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AimsThe ovine stifle is an established model for evaluation of knee treatments, such as meniscus replacement. This study introduces a novel ovine gait simulator for pre-testing of surgical treatments prior to in vivo animal trials. Furthermore, we describe a pilot study that assessed gait kinematics and contact pressures of native ovine stifle joints and those implanted with a novel fiber-matrix reinforced polyvinyl alcohol-polyethylene glycol (PVA-PEG) hydrogel meniscus to illustrate the efficacy of the simulator.MethodsThe gait simulator controlled femoral flexion-extension and applied a 980N axial contact force to the distal tibia, whose movement was guided by the natural ligaments. Five right ovine stifle joints were implanted with a PVA-PEG total medial meniscus replacement, fixed to the tibia via transosseous tunnels and interference screws. Six intact and five implanted right ovine stifle joints were tested for 500 k gait cycles at 1.55 Hz. Implanted stifle joint contact pressures and kinematics in the simulator were compared to the intact group. Contact pressures were measured at 55° flexion using pressure sensitive film inserted sub-meniscally. 3D kinematics were measured optically across two 30-s captures.ResultsPeak contact pressures in intact stifles were 3.6 ± 1.0 MPa and 6.0 ± 2.1 MPa in the medial and lateral condyles (p < 0.05) and did not differ significantly from previous studies (p > 0.4). Medial peak implanted pressures were 4.3 ± 2.2 MPa (p > 0.4 versus intact), while lateral peak pressures (9.4 ± 0.8 MPa) were raised post medial compartment implantation (p < 0.01). The range of motion for intact joints was flexion/extension 37° ± 1°, varus/valgus 1° ± 1°, external/internal rotation 5° ± 3°, lateral/medial translation 2 ± 1 mm, anterior/posterior translation 3 ± 1 mm and distraction/compression 1 ± 1 mm. Ovine joint kinematics in the simulator did not differ significantly from published in vivo data for the intact group, and the intact and implanted groups were comparable (p > 0.01), except for in distraction-compression (p < 0.01).ConclusionThese findings show correspondence of the ovine simulator kinematics with in vivo gait parameters. The efficacy of the simulator to evaluate novel treatments was demonstrated by implanting a PVA-PEG hydrogel medial meniscal replacement, which restored the medial peak contact pressures but not lateral. This novel simulator may enable future work on the development of surgical procedures, derisking subsequent work in live animals.

Purpose: To characterize changes in subfoveal choroidal thickness in preterm infants from 30 to 60 weeks' postmenstrual age (PMA). Design: The prospective, observational Study of Eye Imaging in Preterm infantS (BabySTEPS) enrolled infants eligible for retinopathy of prematurity screening per the American Association of Pediatrics guidelines. Subjects: Infants imaged with an investigational, handheld OCT at ≥ 4 distinct imaging sessions between 30 to 60 weeks' PMA as part of BabySTEPS. Methods: Average choroidal thickness across the central subfoveal 1 mm in each eye at each time point was measured using custom segmentation software, and errors were manually corrected by a trained grader. We prospectively collected birth history data. A segmented mixed model was used to analyze the change in choroidal thickness as a function of PMA, birth weight, and gestational age (GA). Main Outcome Measures: Characterization of normative subfoveal choroidal thickness values and choroidal growth rate between 30 to 60 weeks' PMA. Results: We included 592 imaging sessions of 79 preterm infants (152 eyes). Mean (± standard deviation) GA was 27.5 ± 2.5 weeks. Mean choroidal thickness was 141.4 ± 34.5 μm at 30 weeks, 272.2 ± 83.9 μm at 38 weeks, and 306.2 ± 77.4 μm between 56 and 60 weeks. Between 30 and 60 weeks' PMA, choroidal growth followed a biphasic model, with a linear growth rate of 14.8 μm per week (95% confidence interval [CI], 13.6–16.0) from 30 until 38.4 weeks, then cessation of growth, with a growth rate of 0.3 μm per week (95% CI, −1.1 to 1.6) from 38.4 to 60 weeks. Infants with extremely low birth weight (ELBW; < 1000 g) and extremely preterm (GA < 28 weeks) infants had significantly slower initial growth rates compared with very low and low birth weight and very preterm and preterm infants (ELBW 13.0 vs. 21.0 μm per week; P < 0.0001 and extremely preterm 13.2 vs. 18.0 μm per week; P = 0.003). Conclusions: Preterm infant choroidal thickness experiences rapid linear growth from 30 to 38 weeks' PMA, at which time growth nearly stops. These foundational measurements and identification of the impact of extremes of low birth weight and prematurity on choroidal development will be essential as researchers begin to understand the role of choroidal development in ocular and retinal health in human infants. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.

