Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

42 Stabilization of the Sacroiliac Joint with the Sacroiliac Bone Surgical Implant

Fred H. Geisler and Jake P. Heiney

Abstract

This chapter summarizes both the surgical technique of minimally invasive surgical (MIS) sacroiliac joint (SIJ) fusion and the clinical literature. Low back pain (LBP) in the United States is the second most common reason for primary care visits after the common cold. LBP, in addition to physical disability and lost income, increases the risk of falls in the elderly. The SIJ is a known cause of pain referred to the lumbar–pelvic region that often presents as clinically similar to pain presentation from the lumbar spine or hip regions. The SIJ is the largest joint and has high shear forces with a relatively small amount of translation and rotation. There is extensive evidence that suggests the SIJ can be a pain generator, possibly the primary one, in 15 to 30% of LBP-diagnosed patients. Patients failing to achieve postoperative pain and mobility goals after lumbar spinal arthrodesis may have an SIJ pain generator. Known etiologies of SIJ pain include degenerative sacroiliitis, residual adjacent segment degeneration, and misdiagnosis after a spinal fixation procedure. Although there is only modest evidence that nonsurgical treatments are effective for any length of time, they comprise the predominant form of current clinical care. In recent years, MIS methods have become available for treatment of SIJ pain. Compared to open SIJ surgery, minimally invasive techniques involve less blood loss, shorter hospital stays, and less perioperative morbidity. Reports of MIS SIJ fusion support the improved clinical outcomes, earlier postoperative weight bearing, and improved patient satisfaction compared to open surgical techniques.

Keywords: sacroiliac joint, minimally invasive surgery, sacroiliac joint arthrodesis, degenerative sacroiliitis, sacroiliac joint disruption, sacroiliac joint dysfunction, low back pain, sacroiliac joint pain, pelvic girdle pain, titanium sacroiliac implant, previous spine surgery

42.1 Introduction

Low back pain (LBP) is a common health issue and one of the top three health issues in developed countries.¹ In the United States, after the common cold, LBP is the second most common reason for visits to primary care physicians.² Annual expenditures for chronic back pain have been estimated to exceed $100 billion per year in the United States.³ In addition to pain, disability, and lost income, LBP has also been noted to increase falls in the elderly; falls can cause hip and/or spinal fractures with an increase in morbidity and mortality.⁴

42.2 Indications and Contraindications

Pain in the lumbopelvic region can result from pathology in the lumbar, hip, or sacroiliac (SI) joint. Not only do the clinical symptoms of these areas overlap, but also often a patient has degenerative changes in more than one of these three areas. The SI joint is the largest joint in the human body and is subject to shear forces of up to 4800 N, with rotational movement of up to 4 degrees and translation capacity of 1.6 mm.⁵ Studies in healthy volunteers have helped to validate the SI joint as a cause of pain and define its innervation.⁶^,⁷ Substantial evidence suggests that the SI joint may be the pain generator in 15 to 30% of patients diagnosed with LBP.⁸^,⁹^,¹⁰^,¹¹ Etiologies of SI joint pain include degenerative sacroiliitis, inflammatory arthritis, SI joint disruptions from trauma or related to pregnancy, anatomical abnormalities such as leg length inequality and scoliosis, adjacent segment degeneration as a result of lumbar and lumbosacral spinal fixation procedures, infection, tumor, gout, and idiopathic causes.¹²^,¹³

Unfortunately, persistent or significant residual pain and disability are common after lumbar surgical procedures. There tends to be a higher frequency and severity of these problems after a lumbar spinal arthrodesis than after a simple lumbar decompression. Degeneration and dysfunction of the SI joint with pain can be the cause of either the reported postoperative pain or the failure to improve as a result of possible misdiagnosis or the presence of additional pain generators. It is interesting to note that the SI joint is the inferior adjacent segment for the L5-S1 lumbar level.¹⁴^,¹⁵^,¹⁶^,¹⁷ Radiographic evidence of SI degeneration has been reported in up to 75% of lumbar spinal fusion patients.¹⁸ The SI joint has also been reported to be the pain generator in 43% of patients with new onset or persistent pain after lumbar spinal fusion.¹⁹ The conclusion of a literature review on the correlation of LBP and SI joint pain indicates that the SI joint not only plays an important role in LBP, but also appears to be under-diagnosed.

