Can Robotic-Arm Assistance Decrease Iatrogenic Soft-Tissue Damage During Direct Anterior Total Hip Arthroplasty?

INTRODUCTION: Manual techniques for total hip arthroplasty (THA) have been widely utilized and proven to be clinically successful. However, the use of advanced computed tomography (CT) scan-based planning and haptically-bounded reamers in robotic-arm assisted total hip arthroplasty (RTHA) holds promise for potentially limiting surrounding soft-tissue damage. This cadaver-based study aimed to compare the extent of soft-tissue damage between a robotic-arm assisted, haptically-guided THA (RTHA) and a manual, fluoroscopic-guided THA (MTHA) direct anterior approach. MATERIALS AND METHODS: There were six fresh-frozen torso-to-toe cadaver specimens included, with two surgeons each performing three RTHA and three MTHA procedures. One hip underwent an RTHA and the other hip received an MTHA in each cadaver. Postoperatively, one additional surgeon, blinded to the procedures, assessed and graded damage to nine key anatomical structures using a 1 to 4 grading scale: (1) complete soft-tissue preservation to <5% of damage; (2) 6 to 25% of damage; (3) 26 to 75% of damage; and (4) 76 to 100% of damage. Kruskal-Wallis hypothesis tests were used to compare soft-tissue damage between RTHA and MTHA cases and adjusted for ties. RESULTS: Pooled analysis of the gluteus minimus, sartorius, tensor fascia lata, and vastus lateralis muscle grades demonstrated that cadaver specimens who underwent RTHA underwent less damage to these structures than following MTHA (median, IQR: 1.0, 1.0 to 2.0 vs. 3.0, 2.0 to 3.0; p=0.003). Pooled analysis of the calculated volumetric damage (mm3) for the gluteus minimus, sartorius, tensor fascia lata, and vastus lateralis muscles demonstrated that the cadaver specimens that underwent RTHA underwent less damage to these structures than those that followed MTHA (median, IQR: 23, 2 to 586 vs. 216, 58 to 3,050; p=0.037). CONCLUSION: This cadaver-based study suggests that utilizing RTHA may lead to reduced soft-tissue damage compared with MTHA, likely due to enhanced preoperative planning with robotic-arm assisted software, real-time intraoperative feedback, haptically-bounded reamer usage, reduced surgical steps, as well as ease of use with reaming. These findings should be carefully considered when evaluating the utilization of robotic-arm assisted THA in practice.

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.

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.

COVID-19 in Patients With Rheumatic Diseases: Is There a Need to Worry?

BACKGROUND/OBJECTIVES: SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2), first described in December 2019, has infected more than 33 million people and claimed more than 1 million deaths worldwide. Rheumatic diseases are chronic inflammatory diseases, the prevalence and impact of which in COVID-19 patients are poorly known. We performed a pooled analysis of published data intending to summarize clinical presentation and patient outcomes in those with established rheumatic disease diagnosis and concurrent COVID-19. METHODS: PubMed and Google Scholar were searched to identify studies reporting data about rheumatic disease patients who were diagnosed with SARS-CoV-2 infection and published until July 22, 2020. Random-effects models were used to estimate the pooled incidence and rates of hospitalization, intensive care unit admission, and mortality among these patients, and interstudy heterogeneity was identified using I2 statistics with greater than 75% value indicating substantial interstudy variation. RESULTS: Twenty studies were included, giving a total sample size of 49,099 patients positive for SARS-CoV-2. Of 49,099 COVID-19 patients, a total of 1382 were also diagnosed with a rheumatic disease in the past. The random-effects pooled prevalence of COVID-19 among rheumatic disease patients was found to be 0.9%. The rates of hospitalization, intensive care unit admission, and mortality were 70.7%, 11.6%, and 10.2%, respectively. CONCLUSIONS: Although the prevalence of SARS-CoV-2 infection is not dramatically high in rheumatic disease patients, concurrent COVID-19 does seem to play a role in determining disease severity and outcomes to some extent. Further studies are needed to give conclusive evidence about whether this subset of the population is at a higher risk of COVID-19 and related outcomes compared with the population at large.

Obesity a predictor of outcomes of COVID-19 hospitalized patients-A systematic review and meta-analysis.

