Acetabular Rim Variants

Abstract

Background and Indications:

Acetabular rim ossification variants have a reported incidence of 17%. These variants include labral calcifications, os acetabuli or acetabular rim fractures, and labral ossification. Labral calcifications are small soft calcification deposits within the labrum in patients with femoroacetabular impingement (FAI). The overall cause is unknown. For acetabular rim fractures/os acetabuli, there are several proposed causes, including unfused secondary ossification center (true os acetabuli) and repetitive microtrauma leading to a stress fracture of the acetabulum (acetabular rim fractures). Surgical intervention can include excision versus fixation. Labral ossification involves circumferential ossification of the labrum that is contiguous with the lateral edge of the acetabular rim. Surgical intervention can include labral debridement, repair, or reconstruction.

Technique Description:

In labral calcification debridement, the superior aspect of the labrum is incised with a radiofrequency device or a beaver blade, and a shaver is reintroduced to remove the calcifications. For acetabular rim fractures/os acetabuli, if excision would lead to iatrogenic dysplasia, then the decision to fix the os back to the acetabulum is made. Several techniques for fixation have been described, including the suture-on-screw technique and the all-suture anchor suture–staple configuration. For labral ossification, surgical decision-making depends on the degree of ossification and the quality of the remaining labrum. If adequate labrum is available, then acetabuloplasty and labral repair are indicated. If inadequate, then acetabuloplasty and labral reconstruction are often chosen.

Results:

One study reported superior results with excision of the os acetabuli and correction of bony impingement with labral repair compared to FAI alone. A second study demonstrated that patients with labral ossification had significantly lower patient-reported outcomes (PROs) preoperatively but similar improvement postoperatively to patients without labral ossification. Another study showed that patients with symptomatic FAI and labral calcifications can be effectively treated with hip arthroscopy at a 2-year follow-up.

Discussion/Conclusion:

Acetabular rim ossification variants are common among patients with FAI. The accurate diagnosis and management of these patients are paramount. With appropriate treatment, patients achieve similar improvement in PROs as compared to those with FAI alone.

Patient Consent Disclosure Statement:

The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

We will discuss acetabular rim variants and present 3 unique case examples of different acetabular rim pathologies addressed with hip arthroscopy. Here are our disclosures. The following topics will be covered in this video. Radiopaque structures resembling an ossicle located around the acetabular rim have long been described in the literature. ¹¹ Acetabular rim variants include secondary ossification centers, acetabular rim fractures, labral calcifications, and labral ossification. The reported radiographic prevalence of acetabular rim ossicles ranges from 4% to 41% in patients with symptomatic femoroacetabular impingement (FAI) and 7% to 13% in asymptomatic patients.^{1,3-6,14,16,19,20,23,24}

Background

Os acetabuli and acetabular rim fractures are bone fragments located at the acetabular rim. True os acetabuli arise from unfused secondary ossification centers. Acetabular rim stress fractures typically occur in the setting of FAI. ¹³ True os acetabuli have a round shape and an oblique or horizontal radiolucent line relative to the acetabular roof.^16,18,21 Acetabular rim stress fractures have a perpendicular fracture line relative to the acetabular roof.^8,15,16 Surgical management can include direct removal, trimming or decompression, or fixation. Surgical management of symptomatic os acetabuli and acetabular rim stress fractures may be required for some patients who have unsuccessful conservative treatment. When evaluating these conditions, it is critical to pay attention to the lateral center-edge angle. Often, these os can be completely excised as part of a FAI correction procedure. However, if removing the bone fragment would result in loss of acetabular coverage and stability, then fixation may be needed.

Labral calcifications are small radiodensities adjacent to the lateral edge of the acetabulum.^10,12,21,22 They can be associated with calcium deposition disease. The overall pathogenesis is unclear, with possible traumatic, genetic, and local metabolic factors playing a role. Treatment of labral calcifications can include debridement as a part of FAI surgery. Overall, these patients do well, and 2-year outcomes are similar to those undergoing hip arthroscopy for FAI without labral calcifications.

Labral ossification relates to circumferential ossification of the labrum that is contiguous with the lateral edge of the acetabular rim. ¹⁷ Labral ossification can be a cause of pincer impingement due to osseous transformation of labral soft tissues.^2,9 The etiology is unclear, but there is an association with HLA B-27. Labral ossification can be treated surgically with labral debridement, repair, or reconstruction. Studies have shown that these patients can do well following hip arthroscopy, but they may have lower preoperative outcome scores compared to those without labral ossification.

Labral reconstruction may be considered when there is 2 to 3 mm or less of labrum about the anterosuperior aspect of the acetabulum. ⁷ We will now show a case presentation to help illustrate these different conditions.

