A thirty-one-year-old woman was referred to our clinic with persistent left hip pain after surgical dislocation. Initially, the patient had presented to an outside institution with a three-year history of progressive left groin pain that failed to improve with conservative treatment. Preoperative imaging had included an anteroposterior pelvic radiograph, a false-profile radiograph, and a magnetic resonance arthrogram (MRA) (Figs. 1-A through 1-E). The patient had undergone a surgical dislocation of the left hip with acetabuloplasty, labral refixation, and femoral osteochondroplasty for pincer impingement at an outside hospital one year prior to presenting at our clinic.
Postoperatively, the patient had noted worsening of the hip pain. Three months postoperatively, radiographs had demonstrated mild subluxation of the femoral head and delayed union of the greater trochanter osteotomy site (Fig. 2). The patient had been managed conservatively at this time. Over the next nine months, the pain had failed to improve. More than one year postoperatively, an MRA had demonstrated increased subluxation of the femoral head (Fig. 3-C).
The patient was subsequently referred to our institution. At presentation, she had a modified Harris hip score of 56.1 and a University of California at Los Angeles (UCLA) activity score of 3. She reported moderate pain and a walking limitation of two to three blocks. Physical examination at presentation demonstrated a positive Trendelenburg sign and a moderate limp. Range of motion of the left hip was 105° of flexion, 35° of internal rotation at 90° of hip flexion, 60° of external rotation at 90° of hip flexion, 50° of abduction, 20° of adduction, 70° of external rotation in hip extension, and 30° of internal rotation in hip extension. She demonstrated a positive anterior impingement sign, positive apprehension sign, and negative Patrick test.
Radiographs obtained when the patient presented to our institution more than one year after the initial surgery demonstrated increased subluxation of the femoral head (Figs. 3-A and 3-B). The lateral acetabular sourcil had postoperative changes consistent with the prior acetabuloplasty. The left hip had a lateral center-edge angle (LCEA) of 3.1° (13.9° with simulated reduction of the femoral head) and an acetabular inclination of 13.1°. A false-profile view demonstrated anterior subluxation of the hip and an anterior center-edge angle (ACEA) of 4.1° (7.4° with simulated reduction of the femoral head). Additionally, the trochanteric osteotomy showed evidence of persistent radiolucency and broken/loose implants, which were concerning for nonunion. The contralateral hip had an LCEA of 19.2° and an acetabular inclination of 11.5°.
A preoperative three-dimensional computed tomography (CT) scan was obtained to assist in planning the reorientation of the remaining acetabulum (Figs. 4-A and 4-B), and it confirmed trochanteric nonunion. Given the substantial acetabular deficiency in addition to the hip subluxation, the patient underwent a PAO with use of a modified Smith-Petersen approach, as previously described in the literature3,4. Lateral reorientation of the acetabulum was limited by the substantial acetabular deficiency. Some degree of acetabular retroversion was needed in the correction because of the profound anterolateral insufficiency. Final reorientation allowed congruent reduction and stability of the hip. The osteotomy was fixed with 4.5-mm screws. The contour of the femoral head-neck junction was visualized through an arthrotomy, and a small revision osteoplasty was performed. The acetabular labrum was inspected and probed, and was found to be stable. Additionally, the trochanteric osteotomy site was explored through a lateral approach, and no gross evidence of motion was observed. Given the radiographic evidence of nonunion, the implants were removed, the osteotomy site was perforated multiple times with a drill bit, and revision fixation was placed across the osteotomy.
The patient did well postoperatively, and radiographic follow-up demonstrated concentric reduction of the hip. Measurements included an LCEA of 33.2°, an acetabular inclination of 5.3°, and an ACEA of 27.4°. At the two-year follow-up, radiographs demonstrated healing of the PAO and trochanteric osteotomy sites, with no evidence of joint space narrowing (Figs. 5-A and 5-B). The patient walked without a limp and had a negative Trendelenburg sign. She was able to return to prior activities, including jogging, horseback riding, and doubles tennis (UCLA hip score of 9). Range of motion of the left hip was 100° of flexion, 15° of internal rotation at 90° of hip flexion, 60° of external rotation at 90° of hip flexion, 50° of abduction, 20° of adduction, 15° of internal rotation in hip extension, and 60° of external rotation in hip extension. The modified Harris hip score increased to 95.7. The patient reported slight occasional pain, no limp, and unlimited walking ability.
To our knowledge, this is the first case report of iatrogenic hip subluxation treated successfully with acetabular reorientation. This case highlights several important features in the diagnosis and treatment of prearthritic hip disease. Most importantly, the diagnostic differentiation of acetabular dysplasia and FAI can be challenging and is important in optimizing surgical treatment. Secondly, PAO can be an effective treatment for iatrogenic hip dysplasia and/or instability.
