P ITFALLS

• If soft tissue imbalance is due to disruption of a collateral ligament, then additional release of the opposite collateral soft tissue constraints will further increase instability. Collateral ligament disruption requires repair or reconstruction and use of an implant that is constrained to varus and valgus stress.

   

• Mediolateral soft tissue imbalance or collateral ligament disruption may not be readily apparent during varus and valgus stress testing. In extension, the hamstring tendons and posterior capsule are tight, which provides stability during varus and valgus stress. Stress testing that is done in slight flexion (approximately 30°) reduces posterior soft tissue tension and permits an accurate assessment of collateral ligament support.

Soft Tissue Balancing in Revision TKA

Indications

• Removal of periarticular scar tissue is a routine part of the exposure for most revision total knee arthroplasties (TKAs). However, release of contracted medial or lateral collateral ligaments may be necessary for management of fixed varus or valgus deformity, and release or resection of contracted posterior capsular soft tissue is required to correct flexion contracture.

• Occasionally collateral ligament reconstruction or advancement may be necessary to provide adequate ligament soft tissue support.

  Examination/Imaging

• The preoperative knee exam and radiographs are important to determine if any fixed soft tissue contracture or collateral ligament instability is present.

  Controversies

  • Valgus deformity may be treated with lateral soft tissue release and an implant that is not constrained to varus and valgus stress. However, correction of valgus deformity is also associated with risk of peroneal nerve injury as a result of posterior and lateral soft tissue lengthening. Alternatively, vagus deformity can be treated with use of a fully constrained implant without soft tissue release in order to minimize the risk of nerve injury.

   

• Passive range of motion should demonstrate any fixed flexion contracture, which will require posterior soft tissue release. Limited flexion is consistent with contracture of the extensor mechanism and may require extensile exposure (tibial tubercle osteotomy or rectus snip) to adequately mobilize the extensor mechanism during revision TKA.

• Varus and valgus stress testing should be done in full extension, 30° of flexion, and 90° of flexion to fully assess collateral ligament integrity and mediolateral soft tissue balance.

• Varus and valgus stress radiographs may be helpful to differentiate instability due to soft tissue laxity from that due to implant loosening and to determine if there is collateral ligament disruption.

  • The valgus stress radiograph in Figure 1A shows complete medial collateral ligament (MCL) disruption. A varus stress radiograph of the same knee (Fig. 1B) demonstrates an intact lateral collateral ligament (LCL).

  • The varus stress radiograph in Figure 2A shows a lax attenuated LCL, whereas the corresponding valgus stress radiograph (Fig. 2B) shows an intact MCL. The varus-valgus soft tissue imbalance can be expected to require MCL release to provide symmetric MCL and LCL tension.

     

     

     

     

     

     

     

     

    Soft Tissue Balancing in Revision TKA

     

     

     

     

     

     

    265

     

    A

    FIGURE 1

     

    B

     

    A

    FIGURE 2

     

    B

     

     

    266

     

    Treatment Options

    • Fixed flexion contracture can be treated with posterior soft tissue release, removal of more bone from the distal femur, or both.

    • Varus or valgus soft tissue imbalance with an attenuated but intact MCL or LCL can be treated with either release of the contracted soft tissue on the opposite side of the joint to balance collateral soft tissue

      tension or, alternatively, use of a constrained implant without soft tissue balancing.

    • Complete loss of collateral ligament support can be treated with use of a constrained implant, ligament reconstruction, or both.

     

    Soft Tissue Balancing in Revision TKA

     

    Surgical Anatomy

• The posterior soft tissues that may require release for treatment of flexion contracture include the posterior synovium and capsule, posterior cruciate ligament (PCL), popliteus tendon, and medial and lateral gastrocnemius tendons.

• The popliteal artery, nerve, and vein are at risk during posterior dissection.

  • These structures are grouped together in the midline posterior to the PCL. In Figure 3, an arteriogram showing occlusion of the popliteal artery demonstrates the midline location of the neurovascular structures posterior to a TKA.

  • During primary TKA, the PCL is easily visualized in the midline of the posterior compartment of the knee. Figure 4 shows an intraoperative view of the flexion space in a primary TKA. A laminar spreader distracts the medial compartment. The popliteal artery, vein, and nerve lie deep to the PCL (Fig. 4, arrow) in the midline of the posterior compartment.

  • In a revision TKA, the anatomy is distorted; the PCL is frequently absent and a synovial layer of variable thickness may be adherent to the posterior capsule. In the intraoperative view of the flexion space in a revision TKA seen in Figure 5, cystic defects are present in the distal femur from osteolysis, the PCL is not present, and the posterior synovium is discolored and thickened.

• Medial soft tissue constraints include the superficial and deep MCL, medial capsule, semitendinosus tendon, and pes anserinus tendon.

  • The medial capsule and deep MCL insert on the tibia at or slightly distal to the joint line and are elevated as part of the surgical exposure of the knee.

  • The superficial MCL provides the primary restraint to varus stress and has a broad insertion on the proximal tibia distal to the joint line.

