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Sagittal spine and lower limb movement during sit-to-stand in healthy young subjects
Gait & Posture 22 (2005) 338–345 www.elsevier.com/locate/gaitpost
Sagittal spine and lower limb movement during sit-to-stand in healthy young subjects Elizabeth A. Tully*, Mohammad Reza Fotoohabadi, Mary P. Galea School of Physiotherapy, The University of Melbourne, Parkville, Vic. 3010, Australia Received 14 April 2004; received in revised form 22 July 2004; accepted 19 November 2004
Abstract This study aimed to determine the sagittal movement relationships between thoracic, lumbar spine and hip joints during sit-to-stand (STS). Forty-seven healthy young adults were videotaped performing STS at their preferred speed from a chair set at 100% knee height. Forward trunk lean prior to buttock lift-off (LO) was accomplished by concurrent lumbar and hip flexion (1:3). As the lumbar spine flexed the thoracic spine extended, resulting in a LO trunk angle of 45.78 (5.88) with respect to a horizontal reference. Following LO, the hip(s) and lumbar spine extended and the thoracic spine flexed, with the standing thoracic angle approximating the initial thoracic posture in sitting. # 2004 Elsevier B.V. All rights reserved. Keywords: Sit-to-stand; Movement analysis; Thoracic spine; Lumbar spine
1. Introduction The ability to stand up from sitting on a chair is an essential prerequisite for walking and therefore independent function [1]. Inability to effectively perform sit-to-stand (STS) can lead to severe mobility impairment, for example, in young children with cerebral palsy [2], and in older people experiencing musculo-skeletal problems [3–5]. Inability to perform this essential activity may lead to dependence, institutionalization and even death in elderly subjects [6]. Although a seemingly simple task, STS requires the coordinated interaction of linked body segments to transport effectively the body’s centre of mass in a horizontal then vertical direction while maintaining balance over a small base of support, the feet. The basic kinematics include flexion of the trunk and hips to bring the centre of mass forward, followed by bilateral extension of the lower limb joints and trunk extension to raise the body mass in a vertical direction over the feet [7]. Previous STS studies have investigated various aspects of this task, such as the total time taken, velocity and * Corresponding author. Tel.: +61 3 8344 4171; fax: +61 3 8344 4188. E-mail address: [email protected] (E.A. Tully). 0966-6362/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2004.11.007
acceleration of body segments [7,8], and the kinematics (joint angles) and kinetics (joint moments) of the lower limb joints before and after buttocks ‘lift-off’ (LO) [8–10]. Although sagittal trunk movement during STS has been measured with respect to a horizontal reference [11,12], the contribution of the thoracolumbar spine has not been subjected to any detailed analysis since few models have included markers on the spine. In most studies the spine has been viewed as a rigid body, the ‘trunk segment’, defined by a straight line joining markers on the first thoracic and first sacral spine [13], or shoulder and greater trochanter [12,14– 16], a method which fails to clarify the respective contribution of hip and thoracolumbar spine to the measure of sagittal trunk angle. In some studies the mobile lower cervical joints have been included as part of the trunk segment [7,17]. Nikfekr et al. [18] placed markers along the midline spine at the level of C7, T3, T6, T9, T12 and the sacrum. However, these authors chose to measure whole trunk kinematics (C7–sacrum), and although linear displacement of the spinal markers was measured in vertical and lateral directions no thoracic or lumbar spinal angles were calculated. It appears that the results of previous studies have influenced assessment and training of patients with
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dysfunctional STS. For example, it is suggested that there should be ‘no flexion within the upper body throughout the (STS) action’ [19], and that ‘flexing the lumbar spine instead of the hips’ [19] is a poor STS technique. However, Schenkman et al. [20] included a marker on the pelvis and demonstrated that during trunk forward lean seven of their nine healthy subjects flexed the trunk segment on the pelvis by an average of 168, indicating some degree of spinal flexion in the pre LO phase. Error has also occurred in measurement of sagittal ‘hip’ joint angle from the frequently used marker combination shoulder, greater trochanter and knee. This measure is contaminated by inclusion of the joints of the thoracolumbar spine [7,8,12], with possible shoulder girdle protraction further compounding the error. As a result of these measurement methods, the coordinated movements of the thoracolumbar spine and hip joints demonstrated in other functional movements of the trunk and lower limbs, for example, flexing the thigh towards the chest as in stepping up a high step [21] or toe touching from upright standing [22], have not been determined during STS. Therefore this study used computer-aided video analysis of STS with a revised model of reference marker placement, to determine (i) the sagittal plane contribution of the lumbar and thoracic spine to trunk movement, (ii) the movement interaction between the lumbar spine and pelvi-femoral or ‘true’ hip joint, and (iii) the coordination of hip and knee joints during STS in healthy young subjects.
