Inter- and intra-rater reliability of vertebral fracture classifications in the Swedish fracture register

Table 1 Rater experience level and time between the test occasions

	Experience level	Time between first and second test for cervical fractures	Time between first and second test for thoracolumbar fractures
Rater 1	Senior consultant in orthopaedics and spine surgery as well as responsible for the vertebral fracture classification in the Swedish Fracture Register.	1 mo	7 mo
Rater 2	Senior consultant in orthopaedics and spine surgery.	1 mo	7 mo
Rater 3	Specialist in orthopaedics.	7 mo
Rater 4	Resident in orthopaedics.	7 mo
Rater 5	Medical student, trained by Rater 1 to be knowledgeable on the topic.	1 mo	1 mo
Rater 6	Resident in orthopaedics.		1 yr
Rater 7	Resident in emergency medicine.		1 yr

Raters 1, 2 and 5 were actively working with classifications and vertebral fractures in the time between the tests while Raters 3, 4, 6 and 7 were not.

Table 2 Distribution of fractures according to the gold standard

			Number of patients	Number of patients with signs of ankylosing spinal disorder
Cervical spine	C1-Th1		50	6
	C1	Posterior arch	2	0
		Burst	5	1
		Lateral mass	1	0
	C2	Odontoid	11	1
		Hangman’s	2	0
		Unclassifiable	4	0
	C3-Th1	Compression	13	3
		Burst	0	0
		Translation/rotation	7	2
		Other	11	0
		Unclassifiable	2	0
Thoracolumbar spine	Th2-L5	Injury through axial compression (A-type injuries)	40	6
		Injury through anterior and posterior structures causing displacement (C-type injuries)	10	10
	Th2-L5 A-type injuries	Wedge shaped compressions	17	2
		Fracture through the middle part of the vertebral body	2	0
		Burst fracture	21	4
	Th2-L5 B-type injuries1	No injury of posterior structures	24	1
		Rupture of the posterior tension band structures through bone	9	4
		Rupture of the posterior ligament	5	0
		Unable to assess	2	1
	Th2-L5 C-type injuries	Hyperextension injury without translation	9	9
		Translation injury/dislocation through bone or disc/ligament	1	1

¹Classification of B-type injuries are only assessed in patients with A-type injuries. C: Cervical vertebra; L: Lumbar vertebra; Th: Thoracic vertebra.

Table 3 Inter-rater reliability compared to the gold standard shown as kappa value (asymptotic standard error) for vertebral fracture classifications

