a certain total dose of growth hormone by increasing the injection frequency. The period of hormone administration was 10 or 5 days followed by a 10 days withdrawal period. When the growth hormone was administered alone or in association with L-thyroxine for 10 days, the optimum injection frequency for growth hormone was found to be 1 inj./day in hypophysectomized rats and 2 inj./day in thyroxine-treated hypophysectomized rats. When the administration period was 5 days for growth hormone given in association with L-thyroxine, the growth stimulation induced by one daily growth hormone injection was the same as that induced by two or four daily injections of the same total dose. An increase in the administration frequency for a total daily dose of thyroxine from 1 to 2 inj./day did not increase the longitudinal bone growth either when thyroxine was given alone or in association with growth hormone.

Femoral head vitality was evaluated by tetracycline labeling and 99mTc-MDP scintimetry in 317 femoral neck fractures before and after internal fixation with two hook-pins. The preoperative vitality was about the same as that observed by others using comparable methods. The postoperative vitality was reduced in five of 81 undisplaced fractures and in 76 of 236 displaced fractures. These data would predict a rate of avascular healing complications of 7% in undisplaced and 32% in displaced fractures treated with hook-pins.

To study the in vivo effects on bone formation in standardized bone growth and remodelling systems, a moderate supplement of vitamin D metabolites was given adolescent rats on a standard diet. Comparison wit other hormones previously shown to stimulate the bone formation in these systems is thereby facilitated. Female rats (10 animals per group) were given one daily subcutaneous injection of 1.5 micrograms/kg 25-OHD3 or 0.04 microgram/kg 1,25-(OH)2D3 for 20 days (75-94 days of age). Controls were given 0.5 ml solvent. Tetracycline was used as intravital marker to determine the longitudinal bone growth of proximal tibia as well as the apposition and resorption of cortical bone in the femur diaphysis. The osteoclasts were counted in the metaphysis and diaphysis of the ribs. Vitamin 1,25-(OH)2D3 resulted in retardation (p $0.05) of the accumulated longitudinal bone growth. A similar but insignificant tendency was found for 25-OHD3. The body weight and the periosteal and endosteal bone formation at various levels along the femoral shaft were unchanged compared to the controls. The total cortical width was somewhat lower in the distal femur for 1,25-(OH)2D3. In the proximal femur 25-OHD3 resulted in a somewhat thicker cortical bone. Most levels along the femur, however, showed no differences. The osteoclast count showed an increased number (p $0.05) in the cortex of the rib in the rats given 1,25-(OH)2D3. Compared to growth hormone, which is the major bone growth stimulating agent, the influences on bone formation of the vitamin D metabolites were minor and predominantly negative.

Opinions differ concerning the treatment of choice for severe slipped capital femoral epiphysis, probably due to the lack of long-term follow-up evaluations on the different methods of treatment. A series of 33 patients with severe slipped capital femoral epiphysis, treated per primam with wedge osteotomy of the femoral neck, were radiographically and clinically reexamined an average of 28 years (range, 16-32 years) after the operation. Segmental collapse and/or chondrolysis developed in ten patients. Nine of these patients were available for reexamination and all had severe arthrosis with poor function. Arthrosis developed in nine of the 19 patients without signs of segmental collapse or chondrolysis; these patients had a satisfactory joint function. This series was compared with another series (from the same orthopedic departments) of patients with severe slip without any primary treatment. The long-term results in these two groups were similar; consequently, the value of realignment by wedge osteotomy of the femoral neck is questionable.

