3D Computer graphical anatomy study of the femur: a basis for a new nail design

Associations between femoral 3D curvature and sagittal imbalance of spine

Background

The sagittal imbalance (SI) of spine triggers compensatory mechanisms (CMs) of lower extremity (LE) to restore trunk balance. These CMs can cause long-period stress on the femur and may possibly alter the femoral morphology. This cross-sectional observational study aimed to answer the following questions: (a) Do SI subjects exhibit greater femoral bowing compared to subjects with sagittal balance? (b) Are there associations between femoral bowing and CMs of LE in SI subjects?

Methods

Subjects who underwent biplanar full body radiographs with the EOS imaging system between January 2016 and September 2021 were recruited. Sagittal parameters included T1-pelvic angle (TPA), pelvic incidence (PI), pelvic tilt (PT), sacral slope, lumbar lordosis (LL), PI-LL, and PT/PI ratio. LE parameters were femoral obliquity angle (FOA), knee flexion angle (KA), and ankle dorsiflexion angle. Femoral bowing was quantified as 3D radius of femoral curvature (RFC). Associations between 3D RFC and the radiographic parameters were analyzed.

Results

A total of 105 subjects were included, classified into balance group (TPA < 14°, n = 40), SI group (TPA ≥ 14° and KA <5°, n = 30), and SI with knee flexion group (TPA ≥ 14° and KA ≥ 5°, n = 35). 3D RFC was significantly lower in SI with knee flexion group compared to the other two groups (both p < 0.001). Stepwise linear regression showed that age, SI and knee flexion, femoral length (FL), FOA, and KA were independent predictors for 3D RFC.

Conclusion

Greater femoral bowing is observed in subjects with SI and knee flexion compared to the balanced population. CM parameters, including KA and FOA, are associated with 3D RFC. Further longitudinal study is needed to investigate the cause-and-effect relationship between SI, CMs of LE, and femoral bowing.

Design of well-matched end-structure of anatomical proximal femoral locking plate based on computer-assisted imaging combined with 3D printing technology: a quality improvement study

BACKGROUND

The extramedullary locking plate system was the common internal fixation method for hip fractures. However, common plates were poorly matched to femur, which was because they were designed based on anatomical parameters of the Western populations. Therefore, the aim was to design an end-structure of the anatomical proximal femoral locking plate that closely matched the anatomy of the Chinese population.

MATERIALS AND METHODS

From January 2010 to December 2021, consecutive patients aged 18 years and older who underwent a full-length computed tomography scan of the femur were included. The end-structure (male and female model) of the anatomical proximal femoral locking plate was designed based on anatomical parameters of femurs that were measured in three-dimensional space using computer-assisted virtual technology. The match degree between the end-structure and femur were evaluated. Inter-observer and intra-observer agreement for the evaluation of match degree was assessed. The matching evaluation based on a three-dimensional printing model was regarded as the gold standard to assess the reliability.

RESULTS

A total of 1672 patients were included, with 701 men and 971 women. Significant differences were seen between male and female for all parameters of the proximal femur (all P <0.001). All match degree of end-structure was over 90%. Inter-observer and intra-observer agreement was almost perfect (all kappa value, >0.81). The sensitivity, specificity, and percentage of correct interpretation of matching evaluation in the computer-assisted virtual model was all greater than 95%. From femur reconstruction to completion of internal fixation matching, the process takes about 3 min. Moreover, reconstruction, measurement, and matching were all completed in one system.

CONCLUSIONS

The results showed that based on the larger sample of femoral anatomical parameters, a highly matching end-structure of anatomical proximal femoral locking plate for Chinese population could be designed with use of computer-assisted imaging technology.

