Imaging changes following surgery for ischiofemoral impingement

Abstract

Partial resection of the lesser trochanter (LT plasty) has been increasingly recommended to treat ischiofemoral impingement. However, there is a lack of studies on the imaging findings following LT plasty. The purpose of this study was to assess magnetic resonance imaging (MRI) changes on the lesser trochanter and surrounding musculotendinous structures following LT plasty to treat ischiofemoral impingement. Twenty-one patients (21 hips) were studied. The LT length and cross-sectional area of the iliopsoas muscle were measured on MRI before and after surgery. The MRIs were performed on average 11 months (range, 3 to 25 months) after surgery. The mean ± standard deviation amount of LT resected (difference between pre- and postoperative LT length) was 7.3 mm ± 2.5 mm. The iliopsoas cross-sectional area decreased after the LT plasty in 95% of the hips (20/21) by an average of 35% ± 16%. The reduction in iliopsoas size had no significant correlation with improvement on the modified Harris Hip Score at a mean follow-up of 17 months after surgery (r = -0.13, P = 0.58). The iliopsoas muscle size decreased on average 35% following endoscopic LT plasty. The decrease was not correlated with midterm functional outcomes.

Keywords: Arthroscopy; femoral osteotomy; hip; ischiofemoral impingement; ischium; magnetic resonance imaging.

Figure 1.

Hip extension testing in a patient with ischiofemoral impingement in the left hip and surgically treated ischiofemoral impingement in the right hip. (a) Start position with the left hip in neutral rotation and neutral abduction. (b) Limited hip extension with compensatory lumbopelvic movement, with recreation of hip and low-back pain. (c) Adding abduction allows extension without lumbopelvic compensation by providing a pain-free clearance between the lesser trochanter and ischium. (d, e) Postoperative examination following LT plasty. The right hip is extended in neutral abduction/rotation without lumbopelvic compensation.

Figure 2.

Endoscopic treatment of ischiofemoral impingement in the left hip. (a) The leg is positioned in internal rotation and the peritrochanteric space is accessed through the anterolateral (AL) and auxiliary proximal (AuxP). (b) In sequence, an auxiliary distal portal (AuxD—black arrow) is placed at the level of the lesser trochanter under fluoroscopic guidance.

Figure 3.

Endoscopic lesser trochanter plasty. (a) The lesser trochanter (LT) is anterior to the quadratus femoris muscle (QFM) and is located under fluoroscopic guidance. In a minority of the patients, the LT is anterior to the adductor minimus muscle. (b) A small window is created in the QFM to expose the posterior surface of the LT. (c) LT plasty is performed keeping the burr within the osseous limits and preserving as much as possible of the anterior insertion of the iliopsoas muscle.

Figure 4.

Assessment of the ischiofemoral space and lesser trochanter (LT) length. (a) Preoperative axial MRI. The yellow line represents the ischiofemoral space. (b) Preoperative LT length. A line is drawn along the reminiscent of the LT growth plate (blue line). A second line is drawn (red line) from and perpendicular to the first line. The length of the red line represents the LT length. (c) Postoperative LT length.

Figure 5.

Axial MRI through the pelvis showing the cross-sectional area of the right iliopsoas muscle. (a) Preoperative MRI. The yellow area represents the cross-sectional area of the iliopsoas muscle. (b) Postoperative MRI. The green area represents the cross-sectional area of the iliopsoas muscle 17 months after LT plasty.