Ligament balancing of a severely deformed knee is the essence of a successful total knee arthroplasty (TKA). Even in knees with minimal deformity, some ligament releases are necessary. Load transfer through a correctly aligned and balanced knee will optimize the longevity of the knee arthroplasty and minimize polyethylene wear.
In a knee with a fixed varus or valgus deformity, it often is necessary to surgically release the structures on the concave side of the knee to restore alignment and appropriate soft tissue tension. Satisfactory ligament release is achieved only when the ligaments are of relatively equal tension on the medial and lateral sides of the knee with the mechanical axis passing through the center or slightly lateral to the center of the knee. Once the ligaments are balanced adequately, the structures on the contracted side should be no tighter than the unreleased structures on the opposite side of the knee. The knee should open 2 to 3 mm when varus and valgus stresses are applied.
Varus knee deformity is far more frequent than valgus deformity. The soft tissue contractures with a fixed varus deformity often include static stabilizers and dynamic stabilizers. Static stabilizers are the ligamentous and fascial structures, and dynamic stabilizers are the semimembranosus and pes tendon group. As a rule, the dynamic stabilizers must be released to achieve a balanced knee. The musculotendonous structures are more compliant and usually do not require surgical release. Deep and superficial medial collateral ligament (MCL) releases have been necessary in more than 50% of TKAs done at my clinic for angular deformity.
At my institute, three methods of ligament releases are used for varus deformity: (1) stripping the soft tissue insertions from the medial side of the tibia; (2) selectively dividing the superficial and deep MCL at the joint line; and (3) releasing the collateral ligaments from the femur by doing an epicondylar osteotomy.
Soft Tissue Stripping
Historically, fixed varus deformity has been corrected by releasing the collateral ligaments and, in some instances, releasing the tendon attachments to the medial tibial flare. Medial collateral ligament stripping can be done before or after the bone resections made for the knee arthroplasty.
As part of the standard surgical exposure of the knee, the capsular attachments to the medial tibial flare are raised with a scalpel or cautery to the midcoronal line of the tibia. Additional ligament releases are indicated when the knee cannot be brought into correct alignment with equal tension in the soft tissue elements on both sides of the knee.
In varus knee posturing, the major contracted and deforming force is the superficial MCL. A periosteal elevator commonly is used to strip the superficial MCL from the tibia. This release requires ligament stripping distal to the pes anserine insertion, usually raising a periosteal sleeve to the diaphyseal region of the proximal tibia. For the medial capsular sleeve to be fully released in a subperiosteal manner, the stripping must extend distally and anteriorly on the medial side of the tibia. On most occasions, the release is not complete until the superficial MCL is detached completely from its tibial insertion.
Release of the pes anserine and semimembranosus tendons that insert on the medial tibial flare is optional with a conventional stripping for fixed varus deformity. The pes anserine tendons can be elevated when the medial sleeve is released. If it is contracted, the broad tendon sheath of the semimembranosus can be released without releasing the tendon from the tibia. However, preservation of these tendon insertions provides some dynamic rotational stability to the medial side of the knee. When preserved, these dynamic stabilizers relax and stretch with the restoration of physical activities after TKA.
In a severely deformed varus knee with a large flexion contracture, additional ligament stripping from the posteromedial flare of the tibia may be necessary. This stripping often includes releasing the posterior capsule from the top of the tibia and dividing the intermuscular septum along the medial ridge of the tibial shaft. In addition, the posterior capsule may need to be released from the back of the femur to allow full correction of a fixed flexion contracture.
One advantage of tibial stripping for varus deformity is that secondary scarring with periosteal healing will restore medial stability. In essence, a Grade 3 tear of the MCL is created in an area with excellent potential for secondary scar tissue formation. However, the soft tissue dissection is fairly extensive with this technique, potentially increasing the patient’s pain and swelling.
Joint Line Release
Dividing the superficial and deep MCL at the joint line is a simple alternative method for releasing the collateral ligaments on the medial side of the knee. It must be emphasized that the posterior oblique ligament and posteromedial joint capsule must be preserved to provide residual stability to the medial side of the knee. The division of the MCLs particularly is useful to treat moderate varus deformity.
