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Rheumatology Advance Access originally published online on April 4, 2007
Rheumatology 2007 46(6):1024-1028; doi:10.1093/rheumatology/kem017
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© The Author 2007. Published by Oxford University Press on behalf of the British Society for Rheumatology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Ankle/hindfoot arthrodesis in rheumatoid arthritis improves kinematics and kinetics of the knee and hip: a prospective gait analysis study

R. J. Weiss1, E. Broström2, A. Stark1, M. C. Wick3 and P. Wretenberg1

1Department of Molecular Medicine and Surgery, Section of Orthopaedics and Sports Medicine, Karolinska Institutet, Stockholm2Department of Women and Child Health, Karolinska Institutet, Stockholm3Department of Medicine, Section of Rheumatology, Karolinska Institutet, Stockholm, Sweden.

Correspondence to: Rüdiger J. Weiss, Department of Orthopaedic Surgery, Karolinska University Hospital, Karolinska Institutet 171 76 Stockholm, Sweden. E-mail: rudiger.weiss{at}karolinska.se


   Abstract
Top
 Abstract
Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
Objectives. To evaluate the effects of ankle/hindfoot arthrodesis in rheumatoid arthritis (RA) patients on gait pattern of the knee and hip.

Methods. In this prospective follow-up study, 14 RA patients scheduled for ankle/hindfoot arthrodesis (talo-calcaneal, talo-navicular, calcaneo-cuboid and/or talo-crural joints) and 14 age- and sex-matched healthy controls were included. Three-dimensional gait analyses of joint angles, moments and work were performed at the index operation and after 13 months of follow-up. Each patient underwent clinical assessments of pain while walking, overall evaluation of disease activity, Health Related Quality of Life Questionnaire (EQ-5D), activity limitations, maximum walking distance, difficulty with walking surface and gait abnormality. For comparisons of pre- vs post-operative conditions, Wilcoxon's matched pairs test and Friedman ANOVA by rank test were used.

Results. At follow-up after ankle/hindfoot fusion surgery, RA patients demonstrated a statistically significant improvement in mean range of joint motions, moments and work in the overlying joints such as the knee and hip. Moreover, there was significantly less pain, disease activity, activity limitation, difficulty with walking surface and gait abnormality. EQ-5D and maximum walking distance were also significantly improved at follow-up.

Conclusions. Our results demonstrate that ankle/hindfoot arthrodesis in RA is an effective intervention to reduce pain and to improve Health Related Quality of Life and functional ability. Moreover, the overlying leg joints experience an improvement in joint motion, muscle-generated joint moments and work during walking. Three-dimensional gait analysis may assist future investigations of the effects of orthopaedic surgery on functional mobility in RA to prevent irreversible disablement.

KEY WORDS: Arthrodesis, Kinematics, Kinetics, Rheumatoid arthritis, Three-dimensional gait analysis


   Introduction
Top
 Abstract
 Introduction
Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 
In rheumatoid arthritis (RA), pain and soft tissue swelling in the involved joints are characteristic early features, often leading to fixed structural deformities later in the disease course [1]. In 80–90% of patients with longstanding inflammatory disease, foot involvement is a common localization of RA [2, 3] and the hindfoot, in particular at the subtalar joint, is an identified area of frequent orthopaedic problems [4]. Mid-foot and ankle-joint involvements are believed to be less commonly involved [5, 6].

RA patients who suffer from pain, stiffness and disability in the foot often seek relief via orthopaedic surgery as a last option following unsuccessful medicinal anti-rheumatic therapy. The aim of modern surgical treatments such as arthrodesis, the most established treatment for rheumatic destructions in the foot, is primarily to resolve pain and improve physical function. Hindfoot arthrodesis in RA gives a high frequency of pain-relief, regardless of whether radiographs show the arthrodesis to be fully healed, i.e. already fibrotic consolidation appears to be sufficient for relieving pain [7].

Recent studies have reported similar satisfaction and union rates following ankle arthrodesis in RA patients compared with patients with osteoarthritis [8, 9]. Hindfoot arthrodesis in patients with osteoarthritis and other foot deformities has been shown to improve the range of motion of the ipsilateral knee joint [10, 11]. Nevertheless, until now little attention has been given to the consequences of ankle/hindfoot arthrodesis in RA on kinematic and kinetic gait changes of the overlying joints such as the knee and hip. This might be due to the general difficulty of functional assessment of RA and the often unpredictable, progressive nature of this disease.

