Preoperative gait characterization of patients with ankle arthrosis
Introduction
Pain and loss of motion associated with degenerative joint disease (DJD) of the ankle can result in devastating consequences. Causes of these degenerative changes include traumatic injuries, abnormal ankle joint biomechanics (i.e. chronic ankle instability), and less commonly primary osteoarthritis, rheumatoid arthritis, inflammatory arthropathy, hemochromatosis, infection, neuropathic arthropathy, and tumor [1], [2], [3]. The true prevalence of ankle DJD has been difficult to define as a result of variation in degenerative changes per etiology and clinical correlation. Lindsjo et al. [4], in a follow-up study of 306 operatively treated ankle fractures, reported the development of posttraumatic arthritis in 14% of patients [3], [4]. Traumatic injury of the ankle is the most common etiology associated with DJD [3]. Development of post traumatic ankle arthrosis is precipitated by chronic eccentric loading (progressive uneven wear) of the joint as a result of angular deformity [5]. Fractures associated with posterior malleolar injuries are more prone to develop DJD when the posterior malleolus has not been anatomically reduced [2], [3], [5], [6]. Chronic ankle instability leading to degenerative changes is due to lateral ligament laxity resulting in damage to the medial side [3], [7]. All of these pathologies cause irreversible destruction of the tibiotalar articular cartilage, chronic cartilage overloading from articular incongruity, and eventual destruction of the joint space, resulting in pain and deformity.
In order to examine how the DJD affects foot and ankle motion, it is important to understand normal foot and ankle motion. Ankle motion has been described in relation to phases of the gait cycle and is commonly referred to as “the three rockers” of foot and ankle motion [6], [8], [9], [10], [11], [12], [13], [14], [15]. The first rocker occurs during the loading response phase of the gait cycle; starting the gait cycle at heel strike or initial contact (0%), the ankle joint undergoes rapid plantar flexion which is at a maximum at 7% of the cycle, concluding with the foot flat on the floor (first rocker or initial double limb support). Next, the ankle progressively dorsiflexes until roughly 30% of the gait cycle (second rocker or single limb support), then as the heel lifts, active plantarflexion continues until reaching a maximum at toe-off (∼25°) or 60% of the gait cycle (third rocker or double limb support). The second rocker occurs during the midstance phase of the gait cycle and the third rocker occurs during the terminal stance phase of the gait cycle. During terminal stance phase, the foot acts as a rigid lever for toe off. Finally, during early swing phase, the ankle joint rapidly dorsiflexes which allows the foot to clear the floor and positions the foot for the next heel strike [6], [8], [12], [13], [14], [15]. Root et al. [16] as well as several other authors [13], [17] also have described foot and ankle motion during gait in relation to the pronation/supination cycle.
The contact area and distribution of force within the ankle joint changes throughout the gait cycle. Stauffer et al. [9] reported that forces transmitted across the ankle joint reach a peak at approximately 40% of the gait cycle. This is the period when transition from dorsiflexion to plantarflexion occurs and forces have been shown to reach as much as 4.5 times body weight [6], [9], [10]. In a normal ankle joint, as the amount of plantar flexion increases and contact area decreases, the plantar pressure (force per unit area) also increases [3]. To compensate for pain caused by forces transmitted across a pathologic ankle joint, the patient may adjust aspects of their gait pattern to redistribute these forces.
