Abstract
Background
Two-dimensional (2D) analysis has the potential to identify individuals at risk for knee injury by measuring genu valgus during sport related tasks. The reliability of 2D mobile motion analysis in measuring genu valgus during a single leg hop test on individuals with anterior knee pain has not been examined.
Purpose
To assess the reliability and concurrent validity of 2D mobile motion analysis and compare it to visual observation while analyzing dynamic genu valgus during a single leg hop test in subjects with anterior knee pain.
Study Design
Cohort study; repeated measures
Methods
Nineteen subjects experiencing anterior knee pain completed a single leg hop test with both lower extremities. Two investigators independently estimated the degrees of genu valgus with visual observation alone during the subjects' single leg hop. After the visual estimation, the investigators watched the video again using the 2D Spark Motion Pro™ application to pause the video and measured the amount of knee valgus with a virtual goniometer tool on the application. Interrater reliability was calculated using intraclass correlation coefficients (ICC) model 2, k and intrarater rater reliability using model 3, k. Minimal detectable change, concurrent validity and limits of agreement were calculated.
Results
Visual observation alone demonstrated interrater reliability ICCs of 0.682-0.685 on the symptomatic and non-symptomatic lower extremities respectively. The interrater reliability using the 2D application had ICC's of 0.927 and 0.792 on the symptomatic and non-symptomatic lower extremities respectively. The concurrent validity for 2D analysis and visual observation on the symptomatic lower extremity had ICC values of 0.96 (rater A) and 0.85 (rater B). The non-symptomatic lower extremity demonstrated concurrent validity ICC values of 0.95(rater A) and 0.65(rater B). The standard error of measurement(SEM) was 3.898 and 3.258 for the symptomatic and non-symptomatic lower extremity(LE) respectively for visual observation. When using the Spark Motion Pro™ application the SEM was 1.648 and 2.718 for the symptomatic and non-symptomatic LE respectively. The minimal detectable change (MDC) using visual observation alone was 5.58 and 4.68. When using the application, it was noted at 2.328 and 3.838 on the symptomatic and non-symptomatic LE respectively.
Conclusion
The results of this study support the use of a 2D mobile application as a reliable tool for measuring knee valgus in symptomatic subjects and offers reduced error (SEM = 1.648) when compared to visual observation alone (SEM = 3.898).
Level of evidence
2B
Keywords: genu valgus, injury prevention, injury screening, two-dimensional
INTRODUCTION
According to the National Collegiate Athletic Association (NCAA), lower extremity injuries comprise more than 50% of all total injuries occurring in collegiate athletes.1 Approximately 37% of these were caused by non-contact mechanisms. Throughout a ten-year study, Majewski et al.2 followed 17,397 athletes during their athletic careers. They discovered 40% of the total injuries that occurred were related to the knee joint, with anterior cruciate ligament (ACL) tears comprising 20.3%, medial meniscal tears accounting for 10.8%, lateral meniscus tears 3.7%, medial collateral ligament tears 7.9%, and lateral collateral ligament injuries 1.1%. In a study evaluating running related injuries, 42.1% of the injuries involved the knee joint.3
The risk for knee injury with increased dynamic valgus during landing has been evaluated over the last two decades.4-8 Movement patterns that result in hip adduction, hip internal rotation, tibial abduction and foot pronation have been related to anterior knee pain and patellofemoral pain syndrome during dynamic sport related tasks.3,6,8,9,10 Specifically, in a prospective study of 205 female athletes followed by Hewett et al.,6 hip abduction moments had a sensitivity of 78% and specificity of 73% for predicting ACL injury.6 A 2.5 time increase in knee abduction moments (p<.001) in athletes who went on to suffer an ACL injury was discovered by the authors .6 There is strong evidence to suggest that incorporation of injury prevention programs has the potential to reduce knee injury rates.11,12,13 These programs, which include neuromuscular and proprioceptive training have been found to reduce knee and ACL injury by 26.9% and 50% respectively.12 Therefore, effort must be made to identify reliable methods in which to recognize faulty movement patterns and initiate interventions to reduce probability for injury.
