Bioprinting that can quickly generate custom-shaped organ-like constructs opens up a new horizon for tissue engineering and regenerative medicine. The importance of bioinks cannot be overemphasized in advancing bioprinting development. Superior to conventional static bioink, dynamic bioink, mimicking the natural extracellular matrix, possesses reversible dynamic molecular networks that provide cellular activity and growth and thus enhance the maturation of bioprinted organ-like constructs, which has gained lots of attention and developed rapidly in the past decade. This paper completely summarizes the progress of dynamic bioink in bioprinting. First, we outline the molecular design principle of dynamic bioinks, involving two main patterns: supramolecular force and reversible chemical bonding. Then, key factors of dynamic bioinks in advancing bioprinting, including printability, structural stability, and modulation of cell behavior, are highlighted. Finally, the review further discusses the challenges and perspectives in fabricating tissues and organs with dynamic bioinks, aiming to offer an illuminating insight into bioprinting.

Regeneration of articular cartilage defects remains challenging owing to its inherently limited endogenous cell source and self-renewal capacity. Although cell therapy has shown promise in regenerating articular cartilage, maintaining cellular functional activity and precisely delivering cells to the defect site remain significant obstacles. Herein, we present a bioprinting strategy to fabricate a cartilage precursor cell (CPCs)-loaded gelatin-based scaffold, which can precisely deliver cells, maintain cellular function, and thus enhance cartilage regeneration. First, benefiting from the modification of quadruple-hydrogen-bonded ureyl pyrimidinone (UPy), gelatin modified with UPy (Gel-UPy) bioink demonstrated a temperature-programmable viscosity, enabling cell-holding stability during the printing process, and extrudable printability at a near physiological temperature. Then, through the enzymatic solidification of transglutaminase (TG), the bioprinted cell-laden scaffold (Gel-UPy@TG) was enhanced in substantial mechanical stability while maintaining a high cell survival rate. Finally, when implanted in a full-layer cartilage defect model of rabbit femoral trochlea, the bioprinted scaffold preserved the chondrogenic capacity of CPCs in the defect site and communicated with the surrounding cells, thereby accelerating the repair process of cartilage defects.

This study aimed to elucidate the correlation between the degree of fat infiltration (FI) in thoracic paraspinal muscles and thoracic vertebral degeneration (TVD). This cross-sectional study comprised 474 patients who underwent standard thoracic computed tomography (CT) scans. The FI was quantified as the percentage of adipose tissues within the cross-sectional area of thoracic paraspinal muscles. Thoracic vertebra was assessed in terms of osteoporosis, ossification of the anterior longitudinal ligament (OALL), ossification of the posterior longitudinal ligament (OPLL), intervertebral disc calcification, intervertebral disc cavity, and facet joint osteoarthritis (FJO). Logistic regression, linear regression, subgroup, and receiver operating characteristic (ROC) analyses were assessed to evaluate the association between FI and TVD. Multivariate logistic regression revealed that more severe FI was closely associated with more serious osteoporosis (P < 0.001). Furthermore, after adjusting for only age, higher FI was significantly associated with nastier FJO (P < 0.05). In male patients, severe FI was greatly associated with worse osteoporosis (P < 0.05). In female patients, severe FI maintained close correlations with more severe osteoporosis and FJO (P < 0.05). Furthermore, in patients aged < 60 or ≥ 60 years, higher FI had a strong correlation with more severe osteoporosis (P < 0.001). In patients aged < 60 years, higher FI was associated with worse intervertebral disc calcification, OALL, and FJO (P < 0.05). Meanwhile, in patients aged ≥ 60 years, increased FI was only associated with severe OPLL (P < 0.05). Multivariate linear regression showed that FI negatively correlated with bone mineral density in the general population and different sex and age groups (P < 0.001). ROC analysis indicated that FI could predict the occurrence of TVD (P < 0.05). Higher FI is associated with more severe TVD. Studies on TVD are currently limited; therefore, this study enriches the related research on TVD, and our findings would facilitate the early prediction and diagnosis of TVD in clinical practice. Furthermore, our findings indicate that thoracic spine pain (TSP) caused by TVD can be prevented, potentially improving the prognosis of patients with TSP.

