Original Article

Minimally Invasive Sacroiliac Joint Fusion Using a Novel Hydroxyapatite-Coated

Screw: Preliminary 1-Year Clinical and Radiographic Results of a 2-Year ProspectiveStudy

Louis H. Rappoport1, Ingrid Y. Luna2, Gita Joshua2

-OBJECTIVE: Proper diagnosis and treatment of sacroiliacjoint (SIJ) pain remains a clinical challenge. Dysfunction ofthe SIJ can produce pain in the lower back, buttocks, andextremities. Triangular titanium implants for minimally inva-sive surgical arthrodesis have been available for severalyears, with reputed high levels of success and patientsatisfaction. This study reports on a novel hydroxyapatite-coated screw for surgical treatment of SIJ pain.

-METHODS: Data were prospectively collected on 32consecutive patients who underwent minimally invasiveSIJ fusion with a novel hydroxyapatite-coated screw.Clinical assessments and radiographs were collected andevaluated at 3, 6, and 12 months postoperatively.

-RESULTS: Mean (standard deviation) patient age was55.2 � 10.7 years, and 62.5% were female. More patients(53.1%) underwent left versus right SIJ treatment, meanoperative time was 42.6 � 20.4 minutes, and estimatedblood loss did not exceed 50 mL. Overnight hospital staywas required for 84% of patients, and the remaining pa-tients needed a 2-day stay (16%). Mean preoperative visualanalog scale back and leg pain scores decreased signifi-cantly by 12 months postoperatively (P < 0.01). Mechanicalstability was achieved in 93.3% (28/30) of patients, and allpatients who were employed preoperatively returned towork within 3 months. Two patients who required revisionsurgery reported symptom improvement within 3 weeksand did not require subsequent surgery.

-CONCLUSIONS: Positive clinical outcomes are reported1 year postoperatively after implantation of a novel implant

Key words- Sacroiliac joint- Sacroiliac joint dysfunction- SI joint fusion

Abbreviations and AcronymsHA: HydroxyapatiteMIS: Minimally invasive surgeryODI: Oswestry Disability IndexSIJ: Sacroiliac jointVAS: Visual analog scale

WORLD NEUROSURGERY 101: 493-497, MAY 2017

to treat sacroiliac joint pain. Future clinical studies withlarger samples are warranted to assess long-term patientoutcomes.

INTRODUCTION

he sacroiliac joint (SIJ) represents a complex syndesmoticjoint composed of hyaline cartilage, fibrocartilage, and

Tsynovium and transmits complex forces from the lumbar

spine to the pelvis.1,2 The SIJ is prone to degenerative changessimilar to those seen in synovial joints, leading to pain and SIJdysfunction. Typical symptoms of SIJ pain manifest in the lumbarspine to the lower extremities and include low back pain thatradiates to the ipsilateral thighs, buttock, groin, and legs.3

Patients often describe hemipelvis through-and-through painand increased pain with torsional activities.Historically, SIJ pain has been confused with lower lumbar pain

yet treated similarly. However, surgeons currently support thetheory that SIJ pain could generate pain in the lower back, but-tocks, and legs.1 Sembrano et al.4 reported that in almost 15% ofpatients presenting with low back pain, the pain was of SIJ origin,and the SIJ was the sole source of pain in 5% of these patients.Katz et al.2 concluded that SIJ dysfunction may elicit new painin the lower back, groin, and legs in patients who haveundergone lumbosacral fusion. Despite increasing interest in theSIJ as a pain generator, the prevalence of this condition isunknown.Fluoroscopically guided intra-articular injection represents the

standard for clinical diagnosis of SIJ pain and dysfunction. Greaterthan 75% reduction in pain within 15e45 minutes of injection

From the 1Arizona Spine Consultants, Phoenix, Arizona; and 2Musculoskeletal Education andResearch Center (MERC), A Division of Globus Medical, Inc., Audubon, Pennsylvania, USA

To whom correspondence should be addressed: Louis H. Rappoport, M.D.[E-mail: lhr4spine@aol.com]

Citation: World Neurosurg. (2017) 101:493-497.http://dx.doi.org/10.1016/j.wneu.2017.02.046

Journal homepage: www.WORLDNEUROSURGERY.org

Available online: www.sciencedirect.com

1878-8750/$ - see front matter ª 2017 Elsevier Inc. All rights reserved.

