Pure high-offset stems can cause an unexpected increase in femoral length in robotic-assisted primary total hip arthroplasty

Table 1 Descriptive statistics of modeled femurs

Measure	Mean	SD	Median	IQR
Anatomical axis (mm)	438	29.5	438	414-454
Native mechanical axis (mm)	431	29.0	427	407-450
Native femoral neck length (mm)	48.4	5.2	44.9	45.7-51.9
Native aMFA (degrees)	6.3	0.6	6.3	6.1-6.8

aMFA: Anatomical mechanical femoral axis; IQR: Interquartile range.

Table 2 Rate and degree of leg length difference between each implant option, n (%)

Leg length difference in millimeters	Median (mm)	0	1	2	3	4	5
Standard vs high offset	1	5	35	3	-	-	-
High offset vs plus head	2	-	-	29	13	1	-
Standard vs plus head	3	-	-	-	31	11	1

Where standard denotes a standard insignia stem with a neutral head, high-offset denotes a high-offset insignia stem with a neutral head, and plus head denotes a standard insignia stem with a + 5 mm head.