The role of arthroscopic treatment of femoroacetabular impingement (FAI) in mild or borderline hip dysplasia (lateral center edge angle=18–25) is controversial. It is recommended to combine capsular plication with femoral neck osteoplasty and suture repair of the labrum. Few studies have investigated which radiological parameters are associated with failure of this procedure.

A larger number of radiological signs of mild or borderline hip dysplasia than radiological signs of FAI negatively influence the outcomes of arthroscopic treatment.

This was a retrospective study done with data collected prospectively after a minimum of 2 years’ follow-up in patients who underwent arthroscopic treatment of FAI due to cam impingement combined with mild to moderate hip dysplasia. Patients with hip osteoarthritis graded as ≥ Tönnis 2 were excluded. Functional outcome scores (mHHS and NAHS) were determined along with the need for reoperation. Three groups were defined based on the outcomes: success (mHHS ≥ Patient Acceptable Symptomatic State [PASS]); moderate improvement (improvement in mHHS + mHHS<PASS) and failure (worsening of the mHHS). Demographic data, radiographic parameters (LCEA, Tönnis angle, alpha angle, offset, FEAR index, Shenton's line, Cliff sign, anterior wall index [AWI], posterior wall index [PWI]) and intraoperative findings were compared between these three groups. The area under the curve (AUC) for the most relevant data identified during the univariate analysis were then modeled to define which factors were the best at predicting failed arthroscopic treatment a posteriori.

The study analyzed 39 patients. The mean mHHS was 76±15 [40–92]. The “success” group consisted of 21 patients (56%, 21/39), the “moderate improvement” group of 12 patients (31%, 12/39) and the failure group of 6 patients (13%, 6/39) (2 subsequently underwent total hip replacement, 4 underwent shelf acetabuloplasty). The FEAR index was significantly higher and the AWI and VCE were significantly lower in the “failure” group. The FEAR index was the best predictive factor; an index ≥ 4° detected 100% of failures with 96% specificity. The patients in the “moderate improvement” group were significantly older (37 years±8 [18–45]<p= 0.04) with a significantly higher offset (2mm±3 [−5–5]<p=0.004); an offset ≥ 2mm could detect 73% of them with a specificity of 72%.

A FEAR index ≥ 4° and offset ≥ 2mm is best able to detect patients at risk of failure and unsatisfactory results, respectively, in the mild clinical cam-type impingement in a population of FAI patients.

IV, retrospective series.