Purpose <p>Evaluate a modification of the original modified Dunn technique, for unstable slipped capital femoral epiphysis (SCFE), where the proximal femoral epiphysis is not dislocated from the acetabulum.</p> Methods <p>We compared two cohorts of patients with unstable SCFE: one operated with dislocation of the femoral epiphysis (DG) and the other without (NDG). Groups were compared demographically and radiographically. Femoral head bleeding was determined after reduction of the slip. Operative time, development of AVN and other complications were registered. The influence of surgical technique and covariates on the slip correction was modeled by a generalized linear mixed model. The risk of necrosis was modeled by logistic regression.</p> Results <p>The groups (20 patients each) were similar regarding age (<i>p</i> = 0.8), time until operation (<i>p</i> = 0.8), gender (<i>p</i> = 1), laterality (<i>p</i> = 1) and race (<i>p</i> = 0.45). Operative time was longer in DG (<i>p</i> = 0.07). Not dislocating the head reduced Southwick angle correction by 3.74 degrees (<i>p</i> = 0.04). Femoral head bleeding was associated with an 85.14% reduction in AVN odds (<i>p</i> = 0.04). Shorter operative time (&lt; 200&#xa0;min) decreased AVN rate by 44% (<i>p</i> = 0.37). Both surgical techniques had similar complication rates, including 20% AVN (<i>p</i> &gt; 0.05).</p> Conclusion <p>Not dislocating the femoral head in the modified Dunn technique presents similar AVN rates when compared to the original operation, shortens the operative time but provides a lower degree of Southwick angle correction. Femoral head bleeding following slip reduction is a good prognostic indicator for AVN occurrence.</p> Level of evidence <p>Level III—Retrospective comparative study.</p>