2. Methods and subjects 2.1. Subjects Forty seven healthy physiotherapy students (27 female, 20 male), mean age 20.1 (2.8) years, range 18–30 years, mean height 168.5 (8.4) cm, and BMI 20.7(2.3) kg/m2
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volunteered for this study. Written consent was obtained from all subjects and ethics approval for this research was obtained from the Human Research Ethics Committee of The University of Melbourne. The volunteers were screened to exclude those with any identifiable movement dysfunction, a history of significant spinal, hip, or knee pathology or vertebrofemoral pain requiring treatment during the preceding 6 months. 2.2. Model of marker placement Ten light reflective markers were attached over the midline thoracolumbar spine and right lower limb of standing subjects using non-irritant adhesive discs. Markers were positioned on each subject as described in Table 1 and illustrated in Fig. 1. Spherical reflective markers 3.5 cm in diameter were attached over relevant spinous processes and pelvic landmarks. Markers located over the lateral aspect of the right lower limb comprised flat circular discs 3.5 cm in diameter cut from a roll of retro-reflective tape. All markers had a 4 cm black base to maximize the contrast between the marker and the subject’s skin. To locate the first thoracic spinous process (T1), the subject was asked to flex their head and neck while the examiner kept a finger on the spinous processes thought to be C6 and C7. The spinous process of C6 was felt to move forward while that of C7 remained stationary. Having located the spinous process of C7 that of T1 was found by palpation of the next caudal level. At the thoracolumbar junction, the location of the first lumbar spinous process (L1) was determined by first placing a mark on the skin corresponding to the midpoint of a line joining the posterior superior iliac spines (S2). A second mark was placed over the lumbar spinous process at the level corresponding to the highest point of the iliac crest, deemed to be at the level of L4, based on the previous radiographic work of Hamilton et al. [23]. The line joining these two points was then projected superiorly by the same distance
Table 1 Location of skin reference markers on midline thoracolumbar spine and right lower limb Marker location
Abbreviation
Marker placement
T1 spinous process Spinous process of 3rd thoracic vertebra L1 spinous process Spinous process of 11th thoracic vertebra Posterior superior iliac spine
T1 T3 L1 T11 PSIS
Anterior superior iliac spine Two-third thigh
ASIS 2/3 thigh
Supracondylar thigh
SC
Lateral tibial condyle Lateral malleolus
LTC LM
Spinous process of the first thoracic vertebra 3 cm below the T1 marker Spinous process of first lumbar vertebra 3 proximal to the L1 marker Distal aspect of the right posterior superior iliac spine, at the level of the spinous process of S2 Anterior superior iliac spine Junction of the proximal one-third with the distal two-thirds of a line joining the midpoint of the lateral knee joint line and the apex of the greater trochanter At the junction of the distal one-quarter and proximal three quarters of a straight line joining the apex of the greater trochanter to the midpoint of the lateral knee joint line Anterior aspect of the neck of the fibula 10 cm above the tip of fibula malleolus
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Fig. 1. Starting position of the sit-to-stand movement. See Table 1 for details of marker locations. Note the positioning of the upper limbs, and in the seated position, the horizontal position of the thighs.
and this proximal point was deemed to be the spinous process of L1. Since the location of the markers 3 cm distal to T1 and 3 cm proximal to L1 may vary with the height of the subject they were named T3 and T11, respectively, for convenience, although they were not necessarily over the correct spinous process. 2.3. Experimental procedure Subjects with bare feet were instructed to stand up from an adjustable-height backless chair at a self-selected speed, arms folded across the chest. Although it was anticipated that having the subjects arms folded across the chest might have some effect on motor performance, the position was adopted to avoid obstructing the camera’s view of the markers. The height of the seat was standardized to the length of the subject’s leg from floor to mid-lateral knee joint line, so that the long axis of the thigh was in the horizontal plane (Fig. 1). Following two to three practice trials the movement was videotaped from the right side using a single video camera placed at a distance of 7 m and perpendicular to the sagittal plane, and with the centre of the field of view at the level of the greater trochanter in standing. The movement was repeated if the examiner was not satisfied that it was performed without unwanted or unnatural actions. A 300 W light attached to the camera tripod illuminated the reflective markers against a dark background. The automatic digitization mode of the two dimensional Peak Motus (Peak Motus Motion Analysis System, PEAK Performance Technologies Inc., Englewood, CO, USA) was used to analyze the STS movement from the videotape at 50 frames/s. The location of each reference marker was automatically recorded in two-dimensional space. Sagittal thoracic, lumbar, hip and knee angles were calculated following filtering of the raw data using a robust low pass Butterworth filter set at 6 Hz. The accuracy and reliability of Peak for uniplanar measurement of joint angles has previously been established [24]. All angular data were
then imported into the Microsoft Excel program and used in conjunction with Kaleidagraph Version 3.8 (Synergy Software) to normalize the data to 100% movement duration. This process was necessary to compensate for the different amounts of time used by each subject to complete the movement, and involved converting the time taken to complete each STS into a 100% scale with 1% increments. The angles at each 1% increment over the total test duration were then recalculated for each subject. Three events were defined to provide reference points during the movement; (i) the ‘start’ of STS was defined as the commencement of horizontal (X) displacement of the T1 marker; (ii) ‘LO’ at the point of 10% of the vertical (Y) displacement of the proximal (2/3Th) thigh marker, as described by Mourey et al. [9], and (iii) the end of STS at the point of maximal vertical (Y) displacement of the T1 marker. Fig. 2 shows the method used to calculate sagittal thoracic, lumbar and lower limb joint angles. Sagittal thoracic angle was calculated from the relative angle between the straight lines defined by T1–T3 and T11–L1. Likewise lumbar angle was calculated from the relative angle between the straight line defined by T11–L1 and a line perpendicular to the line joining the right PSIS–ASIS markers (representing the plane of the pelvis). A zero thoracic spine angle was defined when the straight line T1– T3 and T11–L1 were co-linear. A zero lumbar spine angle was defined when the straight line T11–L1 was perpendicular to the line joining the right PSIS–ASIS. Any spinal angle anterior to the zero position was defined as flexion, whereas a posterior angle was defined as extension. The
Fig. 2. Diagram illustrating method of calculation of thoracic, lumbar, and hip flexion–extension angles. (See text for details).
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‘true’ hip flexion–extension angle was measured between the long axis of the femur (2/3Th–SC) and the plane of the pelvis (PSIS–ASIS). Sagittal knee angle was measured between the long axes of the thigh and leg (2/3Th–SC–LTC– LM). Similar conventions were used to describe hip and knee flexion and extension from the anatomical reference. All flexion (extension) angles were given positive (negative) values for statistical purposes. 2.4. Data analysis For the purpose of analysis STS was divided into a preLO, and a post-LO phase. Mean and standard deviation were calculated for total STS duration. Excursion (end minus start angle), range (maximum minus minimum angle), and sagittal angles at LO were calculated for the thoracic, lumbar spine, hip and knee joints. The relative contributions of hip and lumbar flexion during the pre and post-LO phases were displayed using hip to lumbar ratios, i.e., for each phase the range of hip movement was divided by lumbar range. Descriptive statistics were obtained using Excel 97 (Microsoft Corporation) and Kaleidagraph 3.08 (Synergy software).
