The Foot Intrinsics in Lateral Knee Pain After Tennis

Dear reader,

A few days ago I saw a young client in his early twenties who had started to feel pain on the lateral side of his right knee after playing tennis. At first glance, many people would look only at the knee and begin the usual local drama there. But the body is rarely so simple. The knee often suffers from a problem that was born lower down and then pushed upward through the chain.

On assessment, what stood out to me was a flat overpronated foot, together with very tight hamstrings and a very tight gluteus medius. That pattern immediately made me think about inhibition of the foot intrinsic muscles. In my view, this was not just a tennis knee story. It was a foot to knee to hip load sharing story.

The foot intrinsic muscles are the small muscles that begin and end within the foot itself. They are different from the larger extrinsic foot muscles, which start in the lower leg and send long tendons into the foot. The intrinsic muscles are the local organisers. They give the foot its fine control, subtle stability, toe coordination, arch support, and sensory responsiveness. They are small, yes, but biomechanically they behave like intelligent engineers working quietly underneath the body.

These muscles are arranged in layers. In the first layer we find abductor hallucis, flexor digitorum brevis, and abductor digiti minimi. Abductor hallucis helps support the medial longitudinal arch and stabilises the big toe side of the foot. Flexor digitorum brevis helps flex the lateral four toes and contributes to grounding and forefoot control. Abductor digiti minimi supports the lateral border of the foot and helps stabilise the little toe side.

In the second layer sit quadratus plantae and the lumbricals. Quadratus plantae helps correct the pull of flexor digitorum longus so the toes flex with better direction and less chaos. The lumbricals help control the metatarsophalangeal joints and interphalangeal joints, assisting fine toe coordination during stance and push off.

In the third layer we find flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis. Flexor hallucis brevis helps stabilise the big toe during propulsion and supports the medial forefoot. Adductor hallucis helps maintain transverse arch integrity and stabilises the big toe during stance and push off. Flexor digiti minimi brevis assists the little toe and lateral forefoot stability.

In the fourth layer are the dorsal and plantar interossei. These small but crucial muscles control toe spreading and toe approximation, improve forefoot stability, and help the foot adapt to subtle changes in the ground. Together, all these muscles make the foot more than a passive platform. They turn it into an active sensory and mechanical base.

From an evolutionary point of view, these muscles matter enormously. The human foot did not evolve merely to fit into shoes, stand on polished floors, and rush across pavement between office, gym, and sofa. It evolved for variable terrain, barefoot adaptation, unstable natural surfaces, climbing, walking long distances, changing direction, and responding constantly to the texture of the earth. The intrinsic muscles helped the foot behave as a responsive tripod, a spring, and a stabiliser all at once. They supported arch integrity, helped distribute force, and allowed the body to transfer load upward with far better economy.

In natural conditions, the foot was asked to work. In modern conditions, the foot is often cushioned, confined, flattened, and underchallenged. That is one reason why I keep seeing intrinsics that appear sleepy, underused, and mechanically unconvincing. The foot still looks like a foot, but it is often no longer behaving like the full biological masterpiece it once needed to be.

When the intrinsic muscles are inhibited, the arch is more likely to collapse too easily during loading. In this client, that overpronated pattern likely reduced the foot’s ability to control the rate and quality of internal rotation travelling upward from the ground. Once the foot drops too easily, the tibia often follows into increased internal rotation. Then the knee is no longer receiving load through a clean, balanced line. The femur may drift into poorer control above it. The pelvis then has to negotiate the consequences.

This is where the gluteus medius becomes interesting. Gluteus medius is one of the key muscles responsible for frontal plane pelvic control and for helping stabilise the femur during stance. If the foot below is unstable and the femur begins to lose ideal alignment, gluteus medius often works harder to hold things together. Over time it can become tight, overactive, and fatigued. It tries to protect the chain from collapse, but in doing so it also tells us that the lower system is not sharing load well enough.

The hamstrings fit into this pattern too. When the lower limb is losing efficiency, the hamstrings often increase resting tension to help control deceleration and rotational forces. They become part stabiliser, part emergency assistant. Useful, but not elegant. When they stay tight, they can further disturb the rhythm between pelvis, femur, and tibia. Then the knee sits in the middle of a very poorly negotiated family argument.

Now place that body into tennis. Tennis demands acceleration, braking, side stepping, cutting, pivoting, and repeated changes of direction. It is unforgiving of a lazy foot. A foot with poor intrinsic support may still cope during ordinary walking or gym routines for a while, but tennis exposes weak links quickly. Every cut and push off asks the foot to absorb force, organise it, and send it upward with timing. If that first link is unstable, the whole chain becomes more wasteful.

That is why lateral knee pain in this case makes sense to me. I do not see the knee as the origin. I see it as the region that began protesting once the foot failed to provide a strong enough foundation and the hip began tightening to compensate. The lateral knee is often where the consequences become noticeable, especially when rotational control is poor and the body is repeatedly forced into high speed directional changes.

This is why foot intrinsics are not a minor anatomical curiosity. They are foundational for full chain balance. They help the foot maintain shape under load. They improve contact with the ground. They support the arches. They coordinate the toes during stance and propulsion. They assist force absorption. They contribute to balance, posture, and clean transfer of energy upward. Without them, the ankle becomes less organised, the tibia less controlled, the knee less protected, and the hip more burdened.

In the JANMI view, this matters deeply. The body is not a collection of isolated complaints. It is a connected load sharing system. The sole of the foot is the first conversation with gravity. If that conversation is clumsy, the knee and hip will eventually hear about it.

So in this young tennis player, the lateral knee pain was not just about the knee. It was a message from the full chain. The foot had likely lost some of its intrinsic authority. The hamstrings had tightened to help stabilise what the base was not controlling well enough. The gluteus medius had become tense trying to protect alignment higher up. The knee, caught in the middle, became the loudest voice in the room.

And that is often the modern tragedy of movement. We blame the part that hurts, while ignoring the part that forgot how to work.

This content is for educational purposes only and does not replace an individual assessment by a qualified professional.

Until next time,

Paulius