Soft Tissue Balancing during Total Knee Arthroplasty

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CHAPTER SYNOPSIS

Soft tissue balancing during total knee arthroplasty (TKA) is an important step for optimizing the outcome of the procedure and providing a stable, durable joint. Soft tissue contractures from coronal plane deformities can pose a difficult problem, and a surgeon should have a standard approach to balancing varus and valgus deformities in the operating room. The purpose of this chapter is to review techniques used to balance both varus and valgus knee deformities during primary TKA. Clinical outcomes will also be reviewed to provide the reader a comprehensive viewpoint of this complex topic.

IMPORTANT POINTS

1

Instability after primary TKA is one of the major factors for early revision and poor outcomes.
2

Intraoperative assessment of soft tissue balancing, using either a spacer block, laminar spreaders, or trial components, is a critical step in achieving stability of the knee.
3

With careful assessment of the flexion and extension gaps following bone cuts and osteophyte excision, most deformities can be successfully balanced using an algorithm of differential medial and lateral soft tissue releases.
4

Most flexion contractures of less than 15 degrees can be corrected through soft tissue releases alone without changing the joint line by increasing the distal femoral resection.

CLINICAL PEARLS

1

In a varus knee, release of anteromedial structures tends to have a greater effect on the flexion gap, while release of more posterior structures on the medial side tends to have a greater effect on extension.
2

In a valgus knee, structures inserting near the lateral epicondyle affect the flexion and extension gap, while the iliotibial band has a greater effect on extension, and the popliteus has a greater effect on flexion.
3

The addition of posterior cruciate ligament release in a posterior stabilized knee increases the flexion gap to a greater degree while having little effect on the extension gap.
4

Removal of osteophytes, including posterior femoral condylar osteophytes, should be performed prior to assessing soft tissue balance, to avoid unnecessary release.
5

Balancing deformity in a varus knee is typically performed on the tibial side of the joint, while balancing in a valgus knee is performed on the femoral side.

CLINICAL PITFALLS

1

One should always err on the side of less release initially to avoid overcorrection.
2

If a complete medial release and posterior cruciate ligament sacrifice are carried out, the flexion gap may be significantly larger than the extension gap, causing the jump height of the post to be exceeded.
3

Allowing the flexion space to dictate femoral rotation in the face of significant medial or lateral release for deformity may lead to excessive malrotation of the femoral component.
4

The origin of the popliteus lies inferior and anterior to the lateral collateral ligament origin. This must be considered when releasing the lateral collateral ligament to avoid concomitant release of the popliteus.
5

Increasing the distal femoral resection to improve a flexion contracture may raise the joint line and result in mid-flexion instability.

VIDEO AVAILABLE

1

Computer assisted TKA.

HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

Proper soft tissue balancing during total knee arthroplasty (TKA) is paramount to ensure the long-term success of the operation. Instability after a primary total knee replacement has been reported as one of the major factors leading to early revision and poor outcomes. Therefore, the surgeon must be prepared to properly balance the knee in both flexion and extension since even a minimal coronal deformity may necessitate some degree of soft tissue release for balancing and improved stability.

Testing for soft tissue balancing during TKA was first popularized by Freeman and Insall with a spacer block or lamina spreader assessment of the extension and flexion gap of the knee intraoperatively. For arthritic knees with significant varus or valgus deformity, this becomes an essential step during TKA to optimize the mechanical stability of the knee replacement. An inadequate soft tissue release of the knee is usually associated with either instability or recurrence of deformity in the postoperative period. On the other hand, an overzealous release may produce instability on the contracted side of the joint or an increased flexion space that may lead to knee instability in flexion with a cruciate retaining (CR) implant or to post dislocation in the posterior stabilized (PS) knee due to exceeding the jump height in flexion.

Many studies have reported on the effects of variable soft tissue releases in flexion and extension. These cadaveric studies have usually been performed on knees without significant deformity. Although these studies provide a useful anatomic map of the effective sequential soft tissue release on flexion and extension gaps, they may not completely simulate operating room scenarios.

This chapter reviews clinical studies reporting outcomes of TKA in the varus and valgus knee and refers to past basic science reports to extend recommendations on soft tissue balancing techniques in the operating room. These guidelines, along with the authors’ preferred methods, are reported to give an overview of the importance of soft tissue balancing and techniques of sequential soft tissue release during TKA.

REVIEW OF BASIC SCIENCE AND SOFT TISSUE BALANCING

Several anatomic studies have been published involving cadaveric models and testing techniques to measure the effects of differential anatomic structure releases about the knee. If we consider those studies that have described medial release techniques for the varus knee, one can realize several key concepts. By breaking down the medial structures of the knee into anterior (superficial medial collateral ligament fibers [SMCLs]) and posterior (the posterior oblique ligament [POL] and semimembranosus [SM] fibers that coalesce into the posterior capsule), it has been observed that releases of the anterior structures tend to effectively increase the flexion gap more than the extension gap, while those structures more posterior tend to increase the extension gap more than the flexion gap. The addition of a posterior cruciate ligament (PCL) release for a PS knee increases the flexion gap far more than the extension gap when a complete medial release is realized.

