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Measurement of the Knee Flexion Angle With a Smartphone-Application is Precise and Accurate
The Journal of Arthroplasty 28 (2013) 784–787
Contents lists available at SciVerse ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Measurement of the Knee Flexion Angle With a Smartphone-Application is Precise and Accurate Jean-Yves Jenny MD Center for Orthopedic and Hand Surgery, University Hospital Strasbourg, France
a r t i c l e
i n f o
Article history: Received 27 August 2012 Accepted 16 November 2012 Keywords: knee range of motion measurement navigation Smartphone
a b s t r a c t We hypothesized that the measurement of the knee flexion angle measured with a specific Smartphone application was different from the reference measurement with a navigation system designed for total knee arthroplasty (TKA). Ten consecutive patients operated on for navigation assisted TKA were selected. Six navigated and 6 Smartphone measurements of knee flexion angle were obtained for each patient. The paired difference between measurements and their correlation were analyzed. The mean paired difference between navigated and Smartphone measurements was − 1.1° ± 6.8° (n.s.). There was a significant correlation between both measurements. The coherence between both measurements was good. The intra-observer and inter-observer reproducibility were good. The Smartphone application used may be considered as precise and accurate. The accuracy may be higher than other conventional measurement techniques. © 2013 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) is a successful treatment for endstage osteoarthritis. One of the major goals of this procedure is to restore an adequate range of motion, correcting for flexion contracture and achieving a high flexion angle. Range of motion has a relevant impact on gait [1] and knee function [2], and is frequently used as a monitoring tool for rehabilitation [3,4]. Therefore, measurement of range of motion is a relevant point for evaluation of a TKA, and this evaluation is a critical item of any knee scoring system [5–8]. Smartphone technology may be used in a lot of different ways. Most recent devices involve gyroscopes which may be used as angular measurement tools with the help of specific applications [9]. This technique is readily available, with virtually no additional cost, and may improve the precision and accuracy of the measurement while being easier to use than specific digital techniques. The basic hypothesis of this study was that the measurement of the knee flexion angle measured with a specific Smartphone application was different from the reference measurement with a navigation system designed for TKA. Material and Methods The study was approved by the institutional review committee. Ten consecutive patients operated on for end-stage osteoarthritis by
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2012.11.013. Reprint requests: Jean-Yves Jenny, MD, Center for Orthopedic and Hand Surgery (CCOM), 10 avenue Baumann, F-67400 Illkirch, France. 0883-5403/2805-0014$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2012.11.013
navigation assisted TKA were selected for the present study after giving their informed consent. Following pre-operative items were recorded: age, gender, body mass index (BMI), knee assessment by the Knee Society Score (KSS) [6], severity of the degenerative changes according to Ahlback [10], mechanical femoro-tibial angle measured on full leg X-ray with unipodal support (varus angles were considered as positive and valgus angles as negative values). The navigation system used (OrthoPilot, Aesculap, Tuttlingen, FRG) and the technique of navigation have been described elsewhere [11]. The data registration for the present study was performed after the TKA implantation. A free angle measurement application (Angle, Smudge Apps) was downloaded to the Smartphone from the Apple Application store. The Smartphone was placed in a sterile plastic bag routinely used for protecting the camera during arthroscopic surgery. The knee was positioned at full extension, 30 ± 2°, 60 ± 2°, 90 ± 2°, 110 ± 2° and at maximal flexion angle, according to the navigated measurement. At each step, the Smartphone measurement of the knee flexion angle was performed by putting the device on the anterior surface of the thigh proximal to the skin incision (Fig. 1), and on the anterior surface of the distal tibia distal to the skin incision (Fig. 2); the device displayed the angle compared to the horizontal line in both positions (Fig. 3); knee flexion angle was calculated as the sum of the two measurements. The registration process was repeated twice by the operating surgeon, and once by the assistant surgeon. For each set of measurement, 6 navigated and 6 Smartphone measurements were obtained for each patient, giving 60 navigated and 60 Smartphone measurements for the whole material. The paired difference between each navigated and Smartphone measurement
J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
Fig. 1. Position of the Smartphone on the distal femur.
