Distal Femoral Physeal Injuries

Distal Femoral Physeal Injuries are relatively uncommon but HIGH STAKES injuries.

• Epidemiology:
  • Account for 1-5% of all physeal injuries.
  • Mean age 11-13 years (adolescent growth spurt).
  • Boys greater than Girls (higher energy mechanisms).
• Mechanism:
  • Hyperextension (popliteal artery at risk).
  • Varus/Valgus Stress (sports injuries, MVA).
  • Direct Trauma.

Physeal Anatomy

• The distal femoral physis is the largest physis in the body.
• It is undulating (mamillary processes interdigitate with metaphysis), providing some inherent stability but also predisposing to irregular arrest patterns.
• The physis is completely intracapsular (no perichondral ring protection medially and laterally near the collaterals).

Growth Contribution

• 70% of femoral length (approximately 1cm/year near peak growth).
• 35% of total lower limb length.
• Loss of even 1-2 years of growth equates to 1-2cm LLD.

Vascular Anatomy

• The popliteal artery is tethered by the genicular branches as it passes through the popliteal fossa.
• In hyperextension injuries, the artery can be stretched over the posterior metaphysis.
• Vascular injury rate: approximately 2% for displaced fractures.

The birth-injury scenario flags that in a neonate the epiphysis is unossified — worth developing, because this injury is radiographically occult and classically misdiagnosed.

• Why it is occult. At birth the distal femoral epiphysis is only just ossifying (a small ossific nucleus) and the separation is largely through cartilage, so a plain radiograph shows no obvious fracture line — only subtle displacement of the metaphysis relative to the barely-visible epiphysis.
• The classic mimics. A swollen, pseudoparalysed, irritable knee in a neonate is mistaken for septic arthritis of the knee, congenital knee dislocation, or a fracture elsewhere; the true diagnosis (physeal separation) is missed if the film is read as "normal".
• How to confirm it. Ultrasound is the key test — it shows the cartilaginous epiphysis displaced relative to the metaphysis (with an effusion) and needs no radiation; MRI or a gentle arthrogram are alternatives, and comparison with the other knee helps.
• Context and management. It follows a difficult (often breech) delivery, and — as with any unexplained infant fracture — non-accidental injury must be considered if the history does not fit. Management is gentle splinting in flexion; prognosis is excellent with rapid remodelling and low arrest risk (unlike the older child), so aggressive reduction is avoided.

Key Surgical Points

• Single reduction attempt preferred to minimize additional physeal damage.
• Avoid excessive periosteal stripping to preserve blood supply.
• If crossing the physis is unavoidable, use smooth wires and remove early.
• Document neurovascular status before and after reduction.

• Immobilization: Long leg cast for 6 weeks minimum.
• Weight Bearing: Non-weight bearing initially, then protected WB.
• Pin Removal: 4-6 weeks (smooth wires). Screws can be left in situ.
• Follow-Up Schedule:
  • Weekly X-rays for first 2-3 weeks.
  • 6-week X-ray (assess healing).
  • 6-month and 12-month X-rays (scanograms to assess growth).
  • Annual follow-up until skeletal maturity.

Phase 1: Immobilization (0-6 weeks)

• Long leg cast. Knee in 20-30 degrees of flexion.
• Non-weight bearing on affected limb.
• Encourage toe wiggling and calf pumps to prevent DVT.
• Hip and ankle ROM exercises (within cast constraints).

Phase 2: Early Mobilization (6-10 weeks)

• Cast removal at 6 weeks if healing confirmed.
• Hinged knee brace initially.
• Partial weight bearing progressing to full weight bearing.
• Active and passive ROM for the knee.
• Quadriceps and hamstring isometrics.

Phase 3: Strengthening (10-16 weeks)

• Progressive resistance exercises.
• Closed kinetic chain exercises (squats, leg press).
• Proprioception and balance training.
• Gait normalization.

Phase 4: Return to Activity (4-6 months)

• Sport-specific training.
• Full ROM and greater than 90% strength.
• Clearance by surgeon (confirm no growth disturbance).

• Growth Arrest: Occurs in 30-50% of cases, regardless of type.
• Type I/II: Still have significant arrest risk (25-35%).
• Type III/IV: Higher arrest risk (40-60%).
• Prognosis depends on: Quality of reduction, amount of growth remaining, and size of any physeal bar.
• Functional Outcomes: Generally good if LLD and angular deformity are managed.

Global epidemiology

• Distal femoral physeal fractures represent roughly 1-5% of all physeal injuries and under 1% of paediatric fractures, but carry disproportionate morbidity.
• Peak incidence is in adolescence (mean age 10-13 across published series), male predominant, typically from sport, road traffic or high-energy mechanisms.
• Clinically significant growth disturbance requiring secondary surgery occurs in around 5% across all lower-limb physeal fractures, but is concentrated in the distal femur — older single-centre distal-femur series report overall complication rates of 36-40%.

Side-by-side guidance (principles converge globally)

There is no major guideline disagreement: all converge on anatomical reduction, physeal-respecting fixation, urgent neurovascular assessment for displaced (hyperextension) patterns, and surveillance to maturity. Debate is confined to nuances (prophylactic pinning of non-displaced fractures, transphyseal screw use).

Registry and resource notes

• Paediatric physeal fractures are not captured by arthroplasty registries (NJR, AJRR, AOANJRR); evidence rests on single- and multi-centre cohorts rather than implant registries.
• High-resource settings: ready access to fluoroscopy, CT/MRI for bar mapping, EOS/low-dose scanograms for growth monitoring, and on-site vascular surgery for hyperextension injuries.
• Limited-resource settings: reliance on plain radiographs and clinical leg-length monitoring; physeal bar resection, guided growth and limb-reconstruction services may be unavailable, shifting practice toward contralateral epiphysiodesis or osteotomy for established deformity. Delayed presentation and missed neurovascular compromise are greater risks.