3. Results 3.1. STS duration
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Fig. 4 demonstrates the angular movement relationships between the thoracolumbar spine, hip and knee joints during the pre and post-LO phases. It can be seen from Figs. 3 and 4 that sagittal trunk displacement before and after LO comprised a concurrent but opposite flexion–extension of the thoracic and lumbar spine in conjunction with sagittal hip movement. During forward trunk lean the thoracic spine extended as the lumbar spine and hip joint(s) flexed, producing a maximum trunk angle of 45.668 with respect to a horizontal reference (5.84)8. The lumbar spine reached its maximal flexion angle prior to LO at 32% STS duration, while the thoracic spine continued to extend until LO commenced (42% STS duration). Flexion of the hip joint and lumbar spine was concurrent with the lumbar spine increasing its contribution as forward trunk lean progressed. On average, maximal hip flexion angle occurred close to LO at 39% STS duration, with the ratio of hip to lumbar flexion during the pre-LO phase being 3.1:1, i.e., for every 3.18 of hip flexion there was 18 of lumbar flexion. Following LO the hip(s) and lumbar spine extended with the hip extending more rapidly than the lumbar spine, the ratio of hip to lumbar spine movement being 2.6:1 in this phase. The thoracic spine flexed as the lumbar spine and hips extended, with the sagittal thoracic angle in standing returning to that of the initial sitting posture. At LO, both hip and knee joints were flexed to approximately the same degree (98.18:100.48), after which the both joints were locked together in a linear pattern of extension.
In this group of young healthy adults the mean time to stand up from sitting at a self-selected speed was 2.04 (0.39) s (range 1.30–3.18 s).
4. Discussion
3.2. Angular movement
4.1. Measurement issues
The excursion and range of movement of sagittal thoracic, lumbar, hip and knee joints during STS are shown in Table 2. Note the substantial range through which the lumbar spine moved during STS (37.78) Fig. 3a–d illustrate the mean (S.D.) sagittal thoracic and lumbar spine, hip and knee joint angles at 1% time intervals throughout the movement. LO occurred at 41.2% of STS duration, which corresponded to 38 knee extension from a sitting knee flexion angle of 100.48. Other sagittal angles at LO were: thoracic spine 17.78 (9.48), lumbar spine 19.38 (9.98); hip 98.18 (8.18).
This study has provided a description of the sagittal movement relationships between the thoracolumbar spine, hip and knee joints during STS in a group of healthy young adults. The use of computer aided video analysis, and an improved model for sagittal plane measurement of thoracolumbar and lower limb joint angles [22,25] facilitated this process. A two-dimensional analysis was considered adequate since it has been demonstrated that STS is primarily a sagittal plane activity in healthy subjects, with only small amounts of trunk rotation, trunk lateral flexion, and lateral shift [26].
Table 2 Excursion and range (degrees) of sagittal thoracic and lumbar spine, hip and knee joints during STS in healthy young adults (n = 47) Joint/region
Start
Thoracic spine Lumbar spine Hip joint Knee joint
32.2 14.5 76.9 104.3
End (9.3) (9.4) (7.3) (6.3)
Negative values denote extension.
31.1 (8.7) 16.2 (8.3) 2.1 (7.4) 0.04 (6.4)
Excursion 1.1 30.7 74.8 104.3
Maximum 32.2 21.5 98.9 104.8
(9.3) (9.2) (6.5) (5.2)
Minimum 17.6 (9.1) 16.2 (8.3) 2.1 (7.4) 0.04 (6.4)
Range 14.6 37.7 96.8 104.8
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Fig. 3. Means 1S.D. (n = 47) representing the change in flexion–extension angle throughout sit-to-stand in the thoracic (a) and lumbar spine (b), hip (c) and knee joints (d). LO indicates the point of lift-off.
Fig. 4. Mean line plots (n = 47) illustrating the angular movement relationships throughout sit-to-stand between the thoracic and lumbar spine, hip and knee joints. The vertical dotted line indicates the point of lift-off.
Key advantages of the model of marker placement used in this study were: (i) it enabled the separate sagittal contributions of the thoracic, lumbar spine and hip joints to be identified during STS, (ii) error in measurement of hip flexion angle from markers located on the shoulder, greater trochanter and knee was avoided by measurement of the angle of the femur with respect to the plane of the pelvis, and (iii) errors in hip and knee flexion–extension angles associated with skin movement on the lateral thigh were minimized by placement of markers away from regions of maximal skin movement on the thigh during flexion. It has been demonstrated that significant anterior displacement of the traditional greater trochanter marker, and to a lesser extent posterior displacement of a lateral femoral epicondyle or mid-lateral knee joint marker is responsible for up to 20% error in hip and knee angles during sagittal plane analysis [25]. It is acknowledged that in this study cephalad movement of the ASIS marker during hip flexion may have added 5% error on average to measurement of sagittal hip angle [25]. However, we had the advantage of using lean
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subjects (mean BMI < 21) in whom skin movement and subsequent errors would be minimal. The method of locating L1 in the spinal component of the model was adopted because of the lack of accuracy or reliability associated with methods involving counting lumbar spinous processes [27–30]. The main purpose of this method was to achieve a reliable technique for determining the approximate location of L1 that takes into account the height of the subject. The results of a small, unpublished ultrasound study by a colleague (A. Schache, personal communication) suggest that the method is essentially valid, since on average the proximal landmark represented the spinous process of L1 in a group of young healthy adults. However, the validity and reliability of this method requires further investigation. In this study, relatively large variations were evident in mean sagittal lumbar and thoracic spine angles (S.D. > 50% and 30% mean angle, respectively). Thus, despite efforts to achieve reliable identification of L1 for example, surface anatomy errors may have occurred. Alternatively, there may have been genuine inter-subject variation in thoracolumbar posture or movement. Extreme variability in sagittal plane spinal curvature in standing has been noted previously by Stagnara et al. [31], who suggested that the differences in spinal curvature between subjects was so great that the average curve values were of little use as normative values. Although this study group was extremely homogenous in terms of age, gender, and weight each individual may have a unique sagittal thoracolumbar alignment possibly influenced by the posture of the pelvis. It is acknowledged that there remain some largely insurmountable problems from skin movement over the vertebral spinous processes; however, as noted by Lundberg [32], the fascia over the spinous processes is relatively rigidly fixed to bone, and thus skin movement will follow bone movement more closely than in many other regions. Gadjdosik et al. [33] suggested that errors introduced by skin movement over spinous processes are likely to be systematic, leading at worst to a relatively constant bias in the obtained results.