Distraction osteogenesis, or the Illizarov technique, induces bone regeneration using distractive mechanical forces. Nevertheless, Wolff's law holds that bone adapts to reverse compressive mechanical loads, growing denser in areas of high pressure and resorbing in zones of low pressure. These two forms of new bone formation together suggest that mechanical stimuli play an important role in bone remodeling and regeneration. The therapeutic efficacy of distraction osteogenesis has been recognized in orthopedics and maxillofacial surgeries. Distraction osteogenesis was even used for the regeneration of various other tissues/organs, such as blood vessels and skin (e.g., in the treatment of limb ischemic diseases and foot ulcers), suggesting the principle of distraction histogenesis. However, the underlying mechanisms, particularly those of the cross-organ effects and in terms of mechanotransduction, remain poorly understood. Thus, this review aims to explore the recent advances in research on musculoskeletal regeneration and its association with mechanosensitive channels from a new interdisciplinary application perspective. The contents can provide insights into potential research directions for understanding the molecular mechanisms of musculoskeletal regeneration and its clinical applications.

The musculoskeletal system, the primary load-bearing structure of the human body, plays a crucial role in mechanotransduction, a process comprising mechanosensation, mechanotransduction, and mechanical effect. Aging leads to loss of ability of mechanosensitive cells to sense mechanical stimuli, disruption of transduction pathways, SASP and adiposity accumulation. At the mesoscopic level, bone, cartilage, and muscle differentiation decline, while adipogenesis increases, leading to extracellular matrix and structural aging, ultimately manifesting as macroscopic musculoskeletal degeneration. This review explores intercellular crosstalk and mechanotransduction alterations in aging from a mechanobiological perspective, providing insights into potential therapeutic targets for bone aging and osteoporosis. It also introduces the mesoscopic scale definition and trans mesoscopic transplantation therapy as novel strategies for fracture treatment, postoperative rehabilitation, and bone regeneration, offering innovative directions for future musculoskeletal research. The translational potential of this article:This article systematically reviews the effects of aging on the musculoskeletal system from a mechanobiological viewpoint, covering from microscopic molecular signaling to macroscopic spatial structural alterations, and proposes new strategies to complement the principles of AO therapy, optimization of braking, new insights into tumor metastasis and weight-bearing, and a new strategy for trans mesoscopic transplantation therapy. These insights will contribute to optimizing the management of geriatric fragility fractures in the elderly, exploring innovative therapies for the treatment of diseases of the aging musculoskeletal system, and facilitating the development of integrative therapies and precision medicine in the field of orthopaedics.

Bone loss and microstructural destruction in elderly men are associated with fractures and high mortality. While testosterone (Tes) is considered to be possibly protective, its regulatory mechanism in bone remodeling remains unclear. Here, bone microarchitectural analysis indicates that elderly men exhibit reduced cortical and trabecular thickness with elevated cortical porosity, particularly at the superior femoral head near the medial acetabulum. Serum profiling of 352 individuals showed that low Tes levels (<9.415 nmol·L −1 ) are associated with higher risk of bone loss. In vivo, tail‐suspended mice lacking osteoblastic androgen receptor (AR) displayed similar femoral deterioration, with decreased trabecular bone and increased cortical porosity. Mechanistically, Tes enhances osteoblastic differentiation via AR‐mediated upregulation of tenascin‐C (TNC). Molecular docking suggests the fibrinogen C‐terminal domain of TNC inhibits osteoclastogenesis by binding integrin αV, blocking adhesion of RGD‐containing proteins. A synthetic peptide (pep2) mimicking this domain preserved bone architecture in osteoblast‐specific Ar ‐knockout, tail‐suspended mice. Moreover, elevated serum extracellular vesicle amyloid precursor protein, secondary to Tes‐AR‐TNC decline and osteoclast overactivation, emerged as a biomarker of bone loss when combined with low Tes. This study identifies the Tes‐AR‐TNC axis as a key regulator of male bone remodeling, offering insights into fracture risk assessment and targeted interventions in bone destruction.

