| for people with instability | 4 | purpose |
| to provide protection | 2 | purpose |
| to stabilize the spine | 2 | purpose |
| fusion → be → necessary | 16 |
| fusion → be → required | 9 |
| fusion → become → necessary | 3 |
| negative | neutral | positive |
| 0.144 | 0.770 | 0.086 |
| Raw frequency | 28 |
| Normalized frequency | 0.657 |
| Modifier score | 0.400 |
| Perplexity | 214.431 |