Stride length–cadence relationship is disrupted in below-knee prosthesis users

The aim of this study was to evaluate the linearity of the relationship between stride length and cadence (STRIDE_LC) over three self-selected speeds (normal, slow, fast) in below-knee prosthesis users (n = 14, 11 men, mean age 43 ± 12 years, mean time since amputation 9.2 ± 6.9 years) in comparison to controls (n = 20, 11 men, mean age 43 ± 17 years). The step length–cadence relationship (STEP_LC) was also calculated for the prosthetic and intact legs in prosthesis users and compared to the dominant leg of controls. The goodness of linear fit (R²) and slope over 3 speeds were used as outcome measures. Prosthesis users walked significantly slower than controls (slow-fast speed means 82–131 vs. 97–169 cm/s, respectively, ANOVA p < 0.0001) due to both lower cadence (42–53 vs. 47–63 strides/min, p < 0.0001) and shorter stride length (116–149 vs. 123–161 cm, p < 0.0001). The R² of STRIDE_LC relationship in below-knee prosthesis users (0.76 ± 0.13) was significantly lower than in controls (0.91 ± 0.03, p < 0.001). The R² values of STEP_LC relationship between the prosthetic and intact legs in prosthesis users were correlated (r = 0.85, p < 0.001) and both (0.67 ± 0.19, 0.58 ± 0.21, respectively) were significantly smaller than in the dominant leg of controls (0.86 ± 0.04, p < 0.01). The slopes of STRIDE_LC and STEP_LC were not different. The R² of 0.84 for STRIDE_LC best discriminated prosthesis users from controls with high sensitivity (71%) and specificity (95%). The results indicate that coupling between stride/step length and cadence is disturbed in prosthesis users. Upon further investigation, the goodness of linear fit may prove to be useful in assessing prosthetic design, optimizing prosthetic fit, and predicting clinical outcomes.     

Multidetector CT predictors of prosthesis–patient mismatch in transcatheter aortic valve replacement

BackgroundProsthesis–patient mismatch (PPM) is a predictor of mortality after aortic valve replacement (AVR).ObjectiveWe examined whether accurate 3-dimensional annular sizing with multidetector CT (MDCT) is predictive of PPM after transcatheter AVR (TAVR).MethodsOne hundred twenty-eight patients underwent MDCT then TAVR. Moderate PPM was defined as an indexed effective orifice area ≤0.85 cm²/m² and severe ≤0.65 cm²/m². MDCT annular measurements (area, short and long axis) were compared with the size of the selected transcatheter heart valve (THV) to obtain (1) the difference between prosthesis size and CT-measured mean annular diameter and (2) the percentage of undersizing or oversizing (calculated as 100 × [MDCT annular area – THV nominal area]/THV nominal area). In addition, the MDCT annular area was indexed to body surface area. These measures were evaluated as potential PPM predictors.ResultsWe found that 42.2% of patients had moderate PPM and 9.4% had severe PPM. Procedural characteristics and in-hospital outcomes were similar between patients with or without PPM. THV undersizing of the mean aortic annulus diameter was not predictive of PPM (odds ratio [OR], 0.84; 95% CI, 0.65–1.07; P = .16; area under the receiver-operating characteristic curve [AUC], 0.58). THV undersizing of annular area was not predictive of PPM (OR, 0.96; 95% CI, 0.80–1.16; P = .69; AUC, 0.52). Indexed MDCT annular area was, however, predictive of PPM (OR, 0.24; 95% CI, 0.10–0.59; P < .001; AUC, 0.66).ConclusionsPPM is frequent after TAVR. Appropriate annular oversizing does not reduce the rate or severity of PPM. Patient annulus size mismatch, identified by indexed MDCT annular area, is a significant predictor of PPM.     

Does stress shielding occur with the use of long-stem prosthesis in total knee arthroplasty?

A retrospective study conducted to evaluate the possible occurrence of stress shielding with the use of long-stem tibial prosthesis in total knee arthroplasty. Forty-one patients were reviewed (twenty-three standard prosthesis, eighteen long-stem prosthesis) and forty-one unoperated knee of the contralateral limb). Patients underwent bone mineral density assessment with a dual-energy X-ray absorptiometry (DEXA) bone densitometer for the hip and bilateral knees. The mean time interval between surgery and the DEXA assessment was 87.7 months. There was no significant statistical difference (P > 0.05) in the bone mineral density patterns of the tibia with the use of either standard or long-stem prosthesis. The utilization of the long-stem prosthesis to off-load the tibia is not associated with any significant bone mineral density changes or stress shielding.     

