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Factors affecting the rectus femoris-patellar tendon Q-angle, measured using a computed tomographic scan
JT.Orthop (1999) 4:73–77Q-angle using CT Ando: Sci Factors affecting
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Factors affecting the rectus femoris-patellar tendon Q-angle, measured using a computed tomographic scan Takeo Ando Department of Orthopaedic Surgery, Yashima General Hospital, 1857-1 Yashima-nishi, Takamatsu 761-0113, Japan
Abstract: We devised a method to measure the Q-angle (the angle between the rectus femoris and the patellar ligament), using computed tomography (CT), in 1993. In this study, I investigated the lateral shift at each point forming the angle as factors affecting the Q-angle. The study group consisted of 83 patients with recurrent patellar dislocation (83 lower limbs) and a control group of 55 healthy people (55 lower limbs). A lateral shift was found in the anterosuperior iliac spine (ASIS) in the dislocation group compared with the control group (P , 0.01). A lateral shift was also found in the anteroinferior iliac spine (AIIS) in the dislocation group compared with the control group (P , 0.05). A medial shift was found in the bottom of the groove of the femoral condyle in the dislocation group compared with the control group (P , 0.001). A lateral shift was also seen in the tibial tubercle of the dislocation group in comparison with the control group (P , 0.0001). Lateral shift of the tibial tubercle may be the main factor influencing the Q-angle, as measured by CT. Key words: computed tomography, patella, dislocation
Introduction The Q-angle, defined as the angle between the rectus femoris and the patellar ligament, is larger in patients with recurrent patellar dislocation.6 Conventionally, the Q-angle is regarded as being formed by a line connecting the anterosuperior iliac spine (ASIS) and the center of the patella and a line connecting the center of the patella to the middle of the anterior tibial tubercle, and is meaOffprint requests to: T. Ando Received for publication on April 7, 1998; accepted on Sept. 20, 1998 No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the contents of this article. No funds were received in support this study.
sured with a goniometer.6 In patients with recurrent patellar dislocation, the patella is subluxated during knee extension, and the Q-angle is smaller and may not represent a true cause of dislocation. Measurement error, attributable to thickened soft tissue, however, prevents accurate measurement of the Q-angle. We devised a new method to measure the Q-angle, using computed tomography (CT), in 1993.1 We defined the Q-angle as the angle formed by connecting the anteroinferior iliac spine (AIIS), the bottom of the groove of the femoral condyle, and the tibial tubercle. The measurement error was smaller than with the conventional method, because the bottom of the femoral condyle was used as the reduction point of the patella, soft tissue, and lower limb rotation. In this present study, I investigated the presence or absence of lateral shift at each point forming the angle as factors affecting the Q-angle, measured by CT. Factors reported to affect the Q-angle, measured by conventional methods,6 are lateral shift of the tibial tubercle7,9 and a wide pelvis.12 We have reported previously on the medial shift of the bottom of the groove of the femoral condyle.1 Other factors have also been reported.2,3,4,8,11,14,15 In this study, I precisely measured the lateral shift at each point as factors affecting the Q-angle, using CT, and calculated them. This obviated the measurement error caused by soft tissues. A group with recurrent patellar dislocation (dislocation group) was compared with a control group. Conventionally, proximal10 or distal5,13,14 realignment is the treatment of choice for recurrent patellar dislocation. I examined the factors that influenced the Q-angle, and discuss the treatment of choice for this condition.
Subjects The Q-angle was measured in 83 abnormal limbs in 83 patients (dislocation group; 14 men and 69 women, aged
74
T. Ando: Factors affecting Q-angle using CT
13–38 years; mean, 19.9 years) at Yashima General Hospital. These patients had no history of prior surgery and no history of other lower limb disorders. The Qangle was also measured unilaterally in 55 lower limbs in a control group of 55 people with no history of patellar dislocation, knee pain, or exercise-related pain (17 men and 38 women, aged 14–31 years (mean, 20.3 years). There were 42 right and 41 left limbs in the dislocation group and 28 right and 27 left limbs in the control group.
