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Thermal shrinkage should be used with caution
Burn wounds take longer to heal; stimulating a healing response without killing tissue may be the best approach.
The role of thermal
energy in modifying connective tissues for the treatment of shoulder capsular
laxity may be more suited to that of a low-level stimulant for inducing
biological repair rather than an aggressive mechanism for primary tissue
shrinkage.
Thermal modification of connective tissue can take longer to heal than incision wounds. An additional effect of thermal shrinkage is that it results in an alteration in molecular structure.
“This modified tissue is dead. There’s no question about it; in order to shrink it you have to kill it,” said William Rodkey, DVM, director of basic science, Steadman Hawkins Sports Medicine Foundation, Vail, U.S.A.
“It has to then either be replaced or remodeled through the normal wound healing process. The surgeon must weigh the extent of the tissue shrinkage against the degree of damage required to achieve that shrinkage,” he said.
Helix breakdown
When heat is applied to collagen tissue either by laser, monopolar or bipolar radiofrequency (RF) energy, it becomes denatured and its triple helix formation unwinds. During this unwinding, it turns into a gel.
Bonds begin to break down at about 60ºC and tissue shrinkage starts at about 65ºC.
At roughly 65ºC it takes 10 minutes to get 10% shrinkage, but at 80ºC, 10% shrinkage occurs in about a minute and a half, according to Rodkey, who spoke at the 11th ESSKA Congress in Athens. Rodkey presented the information on behalf of Steven Arnoczky, DVM.
“The cells start to die at about 45ºC. Not only is the shrunken tissue dead, but the surrounding tissue may be dead as well,” he said.
The path of least resistance
The RF current always follows the path of least resistance in its return to the electrode, Rodkey said.
“Different tissues have different impediments to inhibit this current,” Rodkey said. Tissues such as capsular tissue, articular cartilage and bone influence the temperature and time needed to get the shrinkage effect.
From the cell’s point of view, heat is heat. “The cell doesn’t care whether it’s laser heat, monopolar RF, bipolar RF or a branding iron,” Rodkey said, noting that the key element is the physician on the other end of the probe.
Death and responses
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COURTESY OF JEFFREY L. HALBRECHT |
Tissue shrinkage is accompanied by cell death, morphologic changes and a decrease in tissue stiffness. Because of decreased stiffness, tissue that has been shrunken is more susceptible to stretching out.
Thermal heating stimulates a response similar to that of a skin burn, resulting in a local injury with a generalized repair response including fibroplasia and increased collagen deposition. Burn injuries take longer to heal than incision injuries, he said.
Tissue after heating is acellular and must undergo an extensive repair process before fibroplasia starts to take over. This process usually takes a minimum of 12 weeks.
Surgeons may see a decrease in collagen fiber diameter during remodeling. “There’s a dead period before the repair of tissue during which smaller fibers can be seen. The histologic appearance alone may not really reflect on the biomaterial status of that tissue,” Rodkey said.
This healing tissue is mechanically compromised and can stretch out, even in response to normal physiological loads. “We don’t know when or if at all [the tissue] returns to normal material properties,” he said.
Reasons for improvement
Rodkey cited three factors for the therapeutic efficacy of the treatment. One may be that the initial capsular shrinkage and subsequent joint stabilization may provide early improvement. Another factor may be capsular thickening in a cicatrix secondary scar formation. A third may be the loss of some pain receptors.
“You’re killing the nerves along with the other cells, so you may actually be destroying some of the sensory receptors. ... That may give the patient more of a feeling of well-being as well,” he said.
No longer recommended
Clinical studies presented in the last year have shown a high rate of unsatisfactory overall results with thermal shrinkage, Rodkey said.
“Due to the very high long-term failure rate, we can no longer recommend thermal shrinkage for partial tear of the ACL [anterior cruciate ligament],” said Jeffrey L. Halbrecht, MD, at the American Academy of Orthopaedic Surgeons 71st Annual Meeting in San Francisco. A report on that study appeared in the May issue of Orthopaedics Today [“Long-term results poor for thermal shrinkage”].
Halbrecht and colleagues from the California Pacific Medical Center in San Francisco conducted a study to determine if thermal shrinkage using a radiofrequency technique could successfully stabilize partial tears of the ACL.
The study was designed as an uncontrolled prospective study with one-year and five-year follow-up with strict inclusion criteria. “We only performed thermal shrinkage on patients who had bony attachments at the femur and tibia and less than 50% disruption of the ACL,” Halbrecht said. “We had to be able to visualize tissue response to thermal shrinkage intraoperatively, and patients had to be willing and able to comply with rigorous postop rehab.”
Patient evaluation
Patients were evaluated with KT1000 arthrometer preoperatively and intraoperatively before and after the shrinkage, and at one and five years, he said. Researchers determined clinical scores using Lysholm, Cincinnati and satisfaction criteria. “Failures were determined either by verified disruption or more than 5 mm difference KT1000 manual max compared to normal,” Halbrecht said.
There were 19 patients who underwent thermal shrinkage — 14 had partial tears and five had stretched grafts. The average age of the patients was 36 years (seven women and 12 men). Researchers performed the procedure using a monopolar radiofrequency probe.
At five years, 11 of the 14 patients (79%) had failed, requiring complete reconstruction. “When we look at the three patients who had not failed, they still had some improvement in their numbers [according to] the KT1000, Lysholm and Cincinnati tests,” he said. “But there was a clear trend toward decreasing scores between one and five years.”
Tissue status
The initial degree of shrinkage may have no effect on the long-term or even short-term status of the tissue, which should lead to protection and immobilization concerns. Thermal wounds take longer to heal than incisions. “You have to attempt to balance the stresses that you need for remodeling against those which may actually disrupt the tissues once they’ve been shrunken,” Rodkey said.
The “one-wound, one-scar” goal still holds when it comes to rehabilitation. “It suggests that the soft tissue response to trauma will actually contribute to the joint stabilization,” Rodkey said. With atraumatic arthroscopy, thermal modification may be a way to add trauma and stimulus to get to the one-wound, one-scar concept.
A year after the shrinkage, researchers can observe capsular thickening and cicatrix formation. Scar tissue can develop perpendicular to the normal pattern of the capsular fibers. “That makes you wonder if you’re getting the scar at 90º, how long will this actually last and how functional is it?” he said.
“We need to worry about modulations of the scar formation during the remodeling. … Perhaps we can do the initial shrinkage just to initiate a secondary response that would start a cascade of healing rather than just a gross shrinkage of all the tissue.
“Until the basic science and the clinical research have been conducted, the use of thermal energy to treat degenerative cartilage or lax ACL should be considered experimental and should be done with a great deal of caution,” he said.
Correspondent Lou Koury contributed to this article.
For more information:
- Halbrecht JL. Long-term failure of thermal shrinkage for partial tears of the ACL. Presented at the American Orthopaedic Society for Sports Medicine Specialty Day. March 13, 2004. San Francisco.
- Rodkey W. Lecture 7. Basic science of thermal shrinkage. Presented at the 11th ESSKA Congress and 4th World Congress on Sports Trauma. May 5-8, 2004. Athens.