A PROTOCOL TO DETERMINE THE CARRYING ANGLE VALUE OF THE ELBOW JOINT : a Study of Repeatability Maria L. Zampagni, D. Casino S. Zaffagnini, A. Visani and M. Marcacci Laboratorio di Biomeccanica- Istituti Ortopedici Rizzoli
1.1 Introduction In clinical practice the carrying angle is measured in full extension and an increase in its value could be attributed to previous trauma or developmental abnormality . Flynn developed criteria to grade the satisfaction of reduction of supracondylar fractures of the humerus based on the evaluation of the carrying angle . Measurement of this angle is important in the etiopathogenesis of various types of fractures seen around the elbow in the diagnosis of disease of the lateral ( tennis elbow) and medial (golf elbow) epycondyles [3,4].  Cain EL Jr, Dugas JR, Wolf RS, Andrews JR. Am J Sports Med. 2003 Jul-Aug;31(4):621-35.  Flynn, J Bone Joint Surg Am 1974;56:263–72.  Ikeda M, Sugiyama K, Kang C, Takagaki T, Oka Y., J Bone Joint Surg Am. 2006 Mar;88(1 Suppl 1):11-23.  A Foead, R Penafort, A Saw, S Sengupta, Journal of Orthopaedic Surgery 2004;12(1):76–82.
STANDARD GONIOMETER 1.2 Introduction Recently Van Roy (2005) reported the mechanical implication of the carrying angle with the upper limb functionality  Usually this measurement was and still is performed by radiograph or standard goniometer. Amount of force transmitted across joint depends on the loading configurations and the angular orientation of the joint  Van Roy et al. Ergonomics. (2005) Vol. 48, Nos. 11-14, 1645-1656
The purpose of this study • To adopt an accurate and non invasive experimental method in orderto estimate the carrying angle in an in-vivo set-up using an electrogoniometer (FARO Arm), which digitalises the 3-D coordinates of the anatomical landmarks. • We performed an experimental analysis of reliability bycomparing our values to those found in the literature and by a standard goniometer usually adopted in clinical settings [6,7].  Yilmaz E, Karakurt L, Belhan O, Bulut M, Serin E, Avci M., Orthopedics. 2005 Nov;28(11):1360-3.  Ruotolo C, Price E, Panchal. J Shoulder Elbow Surg. 2006 Jan-Feb;15(1):67-71.
2. Approach to the problem EXPERIMENTAL PROCEDURES FARO Arm • It can collect data continuously a rate of 50 Hz or point–by-point at user`s request with 0.3mm/0.3accuracy in a spherical workspace • of 1.8 diameter around its base  S. Martelli, Comput Methods Programs Biomed. 70 (3), 2003, 223-40.  S. Martelli, S. Zaffagnini, B. Falcioni, M. Marcacci. Computer Methods and Programs in Biomedicine, 62, 2000, 77-86.
Landmark points acquisition by Faro Arm   By Cardan decomposition method we obtained the three components of the angle formed between the arm and the forearm. The rotation around the z-axis is the flexion-extension, the rotation around the x-axis is the carrying angle, the rotation around the y-axis is the prono-supination.     Wu G, et al., ISB recommendation on definitions of joint coordinate systems of various joints for the reporting of human joint motion. J Biomech. 2005; May 38(5): 981-992. Anglin C, Wyss UP. Review of arm motion analyses. Proc Inst Mech Eng [H]. 2000;214 (5) :541-55.
DATA ANALYSIS The reliability of the method was analysed: • By change in the mean Typical error • Retest Correlation : • a) Pearson`s correlation coefficient and ICC (Interclass Correlation Coefficient) • b) Limit of Agreement
3. 2 Results REPEATABILITY by standard goniometer REPEATABILITY by Faro Arm ICC=0.76 p<0.000 95% CI= [0.606- 0.864] ICC=0.85 p<0.000 95% CI= [0.728 - 0.910]
3. 3 Results Inter-operator REPEATABILITY by Faro Arm (unskilled vs skilled operator)
4.1 Discussion • For the first time our method has allowed us to identify the carrying angle in-vivo by anatomical landmarks. • Our protocol was more repeatable especially considering that our measurements were calculated blindly without being influenced by the visualization of the value (which is immediately available after the acquisition). • However, a part of the reliability of this method could also be attributed to the skilled user who was able to determine the correct position of the anatomical landmark points that, when not performed accurately, can be an important source of error .  Stokdijk et al. J Biomech (2000) 33; 1139-1145.
FUTURE WORKS To estimate the carrying angle in an in-vivo set-up in order to identify the individual model of the flexion extension movement. The carrying angle values during the flexion extension movement by Vicon System
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