1. Francisco Angulo Parker, MD PGY3 UKY PM&R
Knee hyperextension after hamstring lengthening in cerebral palsy: Incidence, predictive factors and cost in gait efficiency
Francisco Angulo Parker, MD
PGY3
UKY PM&R

2. Cerebral Palsy
Cerebral palsy (CP) is the leading cause of childhood disability affecting function & development
Overall estimated prevalence of CP is cases per 1000 live births
Criteria for CP:
Static Brain lesion
Neuro-motor control deficit that affects movement or posture
Immature brain

3. Hamstring Lengthening
Goal of surgery in ambulatory patients
To improve gait efficiency
To improve knee flexion deformity
To increase knee extension at the end of swing phase and at heel strike
Crouching gait

4. Descriptive statistics
No. (%)
Gender
Male
97 (66%)
Female
50 (34%)
GMFCS 1
26 (17.7%)
GMFCS 2
48 (32.7%)
GMFCS 3
73 (49.7%)
Mean(std)
Age at surgery
12. 1 (3.2) years
Duration b/w surgery & post op gait analysis
1.4 (1.1) years

5. BACKGROUND KINEMATICS IN GAIT EFFICIENCY
POOR DATA PREDICTING KNEE HYPEREXTENSION
REGARDED AS POOR OUTCOME
AVAILABILITY OF DATABASE
SERIES OF STUDIES FROM SAME
DATABASE

6. Objectives
Incidence
Can we predict it? What are the predictive variables?
Cost of knee hyperextension in gait efficiency

7. Methodology Retrospective, case control study.
Regression analysis for predicting variables.

8. population

9. Population Diagnosis Frequency CP hemiplegia 2 CP diplegia 142 HSP 5
parplegia 3
fredrichs ataxia 1
Total
153

10. Population Characteristics Gender Previous Hamstring 93 males
49 female
Previous Hamstring
No: 110
Yes: 32

11. Population Procedures 33 only HS lengthening 34 TAL and HS lengthening
30 Rectus transfer and HS lengthening
27 TAL, HS lengthening and rectus transfer

12. Incidence of knee hyperextension
284 knees (142 patients)
Hyperextension considered 0 deg and above pass full extension
11.5% of the knees showed hyperextension post HS lengthening

13. Variable analysis for prediction
Preop GMFCSLevel
Age at surgery
Other simultaneous surgery (yes/no)
Simultaneous RECTUS (yes/no)
Preop L Popliteal angle
Preop L Knee extension
Preop L Knee flexor tone
Preop L hip extensor
Preop L knee Flexor
Preop L knee Extensor
PRE L 0 = knee flexion at initial contact preop
PRE L 30 = knee flexion at mid-stance preop
Change HT change in height from preop to post op
Change WT change in weight from preop to post op

14. Variables in the EquationB
S.E.
Wald df
Sig.
Exp(B)
Step 1a
preGMFCSLevel
1.027
.424
5.854 1
.016
2.793
age_atsurgery
-.131
.087
2.262
.133
.877
othersimultaneoussurgery
-.253
.199
1.620
.203
.776
simultaneous_RECTUS
.316
.614
.266
.606
1.372
Preop__Popliteal_angle
.057
.027
4.533
.033
1.059
Preop__Knee_extension
.013
.039
.114
.736
1.013
Pre_op__Knee_flexor_tone
.382
.273
1.966
.161
1.466
Pre_op__hip_extesor_control
.310
.196
2.516
.113
1.364
Pre_op__knee_Flexor_control
.024
.241
.010
.921
1.024
Pre_op__knee_Extensor_control
-.476
.345
1.906
.167
.622
PRE__0
-.049
3.225
.073
.953
PRE__30
-.046
.023
4.070
.044
.955
changeHT
.009
.040
.053
.818
1.009
changeWT
.034
.037
.861
.354
1.035
timetofollowup
-.060
.164
.134
.715
.942
Constant
-1.339
3.043
.194
.660
.262

15. Variable analysis for prediction
Statistically significant P=<0.05
Pre GMFCS
Pre op angle
Pre operative knee flexion at midstance
Clinically significant
Significant results only present in Pre operative knee flexion at midstance

16. Gait Stance phase (1) Swing phase (1)
Limb of interest in contact with ground
60% of gait when walking
Heel strike
loading response - foot plantar flexes to ground
midstance - tibia shifts forward over plantigrade foot
terminal stance – heel rise
preswing
Swing phase (1)
Limb of interest in air
40% of gait when walking
Initial swing – begins with toe off, limb moves forward
Midswing – when limb passes grounded limb
Terminal swing – also known as deceleration, slow down towards heel strike
Both feet are on ground during initial contact and during the end of swing phase at terminal stance as the body weight is shifted onto the other limb and the heel rises from the floor in preparation for push off
**tight hamstrings effect all phases of gait

17. Results Pre-operative knee flexion at midstance Not hyperextended.
Mean:
SD: 16.2
Hyperextended
Mean: 23.9
SD: 17.59

18. Gait efficiency
Measured by Oxygen consumption pre and post bilateral hamstring lengthening
Same database
 Only 78 subjects with preop and post op oxygen consumption data

19. Gait efficiency Oxygen consumption
Amount of oxygen consumed per kg of body weight over time (mL/kg-min)
Total power required to keep the body in motion
Related to the level of effort it takes to walk
Does not take walking velocity into account

20. Results Group Statistics post_Hyper_R N Mean Std. Deviation
post_Hyper_R N
Mean
Std. Deviation
Std. Error Mean
PreO2ConsumptionExercise
not hyper 69
18.938
3.8794
.4670
hyper 9
19.422
3.2468
1.0823
Pre02Cost
.6293
.30379
.03657
.7344
.24895
.08298
PostO2ConsumptionExercise
17.233
3.4472
.4150
17.722
4.1176
1.3725
Post02Cost
.5419
.19304
.02324
.6233
.20062
.06687
Change_O2_cost
-.0874
.21070
.02536
-.1111
.12830
.04277
Change_O2_Consum
.47906
.91120

21. Conclusion
Incidence of knee hyperextension after hamstring lengthening in our population is 11.5%
Significant variable: knee flexion at midstance
Statistical and clinical significance at a mean of 23.9 degrees when compared to a mean of 35.4 degrees
No significant change in Oxygen consumption in hyperextended vs non-hyperextended knees

22. discussion
Clinical follow up at 1.5 years after surgery. Long term observance should be considered
Insufficient knee flexion at midstance would bring up the incidence to approximately 25%
What is the efficiency cost in chronic knee hyperextension?
Overall, the prediction of hyperextension continues to be difficult

23. references
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