• Lateral soft tissue constraints include the fibular collateral ligament, posterolateral capsule, popliteus tendon, iliotibial band, and biceps tendon. The peroneal nerve lies posterior to the biceps tendon and crosses laterally over the fibular head. It is at risk by direct trauma during surgical dissection of the lateral soft tissue structures or by stretching from correction of fixed valgus deformity.

   

   

   

   

   

  Soft Tissue Balancing in Revision TKA

   

   

   

   

   

   

  267

   

  FIGURE 3

   

  FIGURE 4

   

  FIGURE 5

   

   

   

  P EARLS

  • A leg holder device maintains the knee in a flexed position without the need for an assistant to hold the lower leg.

     

    P ITFALLS

  • Particularly for large patients, the lower extremity may externally rotate when the patient is positioned supine. A sandbag or bolster can be placed under the ipsilateral hip to minimize external rotation of the lower leg. However, elevation of the ipsilateral pelvis also medializes the anterior superior iliac spine, which may make assessment of limb alignment more difficult.

   

  Soft Tissue Balancing in Revision TKA

   

  Positioning

• The patient is positioned supine with a tourniquet applied on the thigh as proximal as possible.

• The knee is positioned in varying amounts of flexion during surgery.

  Portals/Exposures

• The knee is exposed using a medial parapatellar arthrotomy, and retropatellar adhesions are released.

• If patellar ligament avulsion from the tibial tubercle may occur, the exposure should be extended distally with a tibial tubercle osteotomy or proximally with

  a rectus snip or V-Y turndown of the quadriceps tendon.

• A long tibial tubercle osteotomy provides wide exposure and permits patellar eversion (Fig. 7).

   

   

   

  268

   

   

   

  Equipment

  • A number of leg positioning devices are commercially available that consist of a foot holder that is attached to the leg, and a plate that is attached to the operating room table to secure the foot holder, as seen with the Alvarado (Zimmer, Warsaw, IN) leg holder (Fig. 6).

   

  FIGURE 6

   

   

  FIGURE 7

   

   

   

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  Soft Tissue Balancing in Revision TKA

   

  FIGURE 8

   

   

  P EARLS

  • A lateral retinacular release may further mobilize the extensor mechanism. The medial proximal tibia is dissected in a subperiosteal fashion to facilitate tibial external rotation and lateral patellar subluxation or eversion.

     

  • Placing a pin or staple in the tibial tubercle can protect the patellar ligament from avulsion during lateral patellar retraction.

     

    P ITFALLS

  • If a tibial tubercle osteotomy is performed, the osteotomy length should be adequate to permit reattachment of the bone with wires or screws (see Fig. 7).

     

  • The anterior compartment muscles (Fig. 8, between arrows) should remain attached to the osteotomized bone fragment to maintain vascularity and provide a distal soft tissue tether to resist proximal migration of the bone.

   

   

  Instrumentation

  • Tibial tubercle osteotomy can be performed with an oscillating saw or sharp osteotome. A thin saw blade should be used to minimize bone loss when making the osteotomy.

   

   

  Controversies

  • If extensile exposure is needed, distal extension using a tibial tubercle osteotomy provides wider exposure than proximal transection of the rectus tendon. However, osteotomy nonunion or pain from retained hardware can occur after tibial tubercle osteotomy.

  • Complications from a rectus snip are rare. However, V-Y turndown of the extensor mechanism devascularizes the rectus tendon, which may result in quadriceps weakness and extensor lag.

   

  Soft Tissue Balancing in Revision TKA

   

  Procedure

  Step 1: Posterior Soft Tissue Release

• Posterior soft tissue release is performed with the knee in flexion.

• A laminar spreader (Smith and Nephew, Memphis, TN) is placed in either the medial or lateral compartment to distract the femur and tibia (Fig. 9). The synovium and posterior capsule in the medial compartment are then débrided (Fig. 10).

• The PCL, if present, is resected (Fig. 11).

• The posterior capsule and gastrocnemius tendons can be elevated from the femur using a curved osteotome (Fig. 12).

• After posterior release, the size of the flexion space is increased (Fig. 13).

   

   

   

   

  270

   

   

  P EARLS

  • A broad laminar spreader is helpful to distribute the distraction force over a large area of bone and minimize damage to the posterior femur and proximal tibia.

     

  • Use of a clamp to grasp and pull the synovium and capsule anteriorly permits posterior soft tissue débridement.

     

    P EARLS

  • The popliteal artery, nerve, and vein are at risk during posterior soft tissue release.

   

  Controversies

  • Flexion contracture may be treated with posterior soft tissue release or removal of bone from the distal femur or both. Posterior soft tissue release is associated with a risk of injury to the neurovascular structures. Removal of bone from the distal femur is associated with joint line elevation, which can result in patella infra. However, for severe flexion contractures, both soft tissue release and distal femoral resection are usually required.

   

  FIGURE 9

   

   

   

  FIGURE 10

   

   

   

   

   

  Soft Tissue Balancing in Revision TKA

   

   

   

   

   

   

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  FIGURE 11

   

  FIGURE 12

   

  FIGURE 13

   

   

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  Soft Tissue Balancing in Revision TKA

   

  Step 2: Medial Soft Tissue Release

• The medial soft tissue release consists of a sequential subperiosteal dissection of the medial soft tissue sleeve from the proximal tibia.

