Osteoid osteomas are small lesions that may be difficult to identify at the time of open surgery. Computed tomography (CT)-guided minimally invasive procedures with either drilling or radiofrequency ablation have greatly enhanced the success rate of removing the lesions1.
Image-guidance systems with sophisticated software are used in orthopaedic surgery to improve precision in orientation to perform osteotomies and to place endoprostheses and screws. During tumor surgery, identification of anatomic references is required for margin resection and to allow reconstruction.
We have adapted the StealthStation (Medtronic) treatment guidance system to assist with precision in complex bone tumor surgery and other complex orthopaedic procedures. The CT dataset concerning the organ of interest needs to have at least four fixed points that can be traced by an optical system as reference during the procedure, allowing for an accuracy of 1 mm under the best conditions. The most advanced mobile CT systems (e.g., O-arm Surgical Imaging System; Medtronic) allow data acquisition in the operating room, which is transferred to the navigation system; if needed, additional data acquisition and control are possible. However, the resolution of these systems is lower than with standard CT scanners, and there is a higher risk of radiation exposure for the staff in the operating room. Furthermore, their use is limited because of their high cost.
This case report describes a patient with a subchondral acetabular osteoid osteoma that we believed could not be safely resected with a standard CT-guided procedure or a minimally invasive open approach. We used visual guidance combined with electronic data processing to successfully treat this osteoid osteoma of the acetabulum following several unsuccessful prior CT-guided interventions. The patient was informed that data concerning the case would be submitted for publication, and she provided consent. Patient confidentiality was protected according to the Health Insurance Portability and Accountability Act (HIPAA) of the United States.
A twenty-year-old woman presented with increasing pain in the left hip joint caused by an osteoid osteoma in the subchondral anterolateral part of the acetabulum. She had had three prior core biopsies (performed by the senior author [G.U.E.] in a standard CT scanner) that revealed the pathology of the osteoid osteoma. These interventions had been performed with the instruments directed coaxially to the CT planes, which was important to avoid any damage to the acetabular cartilage. Because of persistent symptoms, the patient presented to another institution, where the fourth intervention was performed with the O-arm Surgical Imaging System. This system was equipped with optical navigation in order to direct the drill obliquely to remove the lesion; however, the osteoid osteoma was missed completely, and postintervention magnetic resonance images (MRIs) showed osteonecrotic changes of the femoral head (Figs. 1-A and Fig. 1-B).
At that time, one option could have been a large open approach, either with surgical hip dislocation or a retroperitoneal approach. With the changes of the femoral head that were seen following the last intervention, we believed that any larger procedure would carry a risk for additional femoral head damage, and we wanted to use visual intra-articular guidance. Because we had had prior experience with not recognizing osteoid osteomas of the acetabulum at surgical hip dislocation because of the covering articular cartilage, it was decided to use CT-based navigation in combination with arthroscopy to remove the osteoid osteoma.
The patient was placed in the lateral decubitus position under general anesthesia in the CT scanner in the radiology department. Four Apex Pins (Stryker) were inserted in the left hemipelvis (one in the left pubic bone, one lateral to the anterior superior iliac spine, and two in the left iliac crest) (Fig. 2-A). A high-resolution CT scan was taken, and the data were transferred to the StealthStation treatment guidance system. In order to avoid any contact with the Apex Pins and to keep them in the same position, the patient was positioned on a traction table and transferred to the operating room.
According to our standard operative protocol, developed by Herzog2, hip arthroscopy was performed over an anterolateral portal from extra to intra-articular, avoiding iatrogenic chondrolabral damage (Fig. 2-A). After a T-shaped capsulotomy and application of axial traction by a fixation device (VACOped; OPED AG), the navigated 70° arthroscope (Storz) was introduced into the acetabulum. The arthroscopic view presented minor irregularities of the chondral surface of the acetabular roof, suggesting remnants of the earlier procedures rather than the subchondrally located osteoid osteoma. Axial traction was temporarily reduced and was reinstituted following the next step.
