Abstract
Objectives:
The rate of revision medial ulnar collateral ligament (UCL) reconstruction continues to rise annually, and two common modes of failure for are inadequate healing at the bone-tendon interface or bony fracture through drill tunnels. Although, vascularity may play a critical role in these processes, the intra-osseous blood flow to the medial epicondyle (ME) and sublime tubercle (ST) remains undefined. The purpose of this work was to better understand the vascularity of the ME and ST at baseline and to quantify vascular disruption caused by tunnel drilling for the two most common UCL reconstruction techniques: the Figure of Eight and Docking.
Methods:
Eight matched pairs (16 total specimens) of fresh-frozen cadaveric upper extremities were randomized to one of the two study groups: Docking or Figure of Eight UCL reconstruction. One elbow in each pair underwent drilling of the medial epicondyle and sublime tubercle by the assigned technique, while the contralateral elbow underwent surgical exposure without drilling to serve as a matched control. For all specimens, the brachial artery was cannulated 10 cm distal to the greater tuberosity, and the ulnar artery was cannulated 10 cm proximal to the wrist. All identified remaining vessels were tied off. Pre- and post- gadolinium MRI scans were performed on all study elbows to quantify intra-osseous vascularity by contrast enhancement, which was compared to the contralateral elbow as a matched control. Intra-osseous flow is quantified within a standardized region of interest (ROI) using customized IDL 6.4 software (Exelis, Boulder, Colorado). Following MRI, contrast-enhanced polyurethane latex was injected into all vessels and CT with 3D reconstruction and gross dissection was performed to correlate findings with the MRI and assess vessel integrity.
Results:
MRI quantification revealed drilling of the ulnar tunnels (which was the same for each group) had a minimal impact on intra-osseous vascularity of the ulna with maintenance of 96% and 99% (p=0.448) of blood flow for the Docking and Figure Eight techniques respectively (Table 1). However, perfusion to the medial epicondyle was reduced 14% (to 86% of baseline) for the Docking Technique and 60% (to 40% of baseline) for the Figure Eight technique (Figure 1). This resulted in a mean difference of 46% in reduced perfusion between the two techniques (p=0.012). Subsequent CT analysis and gross dissection revealed increased disruption of small perforating vessels of the posterior aspect of the medial epicondyle for the Figure of Eight Technique (Figure 1).
Conclusion:
Although tunnel drilling in the sublime tubercle appears to have minimal effect on intra-osseous vascularity of the proximal ulna, both the Docking Technique and the Figure of Eight Technique reduce flow in the medial epicondyle. This reduction is four times greater for the Figure of Eight Technique, and these findings may have important implications for UCL reconstruction surgery.