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4.2. Temporal aspects In this study, the mean time for young healthy adults to stand up from sitting of 2.0 0.3 s was slower than in other studies where healthy subjects performed STS at their natural speed (1.6 0.3 s, 1.7 0.5 s, 1.8 0.3 s) [10,33,34]. It is difficult to compare STS duration across studies since researchers have used different starting foot positions, arm positions, and in particular different definitions for the start and/or end of the movement. On average LO occurred at 41.2% of STS duration. Table 3 shows that in previous studies LO occurred between 30% and 45% STS. The various methods of determining this event make comparison difficult. The latter includes visual estimation of ‘buttocks off’ [34], pressure sensors under the buttocks [8,10], and force plates under the patient’s feet [35], or the front legs of the chair [36]. 4.3. Hip–spine interaction The apparent lack of concern for details of the spinal contribution to STS is surprising, since during rehabilitation of patients with neurological conditions, such as stroke for example, the alignment/movement of the trunk is regarded as having major implications for effective completion of the task. A component of STS considered as critical is ‘flexion of the extended trunk at the hips’ to move the body mass forward in the pre-LO phase (19 p 143), with ‘flexion of the spine instead of at the hips’ (19 p 143) being considered a common motor problem. In contrast our data indicate that both the hips and lumbar spine flex concurrently to bring the body mass forward prior to LO, with the lumbar spine contributing 18 for every 3.18 hip flexion. Ikeda et al. [37] p 473, noted that while the trunk was flexing forward older subjects did not extend their heads as much as younger subjects, so that the older group was facing down at LO. The authors were unclear as to the reason but suggested that the change may be due to an ‘inability to straighten’. Similarly Papa and Cappozzo [10] noted
Table 3 Results of studies showing LL event as a percentage of the total time taken to stand up from sitting Author
Definition of LO
%STS
Present study
At 10% of vertical displacement of proximal thigh marker
41.2
Papa and Cappozzo [10]
Beginning of seat unloading Seat load cell drops to zero
38 45
Alexander et al. [11] Bharami et al. [35] Baer and Ashburn [26] Pai and Rogers [15] Nuzik et al. [34] Roebroeck et al. [7] Khemlani et al. [41] Shepherd and Gentile [8]
Maximum anterior position of head Minimum value of horizontal component of GRF When thighs leave the seat Force plate Visual detection of buttocks LO Largest backward value of horizontal component of GRF At thighs off At thighs off recorded by seat switch under ischial tuberosities
41 40.6 37 37 35 35 31 30
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increased flexion of the trunk segment in elderly subjects during the pre-LO phase. Our study showed that in healthy young subjects it is the thoracic spine that extends as the hips and lumbar spine flex to produce trunk forward lean. Thus, it is possible that in elderly subjects a loss of thoracic extension mobility may make it more difficult to position the head during trunk forward lean. Despite any compensatory neck extension, the subject may not be able to achieve a horizontal position of the eyes/gaze at LO, thereby compromising balance. Mean trunk angle at LO of 45.78 (5.88) was difficult to compare with previous studies largely due to differences in method of angle calculation, with a wide range (348, 378, 758, 908, 1178) being reported [1,3,11,14]. The 3.1:1 ratio of hip to lumbar spine movement during forward flexion of the trunk in the pre LO phase was similar to that demonstrated in other studies of healthy young subjects by our group. These include toe touching from upright standing (ratio 3:1) where the chest is brought towards the extended knees [22], and open chain hip flexion (ratio 3:1) where the bent knee is moved towards the chest as in stepping up a high step [21]. Bohannon et al. [38] demonstrated that hip and pelvic motion were concurrent during hip flexion from supine, with posterior pelvic rotation contributing 1/4–1/3 of the total movement of the thigh. Thus, the interdependent relationship between movement of the hips and lumbar spine during hip flexion is further supported by the results of the current study. Although it appears that previous authors have ignored the contribution of the thoracolumbar spine to trunk forward lean, these results do confirm the importance of the hip joint in bringing the body mass forward prior to LO.
4.4. Hip–knee interaction It has been reported that the acromion continues to move forward after LO [10]. This has been interpreted by some authors as continued hip flexion due to location of reference markers on the shoulder/ acromion, greater trochanter and knee [7,8,12]. For example, it has previously been stated that the extension phase of STS starts at the knee while the trunk is still flexing at the hip [39], although more recently these authors have described the sequence as knee extension followed by hip extension [8] as demonstrated in our study. Mean knee angle at LO (100.48 5.988) was similar to that demonstrated in other studies of STS using healthy subjects and similar procedures [17]. With seat height adjusted to shank length both hip and knee joints were flexed to approximately the same degree at LO. Following LO the hip and knee joints extended together in a linear pattern to raise the body mass to the standing position. The almost simultaneous onset of knee and hip extensor muscles, with peak muscle activity [40,41] and extensor torque [35] around LO reflects this movement pattern.
5. Conclusion For appropriate facilitation of STS in patients with movement dysfunction, clinicians need to be aware of the sagittal contributions of the thoracic and lumbar spine to the forward and upward movement of the trunk, and of the coordinated movement between the hip joint(s) and lumbar spine during the movement. This study has provided the basis for examination of the thoracolumbar contribution to STS in subjects with pathology.