ObjectiveTo compare the biomechanical characteristics of axial traction and suspensory traction in the process of preoperative correction of cervical kyphosis.MethodsAn intact three-dimensional finite element digital model of C2-T2 with cervical kyphosis was established. The head gravity and moment were applied to the finite element model to simulate the force of skull traction and the force of suspensory traction. The changes of cervical kyphotic angle, the length of cervical spinal canal and the stress distribution of each vertebral body were analyzed under two traction modes.ResultsThe kyphotic angles of the kyphotic segments were reduced by both tractions. The C2-C5 kyphotic angle was 41° before traction, and decreased to 32° and 26° after axial traction and suspensory traction, respectively. The length of C3-C7 cervical spinal canal was 61.3 mm before traction. After axial traction, the length of C3-C7 cervical spinal canal increased to 61.8 mm; after suspensory traction, it decreased to 59. 6 mm. The high stress area of each vertebral body was located in the anterior longitudinal ligament attachment area of the vertebral body during both two kinds of traction. The maximum Mises stress of C2-C7 vertebral body in suspensory traction is generally small relative to axial traction.ConclusionCompared with axial traction, suspensory traction has better kyphotic corrective effect, while reduces the length of the cervical spinal canal and the stress on the cervical vertebral body, which decreases the possibility of nerve damage and iatrogenic fracture during traction from a biomechanical point of view.

OBJECTIVE:Lateral lumbar interbody fusion technology may have a protective effect on the paravertebral and spinal ligaments during surgery, resulting in positive effects on bone mineral density (BMD). However, evidence is lacking on the change in vertebral bone density of patients. The changes in bone density in patients after lumbar fusion surgery are closely related to the occurrence of mechanical complications such as proximal border kyphosis, screw extraction, and adjacent vertebral fractures. Therefore, the aim is to investigate the changes in the volumetric bone mineral density (vBMD) of the adjacent vertebral cancellous bone and endplate at the fusion level in patients undergoing lateral lumbar interbody fusion (LLIF). METHODS:The medical records of patients with lumbar degenerative diseases who underwent LLIF surgery in our hospital from March 2018 to October 2021 were retrospectively examined. The volumetric BMD of the cancellous bone and endplate adjacent to the lumbar fusion segment was measured before the operation and during postoperative follow-up. The measured volumetric BMD included the level of the upper/lower instrumented vertebra and the endplate (UIV + 1; LIV + 1; UIV + 1e; and LIV + 1e). Shapiro-Wilk test, one-way ANOVA, Mann-Whitney test, Fisher exact test, univariable, and receiver operating characteristic (ROC) curve analysis were executed in this study. RESULTS:A total of 32 patients were included in the study, including 27 women and 5 men, with a mean age of 60.1 ± 7.1 years. The preoperative vBMD values in the UIV + 1, LIV + 1, UIV + 1e, and LIV + 1e groups were greater than those at the postoperative follow-up (131.9 ± 34.8 vs. 115.8 ± 30.8; 134.8 ± 37.0 vs. 117.2 ± 32.1, p < 0.001; 312.9 ± 79.3 vs. 287.7 ± 85.2, p = 0.007; 314.7 ± 71.4 vs. 296.1 ± 59.8, p = 0.042). The vBMD changes and rates of change in the cancellous and endplate regions were 16.1% ± 17.7% (11.4% ± 13.0%), 12.2% ± 12.1% (17.3% ± 17.5%), 11.4% ± 18.3% (-25.2% ± 49.2%), and 7.2% ± 18.5% (-18.6% ± 49.8%) in the UIV + 1, LIV + 1, UIV + 1e, and LIV + 1e groups, respectively. There was no significant difference in the preoperative vBMD, postoperative vBMD, or percent vBMD change between UIV + 1 and LIV + 1. However, there was a significant difference in the endplate vBMD at follow-up (p = 0.035). CONCLUSION:We evaluated the changes of vBMD of the cancellous bone and endplates adjacent to the vertebral body, cephalad or caudal to the fused level in LLIF patients through QCT, and can provide a new approach for reducing the occurrence of mechanically related complications after vertebral fusion surgery.

