2015 ISAKOS Biennial Congress ePoster #312

Reliability of Lower Limb Angle Measurements Using a Tablet-Based System

Felipe Andai, MD, Santiago, RM CHILE
Jose A. Alemparte, MD, Santiago CHILE
Ignacio Mujica, MD, Santiago, RM CHILE
Alejandro Viacava, MD, Santiago CHILE
Cristóbal Moreno, MD, Santiago CHILE

Clínica Santa María, Santiago, CHILE

FDA Status Not Applicable

Summary: We studied inter and intra-rater reliability of lower limb alignment angle measurements, finding an excellent agreement.




To evaluate the reliability of lower limb frontal plane alignment measures obtained from radiographs measured digitally using a tablet-based system (Bone Ninja).


Standard measurements used in the planning of deformity correction surgeries around the knee, incuding mechanical axis angle, medial proximal tibal angle and lateral distal femoral angle were measured on 40 hip-to-ankle radiographs by four different raters using the “Bone Ninja” App (LifeBridge Health, Baltimore, MD) in an iOs environment (iPad, Apple Inc. Cupertino, CA)). To analyze the intra-rater agreement one of the raters (IM) repeated the measurements 4 weeks later. Additionally, to obtain the “gold standard” values the same radiographs were measured in a PACS software (VuePACS, Carestream Health, Rochester, NY).


Intraclass Correlation Coefficients (ICC) ranged from 0,80 to 0,91 indicating excellent inter-rater reliability. The test-retest ICCs (0,89-0,86) indicated excellent intra-rater reliability. The agreement between Bone Ninja and PACS measurements (ICCs from 0,82 to 0,94) was also excellent.


Bone Ninja can be reliably used for lower limb deformity correction planning. Its stability (inter-observer agreement), and repeatability (intra-observer agreement) are excellent. The agreement with the "gold standard" suggests that both methods can be used interchangeably.

Clinical Relevance
This study offers a statistical validation of a new measurement method based on a device that offers portability and affordability, allowing precise planning of limb deformity correction surgeries.