Insertion sites of iliosacral screws on the posterior ilium: Implications for posterior pelvic fixation.

OBJECTIVES: Lateral compression type II pelvic ring injuries can be treated with fixation through open or percutaneous approaches depending on the injury pattern and available osseous fixation pathways. The start site of iliosacral screws to stabilize these injuries should be on the unstable posterior iliac fragment; however, our understanding of start sites for iliosacral screws has not been developed. The purpose of this study is to provide an analysis of iliosacral screw start sites on the posterior ilium to help guide treatment of pelvic ring injuries. METHODS: One-hundred and seventeen consecutive patients at an academic level I trauma center with pelvic ring injuries who underwent surgical treatment with iliosacral screws were included in the final analysis. The start sites of iliosacral screws with confirmed intraosseous placement on a postoperative computed tomography were mapped on the posterior ilium and analyzed according to the sacral segment and type of iliosacral screw. RESULTS: One-hundred and seventeen patients were included in the final analysis. Of the total of 272 iliosacral screw insertion sites analyzed, 145 (53%) were sacroiliac-style screws and 127 (47%) were transsacral screws. The insertion sites for sacroiliac-style screws and transsacral screws at different sacral segment levels can vary but have predictable regions on the posterior ilium relative to reliable osseous landmarks. CONCLUSIONS: Iliosacral screws start sites on the posterior ilium have reliable regions that can be used to plan posterior fixation of pelvic ring injuries.

Does local fat thickness correlate with post-operative infection in open reduction and internal fixation of acetabulum fractures?

PURPOSE: Obesity is an epidemic which increases risk of many surgical procedures. Previous studies in spine and hip arthroplasty have shown that fat thickness measured on preoperative imaging may be as or more reliable in assessment of risk of post-operative infection and/or wound complications than body mass index (BMI). We hypothesized that, similarly, increased local fat thickness at the surgical site is a predictor of wound complication in acetabulum fracture surgery. METHODS: Patients who underwent open reduction and internal fixation (ORIF) of an acetabulum fracture through a Kocher-Langenbeck (K-L) approach at a single institution from 2013 to 2020 were identified. Pre-operative CT scans were used to measure fat thickness from the skin to the greater trochanter in line with the surgical approach. Post-operative infections and wound complications were recorded and associated with fat thickness and BMI. RESULTS: 238 patients met inclusion criteria. 12 patients had either infection or a wound complication (5.0%). There was no significant association with BMI or preoperative fat thickness on post-operative infection or wound complication (p-value 0.73 and 0.86). CONCLUSIONS: There is no statistically significant association of post-operative infection or wound complications in patients with increased soft tissue thickness or increased BMI. ORIF of acetabulum fractures through a K-L approach can be performed safely in patients with large subcutaneous fat thickness and high BMI with low risk of infection or wound complications.

Bladder Repair With Irrigation and Debridement and Open Reduction Internal Fixation of the Anterior Pelvic Ring Is Safe and Decreases Risk of Infection in Pelvic Ring Injuries With Extraperitoneal Bladder Ruptures.

OBJECTIVES: To determine the incidence of infection in nonoperative versus operative management of extraperitoneal bladder ruptures in patients with pelvic ring injuries. DESIGN: A retrospective cohort study of 2 prospectively collected trauma registries. SETTING: Two Level 1 trauma centers. PATIENT SELECTION CRITERIA: Patients with operative pelvic ring injuries, 68 (6%) had extraperitoneal bladder ruptures. OUTCOME MEASURES AND COMPARISONS: The primary outcome was the incidence and associated risk factors of deep pelvic infection requiring return to OR for surgical debridement. Secondary outcomes included quality of reduction, other complications, and radiographic union. Comparisons were made based on the status of any associated bladder injury. RESULTS: Of 1127 patients with operative pelvic ring injuries, 68 patients had extraperitoneal bladder ruptures, 55 had bladder repair and 13 did not. Of those 13 without repair, none had ORIF of the anterior pelvic ring. Patients without bladder repair had an increased odds of infection 17-fold compared to patients who did have a repair performed (OR 16.9, 95% CI 1.75 - 164, P = 0.01). Other associated factors for deep pelvic infection included use of suprapubic catheter ( p < 0.02) and a closed reduction of the anterior ring ( p < 0.01). Patients undergoing anterior ring ORIF and bladder repair had improved reductions and no increased infection risk. CONCLUSIONS: Operative repair of extraperitoneal bladder ruptures decreases risk of infection in patients with pelvic ring injuries. Additionally, ORIF of the anterior pelvic ring does not increase the risk of infection and results in better reductions compared to closed reduction. Treatment algorithms for these combined injuries should consider recommending early bladder repair and anterior pelvic ORIF. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Obstetricians are likely to elect for cesarean section in women with retained pelvic implants: a radiographic survey study.

