Suture-Staple Fixation of Os Acetabuli: Description of a Novel Fixation Technique Using Linked Knotless Suture Anchors

Abstract

Background:

An os acetabuli is a bone fragment of the acetabular rim. Several stabilization techniques have been described in the literature including the use of canulated headless compression screws, sutures placed over screws, and knotted suture anchors; however, the use of screws near the joint could either lead to irritation or increased joint surface wear if placed improperly.

Indications:

Fixation of an os acetabuli is indicated when removal of the os would result in under-coverage of the femoral head which would in turn lead to a rapid onset of arthritis.

Technique Description:

This novel technique for os acetabuli fixation uses knotless suture anchors to create a “suture-staple” construct. Following the debridement of fibrous tissue and labral repair, reduction of the acetabular os is accomplished and confirmed on intraoperative fluoroscopy. Knottless FiberTak™ Suture Anchors are placed in the anterior and the posterior aspects of the os, and the anchor suture of one anchor is passed through the pass suture of the second anchor to create a “suture-staple” configuration.

Results:

Maintenance of reduction and pain-free motion of the hip was confirmed at 3-month clinic follow-up. The x-rays obtained at this time revealed no evidence of arthritis and appropriate coverage of the hip joint.

Discussion/Conclusion:

Outcomes of other methods of os fixation are largely lacking; however, outcomes using a knotted suture anchor technique in 3 patients with 1-year follow-up seem to indicate fully healed os fragments in all patients with improvement in patient-reported outcomes scores. Longer-term follow-up will be needed to ensure this similar technique produces similar outcomes.

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

My name is Vaib Tadepalli and on behalf of myself and my coauthors, I will be discussing Suture-Staple Fixation of Os Acetabuli: Description of a Novel Fixation Technique Using Linked Knotless Suture Anchors.

Neither I nor any of my authors have any relationships to disclose with either the companies or products listed in this presentation.

In this presentation, we will be introducing the concept of an os acetabuli and discussing indications for os fixation. We will also discuss current acetabular os fixation mechanisms and documented outcomes of these fixation strategies. We will finish the presentation by walking through a case which illustrates the suture-staple technique.

An acetabular os is an osseous fragment that is located within or adjacent to the acetabular rim. It is indicated here in blue. An acetabular os may develop as a result of rim fatigue secondary to repetitive contact in cases of femoroacetabular impingement. In some cases, the fragment can be large and contribute to symptoms from femoroacetabular impingement (FAI). ¹

When symptomatic, surgery may be indicated for os acetabuli. While addressing the underlying femoroacetabular impingement is fundamental to the surgical treatment of a symptomatic os acetabuli, what to do with the os is less straightforward. The os can be fixed back to the rim, partially excised, or completely excised. Measuring the center-edge angle with and without the os helps to provide guidance for treatment. The center-edge angle (CEA) measures the angle created between a vertical line through the center of the femoral head and a line running between the center of the femoral head and the outer edge of the acetabulum. A CEA >25° indicates normal hip coverage, while a CEA <20° suggests insufficient hip coverage. A CEA between 20° and 25° suggests a mildly dysplastic hip joint and predisposes the patient to an early onset of hip arthritis. Os fixation is indicated when removal of the os would result in a CEA <25°. ²

Prior fixation techniques have been described to anchor the acetabular os. These techniques include using a canulated headless compression screw which can be introduced over a guidewire.^3,4 A suture-on-screw method is also documented with the screw providing os fixation while the accompanying suture can be used to address a concomitant labral tear. ⁵ Given the concern for possible hardware placement within the joint in both of these techniques, a suture bridge technique has also been described. ⁶

The outcomes of these fixation techniques are largely documented in case reports, given the low incidence of os fixation. Screw fixation appears to show decrease in pain and improve functional outcomes relative to baseline. ⁵ Suture fixation has been documented to show good interval healing and improvement in patient-reported outcomes score at 1 year in a sample of 3 patients. ⁶

Next, we will discuss the case presentation.

This is a preoperative x-ray taken of the patient in this case which clearly demonstrates a large acetabular os in setting of FAI. In this x-ray, it can be seen how the presence of the os results in impingement of the femoral head-neck junction during flexion of the hip. In this case, as previously discussed, full removal of the acetabular os would result in significant under coverage of the hip joint with a CEA <25°. Therefore, stabilization of the os is indicated.

