The influence of implant design and limb alignment on in vivo wear rates of fixed-bearing and rotating-platform knee implant retrievals.

Analysis of polyethylene (PE) wear in knee implants is crucial for understanding the factors leading to revision in total knee arthroplasty. Importantly, current experimental and computational methods for predicting insert wear can only be validated against true in vivo measurements from retrievals. This study quantitatively investigated in vivo PE wear rates in fixed-bearing (FB) (n = 21) and rotating-platform (n = 53) implant retrievals. 3D surface geometry of the retrievals was measured using a structured light scanner. Then, a reference surface that included the deformation, but not the wear that the retrievals had experienced in vivo, was constructed using a fully automatic surface reconstruction algorithm. Finally, wear volume was calculated from the deviation between the worn and reconstructed surfaces. The measurement and analysis techniques were validated and the algorithm was found to produce errors of only 0.2% relative to the component volumes. In addition to quantifying cohort-level wear rates, the effect of mechanical axis limb alignment on mediolateral wear distribution was examined for a subset of the retrievals (n = 14 + 26). Our results show that FB implants produce significantly (p = 0.04) higher topside wear rates (24.6 ± 10.1 mm3/year) than rotating-platform implants (15.3 ± 8.0 mm3/year). This effect was larger than that of limb alignment, which had a smaller and nonsignificant influence on overall wear rates (+4.5 ± 11.6 mm3/year, p = 0.43). However, increased varus alignment was associated significantly with greater medial compartment wear in both the FB and rotating-platform designs (+1.7 ± 1.3%/° and +1.8 ± 1.6%/°). Our findings emphasize the importance of implant design and limb alignment on wear outcomes, providing reference data for improving implant performance and longevity.

Cognitive and biomarker responses in healthy older adults to a 18-hole golf round and different walking types: a randomised cross-over study.

Introduction: The global burden of age-related cognitive decline is increasing, with the number of people aged 60 and over expected to double by 2050. This study compares the acute effects of age-appropriate cognitively demanding aerobic exercises involving walking, on cognitive functions and exerkine responses such as brain-derived neurotrophic factor (BDNF) and cathepsin B (CTSB) in older, healthy adults. Methods/design: Healthy older golfers (n=25, 16 male and 9 female, 69±4 years) were enrolled in a 5-day randomised cross-over study and completed three different exercise trials (18-hole golf round, 6 km Nordic walking, 6 km walking) in a real-life environment, in random order and at a self-selected pace. Differences in cognition (the Trail-Making Test (TMT) AB) and exerkines (BDNF and CTSB) were analysed within groups using the Wilcoxon signed-rank test and between groups using the Kruskal-Wallis test. Results: All exercise types resulted in a significant decrease in the TMT A-test (p<0.05; golf: -4.43±1.5 s, Nordic walking: -4.63±1.6 s, walking: -6.75±2.26 s), where Nordic walking and walking demonstrated a decrease in the TMT B-test (p<0.05; Nordic walking: -9.62±7.2 s, walking: -7.55±3.2 s). In addition, all exercise types produced significant decreases in the TMT AB test scores (p<0.05), and Nordic walking (p=0.035) showed decreases in the TMTB-TMTA-test. There were no immediate postexercise changes in the levels of BDNF or CTSB. Conclusion: Acute bouts of golf, Nordic walking and walking improved cognitive functions irrespective of exerkines in healthy older adults. In addition, Nordic walking and walking in general enhanced executive functions. No significant effects were seen on the levels of BDNF and CTSB. Trial registration number: ISRCTN10007294.

Is malunion of the greater tuberosity after reverse shoulder arthroplasty in patients with complex proximal humerus fracture associated with worse clinical outcomes? A prospective cohort study.

