A slipped capital femoral epiphysis (SCFE) is classified as unstable if the patient has such severe pain that walking is not possible even with crutches, regardless of the duration of the symptoms.¹ Treatment of unstable SCFE is more difficult than that of stable SCFE because of the risk of damage to the blood supply to the capital femoral epiphysis and subsequent development of osteonecrosis of the femoral head. There are several controversies surrounding the best strategy for the management of an acute, severely displaced, and unstable SCFE.

The etiology of osteonecrosis of the femoral head: The blood supply to the femoral head is provided by the terminal branches of the medial femoral circumflex artery. To date, the pathogenesis of osteonecrosis in acute severely displaced SCFE remains unclear. Damage to the ascending branches of the medial femoral circumflex artery can occur at the time of the injury, although most authors believe that this is a rare event. However, there are reports of surgical observation of a completely torn periosteum flap containing the vessels to the femoral head.² Kinking of the vessels has been shown to cause blood flow disruption in preoperative angiographic imaging of unstable SCFE.³ Increased pressure from an intracapsular hematoma has also been reported as a factor in the increased risk for osteonecrosis, through a tamponade effect. One study reported that measured pressures from the hip joint with unstable SCFE were higher than those of the contralateral unaffected hip.⁴ Another study showed that the blood supply, assessed by an intracranial pressure probe, can be restored after capsular decompression.⁵ However, a systematic review of the literature did not find that capsular decompression was associated with decreased occurrence of osteonecrosis.⁶ It is possible that the blood supply to the femoral head in patients that develop an acute and unstable SCFE is more tenuous.

If these proposed factors are the cause of osteonecrosis in unstable SCFE, timing of treatment may play a role in the development of osteonecrosis. Theoretically, an acute to severely displaced unstable SCFE functions as an intracapsular femoral neck fracture. In the adult literature, surgical intervention for intracapsular femoral neck fractures has been recommended to be performed as early as possible because of the lower risk of developing osteonecrosis of the femoral head. However, in SCFE, the issue of timing as a factor in the development of osteonecrosis also remains a controversial topic.

Ideally, surgical treatment of an acute, severely displaced, and unstable SCFE would allow for stabilization of the epiphysis with improvement of the deformity in order to avoid future problems related to femoral acetabular impingement. Treatment options for an acute, severely displaced, and unstable SCFE include in situ fixation, closed reduction and percutaneous fixation, and open reduction with realignment.

In situ fixation without reduction or following an inadvertent reduction after positioning on the surgical table can be performed on a radiolucent table or a fracture table. Most authors favoring the use of a fracture table would argue that it allows for gentle positioning of the leg with the patella pointing upward to facilitate an inadvertent nonforced improvement of the epiphysis alignment. Unfortunately, treatment outcomes after in situ fixation for acute, severely displaced, and unstable SCFE are associated with high rates of osteonecrosis, varying from 3% to 60%.⁷

The number of screws used to fix the epiphysis in cases of unstable SCFE remains somewhat controversial. The placement of two cannulated screws instead of one single screw will add stability to the fixation and is our preferred method of fixation for an acute, severely displaced, and unstable SCFE. The technique for percutaneous fixation is similar to that described for stable SCFE, which has been discussed in the previous chapter.

Percutaneous fixation following closed reduction and capsular decompression has recently been gaining popularity given its universal application and relatively easy technique.⁵ In situ pinning has been the mainstay of SCFE treatment for decades, and our technique is described in Chapter 6. Briefly, the patient is positioned supine on a radiolucent table or on a fracture table. We prefer the radiolucent flat-top table, and we place a large gel roll under the patient’s ipsilateral scapula to facilitate neutral positioning of the lower extremity with the patella pointing upward. Closed reduction of the SCFE can be performed with longitudinal traction followed by flexion and internal rotation; however, it is our preference to simply position the leg in neutral rotation and fix the epiphysis in situ without forceful reduction. Once the epiphyseal alignment is confirmed by fluoroscopy, a guide wire is inserted in the anterolateral aspect of the proximal femur distal to the intertrochanteric line. The guide wire is gradually advanced toward the center of the epiphysis in the AP and lateral projection (Figure 7.2). To obtain a lateral image, we strongly recommend rotation of the C-arm about 45° to 60° and simply flex the hip, avoiding external rotation and abduction that could displace the epiphysis and bend the guide wire. The screw length is determined, and a drill is advanced just past the physis to avoid penetration of the wire into the joint (Figure 7.3). During drilling, it is important to clear the flutes of bone to avoid heat necrosis of the bone, which can cause osteonecrosis. The screw is then inserted, and an intracranial pressure (ICP; Integra Camino; Integra Life Sciences) probe is introduced through the screw to monitor for pressure changes in the femoral head (Figure 7.4). In the case of absent waveform, a percutaneous capsulotomy is performed by introducing either a pair of scissors or a Cobb in the lateral aspect of the hip capsule. The surgeon then slides the Cobb medially to open the capsule while the intracapsular hematoma is expected to drain out of the wound (Figure 7.5). After decompression of the intracapsular hematoma, the changes in pressure and to the femoral head can be captured by the ICP monitor that should show a waveform that corresponds to the patient’s heart rate.