Prosthetic replacement of the medial meniscus in cadaveric knees: does the prosthesis mimic the functional behavior of the native meniscus?

Meniscus replacement by a polymer meniscus prosthesis in dogs resulted in generation of new meniscal tissue. HYPOTHESIS: Optimal functioning of the prosthesis would involve realistic deformation and motion patterns of the prosthesis during knee joint motion. STUDY DESIGN: Controlled laboratory study. METHODS: The movements of the meniscus were determined during knee joint flexion and extension with and without internal and external tibial torque by means of roentgen stereophotogrammetric analysis. Subsequently, the meniscus in 6 human cadaveric knee joints was replaced by a meniscus prosthesis. RESULTS: All different parts of the meniscus showed a posterior displacement during knee joint flexion. The anterior horn was more mobile than the posterior horn. The prosthesis mimicked the movements of the meniscus. However, the excursions of the prosthesis on the tibial plateau were less. The knee joint laxity was not significantly higher after replacement with the meniscus prosthesis. CONCLUSIONS: The prosthesis approximated the behavior of the native meniscus. Improvement in both the gliding characteristics of the prosthetic material and the fixation of the prosthesis may improve the function. CLINICAL RELEVANCE: The meniscus prosthesis needs to be optimized to achieve a better initial function in the knee joint.     

Unicompartmental knee prosthesis implantation with a non-image-based navigation system: rationale,technique, case-control comparative study with a conventional instrumented implantation

The accuracy of implantation is an accepted prognostic factor for the long-term survival of unicompartmental knee prostheses (UKP). We developed a non-image-guided navigation system for UKP implantation without any extramedullary or intramedullary guiding device. The 30 patients operated on with the navigation system (group A) were matched to 30 patients operated on with the conventional technique (group B) using age, sex, body mass index, preoperative coronal mechanical femorotibial angle, and severity of the preoperative degenerative changes. All patients had a complete radiological examination in the first 3 months after the index procedure, with anteroposterior and lateral plain knee radiographs and anteroposterior and lateral long leg radiographs. Coronal femorotibial mechanical angle and both coronal and sagittal orientations of the femoral and tibial components were measured. There were no significant differences in the mean numerical values of all measured angles except for the sagittal orientation of the tibial component, with a significant excessive posterior tibial slope in group B. There was a significant increase in the rate of prostheses implanted in the desired angular range for all criteria except the coronal mechanical femorotibial angle in group A. An optimal implantation with all optimal items was obtained by 18 cases in group A and 6 cases in group B. Navigated implantation of a UKP with the used, non-image-based system improved the accuracy of the radiological implantation without any significant inconvenience and with little change in the conventional operative technique. The only inconvenience was a 20-min longer operative time. This improvement could be related to a longer survival of such implanted prostheses.     

Do more MRI findings imply worse disability or more intense low back pain? A cross-sectional study of candidates for lumbar disc prosthesis

Objective

To examine whether combined magnetic resonance imaging (MRI) findings are related to the degree of disability and low back pain (LBP) in candidates for lumbar disc prosthesis surgery.

Materials and methods

This cross-sectional study included 170 disc prosthesis candidates (mean age 41 years; 88 women) with chronic non-radicular LBP and localized disc degeneration. Experienced radiologists rated Modic changes and disc findings at L4-S1 on pre-treatment MRIs. An MRI total score (0–10) for findings at L4/L5 plus L5/S1 was calculated for Modic type I and/or II changes, a posterior high intensity zone (HIZ) in the disc, dark/black nucleus pulposus signal, and ≥40 % disc height decrease. We analyzed the relationship of the MRI total score to the Oswestry Disability Index (ODI) (n?=?170) and LBP intensity scores (0–100 visual analogue scale, n?=?165) using multiple linear regression and adjusting for age, gender, body mass index, smoking, and anxiety/depression.

