Medial-lateral dimension, volume of femoral component may affect soft tissue balance in TKA
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Published results showed intraoperative soft tissue balance in posterior stabilized total knee arthroplasties may be affected by the medial-lateral dimension and volume of the femoral component, which may be greater with the use of narrower-size implants.
Researchers inserted standard and narrow femoral trial implants in 30 patients with varus osteoarthritis undergoing posterior stabilized TKA (Persona, Zimmer Biomet) using an image-free navigation system. Researchers measured patient soft tissue balance and performed subgroup analysis to assess the influence of narrow implants on soft tissue balance.
Results showed significant larger joint component gaps at all measured flexion angles except at 60° among the narrow trial group. In a subgroup analysis based on the size of the implant used after the trials, researchers found significantly larger joint component gaps in the narrow trial group at 30°, 120° and 135° flexion vs. the standard trial group with the standard-size implant. Similarly, the narrow trial group had significantly larger joint component gaps for the narrow-size implant at all measured flexion angles except at 0° and 60° compared with the standard trial group, according to results. Researchers noted significantly larger varus ligament balance in the narrow trial group at 45° and 60° flexion. Although the narrow and standard trial groups had comparable varus angles for standard-size implants, results showed significantly larger varus angles for narrow-size implants at 45°, 60° and 120° flexion among the narrow trial group.
“The findings of this study have important clinical relevance as they may help surgeons predict the soft tissue balance after a narrow femoral implantation in [posterior stabilized] PS TKA,” the authors wrote. “In cases with risk of [medial-lateral] ML overhang, surgeons should know the effect of selecting a narrower-size implant and should manage the soft tissue balance accordingly. The effect of other narrow femoral implants in PS TKS should be investigated in future studies.” – by Casey Tingle
Disclosures: Ishida reports he received financial or material support from Zimmer Biomet. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Simon W. Young, MBChB, FRACS, MD
Femoral component size in the sagittal plane is commonly considered and understanding effects of anterior vs. posterior referencing on the flexion gap and patellofemoral joint is a fundamental principle of knee arthroplasty technique. Kazunari Ishida, MD, and co-authors investigate a more novel consideration – that the medio-lateral femoral component size and overall component volume may also affect soft tissue balance. This is relevant as a number of manufacturers now offer a “narrow-width” option for a given femoral component size, mainly to accommodate the often narrower femoral width ratio seen in female patients.
In 30 female TKA patients assessed with an intraoperative navigation system, they found narrower femoral components had significantly larger joint component gaps than standard-width components. The effect was greater when a standard-size component caused bony overhang.
While the clinical impact of their findings is unknown, surgeons should be aware that when choosing a narrower-width femoral component to avoid bony overhang that the soft tissue balance will be affected and to manage this appropriately.
Auckland, New Zealand
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