Uniportal Endoscopic-Assisted Direct Pars Repair Using the Smiley Face Rod Method for Lumbar Spondylolysis
Article information
Abstract
Lumbar spondylolysis is a common cause of low back pain among young athletes. Although direct pars repair using the Smiley Face Rod method provides stable fixation, conventional approaches require muscle dissection, which may delay postoperative recovery. This report describes a novel ultraminimally invasive technique that combines uniportal endoscopic assistance with this robust fixation system. A 20-year-old male gymnast presented with bilateral L5 terminal-stage spondylolysis that was refractory to 6 months of conservative treatment. Uniportal endoscopic-assisted direct pars repair was performed. Through a single 8-mm portal, the pars defects were meticulously debrided and decorticated under direct endoscopic visualization. Autologous iliac crest bone graft was then delivered into the defects through the endoscope’s sheath. Subsequently, percutaneous pedicle screws were inserted through bilateral 2- to 3-cm incisions and connected with a subcutaneously tunneled U-shaped rod to achieve compression across the defects. The patient’s low back pain resolved immediately after surgery. Computed tomography confirmed bony union at 3 months, at which point the patient returned to competitive gymnastics. This uniportal endoscopic-assisted technique for the Smiley Face Rod method is technically feasible and may represent a promising approach that minimizes iatrogenic soft tissue injury. This ultra-minimally invasive strategy may offer advantages for elite athletes by facilitating rapid pain relief and enabling an early return to sport.
INTRODUCTION
Lumbar spondylolysis, a stress fracture of the pars interarticularis, is a primary cause of low back pain in adolescent athletes [1,2]. For patients whose symptoms persist despite at least six months of conservative management, surgical intervention is a viable option [3]. While spinal fusion eliminates motion, direct repair of the pars defect is a more logical alternative for young patients, as it preserves the motion segment and may prevent adjacent segment disease [4].
Among various direct repair methods, pedicle screw-based constructs, such as the "Smiley Face Rod" method, have demonstrated superior biomechanical stability and high fusion rates [4]. This technique provides robust compression across the pars defect, which is crucial for achieving solid bony union [5-9]. However, conventional open or even muscle-sparing minimally invasive surgery for this procedure requires paraspinal muscle dissection and retraction, which can cause muscle atrophy, postoperative pain, and a delayed return to sport [5,9].
The uniportal endoscopic spine surgery is an ultraminimally invasive technique that utilizes a small percutaneous portal, minimizing damage to the surrounding musculoskeletal structures [10]. This approach has been associated with less postoperative pain, shorter hospital stays, and faster recovery [11]. This technical note describes our novel surgical technique that combines the biomechanical advantages of the Smiley Face Rod method with the minimal invasiveness of the uniportal endoscopic-assisted approach, illustrated by a case of an elite gymnast.
TECHNICAL NOTE
1. Indications and Contraindications
The indications for this procedure are symptomatic progressive or terminal stage spondylolysis that has been refractory to conservative care, including activity modification, bracing, and directed physiotherapy. Ideal candidates are typically 40 years of age or younger, have high athletic demands, and present with Grade 0–I spondylolisthesis. This age cutoff is not absolute; it reflects the tendency for younger patients to have better disc preservation and bone healing potential, and less facet degeneration. Final eligibility should be based on imaging evaluation of the disc and facet joints. Clinically, the pain should be responsive to a local anesthetic pars block, with focal tenderness over the defect and pain provoked by extension and rotation maneuvers. Relative contraindications include advanced disc degeneration, dynamic instability, or a slip of grade II or greater. Additionally, severe sagittally oriented clefts not amenable to compression bridging or a large pars gap where direct compression is unlikely to achieve union may be unsuitable for this technique [8]. Active infection or coagulopathy are absolute contraindications.
2. Preoperative Planning
Thorough preoperative planning is essential. Thin slice computed tomography (CT) with multiplanar reconstructions is performed to characterize the cleft orientation, degree of sclerosis, and gap length. A three-dimensional assessment aids in planning the optimal screw trajectory and rod contour. Magnetic resonance imaging (MRI) is used to evaluate the status of the disc and facet joints, as well as to detect any inflammatory bone marrow signal around the defect. To exclude overt instability, standing flexion-extension radiographs are obtained. Based on these images, bilateral pedicle screw lengths and diameters are planned, and a short rod is precontoured to create a shallow "smile" that will span the posterior elements without impinging on adjacent structures.
