Gap Balancing in TKA: Does Technique Matter?
Since Dr. David Liu switched from measured resection to gap balancing, his total knee arthroplasty patients have been happier and their knees have felt more stable. In this article, he reviews his technique.
“The goal of any ligament balancing technique is to achieve a stable and functional range of motion for the patient without over-stressing the soft tissues,” says David W. Liu, MBBS, FRACS, from the Gold Coast Centre for Bone & Joint Surgery in Tugan, Queensland, Australia.
In a presentation at ICJR Australia, Dr. Liu reviewed the technical pitfalls and his own methods for achieving this goal using the gap balancing technique in total knee arthroplasty (TKA). He said that since he switched from measured resection to gap balancing, his patients have been happier and their knees have felt more stable.
So what does gap balancing mean? Dr. Liu stressed that gap balancing does not mean that no ligament releases are made. Instead, the ligament releases are done first and then the surgeon compensates for any imperfections by altering the bony cuts.
Dr. Liu said the key points of gap balancing technique are:
- Accurate proximal tibial resection
- Collateral ligament integrity and function
- Removal of osteophytes
- Ligament releases to correct the deformities prior to making the bone cuts
Which Gap Should Be Balanced First?
The questions surgeons have about the gap balancing technique, he said, include:
- Which gap should be balanced first – extension or flexion?
- How does the surgeon avoid significant joint line shift?
- Does patella position influence gap size?
When only a limited number of component sizes were available, the flexion gap was usually balanced first. This technique had a significant risk of elevating the joint line.
Now that a wide range of component sizes is available in TKA systems, most surgeons balance the extension gap first.
Dr. Liu warned though, that if the extension gap is balanced prior to removal of osteophytes and release of the posterior capsule, there is an increased risk of resecting extra femoral bone, which increases the risk of mid-flexion instability.
Resecting more bone distally improves gap symmetry in extension, but it also raises the joint line, which may negatively affect achieving stability through the full range of motion. For these reasons Dr. Liu prefers not to shift the joint line by more than 2 to 4 mm. 
What Are the Landmarks for Resection?
Dr. Liu uses the intercondylar notch as landmark for resection depth in the distal femur. He has found that this is the landmark with least coefficient of variance (CV) between patients as related to resection depth. The amount resected from the notch should equal the thickness of the prosthesis.
The intercondylar notch is a useful landmark for the resection depth of the distal femur  because:
- It is in the midline of the knee.
- It is unaffected by the degree of varus or valgus.
- The articular cartilage in the notch is usually well preserved.
Dr. Liu has found, however, that the overall amount of resection varies slightly between varus and valgus knees.
Does Patella Position During Ligament Balancing Matter?
Some instrument systems do not allow the surgeon to reduce the patella during gap balancing. Dr. Liu cited studies, [3,4] however, that found the position of the patella does influence the gap measurements.
Patella eversion results in smaller gaps in both flexion and extension, so keeping the patella reduced is important during this stage of the procedure, Dr. Liu said.
What Are the Ideal/Standard Goals of Balancing?
Is balancing in extension and 90° of flexion enough? What distraction force should be used?
A study  of computer-navigated TKA found that even though the knee was properly balanced and the gaps were rectangular in both flexion and extension, 36% of the patients had laxity at 45° and 120° of flexion.
Distraction force needed is another variable affecting balance, Dr. Liu said. For example, the stiffness of the lateral side of the knee is lower than that of the medial side, which leads to a larger lateral gap with increased distraction force. 
Dr. Liu has initiated research into distraction force to determine if there are any predictors of how much distraction force is needed to achieve a rectangular 9-mm gap. His initial results found age, BMI, gender and preoperative flexion to be significant predictors.
The theory of gap balancing is to position the femoral component parallel to the resected proximal tibia with equal collateral ligament tension. But Dr. Liu warned surgeons to be aware of the pitfalls:
- Joint line elevation
- Patella position during balancing
- Unresolved issues and variables such as balancing angles and distraction force
Click the image below to watch Dr. Liu’s presentation.
- David W. Liu, FRACS, James F. Reidy, MBBS, Elaine M. Beller, BSc, MAppStat. The Effect of Distal Femoral Resection on Fixed Flexion Deformity in Total Knee Arthroplasty. Journal of Arthroplasty January 2016, Volume 31, Issue 1, Pages98–102
- Shinichi Kuriyama, Katsufumi Hyakuna, Satoshi, Inoue, Yasuyuki Tanaka, Yasuyuki Tamaki, Hiromu Ito, Shuichi Matsuda. Is a “sulcus cut” technique effective for determining the level of distal femoral resection in total knee arthroplasty? Knee Surgery, Sports Traumatology, Arthroscopy December 2014, Volume 22, Issue 12, pp 3060–3066
- Jung-Ro Yoon, Kwang-Jun Oh, Joon Ho Wang, Jae-Hyuk Yang. Does patella position influence ligament balancing in total knee arthroplasty? Knee Surgery, Sports Traumatology, Arthroscopy July 2015, Volume 23, Issue 7, pp 2012–2018
- G. Kamei, Y. Murakami, H. Kazusa, S. Hachisuka, H. Inoue, H. Nobutou, K. Nishida, Y. Mochizuki, M. Ochi. Is patella eversion during total knee arthroplasty crucial for gap adjustment and soft-tissue balancing? Orthopaedics & Traumatology: Surgery & Research, Volume 97, Issue 3, Pages 287-291
- Jung-Ro Yoon, MD, PhD, Hyeon-Il Jeong, MD, Kwang-Jun Oh, MD, PhD, Jae-Hyuk Yang, MD, PhD. In Vivo Gap Analysis in Various Knee Flexion Angles During Navigation-Assisted Total Knee Arthroplasty. J. of Arthroplasty December 2013, Volume 28, Issue 10, Pages 1796–1800
- Kanto Nagai, MD, Hirotsugu Muratsu, MD, PhD, Tomoyuki Matsumoto, MD, PhD, Shunsuke Takahara, MD, Ryosuke Kuroda, MD, PhD, Masahiro Kurosaka, MD, PhD, Influence of Intraoperative Soft Tissue Balance on Postoperative Active Knee Extension in Posterior-Stabilized Total Knee Arthroplasty. J. of Arthroplasty July 2015, Volume 30, Issue 7, Pages 1155–1159