In this particular case, the patient was discharged home the next day from surgery with instructions to be non-weight-bearing in the right lower extremity. He was seen 2 weeks following surgery when fixation of the epiphysis was confirmed to be adequate. However, about 4 weeks after surgery, he slipped and fell at home and presented to the emergency room with further displacement of the epiphysis and a broken screw (Figure 7.6). Given the presence of a bent/broken screw and further displacement of the epiphysis, we opted to address this complicated problem using a surgical hip dislocation and a subcapital realignment according to the modified Dunn technique. The bent screw was removed after the femoral neck was exposed following dissection of the retinacular flap (Figure 7.7). The femoral metaphysis was carefully exposed and the callus from the posterior aspect of the neck resected (Figure 7.8). The epiphysis was then reduced onto the metaphysis and fixed with two cannulated
screws (Figure 7.9). Following the modified Dunn procedure, the patient was on a non-weight-bearing protocol for 8 weeks, before resuming ambulation with crutches followed by unrestricted activities. His most recent radiographs at 1.5 years after the modified Dunn procedure showed a completely healed SCFE, and he was released to full activities (Figure 7.10).

Treatment of unstable SCFE using the modified Dunn procedure has potential advantages, including the complete decompression of the intracapsular hematoma and the realignment of the capital femoral epiphysis, while protecting the retinacular flap containing the blood supply to the femoral head. The first study from our center, in collaboration with the University of Berne in Switzerland,
showed promising results with a minimal rate of complications.⁸ However, recent series have reported an overall rate of 25% of osteonecrosis of the femoral head after the treatment of unstable SCFE with the modified Dunn in multiple centers across North America.⁹ Given our previous reported experience,⁸ we continue to favor the modified Dunn procedure for unstable SCFE if surgery is to be performed during the regular hospital hours when we can rely on the orthopedic nursing and scrub technician staff. The modified Dunn technique is performed using a surgical hip dislocation approach with dissection of the extended retinacular flap containing the nutrient vessels to the femoral head, as described by Professor Reynold Ganz.⁸,¹⁰,¹¹

For acute severely displaced unstable SCFE, the patient should be carefully positioned in the lateral decubitus, avoiding internal rotation of the hip, which theoretically puts the retinacular vessels under increased tension as it tries to reduce the slip. The operated leg rests on a flat pillow, and the entire lower extremity and the hemipelvis are draped free (Figure 7.12). A straight incision on top of the greater trochanter slightly anterior to the tip of the trochanter is performed (Figure 7.13). At least two-fifths of the incision should be proximal to the trochanter. The subcutaneous tissue is dissected, exposing the fascia lata and the fascia covering the abductor muscles (Figure 7.14). Opening of the fascia lata can be performed from distal to proximal and from proximal to distal. If performed from distal to proximal, the fascia is opened, and at the tip of the greater trochanter, the surgeon places the index finger under the fascia to feel the interval between the gluteus maximus and the tensor fascia lata muscle. The fascia is then opened in the anterior aspect of the gluteus maximus musculature following the Gibson interval. Historically, this procedure was described through the posterior Kocher-Langenbeck, but currently it is preferred to be performed through the Gibson interval to avoid damage to the gluteus maximus muscle belly. Another option is to perform the split of the fascia from proximal to distal. To do so, the anterior border of the gluteus maximus is identified through the fascia and is opened at that level. Proximally, the fascia and the muscle belly of the gluteus medius can be easily identified, and the interval between the gluteus maximus and the gluteus medius is developed, whereas the fascia lata is split distally in line with the incision.