A Simple Method to Improve Detection of Femoral Nail Abutment in the Distal Femur: A Computer Modeling Study

BACKGROUND

Proximal femur fractures are more frequently treated with long femoral nails. Lateral radiographs are used to assess the nail position in the distal femur. However, because of the asymmetric shape of the distal femur, standard lateral radiographs alone are suboptimal for assessing anteriorly positioned nails in the distal femur. Consequently, instances of nail abutment or even perforation might be missed intraoperatively.

QUESTION/PURPOSE

Using a three-dimensional (3D) modelling approach, we asked: When the nail is in the anterior fifth of the canal, will rotating the femur to align the simulated x-ray beam with the anterior femoral condyles instead of the posterior femoral condyles increase the diagnostic accuracy of detecting nail perforation of the anterior cortex?

METHODS

3D models of 42 unilateral femora from a population sample representative of patients with hip fractures (mean age of 76 ± 7 years, 10 males and 32 females, and 16 left and 26 right femora) were used. The patients had a mean height of 158 ± 9 cm; 27 femora were from Asians and 15 were from Caucasians. Clinically appropriately sized nails had already been virtually implanted previously as part of a quantitative nail fit assessment study. In a preliminary step, the mean angles of inclination of the distal anterior supracondylar region were quantified using four axial sections of the distal femur. For the femora with the nail tip in the anterior fifth of the canal, projections representing a lateral radiograph were generated along with rotated projections at mean angle (5°, 8°) rotations, with the anterior femoral condyles aligned, and anterior femoral condyle alignment followed by internal and external rotation to detect maximum nail perforation. The distance from the nail to the distal anterior cortex was measured for each rotational projection and used to detect anterior nail perforation. The accuracy of detection was assessed using the area under the curve (AUC) of the receiver operating characteristic (ROC) analysis.

RESULTS

Rotating the 3D models by aligning the x-ray beam with the anterior femoral condyles improves the diagnostic ability of detecting anterior nail perforation compared with standard lateral radiographs. The AUC increased with rotation from 0.50 (95% confidence interval 0.50 to 0.50) on the lateral projection to 0.73 (95% CI 0.57 to 0.88, difference = -0.23; p = 0.004) at 5° of rotation, 0.77 (95% CI 0.62 to 0.93, difference = -0.27; p = 0.001) at both 8° of rotation and with the anterior femoral condyles aligned, and to 0.82 (95% CI 0.67 to 0.97, difference = -0.32; p < 0.001) with internal/external rotations past the anterior femoral condyles. There were no differences in accuracy between the four methods of rotation.

CONCLUSION

This study shows that rotating the femur to align the anterior femoral condyles on a lateral radiograph and then internally/externally rotating it, improves the accuracy assessed via the AUC of detecting anterior perforation when long nails are positioned in the anterior fifth of the distal femur.

CLINICAL RELEVANCE

This approach can easily be used in a clinical setting. Intraoperatively, the image intensifier can be rotated around the leg to produce an image with the anterior femoral condyle aligned, providing surgeons with an opportunity to identify and improve the nail's position or exchange the nail while the patient is still under anesthesia.

Potential pitfalls of lateral radiographic assessment of the nail position in the distal femur

INTRODUCTION

Antegrade nailing of proximal femur fractures is a widely accepted treatment that relies on lateral radiographs to assess distal nail positioning. However, the distal femur is trapezoidal in cross section, consequently standard lateral radiographs may be insufficient. This study aimed to utilise 3D modelling to virtually assess the accuracy of lateral radiographs in defining the position of a femoral nail in the distal femur, specifically considering distal cortical encroachment.

MATERIALS AND METHODS

Three-dimensional models of a commonly used nail, were positioned in 3D models of 63 femora, generated from CT scans. Lateral projections, representative of lateral radiographs, were generated and measurements of the closest point distance between the distal nail and anterior inner cortex were recorded. Axial slices through the model at the same distal position were produced for any nails located in the canal's anterior 1/5th and used to quantify the shortest nail to anterior cortex distance.

