Derotational Femoral Osteotomy for Femoral Torsion Abnormalities

Abstract

Hip joint preservation is influenced by 3 primary factors: femoroacetabular impingement, hip dysplasia or instability, and femoral torsion abnormalities. When femoral torsion abnormalities are ignored, patients may not achieve optimal clinical outcomes. A derotational femoral osteotomy is a critical procedure for correcting these torsional abnormalities. The purpose of this article is to provide a standardized and reproducible technique for derotational femoral osteotomy to address excessive femoral antetorsion or retrotorsion in patients experiencing intra-articular hip pain.

When evaluating patients with intra-articular hip pain, it is crucial to consider the 3 primary factors involved with preservation of the hip joint: femoroacetabular impingement (FAI), hip dysplasia/instability, and femoral torsion abnormalities.^1,2 Femoral torsion abnormalities can coexist with FAI or dysplasia, potentially reducing the success of hip arthroscopy and/or periacetabular osteotomy without correction of femoral torsion.³ While excessive femoral antetorsion decreases acetabular coverage, thereby increasing the risk for hip instability, femoral retrotorsion improves coverage but increases the risk of impingement and reduces hip range of motion (notably internal rotation).² Both abnormalities can contribute to labral or cartilage damage, leading to early osteoarthritis or failed hip arthroscopy.³ This article presents a reliable derotational femoral osteotomy (DFO) technique designed to effectively correct femoral torsion abnormalities.

Surgical Technique

Preoperatively, hip preservation candidates undergo axial computed tomography from the pelvis through the knee joints. Femoral torsion is measured based on the Murphy method⁴ (Fig 1). In general, we recommend a DFO in patients with femoral torsion >40° or <0°. However, it is important to consider the inter-relationships between femoral torsion, FAI, and dysplasia. For example, we would also recommend a DFO in a patient with hip dysplasia, hip internal rotation (at 90° of hip flexion) of 50°, and femoral torsion of 35°, as a periacetabular osteotomy alone would not sufficiently stabilize this patient's hip joint.

Fig 1.

Axial computed tomography scan showing measurement of femoral torsion per the Murphy method⁴ in a patient with bilateral excessive femoral antetorsion (right: 46.2°, left: 41.6°).

The patient is placed supine on a postless table typically used for hip arthroscopy (Pivot Guardian, Stryker) with the greater trochanter (GT) partially off the table (Video 1). Internal rotation (IR) at 90° of hip flexion is checked once the patient is under anesthesia. Both feet are secured in well-padded boots. For a retro-torsing DFO, the ipsilateral foot is internally rotated 15° to 25°. For an ante-torsing DFO, the ipsilateral foot is placed in neutral. The contralateral leg is abducted 35° to 45° (depending on the patient's range of motion) in order to allow one of the C-arms (for lateral fluoroscopy) to come in between the legs. An additional C-arm (for anteroposterior [AP] fluoroscopy) is brought in from the contralateral side. Before the patient is prepped and draped, AP and lateral images are obtained to ensure the GT can be adequately imaged in both planes.

The patient is prepped, and an Ioban isolation drape (3M) is placed on the patient to cover the surgical field from the iliac crest to the proximal tibia. An incision is made through the skin and iliotibial band slightly posterior to and approximately 4 fingerbreadths proximal to the tip of the GT. A guidewire (Smith & Nephew) is placed through the incision onto the tip of the GT. AP and lateral images are obtained to ensure the guidewire is appropriately positioned in both planes. On AP fluoroscopy, the guidewire should be aiming straight down toward the lateral side of the intramedullary canal. On lateral fluoroscopy, the guidewire should be aiming straight down the femur (Fig 2). Once confirmed, the guidewire is drilled to the level of the lesser trochanter (LT). AP and lateral fluoroscopy images are obtained to ensure the appropriate position of the guidewire. A tissue protector and opening reamer (12.5 mm) are used to ream over the guidewire to the level of the LT. The reamer and guidewire are then removed, and a ball-tip guidewire is introduced into the canal to a level just proximal to the knee joint (confirmed on AP fluoroscopy) (Fig 3). A ruler is inserted over the guidewire and onto the tip of the GT. If the length of the ball-tip guidewire is between 2 nail sizes, the shorter nail should be selected.

Fig 2.

