Iliopsoas Impingement Risk in Collared Femoral Implants: Beware of Small Femora in the Setting of a Constant Length...

Collared femoral stems have seen a resurgence in total hip arthroplasty (THA) due to improved axial and rotational mechanical stability and lower early complication rates, including periprosthetic fracture. However, the presence of a collar over the femoral calcar may cause pain due to iliopsoas impingement (IPI). The objective of this article was to analyze temporal trends in collared stem use and determine risk factors for associated IPI.

A retrospective institutional review was conducted to assess collared stem utilization and the incidence of IPI resulting in arthroscopic iliopsoas fractional lengthening (IPFL) between 2002 and 2025. Patient demographics, collar design, and implant sizing were analyzed as risk factors for IPFL. A total of 108 IPFLs and 29,070 primary THAs were performed during the study period.

While collared stem use remained relatively stable between 2002 and 2019, there was a significant increase (P = 0.003) in collar usage from 2020 onward, averaging 9.4% annual growth. A rise in IPFL procedures was observed over the same period, with a notable increase in cases involving collar overhang greater than two mm. Namely, collar overhang was observed in none of the IPFL cases in 2015, 16.7% of cases in 2020, and 31.6% of all cases in 2025 (P = 0.031). Constant length collar stems, though comprising only 19.6% of all collared stems implanted during the time period, accounted for 51.7% of collar-related IPFL cases (P < 0.001), with smaller stem sizes (size ≤ three) particularly overrepresented (P < 0.001).

While collared stems offer mechanical advantages in THA, excessive collar overhang, especially in small femora with constant length collar designs, may increase the risk of IPI, resulting in subsequent surgical intervention. Surgeons should remain vigilant about this risk during planning and implant selection. Consideration of collar geometry and awareness of femoral size-related overhang may help reduce the need for secondary interventions.