This study included 172 males and 87 females, with a sex ratio of 1.98. The median age of the 259 patients was 33 years, and the AHO patients had a median age of 16 years; CHO patients had a median age of 41 years. The analysis revealed that there was a significant difference in the age of onset between the AHO and CHO patients (p<0.001), and the age of onset in the AHO patients was younger than that in the CHO patients. Among the 259 patients divided by age group, the top three age groups were 11-15 years old (36 patients), 6-10 years old (25 patients),and 61-65 years old (25 patients), 46-50 years old (24 patients). After being divided according to whether they had AHO or CHO, the age groups with the highest incidence were the 11-15 years old (22 patients) and 61-65 years old (22 patients) groups  Table 1 .
The total numbers of infections in the extremity and trunk sites were 252 (97.30%) and 7 (2.70%), respectively. Among all 259 infections, 246 (94.98%) were single infection, and 13 (5.02%) were multisite infections. The tibia (79 cases, 32.11%) was the most common site of solitary infection, followed by the femur (64 cases, 26.02%) and phalanges (20 cases, 8.13%) ( Figure 1 ).
Before admission, 68 patients had a history of fever, accounting for 26.25% of the total. Among them, 42 patients had fever before admission in the AHO group, accounting for 43.75% of the total number of patients with AHO, and 26 patients had fever before admission in the CHO group, accounting for 15.95% of the total number of patients with CHO. The difference was statistically significant (p=0.018). The number of febrile patients was significantly higher in the AHO group than in the CHO group. Before admission, 85 patients had a history of antibiotic use, accounting for 32.82% of the total, and most of these patients had taken cephalosporins (injection or oral administration).
Etiology analysis revealed that most cases of HO had no obvious cause (183/259, 70.66%); the number of cases caused by soft tissue injury (fall, abrasion, bruise, crush and crush) (34/259, 13.13%) followed the number of cases with no obvious cause. Exercise-induced illness (skipping, dancing, swimming, basketball sprain) and history of heavy physical labor (13/259, 5.02%) was the third most common cause. In addition, some patients exhibited a history of infection before onset (upper respiratory tract infection, chickenpox infection and skin infection); high fever (13/259, 5.02%); a history of being stabbed, punctured or injected (10/259, 3.86%); bite history (5/259, 1.93%); and a history of allergic purpura (1/259, 0.39%)( Figure 2 ).
As shown in  Table 2 , among the preoperative (upon admission) serum inflammatory markers, the rate of ESR positivity was the highest at 67.58% (148/219), followed by hs-CRP at 66.67% (132/198), and the rate of WBC positivity was at 24.90% (63/253). According to the AHO and CHO classifications, the rates of positivity for WBC were 38.30% and 16.98%, the rates of positivity for hs-CRP were 69.33% and 65.04%, and the rates of positivity for ESR were 75.61% and 62.77%, respectively. There were significant differences between the AHO and CHO patients in the WBC levels, and the AHO patients had a higher WBC count than the CHO patients (p<0.001). The baseline age of the AHO patients was significantly younger than that of the CHO patients (p<0.001). To reduce the age-induced bias, we performed age-adjusted analysis. After adjusted, positive rate of ESR showed significant difference (p = 0.014).
The manifestations of inflammation were divided into redness of the skin, swelling, fever, pain and dysfunction according to the consultation and physical examination upon admission. Pain affected the highest number of patients at 222, which was followed by 175 patients with swelling and 44 patients with functional impairment. There were significant differences in the incidence of redness of the skin, swelling, fever, and dysfunction between the AHO and CHO patients (p<0.05), and these clinical symptoms were more common in the AHO patients than in the CHO patients. The baseline age of the AHO patients was significantly younger than that of the CHO patients (p<0.001). To reduce the age-induced bias, we performed age-adjusted analysis. After adjusted, positive rate of swelling symptom showed no significant difference (p = 0.066).
In our study, a total of 171 patients had documented pathogen cultures. The rate of positivity among all cultures was 71.93% (123 cases), of which 78.86% (97 cases) involved single microorganism infections. Among those with single microorganism infections, Gram-positive bacteria accounted for 86.60% (84 cases), Gram-negative bacteria accounted for 13.40% (13 cases), and SA accounted for 63.92% (62 cases), including MSSA 56.70% (55 cases) and MRSA 7.22% (7 cases). Among the polymicrobial infections, 46.15% (12 cases) involved only Gram-positive bacteria, 11.54% (3 cases) involved only Gram-negative bacteria, and the rest were mixed bacterial infections.
