Managing pain in patients with foot and ankle pathology can be a challenge. In addition to nociceptive mechanisms, neuropathic mechanisms can contribute to pain in patients with orthopedic conditions and can be found in 10.5% to 53% of patients with chronic pain, depending on the location of the pathology. Neuropathic mechanisms include peripheral sensitization, central sensitization, reduced descending inhibition, and atrophy of cortical areas. Because preoperative diagnosis of neuropathic pain (NP) can impact therapeutic decision-making, researchers identified the need to understand the prevalence of NP in patients with foot and ankle pathology.
In this study of 533 mostly middle-aged adults, Philadelphia-based researchers used the painDETECT questionnaire to determine the presence of NP symptoms in patients with foot and ankle pathology. While the overall rate of NP symptoms was lower than previously published for hip, knee, and lower back, after sorting according to reason for surgery, they found a similar rate for patients with a history of foot/ankle surgery; significantly, they noted that this subgroup of patients had double the rate of NP symptoms compared to the native feet and ankle group.
Location played a role, with higher rates of NP symptoms in those with more proximal pathology. Rates of NP reported previously were 53% in those with lower back pain and 34% for knee osteoarthritis, compared to 12.4% in this study of patients with ankle and foot pathology. Even within the foot and ankle region, the rate of NP in the ankle and hindfoot regions was higher than the midfoot and forefoot (15.5%, 11.4%, and 7.5% for combined ankle/hindfoot, midfoot, and forefoot, respectively; see Table). The researchers did not find an explanation for this finding, but thought it was part of the peripheral sensitization mechanism and noted the fact that the more proximal the location of the pathology, the more nerves cross the area that can be sensitized.
Regarding the effect of preoperative NP on postoperative function and pain, these researchers suggest that a significant number of foot and ankle patients, both for acute injuries and chronic conditions, have NP symptoms. Based on these findings, a Visual Analog Scale pain level of >7 should alert the physician to check for NP. Similar to previous findings, they also found risk factors for NP symptoms, such as obesity, diabetes, smoking, pathologies in the ankle level, and prior surgery, though not a higher prevalence of symptoms.
In conclusion, the authors encouraged clinicians to evaluate all patients preoperatively and take NP symptoms into account when deciding on an operative intervention and pain management both before and after surgery. While they found the painDETECT a good research tool, they advised that reviewing for allodynia, dysesthesia, rest pain, or radiating pain with every patient is a good clinical practice and should be sufficient.
Source: Sidon E, Rogero R, McDonald E, et al. Prevalence of neuropathic pain symptoms in foot and ankle patients. Foot Ankle Intern. 2019, 40(6) 629–633; © 2019 by the Authors. Reprinted by permission of SAGE Publications, Inc.