Knee Surg Sports Traumatol Arthrosc DOI 10.1007/s00167-013-2782-7
KNEE
Sagittal plane evaluation of patellofemoral movement in patellofemoral pain patients with no evidence of maltracking Rapeepat Narkbunnam • Keerati Chareancholvanich Thossart Hanroongroj
•
Received: 5 March 2013 / Accepted: 16 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose The cause of abnormal patellar kinematics in patients with patellofemoral pain remains unclear. Many patients who develop patellofemoral pain symptoms do not exhibit evidence of maltracking. In these patients, sagittal plane evaluation of patellofemoral movement should be performed. Methods Knee radiographs were obtained for forty healthy volunteers and thirty patients at 0°, 30°, 60°, 90° and 120° of flexion in a standing weight-bearing position. The degree of active patellar movement was measured by a newly developed technique called ‘‘patellar motion angle’’. Three independent examiners sequentially performed all of the measurements under identical conditions. Results A significant decrease in the patellar motion angle was found during deep knee flexion from 90° to 120° in the patient group compared to the volunteer group (mean 18.5° ± 5.8° and 23.6° ± 6.2°, respectively) (P = 0.001). From 0° to 90° of knee flexion, no significant differences in the patellar motion angle were found between the two groups. Conclusion Sagittal plane patellofemoral joint kinematics is an area of interest in the study of the mechanical factors associated with patellofemoral pain. This study demonstrated a decrease in patellar movement during deep knee bending activity in patients with patellofemoral pain. Level of evidence Therapeutic study, Level II. Key words Patellofemoral pain Patellar movement Patellar tracking Radiographic study
R. Narkbunnam (&) K. Chareancholvanich T. Hanroongroj Department of Orthopaedics Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Siriraj Hospital 2 Prannok Road Bangkoknoi, Bangkok 10700, Thailand e-mail: [email protected]
Introduction Patellofemoral pain appears to be one of the most common complaints in patients presenting with knee problems [16]. The causes of this condition remain unclear. Furthermore, there is a lack of understanding with respect to its definition, diagnosis, evaluation and treatment. An imbalance in forces due to soft tissue tension around the patella alters the stress at the patellofemoral joint. Excessive load transfer to the subchondral bone leads to micro-structural damage and an inflammatory process that excites the nociceptive receptors, which causes patellofemoral pain symptoms [5, 9]. Most studies have evaluated patellar movement in the coronal or axial plane, both in a static position (e.g. patellar tilting, patellar translation) and during dynamic movement (patellar tracking) [1, 4, 21, 23, 25–27, 32]. Many patients develop patellofemoral pain symptoms without any significant clinical or radiographic evidence of malalignment or abnormal patellar tracking. In these groups of patients, sagittal plane evaluation of patellofemoral movement should be performed. In this study, we developed a simple method called the ‘‘patellar motion angle’’ to measure the degree of patellar movement in relation to the distal femoral condyle in the sagittal plane. The purpose of this study was to evaluate and compare patellofemoral motion from 0° to 120° of knee flexion during weight bearing in healthy volunteers and patellofemoral pain patients with no clinical evidence of maltracking.
Materials and methods For the study group, forty healthy volunteers from the general population who had reached skeletal maturity and
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had no current or past history of patellofemoral pain or instability were recruited. In the patient group, thirty subjects were recruited based on the clinical diagnosis of patellofemoral pain by 2 senior orthopaedic surgeons. The following diagnostic criteria were adopted based on criteria that have been previously used in patellofemoral pain studies: (1) A history of continuous anterior or retropatellar knee pain for more than 3 months or a history of more than 2 episodes of intermittent pain during the last 6 months; (2) exacerbation of symptoms caused by a least 2 of the following activities: prolonged sitting, ascending or descending stairs, squatting, and kneeling [2, 10, 11]; and (3) positive physical examination findings of patellofemoral pain using one of the following instruments: Clarke’s test (patellar gliding test) [3], the patellar compression test [22], isometric quadriceps contraction [14], the squat test [30], Waldron’s test [31] and the eccentric step test [29]. Subjects were excluded if they met any of the following criteria: (1) evidence of patellofemoral maltracking upon physical examination using the following: the patellar J sign [12] and the positive patellar apprehension test [28]; (2) deformity of the trochlear groove, abnormal patellar tilting or translation indicated by abnormal values of sulcus angle (138° ± 6°) [8], congruence angle (?6°/-6°) [24] or lateral patellar angle (opened laterally) on radiographic study at the 45° axial view [20]; and (3) clinical evidence of a current knee condition other than patellofemoral pain, such as knee ligament instability, patellar tendonitis, joint line tenderness or knee effusion, previous knee trauma or surgery, patellar dislocation or signs of osteoarthritis.
