Intraoperative Monitoring of Epiphyseal Perfusion in Slipped Capital Femoral Epiphysis

Schrader, Tim MD; Jones, Christopher R. MD; Kaufman, Adam M. MD; Herzog, Mackenzie M. MPH

Journal of Bone & Joint Surgery - American Volume:
doi: 10.2106/JBJS.15.01002
Scientific Articles
Abstract

Background: The purposes of this study were to validate an innovative, percutaneous method of monitoring femoral head (epiphyseal) perfusion intraoperatively in patients with slipped capital femoral epiphysis (SCFE) and to investigate an association between intraoperative perfusion and the subsequent development of osteonecrosis.

Methods: A percutaneous screw fixation technique for SCFE was utilized. A fully threaded, cannulated, stainless-steel 7.0-mm screw was inserted into the epiphysis. The guidewire was removed, and a sterile intracranial pressure (ICP) probe was placed through the screw such that the tip was in the epiphyseal bone past the end of the screw. Intraoperative epiphyseal pressure and waveform were recorded. A prospective analysis of patients undergoing percutaneous screw fixation for unstable or stable SCFE or for prophylactic treatment with the use of this technique to evaluate femoral head perfusion was performed.

Results: This technique was used in 23 patients (29 hips, including 15 hips with unstable SCFE, 11 with stable SCFE, and 3 treated prophylactically). Three hips (2 with unstable SCFE and 1 treated prophylactically) in 2 patients were eliminated from the analysis because of technical problems with the ICP monitor. All hips with stable SCFE and the prophylactically treated hips had measurable pulsatile flow that was synchronous with the patient’s heart rate at the initial time of probe insertion. Seven patients (7 hips) with unstable SCFE had measurable, pulsatile flow with initial insertion of the probe, and 6 patients (6 hips) with unstable SCFE had no measurable flow. We were able to demonstrate perfusion following a percutaneous capsular decompression in the patients with no initial flow. All patients left the operating room with measurable femoral head blood flow. At a mean follow-up of 1.6 years for hips with stable SCFE and 2.0 years for those with unstable SCFE, no hip subsequently developed radiographic evidence of osteonecrosis of the femoral head. No complications from the use of the ICP monitor occurred.

Conclusions: Femoral head perfusion in patients with SCFE can be measured intraoperatively using this technique. Demonstrating femoral head perfusion before leaving the operating room was associated with the absence of osteonecrosis postoperatively.

Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Author Information

1Children’s Orthopaedics of Atlanta, Atlanta, Georgia

2Orthopaedic Surgery, The Southeast Permanente Medical Group, Jonesboro, Georgia

3Department of Orthopaedic Trauma Services, Mission Hospital, Asheville, North Carolina

4Children’s Healthcare of Atlanta, Atlanta, Georgia

E-mail address for T. Schrader: tschrader@childrensortho.com

E-mail address for C.R. Jones: chrisjones200@gmail.com

E-mail address for A.M. Kaufman: Adam.Kaufman@msj.org

E-mail address for M.M. Herzog: Mackenzie.herzog@choa.org

Article Outline

Slipped capital femoral epiphysis (SCFE) is a common adolescent hip disorder, in which the capital femoral epiphysis is displaced posteroinferiorly relative to the metaphysis. Displacement can occur gradually with the epiphyseal vasculature adapting as the slip progresses or it can occur suddenly after a variable period of prodromal symptoms. SCFE was classified into 2 groups, stable and unstable, in a study by Loder et al.1. Patients with sudden and severe pain who cannot bear weight on the affected extremity, even with crutches, are classified as having unstable SCFE1.

Osteonecrosis of the femoral head is among the most dreaded complications of SCFE. The overall prevalence of osteonecrosis associated with SCFE is near 0% for hips with stable SCFE with appropriate treatment1-3 and has been reported to range from 0% to 60% for hips with unstable SCFE4-11. The association between unstable SCFE and osteonecrosis has led many surgeons to advocate for early treatment (<24 hours after presentation) for hips with unstable slips12-14 and to recommend against closed manipulation or reduction4,15.

It is hypothesized that disruption of the femoral head blood supply in unstable SCFE develops secondary to increased intracapsular pressure and/or kinking of the lateral epiphyseal vessels2. Herrera-Soto et al. demonstrated a considerable increase in intracapsular hip pressure in patients with acute presentation of unstable SCFE16. The pressures further increased with attempted manipulation and were found to significantly decrease following hip capsulotomy16. Any decrease in intracapsular pressure or realignment of the epiphyseal vessels may increase epiphyseal perfusion and ultimately prevent osteonecrosis. Unfortunately, there is currently no reliable way of directly measuring femoral head perfusion in the intraoperative setting.