was calculated, and all paired differences were analyzed with a paired Student t-test. All navigated and Smartphone measurements were plotted, and the Spearman coefficient of correlation was calculated. The coherence between the data was analyzed according to BlandAltman. The same process was applied for the data of each set of measurement and for every individual patient. The influence of all registered pre-operative items was analyzed with the appropriate statistical test. All tests were performed at a 0.05 level of significance. The intra-observer reproducibility was assessed with the calculation of the intraclass correlation coefficient (ICC) between the two sets of measurements by the operating surgeon. The inter-observer reproducibility was assessed with the calculation of the ICC between the first set of measurements of the operating surgeon and that of the assistant surgeon. Results Ten patients participated to the study. There were 4 men and 6 women, with a mean age of 69 years (range, 57 to 81 years) and a mean BMI of 31 (range, 26 to 34). The mean KSS was 85 points (range, 25 to 150 points). There were 7 grade 2 and 3 grade 3 cases according to Ahlback. The mean mechanical femoro-tibial angle was 5° (range, −6 to 11°).
785
Fig. 3. Measurement of the knee flexion angle displayed by the Smartphone.
gated and Smartphone measurements was good (r = 0.01), with only 6 paired differences higher than 10°. Second Set of Measurements The mean paired difference between navigated and Smartphone measurements was −1.7° ± 6.3° (range, −17 to 13°) (P = 0.05). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001) (Fig. 4). The coherence between navigated and Smartphone measurements was good (r = 0.01), with only 8 paired differences higher than 10° (Fig. 5). Third Set of Measurements The mean paired difference between navigated and Smartphone measurements was − 2.6° ± 7.0° (range, − 16 to 10°) (P b 0.001). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001). The coherence between navigated and Smartphone measurements was good (r = 0.01), with only 9 paired differences higher than 10°. No significant difference was observed between these cases and the other cases with a paired difference smaller than 10°.
First Set of Measurements Reproducibility The mean paired difference between navigated and Smartphone measurements was − 1.1° ± 6.8° (range, − 15 to 16°) (n.s.). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001). The coherence between navi-
Fig. 2. Position of the Smartphone on the proximal tibia.
The ICC between the two sets of measurements by the operating surgeon (intra-observer reproducibility) was 0.81. The ICC between the first set of measurements by the operating surgeon and the set of measurements of the assistant surgeon (inter-observer reproducibility) was 0.79.
Fig. 4. Results: knee flexion angle (degrees) – first set of measurements – correlation between Smartphone and navigated measurements.
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J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
Fig. 5. Results: knee flexion angle (degrees) – first set of measurements – Bland-Altman analysis.
Influence of Initial Status No pre-operative criteria showed a significant influence on the differences between navigated and Smartphone measurements. Individual Analysis The mean of the paired difference of individual navigated and Smartphone measurements was − 2° (range, − 5 to 4°) (P = 0.02). There was a significant correlation between navigated and Smartphone measurements for all individual patients (r 2 = 0.88 to 0.99, P = 0.01 to 0.001). There was a good coherence between navigated and Smartphone measurements for all individual patients. Discussion The basic hypothesis of the present study was partially confirmed. There was no significant difference between the measurement of the knee flexion angle with the Smartphone application and with the navigation system in the first set of measurements, but the difference was significant in the two other sets. However, the mean difference (less than 3°) was not clinically relevant, and only 23/180 measurements had a difference over 10° (13%) with an apparently random fluctuation which was not related to the degree of extension or flexion measured. Furthermore, there was a good correlation and a good coherence between navigated and Smartphone measurements for all sets, and there was a good intra-observer and inter-observer reproducibility of the Smartphone measurements. The precise and accurate measurement of the knee range of motion is a critical point during the clinical evaluation of TKA patients. Due to the potential error in flexion angle measurement, the global knee scoring may be inaccurate, and the comparison between different patients or prosthetic designs may be flawed. Flexion angle may be measured in a clinical setting by visual evaluation and/or mechanical goniometers. Yet fast, easy to perform and inexpensive, this technique may involve a significant lack of precision (up to 20°) [12] and of accuracy (up to 18°) [13]. Radiographic evaluation