For all subjects, lateral knee radiographs were obtained at 0°, 30°, 60°, 90°, and 120° of flexion in the standing position with contraction of the quadriceps. A goniometric ruler with a radiopaque iron stick was attached to an X-ray board, and it was used to guide the subjects’ knee flexion at each angle (see Fig. 1). The greater trochanter, femoral lateral condyle and lateral malleolus were used as the reference points to align the goniometric ruler. After fluoroscopy, the accuracy of the knee flexion angle and rotation was verified. If the quality of any of the radiographs was unacceptable, the procedure was repeated. All of the radiographs were recorded using a digital radiography system. The degree of patellar movement was measured by the patellar motion angle (PMA), i.e. the angle between Blumensaat’s line [7] (set as the reference line at the distal femoral condyle) and the line drawn from the posterior angle point of the intercondylar notch to the inferior point of the patellar articular surface (see Fig. 2). The angles above Blumensaat’s line were recorded as negative, and the angles below Blumensaat’s line were recorded as positive. Differences in the PMA at 0°, 30°, 60°, 90° and 120° of knee flexion were recorded using sequential radiographs. Three independent examiners (senior orthopaedic residents) performed the measurements sequentially for each subject under identical conditions. All of the examiners used the digital radiography system for measuring the PMA. Each examiner was blinded to subjects’ data, as well as to the results of the other examiners. Ethics committee approval for the study was obtained from the ethical review board of Siriraj hospital, Mahidol University, Bangkok, Thailand (588/2551(EC4)). Informed consent documentation was obtained from all participants
Fig. 1 Lateral radiographs at 0°, 30°, 60°, 90° and 120° of knee flexion in the standing position with contraction of the quadriceps. A goniometric ruler with a radiopaque iron rod was attached to an X-ray
board to guide the subjects’ knee flexion at each angle and to verify the accuracy of the knee flexion angle in the radiographic records
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Fig. 2 The degree of patellar movement was measured by the ‘‘patellar motion angle’’ (PMA), the angle between Blumensaat’s line (set as the reference line at the distal femoral condyle) and the line
drawn from the posterior angle point of the intercondylar notch to the inferior point of the patellar articular surface
after complete explanation of the study protocol by a study nurse.
Table 1 The difference in the patellar motion angle at 0°, 30°, 60°, 90° and 120° of knee flexion and interobserver variation as indicated by the intraclass correlation coefficient (ICC)*
Statistical analysis
Patellar motion angle
Volunteer group Mean (SD)
Patient group Mean (SD)
P value
ICC*
95 % CI Lower–upper
0°–30°
21.3 (6.7)
21.0 (8.2)
n.s.
0.829
0.747–0.888
30°–60°
24.5 (6.1)
24.0 (5.2)
n.s.
0.777
0.664–0.855
60°–90°
29.8 (6.2)
30.4 (4.9)
n.s.
0.709
0.528–0.820
90°–120°
23.6 (6.2)
18.5 (5.8)
0.001
0.880
0.704–0.870
0°–120°
99.2 (8.5)
93.8 (11.9)
0.042
0.901
0.877–0.936
Normal PMA and patellar height ratio values were expressed as the mean ± SD. Differences between the volunteer and patient groups were assessed using Student’s t test. Alpha and beta were preset to 0.05 and 0.20, respectively. Interobserver reliability was assessed with the intraclass correlation coefficient (ICC) and its 95 % confidence interval (CI).
