Arthroscopic Excision of Intra-Articular Osteoid Osteoma of the Hip: A Case Series

Purpose: To identify the clinical features of intra-articular osteoid osteoma (OO) of the hip, to evaluate the clinical effect of arthroscopic excision for intra-articular OO, and to summarize the characteristics of revision cases of hip OO and the revision surgery under arthroscopy in these cases. Methods: We retrospectively reviewed the data of 25 patients who underwent arthroscopic excision of hip OO. The case series included 10 patients who underwent revision surgery. Lesion location, presenting symptoms, and symptom duration were analyzed; postoperative improvement was assessed using the modified Harris Hip Score (mHHS) and International Hip Outcomes Tool (iHot-12) score. We examined the reasons for revision surgery and the characteristics of OO progression after the first surgery. Results: The most common presenting symptom was groin pain that was relieved by nonsteroidal anti-inflammatory drugs (NSAIDs). Varying degrees of limitation of range of motion (ROM) were present in all patients. The osteosclerosis around the tumor nest on computed tomography (CT) scan is a characteristic radiographic feature in this disease. However, the classic radiographic feature was apparent on plain x-rays in only 2 of 25 patients. As a kind of efficient radiological method, magnetic resonance imaging (MRI) can help in distinguishing OO from femoroacetabular impingement (FAI), as the latter is characterized by a large effusion and bone marrow edema at the atypical site of impingement. For the patients who had only 1 arthroscopic resection, the mean (+/- standard deviation) mHHS and iHot-12 scores were 70.30 +/- 9.06 (range 51 to 86) and 75.07 +/- 7.69 (57 to 88), respectively. At last follow-up, the mean scores were 98.30 +/- 2.15 (94 to 100) and 97.76 +/- 2.04 (94 to 100). For revision cases, the mean mHHS and iHot-12 scores were 68.55 +/- 3.77 (60 to 72) and 67.88 +/- 5.39 (56 to 76). At last follow-up, the mean scores were 97.11 +/- 2.47 (94 to 100) and 95.22 +/- 1.78 (94 to 100). In the present study, 24 of 25 patients (96%) reached the minimal clinically important difference (MCID) of mHHS, and 21 of 22 patients (95.2%) reached the MCID of iHot-12. Among the revision patients, the most common misdiagnosis at first surgery was FAI. Another feature is that a wrong diagnosis or incomplete intra-articular OO resection can stimulate the tumor and cause an inflammatory reaction and rapidly progressive OA, necessitating prompt revision surgery for complete removal. The degree of joint degeneration was related to the time since the first operation. Conclusion: OO of the hip joint typically presents with pain and limited joint activity. Misdiagnosis as FAI or synovitis is common, and CT scan is very helpful for accuracy diagnosis. Arthroscopic excision appears to be an effective method for the treatment of OO of the hip joint.