www.WORLDNEUROSURGERY.org 493

ORIGINAL ARTICLE

LOUIS H. RAPPOPORT ET AL. MINIMALLY INVASIVE SIJ FUSION WITH A HYDROXYAPATITE-COATED SCREW

indicates that this diagnosis is highly probable.1,2 Conservativetreatment of SIJ pain includes nonsteroidal antiinflammatorydrugs, physical therapy, chiropractic therapy, and rest.1 Ifconservative measures and activity modifications fail, andpatients continue to report disabling pain, SIJ arthrodesis istypically recommended.Open SIJ arthrodesis has been performed since the 1920s;

minimally invasive surgery (MIS) arthrodesis has recently gainedpopularity, and favorable outcomes have been reported.5,6 Trian-gular titanium implants have been used in MIS for several yearsand have resulted in high levels of success and patient satisfac-tion.5,7-10 However, determining effective methods of achievingstability of the SIJ remains a clinical concern for surgeons. Thisstudy served to investigate and report on clinical outcomes of anovel hydroxyapatite (HA)-coated screw with design features thatmake it an alternative to triangular implants, with the goal ofachieving mechanical stability for treatment of SIJ pain anddysfunction.

METHODS

Patient PopulationInstitutional review board approval was obtained to prospectivelycollect data on patients undergoing unilateral minimally invasiveSIJ fusion performed with HA-coated screws. Data were pro-spectively collected on 32 consecutive patients, all of whomreached 12-month follow-up. Patients were invited to participate inthis study if they met all study inclusion and exclusion criteria(Table 1). Diagnosis was based on clinical presentation of SIJdysfunction supported by medical history, physical examination,and lumbar magnetic resonance imaging showing absence ofdisease that would correlate with clinical presentation. If apatient failed to respond to nonoperative treatment (medicationmanagement, activity modification, physical therapy, andtherapeutic injections), then, a diagnostic injection wasadministered to isolate pain to the SIJ and confirm SIJ dysfunction.

Implant System DescriptionThe SIJ fusion system used in the current investigation (GlobusMedical Inc., Audubon, Pennsylvania, USA) consists of acomprehensive set of HA-coated screws and cannulated

Table 1. Study Inclusion and Exclusion Criteria

Inclusion Criteria Exclusion Criteria

Age between 21 and 70 years Previous documentation ofosteopenia or osteomalacia

Diagnosis of sacroiliac joint dysfunction History of metabolic bone disease

Consent provided for sacroiliac jointfusion with the SI-LOK Sacroiliac JointFixation System

Diagnosis of a condition that requirespostoperative medication(s) that mayinterfere with bone/soft tissuehealing

Ability to provide informed consent forstudy participation and to return for allfollow-up visits

Presence of a condition that totallyprecludes the possibility of bonefusion

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instruments designed specifically for use in a lateral approach tothe SIJ. This system offers lag fixation and slotted screw options ina variety of lengths. The graft slot option is designed to optimizeSIJ fusion, and the lag feature allows compression of the SIJ. TheHA coating is designed to promote osseous apposition andthrough-growth. Washers assist the surgeon in determiningproper screw insertion depth.

Surgical TechniquePatients were positioned prone on a Jackson table, and the skinmarked at the alar line and posterior sacrum with lateral fluoro-scopic imaging. An incision of 2e3 cm was made 1 cm distal tothe intersection of the lines with blunt finger dissection to thefascia. The first guide pin was inserted under fluoroscopic guid-ance in all 3 planes across the joint, staying caudal to the alar lineand within the sacrum, beginning near the posterior sacrum andangling approximately 10�e15� downward. An outlet view of pindepth allowed measurement of screw length. The joint was drilledto prepare for screw insertion, and the screw slot packed withautogenous bone graft collected from drill reamings. The screwwas then inserted over the guide pin. A switch to inlet view anduse of the dual parallel pin guide were followed by insertion of thesecond guide pin into the bone. The lateral view was used to checkthe first screw position, and the second guide pin was advancedwhile staying lateral to the S1 foramen on outlet view. Whileremaining on that view, screw length was measured, and thescrew was drilled, packed, and implanted in a similar way to thefirst screw. These steps were repeated for the third screw. Posi-tioning was checked on final inlet, outlet, and lateral views. Allreconstructions included 3 screws and a minimum of 1 slottedscrew (Figures 1 and 2).

Outcome MeasuresPatient demographic and intraoperative data, including age,gender, operative time, estimated blood loss, fluoroscopicexposure time, and duration of hospital stay, were collected.Outcome measures reported by both patients and surgeonsincluded visual analog scale (VAS) scores for back and leg pain,Oswestry Disability Index (ODI) scores, Odom’s criteria, workstatus, and satisfaction with the operative procedure. Outcomemeasures and radiographs were collected preoperatively and at3, 6, and 12 months postoperatively. Mechanical stability of theSIJ was defined as absence of screw loosening and radiolucentgaps at the boneescrew interface, screw migration, andimprovement in patient symptoms by 12 months post-operatively. The presence or absence of intraoperative (infec-tious, vascular, or neurologic) and postoperative complications,such as neurologic deficits or the need for reoperation, wasdocumented.

