BoneMorphing versus freehand localization of anatomical landmarks: Consequences for the reproducibility of implant positioning in total knee arthroplasty

Figures & data

Table I.  Non-exhaustive list of the different criteria that could be required for the six femoral implant positioning parameters.

Pose parameter	Criteria to be met
Tx (DP)	>0: default height from cutting height reference point on medial or lateral side
Ty (ML)	Centered on the cut contours in the ML direction
Tz (AP)	Implant anterior tangency to cut contour or anterior offset equal to ML overlapping offset
Rx (AR)	0°: implant rotation axis aligned on tibia reference rotation axis in axial plane or default offset angle from tibia reference rotation axis in axial plane
Ry (FR)	0°: implant mechanical axis aligned on tibia mechanical axis in sagittal plane or > 0°: default offset angle from tibia mechanical axis in sagittal plane
Rz (VV)	0°: implant mechanical axis aligned on tibia mechanical axis in frontal plane or default offset angle from tibia mechanical axis in frontal plane

Note: A combination of these criteria will be provided as input to the TKA system, depending on the implant manufacturers.

Figure 1. Location on a distal femur and proximal tibia statistical 3D model of the most commonly used landmarks in TKA.

Figure 2. Number of trials in which the TKA implant positioning program system proposed the size in each size category (1, 2, 3, 4, or 5 for the femur (top) and 1, 2, 3, 4, 5, or 6 for the tibia (bottom)) per surgeon (SA: surgeon A; SB: surgeon B, etc.).

Table II.  Mean and standard deviation for each of the five surgeons for the six datasets corresponding to the six degrees of freedom of the femoral implant positioning.

	Translation (mean ± SD) (mm)			Rotation (mean ± SD) (°)
	Tx (DP)	Ty (ML)	Tz (AP)	Rx (AR)	Ry (FR)	Rz (VV)
Surgeon A (N = 7)	− 1.8 ± 0.2	2.9 ± 1.3	− 5.7 ± 0.9	− 1.04 ± 0.9	− 1.3 ± 0.7	0.3 ± 0.9
Surgeon B (N = 7)	− 2.0 ± 0.2	0.5 ± 0.9	− 8.7 ± 1.2	− 2.10 ± 0.9	− 3.7 ± 0.9	1.1 ± 0.1
Surgeon C (N = 3)	− 1.9 ± 0.4	2.4 ± 1.2	− 9.5 ± 1.0	− 1.12 ± 1.2	− 4.7 ± 1.1	0.2 ± 0.6
Surgeon D (N = 6)	− 2.2 ± 0.3	1.3 ± 0.8	− 8.4 ± 0.4	− 2.24 ± 2.2	− 3.4 ± 0.3	0.9 ± 0.1
Surgeon E (N = 5)	− 2.0 ± 0.2	1.1 ± 0.7	− 7.9 ± 0.5	− 2.4 ± 1.4	− 3.7 ± 0.9	1.10 ± 0.1
Union (N = 28)	− 2.0 ± 0.3	1.6 ± 1.4	7.8 ± 1.5	− 1.8 ± 1.6	− 3.2 ± 1.4	0.8 ± 0.6

Note: The datasets were limited to the trials for which the system proposed a size 4 femoral implant, which was the one most frequently suggested. The last row of the graph represents the dataset combining all trials with implant 4 irrespective of the surgeon.

Table III.  Mean and standard deviation for each of the five surgeons for the six datasets corresponding to the six degrees of freedom of the tibial implant positioning.

