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The caregiving environment experienced by 243 premature, low birthweight (LBW) children living in poverty was examined to determine whether the quality of care such children receive affords them some measure of protection from the generally deleterious consequences of poverty and prematurity. Only 26 children were identified as functioning in the normal range for cognitive, social/adaptive, health, and growth parameters at age 3. These children, who showed early signs of resiliency, differed from nonresilient children in that they were receiving more responsive, accepting, stimulating, and organized care. They were also living in safer, less crowded homes. 6 "protective" aspects of caregiving were identified and used as part of a cumulative protection index. Children with less than 3 protective aspects of caregiving present at age 1 had only a 2% probability of being resilient, and only a 6% probability if fewer than 3 were present at age 3. Overall, premature LBW children born into conditions of poverty have a very poor prognosis of functioning within normal ranges across all the dimensions of health and development assessed. However, those raised in a setting with 3 or more protective factors were more likely to show early signs of resiliency.

Cementless revision arthroplasty using allograft technique for massive tibial and femoral defects and delayed implantation after debridement was evaluated for the treatment of chronically infected total knee arthroplasties. Thirty-three knees in 33 patients were treated by implant removal and debridement followed by six weeks of antibiotic-impregnated cement beads and intravenous antibiotics. Cultures of synovial tissue taken at surgery grew Staphylococcus epidermidis in 18 knees, Staphylococcus aureus in five knees, Enterococcus in five knees, Pseudomonas in four knees, and mixed gram-negative organisms in one knee. Intravenous antibiotics were given accordingly. A painfree, nondraining wound was achieved with the first incision and drainage in 28 knees, whereas four knees required one or two subsequent procedures to achieve a dry wound and weight-bearing function. One knee continued to drain after repeated attempts at revision and fusion, and amputation above the knee was done at another institution. Cementless reconstruction using antibiotic-soaked bone graft and rigidly fixed femoral and tibial components was successful in 32 of 33 knees, with intermediate term follow-up examinations. Extensive debridement, followed by a six-week waiting period, produced a dry wound and pain-free knee in most patients. Those who developed recurrent infection responded well to repeat debridement, and all but one have remained free of clinically apparent infection two to eight years after surgery. Repeat debridement, antibiotic-impregnated cement beads, and bone grafting were uncommonly necessary, but the four patients that required them did not lose bone stock with subsequent revisions. All but one patient achieved stable fixation of the implants and good function of the knee.(ABSTRACT TRUNCATED AT 250 WORDS)

Screw fixation of the tibial component offers advantages in fixation in cementless total knee arthroplasty (TKA). In a group of 447 cementless TKA tibial components fixed without screws, 24% had partial undersurface radiolucent lines and 3% had complete radiolucent lines. Both of these parameters were significantly decreased (p < 0.01) when screws were used. In a group of 1442 cementless tibial trays fixed with screws, 4% had partial and 0.1% had complete radiolucent lines. Cyst formation around smooth pegs was also more common in trays fixed without screws. Two of the 5758 screws inserted in 1442 trays developed nonprogressive radiolucent lines, but no case of major osteolysis has been seen. Although screw fixation of cementless tibial components appears to improve the metal-bone interface, the potential for long-term complications still exists. The use of screws should be reserved for difficult fixation problems.

Cementless femoral component fixation with a modular design that achieved tight fit in the proximal and distal femur was evaluated. The base of the femoral neck made the most important contribution, but diaphyseal bony interlock also contributed significantly to immediate torsional fixation. Fluted surface and slotted distal design produced fixation that was superior to fully porous-coated and cemented cylindrical stems. Early cyclical loading improved fixation, and under moderate torsional loads (up to 20 N-m), no measurable interface slippage occurred with the modular implant.

Cutting errors that occur during preparation of the femoral component can deter fixation in cementless total knee arthroplasty. This study evaluated the causes of femoral cutting errors and identified methods to minimize these errors. The cutting error caused by toggle of the saw blade in the guide-slot was measured with wood blocks, a cutting guide with 1.5 mm guide slots, and four kinds of saw blades (narrow and wide blades with thicknesses of standard 1.2 mm and thicker 1.4 mm). Another cause of cutting errors, relative motions between the cutting guide and distal femur due to vibration of the saw blade during bone cuts, was measured with preserved cadaver femurs. Various combined fixation methods with intramedullary rod, pins, and clamps were compared. The maximum cutting error caused by toggle of the saw blade in the slot was significantly reduced by using the thicker 1.4 mm saw blade, but the differences between wide and narrow blades in each thickness were not significant. Mean maximum cutting error at the cutting depth of 5 cm with 1.2 mm thick saw blades was 802 microns, and with 1.4 mm thick saw blades it was 488 microns. In the measurement of relative motion, fixation with only pins or clamps did not provide tight fixation and had deflections from 200 microns to more than 1 mm. The best fixation was obtained by combining fixation methods of intramedullary rod and pins or clamps. This resulted in total movement of less than 100 microns. The results of this study indicate that both toggle of the saw blade in the slot and motion of the cutting guide can cause major cutting errors. Cutting error can be minimized by using thicker saw blades and by fixing the cutting guide to the distal femur with combined fixation methods of a central rod and peripheral pins or clamps.

This study investigated the normal load transfer pattern in the intact proximal femur. Both longitudinal and circumferential strains at eight strain-gauge locations were measured in response to both axial loads (1,000 and 2,000 N) and torsional loads (10 and 20 N . m). Under axial loads, strain magnitudes were large in the proximal regions and decreased distally. Very high compressive longitudinal strain was generated at the surfaces of the proximal medial cortical region, yet circumferential strain at this region was relatively low. Singh osteoporosis classification and femoral head diameter significantly affected the strains in the proximal part of the femur, and femoral head offset significantly affected strain levels in the diaphysis. Under torsional loads, the magnitudes of strain were much smaller than those generated under axial loads, but they increased distally. This study suggests that the proximal part of the femur is equipped for high longitudinal strain but is not equipped to handle high circumferential strain. The diaphysis of the femur is exposed to both axial and torsional loads and is equipped to handle high longitudinal and circumferential strains. Femoral implants that generate high circumferential strain in the proximal femur and high bending stress in the diaphysis are likely to fail mechanically or cause significant bone remodeling. Femoral implants and surgical procedures should be designed to apply load to the femur in a manner in which the femur can handle it best.

