Knock Knees (Genu Valgum)

Definition and Anatomy

Measurement

• 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

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

Causes

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

• 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

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

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

What It Tests

Technique

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

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

Clinical Image (from S Das Manual)

Anatomical Basis

Diagnostic Accuracy

Comparison with Related Tests

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)

Patella Fracture - Clinical Examination

Overview

Mechanism of Injury (Relevant to Examination)

History

• Fall from standing height, direct blow to the anterior knee, or near-fall with forceful quadriceps contraction
• Anterior knee pain, swelling, bruising
• Difficulty weight-bearing or walking
• Inability to extend the knee (suggests extensor mechanism disruption)
• In high-energy trauma: ask about ipsilateral hip, femur, and ligamentous injuries (PCL injury in ~25% of operative patellar fractures)

Inspection

• Swelling of the anterior knee
• Bruising/ecchymosis over the patella
• Skin lacerations or abrasions over the patella - must raise suspicion for an open fracture or traumatic arthrotomy
• Position of the limb - patient often holds knee slightly flexed for comfort
• Inability to actively extend (extensor lag visible)

Palpation

• A tense, tender acute hemarthrosis is the most common finding in displaced fractures
• The absence of a large effusion with a palpable bony defect should raise concern for associated retinacular tears (the blood leaks out through the tear)

• A tender, palpable transverse gap/defect between fracture fragments is the hallmark finding of a displaced patella fracture
• Run the fingertip along the anterior surface of the patella - a step or gap indicates fragment separation

• Point tenderness over the patella
• In undisplaced fractures, tenderness may be the only finding

• Carefully palpate and inspect any overlying lacerations - even a minor abrasion may communicate with the joint

Functional Assessment (Most Important Step)

Extensor Mechanism Test

Critical caveat: The ability to extend the knee does NOT rule out a patella fracture - it only means the retinaculum is intact. Conversely, failure to extend means both fracture and retinacular disruption.

• Aspirate the hemarthrosis (knee joint aspiration)
• Inject local anesthetic into the joint
• Then reassess active extension

Special Tests / Additional Examination Steps

Saline Load Test (if open fracture suspected)

• Indication: any laceration or abrasion overlying the patella
• Technique: aspirate joint, then infuse 150 mL of normal saline into the knee joint
• Positive: saline egresses from the wound, confirming communication with the joint
• Methylene blue can be added to saline to improve detection
• A positive test mandates urgent irrigation and debridement in the operating room

Patellar Height Assessment (on lateral X-ray - Insall-Salvati ratio)

• Patellar tendon length : patella height = 1.02 ± 0.13 (normal)
• Ratio < 1 → patella alta → suggests patellar tendon disruption
• Ratio > 1 → patella baja → suggests quadriceps tendon disruption

Imaging

X-rays (standard views)

1. AP view - note vertical and horizontal fracture lines; inspect distal femur and proximal tibia for associated fractures
2. Lateral view - defines fracture pattern, assesses patellar height (Insall-Salvati ratio), and identifies extensor mechanism injury
3. Tangential/Axial (skyline) view - evaluates patellofemoral joint and articular surface

CT scan

• Recommended for comminuted fractures or when multiple fracture lines are present
• Better delineates articular incongruity and comminution (comminution is typically underestimated on plain X-ray)

MRI / Ultrasound

• If clinical uncertainty remains about extensor mechanism integrity (quadriceps tendon, patellar tendon continuity)

Classification (Descriptive)

Key Examination Summary

Post-Examination

• Splint the knee in slight flexion for comfort
• Apply ice and elevate
• Immobilize until definitive treatment
• Rockwood and Green's Fractures in Adults, 10th Ed 2025, p. 2997-3001