Thirty-nine patients with femoral neck fractures were followed up clinically and radiographically by technetium-99m-methylenediphosphonate (99mTc-MDP) scintimetry two to 20 days and four, eight, 12, 24, and 36 months after surgery or until redisplacement, pseudarthrosis, or segmental collapse occurred. The scintimetric data were calculated by selecting regions of interest on the fractured and intact sides over the femoral head, neck, greater trochanter, and shaft; ratios of fractured/intact side were obtained for each region. Bone metabolism after femoral neck fracture was expressed and analyzed numerically. Prognosis regarding the course of healing could be made with precision by studying femoral head isotope activity shortly after surgery, preferably one to three weeks after operation. Intact femoral head uptake (ratio greater than 1.0) was connected with uneventful healing, while defective uptake (ratio less than 1.0) was observed with healing complications. The vast majority of femoral heads with primary uptake defects showed increased uptake (greater than 1.0) after four months, often as early as six to eight weeks, indicating revascularization. Segmental collapse, as well as redisplacement and pseudarthrosis, appear to be related to femoral head vascular injury. Femoral head uptake in patients in whom healing complications developed secondary to avascularity differed significantly from that in patients with normal healing, except at investigations performed four to eight months after operation. 99mTc-MDP uptake in the femoral neck, trochanter, and shaft areas was increased for all femoral neck fractures. Subsequent normalization was considerably slower in patients with healing complications. A significant difference from normal healing did not occur until 12-24 months after operation. For patients with contralateral hip disease affecting the femoral head ratio, the prognosis regarding complications was made with the aid of the femoral head/shaft ratio on the fracture side.

Various factors that might influence the dose-response effect of growth hormone on the longitudinal bone growth were investigated with tetracycline as intravital marker of the bone growth in hypophysectomized rats. These are of practical importance for the bioassay of growth hormone. The growth response was found to be almost the same for subcutaneous and intraperitoneal injection, whereas the intravenous route resulted in significantly lower growth response. The administration of growth hormone in various volumes subcutaneously did not significantly influence the dose-dependent growth response. Freezing of the dissolved growth hormone or addition of NaOH to the solution had no significant effect on the growth response. Cortisone acetate 0.5 mg/kg given at hypophysectomy increased the post-operative survival somewhat, without having any post-operative depressing influence on the growth hormone-induced longitudinal bone growth. The present investigation showed that in standardized conditions the dose-dependent growth response is constant.

We analyzed the longitudinal growth of the distal tibial and fibular physes and the longitudinal displacement of the distal metaphysis and epiphysis of the fibula relative to the distal metaphysis and epiphysis of the tibia during growth using a roentgenstereophotogrammetric technique in eight children: six with a traumatic growth disturbance in one or both of the distal tibial and distal fibular physes and two with a normal ankle. In the normal ankles the distal fibular metaphysis moved distally in relation to the distal tibial metaphysis and the growth in the distal fibular physis was slower than that in the distal tibial physis. Growth arrest in the distal fibular physis and continued growth in the distal tibial physis resulted in distal displacement of the fibular metaphysis relative to the tibial metaphysis, probably due to traction on the distal ligaments of the fibula or more rapid growth in the proximal fibular physis than in the proximal tibial physis, or both. Valgus deformity of the ankle developed when the growth of the distal tibial physis exceeded the distal sliding of the fibula, as shown by the stereophotogrammetric analyses and orthoroentgenograms. Growth arrest in the distal tibial physis and continued growth in the distal fibular physis resulted in proximal sliding of the fibula, as shown by the roentgenstereophotogrammetric analyses and serial orthoroentgenograms. This mechanism compensated to some extent for the overgrowth of the fibula. Simultaneous growth arrest in both the distal tibial and the distal fibular physis was associated with movement of the distal end of the fibula in a distal direction relative to the tibia, probably due to the more rapid growth in the proximal fibular physis than in the proximal tibial growth plate. Therefore, growth arrest of the distal tibial or fibular physis may result in either proximal or distal sliding of the fibular metaphysis in relation to the tibial metaphysis. Probably growth arrest in the distal fibular physis has a less favorable prognosis than arrest in the distal tibial physis, because after tibial arrest proximal sliding of the fibula may compensate for overgrowth of the fibula better than distal sliding of the fibula can compensate for fibular arrest and overgrowth of the tibia.