Three-dimensional gait analysis, including kinematics and kinetics, could provide objective information about gait changes, such as changes of joint angles, moments and work, which are impossible to quantify in a standard clinical setting. This method may help to quantitatively document disease progression or improvement and may thus offer valuable information for physicians regarding specific therapy considerations in individual RA patients.

The aim of the present study was to evaluate gait changes in the overlying joints and functional outcome after elective ankle/hindfoot arthrodesis of RA patients who had no symptomatic disease progression in the lower limbs during follow-up.


   Materials and methods
Top
 Abstract
 Introduction
 Materials and methods
Results
 Discussion
 Acknowledgements
 References
 
RA patients
Patients were eligible for inclusion if they were scheduled for one or a combination of the following surgical procedures: arthrodesis of the talo-calcaneal (subtalar), talo-navicular, calcaneo-cuboid and/or talo-crural joints. RA patients were recruited from the orthopaedic out-patient clinic at the Department of Orthopaedic Surgery at Karolinska University Hospital. All patients fulfilled the 1987 revised American College of Rheumatology (ACR) criteria for RA [12]. All patients received ongoing medication and none had received intra-articular steroid injections for at least three weeks prior to the gait analysis examination. None of the RA patients used walking aids.

Age, sex, RA disease duration and medication were recorded for each patient. Each patient underwent a standardized clinical evaluation, which included the assessment of patient's pain at walking (0–100 mm visual analogue scale, 0 = no pain) giving an average-score of pain in the ankle/hindfoot. Moreover, patient's overall evaluation of disease activity (0–100 mm visual analogue scale, 0 = no disease activity) and the Health-Related Quality of Life Questionnaire EuroQol (EQ-5D) (0–1, 1 = full health) [13] were recorded. According to a modified Kitaoka ankle-hindfoot scale [14], we evaluated activity limitations/support requirement (0–10, 10 = no limitations/no support), maximum walking distance (0–5, 5 = more than 3 km), difficulty with walking surface (0–5, 5 = no difficulty on any surface) and gait abnormality (0–8, 8 = none/slight). Patients experiencing symptomatic disease progression of the ipsilateral knee or hip or of the contralateral lower limb during follow-up were excluded from the study. Pre-operatively and at follow-up, conventional plain radiographs of the weight-bearing ankle and foot joints were obtained in anterior–posterior and lateral views.

Normative data were gathered from a cohort of age- and sex-matched healthy adults without musculoskeletal disease, recruited from employees of the Orthopaedic clinic at Karolinska University Hospital. None of the RA patients and controls had any history of neurological disease or gross motor delay. The study design, which was approved by the local Ethical Committee of Stockholm North, was explained to the RA patients and controls and written informed consent was obtained from all probands.

Gait analysis
All RA patients were asked to walk barefoot along a 10 m long walkway at a self-selected walking speed. In order to avoid morning stiffness, gait analyses were performed in the afternoon. In accordance with the biomechanical gait model (Plug In Gait, Vicon Motion Systems), 34 reflective markers (25 mm) were attached by the same investigator (E.B.) bilaterally onto the patient's skin over standardized bony landmarks (head, trunk, arms, pelvis, legs and feet) (Fig. 1). A three-dimensional motion analysis system with six cameras (Vicon, Motion System, Oxford, UK) was used. Three complete walking trials were performed to obtain kinematic, kinetic and time–distance parameters. All data were averaged across trials. Two force plates (40 x 60 cm, 9281CA, Kistler, Basel, Switzerland) were used to collect ground reaction forces. Gait tests were performed repetitively until force plate data for each side were collected. The floor and the force plates were covered with the same film. Thus, the force plates were not easily distinguishable to avoid biasing that subjects may hit the force plates in an unnatural way. Walking speed (s–1), stride length, step length and cadence were normalized to height, whereas joint moments were normalized to weight. A walking trial was considered complete if the patient's right or left foot had a clean contact on the force plate.


Figure 1
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  		FIG. 1. Reflective markers are attached bilaterally onto the patient's skin over standardized bony landmarks.

 
The Vicon Plug In Gait model was used for the evaluation of all parameters. The lower body was modelled as seven segments (pelvis, 2 thighs, 2 shanks and 2 feet) and the upper body was considered as one segment. A normal gait cycle was defined from initial heel-to-heel contact with the same limb. We only analysed the side for scheduled surgery of the RA patients.