Results Forty healthy volunteers (8 males and 32 females) and thirty patients (5 males and 25 females) with patellofemoral pain were recruited for this study. The mean (standard deviation, SD) of age (years), height (cm) and bodyweight (kg) values in the volunteer and patient groups were as follows: 37.1 (7.6) and 36.1 (6.8) years; 165 (7.2) and 163 (6.9) cm; 59 (11.2) and 62 (12.4) kg, respectively. The patellar position values in relation to Blumensaat’s line at 0°, 30°, 60°, 90° and 120° of knee flexion were -48.7, -29.5, -6.9, ?24 and ?45.4 ((-) = above, (?) = below Blumensaat’s line), respectively, in the volunteer group and -51.1, -30.4, -9, ?22.4 and ?40.2 ((-) = above, (?)=below Blumensaat’s line), respectively, in the patient group.
n.s. not significant *P \ 0.05
The patellar motion angle (PMA) represents the degree of patellar movement around the distal femoral condyle, and it is calculated as the difference in the angle between the patellar positions at each knee flexion angle (see Table 1). The patellar motion angles were not equal to the degree of knee flexion. From 0°–30° to 0°–60° of knee flexion, the patellar motion angle was approximately 20°– 24° when the knee joint motion was 30°. The PMA increased to 30° when knee flexion was between 60° and 90°. In this range of motion, patellar motion was equal to knee joint motion. From 0° to 90° of knee flexion, no significant differences were found in the PMA between the volunteer and patient groups. During deep knee flexion from 90° to 120°, the mean patellar motion angle was 23.6° (SD = 6.2) in the volunteer group and 18.5° (SD = 5.8) in the patient group. In this range of motion, a significant
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difference was found in the patellar motion angle between the 2 groups (P = 0.001), and the patellar motion angle was decreased in the patient group compared to the volunteer group. Interobserver variation in the PMA, as determined by the intraclass correlation coefficient (ICC) with a 95 % confidence interval (CI), is shown in Table 1. All of the range of motion measurements had good reliability (ICC 0.7–0.9; 95 % CI 0.5–0.8).
Discussion Patellofemoral pain syndrome has a characteristic pattern that includes the following characteristics: (1) the pain is aggravated by deep knee flexion during weight-bearing activity, (2) the incidence of patellofemoral pain syndrome is more common in females than in males, (3) patellofemoral pain symptoms are not directly related to the size or degree of a cartilage lesion, and (4) the pain can occur in patients with patellofemoral maltracking and those with normal patellofemoral tracking. Many studies have evaluated patellar kinematics to identify an abnormal patellar movement pattern in patients with patellofemoral pain [16, 21, 25, 32]. Coronal plane movement can be used to assess patellar tracking, patellar translation, tilting and spinning. Maltracking has been reported to be strongly associated with patellofemoral pain, and it is typically characterized by excessive lateral translation or tilting at nearly full knee extension at 15°–45° [21, 23, 25–27]. Unfortunately, this theory has limited utility to explain why pain symptoms usually only occur when the patient is performing deep knee bending activities and why the pain occurs in patients with normal tracking. In the sagittal plane, patellar height ratios play a major role in determining the static relation of the patellofemoral joint. Several patellar height measurement methods have been described; however, no single method has been accepted as the standard. Many studies have proposed that patellar height ratios are weakly correlated with patellofemoral pain [15, 17–19]. The limitations of these methods are that the measurements cannot be performed during deep knee bending; most of these methods exhibit good accuracy in a specific range of motion, from slight flexion to not more than 60° of flexion. To evaluate patellofemoral movement in the sagittal plane, a simple measurement method involving sequential lateral radiographs was used in the present study. Patellar motion angles (PMAs) can accurately indicate the degree of patellar motion in relation to the trochlear groove of the distal femoral condyle. This measurement method is not limited by patellar shape, including the ‘‘long-nosed’’ or ‘‘Cyrano’’ type as described by Grelsamer et al. [13],