Methods A CT scan was performed with the patient in a supine position and the knees extended and relaxed, as in Insall’s method.6 Abduction of the hip was 0°, and rotation of the leg was neutral. Initially, a CT scan of the plane of the pubic symphysis (PS) was made, and this was considered as the origin for setting. Tomographic pictures were recorded of the ASIS, the anteroinferior iliac spine (AIIS), the femoral subtrochanterica, the center of the patella, and the anterior tibial tubercle (Fig. 1). Because of the requirements for radiographic measurement, the sliding table for CT was not moved, except along the major axis of the table, and the tomographic picture could not be expanded or reduced. A personal computer and digitizer were used to measure the center of the bony prominence of the ASIS, the center of the bony prominence of the AIIS, the center of the femoral subtrochanterica (F), the bottom of the groove of the femoral condyle (G) and the center of the bony prominence of the tibial tubercle (T), using CT scan of the lower limbs. During measurement, the origin was the PS, and each of the above points on the CT of the lower limb were measured. Allowing for the reduced scale of the picture, the coordinates of each point were measured. The method used for calculation of the lateral shift of the ASIS is shown in Fig. 2. First, tomographic pictures of the planes of the PS and the ASIS were superimposed on one another. A straight line connecting the bilateral ASISs was established, and a perpendicular line was drawn from the PS toward this line. The distance between the ASIS and the intersection of the perpendicular line with was defined as the lateral shift of the ASIS. In the same manner, the lateral shift of the AIIS and F were calculated (Fig. 2). To take individual differences into consideration, lateral shift was divided by the length of the lower limb; namely, the distance from the ASIS to the medial malleolus of the ankle, and the resulting values were studied. The method for calculation of lateral shift at the bottom of the groove of the femoral condyle (G) is
Fig. 1. Computed tomography (CT) sites. CT scans were made along the planes of the anterosuperior iliac spine (ASIS), the anteroinferior iliac spine (AIIS), the femoral subtrochanterica (F ), the patellar center (P), and the tibial tubercle (T), G, Groove of femoral condyle
shown in Fig. 3. A tomographic picture was taken along the plane of the center of the patella. The width of the femoral condyle was measured along a line parallel to the posterior tangential line of the femoral condyle. This distance was defined as C. Similarly, the distance between G and the medial edge of the femoral condyle was defined as D. The lateral shift of the bottom of the femoral condyle was expressed as D/C 3 100 (%). The method for the calculation of lateral shift at T is shown in Fig. 4. A tomographic picture was taken along the plane of the tibial tubercle. The width of the tibial condyle was measured along a line parallel to the posterior tangential line of the tibial condyle. This distance was defined as A. Similarly, the distance between T and the medial edge of the tibial condyle was defined as B. The lateral shift of T was expressed as B/A 3 100 (%). From these lateral shifts, I examined whether each of these point in the dislocation group deviated medially or laterally in comparison with those in the control group.
T. Ando: Factors affecting Q-angle using CT
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Fig. 3. Method for measurement of lateral shift of G, using CT scan. The lateral shift was calculated as D/C 3 100(%). For definitions of D and C, see text
Fig. 2. Method for measurement, of lateral shift of ASIS, AIIS and F. A perpendicular line was drawn from the pubic symphysis (PS) to a straight line connecting the bilateral points of ASIS, AIIS and F. The distance between the cross point and the affected point was regarded as the lateral shift
Fig. 4. Method for measuring lateral shift of the tibial tubercle, using CT scan. The lateral shift was calculated as B/A 3 100(%). For definitions of B and A, see text
All calculations of the various indexes and distances were performed with a personal computer (NEC PC9801 series, PHOTRON MPC-8501). Results The mean lateral shift of the ASIS was 115 6 7 mm in the control group and 115 6 11 mm in the dislocation group (Fig. 5), with no significant difference between the two groups. The mean lateral shift of the AIIS was 95 6 7 mm in the control group and 92 6 9 mm in the dislocation group, with no significant difference between two groups. The mean lateral shift of F was 110 6 7 mm in the control group and 104 6 10 mm in the dislocation group, significantly smaller than that in the control group (P , 0.01).
