Poster 110: Depth of Tissue Necrosis Following Footprint Preparation with Arthroscopic Radiofrequency Ablation

Abstract

Objectives:

Successful rotator cuff repair depends upon both secure fixation and biologic integration at the bone-tendon interface. Viable osteocytes and sound bony architecture contribute to the mechanical stability of suture anchor repair constructs. Furthermore, because tendons are hypovascular, preserving the microvasculature of the underlying bone bed is important. To create the bone-tendon interface, shoulder surgeons typically employ three different techniques to clear soft tissue from the footprint prior to rotator cuff repair: mechanical debridement, radiofrequency coagulation, and radiofrequency ablation. Conventional radiofrequency devices use radiofrequency energy to vaporize tissue, often in the setting of tumor resection to kill cancerous tissue. In arthroscopy, bipolar radiofrequency wands capitalize on the saline environment, passing radiofrequency waves through the conductive saline medium creating high energy ions. The result is a plasma field that can gently dissolve tissue with limited heat penetration to the surrounding environment, which is referred to as “coblation.” However, the extent to which this energy penetrates the adjacent tissue, potentially damaging nearby vasculature and osteocytes, is unknown. This study aims to explore the histological depth of tissue necrosis caused by arthroscopic radiofrequency ablation wands in comparison to a mechanical shaver.

Methods:

6 bovine metacarpal bones were collected one hour after devascularization and submerged in normal saline. Footprints were created by a radiofrequency ablation wand, at both the coagulation and ablation settings, and a mechanical shaver. Preparation was performed at 5 and 15 seconds. After the specimens were processed and prepared as hematoxylin and eosin-stained microscopic slides, each footprint was evaluated microscopically by a fellowship-trained pathologist. Depth of tissue destruction, preservation of periosteum, and osteocyte necrosis were evaluated histologically compared to the control sections for each treatment method.

Results:

Both the coagulation and ablation settings on the radiofrequency ablation wand were compared to the sections debrided with the mechanical shaver and the control sections. The ablation setting removed significantly more tissue than the coagulation setting at 5 seconds and 15 seconds of energy exposure (0.67 mm vs. 2.3 mm; P = .001 and 1.5 mm vs. 3.58 mm; P = .012) (table 1). While the depth of soft tissue destruction increased with time, the difference between 5 and 15 seconds for either treatment was not significant (0.67 mm vs. 1.5 mm; P = ,088, 2.3 mm vs. 3.58 mm; P = .051). The periosteum was rarely breached by any treatment and was seen to be well preserved in most sections. Osteocytes remained viable in the central area of treatment, and the normal cortical bone architecture was maintained. Compared to the control bone sections (figure 1) there was one section treated with ablation for 15 seconds that showed complete loss of overlying soft tissue in the treatment area and necrotic osteocytes at a depth of 0.5 mm from the treatment area (figure 2, 3).

Conclusions:

When used appropriately, arthroscopic radiofrequency ablation techniques effectively debride soft tissue from the rotator cuff footprint while preserving the underlying periosteal vasculature and cortical osteocytes. However, our results do show that local tissue destruction increases with degree of radiofrequency energy and exposure time which can lead to necrosis of the underlying tissues including the periosteum, osteocytes, and microvasculature. This has the potential to impair the biologic tendon-to-bone healing as well as the integrity of the mechanical repair construct, which would ultimately lead to failure of the repair. Thus, it is important for surgeons to be cautious while using arthroscopic radiofrequency techniques while preparing tendon footprints.

TABLE 1.

Depth of Soft Tissue Destruction by Treatment in millimeters (mm)

Figure 1.

Control, 20X. Histologic section demonstrating normal- periosteum, bony architecture, and viable osteocytes. White arrow: intact periosteum. Black arrow: Viable osteocyte.

Figure 2.

Ablation 15 seconds, 10X. White arrow: intact periosteum. Black arrow: treatment area with complete loss of periosteum

Figure 3.

Ablation 15 seconds, 20X. Histologic section demonstrating necrotic osieocytes at a depth of 0.5 mm below the treatment area.j White arrow: zone of necrotic osteocytes. Black arrow: viable osteocyie