The following maximum peak values of the patient's ensemble gait cycle were analysed: angles for hip- (flexion, extension, abduction, adduction, external rotation and internal rotation), knee- (flexion and extension) and ankle-motion (dorsiflexion and plantarflexion). Moreover, hip, knee and ankle internal joint moments were recorded. Joint power, calculated as the product of joint moment and angular velocity, is defined as the rate of joint work done. As such, joint work was calculated from the area of the joint power profile, wherein positive power, or power generation, corresponds to concentric muscle action and negative power or power absorption corresponds to eccentric muscle action. Positive work was calculated as the sum of positive power area and negative work as the sum of negative power area with respect to time throughout the gait cycle.

Statistical analysis
The non-parametric Wilcoxon's matched pairs test was used to assess gait analyses parameters before and after ankle/hindfoot arthrodesis. The Friedman ANOVA by rank test was used to compare pain at walking, EQ-5D and the modified Kitaoka scale [14] at two time points, pre- and postoperatively. Mann–Whitney U-test was used for comparisons of post-operative gait parameters of the RA group with age- and sex-matched healthy controls. All values are presented as means (±S.D.). The level of significance was P ≤ 0.05. All statistical analyses were performed using Statistica 6.0 (StatSoft Inc., USA).


   Results
Top
 Abstract
 Introduction
 Materials and methods
 Results
Discussion
 Acknowledgements
 References
 
Demographic characteristics of patients and controls (Table 1)
Twenty RA patients (18 females and 2 males) participated in the pre-operative gait analysis. Of these 20 patients, 6 (all females) had to be excluded: five patients due to symptomatic disease progression of the ipsilateral or contralateral lower limbs; 2 underwent total joint arthroplasty and 3 had severe pain in joints of the lower limbs other than the operated foot; and 1 patient had a fracture. Hence, 14 RA patients completed the follow-up gait analysis. Demographic data of the RA patients and the age- and sex-matched healthy subjects are shown in Table 1. There were no statistically significant differences in age, bodyweight or height between the two groups. The mean (S.D.) follow-up time from the index operation was 13.3 (1.7; range 11–16) months.


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  		TABLE 1. Demographic characteristics of patients and controls

 
At the index operation, 11 patients were given disease-modifying anti-rheumatic drugs (DMARDs), 10 received non-steroidal anti-inflammatory drugs (NSAID), 5 received prednisolone, 4 anti-tumour necrosis factor-{alpha} (anti-TNF{alpha}) therapy, 2 received propoxyphene and 2 opiodes. During follow-up, all patients had stable anti-rheumatic treatment based on clinical rheumatological considerations.

Surgical procedures
The following surgical procedures were performed: 6 talo-crural, 2 talo-calcaneal (subtalar), 1 subtalar with talo-navicular, 3 talo-navicular and 2 triple (talo-calcaneal, talo-navicular and calcaneo-cuboid) arthrodeses. One post-operative complication occurred, an infection related to internal fixation. This patient underwent hardware removal and was free from infection at follow-up. Conventional X-rays did not reveal any non-union for the study group at follow-up (data not shown).

Disease characteristics (Table 2)
The mean disease duration (S.D.) before the pre-operative gait analysis was 13 (9) years (range 3–34 years) and 7 (50%) patients had had the diagnosis of RA for more than 10 years. At follow-up, a statistically significant decrease in both pain at walking and patient's assessment of disease activity, as well was a significant increase in EQ-5D was observed. According to the modified Kitaoka ankle-hindfoot scale [14], activity limitations/support requirement, maximum walking distance, difficulty with walking surface and gait abnormality significantly improved post-operatively.


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  		TABLE 2. Disease characteristics of the RA patients pre- and post-operatively

 
Kinematics (Tables 3 and 4)
The pre-operative hip extension angle was 4.0° and markedly improved to 13.4° following surgery (P = 0.01). Knee flexion changed from 44.5° pre-operatively to 49.2° post-operatively (P = 0.04). There were no statistically significant differences between pre- and post-operative hip flexion (P = 0.2), knee extension (P = 0.43), ankle dorsiflexion (P = 0.33) and ankle plantarflexion (P = 0.82). There were no statistically significant differences in the frontal or transverse planes between pre- and post-surgical kinematic parameters (data not shown).