Anteroposterior (A) and lateral (B) fluoroscopy images of the starting guidewire in an appropriate position during a derotational femoral osteotomy performed in a right hip in the supine position.

Fig 3.

Anteroposterior fluoroscopy image of a right femur showing the ball-tip guidewire (black arrow) advanced to a level just proximal to the knee joint.

Next, a spinal needle is inserted perpendicular to the skin at the location of the planned osteotomy site. This should be just proximal to the isthmus and is confirmed with AP fluoroscopy (Fig 4A). A small longitudinal incision is made at this location and dilated with a clamp. A 2.5-mm-long drill bit is used to drill holes circumferentially at the osteotomy site. AP fluoroscopy is used before the surgeon drills each hole to ensure that the drill bit is entering at the same level each time (Fig 4B). The surgeon should drill as many circumferential holes as possible to make it easier to complete the osteotomy when appropriate.

Fig 4.

Anteroposterior fluoroscopy image of a right femur showing a spinal needle (red arrow) localizing the appropriate position of the osteotomy just proximal to the isthmus (A) and a 2.5-mm drill bit (black arrow) entering at the same level as previously drilled holes for the osteotomy (B).

The tissue protector is inserted over the ball-tip guidewire onto the tip of the GT, and the canal is sequentially reamed, beginning with a 9-mm reamer. The entire length of the ball-tip guidewire should be reamed. Once there is an appropriate amount of “chatter,” the diameter of the nail should be selected as 1.5 cm below the final reamer size. A 14-mm reamer is then used to ream just through the tip of the GT.

An intramedullary nail (Trigen Meta-Tan; Smith & Nephew) with length and diameter selected above is introduced over the guidewire and stopped proximal to the osteotomy site.

A spinal needle is inserted perpendicular to the skin at the distal end of the GT (confirmed with AP fluoroscopy). A perfect lateral fluoroscopy image should be obtained showing the spinal needle entering the posterior side of the GT below the nail. Once confirmed, a small incision is made at the location of the spinal needle and dilated with a clamp. A 6-mm Schanz pin is introduced at the same angle at which the spinal needle was entering the patient. The Schanz pin is drilled in a few millimeters, and AP/lateral images are obtained to confirm the appropriate position. Once confirmed, the Schanz pin is advanced just until it breaks the medial femoral cortex (Fig 5).

Fig 5.

Anteroposterior (A) and lateral (B) fluoroscopy images of a right femur showing the proximal Schanz pin entering at the distal end of the greater trochanter and posterior to the intramedullary (IM) nail.

Next, a spinal needle is inserted perpendicular to the skin at the site where the distal Schanz pin will be introduced. This should be distal to the osteotomy site but proximal to where the distal interlocking screw holes will be. Once confirmed with AP fluoroscopy, a small incision is made and dilated with a clamp. Another 6-mm Schanz pin is introduced at the same anterior-posterior angle as the proximal Schanz pin and advanced into the medial cortex.

The ball-tip guidewire is pulled back to a level just proximal to the osteotomy site. A quarter-inch osteotome is introduced through the osteotomy incision and is carefully malleted circumferentially at the same level as the drill holes (confirmed on AP fluoroscopy). It is important not to mallet the osteotome too deeply into the canal during this step as the osteotome can become stuck. Meanwhile, an assistant should hold the ball-tip guidewire and be prepared to quickly advance the guidewire past the osteotomy site as soon as the osteotomy is completed. Once the osteotomy is completed, the ball-tip guidewire is advanced to the distal femur, and AP/lateral images are obtained to ensure the guidewire is in the intramedullary canal.

An unscrubbed assistant uses fine traction to slightly distract the osteotomy. The same assistant then rotates the foot (internally for an ante-torsing DFO or externally for a retro-torsing DFO). A goniometer (Innomed) is used to measure the angle between the 2 Schanz pins, with a general goal of correcting to 20° of femoral antetorsion (Fig 6). If the angle between the pins is not appropriate, the foot can be rotated again and the angle remeasured. Once the appropriate angle is achieved, the surgeon can begin malleting the nail past the osteotomy site. Once the nail is past the osteotomy site, the angle between Schanz pins should be remeasured, and if necessary, the foot can be rotated again to achieve a more optimal angle.

Fig 6.

Use of a large goniometer (yellow star; Innomed) to measure the angle between proximal and distal Schanz pins following rotational correction in a right hip.

