A Novel Technique for Spondylolysis Repair With Pedicle Screws, Rod and Polyester Band

Case Report With Technical Note and Systematic Literature Review

Pedro Berjano, MD, PhD; Gabriele Ristori, MD; Maryem-Fama Ismael Aguirre, MD; Francesco Langella, MD; Marco Damilano, MD; Riccardo Cecchinato, MD; Alvin Pun, MD; Claudio Lamartina, MD

Disclosures

Spine. 2020;45(24):E1682-E1691. 

In This Article

Discussion

In case of spondylolysis, surgery is indicated when nonoperative measures have failed, after an attempt of at least 6 months. Direct repair of a spondylolysis by direct pars osteosynthesis is the widely preferred method of treatment in absence of severe disc degeneration or instability.

The novel SRB technique presented in this paper is a modification of the Scott technique with additional advantages. It utilizes three components to form a construct to repair the spondylolysis: pedicle screws, rod and polyester band. Polyester is a synthetic polymer made of purified terepthalic acid (PTA) or dimethyl terephthalate (DMT) and monoethylene glycol (MEG). Soft, woven, and flat polymeric bands, which are secured to the metal rod using a metal clamp, have been introduced in the last decade improving the sublaminar wiring technique.[38,31,42]

Unlike the Scott technique, which demands extensive muscle stripping and excising the iliolumbar ligament to expose the transverse process during the procedure,[23,43] the SRB technique requires minimal soft tissue dissection and reduces blood loss. Easy surgical access to the spinous process allows the surgeon to pass the polyester band under the base of the spinous process. There is no penetration of the band into the canal, and by looping the band over a transverse rod, instead of transverse processes, the risk of neurological injuries is reduced.

In earlier techniques utilizing wire as part of the construct for the repair of the spondylolysis, the variable strength of the bone, and the relatively small surface area of the wire can cause cut through of the spinous process or transverse process and bone absorption, leading to loosening of the construct and loss of stability.[44,45]

The flat profile and soft, flexible nature of polyester systems distributes contact forces over a greater area lowering the risk of cable pull-out in comparison to metal cables.[46] The gradual application of tension intraoperatively to the band allows for progressive compression across the isthmus.

In a mechanical study,[47] the tensile strength and stiffness of a polymer cable were found to be substantially greater than a titanium. These mechanical properties can potentially reduce the risk of implant failure. The other disadvantages of using metal wire as cerclage wires for the repair of spondylolysis, potentially include the low fatigue strength, cable fraying, and fragmentation that can lead to non-union.[48] There will not be any metal wear particles generated from the polymer band.

Using the SRB technique, the construct will also not be prone to dislodgement unlike a construct that utilizes hooks.[49,50] Furthermore, there are no screws across the pars defect. This allows for a greater area of bony contact as well as not hindering the bone graft to promote higher fusion rate.[37]

The application of the horizontal rod and polyester band outside the spinal canal and away from the transverse processes is relatively straightforward, making the procedure potentially easy to learn.

The potential disadvantages of performing the SRB technique for the repair of spondylolysis include the cost and availability of the polyester band compared with other previous techniques. Furthermore, if the polyester band is passed under the tip, instead of the base of the spinous process, it can introduce rotation forces across the posterior elements that potentially affect the facet joint. Further studies should be necessary to evaluate the cost-effectiveness and the clinical outcomes of this technique.

Previous Techniques Review

The purpose of this systematic review was to provide an overview of all the original surgical techniques historically described to treat spondylolysis. The research identified 21 studies describing new surgical procedures suggesting, on the one hand, a wide range of possibilities, on the other hand, the lack of scientific consensus. In particular, the research highlighted six main approaches and two combinations of original techniques. The results vary from good to excellent for all methods.

Isthmic Direct Screwing. In 1970, Buck[30] described an internal fixation with screws penetrating directly through the pars interarticularis, with good or excellent outcomes in 88% of cases. Achieving accurate placement of the screws was challenging, with a lengthy learning curve, and complications occurred in up to 40% of cases, most commonly related to screw loosening or misplacement. In this technique, the screw itself occupied much of the space of the defect in the region of the isthmus, decreasing the available area for bone grafting and fusion.[51]

In the last decades, minimally invasive surgery and modifications of the original techniques have been described. These techniques employ similar muscle sparing approaches that are more likely to maintain the continued function of the multifidus muscle. Muscle degeneration, an undesirable complication especially for sports players, can therefore be reduced.