This study prospectively examined nine human volunteers who underwent unilateral cementless total knee arthroplasty and had 600 mg of tobramycin powder added to their wound just prior to fascial closure. Serum levels of tobramycin were measured at 30 minutes, 4 hours, 8 hours, and 12 hours after surgery. Tobramycin levels in the reinfused whole blood were measured with each reinfusion. Patients were reinfused up to 12 hours after surgery and then the reservoir was left to suction drainage. All patients had significant levels of serum tobramycin 30 minutes after surgery. The average serum level was 5.5 micrograms/ml (range, 3.0-10.6 micrograms/ml). This level was achieved prior to any reinfusion and represented systemic absorption of tobramycin from the bleeding surfaces of the muscle and bone. All patients received at least one reinfusion of 400 ml of whole blood in the first 8 hours after surgery. Two thirds of the patients received a second reinfusion within the same time frame. Serum tobramycin levels measured post-reinfusion indicated that the risk of attaining potential toxic levels of aminoglycoside was not dependent on reinfusion, but on absorption from the wound. The dose of tobramycin in the drain was measured and found to be excessive and potentially toxic (range, 27-312 mg; average, 132 mg). Despite this fact, reinfusion was not as likely to produce toxic serum levels as was local uptake of the antibiotic. Although no patient in this series had any complaints relating to the high dose of tobramycin (deafness or renal failure), caution should be exercised when using antibiotics in a reinfusion system.(ABSTRACT TRUNCATED AT 250 WORDS)

This study investigated strain distribution changes in the proximal femur after implantation of a flexible composite femoral component (carbon composite material, modulus of elasticity = 18.6 GPa), a titanium alloy implant (E = 100 GPa), and a stainless steel implant (E = 200 GPa). Transverse as well as longitudinal strain was measured using bipolar strain gauges at eight locations on the proximal femur under both physiologic axial (1000 N and 2000 N) and physiologic torsional (10 N-m and 20 N-m) loads. Under axial load, longitudinal compressive strain at the calcar region was significantly greater in intact femurs and the carbon composite stem specimens than in the two metal stem specimens. The difference between intact femurs and the carbon composite stem specimens was not significant. Stress shielding in the proximal lateral region of the femur, however, was still apparent even in the carbon composite stem specimens. Without seating of the stem collar on the femoral neck, longitudinal compressive strain was not generated at the calcar region, and transverse tensile strain at this region was increased. With conventional implant design, the stem collar was still necessary even in the flexible composite stem to provide near normal longitudinal compressive strain in the calcar region. Under torsional load, proximal strain in intact femurs was small and the proximal strain levels observed after either carbon composite or titanium alloy stem implantation were greater than strain levels before implantation. It seemed unlikely that torsional stress relief played a significant role in proximal bone loss after total hip arthroplasty. Both longitudinal and transverse strains at the calcar region under torsional load were significantly greater in the carbon composite stem specimens than in both intact femurs and the titanium alloy stem specimens, suggesting that these abnormally high proximal stresses may cause high proximal micromotion of the implant, and even bone fracture. Proximal implant design seems to be of paramount importance with flexible composite femoral components to avoid excessive proximal stress concentration under torsional load and to provide near normal strain distribution in the proximal femur.

Objective: To determine the epidemiology, clinical characteristics, and outcomes for low birth weight (LBW) infants with growth deficiency, or failure to thrive (FTT, the term commonly used by pediatric providers to describe growth deficiency or faltering in early childhood)., Design: Three-year prospective cohort study with matched case-control study of outcomes., Setting: Eight large university hospital sites throughout the United States., Sample: 914 LBW infants inborn at the sites and meeting study criteria., Results: FTT was a common condition in this cohort, with 180 (19.7%) of 914 LBW infants meeting case criteria by 30 months. New cases of FTT peaked at 8 months gestation-corrected age. In addition to expected differences in growth between infants with and without FTT, infants with FTT had lower developmental indices and less stimulating home environments. At 36 months, FTT infants had lower IQ scores and were much smaller than infants without FTT., Conclusions: Growth deficiency, or FTT, is a common clinical condition for those involved in the follow-up care of LBW infants. Worse cognitive and growth outcomes were observed for those meeting the restrictive case criteria employed in this study. More than 80% of the cases in this LBW cohort did not involve any chronic medical disorders, but several biological and environmental differences were found between those who developed FTT and those who did not.

Because of its proven effectiveness in reducing the need for banked blood transfusions following total joint arthroplasty, the indications for postoperative blood retrieval were expanded to include seven cases of infected total knee or hip arthroplasties where a one-stage exchange procedure was performed. Each joint had been aspirated after surgery and had positive cultures but no gross pus at the time of revision surgery. Each of the operations included debridement with reimplantation of a cementless prosthesis under cover of intravenous antibiotics for 48 hours followed by oral treatment until discharge. Antibiotic-soaked morselized bone graft was used in all patients to restore deficient nonstructural bone. Wound drainage blood was retrieved and reinfused during the first 8 hours after surgery, averaging 958 cc. Banked blood usage averaged 2.4 U (88% homologous) with an average blood loss of 1,974 cc. One patient experienced shaking chills during a second reinfusion of 600 cc of blood without stoppage of the transfusion. Wound hematoma occurred in one patient but did not require surgical evacuation. No patient developed evidence of septicemia.