Coronavirus disease 2019 (COVID-19) pandemic is a global health crisis. Very few studies have reported association between obesity and severity of COVID-19. In this meta-analysis, we assessed the association of obesity and outcomes in COVID-19 hospitalized patients. Data from observational studies describing the obesity or body mass index and outcomes of COVID-19 hospitalized patients from December 1, 2019, to August 15, 2020, was extracted following PRISMA guidelines with a consensus of two independent reviewers. Adverse outcomes defined as intensive care units, oxygen saturation less than 90%, invasive mechanical ventilation, severe disease, and in-hospital mortality. The odds ratio (OR) and 95% confidence interval (95% CI) were obtained and forest plots were created using random-effects models. A total of 10 studies with 10,233 confirmed COVID-19 patients were included. The overall prevalence of obesity in our study was 33.9% (3473/10,233). In meta-analysis, COVID-19 patient with obesity had higher odds of poor outcomes compared with better outcomes with a pooled OR of 1.88 (95% CI: 1.25-2.80; p = 0.002), with 86% heterogeneity between studies (p < 0.00001). Our study suggests a significant association between obesity and COVID-19 severity and poor outcomes. Our results findings may have important suggestions for the clinical management and future research of obesity and COVID-19.

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.

Comparison of Iatrogenic Soft Tissue Trauma in Robotic-Assisted versus Manual Partial Knee Arthroplasty.

Partial knee arthroplasty (PKA) is performed to treat end-stage osteoarthritis in a single compartment. There are minimal data characterizing soft-tissue injuries for PKA with robotic and manual techniques. This cadaver study compared the extent of soft-tissue trauma sustained through robotic-arm assisted PKA (RPKA) and manual PKA (MPKA). Five surgeons prepared 24 cadaveric knees for medial PKA, including six MPKA controls and 18 RPKA assigned into three different workflows: RPKA-LB (six knees) - RPKA with legacy burr; RPKA-NB (six knees) - RPKA with new burr design; and RPKA-NBS (six knees) - RPKA with new burr design and oscillating saw. Two surgeons estimated trauma to the patellar tendon, quadriceps tendon, anterior cruciate ligament (ACL), medial collateral ligament (MCL), medial capsule, posterior capsule, and posterior cruciate ligament (PCLs) using a five-grade system: Grade 1 - complete soft tissue preservation; Grade 2 - ≤25%; Grade 3 - 26 to 50%; Grade 4 - 51 to 75%; and Grade 5 - ≥76% trauma. A total trauma grade was assigned by summing the grades. Kruskal-Wallis statistical tests were used to assess outcomes. When compared to the MPKA group, all RPKA subgroups had lower total trauma grading (p<0.01), lower posterior capsular damage (p<0.01), and less severe ACL damage (p<0.01). The analysis demonstrated no significant difference between the three RPKA workflows. As this study was performed using cadaveric specimens, additional investigations are necessary to determine associations between robotic or manual-assisted technique, observed soft tissue damage, and postoperative clinical outcomes following PKA.

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.

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.

Development and Verification of a Porous Acetabular Shell Design Manufactured Using Additive Technology.

INTRODUCTION: Porous surface acetabular shells have been successfully used in cementless total hip arthroplasty. Recent advances in additive manufacturing have provided opportunities to optimize the shell designs. The current study describes the design and verification of a new acetabular shell design. MATERIALS AND METHODS: Additive manufacturing technology was used to fabricate acetabular shells using Ti6Al4V powder. A large computed tomography (CT) database was used to verify the screw hole location to ensure the screw trajectories were directed in the safe zone. Benchtop stability tests were conducted to compare the fixation stability of the new shell design to a clinically successful design. RESULTS: Shells were designed with an average pore size of 434 microns, surface porosity of 76%, and a coefficient of friction of 1.2. The CT analysis of various shell orientations demonstrated that at least two useful screws were typically directed toward the acetabular safe zone. The sawbone testing showed that the fixation stability of the new shell was either better or equivalent to the clinically successful design under two different bone preparation conditions. CONCLUSIONS: Using additive manufacturing technology, thin walled acetabular shells were fabricated which allowed for at least two ancillary fixation screws in the safe zone. The thin walls enable the use of a 36mm femoral head with a 48mm diameter shell which may enhance the joint stability in small stature patients. The equivalent or better fixation stability of the new design indicates that good initial fixation may be expected in vivo.

Tibial shaft anatomy differs between Caucasians and East Asian individuals.