The first author to describe a minimally invasive technique was Higashino,[20] who in 2007 added the use of a spinal endoscope to Buck screwing procedure.

In 2008, Brennan et al[21] reported a minimally invasive variation of Buck technique, by using intraoperative 3D imaging and frameless navigation. In a similar manner, Wilson et al[24] in 2016 reported a percutaneous variation using a compression screw to achieve maximal compression over the defect.

Wiring. In 1987, the Scott technique showed good subjective results reported in 80% of cases. This technique requires greater surgical exposure, with extensive stripping of the muscle in order to expose the transverse process completely. A complication rate of 14% is reported in the literature. The fragility of the fixation method and anchors obliged patients to wear a postoperative brace for 3 months to avoid wire or anchor breakage, reported in several cases.[52–54]

Several modifications of Scott technique were proposed. In particular, Salib and Pettine[29] and Songer and Rovin[40] using a combination of tension band wiring and pedicle screws, eliminated the need to pass the wire around the transverse process providing at the same time a solid fixation with excellent results and less surgical exposure.

Butterfly Plate. In the 1980s, Louis developed a technique of temporary fixation of the lumbosacral junction.[34] The advantages are a large area available for the bone graft and the avoidance of possible shortening of the pars interarticularis, as could happen with techniques that apply compression over this area. The authors reported 86% of good results and a fusion rate of 95% of the cases. Implant removal 1 year later as a secondary procedure is mandatory and postoperative bracing is advised for 3 months.

Hook-screw Construct. With the introduction of "Hook-Screw" construct, Morscher et al[41] introduces several advantages. The fixation did not depend on the shape of the isthmus defect; it allowed for maximal grafting of the defect and it would exert a compressive force across the lamina. Despite this, numerous problems were reported such as the difficulty in screw placement with a 15% risk of error, screw loosening and breakage,[55] a high risk of non-healing, with a complication rate of up to 44%. The small screw purchase in the base of the superior articular process seems responsible for the many cases of screw pullout and consequent non fusion.

A biomechanical evaluation shows that interbody flexion, extension, and torsional stiffness were the highest for the pedicle screw-hook construct, in respect to other fixation systems.[23] The first to introduce pedicle screw-hook fixation was Taddonio[56] using the Cotrel-Debousset system. Later, different authors presented their own device variations: Tokuhashi and Matsuzaki,[27] with the Isola pediculolaminar system, reported with good clinical results, without implant failure or breakage and Kakiuchi,[35] with the Texas Scottish Rite Hospital (TSRH) system, proposed a more rigid fixation.

Shaped Rod. Firstly Gillet and Petit[31] and later Ulibarri et al[23] proposed the association of pedicle screws and V- or U-shaped rod, respectively. The authors reported good to excellent results in 70% of cases, without significant complications. The biomechanical evaluation of Ulibarri variation, based on U-shaped modular linkage with multiaxial pedicle screws, revealed the least displacement across the pars defect.

Laminar Screw. In an attempt to provide a stiffer construct for higher defect-healing rates, in 2012 Patel et al[25] devised a pedicle screw–intralaminar screw construct. This relatively simple system also presented the advantage of being entirely outside of the spinal canal, decreasing the chance of a neurological injury. There was not a significant difference in stiffness between the pedicle screw–hook and pedicle screw–intralaminar screw techniques in any of the testing modes.

Combination Techniques. In the past decades, a combination of screws, rod and band cerclage were performed to offer multiple modifications aimed to reduce the invasiveness and improve the fusion rate. In particular, Tan et al[33] in 2002 and Goldstein et al[36] in 2016 provided muscle-sparing procedures reporting excellent safety and reliability.

The vast majority of the published studies presenting a new surgical technique, or its modification, are based on clinical case reports and technical note studies that reduce the quality of our research for their low level of evidence. To ascertain the validity of eligible study, only papers describing original surgical procedures were included in the systematic process. We did not perform the quality assessment of the selected studies since the inclusion criteria were strict enough to avoid the inclusion of low-quality papers. All these biases, along with the retrospective nature of studies, may influence the evaluation and the power of results.

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