Early retrieval prior to gross failure of implants can provide valuable information for critical issues in total joint arthroplasty. To evaluate fixation of the femoral component in total hip arthroplasty, two femoral specimens--one Mallory-Head (Biomet, Warsaw, IN) specimen and one AML (DePuy, Warsaw, IN) specimen--were retrieved after 2-8 years of successful use in active patients. Radiographs were made and evaluated for trabecular apposition to the porous-coated areas of the stem, then torsional and axial load tests were performed for each specimen to determine micromotion and displacement at the bone-implant interface. Both implants had radiographic signs of bone ingrowth. No permanent rotational displacement was found in either specimen during torsional load testing, but rotational and axial micromotion were found in both. These findings indicate excellent fixation of implant to bone, and no slippage at the bone-implant interface. The Mallory-Head implant had much greater elastic displacement than the AML, and histological examination showed cancellous bone ingrowth into the porous-coated portion of the Mallory-Head stem. The AML implant, which withstood much higher torsional loads, was found upon histological evaluation to have dense cortical-cancellous bone ingrowth. Strength of attachment of the metal implant to bone was good in both specimens, and neither had slippage at this interface. Differences in mechanical behavior can be attributed to the type of bone supporting the implant. The Mallory-Head implant had a severely worn titanium femoral head, so the joint was full of particulate metal debris.(ABSTRACT TRUNCATED AT 250 WORDS)

Objective: To explore the impact of young maternal age, coresidency with infant's grandmother, and other familial and environmental factors on development of low-birth-weight (LBW) infants., Design: Prospective cohort analyses., Setting: Eight medical institutions in different geographical locations participating in the Infant Health and Development Program., Participants: Control population of 272 LBW, preterm infants enrolled in the Infant Health and Development Program born to mothers aged 15 to 24 years., Main Outcome Measure: Child cognitive, behavioral, and health outcomes at 36 months' gestation-corrected age., Results: Maternal age was not significantly related to child development. Coresidence with infant's grandmother was associated with improved cognitive and health outcomes. Maternal ethnicity, maternal verbal ability, and other environmental factors were also associated with child outcomes., Conclusions: Findings of this study support the need for programs that include the extended family of at-risk infants, providing education and literacy skills to the mothers and encouraging participation of all care givers of the child.

One hundred thirty-five knees with valgus deformity were treated with a minimally constrained, cementless total knee replacement using intramedullary alignment for the femur and tibia. Mean valgus angle before surgery was 16 degrees; mean valgus angle after surgery was 7 degrees. Neither alignment nor varus-valgus stability deteriorated during the six-year follow-up period, but the knees with greater than 25 degrees deformity had a tendency to increase posterior laxity. Severely deformed knees required bone grafting of the medial femoral and tibial surfaces. A technique was developed to resect the distal femur measured from the medial femoral condyle and to maintain joint line position. Patellar subluxation and dislocation occurred in fewer than 1% of the cases. Despite the absence of rotational constraint at the articular surface, there was no tendency for patellar stability to deteriorate over time.

Wear characteristics of metal-backed, polyethylene patellar components were tested using cobalt-chromium, titanium alloy (Ti), and ion-implanted titanium alloy (IITi) articular surfaces. Patellar components were cycled in a bovine serum bath at 3 Hz for 1 million cycles, under a compressive load that varied from 343 N at 0 degree flexion to 2255 N at 120 degrees flexion. After testing, the polyethylene articular surfaces of the patellar components were evaluated for wear and graded using a subjective numbering system. Overall wear damage to the polyethylene surface was much worse with both Ti and IITi than with cobalt-chromium. Differences in mean wear scores were statistically significant when cobalt-chromium was compared with either Ti or IITi, but there were no statistically significant differences between Ti and IITi. Polyethylene surfaces that articulated against Ti femoral surfaces had more severe scratching. The IITi test group had areas of delamination not observed in the other test groups. Subjective evaluation of the metal surfaces showed evidence of wear damage as well. The metal articular surface of IITi resisted scratching as long as the treated surface was intact. In the high-stress areas, however, such as the edges of the intercondylar notch, the ion-implanted surface quickly wore away, exposing the untreated titanium alloy. The cobalt-chromium femoral articular surface had the least amount of scratching and no evidence of loss of metal.

Standard range of motion (S-ROM) modular total hip femoral stem has been designed to achieve precise fit in the diaphysis and metaphysis. This study compares torsional fixation of the S-ROM stem implanted with tight fixation of both the metaphyseal and diaphyseal components, tight metaphyseal and loose diaphyseal fixation. The mean load to failure was significantly greater in those implanted with tight fixation proximally and distally. Rotational micromotion was significantly decreased by fixation proximally, but permanent rotational displacement was improved primarily by distal fixation. Tight proximal and distal fixation were necessary to control both micromotion and permanent rotational displacement caused by torsional loading. Clinical success of this implant will depend on achieving tight proximal and distal fixation.

Carbon-fiber-reinforced-carbon composite material is an attractive implant material because its modulus of elasticity can be made similar to that of cortical bone. This study investigated the effect of femoral prosthesis elastic modulus on cementless implant fixation. Distal, as well as proximal, relative micromovements between implant and bone were measured in two testing protocols (axial-load and torsional-load), comparing identically shaped carbon composite (modulus of elasticity = 18.6 GPa), Ti6Al4V (100 GPa), and 630 stainless steel (200 GPa) prostheses. In the axial-load test, proximal mediolateral micromotions were significantly larger in the flexible composite stem than in the two metals. In the torsional-load test, rotational micromotions and "slop" displacements in the flexible stem were significantly larger proximally and significantly smaller distally than in the two metals. While these results suggest that proximal stress transfer may be improved by a flexible stem, they raise the possibility of increased proximal micromotion, and suggest that improved proximal fixation may be necessary to achieve clinical success with flexible composite femoral components.