Indications and Technique Description

Our first case is a 29-year-old man with worsening right hip pain. He has had pain for many years. He denies any trauma, and his pain is primarily located in the anterior groin. He has had extensive formal supervised physical therapy with minimal benefit. On physical examination, he has limitations in range of motion of the right hip with flexion to 90°, external rotation to 30°, and internal rotation to 10°. He has a positive Stinchfield sign and pain with flexion abduction and external rotation and flexion adduction and internal rotation. Anteroposterior (AP) and 45° Dunn radiographs of his bilateral hips demonstrate a right hip acetabular rim stress fracture in the setting of FAI with cam impingement. He has an increased lateral center-edge angle when including the acetabular rim stress fracture os. However, complete removal of the os would lead to undercoverage. Coronal and sagittal magnetic resonance imaging (MRI) of the right hip demonstrates a perpendicular fracture line in relation to the acetabular roof consistent with an acetabular rim stress fracture. There is associated acetabular labral tearing, and the labrum is attached to the os itself. Three-dimensional computed tomography scan images of the right hip again demonstrate the geometry of the acetabular os and are helpful in understanding the size and location of the os in space. Given this patient has had unsuccessful conservative treatment, he was indicated for surgery with hip arthroscopy, acetabular os trimming followed by fixation, acetabuloplasty, and femoroplasty. We planned to fix the os using a suture staple technique. This is our initial intraoperative AP fluoro shot. As the hip is brought into flexion and extension, we can appreciate impingement of the os to the femur. As we further take the hip through a range of motion, we can appreciate the impingement of the os leading to levering of the hip. Upon entering the hip joint, we can appreciate the relationship of the labrum, which is attached directly to the os. After carefully reflecting the labrum from the os, the mobility of the bone fragment is apparent. We then proceed with careful trimming and decompression of the os with a high-speed burr. We use fluoroscopy to ensure appropriate resection of the os. Here we can see sequential fluoro shots demonstrating os takedown before fixation. The labrum is then repaired using knotless anchors. We proceed with fixation of the remaining os using a suture staple technique with suture anchors through the os bony fragment. Here is our final labral repair and os fixation with restoration of the suction seal. We also proceed with femoroplasty for this case with resection of his cam impingement. Here are side-by-side fluoro shots demonstrating the os pre- and postoperatively, and here are the patient’s postoperative x-rays.

Our next case is a 35-year-old woman with left hip pain. She fell off a horse 9 months ago and has had worsening pain since. Comprehensive nonoperative treatment has failed. On physical examination, she has left hip flexion to 100°, external rotation (ER) at 90° to 50°, and internal rotation (IR) at 90° to 20°. She has pain with flexion adduction and internal rotation. Here is her preoperative AP radiograph, which demonstrates pincer-type FAI with para-acetabular densities suggestive of labral calcifications. Additional x-ray views confirm these findings. MRI reveals tearing throughout the anterior superior acetabular labrum. This video shows the patient’s labrum after entering the joint when viewing from an anterolateral portal. Here we can appreciate the calcific deposits within the labrum. A blade is used to carefully incise the area of the labral calcification. The calcifications are then carefully debrided from the labrum using a shaver. We take great care to protect the labral tissue and remove only the calcifications. Once the calcifications are all removed, we then proceed with labral repair in the standard fashion. Here are intraoperative fluoro shots confirming pincer resection and removal of the labral calcifications. Here are the patient’s postoperative radiographs.

Last, we have a 49-year-old woman with worsening bilateral hip pain, with the left greater than the right. This has been atraumatic in nature, and she has been having pain for years. Comprehensive nonoperative treatment has failed. Her physical examination demonstrates flexion to 110°, ER at 90° to 50°, and IR at 90° to 20°. She has pain with flexion adduction and internal rotation and flexion abduction and external rotation. AP and Dunn view radiographs demonstrate left hip pincer-type FAI with labral ossification. The patient’s MRI demonstrates ossification of the labrum as well. Intraoperative fluoroscopic assessment demonstrates impingement secondary to labral ossification and pincer-type FAI. Upon entering the joint, there is clear ossification of the labrum with associated tearing. We elect to proceed with labral reconstruction given ossification of the labrum. It is the senior author’s preference to proceed with debridement and reconstruction when there is labral deficiency. A shaver is used to debride and remove the native labrum. The area of pincer impingement is localized with intraoperative fluoroscopy before being removed with a high-speed burr. This fluoro shot demonstrates pincer resection after takedown. We can here see the labrum resection and rim preparation with a high-speed burr to help prepare for our labral reconstruction. Here the native labrum is removed and the rim prepared for labral reconstruction.

Discussion

This video demonstrates our final reconstruction. In this case, a tensor fascia lata allograft was used to reconstruct the labrum. Postoperative x-ray demonstrates resection of the pincer impingement. Overall, our postoperative protocol involves 50% weightbearing on crutches for 4 weeks. We typically keep our rehabilitation protocol consistent between our hip arthroscopy cases, including labral reconstruction. We do not routinely brace our patients postoperatively. At the 6-week mark, we focus on working to normalize motion, strength, and gait. At the 12-week point, patients can typically begin some return to sport-specific training. Here are our references. Thank you.