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NASA’S Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at the near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth1. Bennu is a low-albedo B-type asteroid2 that has been linked to organic-rich hydrated carbonaceous chondrites3. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Therefore, the primary mission objective is to return a sample of Bennu to Earth that is pristine—that is, not affected by these processes4. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu’s global properties, support the selection of a sampling site and document that site at a sub-centimetre scale5,6,7,8,9,10,11. Here we consider early OSIRIS-REx observations of Bennu to understand how the asteroid’s properties compare to pre-encounter expectations and to assess the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modelling of Bennu’s thermal inertia12 and radar polarization ratios13—which indicated a generally smooth surface covered by centimetre-scale particles—resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-metre-diameter patches of loose regolith with grain sizes smaller than two centimetres4. We observe only a small number of apparently hazard-free regions, of the order of 5 to 20 metres in extent, the sampling of which poses a substantial challenge to mission success.

Background After an anterior cruciate ligament reconstruction (ACLR), mounting evidence suggests that open kinetic chain (OKC) strengthening is safe, reduces the risk of anterior knee pain, and significantly improves the quadriceps strength. However, clinicians are reluctant to use OKC knee strengthening exercises mainly due to the strong beliefs that they might increase graft laxity. The objective of this scoping review is to identify the key criteria employed in the scientific literature for the safe introduction of OKC quadriceps strengthening following ACLR. Methods A scoping review of the literature was conducted on the online databases MEDLINE (PubMed), ScienceDirect, Embase and CINAHL Library online. Data regarding time-based criteria and/or clinical based criteria allowing OKC exercises introduction following ACLR were searched for. Only studies involving patients who performed quadriceps strengthening using any type of OKC exercises were included, regardless of the type, resistance location, load magnitude, type of muscle contraction, knee range of motion, or duration of the strengthening protocol. Results Twenty-six studies met the inclusion criteria. Twenty-one employed time-based criteria for the introduction of OKC exercise. The median time from when OKC was permitted was 15 postoperative days (range 1–270 days), while the mean time was 31.6 ± 56.7 postoperative days. In 30.7% of the studies additional clinical examination components were used. These components included range of motion (0-100°), numeric pain scale score < 2 or 3, absence of joint effusion (assess by the stroke test), full knee active extension (assess by the straight leg raise), and walking without crutches for the decision-making regarding OKC exercise introduction. Conclusion Less than one study in 3 reported clinical criteria for the introduction of OKC exercise. This highlights the absence of consensus among surgeons and physiotherapists, thereby hindering their ability to make informed decisions based on scientific evidence. Although the use of OKC exercise appears to be safe, precautions to maintain the integrity of the surgical repair need to be implemented. The establishment of valid criteria is crucial to support evidence-based decision-making. Key Points Open kinetic chain (OKC) exercises are generally safe and can significantly improve quadriceps strength without increasing the risk of graft laxity after anterior cruciate ligament reconstruction (ACLR). The majority of studies (80.7%) used time-based criteria for introducing OKC exercises, with a median time of 15 postoperative days. Combining clinical and temporal criteria ensures safe and effective integration of OKC exercises in ACLR rehabilitation.

To determine whether quadriceps and hamstring strengthening in a rehabilitation program involving early open kinetic chain (OKC) and/or closed kinetic chain (CKC) knee joint exercises had an influence on graft laxity at 1, 3, and 6 months after anterior cruciate ligament reconstruction (ACLR). Retrospective study. Two groups (n = 53) of ACLR patients (combination of OKC and CKC exercises group compared to a CKC exercise group) were recruited. OKC protocol was introduced at 2 weeks post-operatively without external resistance and progressed at 4 weeks with load. Comparative ACL graft laxity measurement and isokinetic strength testing were prospectively performed up to 6 months in both groups. No significant differences were observed in the knee laxity at 1 (p = 0.263), 3 (p = 0.263), and 6 months (p = 0.256) follow up between the groups. Similarly, no significant results were observed in within-group knee laxity between 1 and 6 months after ACLR in the intervention (p = 0.155) and control group (p = 0.690). The early initiation of OKC along with CKC exercises doesn't seem to increase the ACLR graft laxity as compared to a rehabilitation program with only CKC exercises. •Early OKC can be used in full ROM and seems to be safe•Early OKC following specific inclusion criteria did not show any complications•Early high volume training should be introduced with OKC and CKC after surgery•Early high volume training seems to be safe

Background: Open kinetic chain (OKC) exercise is an effective method to improve muscle function during rehabilitation after anterior cruciate ligament reconstruction (ACLR); however, there is controversy about its use in the early phase of rehabilitation. Purpose: To determine (1) whether the use of OKC and closed kinetic chain (CKC) exercises improves quadriceps and hamstring strength in the early phase of rehabilitation after ACLR and (2) whether the early use of OKC exercise affects graft laxity at 3 and 6 months postoperatively in patients with a hamstring tendon graft. Study Design: Cohort study; Level of evidence, 3. Methods: This study included an intervention group that underwent OKC + CKC exercises (n = 51) and a control group that underwent CKC exercise only (n = 52). In the intervention group, OKC exercise for the quadriceps and hamstring was started at 4 weeks after ACLR. At 3 and 6 months postoperatively, isokinetic testing was performed to calculate the limb symmetry index (LSI) and the peak torque to body weight ratio (PT/BW) for the quadriceps and hamstring. Anterior knee laxity was measured by an arthrometer. Results: At 3 and 6 months postoperatively, quadriceps strength was higher in the intervention group than in the control group for the LSI (3 months: 76.14% ± 0.22% vs 46.91% ± 0.21%, respectively; 6 months: 91.05% ± 0.18% vs 61.80% ± 0.26%, respectively; P < .001 for both) and PT/BW (3 months: 1.81 ± 0.75 vs 0.85 ± 0.50 N·m/kg, respectively; 6 months: 2.40 ± 0.73 vs 1.39 ± 0.70 N·m/kg, respectively; P < .001 for both). There were similar findings regarding hamstring strength for the LSI (3 months: 86.13% ± 0.22% vs 64.26% ± 0.26%, respectively; 6 months: 91.90% ± 0.17% vs 82.42% ± 0.24%, respectively; P < .001 at three months, P = .024 at 6 months) and PT/BW (3 months: 1.09 ± 0.36 vs 0.67 ± 0.39 N·m/kg, respectively; 6 months: 1.42 ± 0.41 vs 1.07 ± 0.39 N·m/kg, respectively; P < .001 for both). No significant difference in laxity was observed between the intervention and control groups at 3 or 6 months. Conclusion: Early use of OKC exercise for both the quadriceps and the hamstring, in addition to conventional CKC exercise, resulted in better correction of quadriceps and hamstring strength deficits without increasing graft laxity.