PURPOSE: To assess patient outcomes following reverse shoulder arthroplasty in patients with complex proximal humerus fracture and the clinical implications of greater tuberosity malunions. METHODS: This prospective study included 56 patients who underwent RSA (DELTA XTEND™, DePuy Synthes, Warsaw, IN, USA) to treat proximal humerus fractures. We used a standardized suture technique to reattach the tuberosities. Demographic, comorbidity, and radiological parameters were collected. Assessments at 2-year follow-up (n = 49) are given as follows: range of motion (ROM), pain level, Constant Murley scores (CS), subjective shoulder value (SSV), and tuberosity healing. RESULTS: Anatomic tuberosity healing was achieved in 31 (55%) patients (group 1), 14 (25%) had a malunion (group 2), and complete migration occurred in 11 (20%) (group 3). No statistically significant differences between groups 1 and 2 were detected: CS (p = 0.53), SSV (p = 0.07), ROM (forward flexion (FF) p = 0.19, internal rotation (IR) p = 0.34, and external rotation (ER) p = 0.76). Group 3 had poorer outcomes (median [IQR]) than group 1: CS (59 [50-71]) vs. 72 [65-78]), FF (120 [100-150]) vs. 150 [125-160] and ER (- 20 [- 20 to 10] vs. 30 [20-45], respectively. Three complications (group 1) occurred: one-stage revision after low-grade infection, haematoma due to early rivaroxaban intake, and open reduction and internal fixation for acromion insufficiency fracture. No patients showed signs of stem or glenoid loosening after 2 years. CONCLUSION: Cases with complete superior migration experienced poorer clinical outcomes than those with anatomic healing. Despite a relatively high malunion rate, the outcomes were not significantly worse in these patients compared to anatomically healed GT cases.

Comparable in vivo joint kinematics between self-reported stable and unstable knees after TKA can be explained by muscular adaptation strategies: A retrospective observational study.

Background: Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to total knee arthroplasty (TKA) revision. Nevertheless, subjective knee instability is not well defined clinically, plausibly because the relationships between instability and implant kinematics during functional activities of daily living remain unclear. Although muscles play a critical role in supporting the dynamic stability of the knee joint, the influence of joint instability on muscle synergy patterns is poorly understood. Therefore, this study aimed to understand the impact of self-reported joint instability on tibiofemoral kinematics and muscle synergy patterns after TKA during functional gait activities of daily living. Methods: Tibiofemoral kinematics and muscle synergy patterns were examined during level walking, downhill walking, and stair descent in eight self-reported unstable knees after TKA (3M:5F, 68.9 ± 8.3 years, body mass index [BMI] 26.1 ± 3.2 kg/m2, 31.9 ± 20.4 months postoperatively), and compared against 10 stable TKA knees (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2). For each knee joint, clinical assessments of postoperative outcome were performed, while joint kinematics were evaluated using moving video-fluoroscopy, and muscle synergy patterns were recorded using electromyography. Results: Our results reveal that average condylar A-P translations, rotations, as well as their ranges of motion were comparable between stable and unstable groups. However, the unstable group exhibited more heterogeneous muscle synergy patterns and prolonged activation of knee flexors compared to the stable group. In addition, subjects who reported instability events during measurement showed distinct, subject-specific tibiofemoral kinematic patterns in the early/mid-swing phase of gait. Conclusions: Our findings suggest that accurate movement analysis is sensitive for detecting acute instability events, but might be less robust in identifying general joint instability. Conversely, muscle synergy patterns seem to be able to identify muscular adaptation associated with underlying chronic knee instability. Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

The Biomechanics of Cartilage-An Overview.

Articular cartilage (AC) sheathes joint surfaces and minimizes friction in diarthrosis. The resident cell population, chondrocytes, are surrounded by an extracellular matrix and a multitude of proteins, which bestow their unique characteristics. AC is characterized by a zonal composition (superficial (tangential) zone, middle (transitional) zone, deep zone, calcified zone) with different mechanical properties. An overview is given about different testing (load tests) methods as well as different modeling approaches. The widely accepted biomechanical test methods, e.g., the indentation analysis, are summarized and discussed. A description of the biphasic theory is also shown. This is required to understand how interstitial water contributes toward the viscoelastic behavior of AC. Furthermore, a short introduction to a more complex model is given.

Limited reliability of grading scapular notching according to Nerot-Sirveaux on anteroposterior radiographs.

