Is pre-operative block-test with lidocaine injection efficient in predicting the functional result of revision total hip arthroplasty?

Background: While performing a hip joint aspiration for culture, a lidocaine diagnostic injection called block test can be performed during the investigation of painful total hip arthroplasties (THA). This test was formerly applied to limited series in pre-operative and without assessing the predictive value on the results of THA revision. Therefore we investigated a consecutive series of THA revisions who underwent pre-operative aspiration-block test to determine if patients with pre-operative positive block test (disappearance of symptoms) have a better clinical improvement after revision.

Hypothesis: The positive pre-operative block test has a positive predictive value greater than 80% in predicting the favourable result of THA revisions.

Materials and methods: We reviewed 152 patients who had a hip aspiration associated with a block test before their THA revision. The patients were evaluated according to the Oxford hip score (OHS). The primary outcome was considered positive if the patient presented an improvement in the OHS greater than the Minimal Clinically Important Difference (MCID; 9 points) and/or if the postoperative OHS was higher than the Patient Acceptable Symptom State (PASS, defined as 39/48).

Results: Block tests were positive for 61.2% (93/152) of patients. The median improvement in the OHS was 23.0 [IQR 16.0; 30.0] if the block test was positive versus 16.0 [IQR 4.0; 17.0] if negative (p = 0.002). The primary outcome after revision was strongly associated with block test positivity (p < 0.0001). The positive block test had a 67.7% sensitivity, 73.3% specificity, 91.4% Positive Predictive Value and 37.3% Negative Predictive Value for significant improvement after revision surgery.

Conclusion: Hip joint aspiration for culture with concomitant block test seems to be an interesting tool in predicting outcomes of revision surgery for painful THA.

Level of evidence: IV; retrospective study.