Adam Rupp MD and Dawood Sayed MD The University of Kansas Medical Center, Kansas City, KS, USA Low back pain (LBP) is one of the most common presenting symptoms and creates a huge burden functionally to the patient and financially to the economy. Roughly 70–85% of people will develop LBP at some point in their lives [1]. Interestingly, one of the most common causes of LBP is actually sacroiliac joint (SIJ) dysfunction ranging from 15–30% of all cases [2]. This is especially true after having a lumbar or lumbosacral fusion surgery [3]. Roughly 75% of patients at 5-years post-lumbar fusion will have evidence of SIJ degeneration on imaging [4]. Conservative treatments for SIJ pain include intra-articular injections and radiofrequency ablation (RFA). If long-term pain management is not achieved, the next step is surgical fusion. SIJ fusion aims to stabilize the joint and reduce further inflammation and laxity. Minimally invasive procedures have largely replaced open SIJ fusion surgeries. Although there are lower rates of complications and shorter post-operative recovery times, MIV procedures are not without risk. Complications can range from minor muscle irritation to hardware infections. In this chapter, we will discuss basic anatomy, indications, and techniques with a focus on complications and prevention related to MIV SIJ fusion. The SIJ is a complex assimilation between the legs and the spine that is primarily a transition point for forces originating from the lower extremities. The bony anatomy consists of the sacrum centrally, the ilium bilaterally, the coccyx caudally and the L5 vertebrae cephalad. The sacrum is a continuation of the vertebral column consisting of four fused sacral vertebrae. There are 16 foramina (8 posterior, 8 anterior) which transmit the sacral spinal nerves. The articular surface of the sacrum is C- or L-shaped with the discontinuation facing posteriorly. The SIJ and pelvis are surrounded by strong ligaments that add to their overall strength but these can also be the etiology of pain, most notably the interosseous and posterior ligaments [5]. The pelvic girdle has numerous muscular insertions, but despite these attachments, the SIJ has very little intrinsic motion. The motion is limited to counternutation and nutation, the latter is described as “nodding forward” as the cephalic sacral bases move anteriorly while the caudad end moves minimally posterior [6]. This limited motion can still cause discomfort due to the dense innervation of the joint. These nerves include the medial branches of the dorsal rami L4, L5, S1–S3 (most important for sensation) and ventral rami L4–S2. The SIJ also has a rich blood supply, mostly supplied by the superior gluteal and lateral sacral arteries. The superior gluteal arteries traverse laterally above the piriformis hugging the posterior iliac crest directed toward the anterior superior iliac spine [6, 7] (Figures 61.1–61.6). Figure 61.1 Pelvic neurovascular anatomy. (Source: https://www.kenhub.com/en/library/anatomy/lower-extremities-arteries-and-nerves.) MIV SIJ-stabilization candidates should fulfill strict inclusion criteria that include the following: The previous standard of care for SIJ stabilization was open fixation. However, with variable success and high complication rates, open surgeries have largely been replaced with MIV stabilizations. MIV SIJ fusion can be performed using the lateral or posterior approach. The lateral approach was developed and studied first, however, new posterior techniques are becoming increasingly more popular. Both techniques are performed with the patient in the prone position with chest roles to elevate the chest and pelvis, while radiography is obtained to identify relevant anatomy (Figures 61.2a–c). Prophylactic antibiotics should be given prior to incision [10, 11]. The lateral approach typically requires general sedation while the posterior approach can be performed with conscious sedation. Figure 61.2 (a– c) Sacral fluoroscopic anatomy. Lateral approach (SI bone iFuse system): In the lateral view, identify and mark 1 cm inferior to the posterior sacral wall and sacral ala. At the intersection, create a 3-cm incision moving caudally down to the fascia. In the inlet view, introduce the guide pin slightly into the ilium, aiming for the middle third of the sacral body. Switch to outlet view and continue positioning the pin to just above the S1 foramen. Slide the tissue dilator over the pin and lightly guide it through the muscle and fascia, taking care to minimally separate the fibers. Slide the soft-tissue protector over the steinmann pin to the cortex. Use the depth gauge to determine appropriate implant size. Switch to outlet view and slide the drill over the pin, advance until just past the sacral cortex (this point may not be to the end of the pin). Withdraw the drill taking care not to retract or advance the pin. Slide the broach assembly over the steinmann pin and lightly tap until it crosses the joint (again it may not reach the end of the pin). Carefully remove broach. Place implant assembly over the pin, lightly tap until it reaches the end of the pin. In outlet oblique view, ensure the lateral wall of the foramen has not been breached. Important, leave the pin in place when setting up the second pin, this will ensure correct alignment and spacing. Place the parallel pin guide over the initial steinmann and aim the second pin for the middle of the sacral body in inlet view. In outlet view, position the second pin aiming for the first sacral foramen. Once the second pin is in place, the first steinmann can be removed. Repeat the above steps for the second and third implant (Figure 61.3). In outlet view, the third implant is directed between the S1 and S2 foramina [12–17]. Figure 61.3 Lateral approach fusion. Posterior approach (linq allograft system): In oblique view, identify target anatomy superimposing the anterior and posterior joint lines and finally marking the midpoint of the SIJ. Create a stab incision and place the steinmann pin into the joint coaxially. In lateral view, advance the pin to the anterior sacral cortical line. Expand the incision to accommodate the tissue dilators. In oblique view, slide them over the pin until fully seated within the joint. Remove the internal dilator and the guide pin. Place the joint decorticator into the outer dilator, tap using a mallet until fully within the joint. Remove the decorticator using the built-in reverse slap hammer. Fill the implant graft window with DBM putty. Slide the implant into the outer dilator and tap with the mallet until fully seated in the joint. Remove all hardware and close incision [18–22] (Figure 61.4). Figure 61.4 Posterior approach fusion. (Source: LinQ™ – SI Joint Stabilization System by PainTEQ – Where Intervention Meets Innovation.) Complications from MIV sacral stabilization procedures are uncommon ranging from 4–14%. Typical complications include those that are likely with all procedures/surgeries such as anesthetic reactions, bleeding, infection, and PE. However, complications specific to MIV SIJ can be categorized into the following: procedural and post-operative [23, 24]. Trochanteric bursitis/gluteal tendinopathy:
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Complications of Sacroiliac Joint Stabilization
Introduction
Anatomy
Indications
Contraindications
Technique
Complications
Category
Complications
Procedural
Trochanteric bursitis, piriformis syndrome, hematoma, malpositioning, nerve injury, vascular disruption
Post-operative
Hardware complications, wound infection, hardware infection, bone fracture, abnormal periosteal bone growth
Procedural
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