Three‐and‐a‐Half‐Year Follow‐Up After Sacroiliac Joint Fusion With Preexisting Ipsilateral Total Hip Arthroplasty: A Case Report

ABSTRACT

Sacroiliac joint fusion was performed in a patient with a preexisting ipsilateral total hip arthroplasty, with no hip dislocation and unrestricted return to farm work at 3.5 years. Fusion eliminates sacroiliac motion and raises hip contact stress, so adjacent joint health warrants preoperative assessment.

This case documents SIJ fusion performed in a patient with preexisting ipsilateral THA without hip complications through 3.5 years. The patient achieved his primary functional goal of returning to farming. He continued full‐time work at final follow‐up in a physically demanding occupation with no activity restrictions, no THA dislocations, and stable implant positioning for both systems.

1. Introduction

Sacroiliac joint (SIJ) dysfunction accounts for approximately 15%–30% of chronic low back pain cases, with minimally invasive SIJ fusion demonstrating excellent safety and efficacy when conservative treatment fails [1, 2, 3]. The interaction between SIJ pathology and hip arthroplasty represents a complex bidirectional relationship with significant clinical implications.

Recovery time after SIJ fusion using triangular titanium implants is typically characterized by initial mobilization within days. Most patients resume light activities within 2–6 weeks and achieve substantial functional recovery by 6 months [2]. Patients are allowed to bear weight as tolerated soon after surgery, but restrictions on high‐impact activities are common for the first 6–12 weeks [2]. Most adverse events are mild and perioperative, while rates of serious complications are low [4, 5]. In clinical trials, significant improvements in pain and disability appear as early as 6 weeks postoperatively and continue through 6 and 12 months [5].

Research demonstrates that patients with previous SIJ arthrodesis face approximately double the risk of hip dislocation following subsequent total hip arthroplasty (THA) compared to those without prior SIJ fusion, an effect attributed to altered pelvic biomechanics and diminished spinopelvic mobility following SIJ fixation [6, 7].

In the opposite direction, SIJ degenerative changes are frequently observed in patients requiring THA, though the severity of SIJ osteoarthritis does not appear to significantly impact immediate functional outcomes following hip replacement [8]. However, SIJ fusion performed as part of extensive spinal constructs has been identified as a contributing factor to accelerated hip joint degeneration, likely through modified load distribution patterns and adjacent segment disease progression [9, 10].

THA stability depends on several parameters that each shape the functional arc of the prosthetic hip. These include spinopelvic mobility, acetabular inclination and anteversion, femoral head diameter, surgical approach, prior dislocation history, and lumbar degenerative disease [6, 7, 11]. Pooled biomechanical data place intact sacroiliac motion at 1.9° of flexion‐extension, 0.9° of lateral bending, and 1.3° of axial rotation [12]. Though small, this range is necessary for normal pelvic kinematics. Fusion eliminates it and redistributes load to adjacent joints, where compensation falls short of the loss. Lumbar fusion costs a mean 18° of lumbar mobility and returns only 7° of compensatory hip motion [13]. Finite element modeling shows that unilateral SIJ fusion lowers hip joint reaction force by 2% yet raises hip contact stress by 3.7% [10]. Degeneration at L5‐S1 may constrain pelvic tilt further and shift demand onto the hip [9]. The combined range of motion (ROM) consequences of SIJ fusion and preexisting arthroplasty have not been characterized.

Our institutional analysis of 105 consecutive SIJ fusion cases revealed only one patient (0.95%) with preexisting THA [14]. Pooled individual‐level data from four prospective multicenter trials place preexisting THA prevalence at 2.8% and subsequent THA incidence at 2.3% over 3.4 years of follow‐up, against general population estimates of 0.83% and 0.1% to 0.5% [15]. THA prevalence reaches 16.4% in adult spinal deformity, a population that is older and more extensively instrumented [16]. The combination is uncommon in absolute terms yet more frequent than population rates predict. Radiographic SIJ osteoarthritis is present in approximately 40% of THA candidates, yet few require both procedures [8]. While research has concentrated on examining THA outcomes following SIJ fusion, less is known about how preexisting THA affects SIJ fusion outcomes. Here, we present detailed 3.5‐year follow‐up of SIJ fusion in a patient with preexisting ipsilateral THA. Reports of this operative order remain sparse.

Written informed consent from the patient was obtained for publication according to journal guidelines.