		Kappa
		Cervical spine					Thoracolumbar spine
		C1-Th1	C1	C2	C3-Th1	Signs of ankylosing spinal disorder1	Th2-L5	Th2-L5 A-type injuries	Th2-L5 B-type injuries	Th2-L5 C-type injuries	Signs of ankylosing spinal disorder1
Test 1, Rater	1	0.59 (0.07)	0.61 (0.10)	0.81 (0.07)	0.78 (0.06)	0.81 (0.13)	0.64 (0.08)	0.88 (0.06)	0.70 (0.08)	0.72 (0.10)	0.91 (0.07)
	2	0.59 (0.07)	0.72 (0.10)	0.89 (0.06)	0.71 (0.07)	0.91 (0.09)	0.67 (0.07)	0.86 (0.06)	0.64 (0.08)	0.89 (0.08)	1.00 (0.00)
	3	0.51 (0.07)	0.79 (0.10)	0.66 (0.08)	0.66 (0.07)	0.67 (0.15)
	4	0.47 (0.07)	0.86 (0.09)	0.74 (0.07)	0.61 (0.07)	0.32 (0.11)
	5	0.59 (0.07)	0.93 (0.07)	0.74 (0.07)	0.73 (0.07)	0.77 (0.13)	0.44 (0.08)	0.67 (0.08)	0.63 (0.09)	0.57 (0.11)	0.91 (0.07)
	6						0.46 (0.08)	0.76 (0.08)	0.49 (0.09)	0.81 (0.09)	0.75 (0.10)
	7						0.45 (0.08)	0.67 (0.08)	0.48 (0.09)	0.61 (0.13)	0.31 (0.13)
Test 1 Mean		0.55 (0.06)	0.78 (0.12)	0.77 (0.08)	0.70 (0.07)	0.70 (0.23)	0.53 (0.11)	0.77 (0.10)	0.59 (0.10)	0.72 (0.13)	0.77 (0.27)
Test 2, Rater	1	0.70 (0.07)	0.93 (0.07)	0.81 (0.07)	0.80 (0.06)	0.81 (0.13)	0.58 (0.08)	0.82 (0.07)	0.76 (0.07)	0.77 (0.09)	0.91 (0.07)
	2	0.65 (0.07)	0.65 (0.10)	0.89 (0.06)	0.78 (0.06)	0.77 (0.13)	0.60 (0.08)	0.82 (0.07)	0.62 (0.08)	0.78 (0.10)	0.86 (0.08)
	3	0.26 (0.06)	0.66 (0.09)	0.56 (0.07)	0.45 (0.07)	0.52 (0.14)
	4	0.44 (0.07)	0.72 (0.10)	0.65 (0.08)	0.63 (0.07)	0.20 (0.08)
	5	0.63 (0.07)	1.00 (0.00)	0.85 (0.07)	0.70 (0.07)	0.74 (0.15)	0.69 (0.07)	0.82 (0.07)	0.76 (0.07)	0.82 (0.10)	0.95 (0.05)
	6						0.35 (0.08)	0.58 (0.09)	0.46 (0.09)	0.51 (0.13)	0.70 (0.11)
	7						0.18 (0.07)	0.34 (0.09)	0.41 (0.10)	0.52 (0.14)	0.38 (0.13)
Test 2 Mean		0.54 (0.18)	0.79 (0.16)	0.75 (0.14)	0.67 (0.14)	0.61 (0.25)	0.48 (0.21)	0.62 (0.21)	0.60 (0.17)	0.68 (0.15)	0.76 (0.23)

For test 1 and 2 mean kappa (standard deviation) is shown. ¹Ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis. C: Cervical vertebra; L: Lumbar vertebra; Th: Thoracic vertebra.

Table 4 Intra-rater reliability for vertebral fracture classifications shown as kappa value (asymptotic standard error) for all raters. Raters are compared to themselves.

		Kappa
		Cervical spine					Thoracolumbar spine
		C1-Th1	C1	C2	C3-Th1	Signs of ankylosing spinal disorder1	Th2-L5	Th2-L5 A-type injuries	Th2-L5 B-type injuries	Th2-L5 C-type injuries	Signs of ankylosing spinal disorder1
Rater	1	0.72 (0.07)	0.67 (0.10)	0.93 (0.05)	0.80 (0.06)	1.00 (0.00)	0.59 (0.08)	0.76 (0.08)	0.69 (0.08)	0.84 (0.09)	1.00 (0.00)
	2	0.62 (0.07)	0.72 (0.10)	0.93 (0.05)	0.75 (0.07)	0.70 (0.14)	0.62 (0.07)	0.83 (0.07)	0.64 (0.08)	0.90 (0.07)	0.86 (0.08)
	3	0.40 (0.07)	0.86 (0.09)	0.63 (0.07)	0.55 (0.07)	0.66 (0.12)
	4	0.44 (0.07)	0.79 (0.10)	0.64 (0.08)	0.53 (0.07)	0.72 (0.10)
	5	0.72 (0.07)	0.93 (0.07)	0.78 (0.07)	0.82 (0.06)	0.85 (0.10)	0.60 (0.08)	0.75 (0.07)	0.78 (0.08)	0.69 (0.10)	0.95 (0.05)
	6						0.32 (0.07)	0.52 (0.09)	0.37 (0.10)	0.49 (0.14)	0.60 (0.13)
	7						0.16 (0.07)	0.31 (0.09)	0.32 (0.10)	0.47 (0.17)	0.63 (0.19)

¹Ankylosing spondylitis or diffuse idiopathic skeletal hyperostosis. C: Cervical vertebra; L: Lumbar vertebra; Th: Thoracic vertebra.