3. Patient Positioning and Setup
The patient is placed in the prone position on a radiolucent table with chest and pelvic bolsters to ensure the abdomen remains free of pressure. While neuromonitoring is optional, the use of biplanar fluoroscopy is mandatory throughout the procedure. Prophylactic antibiotics are administered according to institutional protocol. Prior to incision, the midline and pedicle projections are marked on the skin under fluoroscopic guidance (Figure 1).
Skin markings for the following structures. A and B: Incisions for the 8-mm portal used in uniportal endoscopy. C: Incision for percutaneous pedicle screws (PPS) (2 cm). D: Incision for PPS placement and iliac bone harvesting (3 cm). E and F: Pedicle morphology. G and H: Iliac bone morphology.
4. Surgical Technique
1) Uniportal endoscopic access and pars preparation
The procedure begins with the uniportal endoscopic access and preparation of the pars defect (Figure 2A). An 8-mm skin incision is created directly over the pars interarticularis under fluoroscopy. On the anteroposterior view, the portal is centered over the pars defect line, slightly paramedian to the midline (Figure 1A and B). Under continuous saline irrigation, the endoscope is introduced, providing a clear, magnified view of the pars defect (Figure 2B). Fibro-sclerotic tissue from the pseudoarthrosis and the sclerotic rims of the defect are meticulously removed using endoscopic punches and a 2-mm diamond burr until bleeding cancellous bone is visualized on both edges. This thorough decortication of the cleft edges is critical for creating a vascular bed conducive to fusion, while carefully preserving cortical integrity (Figure 2C).
Intraoperative photographs. (A) Intraoperative photograph showing skin entry into the pars interarticularis defect using uniportal endoscopy. (B) Endoscopic view demonstrating exposure of the pars cleft after removal of fibrous tissue and synovial membrane (view from the left side). (C) Endoscopic view following decortication, with exposure of bleeding cancellous bone (view from the left side). (D) Photograph of harvested cancellous iliac bone and intraoperative image demonstrating graft delivery into the pars defect through the endoscope’s outer sheath.
2) Percutaneous pedicle screws
Next, percutaneous pedicle screws (PPS) are placed. Through short, 2-cm bilateral paramedian incisions following a Wiltse muscle-sparing approach, guidewires are inserted, and pedicle screws are placed under fluoroscopy. Either a standard or cortical trajectory can be used as planned preoperatively. The depth of the screw heads is confirmed to ensure a low-profile trajectory for the short rod, avoiding any violation of the facet joints.
3) Autograft preparation and delivery
Cancellous autograft was harvested from the posterior iliac crest using a bone harvesting cannula through one of the PPS incisions. Depending on the size of the pars defect, approximately 2–3 mL of cancellous graft was packed into each side through the endoscope’s outer sheath and gently tamped to fill the cleft (Figure 2D). After graft placement, continuous irrigation was minimized and the endoscope was not reintroduced for additional imaging because renewed irrigation can wash out the cancellous graft.
4) Smiley face rod insertion and compression
Finally, the Smiley Face Rod is inserted and compression is applied. The most important step is to contour the U-shaped smiley rod under fluoroscopy so that it precisely matches the depth and mediolateral position of both tulip heads, allowing smooth engagement without excessive force. The contoured short rod is passed subfascially to connect both screw heads under fluoroscopic guidance. Compression across the pars defects is then applied gradually, and final tightening is performed only after confirming appropriate construct alignment and controlled defect closure under fluoroscopy. Final fluoroscopy images are taken to verify the construct's position and ensure there is no interlaminar or facet impingement (Figure 3). The small incisions are closed with absorbable sutures or skin adhesive.
Preoperative and postoperative radiographs. (A) Preoperative anteroposterior plain radiograph. (B) Preoperative lateral radiograph demonstrating the pars defect. (C and D) Preoperative oblique radiographs demonstrating the pars defect (Scotty dog sign). (E) Postoperative anteroposterior radiograph demonstrating appropriate positioning of the pedicle screws and contoured rod. (F) Postoperative lateral radiograph demonstrating appropriate implant positioning and resolution of the pars defect through compression of the lamina achieved by the rod. (G and H) Postoperative oblique radiographs.
5. Case Presentation
A 20-year-old male elite gymnast presented with extension-provoked low back pain that had persisted for over six months. He was diagnosed with bilateral L5 terminal-stage spondylolysis. His symptoms were refractory to a structured course of rest, bracing, and targeted physiotherapy. Diagnostic pars block injections repeatedly produced temporary pain relief, but the symptoms consistently recurred, preventing him from competing. Imaging confirmed the diagnosis; CT showed bilateral L5 pars defects with sclerotic margins consistent with terminal-stage spondylolysis, defined as a persistent pars cleft and pseudoarthrosis with sclerosis on CT [12] (Figure 4A), while MRI demonstrated preserved disc height (Pfirrmann Grade II) and pericleft bone marrow edema, with no spondylolisthesis.
