We treated 50 patients with fractures of the waist of the scaphoid in a below-elbow plaster cast for up to 13 weeks. Displacement of the fragments was assessed independently by two observers using MRI and radiographs performed within two weeks of injury.

The MRI assessments showed that only the measurement of sagittal translation of the fragments and an overall assessment of displacement had satisfactory inter- and intra-observer reproducibility and revealed that nine of the 50 fractures were displaced. Only three of the 49 fractures with adequate follow-up failed to unite, and all were displaced with more than 1 mm of translation in the sagittal plane. If the MRI assessment of displacement of the fracture was used as the measurement of choice, assessment of displacement on the initial scaphoid series of radiographs showed a sensitivity of between 33% and 47% and a positive predictive value of between 27% and 86%. Neither observer was able correctly to identify more than 33% to 47% of the displaced fractures from the plain radiographs. Although the overall assessment of displacement and gapping and translation in the coronal plane on the plain radiographs influenced the rate of union, none of these parameters identified all three fractures which failed to unite.

We conclude that the assessment of displacement of scaphoid fractures on MRI can probably be used to assess the likelihood of union although the small number of nonunions limits the power of the study. In contrast, the assessment of displacement on routine radiography is inaccurate and of less value in predicting union.

Objective: To assess the intra- and inter-observer reproducibility of a number of commonly used radiological measurements in pre- and post-operative patients with thoracic adolescent idiopathic scoliosis (AIS). Reproducibility of measures other than Cobb angle and vertebral rotation have not been studied and particularly there are no reports of reproducibility in patients after instrumentation.

Design: Repeat measurement of radiographs before and after surgery by 2 observers.

Subjects: 30 patients with thoracic AIS were selected from a scoliosis database at random: 15 treated with posterior USS and 15 with anterior instrumentation (8 Zielke / 7 anterior USS).

Outcome measures: The pre-operative AP radiograph, supine lateral bending radiograph and the post-operative AP radiograph at 6 months were selected for each patient. Two observers (MM beginner, AAC experienced) obtained the following measurements from the radiographs: Cobb angle, apical vertebral rotation (AVR, Perdriolle), apical vertebral translation (AVT) to the T1-S1 line, and frontal plane imbalance (FPI). With all marks removed, the radiographs were re-measured by each observer at least one week later. Repeatability was calculated using the method described by Bland and Altman (BMJ 1996). This method is a widely accepted anthropometrical technique but has not previously been used for assessing scoliosis measurements. It was assessed as 95% reproducibility. The co-efficient of reliability (r) expresses the proportion of the observed variability that is not due to error, i.e. higher is better. This was calculated as a means of assessing the usefulness of our measurements and to enable us to compare them.

Results: Intra-observer repeatability (MM vs. AAC): Whether the instrumentation was anterior or posterior had no effect on Cobb angle, AVT or FPI repeatability. AVR however was worse for posterior instrumentation 19° vs. 12°. “r” was > 90% for Cobb angle, AVT and PFI. But, for AVR r measured pre-op 52-92% and post-op 38–69%.

There was no relationship between repeatability and the measurement size.

Conclusions: Measurement reproducibility / error is slightly worse than previously suspected. E.g. a 5–6° curve progression is thought to be significant. We suggest that this could be due to measurement error and the figure should be 6–8°. There is no learning curve for the technique used to measure Cobb angle, AVT and FPI. AVR (Perdriolle) however requires experience. Cobb angle measurement error post-op is similar to pre-op. The Perdriolle method has greater error post-op especially in posterior instrumentation.