There are three clinical endpoints for decompression surgery: severe pain, radiographic progression to collapse, and THA . If THA is used as the endpoint on the decompression side, the survival rate of multiple drilling decompression was 80% (Figure 1), which was similar to the results of previous studies [11, 12]. Therefore, it can be suggested that one-stage THA and multiple drilling decompression were effective for patients with bilateral ONFH at different stages. And decompressed side can obtain early non-weight-bearing function training, which benefits from distributing the whole body weight load to the hip of one-stage THA . If the progression of necrosis or severe pain is used as the endpoint, the success rate of decompression surgery in our study would be 86.7% (Figure 2). Two of the 6 patients who underwent THA re-operation had no significant progression of joint disease in the decompressed hip and no severe pain. However, the patients felt discomfort, slight pain on the decompression side, or had function that was not as good as that of the hip joint on the replacement side. This is a problem should be mentioned. This may become an important factor affecting the success rate of head preservation surgery.
We compared HHS and OHS on the decompressed and replaced sides, and found no significant difference in OHS between the two sides. However, for HHS, the difference between the two sides was statistically significant. We analyzed HHS according to the module analysis and found that the pain module score of the decompressed side was lower than that of the replaced side; however, the functional module score was not significantly different. These results indicated that most patients still had slight pain after decompression. Liu et al showed that patients who underwent femoral head decompression had significantly improved pain symptoms; the postoperative visual analog scale score was about 3 points in their study, which was considered mild pain , and this result is similar to ours. The main causes of pain before femoral head collapse are intraosseous pressure, bone marrow edema, accumulation of microfractures, disruption of mechanical loading, articular cartilage injuries ranging from various stages of chondromalacia to chondral flaps to loose bodies and fraying or tearing. Femoral head decompression can relieve bone marrow edema, but decompression does not address other intraarticular changes. THA is an open surgery that involves the removal of the femoral head and pain caused by these mechanical changes, which fundamentally resolves the intraarticular injuries and replaces the friction interface. This causes marked pain relief of the hip joint on the replaced side postoperatively. The decompressed side had less pain symptoms before surgery, which was not markedly relieved postoperatively. Thus, the patient’s expectation was not met, resulting in lower postoperative satisfaction.
For the patient’s hip mobility, we focused on the difference between the internal and external rotations of the decompression and replacement sides. Early symptoms of ONFH are often pain and the limitation of internal rotation . Decompression surgery does not interfere with structures of the hip joint. Thus, postoperative inflammation of the hip joint still exists, and even progresses further. The preoperative internal rotation activity of the hip joint is limited and is not significantly improved by surgery. In THA, the hip joint is thoroughly cleaned and loosened, and the hip joint activity is improved. Moreover, there is more preoperative activity on the replaced side than on the decompressed side, so the improvement of the hip joint activity on the replaced side is more notable. In this study, the degree of internal rotation of the hip was better on the replaced side than on the decompressed side. Therefore, we believe that this limitation in the internal rotation of the hip joint postoperatively affected the postoperative satisfaction.
We also performed a bilateral one-leg standing test to compare the time of standing on one side. In this study, compared with the replaced side, the decompressed side had a shorter standing time. When standing on one leg, the gluteal muscles (gluteus maximus, gluteus medius, and gluteus maximus) are the main supports . When the strength of the gluteal muscles is insufficient on one side of the patient, their supportive ability is poor, thus reducing the standing time on one foot. It was suggested that when the hip undergoes decompression, the affected limb should not undergo weight bearing for at least 3 months. Thereafter, weight bearing should be restored based on the recovery process. However, the replacement side can resume weight bearing after surgery. The limbs on the decompression side will have different degrees of gluteal muscle atrophy, which may cause hip joint fatigue and soreness in advance due to the insufficient strength of the gluteal muscle on the decompression side. The patient’s satisfaction with the surgical outcome is then reduced.
Psychological factors also have important effects on the postoperative satisfaction of patients . Patients may have residual discomfort or partial dysfunction after decompression. In this study, patients still felt hip discomfort on the decompressed side when comparing their two hips at the same time. As a result, the postoperative patient satisfaction was lower for the decompressed side than for the replacement side. With the continuous improvement of living standards, patients have increasing requirements for quality of life. Although the postoperative function of the decompression side can fully meet the functional needs of the hip joint in patients’ daily lives, the residual mild pain or partial dysfunction after surgery occasionally makes the patient feel uncomfortable, making some patients prefer THA over decompression.
This study has some limitations. First, the sample size of this study was relatively small, and further investigation is needed using larger samples. Second, in the study, only postoperative pain and some functions in the patients were compared. The factors we studied were too simple. Whether other factors also affect patient satisfaction with decompression surgery requires further study.