An Ovine Model of Intramedullary Nailing Through the Pediatric Distal

Femoral Physis

Derrick M. Knapik, MD, Raymond W. Liu, MD

SIGN Fracture Care International Conference

September 23, 2016

Rainbow Babies and Children’s Hospital

Case Western Reserve University

Femur Fractures

Resource Poor Hospital

Operating Room Waiting Area Operating Room

Significant Impact of Injury

SIGN International

Retrograde Femoral Nail

Antegrade Femoral Nail

-No XRAY-No Intra-Operative Power

Distal Femoral Fractures

RETROGRADE NAIL

ANTEGRADENAIL

ANTEGRADENAIL

✓

✓

Retrograde Femoral SIGN Nail

? Are these nails safe for use in children?

Two sizes (7 mm & 8 mm)

Open growth plates with multiple years of growth remaining

Not widely used in pediatric patients

Growth Plate Violation

Limb Shortening Angular Deformity

Purpose

What magnitude of an immature, distal femoral growth plate’s cross sectional area can be violated with a retrograde, centrally located and perpendicularly placed implant without causing significant growth arrest?

Hypothesis

With increasing implant diameter, once a certain area of the growth plate is violated, growth arrest will occur

Rabbit Model3% no inequality in femoral lengths7% femoral shortening

JBJS (Br.), 1988

Sheep Model

• Fracture repair (Malhotra, Front. Surg., 2014)

• Limb lengthening (Forriol, Strat Traum Limb Recon., 2010)

• Osteoporosis (Turner, Vet J. 2002)

• Osteoarthritis (Burger, Lab Animals., 2007)

• Spinal surgery (Wilke, Spine, 1997)

Dorsett Sheep

Sheep Growth

• Puberty: 5-8 months of age– Operation: 3 months of age

• Insertion of a intramedullary

implant

– Euthanasia: 5.5 months of age

• 10 weeks of growth post-op

• No fractures!!– Testing the safety profile of

implants inserted across the

distal femoral growth plate

Estimating Femoral Length

• 160 mm at full growth(Salami et al., Int. J. Morphol, 2011)

• Multiplier from human studies(Paley et al., JBJS (Am), 2000)

– 3 months(sheep) =7 years (humans)

• 160mm/1.56=102 mm

– 5.5 months(sheep) =13 years (humans)

• 160mm/1.13=141 mm

Total Growth: ~ 39 mm (141mm – 102mm)

70% @ distal femur:

Distal Femur: ~ 27 mm

3 months 5.5 months

39 mm

Significant Growth Inhibition

• Assigned 25% Inhibition of

Growth = Clinically Significantly

39 mm x 0.25=9.75 mm

Comparable to humans(McCaw, Brit J Sport Med,1991)

(Gurney, Gait Posture, 2002)

5.5 months 5.5 months

9.75 mm

*

Range of Violation

Makela et al. (JBJS Br, 1988): Rabbits Drill holes 3% of the cross-sectional area=no arrestDrill holes 7%= growth arrest

3%

8%

TO

Liu et al. JPO, 2013

Guzzanti et al. (JBJS Br, 1994): Rabbits ACL Repair; 3% violation=no arrest

Power Analysis

• Power analysis: 3 limbs per increment

• 3 sheep @ 3%

• 3 sheep @ 4%

• 3 sheep @ 5%

• 3 sheep @ 6%

• 3 sheep @ 7%

• 3 sheep @ 8%

1 sheep= 1 operative limb, 1 control limb

Implant Selection

AB

LATERAL POSTERIOR-ANTERIOR

KNEE KNEETIBIA FEMUR

FEMUR

Implant Selection

Area (Circle): πr2

A

B

Area (Ellipse): πAB

? %AreaSteinman Pin (πr2)

AreaPhysis (πab)

x (ab)√rSteinman Pin ? %

(3-8%)

(3-8%)

