Is Knock Knees Allowed in NDA? 2026 Rules for Army, Navy & Air Force

Wing-by-Wing Decision Table

The table below shows how each wing of the armed forces treats knock knees (genu valgum) and the applicable thresholds for 2026.

What Is Genu Valgum (Knock Knees)?

Genu valgum is a lower-limb alignment condition where the knees angle inward toward each other when the legs are straightened. When the knees are touching, the ankles remain apart — this gap between the inner ankle bones is what the Service Medical Board measures.

In normal alignment, the centre of the hip, knee, and ankle fall on a straight line. In knock knees, the femoral condyles (lower end of the thigh bone) converge inward, shifting the mechanical axis of the leg. Mild knock knees are physiologically normal in children up to around age 7 and typically resolve by early teens. When it persists into adulthood or is structurally significant, it becomes relevant for military medical standards.

How the Intermalleolar Distance Is Measured

The candidate stands upright on a flat surface with both knees touching (knees together, feet as close together as possible). The examiner measures the horizontal gap between the internal malleoli — the bony prominences on the inner side of each ankle. This distance is the intermalleolar distance, the key measurement for assessing knock knees.

How Knock Knees Are Tested at the SMB

At the Service Medical Board (SMB), the physical examination for lower-limb alignment follows a standard protocol:

• Standing inspection: The candidate removes footwear and stands on a flat surface. The examiner observes the lower-limb alignment from the front — checking whether the knees converge inward relative to the hip and ankle.
• Knees together, measurement: The candidate is asked to place their knees together firmly. The examiner measures the gap between the internal malleoli (inner ankle bones) using a calibrated measuring instrument or tape measure.
• Functional gait assessment: The examiner may ask the candidate to walk normally to assess any functional gait abnormality caused by the knee alignment.
• Palpation: The knee joint is palpated for pain, swelling, or ligamentous instability, which would indicate a co-existing pathology.
• X-ray (if significant): In cases where the deformity is significant or the cause is unclear, standing X-rays of both lower limbs (long-leg alignment films) may be ordered to measure the mechanical axis deviation and assess bone structure.

Bow Legs (Genu Varum) — Rules & Thresholds

Bow legs (genu varum) is the opposite of knock knees: the legs bow outward, creating a gap between the knees when the feet are placed together. The measurement used here is the intercondylar distance — the gap between the inner surfaces of the knee joints (medial femoral condyles) when the candidate stands upright with feet together.

The key distinction between knock knees and bow legs is the measurement point: knock knees = gap at ankles (intermalleolar), bow legs = gap at knees (intercondylar).

Genu Recurvatum (Hyperextension of the Knee)

Genu recurvatum refers to hyperextension of the knee — the knee bending backwards beyond the neutral (straight) position. It is assessed by asking the candidate to stand with knees fully extended and measuring the degree of backward bend.

Related Lower-Limb Conditions — Full Table

The NDA medical board assesses several related foot and lower-limb conditions alongside knock knees. The table below summarises the key thresholds and outcomes.

NDA Navy — "Acceptable Defects on Entry" Explained

NDA Annexure B para 21 lists certain minor physical defects that are explicitly accepted at recruitment for the Navy, provided they do not cause functional limitation. The underlying philosophy is that these conditions — while deviating from ideal anatomical norms — are not expected to impair a sailor's operational effectiveness.

For knock knees, the relevant provision is para 21(a): knock knees with an intermalleolar gap of less than 5 cm are recorded in the medical file as an "acceptable defect on entry." This means:

• The candidate is accepted into Navy training despite the condition.
• The condition is documented — it does not disappear from the record.
• If the condition worsens or causes functional problems during service, it may be reviewed.
• The candidate must not have any other disqualifying condition alongside the knock knees.

Can Knock Knees Be Fixed Before the NDA Medical?

Mild physiological knock knees in adolescents often resolve naturally by late teens as bone growth completes. If you are 17–19 years old and have mild knock knees, your measurement may improve on its own without any intervention.

For structural knock knees (those that do not resolve spontaneously), the following options exist:

• Guided growth (children/early teens): An orthopaedic surgeon inserts a small implant that slows growth on one side of the growth plate, gradually straightening the leg. This is only possible while the growth plates are still open (typically before age 14–15).
• Corrective osteotomy (adults): A surgical procedure to cut and realign the bone. Recovery involves 3–6 months of rehabilitation and potentially longer before full functional restoration.

