Image processing for femoral endosteal anatomy detection: description and testing of a computed tomography based program

Femoral Head Size is Correlated With Head Position in Very Elderly Patients

BACKGROUND

In cases of femoral neck fracture, it is often not possible to accurately determine the original position of the head center to assess appropriate restoration of leg length. The aim of this study was to determine the accuracy of predicting the position of the femoral head center based on new and established correlations between the femoral head diameter (FHD) and the distance between the lesser trochanter and the femoral head center (LT-FHC) in the very elderly (aged ≥80 years) as the mainly affected but yet underinvestigated group.

METHODS

The FHD and the LT-FHC distance were determined in 148 subjects (104 males, 44 females); 90 aged ≥80 years and 58 aged <80 years. For each age and gender subgroup one specific (LT-FHC)/FHD ratio was determined. The accuracy of the new determined ratios and the established ratios by others were compared by recalculating the LT-FHC distance of each individual subject.

RESULTS

The FHD and the LT-FHC were significantly correlated, most strongly in elderly females (R = 0.554, P < .001). Using the new age- and gender-specific ratios, the LT-FHC distance could be predicted within 10 mm of the true value in 95% of the cases and in only 77% using previously reported formulas.

CONCLUSION

Age- and gender-specific formulas yield higher accuracy than generic formulas. The formulas presented in this study can offer a practical, easy to use instrument for orthopedic surgeons performing hip arthroplasty in very elderly patients in addition to classic techniques to prevent significant leg-length discrepancy.

Three-Dimensional Analysis of the Characteristics of the Femoral Canal Isthmus: An Anatomical Study

Purpose. To establish a new approach for measuring and locating the femoral intramedullary canal isthmus in 3-dimensional (3D) space. Methods. Based on the computed tomography data from 204 Chinese patients, 3D models of the whole femur and the corresponding femoral isthmus tube were reconstructed using Mimics software (Materialise, Haasrode, Belgium). The anatomical parameters of the femur and the isthmus, including the femur length and radius, and the isthmus diameter and height, were measured accordingly. Results. The mean ratio of the isthmus height versus the femoral height was 55 ± 4.8%. The mean diameter of the isthmus was 10.49 ± 1.52 mm. The femoral length, the isthmus diameter, and the isthmus tube length were significantly larger in the male group. Significant correlations were observed between the femoral length and the isthmus diameter (r = 0.24, p < 0.01) and between the femoral length and the isthmus height (r = 0.6, p < 0.01). Stepwise linear regression analyses demonstrated that the femoral length and radius were the most important factors influencing the location and dimension of the femoral canal isthmus. Conclusion. The current study developed a new approach for measuring the femoral canal and for optimization of customer-specific femoral implants.

Automatic and accurate reconstruction of distal humerus contours through B-Spline fitting based on control polygon deformation

The strong advent of computer-assisted technologies experienced by the modern orthopedic surgery prompts for the expansion of computationally efficient techniques to be built on the broad base of computer-aided engineering tools that are readily available. However, one of the common challenges faced during the current developmental phase continues to remain the lack of reliable frameworks to allow a fast and precise conversion of the anatomical information acquired through computer tomography to a format that is acceptable to computer-aided engineering software. To address this, this study proposes an integrated and automatic framework capable to extract and then postprocess the original imaging data to a common planar and closed B-Spline representation. The core of the developed platform relies on the approximation of the discrete computer tomography data by means of an original two-step B-Spline fitting technique based on successive deformations of the control polygon. In addition to its rapidity and robustness, the developed fitting technique was validated to produce accurate representations that do not deviate by more than 0.2 mm with respect to alternate representations of the bone geometry that were obtained through different-contact-based-data acquisition or data processing methods.

RAPID MANUFACTURING SYSTEM OF ORTHOPEDIC IMPLANTS

This study, aimed the development of a methodology for rapid manufacture of orthopedic implants simultaneously with the surgical intervention, considering two potential applications in the fields of orthopedics: the manufacture of anatomically adapted implants and implants for bone loss replacement. This work innovation consists on the capitation of the in situ geometry of the implant by direct capture of the shape using an elastomeric material (polyvinylsiloxane) which allows fine detail and great accuracy of the geometry. After scanning the elastomeric specimen, the implant is obtained by machining using a CNC milling machine programmed with a dedicated CAD/CAM system. After sterilization, the implant is able to be placed on the patient. The concept was developed using low cost technology and commercially available. The system has been tested in an in vivo hip arthroplasty performed on a sheep. The time increase of surgery was 80 minutes being 40 minutes the time of implant manufacturing. The system developed has been tested and the goals defined of the study achieved enabling the rapid manufacture of an implant in a time period compatible with the surgery time.

Computed tomographic analysis of bone support for three acetabular cup designs

The initial stability and long-term survivorship of cementless acetabular components is partially dependent on bone-prosthesis contact patterns. This study addresses the question: What are the differences in contact patterns for hemispheric, dual geometry, and spiked designs? Quantitative and qualitative assessment of contact patterns was achieved using a novel, nondestructive computed tomography-based analysis. Eighteen cadaveric hemipelvis specimens were randomly assigned to receive one of three cup designs. The mean amount of cup contact was 48.6% in the hemisphere group, 31.9% in the dual geometry group, and 35.1 percent in the spiked group. The hemispheric design showed more contact and a more uniform contact pattern than the dual geometry design. The dual geometry design featured a tight fit at the rim of the implant. In the spiked group, the amount of bone-prosthesis contact was affected by the distance that the spikes advanced into the pelvic bone. This nondestructive imaging technique has potential future uses in in vitro and in vivo studies.

A quantitative analysis of bone support comparing cementless tapered and distal fixation total hip replacements

The purpose of this study was to develop a technique to accurately assess cementless femoral stem-bone contact. Using this technique, differences in contact patterns between tapered (Synergy) and cylindrical distal fixation (Prodigy) cementless stems were explored. Femurs were prepared and the 2 types of femoral stems were implanted. After implantation, the femurs were imaged in a spiral computed tomography scanner and analyzed using novel custom-developed imaging software. This analysis used a geometric deformable-model UNIX-based software that determined bone-prosthesis contact area. The tapered stem features proximal, cancellous bone contact and a 3-point fixation pattern. The cylindrical distal fixation stem demonstrates cortical support in the distal aspect of the stem.

Diversity of proximal femoral medullary canal

To analyze the endosteal dimensions of the proximal femoral medullary canal, we studied 50 cadaver femora using computed tomography and a border detection method from 20 mm above the lesser trochanter, the osteotomy level, down to the isthmus. We documented the presence of a dense calcar septum in 96% of femora studied. In addition to mediolateral, anteroposterior, and neck-oriented dimensions, we calculated canal flare indices (CFIs) between the osteotomy level and the isthmus and metaphyseal canal flare indices (MCFIs) between the osteotomy level and the level 20 mm below the lesser trochanter midpoint to describe the shape of the endosteal cavity. With respect to the canal opening, the anteroposterior and mediolateral planes parallelled each other over the entire region as indicated by the high correlation (r = .7, P < .001) between the CFIs in these directions. The prediction of one dimension from another was unreliable in the metaphyseal region, where bone ingrowth is supposed to occur in a femoral prosthesis. The MCFI seemed to be the best parameter to distinguish the various types of proximal femoral canal shapes. We have described the variability of the proximal femoral endosteal dimensions in detail and find that the wide variation in the shape and size of the proximal femoral medullary canal means that it is almost impossible to achieve 100% cortical contact with the stem, especially in the metaphysis.