Outcome assessment in lumbar spine surgery

Gustavo Zanoli
Acta Orthopaedica. Supplementum 2005, 76 (318): 5-47

BACKGROUND: There is no consensus regarding outcomes assessment in spine patients. When using Health-Related Quality of Life (HRQoL) in assessing outcomes of treatment, normative data for different diagnoses are needed to allow comparisons between existing and future studies. The most used generic instrument for HRQoL evaluation in spine pathologies is SF-36. There is no standard definition of important differences in spine surgery patients and no standard reference for minimal clinically important difference.

OBJECTIVE: The overall aim of this thesis was to increase understanding of some aspects of outcome measurement in patients operated on for lumbar spine problems using existing prospective data available at the spine section of the Orthopedics Department of the University of Lund, and, moreover, to explore potentials and weaknesses in the methodology of retrospectively analysis of prospectively collected observational data.

METHODS: A systematic web-search and review of the literature and a retrospective analysis of prospective cohort data collected within the data collection protocol in use by the Swedish Spine Register. Since 1993 all persons undergoing elective lumbar surgery at the spine section of the Orthopedics Department of the University of Lund were included in the prospective registration protocol either in its first version (1993-1997), which was the source of data for paper III, or in its revised version after 1998. Initial information at baseline (the day before surgery) included age, sex, smoking habits, duration of preoperative back and leg pain in months, duration of preoperative sickleave in months, number of previous operations, patient's working status, diagnostic techniques pre- and postoperatively VAS scores analgesic intake, walking distance. Postoperatively, change in leg and back pain, respectively, was recorded on a 5-point Likert Scale as compared to preoperative status, patient satisfaction was recorded on a 3-point Likert Scale.

RESULTS: The number of proposed outcomes, outcome scores, outcome instruments is incredibly high: no new HRQoL instruments specific for LBP are needed. The data collection protocol of the Swedish Spine Register studied can reliably detect postoperative improvements between large groups of patients such as in a Register. Pain intensity measured on the VAS correlates significantly to other indicators of perceived pain, but correlation is not as strong as it could be if they were all measuring the same construct. HRQoL as measured by SF-36 in patients scheduled for lumbar spine surgery showed a pronounced reduction compared to normal and LBP population. The use of norm-based scoring for SF-36 can help interpretation and simplify graphic representation of the findings. SF-36 outcomes 1-year after surgery for lumbar spine disorders are improved, although other factors or natural history could contribute to this improvement. The global effect of spine surgery in our sample is quite similar to effect sizes of very successful orthopedic interventions. The use of standardised outcome measures allows international comparisons, although caution should be used in the interpretation of differences.

CONCLUSIONS: Without the need of additional expensive data collection and using limited economic resources an increased understanding of some aspects of outcome measurement in patients operated on for lumbar spine problems has been achieved. Reference values and more speculative data (such as effect sizes and MCIDs) have been presented. The ecological methodology has been presented and discussed: with a clear respect for its limitations, it could be used to obtain relevant information also in other clinical fields.

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