AN EXPLORATION OF FOOT KINEMATICS AND LOWER EXTREMITY NEUROMUSCULAR FUNCTION IN MIDDLE-AGED PATIENTS WITH PLANTAR HEEL PAIN

Abstract

Plantar heel pain (PHP) afflicts 7.3% of adults over the age of 35, most commonly those aged 45–64, and has an annual treatment cost of $284 million in the United States. PHP is also associated with significant personal costs such as pain-related interference with work-related activities, low physical activity, and decreased health-related quality of life (HRQOL). PHP is an injury caused from mechanical overload which induces inflammation, and ultimately degeneration, at the origin of the plantar aponeurosis. It is signified by pain felt in the heel especially after the first few steps of the morning or by prolonged standing. Although mechanical overload of the plantar aponeurosis is considered the primary mechanism of PHP, the difference within the foot and lower extremity during gait in middle-aged adults with PHP is poorly understood. Therefore, the purposes of this exploratory study were to: identify the kinematic (Chapter 2) and neuromuscular (Chapter 3) gait differences within the foot and lower extremity in middle-aged PHP patients; and determine the association between the gait mechanics, PHP risk factors, and PHP in middle-aged adults (Chapter 4). We hypothesized that patients with PHP would demonstrate: (1) foot and lower extremity differences during loading response, mid/terminal-stance, and push-off phases of gait, (2) lower extremity neuromuscular difference during the early and late stance phases of gait, and (3) the inclusion of gait variables associated with mechanical overload of the plantar aponeurosis with the primary risk factors would improve the ability to predict PHP in middle-aged adults. A convenience sample of 60 adults (aged 45–64; PHP: n = 30; controls: n = 30) participated in the study. All participants completed a series of health and activity questionnaires (SF-36, IPAQ, FAAM, MFPDI), followed by lower limb strength and range of motion (ROM) assessment. Participants then completed barefoot walking trials at self-selected and standardized speeds that were captured using a 14-camera motion capture system and three floor embedded force plates. Joint kinematics were calculated for the hip, knee, and foot. During the walking trials, electromyography (EMG) was recorded from five lower limb muscles. Following walking trials, the kinematic and force plate data were used to calculate stance phase hip, knee, and ankle net joint powers. PHP participants exhibited greater body mass, lower physical activity and HRQOL scores (SF-36, IPAQ, FAAM), and higher pain and disability ratings (MFPDI). They also demonstrated reduced ankle dorsiflexion passive ROM, decreased muscle strength (hip extensors, knee flexor, ankle dorsiflexor, ankle evertor, and hallux flexors), and slower preferred walking speed. Kinematic analysis revealed significant foot ROM differences in the PHP group during the loading response (reduced rearfoot complex lateral rotation, decreased medial midfoot dorsiflexion, increased medial forefoot dorsiflexion) and midstance-terminal stance (reduced rearfoot complex dorsiflexion) subphases. Most of the differences were contrary to the hypothesis and may have been compensatory or pain-avoidant strategies to reduce the plantar aponeurosis strain and pain at impact and when pushing off. Patient reports of heel pain during gait supported this interpretation, with 90% reporting pain at initial contact and during push-off, and 80% reporting heel pain during the gait trials. With respect to neuromuscular function, there were no significant differences in mean lower extremity muscle activation amplitudes between the PHP and uninjured participants, but the PHP patients did exhibit significantly lower peak eccentric plantar flexor ankle power. The peak occurred during the late mid/terminal stance subphase and may function to decrease plantar aponeurosis strain and pain as the activity of the plantar flexors transition from eccentric to concentric activity. Logistic regression analysis examined associations between key kinematic, neuromuscular, and intrinsic/extrinsic risk factors and PHP across six domains: gait kinematics, neuromuscular activation, joint ROM, muscle strength, physical activity, and BMI. Significant predictors of PHP included reduced rearfoot sagittal plane ROM during mid/terminal stance, reduced eccentric ankle plantar flexor power, decreased ankle dorsiflexion passive ROM, and lower physical activity levels. Muscle strength and BMI were not significantly associated with PHP. Collectively, these findings advance the understanding of PHP related gait dysfunction and provide potential outcome measures for interventions aimed at modifying foot mechanics and neuromuscular patterns in patients with PHP. Future prospective studies will be needed to determine if the changes identified in the current study are the cause, or effect, of PHP.