Kinematics During Stair Climbing

For Medical Students

The Principle

Stairs ask the limb to raise or lower the whole body over a fixed step height, which walking on the level does not.

Ascent is concentric work: the muscles shorten to lift the body. Descent is eccentric: the muscles lengthen under load to lower it.

Eccentric control is the harder task and it is where a weak or painful knee fails first, which is why patients describe stairs down before stairs up.

At the Knee

Conventional teaching gives peak knee flexion on stairs as roughly 80 to 90 degrees, considerably more than walking on the level.

On ascent the knee flexes to clear the step, then extends under load as the body rises over the planted foot.

On descent the knee is loaded in flexion while the body lowers, and it reaches its greatest flexion under load at the moment the trailing foot leaves the step.

Both are closed chain tasks on the supporting limb, so the hip and ankle share the work. 3.3.3 covers the chain.

What Changes It

Step height, which sets the flexion required. A deeper step asks for more.

Speed and whether a handrail is used, both of which change the share the knee carries.

Quadriceps function, which is the eccentric brake on descent.

Pain, which reduces the flexion the patient will accept under load.

Clinical Relevance

Ask about stairs separately in each direction, because the two directions test different things.

Difficulty descending points at eccentric quadriceps control and at loaded flexion. Difficulty ascending points at strength through range.

Patellofemoral symptoms commonly appear on stairs before they appear on the level, because the flexion and the load are both greater.

Stairs are a practical functional measure, since they need more range and more control than level walking.

MRCS Level

The Principle

Separate the two directions in the description as well as in the history. Ascent and descent share a range and differ in the type of muscle work and in the timing of peak load.

Peak knee extensor moment on stairs is greater than on the level, and it occurs at a greater flexion angle, which multiplies the joint loading. 3.4.5 covers moments.

The combination of a large flexion angle and a large extensor moment is what makes stairs the discriminating everyday task for the patellofemoral joint.

At the Knee

Peak flexion of roughly 80 to 90 degrees places the knee in the part of the range where rotation and translation are greatest. 3.3.8 covers the zones.

Patellofemoral joint reaction force rises with both the quadriceps force and the flexion angle, and stairs raise both at once. 3.12 covers the joint.

Contact on the tibiofemoral surfaces is further posterior than in level walking, so the loaded area differs as well as the magnitude.

Descent loads the knee in flexion with the limb decelerating, which is the closest everyday task to a controlled landing. 3.3.13 covers landing.

What Changes It

Step geometry, which varies between buildings and is a real source of variation in reported figures.

Handrail use, which reduces the limb's share substantially and is frequently unrecorded.

Quadriceps strength and endurance, which determine eccentric control on descent.

Patellar height and trochlear morphology, which set how the rising patellofemoral load is distributed.

How It Is Measured

Instrumented staircases with force plates in the steps are the laboratory method, and they fix a step geometry that may not match the patient's.

Optical capture on a standard stair rig measures the kinematics, over a few steps.

Timed stair tests measure performance rather than kinematics and are what is usually available clinically.

Handrail use and step height are the two variables most often unreported, which limits comparison between studies.

Clinical Relevance

Record the direction, the step height and whether a handrail was used when documenting stair ability.

Expect patellofemoral pathology to present on stairs, given the simultaneous rise in angle and quadriceps force.

Test eccentric quadriceps control when descent is the problem.

Treat a timed stair test as a performance measure rather than a kinematic one.

FRCS Level

At the Knee

Treat stair function as a discriminating outcome measure, since it needs more range and more eccentric control than the tasks most patients recover first.

The anterior knee pain that follows patellofemoral overload presents on stairs, which is a loading argument and is why stair questions appear in most outcome scores.

Mid to deep flexion loading on stairs is the condition that exposes a mid flexion instability or an unfavourable contact path. 3.3.8 covers mid flexion.

What Changes It

Patellar height and trochlear geometry, native or reconstructed, which set the patellofemoral load distribution.

Component position and joint line in replacement, which change the extensor lever arm through the loaded range.

Tibial slope and alignment, which change the loading the posterior contact sees.

Quadriceps capacity, which is modifiable and is frequently the limiting factor rather than the mechanics.

How It Is Measured

Outcome scores include stair items and measure the patient's account rather than the mechanics.

Instrumented stair analysis quantifies moments and kinematics in a laboratory and in a fixed step geometry.

Fluoroscopic step up studies give bone level kinematics for a single step, which is the method behind several arthroplasty kinematic comparisons.

No clinical measurement separates quadriceps capacity from mechanical restriction on stairs, which is where examination decides.

Clinical Relevance

Use stair function rather than level walking when judging whether a knee has recovered.

Investigate anterior knee pain on stairs as a patellofemoral loading problem first.

Consider mid flexion instability in a replaced knee whose only complaint is stairs.

Exclude quadriceps weakness before attributing stair difficulty to the mechanics.