In this method, bone resections are done first to allow access to and tensioning of the MCL. The release is done through the bed of the removed medial meniscus. The knee is placed in extension and a laminar spreader is inserted to tense the MCL. The tightest portion of the superficial MCL, usually the central third, is identified by digital palpation or by palpation with a blunt instrument. A cautery is used to divide only this tight band, directly dividing its fibers through the bed of the resected meniscus. The release is continued until tension on the laminar spreader is reduced and the deformity is corrected.
The posterior capsule and the posterior oblique ligament are not released with this technique. These structures preserve stability of the medial side of the knee. Tendon structures such as the semimembranosus also are preserved. The tissue reaction is minimal as compared with conventional MCL stripping because of the reduced tissue dissection with this technique.
If the release seems to be too extensive, the MCL can be repaired with ligament sutures.
Releasing the collateral ligaments from the femur by doing an epicondylar osteotomy particularly is useful in treating severe varus deformity with a fixed flexion contracture of the knee. Epicondylar osteotomy can be done either before or after bone resections. The MCL is not damaged with this procedure. Stability is restored when the epicondyle is reattached to the medial femoral condyle, often in a distal and somewhat posterior position from its original location.
The medial epicondylar osteotomy is done with the knee placed in 90° flexion. The osteotomy is done with a 1 1/4 inch osteotome directed in the long axis of the femur. A wafer of bone approximately 1 cm thick by 4 cm in diameter is separated from the condyle. The insertion of the adductor magnus tendon provides proximal stability to the osteotomized segment of bone while the knee is in extension. The knee is temporarily unstable in flexion on the medial side. To fully correct the flexion contracture, additional release of the posteromedial corner of the knee often is needed. This is accomplished by hinging the osteotomized fragment of bone posterior to the medial femoral condyle. A cautery or scalpel then is used to transect the contracted posteromedial joint capsule along its attachment to the distal femur.
The deep and superficial MCLs are not damaged with an epicondylar osteotomy. Stability in extension is maintained by the proximal to distal continuity of the collateral ligaments and the adductor magnus tendon. In some instances, the osteotomy alone is not adequate to fully relax a severe fixed varus deformity. In such cases, contracted portions of the MCL must be released distal to the osteotomized wafer of bone.
After implantation of total knee components, the epicondylar osteotomy is repaired. The epicondyle is reattached to the medial femoral condyle with #2 or heavier nonabsorbable sutures. The repair is done with the knee in 90° flexion to ensure proper placement of the osteotomized wafer of bone. Sutures are placed through the epicondyle and then beneath a bridge of metaphyseal cortical bone that represents the junction between the anterior femoral resection for the femoral component and the adjacent epicondylar ostoeotmy. A minimum of two, but preferably three, sutures are placed, and stability is tested by flexing and extending the knee. Suture repair of the epicondyle restores knee stability in flexion by preventing posterior displacement of the bone fragment and maintaining the femoral origin of the MCLs.
All three techniques for balancing the varus knee have proven successful. Ligament stripping done before or after bone resection works well as a medial release and is a technique familiar to most orthopaedic surgeons. The joint line release is simple and works exceptionally well for mild to moderate varus deformity. Bone resections must be done first to allow space for insertion of a laminar spreader. An epicondylar osteotomy is best for treating the most severe deformities. The epicondylar osteotomy also aids in the exposure of severely ankylosed knees and enhances access to the contracted posterior capsular structures in knees with major flexion contractures.
The Posterior Cruciate Ligament
The varus knee frequently presents with a contracture of the posterior cruciate ligament (PCL), and on rare occasions, even the popliteus tendon. Most commonly, a contracted PCL presents as increased femoral roll-back when the knee is examined with trial implants in place. When the PCL is balanced correctly and the knee is in 90° flexion, the femoral component should center over the tibial component in the sagittal plane. A femoral component that articulates with the posterior 1/3 of the tibial component is indicative of a contracted PCL. If the tibial component is not anchored to the tibia and the PCL is contracted, the front of a trial tibial component will lift off the resected tibia. Chmell and Scott refer to this means of assessing PCL balance as the “POLO” test, an acronym for “pull out, lift off.”
