2012 Annual Conference

Atkins, Lee T.

Texas Tech University Health Science Center, Lubbock, Texas

Background: The two most commonly reported lower limb injuries among runners are patellofemoral pain syndrome (PFPS) and iliotibial band syndrome (ITBS). Excessive frontal plane hip motion during running has been reported to contribute to the etiology of both of these conditions. Traditionally, accurate and objective assessment of hip kinematics during running has required expensive and complex equipment and procedures that are not readily available to clinicians. We have developed an inexpensive and simpler technique that uses commercially available technology. However, the reliability and accuracy of this technique have not been established. The purpose of the study was to examine the reliability and accuracy of frontal plane hip kinematics during running measured using commercially available video and iPhone technology.

Participants: The study consisted of two convenience samples. The first sample included 10 subjects (5 females and 5 males) with a mean±SD age of 26±3.5 years, ranging from 22 to 34 years. The second sample included 6 clinician raters (3 licensed physical therapists, 3 student physical therapists).

Methods: Posterior view video images of subjects running on a treadmill were obtained using a commercially available video camera. A Vicon Motus system simultaneously recorded frontal plane positions of reflective markers placed on the pelvis and legs. Reference angles and excursions were calculated using a custom Matlab algorithm. Clinical measures were obtained by displaying images on a video monitor while raters measured contralateral pelvic drop (CPD) and hip adduction (ADD) angles and excursions using a straight edge and an iPhone running a free inclinometer application. Each rater obtained measures on two days about one week apart. These two measures were examined for intrarater reliability using the intraclass correlation coefficient (ICC_3,1).  The mean of each rater's score was used to determine interrater reliability using ICC_2,2. To investigate accuracy, the raters’ measures were compared to the reference measures using ICC_2,2 for agreement, 95% limits of agreement (LA), and mean absolute differences (MAD).

Results: The ICC values for interrater and intrarater reliability ranged from 0.93 to 1.00 for the CPD and ADD angle measures and 0.82 to 0.99 for the CPD and ADD excursion measures. The accuracy ICC values of all measures ranged from 0.89 to 0.99 with acceptable LA. The MAD between the reference and rater measures ranged from 0.5° to 1.4°.

Conclusion: This study demonstrated that inexperienced student and licensed physical therapists can accurately and reliably measure 2-dimensional frontal plane hip kinematics during running following a short training session using this simple, low cost novel technique.

Clinical Relevance: Considering that an increase in CPD and ADD angles of 2.3° to 5.1° have been reported for subjects with PFPS and ITBS compared to healthy controls, this technique is sufficient for detecting such differences as indicated by the MAD between rater and reference angle measures which ranged from 0.5° to 1.0°. The mean±standard deviations of CPD and ADD angles for the subjects in this study were 6.0±3.5° and 14.6±4.1°, respectively. Additionally, because of the hip abductor muscles’ role in controlling frontal plane hip motion during the stance phase of running, excursion values should be of interest to the clinician as a surrogate measure of their functional activation. For this study, excursion measures were accurate within +/- 1.4° of the reference standard, supporting its use clinically as a useful addition to angle measures and the overall clinical examination. The angle and excursion reliability ICC values (ICC≥0.93 and ICC≥0.82 respectively) demonstrate that this technique provides the clinician with precise and reliable kinematic data that can be used to educate patients about their progress and assess the effectiveness of interventions aimed at reducing these angles regardless of whether or not the same clinician took all the measures.