This article is more than 5 years old. Information may no longer be current.
Loose implants signal risk of proximal femoral remodeling
A research team found up to 21% incidence of varus femoral remodeling in the hip revisions they studied.
Click Here to Manage Email Alerts
In results of a retrospective study conducted at Rush University Medical Center in Chicago, investigators found more than 20% of total hip arthroplasty cases requiring a revision had clinically-relevant remodeling of the proximal femur.
Investigators defined varus femoral remodeling (VFR) to be present if the proposed revision stem fit the diaphysis distally, but was positioned outside the proximal metaphysis
“It is critical that revision total hip arthroplasty (THA) surgeons understand the concept of VFR as these deformities can complicate the insertion of a revision femoral component, leading to undersizing of the stem or periprosthetic fracture,” Jared R.H. Foran, MD, of Golden, Colo., said at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons.
Foran and colleagues reviewed radiographs for 205 consecutive THA cases for which revisions were indicated, excluding those with a periprosthetic fracture or infection without loosening. They graded the remaining films for Paprosky class, which is a femoral defect classification, and presence of VFR, and used a template to determine which stems met the definition of VFR.
“Unexpectedly, we found 5% of femurs actually had valgus remodeling … the distal aspect of the stem fit the diaphysis distally, but lied outside the medial cortex proximally,” Foran said. “That has never been previously described to our knowledge, and thus, proximal femoral remodeling (PFR) is probably a better term than varus remodeling.”
Risk factors identified
The findings elucidated key risk factors associated with PFR, which Foran encouraged joint replacement surgeons to better understand: “Proximal femoral remodeling prevalence is up to 21%. The major risk factors include worsening bone loss (i.e., increasing Paprosky class), loose femoral components, fully-porous coated diaphyseal engaging stems and cemented femoral components.”
Each increase in Paprosky class raised the risk of remodeling by a factor of more than three. Based on the presentation and abstract, other important remodeling risk factors were the presence of loose as opposed to well-fixed implants and male gender. Implant longevity was only a very weak risk factor for remodeling, Foran said.
Managing proximal femoral remodeling and deformity
Extended trochanteric osteotomies (ETOs) were performed in 59% of femurs with varus remodeling and 55% of those with valgus remodeling, but he noted that one weakness of the study was that the actual reasons for the ETOs were not clear from the data, and were not necessarily performed to compensate for remodeling.
Foran also noted that remodeling into retroversion is likewise commonly seen at the time of femoral revision, and that using plain radiographs, the authors may not have been able to fully define what are oftentimes complex, three-dimensional deformities.
“Nonetheless, surgeons performing femoral revisions must be aware that proximal femoral remodeling into varus, valgus and/or retroversion occurs frequently, and they should be ready to manage such deformities to optimize both stability of the revision implant and recreate appropriate anteversion to avoid a dislocation postoperatively” Foran said. “Such deformities may require an osteotomy to correct or a modular implant to compensate for these deformities to optimize joint stability.” – by Susan M. Rapp
Reference:
- Foran JRH, Brown NM, Della Valle CJ, et al. Varus remodeling of the femur in revision total hip arthroplasty Paper #187. Presented at the 2011 Annual Meeting of the American Academy of Orthopaedic Surgeons. Feb. 15-19. San Diego.
- Jared R.H. Foran, MD, can be reached at Panorama Orthopedics & Spine Center, 660 Golden Ridge Rd., Suite 250, Golden, CO 80401; 303-233-1223; email: thepractice@panoramaortho.com.
- Disclosure: He has no relevant financial disclosures.
