Gait analysis with a novel integrated measurement system
for functional assessment of subtalar coalition
1
C. Giacomozzi1, M.G. Benedetti2, A. Leardini2, V. Macellari1, S. Giannini2
Biomedical Engineering Laboratory, Istituto Superiore di Sanità, Rome, Italy
2
Movement Analysis Laboratory, Istituti Ortopedici Rizzoli, Bologna, Italy
Introduction
Only a few specific studies have been conducted up to now to perform an objective analysis of the foot
functional abnormalities during gait in subtalar coalition patients. In general, clinical results are
satisfactory (Kitaoka et al, 1997; Pachuda et al., 1990; Vincent, 1998) while the rate of functional
recovery after surgery is not clearly documented.
The complex motion between the foot bone segments has been observed by means of three-dimensional
tracking systems. Non-invasive stereophotogrammetric techniques have been widely employed (Liu et al.,
1997; Leardini et al., 1999) but a further step towards the complete characterisation of foot loading
requires the integration of kinematics and kinetics measurements.
A piezo-dynamometric integrated system had been developed (Giacomozzi, Macellari, 1997) and then
expanded to kinematics measurements and successfully tested (Giacomozzi et al, 2000). This instrument
simultaneously estimates the ground reaction force resultants and the pressure distribution throughout the
foot-to-floor contact area and on any selected subarea of the footprint. Moreover, a detailed and
synchronised description of several shank and foot segment kinematics is also obtained using an
anatomical-based tracking system (Leardini et al., 1999). The projection of a number of anatomical
landmarks on the footprint would allow an anatomically-based selection of the subareas of interest and a
better estimate the relevant local forces and moments (Giacomozzi et al, 2000).
The aim of the present study is to assess, the foot function in a group of patients with subtalar coalition
and in a group of patients operated for subtalar coalition by means of this novel gait analysis system. The
particular set up presented in this study is supposed to provide considerable insight into the biomechanical
effects of this pathology on gait patterns and into the effectiveness of relevant surgical treatments.
Methods
Eight patients with subtalar coalition were evaluated. Three females patients, mean age 17.0 years, were
affected by rigid symptomatic valgus pes planus due to subtalar coalition and non operated (NOP: Non
OPerated patients). Five patients, 4 males and 1 female, were evaluated after surgical removal of the
coalition (OP : OPerated patients; mean age 17.6 years, mean follow-up 28.8 months). In all the cases
clinical/functional assessment was performed with the Mazur scoring system modified (Mazur et al,
1979). All the patients agreed to participate to the study giving their informed consensus. Five healthy
young subjects (CHV: Control Healthy Volunteers) were evaluated with the same techniques as a control.
The integrated measurement system consisted of an Elite stereophotogrammetric system (BTS, Milan,
Italy) calibrated in a field of 60x50x40 cm3, a Kistler 0.4m x 0.6m force platform (Kistler Instrumente
AG, Switzerland), and a customised pressure platform (81 x 121 resistive sensors, frequency 100 Hz;
Macellari, Giacomozzi, 1996). The pressure platform, 3mm thick, was rigidly fastened on the top of the
force platform so as to obtain a piezo-dynamometric platform in which the forces are transmitted
unaltered from the former to the latter (Giacomozzi, Macellari, 1997). Position, ground reaction force
(GRF), pressure data and kinematic data were synchronised and collected at 100 Hz (Giacomozzi et al,
2000). Spatial re-alignment between position, pressure and force data was obtained by simple rototranslations of the relevant co-ordinate systems. The accuracy of the overall system was calculated by
means of an ad hoc experiment termed ‘MAL spot check’ (Della Croce, Cappozzo, 2000).
