The lateral view head-neck index (LVHNI): A diagnostic tool for the sequelae of slipped capital femoral epiphysis

SummaryIntroductionIt is a well-known fact that slipped capital femoral epiphysis (SCFE) is one of the causes of premature hip osteoarthritis and anterior femoroacetabular impingement. But there are no reliable, published diagnostic methods to measure the residual deformity of slipped capital femoral epiphysis. We propose using the lateral view head-neck index (LVHNI) measurement on a specific lateral X-ray view of the hip for this purpose.HypothesisThe LVHNI can detect and quantify the posterior translation of the femoral head and this index can be measured reliably.Materials and methodsA prospective radiography study was performed by three observers. The hip X-rays of patients who were being treated by arthroplasty for hip osteoarthritis (total hip replacement or hip resurfacing) between January 2010 and December 2011 were analyzed. The LVHNI, which quantifies the posterior translation of the femoral head, was measured on a lateral view of the hip in 45° flexion/45° abduction/30° external rotation. The presence of a pistol grip deformity on A/P X-rays was also assessed.ResultsThe analysis was performed on 131 hips in 120 patients having an average age of 61 years (range 37–91). The chosen LVHNI threshold of 9% resulted in a sensitivity of 89.1% (95% CI: 78.8%–95.5%) and a specificity of 82.4% (95% CI: 71.2%–89.7%) for detecting the presence of a pistol grip deformity. Twenty percent of the hips with no visible deformity on A/P X-rays had a pathological index value. The inter-observer reproducibility was good for the LHNI [intraclass correlation coefficient (ICC): 0.61; 95% CI: 0.51–0.71] and for detecting a pistol grip deformity (ICC: 0.74; 95% CI: 0.62–0.85). The intra-observer reproducibility was excellent for the LHNI (ICC: 0.78; 95% CI: 0.57–0.88) and the pistol grip deformity (ICC: 0.85; 95% CI: 0.74–0.92).ConclusionThe LVHNI is a reliable and reproducible tool to identify deformities secondary to SCFE on specific lateral femoral neck X-rays. If the index value is greater than 9%, SCFE sequelae may be present. In addition, this study showed that 20% of hips with normal A/P X-rays had a pathological index.Level of evidenceLevel IV, prospective diagnostic study without control group.