	Translation (mean ± SD) (mm)			Rotation (mean ± SD) (°)
	TX (DP)	TY (ML)	TZ (AP)	RX (AR)	RY (FR)	RZ (VV)
Surgeon A (N = 5)	13.8 ± 0.3	2.0 ± 0.5	7.2 ± 0.2	0.1 ± 1.7	− 4.9 ± 0.2	− 0.69 ± 0.1
Surgeon B (N = 7)	13.0 ± 0.9	3.1 ± 0.9	6.4 ± 0.6	− 5.8 ± 2.9	− 5.5 ± 0.2	− 0.28 ± 0.2
Surgeon C (N = 4)	14.1 ± 0.7	1.1 ± 1.4	8.3 ± 1.9	11.1 ± 12.1	− 4.7 ± 0.5	− 0.42 ± 0.3
Surgeon D (N = 4)	13.7 ± 0.1	3.7 ± 0.7	7.0 ± 0.4	− 7.6 ± 1.7	− 5.0 ± 0.3	0.10 ± 0.1
Surgeon E (N = 3)	13.5 ± 0.4	1.8 ± 0.3	7.4 ± 0.4	− 3.4 ± 9.3	− 5.0 ± 0.7	− 0.47 ± 0.8
Union (N = 23)	13.6 ± 0.5	2.5 ± 1.3	7.2 ± 1.0	− 1.9 ± 9.1	− 5.1 ± 0.5	− 0.3 ± 0.3

Note: The datasets were limited to those trials for which the system proposed a size 4 tibial implant, which was the one most frequently suggested. The last row of the graph represents the data set combining all trials with implant 4 irrespective of the surgeon.

Figure 3. 3D visualization of the large variability for different landmarks acquired manually. For visualization only, these manual landmarks have been displayed on the BoneMorphing 3D models (color version available at online).

Table IV.  Range of values and standard deviation in mm as described in the methods for landmarks digitized with the pointer for each operator.

	Bony landmarks
	Top of the femoral notch		Medial posterior condyle		Medial epicondyle		Middle of tibial spines		ATT
Direction	ML		3D		3D		3D		3D
	R	SD	R	SD	R	SD	R	SD	R	SD
Surgeon A (N = 8)	5.2	1.8	6.6	2.8	12.9	3.9	11.2	3.4	5.2	1.9
Surgeon B (N = 10)	5.6	1.3	5.0	2.2	13.2	5.4	8.5	2.1	7.6	2.0
Surgeon C (N = 5)	2.6	1.17	8.6	2.97	11.2	5.4	6.9	2.71	11.1	4.1
Surgeon D (N = 6)	15.5	5.8	3.1	1.6	10.9	3.6	8.1	3.4	4.5	1.5
Surgeon E (N = 6)	6.6	2.4	9.5	3.2	8.4	3.3	5.7	2.3	12.7	4.9
Union (N = 35)	15.5	2.2	14.47	3.3	23.62	5.0	13.43	2.2	20.4	4.5

Note: The Direction line indicates the direction of interest in which the variability was studied. 3D indicates that the method for computing point variability was applied. ML, AP, or DP indicates that the real number variability computation method was applied. The last row of the graph represents the dataset combining all 35 trials.

Table V.  Standard deviation (°) of the femoral ML direction serving as reference for the femoral AR for each acquisition method and anatomical direction definition.

	Femoral rotation reference axis
	Epicondylar axis		Whiteside's Line		Posterior condyles axis
Acquisition method	Pointer	BM	Pointer	BM	Pointer	BM
Surgeon A (N = 8)	3.0	2.9	2.6	1.8	1.2	0.9
Surgeon B (N = 10)	3.1	2.9	1.8	2.2	1.0	0.5
Surgeon C (N = 5)	3.4	2.8	2.9	2.7	1.3	1.0
Surgeon D (N = 6)	2.6	5.4	2.7	2.5	2.3	0.4
Surgeon E (N = 6)	3.4	3.5	2.7	2.8	1.7	1.2
Union (N = 35)	3.5	4.0	3.6	2.6	1.6	0.9

Figure 4. X coordinates (proximal to distal axis, in mm) of the tibial medial plateau for each surgeon and acquisition method (pointer or BoneMorphing). The last column of the graph is the dataset combining all 35 trials (SA: surgeon A; SB: surgeon B, etc.).

Figure 5. ML size (in mm) of the tibia at the cut level for each surgeon and acquisition method (pointer or BoneMorphing). The last column of the graph is the dataset combining all 35 trials (SA: surgeon A; SB: surgeon B, etc.).