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because the reference landmark of the patella is at the inferior point of the patellar articular surface. The conceptual basis of this method is to represent the true relationship between patellofemoral articulations similar to the ‘‘patellotrochlear index’’ [6], which measures the patellar height in extension by magnetic resonance imaging, while the PMA is intended to study the patellofemoral position in varying degrees of knee flexion. Good to excellent interobserver reliability was shown in the present study. The results of this study showed that the degree of patellar motion around the distal femoral condyle was less than the degree of knee flexion. Only from 60° to 90° were knee flexion and the patellar motion angle equal. This result is revealing with regard to the normal kinematics of patellar movement in the sagittal plane. By comparing the patient and healthy volunteer groups, a significant decrease in the patellar motion angle was found during deep knee flexion from 90° to 120° in the patient group. From 0° to 90° of knee flexion, no significant differences were found in the patellar motion angle between the two groups. This result can be correlated with pain symptoms that are aggravated by deep knee flexion activities. There were also some limitations in the PMA measurement method. This method requires strict control of the knee flexion angles during radiographic examination because this factor has a direct effect on the PMA. We recommend the use of bony alignment to recheck the accuracy of the knee flexion angles for each radiographic study as our preferred method, as previously described. For this reason, PMAs may not be practical to use as a diagnostic tool in clinical settings. However, the concept of this method may be suitable for use in further studies that aim to define the causes of patellofemoral pain syndrome. The concept of decreased patellar motion in the sagittal plane during deep knee flexion activities in patients with patellofemoral pain syndrome which can be measured from the PMA as in this study has implications regarding treatment strategies for these groups of patients. Stretching exercises or surgical procedures that aim to increase the flexibility of the quadriceps and the patellar tendon should be considered as a principle of treatment.
Conclusion This study focused on sagittal plane patellofemoral joint kinematics with regard to the mechanical factors involved in patellofemoral pain. The new ‘‘patellar motion angle’’ assessment that was developed in this study is a simple and a reliable measurement method. Decreases in the patellar motion angle in the sagittal plane during deep knee bending activities were observed in patients with patellofemoral
Knee Surg Sports Traumatol Arthrosc
pain compared to the healthy volunteers. Abnormal patellar kinematics in the sagittal plane should be investigated further to evaluate the actual pathophysiology of the pain in patients with patellofemoral pain syndrome. Conflict of interest Ethical standard
None. Ethics committee approvals were obtained.
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15. Haim A, Yaniv M, Dekel S, Amir H (2003) Patellofemoral pain syndrome, validity of clinical and radiological features. Clin Orthop Relat Res 451:223–228 16. Ireland ML, Willson JD, Ballantyne BT, Davis IM (2003) Hip strength in females with and without patellofemoral pain. J Orthop Sports Phys Ther 33:671–676 17. Kannus PA (1992) Long patellar tendon: radiographic sign of patellofemoral pain syndrome: a prospective study. Radiology 185:859–863 18. Kujala UM, Osterman K, Kormano M, Nelimarkka O, Hurme M, Taimela S (1989) Patellofemoral relationships in recurrent patellar dislocation. J Bone Joint Surg Br 71:788–792 19. Laprade J, Culham E (2003) Radiographic measures in subjects who are asymptomatic and subjects with patellofemoral pain syndrome. Clin Orthop Relat Res 414:172–182 20. Laurin CA, Levesque HP, Dussault R et al (1978) The abnormal lateral patellofemoral angle. J Bone Joint Surg Am 60:55–60 21. MacIntyre NJ, Hill NA, Fellows RA, Ellis RE, Wilson DR (2006) Patellofemoral joint kinematics in individuals with and without patellofemoral pain syndrome. J Bone Joint Surg Am 88:2596–2605 22. Malek MM, Mangine RE (1981) Patellofemoral pain syndromes: a comprehensive and conservative approach. J Orthop Sports Phys Ther 2:108–116 23. McNally EG, Ostlere SJ, Pal C, Phillips A, Reid H, Dodd C (2000) Assessment of patellar maltracking using combined static and dynamic MRI. Eur Radiol 10:1051–1055 24. Merchant AC (1990) Patellofemoral malalignment and instabilities. In: Ewing JW (ed) Articular cartilage and knee joint function: basic science and arthroscopy. Raven Press Ltd, New York, pp 79–91 25. Nha KW, Papannagari R, Gill TJ (2008) In vivo patellar tracking: