Although several studies have identified risk factors for local recurrence [24, 25] in TSGCT, none have analyzed possible risk factors for osteochondral destruction and progression in combination with those for local recurrence. Given that TSGCT is a benign neoplasm , the primary endpoint of treatment should be to maintain the function of involved joints. Surgery to reduce the recurrence rate in TSGCT occasionally causes morbidity of involved joints. This makes it important to analyze factors influencing local recurrence and osteochondral destruction together.
Previous studies reported that TSGCT has a high local recurrence rate of 16-30% [10, 11, 24], with the rate high in the diffuse type [10, 11], and in knee lesions [11, 24]. These results are consistent with those in the present study, and the local recurrence free survival rate in the present study was also comparable with that noted in past reports [10, 11], indicating that the quality of treatment in our institutions is roughly equal to that reported elsewhere. The treatment modality for primary/recurrent TSGCT has been surgical excision of tumors, but is now being partially changed to watchful observation, particularly for recurrent tumors if morbidity is expected with surgical treatment in our institutions. Recently, arthroscopic surgery has been applied to TSGCT surgery, particularly for knee involvement [26, 27, 28, 29]. Several previous reports described comparable results to open surgery regarding local recurrence [27, 28], whereas others described inferior results [26, 29]. Most recent studies also reported conflicting results regarding the clinical outcome of arthroscopic surgery (Table 5) [30, 31]. Although the local recurrence rate was higher in arthroscopic surgery than that in open synovectomy in the present study, there was no significant difference probably due to the small numbers of cases, shorter follow-up period, and possible selection bias (easy to approach cases) in cases with arthroscopic surgery. Most of the previous studies describing arthroscopic surgery reported the results of local recurrence, but not the functional results, which seem to be superior in arthroscopic surgery as compared with open synovectomy. A recent study reported postoperative function, but unfortunately only 6 of 206 cases were surgery with arthroscopy (Table 5) . Focusing on the results of local recurrence, arthroscopic surgery may have a disadvantage compared to open synovectomy. However, again, the advantage of arthroscopic surgery for the preservation of involved joint function, particularly that of knee joints needs to be considered.
Few studies have mentioned or investigated the progression of osteochondral destruction after surgery. Multivariate analysis showed osteochondral destruction at the initial examination and local recurrence to be independent risk factors for the progression of osteochondral destruction in the present study. Local recurrence itself sometimes causes pain and limitation of range of motion, while osteochondral destruction often impairs the patient QOL. Although the local recurrence rate was higher in cases with arthroscopic surgery compared with open synovectomy, osteochondral destruction was attributable to arthroscopic surgery in only a single case, although the follow-up period was short. The results of our previous report indicated that repeated surgery for local recurrence was a significant risk factor for progression of osteochondral destruction . However, the results of the present study did not show repeated surgery to be a risk factor for osteochondral destruction. This difference between the previous and present studies is related to the transition over time of the treatment procedure for TSGCT of the anterior knee from open total synovectomy to arthroscopic surgery.
Sharma et al.  reported that repeated surgery could salvage relapses, but was associated with morbidity after additional surgeries. They also cited Chin et al’s study in which complications such as stiffness, contractures, and reflex sympathetic dystrophy were noted more frequently with open procedures . Because TSGCT is a benign tumor, invasive treatment is not always needed to only reduce the local recurrence rate. Although recurrence and its effects on the subsequent clinical features after arthroscopic surgery should be further analyzed in the future, this procedure, particularly for knee location, may be an appropriate technique to reduce osteochondral destruction.
Other than knee joints, hip joints have also previously been reported to be destroyed by TSGCT  and the results of the present study agreed. A previous study reported the underlying mechanism of osteochondral destruction in diffuse type TSGCT. Namely, TSGCT invades bone from the attachment site of the articular capsule or ligaments where articular cartilage is bare . Furthermore, previous studies including our previous report indicated that osteochondral destruction often occurs in joints with a small articular cavity such as hip and ankle [12, 15, 21]. These previous results are consistent with the findings of the current study in which diffuse-type and joints other than knee were independent factors associated with the initial joint destruction. Diffuse type TSGCT could invade bone at areas bare of cartilage, with joints other than knees having low joint capacity. In these joints, reconstruction procedures for joints including total joint arthroplasty and arthrodesis are appropriately selected depending on the individual circumstances.
Several limitations are present in the present study. First, it focused on a limited number of patients due to the rarity of this disease, who were analyzed retrospectively. Exclusion of cases followed up for less than 12 months and with insufficient medical records reduced the number of localized cases such as those with finger or toe involvement. Because the present study focused on the factors associated with local recurrence and osteochondral destruction causing possible functional impairment, cases with relatively large joints were selected as targets for investigation. Compared with previous reports, the present eighty cases represent a relatively high number, and analyses for osteochondral destruction have rarely been performed. The second limitation is that numerical evaluations of patients’ function after surgery, local recurrence, and osteochondral destruction were not performed, and the occurrence of osteochondral destruction is not necessarily consistent with the onset of pain. In future studies, function in addition to the presence of pain should be analyzed for not only surgically treated patients, but also those treated conservatively including watchful observation. The third limitation was the presence of slight differences in treatment strategies among the treatment periods and institutions. The final treatment modality was determined by the physicians and patients based on close counseling at each institution, and in some institutions full-time orthopedic surgeons specializing in arthroscopic surgery are not available. Indications for specific surgical procedure, arthroscopic surgery or open surgery, differ among cases. These factors may have influenced the outcome. Although the efficacy of radiotherapy for TSGCT has been reported [33, 34], it has in general not been chosen in this context at our institutions, or in our country.