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The pattern of motion of the longitudinal arch of the foot
The FOOZ(1994) 4, 151-154 0 1994 Longman
Group
Ltd
r
-
I
The pattern of motion of the longitudinal arch of the foot I. G.
Winson, A. Lundberg, C. Bylund
Department of Orthopaedics, Southmead Hospital, Bristol, UK, Department of Orthopaedics, Karolinska Hospital, Stockholm, Sweden, and Department of Radiology, Danderyd Hospital, Stockholm, Sweden SUMMA R Y. We studied motion of the longitudinal arch of the foot using roentgen stereophotogrammetric analysis. Motion was analysed iu response to great toe dorsiflexion, maximum plantarlIexion/supination and heel raise, all actions previously stated to alter the height of the longitudinal arch. The largest amounts of motion were seen in the talonavicular joint (ranging from 37.1” to 14.2”) This included significant amounts of plantarflexion, adduction (or internal rotation) and supiuation occuring during the process of arch raising. This pattern of motion was seen in all forms of arch raising activity studied. Forced great toe dorsiflexion induced the maximum motion seen in the talonavicular joint. Motion of a significant degree was also induced in the talocalcaneal joint (17.9-8.6). Anterior to this motion was less (10.1-3.5” for the total motion in the naviculo-cuueiform joint and 8.0-3.0” for the cuneiform-metatarsal joint) and in the longtudinal plane these joints went into pronation. From a clinical point of view, it is important to recognize the role of the talonavicular joint in arch motion and that the involvement of the talonavicular joint in this sort of activity occurs in all three planes.
The occurrence of motion in the longitudinal arch of the foot induced by dorsiflexion of the great toe is widely accepted.‘,2 Though it is well recognized that with increasing dorsiflexion the arch rises, the distribution of motion in the joints involved is largely unknown. Similarly, the motion which occurs as a consequence of other stimuli which tend to raise the longitudinal arch has not been accurately recorded in vivo, mainly due to the limited availability of methods for kinematical analysis with adequate accuracy for detailed analysis of the relative motion of the small bones involved. Several previous studies have established that motion is available in three component parts, so-called triplane motion, in the various joints of the hindfoot.3-7 It has further been suggested and demonstrated that changes in the height of the longitudinal arch are an integral part of the normal behaviour of the foot during the stance phase of gait.*-” There is, however, little information on the distribution of motion between the various joints. The aim of the study was to analyse the motion occurring in the talocural, talocalcaneal, talonavicular, naviculo-cuneiform and first tarsometatarsal joints in different forms of arch raising, to elucidate the pattern of motion occuring in the various parts of the arch. In order to analyse the three-dimensional motion in these small joints, the technique of roentgen stereophotogrammetric analysis (RSA) has been used. The accuracy of this technique has been previously established. 11,12The accuracy established by these studies allows for the measurement in
angular changes of less than 1”. The technique has also been used in studies of the kinematics of the ankle-foot complex.’ It is thereby intended to demonstrate in life the ranges and direction of motion available in the longitudinal arch during arch raising activities.
MATERIALS AND METHODS We performed the study by RSA in 6 healthy volunteers. Ages ranged from 24 to 36 years and weight from 56 to 83 kg. None had any previous or present foot complaints, and all subjects had clinically normal feet except one (subject no. 2) who had an asymptomatic planovalgus foot. Prior to examinations, at least three radio-opaque markers (Tantalum, spherical balls, 0.8 mm in size) were introduced into each of the tibia, the talus, the calcaneus, the navicular, the medial cuneiform, the cuboid and the first, third and fifth metatarsal bones of the examined foot (Fig. 1). Stiffness was in no case present for more than 3 days after introduction of the markers, and the RSA examinations were performed at least 2 weeks after this time. RSA examinations The subjects were asked to stand with the right foot in the neutral position inside a plexiglass calibration cage, all four sides of which carried radio-opaque markers in known positions. Simultaneous anteroposterior and lateral films were exposed. The subject 151
152 The Foot
Fig. l-The
distribution of markers in the foot.
