Inverse kinematic alignment accommodates native coronal knee alignment better in comparison to adjusted mechanical alignment and restricted kinematic alignment.

PURPOSE: The purpose was to determine the proportion of native non-arthritic knees that fit within the target zones of adjusted mechanical alignment (aMA), restricted kinematic alignment (rKA), and inverse kinematic alignment (iKA), and to estimate adjustments in native coronal alignment to bring outlier knees within the respective target zones. The hypothesis was that the target zone of iKA, compared to the target zones of aMA and rKA, accommodates a higher proportion of native non-arthritic knees. METHODS: The study used measurements obtained from a computed tomography (CT) scan database (SOMA, Stryker) of 972 healthy knees (Caucasian, 586; Asian, 386). Hip knee ankle (HKA) angle, medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were used to estimate the proportions of knees within the patient-specific alignment target zones; and to estimate theoretical adjustments of MPTA, LDFA and soft tissue balance (HKA) to bring outlier knees within target zones. Theoretical adjustments to bring outlier knees within the alignment target zones of aMA, rKA and iKA were calculated by subtracting the native coronal alignment angles (MPTAnative, LDFAnative and HKAnative) from angles on the nearest target zone border (MPTAtarget, LDFAtarget and HKAtarget). RESULTS: Patients were aged 59.8 ± 15.8 years with a BMI of 25.0 ± 4.4 kg/m2. The HKA angles were between 168° and 186°, MPTA between 78° and 98° and LDFA between 79° and 93°. Of the 972 knees, 81 (8%) were in the aMA target zone, 530 (55%) were in the rKA target zone, and 721 (74%) were in the iKA target zone. Adjustments of MPTA, LDFA and HKA angle to bring outlier knees within the target zones, were, respectively, 90, 91 and 28% for aMA, 45, 28 and 25% for rKA, and 25, 23 and 7% for iKA. CONCLUSIONS: There is considerable variability in native knee coronal alignment that corresponds to different proportions of the restricted patient-specific alignment target zones for TKA. Although extension of the MPTA and LDFA target zones with rKA accommodate native knee alignment better than aMA, up to 25% would require adjustment of native HKA angle. By also extending the HKA angle target zone into varus, iKA accommodates a greater proportion (93%) of native limb alignment. LEVEL OF EVIDENCE: IV.

The trochlear sulcus of the native knee is consistently orientated close to the sagittal plane despite variation in distal condylar anatomy.

PURPOSE: The aim of this study was to describe the native trochlear orientation of non-arthritic knees in three planes and to quantify the relationship between trochlear and distal condylar anatomy across race and sex. METHODS: Computed tomography scans of 1578 femora were included in this study. The mediolateral position of the trochlear sulcus, the distal trochlear sulcus angle (DTSA) the medial sulcus angle (MSA) and the lateral sulcus angle (LSA) as well as the mechanical lateral distal femoral angle (mLDFA) were measured relative to a standard reference coordinate system. Multiple linear regression analyses were performed to account for potential confounding variables. RESULTS: The mediolateral position of the trochlear sulcus had minimal mean deviation of the sagittal femoral plane. The mean DTSA was 86.1° (SD 2.2°). Multilinear regression analysis found mLDFA, sex, and age all influence DTSA (p < 0.05), with mLDFA having by far the greatest influence (r2 = 0.55). The medial facet of the trochlear sulcus was found to be flat proximally and more prominent distally. The lateral facet was relatively uniform throughout the arc. CONCLUSION: In non-arthritic knees, due to a strong positive correlation between the DTSA and the mLDFA, the trochlear sulcus is consistently orientated in the sagittal femoral plane regardless of distal condylar anatomy. Minor deviations from the sagittal plane occur in a lateral direction in the middle part and in a medial direction at the proximal and distal part of the trochlea. These findings have relevance regarding the biomimetic design of total knee implants.

Obtaining anatomic motion and laxity characteristics in a total knee design.

