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SUFE Pinning - In Situ Fixation with Single Central Screw

Comprehensive FRCS examination guide to in situ screw fixation for slipped upper femoral epiphysis (SUFE/SCFE), including Loder classification, Southwick angle measurement, screw positioning, and AVN prevention strategies

Core Procedure
intermediate
By OrthoVellum Medical Education Team

Reviewed by OrthoVellum Editorial Team

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High Yield Overview

SUFE IN SITU PINNING

Percutaneous Single Central Screw Fixation | Paediatric

Mnemonic

S-U-F-ESUFE - Risk Factors and Bilateral Risk

Memory Hook:20-40% develop bilateral SUFE - always image both hips at presentation and consider prophylactic pinning

Mnemonic

C-E-N-T-E-RCENTER - Screw Positioning Principles

Memory Hook:Posterior screw malposition risks posterior retinacular vessel injury - the main blood supply to the femoral head

Critical Danger Structures - SUFE Pinning

Posterior Retinacular Vessels

Main blood supply to femoral head arising from MFCA. Run along posterior-superior femoral neck. Highest AVN risk if damaged by posterior screw malposition. Protection: verify center-center on lateral view, avoid posterior cortex penetration.

Femoral Head Articular Cartilage

Subchondral bone penetration causes chondrolysis (acute cartilage necrosis). Presents 2-12 months post-op with stiffness and joint space narrowing. Protection: screw tip 5mm from subchondral bone on both AP and lateral views.

Physis (Growth Plate)

Multiple passes through physis increases trauma and chondrolysis risk. Inadequate thread engagement allows continued slip. Protection: single-pass technique, ALL threads across physis, partially threaded screw for compression.

Lateral Femoral Cutaneous Nerve

Emerges medial to ASIS, courses to anterolateral thigh. Risk with lateral thigh incision for percutaneous approach. Protection: incision distal to vastus ridge (more inferior), blunt dissection through muscle.

Absolute Indications:

  • All SUFE regardless of severity (prevents further slip)
  • Unstable SUFE: emergency surgery within 24 hours
  • Stable SUFE: semi-urgent surgery within days

Prophylactic Contralateral Pinning Indications:

  • Age less than 10 years (60% bilateral risk)
  • Endocrine/metabolic cause:
    • Hypothyroidism (50% bilateral)
    • Renal osteodystrophy (60% bilateral)
    • Growth hormone deficiency (30-50% bilateral)
  • Unable to reliably follow-up (remote, non-compliant)
  • Symptomatic contralateral hip without visible slip

Contraindications to In Situ Pinning:

  • None absolute (even severe slips pinned in situ by most)
  • Relative: severe slip greater than 50 degrees in unstable acute SUFE at experienced centre - consider modified Dunn procedure

Equipment

Essential Equipment:

  • Radiolucent fracture table (Jackson or OSI)
  • C-arm fluoroscopy unit
  • Cannulated screw set (7.0mm or 7.3mm partially threaded)
  • Guidewires (2.4mm or 2.8mm)
  • Cannulated drill bit (matching screw diameter)
  • Depth gauge
  • Power drill

Patient Setup:

  • Supine on fracture table
  • Affected leg in traction boot
  • Hip: 10-15 degrees flexion, 10-20 degrees abduction, neutral rotation
  • Contralateral leg abducted (scissor position)
  • Well-padded perineal post
  • C-arm positioned between legs for biplanar imaging

Critical Check: Confirm ability to obtain perfect AP and lateral views BEFORE prepping

Operative Technique

Step 1: Patient Positioning and Imaging Setup

Position supine on radiolucent fracture table. Apply gentle longitudinal traction through traction boot - DO NOT attempt forceful reduction (risks AVN). Hip position: 10-15 degrees flexion, 10-20 degrees abduction, neutral rotation (avoid internal rotation). Contralateral leg abducted widely for C-arm access.

Critical: Verify ability to obtain TRUE AP (femoral neck perpendicular to beam, lesser trochanter barely visible medially) and TRUE lateral (neck in profile, greater trochanter posterior) views before prepping.

Exam Pearl

EXAM KEY: Positioning for SUFE is NOT about reduction - it's about visualization. Gentle traction only. Forceful manipulation propagates unstable slips and shears retinacular vessels causing AVN. For unstable acute SUFE, use cross-table lateral (shoot-through) rather than frog-lateral to avoid further displacement.