If the patient does not have a limb-length discrepancy, fine traction can be removed once the nail is a few centimeters past the osteotomy site. If the affected extremity is shorter preoperatively, fine traction can be maintained to add length.

Once the nail is close to the distal Schanz pin, the angle between pins should be measured once more. If an appropriate angle is maintained, both Schanz pins are removed, and the nail is further advanced until the proximal tip of the nail is at the level of the tip of the GT. A proximal interlocking screw is placed. A perfect circle technique is used to drill for 2 distal interlocking screws. At this point, the drill bits should be left in place for these distal interlocking screws, and the guide on the proximal nail should be removed.

The surgeon unscrubs, takes the boot off the traction device, and, while under the drapes to maintain sterility, checks hip IR at 90° of hip flexion (Fig 7). Depending on whether or not the patient is also undergoing a periacetabular osteotomy, IR should be in the range of 10° to 30°. If appropriate, the boot is placed back into the traction device, the surgeon rescrubs, and 2 distal interlocking screws are placed.

Fig 7.

The head surgeon has scrubbed out and, while under the drapes, has taken the operative extremity out of the traction device to check hip internal rotation at 90° of hip flexion to ensure that the correction performed is appropriate. Performed on a right hip.

Discussion

The major factors of hip joint preservation include FAI, hip dysplasia/instability, and femoral torsion abnormalities.¹ While it is possible for each factor to cause intra-articular hip pain on its own, it is vital for hip preservation surgeons to consider potential interactions between hip pathologies. Prearthritic hip pain is often multifactorial, and unless each factor is considered and treated as necessary, patients may not achieve optimal outcomes. Our step-by-step guide provides a reproducible method for performing a DFO to correct femoral torsion abnormalities. The advantages and disadvantages of our technique can be found in Table 1, and the pearls and pitfalls are presented in Table 2.

Table 1.

Technique Advantages and Disadvantages

Advantages	Disadvantages
•Surgical technique is reproducible •Can correct excessive femoral antetorsion or retrotorsion •Weightbearing as tolerated immediately postoperatively •Smaller incisions than DFO with plate and screws	•Requires 2 C-arms for most efficiency •Interlocking screws may cause irritation (treated with screw removal)

DFO, derotational femoral osteotomy.

Table 2.

Technique Pearls and Pitfalls

Pearls	Pitfalls
•Circumferential drilling at osteotomy site helps create a controlled fracture and prevents propagation. •Make sure Schanz pins are bicortical and stable to prevent errors in correction measurement. •Have an unscrubbed assistant stand by the patient's feet and provide feedback on goniometer accuracy when measuring the angle between Schanz pins.	•Improper starting guidewire position can make it difficult to advance ball-tip guidewire. •Fracture can displace/shorten if the guidewire is not immediately advanced into the distal femoral segment following completion of the osteotomy.

Several articles5, 6, 7, 8, 9 have examined surgical outcomes for patients with femoral torsion abnormalities who underwent hip arthroscopy without correcting femoral torsion. Sinkler et al.⁵ noted an association with poorer functional outcomes and a higher likelihood of requiring additional procedures in the future for patients with both hip dysplasia and either severe femoral retrotorsion or antetorsion. Marland et al.⁶ found that patients treated for borderline acetabular dysplasia with uncorrected femoral antetorsion had significantly worsened pain scores and were less likely to achieve an improved hip after hip arthroscopy. Hatem et al.⁷ found that proximal DFO enhances not only hip but also spine function in individuals with abnormal femoral torsion. These studies highlight the importance of addressing femoral torsion abnormalities concomitantly during hip preservation surgery.

Addressing femoral torsion abnormalities is critical to optimizing surgical outcomes in patients with intra-articular hip pain. Despite the recognized benefits of DFO in correcting these abnormalities, few articles provide a technique for performing DFO in adult patients. This article provides a reproducible step-by-step technique guide to correcting excessive femoral antetorsion or retrotorsion in patients with prearthritic hip pain.

Disclosures

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: M.J.K. is a consultant or advisor for Smith & Nephew and is a member of the Editorial Board for Arthroscopy. All other authors (A.D.P., K.P.M., B.D.M., K.L.C.) declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplementary Data

Video 1

Step-by-step technique for derotational femoral osteotomy (DFO). DFO is performed in a right hip in the supine position on a distraction table.