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Sagittal spine and lower limb movement during sit-to-stand in healthy young subjects Elizabeth A. Tully*, Mohammad Reza Fotoohabadi, Mary P. Galea School of Physiotherapy, The University of Melbourne, Parkville, Vic. 3010, Australia Received 14 April 2004; received in revised form 22 July 2004; accepted 19 November 2004
Abstract This study aimed to determine the sagittal movement relationships between thoracic, lumbar spine and hip joints during sit-to-stand (STS). Forty-seven healthy young adults were videotaped performing STS at their preferred speed from a chair set at 100% knee height. Forward trunk lean prior to buttock lift-off (LO) was accomplished by concurrent lumbar and hip flexion (1:3). As the lumbar spine flexed the thoracic spine extended, resulting in a LO trunk angle of 45.78 (5.88) with respect to a horizontal reference. Following LO, the hip(s) and lumbar spine extended and the thoracic spine flexed, with the standing thoracic angle approximating the initial thoracic posture in sitting. # 2004 Elsevier B.V. All rights reserved. Keywords: Sit-to-stand; Movement analysis; Thoracic spine; Lumbar spine
1. Introduction The ability to stand up from sitting on a chair is an essential prerequisite for walking and therefore independent function [1]. Inability to effectively perform sit-to-stand (STS) can lead to severe mobility impairment, for example, in young children with cerebral palsy [2], and in older people experiencing musculo-skeletal problems [3–5]. Inability to perform this essential activity may lead to dependence, institutionalization and even death in elderly subjects [6]. Although a seemingly simple task, STS requires the coordinated interaction of linked body segments to transport effectively the body’s centre of mass in a horizontal then vertical direction while maintaining balance over a small base of support, the feet. The basic kinematics include flexion of the trunk and hips to bring the centre of mass forward, followed by bilateral extension of the lower limb joints and trunk extension to raise the body mass in a vertical direction over the feet [7]. Previous STS studies have investigated various aspects of this task, such as the total time taken, velocity and * Corresponding author. Tel.: +61 3 8344 4171; fax: +61 3 8344 4188. E-mail address: [email protected] (E.A. Tully). 0966-6362/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.gaitpost.2004.11.007
acceleration of body segments [7,8], and the kinematics (joint angles) and kinetics (joint moments) of the lower limb joints before and after buttocks ‘lift-off’ (LO) [8–10]. Although sagittal trunk movement during STS has been measured with respect to a horizontal reference [11,12], the contribution of the thoracolumbar spine has not been subjected to any detailed analysis since few models have included markers on the spine. In most studies the spine has been viewed as a rigid body, the ‘trunk segment’, defined by a straight line joining markers on the first thoracic and first sacral spine [13], or shoulder and greater trochanter [12,14– 16], a method which fails to clarify the respective contribution of hip and thoracolumbar spine to the measure of sagittal trunk angle. In some studies the mobile lower cervical joints have been included as part of the trunk segment [7,17]. Nikfekr et al. [18] placed markers along the midline spine at the level of C7, T3, T6, T9, T12 and the sacrum. However, these authors chose to measure whole trunk kinematics (C7–sacrum), and although linear displacement of the spinal markers was measured in vertical and lateral directions no thoracic or lumbar spinal angles were calculated. It appears that the results of previous studies have influenced assessment and training of patients with
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dysfunctional STS. For example, it is suggested that there should be ‘no flexion within the upper body throughout the (STS) action’ [19], and that ‘flexing the lumbar spine instead of the hips’ [19] is a poor STS technique. However, Schenkman et al. [20] included a marker on the pelvis and demonstrated that during trunk forward lean seven of their nine healthy subjects flexed the trunk segment on the pelvis by an average of 168, indicating some degree of spinal flexion in the pre LO phase. Error has also occurred in measurement of sagittal ‘hip’ joint angle from the frequently used marker combination shoulder, greater trochanter and knee. This measure is contaminated by inclusion of the joints of the thoracolumbar spine [7,8,12], with possible shoulder girdle protraction further compounding the error. As a result of these measurement methods, the coordinated movements of the thoracolumbar spine and hip joints demonstrated in other functional movements of the trunk and lower limbs, for example, flexing the thigh towards the chest as in stepping up a high step [21] or toe touching from upright standing [22], have not been determined during STS. Therefore this study used computer-aided video analysis of STS with a revised model of reference marker placement, to determine (i) the sagittal plane contribution of the lumbar and thoracic spine to trunk movement, (ii) the movement interaction between the lumbar spine and pelvi-femoral or ‘true’ hip joint, and (iii) the coordination of hip and knee joints during STS in healthy young subjects.