The shank and foot complex was represented by five rigid segments: shank, calcaneous bone, mid-foot,
1st metatarsal bone, and the proximal phalanx of the hallux. Each segment was tracked by a cluster of
four markers mounted on a Plexiglas plate attached to the segment using metallic clamps and double
sided adhesive tape (Leardini et al., 1999). The anatomical landmark calibration procedure (Cappozzo et
al, 1995) was performed to reconstruct the trajectories of relevant landmarks on the shank and foot
(Leardini et al., 1999). The projections on the transverse plane of these landmarks were superimposed
onto the collected pressure footprint for each sample of the stance phase. Then a reference instant was
identified to determine the footprint subareas on an anatomical basis, taken as the instant when the
summation of all the vertical normalised coordinates is minimum. The rearfoot, midfoot and forefoot subareas were identified accordingly. The local shear and vertical components of the GRF for each selected
subarea were estimated based on an established procedure (Giacomozzi, Macellari, 1997). The force
components were normalised with respect to the patient’s body mass. Contact times for each subarea
were also measured and normalised with respect to the total stance phase. Loading time, peak values and
integrals (expressed as % of body mass times % of stance phase) were finally averaged within each class
of subjects (NOP, OP and CHV).
Results & Discussion
As for the clinical assessment, the score obtained for the three NOP patients was respectively 22, 79 and
84 (mean heel valgus 8°, mean ankle dorsiflexion and plantarflexion 14 and 28°, mean pronation and
supination 5 and 12°). The five OP patients had a mean score of 92 (range 80-100; mean heel valgus 4°,
mean ankle dorsiflexion and plantarflexion 16 and 33°, mean pronation and supination 12 and 27°).
Table 1 reports loading time and force peak values for the total foot, for each of the selected subareas, and
for each of the three populations. In NOP patients an overloading of the entire foot emerges in the vertical
and medio-lateral components, mainly due to the contribution of rearfoot and midfoot subareas only. The
rearfoot is also responsible for the overloading of the entire foot along the medio-lateral axes. Results
from OP patients demonstrated a trend to normalisation of the force along all the three components.
Stance phase in total foot is longer in NOP patients, while is comparable for OP patients and CHV. In the
corresponding subareas, NOP loading time is higher for the rearfoot and lower for the forefoot. NOP
patients showed lower peaks of the GRF vertical and fore-aft components under the forefoot with respect
to CHV, while OP patients clearly showed an overall trend to normalise their loading pattern.
Joint rotation data are presented in Figure 1. In NOP patients, main abnormalities were found at the Ti-Ca
joint in the sagittal (DP) and coronal (PS) planes. The rearfoot shows a trend to a pronated attitude at heel
strike. Afterwards, rearfoot remains in that position with a trend to a premature and slight supination
during terminal stance. There was an evident reduction of the plantarflexion during terminal stance.
Surgery seemed to restore a physiological rearfoot kinematics both in the sagittal and coronal plane. The
Ca-Mi and Mi-Me joints in both patient groups did not show particular abnormal motion, at least in
clinically interpretable terms. Although still within the control band, it is interesting to underline the lack
of Mi-Me plantarflexion at terminal stance and its rigid attitude in PS throughout the stance phase. At the
Me-Ph level, it is evident a very limited DP range of motion in both patient groups.
The foot affected by subtalar coalition substantially works as a rigid flatfoot. Surgery seems to restore a
more regular pattern of rearfoot loading and motion, consistent also with clinical measurements.
Nevertheless, the reduced motion at the Me-Ph remains unchanged, probably associated to the acquired
“metatarsus primus elevatus” deformity.
The present study is certainly limited by the small number of patients and by the fact that NOP and OP
patients were not from the same group. Nevertheless, the excellent clinical scoring, the reduction of pain,
the increased passive range of foot prono-supination, the heel re-alignment and the improved rearfoot
function during gait at the follow-up considered support the effectiveness of the surgical treatment,
although a complete restoration of forefoot kinematics was not achieved.
The novel integrated system for the simultaneous anatomical-based analysis of foot-ground reaction
force, foot pressures and joint kinematics demonstrated to have great potentiality for clinical applications.