OBJECTIVE:The aim of this study was to compare the predictive efficacy of quantitative CT (QCT)-based endplate volumetric bone mineral density (EP-vBMD) and MRI-based endplate vertebral bone quality (EBQ) score for cage subsidence (CS) after lateral lumbar interbody fusion (LLIF). METHODS:A retrospective study was conducted on patients who underwent single-level LLIF in conjunction with pedicle screw fixation at the authors' institution between January 2019 and April 2023. The volumetric bone mineral density (vBMD) was measured based on preoperative CT using phantom-less QCT software. Measurement of the VBQ score was based on preoperative MRI. CS was defined as a decrease of more than 2 mm in the midpoint height of the intervertebral space. The receiver operating characteristic (ROC) curve of the EP-vBMD and EBQ for predicting CS was drawn, and the predictive efficacy of the two methods was compared using the Delong test. Clinical outcomes, including the visual analog scale for low back pain (VAS-BP), VAS for leg pain (VAS-LP), and Oswestry Disability Index (ODI) scores were assessed preoperatively, postoperatively, and at the 1-year follow-up. RESULTS:Ninety-seven patients who underwent LLIF were included in this study, including 31 patients with CS and 66 patients with no CS (NCS). No significant differences were observed between the two groups in VAS-BP, VAS-LP, or ODI scores preoperatively, postoperatively, or at the 1-year follow-up (all p > 0.05). The EP-vBMD of the CS group was lower than that of the NCS group, and EBQ was higher than that of the NCS group. The area under the ROC curve (AUC) of EP-vBMD for predicting CS was larger than that of global and segmental vBMD. The AUC of the EBQ for predicting CS was larger than that of global and segmental VBQ, and the AUC of EP-vBMD was larger than that of the EBQ. The combined prediction model of EP-vBMD and EBQ had the largest AUC value (0.899), but it was not significantly different from EP-vBMD alone (p = 0.547). CONCLUSIONS:The regional endplate BMD assessment based on QCT and MRI can effectively predict CS after LLIF, and it has better predictive efficiency than the global or surgical segmental vertebrae BMD measurement. EP-vBMD is superior to EBQ in predicting CS. The prediction efficiency of EP-vBMD combined with EBQ was better than EBQ alone, but not better than EP-vBMD.

Rationale: Synovial sarcoma (SS) is a rare and highly malignant soft tissue sarcoma. When SS occurs in atypical locations, it can present significant diagnostic challenges. We report a case of paraspinal SS initially misdiagnosed as spinal tuberculosis, highlighting the diagnostic difficulties and the importance of considering SS in the differential diagnosis. Patient concerns: A 23-year-old woman presented with progressively worsening lower left back pain over 3 weeks, accompanied by weakness and numbness in her left lower limb. She was initially misdiagnosed with spinal tuberculosis at 2 different hospitals based on weakly positive anti-tuberculosis antibodies and imaging findings. Despite ongoing anti-tuberculosis treatment, her condition continued to deteriorate. Diagnoses: The first surgery revealed findings inconsistent with spinal tuberculosis, but a tumor could not be excluded. However, the initial pathological biopsy was inconclusive. A second surgery confirmed the diagnosis of SS through histopathological examination. Interventions: The patient underwent a second surgery for mass resection and biopsy confirmation. Unfortunately, by the time the correct diagnosis was made, the disease had metastasized to her lungs, and the optimal window for surgical intervention had been missed. Outcomes: The patient’s delayed diagnosis resulted in extensive diffuse metastasis to both lungs, significantly impacting her survival. Lessons: This case underscores the need to consider malignancies such as SS in the differential diagnosis of spinal lesions, particularly when clinical response to treatment is poor. Early diagnosis and timely surgical intervention are critical to improving patient outcomes. Our literature review provides further insights into the characteristics of paraspinal SS and strategies to prevent misdiagnosis, emphasizing the importance of early and accurate diagnosis to enhance patient survival.

