In the present case series, we determined that a poor pain reduction rate (~ 27%) 3 weeks after the diagnosis of an OVF that caused pain was a factor significantly associated with inadequate pain relief at final follow-up (14 months). Until now, few studies have addressed the process of pain recovery in patients with OVF treated with conservative therapy. Based on the experience of individual doctors in clinical practice or at hospitals managing these patients, wide variations in the initial treatments for OVF—such as drug administration, bracing, bedrest for a set duration, admission to a hospital, and so forth—are among the possible reasons for a lack of reports addressing the course of pain reduction in the past. This wide variation makes it challenging to compare the actual time course of pain reduction between patients who received different therapeutic regimens. In contrast, in this case series we applied a conservative standardized treatment regimen that included 2 weeks of bedrest followed by rehabilitative treatment that required a rigid Jewett spinal brace to be worn; this enabled us to analyze the course of pain reduction over time. We consider this one of the strong points of our present study.
Toyoda and colleagues performed a stepwise cluster analysis using VAS scores and identified four different patterns of lumbar pain progression after OVF . In that report, cluster 4 included the patients who initially exhibited moderate to strong pain without pain reduction over the clinical course. Another cluster included patients with initial moderate pain that was rapidly attenuated. In the present study, patients in the group who experienced an unfavorable level of pain reduction (< 50% at 3 weeks similarly exhibited an inadequate reduction in their pain level 12 weeks after hospital admission for OVF. Results at the final follow-up visit largely overlap with the cluster 4 results in the report of Toyoda et al. Both reports showed that a failure to adequately relieve pain in the relatively early phase of treatment is significantly associated with inadequate pain relief at final follow-up. In other words, the pain reduction rate at a relatively early phase of OVF could be one of the possible predictive factors for the prognosis of pain reduction. Further exploration with a larger prospective cohort in the near future is prerequisite to being able to elucidate the true usefulness of using pain mitigation early in the course of treatment as a predictive factor for pain prognosis in patients with OVF.
Previously, Toyone et al. reported that vertebral instability in the early phase after injury was significantly associated with pain reduction at final follow-up . In the present study, univariate analysis revealed that vertebral instability 3 weeks after diagnosis of OVF was significantly associated with final outcomes; this aligns with the report of Toyone and colleagues. A possible reason for a discrepancy between the two studies is the cutoff of the dichotomous objective variable, ≥ 50% pain reduction. Therefore, it might be considered premature to conclude that vertebral instability is unassociated with final outcome.
The present study has several strengths and limitations. We consider that the ease of evaluation is a strength of our study in addition to only evaluating pain intensity after an appropriate period of conservative therapy. Furthermore, the conservative standardized treatment regimen lends strength to our results. In contrast, the latter approach could hinder the generalizability of our results to patients receiving other types of conservative treatment. The limitations of this study included the small number of patients, a short follow-up period, and the fact that we did not consider other factors associated with the clinical course, such as fracture type and underlying disorders. The retrospective nature of the present study is another possible limitation given that we could not consider the patients who discontinued the study.
Currently, we apply conservative standardized therapy regimens to almost all patients with OVF as a way of screening. If the reduction in pain achieved via initial conservative treatment is inadequate, we consider other treatment options that include surgery. Our study results are encouraging and support our current treatment strategy.