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Anterior Subcutaneous Internal Pelvic Fixation/INFIX: A Systemic Review

Vaidya, Rahul MD, FRCSC; Woodbury, Derrek Msc, DO; Nasr, Kerrelos MD

Author Information
Journal of Orthopaedic Trauma: September 2018 - Volume 32 - Issue - p S24-S30
doi: 10.1097/BOT.0000000000001248



Anterior subcutaneous internal pelvic fixation (ASIPF) was developed to address the shortcomings of external fixation (EXFIX) of the anterior pelvis.1–19 These are pin tract infections (25%–50% of pts),1,2,4,10–15,17,19,20 osteomyelitis (7%),1,2,10,11,14,17 loosening (10%),10,11,14,15,17 loss of reduction (up to 33%),2,4,10 difficulty when used with in patients with obesity,7 and/or patients who attempt to mobilize or sit upright.

Three separate innovations were developed to address this issue in publications and patents from 2007–2012: the Pelvic Bridge,21,22 the internal fixation (INFIX),23,24 and the cross-over pelvic internal fixator.25 All these techniques are used in conjunction with posterior fixation in unstable pelvic ring injuries and have the ability to distract or compress the anterior injury.

The purpose of this article is to review the literature in the use of ASIPF also known as INFIX. We hope to define indications, healing, radiographic parameters, functional outcomes, complications, and direct comparisons to alternate fixation methods including plates, EXFIX, ramus screws, and overall recommendations.


A systematic review of the literature was performed according to the methods described in the Preferred Reporting Items for Systematic Reviews and Meta-analyses statement.26 Studies included were original articles pertinent to our research questions that were published in the English language or with English translation between the years 2007 and Jan 2018.

Medical Subject Heading terms were used with the search string “anterior subcutaneous pelvic fixation or fixator or stabilization” and “Pelvic INFIX.” These terms were searched within PubMed and Google Scholar. Databases and articles were accessed through Wayne State University Library, Detroit, Michigan. Articles, which met the inclusion criteria, were systematically assessed for the relevance of their content (see Figure, Supplemental Digital Content 1, : depicts a flow diagram of the systematic literature search). Initially, titles were screened for primary inclusion and exclusion. All the abstracts obtained were further assessed for eligibility. The full texts of articles, which met the relevance and inclusion criteria, were obtained and reviewed, paying particular attention to relevance for our topic. References of full texts were also reviewed to identify any other potentially relevant studies. The final studies were reviewed according to study design, analysis, and interpretation, as well as validity of results. Because there were only case series and case reports published, the level of evidence was rated as Level 4 case series.


After application of the eligibility criteria, a total of 25 studies were identified. Five studies were removed from the data as we believed that they were duplicate data from the same authors. For these 5 studies, we included only the larger and more recent series.24,25,27–29 That left 20 articles with 496 patients (see Table, Supplement Digital Content 1, There were 17 case series27,30–46 with 4–91 patients and 3 case reports47–49 which were included because of significant complications reported. There was 1 prospective study36 and 3 case–control studies.29,42,44


In all 20 studies, an unstable pelvic injury was the indication for surgical intervention. Eight studies used parts of the OTA/AO50 classification,31,33,39–42,44,45 2 studies used the Young and Burgess (YB) classification,51 8 studies used both,30,34,35,37,43,47–49 and 2 studies36,38 did not elaborate on classification. In 437/496 patients who were classified using the OTA/AO classification, 46.5% were 61-C and 53.5% were 61-B injuries. Only 1 study used the complete OTA/AO50 classification such that the anterior injury could be identified.43 That study reported 28 a, 17 b, 5 c, 21 d, 4 e, 7 f, and 0 g injuries (Figs. 1–5). Two studies excluded symphyseal injuries because of concern for fixation failure47 and a suitable alternative, plating.36,46 Two studies targeted symphyseal injuries,29,44 and the others did not exclude them. Many studies commented on the benefit of using INFIX in combined pelvic/acetabular injuries as opposed to EXFIX because all implants were internal, in open fractures, and in combination with a laparotomy.