Statistical AnalysisDescriptive statistics were reported as mean and standard devia-tion, or as frequency and percentage, when applicable. Significantchanges in VAS and ODI scores from the preoperative time pointwere assessed using repeated-measures analysis of variance.Analysis was performed using SPSS version 20.0.0 software forWindows (IBM Corp., Armonk, New York, USA), and statisticalsignificance was indicated at P < 0.05.

ROSURGERY, http://dx.doi.org/10.1016/j.wneu.2017.02.046

Figure 1. Anteroposterior plain film radiographic viewsat (A) 3-month and (B) 12-month follow-up. This36-year-old man presented with chronic low back painand disabling left leg pain. A left sacroiliac joint fusion

was performed with 3 slotted screws. Note the lack ofdifference in radiopacity within screw slots between3- and 12-month intervals and absence of radiolucentgaps at the boneescrew interface.

ORIGINAL ARTICLE

LOUIS H. RAPPOPORT ET AL. MINIMALLY INVASIVE SIJ FUSION WITH A HYDROXYAPATITE-COATED SCREW

RESULTS

Patient Demographics and Operative DataMean (standard deviation) patient age was 55.2 � 10.7 years, and62.5% were female. A greater number of patients underwent

Figure 2. Anteroposterior plain film radiographic viewsat (A) 3 months and (B) 12 months postoperatively.This 64-year-old woman presented with disabling lowback and left leg pain, and limb numbness. A leftsacroiliac joint arthrodesis was performed with 3

WORLD NEUROSURGERY 101: 493-497, MAY 2017

left versus right SIJ arthrodesis (53.1% vs. 46.9%). Mean operativetime was 42.6 � 20.4 minutes and fluoroscopic time 2.9 � 1.3 mi-nutes, and estimated blood loss did not exceed 50 mL (mean, 12.5�10.5 mL) in all cases. Overnight hospital stay was required for 84% ofpatients, and remaining patients required a 2-day stay (16%).

slotted screws. Note the lack of difference inradiopacity within screw slots between 3-month and12-month intervals and absence of radiolucent gaps atthe boneescrew interface.

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Figure 4. Line graph comparing Oswestry Disability Index (ODI) scoresover 12-month postoperative follow-up (mean � standard deviation) forall patients. *Statistically significant differences from preoperativescores (P < 0.05).

ORIGINAL ARTICLE

LOUIS H. RAPPOPORT ET AL. MINIMALLY INVASIVE SIJ FUSION WITH A HYDROXYAPATITE-COATED SCREW

Clinical Outcome MeasuresMean VAS back pain scores decreased significantly from 55.8 �26.7 mm preoperatively to 28.5 � 21.6 mm, 31.6 � 26.9 mm, and32.7 � 27.4 mm, respectively, at 3, 6, and 12 months post-operatively (P < 0.01). VAS leg pain scores also decreased signif-icantly from 40.6 � 29.5 mm to 19.5 � 22.9 mm, 16.4 � 25.6 mm,and 12.5 � 23.3 mm, respectively, for left leg pain (P < 0.01), andfrom 40.0� 34.1 mm to 18.1� 26.3 mm, 20.6� 25.4 mm, and 14.4� 21.1 mm, respectively, for right leg pain, at 3, 6, and 12 monthspostoperatively (P < 0.05) (Figure 3). Mean ODI scores decreasedsignificantly from 55.6 � 16.1 to 33.3 � 16.8, 33.0 � 16.8, and34.6 � 19.4, respectively, at 3, 6, and 12 months postoperatively(P < 0.01) (Figure 4). Odom’s criteria indicated that theproportion of patients experiencing excellent/good outcomes was78%, 72%, and 76%, at 3, 6, and 12 months, respectively.Mechanical stability was achieved in 93.3% (28/30) of patients.

In all, 36% of patients were retired both before and after surgery. Atotal of 16% of patients were unemployed preoperatively andremained unemployed postoperatively. All patients employedpreoperatively (44%) returned to work within 3 months. One pa-tient (4%) was employed preoperatively but retired after surgery.Mean satisfaction with results of surgery was 8.4 at 3 and 6

months postoperatively, and 8.6 at 12 months postoperatively, ona scale from 1 to 10, with 10 meaning completely satisfied. Ninety-seven percent of patients stated that they would consider havingthe same type of surgery again and would recommend this pro-cedure to a family member or friend.