is accepted as the reference technique [14], but the additional exposure prevents it to be used extensively. Specific digital goniometers have been developed [15,16], but are not commonly used. More sophisticated techniques, such as gait analysis [17,18], are too demanding and can only be performed in experimental studies. More recently, digital imaging with computer image analysis has been proposed [19–21]; these methods were proved to be successful, but might be too time consuming to be used on a routine basis. Navigation systems have proved to be an accurate and precise measurement tool to assess the three-dimensional positioning of the knee joint, including the angle of knee flexion [22]. This allows using such systems as a reference technique to test for precision and
accuracy of other measurement tools. However, such systems are invasive and cannot be used outside the operating room. There are some weak points in this study. Although the total number of measurements is high, only 10 patients have been included, and the results might not be extended to the general population. Specially, the differences might be more significant in patients with higher BMI. The measurement was performed under passive conditions, and the results might be altered in the office environment where patients may actively bend the knee or even squat down; however, the use of navigation is not possible under this office condition to perform further validation. The accepted reference for similar works, i.e. the radiographic measurement, has not been performed; however the bias is probably limited, as navigation systems may be more precise and accurate than radiographic measurement. This study involved only two surgeons, and the results might not be extended to any orthopedic surgeon. The results may be specific to one specific application, on one specific Smartphone. Further study would be needed to verify that these results can be duplicated with other hardware and software combinations. Despite these limitations, the results of the present study may help improving the precision and accuracy of the clinical examination of a TKA and of its scoring. As the differences between the Smartphone measurements and the navigated measurement considered as the reference, the Smartphone application may be considered as precise and accurate. Using this technology to assess the knee range of motion allows an accurate assessment of this item, which is significant in all scoring systems. The accuracy may be higher than other conventional measurement techniques, and especially visual assessment which is most commonly used in the routine practice. Furthermore, this technology may be used to monitor the rehabilitation course by the physiotherapeutist or even the patient him- or herself, avoiding unnecessary postoperative visit or suggesting the occurrence of arthrofibrosis. However, a further study is ongoing to validate this technology by very obese patients, where the potential exists for soft tissues distorting the measurement process. Conclusion The Smartphone application used may be considered as precise and accurate. Using this technology to assess the knee range of motion allows an accurate scoring of this item, which is significant in all scoring systems. The accuracy may be higher than other conventional measurement techniques. References 1. Myles CM, Rowe PJ, Walker CR, et al. Knee joint functional range of movement prior to and following total knee arthroplasty measured using flexible electrogoniometry. Gait Posture 2002;16:46. 2. Miner AL, Lingard EA, Wright EA, et al. Knee range of motion after total knee arthroplasty: how important is this as an outcome measure? J Arthroplasty 2003;18:286. 3. Harmer AR, Naylor JM, Crosbie J, et al. Land-based versus water-based rehabilitation following total knee replacement: a randomized, single-blind trial. Arthritis Rheum 2009;61:184. 4. Irrgang JJ, Ho H, Harner CD, et al. Use of the International Knee Documentation Committee guidelines to assess outcome following anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 1998;6:107. 5. Hefti F, Müller W, Jakob RP, et al. Evaluation of knee ligament injuries with the IKDC form. Knee Surg Sports Traumatol Arthrosc 1993;1:226. 6. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989;248:13. 7. Okuda M, Omokawa S, Okahashi K, et al. Validity and reliability of the Japanese Orthopaedic Association score for osteoarthritic knees. J Orthop Sci 2012 [Epub ahead of print]. 8. Windsor R, Insalll, Warren R. The Hospital for Special Surgery knee ligament rating form. Am J Knee Surg 1988;1:140. 9. Peters FM, Greeff R, Goldstein N, et al. Improving acetabular cup orientation in total hip arthroplasty by using smartphone technology. J Arthroplasty 2012;27:1324. 10. Ahlbäck S. Osteoarthrosis of the knee. A radiographic investigation. Acta Radiol Diagn (Stockh) 1968(Suppl 277):7. 11. Jenny JY, Clemens U, Kohler S, et al. Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case–control study of
J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
12. 13.
14. 15.
16.
