Prone-Position Modified Silfverskiöld Test: Feasibility and Reliability

Gastrocnemius tightness contributes to several foot and ankle pathologies. The Silfverskiöld test, traditionally being performed in supine or sitting positions, differentiates isolated gastrocnemius and combined gastrocnemius-soleus tightness. The senior author of this study has performed a prone-position modification in clinical practice for simplicity, practicality, and ability to provide bilateral comparison. This diagnostic reliability study aims to establish the prone-position modification of the Silfverskiöld test and compare dorsiflexion measurements with established techniques.

Prone-position modification of the Silfverskiöld test is performed with feet extending beyond the couch. Both feet are tested together with passive dorsiflexion first with knees in full extension and then in 90 degrees flexion. After initial evaluation in 5 healthy volunteers, the technique was compared with supine, sitting, and lunge tests in 15 patients with diverse foot and ankle pathologies. A consultant foot and ankle surgeon and musculoskeletal physiotherapist each performed the tests twice. Interobserver and intraobserver reliability were assessed using ICCs (2-way random effects model). Dorsiflexion differences among prone, supine, and sitting positions were examined using repeated measures analysis of variance (ANOVA) with Tukey post hoc testing. Each patient was asked to grade the 4 tests as per degree of comfort during these tests.

The prone-position modification showed good to excellent reliability. Interobserver ICCs were 0.89 (95% CI 0.77-0.97) in full extension and 0.89 (95% CI 0.79-0.97) in 90 degrees flexion. Intraobserver ICCs ranged from 0.94 to 0.97. ANOVA demonstrated no significant differences in dorsiflexion among prone, supine, and sitting positions in full extension (P = .89) or 90 degrees flexion (P = .80), with post hoc testing confirming equivalence. Majority of patients (86.7%) rated the prone test as the most comfortable.

The prone-position modification of the Silfverskiöld test provides reliable, clinically comparable dorsiflexion measurements and is well tolerated. Although findings support its utility, the modest sample size suggests that further validation in larger cohorts is warranted.

Level II, diagnostic reliability study.