Human cadaveric femora were subjected to static and uniaxial dynamic load applied on the femoral head by a simulator. By two transducer-mounted aluminium rings attached to the bone, the static and the dynamic load causing an elastic deformation of 1 mm in the trochanteric region was assessed. A trochanteric fracture was then produced and stabilized by one of three fixation devices, after which the test was repeated. The unfractured femora had the most rigid appearance (static load, 25.9 KN/mm; dynamic load, 33.1 KN/mm). Of the fractured and stabilized specimens, the Jewett nail-plate gave the most rigid fixation (static load, 5.4 KN/mm; dynamic load, 11.5 KN/mm). The least rigid femora were those stabilized by the dynamic Nolok (static, 4.7 KN/mm; dynamic, 9.2 KN/mm) and Hansson (static, 3.2 KN/mm; dynamic 6.1 KN/mm) telescoping devices. Because of the viscoelastic properties of bone, the load applied in a hip simulator should be dynamic; otherwise, the ability of the device to withstand in vivo loading might be underestimated.

The Hennessy Grading System is now used in Sweden for the commercial grading of meat content. An experiment was performed to discover if the Hennessy Grading System could also be used to predict the final meat quality from slaughter line measurements.

In 61 children (30 boys and 31 girls), the growth rates in the distal tibia and fibula were recorded by use of a roentgen stereophotogrammetric technique. The average observation time was about one year and seven months. The growth rates were correlated with chronologic and skeletal age. Adjusting for skeletal age did not significantly change the average growth rates or the scattering of the values. The mean growth rate and the remaining growth from about nine years of age in the boys and eight years of age in the girls were calculated for separate age groups. In the distal tibia in the boys and the girls, the average growth rate decreases from a plateau of about 11 and ten years of age, respectively. Decreasing growth rates were found somewhat later in the distal tibia than in the distal fibula in both the boys and the girls. The growth rates were close to zero at about the same time in the distal tibia and fibula in both sexes. In determining the remaining growth, the large biologic variability indicates the importance of serial measurements on the individual patient. The individual growth charts, together with clinical and radiographic estimation of maturity, provide a guideline for treatment of a patient with growth disturbance of the distal tibia and fibula.

The stimulating effect of different pituitary hormones on longitudinal bone growth was determined with tetracycline as intravital marker in hypophysectomized rats. Growth hormone was found to be the most effective growth stimulating pituitary hormone. At considerably higher doses, thyrotrophic hormone (TSH) and prolactin also showed growth stimulating pituitary hormone. At considerably higher doses, thyrotrophic hormone (TSH) and prolactin also showed growth stimulating activity. TSH exerts its effect via the production of thyroxine, whereas the growth stimulation by prolactin seems to be a direct effect of this hormone, similar to the effect of growth hormone. The LH, FSH, ACTH, MSH, vasopressin and oxytocin preparations did not stimulate longitudinal bone growth.

Using roentgen stereophotogrammetric analysis (RSA), we investigated the talar mobility in 54 ankles during the anterior drawer and adduction tests. Talar tilt was increased in ankles with unilateral symptoms of chronic lateral instability. No other difference in talar tilt and anterior drawer sign was noted comparing ankles with and without symptoms. We conclude that mechanical tests cannot always verify the diagnosis "chronic lateral instability of the ankle".

In a prospective randomized investigation, AO screws (53 cases) and hook-pins (57 cases) were used for femoral neck fracture fixation in 110 cases. The results of the one-week postoperative scintimetry and a four-month radiographic follow-up were analysed. The femoral head vitality according to scintimetry was similar in the two groups, whether undisplaced or displaced fractures. Within four months from the operation, six cases with screw fixation had been subjected to total hip arthroplasty while only one with hook-pins, all because of fracture redisplacement. However, at the four-month control, another more fracture operated on with screws and five more operated on with hook-pins were scheduled for hip arthroplasty. Thus, no difference between the two methods regarding postoperative femoral head vitality or complications in short term follow-up, was noted.