BACKGROUND: Since the introduction of the first total knee designs, a frequent design goal has been to reproduce normal knee motion. However, studies of many currently used total knee designs, have shown that this goal has not been achieved. We proposed that Guided Motion total knee designs, could achieve more anatomic motion than present standard designs. METHODS: Several Guided Motion knees for application without cruciate ligaments were designed using a computer method where the bearing surfaces were generated by the motion required. A knee testing machine was constructed where physiological forces including compressive, shear and torque were applied during knee flexion. The neutral path of motion and the laxity about the neutral path were measured. This evaluation method was a modification of the ASTM standard Constraint Test. RESULTS: The motions of the Guided Motion knees and a standard PS knee were compared with the anatomic motion of knee specimens determined in an earlier study The Guided Motion knees showed motion patterns which were closer to anatomic than the PS knee. CONCLUSIONS: The results provided justification for carrying out further evaluations of functional conditions, using either knee simulators or computer modelling. If anatomic motions could be reproduced in vivo, it is possible that clinical outcomes could be improved.

Coronal and sagittal alignment of the lower limb in Caucasians: Analysis of a 3D CT database.

INTRODUCTION: Lower limb alignment is a major determinant of long-term outcomes after osteotomy or total knee replacement. The aim of this paper is to define the mean values of coronal and sagittal lower limb alignment for Caucasians as a function of sex using 3D reconstructions from CT-scans. MATERIALS AND METHODS: The analysis involved 586 Caucasian patients (269 males and 317 females) who had their hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior proximal tibial angle (PPTA), lateral and medial proximal posterior tibial angles (LPPTA/MPPTA), posterior distal femoral angle (PDFA), and non-weightbearing joint convergence angle (nwJLCA) measured. This analysis was performed using a CT-scan-based modelling system (SOMA). Differences between sexes and morphotypes (neutral, varus and valgus) were analyzed statistically. RESULTS: The mean HKA was 180±2.57°, LDFA 86.1±1.87°, MPTA 86.1±2.15°, PPTA 84.6±2.58°, LPPTA 84.9±3.17°, MPPTA 85.1±3.21°, PDFA 85.3±1.50° and nwJLCA 0.82±1.32°. There was a significant difference between sexes for the HKA (180.3±2.46° and 179.0±2.52°), LDFA (85.6±1.90° and 86.8±1.61°), MPPTA (84.7±3.06° and 85. 6±3.31°). The neutral morphotype was more frequent in women than men (78% vs. 73%), the varus morphotype was more frequent in men than women (20% vs. 7.6%) and the valgus morphotype was more frequent in women than men (15% vs. 6.7%). CONCLUSION: Normal parameters for lower limb alignment in Caucasian patients were described in the coronal and sagittal planes. There was a significant influence of sex in the coronal plane, which was not found in the sagittal plane. LEVEL OF EVIDENCE: IV; retrospective cohort study.

Ethnical Differences in Knee Phenotypes Indicate the Need for a More Individualized Approach in Knee Arthroplasty: A Comparison of 80 Asian Knees with 308 Caucasian Knees.

The purpose of this study was to determine the distribution of functional knee phenotypes in a non-osteoarthritic Asian population. The Stryker Orthopaedic Modeling and Analytics (SOMA) database was searched for CT scans of the lower limb meeting the following inclusion criteria: patient age at time of image >18 and <46 years, no signs of fractures and/or previous surgery and/or degenerative changes, Asian ethnicity. A total of 80 CT scans of 40 patients were included (24 males, 16 females). The hip-knee-ankle angle (HKA), femoral mechanical angle (FMA) and tibial mechanical angle (TMA) were measured. Based on these measurements, each limb was phenotyped according to the previously introduced functional knee phenotype concept. All angles and phenotypes of the present study were compared with previously published data of a non-osteoarthritic Caucasian population (308 legs of 160 patients, 102 males, 58 females). Asian knees had a significantly lower TMA (both genders p < 0.001) but a higher FMA (males p < 0.05, females p < 0.001) than Caucasian knees but showed no difference in the HKA. Asian knees differed significantly with regard to femoral and tibial phenotypes (p < 0.01), but not with regard to limb phenotypes. The high variability of all coronal alignment parameters highlights the importance of a detailed analysis prior to TKA. Ethnical differences underline the need for a more individualized approach in TKA.

