Gap balancing versus measured resection in TKA—Brief comparison of the techniques
Accurate soft tissue tensioning, and appropriate component positioning are critical to the success of TKA. If a knee is not balanced correctly then patient outcomes are compromised. What evidence exists to support surgeons’ use of gap balancing or measured resection? Is one of these techniques superior to the other? The discussion around this question is quite controversial. In Part 1 of this article series we look at the debate surrounding these techniques and compare the two. Does one technique come out on top?
Globally, total knee arthroplasty (TKA) is being performed at a rapidly increasing rate . There have been projections of 3.48 million annual procedures by 2030 in the US alone, which is growth of 673% from 2007 . While a number of problems, such as osteo- and inflammatory arthritis, obesity, tumors, and congenital deformities , could prompt this procedure, especially in the elderly population, the reality is that TKA is increasingly performed on younger, active patients .
The success of TKA is dependent on many factors, but if soft tissue tensioning and component positioning are not accurately achieved then the resulting instability can cause early failure of the implant, pain in the joint, and even necessitate revision . Gustkey et al. found that “balanced joints” were the “most significant contributing factor to improved postoperative outcomes” . Sharkey et al. report that up to 35% of early TKA revisions in the US may be triggered by soft tissue imbalance .
Two techniques for balancing
Historically, there have been two balancing techniques used during TKA: gap balancing or measured resection . These techniques are widely used around the globe, and have each been shown to successfully balance knees and deliver good TKA outcomes; but, each technique has its pros and cons. Part 2 of this article series looks at gap balancing, and Part 3 examines measured resection in more depth. In this article we present a side-by-side comparison of gap balancing and measured resection; what are the benefits and disadvantages of each? Are there indications that suggest the selection of one over the other? Is one technique superior to the other?
We interviewed Mathew Abdel, from the Mayo Clinic in Rochester, US, and Philipp von Roth from the Charité-University Hospital in Berlin, Germany, about gap balancing and measured resection. They offer their unique perspectives on these techniques and assert what they think is really happening in the OR when it comes to the use of gap balancing and measured resection.
In discussion: gap balancing or measured resection?
While gap balancing and measured resection both have their proponents and detractors, the reality is that most surgeons employ a hybridization of the two techniques to establish femoral component rotation and tension soft tissues in total knee arthroplasty (TKA). Why is this the case? Surgeons Matthew Abdel from the Mayo Clinic in the United States and Philipp von Roth from the Charité-University Hospital in Berlin, Germany, discuss the techniques surgeons are using today, might be using in ten years, and what kind of education is best suited to pass on developments in TKA.
What are the long-term risks, if patients do not have a properly balanced flexion and extension gap after TKA?
Matthew P. Abdel (MPA): Foremost, it is important to note that some patients with subtle instability in the sagittal plane may be asymptomatic, while others may have significant limitations. For patients with true flexion instability, they complain of recurrent effusions, an inability to trust the knee, and point tenderness over Gerdy’s tubercle and the region of the pes.
Philipp von Roth (PvR): One has to mention that there is no distinct definition at what point a TKA has to be considered “instable”; a moderate instability can be tolerated by most patients. However, instability negatively influences kinematics of the TKA. This can result in problematic shear forces leading in increased wear of the polyethylene inlay. In most cases, patients cannot verbalize “instability”. They report on a sense of uncertainty when going up or down the stairs or that they could never rely on the knee during daily activities. In addition, some patients note recurrent effusions.
The literature is inconclusive about which one is superior, gap balancing or measured resection? Why is this?
MPA: In reality, most surgeons utilize a hybrid of both techniques.
PvR: In my opinion, this is because the publications are written by orthopedic surgeons who either prefer one or the other technique. Properly applied, both techniques show good results. The key to success lies in recognizing when one or the other technique is not applicable due to bony malformations or ligament injuries and you must resort to the other technique.
It has been pointed out that there are possibly some regional differences regarding which technique is most often used?
MPA: These are not “regional” differences. Rather, there are differences based upon which surgeon or institution an individual trained under.