clinical motions and patellofemoral indices. J Orthop Res 26:1067–1074 26. O’Donnell P, Johnstone C, Watson M, McNally E, Ostlere S (2005) Evaluation of patellar tracking in symptomatic and asymptomatic individuals by magnetic resonance imaging. Skeletal Radiol 34:130–135 27. Powers CM, Ward SR, Fredericson M et al (2003) Patellofemoral kinematics during weight-bearing and non-weightbearing knee extension in persons with lateral subluxation of the patella: a preliminary study. J Orthop Sports Phys Ther 33:677–685 28. Reider B (1999) The orthopaedic physical examination. In: Reider B (ed) The knee. WB Saunders Company, Philadelphia, pp 201–248 29. Selfe J (2000) Peak 5 motion analysis of an eccentric step test performed by 100 normal subjects. Physiotherapy 86:241–247 30. Stickland A (1985) Examination of the knee joint. Physiotherapy 70:144–150 31. Waldron VD (1983) A test for chondromalacia patellae. Orthop Rev 12:103 32. Wilson NA, Press JM, Koh JL (2009) In vivo noninvasive evaluation of abnormal patellar tracking during squatting in patients with patellofemoral pain. J Bone Joint Surg Am 91:558–566
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KNEE
Sagittal plane evaluation of patellofemoral movement in patellofemoral pain patients with no evidence of maltracking Rapeepat Narkbunnam • Keerati Chareancholvanich Thossart Hanroongroj
•
Received: 5 March 2013 / Accepted: 16 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose The cause of abnormal patellar kinematics in patients with patellofemoral pain remains unclear. Many patients who develop patellofemoral pain symptoms do not exhibit evidence of maltracking. In these patients, sagittal plane evaluation of patellofemoral movement should be performed. Methods Knee radiographs were obtained for forty healthy volunteers and thirty patients at 0°, 30°, 60°, 90° and 120° of flexion in a standing weight-bearing position. The degree of active patellar movement was measured by a newly developed technique called ‘‘patellar motion angle’’. Three independent examiners sequentially performed all of the measurements under identical conditions. Results A significant decrease in the patellar motion angle was found during deep knee flexion from 90° to 120° in the patient group compared to the volunteer group (mean 18.5° ± 5.8° and 23.6° ± 6.2°, respectively) (P = 0.001). From 0° to 90° of knee flexion, no significant differences in the patellar motion angle were found between the two groups. Conclusion Sagittal plane patellofemoral joint kinematics is an area of interest in the study of the mechanical factors associated with patellofemoral pain. This study demonstrated a decrease in patellar movement during deep knee bending activity in patients with patellofemoral pain. Level of evidence Therapeutic study, Level II. Key words Patellofemoral pain Patellar movement Patellar tracking Radiographic study
R. Narkbunnam (&) K. Chareancholvanich T. Hanroongroj Department of Orthopaedics Surgery, Faculty of Medicine, Siriraj Hospital, Mahidol University, Siriraj Hospital 2 Prannok Road Bangkoknoi, Bangkok 10700, Thailand e-mail: [email protected]
Introduction Patellofemoral pain appears to be one of the most common complaints in patients presenting with knee problems [16]. The causes of this condition remain unclear. Furthermore, there is a lack of understanding with respect to its definition, diagnosis, evaluation and treatment. An imbalance in forces due to soft tissue tension around the patella alters the stress at the patellofemoral joint. Excessive load transfer to the subchondral bone leads to micro-structural damage and an inflammatory process that excites the nociceptive receptors, which causes patellofemoral pain symptoms [5, 9]. Most studies have evaluated patellar movement in the coronal or axial plane, both in a static position (e.g. patellar tilting, patellar translation) and during dynamic movement (patellar tracking) [1, 4, 21, 23, 25–27, 32]. Many patients develop patellofemoral pain symptoms without any significant clinical or radiographic evidence of malalignment or abnormal patellar tracking. In these groups of patients, sagittal plane evaluation of patellofemoral movement should be performed. In this study, we developed a simple method called the ‘‘patellar motion angle’’ to measure the degree of patellar movement in relation to the distal femoral condyle in the sagittal plane. The purpose of this study was to evaluate and compare patellofemoral motion from 0° to 120° of knee flexion during weight bearing in healthy volunteers and patellofemoral pain patients with no clinical evidence of maltracking.