Patients with varus knee osteoarthritis undergoing high tibial osteotomy exhibit more femoral varus but similar tibial morphology compared to non-arthritic varus knees.

PURPOSE: The aim of this study was to compare alignment parameters between patients undergoing high tibial osteotomy (HTO) for knee osteoarthritis (OA) and non-arthritic controls. METHODS: Pre-operative computed tomography images from 194 patients undergoing HTO for medial knee OA and 118 non-arthritic controls were utilized. All patients had varus knee alignment (mean age: 57 ± 11 years; 45% female). The hip-knee-ankle (HKA) angle, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA) and non-weight-bearing joint line convergence angle (nwJLCA) were compared between "control group" and "HTO group". Femoral and tibial phenotypes were also assessed and compared between groups. Variables found on univariate analysis to be different between the groups were entered into a binary logistic regression model. RESULTS: The mean age was lower (Δ = 4 ± 6 years, p = 0.024), body mass index (BMI) was higher (Δ = 1.1 ± 2.8 kg/m2, p = 0.032) and there were more females (Δ = 14%, p = 0.020) in the HTO group. The HTO group had more overall varus (7° ± 4.7° vs 4.8° ± 1.3°, p < 0.001). There was a significant difference in the mean mLDFA between the two groups with the HTO group having more femoral varus (88.7 ± 3.2° vs 87.3 ± 1.8°, p < 0.001). MPTA was similar between the groups (p = 0.881). Age was found to be a strong determinant for femoral varus (p = 0.03). CONCLUSION: Patients undergoing HTO for medial knee OA have more femoral varus compared to non-arthritic controls while tibial morphology was similar. This will be an important consideration in pre-operating planning for realignment osteotomy in patients presenting with medial knee OA and warrants further investigation. LEVEL OF EVIDENCE: III, retrospective comparative study.

Femoral and Tibial Bony Risk Factors for Anterior Cruciate Ligament Injuries Are Present in More Than 50% of Healthy Individuals.

BACKGROUND: Anterior cruciate ligament (ACL) injuries are multifactorial events that may be influenced by morphometric parameters. Associations between primary ACL injuries or graft ruptures and both femoral and tibial bony risk factors have been well described in the literature. PURPOSE: To determine values of femoral and tibial bony morphology that have been associated with ACL injuries in a reference population. Further, to define interindividual variations according to participant demographics and to identify the proportion of participants presenting at least 1 morphological ACL injury risk factor. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: Computed tomography scans of 382 healthy participants were examined. The following bony ACL risk factors were analyzed: notch width index (NWI), lateral femoral condylar index (LFCI), medial posterior plateau tibial angle (MPPTA), and lateral posterior plateau tibial angle (LPPTA). The proportion of this healthy population presenting with at least 1 pathological ACL injury risk factor was determined. A multivariable logistic regression model was constructed to determine the influence of demographic characteristics. RESULTS: According to published thresholds for ACL bony risk factors, 12% of the examined knees exhibited an intercondylar notch width <18.9 mm, 25% had NWI <0.292, 62% exhibited LFCI <0.67, 54% had MPPTA <83.6°, and 15% had LPPTA <81.6°. Only 14.4% of participants exhibited no ACL bony risk factors, whereas 84.5% had between 2 and 4 bony risk factors and 1.1% had all bony risk factors. The multivariate analysis demonstrated that only the intercondylar notch width (P < .0001) was an independent predictor according to both sex and ethnicity; the LFCI (P = .012) and MMPTA (P = .02) were independent predictors according to ethnicity. CONCLUSION: The precise definition of bony anatomic risk factors for ACL injury remains unclear. Based on published thresholds, 15% to 62% of this reference population would have been considered as being at risk. Large cohort analyses are required to confirm the validity of previously described morphological risk factors and to define which participants may be at risk of primary ACL injury and reinjury after surgical reconstruction.