Purpose: The purpose of this paper is to explore the designed cultural ecology of a hip-hop and computational science, technology, engineering, and mathematics (STEM) camp and the ways in which that ecology contributed to culturally sustaining learning experiences for middle school youth. In using the principles of hip-hop as a CSP for design, the authors question how and what practices were supported or emerged and how they became resources for youth engagement in the space. Design/methodology/approach: The overall methodology was design research. Through interpretive analysis, it uses an example of four Black girls participating in the camp as they build a computer-controlled DJ battle station. Findings: Through a close examination of youth interactions in the designed environment -- looking at their communication, spatial arrangements, choices and uses of materials and tools during collaborative project work -- the authors show how a learning ecology, designed based on hip-hop and computational practices and shaped by the history and practices of the dance center where the program was held, provided access to ideational, relational, spatial and material resources that became relevant to learning through computational making. The authors also show how youth engagement in the hip-hop computational making learning ecology allowed practices to emerge that led to expansive learning experiences that redefine what it means to engage in computing. Research limitations/implications: Implications include how such ecologies might arrange relations of ideas, tools, materials, space and people to support learning and positive identity development. Originality/value: Supporting culturally sustaining computational STEM pedagogies, the article argues two original points in informal youth learning (1) an expanded definition of computing based on making grammars and the cultural practices of hip-hop, and (2) attention to cultural ecologies in designing and understanding computational STEM learning environments.

Aims: Bi-unicondylar arthroplasty (Bi-UKA) is a bone and anterior cruciate ligament (ACL)-preserving alternative to total knee arthroplasty (TKA) when the patellofemoral joint is preserved. The aim of this study is to investigate the clinical outcomes and biomechanics of Bi-UKA. Methods: Bi-UKA subjects (n = 22) were measured on an instrumented treadmill, using standard gait metrics, at top walking speeds. Age-, sex-, and BMI-matched healthy (n = 24) and primary TKA (n = 22) subjects formed control groups. TKA subjects with preoperative patellofemoral or tricompartmental arthritis or ACL dysfunction were excluded. The Oxford Knee Score (OKS) and EuroQol five-dimension questionnaire (EQ-5D) were compared. Bi-UKA, then TKA, were performed on eight fresh frozen cadaveric knees, to investigate knee extensor efficiency under controlled laboratory conditions, using a repeated measures study design. Results: Bi-UKA walked 20% faster than TKA (Bi-UKA mean top walking speed 6.7 km/h (SD 0.9),TKA 5.6 km/h (SD 0.7), p < 0.001), exhibiting nearer-normal vertical ground reaction forces in maximum weight acceptance and mid-stance, with longer step and stride lengths compared to TKA (p < 0.048). Bi-UKA subjects reported higher OKS (p = 0.004) and EQ-5D (p < 0.001). In vitro, Bi-UKA generated the same extensor moment as native knees at low flexion angles, while reduced extensor moment was measured following TKA (p < 0.003). Conversely, at higher flexion angles, the extensor moment of TKA was normal. Over the full range, the extensor mechanism was more efficient following Bi-UKA than TKA (p < 0.028). Conclusion: Bi-UKA had more normal gait characteristics and improved patient-reported outcomes, compared to matched TKA subjects. This can, in part, be explained by differences in extensor efficiency. Cite this article: Bone Joint Res 2021;10(11):723–733.

Aims: In the native hip, the hip capsular ligaments tighten at the limits of range of hip motion and may provide a passive stabilizing force to protect the hip against edge loading. In this study we quantified the stabilizing force vectors generated by capsular ligaments at extreme range of motion (ROM), and examined their ability to prevent edge loading. Methods: Torque-rotation curves were obtained from nine cadaveric hips to define the rotational restraint contributions of the capsular ligaments in 36 positions. A ligament model was developed to determine the line-of-action and effective moment arms of the medial/lateral iliofemoral, ischiofemoral, and pubofemoral ligaments in all positions. The functioning ligament forces and stiffness were determined at 5 Nm rotational restraint. In each position, the contribution of engaged capsular ligaments to the joint reaction force was used to evaluate the net force vector generated by the capsule. Results: The medial and lateral arms of the iliofemoral ligament generated the highest inbound force vector in positions combining extension and adduction providing anterior stability. The ischiofemoral ligament generated the highest inbound force in flexion with adduction and internal rotation (FADIR), reducing the risk of posterior dislocation. In this position the hip joint reaction force moved 0.8° inbound per Nm of internal capsular restraint, preventing edge loading. Conclusion: The capsular ligaments contribute to keep the joint force vector inbound from the edge of the acetabulum at extreme ROM. Preservation and appropriate tensioning of these structures following any type of hip surgery may be crucial to minimizing complications related to joint instability. Cite this article: Bone Joint Res 2021;10(9):594–601.