The purposes of this study were to validate an innovative, percutaneous method of monitoring femoral head (epiphyseal) perfusion in patients with SCFE intraoperatively and to correlate intraoperative perfusion with the subsequent development of osteonecrosis. Our hypothesis was that hips with stable SCFE and prophylactically treated hips would demonstrate femoral head perfusion intraoperatively and that hips with unstable SCFE might or might not have femoral head perfusion.

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Materials and Methods

Patient Selection

Institutional review board approval was obtained. A prospective case series analysis of all patients with SCFE treated by the senior author (T.S.) from February 2011 to February 2014 was performed. Patients who had prior ipsilateral hip pathology or surgery were excluded. Thirty-seven patients were eligible for the study. Fourteen patients, all with stable SCFE, declined to enter the study. Twenty-three patients (29 hips) gave informed consent and were enrolled. Of those patients, 1 gave informed consent for the treatment of an unstable SCFE in 1 hip and then declined to enter the study when the contralateral hip was treated for a subsequent, stable SCFE. Three patients had bilateral SCFE (simultaneous presentation in 2 patients and sequential in 1 patient), and 3 patients had prophylactic treatment of the contralateral hip. Fifteen hips had unstable SCFE, 11 had stable SCFE, and 3 were treated prophylactically. Three hips (2 with unstable SCFE and 1 treated prophylactically) in 2 patients were eliminated from the analysis because of technical problems with the intracranial pressure (ICP) system. One of those patients had both hips excluded, and the other had 1 hip excluded and 1 hip included. The group analyzed included 11 girls (14 hips) and 11 boys (12 hips), with 13 unstable, 11 stable, and 2 prophylactically treated hips in the final analysis. Demographic, symptom, surgical, and outcome information are given in Table I.

SCFE was diagnosed by clinical and radiographic evaluation. Prospectively collected data included patient characteristics, symptom information, and surgical data. Patient characteristics included sex, date of birth, height, weight, body mass index (BMI), medications, and history of hip problems. Symptom information included involved side(s), duration of symptoms, date of SCFE diagnosis, stable versus unstable slip, ambulation status, preoperative slip angle, postoperative slip angle, severity of slip, and grade of slip. Patients were deemed to have an unstable injury if they were not able to bear weight, despite the use of assistive devices. Surgical data that were recorded included the date of surgery, stability of the physis, reduction technique, whether a joint decompression had been performed, and intraoperative monitoring signals from the pressure monitor.

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Surgical Technique

Preoperative imaging and clinical examination confirmed the diagnosis of SCFE (Fig. 1). Surgery was typically performed within 24 hours after presentation to our facility. Several patients with stable SCFE were diagnosed at outside facilities and were then referred to our facility. Patients with unstable SCFE were urgently taken to the operating room once they were medically stabilized.

Patients were placed supine on a radiolucent table. Fluoroscopic imaging was used to assess physeal stability in hips with stable SCFE and to assess whether a positional reduction had occurred in hips with unstable SCFE. If gross physeal instability was demonstrated in stable SCFE, the hip was treated as if it were unstable. If the acute displacement of an unstable SCFE had not reduced with positioning, then a closed manipulation with hip flexion, internal rotation, and traction was performed. The goal was to reduce the acute displacement of an unstable SCFE back to its chronic position. A 3.2-mm threaded guidewire was placed from the anterolateral aspect of the femoral neck across the proximal femoral physis into the epiphysis. Once the guidewire was across the physis, lateral images were made by either positioning the hip in a frog-leg lateral position or rotating the C-arm in order to confirm proper guidewire placement in the epiphysis. The guidewire was measured and overdrilled just past the level of the physis. A fully threaded, stainless-steel 7.0-mm cannulated screw (Smith & Nephew) was inserted past the physis into the epiphysis, stabilizing the physis in hips with unstable SCFE. Fluoroscopic imaging was used to monitor rotation and/or displacement of the epiphysis as the screw was advanced across the physis in hips with unstable SCFE. The guidewire was then removed, leaving the screwdriver engaged in the screw head. A sterile ICP probe (Integra Camino; Integra LifeSciences) (Fig. 2) was zeroed after it was connected to the monitor. The probe was placed percutaneously through the screwdriver shaft and screw (Fig. 3), such that the tip was in the epiphyseal bone past the tip of the screw. Appropriate probe placement was confirmed with fluoroscopy (Fig. 4). Intraoperative epiphyseal perfusion pressure and waveforms were recorded (Fig. 5). Waveforms with measurable, arterial-like pulsations synchronous with the heart rate of the patient were believed to represent femoral head perfusion. If no perfusion was noted on ICP monitoring, then a hip decompression was performed by aspiration with an 18-gauge needle or by advancing Mayo scissors or a Cobb elevator along the anterior aspect of the femoral neck through the same incision (Fig. 6). A decompressed hemarthrosis, dark hematoma mixed with synovial fluid and fat, was typically seen at the level of the skin (Fig. 7). Epiphyseal perfusion was reevaluated after the decompression (Fig. 8). If there was still no perfusion, the capsulotomy was repeated with a Cobb elevator. After confirmation of epiphyseal blood flow, the ICP probe was removed. The guidewire was replaced and the cannulated screw was advanced to its final seating depth (Fig. 9). All hips were treated with a single screw.