PURPOSE: The orientation and distance from the shaft of the femur and tibia to the articular surface centre is important for performing total knee arthroplasty (TKA) with cementless stems. It is important to understand anatomic differences between races to match the tibial and femoral shaft axis to the knee articular surface. Thus, the purpose of this study was to compare knee morphology between Caucasian and East Asian individuals to determine the optimal placement of tibial and femoral stems. METHODS: A retrospective study was conducted on a matched cohort of 50 East Asians (21F, 29M) and 50 Caucasians (21F, 29M) by age and gender. CT scans were obtained in healthy volunteers using < 2-mm slices. The distance from the proximal tibial diaphysis axis to the tibial plateau centre and the distance from the distal femoral diaphysis axis to the centre of distal femoral articular surface were measured separately. Tibial measurements were taken using Akagi's anteroposterior (AP) axis and the widest mediolateral (ML) diameter, and femoral measurements were based on Whiteside's line and the surgical epicondylar axis. RESULTS: The ML distance between the tibial shaft centre and Akagi's line was significantly higher for Asians (9.9 ± 2.7 mm, Caucasians 7.7 ± 3.1 mm, p < 0.001). The distance between the femoral shaft centre and Whiteside's line was lower, although not significantly different (Asians 1.9 ± 1.0 mm, Caucasians 2.2 ± 1.1 mm, n.s.). However, there were no differences in the AP dimension for the femur or tibia comparing Asians to Caucasians in both tibial side (Asians 10.6 ± 3.3 mm vs. Caucasians 10.9 ± 4.0 mm) and femoral side (Asians 18.1 ± 1.7 mm vs. Caucasians 17.5 ± 1.6 mm). CONCLUSION: East Asian individuals have more offset in the ML dimension for the tibia. This finding is clinical relevant, as this dimensional difference should be taken into consideration when designing primary and revision TKA stemmed tibial implants for East Asian individuals. LEVEL OF EVIDENCE: Case-control study, Level III.

Development and Verification of Novel Porous Titanium Metaphyseal Cones for Revision Total Knee Arthroplasty.

BACKGROUND: Porous metaphyseal cones are widely used in revision knee arthroplasty. A new system of porous titanium metaphyseal cones has been designed based on the femoral and tibial morphology derived from a computed tomography-based anatomical database. The purpose of this study is to evaluate the initial mechanical stability of the new porous titanium revision cone system by measuring the micromotion under physiologic loading compared with a widely-used existing porous tantalum metaphyseal cone system. METHODS: The new cones were designed to precisely fit the femoral and tibial anatomy, and 3D printing technology was used to manufacture these porous titanium cones. The stability of the new titanium cones and the widely-used tantalum cones were compared under physiologic loading conditions in bench top test model. RESULTS: The stability of the new titanium cones was either equivalent or better than the tantalum cones. The new titanium femoral cone construct had significantly less micromotion compared with the traditional femoral cone construct in 5 of the 12 directions measured (P < .05), whereas no statistical difference was found in 7 directions. The new porous titanium metaphyseal tibial cones demonstrated less micromotion in medial varus/valgus (P = .004) and posterior compressive micromotion (P = .002) compared with the traditional porous tantalum system. CONCLUSION: The findings of this biomechanical study demonstrate satisfactory mechanical stability of an anatomical-based porous titanium metaphyseal cone system for femoral and tibial bone loss as measured by micromotion under physiologic loading. The new cone design, in combination with instrumentation that facilitates surgical efficiency, is encouraging. Long-term clinical follow-up is warranted.

Anthropometric Computed Tomography Reconstruction Identifies Risk Factors for Cortical Perforation in Revision Total Hip Arthroplasty.

BACKGROUND: The incidence of revision hip arthroplasty is increasing with nearly 100,000 annual procedures expected in the near future. Many surgeons use straight modular tapered stems in revisions; however, complications of periprosthetic fracture and cortical perforation occur, resulting in poor outcomes. Our objective was to identify patient demographics and femoral characteristics that predispose patients to cortical perforation when using the straight modular stems. METHODS: We used a computed tomography database and modeling software to identify patient demographics and morphologic femoral characteristics that predispose patients to cortical perforation during revision hip arthroplasty. Overall, 561 femurs from patients of various backgrounds were used, and statistical analysis was performed via the 2-sample t test. RESULTS: Decreased patient height (mean 163.0 vs 168.8 cm), radius of curvature (818 vs 939 mm), anterior-posterior (8.5 vs 13.8 mm) and medial-lateral (7.9 vs 11.3 mm) width of the isthmus, and distance of the isthmus from the greater trochanter (179 vs 186 mm) were all statistically significant risk factors for cortical perforation (P < .05). CONCLUSION: This study identifies several patient-specific risk factors for cortical perforation during revision hip arthroplasty using straight modular tapered stems and highlights the importance of preoperative planning especially in patients with shorter stature, proximal location of the femoral isthmus, narrow femoral canal, and smaller radius of curvature. Also, when using a mid-length modular tapered stem without an extended trochanteric osteotomy, consideration should be given to using a kinked stem to avoid anterior cortical perforation.