Four fresh-frozen anatomic knee specimens were tested for knee stability, patellar tracking, and patellofemoral contact points with the femoral component positioned in 5 degrees internal, 5 degrees external, or neutral axial rotational alignment of the femoral component referenced on the posterior femoral condyles. The externally rotated specimens had varus-valgus stability of the knee that was closest to the normal control. The internally rotated specimens shifted into valgus alignment with flexion. Patellar tracking also was closest to normal in the externally rotated specimens. Patellofemoral contact was more evenly distributed between the medial and lateral contact areas in the externally rotated specimens than in the internally rotated or in the neutral specimens. Internal rotation of the femoral component in the knee with perpendicular resection of the tibia causes undesirable changes in knee stability, patellar tracking, and patellofemoral contact points. Neutral positioning produces similar but less negative effects on knee stability and patellar kinematics. External rotation improves both patellar tracking and knee stability characteristics.

This is a report of the outcome of cementless revision total knee arthroplasty (TKA), and describes the technique for bone grafting of massive femoral and tibial defects. The technique relies on rigid fixation of the implants using the remaining shell of distal femur and proximal tibia and the diaphysis of each bone for support of the implant. Fifty-six cementless revision TKAs in 56 patients were performed using cementless technique, long-stemmed components, and morselized allograft between April 1985 and April 1989. All knees had major loss of femoral and tibial bone stock. Fixation of the stemmed implants required firm seating on the rim of the femur and tibia. The stem engaged the isthmus of the bone to provide toggle control, and the screws fixed the implant firmly to bone. Two years after surgery, 30 (54%) of the patients had no pain, 17 (30%) had mild pain, five (9%) had moderate pain, and four (7%) had severe pain. All 56 knees had increasing radiodensity in the grafted areas one and two years postoperatively as compared with the one-month roentgenogram. All implants except two achieved stable fixation to bone. Alignment, stability, and comfort of the knee were all improved with cementless revision technique. The overall results of this study are encouraging. Bone stock was reliably reconstructed, and fixation during the short term appears to be durable.

Records of sales revealed that 6172 Ortholoc II cementless total knee femoral components with double bead layers were sold between January 1986 and December 1987. Sixteen thousand two hundred thirty Ortholoc II femoral implants with single bead layers were sold between December 1986 and January 1990. Fractures of the femoral components were reported in 32 knees; all but one occurred in femoral components with porous surfaces consisting of two layers of sintered beads. The overall minimum rate of failure for all sizes with double bead layers was 0.42%. The rate varied with the size of the implant and was much greater in smaller implants. The rate of failure was 0.82% in 852 small components, 0.37% in 2416 medium components, 0.29% in 1729 large components, and 0.09% in 1175 extra-large components. The differences in failure rates were statistically significant for all sizes of implants when compared with other sizes. Sixteen thousand two hundred thirty Ortholoc II components with a single layer of beads were sold worldwide between December 1986 and January 1989. One implant (medium size) failed 18 months after surgery. The minimum rate of failure in the single bead layer implants is 0.006%. This failure rate is statistically significantly less than that of the double bead layer implants. All failures occurred at the junction between one of the bevel surfaces and the distal surface of the implant. In all cases, crack propagation was initiated at the inner surface. This suggests that bending stresses had developed and had opened (straightened) the femoral component.(ABSTRACT TRUNCATED AT 250 WORDS)

Three cementation techniques were investigated to determine their effect on initial fixation of unicondylar tibial components. Twenty-one anatomic specimens were divided into three groups. In Groups A and B, the medial tibial plateau was minimally resected. Group A was drill interdigitated and pulse lavaged, Group B was left "as cut". In Group C, the articular cartilage was curetted, exposing the subchondral bone entirely. An Ortholoc II unicondylar prosthesis was cemented onto the tibias, after which a 981-N load was applied anteromedially at 1 Hz for 10,000 cycles. Measurements for anterior and posterior micromotion were taken at the first cycle, every ten cycles for the first 100 cycles, every 100 cycles for the first 1000, and every 250 cycles thereafter. Measurements for anterior subsidence and posterior liftoff were taken after every 1000 cycles. Group A was found to be significantly better than Group B in anterior micromotion, posterior micromotion, and posterior liftoff in all load cycles. Group A was also found to be significantly better than Group C in anterior micromotion, posterior micromotion, and posterior liftoff in all load cycles. The performance of Groups B and C was highly variable. Both groups had specimens with extreme micromotions in response to low loads. Group A provided consistent and superior results. This study shows that cementation techniques employing multiple-drill-hole interdigitation and pulse lavage produce rigid initial fixation and consistent excellent results. Cementing to the smooth subchondral bone or unlavaged cancellous bone was unreliable.

A series of 23 major load-bearing acetabular allografts done in conjunction with revision total hip arthroplasty were prospectively evaluated. This study includes cases with a minimum 2-year follow-up period. The procedures were performed using noncemented porous-coated acetabular components with pegs. In seven acetabula there was no change in cup position when compared with the initial postoperative roentgenogram (35%). Six acetabula migrated 3-5 mm during the first 2 years, then became stable without further progression (28.6%). In six cases (30%) gross loosening and migration occurred, requiring revision to a larger cup. One case required exchange arthroplasty for infection (5%). All biopsies taken at the time of the revision for failure showed viable bone replacing allograft. If the criteria for success of major superior acetabular allografts include incorporation of the graft and long-term stability of the implant, then the success rate in this series is very low. Only 7 of 20 hips were successful over a relatively short time period. However, if expectations are lowered, and the procedure is considered successful if adequate bone stock is restored to the acetabulum to allow reconstruction with a cementless cup firmly fixed in viable bone, then all but three revisions were successful.

Postoperative wound drainage was aspirated, collected, and transfused in 197 patients undergoing unilateral or bilateral cementless knee arthroplasty using the Solcotrans or the Constavac Blood Conservation blood-retrieval devices. Operative technique, method of hemostasis, and postoperative management were identical in all patients. Drainage-tube suction pressure was minimized, and the duration of drainage collection was less than 8 hours in all patients. In the 153 patients who underwent unilateral total knee arthroplasty (TKA), the amount of blood retrieved and transfused averaged 829 cm3 (59% of total blood lost). For the 44 patients who underwent bilateral procedures, 1,131 cm3 of blood was salvaged (56% of total blood lost). Transfused banked blood averaged 1.7 units (25% homologous) in unilateral cases, while bilateral procedures required 3.0 units (35% homologous). Complications (4%) included wound hematomata in five patients and deep venous thrombosis in two. Transient chills, fever, or tachycardia were seen in four patients at the time of transfusion. Transfusion requirements of banked blood appeared to be significantly reduced, especially in simultaneous bilateral knee arthroplasty, when compared to previous experience in patients who did not undergo postoperative blood retrieval.

