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Fig. 1 The algometer is applied to a bony prominence and pressure is increased until the patient indicates that discomfort has turned to pain, establishing the preoperative pain threshold.
Courtesy of Brian T. Nickel, MD

AAOS Now

Published 1/1/2018

Study Finds Objective Test for Preoperative Pain Predicts Postoperative Opioid Use

Arthroplasty patients with low pain thresholds may benefit from pain management ‘prehab’
A study that used an objective method to measure preoperative pain threshold (PPT) demonstrated that total joint arthroplasty patients with higher preoperative pain tolerance required less narcotic medication after surgery. The study also revealed that one-fifth of the patients received opioid prescriptions from physicians other than their orthopaedic providers in the postoperative period.

The data were presented at the 2017 annual meeting of the American Association of Hip and Knee Surgeons (AAHKS) in Dallas, by Brian T. Nickel, MD, of Duke University Medical Center. The paper, “Battling the Opioid Epidemic with Prospective Pain Threshold,” received the 2017 AAHKS James A. Rand Young Investigator’s Award.

Dr. Nickel and his fellow researchers measured PPTs in patients scheduled to undergo total knee or total hip arthroplasty (TKA/THA) using a pressure algometer, and subsequently recorded the patients’ total opioid consumption (using morphine equivalents for measurement) at 6-week follow-up.

Readings were taken with the algometer, with a maximum force of 20 pounds per square inch at two locations: the surgical joint site (the medial epicondyle for TKA or iliac crest for THA) to measure local pain threshold, and at the contralateral olecranon to measure systemic pain threshold (Figs. 1 and 2). Results revealed a negative correlation between both surgical site PPT (correlation, –0.26; P = 0.047) and systemic PPT (correlation, –31; P = 0.021) and postoperative opioid consumption (Tables 1 and 2). “In other words, the higher a patient’s objectively measured pain threshold, the less narcotics they required in the outpatient setting,” Dr. Nickel said.

The algometer PPT threshold readings ranged from 2.17 to 19.08 at the surgical site and from 3.67 to 14.42 at the systemic site.

Patients were also assessed for PPT via subjective measures (Visual Analog Score, Pain Severity Score, Pain Interference Score), but none of these scores reached significance in correlating to opioid consumption.

‘Prehab’ for pain management?
Dr. Nickel said the results, set against the backdrop of the opioid epidemic (2.4 million Americans have a severe narcotic-use disorder and 19,000 people died from prescription opioid overdose in 2015), have several potentially useful implications for orthopaedic surgeons. Because orthopaedic surgeons constitute the third-highest-prescribing group among physicians, the foremost need is for a more comprehensive, systemic approach to pain and pain medication management that includes coordination with the primary care physician. The results also point to the potential benefit of a prehabilitation (prehab) regimen for high-risk patients, including a preoperative consultation for low-threshold patients who may already be taking opioids—some 30 percent of the patients in this study fit that category—that would resemble the preoperative physical therapy that some patients undergo.

Under a more coordinated approach to pain management and medication in arthroplasty patients, the surgeon would conceivably be removed from the prescribing loop. “We need to determine who is going to be giving these patients their opioids,” Dr. Nickel said. “We need to do a better job communicating and developing a system with the primary care provider. We need to quantify the need, and monitor the dispensing and consumption accordingly.”

Dr. Nickel said he was prompted to undertake the study during his residency when the discharge paperwork for arthroplasty patients would routinely specify a prescription for a seemingly arbitrarily determined 100 opioid pills. “The monolithic process of prescribing 100 opioids for every patient upon discharge seemed incongruous to the need of each patient,” he said. “It appeared that no studies in the literature had investigated preoperative objective metrics with outpatient narcotic need. Yet despite the broad range of thresholds in patients, we continued to prescribe 100 pills to keep things standardized.”

Dr. Nickel said that the study’s findings regarding opioid use by patients before surgery, along with the revelation that 20 percent of the patients were obtaining opioids from prescribers outside the orthopaedic team, point to a need to reevaluate the generalized model of prescribing these drugs.

