Arthroscopic Treatment of Femoral Neck Impingement Cysts Using Biocomposite Anchors in the Setting of Femoroacetabular Impingement

Abstract

Background:

There is no established superior treatment for femoral neck impingement cysts, which may be symptomatic and can create a challenge in the arthroscopic treatment of femoroacetabular impingement. Isolated decompression of these cysts may lead to biomechanical compromise and an increased risk of femoral neck fracture similar to that associated with cortical perforation in osteoplasty of cam lesions, given the remaining focal osseous disruption and cortical discontinuity analogous to a burr perforation.

Indications:

In patients undergoing arthroscopic treatment of femoroacetabular impingement and found to have femoral neck impingement cyst warranting decompression, occlusion of the remaining defect with a biocomposite anchor may improve symptoms related to the impingement cyst as well as reduce the risk of femoral neck fracture.

Technique Description:

This surgical technique video demonstrates the filling of a femoral neck impingement cyst using a case example of a very active middle-aged woman undergoing arthroscopic treatment of femoroacetabular impingement. During cam osteoplasty in the peripheral compartment phase, the cyst is decompressed using a curette. An appropriately sized bioabsorbable suture anchor is secured into the defect and the sutures removed. The osteoplasty is resumed over the screw to achieve contouring of the femoral neck commensurate with an adequate head-neck offset confirmed by dynamic intraoperative hip examination.

Results:

Postoperative imaging from this procedure reveals bony in-fill with gradual dissolution of the biocomposite anchor. In our cohort of patients treated with biocomposite anchors concomitant to arthroscopic treatment of femoracetabular impingement with follow-up ranging from 2 to 12 years, there were no self-reported femoral neck fractures.

Discussion/Conclusion:

We expect that treatment of femoral neck impingement cysts with biocomposite anchors will stimulate bony in-fill of the defect stimulated by the anchor, with a decrease in the risk of femoral neck fracture as compared with an untreated cyst. Further research is needed to strengthen the evidence surrounding comparative treatment of impingement cysts as well as the optimal choice of material in the case of occlusion with a biocomposite anchor.

Graphical Abstract

This is a visual representation of the abstract.

Video Transcript

This technical note describes our technique for the arthroscopic treatment of femoral neck impingement cysts in the setting of femoracetabular impingement (FAI), in which we fill the cyst with a biocomposite suture anchor.

Our disclosures can be seen here.

Bone cysts of the femoral head-neck junction have been noted since as early as 1964 and have been variably described as “reaction areas” or “herniation pits.” The herniation pit was described by Pitt in 1982 as a round or oval subcortical radiolucency with a thin sclerotic margin most commonly located at the proximal anterosuperior femoral neck. ⁷ The etiology was thought to be related to repetitive mechanical stress from the anterior joint musculature and capsule. Impingement cysts are usually first identified incidentally on diagnostic or preoperative imaging, but can also be discovered intraoperatively and can complicate femoral neck osteoplasty during hip arthroscopy for treatment of femoroacetabular impingement. ⁴

The reported prevalence is widely variable, ranging from 4% to 12% in patients without FAI, and from 5% to 33% in patients with FAI.^5,6 There is no consensus on the management of this bony defect, but treatment strategies have included intra-articular steroid injections, activity modification, isolated surgical decompression, and bone grafting.^1,2 In the setting of cam osteoplasty, with or without isolated surgical decompression of the cyst, these lesions may create a cortical defect and act as a stress riser. This may increase the lifetime risk of femoral neck fracture, given their location most often within the principal compressive trabecular system of the femoral head and neck, and their observed tendency to enlarge over time. ³

In this technical note, we will present our preferred technique of treating impingement cysts with a biocomposite suture anchor. The aim is to stimulate bone in-growth and decrease both the lifetime fracture risk and any symptoms caused by these defects.

The patient was an otherwise healthy 46-year-old woman who presented with a 12-month history of left hip pain. She had completed extensive non-operative management in the form of physiotherapy, activity modifications, and injections. She described primarily groin and deep hip pain that was initially only present with running, pilates, and high intensity interval training (HIIT) workout exercises, but that progressed to consistently interfere with activities of daily living. She had no history of prior surgeries on the left hip.

Her focused left hip examination revealed a range of motion with flexion to 120°, external rotation to 35°, internal rotation to 10°, and a flexion abduction external rotation (FABER) distance of 25 cm. She had a positive anterior impingement sign, with no tenderness elicited across the hip joint with palpation. The distal left lower extremity was neurovascularly intact.

The image on the right is of the coronal view magnetic resonance imaging (MRI) of the patient’s left hip, revealing a reduced femoral head-neck offset consistent with cam morphology and a round, subcortical fluid-filled bony defect in the proximal anterosuperior femoral neck, consistent with an impingement cyst.