RESULTS

A significant (p = 0.000) difference exists between the positions of the nail in the lateral projection (- 1.7 ± 1.24 mm) compared with axial position (- 0.23 ± 1.41 mm) with reference to the inner cortical surface. In the lateral projection, 30 nails were located in the canal's anterior 1/5th, of these, 14 nails were identified in the axial position as perforating the inner cortex, with four also perforating the outer cortex surface.

CONCLUSION

Femoral nails are often anteriorly located in the distal femur and reviewed using lateral radiographs. However, this research demonstrates that owing to the geometry of the distal femur, a lateral radiograph may be inadequate for determining the true position of a femoral nail within the distal femur. Accurately assessing the position of femoral nails may help to address and prevent thigh pain, and iatrogenic fracture or perforation which have been associated with anterior positioning.

A novel radiological classification system of the distal femur

INTRODUCTION

In our previous studies, we were able to identify anatomical differences as a predictor for aseptic loosening following primary and revision surgery with the use of rotating hinge prosthesis. This study was performed to answer following question: can a novel radiological classification system of the distal femur be identified?

MATERIALS AND METHODS

A total of 200 patients who received standardized anteroposterior (AP) and lateral views of the knee joint were included in this study. On AP radiographs, we measured the distance between inner diameter of the femur at 20 cm proximally from the knee and at a point 2 cm proximally from the adductor tubercle. The ratio of the inner diameter of the femoral canal at 20 cm proximal of knee joint to the inner diameter of medullary canal at 2 cm proximal of adductor tubercle was used as a novel index ratio. Two observers blindly and independently reviewed the anteroposterior radiographs twice.

RESULTS

Three groups of anatomical classification can be constructed for each sex according to the 25th and 75th percentiles. A higher distribution of Type C was found in female patients. The median intra-observer reliability for rater 1 was 0.995 (IQR 0.994-0.997). We had also a high inter-observer reliability with ICC of 0.997 (95% CI 0.996-0.998).

CONCLUSIONS

The novel classification presents three different types of the knee joint for male and female patients. Type C has a wider inner diaphyseal diameter compared to Type A with a narrow inner diaphyseal diameter.

Notching is less, if femoral component sagittal positioning is planned perpendicular to distal femur anterior cortex axis, in navigated TKA

Purpose

In navigated TKA, the risk of notching is high if femoral component sagittal positioning is planned perpendicular to the sagittal mechanical axis of femur (SMX). We intended to determine if, by opting to place the femoral component perpendicular to distal femur anterior cortex axis (DCX), notching can be reduced in navigated TKA.

Methods

We studied 171 patients who underwent simultaneous bilateral computer-assisted TKA. Femoral component sagittal positioning was planned perpendicular to SMX in one knee (Femur Anterior Bowing Registration Disabled, i.e. FBRD group) and perpendicular to DCX in the opposite knee (Femur Anterior Bowing Registration Enabled, i.e. FBRE group). Incidence and depth of notching were recorded in both groups. For FBRE knees, distal anterior cortex angle (DCA), which is the angle between SMX and DCX, was calculated by the computer.

Results

Incidence and mean depth of notching was less (p = 0.0007 and 0.009) in FBRE versus FBRD group, i.e. 7% versus 19.9% and 0.98 mm versus 1.53 mm, respectively. Notching was very high (61.8%) in FBRD limbs when the anterior bowing was severe (DCA > 3°) in the contralateral (FBRE) limbs.

Conclusion

Notching was less when femoral component sagittal positioning was planned perpendicular to DCX, in navigated TKA.

Level of evidence

Therapeutic level II.