The use of 3D motion capture systems and force plates is well known to be the gold standard for kinematic analysis during movement. This type of system, which is typically used in a laboratory setting, is not universally available. Additionally, use of such systems is costly and requires extensive set-up and education. Two alternate resources available for use in assisting in quantifying joint angles during functional sport specific tasks include 2D video analysis and visual observation. The advantages of these alternatives include applicability, availability, minimal expense, practicality, and ease of use. However, when using visual observation alone, Ekegren et al.14 described the sensitivity of objectifying genu valgus during a drop jump task to range between 67% to 87% when compared to the gold standard of 3D analysis. This resulted in one-third of the tested athletes failing to be labeled as “high risk” who were labeled as such by 3D analysis. Therefore, it was concluded that adequate assessment of knee valgus angles during sport specific tasks is questionable without the use of technological resources. 14
The use of 2D video assessment of human movement has been demonstrated to be a valid and reliable alternative in measuring dynamic movement tasks when 3D analysis is not available.15,16 Munro et al.15 reported intraclass correlation coefficient (ICC) values between .83 and .88 in males and females respectively when measuring the reliability of 2D video analysis of frontal plane projection angles during a drop jump task. They concluded that in the absence of access to 3D motion analysis, this method can be used to reliably quantify genu valgus values. In another study, McLean et al.17 examined 3D analysis vs. a 2D standard video measurement technique to determine its potential to screen for excessive genu valgus in elite basketball players. Although their 2D measurement technique demonstrated greater frontal plane knee angles when compared to 3D measures, the researchers determined 2D analysis to be a reliable method for identifying increased genu valgus. It appears that 2D analysis may appropriately identify athletes who demonstrate an increased risk of injury.17 To the authors knowledge, despite the aforementioned research, no study has evaluated the reliability of 2D motion analysis in measuring genu valgus among individuals with knee pain. The objectives of this study were as follows: To assess the reliability and concurrent validity of 2D mobile motion analysis and compare it to visual observation while analyzing dynamic genu valgus during a single leg hop test in subjects with anterior knee pain.
METHODS
Subjects
Nineteen adult subjects, (female n = 12; male n = 7, average age 28.5 years, + /- 7.29), who were experiencing anterior knee pain for no greater than twelve months, were recruited from the local community using brochures displayed at two hospital based fitness facilities over the course of six months. Anterior knee pain, as characterized by Cook et al.18 was defined as having at least two of the three following characteristics; pain with squatting, peripatellar palpable tenderness and/or pain with resisted knee extension. In addition to anterior knee pain, inclusion criteria consisted of being between 18 and 40 years of age and a pre-symptom score of five or greater on the Tegner activity scale.19 Patients between the ages of 18 and 40 years old were chosen for two reasons. Firstly, to eliminate the need for parental consent and secondly this is the most common age range which the authors treat this population in their clinics. The pre-symptom score of ≥ level 5 on the Tegner scale was chosen based on the Tegner et al.19 recommendation, as the point of tolerance and ability to perform a single leg hop test. Subjects were excluded from the study if they were unable to read or speak English as required for understanding forms and instructions, were currently participating in a structured strength and conditioning program, had a history of knee surgery, or were unable to perform a single leg hop. This study was approved by the Institutional Review Board of Florida Hospital- Adventist Health System and all subjects meeting inclusion criteria consented to participate. Subjects provided demographic information including age, height, mass, dominant leg, symptomatic lower extremity, gender, and health status.
Instruments
The Spark motion Pro™ application was downloaded from the Apple App store to a fourth generation iPad© on the IOS 6.0.1 operating system. The iPad© had a display of 9.7 inches, 2,048 x 1,536-pixel color IPS LCD display with a 4:3 aspect ratio and captured video at 30 frames per second. The iPad© was placed on a 2014 Manfrotto compact, aluminum tripod with the amazon standard identification number (ASIN, B00L6CBKaK). An Adonit Jot Pro fine point precision stylus, (ASIN, B00931K1QK), was used to measure genu valgus with the applications goniometer tool.
Procedures
Upon agreeing to participate and receiving documentation of consent, subjects completed the Tegner activity level scale. The Tegner activity level scale has been used in similar studies to ascertain if a subject will be able to tolerate the single leg hop.19 The Tegner activity scale consists of a self-reporting 10-item level scale ranging from level 0 (sick leave or disability pension because of knee problems) to level 10 (competitive sports-soccer, football, rugby, national elite). The subjects were required to rate themselves at pre-symptom level and current level of function. The single leg hop test has demonstrated ICC's ranging from .93 to .96 for prediction of dynamic knee stability.20 It has the potential to demonstrate insufficiencies in functional knee stability in healthy subjects.20
After completion of the Tegner activity scale, the subject watched an investigator perform a single leg hop in the designated testing area and questions were answered to ensure the subject had a verbal understanding of the expected activity. No cuing on mechanics or posture was provided to avoid coaching bias. The subjects advised the investigator which knee was symptomatic and hopped as far as possible with their non-symptomatic lower extremity while keeping their balance for a minimum of two seconds. If the subject was unable to maintain their balance for at least two seconds, a 30 second rest period was provided and another attempt at the single leg hop was made. Once this reference hop distance was made, athletic tape was placed on the ground to mark this location. The subjects then had a one-minute rest period, while the investigators set up the tripod and equipment for video analysis. The tripod was placed five feet from the reference landing location to maintain universal distance from recording to landing point and avoid variations in depth of field during video analysis angle measurements.