Whiteside et al. used a valgus torque in a cadaveric model to study the effects of releasing the anterior portions and posterior oblique portions of the SMCL on the flexion and extension gaps of the knee, respectively. The PCL was preserved. Release of the anterior portion of the SMCL had a much greater effect on the flexion gap, and release of the posterior oblique portion had a much greater effect on the extension gap. Krackow and Mihalko used a cadaveric knee model under distractive loads to determine the influence of different medial release sequences on the flexion and extension gaps. These changes were referred to as gap kinematics, and the authors determined that releasing the SMCL first allowed for the most effective release. When the SM and pes anserine tendons were released first, the relative correction was small. The authors also noted a significantly larger flexion gap compared with extension with complete release of all medial soft tissue structure studies (SMCL, SM, pes anserine, posterior capsule, and PCL).

On the lateral side of the knee, those structures with attachments on or around the lateral epicondyle (the lateral collateral ligament [LCL] and popliteofibular ligament) when released effectively increase the gap in both flexion and extension. This was first reported by Grood when he described the functional envelope of the knee. The iliotibial band (ITB) as a dynamic structure is only in the coronal plane of movement and, when released, affects extension space almost exclusively. The popliteus affects mainly the flexion gap, since this structure is elongated as the knee is flexed.

For valgus knee releases on the lateral side of the knee, Kanamiya et al. reported on the effects in flexion and extension of each anatomic structure. Using different sequences of release and isolating each structure’s effect on the flexion and extension gap, it was concluded that the ITB and posterolateral capsule mainly affected the extension gap, whereas the LCL had effects on both the flexion and extension gaps. The popliteus was found to have more effect in flexion than extension. Mihalko and Krackow also have reported on different sequences of lateral sided release with similar findings. A two-fold increase in the flexion gap was noted when a full lateral release including the PCL was performed. Lateral flexion instability occurred when a full release of lateral knee structures was performed (including the LCL, popliteus, ITB, lateral gastrocnemius tendon, and posterolateral corner).

The same authors have reported an investigation on the pie crusting technique of the posterolateral corner for balancing in the valgus knee. They found a direct correlation between the number of scalpel blade incisions and the effective release for smaller releases. Larger releases were not realized until the LCL was effectively released. Another study also investigated lateral structural release with a pie crusting technique using a cadaveric model. They reported similar findings but did not investigate the amount of pie crusting.

These anatomic studies can give the surgeon an excellent guide as to how best approach flexion and extension gap imbalances in the operating room. Keeping in mind the principles of medial and lateral releases described in these studies will allow the surgeon to tackle these deformities directly without relying on increased implant constraint for stability.

INTRAOPERATIVE ASSESSMENT OF BALANCING

Two main variations exist in the techniques used to assess ligament balancing intraoperatively. Following completion of all tibial and femoral bony cuts and removal of osteophytes, including posterior femoral condylar osteophytes, some surgeons will assess the flexion and extension gaps under a distractive load using spacer blocks, lamina spreaders, or tensiometers ( Fig. 8-1 ). Another technique involves using the trial prosthetic components as spacer blocks and applying varus and valgus stress in flexion and extension to assess the opening of the associated side of the knee and compare each side for balancing ( Fig. 8-2 ). If the medial and lateral joint gaps are not balanced in both flexion and extension, specific releases should be performed. In a comparison cadaveric study it was concluded that a distractive force and trial component technique were equivalent. These techniques are applicable regardless of what manufacturer or system is used. It is important to remove all osteophytes prior to the assessment of balancing, since medial or lateral osteophytes may increase tension in the surrounding soft tissue structures, and posterior femoral osteophytes may limit extension.

Some surgeons recommend that rotation of the femoral component be dictated by the flexion gap. After soft tissue balancing, the flexion space is balanced by rotating the femoral component to equalize the filling effect of the femoral component in flexion. This technique is often advocated for mobile bearing designed implants to allow gap equalization through femoral bone cuts in flexion to ensure no imbalance and prevent bearing spin out in flexion.

However, if a significant release of the medial or lateral structures in addition to release of the PCL is necessary, this may result in a larger flexion space compared to the extension space. With a varus knee, if a larger flexion space is present after releases are performed, this may suggest an internal rotation of the femoral component in order to balance the flexion space. However, with significant internal rotation of the femoral component, there are concerns that this may lead to patellar maltracking.

One needs to be cognizant of the suggested femoral rotation that the flexion gap may dictate and compare it to the traditional landmarks such as the epicondylar axis and the AP axis described by Whiteside and Arima. If the flexion space is dictating an internally rotated femoral component, then the surgeon should rethink this step. If the flexion gap is excessive, the surgeon may need to consider increasing the constraint of the implant to compensate for the possibility of instability, or if the jump height of a PS knee post is in question.