The use of the ICP probe in the present study was off label as the device had not been approved for this application by the U.S. Food and Drug Administration.

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Postoperative Management

Patients were typically discharged from the hospital after demonstrating partial weight-bearing with crutches. The use of crutches was continued for 6 weeks. Anteroposterior and frog-leg lateral pelvic radiographs were made at every clinic visit (Fig. 10). In cases of unstable SCFE, magnetic resonance imaging (MRI) or bone scan evaluation for osteonecrosis was recommended during the first 6 weeks postoperatively. Radiographs were monitored for sclerosis and/or collapse to signify the development of osteonecrosis.

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Statistical Analysis

Descriptive statistics were calculated for all variables. Differences in variables between the stable and the unstable group and between the group with intraoperative femoral head blood flow and the group with no flow were evaluated. Dichotomous variables were assessed using the Fisher exact test, and continuous variables were assessed using the Wilcoxon rank-sum test. All statistics were analyzed at the 95% significance level.

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Results

There were 13 stable hips (including 2 prophylactically treated) and 13 unstable hips. No significant difference was detected between the stable and unstable groups in terms of sex, affected side, age, height, weight, BMI, or symptom duration (Table II). There was a significant difference between the stable and unstable groups with respect to time from diagnosis to surgery (6.5 versus 1.0 days, respectively; p = 0.01), preoperative slip angle (26.8° versus 53.4°, respectively; p < 0.01), and slip angle change from preoperative to postoperative (4.3° versus 23.4°, respectively; p < 0.01) (Table II). No significant difference between the stable and unstable groups was found with respect to the mean postoperative slip angle (Table II).

Waveforms recorded intraoperatively were similar to arterial tracings with a pulse pressure and were synchronous with the patient’s heart rate. All stable SCFE hips and the prophylactically treated hips had measurable, pulsatile flow with initial insertion of the ICP probe, as did 7 unstable SCFE hips. Six hips with unstable SCFE had no measurable flow. Pressure values at initial placement for hips with stable SCFE, unstable SCFE with flow, and unstable SCFE with no flow are listed in Table III. The 6 hips with no flow had a percutaneous capsular decompression performed. One of them had a needle aspiration, 1 had a decompression with Mayo scissors, and 4 hips had a decompression with a Cobb elevator. After the decompression, measurable, synchronous, pulsatile flow was demonstrated in 4 additional hips. The capsulotomy was repeated with a Cobb elevator in the remaining 2 hips with no flow (both initially decompressed with a Cobb elevator) after which pulsatile, synchronous flow was obtained. After adequate capsular decompression in the hips with unstable SCFE that had had no initial flow, the systolic pressures averaged 41.0 mm Hg (range, 35 to 52 mm Hg), diastolic pressures averaged 33.3 mm Hg (range, 28 to 43 mm Hg), mean arterial pressures averaged 37.0 mm Hg (range, 32 to 47 mm Hg), and pulse pressures averaged 7.7 mm Hg (range, 6 to 8 mm Hg). When the patients left the operating room, all hips had measurable femoral head flow.

Demographic and symptom information for patients with unstable SCFE who had initial flow compared with those with no initial flow are listed in Table IV. There was no significant difference between the unstable group with no initial flow and the unstable group with initial flow in terms of sex, affected side, age, height, weight, BMI, symptom duration, time from diagnosis to surgery, preoperative slip angle, or postoperative slip angle; however, the difference with regard to the slip angle change approached significance (Table IV).

