Intraoperative Imaging of Proximal Femur Fractures


William W. Cross III
Ian P. McAlister


Introduction



  • Clear visualization of the femoral neck with intraoperative fluoroscopy is vital in the treatment of femoral neck fractures and proximal femur fractures.
  • Implant malposition and poor reductions secondary to inadequate imaging are common and may lead to early clinical failures.
  • The proximal femur is highly intolerant to varus malalignment, and every effort should be made to ensure adequate imaging ensues to identify subtle angular deficiencies.
  • Failure to appropriately position implants in the femoral head and neck has led to early failures. Optimal visualization around the spherical femoral head is critical to avoid these complications.

Bony Anatomy Appreciated on Intraoperative Imaging



  • The spherical femoral head requires (at least) orthogonal imaging sequences to assure that implants are safely placed within the subchondral bone and do not penetrate the convex articular surface.

    • Thus, a screw is “safe” if it appears within the femoral head on every image. If it appears to penetrate the femoral head on any image, that screw must be revised to a shorter length or direction.

  • The angle of inclination, also referred to as the neck-shaft angle, and neck version are the most clinically relevant angular measurements when managing fractures of the femoral neck, intertrochanteric, and subtrochanteric regions.
  • Angle familiarity can assist with intraoperative fluoroscopy management.
  • The neck-shaft angle for adults, irrespective of sex, is 129 degrees (±6 degrees) on average.1
  • Male femoral neck anteversion with respect to the shaft is 7.0 degrees ± 6.8 degrees.
  • Female femoral neck anteversion with respect to the shaft is 8.0 degrees ± 10.0 degrees.2
  • The insertion of the short external rotators (posterior trochanteric ridge), the hip abductors (greater trochanter), and the psoas muscle (lesser trochanter) all provide deforming forces for fractures in this region and must be addressed with fracture surgery.
  • The word calcar is derived from the Latin word calcaria, which means a spur or spur-like projection, such as one found on the base of a petal or on the wing or leg of a bird.

    • The calcar femorale is a dense vertical plate of bone within the proximal femur (yellow line in Figs. 17-1 and 17-2).3
    • It originates in the posteromedial aspect of the femoral shaft, under the lesser trochanter, and radiates laterally through the cancellous bone toward the greater trochanter.
    • Clinically, this area of thickened bone helps resist medial compressive loads.
    • Involvement of the calcar is important in distinguishing stable versus unstable fracture patterns.
    • It is this area where implants engage the bone with the most resistance to deformation.


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Figure 17-1



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Figure 17-2


Intraoperative Positioning and Associated Imaging for Proximal Femoral Trauma



  • There are inherent pros and cons of supine versus lateral positioning. This includes advantages or limitations with intraoperative fluoroscopy. Each must be considered when preoperatively planning for positioning and imaging needs.

    • Supine on standard or specialized fracture table
    • Supine on radiolucent table (free-legged)
    • Lateral on radiolucent table (free-legged)
    • Lateral on a fracture table
    • Two C-arm technique for proximal femur surgery

1. Supine Position on Fracture Table



  • Imaging is easiest in this position.

    • Rollover lateral imaging places the shaft, neck, and head in colinear alignment allowing the surgeon to see subtle malreductions in the sagittal plane. Further, placement of the implant into the femoral neck and head can be well visualized (Fig. 17-3).

  • AP pelvis and hip views:

    • Anteroposterior pelvic (AP pelvis) radiograph may be taken in the surgical suite to compare injured and uninjured sides. Further, AP pelvis imaging is important for the assessment of version with direct anterior total hip replacement for displaced femoral neck fractures.
    • In a true AP pelvis, the obturator foramina should appear symmetric.
    • The tip of the coccyx should lie approximately 1 to 3 cm directly superior to the symphysis pubis.
    • The spinous processes should be midline within the vertebrae. The lumbar pedicles should be symmetric but may be challenging to see intraoperatively on the same image as the symphysis on routine AP imaging. This is different for inlet and outlet imaging (Fig. 17-4).
    • AP hip view should include the lesser trochanter, and in many cases, the outline of the piriformis fossa can be detailed (red markings) (Fig. 17-5).

  • Lateral imaging:

    • Standard lateral (parallel to floor lateral)

      • Best for viewing calcar region reduction. Can be challenging to optimize perfect implant positioning into the femoral head.
      • Should be used in conjunction with the rollover lateral. It may lack the accuracy to detect subtle deformities in the sagittal plane (Fig. 17-6).

    • Rollover lateral (inline lateral): places the shaft, neck, and head in colinear alignment allowing the surgeon to see subtle malreductions in the sagittal plane. Further, placement of the implant into the femoral neck and head can be well visualized. Best used for positioning of implant into femoral head. Calcar region not well visualized here. Should be in conjunction with standard lateral (Fig. 17-7).


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Figure 17-3



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Figure 17-4



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Figure 17-5



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Figure 17-6


Case Example: Cannulated screw fixation of femoral neck fracture. Preoperative fluoro imaging sequences demonstrate stable slightly valgus impacted femoral neck fracture with minimal inferior neck comminution and no sagittal plane step-off or angulation (Fig. 17-8).



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Figure 17-8

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Mar 25, 2020 | Posted by in ORTHOPEDIC | Comments Off on Intraoperative Imaging of Proximal Femur Fractures
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