The examples on the left are from a patient with an impingement cyst of the right femoral neck, illustrated on sagittal, coronal, and axial MRI views.

We will now describe our general surgical technique in addressing FAI and related pathologies, leading up to the treatment of the impingement cyst. The first portion of the procedure is demonstrated on a patient undergoing arthroscopy of the right hip.

After standard hip arthroscopy setup and patient positioning is established, standard anterolateral and midanterior portals are placed, which has been described by our team previously. ⁸

After intraoperative assessment, the central compartment is addressed first. The acetabular rim is exposed and acetabuloplasty is performed with a curved 4.5-mm burr for suture bed prep, as demonstrated here. The amount of bone to be resected is predetermined based on preoperative radiographic evaluation. Subspine impingement is also addressed at this time if present.

In this case, minimal labral debridement was performed with excellent tissue volume for solid repair. The first of 3 anchors in this repair was placed at the 1-o’clock position in a looped fashion and tensioned appropriately prior to fixation with arthroscopic knots.

After completion of labral management and any other central compartment pathology, traction is released and the peripheral compartment is addressed with the hip flexed at 45°.

Osteoplasty of the femoral neck is performed with an arthroscopic burr after dynamic evaluation of the hip is performed to identify the location of cam morphology and impingement with the labrum.

While performing the osteoplasty, an impingement cyst was identified at the femoral head-neck junction. In order to avoid a stress riser at this site, our preferred technique is to fill the cyst with an appropriately sized anchor. To do so, a straight or curved curette and burr are used to decompress the cyst. This also helps to determine its direction and extent. The 4.5-mm burr is then used to measure the diameter of the cyst.

A tap is first used to guide in the anchor, followed by anchor placement. We use a TwinFix Ultra HA biocomposite suture anchor (Smith & Nephew, Andover, MA), composed of Poly(L-lactate) (PLL), a slowly absorbed polyester that can stimulate collagen formation, and hydroxyapatite. ⁹ These anchors come in 4.5, 5.5, and 6.5 mm sizes. The smallest possible anchor to fill the defect is used. If the defect is too large for 1 anchor, then 2 may be placed. The sutures are removed, and the anchor is then contoured with an arthroscopic burr until it is flush with the surrounding bony surface. Decompression and contouring are continued. Appropriate resection has been achieved when a dynamic examination is performed intraoperatively to reproduce motions at risk, and complete relief of impingement with preservation of the labral seal in all directions is observed.

Full cam decompression and confirmation with intraoperative dynamic examination are performed as described in previous technical notes. ⁸ Complete contouring of the biocomposite anchor is again confirmed prior to closure of the capsule.

Lastly, capsular closure is performed to preserve stability of the hip joint. In this case, two #2 Vicryl sutures are used, each passed through the capsular leaflets in a double-limb fashion with a suture passer and secured with a Quebec City Slider followed by 4 half hitch knots.

Our postoperative protocol includes placement of a postoperative hip brace and antirotational boots and restriction to <20 pounds of flat-footed weight bearing for 10 to 21 days, or 6 weeks in the case of microfracture. To reduce the formation of adhesions, we prescribe continuous passive motion for at least 2 weeks, 6 to 8 hours per day, with passive range of motion exercises. Stationary biking without restriction is initiated within the first few days after surgery. Hip external rotation and extension are limited for 2 to 3 weeks.

After the patient has progressed from passive motion through active motion to specific strength exercise milestones, they can undergo our sport test to help determine their readiness to return to their previous activities.

These are preoperative and postoperative axial MRIs, with the postoperative imaging performed approximately 1 year after hip arthroscopy for FAI including treatment of an impingement cyst with a biocomposite anchor. In the preoperative image on the left, the characteristic round-shaped, subcortical cyst with a sclerotic rim can be appreciated at the anterosuperior femoral neck. In the postoperative image on the right, the remaining components of the anchor be appreciated with full bony in-fill of the cyst present as well as complete healing of the overlying cortex.

There are currently no published outcomes on this technique, and comparative evidence is lacking. In our population of patients treated with biocomposite anchors concomitant to arthroscopic treatment of FAI with follow-up ranging from 2 to 12 years, there were no self-reported femoral neck fractures and 1 conversion to total hip arthroplasty. The majority of these patients had mixed FAI morphology.

Our expectation is that patients will achieve bony in-fill of the impingement cysts facilitated by the biocomposite anchor and achieve a decreased risk of femoral neck fracture as well as improvement of any symptoms related to the defect. For these reasons, we opt for surgical rather than conservative treatment of these lesions at the time of concomitant hip arthroscopy.