Bony asymmetry in patellofemoral morphology and risk factors of instability are mostly clinically negligible.

PURPOSE: Previous investigations suggested that femoral side-to-side differences were located in the upper femur anatomy. However, little is known about the asymmetry between distal femur and patella. The degree of bony asymmetry in the patellofemoral joint was evaluated using pairs of CT-scans with emphasis on morphometric measurements and risk factors relevant to patellofemoral disorders. METHODS: Patellofemoral morphometric parameters and anatomical risk factors were analyzed from 345 pairs of CT scans to evaluate side-to-side differences for each patient. All measurements were automatized using previously published algorithm-calculated bone landmarks. We analyzed asymmetry based on absolute differences (AD) and percentage asymmetry (AS%). Significant asymmetry was defined as AS% > 10%. RESULTS: Patellar height was found to be highly symmetric (mean AD 0.1 for both Insall-Salvatti and Caton-Deschamps methods, AS% 8% and 9%, respectively). Patellar and femoral morphometric parameters were found highly symmetric, except for the trochlear groove depth. Substantial asymmetry was reported in two patellofemoral risk factors: the lateral trochlear inclination (mean AD 2°, AS% 16%) and the tibial tuberosity-trochlear groove distance (1 mm, 116%). Patellar and femoral morphometric asymmetries were independent of demographics, including age, gender, height, weight and ethnicity. CONCLUSION: Patellar height was found to be highly symmetric and is, therefore, a reasonable index for contralateral templating. While very few patellofemoral morphometric parameters and anatomical risk factors were asymmetric, the mean differences were clinically negligible and independent of demographics. LEVEL OF EVIDENCE: III.

Neutral alignment resulting from tibial vara and opposite femoral valgus is the main morphologic pattern in healthy middle-aged patients: an exploration of a 3D-CT database.

PURPOSE: Given the goal of achieving optimal correction and alignment after knee arthroplasty or high tibial osteotomy, literature focusing on the inter-individual variability of the native knee, tibia and femur with regards to the coronal or sagittal alignment is lacking. The aim of this study was to analyse normal angular values in the healthy middle-aged population and determine differences of angular values according to inter-individual features. The first hypothesis was that common morphological patterns may be identified in the healthy middle-aged non-osteoarthritic population. The second hypothesis was that high inter-individual variability exists with regards to gender, ethnicity and alignment phenotype. METHODS: A CT scan-based modelling and analysis system was used to examine the lower limb of 758 normal healthy patients (390 men, 368 women; mean age 58.5 ± 16.4 years) with available data concerning angular values and retrieved from the SOMA database. The hip-knee-ankle angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior distal femoral angle (PDFA), posterior proximal tibial angle (PPTA) and non weight-bearing joint line convergence angle (nwJLCA) were then measured for each patient. Results were analysed for the entire cohort and based on gender, ethnicity and phenotype. RESULTS: The mean HKA was 179.4° ± 2.6°, LDFA: 85.8° ± 2.0°, MPTA: 85.6° ± 2.4°, PDFA: 85.2° ± 1.5°, PPTA: 83.8° ± 2.9° and nwJLCA: 1.09° ± 0.9°. Gender was associated with higher LDFA and lower HKA for men. Ethnicity was associated with greater proximal tibial vara and distal femoral valgus for Asian patients. Patients with an overall global varus alignment had more tibia vara and less femoral valgus than patients with an overall valgus alignment. CONCLUSION: Even if significant differences were found based on subgroup analysis (gender, ethnicity or phenotype), this study demonstrated that neutral alignment is the main morphological pattern in the healthy middle-aged population. This neutrality is the result from tibia vara compensated by an ipsilateral femoral valgus. LEVEL OF CLINICAL EVIDENCE: III, retrospective cohort study.