The basic concepts involved in cementless fixation of the total hip arthroplasty femoral component have been controversial. Some clinicians advocate fixation only of the proximal portion of the stem so that weight-bearing loads will be transferred proximally, and proximal stress shielding will be avoided. Others advocate distal fixation to ensure rigidity of fixation but concede that it will lead to proximal stress shielding and bone loss. However, clinical evidence suggests that the design of the implant is one important factor in determining stress shielding. When the stem is smooth and cylindrical distally, proximal stress relief does not occur, even when the stem is fixed tightly distally. Because femoral component loosening is the most common clinical problem with cementless total hip arthroplasty, every effort should be made to achieve fixation of the implant. Proximal and distal fixation can be achieved with most of the available implants. For tight proximal fixation, a good proximal implant design and a precise line-to-line preparation technique are critical, but aggressive broaching and interference-fit techniques result in a high rate of proximal femoral fracture during preparation and implantation. When the conditions are good for excellent proximal fixation, a flexible stem should be selected to apply a large amount of stress proximally. The stress transferred through distal fixation will be small in this situation, and the reaming technique of the femoral diaphysis does not need to be very aggressive. Approximately 10 to 20 mm of tight distal fit combined with the 0.5-mm underreaming technique provides sufficient distal fixation, and the chance of distal femoral fracture during insertion of the stem is minimum with this technique. When conditions are unfavorable for excellent proximal fixation, such as in revision hip arthroplasty, or when a proximal deformity or osteoporosis is present, a relatively rigid stem should be selected to avoid overloading proximal fixation and, thus, generating large proximal micromotion. The stress transferred through distal fixation will be large in this situation, and a relatively aggressive but well-controlled reaming technique of the diaphysis is required. Approximately 20 to 40 mm of tight distal fit combined with a 0.5-mm underreaming technique is adequate to obtain sufficient distal fixation and still avoid distal femoral fracture. Implant design features that improve proximal fixation and instrumentation features that improve bone preparation and decrease the risk of failure will broaden the indications for cementless fixation. As fixation and instrumentation improve, more flexible implants can be developed to improve bone preservation and avoid proximal stress relief.(ABSTRACT TRUNCATED AT 400 WORDS)

Rotational loading of the femoral component has recently emerged as a prime factor for causing loosening and failure of total hip replacements. In this study the effect of surgical press-fit technique on torsional fixation of the femoral component was evaluated. The commonly used line-to-line reaming technique was compared to an underreaming technique using both four-fifths and one-third porous-coated anatomic medullary locking (AML) implants. Rotational micromotion, permanent rotational displacement, and slop displacement between bone and implant were measured with linearly variable differential transducers under torsional loading. The line-to-line reamed group showed significantly greater motion than both underreamed groups for all micromotion parameters. This was especially true for the slop displacement test, which revealed large amounts of displacement after a single moderate torsional load, whereas in the underreamed groups significantly less loosening was found. The line-to-line reaming technique did not achieve good rotational fixation of the femoral component. Superior rotational stability was accomplished only when the diaphysis was underreamed and tight diaphyseal fixation was achieved. The extent of the porous coating on the stem did not have a significant effect.

The effects of patellar button position and femoral component design on patellar tracking were investigated roentgenographically and arthroscopically using fresh-frozen adult anatomic specimen knees. Patellar tracking was evaluated for medial/lateral position and tilting angle deviation by comparing preoperative normal values to total knee replacement performance with the following variables: (1) femoral component design; symmetrical total condylar type with a 3-mm central patellar groove and a component with a 3-mm raised lateral patellar flange and 1-mm deepened patellar groove; and (2) patellar button placement; central insertion; and 10-mm medialized insertion. In the roentgenographic study, medialized position of the patellar button allowed the bony portion of the patella to assume its normal lateral position and tilt throughout the knee range of motion. A combination of medialized position of the patellar button and deepening of the patellar groove provided the most anatomically correct position and the most normal tilting of the bony structure of the patella. In the arthroscopic study, the centralized patellar position caused significant lateral tracking and subluxation relative to the femoral component, whereas the medialized position eliminated this tracking disorder. Deepening the patellar groove minimized the intraarticular tracking abnormality and constrained the patellar button in the patellar groove. These results show that the position of the patellar button and femoral component design exert a major influence on patellar tracking.

The effects of a central stem and its length on cementless tibial tray micromovement were investigated using preserved cadaver tibial specimens. For axial loading tests, cyclical compressive loads ranging 50-1000 N were applied to the anterolateral portion of the implanted tray. With subsidence on the loaded side and lift-off on the contralateral side, micromotions on both sides and bending of the tray were measured. The three groups consisted of a stemless group, a 7.5 cm (short) central stem group, and a 15 cm (long) central stem group. For shear loading tests, shear loads ranging 20-250 N were applied to the central portion of the posterior rim of the tray anteriorly for 1,000 cycles. Displacement values for subsidence and micromotion were measured on the medial and lateral side of the trays and compared for each group. For axial tests, the long stem minimized subsidence and lift-off (P < .05) when compared to the stemless group. Although the short stem also tended to prevent contralateral lift-off, no significant difference was shown when compared to the stemless group. However for shear loading, both central stem lengths significantly reduced subsidence and micromotion (P < .05). The authors conclude that the tibial tray with a long stem can achieve better initiation fixation of the implant to bone when compared to the short stem and no stem groups.

