The investigators primary objective is to determine the fracture patterns, displacement-based treatment decisions, immediate and long-term complications, clinical, radiographic and patient reported outcomes of acetabular fractures with open physes.

Hypothesis: This study will demonstrate that more complex and displaced fracture patterns are associated with a greater incidence of complications and poorer outcomes.

The investigators secondary objective is to create a pediatric acetabular registry that can be used to track fracture patterns, displacement-based treatment decisions, immediate and long-term complications, clinical, radiographic and patient reported outcomes of acetabular fractures with open physes.

Hypothesis: This study will demonstrate that more complex and displaced fracture patterns are associated with a greater incidence of complications and poorer outcomes.

Introduction

This document is a protocol for a human research study. This two-phased study will be carried out in accordance with the applicable United States government regulations and the University of Utah and Primary Children's Hospital research policies and procedures. The first phase will consist of a retrospective cohort that will be contacted for follow-up data, while the second phase will consist of the creation of a prospective database.

Background and Current Clinical Data

Pelvic fractures, consisting of the pelvic ring and acetabulum, represent less than 0.2% of all pediatric fractures. Isolated acetabular fractures are estimated to represent 9.8% of pelvic fractures, while combined pelvic ring and acetabular fractures are estimated at 20%. Notably, these injuries occur as a result of high-energy trauma, most commonly during motor vehicle-related accidents.Despite the high-energy forces involved, pediatric patients are less likely to experience fracture-induced hemodynamic instability. This is due to factors such as limited displacement of fractures secondary to pelvis malleability, pelvic ligamentous strength, thickness of the pediatric periosteum and increased responsiveness of the pediatric hemostatic system. Consequently, the patient's life is more likely to be threatened by associated cranial, abdominal, thoracic, and neurological injuries, which occur in more than 60% of cases. Overall mortality rates are estimated between 3.2% to 18%. Acetabular fractures can also occur secondary to lower-energy mechanisms, such as hip dislocations during sports activity. The rarity of pediatric acetabulum fractures has resulted in limited high-quality data regarding clinical and patient reported outcomes (PRO), but the severity of these injuries indicates further observations are necessary.

The outcomes for pediatric acetabulum fractures are reported by a few small studies. Non- surgical and surgical management has resulted in acceptable clinical and radiographic outcomes. Past investigators have reported zero nonunions, one unplanned reoperation, and full return to activity in 18 patients. However, the study is limited by a small cohort and follow-up only to one year, which restricts the ability to observe the development of long-term complications such as arthritis or dysplasia. Other investigators have reported on 21 acetabulum fracture ORIF patients younger than 18 from 2001-2018, displaying favorable functional outcomes. However, only five patients had open physes, which severely limits the findings of the study to skeletally mature adolescents. Similar to adult acetabulum fractures, pediatric patients have a risk of post-traumatic osteoarthritis (PTOA). Additional complications of concern in skeletally immature patients are leg length inequality, hip dysplasia, and hip subluxation. These are secondary to a growth disturbance of the triradiate cartilage, which occurs due to osseous bridging across the cartilage or ossification of a physeal hematoma after injury. Growth disturbance has been reported in 14% of acetabulum fractures, while hip dysplasia has been estimated at 5%. However, the strength of both findings are limited by small sample sizes. Hip subluxation and dislocation are also associated with development of avascular necrosis (AVN) of the femoral head, osteonecrosis of the posterior acetabular wall, and sciatic nerve palsy. Hip reduction within 6 hours is associated with lower rates of AVN due to preservation of femoral head blood flow. While pediatric acetabulum fractures are associated with good outcomes, they are also associated with many potential complications that have lasting consequences for the patient. These outcomes will be best observed through long-term studies of the pediatric population.

There are few studies that report on the long-term PROs of pediatric acetabular fractures. Within the small subset of studies reporting PROs, there are a few tools used, such as the Merle d'Aubigne score, Short Musculoskeletal Functional Assessment, and 36-Item Short Form Survey. While each legacy measure provides specific, beneficial information relative to pelvic and acetabular injury, they are not standardized or widely used in other fracture patterns. The Patient Reported Outcomes Measurement Information System (PROMIS) is an internationally used measurement system developed by the National Institute of Health to produce a T-score standardized to the U.S. general population. PROMIS provides multiple benefits such as reducing patient burden using computer adaptive testing, integration into the electronic medical record, and validity across multiple populations. Using the Swedish Fracture Registry, investigators have identified and reported the PROMIS Scores of 63 pediatric pelvic fractures (31% response rate) at a mean follow-up of 3.5 years. Greater than 85% of respondents reported none or mild concerns in mobility, anxiety, depression, fatigue, peer relationships, pain interference and pain intensity, but PROMIS t-scores were never explicitly listed. Additionally, they failed to mention the number of patients with isolated or concomitant acetabular fractures who completed PROMIS surveys. The Hip Disability and Osteoarthritis Outcome Score (HOOS) is another validated and heavily used PRO, developed to assess the patients' opinion about hip pain related function and quality of life. HOOS has most commonly been used to capture outcomes related to hip osteoarthritis and total hip arthroplasty. To date, HOOS has not been used to describe pediatric acetabular fractures, but would allow for a hip specific assessment and comparison to patients with osteoarthritis. Accurate reporting of pediatric acetabular PROs is warranted, especially with minimal high-quality data on the topic.

Pediatric pelvic fractures are injuries carrying a high mortality and morbidity rate. Acetabulum fractures are a rare subset of pediatric injuries with limited high-quality research in fracture classification and treatment related clinical, radiographic, and patient reported outcomes. In adults, complex fracture patterns in polytraumatic or elderly patients are associated with complications, poor functioning and long-term prognosis. Past investigators reported that 21% of 816 operatively treated displaced acetabular fractures required conversion to THA within 20 years, however half of the conversions occurred within the first 1.5 years. In addition, investigators have reported a 100% three-year conversion rate to total hip arthroplasty (THA) as a result of PTOA if patients were over the age of 60, had femoral head damage, and acetabular impaction. Depending on fracture pattern, pediatric acetabulum fractures may carry a similar risk of PTOA and other complications such as AVN. They may also be associated with poor long-term PROs. This is troublesome for pediatric patients, who would have to live their productive adulthood with poor functioning and quality of life. There is significant progress to be made in identifying the prognosis of pediatric acetabular fractures and identifying factors related to poor outcomes.

Inclusion Criteria:

• Patients aged 18 years or less (at time of injury) with open physes sustaining an acetabular fracture with primary treatment occurring at either University of Utah Hospital or Primary Children's Hospital from 2000-present.
• Informed consent can be obtained from parent, guardian, or family member.

Exclusion Criteria:

• History of metabolic or genetic bone disease (Ricket's, Osteogenesis Imperfecta),
• pathologic fracture,
• non-ambulatory prior to injury, paraplegic,
• hemiplegic, or cognitive impairment that inhibits the participant's ability to answer patient reported outcome surveys.
• Pregnancy

Patients aged 18 years or less (at time of injury) with open physes sustaining an acetabular fracture with primary treatment occurring at either University of Utah Hospital or Primary Children's Hospital from 2000-present.