2. Case History/Examination

A 60‐year‐old male farmer presented with right lower back and leg pain following a fall from a ladder 2.5 years prior. His symptoms significantly impacted farming activities requiring prolonged standing, walking on uneven terrain, and repetitive bending. He had undergone right THA 1.5 years earlier for severe osteoarthritis secondary to hip dysplasia, which provided no relief of his leg pain while his lower back pain persisted. The arthroplasty was performed through a direct‐anterior approach with MAKO robotic assistance using a Stryker Accolade II femoral stem, a 58 mm Stryker Tritanium acetabular shell, and a 36 mm ceramic femoral head on a polyethylene liner. Acetabular inclination and anteversion were not quantified in the prior operative report. Radiographic estimates were approximately 40° of inclination and 15° of anteversion. He denied any THA dislocation events.

Conservative treatments including epidural steroid injections, radiofrequency ablations, and physical therapy provided minimal sustained relief. Right SIJ injection provided excellent pain relief for 1–2 months. A subsequent right SIJ injection produced only 24 h of relief.

Physical examination revealed moderate lumbar spine tenderness with positive Fortin finger test, thigh thrust, pelvic compression, pelvic gapping, Gaenslen's test, and sacral thrust on the right side. FABER test could not be performed due to THA. BMI was 35.6 kg/m². Initial scores: Oswestry Disability Index (ODI) 44%, Visual Analog Scale (VAS) 6/10, PROMIS‐10 Assessment 25.

3. Differential Diagnosis, Investigations and Treatment

Imaging obtained before the index arthroplasty is shown for reference (Figure 1). Radiographs before SIJ fusion demonstrated right SIJ irregularity compared to the contralateral side (Figure 2). Pelvic computed tomography (CT) from the earlier arthroplasty workup already showed vacuum phenomenon in the right SIJ (Figure 3). Additional findings included L5‐S1 disc space loss with lower lumbar facet hypertrophy and no THA complications.

FIGURE 1.

Anterior–posterior pelvis radiograph obtained before the index total hip arthroplasty.

FIGURE 2.

Supine anterior–posterior pelvis radiograph obtained before SIJ fusion, demonstrating irregularity of the right SIJ compared to the contralateral side.

FIGURE 3.

Pelvic CT obtained before the index total hip arthroplasty, showing vacuum phenomenon (Hounsfield units below 0) in the right SIJ.

The patient met criteria for minimally invasive SIJ fusion and underwent right SIJ fusion with triangular titanium implants (iFuse‐3D, SI Bone, Santa Clara, CA) [17]. In a prone position on a four‐poster frame, a percutaneous reference pin was placed in the contralateral posterior superior iliac spine. Intraoperative three‐dimensional images were acquired with an O‐arm and transferred to a Stealth navigation workstation (Medtronic, Minneapolis, MN). Implants were delivered through a small lateral incision overlying the right SIJ, with navigated K‐wire placement followed by sequential soft tissue dilation, drilling, and broaching at each level, as previously described [18]. Three implants were placed: 7.0 × 55 mm cephalad S1, 7.0 × 55 mm inferior S1, and 7.0 × 50 mm S2. Intraoperative two‐dimensional fluoroscopy and three‐dimensional imaging confirmed implant placement (Figure 4). He tolerated the procedure well with no complications and was allowed immediate weight bearing with crutch assistance for the first 3 weeks.

FIGURE 4.

Intraoperative imaging confirming implant placement. Anteroposterior (A) and lateral (B) fluoroscopy. Axial images from the final O‐arm spin, shown proximal to distal, demonstrate the cephalad S1 (C), inferior S1 (D), and S2 (E) implants.

4. Conclusions and Results

Recovery trajectory is detailed in Table 1. At 6 weeks, pain improved to VAS 4.0/10 and ODI decreased to 33% (25% improvement). He could ambulate without assistance and reported at this visit that he had resumed farm work operating tractors. Instrumentation appeared stable on radiographs (Figure 5). At 3 months, continued improvement was noted with VAS 2.5/10 and ODI 29%. He could walk and sleep without pain while progressively returning to farming activities. Implant positioning remained intact (Figure 6).

TABLE 1.

Patient‐reported outcomes and clinical milestones from baseline through 3.5‐year follow‐up.