235 cases compared with 235 conventionally implanted prostheses. J Arthroplasty 2005;20:832. Lavernia C, D'Apuzzo M, Rossi MD, et al. Accuracy of knee range of motion assessment after total knee arthroplasty. J Arthroplasty 2008;23(Suppl 1):85. Lenssen AF, van Dam EM, Crijns YH, et al. Reproducibility of goniometric measurement of the knee in the in-hospital phase following total knee arthroplasty. BMC Musculoskelet Disord 2007;8:83. Edwards JZ, Greene KA, Davis RS, et al. Measuring flexion in knee arthroplasty patients. J Arthroplasty 2004;19:369. Cleffken B, van Breukelen G, Brink P, et al. Digital goniometric measurement of knee joint motion. Evaluation of usefulness for research settings and clinical practice. Knee 2007;14:385. Yaikwawongs N, Limpaphayom N, Wilairatana V. Reliability of digital compass goniometer in knee joint range of motion measurement. J Med Assoc Thai 2009;92:517.
787
17. Favre J, Jolles BM, Aissaoui R, et al. Ambulatory measurement of 3D knee joint angle. J Biomech 2008;41:1029. 18. Huddleston J, Alaiti A, Goldvasser D, et al. Ambulatory measurement of knee motion and physical activity: preliminary evaluation of a smart activity monitor. J Neuroeng Rehabil 2006;3:21. 19. Bennett D, Hanratty B, Thompson N, et al. Measurement of knee joint motion using digital imaging. Int Orthop 2009;33:1627. 20. Naylor JM, Ko V, Adie S, et al. Validity and reliability of using photography for measuring knee range of motion: a methodological study. BMC Musculoskelet Disord 2011;12:77. 21. Russell TG, Jull GA, Wootton R. Can the Internet be used as a medium to evaluate knee angle? Man Ther 2003;8:242. 22. Austin MS, Ghanem E, Joshi A, et al. The assessment of intraoperative prosthetic knee range of motion using two methods. J Arthroplasty 2008;23:515.
Contents lists available at SciVerse ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Measurement of the Knee Flexion Angle With a Smartphone-Application is Precise and Accurate Jean-Yves Jenny MD Center for Orthopedic and Hand Surgery, University Hospital Strasbourg, France
a r t i c l e
i n f o
Article history: Received 27 August 2012 Accepted 16 November 2012 Keywords: knee range of motion measurement navigation Smartphone
a b s t r a c t We hypothesized that the measurement of the knee flexion angle measured with a specific Smartphone application was different from the reference measurement with a navigation system designed for total knee arthroplasty (TKA). Ten consecutive patients operated on for navigation assisted TKA were selected. Six navigated and 6 Smartphone measurements of knee flexion angle were obtained for each patient. The paired difference between measurements and their correlation were analyzed. The mean paired difference between navigated and Smartphone measurements was − 1.1° ± 6.8° (n.s.). There was a significant correlation between both measurements. The coherence between both measurements was good. The intra-observer and inter-observer reproducibility were good. The Smartphone application used may be considered as precise and accurate. The accuracy may be higher than other conventional measurement techniques. © 2013 Elsevier Inc. All rights reserved.