A preliminary form of a new version of the Home Observation for Measurement of the Environment (HOME) is presented. It is designed for use with families of children aged 10-15. The 80-item preliminary version of the Preadolescent HOME (PA-HOME) was field tested on 117 children with varying disabilities. The 80 items were selected from a pool of over 250 items by means of several field tests and accompanying item analyses. Both factor analyses and item analyses were used to help pare down items and produce a scale with acceptable psychometric properties. The psychometric properties of the PA-HOME are quite similar to those reported for the other three versions of the HOME Inventory. It appears to be a reasonably reliable scale with moderate correlations with other measures of the family environment, such as SES, social support, and marital stability. It has low to moderate correlations with measures of child competence in this sample of children with disabilities. The correlations are of the same general magnitude of correlations between the Infant-Toddler, Early Childhood, and Middle Childhood versions of HOME in samples of younger children with disabilities.

The purposes of this study were to evaluate the reliability of intramedullary (IM) instrumentation for unicompartmental total knee replacement and to assess the stability characteristics of the knee after implantation of a relatively unconstrained articular surface. Five adult, human cadaver lower extremities including hip, knee, and ankle were used to evaluate IM alignment. Five adult, fresh-frozen knee specimens were used to evaluate knee kinematics. Long anterioposterior roentgenograms were used to evaluate valgus angle and position of the center of the knee relative to the mechanical axis of the lower extremity. IM instrumentation returned the knee to normal alignment in all cases. The greatest valgus angle change was 3 degrees, and the position of the center of the knee relative to the mechanical axis was not significantly altered. Knee kinematics after unicompartmental knee replacement followed the predicted pattern of normal stability in extension and had slightly less varus-valgus laxity at 30 degrees (p less than 0.01), 45 degrees (p less than 0.01), and 60 degrees (p less than 0.05), and less anteroposterior displacement at 45 degrees (p less than 0.01) and 60 degrees (p less than 0.05). This study offers encouraging evidence that unicompartmental knee replacement with unconstrained components can restore normal knee kinematics, and that alignment can be restored with a high degree of accuracy with an intramedullary alignment system.

Fifty-five total knee arthroplasties (TKAs) in thirty-nine adult (mean age, 62 years) patients with rheumatoid arthritis were studied prospectively for a period of 1-7 years. All of the procedures were performed using cementless fixation of the tibial and femoral components. The Knee Society clinical rating system mean knee scores increased 56 points after operation (mean, 88 points), and the mean functional scores increased 28 points (mean, 64 points). Two revisions (4%) have been required, one for secondary late infection and one for failure of a cementless metal-backed patellar component. Good bone stock was retained in both, allowing for uneventful cementless revision. Forty-two arthroplasties (76%) were completely pain-free, twelve (22%) had mild, occasional discomfort with weight-bearing, and one (2%) had moderate pain at last examination. In this older rheumatoid population, cementless TKA offers good or excellent early clinical results and excellent preservation of bone stock should revision become necessary.

This study evaluated patellar wear with three commonly used metallic surfaces against a polyethylene surface. Wear characteristics of metal-backed patellar components were tested against cobalt chromium, titanium alloy, and ion-implanted titanium alloy (IITi) articular surfaces. Adult bovine serum was used as a lubricant. The specimens were cycled at 2.9 Hz for 1 X 10(6) cycles. The axial load was 343.2 N at 0 degrees flexion and increased to 2255.6 N at 110 degrees flexion. After testing, the polyethylene and metal surfaces were examined for wear using scanning electron microscopy. Patellae tested against the titanium-alloy surfaces had severe abrasion, surface cold flow, and pitting. The patellae tested against IITi were similar to the titanium-alloy group at the edges of the components, and delamination of the surface layers occurred in the high stress areas. The patellae tested against cobalt-chromium alloy had the least wear. Among the three metal surfaces, the titanium surface had the most severe surface abrasion and the cobalt-chromium surface had the least. At higher power magnification (X500), the cobalt-chromium surface had minimal surface abrasion even in the high stress areas. The IITi and titanium surfaces had severe scratching and surface abrasion, but the titanium surfaces were clearly more severely affected. The ion-implanted surface appeared to have been worn away in the high stress areas. Ion implantation does not produce a major improvement in the effect the titanium-alloy surface has on the polyethylene but does improve the wear on the metal surface itself. The cobalt-chromium surface was less damaged than the titanium and IITi and also caused less damage to the polyethylene. This experiment suggests that titanium and ion-implanted titanium are inferior materials to cobalt chromium when used as an articular surface in total knee replacements.

Cementless total knee arthroplasties (TKAs) were prospectively evaluated for pain relief in 1110 knees. The effect of screws in the tibial component, the age of the patients, and the gender of the patients were studied to determine the effect of these parameters on pain relief one and two years postsurgery. The group with screws in the tibial component (Ortholoc II) had a significantly higher percentage of pain-free knees at one year than at two years postsurgery, and the older patients had a significantly higher rate of pain-free knees at one- and two years postsurgery than the younger patients. Older female patients with Ortholoc I TKAs had a significantly higher percentage of pain-free knees than did older male patients at one-year postsurgery, but not at two years. The group with screws in the tibial components (Ortholoc II) had a higher percentage of pain-free knees at one-year postsurgery than did the Ortholoc I knees, but there was no difference between Ortholoc I and II at two-years postsurgery. In the Ortholoc II group, there was also no difference in results among sexes or between patients older and younger than 65 years old. The correlation coefficient was calculated to evaluate the relationship between body weight and the degree of pain after TKA. No significant correlation could be found at one and two years after surgery.

