Study Combines CT and MRI to Probe Predictors of Collapse in Flatfoot Deformity

By: Terry Stanton

A study combined an optimized assessment of soft-tissue structures provided by MRI with the dynamic evaluation of bone structures by weight-bearing CT (WBCT) in patients with flexible adult acquired flatfoot deformity (AAFD). Using the imaging, the investigators sought to assess which soft tissue structures demonstrating MRI signs of degeneration would correlate and influence more positive findings of marked bone collapse, such as such as subtalar joint subluxation, sinus tarsi, and subfibular impingement.

The study, which was displayed earlier this week as Poster 172, observed that some degree of subtalar joint subluxation, as well as sinus tarsi impingement, was found in approximately 70 percent of the 55 patients (56 feet) with flexible AAFD.

In the study, multiple WBCT and MRI variables related to the severity of the deformity were obtained for 20 men and 35 women (mean age, 53 years; range, 20–86 years). Patients were evaluated by four blinded and independent readers for markers of arch collapse (navicular-floor distance and forefoot arch angle), increased valgus alignment of the hindfoot, forefoot abduction (talonavicular uncoverage angle), subtalar joint subluxation, sinus tarsi and subfibular impingement, and soft tissue degeneration (posterior tibial tendon [PTT], spring and talocalcaneal ligaments).

In contrast to the 70 percent prevalence of subtalar joint subluxation and sinus tarsi impingement, subfibular impingement—representing a marker of even more severe collapse of the foot—was found in only 9 percent of the patients, explained Cesar De Cesar Netto, MD, PhD, a fellow at MedStar Union Memorial Hospital in Baltimore. “Regarding MRI findings,” he continued, “we saw an overall more pronounced involvement of the spring and interosseous ligament, with relatively preserved integrity of the PTT.” 

However, involvement of the tendon was the only soft tissue degeneration to influence the presence of sinus tarsi impingement (P = 0.04). Positive findings for subtalar joint subluxation significantly correlated with increased degeneration of the spring ligament (P = 0.004), as well as the interosseous ligament (P = 0.006). The only soft tissue finding to associate with subfibular impingement was involvement of the interosseous ligament (P = 0.02).

“Even though involvement of the spring and interosseous ligaments in patients with AAFD has been already demonstrated in the literature,” Dr. De Cesar Netto said, “the significant and isolated influence of pronounced degeneration of the ligaments as positive indicators of more severe collapse of the bony architecture in AAFD patients, represented by subtalar joint subluxation and subfibular impingement, must be considered as essential findings. When considering the ‘chicken or the egg’ riddle, since we don’t really know which structures degenerate first in AAFD, our results point toward an increased importance of the ligamentous structures in the development and progression of the pathology, with the degeneration of the PTT potentially representing a late finding and only the tip of the iceberg.”

Dr. De Cesar Netto said future prospective and longitudinal studies should further investigate the role of potential predictors for bone collapse and soft tissue degeneration in patients with AAFD, as they could impact treatment and surgical planning, decrease thresholds for additional soft tissue procedures such as a spring ligament reconstruction, and minimize the need for hindfoot fusion procedures.

Dr. De Cesar Netto’s coauthors of “Weight-Bearing CT and MRI Findings of Stage II Flatfoot Deformity: Can We Predict Patients at High-Risk for Foot Collapse?” are Guilherme Honda Saito, MD; Lauren Roberts, MD; Ashraf Fansa, MD; Alessio Bernasconi, MD; Harry G. Greditzer, MD, MSc; Carolyn M. Sofka, MD; Jonathan T. Deland; and Scott J. Ellis, MD. The study was performed at Hospital for Special Surgery, New York, N.Y.

Terry Stanton is the senior science writer for AAOS Now.