Marker location and knee joint constraint affect the reporting of overhead squat kinematics in elite youth football players

Motion capture systems are used in the analysis and interpretation of athlete movement patterns for a variety of reasons, but data integrity remains critical regardless. The extent to which marker location or constraining degrees of freedom (DOF) in the biomechanical model impacts on this integrity lacks consensus. Ten elite academy footballers performed bilateral overhead squats using a marker-based motion capture system. Kinematic data were calculated using four different marker sets with 3DOF and 6DOF configurations for the three joint rotations of the right knee. Root mean squared error differences between marker sets ranged in the sagittal plane between 1.02 and 4.19 degrees to larger values in the frontal (1.30-6.39 degrees) and transverse planes (1.33 and 7.97 degrees). The cross-correlation function of the knee kinematic time series for all eight marker-sets ranged from excellent for sagittal plane motion (>0.99) but reduced for both coronal and transverse planes (<0.9). Two-way ANOVA repeated measures calculated at peak knee flexion revealed significant differences between marker sets for frontal and transverse planes (p < 0.05). Pairwise comparisons showed significant differences between some marker sets. Marker location and constraining DOF while measuring relatively large ranges of motion in this population are important considerations for data integrity.

In Vivo Weight-Bearing Kinematics for Constrained Versus Traditional Bicruciate Stabilized Total Knee Arthroplasty Cohorts Compared to the Normal Knee

BACKGROUND

Constrained inserts in total knee arthroplasty (TKA) may offer additional stability, but can this insert type allow unrestricted movements or will the extra conformity cause kinematic conflict with the cam-post mechanism in deeper flexion? The objective of this study was to evaluate the weight-bearing kinematics of both traditional and constrained bicruciate stabilized (BCS) TKA inserts to determine if the rollback induced by the cam-post mechanism will work in unison with the constrained polyethylene insert.

METHODS

This study used previously published 3-dimensional model fitting techniques to compare weight-bearing flexion and femoro-tibial condylar motion patterns for 20 patients who had a traditional insert, 20 patients who had a constrained insert, and 10 previously published nonimplanted knees, all performing a deep knee bend activity while under fluoroscopic surveillance.

RESULTS

The results from this study indicate that subjects having a bicruciate stabilized TKA experienced similar postoperative kinematics for both constrained and unconstrained insert options, comparable to normal knees.

CONCLUSIONS

Subjects in this study having either a constrained or traditional insert experienced progressive rollback of both condyles, with the lateral condyle rolling more posterior than the medial condyle, leading to axial rotation. Although less in magnitude, these results were comparable to the normal knee in pattern, indicating that kinematic conflict did not occur for subjects having a constrained insert.

Unicondylar knee arthroplasty demonstrating a significant increased risk for aseptic revisions compared to unconstrained and constrained total knee arthroplasty: An analysis of aseptic revisions after unicondylar and primary total knee arthroplasty of the German Arthroplasty Registry

PURPOSE

Due to ageing population, the implantation rate of total knee arthroplasties (TKAs) is continuously growing. Aseptic revisions in primary knee arthroplasty are a major cause of revision. The aim of the following study was to determinate the incidence and reasons of aseptic revisions in constrained and unconstrained TKA, as well as in unicondylar knee arthroplasties (UKAs).

METHODS

Data collection was performed using the German Arthroplasty Registry. Reasons for aseptic revisions were calculated. Incidence and comparison of aseptic revisions were analysed using Kaplan-Meier estimates. A multiple χ2 test with Holm's method was used to detect group differences in ligament ruptures.

RESULTS

Overall, 300,998 cases of knee arthroplasty with 254,144 (84.4%) unconstrained TKA, 9993 (3.3%) constrained TKA and 36,861 (12.3%) UKA were analysed. Aseptic revision rate in UKA was significantly increased compared to unconstrained and constrained TKA (p < 0.0001). In constrained TKA, a 2.0% revision rate for aseptic reasons were reported after 1 year, while in unconstrained TKA 1.1% and in UKA, 2.7% of revisions were identified. After 7 years in constrained TKA 3.3%, in unconstrained TKA 2.8%, and in UKA 7.8% sustained aseptic revision. Ligament instability was the leading cause of aseptic revision accounting for 13.7% in unconstrained TKA. In constrained TKA, 2.8% resulted in a revision due to ligament instability. In the UKA, the most frequent cause of revisions was tibial loosening, accounting for 14.6% of cases, while progression of osteoarthritis accounted for 7.9% of revisions. Ligament instability was observed in 14.1% of males compared to 15.9% of females in unconstrained TKA and in 4.6% in both genders in UKA.