The mainstay of care for SI degenerative pain, as with degenerative pain elsewhere in the body, is nonsurgical care. Nonsurgical treatments for SI joint pain include anti-inflammatory medication, pain medication, activity modification, weight loss, physical therapy, chiropractic care, radiofrequency ablation and SI joint steroid injections.⁸^,²⁰^,²¹ However, there is only modest evidence that any of these nonsurgical treatments is curative or effective for a long period of time.²² When these measures fail to provide significant and lasting symptom relief and the patient has persistent disabling pain, surgical options may be considered.

Surgical treatment for persistent SI joint pain was first reported in the early 1900s.²³ However, mainly due to challenges including blood loss, extended hospital stay, wound size, and difficulty with mobilization (e.g., non-weight bearing status), open surgical repair is typically reserved, even now, for only the most severe cases.²⁴^,²⁵ A major shift in philosophy about surgical management has recently occurred after the development of minimally invasive surgical methods. Compared to open surgery, minimally invasive techniques are typically associated with far less blood loss, shorter hospital stay, and less perioperative morbidity. The better patient post-operative experience after minimally invasive SI joint fusion techniques is attributable to smaller surgical incisions and less soft tissue dissection. Reports of MIS SI joint fusion confirm these postop patient benefits as well as showing improved clinical outcomes, earlier post-operative weight bearing, and overall improved patient satisfaction compared to open surgical techniques.²⁶^,²⁷^,²⁸

There are several published studies regarding minimally invasive fusion of the SI joint.²⁹^,³⁰ The literature describes two significantly different approaches to achieve this goal: a dorsal joint distraction and a lateral transarticular approach. In the dorsal approach, the SI joint is distracted and a structural material (either implant or allograft) is placed posterior to anterior within the joint on decorticated bony surfaces. Using the lateral approach, structural implants are placed across the SI joint with the lateral portion of the implant residing in the ilium and the medial end in the sacrum. Thus, the two techniques differ markedly with respect to the biomechanical stabilization and bony arthrodesis of the SI joint. By far the most common approach reported in the literature is the lateral transarticular approach. With this technique, the SI joint is accessed laterally through a small incision made into the lateral buttocks. This approach typically involves placement of one or more implants across the joint, spanning the ilium and sacrum, under fluoroscopic guidance. SI joint implant systems using both triangular-shaped and screw-based implants have been proposed. The surgical goal is to provide immediate fixation of the joint with subsequent arthrodesis that leads to a mature bony fusion over the long term. Cadaveric and finite element biomechanical studies have demonstrated marked reduction in SI joint motion after lateral, transarticular placement of a series of triangular-shaped implants. No biomechanical studies are known to support stabilization of the SI joint with a dorsal joint distraction technique.

42.2.1 Literature Review

A systematic review with a quantitative meta-analysis (MA) of operative measures and clinical outcomes reported in published prospective or retrospective studies of MIS SI joint fusion using a lateral transarticular technique has been recently performed.³¹ This review was conducted according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.³² The databases PubMed (http://www.ncbi.nlm.nih.gov/pubmed) and Embase (http://www.embase.com) were searched using the terms “sacroiliac joint” AND “fusion.” In addition to database reviews, the bibliographies of previously published systematic reviews were evaluated in an effort to identify any articles not retrieved in the database searches.³³ This review only included articles that were:

• In English.

• Original prospective or retrospective studies.

• Included at least five patients.

• Describing operative and clinical outcomes after MIS SI joint fusion using a lateral transarticular approach for SI joint dysfunction.

It excluded articles that reported:

• Dorsal distraction approach.

• Open surgical technique.

• Fusion of the pubic symphysis.

• Single case reports.

• No clinical data or very limited follow-up.

• Traumatic pelvic ring injuries.

• Ankylosing spondylitis.

• Infection or tumor.

• Studies that solely evaluated imaging.

