Topographic matching of selected donor and recipient sites for osteochondral autografting of the articular surface of the femoral condyles.

The purpose of this study was to define the topography of the articular surface of the femoral condyles and to develop a method for computerized topographic matching of donor and recipient sites for osteochondral transplantation. The condyles of seven fresh cadaveric femurs were mounted on the rotating stage of a laser-based coordinate measuring machine. An anatomic coordinate system defining the articular surface of the condyles was created. Customized software was developed to allow selection and topographic matching of osteochondral graft donor and recipient sites from any location on the surface of the condyles. For cartilage defects within the weightbearing portions of the medial or lateral femoral condyles, grafts taken from sites from the most medial or lateral portions of the patellar groove provided a significantly better topographic match than did grafts taken from the central intercondylar notch.

Femoral ring versus fibular strut allografts in anterior lumbar interbody arthrodesis. A biomechanical analysis.

STUDY DESIGN: A comparison between femoral ring and fibular strut allografts in anterior lumbar interbody arthrodesis, as assessed by biomechanical analysis. OBJECTIVES: To assess the difference in stability and rigidity provided by the femoral ring allograft versus that provided by fibular strut allograft. SUMMARY OF BACKGROUND DATA: Two commonly used techniques for spinal arthrodesis at L4-L5 include the femoral ring allograft and the fibular strut allograft. The postoperative stability has not been evaluated biomechanically. METHODS: An anterior lumbar interbody fusion on seven cadaveric specimens was performed using femoral ring and fibular strut allografts. Biplanar radiography was used to measure the 6 degrees of motion of L4 with respect to L5 during a range of loading maneuvers. RESULTS: When an extension moment was applied, the femoral ring allograft extended 4.2 degrees more than the intact specimen, compared with 1.6 degrees with the fibular strut allograft (P = 0.18). When the flexion moment was imposed, lateral bending increased by 2.2 degrees with the femoral ring, compared with 0.7 degree with the fibular strut allograft (P = 0.06). During lateral bending, increased lateral translation was observed to be 0.9 mm with the fibular strut allograft compared with 1.4 mm with the femoral ring allograft (P = 0.06). CONCLUSIONS: Although not statistically significant, the fibular strut allograft creates a more rigid construct immediately after surgery during flexion-extension, lateral bending angulations, and lateral translation. One should consider using the fibular strut allograft over the femoral ring allograft, as it is more stable and rigid construct in the immediate postoperative period.

Predicting the position of the femoral head center.

To find an accurate method to predict the position of the normal head center in severely deformed hips without a contralateral reference, we studied the relationships between the head center and dimensions of the normal proximal femur using cadaveric specimens. From a large anatomic collection, 32 cadaveric femora with neck-shaft angles ranging from 115 to 146 were selected. The two parameters with the greatest correlation with the height of the femoral head were the height of the neck isthmus (r = .932) and the lowest point of neck saddle (r = .790). Medial head offset was most strongly correlated with the offset of the neck isthmus (r = .945) and the distance from the medullary axis to the outer borders of the medial cortex at the +30% level (r = .861). As a rule of thumb, the height of the head center can be predicted as the height of the midpoint of the neck isthmus plus 10 mm or as the height of the neck saddle with an accuracy of +/-5.1 mm and +/-8.3 mm. The offset of the head center can be predicted as the offset of the midpoint of the neck isthmus plus 15 mm or as the distance from the medullary axis to the medial cortex at the +30% level plus 15 mm with an accuracy of +/-4.6 mm and +/-6.3 mm.

The morphology of the femur in developmental dysplasia of the hip.

We studied the morphometry of 35 femora from 31 female patients with developmental dysplasia of the hip (DDH) and another 15 from 15 age- and sex-matched control patients using CT and three-dimensional computer reconstruction models. According to the classification of Crowe et al 15 of the dysplastic hips were graded as class I (less than 50% subluxation), ten as class I/III (50% to 100% subluxation) and ten as class IV (more than 100% subluxation). The femora with DDH had 10 to 14 degrees more anteversion than the control group independent of the degree of subluxation of the hip. In even the most mildly dysplastic joints, the femur had a smaller and more anteverted canal than the normal control. With increased subluxation, additional abnormalities were observed in the size and position of the femoral head. Femora from dislocated joints had a short, anteverted neck associated with a smaller, narrower, and straighter canal than femora of classes I and II/III or the normal control group. We suggest that when total hip replacement is performed in the patient with DDH, the femoral prosthesis should be chosen on the basis of the severity of the subluxation and the degree of anteversion of each individual femur.

Morphology of the lumbar vertebral endplates.