CONCLUSION

In patients with UKA, aseptic revision rates are significantly higher compared to unconstrained and constrained TKA. Ligament instability was the leading cause of aseptic revision in unconstrained TKA. In UKA, the most frequent cause of revisions was tibial loosening, while progression of osteoarthritis was the second most frequent cause of revisions. Comparable levels of ligament instability were observed in both sexes.

LEVEL OF EVIDENCE

Level III, cohort study.

Survival Analysis and Failure Modes of Total Hip Arthroplasty Using a Cemented Semi-Retentive Acetabular Cup

To reduce the incidence of total hip revisions, there have been continuous efforts to enhance prosthetic materials and designs to optimize implant survival. A primary implant with a constrained acetabular component is often used to minimize the risk of dislocations even though this approach has some drawbacks as reported in the literature. To address these concerns, this study aimed to assess the survivorship and dislocation rate of a semi-retentive cemented acetabular cup when used as a primary implant. The specific cemented cup that we studied was not present in any study that we consulted, so to fill this gap, we conducted a retrospective examination of 527 cemented hip prostheses that utilized the semi-retentive cup between the years 2005 and 2012. We employed Cox multiple regression models for our statistical analysis. The revision due to dislocation occurred in 12.8% of all cases, with a lower incidence of 5% (14 cases) in age groups >70 years than in age groups <70 years (14%-32 cases) (p < 0.001). The survival rates of the semi-retentive cemented acetabular cup were 98.6% (520 cases) at 5 years and 92.2% (487 cases) at 10 years. The survival rates were significantly lower in women than men, with 1.9% (7 cases) toward 0% at 5 years and 8.1% (30 cases) toward 5% (7 cases) at 10 years (p = 0.002). The difference in failure rates between age groups over 70 years (2.3%-10 cases) and age groups under 70 years (11.5%-34 cases) was also statistically significant (p < 0.001). Our study indicates that the semi-constrained design may cause frequent damage to the polyethylene liner due to impingement and wear, which are the primary factors for failure. Also, this implant has a similar risk of revision due to dislocation as reported in studies and may be beneficial as a primary implant in elderly patients with low-demanding lifestyles, muscular insufficiency, and low compliance regarding hip prosthetic behavior, without a major effect on survivorship.

Survivorship of highly constrained prostheses in primary and revision total knee arthroplasty: analysis of 6070 cases

BACKGROUND

Concerns exist about the survival and complication rates of highly constrained total knee arthroplasty (TKA) prostheses. The aims of this study were to determine if there were differences between the revision and complication rates of fully stabilized (FSTKA) and hinged (HTKA) TKA, when used in both primary and revision procedures.

METHODS

Survivorship of all highly constrained TKA prostheses implanted over a 17 year period were analysed by the Australian Orthopaedic Association National Joint Replacement Registry. The primary outcome measure was time to first revision using Kaplan Meier estimates of survivorship.

RESULTS

In the primary setting, the cumulative percent revision at 11 years was higher for HTKA than for FSTKA prostheses (P = 0.014). However, this finding was only significant for patient >75 years. In the revision setting, there were no differences in the revision rates for either category of prosthesis for any age group. For the indication of periarticular/periprosthetic fracture, HTKA resulted in a lower revision rate than FSTKA in both primary and revision cohorts. There were no differences in the rates of revision for infection and aseptic loosening for either prosthesis type in primary or revision settings. The revision risk for periprosthetic fracture was higher after HTKA prostheses.

CONCLUSION

Both FSTKA and HTKA prostheses provide similar outcomes in primary and revision procedures except for the setting of periarticular/periprosthetic fracture, where a HTKA should be used. In elderly patients, a FSTKA prosthesis is recommended as the risk of periprosthetic fracture is higher with a HTKA.