Total knee arthroplasty (TKA) is a successful treatment for endstage osteoarthritis. One of the major goals of this procedure is to restore an adequate range of motion, correcting for flexion contracture and achieving a high flexion angle. Range of motion has a relevant impact on gait [1] and knee function [2], and is frequently used as a monitoring tool for rehabilitation [3,4]. Therefore, measurement of range of motion is a relevant point for evaluation of a TKA, and this evaluation is a critical item of any knee scoring system [5–8]. Smartphone technology may be used in a lot of different ways. Most recent devices involve gyroscopes which may be used as angular measurement tools with the help of specific applications [9]. This technique is readily available, with virtually no additional cost, and may improve the precision and accuracy of the measurement while being easier to use than specific digital techniques. The basic hypothesis of this study was that the measurement of the knee flexion angle measured with a specific Smartphone application was different from the reference measurement with a navigation system designed for TKA. Material and Methods The study was approved by the institutional review committee. Ten consecutive patients operated on for end-stage osteoarthritis by
The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2012.11.013. Reprint requests: Jean-Yves Jenny, MD, Center for Orthopedic and Hand Surgery (CCOM), 10 avenue Baumann, F-67400 Illkirch, France. 0883-5403/2805-0014$36.00/0 – see front matter © 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.arth.2012.11.013
navigation assisted TKA were selected for the present study after giving their informed consent. Following pre-operative items were recorded: age, gender, body mass index (BMI), knee assessment by the Knee Society Score (KSS) [6], severity of the degenerative changes according to Ahlback [10], mechanical femoro-tibial angle measured on full leg X-ray with unipodal support (varus angles were considered as positive and valgus angles as negative values). The navigation system used (OrthoPilot, Aesculap, Tuttlingen, FRG) and the technique of navigation have been described elsewhere [11]. The data registration for the present study was performed after the TKA implantation. A free angle measurement application (Angle, Smudge Apps) was downloaded to the Smartphone from the Apple Application store. The Smartphone was placed in a sterile plastic bag routinely used for protecting the camera during arthroscopic surgery. The knee was positioned at full extension, 30 ± 2°, 60 ± 2°, 90 ± 2°, 110 ± 2° and at maximal flexion angle, according to the navigated measurement. At each step, the Smartphone measurement of the knee flexion angle was performed by putting the device on the anterior surface of the thigh proximal to the skin incision (Fig. 1), and on the anterior surface of the distal tibia distal to the skin incision (Fig. 2); the device displayed the angle compared to the horizontal line in both positions (Fig. 3); knee flexion angle was calculated as the sum of the two measurements. The registration process was repeated twice by the operating surgeon, and once by the assistant surgeon. For each set of measurement, 6 navigated and 6 Smartphone measurements were obtained for each patient, giving 60 navigated and 60 Smartphone measurements for the whole material. The paired difference between each navigated and Smartphone measurement
J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
Fig. 1. Position of the Smartphone on the distal femur.
was calculated, and all paired differences were analyzed with a paired Student t-test. All navigated and Smartphone measurements were plotted, and the Spearman coefficient of correlation was calculated. The coherence between the data was analyzed according to BlandAltman. The same process was applied for the data of each set of measurement and for every individual patient. The influence of all registered pre-operative items was analyzed with the appropriate statistical test. All tests were performed at a 0.05 level of significance. The intra-observer reproducibility was assessed with the calculation of the intraclass correlation coefficient (ICC) between the two sets of measurements by the operating surgeon. The inter-observer reproducibility was assessed with the calculation of the ICC between the first set of measurements of the operating surgeon and that of the assistant surgeon. Results Ten patients participated to the study. There were 4 men and 6 women, with a mean age of 69 years (range, 57 to 81 years) and a mean BMI of 31 (range, 26 to 34). The mean KSS was 85 points (range, 25 to 150 points). There were 7 grade 2 and 3 grade 3 cases according to Ahlback. The mean mechanical femoro-tibial angle was 5° (range, −6 to 11°).
785
Fig. 3. Measurement of the knee flexion angle displayed by the Smartphone.
gated and Smartphone measurements was good (r = 0.01), with only 6 paired differences higher than 10°. Second Set of Measurements The mean paired difference between navigated and Smartphone measurements was −1.7° ± 6.3° (range, −17 to 13°) (P = 0.05). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001) (Fig. 4). The coherence between navigated and Smartphone measurements was good (r = 0.01), with only 8 paired differences higher than 10° (Fig. 5). Third Set of Measurements The mean paired difference between navigated and Smartphone measurements was − 2.6° ± 7.0° (range, − 16 to 10°) (P b 0.001). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001). The coherence between navigated and Smartphone measurements was good (r = 0.01), with only 9 paired differences higher than 10°. No significant difference was observed between these cases and the other cases with a paired difference smaller than 10°.
First Set of Measurements Reproducibility The mean paired difference between navigated and Smartphone measurements was − 1.1° ± 6.8° (range, − 15 to 16°) (n.s.). There was a significant correlation between navigated and Smartphone measurements (r = 0.99, P b 0.001). The coherence between navi-
Fig. 2. Position of the Smartphone on the proximal tibia.
The ICC between the two sets of measurements by the operating surgeon (intra-observer reproducibility) was 0.81. The ICC between the first set of measurements by the operating surgeon and the set of measurements of the assistant surgeon (inter-observer reproducibility) was 0.79.