Cage subsidence after oblique lumbar interbody fusion (OLIF) frequently causes poor outcomes, yet existing predictive models lack accuracy and applicability. This study leveraged the Least Absolute Shrinkage and Selection Operator (LASSO) regression to efficiently identify key predictors of subsidence from quantitative CT vertebral bone quality and endplate-related factors. We analyzed 337 OLIF surgical segments (674 endplates; May 2017-May 2024), observing subsidence in 45.70%. LASSO selected intervertebral disc height correction, intraoperative endplate injury, inferior endplate morphology, and volumetric bone mineral density of the inferior vertebra/endplate as top predictors. These variables informed a multivariable logistic regression model, visualized as a digital nomogram. The model demonstrated excellent predictive performance in training and validation cohorts via ROC, precision-recall, and calibration curves. Decision curve analysis confirmed high clinical utility across risk thresholds, enabling personalized preoperative risk assessment and prevention strategy optimization for OLIF patients.

Bioprinting technology plays a crucial role for constructing tissue substitutes. However, the mismatched scaffold shapes and the poor treatment timeliness limit its clinical translational application. In situ printing technology that prints bioregenerants directly inside patient's body can meet the needs of specific tissue repair. This study develops a smartphone controlled handheld bioprinter for in situ skin wounds dressing. The mini bioprinter can be handheld and placed on any printing surface to create strips, complex patterns, and 3D structures, and can be equipped with microchannel needles to expand functionality. The size of the strips as well as the printing path can be programmed and controlled by the smartphone to ensure the precision of the printed product quality. Furthermore, the device not only allows for smooth switching between different bioinks for printing heterogeneous structure, but also allows for fast and uniform coverage of large wound surfaces. When dealing with complex wounds in vitro & vivo, the printer can effectively fill and precisely close wounds, promoting wound healing. The programmable handheld bioprinter can balance mobility and customizability in the management of skin wounds and is expected to realize its potential for emergency medical treatment in condition-constrained scenarios, such as battlefields or disaster areas.

Tumor therapy has advanced significantly in recent years, but tumor cells can still evade and survive the treatment through various mechanisms. Notably, tumor cells use autophagy to sustain viability by removing impaired mitochondria and clearing excess reactive oxygen species (ROS). In this study, the aim is to amplify intracellular oxidative stress by inhibiting mitochondrial autophagic flux. Multisynergistic environmental-response nanoparticles (ERNs) are engineered by integrating gold nanoparticles and copper peroxide with borosilicate bioactive glass. The controlled release of copper and inhibition of autophagy flux triggered an overabundance and accumulation of oxidative stress within the tumor cells. This stress triggered immunogenic tumor cell death, believed to initiate a systemic immune response. The tumor microenvironment (TME) transitioned back to a normal physiological state as tumor cells are ablated. ERNs responded to the microenvironment changes by depositing hydroxyapatite on the surface and spontaneously enhancing bone regeneration. This innovative formulation facilitates the functional transition of ERNs from "anti-tumor therapy" to "biomineralization" that kills cancers and induces new bone formation. Overall, it is shown that the ERNs effectively eradicate cancers by utilizing chemodynamic therapy, starvation therapy, and immunotherapy.