OTA/AO classification for anterior injuries c1 and c2. An example of a c1 anterior pelvic ring injury (A) preoperative, (B) after fixation, and (C) at follow-up after healing.
OTA/AO classification for anterior injury c3. An example of a c3 anterior pelvic ring injury (A) preoperative, (B) after fixation, and (C) at follow-up after healing.
OTA/AO classification for anterior injuries c4, c5, and c6. An example of a c5 anterior pelvic ring injury (A) preoperative, (B) after fixation, and (C) at follow-up after healing.
OTA/AO classification for anterior injuries c7 and c8. An example of a c7 anterior pelvic ring injury (A1) x-ray, (A2) computed tomography preoperative, (B) after fixation, and (C) at follow-up after healing.
OTA/AO classification for anterior injuries c9 and c10. An example of a c9 anterior pelvic ring injury (A1) x-ray, (A2) computed tomography preoperative, (B) after fixation, and (C) at follow-up after healing.


The technique used for ASIPF varied slightly among studies. Most articles recommend using either mini-open23,31 or percutaneous insertion.34 The fluoroscopic views used commonly were the iliac oblique, obturator outlet, and obturator inlet views,31,52,53 with an insertion site at or just above the anterior inferior iliac spine. Implants used were polyaxial screws,23,25,31 monoaxial screws,54 and Schanz pins;43 the diameter varied from 6.5 to 9 mm, but most commonly 7–8.5 mm screws were reported. The screws should be inserted at least 60 mm into the bone or to the roof of the sciatic notch on the iliac oblique x-ray,52,53 which means using 80–120 mm lengths. In very obese individuals, Schanz pins of 150 mm are useful and can be found with the USS Spine Fracture Module (Depuy Synthes, Paoli, PA).43 A 5.5-to-6.5-mm titanium rod is over-contoured on the abdomen and slid just under the skin at the level of the bikini line55 as demonstrated in an online video.52 Reduction of the pelvis for rotationally unstable injuries can be achieved by compression or distraction using C-rings and laminar spreaders,23,46,56 manipulation by hand with handles on the screws, or a with a femoral distractor.31 For vertically unstable or other complete injuries, the posterior ring was reduced and fixed first. Some authors reported use of anterior inferior iliac spine/supraacetabular implants to aid in this reduction maneuver (this is a topic beyond the scope of this article). Patients were allowed to ambulate on uninjured hemi-pelvises with full weight and toe touch or foot flat on the injured side. Full weight-bearing started on the injured side for a type C injury between 6 and 12 weeks depending on the institution.

Elective implant removal was reported to take place between 10 weeks and 9 months, was reported to be safe, easy, and without complication, but required to be performed in an operative theater unlike an external fixator.46 Several authors have reported implants that were left in indefinitely in individuals who were asymptomatic and did not want another surgical intervention. The long-term effect of this is unknown.


The pelvic fracture healed in 454 of 456 patients (see Table, Supplemental Digital Content 1, where it was reported. Nonunion was reported in 2 studies.33,46 Dahill et al reported 1 anterior nonunion of 41 patients, which was asymptomatic and required no further treatment. Muller et al reported nonunion in 1/36 patients who was schizophrenic, noncompliant, refused further surgery, and ended up in a malunion. Nonunion is a rare event in pelvic fractures.


Radiographic measures of reduction in 1 study43 were by the pelvic deformity index of Lefaivre et al/Keshishyan et al57,58 for lateral compression and vertical shear injuries (39.6% improvement) or symphyseal diastasis for anterior posterior compression (APC) injuries (56.9% improvement, 86% excellent, 14% good) in 83 patients. The Matta 59 criteria were used in 4 studies. They reported 58% excellent, 35% good, and 6.5% poor reductions in 62 overall patients.38–40,45 Fifteen studies did not use any radiographic measures.


Outcome scores were addressed in 6 articles for 197 patients. One used the German pelvic outcome score,33 and 5 used the Majeed score.40,42–45 They reported 87 excellent, 77 good, and 33 fair results.