Once the landing spot was determined and equipment was set-up accordingly, testing began. The subject performed a single leg hop on their non-symptomatic lower extremity to the designated marked location, maintained the landing for two seconds and received a 60 second rest period between each of three trials. The same occurred on the symptomatic lower extremity. If the subject was unable to maintain the qualifications of a successful hop as described above, a rest period of 60 seconds was provided and another hop was performed. When the first three successful hops were completed and recorded on the non-symptomatic lower extremity, a three-minute rest period was provided prior to initiation of the symptomatic lower extremity hop trials.
After all trials and video recording were complete visual estimation of genu valgus was performed. Two investigators blinded to each other's results (both Doctors of physical therapy and familiar with the use of video analysis) visually estimated the degrees of genu valgus during a single video play of each trial hop. Genu valgus was estimated at the point where knee eccentric momentum ended and the subject began their return into knee extension. After each investigator completed the visual estimation alone analysis, the goniometric tool on the application was utilized to measure genu valgus. The same still video image was utilized by the same examiner for both the visual estimation analysis and the goniometric measurement analysis using the application. The reference points used for both visual estimation and goniometric measurements were the anterior superior iliac spine (ASIS), a line bisecting the medial and lateral femoral condyles and a line bisecting the medial and lateral malleoli at the talocrural joint. Frontal plane knee collapse was measured as the difference from a vertical line (180 degrees), with varus recorded as a negative value and valgus as a positive value. Figure 1 demonstrates a subject's single leg hop with associated goniometric measurement using the Spark Motion Pro™ goniometer. The genu valgus measured in Figure 1 using the application was recorded as 19 degrees by subtracting 180 (vertical) from 199.
Figure 1.
Single leg hop test using the Spark Motion Pro™ goniometer for measurement of the degrees of genu valgus.
Statistical methods
SPSS version 15.0 for Windows was utilized for statistical analysis. Descriptive data including mean measurement angles with standard deviations (SD) were calculated for each session. The ICC model 3, k was used for the intrarater component of analysis and model 2, k for the interrater reliability analysis. To analyze whether the Spark Motion Pro™ software can be used reliably between equally trained clinicians, model 2, k was used.21 A value of ≥ 0.75 was classified as having good reliability based on recommendations of Portney and Watkins.21 Values below 0.75 were classified as moderate to poor reliability. The minimal detectable change (MDC) was calculated using the following formula: (MDC?? = 1.96*SEM*). This formula was used to determine the magnitude of change that would exceed the threshold of measurement error at 95% confidence level.21,22 The 95% limits of agreement were calculated by using the formula: 95% limits of agreement = mean difference + /- 2SD. These values were rounded to the nearest degree to reflect the smallest unit of measurement on the virtual goniometric tool on the Spark Motion Pro™ application. An ICC model 3, k was used in the concurrent reliability analysis to determine if both methods of measurement analysis produced comparable results. ICC value interpretations were also based on the guidelines set forth by Portney and Watkins.21
RESULTS
A total of nineteen adult subjects, 12 females and 7 males were recruited. All subjects recruited and initially eligible were able to complete the single leg hop protocol. The average and standard deviation for participants' age, mass, and height is described in Table 1.
TABLE 1.
Demographics (n = 19)
| Variable | Mean (SD) |
|---|---|
| Age | 28.53 (7.29) |
| Height (cm) | 171cm (10.07) |
| Mass (kg) | 69.73kgs (12.35) |
| BMI | 23.67 (2.15) |
| Sex (% Female) | 63.2% |
| Leg Dominance (% Right) | 94.7% |
| Symptomatic LE (% Right) | 42.1% |
SD: standard deviation; BMI: Body Mass Index
The interrater reliability for visual estimation of knee valgus during the single leg hop trials is depicted in Table 2. The ICC for visual estimate alone (Table 2) demonstrates poor reliability (.682-.685). The mean, standard deviation, ICC, SEM, and MDC95 were calculated for the symptomatic (painful) and non-symptomatic (non-painful) lower extremities.
