Quenn RM, Attarian DE, Bolognesi MP, Butler RJ. Bilateral symmetry in lower extremity mechanics during stair ascent and descent following a total hip arthroplasty: A one-year longitudinal study. Clinical Biomechanics, 2015, 30:53-58.
This study captured kinematic and kinetic data on 42 patients on 3 different occasions: pre-operatively, 6 weeks post-operatively, and 1 year post-operatively while climbing up and down stairs. This blog will focus on the data during ascent comparing the operated and non-operated limbs across the 3 data collection intervals.
The authors reported hip motion and muscle moments in the sagittal and frontal planes. There were deficits identified when comparing the surgical limb to the non-surgical limb prior to surgery. In analyzing the surgical limb characteristics over time, for most of the measured variables there was no difference between how the patients climbed stairs pre-operatively compared to the 6-week interval. The statistically significant differences occurred between 6 months and 1 year. Although this is not surprising, the nature of the changes can provide guidance for post-operative rehab programs in order to facilitate better stair climbing and better quality of living.
In the sagittal plane, the amount of hip flexion used to ascend the stairs decreased, while the amount of peak extension increased. The moments created by the hip extensor muscle increased. There are 2 complementary explanations for this. With weak hip extensors, the subjects in this study may have flexed the operated hip more to make stair ascent easier. The flexed position moves the center of mass forward, but it also lengthens the hip extensor muscles. In a lengthened position, the extensor muscles can generate more torque. As the hip extensors gain strength, the need for flexion decreases and the greater extensor torque from the muscle will drive the hip into a more extended position.
This knowledge that increased hip extensor strength facilitates improved function is not surprising, but it does provide strategies for reducing the time for this improvement to occur. There are many training movements (actions) that require the hip extensors to activate. Squatting, lunges with the non-operated leg, and lunges with the operated leg will produce the hip flexion required to activate the hip extensors. Certain lunges would be chosen that create not only hip flexion, but also hip adduction and hip internal rotation. All 3 of these motions will lengthen, activate, and load the posterior-lateral hip muscles. This includes all of the gluteal muscles, the hamstrings, and the adductors. All posterior-lateral hip muscles work in all 3 planes rather than having isolated functions in one plane as some textbooks would suggest.
Recognizing that reaching with the arms can lengthen the muscles (and enhance the torque production), the actions of squatting or lunging with either leg would be coupled with bilateral or unilateral arm reaches in the 3 planes to “turn on” the muscles. This torque enhancement tweak mimics what the patients demonstrated at 6 weeks post-operatively. Once the posterior-lateral hip muscles gain strength, the enhancement created by the reach in each plane would be reduced. This reduction in reaching makes the kinematics of stair ascent more authentic. Following the Applied Functional Science® (AFS) strategy of Tweaking In and Tweaking Out, the direction of the arm reach can eventually be reversed which places the posterior-lateral hip muscles at a disadvantage thereby increasing the challenge to the hip and the rest of the lower extremity.
The progression from more hip flexion to less, and the progression from a less to a more extended hip position documented in this study demonstrates the body’s ability to use resources in order to accomplish a task. As the resources change (greater extensor muscle torque), the system modifies the coordination of parts. The process of tweaking the rehabilitation movements in all 3 planes to facilitate this progression is at the foundation of all Gray Institute® courses.