(A) Paramedian slice of preoperative computed tomography demonstrating the pars interarticularis defect. (B) Paramedian slice of postoperative computed tomography demonstrating resolution of the pars defect through compression of the lamina achieved by the rod. (C) Postoperative computed tomography at 3 months demonstrating bony bridging across the pars interarticularis.
The patient underwent the uniportal endoscopic-assisted Smiley Face Rod procedure as described. The operative time was 135 minutes with an estimated blood loss of only 10 mL. There were no intraoperative complications. The patient experienced immediate postoperative pain relief and was mobilized on the first postoperative day. Because the procedure was minimally invasive and the iliac crest harvest was limited primarily to cancellous bone, donor-site pain was minimal, allowing rehabilitation to begin on postoperative day 1. A brace was used for comfort for 4 weeks. Rehabilitation was staged: weeks 0–4: walking, stretching, and core exercises; weeks 4–8: increased training with gradual return to running; weeks 8–12: sport-specific conditioning; after 12 weeks: progressive return to sport after CT-confirmed bridging and pain-free functional testing.
A CT scan at 3 months confirmed bony bridging bilaterally, and the athlete returned to competition thereafter without restrictions (Figure 4C). No implant-related complications were observed during follow-up.
6. Ethics Statement
This study was conducted in accordance with the Declaration of Helsinki and approved by the institutional review board of Inanami Spine and Joint Hospital (approval number: 20251224). Informed consent for publication was obtained by the participant in this study.
DISCUSSION
This technical note illustrates that the uniportal endoscopic assistance enables direct, magnified visualization for thorough decortication of the pars defect through an 8-mm portal. It also facilitates precise autograft delivery via the endoscopic outer sheath. When combined with a PPS-based Smiley Face Rod compression construct placed through short 2- to 3-cm incisions, the approach minimizes muscle trauma while successfully preserving the index motion segment.
For young athletes with persistent pain after optimized conservative care, direct repair offers the benefit of motion preservation and has high rates of union and return-to-sport, particularly for pedicle-screw-based constructs [5,6,8]. Endoscopic-assisted repairs have previously shown the feasibility of grafting and fixation through minimal portals; our adaptation applies these principles to the Smiley Face Rod construct, merging the biomechanical robustness of PPS compression with the tissue-sparing advantages of endoscopic assistance [13,14].
Endoscopic-assisted pars repair has been reported, but the most appropriate fixation strategy likely depends on disease stage and defect morphology [13,14]. Screw-based fixation across the pars can be suitable for early to progressive-stage defects when reliable screw purchase is possible [13]. In terminal-stage pseudoarthrosis, however, a chronic cleft, sclerosis, and an evident defect gap can limit screw purchase and reduce the feasibility of direct screw fixation. In such cases, endoscopic decortication to a bleeding cancellous bed, cancellous autograft packing, and compression with a Smiley Face Rod construct may provide a practical motion-preserving strategy to stabilize the defect and promote union. Other endoscopic-assisted techniques have also been described using instrumentation that spans adjacent levels [14]. While this may increase stability, it can restrict segmental motion and may increase stress on adjacent segments, which is a particular concern in young athletes. Accordingly, we view the present technique as a minimally invasive option that preserves the index motion segment while providing robust compression across the pars defects in carefully selected terminal-stage cases.
Limitations of this report include the limited case experiences, the dual learning curve required for both endoscopy and PPS placement, and considerations regarding radiation exposure. Patient selection criteria must be strictly followed, considering factors such as disc degeneration, the length and orientation of the pars gap, and any dynamic instability. Future studies should compare the uniportal endoscopic-assisted Smiley Face Rod method with mini-open techniques, focusing on time-to-union, pain trajectories, postoperative paraspinal muscle quality, and radiation dose. Furthermore, standardizing athlete-specific rehabilitation protocols and return-to-play milestones would be beneficial.
In conclusion, this uniportal endoscopic-assisted direct pars repair using a Smiley Face Rod Method is a technically feasible and potentially promising method that minimizes iatrogenic soft tissue injury for lumbar spondylolysis patients. This ultra-minimally invasive approach offers significant advantages for elite athletes to return to sport.
Notes
Conflicts of interest
The authors have nothing to disclose.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.