Measurement of the Posterior Tibial Slope Depends on Ethnicity, Sex, and Lower Limb Alignment: A Computed Tomography Analysis of 378 Healthy Participants.

BACKGROUND: There is no general consensus on the normal and pathological values for the posterior tibial slope (PTS). PURPOSE/HYPOTHESIS: The primary aim of this study was to determine standard values for the PTS in healthy participants using 3-dimensional (3D) computed tomography (CT). A secondary aim was to determine the effect of demographic factors and coronal-plane lower limb alignment on the PTS measurement. The hypothesis was that the PTS would be significantly influenced by demographic factors and coronal-plane lower limb alignment. STUDY DESIGN: Cross-sectional study; Level of evidence, 3. METHODS: A CT-based modeling and analytics system was used to examine and measure lower limb alignment and the PTS in 378 patients (193 male and 185 female; mean age, 58.3 ± 16.4 years [range, 18-92 years]; mean body mass index, 25.0 ± 4.4 kg/m2). The lateral, medial, and global PTS were measured for each patient. All measurements were constructed using algorithm-calculated landmarks, resulting in reproducible and consistent constructs for each specimen. The results were then evaluated based on ethnicity, sex, and hip-knee-ankle (HKA) angle. RESULTS: The study population comprised 219 white and 159 Asian participants. The mean global, medial, and lateral PTS were 6.3° (range, -5.5° to 14.7°; 1% with ≥12°), 6.2° (range, -4.1° to 17.2°; 3% with ≥12°), and 5.3° (range, -4.7° to 16.2°; 2% with ≥12°), respectively. The lateral (Δ = -1.0° [95% CI, 0.6°-1.6°]; P < .0001) and global (Δ = -0.5° [95% CI, 0.0°-0.8°]; P = .0332) PTS were smaller in the female subpopulation. The global PTS was greater (Δ = 1.9° [95% CI, 1.5°-2.3°]; P < .0001) in the Asian subpopulation. The mean HKA angle was 179.6° (range, 170°-190°). The HKA angle was significantly correlated with the medial and global PTS. Specimens with a genu varum knee exhibited a significantly greater global (Δ = 1.2° [95% CI, 0.8°-1.7°]; P < .0001) and medial (Δ = 1.9° [95% CI, 1.3°-2.5°]; P < .0001) PTS. CONCLUSION: The present study gives a benchmark for the physiological values of the PTS in a healthy population and highlights several factors influencing the PTS, such as ethnicity, sex, and alignment. Anatomic variants with a PTS ≥12° were very uncommon (≤3%) in our Asian and white groups and thus could be considered as pathological. The PTS is a crucial anatomic factor for anterior cruciate ligament injuries and reconstruction. A general consensus is lacking regarding the cutoff for abnormal values, thus guiding standard of care. This study investigated the dispersion of global, medial, and lateral posterior plateau tibial angles in a large population representing a range of demographic diversity.

Contralateral preoperative templating of lower limbs' mechanical angles is a reasonable option.