The applicability of the set-up, the reliability in detecting foot loading and motion abnormalities, and the
clinically interpretable form of the results make the system a valuable tool in clinical research. From a
more biomechanical view, the possibility to relate foot anatomical structures with their function appears
highly attractive, providing insight into normal and pathological foot biomechanics and outcome after
treatment.
Total foot
Rearfoot
Midfoot
Forefoot
NOP (s)
(%stance)
0.81 (0.76÷0.92)
100
0.56 (0.37÷0.78)
67.3 (48.7÷84.8)
0.54 (0.30÷0.66)
68.8 (32.6÷86.8)
OP (s)
(%stance)
0.74 (0.65÷0.79)
100
0.44 (0.30÷0.61)
59.5 (39.0÷77.2)
CHV (s)
(%stance)
0.73 (0.68÷0.83)
100
0.40 (0.33÷0.48)
54.5 (48.5÷57.8)
0.35
(0.08÷0.51)
45.5 (8.7÷67.1)
0.42
(0.13÷0.58)
56.1
(20.0÷76.0)
0.37
(0.26÷0.51)
50.0
(38.2÷61.5)
Loading times
0.64 (0.54÷0.71)
87.4 (83.1÷90.7)
0.63 (0.58÷0.73)
86.3 (80.6÷89.7)
Peak (% bm)
Vertical
NOP
105.3 (101.3÷108.1) 91.4 (80.7÷106.5) 26.0 (2.9÷40.3) 82.1 (41.8÷103.9)
OP
112.1 (109.5÷120.3) 89.3 (79.0÷97.4)
22.8 (1.2÷38.9) 101.9 (90.0÷111.9)
CHV
107.7 (104.1÷110.1) 85.7 (73.5÷98.8)
11.4 (6.4÷17.9) 106.7 (101.1÷111.5)
Ant-post
NOP
16.0 (13.4÷20.2)
11.9 (10.1÷13.4)
1.6 (0.3÷2.5)
12.5 (2.8÷14.3)
OP
20.1 (16.9÷24.3)
13.7 (10.7÷16.0)
2.6 (0.1÷5.2)
20.0 (16.9÷24.3)
CHV
21.5 (19.5÷21.6)
12.7 (10.1÷15.1)
0.7 (0.2÷1.2)
21.5 (19.5÷23.4)
Med-lat
NOP
8.5 (6.0÷9.8)
7.0 (4.0÷8.7)
1.7 (0.4÷2.4)
4.8 (4.2÷5.4)
OP
8.1 (4.0÷13.0)
6.7 (4.0÷10.0)
1.3 (0.1÷2.3)
5.3 (3.7÷7.2)
CHV
7.5 (5.7÷10.2)
6.9 (3.5÷10.2)
0.6 (0.2÷1.2)
4.4 (2.1÷5.4)
Table 1: Loading times and force peak values referred to total foot and to each of the selected subareas, for NOP patients, OP
patients, and CHV. Loading times are expressed both as absolute values (s) and as percentage of the total stance phase.
Force peak values of the three GRF components are expressed as percentage of the patient’s body mass.
40
Ti-Ca
PS
DP
20
IE
DP
PS
IE
Mi-Me
0
-20
0
50
DP
Ca-Mi
100
PS
IE
DP
PS
IE
Me-Ph
0
Figure 1: Dorsi-plantar (DP), prono-supination (PS) and internal-external (IE) rotations of the tibio-calcaneal (Ti-Ca),
calcaneo-midfoot (Ca-Mi), midfoot-first metatarsal (Mi-Me), I metatarso-phalangeal (Me-Ph) joints, reported versus
percentage of stance duration. Grey bands represent corresponding mean (solid thin line) plus standard deviation zones.
for each of the four joints. Dorsiflexion, pronation and internal rotation are intended as the positive values of the
rotations. Corresponding means for the NOP (thick solid line) and OP (thick dotted line) patients are superimposed. All
joint rotation measurements are in degrees.
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