was then asked to remove weight from the heel until the underlying skin lost contact with the base of the reference cage (weight thus being carried only by the forefoot). A new set of exposures was made in this position. The heel was then raised further until a 50 mm wooden block could be introduced under the centre of the heel. Another pair of films was then exposed. The subject was then asked to stand with his foot against the firm wall of the calibration cage in such a position that the great toe was passively fully dorsiflexed, and again, further exposures were taken (Fig. 2). Exposures were also made in maximum nonweightbearing voluntary plantarflexion/supination. The positions of all calibration cage markers and all markers in the bones were digitized and fed to a computer programmed to yield relative spatial dis-
placements of the studied bones. The method of undertaking the RSA studies was approved by the ethical committee of the Karolinska Hospital. Data presentation Displacements of the bones between the different input positions are given as total rotations (helical axis rotations) for each studied position (Table 1). These movements are then broken down into component rotations around the axes of a three-dimensional coordinate system (Table 2). These rotations correspond to plantarIIexion/dorsiflexion, supination/pronation and internal/external rotation, respectively. The coordinate system is fixed with its origin in the geometrical centre (centre of gravity) of the proximal segment in each comparison.
RESULTS
Fig. 2-The
position of maximum dorsitlexion of the great toe.
Both progressive heel raise and great toe dorsiflexion induced motion in the joints of the longitudinal arch. In dorsiflexion of the toe, the average amounts of plantarhexion were 19.3” for the talonavicular joint, 10.5” for the talocalcaneal and 3.8” for the naviculocuneiform joint, and this was associated with 1.5” of motion of the first tarsometatarsal joint. This motion was accompanied by 19.6“ internal rotation and 17.4” of supination in the talonavicular joint. The values for the motion occurring in the separate planes in each of the studied joints can be seen in Table 2. This produced maximum total rotation (helical
The pattern Table 1. The total motion
in response
Joints Dorsiflexion Raised
of great toe
heel
Block under
heel
Plantarflexionjsupination
Average
arch of the foot
Talonavicular
Naviculocuneiform
Cuneiform-metatarsal
13.9 6.9 4.7 3.0 16.9 6.9 35.5 7.8
15.7 I.8 8.7 6.0 8.6 4.0 17.9 5.4
33.4 7.0 14.2 10.4 17.6 8.3 37.1 7.0
10.1 6.2 3.5 2. I 9.8 4.5 5.8 1.7
8.0 1.0 3.0 1.8 5.6 1.9 3.8 1.9
deviations
in italics.
to great toe dorsiflexion
Plantarflexion/dorsiflexion Great toe Heel-raise 50 mm block plantarflexion/
Supination/pronation Great toe Heel raise 50 mm block Plantarflexionjsupination External/internal Great toe Heel raise 50 mm block Plantarflexion/supination
Average values in plain type, standard Positive values plantartlexion/supination
153
activities
Talocalcaneal
Joints
Maximum supination
arch raising
of the longitudinal
Talocural
values in plain type, standard
Table 2. Movement in response plantarfiexion and supination
to various
of motion
lifting the heel, with a block under the heel and at maximum
excursion
Talocural
Talocalcaneal
Talonavicular
-10.1 7.2 -2.7 3.3 13.8 7.6 36.6
10.5 4.0 6.3 5.5 6.9 3.1 10.1
19.3 2.8 10.1 8.1 14.7 5.9 15.8
3.8 2.5 0.8 1.9 3.6 2.6 3.8
-1.5 1.3 -0.3 I..? -0.6 1.3 0.5
2.8
6.5
13.7
0.4
0.4
5.2 1.6 1.3 1.7 -5.3 I.6 -2.3 6.2
6.7 4.5 2.6 3.4 1.9 2.1 6.7 5.0
17.4 7. I 7.0 7.0 5.2 1.7 15.2 7.6
-11.2 3.3 -2.7 2.1 - 8.7 3.8 - 5.8 4.5
-6.9 1.2 -2.0 1.6 -5.0 2.0 -0.7 2.7
-2.7 2.7 0.2 2.2 -1.7 1.7 3.7 6.3
6.7 1.8 2.9 3.4 5.6 3.5 11.4 5.6
19.6 6.6 4.8 6.0 9.7 5.2 20.0 7.4
-
2.9 I.3 1.6 1.1 0.9 1.5 -0.6 1.1
Naviculocuneiform
3.4 1.7 -0.6 0.2 - 1.4 1.3 0.5 1.5
into
Cuneiform-metatarsal
deviations in italics. and external rotation.
