Gap balancing versus measured resection in TKA—Evidence for/against gap balancing
When it comes achieving correct femoral component positioning during TKA, one commonly used technique is gap balancing. This method is successfully employed by many surgeons and involves balancing tension and flexion gaps before femoral bone cuts are made. Here, in part 2 of our article series, we explore gap balancing and some of the positive and negative commentary surrounding this technique.
Some schools of thought maintain that the success of total knee arthroplasty (TKA) relies - among other things - on achieving symmetric, balanced flexion and extension gaps . Indeed, soft tissue management has been identified by some as more important to outcomes than bone management .
If femoral component malrotation is present, it can result in decreased patient satisfaction (pain) and implant disfunction  via altered tibiofemoral kinematics [4, 5]. Malrotation can also cause patellofemoral complications and instability. This was directly correlated to the combined (femoral and tibial) internal component rotation by Berger et al.  It has also been suggested that if relative rotational mismatch is kept within ±5° (surgical norms), then knee axial rotation during flexion is more controlled and more likely to deliver a better outcome .
Gap balancing has been shown to produce desirable outcomes, particularly because balancing is done independent of bony anatomy, eliminating confusion around intraoperative landmarking that could be compromised by bone deformities and individual anatomical variation [7, 8].
Matthew Abdel, orthopedic surgeon at the Mayo Clinic in Rochester, US, finds the technique, “particularly useful for patients with distal femoral fractures where anatomic landmarks are displaced and may make a measured resection technique difficult.” Philipp von Roth, orthopedic surgeon at the Charité-University Hospital in Berlin, Germany, feels that the “gap balancing technique is optimal for redressable varus- or valgus deformities and in case of difficulties identifying the anatomical landmarks with intact ligaments.”
Two gap balancing techniques
While measured resection is a technique used to determine femoral component rotation, this article will examine gap balancing and its two recognized sequences, looking at the pros and cons. See our interview on why surgeons use one or the other technique.
In gap balancing, ligaments are released before femoral bone cuts are made . One technique we will discuss involves balancing the flexion gap first; the other technique first balances the joint in extension, then returns to address the flexion gap in relation to the previously balanced extension gap . Both require sequential soft tissue balancing .
Remove all osteophytes
Both techniques demand the removal of all osteophytes (including posterior femoral and tibial) before soft tissue releases. Ramappa et al. reminds surgeons about “the importance of meticulous osteophyte excision” . These bony projections tension adjacent ligaments, which may produce flexion gap asymmetry and femoral component malrotation , and increase the likelihood of interaction between implant components and surrounding tissue, to the detriment of the patient .
Success tied to accurate tibial cuts
The success of gap balancing, for both sequences, hinges on a precise proximal tibial cut; correct depth and alignment on the coronal and sagittal planes is critical to avoid femoral component malrotation . If the resection is varus or valgus then either internal or external rotation, respectively, of the femoral component will occur [7, 8]. This can result in “a mismatch of flexion and extension gap dimensions” . The tibial cut is used as a reference point for femoral resections, further reaffirming the importance of accuracy in the tibial resection.
If you start with the flexion gap
If a surgeon chooses to balance the extension gap first they are looking for parallel alignment of the tibial cut with the transepicondylar axis, which will be perpendicular to the anteroposterior axis. Required soft tissue releases are performed after the joint is correctly tensioned in flexion, using the above alignments to guide releases (Fig. 1). After this, the extension gap addressed .
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- If you start with the flexion gap
- If you start with extension balancing
- Symmetric gaps
- The case for gap balancing
- The case against gap balancing
- When not to use gap balancing
This series of articles was created with the support of the following specialists (in alphabetical order):
Matthew P Abdel MD
Rochester, United States
Philipp von Roth MD
Charité—University Medicine Berlin
This issue was created by Word+Vision Media Productions, Switzerland
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