PURPOSE: Women with a history of pelvic fracture undergo cesarean section (CS) at a higher rate than the general population. The purpose of our study is to query obstetricians on their preferences. METHODS: An electronic survey consisting of 22 radiographs of patients who underwent pelvic fixation was sent to obstetricians at 3 academic medical centers. For each radiograph, a hypothetical scenario was given, and the respondents were asked if they would elect for a vaginal delivery or CS. RESULTS: We collected 58 responses. The overall CS rate was 59%. Respondents were significantly more likely to elect for CS with trans-symphyseal fixation or sacroiliac fixation, independently (p < 0.001). DISCUSSION: Obstetricians are likely to elect for elective CS in the presence of pelvic implants especially in patients with trans-symphyseal and sacroiliac fixation. Based on there is an opportunity for collaboration between orthopedic trauma surgeons and obstetricians.

Percutaneous sacral screw fixation alone sufficient for mildly displaced U-type sacral fractures with preserved osseous fixation pathways.

PURPOSE: To describe U-type sacral fracture characteristics amenable to percutaneous sacral screw fixation. METHODS: U-type sacral fractures were identified from a trauma registry at a level 1 trauma center from 2014 to 2020. Patient demographics, injury mechanism, fracture characteristics, and fixation construct were retrospectively retrieved. Associations between fracture pattern and surgical fixation were identified. RESULTS: 82 U-type sacral fractures were reviewed. Six treated with lumbopelvic fixation (LPF) and 76 were treated with percutaneous sacral screws (PSS) alone. Patients receiving LBF had greater sacral fracture displacement in coronal, sagittal, and axial planes compared to patients receiving PSS alone (P < 0.05), negating osseous fixation pathways. All patients went onto sacral union and there were no implant failures or unplanned reoperations for either group. CONCLUSION: If osseous fixation pathways are present, U-type sacral fractures can be successfully treated with percutaneous sacral screws. LPF may be indicated in more displaced fractures with loss of spinopelvic alignment. Both techniques for U-type sacral fractures result in reliable fixation and healing without reoperations.

Use of 3D Fluoroscopy to Assist in the Reduction and Fixation of Pelvic and Acetabular Fractures: A Safety and Quality Case Series.

SUMMARY: Multidimensional fluoroscopy has been increasingly used in orthopaedic trauma to improve the intraoperative assessment of articular reductions and implant placement. Owing to the complex osteology of the pelvis, cross-sectional imaging is imperative for accurate evaluation of pelvic ring and acetabular injuries both preoperatively and intraoperatively. The continued development of fluoroscopic technology over the past decade has resulted in improved ease of intraoperative multidimensional fluoroscopy use in pelvic and acetabular surgery. This has provided orthopaedic trauma surgeons with a valuable tool to better evaluate reduction and fixation at different stages during operative treatment of these injuries. Specifically, intraoperative 3D fluoroscopy during treatment of acetabulum and pelvis injuries assists with guiding intraoperative decisions, assessing reductions, ensuring implant safety, and confirming appropriate fixation. We outline the useful aspects of this technology during pelvic and acetabular surgery and report its utility with a consecutive case series at a single institution. The added benefits of this technology have improved the ability to effectively manage patients with pelvis and acetabulum injuries.

Iliosacral Screws Can be Placed With Precision by Adjusting the Pelvic Inlet Between S1 and S2.