The pelvic surface of the acetabulum was then exposed over an ilioinguinal approach, avoiding damage to the lateral femoral cutaneous nerve (Fig. 2-B), and laterally to the iliopsoas muscle, protecting the femoral nerve. With use of the navigation system, a threaded Kirschner guidewire was introduced from the pelvic brim and targeted at the osteoid osteoma. Under arthroscopic control, the guidewire was advanced until its tip appeared within the acetabular chondral surface (Fig. 3). With use of a cannulated biopsy drill (Exner-Zihlmann ZSB), the osteoid osteoma was overdrilled under simultaneous navigational guidance of the 10-mm drill and navigated arthroscopy, avoiding perforation of the chondral surface (Figs. 4-A, Fig. 4-B, and Fig. 4-C). No image intensifier or fluoroscopy was used in the operating room. Histopathologic examination of the drill-core material confirmed the diagnosis of osteoid osteoma (Fig. 5).
Postoperatively, we recommended a temporary reduction of weight-bearing, and wound-healing of the operative approaches was uneventful. The osteoid osteoma pain resolved immediately; some persisting vague pain was attributed to the damage of the femoral head. On MRI examination, the former osteoid osteoma was absent (Fig. 6).
Our patient was initially treated according to accepted standards; however, only the combined application of arthroscopic visual and navigated cross-sectional image guidance was definitively successful. To the best of our knowledge, this combination of a navigated surgical and arthroscopic approach in the subchondral location of an osteoid osteoma has not been reported previously.
Based on fluoroscopy and CT, navigated placement of percutaneous screws in both thoracic spine and pelvic surgery has been shown to have high accuracy3,4. Because of high reliability, CT-based and Iso-C3D-based computer navigation are being used more often in limb-preserving tumor surgery5-8.
Navigated excision of small osteoid osteomas targeted to preserve the surrounding bone structure has been successful in spinal surgery9,10 and in long bones11,12. As a prerequisite for matching the intraoperative osseous surface with the preoperative CT images, a larger soft-tissue exposure is required9. Intraoperative fluoroscopy-based navigation without need for surface registration minimizes the surgical approach but contributes to potential radiation exposure10,12.
In an intra-articular location with arthroscopic visibility and access, direct arthroscopic removal of an osteoid osteoma from the articular surface has been reported previously13,14. In a juxta-articular subcortical location, CT-guided indirect resection of an osteoid osteoma under arthroscopic control preserved the integrity of the overlying cartilage surface15.
In a comparable task that preserves cartilage integrity, computer-assisted retrograde drilling of osteochondrotic lesions of the talus has been developed, with use of preoperative CT scans of the ankle joint after the fitting of a removable cast16. This technique is accurate, but it requires highly technical and qualified personnel. Treatment of an osteochondrotic lesion of the femoral condyle that was not visible with an arthroscope was achieved by means of navigated retrograde drilling after fusion of a preoperative MRI dataset with intraoperative Iso-C3D fluoroscopy17; 2D-fluoroscopic navigation18 and a recent fluoroscopy-free navigation procedure19 were successful in the retrograde drilling of the subchondral bone in osteochondrotic lesions of the talus when the osteochondral focus was arthroscopically identifiable.
In our case, the lower resolution of the O-arm Surgical Imaging System may have provided less precise data, thus allowing the osteoid osteoma to be missed initially. The high-resolution CT used for navigation has a relatively high radiation exposure for the patient, but it resulted in definitive control of the disease without additional radiation exposure to the operating room staff. While the patient was exposed to more radiation with the high-resolution CT, had our procedure been done initially, the patient would not have received radiation during the prior unsuccessful procedures.
Any means to improve precision should be applied in orthopaedic and trauma surgery. The navigation tool described here has been used for many years, especially in neurosurgery, and is available in many hospitals. We have adapted it for bone surgery with the use of Apex Pins, which serve as reference. In addition to the precision of the guidance system, another advantage may be the reduced radiation exposure to the operating room personnel.