Materials and methods For the study group, forty healthy volunteers from the general population who had reached skeletal maturity and
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had no current or past history of patellofemoral pain or instability were recruited. In the patient group, thirty subjects were recruited based on the clinical diagnosis of patellofemoral pain by 2 senior orthopaedic surgeons. The following diagnostic criteria were adopted based on criteria that have been previously used in patellofemoral pain studies: (1) A history of continuous anterior or retropatellar knee pain for more than 3 months or a history of more than 2 episodes of intermittent pain during the last 6 months; (2) exacerbation of symptoms caused by a least 2 of the following activities: prolonged sitting, ascending or descending stairs, squatting, and kneeling [2, 10, 11]; and (3) positive physical examination findings of patellofemoral pain using one of the following instruments: Clarke’s test (patellar gliding test) [3], the patellar compression test [22], isometric quadriceps contraction [14], the squat test [30], Waldron’s test [31] and the eccentric step test [29]. Subjects were excluded if they met any of the following criteria: (1) evidence of patellofemoral maltracking upon physical examination using the following: the patellar J sign [12] and the positive patellar apprehension test [28]; (2) deformity of the trochlear groove, abnormal patellar tilting or translation indicated by abnormal values of sulcus angle (138° ± 6°) [8], congruence angle (?6°/-6°) [24] or lateral patellar angle (opened laterally) on radiographic study at the 45° axial view [20]; and (3) clinical evidence of a current knee condition other than patellofemoral pain, such as knee ligament instability, patellar tendonitis, joint line tenderness or knee effusion, previous knee trauma or surgery, patellar dislocation or signs of osteoarthritis.
For all subjects, lateral knee radiographs were obtained at 0°, 30°, 60°, 90°, and 120° of flexion in the standing position with contraction of the quadriceps. A goniometric ruler with a radiopaque iron stick was attached to an X-ray board, and it was used to guide the subjects’ knee flexion at each angle (see Fig. 1). The greater trochanter, femoral lateral condyle and lateral malleolus were used as the reference points to align the goniometric ruler. After fluoroscopy, the accuracy of the knee flexion angle and rotation was verified. If the quality of any of the radiographs was unacceptable, the procedure was repeated. All of the radiographs were recorded using a digital radiography system. The degree of patellar movement was measured by the patellar motion angle (PMA), i.e. the angle between Blumensaat’s line [7] (set as the reference line at the distal femoral condyle) and the line drawn from the posterior angle point of the intercondylar notch to the inferior point of the patellar articular surface (see Fig. 2). The angles above Blumensaat’s line were recorded as negative, and the angles below Blumensaat’s line were recorded as positive. Differences in the PMA at 0°, 30°, 60°, 90° and 120° of knee flexion were recorded using sequential radiographs. Three independent examiners (senior orthopaedic residents) performed the measurements sequentially for each subject under identical conditions. All of the examiners used the digital radiography system for measuring the PMA. Each examiner was blinded to subjects’ data, as well as to the results of the other examiners. Ethics committee approval for the study was obtained from the ethical review board of Siriraj hospital, Mahidol University, Bangkok, Thailand (588/2551(EC4)). Informed consent documentation was obtained from all participants
Fig. 1 Lateral radiographs at 0°, 30°, 60°, 90° and 120° of knee flexion in the standing position with contraction of the quadriceps. A goniometric ruler with a radiopaque iron rod was attached to an X-ray
board to guide the subjects’ knee flexion at each angle and to verify the accuracy of the knee flexion angle in the radiographic records
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Fig. 2 The degree of patellar movement was measured by the ‘‘patellar motion angle’’ (PMA), the angle between Blumensaat’s line (set as the reference line at the distal femoral condyle) and the line
drawn from the posterior angle point of the intercondylar notch to the inferior point of the patellar articular surface
after complete explanation of the study protocol by a study nurse.