PvR: Everyone does only what he has learned and does best! The pioneers of TKA come from North America. The implantation about 30-40 years ago was done almost exclusively by the measured resection technique. As such, this technique is very common there.
Many surgeons recommend a hybrid approach. What educational support is needed to disseminate and encourage a hybridized technique?
MPA: The key includes cadaver labs and simulation-based labs.
PvR: The broad introduction of new techniques can be achieved by the digitalization and visualization of surgical processes. A screen in the OR could show the next step of the procedure. The surgeon is forced to actively evaluate every step of the operation. This can not only increase patient safety but also can help introduce new techniques in a standardized manner.
Information at: https://www.jnj.com/media-center/press-releases/johnson-johnson-medical-gmbh-to-acquire-surgical-process-institute and http://sp-institute.com/en/.
Ten years from now: what technique will TKA surgeons be using to achieve accurate alignment and soft-tissue tensioning?
MPA: Most surgeons will be using a hybrid technique. I anticipate that advanced technologies like robotically-assisted surgery and sensor technology will evolve both techniques to a true “patient-specific” knee based upon not only bony anatomy, but also soft-tissue laxity in both static and dynamic arcs of motion.
PvR: The hybrid technique reduces the disadvantages and better exploits the advantages of the respective technique. As such, I believe that in 10 year the hybrid technique will be most commonly used. Next generation robotics and navigation tools might improve the implantation process.
About the interviewees
In brief: gap balancing
After a perpendicular cut of the tibia, the tension of the intact collateral ligaments guide the femoral bone cuts . There are two strategies surgeons employ; generally they either balance the flexion gap first, or first balance the joint in extension, then balance the flexion gap. The goal is to obtain rectangular, evenly tensioned, and symmetrical flexion and extension gaps . This is preferably done via soft tissue releases and spacer blocks, not bone cuts .
Pros of gap balancing
When correctly performed, this technique has been shown to result in good femoral rotation [9, 10], and deliver flexion gap stability . It has been associated with a lower rate of condylar lift-off , coronal stability [13, 14], and good patellar tracking . Gap balancing provides some flexibility to surgeons when flexion space releases have unpredicted results [16, 17]. The technique also allows for adjustments to rotation under tension that can help compensate for lateral laxity, if it is encountered intraoperatively . Three  and five-year  follow-ups of gap balanced TKA patients found good functionality and outcomes at both times.
Cons of gap balancing
However, gap balancing does have some disadvantages. The success of the technique hinges on precise proximal tibial resection as balancing is done in relation to this surface . Balancing is done in 90° flexion and 0° extension, but not always at midflexion, which might cause midflexion instability [16, 20]. The patella is subluxed during tensioning which mean the gap could be wrongly sized or misbalanced and externally rotate the femur , and if collateral ligaments are not intact, then rotational errors could be introduced . Additionally, the technique may not provide flexibility in cases with fixed, non-reducible deformities .
In brief: measured resection
Measured resection involves setting femoral component rotation through the use of bony landmarks, then soft tissue are adapted through releases of the passive stabilizers after femoral cuts are made [21, 22, 23]. These landmarks are the: transepicondylar axis (TEA) (surgical and anatomical); anterioposterior axis (AP) or ‘Whiteside’s line’; and posterior condylar axis (PCA) (Fig. 1) [12, 16, 24]. It is recommended that the landmarks be used in combination and not singularly . Each of these axes have their associated sequence of balancing steps and some unique tools.
Figure 1. Boney landmarks. As posted on: Talbot S. Femoral Rotation: Let’s Just Use the Posterior Condyles? July 13, 2017. Available at: https://totalkneealignment.blog/2017/07/13/femoral-rotation-lets-just-use-the-posterior-condyles/. Accessed: January 15, 2018.
Pros of measured resection
Measured resection has been shown to be, “reliable and accurate in determining femoral component rotation” , and “durable and successful” . If surgeons reference all bony landmarks (TEA, AP axis, and PCA), versus using a singular axis, they are more likely to optimize component placement . The technique handles cases of patellar infera well , and provides better accommodation for ligament balancing for fixed deformities . In addition, the use of measured resection has been shown to decrease reduction of the post-operative joint line position .