2. Methods and subjects 2.1. Subjects Forty seven healthy physiotherapy students (27 female, 20 male), mean age 20.1 (2.8) years, range 18–30 years, mean height 168.5 (8.4) cm, and BMI 20.7(2.3) kg/m2
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volunteered for this study. Written consent was obtained from all subjects and ethics approval for this research was obtained from the Human Research Ethics Committee of The University of Melbourne. The volunteers were screened to exclude those with any identifiable movement dysfunction, a history of significant spinal, hip, or knee pathology or vertebrofemoral pain requiring treatment during the preceding 6 months. 2.2. Model of marker placement Ten light reflective markers were attached over the midline thoracolumbar spine and right lower limb of standing subjects using non-irritant adhesive discs. Markers were positioned on each subject as described in Table 1 and illustrated in Fig. 1. Spherical reflective markers 3.5 cm in diameter were attached over relevant spinous processes and pelvic landmarks. Markers located over the lateral aspect of the right lower limb comprised flat circular discs 3.5 cm in diameter cut from a roll of retro-reflective tape. All markers had a 4 cm black base to maximize the contrast between the marker and the subject’s skin. To locate the first thoracic spinous process (T1), the subject was asked to flex their head and neck while the examiner kept a finger on the spinous processes thought to be C6 and C7. The spinous process of C6 was felt to move forward while that of C7 remained stationary. Having located the spinous process of C7 that of T1 was found by palpation of the next caudal level. At the thoracolumbar junction, the location of the first lumbar spinous process (L1) was determined by first placing a mark on the skin corresponding to the midpoint of a line joining the posterior superior iliac spines (S2). A second mark was placed over the lumbar spinous process at the level corresponding to the highest point of the iliac crest, deemed to be at the level of L4, based on the previous radiographic work of Hamilton et al. [23]. The line joining these two points was then projected superiorly by the same distance
Table 1 Location of skin reference markers on midline thoracolumbar spine and right lower limb Marker location
Abbreviation
Marker placement
T1 spinous process Spinous process of 3rd thoracic vertebra L1 spinous process Spinous process of 11th thoracic vertebra Posterior superior iliac spine
T1 T3 L1 T11 PSIS
Anterior superior iliac spine Two-third thigh
ASIS 2/3 thigh
Supracondylar thigh
SC
Lateral tibial condyle Lateral malleolus
LTC LM
Spinous process of the first thoracic vertebra 3 cm below the T1 marker Spinous process of first lumbar vertebra 3 proximal to the L1 marker Distal aspect of the right posterior superior iliac spine, at the level of the spinous process of S2 Anterior superior iliac spine Junction of the proximal one-third with the distal two-thirds of a line joining the midpoint of the lateral knee joint line and the apex of the greater trochanter At the junction of the distal one-quarter and proximal three quarters of a straight line joining the apex of the greater trochanter to the midpoint of the lateral knee joint line Anterior aspect of the neck of the fibula 10 cm above the tip of fibula malleolus
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Fig. 1. Starting position of the sit-to-stand movement. See Table 1 for details of marker locations. Note the positioning of the upper limbs, and in the seated position, the horizontal position of the thighs.
and this proximal point was deemed to be the spinous process of L1. Since the location of the markers 3 cm distal to T1 and 3 cm proximal to L1 may vary with the height of the subject they were named T3 and T11, respectively, for convenience, although they were not necessarily over the correct spinous process. 2.3. Experimental procedure Subjects with bare feet were instructed to stand up from an adjustable-height backless chair at a self-selected speed, arms folded across the chest. Although it was anticipated that having the subjects arms folded across the chest might have some effect on motor performance, the position was adopted to avoid obstructing the camera’s view of the markers. The height of the seat was standardized to the length of the subject’s leg from floor to mid-lateral knee joint line, so that the long axis of the thigh was in the horizontal plane (Fig. 1). Following two to three practice trials the movement was videotaped from the right side using a single video camera placed at a distance of 7 m and perpendicular to the sagittal plane, and with the centre of the field of view at the level of the greater trochanter in standing. The movement was repeated if the examiner was not satisfied that it was performed without unwanted or unnatural actions. A 300 W light attached to the camera tripod illuminated the reflective markers against a dark background. The automatic digitization mode of the two dimensional Peak Motus (Peak Motus Motion Analysis System, PEAK Performance Technologies Inc., Englewood, CO, USA) was used to analyze the STS movement from the videotape at 50 frames/s. The location of each reference marker was automatically recorded in two-dimensional space. Sagittal thoracic, lumbar, hip and knee angles were calculated following filtering of the raw data using a robust low pass Butterworth filter set at 6 Hz. The accuracy and reliability of Peak for uniplanar measurement of joint angles has previously been established [24]. All angular data were
then imported into the Microsoft Excel program and used in conjunction with Kaleidagraph Version 3.8 (Synergy Software) to normalize the data to 100% movement duration. This process was necessary to compensate for the different amounts of time used by each subject to complete the movement, and involved converting the time taken to complete each STS into a 100% scale with 1% increments. The angles at each 1% increment over the total test duration were then recalculated for each subject. Three events were defined to provide reference points during the movement; (i) the ‘start’ of STS was defined as the commencement of horizontal (X) displacement of the T1 marker; (ii) ‘LO’ at the point of 10% of the vertical (Y) displacement of the proximal (2/3Th) thigh marker, as described by Mourey et al. [9], and (iii) the end of STS at the point of maximal vertical (Y) displacement of the T1 marker. Fig. 2 shows the method used to calculate sagittal thoracic, lumbar and lower limb joint angles. Sagittal thoracic angle was calculated from the relative angle between the straight lines defined by T1–T3 and T11–L1. Likewise lumbar angle was calculated from the relative angle between the straight line defined by T11–L1 and a line perpendicular to the line joining the right PSIS–ASIS markers (representing the plane of the pelvis). A zero thoracic spine angle was defined when the straight line T1– T3 and T11–L1 were co-linear. A zero lumbar spine angle was defined when the straight line T11–L1 was perpendicular to the line joining the right PSIS–ASIS. Any spinal angle anterior to the zero position was defined as flexion, whereas a posterior angle was defined as extension. The
Fig. 2. Diagram illustrating method of calculation of thoracic, lumbar, and hip flexion–extension angles. (See text for details).
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‘true’ hip flexion–extension angle was measured between the long axis of the femur (2/3Th–SC) and the plane of the pelvis (PSIS–ASIS). Sagittal knee angle was measured between the long axes of the thigh and leg (2/3Th–SC–LTC– LM). Similar conventions were used to describe hip and knee flexion and extension from the anatomical reference. All flexion (extension) angles were given positive (negative) values for statistical purposes. 2.4. Data analysis For the purpose of analysis STS was divided into a preLO, and a post-LO phase. Mean and standard deviation were calculated for total STS duration. Excursion (end minus start angle), range (maximum minus minimum angle), and sagittal angles at LO were calculated for the thoracic, lumbar spine, hip and knee joints. The relative contributions of hip and lumbar flexion during the pre and post-LO phases were displayed using hip to lumbar ratios, i.e., for each phase the range of hip movement was divided by lumbar range. Descriptive statistics were obtained using Excel 97 (Microsoft Corporation) and Kaleidagraph 3.08 (Synergy software).