Table 1 The difference in the patellar motion angle at 0°, 30°, 60°, 90° and 120° of knee flexion and interobserver variation as indicated by the intraclass correlation coefficient (ICC)*
Statistical analysis
Patellar motion angle
Volunteer group Mean (SD)
Patient group Mean (SD)
P value
ICC*
95 % CI Lower–upper
0°–30°
21.3 (6.7)
21.0 (8.2)
n.s.
0.829
0.747–0.888
30°–60°
24.5 (6.1)
24.0 (5.2)
n.s.
0.777
0.664–0.855
60°–90°
29.8 (6.2)
30.4 (4.9)
n.s.
0.709
0.528–0.820
90°–120°
23.6 (6.2)
18.5 (5.8)
0.001
0.880
0.704–0.870
0°–120°
99.2 (8.5)
93.8 (11.9)
0.042
0.901
0.877–0.936
Normal PMA and patellar height ratio values were expressed as the mean ± SD. Differences between the volunteer and patient groups were assessed using Student’s t test. Alpha and beta were preset to 0.05 and 0.20, respectively. Interobserver reliability was assessed with the intraclass correlation coefficient (ICC) and its 95 % confidence interval (CI).
Results Forty healthy volunteers (8 males and 32 females) and thirty patients (5 males and 25 females) with patellofemoral pain were recruited for this study. The mean (standard deviation, SD) of age (years), height (cm) and bodyweight (kg) values in the volunteer and patient groups were as follows: 37.1 (7.6) and 36.1 (6.8) years; 165 (7.2) and 163 (6.9) cm; 59 (11.2) and 62 (12.4) kg, respectively. The patellar position values in relation to Blumensaat’s line at 0°, 30°, 60°, 90° and 120° of knee flexion were -48.7, -29.5, -6.9, ?24 and ?45.4 ((-) = above, (?) = below Blumensaat’s line), respectively, in the volunteer group and -51.1, -30.4, -9, ?22.4 and ?40.2 ((-) = above, (?)=below Blumensaat’s line), respectively, in the patient group.
n.s. not significant *P \ 0.05
The patellar motion angle (PMA) represents the degree of patellar movement around the distal femoral condyle, and it is calculated as the difference in the angle between the patellar positions at each knee flexion angle (see Table 1). The patellar motion angles were not equal to the degree of knee flexion. From 0°–30° to 0°–60° of knee flexion, the patellar motion angle was approximately 20°– 24° when the knee joint motion was 30°. The PMA increased to 30° when knee flexion was between 60° and 90°. In this range of motion, patellar motion was equal to knee joint motion. From 0° to 90° of knee flexion, no significant differences were found in the PMA between the volunteer and patient groups. During deep knee flexion from 90° to 120°, the mean patellar motion angle was 23.6° (SD = 6.2) in the volunteer group and 18.5° (SD = 5.8) in the patient group. In this range of motion, a significant
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difference was found in the patellar motion angle between the 2 groups (P = 0.001), and the patellar motion angle was decreased in the patient group compared to the volunteer group. Interobserver variation in the PMA, as determined by the intraclass correlation coefficient (ICC) with a 95 % confidence interval (CI), is shown in Table 1. All of the range of motion measurements had good reliability (ICC 0.7–0.9; 95 % CI 0.5–0.8).
