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.
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.
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.
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.
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.
1. Loder RT, Richards BS, Shapiro PS, Reznick LR, Aronson DD. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg Am. 1993 ;75(8):1134–40.
2. Maeda S, Kita A, Funayama K, Kokubun S. Vascular supply to slipped capital femoral epiphysis. J Pediatr Orthop. 2001 ;21(5):664–7.
3. Edouard C, Raphaël V, Hubert Dle P. Is the femoral head dead or alive before surgery of slipped capital femoral epiphysis? Interest of perfusion magnetic resonance imaging. J Clin Orthop Trauma. 2014 ;5(1):18–26. Epub 2014 Mar 31.
4. Tokmakova KP, Stanton RP, Mason DE. Factors influencing the development of osteonecrosis in patients treated for slipped capital femoral epiphysis. J Bone Joint Surg Am. 2003 ;85(5):798–801.
5. Kennedy JG, Hresko MT, Kasser JR, Shrock KB, Zurakowski D, Waters PM, Millis MB. Osteonecrosis of the femoral head associated with slipped capital femoral epiphysis. J Pediatr Orthop. 2001 ;21(2):189–93.
6. Fallath S, Letts M. Slipped capital femoral epiphysis: an analysis of treatment outcome according to physeal stability. Can J Surg. 2004 ;47(4):284–9.
7. Sankar WN, McPartland TG, Millis MB, Kim YJ. The unstable slipped capital femoral epiphysis: risk factors for osteonecrosis. J Pediatr Orthop. 2010 ;30(6):544–8.
8. Parsch K, Weller S, Parsch D. Open reduction and smooth Kirschner wire fixation for unstable slipped capital femoral epiphysis. J Pediatr Orthop. 2009 ;29(1):1–8.
9. Chen RC, Schoenecker PL, Dobbs MB, Luhmann SJ, Szymanski DA, Gordon JE. Urgent reduction, fixation, and arthrotomy for unstable slipped capital femoral epiphysis. J Pediatr Orthop. 2009 ;29(7):687–94.
10. Zaltz I, Baca G, Clohisy JC. Unstable SCFE: review of treatment modalities and prevalence of osteonecrosis. Clin Orthop Relat Res. 2013 ;471(7):2192–8.
11. Ziebarth K, Zilkens C, Spencer S, Leunig M, Ganz R, Kim YJ. Capital realignment for moderate and severe SCFE using a modified Dunn procedure. Clin Orthop Relat Res. 2009 ;467(3):704–16. Epub 2009 Jan 14.
12. Kalogrianitis S, Tan CK, Kemp GJ, Bass A, Bruce C. Does unstable slipped capital femoral epiphysis require urgent stabilization? J Pediatr Orthop B. 2007 ;16(1):6–9.
13. Gordon JE, Abrahams MS, Dobbs MB, Luhmann SJ, Schoenecker PL. Early reduction, arthrotomy, and cannulated screw fixation in unstable slipped capital femoral epiphysis treatment. J Pediatr Orthop. 2002 ;22(3):352–8.
14. Peterson MD, Weiner DS, Green NE, Terry CL. Acute slipped capital femoral epiphysis: the value and safety of urgent manipulative reduction. J Pediatr Orthop. 1997 ;17(5):648–54.
15. Casey BH, Hamilton HW, Bobechko WP. Reduction of acutely slipped upper femoral epiphysis. J Bone Joint Surg Br. 1972 ;54(4):607–14.
16. Herrera-Soto JA, Duffy MF, Birnbaum MA, Vander Have KL. Increased intracapsular pressures after unstable slipped capital femoral epiphysis. J Pediatr Orthop. 2008 ;28(7):723–8.
17. Rhoad RC, Davidson RS, Heyman S, Dormans JP, Drummond DS. Pretreatment bone scan in SCFE: a predictor of ischemia and avascular necrosis. J Pediatr Orthop. 1999 ;19(2):164–8.
18. Beck M, Siebenrock KA, Affolter B, Nötzli H, Parvizi J, Ganz R. Increased intraarticular pressure reduces blood flow to the femoral head. Clin Orthop Relat Res. 2004 ;(424):149–52.
19. Swiontkowski M, Tepic S, Ganz R, Perren SM. Laser Doppler flowmetry for measurement of femoral head blood flow. Experimental investigation and clinical application. Helv Chir Acta. 1986 ;53(1-2):55–9.
20. Swiontkowski MF, Tepic S, Perren SM, Moor R, Ganz R, Rahn BA. Laser Doppler flowmetry for bone blood flow measurement: correlation with microsphere estimates and evaluation of the effect of intracapsular pressure on femoral head blood flow. J Orthop Res. 1986;4(3):362–71.
21. Nötzli HP, Swiontkowski MF, Thaxter ST, Carpenter GK 3rd, Wyatt R. Laser Doppler flowmetry for bone blood flow measurements: helium-neon laser light attenuation and depth of perfusion assessment. J Orthop Res. 1989;7(3):413–24.
22. Ibrahim T, Mahmoud S, Riaz M, Hegazy A, Little DG. Hip decompression of unstable slipped capital femoral epiphysis: a systematic review and meta-analysis. J Child Orthop. 2015 ;9(2):113–20. Epub 2015 Mar 17.
Copyright 2016 by The Journal of Bone and Joint Surgery, Incorporated
23. Loder RT. What is the cause of avascular necrosis in unstable slipped capital femoral epiphysis and what can be done to lower the rate? J Pediatr Orthop. 2013 ;33(Suppl 1):S88–91.