Lateral Femoral Cutaneous Nerve Injury

The most common complication that was reported was lateral femoral cutaneous nerve (LFCN) injury or irritation in 123 of 467 patients (26.3%). Thirteen studies stated that the injury was temporary and resolved. Three believed that it was a persistent issue.33,41,46 This issue seemed to be tolerated well in most patients and is often described as paresthetic or numb and resolves with removal of the implant.30,31,36,37,39,40,42–45 In 1 case,36 the LFCN irritation was a reason for early implant removal and in 1 instance occurred at the removal surgery.43

Femoral Nerve Palsy

Femoral nerve palsy has been reported as a complication in 5 reports35,39–42 in 10 patients. Hesse et al35 reported on 6 patients who had 8 femoral nerve palsies, which was the subject of this article. One patient had it recognized early, and in 5 patients, it was recognized late, presenting as leg buckling when walking. They were all treated with INFIX removal, and at the latest follow-up, 2 of 8 femoral nerves were normal, 5 of 8 were still recovering, and 1 did not recover. The authors believed that it may be due to seating the bar too deep in patients with obesity, leading to compression of the femoral nerve. The other 4 cases were reported in case series of ASIPF use, were all discovered early in the postoperative period, had the INFIX removed39,41,42 or readjusted,40 3 cases had full recovery, and 1 partial recovery. The incidence of this complication in the reported series of pelvic cases using ASIPF is 4/487 or 1% (this does not include the article by Hesse et al, which has only femoral nerve palsy cases). We recommend an early postoperative examination after INFIX to ensure that these instances are caught and corrected. As with many procedures, there is a learning curve, and placing the screws and bar too deep is likely the problem.

Vascular Occlusion

Vascular occlusion was reported in 1 case. Seating the bar too deep can also lead to vascular occlusion,39,43,48 and removal or repositioning of the screws to a higher level off the bone along with the rod solves the issue. In this case, it was recognized early and was treated expediently with resolution of the problem. We recommend keeping the screw heads high to the level of the skin and keeping the bar superficial.

Heterotopic Ossification

Heterotopic ossification (HO) was reported in 120 of 332 cases.30,31,33,34,36,38–40,43,44 It was reported to be asymptomatic in all of them except 2.43 One patient who had severe HO declined removal and was ultimately satisfied. A second patient had severe HO unrelated to the INFIX but to a massive soft-tissue injury. In the same study,43 older age (analysis of variance 0.007) and higher injury severity score (0.05) were found to be risk factors for developing HO. The length of time the INFIX was in place, Glasgow Coma Scale, sex, race, and Majeed score showed no significant relationship with the development of HO. HO is usually asymptomatic and requires no treatment. It can be removed at the time of implant removal if there is excessive formation.


Infection at the surgical site was reported in 15 of 496 cases (3%).30,32,33,36,41,43,45,46 In 9/15 cases, the infection occurred before 10 weeks, and in 3/15 cases, it occurred late after 6 months. Timing was not described in 3 cases. The implant was removed in 1030,33,43 cases, followed by culture-specific antibiotics. In 2 early cases,30,33 the infection was treated with culture-specific suppressive antibiotics and it resolved to allow for explantation at the usual time. Early removal of the hardware because of infection did not result in a loss of reduction in any case, likely due to the solid posterior fixation. Although not explicitly described in the literature, the utilization of irrigation and debridement at the site of infection either at the time of explant or before may have played a vital component in the overall treatment. Infections resolved in all cases, with no reports of osteomyelitis at the latest follow-up.

Early Revision Implant Failure Loss of Reduction

Early reoperations occurred in 36/496 cases (7.3%). The reasons for early reoperation was that the implant was placed too deep (patient had discomfort) in 4 patients, loss of fixation in 9, infection in 8, femoral nerve palsy in 10, LFCN irritation (not tolerated by patient) in 1, vascular occlusion in 1, and bladder incarceration in a symphysis pubis disruption in 1. Of these complications, 16/496 (3%) were likely caused by the screws and bar placed too deep and compressing the underlying structures, resulting in discomfort, femoral nerve palsy, or vascular occlusion. It is important to place the screws well off the bone and have the rod above the fascia to a point just under the skin.