VARUS KNEE ANATOMY AND STRUCTURAL RELEASE TECHNIQUES

All osteophytes should be removed prior to undertaking any soft tissue releases. Alleviating impingement of soft tissue structures from impeding osteophytes alone can often be sufficient to provide a balanced flexion and extension gap. Available soft tissue supporting structures about the knee can be classified as dynamic (musculotendinous) or static (capsular or ligamentous). On the medial aspect of the knee, the dynamic stabilizers are the pes anserine tendons and the SM, with the static stabilizers being the SMCL, POL, and the capsule.

The SMCL has its tibial insertion on the medial aspect of the upper tibia and femoral insertion on the medial epicondyle. The SMCL is released off of the tibial insertion using a subperiosteal technique to release the insertion from just medial to the pes anserine tendon insertion to the medial aspect of the upper tibia. The release may need to be taken to a distance of up to 6 to 8 cm distal to the joint line to obtain an effective release. The surgeon may elect to release a shorter distance (4 cm) initially, depending on how much correction is needed. One should always err on the side of less release initially ( Fig. 8-3 A ). The SMCL has been shown to affect both flexion and extension, but if one releases only the anterior portion, it has been shown to affect the flexion space more than the extension space and can be used in specific situations to aid in ligament balancing.

Alternatively, division of the SMCL has been described at the level of the joint. This technique identifies the contracted portion of the ligament, while the medial aspect of the joint is held under distraction with a laminar spreader. It should be emphasized that the POL and the posterior capsule should not be released when this technique is used due to the possible destabilization of the medal soft tissue sleeve. Therefore, this technique should be used for minor varus deformity cases.

The POL fibers of the medial collateral ligament run in an oblique fashion from the upper aspect of the SMCL fibers to the posteromedial aspect of the proximal tibial flare ( Fig. 8-3 B ). This structure is released by taking the insertion off subperiosteally from the medial apex of the tibial cut, directing the release at a 45-degree angle posteriorly. The POL is then released subperiosteally to the posterior aspect of the proximal tibia. The POL has been shown to affect mainly the extension space when released in cadaveric studies.

The SM has a complex attachment to the posteromedial aspect of the tibia, with five described insertion sites. The blending of the tendon to the posteromedial aspect of the tibia and posterior capsule is the area targeted for release if necessary. Release of this structure is usually only necessary in the significant varus deformity case. To release the SM, a subperiosteal technique is used to release its insertion from the posteromedial aspect of the proximal tibia. This will then allow the tibia to be externally rotated and allow easier access to the posteromedial aspect of the tibial resection. Before release of this structure, osteophytes in this region should be removed ( Fig. 8-3 C ). The posterior nature of its blended insertion with the capsule means its release will affect the extension space more than the flexion space.

The insertions of the sartorius, gracilis, and semitendinosis lie in order from superior to inferior just medial to the proximal portion of the anterior crest of the tibia. Collectively, these pes anserine tendons are usually not considered the first line of release for balancing the medial aspect of the joint, and their release is usually not used except for when a significant varus deformity is present. These tendons are released subperiosteally from the proximal tibia and have been shown to affect extension more than flexion.

A procedure involving osteotomizing the medial epicondyle has also been reported to aid in balancing and exposure of the combined varus and flexion contracted knee. The technique involves osteotomizing the epicondyle, removing the attachments of the SMCL and adductors with a 2 × 2–cm portion of bone. Eversion of this bony fragment improves exposure of the medial structures and releases these structures for balancing purposes. The epicondylar bone is repaired in appropriate ligamentous tension using two large sutures through the epicondylar fragment and condylar bone. If the posterior portion of the tibia is difficult to expose, one can consider performing a medial epicondylar osteotomy, but one should remember that the flexion gap may be affected more than the extension gap due to the loss of proximal support from the adductors in flexion. If this technique is used, we recommend that the PCL be preserved to limit the potential increase in flexion space. This technique may have a high fibrous union rate due to the fact that the structures are not effectively elongated as when they are released from the tibial insertion, and therefore excess motion of the structures on the epicondyle may result.

One of the senior authors (K.A.K.) uses a bone resection technique of the medial tibial plateau and downsizing of the tibial baseplate. This technique provides soft tissue balancing in the varus knee without interrupting the SMCL insertion on the tibia. The technique involves downsizing and lateralization of the tibial tray on the proximal tibia when acceptable ( Fig. 8-4 ). Excess proximal tibial bone around the periphery of the medial aspect of the tibial tray is then removed to effectively allow more excursion of the soft tissue sleeve. This may allow for a more normal soft tissue attachment to be preserved distal to the joint line. The final effect is one of releasing the contracted medial soft tissue sleeve along with relative medialization of the tibial tubercle, which may enhance patellar tracking.