Prosthetic joint line position after total knee arthroplasty (TKA) was investigated using sagittal roentgenograms obtained from six fresh frozen cadaver knees. A specially designed knee testing device was developed that allowed for a controlled flexion angle while maintaining a constant quadriceps force. Pre- and postoperative roentgenograms were obtained from 30 degrees to 120 degrees in 15 degrees intervals. Steinman pins inserted into the medial femoral condyle and patella were used as reference points in the roentgenograms. A displacement vector between the medial femoral condyle and tibial plateau was used to analyze the tibiofemoral joint relationship. The functional patellar length (Insall-Salvati ratio), was used to determine correct patellar height. Another displacement vector was used to measure the patellofemoral joint relationship, and the angle between the patellar cut surface and femoral long axis was also calculated. Bone resection thickness from the femoral, tibial, and patellar surfaces was equal to the prosthetic thickness. This reconstructive scheme produced correct ligament balance and flexibility of the knee without the aid of tensioning devices or special measurements. Patellar tracking appeared to be identical before and after surgery. This accurate but simple surgical technique also reproduced normal knee extensor mechanisms that may influence longevity and long-term results of TKA.

Tibial tubercle osteotomy provides a safe and reliable means of extensile exposure of the knee. A technique was developed using a long osteoperiosteal segment including the tibial tubercle and upper tibial crest leaving lateral muscular attachments intact to this bone fragment. The bone fragment was reattached to its bed with two cobalt-chromium wires passed through the fragment and through the medial tibial cortex. The procedure was used in 71 knees to expose the joint for total knee arthroplasty, and the follow-up period was one to five years. All healed uneventfully, and no significant complications occurred. Mean postoperative flexion was 97 degrees. No extension lag occurred, and mean flexion contracture was 2.5 degrees. Excellent exposure can be achieved by means of a viable bone flap below the knee. Early rehabilitation and weight bearing can be done with low potential for complications.

Using a special knee-testing device, ten knees obtained at autopsy were subjected to varus-valgus, anterior-posterior, and flexion-rotation analysis in the intact state and after total knee arthroplasty. The ten knees showed no significant change in stability after knee replacement when the joint line was maintained in its natural position. When the femoral component was repositioned 5 mm proximally and 5 mm anteriorly, a significant increase in laxity occurred during midflexion. When the joint line was shifted 5 mm distal and 5 mm posterior to its anatomic location, significant tightening occurred in midrange of motion. Coupled rotation of the tibia with knee flexion was decreased after surgery in all knees with no specific relationship to joint line position. Coupled rotation with varus-valgus testing, however, remained within the normal range through the first 30 degrees of flexion only when the joint line was restored to its normal anatomic position. Stability in condylar knee arthroplasty is in part dependent on position of the joint line. Surgical techniques that rely on restoring the flexion and extension gap without regard to joint line position may result in alteration of varus-valgus or anterior-posterior displacement in midrange flexion.

Aseptic loosening of tibial components remains a serious problem in uncemented total knee arthroplasties. Achieving rigid initial fixation of porous-coated components is one of the most important factors in promoting bone ingrowth. The results of a biomechanical study for micromovement of the tibial component under posteroanterior shear and axial compressive loading are presented. Forty anatomic specimen tibiae were stress tested on a servohydraulic mechanical test machine to evaluate the effects of screws and a sleeve on initial fixation of the uncemented total knee tibial component. Twenty specimens were used for posteroanterior shear loading and 20 for anterolateral axial compressive loading. Four cancellous screws were inserted through holes of the tibial tray to pierce the cortex of the proximal tibia. The methylmethacrylate sleeve was applied to the central stem. Rigidity of fixation was significantly improved by the combination of screws and a sleeve. Bone strength was also an important factor affecting the quality of fixation.

A cementless hip stem that allows screw fixation of the collar to cortical bone in the calcar region was found to achieve enhanced rotational stability when implanted in preserved cadaveric human femora. Although the implants with screws showed less tendency for subsidence than the implants without screws, rotational micromotion was not found to be statistically different under light loading conditions. When implanted in composite bone, the addition of screws in the configuration tested was associated with significant metal-on-metal wear during combined compression and rotational cyclic loading. This finding is of concern due to potential wear particle toxicity and possible lowered fatigue life of the prosthesis. Therefore, specific design changes are recommended.

Rotational loosening has recently emerged as an important cause of failure of the femoral component of total hip arthroplasties. This study was designed to investigate the role played by torsional loads in loosening of cementless femoral components and to evaluate three cementing techniques involving a combination of canal irrigation, manual insertion, and vacuum mixing combined with pressure injection of the cement for their ability to improve rotational fixation. Rotational micromotion and subsidence were measured in 24 preserved human anatomic specimen femora. Acoustic emission (AE) technique was applied as a non-destructive method for evaluating material failure during loading. From the micromovement data, torque to 50 mu subsidence and torque to failure were surprisingly low with cementless fixation and with poor cement technique but were markedly improved with pulsed irrigation. Further improvement was achieved by pressure injection and vacuum mixing of the cement. However, AE was detected even in the most carefully performed cement specimens under torsional-loading conditions commonly occurring in daily activities. These signs of microfailure of the cement mantle at relatively low torsional loads suggest that the mode of failure of deeply penetrated cement is by microfracture of the cement mantle. The poor performance suggests that cementless fixation of intramedullary stems provides unsatisfactory fixation against torsional loading. There is need for major improvements in fixation mechanisms and techniques. The signs of failure of the cement mantle at normally occurring torsional loads suggest that even the best cement technique is prone to failure in torsion when exposed to normal daily use.

The hydrogen washout technique was used to investigate the role of synovial diffusion versus vascular perfusion in the nutrition of monkey flexor tendons within the digital sheath. There was no significant difference in the uptake and washout of hydrogen tracer by tendons in contact with synovium but detached from the surrounding vasculature, compared to control tendons. However, there was insignificant uptake of tracer by tendons with intact vasculature, but separated from synovium. Synovial diffusion is a primary nutrient pathway of monkey flexor tendons within the digital sheath.