axis rotation) for toe dorsiflexion of 33.4” for the talonavicular joint (Table 1). This value for total rotation is comparable with motion seen in maximum non-weightbearing plantarflexion and supination of the foot as a whole. The induced triplane motion in heel raising and with the block under the heel induced comparable directions of rotation in all planes (Table 2), between the various joints. The absolute values were rather less with these input measures. For example, the maximum talonavicular rotation with the 50 mm block was 17.6”.
DISCUSSION
The motion of the longitudinal arch in toe dorsiflexion was first commented upon in detail by Hicks.
The motion has been assumed to occur around an oblique axis in space (i.e. to comprise components relating to different [often referred to as X, y, and z] axes of a spatial coordinate system). The plantartlexion component (being the only component assessed previously) has been stated to be approximately 10” in passive toe dorsiflexion in cadaveric specimens.’ This study shows that nearly twice as much motion can be seen in normal individuals. Under in vivo conditions, toe dorsitlexion also occurs not only with the foot in a neutral position, but more often with the foot plantarflexed, after heel-off during the stance phase of gait. The amount of plantarflexion of the talonavicular joint occurring between neutral and the heel-block position, which reflects similar circumstances in our study, was 14.7”. Resulting supination and internal rotation of the
154 The Foot
talonavicular joint reached high values, which is in concordance with the data previously presentedI on the direction of the second subtalar joint axis. It is a potentially significant finding that the pattern of motion in the arch induced by toe dorsiflexion is different from that seen in supination of the foot.’ In a previous examination of metatarsal mobility undertaken by the authors,14 maximum voluntary dorsiflexion and pronation induced plantarflexion rather than dorsiflexion in the joints of the arch as one might expect. This suggests that common factors must exist in the apparently contrary activities. This may be explained by the subjects using their toe extensors to reach the position, creating a motion pattern similar to that seen in toe dorsiflexion. However, in this study, easing weight off the heel without actually raising it off the ground also induced a similar pattern, in this case without concomitant dorsiflexion of the toes, and presumably without the increased effect of extensor activity. This is still compatible with previous observations on the position of the longitudinal arch and the available dorsiflexion of the toe with the foot under load in different positions of the talocural joint. This may indicate that factors other than the windlass effect of the plantar aponeurosis may influence the biomechanics of arch raising. It would appear that the longitudinal arch in a neutral standing position is at its lowest level allowed by simple dorsiflexion of the joints which go to make up its constituent parts. Motion which occurs from this position in this plane is thus almost exclusively plantarflexion in most circumstances. Other elements of motion, notably supination (motion occurring around the longitudinal axis), are clearly important in producing a visible raise in the longitudinal arch. It has to be noted that the data produced by this study are limited by virtue of the invasive nature of the study. It would clearly be inappropriate to study large numbers of normal individuals in this manner. The accuracy of the study technique, however, means that the observations made represent a true representation of the ranges of motion in normal individuals under these circumstances and thereby provides unique data. The difference between these figures and cadaveric studies demonstrates the difference between in vivo and in vitro studies. Study of the standard deviation figures would suggest a good deal of difference in the performance of individuals. This in turn illustrates the difficulties in defining ‘normal’ foot function.