Seventy-two patients treated with closed reduction and hip spica for slipped capital femoral epiphysis (physiolysis colli femoris; PCF) were evaluated by questionnaire 25 to 66 years after primary treatment. Fifty-seven cases were examined with the use of clinical and radiographic methods. Pain and restricted hip function were obvious in most patients. In 25 of 72, an operation had been done in adult life for coxarthrosis. In a previously investigated group of PCF patients not actively treated, only two of 49 had had surgical treatment of coxarthrosis. Thus the results of closed reduction and hip spica are unfavorable, compared with those of nontreated cases. The results suggest a harmful influence of both reduction and hip spica.

In 30 fresh fractures of the femoral neck, the preoperative femoral-head tracer uptake in Tc-99m MDP scintimetry was compared with the uptake of peroperatively obtained femoral-head biopsies and correlated to intravital bone staining by tetracycline, infused concurrently. Bone uptakes of Tc-99m MDP and tetracycline were shown to correlate well. Total absence of Tc-99m MDP uptake in the femoral-head biopsy corresponded to a scintigraphic uptake ratio of 0.7 (fractured over contralateral head), whereas a normal Tc-99m MDP biopsy uptake corresponded to a ratio of 1.5. This suggests that in Tc-99m MDP scintimetry of a normal hip, less than half of the emission ascribed to the femoral head is derived from the femoral head itself.

In 300 femoral neck fractures treated with hook-pin internal fixation, no perioperative mortality and no deep infection was seen. Eighty-four patients (28%) died within two years of the date of fracture. At two-year follow-up examination, 56 of 300 cases (19%) had developed radiographic healing complications, i.e., redisplacement, nonunion, or segmental femoral head collapse (26% of the survivors). Three of 85 undisplaced fractures (4%) developed segmental collapse (5% of the survivors) while among displaced fractures, radiographic evidence of malhealing was found in 53 of 215 cases (25%; 35% of survivors) at two-year follow-up examination. In the total series, secondary hip arthroplasty was performed in 34 cases (11%). Atraumatic reduction and internal fixation are recommended as primary treatment in femoral neck fractures.

The spatial location of points in an object can be determined by roentgen stereophotogrammetry. A technique of high accuracy was applied in a determination of the daily skeletal growth of young rabbits. The tibia was labelled with tantalum markers on each side of the growth zones, and the increasing distance between these markers due to longitudinal bone growth was measured. Three different types of markers were tested, and the methodologic error was estimated. It varied between 30 and 43 micrometer for one growth interval, depending on the type of marker used. The method has clinical implications currently under investigation.

Forty-nine cases of slipped capital femoral epiphysis or physiolysis colli femoris (PCF) without primary treatment were evaluated 20-60 years after diagnosis by questionnaire and in 44 cases by clinical and radiographic reexamination. The cases represent PCF cases without primary treatment from three different orthopedic centers from 1910 to 1960. Only a few had restrictions in working capacity or social life. Two of these 49 cases have required surgery because of secondary arthrosis, far fewer than were found in a comparable group of cases treated with closed reduction and hip spica.

Scintimetry with 99Tcm MDP was performed in 32 growth regions in 8 children with localized growth disturbances after surgery or injury. The results were compared with the simultaneously performed growth rate analysis using roentgen stereophotogrammetry. A quantitative and qualitative analysis of the nuclide bone images of the anterior view was performed. Numeric ratios, obtained by comparing count rate levels of injured or operated growth region with the corresponding contralateral region, are presented and a satisfactory correlation with the roentgen stereophotogrammetric growth rate analysis was found. Nuclide bone-imaging of growth regions at the knee and ankle provides valuable and significant information about growth and was found to be a clinically useful method when combined with standard radiographic techniques to evaluate growth conditions.

The effect of ligamentous injuries on the stability of the knee joint has been measured or estimated in clinical and anatomical investigations. In order to assess knee instability under reproducible conditions, external transducers (Markolf et al. 1978) or radiographic techniques (Jacobsen 1981; Torzilli et al. 1981) have been introduced to register the effect of standardized forces. An increased mean sagittal laxity in a group of patients with a previous rupture of the anterior cruciate ligament (ACL) has been established in some investigations, but the diagnostic accuracy has been variable. The purpose of this study was to measure the three dimensional in vivo translations and rotations of the tibia in the ACL deficient knee using roentgen stereophotogrammetric analysis.