STUDY DESIGN: The dimensions and shapes of vertebral body endplates of inferior L4, inferior and superior L5, and superior S1 were analyzed. Computed tomographic scans parallel to each endplate were used to develop a standardized geometric model of the boundaries of each vertebral body. OBJECTIVES: To provide a detailed analytic and geometric model of the vertebral endplates from the inferior surface of L4 to the superior surface of S1. SUMMARY OF BACKGROUND DATA: Although measurements of the sagittal and maximum transverse diameters of the vertebral bodies have been well documented, no study offers a complete geometric description of the shape of the endplates. Also, information acquired using the techniques of previous published reports may not provide measurements as accurate as those of the current investigation. METHODS: Twenty-five men and 21 women were studied. Computed tomographic scans of the endplates were digitized. The data were interpolated, and multivariate regression equations were derived to devise a standardized model. Measurements were taken, and the data were curve fitted to give best-fit equations for the standardized models. RESULTS: The endplates resembled a cardioid at the inferior L4 level and became more elliptical toward the superior S1 level. The sagittal and transverse diameters of the endplates of inferior L4, superior and inferior L5, and superior S1 are provided and compared with those reported in previous studies. CONCLUSION: Although the female endplates are smaller than their male counterparts, the overall shapes are similar.

A comparison of alternative methods of measuring femoral anteversion.

PURPOSE: Although CT scans are widely believed to provide the most accurate measurements of femoral anteversion, any estimate of the anteversion of the femur depends on the accuracy of the calculated axis of the femoral neck. We devised a method to measure the anteversion of the femur precisely using a 3D femoral computer model reconstructed from digitized femoral contours. Using this method, we compared the accuracy of three popular methods of anteversion measurement based on CT scans. METHOD: The three popular CT methods were as follows: (a) the classic method of Weiner et al., based on a single CT image; (b) the method of Reikerås et al., in which the neck axis is defined by two superimposed images of the femoral head and neck; and (c) the method of Murphy et al., utilizing centroids of the head and the medullary canal. The accuracy of the single slice method was also examined using slices taken at four different neck slice levels within the proximal femur. CT scans of 30 femora were obtained using a helical CT scanner and reconstructed using custom software. RESULTS: Based on the 3D model, the true anteversion of the femora averaged 19.8 +/- 9.3 degrees (SD). Using the method of Weiner et al., the anteversion of the femora was underestimated by an average of 6.4 degrees (predicted value 13.4 +/- 10.4 degrees). Conversely, Murphy et al.'s method overestimated anteversion by an average of 6.3 degrees with an average value of 26.0 +/- 9.1 degrees. The difference between the true anteversion and the values predicted by both of these methods was statistically significant (p < 0.001). The average anteversion measured according to the method of Reikerås et al. was 17.8 +/- 8.9 degrees, 2.0 degrees less than the true anteversion of the sample (p < 0.005). Anteversion angles predicted from a slice just below the inferior edge of the head averaged 18.3 +/- 9.5 degrees, only 1.5-3.1 degrees less than the true anteversion of the femur (p = 0.14). CONCLUSION: The single slice CT method has sufficient accuracy for use, provided the slice is taken just below the femoral head. In cases with a femoral head deformity or a valgus neck or where difficulty is encountered in positioning the patient, 3D reconstruction appears essential for accurate measurement of anteversion.

Optimal location of a single distal interlocking screw in intramedullary nailing of distal third femoral shaft fractures.

OBJECTIVE: This biomechanical study was done to determine the effect of the level of a single distal screw in a static intramedullary (IM) femoral nail on the stability of fixation of a fracture in the distal third of the femur. DESIGN: Fifteen composite fiberglass femora were osteotomized transversely in the distal third of the femur. A Grosse-Kempf nail was implanted into the femurs, which were divided into three groups of five specimens. Single screw distal nail locking was varied distal to the osteotomy site for each group at 2.5, 5.0, and 7.5 centimeters, respectively. INTERVENTION: All instrumented femurs were mounted on a servohydraulic testing machine and fitted with transducers to measure axial, rotational, and bending displacements. Specimens were cyclically loaded (one hertz) in simultaneous torsion (moment: +/- 10 newton-meters) and axial compression (amplitude: 2,000 newtons) for 500 cycles with a 250-pound abductor force. MAIN OUTCOME MEASUREMENT: Data from linear and rotational transducers were sampled at 100 hertz for five cycles before cycling, every 100 cycles of loading, and immediately after cycling. Custom computer software was developed to convert transducer signals into static and dynamic measurements of axial motion (in millimeters), rotation (in degrees), and angulation (in degrees). RESULTS: Osteotomy site dynamic rotation increased significantly in specimens locked at 7.5 centimeters when compared with the 2.5-centimeter group. There was minimal difference between the stability of the 5.0-centimeter and 7.5-centimeter groups. There was no significant change in position at the fracture site before or after cyclic loading with respect to axial shortening, rotation, or bending. Both dynamic axial and angular displacements were also unaffected by screw position. CONCLUSION: The location of a single distal interlocking screw in static IM nail fixation of distal third femur fractures can significantly affect rotational stability but not axial or angular fixation.

Biomechanical consequences of sequential plantar fascia release.

Plantar fascia release has long been a mainstay in the surgical treatment of persistent heel pain, although its effects on the biomechanics of the foot are not well understood. With the use of cadaver specimens and digitized computer programs, the changes in the medial and lateral columns of the foot and in the transverse arch were evaluated after sequential sectioning of the plantar fascia. Complete release of the plantar fascia caused a severe drop in the medial and lateral columns of the foot, compared with release of only the medial third. Equinus rotation of the calcaneus and a drop in the cuboid indicate that strain of the plantar calcaneocuboid joint capsule and ligament is a likely cause of lateral midfoot pain after complete plantar fascia release.