The relationship between regional bone blood flow (measured using the hydrogen washout method) and regional osteoblastic activity (inferred from presence of osteoblasts on histological sections) was studied in the rabbit tibia. The rate of blood flow in epiphyses with marked osteoblastic activity (0.283 +/- .053 ml/min/ml) was significantly faster than that in epiphyses with minimal activity (0.097 +/- .007 ml/min/ml). Metaphyseal blood flow was significantly faster in areas with marked activity (0.253 +/- 0.040 ml/min/ml) than those with moderate (0.153 +/- .007 ml/min/ml) or minimal (0.126 +/- 0.013 ml/min/ml) osteoblastic activity. Diaphyseal bone blood flow was significantly faster in immature (0.082 +/- 0.005 ml/min/ml) than in mature (0.062 +/- 0.004 ml/min/ml) animals. The results indicate that there is a positive association between regional bone blood flow rate and osteoblastic activity in normal bone.

The podiatrist specializing in biomechanical therapy must begin with a solid foundation of standardized definitions in order to discuss theories of mechanical foot treatment as they have been presented and developed over the past century. Equally important, is the building of a working knowledge and familiarity with the wide variety of available materials and their diverse properties. In addition, in order to arrive at an accurate biomechanical diagnosis, the clinician must evaluate the patient from static, dynamic, and radiographic perspectives. One must also keep current in regard to various technological advances in casting and fabrication of orthotic devices, as well as in new developments in biomechanical theory and associated therapy. It also must be kept in mind that functional foot orthoses are not 100 per cent efficient, therefore, their shape, fabrication, and composition should all be devised and prescribed with specific goals for total body mechanics.

Collar seating and tight distal stem fit were evaluated for their effects on micromotion of the implant in the proximal femur. Collared and collarless implants were inserted with a cementless technique in 42 preserved femoral specimens from adult cadavers and cyclically axially loaded in a 9 degree valgus position. Micromotion was registered with dial indicators. Micromotion was minimized distally and proximally by achieving tight distal fixation. Collar seating prevented distal migration and failure of fixation, but it did not have a detectable effect on mediolateral or anteroposterior proximal micromotion. Toggle appears to be controlled primarily by the distal portion of the stem. Axial load transfer appears to be primarily controlled by collar seating. The least micromotion was achieved with a tight fit distally.

Hydrogen gas was used as a tracer to identify the barrier to material transfer at bone-cartilage interface in the rabbit knees in vivo. The transfer of hydrogen molecules from subchondral bone to articular cartilage was detected by means of platinum electrodes which were placed in varying depths in articular cartilage and subchondral bone. Hydrogen transfer was obstructed at the osteochondral junction in mature animals, while in immature animals there was no such barrier present in the bone-cartilage interface. The metabolism of articular cartilage in mature animals may be isolated from that of the underlying bone. All layers of the mature cartilage including those in the zone of calcified cartilage can receive nourishment and be maintained from the synovial fluid alone.

The hydrogen washout technique was applied to an experimental model of microvascular repair to evaluate its potential use in determining blood flow after microvascular surgery. Three blood flow measurements were obtained in each of 10 rat hindlimbs with the hydrogen washout technique: a control, a reading with arterial flow disrupted, and a final reading after standard microvascular repair of only the saphenous artery. After repair, flow rate was 0.115 ml/minute/ml compared to 0.008 ml/minute/ml for the disrupted reading (p less than .01). The practical clinical applicability of the hydrogen washout technique for evaluating blood flow in the fingertip was tested on five human volunteers. Ischemia in the upper extremity was produced with a pneumatic tourniquet. The hydrogen washout technique and the Doppler pulse monitor were used simultaneously to evaluate circulation in the small finger. Hydrogen uptake occurred simultaneously with return of clinical signs of tissue perfusion during gradual tourniquet deflation. The Doppler pulse returned while clinical signs of ischemia remained. The use of hydrogen washout in monitoring three patients following microvascular surgery has shown it to be accurate in predicting survival. It has, thus far, proven itself to be easily repeatable and reliable both intraoperatively and postoperatively.

Unicompartmental osteoarthritis was produced by applying varus stress to moving rabbit knee joints. Degenerative changes were confined to the medial tibial and the medial femoral articular surfaces. Within the range of varus stress used, duration appears to be more important than magnitude of varus stress in determining the severity of cartilage damage. The calcified zone remained histologically unchanged despite advanced changes in the noncalcified zone superficial to the tidemark. Intrachondral degenerative cysts were frequently found in the basilar layers of the noncalcified cartilage adjacent to the tidemark where shear stresses were likely to be highest and diffusible nutrients least available. Highly cellular cartilaginous tissue was noted in the subchondral marrow spaces in the specimens with advanced cartilage degeneration. These areas appeared to be continuous with the overlying degenerated cartilage through gaps in the calcified cartilage. Subchondral bone did not show remarkable trabecular thickening despite advanced degenerative changes in the articular cartilage.

The effect of posterior tibial slope was evaluated in a rotationally unconstrained anterior cruciate ligament-sacrificing total knee replacement (Ortholoc, Dow Corning Wright, Arlington, TN). Sloping the surface 7 degree posteriorly loosened the knee to varus-valgus and anterior-posterior stress in flexion. Eliminating posterior slope improved varus-valgus stability in flexion but slightly increased anterior-posterior laxity in extension. Values for the 3 degree posterior slope knee were between the values for 0 degree and 7 degree sloped surfaces, but not significantly different statistically from either. Total knee replacement designs with a posterior tibial slope are likely to promote anterior-posterior and varus-valgus laxity in flexion, and those with no posterior slope or 3 degree posterior slope are most likely to achieve normal stability in flexion and extension.

The nutrient pathways of flexor tendons within the flexor sheath were studied using the hydrogen washout technique. Hydrogen uptake and decay of a free segment of flexor tendon detached from its blood supply were not significantly different from an intact tendon lying in the synovial bed. There was no hydrogen uptake by flexor tendons which were mechanically separated from the synovial bed, even though muscular, periosteal and vincular attachments were intact. We concluded from this study that the synovium of the flexor tendon was a significant nutrient pathway for the flexor tendon and that the blood vessels did not appear to play a significant role in the nourishment of the flexor tendon.