3. Results 3.1. STS duration
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Fig. 4 demonstrates the angular movement relationships between the thoracolumbar spine, hip and knee joints during the pre and post-LO phases. It can be seen from Figs. 3 and 4 that sagittal trunk displacement before and after LO comprised a concurrent but opposite flexion–extension of the thoracic and lumbar spine in conjunction with sagittal hip movement. During forward trunk lean the thoracic spine extended as the lumbar spine and hip joint(s) flexed, producing a maximum trunk angle of 45.668 with respect to a horizontal reference (5.84)8. The lumbar spine reached its maximal flexion angle prior to LO at 32% STS duration, while the thoracic spine continued to extend until LO commenced (42% STS duration). Flexion of the hip joint and lumbar spine was concurrent with the lumbar spine increasing its contribution as forward trunk lean progressed. On average, maximal hip flexion angle occurred close to LO at 39% STS duration, with the ratio of hip to lumbar flexion during the pre-LO phase being 3.1:1, i.e., for every 3.18 of hip flexion there was 18 of lumbar flexion. Following LO the hip(s) and lumbar spine extended with the hip extending more rapidly than the lumbar spine, the ratio of hip to lumbar spine movement being 2.6:1 in this phase. The thoracic spine flexed as the lumbar spine and hips extended, with the sagittal thoracic angle in standing returning to that of the initial sitting posture. At LO, both hip and knee joints were flexed to approximately the same degree (98.18:100.48), after which the both joints were locked together in a linear pattern of extension.
In this group of young healthy adults the mean time to stand up from sitting at a self-selected speed was 2.04 (0.39) s (range 1.30–3.18 s).
4. Discussion
3.2. Angular movement
4.1. Measurement issues
The excursion and range of movement of sagittal thoracic, lumbar, hip and knee joints during STS are shown in Table 2. Note the substantial range through which the lumbar spine moved during STS (37.78) Fig. 3a–d illustrate the mean (S.D.) sagittal thoracic and lumbar spine, hip and knee joint angles at 1% time intervals throughout the movement. LO occurred at 41.2% of STS duration, which corresponded to 38 knee extension from a sitting knee flexion angle of 100.48. Other sagittal angles at LO were: thoracic spine 17.78 (9.48), lumbar spine 19.38 (9.98); hip 98.18 (8.18).
This study has provided a description of the sagittal movement relationships between the thoracolumbar spine, hip and knee joints during STS in a group of healthy young adults. The use of computer aided video analysis, and an improved model for sagittal plane measurement of thoracolumbar and lower limb joint angles [22,25] facilitated this process. A two-dimensional analysis was considered adequate since it has been demonstrated that STS is primarily a sagittal plane activity in healthy subjects, with only small amounts of trunk rotation, trunk lateral flexion, and lateral shift [26].
Table 2 Excursion and range (degrees) of sagittal thoracic and lumbar spine, hip and knee joints during STS in healthy young adults (n = 47) Joint/region
Start
Thoracic spine Lumbar spine Hip joint Knee joint
32.2 14.5 76.9 104.3
End (9.3) (9.4) (7.3) (6.3)
Negative values denote extension.
31.1 (8.7) 16.2 (8.3) 2.1 (7.4) 0.04 (6.4)
Excursion 1.1 30.7 74.8 104.3
Maximum 32.2 21.5 98.9 104.8
(9.3) (9.2) (6.5) (5.2)
Minimum 17.6 (9.1) 16.2 (8.3) 2.1 (7.4) 0.04 (6.4)
Range 14.6 37.7 96.8 104.8
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Fig. 3. Means 1S.D. (n = 47) representing the change in flexion–extension angle throughout sit-to-stand in the thoracic (a) and lumbar spine (b), hip (c) and knee joints (d). LO indicates the point of lift-off.
Fig. 4. Mean line plots (n = 47) illustrating the angular movement relationships throughout sit-to-stand between the thoracic and lumbar spine, hip and knee joints. The vertical dotted line indicates the point of lift-off.
Key advantages of the model of marker placement used in this study were: (i) it enabled the separate sagittal contributions of the thoracic, lumbar spine and hip joints to be identified during STS, (ii) error in measurement of hip flexion angle from markers located on the shoulder, greater trochanter and knee was avoided by measurement of the angle of the femur with respect to the plane of the pelvis, and (iii) errors in hip and knee flexion–extension angles associated with skin movement on the lateral thigh were minimized by placement of markers away from regions of maximal skin movement on the thigh during flexion. It has been demonstrated that significant anterior displacement of the traditional greater trochanter marker, and to a lesser extent posterior displacement of a lateral femoral epicondyle or mid-lateral knee joint marker is responsible for up to 20% error in hip and knee angles during sagittal plane analysis [25]. It is acknowledged that in this study cephalad movement of the ASIS marker during hip flexion may have added 5% error on average to measurement of sagittal hip angle [25]. However, we had the advantage of using lean
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subjects (mean BMI < 21) in whom skin movement and subsequent errors would be minimal. The method of locating L1 in the spinal component of the model was adopted because of the lack of accuracy or reliability associated with methods involving counting lumbar spinous processes [27–30]. The main purpose of this method was to achieve a reliable technique for determining the approximate location of L1 that takes into account the height of the subject. The results of a small, unpublished ultrasound study by a colleague (A. Schache, personal communication) suggest that the method is essentially valid, since on average the proximal landmark represented the spinous process of L1 in a group of young healthy adults. However, the validity and reliability of this method requires further investigation. In this study, relatively large variations were evident in mean sagittal lumbar and thoracic spine angles (S.D. > 50% and 30% mean angle, respectively). Thus, despite efforts to achieve reliable identification of L1 for example, surface anatomy errors may have occurred. Alternatively, there may have been genuine inter-subject variation in thoracolumbar posture or movement. Extreme variability in sagittal plane spinal curvature in standing has been noted previously by Stagnara et al. [31], who suggested that the differences in spinal curvature between subjects was so great that the average curve values were of little use as normative values. Although this study group was extremely homogenous in terms of age, gender, and weight each individual may have a unique sagittal thoracolumbar alignment possibly influenced by the posture of the pelvis. It is acknowledged that there remain some largely insurmountable problems from skin movement over the vertebral spinous processes; however, as noted by Lundberg [32], the fascia over the spinous processes is relatively rigidly fixed to bone, and thus skin movement will follow bone movement more closely than in many other regions. Gadjdosik et al. [33] suggested that errors introduced by skin movement over spinous processes are likely to be systematic, leading at worst to a relatively constant bias in the obtained results.
