Knock knees

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Knock Knees (Genu Valgum)

Knock knees, or genu valgum, is a lower limb alignment deformity in which the knees angle inward (medially) while the feet and ankles remain apart. The term "knock knee" describes how the knees "knock" together during walking.

Left (a): normal alignment with the mechanical axis passing through the center of the knee. Right (b): genu valgum - knees deviate medially relative to the mechanical axis.

Definition and Anatomy

In genu valgum, the center of the knee joint lies medial to the mechanical axis (the line from the center of the femoral head to the center of the ankle). This causes unbalanced loading on the knee joint - specifically overloading the lateral compartment and placing abnormal tension on the medial structures. Over time, this asymmetric load leads to lateral compartment osteoarthritis and stretching of medial ligaments.

The femorotibial angle normally measures about 174° in the coronal plane. In genu valgum, this angle increases (more valgus). - General Anatomy and Musculoskeletal System (Thieme Atlas), p. 431

Measurement

The intermalleolar distance is the standard clinical measure:

With the medial sides of the knees touching, measure the gap between the medial malleoli
>5 cm intermalleolar distance is considered abnormal
An intercondylar distance >3 cm (with feet together) indicates genu varum by comparison

"In case of genu valgum or knock knee, the degree of deformity can be estimated by the intermalleolar separation present when the inner sides of the knees are kept in apposition." - S Das Manual on Clinical Surgery, p. (examination section)

Physiological vs Pathological

Physiological (Normal Developmental)

Up to 10° of genu valgum is normal in children up to 2 years of age
Maximum valgus is typically seen between ages 3-4 years
Up to 15° at the knee is common in children aged 2-6 years
Spontaneous correction to straight legs occurs by school age (around 7 years)
Cases within the physiologic range do NOT require treatment
Miller's Review of Orthopaedics 9th Edition, p. 278

Pathological

Knock knees that persist beyond age 6, are severe (>15° or intermalleolar gap >10 cm), or are unilateral warrant further evaluation.

Causes

Category	Examples
Physiological	Normal developmental variant (ages 2-6)
Metabolic bone disease	Rickets, renal osteodystrophy (most common pathological bilateral cause), endemic fluorosis
Skeletal dysplasias	Dwarfism (disproportionate short trunk type), Morquio syndrome, osteochondromas
Connective tissue	Osteogenesis imperfecta (repeated fractures), ligamentous laxity
Trauma/Infection	Proximal tibial fractures (Cozen phenomenon), infections stimulating asymmetric physeal growth
Degenerative	Lateral compartment OA (loss of lateral articular cartilage leads to secondary valgus)
Syndromic	Proteus syndrome, neurodevelopmental disorders with rickets
Hormonal	Klinefelter syndrome (tendency to genu valgum due to tall stature and ligamentous laxity)

Clinical Features

Knees touch/knock together while walking and standing
Ankles remain spaced apart when knees are together
Awkward or waddling gait
Difficulty standing with feet together
Knee pain (lateral compartment) in pathological cases
In children: may coincide with flat feet (pes planus)
Associated femoral anteversion and external tibial torsion can worsen the apparent deformity

Investigations

Standing AP radiograph of lower limbs (full-length) - to measure the mechanical and anatomical axes and femorotibial angle
Weight-bearing PA knee X-ray in adults to evaluate joint space (lateral compartment narrowing)
Blood work if metabolic cause suspected: calcium, phosphate, ALP, PTH, vitamin D, renal function
Urine keratan sulfate if Morquio syndrome suspected

Treatment

Conservative

Observation for physiological genu valgum (2-6 years of age) - resolves spontaneously
Treat underlying metabolic cause (e.g., vitamin D supplementation for rickets)
Conservative treatment is ineffective in pathological genu valgum - braces (e.g., used in osteogenesis imperfecta) are cumbersome and may promote ligamentous laxity

Surgical - Indications

Surgery is considered when:

Child is older than 10 years AND
Intermalleolar distance >10 cm OR valgus angulation >15°
Significant patellar instability secondary to genu valgum
Rapidly progressive deformity

Surgical Options

Option	Principle	Best For
Hemiepiphysiodesis (guided growth)	Temporary compression of medial distal femoral physis (Heuter-Volkmann law: compression inhibits growth)	Children with open physes; gradual correction by differential growth
Stapling / 8-plate	Hardware placed across medial physis to retard medial growth	Skeletally immature patients
Osteotomy	Bone cut at the site of deformity to realign mechanical axis	Skeletally mature patients; severe/fixed deformities
Distal femoral osteotomy	Corrects femoral component of valgus	Adults; also used for recurrent patellar instability in genu valgum (Moran et al., 2024)

Guided growth (hemiepiphysiodesis) relies on the Heuter-Volkmann principle that growth is inhibited by increased compression, and returns to normal once the hardware is removed. - Miller's Review of Orthopaedics 9th Edition

A 2025 systematic review (Hong & Loh, PMID 40966823) confirms guided growth is effective for pediatric knee alignment correction.