Fig. 5. Lateral shift of ASIS, AIIS, and F. There were no significant (NS) differences in ASIS and AIIS positions between the control (Con.) and dislocation (Dis.) groups
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Fig. 6. Lateral shift of ASIS, AIIS, and F (corrected by length of lower limb; see text). The ASIS and AIIS showed significant lateral shifts in the dislocation (Dis.) group compared with controls (Con.) (P , 0.01 and P , 0.05, respectively)
To take each case and individual differences into consideration, lateral shifts of the ASIS, AIIS, and F were divided by the length of the lower limb and the corrected results were studied. The mean corrected value for ASIS in the dislocation group was 15.1 6 1.7%, significantly greater than that in the control group (13.8 6 0.8%; P , 0.01) (Fig. 6). The mean corrected value for AIIS in the dislocation group was 12.0 6 1.2%, significantly greater than that in the control group (11.4 6 0.9%; P , 0.05). The mean corrected value for F in the dislocation group was 13.6 6 1.4%, not significantly different from the value in the control group (13.3 6 1.0%). The mean lateral shift of the bottom of the groove of the femoral condyle was 49 6 5% in the control group and 46 6 6% in the dislocation group (Fig. 7). The bottom of the groove in the dislocation group was located 3% more medially than that in the control group (P , 0.001). The mean lateral shift of the tibial tubercle was 64 6 6% in the control group and 79 6 9% in the dislocation group (Fig. 8). The bottom of the tibial tubercle in the dislocation group was located 15% more laterally than in the control group (P , 0.0001).
Discussion In this study, there were no significant differences between the control and dislocation groups in lateral shift of the ASIS and the AIIS. However, when these shifts were divided by the length of the lower limb, there was a significant shift of both the ASIS (P , 0.01) and the AIIS (P , 0.05). This was assumed to be caused by differences in individual anatomy, by the older age of
T. Ando: Factors affecting Q-angle using CT
Fig. 7. In the control group, the bottom of the groove of the femoral condyle was located almost at the center of the femoral condyle. The bottom of the groove of the femoral condyle was located 3% more medially in the dislocation (Dis) group compared with the control (Con.) group (P , 0.001). Med., medial; Lat., lateral
Fig. 8. The tibial tubercle was located 15% more lateral in the dislocation (Dis.) group than in the control (Con.) group (P , 0.0001). Med., media; Lat., lateral
the control group (more time elapsed after epiphyseal arrest), and by the greater ratio of men in the control than in the dislocation group. Accordingly, lateral shift was divided by the length of the lower limb for correction and the corrected values were used in this study. Factors affecting the Q-angle were examined using CT. These were; a wide pelvis12 (namely, lateral shift of the ASIS and the AIIS), medial shift of the bottom of the groove of the femoral condyle,1 and lateral shift of the tibial tubercle.7,9 These were measured with CT, which allows for accurate measurement, unhindered by the presence of soft tissues. The results were then calculated with a computer. As for lateral shift of the bottom of the groove, the dislocation group showed a significant
T. Ando: Factors affecting Q-angle using CT
77
Table 1. Correlation between lateral shift at various sites (corrected by the length of the lower limb) and the Q-angle measured by CT Site of lateral shift ASIS AIIS F G T
Correlation coefficient 0.33 0.31 0.14 20.33 0.54
For definition of Q-angle, see text CT, Computed tomography; ASIS, anterosuperior iliac spine; AIIS, anteroinferior iliac spine; F, femoral subtrochanterica; G, bottom of groove of the femoral condyle; T, tibial tubercle
medial shift (P , 0.001). With respect to the lateral shift of the tibial tubercle, the dislocation group showed a significant lateral shift (P , 0.0001). I also investigated for a correlation between the Qangle (the angle formed by the AIIS, G, and T) measured by CT and lateral shift at each point (corrected by the length of the lower limb). Table 1 shows the correlation coefficient with lateral shift at each point. The lateral shift of the tibial tubercle had a higher correlation than the other shifts. These results indicated that lateral shift of the tibial tubercle could be the main factor influencing the Q-angle as measured by CT. Taking into consideration these measurements, I concluded that distal rather than proximal realignment should be emphasized as a therapeutic method. However, as the measurements of individuals differ, the measurement of lateral shift at these points should be useful for deciding on the treatment.
