Although PVNS occurs most commonly in larger joints, it can still arise in other parts of the body, which can be seen in the spine, temporomandibular joint [15, 16]. Regardless of where PVNS occurs, the traditional treatment is synovectomy, which can be done by opening or endoscopic surgery. Although the opening method has a wider field of view than endoscopic surgery, which can bring the advantage of relatively complete debridement of diseased synovial tissue, it is more invasive than the endoscopic technique. Both two treatments can achieve satisfactory PRO from short- to long-term follow-up [17,18,19]. A case series study of 14 hips PVNS conducted by Nazal et al.  indicated that endoscopic management was an effective method with a survival rate of 93% (13/14), 1 (7%) recurrence, and 0 arthroplasty. A retrospective study of 13 hip PVNS cases that underwent arthroscopy reported only 1 case converted to THA at 6 years postoperatively because of progressive osteoarthritis . However, a retrospective study by Schwartz  found that the recurrence of treatment for PVNS endoscopically is higher than open surgery, especially for diffuse type. The higher failure rate of treatment for hip PVNS might be explained by periarticular destruction within the closure capsule and the difficulty of surgical resection .
Mankin et al.  put forward that total hip arthroplasty was the only treatment choice by analyzing 12 cases of hip PVNS treated from 1972 to 2009. However, a retrospective study conducted by Tibbo et al.  of case series of 25 PVNS patients who underwent arthroplasty found that the 5- and 10-year survivorship free from any revision were 83 and 63%, respectively. However, following the THA, 19 patients (76%) sustained at least 1 complication, most commonly aseptic loosening. Besides, another retrospective study of 16 hip PVNS patients underwent arthroplasty with an average follow-up of 16.7 years conducted by Vastel et al.  reported 1 case of recurrence and 9 cases of revision. Although this suggests that arthroplasty for hip PVNS had a comforting recurrence rate, the higher rate of complication in arthroplasty might make endoscopic treatment the preferred choice. In our study, due to continuing progression of osteoarthritis, 3 cases converted to THA eventually. But, compared with other patients’ status in our study, patients with more severe joint injury were not converted to THA at the latest follow-up. Previous joint damage might be attributed to secondary injury or PVNS, however, in most conditions, it is hard to explain the outcome when trying to determine whether the symptom might be due to recurrent disease or progression of secondary joint damage . The secondary damage cannot be reversed, nor can it prevent the progression of osteoarthritis. Therefore, based on the condition of affected joints, the surgeon must fully consider the decision to perform less invasive endoscopic surgery or perform total hip arthroplasty.
Because of the infiltrative nature and incomplete resection of PVNS, postoperative adjuvant therapy, such as brachytherapy injection, or external beam radiation, was recommended after resection, especially for diffuse-type PVNS . However, Stephan et al.  did not suggest postoperative adjuvant radiotherapy for PVNS patients because of the possible toxic properties of radiotherapy.
A retrospective study of 14 knee PVNS patients who underwent radiotherapy showed 11 patients had good or excellent limb outcomes . A study of 7 PVNS patients (5 knees, 1 hip, 1 wrist) who underwent radical surgery and postoperative radiotherapy showed that 6 patients had asymptomatic limb function and excellent quality of life at average 29 months follow-up . Besides, Horoschak et al.  conducted a retrospective study of 17 PVNS patients with 18 lesion sites (12 sites of knee, 3 sites of ankle, 2 sites of hand, and 1 site of spine) treated with postoperative radiotherapy and found that the initial local control rate was 75% with an average follow-up of 46 months. Furthermore, a study demonstrated that 41 of 50 PVNS patients (20 cases of knee, 9 cases of ankle, 7 cases of foot, 6 cases of hand, 4 cases of hip,4 cases of wrist) underwent radiotherapy after surgical resection can gain long-term (mean follow-up period of 94 months) good/excellent functio n. No complication or serious complication was found in any of the above studies. It follows that, for the treatment of PVNS patients, postoperative adjuvant radiotherapy might be an effective management that can achieve satisfactory short- to long-term prognosis with no severe complication. However, the optimal dose used for the treatment of PVNS is unclear now. Some studies reported that radiotherapy for PVNS using low dose as 16–20 Gy can achieve the outcome of no recurrence , whereas other studies using dose as high as 50 Gy with no complications [26, 27]. In our study, the using dose for PVNS was 10–30 Gy with no complication.
With the persistent development of radiotherapy, the adjuvant method has developed from traditional treatment to three-dimensional conformal radiotherapy(3D-CRT), intensity modulated radiotherapy (IMRT), and other novel radiotherapy technologies. Those emerging technologies have the advantages of precise positioning and accurate design.
Radiotherapy has been used widely for refractory cases in the knee joint, but there are few cases in the setting of radiotherapy of hip PVNS exist in the contemporary literature. To our best knowledge, this is the first study aimed to compare the clinical outcomes of hip PVNS patients who underwent CRT or IGRT followed by synovectomy endoscopically with those who received isolated synovectomy. In this study, we found a higher rate of hip joint survivability of the RT group than NRT group, which might provide the evidence that adjuvant radiotherapy treatment after endoscopic synovectomy for hip PVNS can be an effective and safe method.
There are several important limitations of this study. First, though the size of the sample is relatively large for known reports of a single center, the total sample size was still small, and there is a bias in patients’ choice of radiotherapy, thus more patients were needed to compare the results. Second, though satisfactory average mid-term PRO gained in our study, the long-term outcome remains to be seen. Third, the time span of this study was more than 11 years, which may affect the outcomes because of the improvement of surgery and radiotherapy technology. Fourth, treatment for concomitant pathology were performed, which made it difficult to distinguish whether the improved PRO was due to the treatment of PVNS or other hip lesions.