The Link Between Total Knee Arthroplasty (TKA) and the Hindfoot

The knee lies midway along the mechanical axis between the hip and the foot, so it’s unsurprising that TKA alignment can impact foot and ankle function. It has been long known that the subtalar joint is crucial in accommodating ankle fusion, so it’s not unexpected that TKA alignment also affects it. 

Subtalar dysfunction correlates to the amount of varus knee correction and BMI

Using varus knee arthritis as their clinical model, authors of the study Risk Factors for Foot and Ankle Pain After Total Knee Arthroplasty and the Role of Subtalar Joint Motion Capacity, studied 184 TKA. They used radiographic data, patient-reported outcomes, and measurements of ankle and subtalar joint motion to conduct their research. 

Patients were divided into two groups, based on their post-surgery American Orthopedic Foot and Ankle Society hindfoot sores: 

• Group 1: 142 patients who did not have deteriorating hindfoot scores after surgery. They had a mean pre-operative varus angle of 11.5 degrees and a mean Body Mass Index of 26.7.

• Group 2: 42 patients who experienced a deterioration in their post-operative hindfoot scores. They had a mean pre-operative varus angle of 14.2 degrees and a mean BMI of 29.5.

Motion: There is a significant difference, with Group 2 showing comprised subtalar motion pre- and post-operatively. 

What did we learn?

High preoperative knee varus degree and BMI values, especially diminished preoperative subtalar joint motion capacity together with these values, are risk factors for postoperative foot and ankle pain after TKA. Discussing these risks is a great way to strike up a collaborative conversation with your TKA colleagues.