Operative

Femoral NotchAbove PCL Origin

Medial Parapatellar

Procedure

Pre-Drilling Implant

KNEE

TIBIA

FEMUR

KNEE

TIBIA

FEMUR

Implant Insertion

Procedure

Cortical Violation

N=4 Specimens

Intramedullary Reamer

TIBIA

FEMUR

SIGN Hand-Held Reamer

REAMER

Cortical Violations: N=0

Operative

Hammer Down Implant K-Wire Placement

KNEE

TIBIA

FEMURKNEE

TIBIA

FEMUR

Post-Operative Course

• No immobilization, no weight-bearing restrictions

• Repeat X-rays to assess distal femoral growth

– 4 weeks post-op

– 8 weeks post-op

– 10 weeks post-op

• Euthanasia (10 weeks) Harvesting bilateral femurs

0 Weeks 4 Weeks

8 Weeks 10 Weeks

36.5mm

48mm

42.5mm

39.5mm

Specimen: 907Nail: 7.0mmViolation: 3%

Total Growth: 11.5mm

0 Weeks 4 Weeks

8 Weeks 10 Weeks

22.8mm

33.9mm

31.6mm

29.4mm

Specimen: 913Nail: 7.0mmViolation: 8%

Total Growth: 11.1mm

Radiographic Growth (mm)

0

4

8

12

16

0.03 0.04 0.05 0.06 0.07 0.08

Tota

l Gro

wth

(Fin

al-I

nit

ial L

en

gth

) in

mili

met

ers

Percentage of Growth Plate Violation

Radiographic Growth (mm)

Specimen 908

Gross Femoral LengthWeinberg and Liu, JPO, 2015Alpak et al., Turk. J Vet. Anim. Sci, 2009

Femoral Head to Medial Femoral Condyle“MEDIAL LENGTH”

Greater Trochanter to Lateral Femoral Condyle“LATERAL LENGTH”

LATERAL

MEDIAL

Mitutoyo Digital Calipers

Gross Femoral Lengths

(+) = Control > Operative (-) = Operative > Control

CONTROL-OPERATIVE CONTROL-OPERATIVE

Gross Femoral Length

-4

-2

0

2

4

6

0.03 0.04 0.05 0.06 0.07 0.08

Gro

ss D

iscr

ep

ancy

in L

en

gth

(C

on

tro

l-O

pe

rati

ve)

in m

m

Percentage of Growth Plate Violation

Lateral Sided Discrepancy

-2

0

2

4

6

8

0.03 0.04 0.05 0.06 0.07 0.08G

ross

Dis

cre

pan

cy in

Le

ngt

h(C

on

tro

l-O

pe

rati

ve)

in m

mPercentage of Growth Plate Violation

Medial Sided DiscrepancySpecimen 908

Specimen 908

Specimen 908

Percutaneous EpiphysiodesisUsing TransphysealScrews(PETS)

Limitations

• Femoral length >160mm in all specimens

– No standardized value for Dorsett sheep

• Multiplier method unreliable?

– Needed to measure femoral length every month

• Distal femoral growth plate in sheep does not grow like in humans?

– More like a humerus where the majority of growth occurs proximally?

Growth Inhibition?FE

MO

RA

L G

RO

WTH

RAT

E (m

m/d

ay)

TIME (days)

NORMAL FEMORAL GROWTHINSERTION OF IMPLANT

RATE OF INHIBITION?

PLATEAU?

IMMEDIATEDECLINE?

Conclusions

• Growth appears to continue at the distal femoral physis when 3 to 7% of the growth plate is violated

– No evidence of significant growth arrest, but trending towards arrest with violation at 8%

• Insertion of a nail across the distal femoral growth is safe in the normal size range (3-7%)

– Violating 8% of the growth plate in children is extreme and unlikely to be performed

Clinical Recommendations

• Implant Insertion

– Smallest hand reamer for pilot hole to avoid large oblique passage

– 8 mm reamer (*do not over-ream!)

– 8 mm SIGN nail

• Safe for use in all children

• For Age 12 and up, a 10mm nail can be safely considered

Clinical Recommendations

• Implant Removal

– At 3-4 months if adequate healing is present

– Can harvest fat from the abdomen

• 4 cm incision, level of umbilicus, laterally centered at mid-thigh

• 1 cm x 1 cm x 4 cm portion of fat

– Implant may be retained, however we do not yet have enough data

Clinical Recommendations

• Follow Up Imaging– AP/Lateral at 3-4 months to monitor healing

– If concerned for growth arrest, obtain contralateral AP/Lateral Knee and Standing AP Pelvis (*knees fully extended!!)

– Otherwise, AP/Lateral bilateral knees and standing AP pelvis 6 months following removal

– If + growth arrest, consider bilateral distal femoral epiphysiodesis

– Ideally, 1 year following surgery as growth disturbances can be subtle

Thank You

Questions?