As shown in  Table 3 , among the 202 strains of pathogenic microorganisms detected, 160 strains were Gram-positive bacteria, 41 strains were Gram-negative bacteria and 1 strain was fungi. The top three were MSSA with 100 strains (49.50%), MRSA with 13 strains (6.44%), and MRSE with 9 strains (4.46%). The top three pathogenic bacteria in the AHO group were 53 strains of MSSA, 8 strains of MRSA and 3 strains of MRSE. SA accounted for 75.61% (31/41) of the single microorganism infections in AHO patients. The top three pathogenic bacteria cultured in the CHO patients were 47 strains of MSSA, 6 strains of MRSE and 6 strains of Enterobacter cloacae. SA accounted for 55.36% (31/56) of the single microorganism infections in the CHO patients.
Through the analysis of drug susceptibility results it was observed that, among the Gram-positive bacteria ( Table 4 ), MSSA was most sensitive to linezolid (99%), followed by vancomycin (98%), oxacillin (98%) and rifampicin (98%). The MRSA strains were most sensitive to linezolid (100%), vancomycin (100%), and rifampicin (100%). The MRSE strains were most sensitive to linezolid (100%) and vancomycin (100%). Regarding Gram-negative bacteria ( Table 5 ), E. cloacae was most sensitive to aztreonam (100%) and piperacillin/tazobactam sodium (100%). Escherichia coli was most sensitive to piperacillin/tazobactam sodium (100%). Pseudomonas aeruginosa was most sensitive to ciprofloxacin (85.71%) and imipenem (85.71%).
The treatment of hematogenous osteomyelitis usually includes conservative treatment and surgical treatment. Surgical treatment is usually divided into debridement (including simple debridement, debridement plus drip drainage, and debridement plus VSD suction), bone cement (nonabsorbable bone cements, such as PMMA; absorbable bone cement, such as calcium sulfate (CS); and calcium phosphate/calcium sulfate (CS/CP)) and amputation in some patients with severe infections ( Table 6 ).
Regarding the antibiotics given on admission, 235 patients (90.73%) received intravenous antibiotics, and 24 patients (9.27%) received oral antibiotics. Regarding intravenous antibiotic therapy, 96 patients (40.85%) received single antibiotic therapy, of which cefazolin (25 patients,26.04%) was the most commonly used antibiotic.
All patients were followed up for at least 12 months; 31 patients (11.97%) were lost to follow-up, and 18 patients (6.95%) had amputations in the hospital. A total of 189 patients(90%) were in remission, and 21 patients (10%) were in relapse. Among them, after conservative treatment, the remission rate was 90%, the remission rate of the patients with one-stage debridement was 88.18%, the remission rate of the patients with one-stage debridement plus antibiotic-loaded PMMA bone cement exclusion was 88.24%, and the patients who had CS or CS/CP had a 100% remission rate.
Treatment of severe patients with sepsis and pulmonary infection. 15 of our patients (5.80%) had coexisting pulmonary infections. For patients with pulmonary infection, the precise diagnosis should be made first to avoid a missed diagnosis or a misdiagnosis. In addition to surgical treatment of local infections of the limbs, systemic intravenous therapy should be combined with appropriate antibiotics. In this subset of patients, we found that oxacillin was very effective unlike other antibiotics. All patients were successfully treated, and the lung infection was cured,such as case 1( Figure 3 ).
The total Financial burden for the hospitalized patients with hematogenous osteomyelitis was 8,832,910 RMB. The median total cost for the hospitalized patients with hematogenous osteomyelitis was 25,754 RMB (11,502 RMB, 47,661 RMB). Among the main costs of the patients with hematogenous osteomyelitis, pharmaceutical costs accounted for the largest proportion (36.17%), followed by material costs (24.06%), anesthesia and surgery costs (17.47%), diagnosis costs (16.10%), comprehensive care costs (5.02%) and blood product costs (1.17%)( Table 7 ).