A contracted or tight PCL can be treated either by sacrificing the PCL and using a PCL-substituting implant, or by selectively balancing the PCL. There are three methods for balancing the PCL: (1) release the PCL from its insertion to the tibia; (2) release fibers of the PCL origin on the medial femoral condyle; or (3) osteotomize the tibial insertion with a V-shaped segment of bone from the back of the tibia. Capsular attachments in continuity with the osteotomized segment of bone preserve stability to the PCL. After release of a contracted PCL, the femur should center over the tibial component with the knee at 90° flexion.
THE VALGUS KNEE
The anatomy of the distal femur is altered in the valgus knee. The lateral femoral condyle is abnormally small, and therefore is considered dysplastic. Instead of the normal angular relationship of the distal femur relative to the femoral shaft (average, 9° valgus), the alignment of the condyles in a valgus knee is commonly 12° valgus to as much as 20° valgus to the anatomic axis of the femur. Instruments for TKA restore axial alignment to 6° distal femoral valgus by removing very little bone from the lateral femoral condyle and removing a relatively thick resection of bone from the medial condyle. Therefore, not only are lateral ligaments contracted and the medial ligaments stretched with valgus deformity, but these asymmetric bone resections to restore alignment further aggravate ligament imbalance.
Bone Resections: Valgus Knee
In the valgus knee, ligaments on the medial side (convex side) may be stretched but are intact. Because ligaments on the medial side will not be released, flexion and extension balance on the medial side must be achieved through balanced femoral bone cuts. The amount of bone removed from the end of the medial femoral condyle must be equal to the amount of bone removed from the back of this condyle. First, bone is removed distally from the medial condyle to restore correct axial alignment. The thickness of this resected bone is measured, and to achieve optimal ligament balance, an equal amount of bone then is resected from the posterior condyle. Preoperatively, the surgeon should template the medial femoral condyle on the lateral radiograph and plan a posterior femoral resection equal to the planned distal resection from the medial femoral condyle. Templating also will allow the surgeon to anticipate and plan for the variable amount of bone that must be removed to restore correct axial alignment of the knee.
When dealing with valgus knees, large resections of bone from the medial femoral condyle go together with small bone resections from the lateral femoral condyle to restore correct axial alignment. The extra thick piece of bone removed from the back of the medial femoral condyle and relatively small piece of bone from the back of the lateral femoral condyle create external rotation of the femoral component. This external rotation is beneficial to stability of the patellofemoral joint when correcting valgus knee deformity.
Lateral Ligament Releases
The major ligaments on the lateral side of the knee are the lateral collateral, arcuate, and fabellofibular ligaments. These ligaments all insert into the fibular head. Only the LCL and the popliteus tendon have their origin from the lateral femoral epicondyle. These two soft tissue structures exclusively provide lateral side knee stability in flexion. Therefore, knee instability in flexion is created if the LCL and the popliteus tendon are released. Whenever the LCL is released, the popliteus tendon must be preserved for flexion stability.
In most valgus knees, it is necessary to release the LCL and, in many instances, to also release the arcuate and fabellofibular ligaments. All three ligaments contribute to the fixed valgus deformity. Cases of mild to moderate valgus deformity may require release of only the LCL. In cases of more severe valgus, the three lateral ligaments and the iliotibial band all may require release. In all instances, the popliteus tendon should be preserved.
In the knee with severe valgus deformity, bone resections must be done first. With the knee in extension, a lamina spreader is inserted into the cavity made by the bone resections, and the most contracted ligament structures are identified. In most valgus knees, the LCL is the tightest structure. Under direct vision and under the tension created by the laminar spreader, the longitudinally oriented fibers are transected with either a cautery or scalpel at the joint line. After release of the LCL, the arcuate and/or fabellofibular ligament often is the next tightest structure. To release these ligaments, the inferior border of the popliteus tendon may need to be raised as the arcuate and fabellofibular ligaments cross the joint space behind the popliteus tendon. A lamina spreader is opened to tense these structures. The use of a cautery is the easiest way to divide the longitudinally oriented fibers. Working inferior to the tendon preserves the popliteus tendon.