INFIX Versus Alterate Fixation

There were 3 case–control studies that compared INFIX directly with another fixation method in a study of pelvic fractures with symphyseal injuries comparing 28 patients treated with open reduction internal fixation (ORIF) (symphyseal plating) with 24 patients with INFIX. They concluded that plating provides better reduction of the pubic symphysis and that plates had a higher infection rate and require only 1 surgery. Outcomes scores were similar.

Bi et al42 compared a modified ASPIF (MASPIF) in 21 cases with a third pedicle screw connected from the bar to the symphysis with EXFIX in 22 cases. They found that the operation time for the EXFIX group was significantly less than that in the MASPIF group (P < 0.0001). In EXFIX, 6 patients developed an infection, 3 loss of fixation, and 2 loosening. None of these complications occurred in MASPIF. Temporary LFCN irritation occurred in 3 MASPIF and 2 EXFIX patients. One patient experienced femoral nerve palsy in MASPIF, which resolved after removal. Fractures of all patients healed well and Majeed scores were similar.

Wang et al44 compared ORIF versus MASPIF in a group of OTA/AO type B injuries. Blood loss, operating time, and hospitalization duration were less (all P < 0.001) in the MASPIF group. The clinical outcomes (6 months or greater follow up) were as follows: MASPIF excellent and good in 80.8% and moderate in 19.2%; and ORIF excellent and good in 65.4%, moderate in 29.0%, and poor in 5.6%. No patient experienced nonunion, delayed union, superficial infection, or deep surgical wound infection. Two patients had temporary LFCN irritation in MASPIF. There were 2 superficial wound infections in the ORIF group.


Physicians are always seeking better ways to provide treatment to their patients. It was this spirit that led to the development of the INFIX device as an alternative to the widely used external fixator for definitive fixation of anterior pelvic ring injuries. Our systemic review found 17 case series and 3 case reports, which included 496 patients. The articles were from the United States, Germany, Great Britain, Switzerland, China, India, and Australia. The average follow-up was 6 months to 34.9 months. We hoped to get a consensus on indications, healing, radiographic parameters, functional outcomes, complications, and direct comparisons to alternate fixation methods including plates, EXFIX, ramii screws, and overall recommendations.

The indications for anterior fixation with INFIX were OTA 61-B and 61-C fractures in conjunction with posterior fixation. Two articles excluded isolated symphyseal injuries,36,46 whereas most series did not. A direct comparison of plates versus INFIX for symphyseal injuries reported better reductions with plates, which also requires only a single surgery, whereas a second article reported less operating room time, blood loss, and hospital duration (P < 0.001) for the modified INFIX versus plates. Majeed scores were similar in both series. We believe that any anterior injury that requires fixation can be treated with INFIX successfully with the appropriate posterior fixation but that isolated symphyseal injuries may be better served by ORIF with plates.

Healing after INFIX application was reported in 454/456 patients or 99.6%. We believe that this is true of pelvic fractures in general, which has a high rate union than the implants used in this study.

Radiological parameters used were the modified Keshishyan cross method 57,58 in 1 article43 and the Matta technique in 4 articles.38–40,45 The Keshishyan cross method is a good method to judge reductions and pelvic symmetry. However, it fails in APC injuries because a symmetrically displaced pelvis, as in an APC 3 injury, may have a very low value and its reduced counterpart could be the same as long as each side is symmetric. Also, pelvic binders used before x-rays can mask the original deformity. In these injuries without much vertical displacement, symphyseal widening may be enough as a measurement.43 The Matta technique when used preoperatively and postoperatively can assess correction but not by 1 number or value, and the articles in this series used it only postoperatively. Unfortunately, correlating radiological deformity with functional outcomes is not something that has been done well for these injuries.