Complications and ReoperationsOne patient required revision surgery for screw loosening at 11months postoperatively; a second patient required revision 3months postoperatively to remove the cephalad screw and to addan additional caudal screw as the result of bony deficiency/dysplasia. Both patients reported symptom improvement within 3weeks, and neither required subsequent revision surgery.

DISCUSSION

Over the past decade, surgeons have come to recognize the SIJ as apotential source of low back pain. However, SIJ pain may mimic

Figure 3. Bar graph of visual analog scale (VAS) scores for all patientsfrom preoperative assessment to 12-month postoperative follow-up (barheight indicates mean value and error bars � 1 standard deviation).*Statistically significant differences from preoperative scores (P < 0.05).

496 www.SCIENCEDIRECT.com WORLD NEU

pain from other sources, making definitive diagnosis challengingand complex. Medical history, physical examination, and diag-nostic imaging can be used as adjunctive diagnostic tools for SIjoint disorders, but none of these is specific enough to confirmpathognomonic evidence of SIJ pain.1 The current consensus isthat fluoroscopically guided intra-articular injection representsthe gold standard for diagnosis and that diagnosis is highlyprobable if greater than 75% reduction in pain is experiencedwithin 45 minutes of injection.1,2 If nonoperative treatment doesnot resolve disabling SIJ pain, SIJ arthrodesis is usuallyrecommended.The current investigation highlights the use of a novel implant

to surgically manage SIJ pain, with positive reports on clinicaloutcomes. The 32 patients in this sample experienced statisticallysignificant decreases in VAS and ODI scores from preoperatively toas early as 3 months postoperatively, and these improvementswere maintained throughout 12 months of follow-up. Further, allpatients who were employed preoperatively returned to workwithin 3 months, patient satisfaction scores were high, and mostpatients indicated that they would recommend the procedure toothers.The findings of this study are consistent with those of historical

controls presented in the published literature for arthrodesis ofthe SIJ (Table 2).5,7,9,11,12 Although 2 complications required revi-sion surgery (one after screw loosening and another for removal ofa screw because of bony deficiency/dysplasia), the reoperationrates are comparable with those of other MIS SIJ arthrodeses.Further, the design of the implant offers potential benefit for SIjoint fusion, such as graft slots that may help expedite joint sta-bilization and biological fusion, the security of a fully threadedconnection, and a lag feature that allows compression of the SIjoint.Plain film radiographs are not reliable for assessment of

osseous fusion across the SI joint; therefore, the absence of screwloosening, radiolucent gaps, and screw migration, in combinationwith symptom improvement, was considered to be a sign of me-chanical stability. Although the imaging end point in the pub-lished literature8 is 30% bone apposition to both the iliac andsacral sides of 2 of 3 implants, we believe that mechanical

ROSURGERY, http://dx.doi.org/10.1016/j.wneu.2017.02.046

Table 2. Literature Comparison for Sacroiliac Joint Arthrodesis

Reference Study Type SystemNumber ofPatients

Follow-Up(months)

ClinicalOutcomeMeasures Satisfaction

ReoperationRate, n (%)

Wise and Dall,200812

Prospective Threaded titanium cage (Medtronic,Memphis, Tennessee, USA)

13 Average 29.5 VAS 77% would have surgeryagain

1/13 (7.7)

Khurana et al.,200911

Consecutivecase study

Hollow modular anchorage screws(Aescalup Ltd., Tuttlingen, Germany)

15 Average 17 SF-36, Majeedscoring system

— 0

Rudolf andCapobianco, 20149

Retrospective iFuse Implant System(SI-BONE Inc., San Jose, California, USA)

50 Average 40 QOLquestionnaire,NRS 0e10

91% satisfied (3months)

4/50 (8)

Cummings andCapobianco, 20137

Retrospective iFuse Implant System(SI-BONE Inc., San Jose, California, USA)

18 Average 12 VAS, ODI, SF-12 56% very satisfied; 83%would definitely have

surgery again

1/18 (5.6)

Ledonio et al.,20145

Retrospective iFuse Implant System(SI-BONE Inc., San Jose, California, USA)

22 Average 13 ODI — 2/22 (9)

Current study, 2016 Prospective SI-LOK (Globus Medical, Inc., Audubon,Pennsylvania, USA)

32 12 VAS, ODI, Odom’scriteria

8.6 (of 10; 97%) wouldhave the same surgery

again

2/32 (6.3)

VAS, visual analog scale; SF, Short Form; QOL, quality of life; NRS, numerical rating scale; ODI, Oswestry Disability Index.