Fig. 4. Results: knee flexion angle (degrees) – first set of measurements – correlation between Smartphone and navigated measurements.
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J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
Fig. 5. Results: knee flexion angle (degrees) – first set of measurements – Bland-Altman analysis.
Influence of Initial Status No pre-operative criteria showed a significant influence on the differences between navigated and Smartphone measurements. Individual Analysis The mean of the paired difference of individual navigated and Smartphone measurements was − 2° (range, − 5 to 4°) (P = 0.02). There was a significant correlation between navigated and Smartphone measurements for all individual patients (r 2 = 0.88 to 0.99, P = 0.01 to 0.001). There was a good coherence between navigated and Smartphone measurements for all individual patients. Discussion The basic hypothesis of the present study was partially confirmed. There was no significant difference between the measurement of the knee flexion angle with the Smartphone application and with the navigation system in the first set of measurements, but the difference was significant in the two other sets. However, the mean difference (less than 3°) was not clinically relevant, and only 23/180 measurements had a difference over 10° (13%) with an apparently random fluctuation which was not related to the degree of extension or flexion measured. Furthermore, there was a good correlation and a good coherence between navigated and Smartphone measurements for all sets, and there was a good intra-observer and inter-observer reproducibility of the Smartphone measurements. The precise and accurate measurement of the knee range of motion is a critical point during the clinical evaluation of TKA patients. Due to the potential error in flexion angle measurement, the global knee scoring may be inaccurate, and the comparison between different patients or prosthetic designs may be flawed. Flexion angle may be measured in a clinical setting by visual evaluation and/or mechanical goniometers. Yet fast, easy to perform and inexpensive, this technique may involve a significant lack of precision (up to 20°) [12] and of accuracy (up to 18°) [13]. Radiographic evaluation is accepted as the reference technique [14], but the additional exposure prevents it to be used extensively. Specific digital goniometers have been developed [15,16], but are not commonly used. More sophisticated techniques, such as gait analysis [17,18], are too demanding and can only be performed in experimental studies. More recently, digital imaging with computer image analysis has been proposed [19–21]; these methods were proved to be successful, but might be too time consuming to be used on a routine basis. Navigation systems have proved to be an accurate and precise measurement tool to assess the three-dimensional positioning of the knee joint, including the angle of knee flexion [22]. This allows using such systems as a reference technique to test for precision and
accuracy of other measurement tools. However, such systems are invasive and cannot be used outside the operating room. There are some weak points in this study. Although the total number of measurements is high, only 10 patients have been included, and the results might not be extended to the general population. Specially, the differences might be more significant in patients with higher BMI. The measurement was performed under passive conditions, and the results might be altered in the office environment where patients may actively bend the knee or even squat down; however, the use of navigation is not possible under this office condition to perform further validation. The accepted reference for similar works, i.e. the radiographic measurement, has not been performed; however the bias is probably limited, as navigation systems may be more precise and accurate than radiographic measurement. This study involved only two surgeons, and the results might not be extended to any orthopedic surgeon. The results may be specific to one specific application, on one specific Smartphone. Further study would be needed to verify that these results can be duplicated with other hardware and software combinations. Despite these limitations, the results of the present study may help improving the precision and accuracy of the clinical examination of a TKA and of its scoring. As the differences between the Smartphone measurements and the navigated measurement considered as the reference, the Smartphone application may be considered as precise and accurate. Using this technology to assess