OBJECTIVES: To determine: 1) the natural incidence of sacral inlet angle differences between S1 and S2 and 2) implications for iliosacral screw placement with a technique to improve the accuracy of the intraoperative fluoroscopic inlet for S1 and S2. DESIGN: Combined retrospective and prospective cohort reviews. SETTING: Regional Level 1 trauma center. PATIENTS/PARTICIPANTS: After exclusion criteria, 300 patients with uninjured pelvic rings to determine the natural incidence of S1 - S2 angle differences and 33 patients treated with iliosacral screws over the study period. INTERVENTION: None in the retrospective cohort. In the prospective cohort all patients underwent fluoroscopically assisted iliosacral screw fixation. MAIN OUTCOME MEASUREMENTS: Radiographic determination of S1 - S2 angle differences above 10 degrees in a natural population for the retrospective cohort. In the prospective, operative cohort the outcome of interest was the safety of iliosacral screws in S1 and S2 as determined on intraoperative fluoroscopy and postoperative CT scan.Results: In the retrospective cohort, 180/300 (60.0%) had S1 - S2 inlet angle differences above 10 degrees. In the operative cohort, 19/33 (57.6%) had S1 - S2 inlet angle differences above 10 degrees. Of the iliosacral screws in S1 and S2 placed using the described imaging technique, all (69/69, 100%) were safe. CONCLUSIONS: A normal population determined that differences in the inlet angle between S1 and S2 are common. An operative cohort was treated using preoperative CT-based planning to define different intraoperative fluoroscopic inlet views for S1 and S2, if a larger difference existed. Using this technique, 69/69 (100%) of iliosacral screws were either intraosseous or juxtacortical and safe. LEVEL OF EVIDENCE: Level V. See Instructions for Authors for a complete description of levels of evidence.

Pelvic ring injuries: recent advances in diagnosis and treatment.

Pelvic ring injuries typically occur from high-energy trauma and are often associated with multisystem injuries. Prompt diagnosis of pelvic ring injuries is essential, and timely initial management is critical in the early resuscitation of polytraumatized patients. Definitive management of pelvic ring injuries continues to be a topic of much debate in the trauma community. Recent studies continue to inform our understanding of static and dynamic pelvic ring stability. Furthermore, literature investigating radiographic and clinical outcomes after nonoperative and operative management will help guide trauma surgeons select the most appropriate treatment of patients with these injuries.

Imaging of Pelvic and Acetabular Trauma: Part 1, Osseous Findings.

Pelvic ring injuries and acetabular fractures are complex injuries and are often challenging to treat for a number of reasons. Orthopaedic trauma surgeons critically evaluate pelvic radiographs and CT images to generate an appropriate detailed injury and patient-specific preoperative plan. There are numerous crucial osseous details that surgeons should be aware of. Often, some of the most important factors that affect patients in treatment timing decisions, assessing reduction strategies, and deciding and inserting fixation constructs may be subtle on preoperative imaging. The radiographic and CT imaging findings covered subsequently should be sought out and appreciated preoperatively. Combining all the available osseous information helps the surgeon predict potential pitfalls and adjust surgical plans before incision. Ensuring a methodical and meticulous imaging review allows for the development of a detailed preoperative plan and helps avoid intraoperative missteps. This process will inherently streamline the surgical procedure and optimize the patient's surgical care. Maximizing the accuracy of the preoperative planning process can streamline the treatment algorithm and ultimately contribute to the best possible clinical outcome.

Oblique anterior pelvic external fixator for intraoperative reduction of rotationally unstable pelvic ring injuries.

Incomplete sacroiliac joint injuries are often associated with external rotation and extension deformities on the injured hemipelvis. To appropriately correct this deformity, an oblique reduction force from caudal to cranial and lateral to medial is helpful. These injuries are often associated with traumatic disruption of the pubic symphysis. However, in injuries without traumatic disruption to the pubic symphysis, a two-pin oblique anterior external fixator can be used to obtain and maintain reduction of the sacroiliac joint, while percutaneous fixation is subsequently placed. Through a small case series and three specific patient examples, we demonstrate that the oblique anterior external fixator frame is a simple and effective strategy with the reduction and stabilization process of these multiplanar hemipelvis deformities.

Imaging of Pelvic and Acetabular Trauma: Part 2, Soft-Tissue Findings.