Outcome scores were reported only in 6 articles and 197/496 patients (40%). They reported 87 excellent, 77 good, and 33 fair results. Without conformity and a breakdown of the scores, it is difficult to know where the shortcomings are with the treatment of these injuries. Also, many pelvic ring injuries are associated with multiple other injuries that affect overall outcome43 and make it impossible to assess treatment.

This study correlates the complications of INFIX, which seems to be universally similar. The rates are as follows: LFCN injury 123 of 467 patients (26.3%), which improves with removal of the implant but may rarely be permanent and irritating; HO 120/332 cases (36%) is usually asymptomatic; infection 15/496 cases (3%), which can be treated with irrigation and debridement, removal, culture-specific antibiotics, and perhaps retention early on (until you feel safe with removal for up to 4 weeks postoperatively); early reoperations occurred in 36/496 cases (7.3%); femoral nerve palsy 1% in 4/487 (early diagnosis crucial for outcome); and vascular occlusion 1/497 (again corrected by removing the bar or elevating it).

Many of these complications could be avoided with familiarity with the technique, making sure that the bar and screws are not placed too deep or placing adequate posterior fixation.46 Better implants, C-clamps, monoaxial screws, or Schanz pins (USS FRACTURE; Depuy Synthes) can avoid problems such as loosening, especially in APC 3 injuries. Long screws or Schanz pins can avoid compression of the underlying structures in patients with obesity.

The 26.3% incidence of LFCN irritation, which is prevalent in every series, does not have a solution. However, it is usually self-limiting and improves once the implant is removed. HO is also present in 36% of cases but usually asymptomatic. It can be excised at the time of implant removal.

Matta59 believed that INFIX of the anterior pelvic ring, although safe and reliable, should be reserved for symphysis pubis dislocations and only a minority of pubic ramus fractures. Yet, fixation front and back is the norm nowadays for completely unstable injuries and many partially stable injuries with ramii fractures or symphyseal injury.

The ideal fixation for symphyseal injuries is likely plates and screws and for ramii fractures EXFIX, ramii screws, or ASIPF. We believe that despite the secondary surgery for ASPIF, it is superior to EXFIX in strength, incidence of infection, patient comfort, and failure of treatment. Both supraacetabular EXFIX and INFIX have an incidence of LFCN irritation. Many times the device can be removed at a secondary surgery for other injuries in polytraumatized patients.

Authors of 15 of 17 series believed ASPIF, a valuable tool for reduction and fixation in unstable pelvic ring injuries, is well tolerated by patients, allowing good mobility with acceptable complications and outcomes. One report felt there was high rate of LFCN palsy and found that some patients do not tolerate the implant very well.36 A second article noted a “high risk of LFCN injury” and cautioned against the liberal use of the INFIX in patients with stable fractures where conservative treatment may be more appropriate but that “Most complications occurring from INFIX are self-limiting.”41

The limitation of this study is that the literature reports only 1 prospective series, 3 retrospective case control series, and 14 retrospective series. Very few reports use the complete OTA/AO classification, which includes the anterior injury description, which this paper is about and would help identify what injuries are being taken care of (Figs. 2–5). Radiographic parameters were reported in only 5 and outcome measures in 6 reports. However, the reports were consistent in attempting to describe pelvic instability (OTA/AO or Young and Burgess) and complications. We included any case report that reported a significant complication as well.29,54,60–62


The use of ASPIF has been reported in North America, Europe, Asia, and Australia. Most authors report it as a valuable tool for reduction and fixation in unstable pelvic ring injuries, which is biomechanically sound, well tolerated by patients, allowing good mobility with acceptable complications and outcomes. There is a learning curve; LFCN nerve irritation, HO, and the need for a secondary surgery are its negatives.


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pelvic ring injury; pelvic fracture; anterior pelvic ring injury; anterior fixation; anterior subcutaneous pelvic fixation; INFIX; complications; outcome scores; outcome parameters; radiographic outcomes; systemic review; heterotopic ossification; infection; symphyseal disruption; ramii fractures; biomechanic stability; pelvic reduction; OTA/AO classification; Young and Burgess classification; external pelvic fixation

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