Femur morphology in healthy infants and young children

The objective of this study was to characterize femur morphology in healthy infants and young children. Anterior-posterior (AP) radiographs of the femur from children age 0-3 years with no history of bone disease were obtained from two children's hospitals and one medical examiner's office. Femur morphological measures (bone length, minimum diaphysis diameter, growth plate width, and femur radius of curvature) and sectional structural measures were determined. Measures were described and compared based on subject age and mass. Relationships between measures and age and mass were evaluated. The 169 AP femur radiographs were obtained from 99 children (59.6% males, median age = 12.0 months, IQR = 0-27.5 months, median body weight = 10.0 kg, IQR = 4.4-15.6 kg). Femur length (r_s  = 0.97, p < 0.001; r_s  = 0.89, p < 0.001), trochanter width (r_s  = 0.86, p < 0.001; r_s  = 0.85, p < 0.001), minimum diaphysis diameter (r_s  = 0.91, p < 0.001; r_s  = 0.87, p < 0.001), and growth plate width (r_s  = 0.91, p < 0.001; r_s  = 0.84, p < 0.001) increased with age and weight, respectively. Cross-sectional area (r_s  = 0.87; r_s  = 0.86; p < 0.01), polar moment of inertia (r_s  = 0.91; r_s  = 0.87; p < 0.001), moment of inertia (r_s  = 0.91; r_s  = 0.87; p < 0.001), polar modulus (r_s  = 0.91; r_s  = 0.87; p < 0.001) and medullary canal diameter (r_s  = 0.83, p < 0.001; r_s  = 0.73, p < 0.001) at the minimum diaphysis also increased with age and weight, respectively. Changes during rapid bone growth are important to understanding fracture risk in infants and young children as they transition to independent walking. Femur length, trochanter width, minimum diaphysis diameter and growth plate width increased with age and weight. Structural properties associated with fracture resistance also increased with age and weight.

A comparison between Asians and Caucasians in the dimensions of the femoral isthmus based on a 3D-CT analysis of 1189 adult femurs

INTRODUCTION

For successful intramedullary implant placement at the femur, such as nailing in unstable proximal femur fractures, the use of an implant that at least reaches or exceeds the femoral isthmus and yields sufficient thickness is recommended. A number of complications after intramedullary femoral nailing have been reported, particularly in Asians. To understand the anatomical features of the proximal femur and their ethnic differences, we aimed to accurately calculate the femoral isthmus dimensions and proximal distance of Asians and Caucasians.

METHODS

In total, 1189 Asian and Caucasian segmented 3D CT data sets of femurs were analyzed. The individual femoral isthmus diameter was precisely computed to investigate whether gender, femur length, age, ethnicity or body mass index have an influence on isthmus diameters.

RESULTS

The mean isthmus diameter of all femurs was 10.71 ± 2.2 mm. A significantly larger diameter was found in Asians when compared to Caucasians (p < 0.001). Age was a strong predictor of the isthmus diameter variability in females (p < 0.001, adjusted r² = 0.299). With every year of life, the isthmus showed a widening of 0.08 mm in women. A Matched Pair Analysis of 150 female femurs showed a significant difference between isthmus diameter in Asian and Caucasian femurs (p = 0.05). In 50% of the cases the isthmus was found in a range of 2.4 cm between 16.9 and 19.3 cm distal to the tip of the greater trochanter. The female Asian femur differs from Caucasians as it is wider at the isthmus.

CONCLUSIONS

In absolute values, the proximal isthmus distance did not show much variation but is more proximal in Asians. The detailed data presented may be helpful in the development of future implant designs. The length and thickness of future standard implants may be considered based on the findings.

Effects of ethnicity on proximal femoral intramedullary nail protrusion-a 3D computer graphical analysis

INTRODUCTION

Antegrade nailing of proximal femur or femoral shaft fractures is a proven treatment with good to excellent results. Nonetheless, clinical evidence from Asia indicates that proximal femur nails can be too proud at the greater trochanter (GT) causing irritation for some Asian patients. This study aimed to identify any significant differences in proximal nail misfit for a set of Asian and Caucasian femora.