While acetabular dysplasia and FAI may be differentiated based on the history and physical examination findings, this distinction is commonly not apparent5-6. Symptoms consistent with labral tears in active young adults can be present with both diagnoses. The potential difficulty in establishing an accurate diagnosis underscores the importance of radiographic and three-dimensional imaging. For radiographic assessment, we utilize a combination of anteroposterior pelvic, Dunn, frog-leg lateral, and false-profile radiographs7,8. Nonetheless, radiographic features of dysplasia and FAI have overlap. Specifically, hips with underlying acetabular dysplasia often have a proximal femoral morphology similar to those in patients with cam-type FAI9. Acetabular retroversion and coxa profunda are additional parameters commonly associated with FAI but also observed in dysplastic hips10,11.
Retrospective review of the preoperative radiographic imaging (Figs. 1-A, 1-B, and 1-C) obtained for our patient demonstrates features most consistent with borderline acetabular dysplasia (LCEA of 20°, acetabular inclination of 10°, and ACEA of 16.4°). The preoperative anteroposterior pelvic radiograph with increased pelvic tilt demonstrates an apparent positive crossover sign. Accurate assessment of acetabular version is not possible on radiographs with altered pelvic tilt12. In this situation, repeat radiographs with adjustment of the projection or three-dimensional imaging can be utilized for the assessment of version. In our patient, the axial MRA image (Fig. 1-E) is not suggestive of acetabular retroversion. The apparent retroversion in the anteroposterior pelvic radiograph results in projection of the anterior wall lateral to the edge of the acetabular sourcil. Measurement of the LCEA should be performed relative to the lateral acetabular sourcil (20°), not the lateral projection of the anterior wall (37.1°).
Surgical hip dislocation and hip arthroscopy are both effective techniques for treating FAI. Surgical hip dislocation allows for treatment of relatively severe femoral or acetabular deformities. In our patient, the initial surgical dislocation appears to have been chosen to allow treatment of the apparent acetabular overcoverage. However, this treatment worsened the underlying acetabular dysplasia and resulted in hip subluxation and progressive symptoms. Additionally, imaging on presentation at our institution was suggestive of a trochanteric nonunion. Intraoperative assessment in this case did not reveal gross motion at the osteotomy site, suggesting fibrous union. The osteotomy site was perforated multiple times with a drill bit without complete takedown, and revision fixation was inserted. Postoperative radiographs demonstrated healing of the osteotomy site. The incidence of trochanteric nonunion after surgical dislocation is 0% to 3%13-16. A recent multicenter study reported an incidence of 1.8% in 334 hips16. A step-cut trochanteric osteotomy may increase the stability of trochanteric fixation and decrease rates of nonunion17.
Hip stability involves a combination of osseous, labral, ligamentous, and muscular restraints18. Acetabular rim trimming, labral resection, and capsulotomy alter these stabilizing structures. Hip subluxation or dislocation has been previously reported after arthroscopic treatment of FAI, although it is described infrequently19-21. Benali and Katthagen21 reported a case of hip subluxation with underlying mild acetabular dysplasia after arthroscopic labral resection, and Mei-Dan et al.22 reported a case of hip subluxation with underlying dysplasia that occurred following hip arthroscopy in a patient who underwent labral repair without pincer resection. Both of these patients required total hip arthroplasty. Matsuda20 reported a case of hip dislocation after arthroscopic acetabular rim trimming and labral refixation. The patient was treated with mini-open capsulorrhaphy and had a good result at the fifteen-month follow-up. Ranawat et al.19 reported a traumatic hip dislocation following hip arthroscopy in a patient with underlying capsular laxity that was treated with arthroscopic capsular plication without recurrent instability at early follow-up. These previous reports suggest that acetabular rim trimming should not be performed in the dysplastic hip. Similarly, in pincer-type impingement, acetabular rim trimming should be performed judiciously to avoid creation of subtle or overt hip instability. In borderline cases, an adequate osteoplasty on the femoral side of the acetabulum can effectively eliminate impingement and avoid the risk associated with excessive acetabular resection. Dynamic intraoperative assessment is required to ensure that impingement has been adequately eliminated without excessive osseous resection. When major acetabular retroversion is present in association with borderline or definite acetabular dysplasia, a reverse PAO may be required23.
We present a case of iatrogenic hip instability treated with PAO with an excellent early clinical outcome. Other authors have reported capsulorrhaphy for postarthroscopic hip instability19-20. Anderson et al. reported five cases of planned staged PAO after surgical dislocation with acetabular rim trimming24. In the setting of structural instability from acetabular insufficiency, we recommend acetabular reorientation with a PAO. In our patient, hip subluxation was associated with major acetabular deficiency, and a soft-tissue procedure alone would have been inadequate. At the two-year follow-up, the patient had an excellent clinical outcome with minimal hip symptoms and without residual instability. The long-term durability of this reconstruction remains uncertain. Although the PAO substantially improved the structural anatomy of the hip, the hip is still abnormal. This case emphasizes the challenges in diagnosing and treating prearthritic hip disease, and highlights the potential for iatrogenic instability associated with excessive open or arthroscopic acetabuloplasty.
Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.