The iliotibial band also may require release to achieve full correction of valgus knee deformity. The iliotibial band has an expansion from behind the biceps muscle to the lateral retinaculum, and it attaches directly to the lateral side of the femur through the lateral intermuscular septum. The iliotibial band is isolated by first dividing the intermuscular septum along the lateral border of the femur. By dividing the intermuscular septum, the expansion of the iliotibial band around the biceps muscle is evident. The iliotibial band is transected until it no longer contributes to the valgus knee deformity.
Femoral Rollback and Condylar Rotation
The PCL usually is not contracted in the valgus knee. However, when a large distal femoral resection from the medial femoral condyle is necessary to restore axial alignment, joint line elevation increases femoral rollback. In such knees, a PCL release or a PCL-substituting prosthesis should be selected.
Ligament releases and ligament balancing are unique aspects of joint replacement surgery. Comfort with these procedures comes only with experience and frequent exposure to difficult cases. Under no circumstances should total knee arthroplasties be done for knees with severe deformity by surgeons who lack the expertise and skill to achieve ligament balance in concert with correction of fixed deformity.
The correction of angular deformities with ligament releases is done variably by different surgeons with little scientific evidence to support any specific technique. The few scientific studies that have been done have either examined the influence on knees from cadavers without fixed deformity or reported the clinical outcome of TKA cases with correction of fixed deformities.
Knees from cadavers without deformity have been studied to establish the contribution of different structures in knee stability. 3–5 In these studies, selective ligament releases were done and stability was analyzed by evaluating the residual balance between the medial and lateral gaps after each release. Matsueda et al 4 reported that release of the anteromedial sleeve 8 cm from the medial joint line created the most significant increase in coronal angulation on the medial side. In reference to valgus deformity, Krakow and Mihalko 3 showed that early LCL release provided a more uniform release of the joint gap. In a study by Peters et al, 5 LCL sacrifice after popliteus tendon sacrifice produced marked lateral flexion and extension gap asymmetry.
Clinical outcome studies also examined the influence of ligament releases on the outcome of TKA. In one study, 473 arthroplasties were divided into six separate groups according to the degree of varus or valgus preoperative deformity. 2 Five of the six groups showed no difference in the mean Hospital for Special Surgery score. The exception was the group with preoperative deformity of 6° to 10° varus, which performed better than the group with a preoperative deformity of greater than 10° valgus. In another study of 231 valgus knees corrected with lateral ligament releases, no cases of clinical instability occurred, and joint stability did not deteriorate with time. 6
Chmell MJ, Scott RD: Balancing the posterior cruciate ligament during posterior cruciate retaining total knee arthroplasty: Description of the POLO test. J Orthop Tech 4:12–15, 1996.
2. Faris PM, Herbst SA, Ritter MA, Keating EM: The effect of preoperative knee deformity on the initial results of cruciate-retaining total knee arthroplasty. J Arthroplasty 7: 527–530, 1992.
3. Krackow KA, Mihalko WM: Flexion-extension joint gap changes after lateral structure release for valgus deformity correction in total knee arthroplasty: A cadaveric study. J Arthroplasty 14: 994–1004, 1999.
4. Matsueda M, Gengerke TR, Murphy M, Lew WD, Gustilo RB: Soft tissue release in total knee arthroplasty: Cadaver study using knees without deformities. Clin Orthop 366: 264–273, 1999.
5. Peters CL, Mohr RA, Bachus KN: Primary total knee arthroplasty in the valgus knee: Creating a balanced soft tissue envelope. J Arthroplasty 16: 721–729, 2001.
6. Whiteside LA: Selective ligament release in total knee arthroplasty of the knee in valgus. Clin Orthop 367: 130–140, 1999.