OTA 2008 Posters

Scientific Poster #118 Upper Extremity OTA-2008

Quantitative Assessment of the Vascularity of the Proximal Humerus Using Gadolinium-Enhanced Magnetic Resonance Imaging in a Cadaveric Model

Carolyn M. Hettrich, MD1 (n); Sreevathsa Boraiah, MD1 (n); Jonathan P. Dyke, MD2 (n);
David L. Helfet, MD1 (n); Dean G. Lorich, MD1 (n);
1Hospital for Special Surgery, New York, New York, USA;
2Weill Cornell Medical College, New York, New York, USA

Purpose: The current consensus in the literature, based on a study by Gerber et al, is that the anterolateral branch of the anterior circumflex artery (ACA) provides the main blood supply to the humeral head. One clinical study showed that the ACA is disrupted in 80% of proximal humerus fractures; however, clinical avascular necrosis (AVN) is rare phenomenon. As a result of this discrepancy, we performed a volumetric analysis to determine the relative contribution of the ACA and posterior circumflex artery (PCA) to the humeral head that can lead to improved prediction of AVN.

Methods: In 24 fresh-frozen cadaveric shoulders (12 matched pairs), we cannulated the axillary artery just proximal to the thoracoacromial branch and ligated the brachial artery distally in the forearm. For each pair of shoulders, one served as a control with intact vasculature, and in the contralateral side, either the ACA or the PCA was ligated. Gadolinium (Gd-DTPA) was injected through the cannulated axillary arteries and MRI was performed at 0 and 20 minutes postinjection. After completion of the MRI, a urethane polymer (PMC-780, Smooth-On Inc) was injected into the specimens, and after polymerization, the specimens were grossly dissected to visualize the vessels and confirm successful ligation. For volumetric analysis, the gadolinium uptake was quantified in each quadrant using a custom automated program. Student t tests were used to compare the gadolinium uptake between the control and ligated sides, as well as differences between the ligated ACA group and the ligated PCA group.

Results: The average increase in signal intensity/voxel was 0.51, 0.18, 0.61, and 0.67 in quadrants 0, 1, 2, and 3, respectively, on the control side. The average increase in signal intensity/ voxel was 0.54, 0.21, 1.10, and 0.87 in quadrants 0, 1, 2, and 3 with the ACA ligated (PCA patent); and 0.47, 0.40, 0.43, and 0.31 in quadrants 0, 1, 2, and 3 with the PCA ligated (ACA patent). The PCA overall supplied 59.2% of the blood supply to the humeral head, with the ACA supplying 36.3% (P <0.05). The PCA also supplied significantly more of the blood supply in quadrants 2 and 3 (P <0.05). Qualitatively, the PCA had a much larger diameter, was more redundant, and less closely adhered to the humeral head. The ACA was smaller and intimately adhered to the capsule.

Conclusion: Volumetric analysis demonstrates that the PCA supplies 59.2% of the blood supply to the humeral head, versus 36.3% in the ACA. This, along with the physical characteristics, are consistent with the clinical finding that the PCA is uninjured in 85% of patients after proximal humerus fracture and that resulting clinical AVN is a relatively rare occurrence.

If noted, the author indicates something of value received. The codes are identified as a-research or institutional support; b-miscellaneous funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts disclosed, and *disclosure not available at time of printing.

• The FDA has not cleared this drug and/or medical device for the use described in this presentation   (i.e., the drug or medical device is being discussed for an “off label” use).  ◆FDA information not available at time of printing. Δ OTA Grant.