INTRODUCTION: Incidences of scapular notching (SN) in reverse shoulder arthroplasty (RSA) range between 0% and 96%, and controversy remain as to its relevance for patient outcome. We assessed the reliability of scapular notching (SN) grading based on the Sirveaux classification system using anteroposterior radiographs. MATERIALS AND METHODS: 206 RSA procedures with 5-year postoperative anteroposterior shoulder radiographs were classified independently by seven assessors according to Sirveaux (session 1). After a review meeting, three assessors re-classified the radiographs along with quality criteria (session 2). SN grading by the majority of assessors was taken as the reference. Classification interobserver reliability was analyzed using Kappa statistics. RESULTS: The incidence of SN was estimated at 53% and 37% at the first and second sessions, respectively. Interobserver reliability Kappa coefficients resulting from the first and second sessions were 0.27 and 0.43, respectively. Case selection based on radiographic quality criteria did not improve SN grading reliability in the second session. CONCLUSION: Agreement between individual surgeons was low when grading SN in RSA according to Sirveaux using anteroposterior radiographs. Consensus among several assessors may increase reliability in research settings.

Effect of plane of arm elevation on glenohumeral kinematics: a normative biplane fluoroscopy study.

BACKGROUND: Understanding glenohumeral motion in normal and pathologic states requires the precise measurement of shoulder kinematics. The effect of the plane of arm elevation on glenohumeral translations and rotations remains largely unknown. The purpose of this study was to measure the three-dimensional glenohumeral translations and rotations during arm elevation in healthy subjects. METHODS: Eight male subjects performed scaption and forward flexion, and five subjects (three men and two women) performed abduction, inside a dynamic biplane fluoroscopy system. Bone geometries were extracted from computed tomography images and used to determine the three-dimensional position and orientation of the humerus and scapula in individual frames. Descriptive statistics were determined for glenohumeral joint rotations and translations, and linear regressions were performed to calculate the scapulohumeral rhythm ratio. RESULTS: The scapulohumeral rhythm ratio was 2.0 ± 0.4:1 for abduction, 1.6 ± 0.5:1 for scaption, and 1.1 ± 0.3:1 for forward flexion, with the ratio for forward flexion being significantly lower than that for abduction (p = 0.002). Humeral head excursion was largest in abduction (5.1 ± 1.1 mm) and smallest in scaption (2.4 ± 0.6 mm) (p < 0.001). The direction of translation, as determined by the linear regression slope, was more inferior during abduction (-2.1 ± 1.8 mm/90°) compared with forward flexion (0.1 ± 10.9 mm/90°) (p = 0.024). CONCLUSIONS: Scapulohumeral rhythm significantly decreased as the plane of arm elevation moved in an anterior arc from abduction to forward flexion. The amount of physiologic glenohumeral excursion varied significantly with the plane of elevation, was smallest for scaption, and showed inconsistent patterns across subjects with the exception of consistent inferior translation during abduction.

Factors influencing intra-articular fluid temperature profiles with radiofrequency ablation.

BACKGROUND: Radiofrequency ablation devices are being used increasingly in arthroscopic surgery. However, there are concerns that excessive temperatures may damage the articular cartilage. The purpose of this study was to investigate the temperature profiles that occur within the glenohumeral space with the use of one commercially available radiofrequency ablation probe. METHODS: Ten fresh-frozen human cadaver shoulder specimens were used. Intra-articular temperatures were measured at different time intervals over a two-minute period at a distance of 1, 3, 5, and 10 mm away from the probe. The radiofrequency probe was activated throughout the range of machine power settings, and irrigation fluid flow was varied (no flow, a flow at 60 mm Hg without suction, and a flow at 60 mm Hg with suction). RESULTS: Temperatures deleterious to articular cartilage chondrocytes (i.e., those in excess of 50 degrees C) were seen with an increased duration of application, a decreased distance between the thermometer and the probe, and a decreased irrigation fluid flow rate. The highest recorded irrigation fluid temperature reached >80 degrees C after two minutes in a no-flow setting. The flow rate was found to be the most significant predictor of intra-articular temperature profiles. The various machine power settings had no apparent influence on temperature, meaning that higher probe settings are not necessarily associated with higher temperature profiles. CONCLUSIONS AND CLINICAL RELEVANCE: These results demonstrate the importance of the management of the irrigation fluid flow rate across the joint during arthroscopic procedures that involve radiofrequency ablation. Even short intervals of limited flow could lead to supraphysiological temperature profiles and potentially to cartilage damage.