Jaffe introduced OO on 5 cases of benign bone tumor in 1935. Approximately one out of ten cases of OO are intra- or juxta-articular . It is not difficult to recognize the regular lesion based on the characteristic clinical, radiological and histological pictures. However, it is still a challenge if the position is located in the joint capsules, which may produce a variety of nonspecific manifestations and confusing radiological features .
OO occurs predominantly in the appendicular skeleton. According to the Musculoskeletal Tumor Society staging system, the lesion was classified as cortical, cancellous, and subperiosteal [19, 20]. The hip was the most commonly affected joint, accounting for 28%-40% of all cases . In our study, lesions were seen in most of the functional joints, with the hip being the most prominent (63.33%). The tricking point of intra- and juxta-articular lesions lies in their insidious clinical manifestations, which leads to delayed diagnosis and thus makes the children's pain unable to be resolved. It was worth noticing that the physis lesions can cause limb length discrepancy with potential coronal and/or sagittal malalignment
Pain is the most common symptom, even the lesion involved joints. The clinical manifestation can be subtle, such as the patient can present with referred pain in the knee if the lesion is involved in the hip. Synovitis is another feature when the articular lesion continues to progress. Joint pain, flexion contracture, decreased range of motion, and a limp or antalgic gait can also be seen in these patients. In the present study, most patients presented with pain as the primary symptom, although the location was variable and influenced by status. However, loss of function took the form of decreased range of motion of the affected joint, including a limp, abnormal range of motion, and uncomfortable when playing. Pain with activity and abnormal range of motion was significantly different between intra- and juxta-articular patients. This may attribute to the constant friction on the intra-articular lesion. More severe synovitis can cause more pronounced pain; other than that, long-standing inflammation may damage the cartilage on the joint surface[7, 23]. From that, consistently abnormal range of motion also obviously influenced the complications. Therefore, we suggest that in the case of suspected intra-articular cases, the relevant examinations should be actively improved to avoid permanent damage to the intra-articular structures
Plain radiography is warranted when children are complaining of pain or limited range of motion. The manifestation is different from the traditional cortical lesion, and the surrounding reactive sclerosis can be minimal or absent in intra- and juxta-articular OO. The nidus is not visualized on plain films, but additional findings such as loss of function often remind the physician to take further imaging workup. The sensitivity of Technetium-99-labeled bone scintigraphy is 100% for confirming the diagnosis of OO. So, if the bone scan imaging is positive, limited-field, thin-cut CT scans should be the next imaging modality for more precise localization. CT is the modality of choice for diagnosis and specifying the location of the lesion. In the present study, all patients had CT scans, but not all patients had the classical image of the nidus, so multiple CTs was performed. The reasons why we must do CT are as follows: 1. CT can help us locate the lesion accurately and facilitate subsequent surgical operations; 2. 2. CT can exclude other diseases with similar clinical manifestations, such as synovitis, bone tuberculosis, infection, etc. MRI is also a reliable method of visualizing the nidus since it is more sensitive to detecting reactive changes in soft tissue. Germann et al claimed that MRI was excellently suited for diagnosing intra- and extra-articular OO because the joint effusion and synovitis were distinguished between the intra- and extra-articular. However, it was not easy to separate the soft tissue edema and synovitis from intra- and juxta-articular OO.
Although non-operative treatment can be considered as an option since some patients might heal spontaneously, in our center, all patients underwent surgical resection since symptoms persisted, even with NSAIDs. Moreover, in children with growth potential, the continued presence of these tumors can lead to undesired complications, such as limb length discrepancies or osteoarthritis. In this study, four patients (13.33%) had performed secondary surgeries (Fig. 2). The reasons were as following: 1) the resection was incomplete; 2) The location of the lesion was inaccurate during the operation; More physicians proposed to perform excision for intra-articular locations of the tumor [24, 28–31]. Over the years, CT-guided techniques, including trephine excision, cryoablation, radiofrequency ablation, and laser thermocoagulation, were reported to be a successful and low risk [32–35]. However, although this procedure is minimally invasive, it entails some problems, such as it is difficult to obtain an intraoperative tumor specimen, which is still a gold stand for definitive diagnosis of OO on histological examination.