Femoral neck version affects medial femorotibial loading

Sex differences in femoral deformity determined using three-dimensional assessment for osteoarthritic knees

PURPOSE

To characterize femoral deformities and determine sex differences in varus knee osteoarthritis (OA), femoral morphology and limb alignment were evaluated by using three-dimensional (3D) assessment, comparing healthy, elderly volunteers with osteoarthritic knees.

METHODS

A total of 178 lower limbs of 169 subjects with knee osteoarthritis (136 women, 33 men; mean age 74.9 ± 5.2 years) and 80 lower limbs of 45 healthy, elderly subjects (24 women, 21 men; mean age 65 ± 4.9 years) were examined. A 3D extremity alignment assessment system was used to examine the subjects under weight-bearing conditions on biplanar long-leg radiographs using a 3D-to-2D image registration technique. The evaluation parameters were (1) femoral bowing in the coronal plane, (2) femoral bowing in the sagittal plane, (3) femoral neck anteversion, (4) hip-knee-ankle angle, and (5) femoral torsion.

RESULTS

Higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis were observed in women with OA compared with healthy subjects. No difference in the higher varus malalignment, no alteration in the femoral anterior bowing, and no difference in the lower femoral neck anteversion were found between men and women when comparing healthy and OA subjects.

CONCLUSIONS

The higher femoral lateral bowing and slightly higher femoral internal torsion in the proximal diaphysis in women are possibly a structural adaptation to mechanical use. The clinical significance is that the femoral deformities and the sex differences in knee OA have the potential to improve the understanding of the aetiology of primary varus knee OA.

LEVEL OF EVIDENCE

IV.

An Innovative Method of Assessing the Mechanical Axis Deviation in the Lower Limb in Standing Position

INTRODUCTION

Various methods of measuring mechanical axis deviation of lower limb have been described including radiographic and CT scanogram, intraoperative fluoroscopy with the use of an electrocautery cord. These methods determine the mechanical axis in a supine, non-weight bearing position. Although long cassette standing radiographic view is used for the purpose but is not available at most centres. A dynamic method of determining the mechanical axis in a weight bearing position was devised in this study.

AIM

The aim of the study was to describe a simpler and newer method in quantifying the mechanical axis deviation in places where full length cassettes for standing X rays are not available.

MATERIALS AND METHODS

A pilot study was conducted on 15 patients. The deviation from the mechanical axis was measured using a manually operated, hydraulic mechanism based, elevating scissor lift table. Patient was asked to stand erect over the elevating lift table with both patellae facing forward and C-arm image intensifier was positioned horizontally. Radiological markers were tied to a radio-opaque thread and placed at the centre of head of the femur and another at the centre of the tibio-talar joint. C-arm views of the hip, ankle and knee joint were taken to confirm the correct position of the marker by varying the height of the lift table.

RESULTS

The mechanical axis deviation values were recorded by measuring distance between the centre of the knee and radio-opaque thread in cm. This was measured in each case both clinically and from the image on the monitor. The two values were found to be statistically same. Pain was measured on VAS. Mechanical axis deviation values and VAS score were found to be positively significantly correlated.

CONCLUSION

This technique is dynamic, unique and accurate as compared to other methods for assessing mechanical axis deviation in a weight bearing position.

Soft-tissue balance in short and straight stem total hip arthroplasty

The growing numbers of short stem hip implants have redefined total hip arthroplasty with new stem geometries and possible functional differences. Several systematic reviews have reported good clinical results with this new class of stems, although kinematic alterations are still unclear in many aspects. The good clinical results obtained at the authors' institution led to the current study. The authors hypothesized that the geometric alignment of the prosthetic components may be closer to the anatomy of the healthy hip joint, thus leading to better function and clinical satisfaction. An examination via finite element analysis was chosen to model the hip joint and virtually implant a short and a standard straight stem. Findings indicated that anchoring of the short stem allowed favorable positioning in the proximal femur, with the femoral head already in the center of the cup. This positioning was not possible for the straight stem, which required further reduction of the femur by a significant translation into the cup, leading to abnormal soft-tissue balancing. The results from the simulation showed an absolute average deviation of ligamentous fiber strains of 6% for the short stem in 30° of flexion and extension versus 29% and 36% for the standard straight stem in 30° of flexion and extension, respectively. A femoral neck guided orientation of the short stem implant seems to allow a more anatomical reconstruction and thus a more balanced hip in terms of the modeled soft tissues. In contrast, the straight stem alters the head position and induces nonphysiological capsular strains.

Proximal femoral morphology and the relevance to design of anatomically precontoured plates: a study of the Chinese population

Adequately shaped femoral plate is critical for the fixation of fracture in the pertrochanteric regions. Lateral aspect of greater trochanter is an important region where the proximal femoral plate anchored. However, little is known regarding the morphology of greater trochanter. The objective of this study was to measure main dimensions of greater trochanter and other regions in the proximal end of the femur to provide an anatomical basis for the design of the proximal femoral plate. Anthropometric data on the proximal femur were performed utilizing three-dimensional computational modeling. Computed tomography images of healthy femurs in 53 women and 47 men were contributed to three-dimensional femur modeling. All data were compared between male and female femora. The results showed that mean values for male group were found to be greater in most of measured femoral dimensions. Oppositely, females demonstrated higher neck-shaft angle on anteroposterior view and femoral anteversion angle. The anthropometric data can be used for the anatomical shape design of femoral plates for osteosynthesis of fractures in the trochanteric regions. A distinct plate design may be necessary to accommodate differences between the genders.

A morphometric study of normal and varus knees

PURPOSE

The aim of the study was to investigate varus and normal knee morphologies to identify differences that may affect knee replacement alignment or design for varus knees.

METHODS

Computed tomography scans of varus and normal knees were analyzed, and geometric shapes, points and axes were fit to the femur and tibia independently. These points were then projected in the three anatomical planes to measure the variations between the two groups.

RESULTS

In the femur, varus knees had less femoral anteversion (p < 0.0001) and a larger medial extension facet (p < 0.05) compared with normal knees. In the tibia, the tubercle was found to be externally rotated in varus knees (12°), with a significant increase in the coronal slope (p = 0.001) and the extension facet angle (p = 0.002).

CONCLUSIONS

The study highlighted the differences and similarities found between the two groups, which raises awareness on changes required during surgical intervention and component placement or design for a varus knee. This is particularly relevant for the design of patient-specific instrumentation and implants.

LEVELS OF EVIDENCE

Diagnostic study, Level III.