A Safe Overhang Limit for Unicompartmental Knee Arthroplasties Based on Medial Collateral Ligament Strains : An In Vitro Study

Excessive tibial component overhang during unicompartmental knee arthroplasty (UKA) may cause medial collateral ligament (MCL) impingement, which, in turn, may lead to medial knee pain [Chau et al. Tibial component overhang 226 following unicompartmental knee replacement—does it matter? The Knee. 2009;16(5):310-3]. This study examines MCL loads in 6 human cadaveric knees for different levels of overhang using a robotic testing system. The results indicated no statistically significant difference between the baseline MCL load (no overhang) and the 2-mm overhang (P = .261). However, there were significant differences in MCL load between 2- vs 4-mm (P = .012) and 2- vs 6-mm overhang (P = .022). The loads were almost doubled from 2 to 4 mm of overhang. We conclude that, to minimize pain from excessive MCL loading, surgeons should avoid tibial component overhang greater than 2 mm in unicompartmental knee arthroplasties.     

悬突及其与牙周病关系的调查研究

目的 :评价窝洞充填并发悬突的影响因素 ,分析其与牙周病的关系 ,并提出防治措施。方法 :采用流行病学调查方法 ,收集 1998年 7月至 12月间来本院就诊并确诊窝洞充填一年以上的 180 0颗后牙临床病例 ,就其并发悬突的相关资料进行综合分析。结果 :悬突的发生与年龄、性别、就诊医院及充填时间无明显关系 ;不同材料 ,不同洞型悬突发生率不同 ,且均有统计学意义 ;邻近悬突处的GI、PD明显高于对照组 ,且与充填时间和充填材料相关。结论 :悬突的发生以银汞合金最高 ,好发于II类洞 ;悬突对牙周的损害程度与充填时间及充填材料密切相关。     

Tibial component overhang following unicompartmental knee replacement—Does it matter?

As implants are made in incremental sizes and usually do not fit perfectly, surgeons have to decide if it is preferable to over or undersize the components. This is particularly important for unicompartmental knee replacement (UKR) tibial components, as overhang may cause irritation of soft tissues and pain, whereas underhang may cause loosening.One hundred and sixty Oxford UKRs were categorised according to whether they had minor (< 3 mm, 70%) or major (≥ 3 mm, 9%) tibial overhang, or tibial underhang (21%). One year post surgery, there was no significant difference in outcome between the groups. Five years after surgery, those with major overhang had significantly worse Oxford Knee Scores (OKS) (p = 0.001) and pain scores (p = 0.001) than the others. The difference in scores was substantial (OKS = 10 points). There was no difference between the ‘minor overhang’ and the ‘underhang’ group.We conclude that surgeons must avoid tibial component overhang of 3 mm or more, as this severely compromises the outcome. Although this study showed no difference between minor overhang or underhang, we would advise against significant underhang because of the theoretical risk of component subsidence and loosening.     

The Effects of Overhang Forming Direction on Thermal Behaviors during Additive Manufacturing Ti-6Al-4V Alloy

Selective laser melting was recently introduced to fabricate complex parts that are likely to contain overhangs. Process parameters, scanning strategies, support structures, and fast prediction techniques are being frequently studied, but little information about overhang forming direction has been reported. In this study, the effects of overhang forming direction in the working plane on temperature evolution and distortion processes during selective laser melting of Ti-6Al-4V alloy were examined by means of numerical simulation and experimental verification. We found that forming from different directions can lead to significant differences in the early stage of the overhang building process, which were verified by both the simulations and the experiment. Some analyses were performed when enough layers had been built and suggestions are also given.     

Posterior Bearing Overhang Following Medial and Lateral Mobile Bearing Unicompartmental Knee Replacements

This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement (OUKR) (Oxford Phase 3, Zimmer Biomet). The Oxford components are designed to be fully congruent, however knee movements involve femoral rollback, which may result in bearing overhang at the posterior margin of the tibial implant, with potential implications for; pain, wear, and dislocation. Movement is known to be greater, and therefore posterior overhang more likely to occur, with; lateral compared to medial implants, anterior cruciate ligament (ACL) deficiency (ACLD) compared to ACL intact (ALCI), and at extremes of movement. Twenty‐four medial, and 20 domed lateral, OUKRs underwent sagittal plane knee fluoroscopy during step‐up and forward lunge exercises. The bearing position was inferred from the relative position of the femoral and tibial components. On the basis of the individual component sizes and geometry the extent the posterior part of the bearing which overhung the posterior part of the tibial component was calculated. There was no significant posterior overhang in knees with medial implants. Knees with lateral domed implants exhibited overhang at flexion angles beyond 60°, the magnitude of which increased with increasing flexion angle, reaching a maximum of 50% of the bearing length at 140° (range 0–140°). This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1938–1945, 2019     

Morphometric Assessment of Resected Femoral Cut Surface in Korean Knees and Its Fitting With Western-Designed Femoral Components

BackgroundThis study aimed at assessing the morphometry of resected femurs in Korean patients during total knee arthroplasty (TKA) and comparing these measurements with current Western-designed femoral component dimensions.MethodsThis single-blind, prospective, randomized, controlled trial involved intraoperative measurements for 271 femoral component implantations from 3 contemporary TKA systems, with 2 systems offering narrow sizing options. The difference between femoral component dimensions and the resected surface of distal femur was measured in millimeters at 5 distinct zones.ResultsOverhang of standard femoral component was common in the anterior-medial condyle and anterior-lateral condyle ranging from 50.8% to 99.0% and 21.5% to 88.0%, respectively. With narrow femoral components, the rate of overhang reduced to 21.5%-30.2% and 9.2%-32.1%. Conversely, underhang rates were higher over the anterior flange width, middle medial-lateral and posterior medial-lateral zones. Standard components displayed higher underhang rates at these zones compared to narrow components. The good fit rate for femoral component was low among the 3 systems ranging from 1.0% to 56.0%. System with narrow option sizing increases the underhang rates in males, while improving the component fit among females at similar zones with rate ranging from 5.2% to 52.9%.ConclusionCurrently available TKA implant designs may not provide a perfect match for the distal femoral shape of the Korean population. The availability of implants with standard and narrow options can substantially improve the optimal fitting of femoral components in the Korean population.     

