JHS - 2026-08-19 - Journal Article
Radiographic Scaphoid Waist Index and Nonunion After Scaphocapitate Fusion for Kienböck Disease.
Nishimura K, Ward C, Tunaboylu MF, Emanuels AF, Moran SL
Topics
Key Takeaway
Scaphoid waist index (WI) was numerically lower in wrists with nonunion after scaphocapitate fusion for Kienböck disease (median 0.365 vs 0.429), but the bootstrap 95% CI crossed zero, leaving the association unconfirmed in this n=22 cohort.
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Summary
This study asked whether a lower preoperative radiographic scaphoid waist index predicts nonunion after scaphocapitate fusion for Kienböck disease, using retrospective lateral radiograph measurements by two independent observers in 22 eligible wrists. Nonunion occurred in 5 of 22 wrists (23%), and median WI was lower in the nonunion group (0.365 vs 0.429), but the Hodges-Lehmann median difference of -0.0568 had a bootstrap 95% CI of -0.0981 to 0.0087, crossing zero. The exploratory type I vs type II dichotomization yielded an OR of 9.60 with an exact 95% CI of 0.64–510.98, rendering it statistically uninformative.
Key Limitation
Exclusion of 76 of 98 cases due to unrecoverable imaging or short follow-up creates a highly selected cohort that almost certainly does not represent the true operative population, making both the 23% nonunion rate and the WI-nonunion signal unreliable.
Original Abstract
PURPOSE
To evaluate whether lower radiographic scaphoid waist index (WI), measured on routine preoperative lateral wrist radiographs, is associated with nonunion after scaphocapitate fusion for Kienböck disease.
METHODS
We performed a retrospective chart and imaging review of patients who underwent scaphocapitate fusion for Kienböck disease within a single integrated multicampus health system (1996-2025). The primary outcome was nonunion. Symptomatic adjacent-joint osteoarthritis within 1 year was evaluated separately as a descriptive secondary outcome. WI was measured independently by two observers on preoperative lateral radiographs. Rater-averaged WI was analyzed as a continuous variable. A conservative dichotomized scaphoid type analysis was performed exploratorily, with type II assigned only when both observers measured WI < 0.40.
RESULTS
Of 98 scaphocapitate fusions identified, 22 met inclusion criteria after excluding cases with nonretrievable archived imaging or follow-up <1 year. Median available postoperative follow-up was 23.7 months (interquartile range [IQR]: 14.4-41.2 months); range, 12.0-185.4 months. Nonunion occurred in 5 of 22 wrists (23%). Rater-averaged WI was numerically lower in wrists with nonunion than in wrists without nonunion: median 0.365 (IQR: 0.364-0.365) versus 0.429 (IQR: 0.375-0.452). The Hodges-Lehmann median difference was -0.0568, with a bootstrap 95% CI: -0.0981 to 0.0087. In the exploratory conservative dichotomized analysis, nonunion occurred in four of nine scaphoid type II wrists and 1 of 13 scaphoid type I wrists; the odds ratio estimate was imprecise and included the null (OR: 9.60; exact 95% CI: 0.64-510.98). Symptomatic adjacent-joint osteoarthritis occurred in two wrists.
CONCLUSIONS
In this small, selected cohort, rater-averaged radiographic WI was numerically lower in wrists with nonunion, suggesting a preliminary, hypothesis-generating WI-nonunion signal. The conservative scaphoid type I versus type II dichotomization was imprecise and should not be interpreted as definitive. Larger studies with more complete follow-up and adjustment for technical and clinical confounders are needed.
TYPE OF STUDY/LEVEL OF EVIDENCE
Prognostic III.