In this case, standard supine hip arthroscopy setup is used on a postless table. Anterolateral and midanterior portals are established. In the arthroscopic video here, the femoral head is seen on the right and the acetabular os is seen on the left. The damaged labral tissue and chondral delamination are debrided using a motorized shaver prior to repair. A radiofrequency (RF) wand is used to carefully open the capsulolabral recess and expose the acetabular rim and acetabular os. The os can be identified as an unstable bony fragment within the capsulolabral tissue in the subspine region. Fluoroscopy can assist in localizing the fragment. The RF wand is used to fully expose and visualize the acetabular os by removing the overlying capsular tissue. It is important not to damage the labrum in the process of exposing the os.

After the overlying tissue is removed and the os is completely visualized, the anterior and posterior margins are established. Instability of the os is appreciated, given the motion seen here as it is probed by the shaver.

Following exposure of the os, it is prepared for attachment to the acetabulum as shown here. This consists of debridement of the fibrous tissue between the posterior surface of the os, and the anterior surface of the acetabular rim where the os will be fixed. In this case, the overhanging os is contributing to a pincer mechanism and the prominent edge is burred down to be flush with the adjacent acetabulum during a concurrent acetabuloplasty.

Following preparation of the os the first knotless FiberTak™ suture anchor (Arthrex, Naples, FL, USA) is placed on the posterior edge of the os taking special care to deploy the anchor in the stable acetabular rim. Following this, a second anchor is placed on the anterior edge of the os using the drill guide to reduce the os while drilling and inserting the anchor.

Now the placement of both suture anchors is observed. The anterior anchor is visualized on the right-hand side of the screen while the posterior anchor is visible on the left.

Following placement of both suture anchors, the suture from the posterior anchor, as indicated here on the left of the screen, is brought through the pass suture from the anterior anchor as shown here, and it is pulled through the anterior anchor and cinched down as seen here.

In a similar fashion, the suture from the anterior anchor is brought through the pass suture of the posterior anchor as seen here. Once again, it is cinched down to create this knotless suture-staple construct that is anchoring the os to the acetabular rim. After the anterior suture is brought through the posterior anchor, the construct can be seen as shown here.

After the suture anchors have been linked together, the stability of the os fixation is tested using the RF wand as shown here. From this clip, we can see that the os is stable in this configuration.

To further demonstrate the construct created by these suture anchors we have a pelvis model in which a similar os acetabuli has been created. First the os is reduced and the anterior anchor is placed as shown.

After that anchor is in place, the posterior anchor is drilled and placed. It should be noted that these anchors consist of one black-and-white striped passing suture and one blue-and-white striped anchor suture.

The anchor suture from the posterior anchor is passed through the passing suture of the anterior anchor and cinched down to create the first half of the “suture-staple configuration” as seen here.

Then the process is repeated with the anchor suture from the anterior anchor passed through the passing suture of the posterior anchor further stabilizing the os and finalizing the suture-staple configuration of this fixation technique.

Regarding the postoperative protocol, for the first 2 weeks, the patient is instructed to remain 50% weightbearing on the operative extremity while using crutches. They are instructed to maintain the operative extremity foot flat on the floor and limit hip flexion to 90°. Therapy at this point is limited to isometric exercises and gentle range of motion.

From 2 to 6 weeks postoperative, the patient is slowly advanced to being weightbearing as tolerated weaning from two crutches to one crutch on the contralateral side. Therapy, in this period, is geared toward increasing range of motion and strength.

With regards to our patient, at 3 weeks follow-up, the patient experienced full painless range of motion of the hip. Radiographs at this point show appropriate coverage of the femoral head and show no early indications of arthritis. Bridging callus is in place between the acetabular os and the pelvis suggesting adequate healing. At 3-month follow-up visit, the patient continued to have full painless range of motion of hip, and radiographs continue to demonstrate stable fixation.

The preoperative and postoperative x-rays for this case can be shown here. Resection of the os would have resulted in a CEA indicated by the red and blue lines as shown with an angle of roughly 23°. Current CEA is measured at 35° as shown by the angle made by the green and blue lines.

These are the references used.

Thank you very much for your time.