Critical Positioning Points

  • NEVER forcefully reduce stable chronic slips
  • Gentle traction only for unstable acute slips
  • Cross-table lateral for unstable SUFE (frog-lateral risks further displacement)
  • Protect genitals from perineal post pressure

Step 2: Fluoroscopic Assessment and Entry Point Planning

Before incision, plan screw trajectory on fluoroscopy:

AP View Analysis:

  • Identify physeal line
  • Confirm Klein's line abnormality
  • Plan entry point: anterolateral femoral neck, 1-2cm distal to vastus ridge

Lateral View Analysis:

  • Assess severity of posterior slip
  • Plan trajectory to center of epiphysis
  • Account for posterior displacement

Entry Point Marking:

  • Place guidewire on skin surface
  • Adjust until overlying planned entry point on both AP and lateral
  • Mark skin

Screw Length Estimation:

  • Measure from entry point to center of epiphysis
  • Typical length 80-100mm in adolescents

Exam Pearl

EXAM KEY: Center-center positioning is the SINGLE MOST IMPORTANT technical step. Screw must bisect the femoral head exactly in the center on BOTH AP and lateral views. Posterior malposition has highest AVN risk (damages posterior retinacular vessels). Anterior malposition damages anterior retinacular vessels. Superior/inferior malposition causes eccentric loading and early physeal closure.

Step 3: Percutaneous Approach

Make 1-2cm stab incision at marked entry point on anterolateral thigh. Divide skin and subcutaneous tissue. Bluntly spread vastus lateralis muscle fibres with haemostat. Palpate anterolateral femoral neck bone surface.

Limited Open Alternative (if obese or revision):

  • 2-3cm longitudinal incision
  • Incise fascia lata
  • Split vastus lateralis (safe - nerve enters posteriorly)
  • Direct palpation of entry point

Exam Pearl

Percutaneous vs Open Decision: Percutaneous is standard for primary SUFE in non-obese patients with good fluoroscopy. Limited open preferred if: obese (thick soft tissues), revision surgery, or aspiration needed (unstable SUFE - decompress haemarthrosis to reduce tamponade effect on blood supply).

Step 4: Guidewire Insertion

Advance guidewire (2.4mm or 2.8mm depending on screw system) under continuous biplanar fluoroscopy:

Technique:

  1. Start perpendicular to bone at entry point
  2. Angle toward center of epiphysis
  3. Advance 2-3mm → check AP → advance 2-3mm → check lateral
  4. Repeat iteratively across physis into epiphysis
  5. Final position: center-center, perpendicular to physis, tip 5mm from subchondral bone

Common Errors:

  • Too posterior (lateral view): highest AVN risk - redirect anteriorly
  • Too anterior: anterior vessel injury risk
  • Too superior/inferior: eccentric loading, early physeal closure
  • Inadequate depth: threads won't engage epiphysis

Guidewire Dangers

  • Minimize passes: each physeal pass increases chondrolysis risk
  • Avoid posterior: posterior retinacular vessels are main blood supply
  • Monitor subchondral distance: avoid joint penetration
  • Hold guidewire stable: prevents advancement with screw

Step 5: Screw Length Measurement

With guidewire optimally positioned:

  • Slide depth gauge over guidewire until seated against bone
  • Read calibrated depth marks
  • Select partially threaded cannulated screw (7.0mm or 7.3mm)
  • Thread length must exceed epiphyseal thickness (typically 16-32mm)

Exam Pearl

Thread Engagement Critical: ALL screw threads must cross the physis into the epiphysis. If smooth shank (not threads) crosses the physis, there is NO fixation of the epiphysis and slip can progress. Partially threaded screws compress the physis - threads pull epiphysis toward metaphysis while smooth shank slides through cortex.

