This study measured knee motion in three planes during common daily activities in 30 normal men using electrogoniometry. Activities included stair climbing, sitting, tying a shoe, and lifting an object with and without body-mechanics instruction. It also tested whether lower-extremity segment length correlates with the flexion required for each task.
The core clinical lesson: stop treating 90 degrees of knee flexion as the finish line for rehabilitation or arthroplasty outcomes. This data shows sitting needs 93 degrees, tying a shoe needs 106 degrees, and lifting correctly needs 117 degrees. A patient who plateaus at exactly 90 degrees will still struggle with these tasks.
A realistic functional target is closer to 110 to 117 degrees for male patients, and taller patients with longer limb segments need even more. The lifting finding has a practical corollary for back care: patients who are not coached to bend the knees substitute spine flexion and load the lumbosacral junction.
When full flexion cannot be achieved, teach compensations such as a higher chair, using the arms to rise, or flexing the uninvolved knee.
This study measured knee motion in three planes during common daily activities in 30 normal men using electrogoniometry. Activities included stair climbing, sitting, tying a shoe, and lifting an object with and without body-mechanics instruction. It also tested whether lower-extremity segment length correlates with the flexion required for each task.
The core clinical lesson: stop treating 90 degrees of knee flexion as the finish line for rehabilitation or arthroplasty outcomes. This data shows sitting needs 93 degrees, tying a shoe needs 106 degrees, and lifting correctly needs 117 degrees. A patient who plateaus at exactly 90 degrees will still struggle with these tasks.
A realistic functional target is closer to 110 to 117 degrees for male patients, and taller patients with longer limb segments need even more. The lifting finding has a practical corollary for back care: patients who are not coached to bend the knees substitute spine flexion and load the lumbosacral junction.
When full flexion cannot be achieved, teach compensations such as a higher chair, using the arms to rise, or flexing the uninvolved knee.