Summary I precisely measured the lateral shift of the anterosuperior iliac spine, the anteroinferior iliac spine, the bottom of the groove of the femoral condyle, and the tibial tubercle, using CT and calculated them based on these measurements. In patients with recurrent patellar dislocation, there was a significant difference in lateral shift at the anterosuperior iliac spine (P , 0.01), at the anteroinferior iliac spine (P , 0.05), and at the tibial tubercle (P , 0.0001) compared with findings in controls. In the patients with recurrent patellar dislocation, there was also a
significant difference in medial shift at the bottom of the groove of the femoral condyle compared with findings in controls (P , 0.001). I concluded that lateral shift of the tibial tubercle may be the main factor affecting the Q-angle as measured by CT and that distal realignment should be the treatment of choice. Acknowledgments. The author thanks Professor Hajime Inoue, M.D., of the Department of Orthopaedic Surgery, Okayama University School of Medicine, Okayama, Japan, for his critical review of the manuscript.
References 1. Ando T, Hirose H, Inoue M, et al. A new method using computed tomographic scan to measure the rectus femoris-patellar tendon Q-angle; comparison with conventional method. Clin Orthop 1993;289:213–9. 2. Bowker JH, Thompson EB. Surgical treatment of recurrent dislocation of the patella: A study of 48 cases. J Bone Joint Surg Am 1964;46:1451–61. 3. Carter C, Sweetnam R. Familial joint laxity and recurrent dislocation of the patella. J Bone Joint Surg Br 1958;40:664–7. 4. Gunn DR. Contracture of the quadriceps muscle: A discussion on the etiology and relationship to recurrent dislocation of the patella. J Bone Joint Surg Br 1964;46:492–7. 5. Hauser EDW. Total tendon transplant for slipping patella. Surg Gynecol Obstet 1938;199–214. 6. Insall J, Falvo KA, Wise DW. Chondromalacia patellae. J Bone Joint Surg Am 1976;58:1–8. 7. Insall J. Current concepts review. Patellar pain. J Bone Joint Surg Am 1982;64:147–52. 8. Jeffreys TE. Recurrent dislocation of the patella due to abnormal attachment of the ilio-tibial tract. J Bone Joint Surg Br 1978;45:740–3. 9. Larson RL. Subluxation-dislocation of the patella. In: The injured adolescent knee. Kennedy JC, editor. Baltimore: Williams and Wilkins, 1979:161–204. 10. Maquet PGJ. Biomechanics of the knee. With application to the pathogenesis and the surgical treatment of osteoarthritis. With 184 figures. Berlin: Springer-Verlag, 1976. 11. Mariani PP, Caruso I. An electromyographic investigation of subluxation of the patella. J Bone Joint Surg Br 1979;61:169–71. 12. Outerbridge RE. Further studies on the etiology of chondromalacia patellae. J Bone Joint Surg Br 1964;46:179–90. 13. Roux D. Recurrent dislocation. In: Crenshaw AH, editor. Campbell’s operative orthopaedics, vol. 1. 4th ed. Saint Louis: CV Mosby, 1963:352–55. 14. Trillat A, Dejour H, Couette A. Diagnostic et traitement des subluxations rècidivantes de la rotule. Rev Chir Orthop 1964;50:813–24. 15. Wiberg G. Roentgenographic and anatomic studies on the femoropatellar joint: With special reference to chondromalacia patellae. Acta Orthop Scand 1941;12:319–410.