Discussion Patellofemoral pain syndrome has a characteristic pattern that includes the following characteristics: (1) the pain is aggravated by deep knee flexion during weight-bearing activity, (2) the incidence of patellofemoral pain syndrome is more common in females than in males, (3) patellofemoral pain symptoms are not directly related to the size or degree of a cartilage lesion, and (4) the pain can occur in patients with patellofemoral maltracking and those with normal patellofemoral tracking. Many studies have evaluated patellar kinematics to identify an abnormal patellar movement pattern in patients with patellofemoral pain [16, 21, 25, 32]. Coronal plane movement can be used to assess patellar tracking, patellar translation, tilting and spinning. Maltracking has been reported to be strongly associated with patellofemoral pain, and it is typically characterized by excessive lateral translation or tilting at nearly full knee extension at 15°–45° [21, 23, 25–27]. Unfortunately, this theory has limited utility to explain why pain symptoms usually only occur when the patient is performing deep knee bending activities and why the pain occurs in patients with normal tracking. In the sagittal plane, patellar height ratios play a major role in determining the static relation of the patellofemoral joint. Several patellar height measurement methods have been described; however, no single method has been accepted as the standard. Many studies have proposed that patellar height ratios are weakly correlated with patellofemoral pain [15, 17–19]. The limitations of these methods are that the measurements cannot be performed during deep knee bending; most of these methods exhibit good accuracy in a specific range of motion, from slight flexion to not more than 60° of flexion. To evaluate patellofemoral movement in the sagittal plane, a simple measurement method involving sequential lateral radiographs was used in the present study. Patellar motion angles (PMAs) can accurately indicate the degree of patellar motion in relation to the trochlear groove of the distal femoral condyle. This measurement method is not limited by patellar shape, including the ‘‘long-nosed’’ or ‘‘Cyrano’’ type as described by Grelsamer et al. [13],
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because the reference landmark of the patella is at the inferior point of the patellar articular surface. The conceptual basis of this method is to represent the true relationship between patellofemoral articulations similar to the ‘‘patellotrochlear index’’ [6], which measures the patellar height in extension by magnetic resonance imaging, while the PMA is intended to study the patellofemoral position in varying degrees of knee flexion. Good to excellent interobserver reliability was shown in the present study. The results of this study showed that the degree of patellar motion around the distal femoral condyle was less than the degree of knee flexion. Only from 60° to 90° were knee flexion and the patellar motion angle equal. This result is revealing with regard to the normal kinematics of patellar movement in the sagittal plane. By comparing the patient and healthy volunteer groups, a significant decrease in the patellar motion angle was found during deep knee flexion from 90° to 120° in the patient group. From 0° to 90° of knee flexion, no significant differences were found in the patellar motion angle between the two groups. This result can be correlated with pain symptoms that are aggravated by deep knee flexion activities. There were also some limitations in the PMA measurement method. This method requires strict control of the knee flexion angles during radiographic examination because this factor has a direct effect on the PMA. We recommend the use of bony alignment to recheck the accuracy of the knee flexion angles for each radiographic study as our preferred method, as previously described. For this reason, PMAs may not be practical to use as a diagnostic tool in clinical settings. However, the concept of this method may be suitable for use in further studies that aim to define the causes of patellofemoral pain syndrome. The concept of decreased patellar motion in the sagittal plane during deep knee flexion activities in patients with patellofemoral pain syndrome which can be measured from the PMA as in this study has implications regarding treatment strategies for these groups of patients. Stretching exercises or surgical procedures that aim to increase the flexibility of the quadriceps and the patellar tendon should be considered as a principle of treatment.
Conclusion This study focused on sagittal plane patellofemoral joint kinematics with regard to the mechanical factors involved in patellofemoral pain. The new ‘‘patellar motion angle’’ assessment that was developed in this study is a simple and a reliable measurement method. Decreases in the patellar motion angle in the sagittal plane during deep knee bending activities were observed in patients with patellofemoral
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pain compared to the healthy volunteers. Abnormal patellar kinematics in the sagittal plane should be investigated further to evaluate the actual pathophysiology of the pain in patients with patellofemoral pain syndrome. Conflict of interest Ethical standard
None. Ethics committee approvals were obtained.
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