In all included studies, patients were diagnosed with SI joint pain using a common approach based on history, physical examination findings³⁴ ( Fig. 42.1), and diagnostic SI joint block. All of the included studies reported on patients with degenerative sacroiliitis (i.e., osteoarthritic degeneration of the SI joint) or SI joint disruptions (i.e., joint disruption as a result of isolated SI trauma, pregnancy, or other causes).

Fig. 42.1 Provocative tests were used in the clinical examination that correlated with sacroiliac joint (SIJ) painful dysfunction. Most authors want three of five tests to be positive to justify proceeding with diagnostic injections of the SI joint for definitive diagnosis. (Adapted from SI-BONE 2017.³⁴)

Fig. 42.2 Multiple authors have studied the visual analog scale (VAS) pain relief after the SI-Bone procedure. There are two noteworthy points in the composite presentation of these reported outcomes. First, there is uniform agreement that a profound initial drop in the VAS in time coincidence with the surgery appears to last as long as the follow-up period. The second point is that there is a low level of residual pain remaining after this operation, which could be due to either degenerative joint disease sources other than the treated sacroiliac joint (SIJ) or the SIJ fusion only relieved a significant portion of the pain in the treated SIJ. (Adapted from Heiney et al 2015.³¹)

Fig. 42.3 Multiple authors have reported a significant decrease in the Oswestry Disability Index, a clinical scale known to correlate with increased function.

Search results yielded 241 records from PubMed and 297 from Embase that were examined. Of these, the study design and number are as follows:

• Ten retrospective single-center case series.¹²^,³⁵^,³⁶^,³⁷^,³⁸^,³⁹^,⁴⁰^,⁴¹^,⁴²^,⁴³

• Two prospective single-center case series.⁴⁴^,⁴⁵

• One multicenter retrospective case series.⁴⁶

• One single center.²⁷

• Two multicenter²⁶^,²⁸ comparative cohort studies.

• One prospective single-arm study.²⁴

• One prospective multicenter randomized controlled trial.⁴⁷

Two types of implants are represented: (1) 3 studies reported the use of a single hollow modular anchorage (HMA) screw packed with demineralized bone matrix and (2) 15 described the placement of a series (typically 3) of triangular, porous titanium plasma spray (TPS) coated implants (iFuse Implant System, SI-BONE, Inc., San Jose, CA). After eliminating the overlap in patient cohorts across studies described earlier, the sum of the literature represents 12 unique studies from 4 different countries with a total of 432 patients: 368 patients from 10 cohorts using triangular TPS-coated implants and 64 patients from 2 cohorts using HMA screws.

Reported operative parameters were procedure time, estimated blood loss (EBL), and hospital length of stay (LOS). The random effects meta-analysis (RMA) mean (95% confidence interval [CI]) procedure time was 59 minutes (50.9–66.9; range 27–78 minutes), with substantial heterogeneity across studies. The RMA mean EBL was 36.9 mL (31.4–42.38), with moderate heterogeneity across studies. Mean hospital LOS, reported in nine studies, ranged from 0.78 to 6.9 days (range 0–7 days). The RMA mean LOS was 1.7 days (1.2–2.2), with significant heterogeneity across studies.

Pain severity was reported in all studies. These are summarized in Fig. 42.2 for the iFuse triangular implant series and the HMA screw results. Outcomes at 36 months, where available, were significantly different (p< 0.0001) by implant type: mean (standard deviation [SD]) score was 2.0 (1.9) for the triangular implant and 4.6 (2.5) for the HMA screw.

ODI was used in several studies and is summarized in Fig. 42.3. Although both groups were similar in terms of baseline disability, the triangular implant cohort showed an improvement of 2.7 times that of the HMA screw cohort (baseline: 59, 54.1; 36-month: 16, 45 for the HMA screw and triangular implant, respectively).