MATERIALS AND METHODS

Two nails (Gamma3, TFNA) were virtually inserted into 63 femoral 3D models (28 Japanese, 4 Thai, 31 Caucasian). In AP, the entry point was 4° lateral for Gamma3 and 5° for TFNA; laterally the same location was used for both. Insertion depth was controlled by aligning the lag screw centre head. The distance of the nail end from the GT was measured at five (medial, lateral, anterior, posterior and centre) reference points (RPs). The correlation between GT height, CCD angle and proximal nail distance to GT was analysed.

RESULTS

There was no significant difference between either nail (p = 1.0). The TFNA was overall less prominent than the Gamma3, and significantly less prominent at all RPs except lateral. The Asian femora were 3.76 (p = 0.016) times more likely to have the nail protruding proximally. The Asian subjects were shorter (p < 0.05) than the Caucasians. Their GT height was slightly shorter and CCD angles larger compared to Caucasian (Asian: 41.1 mm, 128.1°, Caucasian: 42.2 mm, 126.4°), but the differences were not significant (p = 0.36). Stature, GT height and CCD angle significantly correlated with nail distance to GT.

CONCLUSIONS

This study illustrated a significantly increased incidence of proximal nail protrusion in Asian compared to Caucasian femora, corroborating clinical findings. The combination of shorter stature and GT height and a larger CCD angle in Asians likely contributes to this difference.

Biomechanical analysis of peri‑implant fractures in short versus long cephalomedullary implants following pertrochanteric fracture consolidation

INTRODUCTION

Pertrochanteric femur fracture fixation with use of cephalomedullary nails (CMN) has become increasingly popular in recent past. Known complications after fracture consolidation include peri‑implant fractures following the use of both short and long nails, with fracture lines around the tip of the nail or through the interlocking screw holes, resulting in secondary midshaft or supracondylar femur fractures, respectively. Limited research exists to help the surgeon decide on the use of short versus long nails, while both have their benefits. The aim of this biomechanical study is to investigate in direct comparison one of the newest generations short and long CMNs in a human anatomical model, in terms of construct stability and generation of secondary fracture pattern following pertrochanteric fracture consolidation.

METHODS

Eight intact human anatomical femur pairs were assigned to two groups of eight specimens each for nailing using short or long CMNs. Each specimen was first biomechanically preloaded at 1 Hz over 2000 cycles in superimposed synchronous axial compression to 1800 N and internal rotation to 11.5 Nm. Following, internal rotation to failure was applied over an arc of 90° within one second under 700 N axial load. Torsional stiffness as well as torque at failure, angle at failure, and energy to failure were evaluated. Fracture patterns were analyzed.

RESULTS

Outcomes in the study groups with short and long nails were 9.7 ± 2.4 Nm/° and 10.2 ± 2.9 Nm/° for torsional stiffness, 119.8 ± 37.2 Nm and 128±46.7 Nm for torque at failure, 13.5 ± 3.5° and 13.4 ± 2.6° for angle at failure, and 887.5 ± 416.9 Nm° and 928.3 ± 461.0 Nm° for energy to failure, respectively, with no significant differences between them, p ≥ 0.17. Fractures through the distal locking screw holes occurred in 5 and 6 femora instrumented with short and long nails, respectively. Fractures through the lateral entry site of the head element were detected in 3 specimens within each group. For short nails, fractures through the distal shaft region, not interfacing with the implant, were detected in 3 specimens.

CONCLUSION

From a biomechanical perspective, the risk of secondary peri‑implant fracture after intramedullary fixation of pertrochanteric fractures is similar when using short or long CMN. Moreover, for both nail versions the fracture pattern does not unexceptionally involve the distal locking screw hole.