Twenty-four hips had a mean follow-up of 1.9 years (range, 0.7 to 4.2 years). Two patients (2 stable hips) were lost to follow-up. The mean time to the most recent follow-up visit for the stable SCFE group was 1.6 years (range, 0.7 to 2.5 years), and the mean time to the most recent follow-up evaluation for the unstable SCFE group was 2.0 years (range, 0.9 to 4.2 years). At the most recent follow-up, no patient had subsequently developed radiographic evidence of femoral head osteonecrosis. Five patients (7 hips, including 6 with unstable SCFE and 1 prophylactically treated) had bone scans within 6 weeks of surgery. Four of these hips had no perfusion with initial probe placement. All bone scans demonstrated perfusion of the epiphysis. One patient had an MRI scan at 6 weeks after surgery. She had an unstable SCFE with flow on initial probe placement, and the study also demonstrated perfusion of the epiphysis.

No complications from the use of the ICP monitor were noted. There were no wound complications, deep venous thromboses, or deep infections. One patient with an unstable SCFE had progression of the epiphyseal slip after initial treatment. He was treated with removal of the screw, repeat closed reduction, and hardware revision utilizing 2 screws. Pulsatile flow was demonstrated with a probe at the time of revision before and after closed reduction. Only his initial surgery is included in the data analysis. The physis closed without further progression of the deformity, and he had not developed osteonecrosis during a follow-up period of 11 months.

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Discussion

Femoral head perfusion in patients with SCFE has been assessed preoperatively using MRI, bone scanning, and angiography2,3,17; however, the positive predictive value of preoperative perfusion for the absence of osteonecrosis postoperatively is not 100%. Measuring blood flow and pressure at the level of the femoral epiphysis intraoperatively provides a more accurate representation of the actual perfusion that the femoral head experiences and might guide further operative measures to help avoid osteonecrosis.

Laser Doppler flowmetry (LDF) is a technique for measuring blood flow within the femoral head in an environment of changing intracapsular pressure18-20. The technique involves drilling a hole into the femoral head to the level of the subchondral bone and placing a laser probe18. Using a high-power Doppler source and a standard flowmeter, real-time analysis of femoral head blood flow is performed. Pulsatile signals are then converted to flux units (a product of the concentration and velocity of erythrocytes within a defined volume under the probe21). LDF has primarily been used in adults during surgical dislocation procedures. The Camino ICP system works by reading the change in the refraction of light between 4 fibers within the probe. The refraction of light is changed when a diaphragm on the tip is depressed by the surrounding tissue. The two techniques are similar in that both provide qualitative and semiquantitative analysis of flow to the femoral head. However, our ICP probe technique directly measures pressure at the femoral head, which is recorded as a pulsatile pattern when flow is present. Additionally, our technique is less invasive in that our probe is able to fit directly down the shaft of a cannulated screw without drilling an “additional” or unnecessary hole into the bone. Lastly, the ICP system is likely more readily available and does not require additional personnel.

Intraoperative factors such as intracapsular pressure and positional changes clearly have a role in the development of osteonecrosis. This study provides a percutaneous, intraoperative method for directly monitoring blood flow within the femoral head in hips with SCFE. In our study using this method of monitoring intraosseous pressure during SCFE stabilization, no patient had developed osteonecrosis at a mean follow-up of 1.9 years.

Herrera-Soto et al. demonstrated that hips with an unstable SCFE had intracapsular hip pressures that were increased to a level consistent with an intra-articular compartment syndrome16. A hip capsulotomy, which can significantly decrease intracapsular pressure, can be performed16; however, the extent of capsular decompression is difficult to quantify, frequently is not reported in the literature, and can be performed with many different instruments using either an open or percutaneous technique. The current technique allows the surgeon to better assess the adequacy of any type of capsular decompression on the basis of intraoperative monitoring information.

When this protocol was used, perfusion was noted with insertion of the probe in all hips with a stable SCFE and in the prophylactically treated hips. This correlates well with the nearly 0% prevalence of osteonecrosis in stable slips in the literature1-3. Six of 13 hips with an unstable SCFE that had no initial perfusion using the ICP probe were identified intraoperatively, and capsular decompression was performed. All but 2 patients had perfusion restored. These 2 hips might otherwise have developed osteonecrosis secondary to inadequate capsular decompression, yielding a potential osteonecrosis rate of 15.4%. This potential rate compares well with the 16.2% rate of osteonecrosis found in a recent meta-analysis of unstable SCFE22. We believe that demonstrating femoral head perfusion before and after a capsular decompression is paramount in the prevention of osteonecrosis.

