Researchers from the Dartmouth-Hitchcock Medical Center hypothesized that thigh circumference, more than, for example, body mass index (BMI), make the direct anterior approach more difficult since it may be affecting component positioning.
The study, “Does the thigh circumference affect the positioning of the acetabular component when using the direct anterior approach in total hip arthroplasty?” was published in the April 30, 2019 edition of The Bone and Joint Journal.
Wayne Moschetti, M.D., M.S., section chief of the Division of Adult Reconstructive Surgery and assistant professor at the Geisel School of Medicine, Dartmouth, Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire explained to OTW how this question came up, “During anterior hip replacement I was noticing that the handle to the acetabular reamer and insertion handle for the acetabular implant were commonly contacting the patient’s thigh while preparing and inserting the acetabular component.”
“This contact, I was concerned, could adversely affect the preparation of the acetabular socket and position of the final implant. Due to this impingement between the handle and the thigh, I thought it was possible that the cup may be positioned more vertical and anteverted then I was aiming for.”
The researchers categorized thigh circumference into quartiles and then evaluated the data for non-linear relationships and improve the ability to interpret the data. They created quartiles for each level of thigh circumference (10 cm, 20 cm, and 30 cm distal to the anterior superior iliac spine). They used the smallest quartile as the reference group in all models and they made sure that there were equal numbers of patients in each quartile.
The Four Quartiles of Thigh Circumference:
20 cm distal to the anterior superior iliac spine, cm (reference: < 50)
50 to 54 cm distal
54.5 to 58 cm distal
59 to 78 cm distal
“From this you might conclude the smallest thigh circumference were those < 50cm and the largest were 59-78cm but the thighs were distributed evenly among groups.”
“Most importantly, we did see an associated increase in inclination and anteversion as thigh circumference increased. Now this did not lead to component malpositioning leading to our conclusion that total hip arthroplasty (THA) can be performed using the DAA [direct anterior approach] in patients with large thigh circumference safely.”
“It is important to note though that these findings were in a high-volume surgeon experienced with the approach and the average inclination was 40° (ideal target). For a surgeon with less reliable acetabular cup position the tendency for increase inclination and anteversion could theoretically make it more likely that the components get malpositioned if they are routinely further away from that 40° target.”
“The direct anterior approach for THA is a reliable procedure in experienced surgeons’ hands and attention should be placed on implant positioning in patients with larger thigh circumferences as there may be a tendency towards increased inclination and abduction. Understanding this relationship can allow for intra-operative accommodations to adequately place components.”
“It [this study] supports the use of the direct anterior approach for THA in patients with larger thigh circumference but one must make note of the potential for increased inclination and abduction. BMI was correlated with increase thigh circumference which is important to consider during surgical planning in patient with elevated BMIs.”