Pelvic ring injuries and acetabular fractures can be complex and challenging to treat. Orthopaedic trauma surgeons scrutinize pelvic radiographs and accompanying CT images for the osseous details that help create a thorough patient-specific preoperative plan. While the osseous details are incredibly important, the surrounding soft-tissue structures are equally as critical and can have a tremendous effect on both the patient and the surgeon. These findings may change surgery timing, dictate the need for additional surgeons or multidisciplinary teams, and determine the treatment sequence. The structures and potential clinical findings reviewed and demonstrated through example images should be sought out during physical examination and correlative preoperative imaging review. Combining all the available osseous and nonosseous information with a detailed approach helps the surgeon predict potential pitfalls and adjust surgical plans before incision. Maximizing the accuracy of the preoperative planning process can streamline treatment algorithm development and ultimately contribute to the best possible clinical patient outcome.

Assessment of sacral osseous fixation pathways for same-level dual transiliac-transsacral screw insertion.

INTRODUCTION: The purpose of this study is to (1) describe a pre-operative planning technique using non-reformatted CT images for insertion of multiple transiliac-transsacral (TI-TS) screws at a single sacral level, (2) define the parameters of a sacral osseous fixation pathway (OFP) that will allow for insertion of two TI-TS screws at a single level, and (3) identify the incidence of sacral OFPs large enough for dual-screw insertion in a representative patient population. METHODS: Retrospective review at a level-1 academic trauma center of a cohort of patients with unstable pelvic injuries treated with two TI-TS screws in the same sacral OFP, and a control cohort of patients without pelvic injuries who had CT scans for other reasons. RESULTS: Thirty-nine patients had two TI-TS screws at S1. Eleven patients, all with dysmorphic osteology, had two TI-TS screws at S2. The average pathway size in the sagittal plane at the level the screws were placed was 17.2 mm in S1 vs 14.4 mm in S2 (p = 0.02). Twenty-one patients (42%) had screws that were intraosseous and 29 (58%) had part of a screw that was juxtaforaminal. No screws were extraosseous. The average OFP size of intraosseous screws was 18.1 mm vs. 15.5 mm for juxtaforaminal screws (p = 0.02). Fourteen millimeters was used as a guide for the lower limit of the OFP for safe dual-screw fixation. Overall, 30% of S1 or S2 pathways were ≥ 14 mm in the control group, with 58% of control patients having at least one of the S1 or S2 pathways ≥ 14 mm. CONCLUSIONS: OFPs ≥ 7.5 mm in the axial plane and 14 mm in the sagittal plane on non-reformatted CT images are large enough for dual-screw fixation at a single sacral level. Overall, 30% of S1 and S2 pathways were ≥ 14 mm and 58% of control patients had an available OFP in at least one sacral level.

Upper sacral segment fixation with converging iliosacral screws: A technical trick for preoperative planning and case series.

INTRODUCTION: There are some situations where pelvic surgeons may want to place iliosacral screws with differing trajectories (Sacroiliac and Sacral styles) but may not be able to because of overlapping trajectories. HYPOTHESIS: Sacroiliac and Sacral style screws can be placed in S1 in select patients by using a preoperative planning technique off the 3D reconstructed surface rendered preoperative CT scan. MATERIALS/METHODS: Retrospective review of all patients receiving iliosacral screws using the described technique. RESULTS: Six patients received iliosacral screws using the described technique. When the preoperative planning technique demonstrated feasibility, all screws were able to be safely placed. DISCUSSION: Placing Sacroiliac and Sacral style screws within S1 may be ideal in some injury patterns. The described technique allows pelvic surgeons facile in iliosacral screw techniques to preoperatively plan for this construct. LEVEL OF EVIDENCE: VI; Retrospective case series.

When the Physician Becomes the Patient: Considerations for Work, Life, and Leadership.

Most orthopaedic surgeons are unprepared for serious medical illnesses. In such cases, the unique work-related and personal considerations for orthopaedic surgeons affect their career, their practice partners, and their patients. Planning together as an orthopaedic business organization for such issues can provide a framework to better navigate these difficult situations. Understanding the considerations and stressors from the individual's perspective can help provide the appropriate level of support while maintaining privacy. Throughout these considerations, open communication regarding expectations and concerns and expressions of empathy are the cornerstones of dealing with physician illness. Being a physician-patient adds complexity to an already difficult and stressful profession. Further dialogue regarding the physician-patient experience can help increase awareness of this issue and allow organizations to create a structure to best manage this almost inevitable occurrence.