Prosthetic Hip ROM from Multibody Software Simulation

The pre-operative planning of a hip arthroplasty entails the choice of the prosthetic hip model and of the position of both joint components with reference to bone. Assessing the impact of geometrical factors on the final hip range of motion (ROM) is not trivial, since it requires performing 3D evaluations. Nonetheless, it deserves to be studied since hip impingement and dislocation are still relevant complications in hip arthroplasty. This work pertains a numerical model for the assessment of the hip ROM in relation to cotyle position. External/internal rotation is considered as a benchmark, and multiple combinations of acetabular anteversion/inclination are considered. According to results, over two hundred different geometric configurations can be examined in few minutes, and the cotyle position can be so optimized with relevant benefits in term of hip ROM.

Indications, surgical approach, reduction, and stabilization techniques of distal radius fractures

Distal Radius fractures (DRF) are one of the most common injuries in the upper extremity and incidence is expected to rise due to a growing elderly population. The complex decision to treat patients operatively or conservatively depends on a large variety of parameters which have to be considered. No unanimous consensus has been reached yet, which operative approach and fixation technique would produce the best postoperative functional results with lowest complication rates. This article addresses the available evidence for indications, approaches, reduction, and fixation techniques in treating DRF.

An increase in the risk of excessive femoral anteversion for relatively younger age and types of femoral morphology in total hip arthroplasty with direct anterior approach

BACKGROUND

Direct anterior approach (DAA) is known to diminish a dislocation risk and widely used for total hip arthroplasty (THA). On the other hand, anterior dislocation due to increasing stem anteversion and cup anteversion is an important complication.

METHODS

A retrospective analysis of 140 (male/female: 10/130) consecutive patients with 149 hips who had undergone primary THA in the period between 2011 and 2015 was conducted. Factors including age, gender, body mass index (BMI), and primary diagnosis were examined. Radiographic parameters including the Dorr proximal femoral types, cortical thickness index (CTI), canal flare index (CFI), and canal to calcar index were measured. To investigate relationships of combined anteversion (CA) with other factors, a stepwise regression analysis was performed.

RESULTS

The mean age, BMI, and the follow-up period were 69.5 ± 10.3 years old, 23.4 ± 3.4 kg/m², and 48.2 ± 13.6 months, respectively. The proximal femurs of the 149 hips were categorized as Dorr type A ( n = 33), type B ( n = 110), and type C ( n = 6). The mean CTI, CFI, and canal to calcar index were 0.56 ± 0.08, 4.15 ± 0.83, and 0.46 ± 0.09, respectively. The mean stem varus angle, radiographic inclination, and radiographic anteversion of the cup were 0.19 ± 1.63, 40.9 ± 6.0°, and 12.7 ± 3.5°, respectively. Stem anteversion measured by computed tomography (CT) axial image was 17.7 ± 12.0°. The mean radiographic inclination, radiographic anteversion (CTRA), and anatomical anteversion analyzed by Kyocera 3-D template were 40.8 ± 7.2°, 19.8 ± 6.6°, and 28.8 ± 10.0°, respectively. Mean CA defined as the sum of stem anteversion and CTRA was 37.5 ± 14.5°. To investigate relationships of CA with other factors, a stepwise regression analysis was performed and resulted in a model with age ( p < 0.001). In the same way, stem anteversion and CTRA were analyzed; only for the stem anteversion, the stepwise selection process resulted in a model with age ( p < 0.001) and the Dorr types ( p = 0.047).

CONCLUSION

The risk of excessive femoral anteversion increases for relatively younger age and for types of femoral morphology according to the Dorr classification, moreover with an increase of CA in DAA-THA with cementless tapered-wedge stem.

Three-dimensional geometrical modelling of the femoral intramedullary cavity using ring cyclide model

Objectives

This study aims to investigate if geometrical modelling in addition to three-dimensional (3D) modelling will standardize models and allow performing mathematical calculations easily for the compatibility of femoral implant curvature.

Patients and methods

The study included 50 subjects (27 males, 23 females; mean age 55 years; range, 21 to 84 years). The femoral shaft intramedullary cavity was resembled into a chord of the ring cyclide, where the rotational radius was centered at its smallest radius. A 3D evaluation of the left femoral computed tomography data of the subjects was used to investigate the population parameters. The fitting was defined as being between the anterior and posterior border radii in the sagittal plane.

