Kinematics During Landing

For Medical Students

The Principle

A body falling has energy that has to go somewhere when it meets the ground. The limb absorbs it by flexing against muscle control.

Flexing further over a longer time reduces the peak force, because the same energy is absorbed more gradually. A stiff landing concentrates it instead.

Dropping onto a straight leg and dropping into a crouch are the two extremes. The second is mechanically much gentler on the joint.

At the Knee

The knee contacts the ground in relatively little flexion and then flexes rapidly. The rate of flexion is what distinguishes landing from every other task.

The total flexion reached is the absorbing distance. A soft landing reaches considerably more flexion than a stiff one.

Landing is rarely purely sagittal. The knee commonly moves into some valgus and some rotation at the same time, particularly when the landing is unbalanced or on one leg.

That combination of flexion, valgus and rotation is the kinematic pattern described in non contact cruciate injury. 3.2.9 covers coupled motion.

What Changes It

Landing height and body mass, which set the energy to be absorbed.

Technique, which is the amount and timing of flexion and is trainable.

Fatigue, which reduces the flexion achieved and therefore the absorption.

One leg against two, since a single leg landing doubles the share the limb takes.

Clinical Relevance

A landing can be made mechanically safer by changing how it is performed, which is the mechanical basis of warm up and technique programmes. 3.1.5 covers injury prevention.

The knee that collapses inwards on landing is showing the pattern associated with cruciate injury rather than the injury itself.

Landing tasks are used in return to sport testing because they load the knee in the way injury occurs.

Sport specific application belongs to 3.15, and management to Section 6.

MRCS Level

The Principle

Describe landing by its absorbing capacity rather than by its range. The relevant quantities are the flexion achieved, the time taken and the resulting peak force.

Energy absorption is distributed between the hip, knee and ankle, and the distribution is trainable. A limb that absorbs more proximally loads the knee less. 3.4.8 covers absorption.

The kinematic pattern associated with injury is usually described as dynamic knee valgus: hip adduction and internal rotation, knee valgus and tibial external rotation, with relatively little knee flexion.

At the Knee

Peak knee flexion and the time to reach it together determine the loading rate, which is the quantity that distinguishes a stiff landing.

The knee is in early flexion at the moment of peak force, which is where the cruciate is least protected by congruence and most loaded by quadriceps contraction. 3.7 covers anterior cruciate biomechanics.

Coronal plane motion at the knee is largely a consequence of hip and trunk position rather than of knee muscle action, which is why prevention programmes train the hip.

Single leg landing produces greater coronal and transverse motion than double leg, which is why testing uses it.

What Changes It

Hip abductor and extensor function, which control the coronal and transverse position the knee lands in.

Trunk control, which moves the centre of mass relative to the knee.

Fatigue, which reduces flexion and increases coronal motion in a measurable way.

Footwear and surface, which change the loading rate independent of technique.

How It Is Measured

Drop vertical jump with optical capture and force plates is the standard laboratory assessment and measures a prescribed task.

Two dimensional video with frontal plane projection angle is used in practice and confounds valgus with rotation, which is a known limit rather than a fault.

Single leg hop tests measure performance and symmetry rather than kinematics, and they are what return to sport criteria mostly use.

Loading rate requires a force plate, so technique can be assessed by video and loading cannot.

Clinical Relevance

Assess the hip and trunk when a knee lands in valgus, since the knee position is largely set proximally.

Test under fatigue where the activity involves it, because the pattern worsens.

Read a video frontal plane angle as a screening measure rather than a measurement of valgus.

Use landing tasks in return to sport assessment because they reproduce the injury loading.

FRCS Level

At the Knee

Treat landing kinematics as a modifiable risk factor and as an imperfect predictor. Conventional teaching holds that the pattern is associated with injury and that screening an individual from it has limited predictive value.

The mechanical argument for prevention programmes rests on changing the pattern, and the evidence for them rests on injury rates rather than on measured kinematics.

After reconstruction, asymmetrical landing kinematics persists in many patients with normal laxity, which is a kinematic deficit with a functional consequence. 3.11 covers the anterolateral constructs.

What Changes It

Neuromuscular training, which is the modifiable element and the basis of prevention.

Graft choice and donor site, which affect the muscle available for absorption.

Bony morphology, slope and lateral plateau shape, which change what a given landing does to the joint.

Fear and confidence, which change movement strategy independently of capacity.

How It Is Measured

Drop jump analysis gives the kinematics and the loading, in a laboratory and in a prescribed task that is not the sporting movement.

Prospective cohort studies linking screening measures to subsequent injury are where the predictive value question is answered, and the reported performance is modest.

Limb symmetry indices measure performance and are the usual return to sport criterion, with a recognised ceiling effect when both limbs deconditioned.

No measurement identifies an individual who will reinjure, which is the limit worth stating in counselling.

Clinical Relevance

Prescribe neuromuscular training on the evidence of injury rates rather than of kinematic change.

Expect asymmetrical landing kinematics to persist after reconstruction with normal laxity.

Interpret limb symmetry against a preinjury or uninjured comparator where one exists, given the ceiling effect.

State that screening does not identify the individual at risk, while the population association stands.