In previous studies, dynamic foot and ankle motion data was obtained using mathematical modeling, cadaveric specimen measurements, or less sophisticated methods of gait analysis [9], [18], [19], [20], [21]. Most of these studies treat the ankle joint complex as a single articulation and may exclude other foot segments. Stauffer et al. [9] investigated motion analysis in normal, diseased and prosthetic ankle joints. These authors found cadence and ankle motion in the sagittal plane (dorsiflexion/plantarflexion) to be reduced in diseased and prosthetic ankle joints as compared to normal. Mazur et al. [20] examined 12 patients following ankle arthrodesis (fusion of the tibiotalar joint) using a three marker system to model the ankle–foot complex. The authors reported dorsiflexion/plantarflexion motion during gait in the fused ankles compared to normal and decreased walking speed, with cadence unchanged from normal. Both studies ignored motion distal to the ankle joint and only addressed motion in the sagittal plane. Buck et al. [21] analyzed the gait pattern of 19 patients following ankle arthrosis (fusion of the tibiotalar joint) using three-dimensional electrogoniometers mounted on the distal tibia and heel of a shoe. Foot switches were also used to obtain temporal parameters. This study showed a reduction in sagittal motion during gait following ankle arthrodesis as well as diminished varus-valgus motion in the coronal plane. Westblad et al. [18] and Arndt et al. [19] in two separate studies compared skin markers to markers placed directly into bone using intracortical pins and found that superficial markers provided an acceptable kinematic representation of dorsiflexion/plantarflexion (sagittal motion).
Wu et al. [22] recently examined foot and ankle motion following ankle arthrodesis (fusion of the tibiotalar joint) using a three-segment rigid body. This study compared 3D kinematics from 10 patients following ankle arthrodesis with 10 normal subjects. Temporal parameters were obtained using pressure sensitive foot switches attached to the heel, first and fifth metatarsals, and hallux. The results of this study agreed with the previously reported findings with increased stance phase and generalized decreased range of motion in the sagittal, coronal, and transverse planes.
Johnson et al. [13], [23] described normal foot and ankle motion using the Milwaukee Foot Model (MFM), a four segment rigid-body model described by Kidder and coworkers [23], [24], [25], [26] The four segments described in this foot model are tibia/fibula, hindfoot, forefoot, and hallux. Three-dimensional kinematic assessment of these segments were performed on five normal adult subjects; surface marker data was referenced to bony landmarks via anteroposterior, lateral, and modified coronal hindfoot alignment [25] radiographs.
Currently the effect of degenerative joint disease on gait is poorly understood. To our knowledge, this is the first study to quantitatively describe the kinematic changes during gait as a result of ankle arthritis. This information provides a quantitative baseline to better understand the dynamics of this deformity and accurately measure disease progression. The purpose of this study is to examine the characteristics of foot and ankle motion during gait of patients with ankle arthritis prior to surgical intervention. We hypothesize that reduced foot–ankle ROM will be observed in multiple segments and in multiple planes during the gait cycle. The Milwaukee Foot Model, including radiographic assessment, was employed for kinematic analysis [13], [24], [25], [26], [27].
Section snippets
Materials and methods
This is a cross sectional, descriptive study consisting of 34 pre-operative patients (35 ankles) diagnosed with ankle arthrosis (“DJD”) and 25 patients with no known ankle pathology (“Normal”). All DJD patients were evaluated by the same surgeon. The ankle arthrosis (Table 1, Table 2) patient population was collected between the years 2000–2004. This group consisted of 19 males and 15 females (mean age 56 years, range 32–75 years old). The Normal population was drawn from a previously collected
Results
Studies [28], [29], [30] have shown that gait pattern matures by age 7. In the current study, both patient populations have reached a mature gait pattern so the 15-year age difference between groups would not be expected to result in altered gait patterns.
Unless otherwise specified, all changes discussed were significant at p < 0.001.
Discussion
Several authors have attempted to describe the effects of treatment of degenerative joint disease (arthrodesis or joint replacement) on motion about the ankle joint [9], [11], [18], [19], [20], [21], [22]. Currently there have been no quantitative studies on pre-operative DJD kinematics. Examination of the dynamic differences between motion of patients with DJD of the ankle and normals helps to characterize the pathomechanics of this condition. While not currently available, anticipated
Conclusion
This study presents multi-segment foot and ankle kinematic data calculated from a population of 34 subjects with DJD. We found significant decreases in temporal–spatial parameters (walking speed, cadence, and stride length). There was also decreased triplanar motion of the hindfoot and forefoot as well as decreased tibial (sagittal) motion compared to normal. This assessment of patient results reveals quantitative characteristics in a population ambulating with structural deformity and severe
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