References 1. Hicks J H. The mechanics of the foot II. The plantar aponeurosis and the arch. J Anat 1954; 88: 25-30. 2. Rose G K, Welton E A, Marshall T. The diagnosis of the flat foot in the child. J Bone Joint Surg 1984; 66B: 71. 3. van Langelaan E J. A Kinematical analysis of the tarsal joints. An X-ray photogrammetric study. Acta Orthop Stand 1983; 54 (suppi 204). 4. Lundbere. A. Goldie I. Kalin B 0. Selvic G. Kinematics of the ankle/foot complex. Plantar flexion and dorsi-flexion. Foot Ankle 1989; 9: 194. 5. Lundberg A, Svensson 0 K, Bylund C. Goldie I, Selvic G. Kinematics of the ankle/foot complex. Part 2: pronation and supination. Foot Ankle 1989; 9: 248. 6. Lundberg A, Svensson 0 K, Bylund C, Goldie I, Selvic G. Kinematics of the ankle/foot complex. Part 3: influence of leg rotations. Foot Ankle 1989; 9: 304. I. Lundberg A, Svensson 0 K, Nemeth G. Selvik G. The axis of rotation of the ankle joint. J Bone Joint Surg 1989; 71B: 94-99. 8. Elftman H. The transverse tarsal joint and its control. Clin Orthop 1960; 16: 41. 9. Isman R E, Inman V T. Anthropometric studies of the human foot and ankle. Biomechanics Laboratory, University of California, Berkeley, Technical Report, May 1968. 10. Sarafian S K. Functional characteristics of the foot and plantar aponeurosis under tibio-talar loading. Foot Ankle 1987; 8: 4. 11. Selvik G, Alberius P, Aronsson A S. A roentgen stereophotogrammetric system. Construction, calibration and technical accuracy. Acta Radio1 Diagn 1983: 24: 343-352. 12. Lundberg A, Bylund C, Selvik G, Winson I G. Accuracy of roentgen stereophotogrammetric analysis in joint kinematics. European Journal of Clinical Musculo-Skeletal Research 1994 (in press). 13. Hicks J H. The mechanics of the foot 1. The joints. J Anat 1953; 81: 345-351. 14. Winson I G. Lundberg A, Bylund C. Metatarsal motion. The Foot 1994 (in press).
The authors Ian G. Winson MB, ChB, FRCS Consultant Orthopaedic Surgeon Southmead Hospital Southmead Road Westbury-on-Trym Bristol UK Arne Lundberg MD, PhD Department of Orthopaedics Karolinska Hospital Stockholm Sweden Carin Bylund MD Department of Radiology Danderyd Hospital Stockholm Sweden Correspondence to Mr I. G. Winson.
Group
Ltd
r
-
I
The pattern of motion of the longitudinal arch of the foot I. G.
Winson, A. Lundberg, C. Bylund
Department of Orthopaedics, Southmead Hospital, Bristol, UK, Department of Orthopaedics, Karolinska Hospital, Stockholm, Sweden, and Department of Radiology, Danderyd Hospital, Stockholm, Sweden SUMMA R Y. We studied motion of the longitudinal arch of the foot using roentgen stereophotogrammetric analysis. Motion was analysed iu response to great toe dorsiflexion, maximum plantarlIexion/supination and heel raise, all actions previously stated to alter the height of the longitudinal arch. The largest amounts of motion were seen in the talonavicular joint (ranging from 37.1” to 14.2”) This included significant amounts of plantarflexion, adduction (or internal rotation) and supiuation occuring during the process of arch raising. This pattern of motion was seen in all forms of arch raising activity studied. Forced great toe dorsiflexion induced the maximum motion seen in the talonavicular joint. Motion of a significant degree was also induced in the talocalcaneal joint (17.9-8.6). Anterior to this motion was less (10.1-3.5” for the total motion in the naviculo-cuueiform joint and 8.0-3.0” for the cuneiform-metatarsal joint) and in the longtudinal plane these joints went into pronation. From a clinical point of view, it is important to recognize the role of the talonavicular joint in arch motion and that the involvement of the talonavicular joint in this sort of activity occurs in all three planes.
