Recovery after multilevel lumbar interbody fusion is similar between patients who receive weekly teriparatide and bisphosphonate therapy, according to study results published in Spine. Bone contact status after surgery was more predictive of bone fusion rates.
Weekly teriparatide has been shown to help achieve effective bone union after single-level lumbar interbody fusion. In a multicenter prospective randomized study, researchers aimed to determine whether weekly teriparatide improved bone union in patients who underwent multilevel lumbar interbody fusion and how the results compared with results achieved with standard bisphosphonate treatment. They also sought to determine the effect of bone contact status following surgery on recovery.
Patients (N=104) were recruited from 3 university hospitals in Japan and were ≥50 years of age, osteoporotic, and at high risk for fracture or lumbar degenerative disease. Patients were randomly assigned to the weekly teriparatide group (n=50; mean age, 72.5 years; 82% women) or bisphosphonate group (n=54; mean age, 72.0 years; 77.8% women). Teriparatide was administered subcutaneously from 1 week to 6 months postoperatively. Bisphosphonate therapies were administered either once monthly or once every 4 weeks with no dosage form restrictions. Of the patients who initiated teriparatide and bisphosphonate therapy, 47 and 52 completed treatment, respectively.
Bone fusion was assessed by dynamic x-ray and 3-dimensional computed tomography immediately after surgery and at 2, 4, and 6 months after the procedure. A fusion score was assigned based on stage: complete fusion (1 point), moderate fusion (2 points), and nonfusion (3 points). A total fusion score was assigned based on both sagittal and coronal views, for a total score range of 2 to 6 points. Bone contact status was evaluated within 2 weeks of surgery and was defined as a state in which the vertebral body and the transplanted bone were in contact at ≥50% of the endplate.
At 2, 4, and 6 months postoperation, bone fusion scores were 3.9±0.2, 3.3±0.2, and 3.8±0.2 points in the weekly teriparatide group, respectively, and 4.1±0.1, 3.4±0.1, and 4.2±0.2 in the bisphosphonate group, respectively. At 6 months, the rate of bone fusion tended to be higher in the weekly teriparatide group compared with the bisphosphonate group (46.8% vs 32.7%), though this difference was nonsignificant. Clinical outcomes, as assessed by the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire and the Oswetry Disability Index, were significantly improved in both groups at 6 months compared with baseline levels but were not different between groups.
Bone contact status was associated with a significantly higher rate of bone fusion at 2 (P <.001), 4 (P <.001), and 6 months (P =.001). At 6 months postoperation, fusion rates in patients with bone contact after surgery were 5 times higher than those in patients without bone contact (47.4% vs 9.5%). All patients without bone contact after surgery who achieved bone fusion at 6 months (n=2) had received weekly teriparatide.
A lower rate of bone fusion was observed for patients who received multilevel lumbar interbody fusion (46.8%) compared with that in patients who received single-level lumbar interbody fusion (69.0%; P <.001), which correlated with higher bone fusion scores for the multilevel group at 2, 4, and 6 months postoperative (P <.05 for all).
The researchers noted that the small sample size and short postoperative observation period represented limitations to the study. Given the lack of research on the effects of these therapies on bone fusion after surgery, it is unclear whether the 6-month observation period allowed for meaningful evaluation of effects.
Although teriparatide improved patient outcomes following bone fusion, the researchers concluded that there was no significant improvement over the bisphosphonate group with regard to bone fusion rates or bone fusion scores. Bone contact status immediately after surgery, however, was significantly correlated with bone fusion outcomes. Additionally, as they expected, bone fusion was more difficult to achieve following multilevel lumbar interbody fusion than after single-level lumbar interbody fusion. The study authors noted that “[c]areful cartilage endplate dissection and adequate bone grafting are therefore needed to improve bone fusion rate when performing [multilevel interbody lumbar fusion].”
Oba H, Takahashi J, Yokomichi H, et al. Weekly teriparatide versus bisphosphonate for bone union during six months after multi-level lumbar interbody fusion for osteoporotic patients: a multicenter, prospective, randomized study [published online February 11, 2020]. Spine. doi:10.1097/BRS.0000000000003426