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Factors affecting the rectus femoris-patellar tendon Q-angle, measured using a computed tomographic scan Takeo Ando Department of Orthopaedic Surgery, Yashima General Hospital, 1857-1 Yashima-nishi, Takamatsu 761-0113, Japan
Abstract: We devised a method to measure the Q-angle (the angle between the rectus femoris and the patellar ligament), using computed tomography (CT), in 1993. In this study, I investigated the lateral shift at each point forming the angle as factors affecting the Q-angle. The study group consisted of 83 patients with recurrent patellar dislocation (83 lower limbs) and a control group of 55 healthy people (55 lower limbs). A lateral shift was found in the anterosuperior iliac spine (ASIS) in the dislocation group compared with the control group (P , 0.01). A lateral shift was also found in the anteroinferior iliac spine (AIIS) in the dislocation group compared with the control group (P , 0.05). A medial shift was found in the bottom of the groove of the femoral condyle in the dislocation group compared with the control group (P , 0.001). A lateral shift was also seen in the tibial tubercle of the dislocation group in comparison with the control group (P , 0.0001). Lateral shift of the tibial tubercle may be the main factor influencing the Q-angle, as measured by CT. Key words: computed tomography, patella, dislocation
Introduction The Q-angle, defined as the angle between the rectus femoris and the patellar ligament, is larger in patients with recurrent patellar dislocation.6 Conventionally, the Q-angle is regarded as being formed by a line connecting the anterosuperior iliac spine (ASIS) and the center of the patella and a line connecting the center of the patella to the middle of the anterior tibial tubercle, and is meaOffprint requests to: T. Ando Received for publication on April 7, 1998; accepted on Sept. 20, 1998 No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the contents of this article. No funds were received in support this study.
sured with a goniometer.6 In patients with recurrent patellar dislocation, the patella is subluxated during knee extension, and the Q-angle is smaller and may not represent a true cause of dislocation. Measurement error, attributable to thickened soft tissue, however, prevents accurate measurement of the Q-angle. We devised a new method to measure the Q-angle, using computed tomography (CT), in 1993.1 We defined the Q-angle as the angle formed by connecting the anteroinferior iliac spine (AIIS), the bottom of the groove of the femoral condyle, and the tibial tubercle. The measurement error was smaller than with the conventional method, because the bottom of the femoral condyle was used as the reduction point of the patella, soft tissue, and lower limb rotation. In this present study, I investigated the presence or absence of lateral shift at each point forming the angle as factors affecting the Q-angle, measured by CT. Factors reported to affect the Q-angle, measured by conventional methods,6 are lateral shift of the tibial tubercle7,9 and a wide pelvis.12 We have reported previously on the medial shift of the bottom of the groove of the femoral condyle.1 Other factors have also been reported.2,3,4,8,11,14,15 In this study, I precisely measured the lateral shift at each point as factors affecting the Q-angle, using CT, and calculated them. This obviated the measurement error caused by soft tissues. A group with recurrent patellar dislocation (dislocation group) was compared with a control group. Conventionally, proximal10 or distal5,13,14 realignment is the treatment of choice for recurrent patellar dislocation. I examined the factors that influenced the Q-angle, and discuss the treatment of choice for this condition.
Subjects The Q-angle was measured in 83 abnormal limbs in 83 patients (dislocation group; 14 men and 69 women, aged
74
T. Ando: Factors affecting Q-angle using CT
13–38 years; mean, 19.9 years) at Yashima General Hospital. These patients had no history of prior surgery and no history of other lower limb disorders. The Qangle was also measured unilaterally in 55 lower limbs in a control group of 55 people with no history of patellar dislocation, knee pain, or exercise-related pain (17 men and 38 women, aged 14–31 years (mean, 20.3 years). There were 42 right and 41 left limbs in the dislocation group and 28 right and 27 left limbs in the control group.
