To investigate the safety and effect of zoning laminectomy for the ossification of thoracic ligamentum flavum.

From November 2011 to December 2014, 34 patients (15 males, 19 females; 41-76 years old, average 55.0±8.1) with ossification of thoracic ligamentum flavum (OLF) were treated by zoning laminectomy. The course of disease ranged from 1 month to 123 months (average 16.5 months). According to the anatomical characteristics and the pathological ossification process of the thoracic ligamentum flavum, we proposed the concept of "zoning", which divided each segmental thoracic OLF into three zones: "safety zone", "middle zone" and "risk zone". From the features of anatomy of LF and process of OLF development, we found there is no or less cerebrospinal fluid between spinal cord and the tip of each ossified nodular masses in severe OLF, any procedures using instruments in this area have the potential to cause irreversible spinal cord injury, we defined this area as "risk zone", the "null" area of each lamina and lateral and dorsal side of nodular masses as "safety zone", and the other area as "middle zone". From "safety zone" to "risk zone" the spinal canal decreased gradually, different zone needs different surgical strategy: This surgical procedure first removed the "null" area of superior and inferior lamina and dorsal side of each segmental OLF. Next, partially or totally resected the "middle zone", exploring the lateral side of nodular masses, and the "risk zone" was exposed and isolated. Finally, dissected the lateral side of nodular masses, and then the "risk zone" was floated and resected with a directly decompressing the spinal cord. Preoperative and postoperative modified Japanese Orthopedic Association (JOA) score and neurologic functional recovery ratio were used to evaluate the surgical outcomes.

Of the total 83 decompressed OLF segments, 5 (6.0%) located in the upper thoracic spine (T₁-T₄), 8 (9.6%) in the midthoracic spine (T₅-T₈), and 70 (84.4%) in the lower thoracic spine (T₉-L ₁). The followed up ranged from 4 to 40 months, with an average of 21.7±9.9 months. The mean JOA score increased significant from 5.3±2.0 preoperatively to 8.8±1.8 at the final follow-up (t=11.566, P=0.001). Postoperative average JOA neurologic functional recovery rates were 63.2%±24.7%, including excellent in 15 cases, good in 11 cases and fair in 8 cases. The excellent and good rate was 76.5%. Twelve cases had transient CSF leakage because of dural defect. The dural defect was only treated by tightly suturing the paraspinal muscles, the subcutaneous tissue, and the skin layers. The CSF leakage lasted for 6 to 8 days after operation. Two cases with wound infection were treated with debridement and antibiotics and healed completely. One case with thoracic spinal cord transient incomplete paralysis due to a post-operative epidural hematoma was treated with an emergency operation and got recovered neurological function.

Zoning laminectomy has the advantages of safe manipulation and thorough decompression, which is an effective choice for the surgical treatment of thoracic OLF.

Thoracic vertebrae; Ligamentum flavum; Ossification, heterotopic; Treatment outcome