Complications of Untreated Genu Valgum

Lateral compartment knee osteoarthritis
Patellar instability and patellofemoral pain
Abnormal gait biomechanics
Medial ligament and capsule stretching
Compensatory foot deformities (fallen pedal arch)

Key Points Summary

Feature	Detail
Definition	Knees deviate medially; mechanical axis passes medial to knee center
Measurement	Intermalleolar distance (>5 cm abnormal)
Physiological age	2-6 years, peaks at 3-4 years, resolves by age 7
Most common pathological cause (bilateral)	Renal osteodystrophy
Surgical threshold	>10 years old, >15° valgus, or >10 cm intermalleolar gap
Preferred surgery in growing children	Guided growth hemiepiphysiodesis
Preferred in skeletally mature	Osteotomy at site of deformity

Cozens test

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Cozen's test lateral epicondylitis tennis elbow clinical examination procedure

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Cozen's Test (for Lateral Epicondylitis / Tennis Elbow)

What It Tests

Cozen's test is a provocative clinical examination used to diagnose lateral epicondylitis (tennis elbow) - a painful degenerative tendinopathy at the origin of the extensor carpi radialis brevis (ECRB) at the lateral epicondyle of the humerus.

Technique

Cozen's test (A) and Maudsley's test (B) demonstrated clinically

(A) Cozen's test - examiner grasps and stabilizes the forearm while resisting wrist extension. (B) Maudsley's test shown alongside for comparison.

Step-by-step procedure:

The examiner stabilizes the patient's elbow with one hand, with the thumb palpating/pressing over the lateral epicondyle
The patient makes a clenched fist and pronates the forearm
The patient then radially deviates and actively extends the wrist against resistance applied by the examiner's other hand
The elbow is kept in slight flexion or full extension depending on variation

Positive test: Reproduction of sharp pain at the lateral epicondyle (where the common extensor tendons originate)

Rosen's Emergency Medicine, p. 2349
S Das Manual on Clinical Surgery, p. 235

Clinical Image (from S Das Manual)

Cozen's test - S Das Manual on Clinical Surgery

Anatomical Basis

The test stresses the extensor carpi radialis brevis (ECRB) tendon at its origin on the lateral epicondyle. In lateral epicondylitis, histologic examination reveals angiofibroblastic hyperplasia (degenerative tendinopathy, not true inflammation despite the "-itis" name). The wrist extension and radial deviation against resistance maximally load this tendon origin, provoking pain. - Miller's Review of Orthopaedics 9th Ed

Diagnostic Accuracy

Metric	Value
Sensitivity	~74%
Specificity	Poor (low)
Clinical utility	Best used as part of a cluster of tests, not in isolation

Because of its poor specificity, Cozen's test should not be used alone - a positive result must be interpreted alongside history, tenderness to palpation just distal to the lateral epicondyle, and other tests. - Rosen's Emergency Medicine, p. 2349

Comparison with Related Tests

Test	Maneuver	Structures stressed
Cozen's	Resisted wrist extension + radial deviation with clenched fist	ECRB origin at lateral epicondyle
Maudsley's test	Active extension of the middle finger (3rd digit) against resistance, elbow extended	ECRB (via extensor digitorum communis)
Mill's manoeuvre	Passive wrist flexion with forearm pronated	Common extensor tendon stretched passively

All three reproduce pain at the lateral epicondyle when positive for lateral epicondylitis.

"Mill's manoeuvre i.e. the patient's wrist is passively flexed when his forearm is pronated. This gives rise to tremendous pain on the attachment of the common extensor tendons." - S Das Manual on Clinical Surgery, p. 235

Context: Lateral Epicondylitis (Tennis Elbow)

Affects the ECRB origin at the lateral epicondyle
Despite the name, <5% of patients actually play tennis - more common in workers doing repetitive wrist extension (screwdrivers, wrenches, assembly line)
Prevalence in the workforce: up to 14.5%
Symptoms: dull ache along the lateral elbow, worsened by grasping, twisting, turning door handles, or pouring
Tenderness just distal to the lateral epicondyle over the ECRB origin is the most reliable finding on palpation
Treatment: conservative first (rest, NSAIDs, physiotherapy, counterforce bracing); corticosteroid injections have no clear long-term benefit; surgery (open or arthroscopic debridement) for recalcitrant cases - Miller's Review of Orthopaedics 9th Ed

Note on the "Cozen Phenomenon" (Different Context)

The term "Cozen" also appears in orthopaedics in a different context: the Cozen phenomenon refers to progressive valgus deformity (knock knee) following a proximal tibial fracture in children - this is a separate entity and should not be confused with Cozen's test for tennis elbow. - Campbell's Operative Orthopaedics 15th Ed 2026

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