To observe whether cystic changes affects the outcome of hip preservation surgery of early osteonecrosis of the femoral head (ONFH).

Prospective clinical follow-up was conducted to observe the clinical data of patients with early ONFH at Aviation General Hospital from June 2017 to November 2020. According to the evaluation of preoperative imaging (CT and MRI), patients were divided into the cystic changes group, with a total of 32 patients and 37 hips. Patients without cystic changes were assigned to the non-cystic group, with a total of 50 patients and 59 hips. All patients were treated with minimally invasive single approach to double-channel core decompression and bone grafting with structural bone support by the great trochanter. Decompression bone grafting was performed on the inner and lower areas of femoral head necrosis through the inner and lower channels, and decompression bone grafting plus structural bone support was performed on the outer and upper areas of femoral head necrosis through the outer and upper channels. Follow-up was performed at 3, 6, 12 months after surgery and once a year thereafter. Follow-up was terminated if total hip arthroplasty was done, which considered a failure. Data from the preoperative and last follow-up visits were included in the study for data analysis. Hip function was assessed by Harris hip score. Hip function scores, excellent and good rates and hip function scores of patients with different types (C+ L1, L2+ L3) were compared between the two groups. Imaging progression rate and failure rate of 2 groups were compared. All the patients included in the study underwent anteroposterior and lateral hip joint X-ray and CT examination before and during the follow-up. Postoperative imaging evaluation was considered as stable if there was no collapse of femoral head or no aggravation of original collapse, and imaging progress was considered if subchondral fracture or aggravation of collapse occurred. A final THA was considered a failure. Data were processed with Wilcoxon signed-rank test and chi-square test, and kaplan-Meier method was used for survival analysis.

All patients were included in the study and followed up for a mean of (30.6±8.6) months. The Harris hip score of the cystic changes group at the last follow-up was(82.43±16.36) points, significantly higher than that before surgery[(75.67±13.43) points], and the difference was statistically significant (P=0.022). The excellent and good rate increased from 37.84%(14/37) to 62.16%(23/37), and the difference was statistically significant(χ²=4.378, P<0.05). The Harris hip score of the non-cystic group was (81.76±17.68) points at the last follow-up, compared with that before surgery [(82.90±12.77) points], and the difference was not statistically significant (P=0.965). The excellent and good rate increased from 55.93%(33/59) to 62.71%(37/59), and the difference was not statistically significant(χ²=0.562, P>0.05). Before surgery, Harris hip score in the cystic changes group was significantly lower than that in the non-cystic group, and the difference was statistically significant (P=0.021); at the last follow-up, there was no statistically significant difference in Harris hip score between the two groups (P=0.778). In cystic changes group, there was no statistically significant difference in Harris hip score of C+ L1 patients before surgery and at the last follow-up (P=0.417); Harris hip score of L2+ L3 patients was significantly lower before surgery than that at the last follow-up, and the difference was statistically significant (P=0.040). In non-cystic group, there was no statistically significant difference in Harris hip score of C+ L1 patients before surgery and at the last follow-up (P=0.088); there was no statistically significant difference in Harris hip score of L2+ L3 patients before surgery and at the last follow-up (P=0.189). Before surgery, Harris hip score of C+ L1 patients was significantly lower in the cystic changes group than that in the non-cystic group (P=0.022). At the last follow-up, there was no statistically significant difference in Harris hip score between the two groups (P=0.335). Before surgery, there was no statistically significant difference in the Harris hip score of L2+ L3 patients between the two groups(P=0.261). At the last follow-up, there was no statistically significant difference in the Harris hip score of L2+ L3 patients between the two groups (P=0.323). At the last follow-up, the rate of imaging progression was 27.03% (10/37)in the cystic changes group and 22.03%(13/59) in the non-cystic group, and there was no statistically significant difference (χ²=0.311, P=0.577). The imaging progression rate of patients with C+ L1 in the cystic changes group was 38.46%(5/13), which was higher than that in the non-cystic group [4.76%(1/21)], the difference was statistically significant (χ²=4.170, P=0.019). The imaging progression rates of L2+ L3 patients in the cystic changes group and non-cystic group were 20.83%(5/24) and 32.43%(12/37), respectively, and there was no statistically significant difference (χ²=0.974, P=0.324). At the last follow-up, the failure rate was 13.51% (5/37) in the cystic changes group and 11.86% (7/59) in the non-cystic group, and there was no statistically significant difference (χ²=0.000, P>0.05). Kaplan-meier survival curve showed that the overall survival curve of the two groups progressed smoothly, and there was no obvious time boundary associated with clinical failure.

The cystic changes area of the femoral head may affect the hip function and imaging progression of ONFH patients in stage of ARCO Ⅱ or C+ L1, but it is not recommended as a risk factor for the prognosis of ONFH in early stage.