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4.2. Temporal aspects In this study, the mean time for young healthy adults to stand up from sitting of 2.0 0.3 s was slower than in other studies where healthy subjects performed STS at their natural speed (1.6 0.3 s, 1.7 0.5 s, 1.8 0.3 s) [10,33,34]. It is difficult to compare STS duration across studies since researchers have used different starting foot positions, arm positions, and in particular different definitions for the start and/or end of the movement. On average LO occurred at 41.2% of STS duration. Table 3 shows that in previous studies LO occurred between 30% and 45% STS. The various methods of determining this event make comparison difficult. The latter includes visual estimation of ‘buttocks off’ [34], pressure sensors under the buttocks [8,10], and force plates under the patient’s feet [35], or the front legs of the chair [36]. 4.3. Hip–spine interaction The apparent lack of concern for details of the spinal contribution to STS is surprising, since during rehabilitation of patients with neurological conditions, such as stroke for example, the alignment/movement of the trunk is regarded as having major implications for effective completion of the task. A component of STS considered as critical is ‘flexion of the extended trunk at the hips’ to move the body mass forward in the pre-LO phase (19 p 143), with ‘flexion of the spine instead of at the hips’ (19 p 143) being considered a common motor problem. In contrast our data indicate that both the hips and lumbar spine flex concurrently to bring the body mass forward prior to LO, with the lumbar spine contributing 18 for every 3.18 hip flexion. Ikeda et al. [37] p 473, noted that while the trunk was flexing forward older subjects did not extend their heads as much as younger subjects, so that the older group was facing down at LO. The authors were unclear as to the reason but suggested that the change may be due to an ‘inability to straighten’. Similarly Papa and Cappozzo [10] noted
Table 3 Results of studies showing LL event as a percentage of the total time taken to stand up from sitting Author
Definition of LO
%STS
Present study
At 10% of vertical displacement of proximal thigh marker
41.2
Papa and Cappozzo [10]
Beginning of seat unloading Seat load cell drops to zero
38 45
Alexander et al. [11] Bharami et al. [35] Baer and Ashburn [26] Pai and Rogers [15] Nuzik et al. [34] Roebroeck et al. [7] Khemlani et al. [41] Shepherd and Gentile [8]
Maximum anterior position of head Minimum value of horizontal component of GRF When thighs leave the seat Force plate Visual detection of buttocks LO Largest backward value of horizontal component of GRF At thighs off At thighs off recorded by seat switch under ischial tuberosities
41 40.6 37 37 35 35 31 30
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increased flexion of the trunk segment in elderly subjects during the pre-LO phase. Our study showed that in healthy young subjects it is the thoracic spine that extends as the hips and lumbar spine flex to produce trunk forward lean. Thus, it is possible that in elderly subjects a loss of thoracic extension mobility may make it more difficult to position the head during trunk forward lean. Despite any compensatory neck extension, the subject may not be able to achieve a horizontal position of the eyes/gaze at LO, thereby compromising balance. Mean trunk angle at LO of 45.78 (5.88) was difficult to compare with previous studies largely due to differences in method of angle calculation, with a wide range (348, 378, 758, 908, 1178) being reported [1,3,11,14]. The 3.1:1 ratio of hip to lumbar spine movement during forward flexion of the trunk in the pre LO phase was similar to that demonstrated in other studies of healthy young subjects by our group. These include toe touching from upright standing (ratio 3:1) where the chest is brought towards the extended knees [22], and open chain hip flexion (ratio 3:1) where the bent knee is moved towards the chest as in stepping up a high step [21]. Bohannon et al. [38] demonstrated that hip and pelvic motion were concurrent during hip flexion from supine, with posterior pelvic rotation contributing 1/4–1/3 of the total movement of the thigh. Thus, the interdependent relationship between movement of the hips and lumbar spine during hip flexion is further supported by the results of the current study. Although it appears that previous authors have ignored the contribution of the thoracolumbar spine to trunk forward lean, these results do confirm the importance of the hip joint in bringing the body mass forward prior to LO.
4.4. Hip–knee interaction It has been reported that the acromion continues to move forward after LO [10]. This has been interpreted by some authors as continued hip flexion due to location of reference markers on the shoulder/ acromion, greater trochanter and knee [7,8,12]. For example, it has previously been stated that the extension phase of STS starts at the knee while the trunk is still flexing at the hip [39], although more recently these authors have described the sequence as knee extension followed by hip extension [8] as demonstrated in our study. Mean knee angle at LO (100.48 5.988) was similar to that demonstrated in other studies of STS using healthy subjects and similar procedures [17]. With seat height adjusted to shank length both hip and knee joints were flexed to approximately the same degree at LO. Following LO the hip and knee joints extended together in a linear pattern to raise the body mass to the standing position. The almost simultaneous onset of knee and hip extensor muscles, with peak muscle activity [40,41] and extensor torque [35] around LO reflects this movement pattern.
5. Conclusion For appropriate facilitation of STS in patients with movement dysfunction, clinicians need to be aware of the sagittal contributions of the thoracic and lumbar spine to the forward and upward movement of the trunk, and of the coordinated movement between the hip joint(s) and lumbar spine during the movement. This study has provided the basis for examination of the thoracolumbar contribution to STS in subjects with pathology.
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