Failures of treatment of osteoid osteoma (OO) are related to errors in exact localization and incomplete excision of the nidus. Intraoperative Iso-C 3D navigation allows exact localization, excision and confirmation of excision by percutaneous methods.

We report the successful percutaneous excision of OO in 11 patients (extremities-5; spine-6). All patients had a minimally invasive reflective array (MIRA) fixed to the same bone in the extremities and to the adjacent spinous process or body(caudal) in spine, followed by registration of anatomy. A tool navigator was utilized to plan the key hole incision so that the trajectory did not involve important anatomical structure. A sleeve was then introduced which allowed the usage of instruments like a burr and curette to deroof the nidus, curette the nidus and obtain material for histopathology and further burr the cavity to ensure complete eradication of the nidus. During the entire procedure, the tool navigator was used frequently to reconfirm the location and the depth of burring. Following excision, registration using Iso-C 3D C-arm was done to confirm the complete eradication of the nidus.

The age of the patients varied from 10 years to 27 years. In the extremities, location of the MIRA was in the same bone and firm anchorage was obtained using either a single Steinman pin locator (4 patients) or a double pin locator (1 patient). In spine the MIRA was attached to the adjacent spinous process (caudal) in the cervical, thoracic or lumbar region (5 patients) and in sacrum (1 patient) it was attached using a Steinman pin to the adjacent vertebral body. Excellent three-dimensional view of the nidus and localization was possible in all patients. A safe trajectory that avoided anatomical structures was possible in all patients using a tool navigator. The incision ranged from 1 to 4 cms. Adequate material for histology was obtained in ten patients that confirmed the diagnosis of osteoid osteoma and in one patient histopathological confirmation was not possible because the nidus was completely destroyed during the process of deroofing and burring. In ten patients, post excision ISO-C 3D scans confirmed adequate removal and in one patient, it was successful in identifying incomplete removal requiring further excision of the nidus. The average operating time was 62 mins (37–90 mins) and the blood loss was less than 30 cc in all patients. All patients achieved excellent pain relief and were asymptomatic at an average follow up of 3.4 (2.2 – 3.9) years.

Iso-C 3 D navigation offers the advantage of excellent localization of the nidus and percutaneous excision of these tumors, thereby conserving bone in critical locations like the spine and upper end of femur. It also offers the advantage of intraoperative confirmation of adequate excision and allows harvesting the nidus for histological confirmation.

Study Design: An in-vivo serial magnetic resonance imaging study of diffusion characteristics in human lumbar discs over 24 hours in healthy volunteers and patients with low back pain. Objective: Nutrition to the disc is solely by diffusion but no firm data is available on diffusion pattern in humans. This study reports diffusion patterns in a human population studied and documents the 24-hour diffusion pattern.

Methods: T1-weighted images were obtained pre and post-contrast with Gadodiamide-0.3mmol/kg at 5, 10 minutes, 2, 4, 6, 12 and 24hours. Diffusion was calculated by measuring signal intensity values in seven regions of interest (anterior and posterior annulus, anterior, posterior, peripheral (PNP) and central (CNP) parts of nucleus pulposus (NP). Enhancement percentage (EP), Peak enhancement percentage (PEP) and time to achieve PEP (T_max) were calculated.

Subjects: Of the 215 discs in 43 persons (10 volunteers and 33 patients) 96 discs were normal and considered for study.

Results: Diffusion occurred mainly from the endplate (rather than annulus). The mean EP of PNP and CNP at 5 minutes was 6.7, 3.9; 10minutes was 7.5, 4.0; 2 hours was 36.6, 17.9; 4hrs was 42.8, 29.8; 6hrs was 51.7, 40.5; 12hrs was 35.9, 27.8 and 24 hours was 33.3, 27.9. Though PEP was achieved at 6 hours in NP, the CNP lagged behind throughout. Univariate ANOVA showed that there was significant difference (p< 0.0001) in PEP of NP between the age groups of less than ten (72.4) and higher (37.9). The mean PEP at the NP of lower two discs (26.8) was less compared to upper two discs 41.0(p=0.059). Stepwise linear regression analysis showed that diffusion to the CNP was significantly influenced by age (R² =0.324), followed by level of disc (R²=0.5).

Conclusion: This is the first study to document the normal 24-hour diffusion pattern across lumbar discs. The data can form the basis for comparison of diffusion changes in degeneration, Modic’s endplate changes and smoking.