Direct comparison of postoperative monitoring of free flaps with microdialysis, implantable cook-swartz Doppler probe, and clinical monitoring in 20 consecutive patients.

BACKGROUND: There is an increasing demand for successful free tissue transfer, with postoperative monitoring of flaps a key to early salvage. Monitoring methods have ranged from clinical techniques to invasive options, of which two are particularly applicable to buried flaps (Cook-Swartz Doppler probe and microdialysis). The evidence for these options has been represented largely in separate cohort studies, with no single study comparing these three techniques. We aim to perform this comparison in a single cohort of patients. METHODS: A prospective, consecutive cohort study comparing clinical monitoring, microdialysis and the implantable Doppler probe was undertaken. In 20 patients receiving 22 flaps, 21 flaps were monitored with microdialysis, 18 flaps with clinical observation, and 21 flaps with the Cook-Swartz Implantable Doppler probe. Exclusion was based on applicability and availability intra-operatively. Efficacy was assessed through sensitivity, specificity, positive, and negative predictive values. RESULTS: Nineteen of 22 flaps had no suspected anastomotic problems; 3 of 22 flaps were explored for anastomotic problems, with two salvaged and one lost. The implantable Doppler and microdialysis were found to detect flap statistically earlier than clinical assessment, with microdialysis better at detecting flap compromise: 100% specificity (confidence interval 31-100%) when compared to the implantable probe and clinical assessment (67%: 13-98% and 33%: 2-87%, respectively). CONCLUSIONS: Each of the Cook-Swartz Doppler probe, microdialysis and clinical assessment was found suitable for monitoring in free tissue transfer. The implantable Doppler and microdialysis offer the potential for earlier detection of flap compromise.

Coupling of Bone Resorption and Formation in Real Time: New Knowledge Gained From Human Haversian BMUs.

It is well known that bone remodeling starts with a resorption event and ends with bone formation. However, what happens in between and how resorption and formation are coupled remains mostly unknown. Remodeling is achieved by so-called basic multicellular units (BMUs), which are local teams of osteoclasts, osteoblasts, and reversal cells recently proven identical with osteoprogenitors. Their organization within a BMU cannot be appropriately analyzed in common histology. The originality of the present study is to capture the events ranging from initiation of resorption to onset of formation as a functional continuum. It was based on the position of specific cell markers in longitudinal sections of Haversian BMUs generating new canals through human long bones. It showed that initial resorption at the tip of the canal is followed by a period where newly recruited reversal/osteoprogenitor cells and osteoclasts alternate, thus revealing the existence of a mixed "reversal-resorption" phase. Three-dimensional reconstructions obtained from serial sections indicated that initial resorption is mainly involved in elongating the canal and the additional resorption events in widening it. Canal diameter measurements show that the latter contribute the most to overall resorption. Of note, the density of osteoprogenitors continuously grew along the "reversal/resorption" surface, reaching at least 39 cells/mm on initiation of bone formation. This value was independent of the length of the reversal/resorption surface. These observations strongly suggest that bone formation is initiated only above a threshold cell density, that the length of the reversal/resorption period depends on how fast osteoprogenitor recruitment reaches this threshold, and thus that the slower the rate of osteoprogenitor recruitment, the more bone is degraded. They lead to a model where the newly recognized reversal/resorption phase plays a central role in the mechanism linking osteoprogenitor recruitment and the resorption-formation switch. © 2017 American Society for Bone and Mineral Research.