The topic states repeatedly that this physis has the highest growth-arrest rate of any physis and that it is "undulating" — here is why that architecture drives the risk.

• A deeply undulating physis, not a flat disc. Unlike the relatively flat physes of the distal radius or proximal humerus, the distal femoral physis has prominent mamillary processes that interdigitate with the metaphysis in all planes. This interlocking gives some intrinsic stability but means the growth plate is a complex three-dimensional surface, not a clean shear plane.
• The fracture cannot cleave cleanly. In a flatter physis a shear injury propagates through the mechanically weak hypertrophic zone / zone of provisional calcification, sparing the germinal (reserve and proliferative) cells. Across the undulating distal femur the fracture line is forced to cross the germinal and proliferative zones irregularly, directly injuring the growth-producing cells — so even a "benign" Salter-Harris I/II can leave a permanent germinal-layer injury and a bar.
• Highest stakes, fastest growth. Because this physis contributes about 70% of femoral (35% of limb) length at roughly 1 cm/year, any germinal-cell injury translates rapidly into leg-length discrepancy or, if the arrest is partial, angular deformity — which is why the arrest rate (30-50%) stays high whatever the Salter-Harris type, and why surgery does not abolish it (the damage is intrinsic to the injury).
• Practical corollary. This is the mechanistic basis for the topic's core messages: gentle single-attempt anatomical reduction (avoid adding iatrogenic germinal injury), physeal-respecting fixation, and mandatory surveillance regardless of fracture type.

• Prophylactic pinning of non-displaced fractures: High late-displacement risk argues for stabilisation, but many non-displaced fractures heal well in cast — practice varies and no randomised data exist.
• Does surgery reduce growth arrest? Adams/Arkader (2020) showed a lower surgical threshold did NOT lower the complication rate (36% vs 40%), suggesting arrest is largely intrinsic to the injury rather than treatment-modifiable.
• Transphyseal screw fixation: Smooth wires are preferred, but stable SH-II fixation sometimes requires metaphyseal screws; whether brief transphyseal smooth-wire passage independently worsens arrest is debated (Arkader noted a trend, not significance).
• Bar resection vs accept-and-reconstruct: For bars under ~25-50% with growth remaining, resection plus guided growth can restore alignment, but rebound deformity and unpredictable physeal recovery (Masquijo 2020) lead some to favour epiphysiodesis/osteotomy.
• Optimal imaging for arrest detection: MRI maps bars accurately but timing, cost and need for sedation in young children are unresolved versus serial scanograms.

Types of Arrest

• Complete Arrest: Entire physis stops growing. Results in shortening only (no angular deformity).
• Partial (Central) Arrest: Bar in the center. Causes shortening and may cause "tenting" of the physis.
• Partial (Peripheral) Arrest: Bar on one side. Causes angular deformity as the unaffected side keeps growing.

Evaluation

• Scanogram: Leg length measurement.
• MRI: Maps the physeal bar (location, size).
• Bone Age: Estimate remaining growth.

Management Options

• Bar less than 50%, Greater than 2 years growth remaining: Bar excision + fat/PMMA interposition.
• Bar greater than 50%, or Less than 2 years growth remaining: Bar excision will fail. Consider:
  • Contralateral epiphysiodesis (for LLD).
  • Limb lengthening (for significant LLD).
  • Corrective osteotomy (for angular deformity).
  • Guided growth (hemi-epiphysiodesis for angular correction if some growth remains).

What is the distal femoral growth plate? The distal femur (thighbone near the knee) has a growth plate that is responsible for 70% of the thighbone's growth. Injury to this growth plate is serious because it can affect how your child's leg grows.

Why is this injury different? Unlike most other growth plate injuries, the distal femoral growth plate has a HIGH chance (30-50%) of developing problems with growth, even if the treatment is perfect. This may lead to:

• One leg being shorter than the other.
• One leg growing crooked.

What are the treatment options if growth problems occur? If growth problems develop, your doctor may recommend:

• Surgery to remove the damaged area and allow growth to resume.
• Surgery on the opposite leg to slow its growth (so the legs end up the same length).
• Surgery to straighten a crooked leg.

What follow-up is needed? Your child will need regular X-rays for at least 2 years to monitor the growth plate. Please do not miss these appointments, as early detection of problems allows for better treatment.

Reduction Technique

• Apply longitudinal traction with the knee slightly flexed.
• For hyperextension injuries (posterior displacement of the distal fragment), flex the knee and push the distal fragment anteriorly.
• Avoid excessive force. One smooth reduction attempt is better than multiple aggressive attempts.

Pinning Technique

• Enter from the lateral and medial metaphysis, above the physis.
• Direct the wires across the fracture into the epiphysis.
• Diverge the wires for three-point fixation stability.
• Avoid the intercondylar notch (risk of ACL damage).
• Image in two planes (AP and lateral) to confirm position.

Avoiding Iatrogenic Damage

• Use smooth wires (not threaded).
• If threaded screws are used (for epiphyseal fixation), ensure they are parallel to the physis and do not cross it.
• Limit drill passes through the physis.
• Use small diameter implants.

Post-Reduction Checks

• Confirm neurovascular status immediately.
• Document pulses both before and after reduction.
• Obtain X-rays to confirm anatomical reduction.