A Purely Algebraic Justification of the Kabsch-Umeyama Algorithm

The constrained orthogonal Procrustes problem is the least-squares problem that calls for a rotation matrix that optimally aligns two matrices of the same order. Over past decades, the algorithm of choice for solving this problem has been the Kabsch-Umeyama algorithm, which is effectively no more than the computation of the singular value decomposition of a particular matrix. Its justification, as presented separately by Kabsch and Umeyama, is not totally algebraic since it is based on solving the minimization problem via Lagrange multipliers. In order to provide a more transparent alternative, it is the main purpose of this paper to present a purely algebraic justification of the algorithm through the exclusive use of simple concepts from linear algebra. For the sake of completeness, a proof is also included of the well known and widely used fact that the orientation-preserving rigid motion problem, i.e., the least-squares problem that calls for an orientation-preserving rigid motion that optimally aligns two corresponding sets of points in d-dimensional Euclidean space, reduces to the constrained orthogonal Procrustes problem.

On Estimation of Genome Composition in Genetically Admixed Individuals Using Constrained Genomic Regression

Quantifying the population stratification in genotype samples has become a standard procedure for data manipulation before conducting genome wide association studies, as well as for tracing patterns of migration in humans and animals, and for inference about extinct founder populations. The most widely used approach capable of providing biologically interpretable results is a likelihood formulation which allows for estimation of founder genome proportions and founder allele frequency conditional on the observed genotypes. However, if founder allele frequencies are known and samples are dominated by admixed genotypes this approach may lead to biased inference. In addition, processing time increases drastically with the number of genetic markers. This article describes a simplified approach for obtaining biologically meaningful measures of population stratification at the genotype level conditional on known founder allele frequencies. It was tested on cattle and human data sets with 4,022 and 150,000 genetic markers, respectively, and proved to be very accurate in situations where founder poplations were correctly specified, or under-, over-, and miss-specified. Moreover, processing time was only marginally affected by an increase in the number of markers.

Postoperative Numbness: A Survey of Patients After Hip Arthroscopic Surgery

Background:

Hip arthroscopic surgery is a rapidly growing procedure that requires distraction of the leg to access the joint. A frequently reported complication of this procedure is postoperative numbness, with rates between 1% and 20% reported in the literature.

Purpose/Hypothesis:

The purpose of this study was to determine the factors contributing to the development and effect of numbness on functional outcomes. We hypothesized that this complication is underreported and that its prevalence is higher than what has been described in the literature.

Study Design:

Case series; Level of evidence, 4.

Methods:

Patients who had undergone hip arthroscopic surgery between 2012 and 2016 were included, and a telephone survey was conducted to collect data. Data related to the procedure and outcome scores were collected via a systematic chart review for the included patients. Data analysis was conducted for means, SDs, frequencies, and percentages. For comparative statistics, t tests and multiple logistic regression models were used.

Results:

A total of 221 patients (113 male, 108 female; mean age, 39.8 ± 13.34 years) completed the survey out of 362 eligible patients. Overall, 37% (n = 82) of patients reported having experienced some form of numbness after surgery. Approximately 43% (35/82) of the patients reported resolution by 6 weeks postoperatively, and 68% (56/82) of numbness was reported to have completely resolved by 6 months. The duration of surgery was a significant factor for the development of postoperative numbness (P = .010; odds ratio, 2.18) when comparing procedures longer than 50 minutes with procedures shorter than 50 minutes (first incision until closure). Postoperative numbness was associated with a negative effect on the International Hip Outcome Tool–33 (iHOT-33) score that reached statistical significance at the 1-year (numbness, 60.19; no numbness, 74.21; P = .006) and 2-year time points (numbness, 52.04; no numbness, 72.69; P = .01).

Conclusion:

This study confirmed our hypothesis that postoperative numbness is more common in our patient population than the incidence reported in the literature. This adverse event was also shown to be associated with decreased postoperative functional outcomes, as measured by the iHOT-33 at 1 and 2 years postoperatively.

A Comparison of Constrained Item Selection Methods in Multidimensional Computerized Adaptive Testing

The construction of assessments in computerized adaptive testing (CAT) usually involves fulfilling a large number of statistical and non-statistical constraints to meet test specifications. To improve measurement precision and test validity, the multidimensional priority index (MPI) and the modified MPI (MMPI) can be used to monitor many constraints simultaneously under a between-item and a within-item multidimensional framework, respectively. As both item selection methods can be implemented easily and computed efficiently, they are important and useful for operational CATs; however, no thorough simulation study has compared the performance of these two item selection methods under two different item bank structures. The purpose of this study was to investigate the efficiency of the MMPI and the MPI item selection methods under the between-item and within-item multidimensional CAT through simulations. The MMPI and the MPI item selection methods yielded similar performance in measurement precision for both multidimensional pools and yielded similar performance in exposure control and constraint management for the between-item multidimensional pool. For the within-item multidimensional pool, the MPI method yielded slightly better performance in exposure control but yielded slightly worse performance in constraint management than the MMPI method.