Step 6: Screw Insertion

Drilling (if needed):

  • Use cannulated drill over guidewire if bone dense
  • Drill to 5-10mm short of final length
  • Avoid plunging into epiphysis

Screw Placement:

  • Thread partially threaded cannulated screw over guidewire
  • Assistant holds guidewire stable (hemostat on wire prevents advancement)
  • Advance under fluoroscopy until all threads cross physis
  • Compress by continuing to tighten (physis closes)
  • Avoid overtightening (strips soft epiphyseal bone)

Step 7: Final Fluoroscopic Confirmation

AP View Checklist:

  • ☐ Screw bisects center of femoral head
  • ☐ All threads across physis in epiphysis
  • ☐ Tip 5mm from subchondral bone
  • ☐ No superior/inferior cortex penetration

Lateral View Checklist:

  • ☐ Screw bisects center of femoral head
  • ☐ Perpendicular or minimally oblique to physis
  • ☐ Tip 5mm from subchondral bone
  • ☐ NO posterior cortex penetration (critical!)
  • ☐ No anterior cortex penetration

Dynamic Test:

  • Gently internally rotate and flex hip
  • Screw should remain stable (no toggling or backing out)

Step 8: Guidewire Removal

  • Grasp guidewire with needle driver
  • Steady screw head to prevent backing out
  • Withdraw guidewire smoothly
  • Reconfirm screw position on fluoroscopy

Step 9: Prophylactic Contralateral Pinning Decision

Consider Prophylactic Pinning If:

  • Age less than 10 years (up to 60% bilateral)
  • Endocrine/metabolic cause identified
  • Unable to reliably follow-up
  • Symptomatic contralateral hip
  • Physeal widening on contralateral side

If Pinning:

  • Reposition C-arm to contralateral hip
  • Identical technique (easier as anatomy normal)
  • Complete one side fully before starting other

Exam Pearl

Prophylactic Pinning Controversy: 20-40% overall risk of contralateral slip if not pinned. Arguments FOR: prevents second surgery, earlier return to activities. Arguments AGAINST: 60-80% never slip (overtreatment), surgical risk. Consensus: individualize - definitely pin if age less than 10 or metabolic cause; close monitoring acceptable for older children without risk factors.

Step 10: Wound Closure

  • Irrigate with saline
  • Percutaneous: skin closure only (3-0 or 4-0 absorbable subcuticular)
  • Limited open: fascia lata (2-0 Vicryl), subcutaneous (3-0 Vicryl), skin
  • Sterile dressing
  • Remove from traction table with log roll (avoid twisting)

Step 11: Post-operative Care

Immediate (24-48 hours):

  • Neurovascular checks (femoral nerve palsy rare from traction)
  • Bed rest for unstable SUFE (allows physeal stabilization)
  • Mobilize same day for stable SUFE

Weight-Bearing Protocol:

  • Touch weight-bearing (TWB) with crutches for 6 weeks
  • Progress to full weight-bearing at 6 weeks if radiographs stable
  • Activity restrictions: no running/jumping/contact sports for 3-6 months

Follow-up Schedule:

TimingAssessment
2 weeksWound, X-ray both hips
6 weeksX-ray, progress to FWB if stable
3 monthsX-ray, expand activities
Q3-6 monthsUntil physeal closure (18-24 months)
AnnuallyUntil skeletal maturity

Step 12: Screw Removal

Timing: 3-6 months after complete physeal closure

Rationale: Femoral neck continues to grow in girth after physeal closure - if screw left in place, tip progressively approaches/enters joint causing chondrolysis

Technique:

  • Same positioning (fracture table, biplanar fluoroscopy)
  • Percutaneous over screw head
  • Unscrew and remove
  • Protected weight-bearing 6 weeks if large screw or long dwelling time

Complications

SUFE Pinning Complications

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"A 13-year-old obese boy presents with 6 weeks of left groin and thigh pain. He walks with an antalgic gait and externally rotated left leg. On examination, he has limited hip internal rotation and obligate external rotation with hip flexion. How would you assess and manage this patient?"

EXCEPTIONAL ANSWER
This clinical presentation is classic for SUFE - the Drehmann sign of obligate external rotation with flexion is pathognomonic. I would take a focused history clarifying symptom duration, ability to weight-bear, and any prodromal symptoms. I would examine for leg length discrepancy and assess contralateral hip. Essential imaging includes AP pelvis and frog-lateral of BOTH hips - 20-40% are bilateral. I would assess Klein's line on AP (should intersect lateral epiphysis but fails in SUFE), measure Southwick slip angle on frog-lateral (difference between affected and normal side), and classify using Loder stability (can he weight-bear?) and Southwick severity. If he can weight-bear, this is stable chronic SUFE requiring semi-urgent in situ pinning within days using a single partially threaded cannulated screw positioned center-center, perpendicular to physis, with all threads across physis and tip 5mm from subchondral bone. I would assess for endocrine causes with thyroid function tests and consider prophylactic contralateral pinning if risk factors present.
VIVA SCENARIOStandard

EXAMINER

"You are called to see a 12-year-old girl in ED who fell playing netball and now cannot weight-bear on her right hip. X-rays show a SUFE with Southwick angle of 45 degrees. She has been in ED for 4 hours. How would you proceed?"

