Background
The aim of this study is a clinical evaluation of the center of rotation (COR) placement towards a patient’s recovery with respect to daily living ability and mobility. In past experiments ...based on three-dimensional (3D) models, medialization of the COR in total hip arthroplasty (THA) showed a negative influence on muscle strength of the abductors and reaction force of the hip joint. This contradicts paradigms, where reduced hip loading forces are claimed to increase functional outcomes.
Methods
The plain X-rays of 110 patients who underwent THA after a femoral neck fracture between January 2019 and January 2021 were retrospectively evaluated. A Barthel Index on discharge was obtained in 69 cases. 47 patients were available for a follow-up interview concerning the Barthel Index, Parker mobility score (PMS), and pain levels (NRS) 6 and 12 months after surgery.
Results
Medialization of the COR had a significantly negative effect on the need for care (Barthel Index) at patient discharge (Spearman correlation 0.357,
p
= 0.013). The effect on the PMS is still existent at 6 and 12 months (Spearman correlation 0.471,
p
= 0.009 at 6 months; 0.472,
p
= 0.008 at 12 months). Mann–Whitney
U
tests showed that the groups with medialized COR performed significantly worse than the lateralized groups. This was seen for the Barthel Index at discharge and at 6 months after surgery and for the PMS at 6 and 12 months. The accurately reconstructed CORs showed no significant differences from the lateralized rotation centers in need of care and mobility.
The superior COR placement group showed significantly reduced mobility at 12 months in contrast to the inferior COR placement group (
p
= 0.008), and the group of accurately reconstructed rotation centers showed significantly less pain than the inferior COR placement group (
p
= 0.007 after 6 months,
p
= 0.026 after 12 months). Especially the combination of both (superomedialization) leads to reduced mobility (Spearman correlation 0.67,
p
= < 0.001).
Conclusions
COR superior displacement, COR medialization, and the combination of both (superomedialization, Spearman
p
= < 0.001) lead to reduced mobility while inferior displacement showed increased pain. According to our results, we recommend an exact vertical COR restoration, while horizontal medial displacement needs to be avoided.
Level of evidence
III.
Modern computerized planning tools for periacetabular osteotomy (PAO) use either morphology-based or biomechanics-based methods. The latter relies on estimation of peak contact pressures and contact ...areas using either patient specific or constant thickness cartilage models. We performed a finite element analysis investigating the optimal reorientation of the acetabulum in PAO surgery based on simulated joint contact pressures and contact areas using patient specific cartilage model. Furthermore we investigated the influences of using patient specific cartilage model or constant thickness cartilage model on the biomechanical simulation results. Ten specimens with hip dysplasia were used in this study. Image data were available from CT arthrography studies. Bone models were reconstructed. Mesh models for the patient specific cartilage were defined and subsequently loaded under previously reported boundary and loading conditions. Peak contact pressures and contact areas were estimated in the original position. Afterwards we used a validated preoperative planning software to change the acetabular inclination by an increment of 5° and measured the lateral center edge angle (LCE) at each reorientation position. The position with the largest contact area and the lowest peak contact pressure was defined as the optimal position. In order to investigate the influence of using patient specific cartilage model or constant thickness cartilage model on the biomechanical simulation results, the same procedure was repeated with the same bone models but with a cartilage mesh of constant thickness. Comparison of the peak contact pressures and the contact areas between these two different cartilage models showed that good correlation between these two cartilage models for peak contact pressures (r = 0.634 ∈ 0.6, 0.8, p < 0.001) and contact areas (r = 0.872 > 0.8, p < 0.001). For both cartilage models, the largest contact areas and the lowest peak pressures were found at the same position. Our study is the first study comparing peak contact pressures and contact areas between patient specific and constant thickness cartilage models during PAO planning. Good correlation for these two models was detected. Computer assisted planning with FE modeling using constant thickness cartilage models might be a promising PAO planning tool when a conventional CT is available.
Conventional application of these two calculus staples is stretched here, somewhat recreationally, but also to raise solid questions about the role of limit interchange in analysis—without, however, ...delving any deeper than first-year Calculus.
Ecker discusses the little tricks that professors apply in designing shortcuts and problems involving "nice numbers" that lead to easily predictable outcomes. He presents a shortcut that he ...discovered recently.
Abstract Benign paroxysmal positional vertigo is a common cause of disabling vertigo with a high rate of recurrence. Although connections between vitamin D deficiency and osteoporosis, as well as ...between osteoporosis and benign paroxysmal positional vertigo have been suggested respectively in the literature, we are not aware of any publication linking vitamin D and benign paroxysmal positional vertigo. As a hypothesis, we suggest that there is a relation between insufficient vitamin D level and benign paroxysmal positional vertigo. In order to test this hypothesis, in a small retrospective pilot study, 25-hydroxyvitamin D levels in serum of patients with benign paroxysmal positional vertigo and frequency of recurrence after correction of serum level were assessed retrospectively. Patients with idiopathic positional vertigo had a low average serum level of 25-hydroxyvitamin D (23 ng/mL) similar to that of the general Austrian population, which has a high prevalence of hypovitaminosis D. In 4 cases with chronically recurrent severe vertigo episodes, average levels of serum 25-hydroxyvitamin D were even significantly lower than in the other vertigo patients, who had their first episode. Vertigo attacks did not recur after supplementation with vitamin D. We raise the possibility that patients with benign paroxysmal positional vertigo who have low vitamin D levels may benefit from supplementation and suggest further epidemiological investigations to determine the effect of correcting vitamin D deficiency on the recurrence of vertigo. Given the many known benefits of vitamin D, the authors recommend the measurement of vitamin D in patients with benign paroxysmal positional vertigo and supplementation if necessary.
Conventional application of these two calculus staples is stretched here, somewhat recreationally, but also to raise solid questions about the role of limit interchange in analysis -- without, ...however, delving any deeper than first-year Calculus. PUBLICATION ABSTRACT
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