# Obstacle Crossing in Older Adults with Total Knee Arthroplasty at the Initial Swing Phase
###### Abstract  
After undergoing a total knee arthroplasty (TKA) procedure, patients are at a high risk of falling because they present with ineffective mobility within a complex environment, especially during obstacle crossing. Toe clearance (TC) is an important factor to quantify the risks of trip-related falls. The study aimed to investigate TC height and toe trajectory and joint kinematic changes occurring in the lower limb following TKA during obstacle crossing at the initial swing phase. Twenty TKA patients, including those in preoperative and postoperative stages (three and six months), performed obstacle-crossing tasks to compare their performance with 20 healthy controls. Participants walked at self-pace along an 8 m walkway with 2.5, 5, and 10 cm obstacles positioned along the center of the path. For each participant, body segment motions were traced using reflective markers and the kinematics of lower extremity, toe clearance, and gait parameters were analyzed using a 3D-motion analysis system. TKA patients had lower TC height and toe trajectory at six months, slower toe elevation than controls when swing toe crossed 5 and 10 cm obstacles (\(p<0.05\)), and decreased hip and knee flexion (\(p<0.05\)). These altered gait patterns with decreased TC height and toe trajectory were identified as tripping factors as the toe trajectory was close to the ground surface. TKA patients had acquired different lower limb kinematics to maintain adequate TC. At long-term follow-up, there was an increasing trend for patients to trip after surgery. Therefore, more focus is needed on the exercise prescription for rehabilitation programs to improve muscle strength and stepping control. Keywords:gait; kinematics; obstacle; toe clearance; total knee arthroplasty; tripping +
Footnote †: journal: Medical  
skills and are prone to trip-related falls [9]; their walking ability resulted in lesser total knee motion during gait, with lesser knee flexion during swing than the controls [10]. Interestingly, the rate of falling in TKA patients has been shown to range between 12% and 38%, with tripping on an object being the most common reason [11; 12]. The main cause of falls is followed by tripping or stumbling (21%) and slipping (3%) [13]. Tripping occurs when the foot clearance during the swing phase of gait is interrupted by an obstacle or a sudden change in surface level [14] and toe contact with the ground was influenced by a decrease in toe clearance. [15]. Inadequ toe clearance increases the chance of tripping while walking on uneven ground, contributing to falls [16], especially in persons with very fluctuating foot trajectories. Therefore, toe clearance is critical to determine the risk of tripping-associated forward falls [17; 18]. Walking on level ground (24% of all falls) and walking on uneven ground (24% of all falls) were the two most common activities among elderly individuals at the time of the fall [19]. Regarding walking on uneven ground, obstacle crossing is a multi-joint movement that requires accurate swing foot control and increased inter-joint coordination of swing legs [20]. There are a few examples in the literature demonstrating knee kinematics during various functional activities (e.g., level walking at different speeds, semi-squat, mid-squat, step ascent and descent, and sit to stand) three and six months, one year, or more following TKA [21; 22; 23]. These studies show significant decrease in the range of motion of the operated side during gait and walking speed, a deficit in strength, and altered movement patterns. These changes could lead to altered mechanical functions of the joint during walking [24]. One study indicated that knee OA patients had decreased knee flexion and increased ankle dorsiflexion when they swung the toe above the obstacles [25]. Another study reported that patients with TKA displayed a decrease in active knee flexion and an increase in hip hiking to compensate knee flexor work while crossing obstacles [26].