Factors Affecting Wear of Constrained Polyethylene Tibial Inserts in Total Knee Arthroplasty

BACKGROUND

Wear in posterior-stabilized (PS) polyethylene tibial inserts depends on component position, limb alignment, and ligament balancing. Valgus-varus constrained (VVC) inserts are likely to be affected similarly. We aimed to compare wear characteristics of VVC and PS inserts and identify associated factors.

METHODS

This was a retrieval analysis (macroscopic and radiographic) of all 18 VVC liners collected from patients who underwent revision surgery from 1999 to 2011. These patients were matched to another group with PS inserts who underwent revision in the same time period.

RESULTS

There was significantly more damage in the posts of the VVC group (13.0 ± 5.0, compared to 4.7 ± 1.9 in the PS group; P < .001). Within the VVC group, the total damage score and cold flow damage were significantly higher with excessive joint line changes (≥5 mm; P = .01). The excessive joint line elevation was associated with rotational wear pattern of the post (P = .004). Damage scores were increased with femoral component malposition (P = .04), anterior tibial slope (P = .04), and tibial component malposition (P = .04).

CONCLUSION

Joint line elevation, femoral and tibial component malposition, and anterior tibial slope resulted in significantly more wear in the VVC inserts. Joint line elevation of >5 mm resulted in wear of the medial and lateral aspects of the post, femoral valgus resulted in cold flow wear of the anterior post, and tibial valgus and anterior slope resulted in wear of lateral aspect of the post.

The Impact of Wear and Lift-Off on Coronal Plane Alignment in TKA and Implications to Future Constrained Revision: A Retrieval Study

Current discussion exists whether to position a total knee arthroplasty (TKA) in slight undercorrection in varus osteoarthritis. The goal of this study was to analyse the effect of wear and lateral lift-off in primary TKA on coronal plane alignment and the implication to future constrained revision TKA. Seventy-six retrieved tibial inserts were analysed for the ratio of wear (RW), lateral lift-off and implications for future constrained revision surgery according to the coronal plane alignment. The RW significantly affects the coronal plane alignment in TKA. Progressive wear and lateral lift-off were seen with progressive varus alignment. However, there was no difference in constrained revision between mild varus and moderate varus aligned TKAs.

Analysis of composition of microbiomes: a novel method for studying microbial composition

Background

Understanding the factors regulating our microbiota is important but requires appropriate statistical methodology. When comparing two or more populations most existing approaches either discount the underlying compositional structure in the microbiome data or use probability models such as the multinomial and Dirichlet-multinomial distributions, which may impose a correlation structure not suitable for microbiome data.

Objective

To develop a methodology that accounts for compositional constraints to reduce false discoveries in detecting differentially abundant taxa at an ecosystem level, while maintaining high statistical power.

Methods

We introduced a novel statistical framework called analysis of composition of microbiomes (ANCOM). ANCOM accounts for the underlying structure in the data and can be used for comparing the composition of microbiomes in two or more populations. ANCOM makes no distributional assumptions and can be implemented in a linear model framework to adjust for covariates as well as model longitudinal data. ANCOM also scales well to compare samples involving thousands of taxa.

Results

We compared the performance of ANCOM to the standard t-test and a recently published methodology called Zero Inflated Gaussian (ZIG) methodology (1) for drawing inferences on the mean taxa abundance in two or more populations. ANCOM controlled the false discovery rate (FDR) at the desired nominal level while also improving power, whereas the t-test and ZIG had inflated FDRs, in some instances as high as 68% for the t-test and 60% for ZIG. We illustrate the performance of ANCOM using two publicly available microbial datasets in the human gut, demonstrating its general applicability to testing hypotheses about compositional differences in microbial communities.

Conclusion

Accounting for compositionality using log-ratio analysis results in significantly improved inference in microbiota survey data.