PURPOSE: In cases where the femur or tibia exhibits abnormal mechanical angulation due to degenerative changes or fracture, the contralateral leg is often used to complete preoperative templating. The aim of this study was to determine the degree of asymmetry between knee joints in healthy individuals and to determine whether it is affected by differing demographic parameters. METHODS: A CT scan-based modelling and analysis system was used to examine the lower limb of 233 patients (102 males, 131 women; mean age 61.2 ± 15.2 years, mean body mass index 24.9 ± 4.4 kg/m2) The hip-knee angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), posterior proximal tibial angle (ppta) and posterior distal femoral angle (PDFA) were then calculated for each patient. Results were then analysed to calculate femoral symmetry based on absolute differences (AD) and percentage asymmetry (%AS) using a previously validated method. RESULTS: Our results do not demonstrate any considerable asymmetry (percentage of asymmetry > 2%) for all the anatomical parameters analysed: HKA (mean AD = 1.5°; mean AS % = 0.8, n.s), MPTA (AD = 1.1°; AS % = 1.3, n.s), PPTA (AD = 1.4°; AS % = 1.0, n.s), LDFA (AD = 1.2 mm; AS % = 1.4, n.s) and PDFA (AD = 0.9°; AS % = 1.0, n.s). Gender and ethnicity were not associated with significantly higher AD asymmetry. A significant correlation of AD asymmetry was observed between BMI and HKA, BMI and MPTA, and between patients' age and the MPTA. CONCLUSION: This data demonstrate that there is a non-statistically significant mechanical angle asymmetry between the two lower limbs. In cases where contralateral templating is used, such asymmetry will induce minimal (if any) clinical differences. LEVEL OF EVIDENCE: IV.

Virtual reconstruction of the posterior cruciate ligament for mechanical testing of total knee arthroplasty implants.

BACKGROUND: Total knee arthroplasty (TKA) design continues to be refined. As part of the pre-clinical design process, kinematic evaluation under ideal circumstances must be simulated. Previously, this was accomplished mechanically through the use of elastomeric bumpers and human cadaver models, which can be costly and time-intensive. With improved technology, a six-axis joint simulator now allows for virtual ligament reconstruction. The aim of this study was to create and evaluate a virtual posterior cruciate ligament (PCL) model to simulate native knee kinematics for component testing in TKA. METHODS: Three human cadaveric knee specimens were utilized, each mounted in a six-axis joint simulator and the femoral and tibial ligament insertion points digitized. Ligament stiffness and kinematics were first tested with the intact knee, followed by retesting after PCL transection. Knee kinematic testing was then repeated, and the virtual PCL was reconstructed until it approximated that of the intact knee by achieving less than 10% random mean square (RMS) error. RESULTS: A virtual three-bundle PCL was created. The RMS error in anterior-posterior motion between the virtually reconstructed PCL and the intact knee ranged from six to eight percent for simulated stair climbing in the three knee specimens tested, all within our target goal of less than 10%. CONCLUSION: This study indicated that a virtually reconstructed three-bundle PCL with a joint simulator can replicate knee kinematics. Such an approach is valuable to obtain clinically relevant kinematics when testing cruciate-retaining total knee arthroplasty under force control.

Accuracy of Reference Axes for Femoral Component Rotation in Total Knee Arthroplasty: Computed Tomography-Based Study of 2,128 Femora.

