Table 2.

Standard error of measurement and smallest detectable change for long-axis radiographic angles across intra-operator, inter-operator, and test–retest conditions

	Descriptive				SEM [95% CI]			SDC [95% CI]
	Mean	SD	Min	Max	Intra	Inter	Trtest	Intra	Inter		Trtest
Osteoarthritic knee
LDFA	88.9	2.3	84	95	0.6 [0.5–0.6]	0.7 [0.6–0.8]	0.8 [0.7–0.8]	1.8 [1.4–1.7]	2.0 [1.8–2.1]		2.3 [1.9–2.3]
MPTA	87.4	2.7	78	94	0.9 [0.7–0.8]	1.4 [1.2–1.4]	1.2 [1.1–1.3]	2.4 [1.9–2.3]	3.8 [3.4–3.9]		3.4 [2.9–3.5]
JLO	176.3	2.8	168	186	1.1 [0.8–1.0]	1.5 [1.4–1.6]	1.5 [1.3–1.6]	3.1 [2.3–2.9]	4.2 [3.8–4.4]		4.2 [3.6–4.4]
aHKA	1.4	4.1	− 9	12	1.1 [0.8–1.0]	1.6 [1.4–1.6]	1.4 [1.2–1.5]	3.0 [2.3–2.8]	4.3 [3.9–4.5]		4.0 [3.4–4.0]
Knee with total knee arthroplasty
LDFA	90.0	2.3	83	95	0.5 [0.4–0.5]	0.7 [0.6–0.7]	0.8 [0.6–0.8]	1.4 [1.1–1.4]	1.9 [1.7–2.0]	2.1 [1.8–2.2]
MPTA	89.6	2.1	84	95	0.5 [0.4–0.5]	0.6 [0.5–0.7]	0.7 [0.6–0.7]	1.4 [1.0–1.5]	1.8 [1.5–1.9]	1.9 [1.6–2.0]
JLO	179.5	3.0	173	188	0.7 [0.5–0.7]	1.0 [0.9–1.1]	1.0 [0.9–1.1]	2.1 [1.5–2.1]	2.9 [2.5–3.1]	2.9 [2.4–3.0]
aHKA	0.4	3.2	− 9	9	0.7 [0.6–0.7]	0.8 [0.7–0.9]	1.0 [0.8–1.0]	2.0 [1.5–1.9]	2.3 [2.0–2.4]	2.8 [2.3–2.9]

Results are presented as estimates [95% confidence interval]. The criteria are defined as follows: for SEM, Excellent (0.7°), Good (0.7° to 1.1°), Moderate (1.1° to 1.8°), and Poor (> 1.8°); for SDC, Excellent (< 2°), Good (2° to 3°), Moderate (3° to 5°), and Poor (> 5°)

Abbreviations: SEM, standard error of measurement; SDC, smallest detectable change; Intra, intra-operator; Inter, inter-operator; Trtest, test–retest; LDFA, lateral distal femoral angle; MPTA, medial proximal tibial angle; JLO, joint line obliquity; aHKA, arithmetic hip-knee-ankle angle