Anthropometrics Measurement: Inter-Malleoli Distance

Inter-malleoli distance is a simple standing measurement used to record the distance between the ankles when the knees are together. It is most commonly used as a practical measure of ankle separation in people who appear to have a knock-kneed lower-limb alignment, also known as genu valgum.

This measurement can be useful in health, fitness, sport, workplace, rehabilitation and performance settings when lower-limb alignment needs to be documented objectively. It may also provide useful context when reviewed alongside gait, balance, squat mechanics, running, jumping, knee range of motion, hip range of motion, ankle range of motion and lower-limb strength results.

Inter-malleoli distance should not be used on its own to diagnose a condition or decide whether a person is ready for sport, work or activity. It is a simple alignment-distance measure. If a major, painful, progressive, one-sided or concerning alignment finding is present, the result should be interpreted within the appropriate professional scope and broader assessment context.

For Measurz, the main value is repeatability. Measure the same way each time, record the position and compare the result with the person’s own baseline or relevant clinical context.

What Is Inter-Malleoli Distance?

Inter-malleoli distance is the distance between the medial malleoli, or inner ankle bones, when the person stands with the knees together.

In practical terms, it measures the gap between the ankles when the inner knees are touching.

The result is usually recorded in centimetres.

Inter-malleoli distance is typically used when the knees touch but the ankles remain separated. This may describe a knock-kneed alignment pattern. If the ankles touch and the knees are separated, inter-condylar distance is usually the more relevant measurement.

Why It Is Used

Inter-malleoli distance may be used to:

• Record lower-limb alignment
• Measure the gap between the ankles in standing
• Track change over time
• Add context to gait assessment
• Add context to running, jumping or landing assessment
• Add context to squat or lower-limb movement assessment
• Support paediatric growth and alignment monitoring where appropriate
• Compare findings across repeated Measurz assessments
• Provide a simple objective value for progress reports
• Support communication with clients using clear measurable data

It is most useful when measured consistently over time or when used alongside other lower-limb assessment results.

What It Measures

Inter-malleoli distance measures the gap between the ankles when the knees are together.

It may provide useful information about:

• Ankle separation in standing
• Knock-kneed alignment profile
• Lower-limb alignment context
• Change from baseline
• Relationship to gait or movement findings
• Side-to-side visual asymmetry when combined with observation
• Growth or development context in children where appropriate

It does not directly measure:

• Bone structure with precision
• Tibiofemoral angle
• Hip strength
• Knee strength
• Ankle mobility
• Pain source
• Injury diagnosis
• Cartilage, ligament or meniscus status
• Readiness for sport or work
• Functional performance

Inter-malleoli distance is a simple clinical distance measure, not a complete lower-limb alignment analysis.

Equipment Required

To measure inter-malleoli distance in Measurz, you will need:

• Flexible non-elastic measuring tape, ruler or calliper
• Measurz app
• Flat standing surface
• Clear view of the knees and ankles
• Optional skin-safe marker
• Notes field for position, footwear and testing conditions

A rigid ruler or calliper may be easier than a flexible tape if the gap is small. A tape measure can still be used if applied carefully without bending or angling.

How to Measure Inter-Malleoli Distance

1. Prepare the client

Explain the purpose of the measurement clearly.

A useful explanation is:

“We are going to measure the distance between your ankles while your knees are together. This helps us record your lower-limb alignment and compare it over time.”

Ask the client to remove shoes where practical so knee, foot and ankle position can be seen clearly. If shoes must remain on, record this in Measurz.

Before testing, record:

• Footwear condition
• Standing position
• Any pain or discomfort
• Whether the person can stand comfortably
• Any major asymmetry
• Any reason the result may not compare directly with previous sessions

2. Position the client

Ask the client to stand upright on a flat surface.