The erosion of solids caused by cavitating liquids is a result of the concerted collapse of clusters of cavities. In vibratory cavitation equipment the clusters grow and collapse adjacent to a solid surface and are typically of hemispherical or cylindrical form. In the present paper the collapse process of these clusters is described and the collapse equations are developed and solved. The theoretical results are compared with results from high-speed photography of the clusters and with the initial stages of cavitation erosion on metal specimens. Experimental and theoretical results show that the collapse of a cavity cluster is driven by the ambient pressure and the collapse proceeds from the outer boundary of the cluster towards its center. During the collapse the pressure at the inward-moving cluster boundary increases continuously, and at the cluster center it rises significantly above the ambient pressure. Therefore the collapse velocity of the individual cavities increases towards the cluster center, which explains that the erosion, being caused by the individual cavities, occurs predominantly in this region. Likewise, the pressure increase at the cluster boundary explains why materials of even high strength can be eroded by collapse of cavity clusters at atmospheric ambient pressure. Journal of Applied Physics is copyrighted by The American Institute of Physics.

A non-equilibrium, two-phase model for a plane, one-dimensional system is used to calculate the pressure and cavitation development in water containing free gas as cavitation nuclei. Two cases are considered, (i) the field between a vibrating horn and a stationary specimen which is placed at a small distance from the horn, and (ii) a water column in a flat-bottomed tube which is accelerated by axial impact on the tube. The calculations are based on data corresponding to experimental investigations and the calculated developments are compared with the observed cavitation processes.

Twenty patients were examined by standard radiography and roentgen stereophotogrammetric analysis (RSA) during a two-year period after total hip arthroplasty. Eleven of the acetabular components migrated cranially and three femoral components migrated distally. This migration was most rapid during the first four months after operation. Our findings support the possibility that mechanical loosening is initiated by thermal injury during polymerisation of the cement; the less frequent migration of the metallic femoral component compared with the polyethylene acetabular component may be because the metal acts as a heat sink. Standard radiographs were inadequate for assessment of early mechanical loosening, whereas RSA could reveal migration within four months of the arthroplasty.

The degree of faceting of small particles during sintering is discussed with reference to a recent paper by Yacaman, Romeu, Gomez and Munir (1979).

A growing interest has recently been shown in small (< 100 nm) metal particles. Such particles are conveniently made by evaporation in an inert gas atmosphere (see eg. 1,2) and the average particle size is empirically found to increase both with pressure and evaporation temperature.A detailed study was presented earlier on the interaction between single particles of gold (3). The surface energy was found to be the driving force for the whole series of possible adhesion events which include elastic deformation with strain fields visible in the electron microscope (4), plastic deformation with twinning, relative particle rotation and sliding. Nobody has, however, convincingly reported at which position relative to the evaporation source and at what temperature the particle formation and interaction occur. It is the aim with this investigation to start elucidating these processes by using various ferromagnetic materials with different Curie temperatures. These particles have then, in a way, a memory of the actual processes.

In 61 children (30 boys and 31 girls), the growth rates in the distal tibia and fibula were recorded by use of a roentgen stereophotogrammetric technique. The average observation time was about one year and seven months. The growth rates were correlated with chronologic and skeletal age. Adjusting for skeletal age did not significantly change the average growth rates or the scattering of the values. The mean growth rate and the remaining growth from about nine years of age in the boys and eight years of age in the girls were calculated for separate age groups. In the distal tibia in the boys and the girls, the average growth rate decreases from a plateau of about 11 and ten years of age, respectively. Decreasing growth rates were found somewhat later in the distal tibia than in the distal fibula in both the boys and the girls. The growth rates were close to zero at about the same time in the distal tibia and fibula in both sexes. In determining the remaining growth, the large biologic variability indicates the importance of serial measurements on the individual patient. The individual growth charts, together with clinical and radiographic estimation of maturity, provide a guideline for treatment of a patient with growth disturbance of the distal tibia and fibula.