Carlos Luis Benitez MD, Presenter: Nothing to Disclose

Douglas Unis, Abstract Co-Author: Nothing to Disclose

To perform an MR imaging analysis of the postoperative appearance of the tensor fascia lata muscle following a minimally invasive, anterolateral approach for total hip arthroplasty. This analysis uses common MR signs seen on denervation myopathy.

Twenty six (26) patients underwent total hip arthroplasty using the modified Watson Jones anterolateral approach. Patient age ranged from 27 to 81 years (mean: 54.5 years, SD: 12). All surgeries were performed by the same surgeon over a two year period (2006 to 2008). Patients then underwent a postoperative noncontrast MRI. Median time for imaging was 9.3 months from the date of surgery (range, 2.9 to 19.4 months). Each MRI was read by the same musculoskeletal radiologist using PACS. Each examination analyzed the TFL muscle for atrophic change from denervation using three parameters: change in muscle volume, muscle edema and intermuscular fat replacement. The surrounding musculature and contralateral TFL muscle were used as the internal standard controls.

Using maximum muscle cross-section as a volume indicator, patients were categorized into 3 groups: atrophy, hypertrophy, and no change. Atrophy of the TFL muscle was seen in 61.5% of patients (16 subjects). In the atrophy group, 56% (9) showed edema, and 69% (11) had fat replacement. Hypertrophy of the TFL, also a sign of denervation injury, was seen in 11.5% (3 subjects). In the hypertrophy group, none had muscle edema or fat replacement. No volume change was seen in 27% (7 subjects). In this group, only 1 patient had muscle edema and none had fat replacement. At a median of 9.3 months, 74% of patients had signs of denervation of the TFL (atrophy and hypertrophy).

To our knowledge, the present series represents the only MR study on the postoperative appearance of the tensor fascia lata muscle following the modified Watson Jones approach. Most of our patients showed MR signs of postoperative muscle denervation: atrophy (majority) and hypertrophy (minority). Other signs of denervation such as muscle edema and fat replacement were also seen, mostly on the atrophy group.

MR imaging of the postoperative hip arthroplasty is a useful technique to evaluate for the extent of muscle denervation atrophy at the site of the incision.

Benitez, C, Unis, D, MR Imaging of the Postoperative Tensor Fascia Lata Muscle Following a Modified Watson Jones Approach for the Total Hip Arthroplasty.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013506.html