Surgery may restore sensation at great toe
By Emily Delzell
Although some research has described sensory nerve dysfunction as a potential complication of hallux valgus surgery, most patients undergoing the procedure have measureable preoperative deficits—and most of these improve after surgery, according to results from a prospective study epublished in May by Foot & Ankle International.
Researchers at the St. Alphonsus Health System’s Coughlin Foot & Ankle Clinic in Boise, ID, enrolled 57 consecutive patients scheduled to undergo corrective surgery for intractable pain in the first or second metatarsophalangeal joint from a hallux valgus deformity that hadn’t responded to footwear and activity modifications or pain medication. Of these 57 patients, 48 (43 women; mean age, 49 years) returned for the final follow-up at 24 months.
Investigators established patients’ baseline levels of pain, subjective numbness, and other measures, and performed a detailed sensory exam using a Semmes-Weinstein 5.07 monofilament to detect any geometric areas of sensory deficit about the hallux. Researchers repeated the exam at three, six, and 24 months postoperatively.
Preoperatively, 37 patients (77%) had a mean sensory deficit to the monofilament of 893 mm2. At 24 month follow-up the mean deficit was 202 mm2, and 19 patients had complete resolution of numbness; the 28 patients with residual numbness had a mean deficit of 414 mm2. Two patients with no preoperative numbness showed small sensory deficits (44.8 mm2 and 111.4 mm2) at 24 months.
Patients also had improvements from preoperative levels to 24-month follow-up in mean American Orthopaedic Foot and Ankle Society scores (from 59 to 89 on a 100-point scale); mean visual analog scale pain scores (from 5.4 ± 2.3 to 1.1 ± 1.9); mean hallux valgus angle (from 29° to 9°); and mean 1-2 intermetatarsal angle (from 15° to 6°).
“Our study showed that most patients have a measurable sensory deficit before surgery, that most of the deficits improve up to twenty four months after surgery, and that neither the deficit nor its improvement significantly correlate to patient outcomes,” said lead author James Jastifer, MD, an orthopedic surgeon who is now at Borgess Medical Center in Kalamazoo, MI.
Jastifer also noted patients’ subjective experience of numbness didn’t match objective findings. Specifically, 68% of patients who reported no preoperative numbness about the great toe had measurable sensory deficits on monofilament testing. Research published in 2004 by Herron et al found a similar disconnect between subjective and objective sensory deficits in hallux valgus.
Hylton Menz, BPod(Hons), PhD, professor and head of the Lower Extremity and Gait Studies Program at La Trobe University in Bundoora, Australia, said the original injury leading to sensory deficits is most likely due to compression of the medial dorsal cutaneous nerve between the medial exostosis (bunion) and the shoe.
“Following surgery, the sensory deficit area reduced, which suggests that removal of the medial exostosis and realignment of the hallux decompresses the nerve, allowing for at least partial return of normal sensory function,” he said.
Jastifer agreed about the cause of the injury.
“We think the injury develops as the bunion deformity progresses. We also believe, based on these findings, that this nerve injury is reversible,” he said, noting that his group thinks the abnormal plantar pressure loading associated with hallux valgus is also a result of the bunion deformity and its effects on first-ray mechanics.
“Cutaneous sensory deficits are considered to be a relatively common complication of hallux valgus surgery,” Menz said. “The findings suggest that many of these ‘complications’ may in fact be preexisting, and in some cases can actually be improved by surgery. If this is the case, it may provide a sensory explanation as to why some individuals exhibit improvements in balance following hallux valgus surgery.”
A 2013 paper published in the Journal of the American Podiatric Medical Association found improvements in static balance among older adults who had undergone hallux valgus surgery. Researchers found that, compared with patients with hallux valgus who hadn’t had surgery, surgically treated patients had 29% and 63% less center of mass sway during double- and single-support balance assessments, respectively.
Jastifer JR, Coughlin MJ, Doty JF, et al. Sensory nerve dysfunction and hallux valgus correction: a prospective study. Foot Ankle Int 2014 May 7. [Epub ahead of print]
Herron ML, Kar S, Beard D, Binfield P. Sensory dysfunction in the great toe in hallux valgus. J Bone Joint Surg Br 2004;86(1):54-57.
Sadra S, Fleischer A, Klein E, et al. Hallux valgus surgery may produce early improvements in balance control: results of a cross-sectional pilot study. J Am Podiatr Med Assoc 2013;103(6): 489-497.