The client should:

• Stand tall and relaxed
• Keep weight evenly distributed
• Bring the medial femoral condyles, or inner knees, together
• Keep the knees comfortably extended
• Keep feet pointing forward as much as practical
• Avoid forcing the ankles inward or outward
• Avoid twisting the legs to change the result

The position should be natural and repeatable.

3. Confirm the knees are together

Check that the inner knees are touching or as close together as comfortably possible.

Do not force the knees together if this causes pain or discomfort. If the knees cannot touch, record this clearly.

4. Identify the ankle landmarks

Identify the closest points between the inner ankles.

These are the medial malleoli.

The measurement should capture the shortest gap between the medial malleoli, not a diagonal or slanted distance.

5. Measure the distance

Measure the shortest distance between the medial malleoli.

A practical method is:

1. Keep the person standing with knees together.
2. Place the ruler, calliper or tape between the ankles.
3. Measure the shortest distance between the inner ankles.
4. Record the result in centimetres.

Avoid pressing into the skin or changing the person’s ankle or knee position while measuring.

6. Repeat if required

For improved confidence, repeat the measurement.

If values differ, check:

• Knee position
• Knee extension
• Foot direction
• Weight distribution
• Whether the person moved or rotated

Record the average of two close measurements or the most consistent value based on your protocol.

7. Save the result in Measurz

Enter the result into Measurz with clear notes.

Useful notes include:

• Inter-malleoli distance value
• Measurement unit
• Standing position
• Knees together
• Shoes on or off
• Feet pointing forward or natural stance
• Symptoms if relevant
• Any positioning limitation
• Any reason the result may not compare directly with previous sessions

Scoring and Interpretation

The main score is inter-malleoli distance, usually recorded in centimetres.

A larger value means there is a larger gap between the ankles when the knees are together. A smaller value means the ankles are closer together.

Interpretation should consider:

• Age
• Growth stage
• Symptoms
• Whether the finding is one-sided or symmetrical
• Whether the distance is changing over time
• Gait pattern
• Foot position
• Hip range of motion
• Knee range of motion
• Ankle range of motion
• Lower-limb strength
• Balance and functional testing
• Sport or work demands
• Whether the person can stand comfortably

In children, knock-kneed alignment can be part of normal development and often changes over time. In adults, inter-malleoli distance may reflect body structure, previous injury, joint shape, long-term alignment or other factors.

Inter-malleoli distance should not be used as a stand-alone diagnostic measure.

Normative Data, Benchmarks or Reference Values

There are no simple universal norms for inter-malleoli distance that apply to everyone.

In children, some clinical references use less than 8 cm as a broad guide for inter-malleoli distance, but this depends on age and development. It should not be treated as a universal adult standard.

For most Measurz users, the most useful comparisons are:

• The client’s own baseline
• Change over time
• Whether the finding is symmetrical or one-sided
• How the result relates to gait, squat, balance, hop, strength and range of motion findings

If the distance is large, painful, worsening, one-sided or associated with functional concerns, it should be interpreted within the appropriate professional scope and broader assessment context.

Reliability and Validity

Inter-malleoli distance can be reliable when measured consistently.

Reliability improves when:

• The same standing position is used
• The knees are placed together the same way
• Foot position is consistent
• The knees are comfortably extended
• The same measuring tool is used
• The same landmark is used
• The same professional performs the measurement
• The same unit is recorded
• Notes are entered clearly in Measurz

Inter-malleoli distance is valid as a simple measure of the ankle gap in standing. It does not replace more detailed lower-limb alignment assessment, tibiofemoral angle measurement or imaging when those are required.