Posterior Exposure in Kocher-Langenbeck With Gluteus Minimus Debridement vs. the Gibson Approach: A Cadaveric Study.

OBJECTIVE: To quantify the posterior acetabular exposure achieved with the Kocher-Langenbeck (K-L) with gluteus minimus debridement and Gibson approaches. METHODS: A Kocher-Langenbeck approach and a subsequent Gibson approach on the contralateral hip were performed in the prone position on 9 fresh frozen cadavers. Calibrated digital images were obtained of the Kocher-Langenbeck exposure, Kocher-Langenbeck exposure after gluteus minimus debridement, and Gibson exposure. The surface area of the posterior hip and pelvis visualized with each approach was calculated and compared with the contralateral side to assess for the difference between exposures. RESULTS: In 5 of the 9 cadavers, the Kocher-Langenbeck exposure before gluteus minimus debridement yielded an increased exposure in comparison with the Gibson approach, and the exposure was equivocal in 3 specimens. An increase of greater than 10% was considered significant. The exposure increased anteriorly and cranially by an average of 13.1 cm 2 after debridement of the gluteus minimus caudal to the superior gluteal neurovascular bundle in the Kocher-Langenbeck approach. CONCLUSIONS: Debridement of the gluteus minimus caudal to the level of the superior gluteal neurovascular bundle can significantly increase anterior and cranial exposure in the Kocher-Langenbeck approach and provide similar areas of access when compared with that in the Gibson approach.

The Impact of Magnetic Resonance Imaging on the Diagnosis of High-Energy Ipsilateral Femoral Neck and Shaft Fractures.

OBJECTIVE: To evaluate the most common femoral shaft fracture morphology associated with an ipsilateral femoral neck fracture in high-energy blunt trauma using magnetic resonance imaging (MRI). DESIGN: Retrospective review. SETTING: Level 1 trauma center. PATIENTS/PARTICIPANTS: 219 consecutive patients sustaining 228 femoral shaft fractures from high-energy blunt trauma. MAIN OUTCOME MEASUREMENTS: Fracture patterns were analyzed using the OTA/AO classification system. In addition, location of the fracture was measured as the distance from the distal aspect of the lesser trochanter to the center of the femoral shaft fracture. RESULTS: An OTA/AO 31 type fracture was seen in 16.5% (20/121) of patients presenting with OTA/AO 32-A type fractures, 12% (6/50) of patients with OTA/AO 32-B type fractures, and 26.3% (15/57) of patients with OTA/AO 32-C type fractures. The fractures that occurred in the middle or distal third of the femur shaft constituted 95.1% (39/41). CONCLUSIONS: In this cohort, patients with middle and distal third OTA/AO 32-C type fractures had the highest association with an ipsilateral OTA/AO 31 type fracture. OTA/AO 32-A2 and 32-A3 type fractures had the highest association with femoral neck fractures seen only on MRI. The data presented suggest continued usage of the rapid sequence pelvic MRI for all patients with high-energy femoral shaft fractures in whom a femoral neck fracture was not seen on an x-ray or a computed tomography scan. LEVEL OF EVIDENCE: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Is retrograde nailing superior to lateral locked plating for complete articular distal femur fractures?

INTRODUCTION: Nonunion rates for distal femur fractures treated with lateral locked plating (LLP) remains as high as 18-22% despite significant advances with implant design and construct modulation. However, whether treatment of distal femur fractures with rIMN has improved outcomes compared to LLP has not been well characterized. The purpose of this study was to compare outcomes of complete articular distal femur fractures (AO/OTA 33-C) treated with either LLP or rIMN. METHODS: 106 distal femur fractures in 106 patients between January 2014 and January 2018 were identified. Medical records were reviewed to collect patient age, gender, body mass index, sagittal and coronal plane alignment on immediate postoperative radiographs, time to union, incidence of nonunion, and incidence of secondary operative procedures for repair of a nonunion. RESULTS: Of 106 patients, 50 underwent rIMN and 56 underwent LLP. The mean age at the time of injury was 51 years (21 to 86 years) and there were 55 males. Average coronal alignment of 83.7° of anatomic lateral distal femoral angle (aLDFA) and sagittal alignment of <1° of apex anterior angulation in the rIMN group. In the LLP group there was an average of 87.9° of aLDFA and 1.9° of apex anterior angulation (p = .005 and p = .36). Average time to union in the rIMN group was 6 months and 6.6 months in the LLP group (p = .52). Incidence of nonunion in the rIMN group was 11.8% and 27.5% in the LLP group (p = .008). There were 8 secondary procedures for nonunion in the rIMN group and 18 in the LLP group (p = .43). CONCLUSIONS: Our results demonstrated a higher nonunion rate and coronal plane malalignment with LLP compared to rIMN. While prospective data is required, rIMN does appear to be an appropriate treatment for complete articular distal femur fractures with a potentially decreased rate of nonunion .

