Long-Term Outcomes of Femoral Derotation Osteotomy for Individuals With Cerebral Palsy

Excessive anteversion is commonly observed in the CP population. If individuals do not internally rotate their femurs as a compensation for this bony torsion, excessive anteversion decreases the coronal plane moment arm of the hip abductors-a phenomenon often called lever arm dysfunction. Considering that adequate hip abductor strength is a crucial factor for normal walking and many other functional activities, the compensatory mechanism theory hypothesizes that individuals with excessive anteversion will internally rotate their hips to restore the coronal plane moment arms. Excessive internal hip rotation (IHR) is observed in the gait of approximately 50% of individuals with CP. It has been postulated, though, that while IHR may restore hip abductor function, it is cosmetically unappealing and may lead to trips and falls. Therefore, FDOs are considered the standard treatment for correcting excessive anteversion and IHR in individuals with CP. Notably, it is one of the top two orthopedic surgeries performed at Gillette Children's Specialty Healthcare. Among the \~4000 individuals with CP who have been seen in the gait lab, almost 1350 individuals (>2200 limbs) have undergone at least one FDO.

Short-term (\~12 months postoperative) improvements of transverse plane hip rotation during gait range from only 33% to 94%. Despite FDO's widespread use, long-term outcomes of the procedure have only begun to be studied, with our 2016 study the only one that included a control group. Without a control group, the natural history of bony remodeling or gait adaptations is unknown. However, our prior study is limited by two main factors, 1) all data were extracted from our database retrospectively, so the potential for a large bias exists since outcomes reflect only patients with clinically-initiated gait visits, and 2) outcomes of hip abductor function were only measured by hip rotation (or hip abductor moment during gait, which is only available for individuals who can walk without assistive devices), so the true ability of the hip abductors to generate moment has not been tested. Furthermore, the vast majority of individuals were <18 years old at their "long-term" visit (\~5 years after their preoperative gait visit), which precedes the reported gait or functional decline more commonly occurring in one's 20s and beyond.

Counseling families on the long-term outcomes after an FDO is currently not possible and is necessary for families and health-care providers to make informed decisions. It remains unclear whether individuals who receive an FDO experience long-term beneficial effects on function, activity, and comfort as compared to those who receive other or no treatment for their excessive anteversion and/or IHR.

Briefly, anteversion as measured by the trochanteric prominence angle test (TPAT) is the most common method used by clinicians to determine if an FDO is warranted, in addition to anteversion being an important predictor of predicted short-term outcomes after an FDO23. However, data from our lab suggests that there is 10-15° of measurement error associated with this method. As such, our secondary purpose was to compare anteversion as measured by the TPAT to that of a radiographical gold standard, EOS. EOS delivers 4-30 times less radiation to the gonads and lower extremities compared to computed tomography (CT)24, making it very suitable for research purposes. Additionally, accuracy of quantifying femoral anteversion is not compromised versus the current gold standard, CT, with a mean difference of \~3° reported.

• Motion Analysis (Diagnostic test): Gait and Motion Analysis, comprised of 3-dimensional kinematics and kinetics, electromyography, energy expenditure, and physical exam (range of motion, strength, spasticity, etc.)
• sterEOS Imaging of Lower Extremities (Diagnostic test): Bi-planar imaging of the lower extremities to evaluate femoral anteversion and hip dysplasia and subluxation.
• Surveys (Behavioral): 9 surveys assessing function, activity, participation, pain, quality of life, and treatment history.

Primary outcomes

• Gait and Motion Analysis [long-term research visit (on average, ~10 years post-baseline)]: Compare gait kinematics and kinetics across groups
• sterEOS imaging [long-term research visit (on average, ~10 years post-baseline)]: femoral anteversion determined by 3-D reconstruction of bi-planar sterEOS imaging
• Change in Gait and Motion Analysis [baseline (qualifying exam, pre-FDO or gait analysis at which controls matched cases) compared to long-term research visit (on average, ~10 years post-baseline)]: Compare change in gait kinematics and kinetics within groups

Secondary outcomes

• sterEOS imaging [long-term research visit (on average, ~10 years post-baseline)]: Assess hip dysplasia and/or subluxation in qualifying limb across groups
• Number of hip abduction repetitions [long-term research visit (on average, ~10 years post-baseline)]: Assess hip function across groups
• Seconds to complete Timed Up and Go [long-term research visit (on average, ~10 years post-baseline)]: Assess function across groups
• Quality of Life as assessed by WHOQOL-bref [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Pain as assessed by the Brief Pain Inventory [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Fear of Falling as assessed by Falls Efficacy Scale-International [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Hip Function as assessed by Harris Hip Function [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• General Function as assessed by Functional Assessment Questionnaire [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Walking Function as assessed by Function Mobility Scale [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Participation as assessed by Child/Adolescent Frequency of Participation Questionnaire [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey
• Satisfaction with Life as assessed by Deiner Satisfaction with Life Scale [compare scores across groups at long-term research visit (on average, ~10 years post-baseline)]: self-reported survey

Sex: All, ages: 25 Years to any

Inclusion Criteria:

* Diagnosed with bilateral CP (i.e., hemiplegics excluded)
* Minimum age of 25 years presently
* Had a preoperative gait analysis
* Underwent only 1 external, proximal FDO per side
* Minimum 5 years since an FDO
* FDO implants have been removed
* No prior pelvic osteotomy
* Able to speak and read English
* Not pregnant

Control group (-FDO):

* Same as cases, except no FDO
* Matched to cases at baseline (using a matching algorithm)

Exclusion Criteria:

* none

• Tom F Novacheck, MD, Principal investigator, Gillette Children's Specialty Healthcare