Small interprosthetic gaps do not increase femoral peri-prosthetic fracture risk. An in vitro biomechanical analysis.

It has been hypothesized that the interprosthetic gap between ipsilateral hip and knee replacements acts as a stress riser affecting bone fracture behaviour. The aim of this study was to quantify femoral strength and fracture morphology for a wide range of interprosthetic gaps. Seven interprosthetic gaps (0-20cm) were created in artificial femora (N = 6-9/group). All specimens were loaded to failure following a compressive loading protocol. Fracture load and fracture morphology were recorded. Outcomes were compared to femora with a hip implant only (N = 6; reference group). Fracture load was highest for 0 cm gaps. All other interprosthetic gaps had fracture loads similar to that of the reference group. Fracture occurred most frequently with a medial butterfly fragment located at the tip of the hip stem.We conclude that small gaps do not act as stress risers. The specific fracture morphology may benefit from different treatment than peri-prosthetic hip fractures.

Pedicled vascularized rib transfer for reconstruction of clavicle nonunions with bony defects: anatomical and biomechanical considerations.

BACKGROUND: Clavicular nonunions with large bony defects, although rare, are difficult to treat and often result from multiple failed attempts at surgical management. Reconstruction using vascularized bone graft is the accepted standard in cases of large osseous defects. METHODS: An anatomical vascular corrosion study with cadaveric dissections and finite element analyses was designed to assess the feasibility of clavicular reconstruction with a musculo-osteous graft interposition based on a pedicled serratus anterior flap. RESULTS: Rib vascularization through the serratus anterior was demonstrated, so that the thoracic branch of the thoracodorsal artery can been considered a secondary blood supply for the seventh and eighth ribs. Single and double pedicled rib transfers allowed for reconstruction with as much as 8 cm of bone loss. The maximal stress found in the single-rib reconstruction interfaces was located at the medial contact of the plate with the clavicle. It was 2.7-fold higher than the maximal stress of the medial bow of the intact clavicle. Conversely, the double-rib reconstruction had improved mechanical resistance. A case report using a single-rib transfer supported the biomechanical study by showing that the maximal risk of material loosening was located at the medial bone interface. CONCLUSIONS: Double vascularized rib transfer as part of a serratus anterior flap should be used instead of single-rib transfer to reconstruct large clavicle defects. This technique is reproducible and does not require microvascular anastomoses. Therefore, it has potential advantages over free fibula transfer.