The occurrence of motion in the longitudinal arch of the foot induced by dorsiflexion of the great toe is widely accepted.‘,2 Though it is well recognized that with increasing dorsiflexion the arch rises, the distribution of motion in the joints involved is largely unknown. Similarly, the motion which occurs as a consequence of other stimuli which tend to raise the longitudinal arch has not been accurately recorded in vivo, mainly due to the limited availability of methods for kinematical analysis with adequate accuracy for detailed analysis of the relative motion of the small bones involved. Several previous studies have established that motion is available in three component parts, so-called triplane motion, in the various joints of the hindfoot.3-7 It has further been suggested and demonstrated that changes in the height of the longitudinal arch are an integral part of the normal behaviour of the foot during the stance phase of gait.*-” There is, however, little information on the distribution of motion between the various joints. The aim of the study was to analyse the motion occurring in the talocural, talocalcaneal, talonavicular, naviculo-cuneiform and first tarsometatarsal joints in different forms of arch raising, to elucidate the pattern of motion occuring in the various parts of the arch. In order to analyse the three-dimensional motion in these small joints, the technique of roentgen stereophotogrammetric analysis (RSA) has been used. The accuracy of this technique has been previously established. 11,12The accuracy established by these studies allows for the measurement in
angular changes of less than 1”. The technique has also been used in studies of the kinematics of the ankle-foot complex.’ It is thereby intended to demonstrate in life the ranges and direction of motion available in the longitudinal arch during arch raising activities.
MATERIALS AND METHODS We performed the study by RSA in 6 healthy volunteers. Ages ranged from 24 to 36 years and weight from 56 to 83 kg. None had any previous or present foot complaints, and all subjects had clinically normal feet except one (subject no. 2) who had an asymptomatic planovalgus foot. Prior to examinations, at least three radio-opaque markers (Tantalum, spherical balls, 0.8 mm in size) were introduced into each of the tibia, the talus, the calcaneus, the navicular, the medial cuneiform, the cuboid and the first, third and fifth metatarsal bones of the examined foot (Fig. 1). Stiffness was in no case present for more than 3 days after introduction of the markers, and the RSA examinations were performed at least 2 weeks after this time. RSA examinations The subjects were asked to stand with the right foot in the neutral position inside a plexiglass calibration cage, all four sides of which carried radio-opaque markers in known positions. Simultaneous anteroposterior and lateral films were exposed. The subject 151
152 The Foot
Fig. l-The
distribution of markers in the foot.
was then asked to remove weight from the heel until the underlying skin lost contact with the base of the reference cage (weight thus being carried only by the forefoot). A new set of exposures was made in this position. The heel was then raised further until a 50 mm wooden block could be introduced under the centre of the heel. Another pair of films was then exposed. The subject was then asked to stand with his foot against the firm wall of the calibration cage in such a position that the great toe was passively fully dorsiflexed, and again, further exposures were taken (Fig. 2). Exposures were also made in maximum nonweightbearing voluntary plantarflexion/supination. The positions of all calibration cage markers and all markers in the bones were digitized and fed to a computer programmed to yield relative spatial dis-
placements of the studied bones. The method of undertaking the RSA studies was approved by the ethical committee of the Karolinska Hospital. Data presentation Displacements of the bones between the different input positions are given as total rotations (helical axis rotations) for each studied position (Table 1). These movements are then broken down into component rotations around the axes of a three-dimensional coordinate system (Table 2). These rotations correspond to plantarIIexion/dorsiflexion, supination/pronation and internal/external rotation, respectively. The coordinate system is fixed with its origin in the geometrical centre (centre of gravity) of the proximal segment in each comparison.
RESULTS
Fig. 2-The
position of maximum dorsitlexion of the great toe.
Both progressive heel raise and great toe dorsiflexion induced motion in the joints of the longitudinal arch. In dorsiflexion of the toe, the average amounts of plantarhexion were 19.3” for the talonavicular joint, 10.5” for the talocalcaneal and 3.8” for the naviculocuneiform joint, and this was associated with 1.5” of motion of the first tarsometatarsal joint. This motion was accompanied by 19.6“ internal rotation and 17.4” of supination in the talonavicular joint. The values for the motion occurring in the separate planes in each of the studied joints can be seen in Table 2. This produced maximum total rotation (helical
The pattern Table 1. The total motion
in response
Joints Dorsiflexion Raised
of great toe
heel
Block under
heel
Plantarflexionjsupination
Average
arch of the foot
Talonavicular
Naviculocuneiform
Cuneiform-metatarsal
13.9 6.9 4.7 3.0 16.9 6.9 35.5 7.8
15.7 I.8 8.7 6.0 8.6 4.0 17.9 5.4
33.4 7.0 14.2 10.4 17.6 8.3 37.1 7.0
10.1 6.2 3.5 2. I 9.8 4.5 5.8 1.7
8.0 1.0 3.0 1.8 5.6 1.9 3.8 1.9
deviations
in italics.