Cons of measured resection
Much criticism of measured resection revolves around the difficulty of accurate intraoperative identification of bony landmarks [7, 16, 30, 31, 32]. Patients can present with bone loss, unique anatomical variation and/or deformities that distort bony references, which results in a number of issues . Because measured resection requires soft tissue releases after trial component placement, it may create laxity and asymmetry that is difficult to correct .
Comparing the two techniques
As mentioned above, gap balancing and measured resection have both been shown to deliver acceptable outcomes for surgeons and patients. There are also disadvantages to both. There are studies that find one technique superior to the other, and studies that find the techniques’ outcomes comparable. In Table 1 we look at a selection of published studies, identify the evaluated variable, and simplify their conclusion(s). It is by no means an exhaustive list of research that has compared these two techniques.
Table 1. A selected list of comparative studies on the effectiveness of gap balancing and measured resection. The first author of the study is indicated in the first column. The variable being evaluated is identified in the second column. An “X” indicates which technique was suggested as superior or if the study concluded equal effectiveness of the two techniques.
It is interesting to note that in each of the four studies here that evaluate postoperative outcomes, all concluded there were no long-term functional differences between the techniques.
As highlighted by the information in this table, the research does not seem to support one technique over the other in a clear-cut way . Yes, the techniques may result in differences in particular variables (ie, higher or lower joint lines, more or less symmetrical flexion and extension gaps, more or less accurate femoral component rotation), but these differences do not necessarily translate into negative outcomes.
It’s been suggested that scoring systems are not sensitive enough to expose subtleties in outcomes and ongoing patient dissatisfaction may stem from our lack of understanding of patient specific parameters . Philipp von Roth, surgeon at the Charité-University Hospital in Berlin, Germany, reminds us that a thorough examination, consideration of patient-specific anatomy, and a stepwise approach is advised.
“The examination of the patient and—in particular—of the knee is the key to success. Ligamentous integrity, leg axis, and the redressability of a deformation can be captured. In addition, a full leg radiograph is mandatory. Intraoperatively the anatomical landmarks have to be identified and marked in a first step, followed by the evaluation of the ligaments. In case of doubt, a laminar spreader with force and distance information can help evaluate ligamentous integrity in flexion and extension. Latest generation computer-assisted surgery tools also can give feedback on the gaps over the full range of motion.”
So, which technique should surgeons use? Simple answer: Both of them.
Many surgeons prefer a hybrid approach because it combines the positive aspects of each technique, minimizes the disadvantages, and allows for more patient-specific solutions. Sheth et al. writes, “A hybrid technique has been developed that combines the benefits of measured resection and gap balancing and minimizes the limitations associated with both techniques. This hybrid approach has the potential for achieving improved TKA kinematics and refined surgical technique” .
A skilled surgeon can use either technique, or a hybrid approach, to achieve suitable component placement in the coronal, sagittal, and axial planes, and accurately balance soft tissues . As Mayo Clinic, Rochester, US, surgeon Matthew Abdel says, “The key is for a knee surgeon to use the technique he/she is most comfortable with as long as the flexion and extensions gaps are balanced both to varus and valgus loads throughout an arc of motion. Most surgeons use a hybrid of both techniques.”
Further supporting a hybrid approach is Philipp von Roth of the Charité-University Hospital in Berlin, Germany, who also teaches TKA from this perspective. “I would not want to answer the question for or against one technique. Both techniques have their advantages and disadvantages. From my point of view, the combination of both techniques makes sense to reduce the disadvantages and to better exploit the advantages of the respective technique.”
Determining if gap balancing or measured resection is better may be a 30-year-old debate , but the reality is, in the hands of a skilled surgeon, either technique (and most likely a combination of the two) will deliver good outcomes. As technology advances and presents us with improved understanding, new tools, and advanced techniques, perhaps the number of dissatisfied TKA patients will decline. Until there’s a proven new way to establish femoral component rotation and tension soft tissue during TKA, it’s “business as usual“.
This series of articles was created with the support of the following specialists (in alphabetical order):
This issue was created by Word+Vision Media Productions, Switzerland
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