Common Errors and Limitations

Common errors include:

• Not keeping the knees together
• Measuring while the feet are turned out differently
• Letting the person shift weight to one side
• Measuring a diagonal rather than the shortest distance
• Forcing the knees or ankles into position
• Not recording footwear
• Not recording symptoms
• Comparing different standing positions
• Treating the result as a diagnosis

Limitations include:

• It does not measure bone angles directly
• It does not explain the cause of alignment
• It can be affected by foot position
• It can be affected by hip rotation
• It can be affected by knee flexion
• It does not measure strength or function
• It may need broader assessment if findings are concerning
• It should not be used alone for sport, work or treatment decisions

Practical Applications

Inter-malleoli distance may be useful for:

• Lower-limb alignment profiling
• Tracking ankle gap over time
• Paediatric lower-limb observation where appropriate
• Gait assessment context
• Squat and movement assessment context
• Running or landing assessment context
• Supporting lower-limb Measurz reports
• Client education using objective measurements

For example, if inter-malleoli distance changes over time and gait, squat or balance results also change, the combined data may provide more useful context than the distance measurement alone.

How to Record This in Measurz

When recording inter-malleoli distance in Measurz, include:

• Client name
• Test date
• Inter-malleoli distance value
• Measurement unit
• Standing position
• Knees together
• Shoes on or off
• Foot direction
• Symptoms if relevant
• Whether the finding is symmetrical or one-sided
• Any reason the result may not compare directly with previous sessions

For best results, use the same standing setup every time.

Measurz can help organise inter-malleoli distance alongside inter-condylar distance, leg length, knee girth, hip range of motion, knee range of motion, ankle range of motion, strength, balance, hop testing and gait observations.

FAQs

What is inter-malleoli distance?

Inter-malleoli distance is the distance between the inner ankles when the knees are together.

What does it help describe?

It helps describe a knock-kneed alignment pattern, also known as genu valgum.

How should the person stand?

The person should stand upright with the inner knees together, knees comfortably extended and feet pointing forward as much as practical.

What unit should I use?

Centimetres are usually most practical for Measurz recording.

Are there universal norms?

No. There are broad paediatric reference guides, but there are no simple universal norms for everyone.

Is inter-malleoli distance a diagnosis?

No. It is a measurement, not a diagnosis.

Should it be measured with shoes on or off?

Shoes off is usually preferred, but the most important point is to record footwear conditions and repeat them consistently.

Should it be used alone?

No. It should be interpreted alongside other Measurz assessment findings.

Key Takeaways

Inter-malleoli distance measures the gap between the ankles when the knees are together.

It is commonly used to describe knock-kneed lower-limb alignment.

There are no simple universal norms that apply to everyone.

In children, broad age-related reference guides exist, but they should be used carefully.

The result is most useful when compared with the client’s own baseline and broader assessment findings.

Inter-malleoli distance should not be used as a stand-alone diagnosis or readiness measure.

References

Alrayes, M. M., Alruwaili, F. N., Alotaibi, A. M., & Alghamdi, A. A. (2023). Towards a better understanding of knee angular deformities: Clinical assessment and radiographic considerations. Archives of Orthopaedic and Trauma Surgery. https://doi.org/10.1007/s00402-023-05153-w

Arazi, M., Öğün, T. C., Memik, R., & Kutlu, A. (2001). Normal development of the tibiofemoral angle in children: A clinical study of 590 normal subjects from 3 to 17 years of age. Journal of Pediatric Orthopaedics, 21(2), 264–267.

Espandar, R., Mortazavi, S. M. J., & Baghdadi, T. (2010). Angular deformities of the lower limb in children. Asian Journal of Sports Medicine, 1(1), 46–53.

Lohman, T. G., Roche, A. F., & Martorell, R. (Eds.). (1988). Anthropometric standardization reference manual. Human Kinetics.

Marfell-Jones, M., Stewart, A., & de Ridder, H. (2012). International standards for anthropometric assessment. International Society for the Advancement of Kinanthropometry.

Saini, U. C., Bali, K., Sheth, B., Gahlot, N., & Gahlot, A. (2010). Normal development of the knee angle in healthy Indian children: A clinical study of 215 children. Journal of Children’s Orthopaedics, 4(6), 579–586. https://doi.org/10.1007/s11832-010-0297-z