TABLE 2.
Interrater reliability of functional knee valgus using visual estimate during single leg hop
| Rater A Mean angle (SD) | Rater B Mean angle (SD) | ICC 2, k | SEM° | MDC° | |
|---|---|---|---|---|---|
| Symptomatic LE | 6.37(6.89) | 5.35(3.48) | .682 | 3.89 | 5.50 |
| Non-symptomatic LE | 6.46(5.79) | 4.04(3.07) | .685 | 3.25 | 4.60 |
SD: standard deviation; ICC: intraclass coefficient; SEM: Standard error of measurement; and MDC95: minimum detectable change at 95% confidence interval.
Table 3 presents the interrater reliability when using the Spark Motion Pro™ application goniometer function. The ICC when utilizing the Spark Motion Pro™ application (Table 3) with the goniometric function demonstrates good reliability in a range of .792-.927 for both symptomatic and non-symptomatic lower extremities. The ICC using the goniometer on the application demonstrated higher reliability (.927) on the symptomatic lower extremity than the non-symptomatic extremity (.792). Table 4 presents the concurrent validity on the symptomatic extremity when comparing visual estimation and the use of the goniometer. The concurrent validity of the symptomatic lower extremity demonstrated an ICC of 0.96 for rater A and 0.85 for rater B(95% CI: 0.92-0.99; 0.61-0.94 for rater A and B respectively) (Table 4). Table 5 presents the concurrent validity of the non-symptomatic lower extremity (ICC = 0.954 and 0.65; 95% CI: 0.88-0.98, 0.092-0.87 for rater A and B respectively). Reliability tended to be greater when evaluating the symptomatic lower extremity when compared to the non-symptomatic lower extremity.
TABLE 3.
Interrater reliability of functional knee valgus using Spark Motion Pro™ during single leg hop.
| Rater A Mean angle (SD) | Rater B Mean angle (SD) | ICC 2, k | SEM° | MDC° | |
|---|---|---|---|---|---|
| Symptomatic | 5.90(6.07) | 6.63(5.52) | .927 | 1.64 | 2.32 |
| Non-symptomatic | 5.86(5.94) | 4.67(3.91) | .792 | 2.71 | 3.83 |
SD: standard deviation; ICC; intraclass coefficient; SEM: standard error of the measurement; and MDC 95; minimum detectable change at 95% confidence level
TABLE 4.
Concurrent validity of the symptomatic lower extremity using visual assessment and Spark Motion Pro™
| Rater | ICC (3, k) | 95% CI |
|---|---|---|
| A | 0.96 | 0.92-0.99 |
| B | 0.85 | 0.61-0.94 |
ICC: intraclass correlation coefficient; CI: confidence interval
TABLE 5.
Concurrent validity of the non-symptomatic lower extremity using visual assessment and Spark Motion Pro™
| Rater | ICC (3, k) | 95% CI |
|---|---|---|
| A | .954 | 0.88-0.98 |
| B | .650 | 0.092-0.87 |
ICC: intraclass correlation coefficient; CI: confidence interval
DISCUSSION
To date, the reliability of 2D analysis of genu valgus during a single leg hop test has not been evaluated on symptomatic subjects. Therefore, this study evaluated the reliability of 2D video analysis of genu valgus utilizing the Spark Motion Pro™ application vs. visual estimation alone. It also assessed the validity of the applications ability to measure genu valgus during a single leg hop in symptomatic subjects. Higher reliability was noted when using the application on the symptomatic lower extremity when compared to the non-symptomatic lower extremity. This further validates the importance of using technology when evaluating subjects with complaints of anterior knee pain.
The findings of this study are consistent with the results found in other studies that examine the reliability of 2D mobile motion analysis. Mobile motion capture software has the potential to objectively quantify joint angles during video analysis with good reliability. In a study by Krause et al.,23 the researchers found the reliability of Coach's Eye (Tech Smith Corporation, Okemos, MI), to range from .96-.99 when measuring sagittal plane knee motion during a squat maneuver in non-symptomatic subjects. A novel finding of this study includes the identification of increased reliability while using the 2D mobile motion analysis on the symptomatic lower extremity (ICC .927) when compared to the non-symptomatic lower extremity (ICC .792). To the authors knowledge, no study has examined the reliability of 2D mobile motion analysis on subjects with anterior knee pain.
