Jourdan M. Cancienne, MD

AAOS Now

Published 8/1/2019
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Terry Stanton

Study Identifies Outcome Predictors for FAIS Hip Arthroscopy

A study presented at the American Orthopaedic Society for Sports Medicine Annual Meeting in Boston detailed the use of a predictive model for achieving the minimal clinically important difference (MCID) in patients undergoing hip arthroscopy for femoroacetabular impingement syndrome (FAIS).

“With advancements in both the understanding and treatment of nonarthritic hip pain, the paradigm of defining clinical success within the hip-preservation field has shifted from radiographic measurements and survivorship metrics to validated, patient-centered, [and] clinically meaningful differences,” explained Jourdan M. Cancienne, MD, of Midwest Orthopaedics at Rush, who presented the study. “The primary advantage of measuring the MCID compared to patient-reported outcomes (PROs) is that it represents a tangible, clinical treatment target. Thus, we sought to utilize a large, prospectively collected, consecutive series of patients treated for FAIS with a modern hip arthroscopic technique to build and evaluate a statistical model to predict two-year postoperative MCIDs for PRO scores using only preoperative patient data.”

Seeking significance

Although arthroscopic procedures for FAIS have gained wide acceptance, few studies have sought to identify risk factors associated with failure to achieve clinically significant outcomes after hip arthroscopy for FAIS based on MCID criteria, Dr. Cancienne said. A number of studies have detailed statistically significant improvements in certain PROs, such as the modified Harris Hip Score (mHHS), Hip Outcome Score-Activities of Daily Living subscale (HOS-ADL), and HOS-Sport-Specific subscale (HOS-SS) following hip arthroscopy for FAIS. However, it has been suggested that statistical significance of PROs is not necessarily equivalent to clinical significance, leading to the increased usage of MCIDs to determine what changes are meaningful to patients.

The study involved a series of 2,511 patients undergoing primary hip arthroscopy for the treatment of FAIS by a single surgeon over a period of 4.5 years. Inclusion criteria consisted of clinical and radiographic diagnosis of symptomatic FAIS, failure of conservative management (physical therapy, activity modification, oral anti-inflammatories, and, for some patients, fluoroscopically guided intra-articular cortisone injection), and hip arthroscopy to address the FAIS with a minimum of two-year follow-up with PROs. Exclusion criteria consisted of hip arthroscopy for an indication other than FAIS, prior ipsilateral hip surgery, evidence of radiographic osteoarthritis (Tönnis grade > 1), hip dysplasia (lateral center edge angle < 20°), or a history of congenital hip disorders (slipped capital femoral epiphysis, developmental hip dysplasia, etc.).

Demographic data were collected from all patients, including sex, age, operative extremity, body mass index (BMI), sports participation, duration of symptoms, and comorbidities. All patients completed preoperative and minimum two-year postoperative hip-specific PRO instruments, including the HOS-ADL, HOS-SS, and mHHS. In addition, all patients graded their pain levels and visual analog scale (VAS) pain scores at two years postoperatively.

To quantify the clinical significance of outcome achievement of HOS-ADL, HOS-SS, and mHHS, the investigators utilized an anchor-based methodology to calculate the MCIDs for each outcome of interest. They determined this by calculating half the standard deviation (SD) of the VAS pain score in the study patients, as has been described in the literature.

Among 1,103 eligible patients, 898 (81.4 percent) had a minimum of two-year reported outcomes and were entered into the modeling algorithm. The average age and BMI were 32.9 years (SD, 12.2 years) and 25.1 kg/m2 (SD, 5.0 kg/m2), respectively (Table 1). Most patients participated in sports (70.3 percent), and 53.9 percent were self-reported runners. A total of 313 patients (28.4 percent) reported having symptoms lasting more than two years prior to surgery.

Jourdan M. Cancienne, MD

There was a statistically significant difference between preoperative and postoperative alpha angles (anteroposterior, false-profile, and Dunn view), as well as lateral center-edge angle and anterior center edge angle. There was no statistically significant difference between pre- and postoperative Tönnis angles. The majority of patients did not have any arthritic changes seen on plain radiographs (Tönnis grade 0 = 94.2 percent). There was a statistically significant increase in HOS-ADL (65.0 ± 18.8 versus 86.7 ± 16.1), HOS-SS (42.9 ± 22.7 versus 75.1 ± 24.7), and mHHS (57.3 ± 14.8 versus 80.6 ± 16.8;) at two years postoperatively. Furthermore, there was a significant reduction in reported VAS pain score (67.8 ± 20.2 versus 20.9 ± 23.9).

The predictors

The HOS-ADL, HOS-SS, and mHHS threshold scores for achieving MCID were 9.8, 14.4, and 9.14, respectively. With the two-step modeling procedure, the percentages of patients meeting the MCID threshold scores were 74.0 percent for HOS-ADL, 73.5 percent for HOS-SS, and 79.9 percent for mHHS. Although the set of significant predictors differed for each hip-specific outcome measure, there were some similarities. A history of preoperative injections, a history of anxiety/depression, and a high preoperative functional score each had a statistically significant negative association with achieving threshold MCID for all three measures. Preoperative symptom duration of more than two years also had a statistically significantly negative association with achieving threshold MCID for HOS-ADL and HOS-SS. Additionally, despite the inclusion of features describing results of pain provocation and mobility tests, such as a positive trochanteric pain sign and proximal hamstring tenderness to palpation, very few of those features were determined to be predictive. This is noteworthy because it validates that the modeling process could disregard features that theoretically should not have any bearing on achieving threshold MCID.

Statistically significantly predictors of not achieving the HOS-ADL MCID were history of anxiety and depression, preoperative symptom duration of more than two years, age ٣٠ to ٤٥ years, obesity, increased preoperative HOS-ADL, and preoperative injection. Predictors of not achieving the HOS-SS MCID were history of anxiety and depression, preoperative symptom duration of more than two years, increased preoperative HOS-SS, and preoperative injection, whereas participating in running as a sport activity was a predictor of achieving MCID HOS-SS. Predictors of not achieving mHHS MCID included history of anxiety or depression, high preoperative mHHS, and preoperative injection, whereas being female was predictive of successfully achieving MCID. Relatively shorter preoperative symptom durations were associated with successfully achieving MCID for mHHS, including those whose symptoms lasted six to 12 months and/or one to two years.

“These findings have important implications for shared decision-making algorithms and managing preoperative expectations following hip arthroscopy for FAIS,” said Dr. Cancienne.

He and his coauthors are currently looking to develop and employ shared decision-making models, which could be used to help counsel patients on their risk of not achieving a clinically significant outcome. “There is also the opportunity to apply cloud-based solutions like PatientIQ to build outcome registries and fluidly analyze outcomes in real time,” he said.

Dr. Cancienne’s coauthors of “A Predictive Model for Achieving the Minimal Clinically Important Difference Following Hip Arthroscopy” are Benedict Nwachukwu, MD; Edward C. Beck, MD, MPH; Jorge Chahla, MD, PhD; Elaine K. Lee, PhD; and Shane J. Nho, MD, MS.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org.