Three-dimensional (3D) bioprinting has advantages for constructing artificial skin tissues in replicating the structures and functions of native skin. Although many studies have presented improved effect of printing skin substitutes in wound healing, using hydrogel inks to fabricate 3D bioprinting architectures with complicated structures, mimicking mechanical properties, and appropriate cellular environments is still challenging. Inspired by collagen nanofibers withstanding stress and regulating cell behavior, a patterned nanofibrous film was introduced to the printed hydrogel scaffold to fabricate a composite artificial skin substitute (CASS). The artificial dermis was printed using gelatin-hyaluronan hybrid hydrogels containing human dermal fibroblasts with gradient porosity and integrated with patterned nanofibrous films simultaneously, while the artificial epidermis was formed by seeding human keratinocytes upon the dermis. The collagen-mimicking nanofibrous film effectively improved the tensile strength and fracture resistance of the CASS, making it sewable for firm implantation into skin defects. Meanwhile, the patterned nanofibrous film also provided the biological cues to guide cell behavior. Consequently, CASS could effectively accelerate the regeneration of large-area skin defects in mouse and pig models by promoting re-epithelialization and collagen deposition. This research developed an effective strategy to prepare composite bioprinting architectures for enhancing mechanical property and regulating cell behavior, and CASS could be a promising skin substitute for treating large-area skin defects.

Osseointegration implant (OI) surgery is the latest rehabilitation technology for amputees, where a bone-anchored implant obviates the limitations of traditional socket prostheses. The bone mineral density (BMD) in the periprosthetic and other anatomical regions can be used to assess bone remodelling following OI surgery. Currently, limited studies have used BMD measurements in reporting post-operative OI outcomes and the association between the maintenance of BMD and implant efficacy has remained elusive. This review captured and analysed all studies that have reported the BMD as an objective outcome measure in patients with trans-femoral or trans-tibial OI. The PubMed, Medline, Scopus and Web of Science databases were searched using the terms 'amputation', 'osseointegration' and 'bone mineral density'. A total of 6 studies involving human participants were included for analysis. All studies used dual X-ray absorptiometry and/or X-rays for measuring BMD. Rehabilitation of trans-femoral or trans-tibial amputation using OI may help restore healthy BMD by enabling physiological bone loading. However, there is a low correlation between the BMD around the OI and the success of OI surgery or the risk of periprosthetic fractures. This review summarises the current evidence on BMD assessment in OI for lower limb amputee rehabilitation. Despite the great variability in the results, the available evidence suggests that OI may help restore BMD following surgery. The limited evidence calls for further investigation, as well as the development of a standard BMD measurement protocol.

Background/Purpose Routine physical exams often use a chest computed tomography (CT) scan to screen pulmonary nodules, generally it only includes thoracic vertebrae. Phantom-less quantitative computed tomography (PL-QCT) has advantage on retrospective bone mineral density (BMD) assessment, especially for chest CT scan. This study aimed to evaluate the performance of different single vertebrae and different thoracic vertebrae combinations in predicting osteoporosis or osteopenia. Methods 246 patients (mean age of 55.97±14.91; 48% female) who underwent the whole abdominal computed tomography (CT) were involved in this retrospective study. The BMD of lower thoracic and lumbar vertebrae were measured by PL-QCT. Diagnostic performance measures and the receiver operating characteristic (ROC) curves for diagnosing osteoporosis and osteopenia were calculated. Average of L1 and L2 BMD was used as diagnosis standard value of osteoporosis and osteopenia. Results A total of 1230 vertebrae were measured for BMD via this PL-QCT system. The BMD of lower thoracic vertebrae decreased successively from T10 to L2. And the BMD of lower thoracic and lumbar vertebrae are highly correlated. To distinguish osteoporosis from non-osteoporosis (osteopenia + normal), the maximal area under the receiver operating characteristic curve (AUC) was 0.951(BMD average of T10, T11 and T12). At the optimal threshold of 107.85 mg/cc, the specificity was 94.7% at the combination of the entire 3 lower thoracic vertebrae (BMD average of T10, T11 and T12). Conclusions During chest CT scan, BMD of lower thoracic measured by automatic PL-QCT could be a valuable opportunistic osteoporosis diagnosis tool as it has similar performance in comparison with its lumbar counterpart.