Comparison of Head Center Position and Screw Fixation Options Between a Jumbo Cup and an Offset Center of Rotation Cup in Revision Total Hip Arthroplasty: A Computer Simulation Study.

Jumbo acetabular cups are commonly used in revision total hip arthroplasty (THA). A straightforward reaming technique is used which is similar to primary THA. However, jumbo cups may also be associated with hip center elevation, limited screw fixation options, and anterior soft tissue impingement. A partially truncated hemispherical shell was designed with an offset center of rotation, thick superior rim, and beveled anterior and superior rims as an alternative to a conventional jumbo cup. A three dimensional computer simulation was used to assess head center position and safe screw trajectories. Results of this in vitro study indicate that a modified hemispherical implant geometry can reduce head center elevation while permitting favorable screw fixation trajectories into the pelvis in comparison to a conventional jumbo cup.

Changes in Femoral Version During Implantation of Anatomic Stems: Implications on Stem Design.

BACKGROUND: Component positioning in total hip arthroplasty (THA) is among the primary indicators for longevity and success. Acetabular component positioning has been discussed in literature at length; however, femoral component positioning is also important as it contributes to combined anteversion. METHODS: In this study, we examined the changes in femoral anteversion after the implantation of anatomic stem ABG II. A cadaveric study, a computed tomography-based computer modeling study, and a clinical study using a navigation system were conducted to document these changes. RESULTS: These studies demonstrated that the anatomic stem ABG II increased the postimplantation femoral version by approximately 7°. The postimplantation versions followed a bimodal distribution. The computed tomography and navigation data also highlighted that the patient population may roughly be divided into 2 groups: the first group that needs anteverted stem and the second group that needs little or no anteversion in the stem to recreate the desired version and offset. CONCLUSION: Based upon our data, we propose a new anatomic stem design that is offered in 2 version angles of 0° and 7° to help create the desired version and offset.

Development and verification of a cementless novel tapered wedge stem for total hip arthroplasty.

Most current tapered wedge hip stems were designed based upon the original Mueller straight stem design introduced in 1977. These stems were designed to have a single medial curvature and grew laterally to accommodate different sizes. In this preclinical study, the design and verification of a tapered wedge stem using computed tomography scans of 556 patients are presented. The computer simulation demonstrated that the novel stem, designed for proximal engagement, allowed for reduced distal fixation, particularly in the 40-60 year male population. Moreover, the physical micromotion testing and finite element analysis demonstrated that the novel stem allowed for reduced micromotion. In summary, preclinical data suggest that the computed tomography based stem design described here may offer enhanced implant fit and reduced micromotion.

Biomechanical analysis of various footprints of transforaminal lumbar interbody fusion devices.

STUDY DESIGN: A biomechanical finite element modeling study of the human lumbar spine. OBJECTIVE: To evaluate the effects of a transforaminal interbody device's footprint on lumbar spine biomechanics to further examine the potential subtle biomechanical differences not captured in previous studies. SUMMARY OF BACKGROUND DATA: In recent years, the evolution of interbody fusion devices has provided the surgeons with a multitude of options. An articulating transforaminal lumbar interbody fusion (TLIF) device is developed to overcome the surgical challenges associated with insertion of a large footprint interbody device through a small incision. METHODS: A finite element model of the L3-S1 lumbar segment was modified to simulate replacement of various TLIF constructs with different cage designs including an articulating vertebral interbody (AVID) TLIF device and a generic TLIF device placed in different configurations. The instrumented models were subjected to a 400 N follower load along with a 10 N m bending moment at different physiological planes. The kinematics, loads, and stresses were compared among various models. RESULTS: Simulated cage designs provided similar kinematical stability within the treated segments. However, the articulating and double TLIF implants allowed for better load sharing through the anterior column. These implants resulted in lower endplate and pedicle screw stresses and in more homogenous stress distribution across the peripheral region of the endplate. CONCLUSIONS: An articulating, large footprint, peripherally placed TLIF device affords substantial biomechanical advantages. This device may be able to reduce the incidence of subsidence because of its ability to reduce and distribute the endplate stresses in the stronger peripheral region. It may also reduce the posterior hardware failure incidence owing to its ability to reduce the screw stresses as compared with traditional TLIF. Although double TLIF has been demonstrated to have similar biomechanical advantages as the AVID, complications associated with double TLIF (ie, larger surgical incision, longer surgical procedure, placement and alignment challenges) support AVID as a better optimized alternative.