Methods A CT scan was performed with the patient in a supine position and the knees extended and relaxed, as in Insall’s method.6 Abduction of the hip was 0°, and rotation of the leg was neutral. Initially, a CT scan of the plane of the pubic symphysis (PS) was made, and this was considered as the origin for setting. Tomographic pictures were recorded of the ASIS, the anteroinferior iliac spine (AIIS), the femoral subtrochanterica, the center of the patella, and the anterior tibial tubercle (Fig. 1). Because of the requirements for radiographic measurement, the sliding table for CT was not moved, except along the major axis of the table, and the tomographic picture could not be expanded or reduced. A personal computer and digitizer were used to measure the center of the bony prominence of the ASIS, the center of the bony prominence of the AIIS, the center of the femoral subtrochanterica (F), the bottom of the groove of the femoral condyle (G) and the center of the bony prominence of the tibial tubercle (T), using CT scan of the lower limbs. During measurement, the origin was the PS, and each of the above points on the CT of the lower limb were measured. Allowing for the reduced scale of the picture, the coordinates of each point were measured. The method used for calculation of the lateral shift of the ASIS is shown in Fig. 2. First, tomographic pictures of the planes of the PS and the ASIS were superimposed on one another. A straight line connecting the bilateral ASISs was established, and a perpendicular line was drawn from the PS toward this line. The distance between the ASIS and the intersection of the perpendicular line with was defined as the lateral shift of the ASIS. In the same manner, the lateral shift of the AIIS and F were calculated (Fig. 2). To take individual differences into consideration, lateral shift was divided by the length of the lower limb; namely, the distance from the ASIS to the medial malleolus of the ankle, and the resulting values were studied. The method for calculation of lateral shift at the bottom of the groove of the femoral condyle (G) is
Fig. 1. Computed tomography (CT) sites. CT scans were made along the planes of the anterosuperior iliac spine (ASIS), the anteroinferior iliac spine (AIIS), the femoral subtrochanterica (F ), the patellar center (P), and the tibial tubercle (T), G, Groove of femoral condyle
shown in Fig. 3. A tomographic picture was taken along the plane of the center of the patella. The width of the femoral condyle was measured along a line parallel to the posterior tangential line of the femoral condyle. This distance was defined as C. Similarly, the distance between G and the medial edge of the femoral condyle was defined as D. The lateral shift of the bottom of the femoral condyle was expressed as D/C 3 100 (%). The method for the calculation of lateral shift at T is shown in Fig. 4. A tomographic picture was taken along the plane of the tibial tubercle. The width of the tibial condyle was measured along a line parallel to the posterior tangential line of the tibial condyle. This distance was defined as A. Similarly, the distance between T and the medial edge of the tibial condyle was defined as B. The lateral shift of T was expressed as B/A 3 100 (%). From these lateral shifts, I examined whether each of these point in the dislocation group deviated medially or laterally in comparison with those in the control group.
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Fig. 3. Method for measurement of lateral shift of G, using CT scan. The lateral shift was calculated as D/C 3 100(%). For definitions of D and C, see text
Fig. 2. Method for measurement, of lateral shift of ASIS, AIIS and F. A perpendicular line was drawn from the pubic symphysis (PS) to a straight line connecting the bilateral points of ASIS, AIIS and F. The distance between the cross point and the affected point was regarded as the lateral shift
Fig. 4. Method for measuring lateral shift of the tibial tubercle, using CT scan. The lateral shift was calculated as B/A 3 100(%). For definitions of B and A, see text
All calculations of the various indexes and distances were performed with a personal computer (NEC PC9801 series, PHOTRON MPC-8501). Results The mean lateral shift of the ASIS was 115 6 7 mm in the control group and 115 6 11 mm in the dislocation group (Fig. 5), with no significant difference between the two groups. The mean lateral shift of the AIIS was 95 6 7 mm in the control group and 92 6 9 mm in the dislocation group, with no significant difference between two groups. The mean lateral shift of F was 110 6 7 mm in the control group and 104 6 10 mm in the dislocation group, significantly smaller than that in the control group (P , 0.01).