Minimally invasive fusion of the SI joint has been performed with several types of implants using either a dorsal joint distraction technique (titanium cages packed with bone morphogenic protein,⁴⁸ allograft bone dowels,⁴⁹ or autograft iliac bone plugs⁵⁰) or, more commonly, through a lateral transarticular approach using either HMA screws packed with demineralized bone matrix¹²^,³⁷^,⁴⁴ or triangular TPS-coated implants.²⁴^,²⁶^,³⁵^,³⁶^,³⁸^,⁴² As the two techniques are fundamentally different and the body of literature supporting the latter approach is comparatively more substantial, the presented systematic review focused on the lateral transarticular approach only. Compared to open SI joint fusion, MIS SI joint fusion as reported herein is associated with less blood loss, a shorter hospital stay, and improved clinical responses.²⁶^,⁵¹^,⁵²^,⁵³ Not surprisingly, the use of minimally invasive fusion for SI joint pathology has overtaken open approaches.⁵⁴

The analysis of intraoperative outcomes showed mean procedure times of approximately 1 hour, mean EBL of 50 mL, and a mean LOS of approximately 1 day. These procedure-related variables compare favorably to open surgical SI joint fusion cohorts, which reported mean procedure times of 128 to 163 minutes, EBL of 288 to 682 mL, and mean hospital LOS of 3.3 to 5.2 days.²⁶^,²⁷^,⁵¹

In comparison to the modest changes in pain and disability in similar patients treated with nonsurgical management,⁴⁷ improvements after minimally invasive SI joint fusion using a lateral transarticular approach appear to be substantial and clinically important. It is encouraging to see that studies with longer term outcomes consistently showed sustained positive outcomes on visual analog scale (VAS) and Oswestry Disability Index (ODI) over time.⁴⁰^,⁴⁵

42.3 Preoperative Planning

Preoperative planning is essential in SI joint surgery. The OsiriX software is an example of a three-dimensional planning program that is relatively inexpensive and can be loaded onto a personal Apple- or Windows-based computer (OsiriX MD 6.5). This computer program allows synthesis of the inlet and outlet views ( Fig. 42.4), which aids in lining up identical intraoperative views. This program can also make three-dimensional surface reconstructions ( Fig. 42.5) to help guide in the planning of the surgery. The OsiriX program allows the axis to be rotated so that one of the axes is parallel to the posterior cortical lining in the upper part of the sacrum, thus often allowing the planning to be reduced to a two-dimensional problem ( Fig. 42.6). Green lines in Fig. 42.6a show the planned implant positions, and Fig. 42.6b shows the starting point as determined on the lateral X-ray. There are many other medical imaging programs that perform these functions and aid in the organization and planning of MIS surgery. Typically, the radiologist already has such a program integrated in the hospital radiology system, or the surgeon has access to one of the spinal operating room (OR) computer guidance systems (e.g., Medtronic Stealth, BrainLab, Stryker, etc.). The essential point is the importance of preoperative planning, not the particular computer program. OsiriX MD is highlighted as a low-cost alternative in the event hospital programs are unavailable.

Fig. 42.4 (a) Inlet and (b) outlet fluoroscopy images synthesized using the OsiriX program. These images are shown to the radiology technician as an example of what is desired for intraoperative images. Once shown these images, it is often easy for the technician to match them in a short number of exposures and time.

Fig. 42.5 (a,b) Three-dimensional surface reconstructions are often helpful in the visualization of the sacroiliac (SI) joint and the surrounding bone.

The operating room is set up with the patient prone with pressure point areas padded and the lateral portion of the buttocks exposed in the surgical area. While one C-arm is required, two C-arms reduce operating time by quickly providing alternating views in the anteroposterior (AP) and lateral planes. Dual C-arms are set up such that one provides imaging in the pelvic inlet and outlet views and the other provides the lateral view ( Fig. 42.7). As an alternative to the dual fluoroscopies, an intraoperative CT scan with three-dimensional navigation can be used for radiologic guidance. The skin is marked using a plumb line draped over the patient to define true vertical, and a Kirschner wire (K-wire) to define the posterior line of the sacrum ( Fig. 42.8). These are both imaged on the lateral fluoroscopy with the rotation of the image adjusted so that the plumb line wire images are vertical on the screen and superimposed, verifying a true lateral without a rotation component ( Fig. 42.9). As the skin is a tethering point for the implant placement instruments, it is important to place the skin incision in the correct position to minimize its size, and to facilitate surgery.

Fig. 42.6 The trajectory and length of the implants can be estimated from the preoperative planning. (a,b) The superior implant. (c,d) The inferior implant.