Pressurization and centralization enhance the quality and reproducibility of cement mantles.

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.

Anatomic alignment of the patellar groove.

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.

Increased tibial translation after partial sectioning of the anterior cruciate ligament. The posterolateral bundle.

We measured changes in anterior translation of the tibia with sequential sectioning of the bundles of the anterior cruciate ligament and correlated these changes with the clinical examination. Six fresh cadaveric lower extremities were examined by three experienced knee surgeons in a masked fashion with the anterior cruciate ligament intact and after sectioning of the posterolateral bundle, the posterolateral bundle and 50% of the anteromedial bundle, and the entire ligament. Lachman, anterior drawer, and lateral pivot shift tests were performed. Both KT-1000 arthrometer testing (30 pounds) and biplanar radiography demonstrated progressive increases in anterior translation with incremental sectioning of the anterior cruciate ligament. However, significant (P < 0.05) increases in translation were found only after sectioning both the posterolateral bundle and half of the anteromedial bundle and after complete sectioning of the anterior cruciate ligament. The examiners were accurate in their interpretation of the status of the anterior cruciate ligament in 89% of the intact specimens and 80% of completely sectioned ligaments. Only 11% of the examinations correctly diagnosed the anterior cruciate ligament as partially cut when the posterolateral bundle was sectioned. A soft end point to the Lachman examination was noted only after cutting at least 75% of the ligament, but was not always present. Clinical evaluation is accurate in defining intact and completely sectioned anterior cruciate ligaments. However, it is unable to differentiate a sectioned posterolateral bundle from an intact anterior cruciate ligament, or a 75% sectioned ligament from a completely sectioned ligament. The clinical diagnosis of a partial tear of the anterior cruciate ligament is more likely to represent a complete or "functionally complete" tear.

Factors influencing pressurization of the femoral canal during cemented total hip arthroplasty.

Successful cement pressurization with total hip arthroplasty depends on the capacity of the cement gun and its ability to pressurize the canal and the integrity of the intramedullary plug and the proximal seal used to contain the cement bolus during pressurization. In the laboratory, the authors measured the volume of cement delivered by two cement guns (from Zimmer, Warsaw, IN, and Howmedica, Rutherford, NJ) in comparison with typical values for the volume of the medullary canal following standard surgical preparation. The two cement guns studied delivered 93 and 138 mL cement, respectively. In comparison, the volume of the intramedullary canal ranged from 35 to 70 mL using a standard femoral prosthesis (Precision Hip System, Howmedica). Peak pressures developed during cement injection using the cement guns were 73.6 +/- 27.1 psi for the Zimmer system and 47.3 +/- 16.9 psi for the Howmedica system. Both devices were able to sustain a minimum pressure of at least 6.5 psi through cementing when used in conjunction with a flexible pressurizing seal. The mechanical performance of five designs of intramedullary plugs was assessed by monitoring plug displacement during cement pressurization in reamed cortical specimens. The performance of each device was judged by its ability to withstand cement pressures of 50 psi without displacement within the medullary canal. On the basis of this test, the probability that these plugs would exceed this criterion when used with the femur was estimated to range from 24 to 94%. Few of the commercially available plugs were able to withstand cement pressures routinely generated using standard cement delivery systems.

The effect of aging on the shape of the proximal femur.

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.

Partial tears of the anterior cruciate ligament. Are they clinically detectable?

Eight cadaveric lower extremities were examined by three experienced knee surgeons in blinded fashion. The knees were examined with intact anterior cruciate ligaments, sectioned anteromedial bundles, and completely sectioned anterior cruciate ligaments to evaluate detectable laxity changes. Lachman, anterior drawer, lateral pivot shift, and KT-1000 arthrometer testing were performed. Optimized biplanar radiography using a defined spatial coordinate reference system was performed with a 30-pound anterior force at 30 degrees of flexion to confirm clinical findings. Physical examination and arthrometer testing detected no difference between intact and partially sectioned anterior cruciate ligaments; these ligaments were significantly different than completely sectioned ligaments, with the Lachman test being the most sensitive. Despite consistent clinical detection of complete sectioning of the anterior cruciate ligament by both physical examination and arthrometer testing, neither method proved accurate in the diagnosis of isolated tears of the anteromedial bundle, but both did show that partially sectioned anterior cruciate ligament closely resembled intact ligament and differed significantly from completely sectioned ligament, as confirmed by radiologic data. Clinically diagnosed "partial tear" is likely to be complete rupture of the anterior cruciate ligament. Historically, clinically diagnosed partial tears of the anterior cruciate ligament have tended to "progress" to symptomatic instability. Our data imply these patients may have had functionally incompetent ligaments from time of injury and, in fact, were demonstrating the expected natural history of an anterior cruciate ligament-deficient knee.