Practical Advice — Measure Yourself at Home

You can make a preliminary self-assessment of your intermalleolar distance before attending the SMB:

• Step 1: Remove your shoes and socks and stand on a flat, hard floor.
• Step 2: Stand upright with your knees touching each other as firmly as possible, feet pointed straight ahead.
• Step 3: Ask someone to measure the horizontal gap between the inner prominences of your ankle bones (the bony knobs on the inside of each ankle — the medial malleoli).
• Step 4: Take the measurement in centimetres at the widest point between the two inner ankles.

If you are in the borderline range (around 4–6 cm), seeing an orthopaedic surgeon for a formal measurement and functional evaluation before the SMB is advisable. A formal report from a specialist can support your case at the board.

Frequently Asked Questions

• Is knock knees allowed in NDA?

  It depends on the wing. NDA Navy accepts knock knees if the intermalleolar gap is less than 5 cm (listed as an acceptable defect on entry under Annexure B para 21(a)). NDA Air Force rejects candidates if the intermalleolar distance exceeds 5 cm for males or 8 cm for females. NDA Army treats knock knees as a limb deformity and assesses it case-by-case at the Service Medical Board.
• What is the knock knees limit for NDA Navy?

  NDA Navy accepts knock knees where the intermalleolar distance (gap between the inner ankle bones when knees are together) is less than 5 cm. This is explicitly listed as an acceptable defect on entry in Annexure B para 21(a) of the NDA notification.
• What is the knock knees limit for NDA Air Force?

  NDA Air Force (via AFCAT/NDA Air wing guidelines, para 25(g)(x)) rejects candidates whose intermalleolar distance exceeds 5 cm for male candidates or 8 cm for female candidates. Any measurement at or below these thresholds may be accepted, subject to functional assessment.
• How does the army check for knock knees at the medical board?

  At the Service Medical Board (SMB), the candidate stands upright with feet together and knees touching. The examiner measures the gap between the internal malleoli (inner ankle bones) using a calibrated instrument or measuring tape. In significant cases, X-rays of the knee and lower limb may be taken to assess the degree of angulation and rule out structural pathology.
• Can I join NDA Army with knock knees?

  NDA Army assesses knock knees on a case-by-case basis at the Service Medical Board. Unlike Navy (clear 5 cm threshold) and Air Force (clear 5/8 cm rejection threshold), the Army does not publish a single numerical cut-off. The SMB evaluates functional impact, severity, and any underlying cause. Mild physiological knock knees with no functional limitation may be accepted; significant deformity is likely to be rejected.
• What is the difference between knock knees and bow legs for NDA?

  Knock knees (genu valgum) means the knees angle inward and touch while the ankles remain apart — the intermalleolar gap at the ankles is measured. Bow legs (genu varum) is the opposite: the knees bow outward while the feet are together — the intercondylar distance between the knees is measured. NDA Air Force rejects bow legs where the intercondylar distance exceeds 7 cm.
• What is the bow legs (genu varum) limit for NDA?

  For NDA Air Force, bow legs are rejected if the intercondylar distance exceeds 7 cm. NDA Navy lists mild curvature (intercondylar distance up to 7 cm) as an acceptable defect on entry. For NDA Army, bow legs are assessed on a case-by-case basis at the SMB, similar to knock knees.
• Is hallux valgus (bunion) allowed in NDA?

  Hallux valgus (bunion) is rejected if the angle exceeds 20 degrees or if it is associated with a bunion, corns, or callosities causing functional limitation. Hallux rigidus (stiff big toe) is rejected in all cases regardless of severity, as it causes significant functional impairment during military service.

Related Guides

Sources

• NDA & NA Notification — Annexure B para 21(a)(b): Acceptable defects on entry — knock knees (intermalleolar gap <5 cm) and bow legs (intercondylar gap ≤7 cm) (page 59).
• AFCAT 02/2023 — para 25(g)(x)(xi)(xii): Air Force lower-limb standards — intermalleolar distance thresholds for knock knees, intercondylar distance for bow legs, and genu recurvatum criteria.
• NDA Notification Annexure B — Lower limb and foot disqualifiers: hallux valgus, hallux rigidus, hammer toe, polydactyly, club foot, ACL reconstruction, and ligamentous laxity.

This page is for informational purposes only and does not constitute medical or legal advice. NDA medical standards are subject to change with each official notification. Always refer to the most recent NDA notification and, where in doubt, consult a qualified orthopaedic surgeon and refer directly to the official notification published by UPSC.