Symptomatic Ischial Stress Fractures in Elite Athletes Treated With Percutaneous Screws: A Report of 2 Cases.

CASES: Two high-level athletes with symptomatic gluteal pain with explosive movements that had failed nonoperative management were eventually diagnosed with ischial stress fractures. These were treated with percutaneous posterior column screws. Both patients healed their fractures and made full return to sport. CONCLUSION: Ischial stress fractures should be considered in the differential for athletes with persistent gluteal pain. Percutaneous fixation is a minimally invasive and effective method of treating symptomatic ischial stress fractures that have failed nonoperative treatment.

A New Algorithm for Classifying Acetabular Fracture Patterns on Three-dimensional Computed Tomography Reconstructions Markedly Improves Residents' Ability to Correctly Classify Fractures.

INTRODUCTION: CT and three-dimensional (3D) CT reconstructions have been shown to improve the understanding of acetabular fractures. With the increased availability of 3D pelvic CT reconstructions, our goal for this study was to develop an algorithm to aid residents in the classification of acetabular fractures. We hypothesized that the use of a stepwise algorithm will markedly enhance the trainees' ability to correctly identify acetabular fracture patterns. METHODS: This was a multicenter study that included 33 residents. Residents reviewed 15 sets of 3D reconstructions of the 10 acetabular fracture patterns. Residents completed the first round, and the results were collected electronically. Three weeks later, they were asked to classify the fractures a second time with the use of the algorithm. The number of correct responses from the two sessions was analyzed to determine if the algorithm improved residents' ability to correctly classify fracture patterns. RESULTS: Thirty-three residents classified 15 fractures which yielded 495 unique responses. Residents correctly classified 52.5% (260/495) of fractures without the algorithm, which significantly increased to 77.5% (384/495) (P = 0.001) with the algorithm. When stratified by year in residency, all residents were able to correctly classify markedly more fractures with the algorithm. DISCUSSION: Overall, we believe this method is a reproducible diagnostic tool that will assist residents in classifying acetabular fractures. We were able to demonstrate that with the use of this algorithm, residents' ability to correctly classify acetabular fractures is markedly enhanced, regardless of year in training. This algorithm will be a useful adjunct to assist and advance trainees' education and understanding of a complex topic.

Superior gluteal artery injury risk from third sacral segment transsacral screw insertion.

OBJECTIVES: Iliosacral (IS) and transsacral (TS) screws are commonly used to stabilize pelvic ring injuries. The course of the superior gluteal artery (SGA) can be close to implant insertion paths. The third sacral segment (S3) has been described as a viable osseous fixation pathway (OFP) but the proximity of the SGA to the S3 screw path is unknown. METHODS: Fifty uninjured patients with contrasted pelvic computed tomograms (CTA) were identified with an S3 path large enough for a 7.0 mm TS screw. Starting sites for S1 IS or TS, S2 and S3 TS screws were located on the volume rendered lateral CTA image and transferred onto the surface rendered 3D CTA with the SGA clearly visible. The distance from screw start sites to the SGA was measured. A distance less than 3.5 mm was considered likely for injury. RESULTS: The average distances from screw start sites to the SGA were 23.0 ± 7.9 mm for S1 IS screws, 14.3 ± 6.4 mm for S2 TS screws and 25.9 ± 6.5 mm for S3 TS screws. No S1 IS screws, 5 S2 TS screws (10%), and no S3 TS screws were projected to cause injury to the SGA. CONCLUSIONS: The osseous start site and soft tissue path for an S3 TS screw is remote from the SGA. The S1 IS and S3 TS pathways are further away from the SGA while the S2 TS pathway is closer and may theoretically pose a higher injury risk in patients with an available S3 OFP.