Innovations in hip arthroplasty three-dimensional modeling and analytical technology (SOMA).

The modern generations of cementless hip arthroplasty implant designs are based on precise fit and fill of components within the native bony geometry of the proximal femur and the acetabulum for enhanced implant longevity. Variations exist based on a number of population demographics such as age, gender, body mass index, and ethnicity. Recently, establishment of comprehensive electronic computerized tomographic databases from a diverse population worldwide have been key innovations in the field of implant development. This technology provides a potential improvement compared to historical techniques of implant design and manufacturing which involved limited trials on cadavers. Segmentation of the computerized data to generate three-dimensional models allows precise and accurate measurements of anatomical structures and may provide better understanding of anthropometric variations that occur among individuals. Evidence-and population-based computational analyses may provide a better tool for designing orthopaedic implants that deliver an enhanced fit for a more diverse patient population. Moreover, these population-based databases can also verify new designs by means of virtual implantation and analysis on specific or large groups of bones within the database. The aim of this paper is to describe a three dimensional modeling and analytical technology and to review the various applications of this technology in relation to hip arthroplasty.

Design and Verification of a Metaphyseal Filling Stem for Total Hip Arthroplasty Based on Novel Measurements of Proximal Femoral Anatomy.

Background: Cementless metaphyseal filling stems rely on fixation in the medial-to-lateral and anterior-to-posterior (AP) planes. The purpose of this preclinical study was to develop Insignia, a new metaphyseal filling system to match the anatomy of the proximal femur, and then compare it to clinically successful stems in multiple simulations. Methods: In this preclinical study, the geometry of the proximal femur in the AP plane among 1321 healthy subjects was evaluated using computed tomography. This data was then used to design insignia. Preclinical studies were performed to compare the broaching effort required to prepare a canal using this system, assess the reliability of seating heights for the stem, and compare in vitro micromotion testing of the stem under simulated stair climb activity. Results: The proximal femur decreased approximately 50% in the AP plane spanning 20 mm above the lesser trochanter to 30 mm below the lesser trochanter. Additional bench top testing was performed, and the new stem system was found to demonstrate significantly reduced broaching effort (average 6 vs 29 hits, P-value = .000), reliable seating heights on stem placement, and 70% less proximal micromotion on 10,000-cyclic testing (P < .05) compared to another clinically successful metaphyseal filling stem. Conclusions: The AP dimension of the proximal femur decreases nearly 50% throughout its length. Metaphyseal filling stems that match the AP anatomy of the proximal femur may require fewer hits during broaching, yield reproducible seating heights, and reduce micromotion on cyclic testing.

An Advanced Knee Simulator Model Can Reproducibly Be Used for Ligament Balancing Training during Total Knee Arthroplasty.

A critical and difficult aspect of total knee arthroplasty (TKA) is ligamentous balancing for which cadavers and models have played a large role in the education and training of new arthroplasty surgeons, although they both have several shortcomings including cost, scarcity, and dissimilarity to in vivo ligament properties. An advanced knee simulator (AKS) model based on computed tomography (CT) scans was developed in the setting of these challenges with cadavers and previous models. In this study, we compared the ligament balancing between AKS and human cadaveric knees to assess the validity of using the AKS for ligament balancing training during TKA. A CT scan of a TKA patient with varus deformity was used to design the AKS model with modular components, using three-dimensional printing. Three fellowship-trained arthroplasty surgeons used technology-assisted TKA procedure to plan and balance three cadaver knees and the AKS model. Medial and lateral laxity data were captured using manual varus and valgus stress assessments for cadavers and the model in an extension pose (10 degrees of flexion from terminal extension) and between 90 and 95 degrees for flexion. After preresection assessments, surgeons planned a balanced cruciate-retaining TKA. Following bony cuts and trialing, extension and flexion ligament laxity values were recorded in a similar manner. Descriptive statistics and Student's t-tests were performed to compare the cadavers and model with a p-value set at 0.05. Preresection medial/lateral laxity data for both extension and flexion were plotted and showed that the highest standard deviation (SD) for the cadavers was 0.67 mm, whereas the highest SD for the AKS was 1.25 mm. A similar plot for trialing demonstrated that the highest SD for the cadavers was 0.6 mm, whereas the highest SD for the AKS was 0.61 mm. The AKS trialing data were highly reproducible when compared with cadaveric data, demonstrating the value of the AKS model as a tool to teach ligament balancing for TKA and for future research endeavors.