Results

The best fitting radius of implants was in between 90 to 99 cm in 72% of subjects in our sample. These radii values were lower than the mean intramedullary and cortical centerline radii which had only 62% and 50% fittings, respectively, among our population sample. The bowing radii and the smallest intramedullary width increased with the femoral length. These values were not affected by gender.

Conclusion

This modelling may have value for understanding femoral shaft intramedullary cavity geometry and may be a good tool to assess implant fitting.

Secular evolution of femoral morphology from a clinical perspective

INTRODUCTION

Intramedullary nailing is the surgical method of choice for the treatment of proximal femur or femoral shaft fractures. Implant manufacturers aim to design implants fitting for the broadest possible population segment. As complete morphological data sets of long bones are not widely available, anatomical collections of historical dry bone specimens may represent abundant additional sources of morphological three-dimensional (3D) data for implant design, provided they are consistent with present populations. This study aims to investigate secular trends and age-related changes of femoral morphology of the Caucasian population over the past 800 years.

MATERIALS AND METHODS

Computer graphical measurements of 3D-datasets of right and left femora derived from computed tomography (CT) scans, representative of the present Caucasian population, were compared to computer graphical measurements of 3D-datasets of right and left femora derived from CT scans of specimens from a historical medieval European bone collection.

RESULTS

Clinically relevant parameters of historical medieval European femora were found mostly consistent with correlative data of the present Caucasian population. Additionally, for some of the evaluated parameters, particularly anteversion, morphological differences significantly correlated to individual age and sex could be identified, whereas other parameters such as caput-collum-diaphyseal angle or radius of anterior femoral bowing were not correlated to individual age or sex.

CONCLUSION

The findings suggest that more recent historical specimen collections may be a convenient and easily accessible source of new 3D morphological data, as well as to complement existing data, to be used by researchers and manufacturers for the development of intramedullary femoral nails.

An innovative method for measuring the femoral arch

A mismatch between the femoral bow and intramedullary nails causes a series of complications. Previous investigations have sought to determine the curvature of the femur using the radius of the femoral bow. However, the radius of the curvature is affected by femur length. To eliminate the influence of femur length, we instead used an angle to indicate femoral curvatures.Forty patients with intertrochanteric fractures who underwent a surgical procedure at our institution were enrolled in this study. We conducted a lateral X-ray of the contralateral femur before operation. We drew a triangle in the X-ray images using Digimizer software. The tangent values of the acute angle were used to indicate femoral curvature. The tangent values were then compared with the dimensions of currently used nails.The average tangent value of the femurs was 0.0835 ± 0.0147, as measured from the inner cortex and 0.0798 ± 0.0150, as measured from the outer cortex. The tangent values were related to sex, with males having straighter femurs than females, and there was no obvious correlation between tangent values and age or femur length. Tangent value is a reliable method with a high intersurveyor consistency; femur curvatures were significantly greater than the curvatures of currently used nails.

Femoral antecurvation-A 3D CT Analysis of 1232 adult femurs

INTRODUCTION

For optimal treatment of femoral fractures, it is essential to understand the anatomical antecurvation of the human femur. Recent clinical studies have highlighted the problem of distal anterior encroachment or even perforation of the nail tip. The aim of this study was to accurately describe the femoral antecurvation in a large cohort. Another objective was to identify the most important influences on femoral antecurvation, such as age, femur length, gender and ethnicity.

METHODS

A three dimensional modelling and analytical technology was applied for the analysis of 1,232 femurs. Individual femoral antecurvation was precisely computed to determine whether gender, femur length, age, ethnicity or body mass index influence the radius of curvature (ROC).