to great toe dorsiflexion
Plantarflexion/dorsiflexion Great toe Heel-raise 50 mm block plantarflexion/
Supination/pronation Great toe Heel raise 50 mm block Plantarflexionjsupination External/internal Great toe Heel raise 50 mm block Plantarflexion/supination
Average values in plain type, standard Positive values plantartlexion/supination
153
activities
Talocalcaneal
Joints
Maximum supination
arch raising
of the longitudinal
Talocural
values in plain type, standard
Table 2. Movement in response plantarfiexion and supination
to various
of motion
lifting the heel, with a block under the heel and at maximum
excursion
Talocural
Talocalcaneal
Talonavicular
-10.1 7.2 -2.7 3.3 13.8 7.6 36.6
10.5 4.0 6.3 5.5 6.9 3.1 10.1
19.3 2.8 10.1 8.1 14.7 5.9 15.8
3.8 2.5 0.8 1.9 3.6 2.6 3.8
-1.5 1.3 -0.3 I..? -0.6 1.3 0.5
2.8
6.5
13.7
0.4
0.4
5.2 1.6 1.3 1.7 -5.3 I.6 -2.3 6.2
6.7 4.5 2.6 3.4 1.9 2.1 6.7 5.0
17.4 7. I 7.0 7.0 5.2 1.7 15.2 7.6
-11.2 3.3 -2.7 2.1 - 8.7 3.8 - 5.8 4.5
-6.9 1.2 -2.0 1.6 -5.0 2.0 -0.7 2.7
-2.7 2.7 0.2 2.2 -1.7 1.7 3.7 6.3
6.7 1.8 2.9 3.4 5.6 3.5 11.4 5.6
19.6 6.6 4.8 6.0 9.7 5.2 20.0 7.4
-
2.9 I.3 1.6 1.1 0.9 1.5 -0.6 1.1
Naviculocuneiform
3.4 1.7 -0.6 0.2 - 1.4 1.3 0.5 1.5
into
Cuneiform-metatarsal
deviations in italics. and external rotation.
axis rotation) for toe dorsiflexion of 33.4” for the talonavicular joint (Table 1). This value for total rotation is comparable with motion seen in maximum non-weightbearing plantarflexion and supination of the foot as a whole. The induced triplane motion in heel raising and with the block under the heel induced comparable directions of rotation in all planes (Table 2), between the various joints. The absolute values were rather less with these input measures. For example, the maximum talonavicular rotation with the 50 mm block was 17.6”.
DISCUSSION
The motion of the longitudinal arch in toe dorsiflexion was first commented upon in detail by Hicks.