Fig. 1 The algometer is applied to a bony prominence and pressure is increased until the patient indicates that discomfort has turned to pain, establishing the preoperative pain threshold.
Courtesy of Brian T. Nickel, MD
Fig. 2 Jennifer Friend, a clincial research coordinator at Duke University Medical Center department of orthopaedic surgery, takes an algometer reading at the surgical site of a patient scheduled for total knee arthroplasty.
Courtesy of Brian T. Nickel, MD

“The wide distribution of narcotic consumption across all patients raises questions about our current process,” said Dr. Nickel, who noted that before the study, he and his colleagues would have estimated that “2 to 3 percent” of patients would be expected to be receiving those “extra-orthopaedic” prescriptions. “The fact that 20 percent of patients are receiving narcotic prescriptions outside of the surgery team just 6 weeks from surgery is a staggering number and highlights the need for improved interdisciplinary communication.”

Making plans
Dr. Nickel believes the study findings could provide practical guidance in developing a pain management plan for arthroplasty patients, especially those with low thresholds for pain and/or risk for medication misuse. “The finding of a negative correlation between pain threshold and opioid consumption postoperatively can translate into responsible outpatient prescribing by pointing us to provide patients with a high threshold or minimal inpatient consumption with a smaller quantity of narcotics, perhaps 10 to 20 pills. On the other hand, for those with a low threshold and difficulty controlling pain perioperatively, perhaps prescriptions should come only from a pain management team, to avoid multiple prescribers.”

The algometer used in the study (Wagner FPK 20), Dr. Nickel noted, is a “simple, easy tool that anyone can use, for all comers” and costs about $275. The PPT is determined by placing the algometer on “any bony prominence,” he explained. “The moment that discomfort turns to pain and the patients says ‘Stop,’ you get the PPT number.”

One audience member wondered if the fact that close to a third of patients might be taking some dosage of opioids preoperatively might skew the results or hobble the reliability of algometer testing. In response, Dr. Nickel said, “There are countless factors that may impact a patient’s response to the algometer testing, and by no means is any pain test perfect. However, having an objective, simple, reliable, and safe method to stratify patients may help anticipate outpatient narcotic need, preventing overprescription and identifying those at risk for heavy postoperative narcotic use.”

Elaborating on his suggestion that some kind of prehab regimen would be beneficial for selected patients, Dr. Nickel said, “Similar to the way we implement physical prehabilitation to recover from surgical trauma, a narcotic prehab could prove vital to patient education and expectations. It would help clarify the purpose of opioids and the typical duration and quantity of use, and encourage appropriate disposal procedures for excess opioids by reducing the number of excess opioids sitting in medicine cabinets across the country. This is paramount, as a recent government survey performed by the Substance Abuse and Mental Health Services Administration found only 4.4 percent of painkiller abusers obtain their pills from drug dealers; the majority obtain them from friends or relatives.”

Another audience member, noting that some patients may have a genetic disposition toward a low pain threshold, raised the idea of determining the PPT by means of genetic testing.

“Genetic markers have helped revolutionize treatment in many medical fields, but implementing genetic testing in arthroplasty may be cost-prohibitive,” Dr. Nickel said. “That being said, perhaps it could be considered in patients with known pain intolerance or chronic pain issues.”

Dr. Nickel noted that the study has a few limitations. “A potential source of bias is that we relied upon self-reporting for narcotic consumption,” he said. “It would be tremendously difficult to have patients bring in their opioid prescriptions and individually count the unused pills, but perhaps that would be an excellent follow-up study and potentially a responsible method of narcotic disposal. Second, if patients received narcotics from states outside of North Carolina and did not report them [the study relied on the North Carolina narcotic reporting database], those morphine equivalents were not traceable.”

Dr. Nickel’s coauthors are Mitchell R. Klement, MD; William A. Byrd, MD; David E. Attarian, MD; Thorsten M. Seyler, MD; and Samuel S. Wellman, MD.

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org.

Bottom Line

  • Orthopaedic surgeons are the third-highest-prescribing physician group for prescribing opioids.
  • This study used algometer testing at the surgical site and at an ipsilateral (systemic) site in patients scheduled for THA/TKA to establish preoperative pain threshold objectively.
  • The higher a patient’s objective threshold, the less narcotic medication he or she required postoperatively. Subjective pains scores did not correlate significantly.
  • Twenty percent of patients were found to be obtaining opioid prescriptions from outside the surgical team 6 weeks postoperatively.
  • The results point to a need for coordination of pain and pain medication management, including prehab, especially for low-pain threshold patients and/or those at risk for opioid use disorder.