Spontaneous Correction of External Tibiofemoral Rotation ...

Spontaneous Correction of External TibiofemoralRotation and Tibial Tuberosity-Trochlear Groove Distance Occurs After Medial Patellofemoral Ligament Reconstruction in Fixed or Obligatory Dislocators

Alexandra H. Aitchison, BS

Kenneth M. Lin, MD

Sofia Hidalgo Perea, BS

Daniel W. Green, MS, MD

Division of Pediatric Orthopedic SurgeryHospital for Special Surgery, New York, NY

Confidential & Proprietary 1

DISCLOSURES


Alexandra Aitchison, BS, Kenneth M. Lin, Sofia Hidalgo Perea BS:

Have no financial conflicts to disclose

Daniel W. Green, MD, MS:

I receive royalties from Arthex, Inc. and Pega Medical. I am a consultant for Arthrex,

Inc.

Anatomic factors in Patellar Instability

3

Bony morphology: Trochlear dysplasia

Bony alignment: Patella alta, genu valgum, TT-TG, femoral anteversion

Soft tissue integrity: MPFL, generalized laxity

Role of Rotational Deformity in Patellar Instability

Tibiofemoral Rotation Patellar Instability 4

Long bone torsion: femoral anteversion, external tibial torsion

Role of Rotational Deformity in Patellar Instability


Tibiofemoral Rotation: external rotation of tibia in relation to femur through the knee joint

PRiSM 2018

They showed that in pediatric patients with patellar

instability, there was increased intraarticular external

rotation of the tibia in relation to the femur of 7.7 degrees

Spectrum of Clinical Severity

Patellar dislocations are common in the pediatric and adolescent population: up to 69 per 100,000 person-years

Clinical presentation: spectrum of manifestations


Fixed dislocation or

Obligatory dislocation w/flexion

NormalFixed/Obligatory Dislocator“Standard” Instability

One to several traumatic

dislocations

Increased Rotational Deformity with Increasing Clinical Severity


Control: no instability

SPI: standard traumatic patellar instability

FOD: fixed/obligatory dislocator

ICC for TFR (3

observers):

0.962 (95% CI, 0.932-

0.981)

Fixed or Obligatory dislocators

8

Apparent genu valgum in severe rotatory deformity

13yo M with nail patella syndrome,

with fixed right lateral patellar dislocation

Fixed or Obligatory dislocators

Rotatory force vector of extensor mechanism in fixed dislocation

▪ Quadriceps contraction → external rotatory force on the tibia due to lateral location of the

patella


8yo M with trisomy 21,

with fixed right lateral patellar dislocation

Study Objective

• Tibiofemoral rotation is an important anatomic factor in pediatric patellar

instability

• In fixed or obligatory dislocators, there is increased rotational deformity

• External tibial rotation in relation to the femur at the level of the joint


Does intraaricular tibiofemoral rotation change following MPFL Reconstruction?

Is there a difference in rotational change that can be achieved in severe (fixed/obligatory dislocators)

compared to standard traumatic dislocators?

Study Design


Patients

▪ Study period: 4/2009 – 2/2019

▪ Case Control Design

▪ FOD (Fixed/Obligatory Dislocator)

▪ SPI (Standard Traumatic Patellar Instability)

▪ Inclusion: age<18, qualifying diagnosis, MPFLR

and pre and postoperative MRI performed at

study institution

▪ Exclusion: Prior patellar realignment surgery, no

follow-up MRI, and MRI of inadequate quality for

measurement

SPI (N=16)FOD (N=14)

Comparison of pre- and post-op

TT-TG and TFR by MRI

Preoperative MRI

MPFL Reconstruction

Postoperative MRI

Methods


Imaging

▪ 3T MRI scanner

▪ Supine, knee extended

▪ Proton-density axial projection

▪ Blinded measurements by 3

authors

▪ Measurement of TT-TG and TFR

on pre- and post-op MRI

A B

Tibiofemoral rotation (TFR): Angle between posterior

femoral condylar line and posterior tibial line

Posterior condylar line at level

of the widest A-P condylar

diameter

Posterior tibial line at the

level of the PCL insertion

Demographic Data


Total (n=30) SPI (n=16) FOD (n=14) Significance

Age 13.9 years 14.7 years 13.0 years P=0.042

Sex 53% Female 63% Female 43% Female P=0.005

Laterality 57% Right 56% Right 57% Right P=0.89

Time from Surgery

to Postoperative MR

I

2.0 years 1.8 years 2.3 years P=0.39

Greater average age, and greater proportion of females in SPI group


Fixed or obligatory dislocator group

• Significant decrease in TT-TG: 4.0mm

• Significant decrease in External TFR: 5.5°

Standard traumatic instability group

• No significant change in TT-TG

• No significant change in External

TFR

Pre- and Post-Operative Measurements of TT-TG and TFR on MRI

0

2

4

6

8

10

SPI FOD

ExternalTibiofemoralR

otation

(Degrees)

Diagnosis

Pre-op

Post-op

0

4

8

12

16

20

SPI FOD

TT-TG(mm)

Diagnosis

Pre-op

Post-op


P=0.019P=0.846

Change in TT-TGChange in TFR

P=0.025

P=0.896

Pre- and post-operative measurements of TT-TG and TFR on MRI

Discussion

Limitations

▪ Single institution, retrospective study

▪ Tibiofemoral rotation is not yet a commonly used, standardized measurement

▪ Tibiofemoral rotation is a dynamic phenomenon; current study assesses

static rotation


Discussion


Key Findings:

• In standard patellar instability patients, MPFLR did not change TT-TG or TFR

• In fixed/obligatory dislocators, MPFLR led to improvements in both TT-TG and

TFR

• Decreased TT-TG by 4.0mm

• Decreased external TFR by 5.5°

Conclusion:

This is the first study to show that MPFL reconstruction can change intraarticular

tibiofemoral rotation in severe cases of pediatric patellar instability


Thank you!

Contact Information: Daniel W. Green, MD [email protected]

Spontaneous Correction of External Tibiofemoral Rotation ...

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