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Cementing technique has a profound influence on the incidence of aseptic loosening of total hip replacements. Two specific measures that seem to have the greatest impact on the longevity of cemented femoral stems are pressurization of cement and control of mantle thickness, typically through the use of modular centralizing devices attached to the tip of the prosthesis. Two laboratory studies are presented that examine the success of these measures in clinical practice. In the first study, the performance of five designs of intramedullary plugs in resisting migration during pressurization of cement was evaluated in human anatomic specimen femurs. Profound differences were observed between the performance of the different plug designs. In canals larger than 12 to 14 mm, most commercial devices failed to resist pressures greater than 30 to 40 pounds per square inch. Overall, it was estimated that between 6% to 76% of these devices would fail to resist cement pressures of 50 pounds per square inch in clinical practice. The second study examined the role of distal centralizers in the accumulation of air bubbles around the distal tip of the prosthesis during insertion of the stem into the femur. Acrylic replicas of a femoral stem were implanted in cavities simulating the femoral canal. Colored dyes, present within the cement, revealed the complex patterns of cement flow. It was shown that cement, dragged from the top of the femur, forms a thin layer that covers the entire surface of the prosthesis and the distal centralizer. Significant voids were present behind the trailing edges of the distal centralizer in 42% of the cases examined. These studies show that improvements in intramedullary plugs and stem centralizers are needed to increase the reproducibility of cement technique in total hip replacement.

The variability in alignment of the natural patellar groove was determined about various anatomic axes of the femur, using 3 plane radiographs and electronic digitization. After the patellar groove was identified and marked on 15 anatomic specimen femurs, radiographs were taken in the coronal, sagittal, and transverse planes so that principal anatomic axes could be outlined. Through electronic digitization, a 3-dimensional representation of the patellar groove was constructed about the distal anatomic axis, mechanical axis, transepicondylar axes, and transcondylar axes. Regarding these 4 principal anatomic axes, the variability in orientation of the patellar groove was profound in both coronal and transverse planes, typically involving a range of 11 degrees to 16 degrees about the mean. The average orientation most closely approximated the perpendicular to the transepicondylar axis in the coronal plane; however, the range varied extensively. None of the anatomic axes tested proved reliable as a reference axis for proper position of the patellar groove, and this study shows that the orientation of the natural patellar groove is more variable than previously suspected. The failure of femoral components to accommodate this variability may explain many complications associated with the patellar component in total knee arthroplasty.

The design of cementless femoral prostheses is based on the assumption that age and gender do not affect the shape of the proximal femur. To test this hypothesis, standard anteroposterior and lateral radiographs were prepared of 4 sets of 20 femora, obtained from young (range, 40-60 years) and elderly (range, 60-90 years) donors of both genders. The intracortical and extracortical borders of each femur were digitized electronically, and key parameters were measured to define the shape and dimensions of the medullary canal and the position of the femoral head. Systematic differences were observed between the size and shape of male and female femora. Extracortical dimensions were larger in the male femora by 14% to 19%, and endosteal dimensions by 11% to 24%. However, there were no significant differences between the canal shape of young male and young female femora in the coronal, sagittal, or transverse planes. The male femora displayed no significant differences in canal shape or endosteal width as a function of age. Profound differences were observed in the endosteal shape and diaphyseal dimensions of the young and old female femora. The older female femora had wider canals at the level of the isthmus, with a significant reduction in the canal flare index (the ratio between the canal width proximal to the lesser trochanter and at the isthmus). This study demonstrates that cementless femoral prostheses of 1 standard shape cannot provide a close fit to the endosteal contours of young and elderly women.

UNLABELLED The dial osteotomy, an acetabular reorientation procedure based on radiographs, was developed by R. H. Eppright for treatment of hip dysplasia; however, long-term results are not recorded. The aim of this study was to evaluate retrospectively the results of the dial osteotomy as done in 37 patients (44 hips) at an average followup of 12.6 years. Articular pressures with the application of a time and pressure algorithm were calculated from radiographs to correlate calculated intraarticular pressures with progression of degenerative disease. Clinical results at followup were 32 (73%) satisfactory and 12 (27%) unsatisfactory hips. Six (13%) hips failed between 10-20 years (average 14.7 years). A satisfactory result correlated with the preoperative functional score. Radiographically, the anterior center-edge angle increased from an average of 6.7 degrees to 37.9 degrees. At followup, radiographic indices of degeneration indicated that eight (18%) hips had improved, 18 (41%) had stabilized, and 18 (41%) had deteriorated. Severin indices improved in 21 (48%) hips. Joint space width at followup provided the only correlation between radiographic parameters and clinical result. Contact pressures were reduced from 4.45 MPa to 1.12 MPa. The cumulative exposure to articular pressures averaged 61.6 MPa-years, and did not correlate with radiographic parameters or clinical success. LEVEL OF EVIDENCE Therapeutic study, Level IV (case series--no, or historical control group). See the Guidelines for Authors for a complete description of levels of evidence.

This study evaluates the three-dimensional anatomy of the femur with congenital dysplasia of the hip (CDH) in comparison with healthy controls. Computed tomographic scans were obtained from 207 women (154 with dysplasia; 54 healthy controls) with an average age of 51.6 years (range, 18-82 years). Most of the dysplastic joints were classified as Crowe I (43%), or Crowe II or III (48%), with 9% Crowe IV. Individualized three-dimensional computer models of the femur were generated by reconstruction of the CT scans. Dimensional and morphometric parameters were derived by computer analysis of each of the femoral reconstructions. The dysplastic femurs had shorter necks and smaller, straighter canals than the controls. The shape of the canal became more abnormal with increasing subluxation. Detailed analysis showed that the primary deformity of the dysplastic femur is rotational, with an increase in anteversion of 5 degrees to 16 degrees, depending on the degree of subluxation of the hip. The rotational deformity of the dysplastic femur arises within the diaphysis between the lesser trochanter and the isthmus and is not attributable to a torsional deformity of the metaphysis. This study shows that there is a significant difference in the geometry of the normal femurs and those with CDH, even in mild cases. In CDH cases, we recommend the use of modular or specially-designed components to accommodate the shape of the dysplastic canal.