BACKGROUND: Many reference axes are used to evaluate rotation of the femoral component during total knee arthroplasty, including the Whiteside line, surgical transepicondylar axis (sTEA), anatomical transepicondylar axis (aTEA), posterior condylar axis externally rotated 3° (PCA+3°ER), sulcus line, and femoral transverse axis (FTA). There is no consensus about which of these axes is most accurate. METHODS: The Stryker Orthopaedic Modeling and Analytics (SOMA) database was used to identify 2,128 entire-femur computed tomography (CT) scans. The Whiteside line, aTEA, PCA+3°ER, sulcus line, and FTA were constructed according to published guidelines. Every axis was compared with the sTEA, which is widely regarded as the gold standard reference axis for rotation of the distal part of the femur but has low intraobserver and interobserver reliability intraoperatively. RESULTS: The PCA+3°ER differed from the sTEA by a mean (and standard deviation) of 0.60° ± 1.64°; it was the most accurate but also had the highest degree of intersubject variability. The mean PCA-sTEA angle was 2.40°, close to the accepted "rule of thumb" of 3°. This value was significantly higher in women (2.64° ± 1.74°) than in men (2.18° ± 1.52°; p < 0.001). The Whiteside line differed from the sTEA by a mean of 1.90° ± 1.38°, and the sulcus line differed from the sTEA by a mean of 1.94° ± 1.49°; neither of these values varied significantly with sex or ethnicity. The FTA differed from the sTEA by a mean of 2.04° ± 1.50°. Least accurate was the aTEA, which differed from the sTEA by a mean of 2.05° ± 1.33°. The combination of 3 axes that are readily available intraoperatively (the Whiteside line, aTEA, and PCA+3°ER) differed from the sTEA by a mean of 1.80° ± 0.70°. CONCLUSIONS: In the largest study of its kind, analysis of CT scans of 2,128 femora revealed that no 1 axis could serve as a marker of femoral component rotation with both high accuracy and low variability. Utilizing a combination of 3 methods (PCA+3°ER, the Whiteside or sulcus line, and aTEA) to maximize accuracy and sex and ethnic generalizability when positioning the femoral component is recommended. CLINICAL RELEVANCE: A large-scale study using a CT-based biomorphometric database demonstrated that use of a combination of 3 axes (PCA+3°ER, the Whiteside or sulcus line, and aTEA) was the optimal strategy for judging femoral component rotation.

Upper Femur Anatomy Depends on Age and Gender: A Three-Dimensional Computed Tomography Comparative Bone Morphometric Analysis of 628 Healthy Patients' Hips.

BACKGROUND: The knowledge of proximal femur geometry is essential in the understanding and treatment of hip pathologies. Our aim is to evaluate the range of "normal anatomical values of the proximal femur" and their relationship to age, gender, and ethnicity in a cohort of healthy population, using a 3-dimensional computed tomography automated software. METHODS: The pelvis and bilateral femora of 628 healthy individuals (394 males/234 females, mean age 61.5 ± 16.5 years, mean body mass index [BMI] 26.9 ± 5.2 kg/m2) including 2 ethnicities (226 Asians and 406 Caucasians) were assessed with a 3-dimensional computed tomography scan-based system using algorithm-calculated landmarks. The demographic parameters recorded were age, gender, BMI, and ethnicity. The femoral neck-shaft angle (NSA), femoral neck version, femoral offset (FO), and femoral canal flare index (fCFI) were calculated for each individual. Analyses were performed using SPSS version 22. P-values <.05 were considered to indicate statistical significance. RESULTS: Overall, the mean NSA was 124.7° (standard deviation [SD] 6.2), mean femoral neck version was 14.5° (SD 8.1), mean FO was 42.9 mm (SD 6.8), and mean fCFI was 3.4 (SD 0.5). Gender was associated with all parameters, with the females presenting more valgus and anteverted hips. Multivariate analysis revealed a lower NSA and fCFI and a higher FO for older individuals. Ethnicity and BMI were not associated with any parameters. CONCLUSION: Our results showed that there is a direct relationship of age and gender to the variations in the investigated proximal femur anatomical parameters in a large cohort of healthy individuals. Those important gender-based and age-based differences might advocate for more varus and lateralized component to reproduce preoperative anatomy of male and patients older than 50 years.

Stryker Orthopaedic Modeling and Analytics (SOMA): A Review.

Due to the differences in bone morphology between demographics such as age, gender, body mass index, and ethnicity, the development of orthopaedic implants requires a large number of anatomical data from various patient populations. In an effort to assess these demographic variations, Stryker Orthopaedic Modeling and Analytics (SOMA) has been developed. SOMA is a suite of tools which utilizes a comprehensive database of computed tomography scans (CT-scans), plus associated three-dimensional (3D) bone models, allowing the user to assess population differences in bone morphology, bone density, and implant fit for the purposes of research and development. Several additional software tools are currently in development to further analyze bone density and have the potential to enhance component fit. These tools, in combination with the database, have been previously utilized for development of many implant designs and techniques in hip and knee arthroplasty, as well as in trauma surgery.