ORIGINAL ARTICLE

LOUIS H. RAPPOPORT ET AL. MINIMALLY INVASIVE SIJ FUSION WITH A HYDROXYAPATITE-COATED SCREW

stability is a more reliable and concrete term to describe a stableSIJ at 12 months postoperative. Mechanical stability wasachieved in 93.3% (28/30) of patients. All patients reportedsymptom improvement by follow-up at 12 months post-operatively, but 2 patients showed signs of radiographic lucency.Plain radiographs were not available for 2 patients 12 monthspostoperatively, precluding assessment of mechanical stability.Limitations of this study include small sample size and short

follow-up. However, this study is part of a larger 24-month follow-up prospective study, the results of which will be reported on

WORLD NEUROSURGERY 101: 493-497, MAY 2017

completion. Although findings of this study suggest that use ofHA-coated screws offers a viable surgical alternative for patientswho have SIJ pain, additional studies with a greater number ofpatients are needed to determine longer-term outcomes.

CONCLUSIONS

The current study found that use of a novel HA-coated screw totreat SIJ pain and dysfunction yielded positive clinical outcomes,high patient satisfaction, and low complication rates.

REFERENCES

1. Buchowski JM, Kebaish KM, Sinkov V, Cohen DB,Sieber AN, Kostuik JP. Functional and radio-graphic outcome of sacroiliac arthrodesis for thedisorders of the sacroiliac joint. Spine J. 2005;5:520-528.

2. Katz V, Schofferman J, Reynolds J. The sacroiliacjoint: a potential cause of pain after lumbar fusionto the sacrum. J Spin Disord Tech. 2003;16:96-99.

3. Slipman CW, Shin CH, Patel RK, Isaac Z,Huston CW, Lipetz JS, et al. Etiologies of failedback surgery syndrome. Pain Med. 2002;3:200-214.

4. Sembrano JN, Polly DW Jr. How often is low backpain not coming from the back? Spine. 2009;34:E27-E32.

5. Ledonio CG, Polly DW Jr, Swiontkowski MF.Minimally invasive versus open sacroiliac jointfusion: are they similarly safe and effective? ClinOrthop Relat Res. 2014;472:1831-1838.

6. Smith AG, Capobianco R, Cher D, Rudolf L,Sachs D, Gundanna M, et al. Open versus

minimally invasive sacroiliac joint fusion: a multi-center comparison of perioperative measures andclinical outcomes. Ann Surg Innov Res. 2013;7:14.

7. Cummings J, Capobianco RA. Minimally invasivesacroiliac joint fusion: one-year outcomes in 18patients. Ann Surg Innov Res. 2013;7:12.

8. Duhon BS, Cher DJ, Wine KD, Kovalsky DA,Lockstadt H. Triangular titanium implants forminimally invasive sacroiliac joint fusion: a pro-spective study. Global Spine J. 2016;6:257-269.

9. Rudolf L, Capobianco R. Five-year clinical andradiographic outcomes after minimally invasivesacroiliac joint fusion using triangular implants.Open Orthop J. 2014;8:375-383.

10. Sachs D, Capobianco R. Minimally invasivesacroiliac joint fusion: one-year outcomes in 40patients. Adv Orthop. 2013;2013:536128.

11. Khurana A, Guha AR, Mohanty K, Ahuja S.Percutaneous fusion of the sacroiliac joint withhollow modular anchorage screws: clinical andradiological outcome. J Bone Joint Surg Br. 2009;91:627-631.

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12. Wise CL, Dall BE. Minimally invasive sacroiliacarthrodesis: outcomes of a new technique. J SpinDisord Tech. 2008;21:579-584.

Conflict of interest statement: The authors acknowledge thatfunding for this project was provided by the MusculoskeletalEducation and Research Center (MERC), a Division of GlobusMedical, Inc. L.H.R. is a consultant for Globus Medical, Inc.,Orthofix, 4WEB Medical, and Innovasis; receives researchsupport from Globus and Orthofix; and is a member of theSpeakers Bureau for Globus and Orthofix. I.Y.L. and G.J. aresalaried employees of Globus Medical. I.Y.L. performedstatistical analyses.

Received 9 September 2016; accepted 8 February 2017

Citation: World Neurosurg. (2017) 101:493-497.http://dx.doi.org/10.1016/j.wneu.2017.02.046

Journal homepage: www.WORLDNEUROSURGERY.org

Available online: www.sciencedirect.com

1878-8750/$ - see front matter ª 2017 Elsevier Inc. Allrights reserved.

w.WORLDNEUROSURGERY.org 497