Purpose: The aim of this retrospective observational study is to describe the demographic, clinical, and functional characteristics of children and adolescents with spastic cerebral palsy (CP) undergoing Single Event Multilevel Surgery (SEMLS) and changes in their gait efficiency following surgery.

Methods: Seventy-eight participants were included and a total of eighty-four SEMLS analyzed. All the participants were followed by the Children Rehabilitation Unit of the Local Health Authority of Reggio Emilia. Participants met the following requirements: age 4-20 years; hemiplegic or diplegic CP; Gross Motor Function Classification System level I, II or III; 3D gait analysis either before and after surgery. The following parameters were reported: maximum hip and knee extension in the gait cycle, to measure the gait efficiency; normalized maximum power produced by the ankle during push-off phase, to express the propulsive capacity; normalized speed and normalized stride length as global gait performance measure.

Children with Cerebral Palsy (CP) often have gait difficulties due to poor motor control, spasticity, skeletal deformities, and muscle weakness. Their walking is usually slow, tiring, with reduced endurance, and a higher risk of falls. As a result, these children often have limited participation in daily activities and a lower quality of life. Among the most common treatments, functional orthopedic surgery is now considered the "standard of care" for these patients. Many studies have shown that surgery has a positive impact on walking ability.

In the traditional surgical approach, patients undergo multiple operations, each correcting a single issue. For example, fixing a shortened triceps muscle, to allow the foot to fully contact the ground, might be followed by lengthening the knee flexors to enable full knee extension and upright standing. This step-by-step process, where surgeries are often done annually, was called the "birthday syndrome". Some researchers have studied the effects of surgery on specific walking issues. For example, in 2022, Kruger K.R. et al. examined the long-term impact of correcting valgus-pronated feet. Dohin B. et al., in 2020, looked at how lengthening knee flexors and adductors improved in-toeing gait. Krupiński M. et al., in 2015, studied the effect of Achilles tendon lengthening in children with toe-walking (equinus gait). While these studies provided useful insights for clinicians, they often oversimplified the complexity of the underlying problems.

In CP, multiple areas of the body are usually involved in walking difficulties, as seen in crouch gait (walking with bent knees), which can have many causes that influence each other. This often requires surgery on multiple areas at once to improve the overall balance of the body. More recently, surgeons have adopted a technique where multiple deformities are corrected in a single surgery, often involving both lower limbs. This approach, known as single-event multilevel surgery (SEMLS), reduces the number of surgeries compared to the traditional method of addressing one issue at a time. However, as children grow, additional SEMLS procedures may be needed to address new issues that arise, such as muscle tightness. Several studies have shown that these multilevel surgeries can improve walking ability. Saglam Y. et al., in 2016, studied the combination of femoral derotational osteotomy and soft tissue procedures in children with in-toeing gait. In 2022, Pierz K. et al. examined how SEMLS, including knee flexor lengthening combined with other techniques (such as triceps lengthening or tibial derotational osteotomy), improved walking in children with crouch gait. Moreira de Freitas Guardini K. et al., in 2021, also studied a large sample of children undergoing SEMLS, focusing on their clinical characteristics.

Evaluating the effects of surgery requires selecting appropriate outcome measures, which is not always simple. Most studies aim to improve "gait quality" but do not always confirm if the chosen parameters lead to real functional improvements for the patient. Some researchers use measures from physical exams (e.g., range of motion, muscle strength) or biomechanical data from gait analysis (3DGA, the gold standard for assessing gait in children with CP). These studies often focus on how the body moves (kinematics) and on spatiotemporal parameters such as walking speed and step length, along with summary indices. These parameters show changes in the specific area operated on and how the body moves as a whole. They provide information on alignment and symmetry of the legs during movement.

However, a well-aligned structure does not necessarily involve that the system works efficiently, meaning it minimizes energy expenditure during walking. Gait efficiency is especially important in children with CP, as many studies have shown that inefficient gait leads to increased energy consumption and mechanical work. Therefore, it is important to consider not only joint movement and overall performance but also other aspects, since kinematic data and physical exams do not provide information on gait efficiency.

Marconi V. et al. (2014) conducted a prospective study on energy consumption and mechanical work in children with CP after SEMLS. Their study showed a reduction in energy consumption after surgery, but the small sample size (10 children) and mixed group of patients (including hemiplegic, diplegic, and quadriplegic children) limit the generalizability of the results. Marconi V. et al. used the energy calculation method proposed by Willems P.A. et al. (1995), while Van de Walle P. et al. (2012) suggested that joint power calculations might be more valid and sensitive for CP. Other researchers have used indirect measures of efficiency, finding correlations between energy consumption and variables like pelvic vertical oscillation (assessed by the BEQ index, Kerrigan D.C. et al. 1996) or maximum knee and hip extension (Noorkoiv M. et al, 2019). These measures have been used to assess gait efficiency in CP, but not specifically to evaluate the effects of surgery.

The aim of this retrospective observational study is to describe the functional characteristics of children and adolescents with spastic cerebral palsy (CP) undergoing SEMLS and changes in their gait efficiency following surgery.

Methods:

This is a retrospective monocentric observational study. Outcome measures were collected before surgery (T0) and after surgery (T1) in a time span between 8 and 38 months. The surgical recommendation was tailored to the participants' requirements and decided through a comprehensive assessment, which included a standardized physical exam, radiographic studies, and instrumental gait analysis.

Gait analysis was performed by means of a Vicon® system (Oxford Metrics Group, Oxford, UK). The system was equipped with eight optoelectronic cameras, two force plates (AMTI, USA), and two video cameras. All assessments were conducted in the Motion Analysis Laboratory LAMBDA, Azienda USL-IRCCS di Reggio Emilia. The same assessor evaluated all participants.

Age and the level of Gross Motor Function Classification System (GMFCS) were collected before surgery.

The analyses will be conducted by the Statistics and Clinical Studies Office of the USL IRCCS in Reggio Emilia using SAS System, R, or SPSS software, depending on availability at the time. Quantitative and qualitative data will be analyzed and presented using mean, standard deviation (SD), median, interquartile range (IQR), and relative frequencies. Central tendency measures and percentages will be accompanied by 95% confidence intervals (CI). Normality of quantitative data will be assessed with the Shapiro-Wilk test. Appropriate statistical tests will be applied to compare measures between the two time points, T0 and T1.

To assess gait efficiency, the mean maximum extension values will be compared between T0 and T1 in the SEMLS surgery group using the paired Student's t-test or Wilcoxon test, depending on the normality assumption. Without aiming for comparison, the same measurements will also be described for the non-surgical group to observe trends.

For quantitative variable comparisons between the two time points, the paired Student's t-test or Wilcoxon test will be applied based on normality.

Inclusion Criteria:

• diagnosis of diplegic or hemiplegic CP;
• GMFCS levels I, II, or III;
• aged between 4 and 20 years;
• Lower limb Single Event Multilevel Surgery (SEMLS)
• 3D gait analysis before and after surgery

Exclusion Criteria:

• more than one lower limb surgery event between the two gait assessments
• one single gait evaluation

The study population will include patients who attended the Children Rehabilitation Unit of Local Health Authority of Reggio Emilia from 2011 to 2021. The study will focus on patients diagnosed with cerebral palsy who underwent lower limb SEMLS (single-event multilevel surgery) and 3D Gait Analysis before and after surgery.

To protect participant privacy the IPD will not be shared, unless upon reasonable request.