RESULTS

The calculated mean ROC for all femurs was 943 mm. The lowest ROC of 826 mm was found in female Asian femurs. A regression analysis demonstrated that age and femur length could predict the variability of the curvature, with femoral length as most powerful predictor. A matched pair subgroup analysis between Asians and Caucasians could not show any significant differences of ROC values.

CONCLUSIONS

The mean radius of the femoral antecurvation may be smaller than previously reported revealing a significant mismatch between the actual individual anatomy and existing implants. In opposite to existing literature, this study suggests, that antecurvation differences between various ethnicities may exclusively be attributed to differences in femoral length and age. The findings of this study may be found helpful in the development of novel designs for intra- and extramedullary implants.

Deviation of femoral intramedullary alignment rod influences coronal and sagittal alignment during total knee arthroplasty

BACKGROUND

An intramedullary (IM) rod is used to resect the distal femur vertically to the femoral mechanical axis in the coronal plane in many cases of total knee arthroplasties (TKA). The valgus angle between the mechanical axis and the anatomical axis of the distal femur is estimated preoperatively. It is known the deviation of the IM rod in the femoral canal could influence the femoral component alignment. However, there is no published data regarding how many degrees of deviation to make with the IM rod. The purpose of this study is to measure each deviation of the IM rod using three-dimensional (3D) computer simulations.

METHODS

Preoperative CT scans on 30 knees undergoing TKA were studied. The line connecting central points at 10 and 20 cm proximal from the intercondylar notch was defined as the anatomical axis and the point at which the anatomical axis intersects the surface of the distal femur was considered as the entry point of the IM rod. The medio-lateral (ML) and antero-posterior (AP) deviations between the anatomical axis and the IM rod were measured.

RESULTS

The ML and AP deviations were 0.8 and 1.1° on average. The IM rod was deviated medio-laterally more than 1.0° in three knees (10%).

CONCLUSION

Surgeons should note the ML difference of the resection thickness of the distal femur for coronal alignment. If the ML difference varies greatly from the preoperative planning, they need to adjust at most 1.0° of valgus angle to achieve the appropriate coronal alignment. Level of evidence III, Therapeutic.

A cadaveric biomechanical study comparing the ease of femoral nail insertion: 1.0- vs 1.5-m bow designs

INTRODUCTION

Anatomic fit of intramedullary nails was suggested by previous studies to improve significantly when the nail radius of curvature (ROC) is closer to the average femoral anatomy. However, no attempt has been made to investigate the impact of different ROC designs on the nail insertion process. Therefore, this biomechanical study quantitatively compared the ease of insertion between femoral intramedullary nails with a 1.0-m and a 1.5-m bow radius.

MATERIALS AND METHODS

Long TFN-ADVANCED™ (TFNA, 1.0 m ROC) and Proximal Femoral Nail Antirotation nails (PFNA, 1.5 m ROC) were implanted pairwise into seven paired cadaver femora. All bones were reamed 1.5 mm larger than the nail diameter. Using a material testing machine, intramedullary nailing was then performed stepwise with 20-mm steps and a 10-mm/s insertion rate, and force was measured. The nail deformation caused by the insertion was assessed through 3D computer models built from pre- and post-nailing CT scans. The ease of insertion between TFNA and PFNA nails was quantified in terms of insertion force, insertion energy and nail deformation.

RESULTS

There was no significant difference in the peak force generated during nailing between TFNA and PFNA nails (P = 0.731). However, the force measured at the end of insertion (P = 0.002) was significantly smaller in TFNA nails compared to PFNA nails. After implantation, TFNA nails showed significantly smaller deformation when compared to PFNA nails (P = 0.005, both ends aligned). Furthermore, less energy was required to insert TFNA nails; however, the difference was not significant (P = 0.25).

CONCLUSIONS

Compared to PFNA nails, a significant decrease in insertion force and nail deformation was found at the end of insertion for TFNA nails. Results suggest that TFNA having a 1.0-m ROC is easier to insert for the set of femora used in this study compared to PFNA with a 1.5-m ROC.