Abstract-In this paper, a compact printed meandered folded dipole antenna with a volume of 114 mm 3 suitable for implantation in a range of different body tissue types with diverse electrical properties is presented for operation in the 2.36 -2.4 GHz MBAN and 2.4 GHz ISM bands. Its performance was verified and compared against that of a wire dipole and slot loaded monopole antenna in an implant phantom testbed containing tissue equivalent liquids representing body tissues with high and low water content. The antenna was shown to maintain its return loss performance in the 2360 -2400 MHz, 2400 -2483.5 MHz and 2483.5 -2500 MHz frequency bands with equivalent or better performance than a fundamental wire dipole despite having approximately half the physical length.Index Terms-medical body area network, implantable medical devices, implantable antenna, body phantom

Purpose This study aimed to determine whether unrestricted weight-bearing as tolerated (WBAT) following lateral locking plate (LLP) fixation of periprosthetic distal femoral fractures (PDFFs) is associated with increased failure and reoperation, compared with restricted weight-bearing (RWB). Materials and methods In a retrospective cohort study of consecutive patients with unilateral PDFFs undergoing LLP fixation, patients prescribed WBAT were compared with those prescribed 6 weeks of RWB. The primary outcome measure was reoperation. Kaplan–Meier and Cox multivariable analyses were performed. Results There were 43 patients (mean age 80.9 ± 11.7 years, body mass index 26.8 ± 5.7 kg/m2 and 86.0% female): 28 WBAT and 15 RWB. There were more interprosthetic fractures in the RWB group (p = 0.040). Mean follow-up was 3.8 years (range 1.0–10.4). Eight patients (18.6%) underwent reoperation. Kaplan–Meier analysis demonstrated no difference in 2-year survival between WBAT (80.6%, 95% CI 65.3–95.9) and RWB (83.3%, 95% CI 62.1–100.0; p = 0.54). Cox analysis showed increased reoperation risk with medial comminution (hazard ratio 10.7, 95% CI 1.5–80; p = 0.020) and decreased risk with anatomic reduction (hazard ratio 0.11, 95% CI 0.01–1.0; p = 0.046). Immediate weight-bearing did not significantly affect the risk of reoperation compared with RWB (relative risk 1.03, 95% CI 0.61–1.74; p = 0.91). Conclusions LLP fixation failure was associated with medial comminution and non-anatomic reductions, not with postoperative weight-bearing. Medial comminution should be managed with additional fixation. Weight-bearing restrictions additional to this appear unnecessary and should be avoided.

Aims Debate continues regarding the optimum management of periprosthetic distal femoral fractures (PDFFs). This study aims to determine which operative treatment is associated with the lowest perioperative morbidity and mortality when treating low (Su type II and III) PDFFs comparing lateral locking plate fixation (LLP-ORIF) or distal femoral arthroplasty (DFA). Methods This was a retrospective cohort study of 60 consecutive unilateral (PDFFs) of Su types II (40/60) and III (20/60) in patients aged ≥ 60 years: 33 underwent LLP-ORIF (mean age 81.3 years (SD 10.5), BMI 26.7 (SD 5.5); 29/33 female); and 27 underwent DFA (mean age 78.8 years (SD 8.3); BMI 26.7 (SD 6.6); 19/27 female). The primary outcome measure was reoperation. Secondary outcomes included perioperative complications, calculated blood loss, transfusion requirements, functional mobility status, length of acute hospital stay, discharge destination and mortality. Kaplan-Meier survival analysis was performed. Cox multivariate regression analysis was performed to identify risk factors for reoperation after LLP-ORIF. Results Follow-up was at mean 3.8 years (1.0 to 10.4). One-year mortality was 13% (8/60). Reoperation was more common following LLP-ORIF: 7/33 versus 0/27 (p = 0.008). Five-year survival for reoperation was significantly better following DFA; 100% compared to 70.8% (95% confidence interval (CI) 51.8% to 89.8%, p = 0.006). There was no difference for the endpoint mechanical failure (including radiological loosening); ORIF 74.5% (56.3 to 92.7), and DFA 78.2% (52.3 to 100, p = 0.182). Reoperation following LLP-ORIF was independently associated with medial comminution; hazard ratio (HR) 10.7 (1.45 to 79.5, p = 0.020). Anatomical reduction was protective against reoperation; HR 0.11 (0.013 to 0.96, p = 0.046). When inadequately fixed fractures were excluded, there was no difference in five-year survival for either reoperation (p = 0.156) or mechanical failure (p = 0.453). Conclusion Absolute reoperation rates are higher following LLP fixation of low PDFFs compared to DFA. Where LLP-ORIF was well performed with augmentation of medial comminution, there was no difference in survival compared to DFA. Though necessary in very low fractures, DFA should be used with caution in patients with greater life expectancies due to the risk of longer term aseptic loosening. Cite this article: Bone Joint J 2021;103-B(4):635–643.

A wearable stripline-fed circularly polarized dual patch antenna structure that exhibits enhanced into-body gain is presented. The antenna is designed for body-surface repeater solutions and it addresses the problem of marginal into-body deep tissue communication links, where power consumption is of the utmost importance and system link efficiency is critical. Under realistic operation conditions the antenna's circular polarization successfully mitigates implant orientation and polarization mismatch. Polarization loss for linear antennas can be up to 16 dB in anechoic environments and as much as 12.5 dB in a realistic multipath environment, as demonstrated by measured co-and cross-polar forward path gain between implanted and linearly polarized surface antennas. To overcome the body isolating effect of an antenna ground plane and to produce an effective off-body mode, a novel dual aperture stripline feed was developed which also improves the body-mounted antenna radiation efficiency. The antenna provides a 0 dBi off-body gain whilst still maintaining excellent into-body performance. The into-body link was shown to exhibit circular polarization with a maximum isolation of only 1.5 dB between co-and cross-polar measurements in the 2.36-2.4 GHz band. All measurements were carried out using an accurate, next-generation layered phantom tested representative of a wide range of the population.

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