Design: Study on the cases of the united interlocked intramedullary (IM) nailed humeral shaft fractures. Objective: To assess the healing pattern of nailed humeral shaft fracture and to compare it with the results of the other previous authors’ nail-treated large bone fractures. Background data: Based on the relevant previous studies related with healing patterns of the interlocked IM nail-managed humeral shaft fractures, the current age-matched study on the participating callus for union was conceived. The comparative study on the healing patterns between the fractures of non-weight-bearing long bone — the humerus — and other large weight-bearing long bones have never been carried out previously. Materials and methods: Eighty-nine cases of the humeral shaft fractures, fixated with antegrade interlocked IM standard Kuentscher nail were subjected to the study. The patients’ ages ranged from the late teens to 9th decade of life. For the antegrade nailing, two entry points were chosen; conventional entry point in the early series, and rotator cuff interval in the late series. Results: External callus was very rarely formed [12 cases (13.4%)]. It was formed at post-fixation 6.5 weeks on average in cases with unreduced displaced fragment, and proximal interlocking. Radiographic union occurred at post-fixation 17.6 weeks on an average by primary osteonal callus. Conclusion: It was concluded that in most cases union was obtained primarily by the contact or gap healing irrespective of the patients’ ages, and that periosteal participation was very rare or negligible. Use of smaller diameter nail or new development of less rigid IM nail without external nail shape change is thought desirable to induce periosteal callus in early healing stage.
