Computer-assisted analysis of lower limb geometry: higher intraobserver reliability compared to conventional method

Figures & data

Figure 1. Joint orientation angles and axis in the frontal plane according to Paley et al. [5]. [Color version available online.]

Table I.  Nomenclature of joint orientation and axis in the frontal plane according to Paley [9].

mLPFA	mechanical Lateral Proximal Femoral Angle: Angle between the mechanical femoral axis and a line from the tip of the greater trochanter to the hip center.
mLDFA	mechanical Lateral Distal Femoral Angle: Angle between the mechanical femoral axis and a tangent through the two most convex distal points of the femoral condyles.
MPTA	Medial Proximal Tibial Angle: Angle between the mechanical axis of the tibia and a line along the flat portion of the subchondral bone of the tibial plateau.
LDTA	Lateral Distal Tibial Angle: Angle between the mechanical tibial axis and a line through the tip of the medial and lateral talus shoulder.
AMA	Anatomical-Mechanical Angle: Angle between the anatomical and mechanical femoral axes.
JLCA	Joint Line Convergence Angle: Angle between the tangent through the two most convex distal points of the femoral condyles and a line along the flat portion of the subchondral bone of the tibial plateau.
MAD	Mechanical Axis Deviation: Distance of the mechanical axis of the leg from the knee center.

Figure 2. Digital analysis of leg geometry with the planning software. a) The contours of the femur, tibia and talus are drawn digitally. b) Measurement of the joint orientation angles, alignment and leg length by the software. [Color version available online]

Table II.  Standard deviation (SD) after conventional measurement (CM) and computer-assisted analysis (CAA).

	SD CM	SD CAA	SD difference	p-value
mLPFA (°)	1.17	1.12	0.05	0.294
MLDFA (°)	0.65	0.43	0.22	< 0.001
MPTA (°)	0.67	0.47	0.20	< 0.001
LDTA (°)	0.89	0.53	0.36	< 0.001
AMA (°)	0.36	0.29	0.07	0.032
JLCA (°)	0.77	0.58	0.19	< 0.001
MAD (mm)	0.94	0.80	0.14	0.023
Leg length (mm)	0.90	0.96	0.06	0.271

Table III.  Time period for complete analysis of the alignment, axis, joint orientation and leg length.

	CM	CAA	Difference	p-value
Time (min:sec) ± SD (range)	11:46 ± 1:20 (8:17–15:46)	6:34 ± 0:45 (5:00–9:38)	5:11	< 0.001

Table IV.  Leg length before and after calibration with the magnification marker calculated by CAA

CM	CAA	Difference	Magnification
81.29 ± 5.96 cm	77.38 ± 4.94 cm	3.91 ± 2.03 cm	4.6 ± 1.8% (range: 2.7–11.9%)

Paley D, Tetsworth K. Mechanical axis deviation of the lower limbs. Preoperative planning of uniapical angular deformities of the tibia or femur. Clin Orthop 1992; 280: 48–64

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Paley D. Principles of deformity correction. Springer;, Berlin 2001

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