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  		TABLE 3. Motion variables of RA patients (pre- and post-operative) and healthy controls: kinematic and kinetic parameters are angles, moments and work of the hip, knee and ankle. Time–distance parameters such as walking speed, stride length, step length and cadence are shown after normalization to height

 

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  		TABLE 4. Motion variables of RA patients (pre- and post-operative): kinematics of the ankle subdivided by hindfoot and ankle arthrodesis

 
Kinematics of the ankle dorsi- and plantarflexion for the hindfoot and ankle subgroups did not reveal any statistically significant differences (Table 4). There were no statistically significant differences in joint motions between the RA group at follow-up and the control group except for ankle plantarflexion.

Kinetics (Table 3)
Statistically significant differences in pre- compared with post-operative gait analyses were evident for hip flexion moment (0.5 vs 0.7 Nm/kg; P = 0.01), hip extension moment in swing (0.2 vs 0.3 Nm/kg; P = 0.01) and hip external rotation moment (0.06 vs 0.09 Nm/kg; P = 0.04). No statistically significant differences were recorded for hip extension moment (P = 0.25), hip internal rotation moment (P = 0.3) and hip adduction and abduction moments (data not shown). Knee flexion moment (0.2 vs 0.3 Nm/kg; P = 0.04) and knee external rotation moment (0.06 vs 0.08 Nm/kg; P = 0.04) were significantly greater at follow-up. No statistical significant differences were observed for knee extension moment (P = 1.0), knee internal rotation moment (P = 0.4), knee adduction/abduction (data not shown), ankle dorsiflexion moment (P = 0.6) and ankle plantarflexion moment (P = 0.06).

Hip positive work (muscle concentric action) was 0.08 J/kg pre-operatively and 0.12 J/kg post-operatively (P = 0.06). Hip negative work (muscle eccentric action) was 0.11 J/kg pre-operatively and 0.15 J/kg post-operatively (P = 0.05). Knee positive work (0.07 vs 0.09 J/kg; P = 0.02) and knee negative work (0.09 vs 0.14 J/kg; P = 0.03) were significantly greater at follow-up. There were no statistically significant differences in ankle positive work (P = 0.16) or negative work (P = 0.06) following surgery.

All joint moments and work were significantly decreased in the RA group at follow-up in comparison to the healthy controls, except for knee flexion moments, knee internal rotation moments, hip negative work and knee positive work.

Time–distance parameters (Table 3)
There was no statistically significant difference for cadence (P = 0.06) one year after hindfoot arthrodesis. However, normalized walking speed (0.48 vs. 0.57 s–1; P = 0.04), stride length (0.56 vs 0.63; P = 0.04) and step length (0.28 vs 0.32; P = 0.05) were greater at the follow-up gait analysis. All time–distance parameters were still increased in the control group in comparison to post-operative RA group.


   Discussion
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
Acknowledgements
 References
 
In patients with long-term RA, the development of severe, painful and often immobilizing structural deformities of the affected extremities is, despite modern anti-rheumatic therapy regimens, relatively common [15]. It is known from routine clinical practice that inflamed and painful joints not only lead to locally restricted motion, but can, due to abnormal use and forces, also cause other functional abnormalities in over- or underlying joints. The use of orthopaedic surgery, although decreasing during the past 15 years [16], is a surrogate of disease severity. Arthrodesis, the osteosynthetic fusion of two joints, is one of the most common and successful orthopaedic procedures in the RA foot. Functionally, the operated joint is stiffened and consequently also different physical forces are put on neighboured joints. Our cohort's improvements in pain, disease activity, EQ-5D, activity limitations, walking distance, walking surface and gait abnormality after arthrodesis could have been expected since, as mentioned above, arthrodesis represents a solid procedure with reproducible results [8, 9, 17, 18]. To date, the functional and kinetic impacts on the operated and respective neighboured joints post-surgery have not yet been systematically analysed.

Kinematics describes joint movements, including angles of the ankle, knee and hip joint. In this present study, we did not observe a statistically significant alteration in ankle dorsi- and plantarflexion angles when comparing the pre- with the post-operative gait data. This remained unchanged when cases of hindfoot and cases of ankle athrodeses were analysed separately in a subgroup analysis. That may suggest that arthrodesis of the ankle or hindfoot does not influence movement in the operated joints in our cohort, since movement is already limited before surgery due to stiffness and pain. However, it has to be mentioned that the three-dimensional gait analysis system used in this study does not represent the perfect functional foot model as the foot is calculated as one segment only.