Results

The MRI total score was not related to ODI (regression coefficient 0.12, p?=?0.79) or LBP intensity (regression coefficient 0.64, p?=?0.37). When individual MRI findings were analyzed, patients with HIZ at L5/S1 had slightly lower ODI scores (4.7 points, p?=?0.02). In post hoc analyses, results remained unchanged after adding facet arthropathy to the MRI total score and adjusting also for physical workload and physical leisure-time activity.

Conclusions

The combined MRI findings were not related to the degree of disability or the intensity of LBP. These degenerative MRI findings cannot explain variation in pre-treatment disability and pain in patients with chronic LBP accepted for disc prosthesis surgery.     

Reliability of change in lumbar MRI findings over time in patients with and without disc prosthesis—comparing two different image evaluation methods

Objectives

To assess the reliability of change in lumbar magnetic resonance imaging (MRI) findings evaluated retrospectively by direct comparison of images and by non-comparison.

Materials and methods

Pre-treatment and 2-year follow-up MRI was performed in 126 patients randomized to disc prosthesis surgery or non-surgical treatment. Two experienced radiologists independently evaluated progress and regress for Modic changes, disc findings, and facet arthropathy (FA) at L3/L4, L4/L5, and L5/S1, both by non-comparison and by comparison of initial and follow-up images. FA was evaluated at all levels, and other findings at non-operated levels. We calculated prevalence- and bias-adjusted kappa (PABAK) values for interobserver agreement. The impact of an adjacent prosthesis (which causes artefacts) and image evaluation method on PABAK was assessed using generalized estimating equations.

Results

Image comparison indicated good interobserver agreement on progress and regress (PABAK 0.63?1.00) for Modic changes, posterior high-intensity zone, disc height, and disc contour at L3-S1 and for nucleus pulposus signal and FA at L3/L4; and moderate interobserver agreement (PABAK 0.46?0.59) on decreasing nucleus signal and increasing FA at L4-S1. Image comparison indicated lower (but fair) interobserver agreement (PABAK 0.29) only for increasing FA at L5/S1 in patients with prosthesis in L4/L5 and/or L5/S1. An adjacent prosthesis had no overall impact on PABAK values (p?≥?0.22). Comparison yielded higher PABAK values than non-comparison (p?<?0.001).

Conclusions

Regarding changes in lumbar MRI findings over time, comparison of images can provide moderate or good interobserver agreement, and better agreement than non-comparison. An adjacent prosthesis may not reduce agreement on change for most findings.     

Diagnostics of “non-acute” vascular prosthesis infection using <Superscript>18</Superscript>F-FDG PET/CT: our experience with 96 prostheses

Introduction  Vascular prosthesis infection (VPI) is a life-threatening complication that occurs in 0.5–5% of prostheses. Low-grade infections in non-acute patients are a diagnostic challenge requiring a new method with good diagnostic accuracy. The aim of this work was to define the accuracy of ¹⁸F-FDG PET/CT in these settings and to identify essential parameters of the evaluation. Material and methods  PET/CT was performed prospectively in 76 consecutive patients with a total of 96 vascular prosthetic grafts in which infection was suspected. PET/CT scans were analysed in terms of the presence and intensity of focal and diffuse FDG uptake, the presence of an anastomotic pseudoaneurysm, the presence of an irregular boundary of infiltration, a combination of these, and the uptake ratio between the graft and blood background. The gold standard was based on operative/histopathological finding or a clinical follow up of >6 months. Results  Among the various assessed parameters only focal FDG uptake and an irregular graft boundary were significant predictors of VPI. Focal intense FDG uptake together with an irregular boundary of the lesion on CT scan predicted VPI with 97% probability, while smooth lesion boundaries and no focal FDG uptake predicted a probability of VPI of less than 5%. Even in lesions with nondiagnostic inhomogeneous focal FDG uptake (18/96) an irregular boundary effectively helped in decision-making with a probability of 28% (smooth) or 77% (irregular) for VPI. Conclusion  PET/CT gave reliable results with an accuracy >95% in 75% of prostheses. PET/CT can identify those prostheses (25% of prosthesis) for which its diagnostic accuracy is diminished to 70–75%. In our series PET/CT was an excellent diagnostic modality for suspected VPI.