the knee range of motion allows an accurate assessment of this item, which is significant in all scoring systems. The accuracy may be higher than other conventional measurement techniques, and especially visual assessment which is most commonly used in the routine practice. Furthermore, this technology may be used to monitor the rehabilitation course by the physiotherapeutist or even the patient him- or herself, avoiding unnecessary postoperative visit or suggesting the occurrence of arthrofibrosis. However, a further study is ongoing to validate this technology by very obese patients, where the potential exists for soft tissues distorting the measurement process. Conclusion The Smartphone application used may be considered as precise and accurate. Using this technology to assess the knee range of motion allows an accurate scoring of this item, which is significant in all scoring systems. The accuracy may be higher than other conventional measurement techniques. References 1. Myles CM, Rowe PJ, Walker CR, et al. Knee joint functional range of movement prior to and following total knee arthroplasty measured using flexible electrogoniometry. Gait Posture 2002;16:46. 2. Miner AL, Lingard EA, Wright EA, et al. Knee range of motion after total knee arthroplasty: how important is this as an outcome measure? J Arthroplasty 2003;18:286. 3. Harmer AR, Naylor JM, Crosbie J, et al. Land-based versus water-based rehabilitation following total knee replacement: a randomized, single-blind trial. Arthritis Rheum 2009;61:184. 4. Irrgang JJ, Ho H, Harner CD, et al. Use of the International Knee Documentation Committee guidelines to assess outcome following anterior cruciate ligament reconstruction. Knee Surg Sports Traumatol Arthrosc 1998;6:107. 5. Hefti F, Müller W, Jakob RP, et al. Evaluation of knee ligament injuries with the IKDC form. Knee Surg Sports Traumatol Arthrosc 1993;1:226. 6. Insall JN, Dorr LD, Scott RD, et al. Rationale of the Knee Society clinical rating system. Clin Orthop Relat Res 1989;248:13. 7. Okuda M, Omokawa S, Okahashi K, et al. Validity and reliability of the Japanese Orthopaedic Association score for osteoarthritic knees. J Orthop Sci 2012 [Epub ahead of print]. 8. Windsor R, Insalll, Warren R. The Hospital for Special Surgery knee ligament rating form. Am J Knee Surg 1988;1:140. 9. Peters FM, Greeff R, Goldstein N, et al. Improving acetabular cup orientation in total hip arthroplasty by using smartphone technology. J Arthroplasty 2012;27:1324. 10. Ahlbäck S. Osteoarthrosis of the knee. A radiographic investigation. Acta Radiol Diagn (Stockh) 1968(Suppl 277):7. 11. Jenny JY, Clemens U, Kohler S, et al. Consistency of implantation of a total knee arthroplasty with a non-image-based navigation system: a case–control study of
J.-Y. Jenny / The Journal of Arthroplasty 28 (2013) 784–787
12. 13.
14. 15.
16.
235 cases compared with 235 conventionally implanted prostheses. J Arthroplasty 2005;20:832. Lavernia C, D'Apuzzo M, Rossi MD, et al. Accuracy of knee range of motion assessment after total knee arthroplasty. J Arthroplasty 2008;23(Suppl 1):85. Lenssen AF, van Dam EM, Crijns YH, et al. Reproducibility of goniometric measurement of the knee in the in-hospital phase following total knee arthroplasty. BMC Musculoskelet Disord 2007;8:83. Edwards JZ, Greene KA, Davis RS, et al. Measuring flexion in knee arthroplasty patients. J Arthroplasty 2004;19:369. Cleffken B, van Breukelen G, Brink P, et al. Digital goniometric measurement of knee joint motion. Evaluation of usefulness for research settings and clinical practice. Knee 2007;14:385. Yaikwawongs N, Limpaphayom N, Wilairatana V. Reliability of digital compass goniometer in knee joint range of motion measurement. J Med Assoc Thai 2009;92:517.
787
17. Favre J, Jolles BM, Aissaoui R, et al. Ambulatory measurement of 3D knee joint angle. J Biomech 2008;41:1029. 18. Huddleston J, Alaiti A, Goldvasser D, et al. Ambulatory measurement of knee motion and physical activity: preliminary evaluation of a smart activity monitor. J Neuroeng Rehabil 2006;3:21. 19. Bennett D, Hanratty B, Thompson N, et al. Measurement of knee joint motion using digital imaging. Int Orthop 2009;33:1627. 20. Naylor JM, Ko V, Adie S, et al. Validity and reliability of using photography for measuring knee range of motion: a methodological study. BMC Musculoskelet Disord 2011;12:77. 21. Russell TG, Jull GA, Wootton R. Can the Internet be used as a medium to evaluate knee angle? Man Ther 2003;8:242. 22. Austin MS, Ghanem E, Joshi A, et al. The assessment of intraoperative prosthetic knee range of motion using two methods. J Arthroplasty 2008;23:515.