Background Thyroid carcinoma is the most common endocrinological malignancy, but its spread to bone is rare. Particularly, bone metastases leading to complete resorption of the humerus are extremely uncommon. We aimed to explore factors affecting treatment decision in humeral metastasis by presenting a case and analyze the possible treatments via conducting a literature review. Case presentation We described a case of a 68-year-old woman experiencing chronic pain in her right upper arm for six years. Clinical, radiological, and pathological evaluations confirmed humeral metastasis from thyroid carcinoma. Surgical treatments like tumor removal or limb amputation were suggested for prolonging life and pain relief, but the patient refused them and pursued conservative managements such as herbal medicine, radioactive iodine ( 131 I) therapy, and Levothyroxine Sodium(L-T4). The humeral destruction aggravated gradually, ultimately leading to complete resorption of her right humerus. The patient could not move her right shoulder, but her forearm motion was almost normal; thus, she could complete most of her daily living activities independently. Surgical treatments such as limb amputation were advised but she still refused them for preservation of the residual limb function and preferred conservative managements. Conclusion A personalized multidisciplinary approach is important for patients with bone metastasis. The balance between limb amputation for life-prolonging and pain relief and limb salvage for preservation of residual function and social and psychological well-being should be considered. Our literature review revealed that some novel surgical treatments and techniques are available for bone metastases. This case adds to our current understanding of bone metastases and will contribute to future research and treatments.

Osteoarthritis (OA) is a debilitating chronic joint disease affecting large populations of patients, especially the elderly. The pathological mechanisms of OA are currently unknown. Multiple risk factors are involved in OA development. Among these risk factors, alterations of mechanical loading in the joint leading to changes in biological signaling pathways have been known as a key event in OA development. The importance of AMPK-β-catenin-Runx2 signaling in the initiation and progression of OA has been recognized in recent years. In this review, we discuss the recent progress in understanding the role of this signaling pathway and the underlying interaction mechanisms during OA development. We also discuss the drug development aiming to target this signaling pathway for OA treatment.

STUDY DESIGN:Retrospective cohort study. OBJECTIVE:To evaluate the effectiveness of pedicle screw trajectory planning based on artificial intelligence (AI) software in patients with different levels of bone mineral density (BMD). SUMMARY OF BACKGROUND DATA:AI-based pedicle screw trajectory planning has potential to improve pullout force (POF) of screws. However, there is currently no literature investigating the efficacy of AI-based pedicle screw trajectory planning in patients with different levels of BMD. METHODS:The patients were divided into 5 groups (group A-E) according to their BMD. The AI software utilizes lumbar spine CT data to perform screw trajectory planning and simulate AO screw trajectories for bilateral L3-5 vertebral bodies. Both screw trajectories were subdivided into unicortical and bicortical modes. The AI software automatically calculating the POF and pullout risk of every screw trajectory. The POF and risk of screw pullout for AI-planned screw trajectories and AO standard trajectories were compared and analyzed. RESULTS:Forty-three patients were included. For the screw sizes, AI-planned screws were greater in diameter and length than those of AO screws ( P <0.05). In groups B-E, the AI unicortical trajectories had a POF of over 200N higher than that of AO unicortical trajectories. POF was higher in all groups for the AI bicortical screw trajectories compared with the AO bicortical screw trajectories ( P <0.05). AI unicortical trajectories in groups B-E had a lower risk of screw pullout compared with that of AO unicortical trajectories ( P <0.05). CONCLUSIONS:AI unicortical screw trajectory planning for lumbar surgery in patients with BMD of 40-120 mg/cm 3 can significantly improve screw POF and reduce the risk of screw pullout.