The motion has been assumed to occur around an oblique axis in space (i.e. to comprise components relating to different [often referred to as X, y, and z] axes of a spatial coordinate system). The plantartlexion component (being the only component assessed previously) has been stated to be approximately 10” in passive toe dorsiflexion in cadaveric specimens.’ This study shows that nearly twice as much motion can be seen in normal individuals. Under in vivo conditions, toe dorsitlexion also occurs not only with the foot in a neutral position, but more often with the foot plantarflexed, after heel-off during the stance phase of gait. The amount of plantarflexion of the talonavicular joint occurring between neutral and the heel-block position, which reflects similar circumstances in our study, was 14.7”. Resulting supination and internal rotation of the
154 The Foot
talonavicular joint reached high values, which is in concordance with the data previously presentedI on the direction of the second subtalar joint axis. It is a potentially significant finding that the pattern of motion in the arch induced by toe dorsiflexion is different from that seen in supination of the foot.’ In a previous examination of metatarsal mobility undertaken by the authors,14 maximum voluntary dorsiflexion and pronation induced plantarflexion rather than dorsiflexion in the joints of the arch as one might expect. This suggests that common factors must exist in the apparently contrary activities. This may be explained by the subjects using their toe extensors to reach the position, creating a motion pattern similar to that seen in toe dorsiflexion. However, in this study, easing weight off the heel without actually raising it off the ground also induced a similar pattern, in this case without concomitant dorsiflexion of the toes, and presumably without the increased effect of extensor activity. This is still compatible with previous observations on the position of the longitudinal arch and the available dorsiflexion of the toe with the foot under load in different positions of the talocural joint. This may indicate that factors other than the windlass effect of the plantar aponeurosis may influence the biomechanics of arch raising. It would appear that the longitudinal arch in a neutral standing position is at its lowest level allowed by simple dorsiflexion of the joints which go to make up its constituent parts. Motion which occurs from this position in this plane is thus almost exclusively plantarflexion in most circumstances. Other elements of motion, notably supination (motion occurring around the longitudinal axis), are clearly important in producing a visible raise in the longitudinal arch. It has to be noted that the data produced by this study are limited by virtue of the invasive nature of the study. It would clearly be inappropriate to study large numbers of normal individuals in this manner. The accuracy of the study technique, however, means that the observations made represent a true representation of the ranges of motion in normal individuals under these circumstances and thereby provides unique data. The difference between these figures and cadaveric studies demonstrates the difference between in vivo and in vitro studies. Study of the standard deviation figures would suggest a good deal of difference in the performance of individuals. This in turn illustrates the difficulties in defining ‘normal’ foot function.
References 1. Hicks J H. The mechanics of the foot II. The plantar aponeurosis and the arch. J Anat 1954; 88: 25-30. 2. Rose G K, Welton E A, Marshall T. The diagnosis of the flat foot in the child. J Bone Joint Surg 1984; 66B: 71. 3. van Langelaan E J. A Kinematical analysis of the tarsal joints. An X-ray photogrammetric study. Acta Orthop Stand 1983; 54 (suppi 204). 4. Lundbere. A. Goldie I. Kalin B 0. Selvic G. Kinematics of the ankle/foot complex. Plantar flexion and dorsi-flexion. Foot Ankle 1989; 9: 194. 5. Lundberg A, Svensson 0 K, Bylund C. Goldie I, Selvic G. Kinematics of the ankle/foot complex. Part 2: pronation and supination. Foot Ankle 1989; 9: 248. 6. Lundberg A, Svensson 0 K, Bylund C, Goldie I, Selvic G. Kinematics of the ankle/foot complex. Part 3: influence of leg rotations. Foot Ankle 1989; 9: 304. I. Lundberg A, Svensson 0 K, Nemeth G. Selvik G. The axis of rotation of the ankle joint. J Bone Joint Surg 1989; 71B: 94-99. 8. Elftman H. The transverse tarsal joint and its control. Clin Orthop 1960; 16: 41. 9. Isman R E, Inman V T. Anthropometric studies of the human foot and ankle. Biomechanics Laboratory, University of California, Berkeley, Technical Report, May 1968. 10. Sarafian S K. Functional characteristics of the foot and plantar aponeurosis under tibio-talar loading. Foot Ankle 1987; 8: 4. 11. Selvik G, Alberius P, Aronsson A S. A roentgen stereophotogrammetric system. Construction, calibration and technical accuracy. Acta Radio1 Diagn 1983: 24: 343-352. 12. Lundberg A, Bylund C, Selvik G, Winson I G. Accuracy of roentgen stereophotogrammetric analysis in joint kinematics. European Journal of Clinical Musculo-Skeletal Research 1994 (in press). 13. Hicks J H. The mechanics of the foot 1. The joints. J Anat 1953; 81: 345-351. 14. Winson I G. Lundberg A, Bylund C. Metatarsal motion. The Foot 1994 (in press).
The authors Ian G. Winson MB, ChB, FRCS Consultant Orthopaedic Surgeon Southmead Hospital Southmead Road Westbury-on-Trym Bristol UK Arne Lundberg MD, PhD Department of Orthopaedics Karolinska Hospital Stockholm Sweden Carin Bylund MD Department of Radiology Danderyd Hospital Stockholm Sweden Correspondence to Mr I. G. Winson.