The present study shows that the acute displacement of an unstable SCFE can safely be reduced back to the previous stable position, as long as an adequate capsular decompression is performed. This technique may not fully restore the anatomy of the proximal portion of the femur to an anatomic position as only the acute displacement of an unstable SCFE is reduced. Consequently, such patients may benefit from evaluation and correction at specialized centers with surgeons trained in complex hip reconstruction techniques. However, this technique allows an unstable SCFE to be reduced and stabilized at most centers with the knowledge that the femoral head is perfused, giving the patient and surgeon time to determine the most appropriate next steps.

Our current protocol utilizes this probe and technique in all patients with an unstable SCFE and in patients with a stable SCFE with intraoperative physeal instability. The ICP monitoring device is widely available in hospitals. It does not require advanced training in complex hip reconstruction techniques. The insertion and utilization of the probe add approximately 5 minutes to the operative time. The probe tip is French size 4 (1.35 mm) in diameter for approximately 60 mm. After 60 mm, the tubing diameter increases to 3 mm. It is therefore recommended that the probe be placed down the screwdriver shaft and screw to ensure that it is compatible with each individual cannulated screw system. The cost of the disposable devices at our institution is roughly $650. There is potential for cost savings when utilizing intraoperative monitoring in patients with an unstable SCFE, since preoperative advanced imaging may be avoided, although that analysis is outside the scope of this study. There are also other pressure monitoring systems that may be utilized. Further investigation into the reliability and effectiveness of different systems is needed.

This technique of percutaneous, intraosseous pressure monitoring has potential application beyond SCFE. Our technique is particularly applicable to the orthopaedic trauma setting when cannulated screw fixation might be indicated for a particular fracture pattern. Examples of such fracture sites include the talar neck, femoral neck, proximal part of the humerus, and scaphoid waist. If the pressure monitoring system indicates poor flow, the surgeon is able to tailor the operative plan appropriately.

This study is not without limitations. Long-term follow-up was not available for patients. While the majority of patients had >1 year of follow-up, 2 patients had <1 year of follow-up and 2 patients were lost to follow-up. Three of 4 patients with limited or no follow-up had a stable SCFE with femoral head perfusion at the time of initial probe insertion. Consequently, we think that the risk of osteonecrosis is very low for these patients. The fourth patient had an unstable SCFE and underwent closed reduction, after which femoral head perfusion was demonstrated on initial probe placement. Slip progression was noted during follow-up, and he underwent revision 3 weeks after the initial surgery. He had femoral head perfusion before and at the conclusion of the revision procedure. At 11 months of follow-up, there was no radiographic evidence of osteonecrosis. Loder stated that “all AVN [avascular necrosis] from the unstable SCFE is very quick, and there have been no cases described occurring later than 12 months from the initial unstable SCFE.”23 Therefore, we included these patients in our analysis. Another limitation is that we relied on plain radiographs to evaluate for osteonecrosis. MRI might have improved the accuracy in this setting; however, plain radiography is the literature standard. Also, we did not evaluate the clinical outcome of these patients with functional questionnaires. Further study is needed to validate the utility of this technique to avoid long-term complications in hips with SCFE.

There are also technical limitations with the use of the ICP probe. The probe did not provide any signal in 3 hips, resulting in exclusion from the analysis. In 1 patient with 1 unstable and 1 prophylactically treated hip, a prong in the mechanical connection between the monitor and the probe bent while being connected and another monitor was not immediately available. Both hips were excluded. This patient had 2.4 years of follow-up without the development of osteonecrosis. The other patient had bilateral SCFE but was symptomatic only on one side. She was unable to bear weight so both hips were classified as unstable, even though one was asymptomatic. The probe used for the asymptomatic, unstable side did not provide any data. A second probe was used for the symptomatic, unstable side, and that hip was included in the data analysis. The patient had 1.5 years of follow-up without the development of osteonecrosis.

We present a procedurally simple and readily accessible percutaneous technique to provide real-time, intraoperative monitoring of femoral head perfusion in hips with SCFE. Using data from the ICP probe, we were able to achieve quantitative femoral head perfusion in a series of 26 hips, including 13 with unstable SCFE, and avoided osteonecrosis in all hips. This method represents a vast improvement over prior methods of predicting or monitoring femoral head blood flow and may accurately guide intraoperative decision-making for patients with SCFE.

Investigation performed at Children’s Healthcare of Atlanta at Scottish Rite, Atlanta, and Children’s Orthopaedics of Atlanta, Atlanta, Georgia

Disclosure: Funding for this project came from a Friends Research Grant of Children’s Healthcare of Atlanta. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a patent and/or copyright, planned, pending, or issued, broadly relevant to this work.

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