35-year-old man with occult lower extremity rotational deformity

Issue: January 2020

ByNicholas A. Trasolini, MD

ByMary Kate Erdman, MD

ByAdam K. Lee, MD

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A 35-year-old man presented to our institution 6 weeks after a motorcycle collision. During this accident, he sustained a right femoral shaft fracture that was managed with closed reduction and retrograde medullary fixation at another institution.

During the index procedure, the fracture was noted to be comminuted making anatomic reduction challenging. Rotational reduction was assessed by comparing rotational profiles of the operative extremity to the contralateral leg. More specifically, a true lateral fluoroscopic image of the uninjured leg was taken, followed by a 90° anteroposterior (AP) view of the hip. These images were compared to the operative extremity and rotation of the fracture was adjusted to match the fluoroscopic profile of the contralateral images.

At our initial evaluation, radiographs indicated the hardware was intact and the patient was pain free in the femur (Figure 1). However, he complained of stark differences in the rotation of his extremities that altered his gait and caused a cosmetic disturbance. He reported he had been participating in physical therapy, but his rotational asymmetry prevented his gait from improving. On initial exam, he was noted to have significant differences in foot progression angles during gait, with the right lower extremity demonstrating excessive external rotation of 25°. On examination of the hips, range of motion was not significantly different. There was less than 10° of internal rotation difference compared with the uninjured extremity and similar external rotation.

What is your next step in workup of this patient?

Thigh-foot-angle measurements, CT rotational profiles

Further physical examination demonstrated side-to-side differences in thigh-foot angles. On the left side, the thigh-foot angle was 10°; on the right side it was 35°. CT rotational profiles were ordered to compare side-to-side rotation between the distal femoral epicondylar axis and the femoral neck version (Figure 2). Rotational profiles demonstrated 26° of anteversion of the right femur compared with 21° of version for the left femur. This 5° side-to-side difference was not consistent with the marked malrotation noted during gait and standing.

Additional CT rotational profiles were performed for the tibias to compare the posterior condylar axis to the bimalleolar axis. The external tibial torsion of the right lower extremity was 53° compared with 34° on the left (Figure 3).

What is your diagnosis?

See answer on the next page.

External tibial torsion

This patient had asymmetrical tibial torsion that was offset by asymmetrical femoral version. When his femoral shaft fracture was treated, the rotation was matched to the contralateral within 5°. This revealed his tibial extorsion, resulting in a postoperative cosmetic and functional deficit.

Treatment

At the time of completed workup, the femoral shaft fracture had united. After discussion with the patient, a decision was made to proceed with correcting side-to-side differences in tibial torsion instead of restoring his preoperative asymmetrical femoral version. The patient underwent a tibial and fibular internal rotation osteotomy with medullary fixation and reamed autograft. Postoperative thigh-foot angles were 10° external bilaterally. The patient was made immediately weight-bearing as tolerated and had cosmetic improvement and improved foot progression angles during gait.

Discussion

Femoral shaft fractures are prone to malrotation during reduction and fixation. The incidence of malrotation, defined as greater than 15°, has been reported in unilateral injuries and bilateral injuries at 37% and 41%, respectively. The osteology of the femur contributes to this clinical challenge. The diaphysis is not only cylindrical but also lacks prominent landmarks that can be identified fluoroscopically. Additionally, there are notable variations in femoral version in the population and side-to-side differences of as much as 11°.

Malrotation can lead to clinically relevant alterations in gait and knee mechanics. External malrotation is particularly troublesome for patients as this deformity shifts the mechanical axis posteriorly and has been associated with decreased functional outcomes, increased forces across the patellofemoral joint and a subsequent risk of osteoarthritis.

Detection of malrotation can be challenging in the clinical setting. On physical exam, inspection of limb alignment alone frequently yields a missed diagnosis. When rotation is assessed in the supine position, malrotation can be missed in up to 42% of cases and 25% of cases are missed when patients are assessed in the prone position. More accurate detection and quantification of malrotation is accomplished by a CT scan. This exam can be isolated to bilateral hips and bilateral knees, bypassing the diaphyseal region of the femur to prevent unnecessary radiation. Two angles measured on the axial view are compared in the same extremity: one angle is subtended by a line tangent to the posterior border of the femoral condyles and the horizontal axis (condylar angle) and the other angle is subtended by a line along the long axis of the femoral neck and the horizontal axis (cervical angle). The difference between the condylar and cervical angles can be compared side to side to measure the respective version of each femur. It is less common to include tibial rotational profiles, but it should be considered in cases where side-to-side differences in thigh-foot angles are noted on physical exam.

Risk factors for malrotation include both injury and surgical characteristics. Fracture patterns that are comminuted, segmental, transverse or associated with bone loss make accurate rotational reduction challenging. Bilateral fractures create a clinical dilemma because most methods to restore femoral version rely on templating from the contralateral. Medullary nailing — the gold standard in treatment of diaphyseal femur fractures — often involves indirect reduction. This technique preserves soft tissues, but eliminates the benefit of direct reduction which can be useful in restoring anatomic rotation. Patient positioning has also been shown to induce deformity. Fracture tables are associated with increased internal rotation deformity while free-legged nailing is associated with an induced external rotation deformity. Many fluoroscopic techniques have been described to reduce the risk of malrotation during fixation of femoral shaft fractures. These range from simple assessment of cortical step difference to more detailed techniques including measured anteversion, lesser trochanter profile, neck horizontal angle and greater trochanter-head contact techniques. These techniques can each obtain accurate version within 5° to 10° of the contralateral extremity.

Asymmetric tibial torsion uncovered after femoral nailing has not previously been described, to our knowledge. In this case, restoring preoperative rotation at the time of initial fracture surgery would not have resulted in composite malrotation. However, matching femoral rotation to the contralateral side uncovered a difference in tibial rotation. In this case, treatment options included revision of femoral rotation or tibial osteotomy to match the contralateral limb. The patient elected for tibial rotational osteotomy and medullary nailing, improving his cosmetic extremity appearance and restoring gait mechanics. This highlights two important principles — that side-to-side differences are common in femoral anteversion and workup of postoperative malrotation should include a thoughtful physical exam with consideration of the entire extremity.

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• For more information:
• Mary Kate Erdman, MD; Adam K. Lee, MD; and Nicholas A. Trasolini, MD, can be reached at Department of Orthopaedic Surgery, Keck Medical Center of the University of Southern California, 1620 San Pablo St., Suite 2000, Los Angeles, CA 90033. Erdman’s email: marykate.erdman@med.usc.edu. Lee’s email: adam.lee@med.usc.edu. Trasolini’s email: nicholas.trasolini@med.usc.edu.
• Edited by Joshua D. Johnson, MD, and Nicholas A. Trasolini, MD. Johnson is a chief resident in the department of orthopedic surgery at Mayo Clinic in Rochester, Minnesota. He will be a musculoskeletal oncology fellow at MD Anderson following residency. Trasolini is the administrative chief resident in the department of orthopedic surgery at Keck Medical Center of the University of Southern California and will be a sports medicine fellow at Rush University Medical Center following residency. For information on submitting Orthopedics Today Grand Rounds cases, please email: orthopedics@healio.com.

Disclosures: Erdman, Lee and Trasolini report no relevant financial disclosures.