P3.259: Dynamic Ultrasound Findings of Hip Microinstability and Its Impact on Post-Injection Pain Relief

Background: Hip microinstability (HMI) due to ligamentous laxity, borderline dysplasia, and/or femoral anteversion is an increasingly recognized source of chronic pain in the hip. Dynamic ultrasound (US) has recently emerged as a promising tool in identifying and diagnosing hip microinstability. Microinstability may result in gait instability, hip pain and apprehension, however, clear diagnostic criteria remain elusive. We aimed to evaluate the relationship between patient and treatment factors and hip microinstability observed on dynamic US.

Methods: Patients at a single institution with acute or chronic hip pain, undergoing dynamic US examination with guided anesthetic and steroid injection performed by 2 physicians from June 2022 to July 2024 were identified. Demographics, diagnoses, and pain scores (out of 10) in seven provocative positions were collected. Examination maneuvers included passive hip flexion (PHF), scour, FADIR (flexion, adduction, and internal rotation), Stinchfield, FABER (flexion, abduction, and external rotation), resisted FABER and psoas stretch.

Results: 62 patients met study criteria, median age 17 years (range 13 to 40 years), majority female, (87.1%), white (82.3%), not Hispanic or Latino (96.7%). 28 patients had microinstability (45.2%). Age and gender were not significantly related to HMI (p=0.899, 0.450). Patients without HMI reported higher baseline pain scores with PHF and FADIR (p=0.002, p=0.028). After injection, patients without HMI reported greater pain relief with PHF than those without HMI (p=0.009), but reduction in FADIR pain were not significantly related to HMI (p=0.735). Specific diagnoses of labral/chondral pathology, femoroacetabular impingement, or hip pain were not significantly related to findings of microinstability (p=0.173). Patients exhibiting findings of hip dysplasia noted on radiographs were subsequently found to have HMI more often than those without evidence of hip dysplasia (p=0.011). There was no significant difference found between HMI and ultimate need for surgery (p>0.999).

Conclusion: Patients without HMI had significantly higher pain scores with pre-injection PHF and impingement (FADIR) maneuvers and greater pain relief with PHF than those with HMI, however, decrease in impingement pain did not significantly relate to HMI status. Physicians can use this information to better counsel patients on the utility and expectations of pain relief with therapeutic intra-articular hip injections. A correlation between hip dysplasia and HMI was also noted in the data, the clinical significance of this may be further investigated in the future. No relationship was found between HMI and the ultimate need for surgical intervention, which may be useful when discussing long term outcomes with patients. Overall, HMI is an important factor that can allow physicians to better counsel patients on the causes of their pain and expectations on the utility of different treatments and the progression of their care.