Use Caution When Assessing Preoperative Leg-Length Discrepancy in Pediatric Patients With Anterior Cruciate Ligament Injuries

Abstract

Background:

Pre- and postoperative standing hip-to-ankle radiographs are critical for monitoring potential postoperative growth arrest and resultant deformities after pediatric anterior cruciate ligament (ACL) reconstruction.

Purpose:

To determine the prevalence of apparent preoperative leg-length discrepancies (LLDs) that resolve at the first postoperative radiographic examination in patients undergoing ACL reconstruction in order to understand what proportion of the noted preoperative deformities may have been inaccurate.

Study Design:

Case series; Level of evidence, 4.

Methods:

A retrospective review of prospectively collected preoperative and first postoperative full-length hip-to-ankle radiographs was performed in a cohort of skeletally immature patients who had an acute ACL injury and underwent subsequent surgical reconstruction. Leg length measurements for both the injured and the uninjured legs were obtained for comparison.

Results:

A total of 112 patients (mean age, 12.7 ± 1.7 years) were included (79 boys and 33 girls). Leg-length measurement interrater reliability among 3 raters for 25 randomly chosen images was nearly perfect (intraclass correlation coefficient, 0.996; 95% CI, 0.994-0.998). At baseline, there was no apparent preoperative LLD (<5 mm) in 48% (n = 54) of participants, while 37% (n = 41) displayed a small apparent LLD (5 to <10 mm), 12% (n = 13) displayed a moderate apparent LLD (10 to <15 mm), and 4% (n = 4) displayed a large apparent LLD (≥15 mm). Of the patients with an apparent preoperative LLD, 66% (n = 38) of them tore their ACL on the leg measuring shorter. At first postoperative radiographs, 48% (n = 28) of patients with an apparent preoperative LLD showed resolution to no LLD: 46% (n = 19) of patients with a small apparent preoperative LLD, 54% (n = 7) of patients with a moderate apparent LLD, and 50% (n = 2) of patients with a large apparent LLD.

Conclusion:

A high percentage of patients (48%) with apparent preoperative LLDs showed resolution to no LLDs by their first postoperative imaging, indicating that preoperative hip-to-ankle radiographs display some false LLDs in patients with recent ACL tears who are unable to fully extend their injured leg and bear weight.