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Does a positioning rod or a patient-specific guide result in more natural femoral flexion in the concept of kinematically aligned total knee arthroplasty?

  • Knee Arthroplasty
  • Published:
Archives of Orthopaedic and Trauma Surgery Aims and scope Submit manuscript

Abstract

Purpose

Flexion of the femoral component in 5° increments downsizes the femoral component, decreases the proximal reach and surface area of the trochlea, delays the engagement of the patella during flexion, and is associated with a higher risk of patellar-femoral instability after kinematically aligned TKA. The present study evaluated flexion of the femoral component after use of two kinematic alignment instrumentation systems. We determined whether a distal cutting block attached to a positioning rod inserted perpendicular to the distal femoral joint line in the axial plane and 8–10 cm into the distal femur anterior and posterior to the distal cortex of the femur in the sagittal plane or a femoral patient-specific cutting guide sets the femoral component in more natural flexion.

Methods

Flexion of the femoral component was measured with respect to the sagittal femoral anatomic axis of the distal diaphysis and the sagittal femoral axis on rotationally controlled long-leg lateral computer scanograms. Measurements were performed on 53 consecutive patients treated with a kinematically aligned TKA performed with a distal cutting block attached to a positioning rod, and 53 consecutive patients treated with a kinematically aligned TKA performed with a femoral patient-specific cutting guide.

Results

The average flexion and variability (±standard deviation) of the femoral component of patients treated with a positioning rod was 1° ± 2° and 7° ± 4° with respect to the anatomic and mechanical axes, respectively, which was 5° less than the average flexion of the femoral component of patients treated with a femoral patient-specific cutting guide of 6° ± 4° and 12° ± 5° (p = 0.0001, p = 0.0001, respectively).

Conclusions

Because a distal cutting block attached to a positioning rod sets the femoral component in 5° less flexion and with less variability than a femoral patient-specific cutting guide, we prefer this instrumentation system when performing kinematically aligned TKA to reduce the risk of patellar-femoral instability. Each surgeon should determine the repeatability of setting the flexion of the femoral component with this instrumentation system.

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Authors and Affiliations

  1. Department of Orthopedic Surgery, Hannover Medical School, Hannover, Germany

    Max Ettinger & Tilman Calliess

  2. Department of Mechanical Engineering, University of California, Davis, Davis, CA, 95616, USA

    Stephen M. Howell

Authors
  1. Max Ettinger
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  2. Tilman Calliess
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  3. Stephen M. Howell
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Correspondence to Max Ettinger.

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The authors have proprietary interests in the materials described in the article. The authors declare that they have no conflict of interest.

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This article does not contain any studies with human participants or animals performed by any of the authors.

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Ettinger, M., Calliess, T. & Howell, S.M. Does a positioning rod or a patient-specific guide result in more natural femoral flexion in the concept of kinematically aligned total knee arthroplasty?. Arch Orthop Trauma Surg 137, 105–110 (2017). https://doi.org/10.1007/s00402-016-2598-2

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  • DOI: https://doi.org/10.1007/s00402-016-2598-2

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