Fig. 5. Lateral shift of ASIS, AIIS, and F. There were no significant (NS) differences in ASIS and AIIS positions between the control (Con.) and dislocation (Dis.) groups
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Fig. 6. Lateral shift of ASIS, AIIS, and F (corrected by length of lower limb; see text). The ASIS and AIIS showed significant lateral shifts in the dislocation (Dis.) group compared with controls (Con.) (P , 0.01 and P , 0.05, respectively)
To take each case and individual differences into consideration, lateral shifts of the ASIS, AIIS, and F were divided by the length of the lower limb and the corrected results were studied. The mean corrected value for ASIS in the dislocation group was 15.1 6 1.7%, significantly greater than that in the control group (13.8 6 0.8%; P , 0.01) (Fig. 6). The mean corrected value for AIIS in the dislocation group was 12.0 6 1.2%, significantly greater than that in the control group (11.4 6 0.9%; P , 0.05). The mean corrected value for F in the dislocation group was 13.6 6 1.4%, not significantly different from the value in the control group (13.3 6 1.0%). The mean lateral shift of the bottom of the groove of the femoral condyle was 49 6 5% in the control group and 46 6 6% in the dislocation group (Fig. 7). The bottom of the groove in the dislocation group was located 3% more medially than that in the control group (P , 0.001). The mean lateral shift of the tibial tubercle was 64 6 6% in the control group and 79 6 9% in the dislocation group (Fig. 8). The bottom of the tibial tubercle in the dislocation group was located 15% more laterally than in the control group (P , 0.0001).
Discussion In this study, there were no significant differences between the control and dislocation groups in lateral shift of the ASIS and the AIIS. However, when these shifts were divided by the length of the lower limb, there was a significant shift of both the ASIS (P , 0.01) and the AIIS (P , 0.05). This was assumed to be caused by differences in individual anatomy, by the older age of
T. Ando: Factors affecting Q-angle using CT
Fig. 7. In the control group, the bottom of the groove of the femoral condyle was located almost at the center of the femoral condyle. The bottom of the groove of the femoral condyle was located 3% more medially in the dislocation (Dis) group compared with the control (Con.) group (P , 0.001). Med., medial; Lat., lateral
Fig. 8. The tibial tubercle was located 15% more lateral in the dislocation (Dis.) group than in the control (Con.) group (P , 0.0001). Med., media; Lat., lateral
the control group (more time elapsed after epiphyseal arrest), and by the greater ratio of men in the control than in the dislocation group. Accordingly, lateral shift was divided by the length of the lower limb for correction and the corrected values were used in this study. Factors affecting the Q-angle were examined using CT. These were; a wide pelvis12 (namely, lateral shift of the ASIS and the AIIS), medial shift of the bottom of the groove of the femoral condyle,1 and lateral shift of the tibial tubercle.7,9 These were measured with CT, which allows for accurate measurement, unhindered by the presence of soft tissues. The results were then calculated with a computer. As for lateral shift of the bottom of the groove, the dislocation group showed a significant
T. Ando: Factors affecting Q-angle using CT
77
Table 1. Correlation between lateral shift at various sites (corrected by the length of the lower limb) and the Q-angle measured by CT Site of lateral shift ASIS AIIS F G T
Correlation coefficient 0.33 0.31 0.14 20.33 0.54
For definition of Q-angle, see text CT, Computed tomography; ASIS, anterosuperior iliac spine; AIIS, anteroinferior iliac spine; F, femoral subtrochanterica; G, bottom of groove of the femoral condyle; T, tibial tubercle
medial shift (P , 0.001). With respect to the lateral shift of the tibial tubercle, the dislocation group showed a significant lateral shift (P , 0.0001). I also investigated for a correlation between the Qangle (the angle formed by the AIIS, G, and T) measured by CT and lateral shift at each point (corrected by the length of the lower limb). Table 1 shows the correlation coefficient with lateral shift at each point. The lateral shift of the tibial tubercle had a higher correlation than the other shifts. These results indicated that lateral shift of the tibial tubercle could be the main factor influencing the Q-angle as measured by CT. Taking into consideration these measurements, I concluded that distal rather than proximal realignment should be emphasized as a therapeutic method. However, as the measurements of individuals differ, the measurement of lateral shift at these points should be useful for deciding on the treatment.