Timepoint	ODI	Change from baseline	VAS	Change from baseline	PROMIS‐10	Functional status	Clinical milestone
Preoperative	44	—	6.0	—	25	Unable to perform farming activities; prolonged sitting, standing, walking worsened symptoms	Baseline assessment
6 weeks	33	↓11 points (25% improvement)	4.0	↓2.0 points (33% improvement)	30	Ambulating without cane; light activities only	Weight bearing as tolerated
3 months	29	↓15 points (34% improvement)	2.5	↓3.5 points (58% improvement)	34	Walking and sleeping without pain; light farm tasks	Activity progression beyond 6–12 week restriction period
6 months	9	↓35 points (80% improvement)	2.5	↓3.5 points (58% improvement)	37	Walking 2 miles; returned to all farming activities without restrictions	Peak functional improvement; substantial recovery milestone
1 year	20	↓24 points (55% improvement)	2.0	↓4.0 points (67% improvement)	31	Continued full farming activities	Post‐knee arthroplasty recovery
3.5 years	38	↓6 points (14% improvement)	3.5	↓2.5 points (42% improvement)	29	Full‐time farming with no restrictions or limitations	Long‐term durability assessment

Note: The patient underwent right total knee arthroplasty between the 6‐month and 1‐year visits.

Abbreviations: ODI, Oswestry Disability Index (0–100%); PROMIS‐10, Patient‐Reported Outcomes Measurement Information System Global Health Scale; VAS, Visual Analog Scale (0–10).

FIGURE 5.

Six‐week postoperative supine anterior–posterior (A) and lateral (B) radiographs showing implant placement without evidence of loosening.

FIGURE 6.

Three‐month postoperative supine anterior–posterior (A) and lateral (B) radiographs showing implant placement without evidence of loosening.

By six months, substantial functional recovery was achieved with ODI 9% (80% improvement from baseline) and VAS 2.5/10, allowing return to all farming activities without restrictions. This exceeded published minimal clinically important difference thresholds [4]. Radiographs showed increased density at the superior aspect of the SIJ with no evidence of implant loosening or migration (Figure 7).

FIGURE 7.

Six‐month postoperative outlet (A) and lateral (B) radiographs showing implant placement without evidence of loosening.

The patient underwent right total knee arthroplasty (TKA) between 6‐month and 1‐year follow‐up. At one year, ODI increased to 20% (likely reflecting knee surgery impact), while VAS was 2.0/10. SIJ instrumentation remained stable (Figure 8).

FIGURE 8.

One‐year postoperative outlet (A) and lateral (B) radiographs showing implant placement without evidence of loosening.

At 3.5‐year follow‐up, the patient reported no restrictions in daily activities or farming work. While ODI (38%) and VAS (3.5/10) scores increased compared to optimal results, pain levels remained substantially improved from preoperative baseline. He expressed satisfaction with functional capacity and denied activity restrictions. Imaging at final follow‐up showed intact SIJ instrumentation without loosening, fracture, or migration (Figure 9). Right THA appeared stable with no complications.

FIGURE 9.

Three‐and‐a‐half‐year postoperative outlet (A) and lateral (B) radiographs showing implant placement without evidence of loosening. THA instrumentation was stable without hardware complication.

5. Discussion

This case addresses the less‐studied scenario of SIJ fusion with preexisting THA. Our patient underwent SIJ fusion without hip dislocation through 3.5 years, in contrast to the increased dislocation risk documented when SIJ fusion precedes THA. His course followed the expected pattern: early mobilization and activity resumption within the 2–6 week window, peak functional gain by 6 months with an 80% reduction in ODI, and maintenance of that benefit through long‐term follow‐up despite later symptom fluctuation.

The biomechanical implications of performing SIJ fusion with established THA may differ substantially from the reverse scenario. SIJ fusion fundamentally alters the spine‐pelvis‐hip kinematic chain by restricting or eliminating SIJ motion, forcing the hip joint to accommodate positional changes that would normally be distributed across multiple spinal and pelvic segments [10]. Loss of SIJ ROM contributes to compensatory hypermobility at adjacent segments or increased stress on the hip joint itself [9]. Unpredictable pelvic positioning during activities of daily living can in turn contribute to impingement and instability [6, 7]. Gait analysis sixmonths after unilateral SIJ fusion shows normalized step width and improved hip motion, though elevated pelvic obliquity and rotation persist [19]. The burden runs in both directions, since lumbar fusion accelerates SIJ degeneration and, when extended to SIJ fixation, accelerates degenerative change at the hip, whereas hip arthroplasty is not itself a risk factor for SIJ degeneration [11]. These findings support assessment of adjacent joint health before SIJ fusion, particularly when an ipsilateral arthroplasty is already in place.

Gait mechanics change after arthroplasty and recover over the first postoperative year [20]. This patient's THA had been in place for 1.5 years before SIJ fusion, so that adaptation and soft tissue healing had already occurred, which may have reduced the risk of acute destabilization.

Farming demands prolonged standing on uneven terrain, repetitive bending, and lifting, all of which load the SIJ and the hip. He resumed tractor work at 6 weeks and returned to unrestricted farming by 6 months, maintaining that capacity through long‐term follow‐up.