Telomeric 3' overhangs in chronic HBV-related hepatitis and hepatocellular carcinoma

Telomeric 3' overhang is a key component of telomere structure, but little is known about its role in hepatocarcinogenesis. We examined the 3' overhang and telomere length, mRNA levels of hTERT, POT1, TRF1 and cytokeratin 19 (CK19) in 41 hepatitis B virus (HBV)-related hepatocellular carcinomas (HCCs) and adjacent non-HCCs of B viral chronic hepatitis/cirrhosis. 3' overhang length was positively correlated with telomere length (p < 0.001). In non-HCCs, the 3' overhang shortened with increasing age (p = 0.043). Twenty-six HCCs had shorter and 15 HCCs had longer 3' overhangs than the adjacent non-HCCs. The mRNA levels of hTERT, POT1 and TRF1 were upregulated in HCCs than in non-HCCs. HCCs with lengthened 3' overhangs expressed higher hTERT mRNA levels than those with shortened 3' overhangs, when compared to 3' overhangs in non-HCCs (p = 0.044). POT1 and TRF1 showed no significant difference according to the 3' overhangs. HCCs with long 3' overhangs had higher mitosis (p = 0.046) and more frequent multipolar mitosis compared to those with short 3' overhangs (p = 0.034). HCCs with high cytokeratin 19 mRNA levels, a marker for hepatic progenitor cells, had longer 3' overhangs than HCCs with low cytokeratin 19 mRNA levels (p= 0.019). In conclusion, the 3' overhang erosion might be closely related to the number of cell divisions in telomerase-negative hepatocytes of chronic hepatitis/cirrhosis. In telomerase-positive HCCs, an altered 3' overhang are involved in HBV-related hepatocarcinogenesis and hTERT might be involved in regulation of 3' overhang.     

Variation of the 3' telomeric overhang lengths in human cells

The telomeric G-rich 3' overhang is important for the maintenance of chromosomal integrity by stabilizing T-loop structure in which the 3' overhang invades the double-stranded telomeric DNA. However, the 3' overhang length has not been examined in different human cell lines, and its regulatory mechanism has not been revealed. In this study, we examined overhang length in 56 human cancerous cell lines and five normal cell lines, originated from various tissues. In cancer cells, relative overhang length existed in a wide range from 23% to 308% and showed no significant association with tissue types although short overhang was noted in brain, cervix, and colorectal cells. Normal cells exhibited overhangs in the range from 92% to 202%, which were relatively longer than those seen in cancer cells (p = 0.002). The overhang length was positively correlated with telomere length (p < 0.001), and showed no correlation with mRNA levels of hTERT, a catalytic protein of telomerase, POT1, an overhang binding protein and TPP1, a POT1 interacting protein. This study demonstrates a broad distribution of overhang length in human cells, suggesting a dynamic regulation of 3' overhang length. The overhang length seems to be closely associated with telomere length and might be regulated by multiple mechanisms.     

Contact-Free Support Structures for the Direct Metal Laser Melting Process

Although Direct Metal Laser Melting (DMLM), a powder bed fusion (PBF) Additive Manufacturing (AM) for metallic materials, provides many advantages over conventional manufacturing such as almost unlimited design freedom, one of its main limitations is the need for support structures beneath overhang surfaces. Support structures are generally in contact with overhang surfaces to physically prop them up; therefore, they need to be removed after manufacturing due to not constituting a part of the main component design. The removal of supports is a process sequence adding extra time and cost to the overall manufacturing process and could result in damaging the main component. In this study, to examine the feasibility of contact-free supports for overhang surfaces in the DMLM process, coupons with these novel types of supports were prepared from CoCrMo alloy powder. This study aims to understand the effect of two parameters: the gap distance between supports and overhang surfaces and the inclination angle of overhang surfaces, on the surface topography and microstructural properties of these surfaces. Visual inspection, roughness measurements, and optical microscopy were utilized as characterization methods The roughness parameters (Ra, Rq, and Rz) were obtained using the focus variation method, and optical microscope analysis was performed on the cross-sections of the overhang surfaces to investigate the sub-surface microstructure and surface topology. Results showed that contact-free supports have a positive effect on decreasing surface roughness at all build angles when the gap distance is correctly set to avoid sintering of the powder in between the overhang and supports or to avoid too large gaps eliminating the desired effect of the higher thermal conductivity.     

Effect of Acetabular Component Positioning on Functional Outcomes in Primary Total Hip Arthroplasty

Background

Acetabular component positioning is crucial to a successful total hip arthroplasty (THA). This study evaluated the effect of absolute acetabular component position as well as acetabular position relative to bony anatomy on patient-reported functional outcomes after primary THA.