Study Design

Prospective cohort study.

Introduction: Intra-operative localisation of small nidus in osteoid osteoma & osteoblastoma is difficult resulting in failed excision. Wide resection is fraught with prolonged operative time, increased bleeding and instability.

Methods: 8 patients (6M & 2F) with a diagnosis of osteoid osteoma(7) and osteoblastom(1) were operated at our centre between 1995–2005. The mean age at presentation was 20.9 years (9–31 yrs). The tumour was localised to cervical(2), thoracic(4) and lumbar(2) posterior elements respectively. All had back/neck pain of varying duration (mean 20 mo; range 6–48 mo). 2 patients presented with thoraco-lumbar scoliosis and 3 had failed treatments. All patients were worked-up with x-rays, CT/MRI and 99m technetium scan to localise lesion. 600 MBq Tech HMDP(hydroxy-methylene-di-phosphate) was administered intra-venously 3 hrs prior to surgery and fluoroscopy was used to confirm anatomical level. A 5 mm cadmium telluride (Cd Te) probe & rate meter were used to scan the area containing lesion and counts per second (cps) recorded. Background count from adjacent area was obtained for comparison purposes. The tumour nidus was then excised & cps from tumour bed and excised specimen recorded.

Results: The mean follow-up was 5.85 years (2–12.33). The mean cps for osteoid osteoma pre-excision was 203.8 (60–515) which fell to 72.5 (10–220) post-excision. The cps reduced from 373 to 40.5 postoperatively for osteoblastoma. Complete excision was recorded every time and all patients reported characteristic disappearance of pre-operative pain. All had discontinued analgesic medication, returned back to normal activities by 3 months and were followed-up at regular intervals for 2 yrs when they filled NDI, ODI & SF-36 questionnaire.

Discussion: Gamma probe guided surgical excision facilitates accurate localisation of lesion, is less invasive warranting minimal bone resection & resultant instability and perhaps most importantly confirmation of complete excision of the tumour nidus consistently every time (esp. failed surgeries).

Immunoscintigraphy using radioisotope-labelled monoclonal antibody prepared against osteosarcoma 791T cells was used to detect a primary osteosarcoma. The eight-centimetre tumour was detected using rectilinear scintigraphy of 131I-labelled antibodies. Image enhancement was achieved by subtraction of blood-pool radioactivity labelled with technetium-99m. The ratio of tumour to non-tumour uptake of radioactivity (5:1) suggested that antibody targeting of therapeutic agents is feasible.