Maykut et al.3 evaluated the reliability of numerous frontal plane kinematic variables during running using Dartfish Motion Analysis Software (Dartfish, Fribourg, Switzerland). The researchers found excellent intrarater reliability for peak knee abduction angles (ICCs: 0.955-0.976), and in terms of concurrent validity, moderate correlations were presented between 2D and 3D measures on the left lower extremity (pearson product correlation coefficient, 0.541; p = .006).
Table 2 demonstrates that when using visual estimation alone, reliability tended to decrease when measuring symptomatic and non-symptomatic lower extremity angles. The SEM and MDC between visual estimation and the Spark Motion Pro™ also demonstrated some differences. The SEM for the symptomatic and non-symptomatic LE was 3.89° and 3.25° respectively during visual estimation. When using the application, this decreased to 1.64° and 2.71° respectively. This demonstrates the increased chance for error in measuring genu valgus when visual estimation is used in isolation. The lower SEM calculated while using the 2D analysis application (1.64°) versus visual estimation (3.89°) demonstrates greater precision in measuring genu valgus when using technological resources. Nevertheless, the error rate is high with both assessment options as the SEM was in some cases close to 33% of the measurement.
Herrington et al.,24 set out to calculate normative values of genu valgus during a drop jump task for non-pathological subjects. The results of their study indicated that valgus measurements should be symmetrical and in the range of 7° to 10° for females and 3° to 8° for males.24 The researchers noted the potential risk for knee injury increases, if genu valgus values are larger than the normative observation. The results of the current study validate the importance of using methods or devices that decrease the opportunity for misclassification of at risk athletes. If valgus measurements are determined to be outside the norm, injury prevention programs and rehabilitation have had some success in decreasing knee injury risk.25,26
The utility of implementation of injury prevention strategies and interventions in the rehabilitation and sports performance settings was demonstrated in a prospective study by Hewett et al.25 The investigators followed 1,263 high school student athletes who were instructed in a six-week injury prevention program that included neuromuscular training, plyometrics, flexibility, and weight training.25 Compared to an untrained group of high school athletes, the results of their findings demonstrated that the untrained group had a 3.6 times higher rate of knee injury than the trained group and untrained female athletes were 4.8 to 5.8 times more likely to experience a serious knee injury than their male counterparts.25 In 2012, Wouters et al.26 analyzed the results of a four-week neuromuscular training program on hip and knee kinematics in sixty nine female runners. The program included visual (mirror), tactile and verbal cues during exercises emphasizing gluteus medius and maximus recruitment. Their results demonstrated a decrease in internal hip moments by 23% (p = 0.007) and knee abduction moments by 29% (P = . 033) when compared to pre-training values. Knee adduction and abduction angles were reduced by 2.1° (P = .050) and 2.7° (p = .0008) respectively.26 The use of 2D mobile motion analysis can provide reliable information informing the determination of individuals (e.g. athletes, patients etc.) who are at risk for knee injury, and according to Hewitt et al.27 can assist in the development of individualized intervention approaches that have demonstrated effectiveness in reducing knee injury rates.27
This study is not without limitations. Physical markers were not used to identify the ASIS, mid-line of the thigh and talocrural joint. This decision was made in an effort to simulate how the Spark Motion Pro™ application may be used in the clinic or on the field.28 An additional limitation to this study includes the limited number of subjects used as well as the exclusion criteria. The limited number of subjects reduced the generalizability of the study findings. Subjects who were participating in a structured strengthening program were excluded from the study. This was to eliminate bias for subjects who may have already been coached or trained for proper landing and jump mechanics.
Future research should include comparing various lower extremity functional hop tests (single leg triple hop for distance, crossover hop for distance, vertical jump) on a larger sample of symptomatic subjects.
CONCLUSION
Two-dimensional mobile motion analysis using the Spark Motion Pro™ application demonstrated higher reliability than visual observation while analyzing genu valgus during a single limb hop in subjects with anterior knee pain. Although good reliability was noted in the non-symptomatic extremity, higher reliability values were achieved when measuring genu valgus on the symptomatic lower extremity. When 3D motion analysis is not available, a mobile motion analysis application could be used as a reliable tool when measuring dynamic knee valgus during a single leg hop test.
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