Clinical studies have demonstrated SIJ stabilization with triangular titanium implants to effectively reduce pain, increase quality of life, and reduce opioid use [2]. In this patient, SIJ fusion and THA coexisted without adverse implant interaction or compromise to either system through 3.5 years. Throughout follow‐up, radiographs demonstrated no evidence of implant loosening or migration for either system. Bony fusion across the SIJ was not confirmed, since postoperative CT was not obtained. An additional notable finding was that the radiographic appearance of the THA remained unchanged, with no occurrence of hip dislocation. Despite a modest increase in reported symptoms at final follow‐up, the patient maintained an unrestricted activity level and continued full‐time farming. Numerical scores did not fully reflect his maintained functional capacity.

While literature extensively documents increased dislocation risk following THA in patients with prior SIJ fusion, outcomes for the reverse sequence of SIJ fusion following THA are largely undescribed. This sequence occurred in 0.95% of SIJ fusion patients at our institution and in 2.8% across four pooled multicenter trials, in which every patient with a unilateral preexisting THA underwent ipsilateral SIJ fusion [14, 15]. This single experience does not establish a favorable risk profile. Given the paucity of published data on this uncommon but clinically relevant scenario, this case suggests that SIJ fusion may be feasible in carefully selected patients with preexisting ipsilateral THA when accompanied by appropriate counseling and surveillance. The key clinical learning points from this case are summarized in Table 2. Multi‐institutional collaboration is needed to better understand biomechanical interactions and long‐term outcomes when these procedures are performed in this sequence.

TABLE 2.

Key clinical learning points.

Clinical domain	Key finding	Clinical significance
Surgical safety	SIJ fusion performed without complications in presence of ipsilateral THA	Suggests a feasible surgical approach in this setting
Diagnostic approach	Standard SIJ fusion evaluation criteria and techniques applicable	No modification of established protocols required
Functional outcomes	Return to high‐demand occupational activities (farming) achieved	Occupational function was restored in this patient
Implant stability	Both SIJ and THA systems remained stable through 3.5‐year follow‐up	Long‐term coexistence without adverse interaction
Outcome assessment	Functional capacity maintained despite numerical score fluctuation	Numerical scores did not fully reflect functional capacity
Research implications	Outcome data for this operative sequence are sparse	Additional case series needed to establish broader patterns

This represents a single case rather than a prospectively designed study. Long‐term outcomes beyond 3.5 years remain unknown. The absence of comparative controls limits definitive conclusions about safety and efficacy relative to isolated SIJ fusion. Postoperative CT was not clinically indicated given his sustained symptomatic improvement and the absence of findings suggesting implant failure. Solid interosseous fusion therefore could not be confirmed. The compensatory mechanisms described above are inferred from published biomechanical modeling rather than measured in this patient. Right TKA between the 6‐month and 1‐year visits confounds interpretation of the later patient‐reported outcome scores. Functional status relied on self‐report and clinical assessment rather than objective work‐capacity testing.

This case documents SIJ fusion performed in a patient with preexisting ipsilateral THA without hip complications through 3.5 years. The patient achieved his primary functional goal of returning to farming. He continued full‐time work at final follow‐up in a physically demanding occupation with no activity restrictions, no THA dislocations, and stable implant positioning for both systems.

Author Contributions

Dustin J. Kress: investigation, writing – original draft, visualization, writing – review and editing, data curation. Jason J. Haselhuhn: investigation, data curation, visualization, writing – original draft, writing – review and editing. Neill B. Hatcher: investigation, data curation, visualization, writing – original draft, writing – review and editing. Kari Odland: writing – review and editing, supervision, project administration, visualization, investigation. David W. Polly Jr: conceptualization, investigation, visualization, writing – review and editing, supervision.

Funding

The authors have nothing to report.

Ethics Statement

This study was conducted in accordance with the ethical principles of the Declaration of Helsinki (World Medical Association, 2024). This study was deemed “Exempt” on (6/7/2024) by the Institutional Review Board (IRB).

Consent

Informed patient consent was obtained for dissemination of the data and imaging reported in this manuscript prior to its initiation.

Conflicts of Interest

D.J.K., J.J.H., N.B.H. and K.O. declare no financial conflicts. D.W.P. has consultancies with SI‐Bone, Globus, Spinal Stabilization Technologies, and Curiteva, royalties from SI Bone and Springer (textbook), research support from SI Bone and Medtronic, and stock in SeeAll AI (< 0.03%).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).