Conversely, our RA patients walked with a significantly increased hip extension and knee-flexion joint range of motion following fusion surgery of the ankle/hindfoot. Maximal hip extension during gait in healthy controls is described to be approximately 10° [19], which was also seen in our control group. The improved patient's range of motion in the hip and knee after arthrodeses when compared to our control group is of clinical significance since this is important for adequate moments during level walking, especially when ankle plantar flexion is limited.

Kinetics describes the forces involved in movement generation and the most commonly discussed parameters are moments of force and work. The moments of force described in the present study are the internal moments created by the leg muscles surrounding each joint as a reaction to the load produced by ground reaction forces and the motion of the leg segments. Hip and knee moments during gait, as described in the recent literature concur with the parameters found in our control group [20]. The improvements of hip flexion moment, hip extension moment in swing and knee flexion moment after foot surgery are not only of statistical but also of clinical significance, as the RA patients experience a normalization of joint moments when comparing to the controls (Table 3) which is crucial to increase forward progression. Work analysis is the complement that describes muscle action over time, which is also improved at the hip and the knee post-operatively. Arthrodesis in our RA patients led to improved joint moments and work in the knee and hip, which is important to provide forward propulsion of the body and advancement of the swing leg. Several investigators [21–24] have reported a strong relationship between leg power and functional performance measures such as time, chair rise, stair climbing, lifting and walking.

Except for cadence, all time–distance parameters such as walking speed, stride length and step length also significantly improved in the RA cohort at follow-up, which was expected. Other studies have reported that RA patients have a decrease in time–distance parameters [1, 25]. The improvement of those parameters may express a more normalized gait pattern and better lower limb function. We aimed to study RA patients at a self-selected walking speed but not to control the cycle time, as would, for example, be the case when probands are walking in time with a metronome. The rationale for controlling the cycle time is that there is some existing evidence in the literature, that walking speed may influence gait parameters [26] and using a controlled cycle time provides a means of reducing the variability. However, subjects are unlikely to walk naturally when trying to keep pace with a metronome. Zijlstra et al. [27] found considerable differences in the gait of normal subjects between natural walking and constrained walking. We are aware that this controversially discussed issue leaves us with some uncertainty of how different walking speeds might influence kinematics and kinetics, putting a certain limitation on our results.

Although this RA patient cohort in our prospective follow-up study was not fully homogeneous, our clinical observations convinced us that ankle/hindfoot arthrodesis may have a general beneficial impact on the overlying joints despite inter-individual differences concerning surgical procedures or involved joints. It is difficult to study RA patient's gait pattern in a prospective follow-up study due to the generalized and progressive nature of the inflammatory disease and also due to the fact that patients with RA have comorbidity, rarely present with only an isolated foot problem. From our own clinical experience, RA patient's feet are usually symptomatic concomitantly with an involvement of the hip and knee joints, which may in turn be worsened by these foot problems. The considerable high exclusion rate (30%) during this follow-up study must be explained by the fact that symptomatic disease progressed in other joints of the lower limbs other than in the operated foot.

In addition, it has to be mentioned that the results of our study are based on the analyses of ankle/hindfoot arthrodesis in a relatively small RA patient cohort, putting a limitation on the generalizability of our results. Nevertheless, our results compellingly demonstrate that in RA patients eligible for ankle/hindfoot arthrodesis, this orthopaedic procedure is an effective intervention to reduce pain in the foot and also to markedly improve Health Related Quality of Life and functional ability. Moreover, joint motion and muscle-generated joint moments and work during walking were improved in the overlying leg joints such as the knee and hip, one year after surgery. Adequate kinematic and kinetic parameters in all joints of the lower limbs have a positive effect on gait and function towards more normal walking pattern.

In conclusion, using modern technology of three-dimensional gait analysis, the results of this present prospective study provided evidence that ankle/hindfoot arthrodesis in RA patients not only significantly improves tenderness and function of the operated joints, but also significantly improves kinematic and kinetic improvements in walking pattern and function of the neighboured overlying joints such as the knee and hip.

Formula


   Acknowledgements
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
References
 
We thank Dr Åsa Bartonek and Dr Elena M. Gutierrez-Farewik for inspiring discussions of the study design and Assoc. Prof. Robert A. Harris for linguistic advice. The study was supported by grants from The Sven Noréns Gåvofond and Teknik Stiftelsen.

The authors have declared no conflicts of interest.


   References
Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 Acknowledgements
 References
 

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Submitted 1 September 2006; revised version accepted 9 January 2007.
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