Summary I precisely measured the lateral shift of the anterosuperior iliac spine, the anteroinferior iliac spine, the bottom of the groove of the femoral condyle, and the tibial tubercle, using CT and calculated them based on these measurements. In patients with recurrent patellar dislocation, there was a significant difference in lateral shift at the anterosuperior iliac spine (P , 0.01), at the anteroinferior iliac spine (P , 0.05), and at the tibial tubercle (P , 0.0001) compared with findings in controls. In the patients with recurrent patellar dislocation, there was also a
significant difference in medial shift at the bottom of the groove of the femoral condyle compared with findings in controls (P , 0.001). I concluded that lateral shift of the tibial tubercle may be the main factor affecting the Q-angle as measured by CT and that distal realignment should be the treatment of choice. Acknowledgments. The author thanks Professor Hajime Inoue, M.D., of the Department of Orthopaedic Surgery, Okayama University School of Medicine, Okayama, Japan, for his critical review of the manuscript.
References 1. Ando T, Hirose H, Inoue M, et al. A new method using computed tomographic scan to measure the rectus femoris-patellar tendon Q-angle; comparison with conventional method. Clin Orthop 1993;289:213–9. 2. Bowker JH, Thompson EB. Surgical treatment of recurrent dislocation of the patella: A study of 48 cases. J Bone Joint Surg Am 1964;46:1451–61. 3. Carter C, Sweetnam R. Familial joint laxity and recurrent dislocation of the patella. J Bone Joint Surg Br 1958;40:664–7. 4. Gunn DR. Contracture of the quadriceps muscle: A discussion on the etiology and relationship to recurrent dislocation of the patella. J Bone Joint Surg Br 1964;46:492–7. 5. Hauser EDW. Total tendon transplant for slipping patella. Surg Gynecol Obstet 1938;199–214. 6. Insall J, Falvo KA, Wise DW. Chondromalacia patellae. J Bone Joint Surg Am 1976;58:1–8. 7. Insall J. Current concepts review. Patellar pain. J Bone Joint Surg Am 1982;64:147–52. 8. Jeffreys TE. Recurrent dislocation of the patella due to abnormal attachment of the ilio-tibial tract. J Bone Joint Surg Br 1978;45:740–3. 9. Larson RL. Subluxation-dislocation of the patella. In: The injured adolescent knee. Kennedy JC, editor. Baltimore: Williams and Wilkins, 1979:161–204. 10. Maquet PGJ. Biomechanics of the knee. With application to the pathogenesis and the surgical treatment of osteoarthritis. With 184 figures. Berlin: Springer-Verlag, 1976. 11. Mariani PP, Caruso I. An electromyographic investigation of subluxation of the patella. J Bone Joint Surg Br 1979;61:169–71. 12. Outerbridge RE. Further studies on the etiology of chondromalacia patellae. J Bone Joint Surg Br 1964;46:179–90. 13. Roux D. Recurrent dislocation. In: Crenshaw AH, editor. Campbell’s operative orthopaedics, vol. 1. 4th ed. Saint Louis: CV Mosby, 1963:352–55. 14. Trillat A, Dejour H, Couette A. Diagnostic et traitement des subluxations rècidivantes de la rotule. Rev Chir Orthop 1964;50:813–24. 15. Wiberg G. Roentgenographic and anatomic studies on the femoropatellar joint: With special reference to chondromalacia patellae. Acta Orthop Scand 1941;12:319–410.