EXCEPTIONAL ANSWER
This is an UNSTABLE SUFE based on inability to weight-bear - this is an orthopaedic emergency. Unstable SUFE has 20-50% AVN risk, which increases with every hour of delay. I would immediately admit her, keep her nil by mouth, provide analgesia, and arrange urgent theatre within 24 hours of symptom onset. I would NOT attempt closed reduction as this risks further damage to the retinacular vessels. In theatre, I would position supine on fracture table with gentle traction only, using cross-table lateral view (not frog-lateral which risks further displacement). I would perform percutaneous in situ pinning with a single 7.0-7.3mm partially threaded cannulated screw, positioned center-center on both AP and lateral views, with all threads across physis and tip 5mm from subchondral bone. Post-operatively, I would keep her on bed rest for 24-48 hours to allow physeal stabilization before mobilising touch weight-bearing. Given moderate slip severity and her young age, I would discuss prophylactic contralateral pinning and arrange endocrine workup.
VIVA SCENARIOStandard

EXAMINER

"A colleague asks your opinion on a 9-year-old boy with a mild unilateral SUFE (Southwick 25 degrees) who is stable and has no obvious endocrine cause. The parents want to know if prophylactic pinning of the other hip is necessary. What would you advise?"

EXCEPTIONAL ANSWER
This is an important shared decision-making discussion. The key factors are: his young age (less than 10 years carries up to 60% bilateral SUFE risk), the 20-40% overall contralateral slip rate, and the implications of close monitoring versus prophylactic surgery. Arguments FOR prophylactic pinning: prevents contralateral slip in a high-risk patient, avoids second surgery and anaesthetic if slip occurs, allows bilateral recovery in same timeframe. Arguments AGAINST: 40% may never slip (overtreatment), surgical risks (AVN 0.5-2%, chondrolysis 1-5%), physeal closure causes slight shortening. Given his age less than 10 years, I would RECOMMEND prophylactic pinning - he is in the highest risk category. However, I would explain both options clearly. If parents decline, I would ensure very close surveillance with bilateral AP pelvis and frog-lateral every 3-6 months until physeal closure, with clear instructions to present urgently with any symptoms. The decision should be documented thoroughly.

SUFE In Situ Pinning - Exam Summary

High-Yield Exam Summary

References

  1. Loder RT, Richards BS, Shapiro PS, et al. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg Am. 1993;75(8):1134-40.

  2. Southwick WO. Osteotomy through the lesser trochanter for slipped capital femoral epiphysis. J Bone Joint Surg Am. 1967;49(5):807-35.

  3. Ziebarth K, Zilkens C, Spencer S, et al. Capital realignment for moderate and severe SCFE using a modified Dunn procedure. Clin Orthop Relat Res. 2009;467(3):704-16.

  4. Aronsson DD, Loder RT, Breur GJ, Weinstein SL. Slipped capital femoral epiphysis: current concepts. J Am Acad Orthop Surg. 2006;14(12):666-79.

  5. Zaltz I, Baca G, Kim YJ, et al. Complications associated with the modified Dunn procedure for SCFE. J Pediatr Orthop. 2014;34(7):661-7.

  6. Lehmann CL, Arons RR, Loder RT, Vitale MG. The epidemiology of slipped capital femoral epiphysis: an update. J Pediatr Orthop. 2006;26(3):286-90.

  7. Sankar WN, Vanderhave KL, Matheney T, et al. The modified Dunn procedure for unstable slipped capital femoral epiphysis: a multicenter perspective. J Bone Joint Surg Am. 2013;95(7):585-91.

  8. Loder RT, Skopelja EN. The epidemiology and demographics of slipped capital femoral epiphysis. ISRN Orthop. 2011;2011:486512.

  9. Imhäuser G. Late results of Imhäuser's osteotomy for slipped capital femoral epiphysis. Z Orthop Ihre Grenzgeb. 1977;115(5):716-25.

  10. Kocher MS, Bishop JA, Weed B, et al. Delay in diagnosis of slipped capital femoral epiphysis. Pediatrics. 2004;113(4):e322-5.