  • The MCL is released by subperiosteal dissection with an electrocautery, an elevator, or an osteotome, or by sharp dissection of the soft tissue from the proximal tibia.

  • The dissection is continued distally (Fig. 14A, lower arrow, and Fig. 14B) as necessary to correct varus and posteriorly (see Fig. 14A, upper arrow, and Fig. 14C) to correct combined flexion and varus deformity.

• The medial soft tissue sleeve is maintained in continuity with the tibial periosteum. The soft tissue is elevated but not detached from the tibia.

• Gradually thicker tibial trial inserts are used with the trial revision components, which stretches the medial soft tissue sleeve until the tension in the lateral and medial soft tissues is equal.

A B

C FIGURE 14

273

P EARLS

• Distal release lengthens the MCL and corrects fixed varus deformity, while posteromedial release of the semitendinosus corrects combined varus and flexion contracture.

   

  P ITFALLS

• Release of the pes anserinus tendon insertion is rarely necessary and may result in instability if the soft tissue sleeve is detached from the periosteum.

   

• If mediolateral soft tissue balance is determined by assessing the size of the medial and lateral soft tissue gaps with a distraction device in place, the gaps may be affected by asymmetric bone loss of either the medial or lateral femur or tibia.

Soft Tissue Balancing in Revision TKA

Step 3: Lateral Soft Tissue Release

• Lateral soft tissue release is performed either as a sequential subperiosteal dissection of discrete soft tissue constraints or with a pie-crusting technique of tight soft tissues.

• Sequential release is performed after stress testing to determine which soft tissues are tight in extension, flexion, or both.

  • If the lateral soft tissues are tight in extension, the iliotibial band or posterior capsule is released.

  • If the lateral soft tissues are tight in flexion, the fibular collateral ligament or popliteus tendon is released.

• A pie-crusting release is performed with use of a laminar spreader to distract the joint surfaces. Tight lateral structures are identified by palpation and released with a series of transverse stab incisions into portions of the tethering lateral soft tissues.

• A transverse stab incision is made in the tight lateral soft tissues at the level of the tibial surface after initial distraction (Fig. 15A).

• The laminar spreader is then further distracted to gradually lengthen the lateral tissues and multiple stab incisions are made (Fig. 15B).

Instrumentation/ Implantation

• Mediolateral soft tissue balance should be assessed by varus and valgus stress testing with trial or final components in place and an unconstrained tibial insert.

Controversies

• Release may be performed using a sequential subperiosteal dissection of medial soft tissues or with a “pie-crusting” technique. However, medial pie-crusting can result in over-release and is usually performed on the lateral side to correct valgus deformity.

A B

FIGURE 15

P EARLS

• With either technique, the release should be performed gradually and tension in the soft tissues assessed at each stage of the release by varus and valgus stress testing with the trial components in place or using a distraction device, to avoid

  over-release.

   

  P ITFALLS

• If the sequential subperiosteal release technique is used, either the fibular collateral ligament or popliteus tendon can be released, but if both are released, lateral instability may occur.

   

• If the pie-crusting technique is used, the fibular head should be palpated to identify the peroneal nerve and avoid risk of direct trauma during the release.

   

• Correction of severe valgus deformity or combined flexion and valgus deformity can result in lengthening the lateral soft tissues, including the peroneal nerve, and result in nerve palsy.

274

Instrumentation/ Implantation

• Mediolateral soft tissue balance should be assessed by varus and valgus stress testing with trial or final components in place and an unconstrained tibial insert.

Soft Tissue Balancing in Revision TKA

Step 4: Ligament Reconstruction

• Reconstruction of an attenuated or disrupted ligament requires distal advancement or proximal recession with reattachment to bone or soft tissue.

  • In Figure 16A, an intraoperative view of a failed TKA during valgus stress testing demonstrates a deficient MCL.

    Controversies

    • In order to avoid lengthening the lateral soft tissues and minimize the risk of peroneal nerve injury, a constrained implant may be used without lateral soft tissue release. However, the constrained implant is associated with greater implant-bone interface stresses and risk of loosening, so this method appears most appropriate for elderly or less active patients.

     

  • The MCL is dissected and remains attached proximally to the femur, but the distal attachment to the tibia is disrupted (Fig. 16B).

  • Krackow sutures are placed in the distal portion of the MCL (Fig. 16C).

  • The MCL is advanced distally and sutured to the deep portion of the medial retinaculum (Fig. 16D). A constrained implant is used to protect the repair during healing.

• The reconstruction should be augmented with autogenous or allograft soft tissue.

   

   

   

  P EARLS

  • A Krackow suture is helpful to gain adequate soft tissue fixation.

     

  • The ligament sutures can be attached to surrounding soft tissue that is fixed to bone, bone anchors, or a screw.

     

  • The stability of the repair should be checked through the entire range of knee motion to ensure the integrity of the reconstruction.

   

   

   

   

   

   

  Soft Tissue Balancing in Revision TKA

   

   

   

   

   

   

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  A

   

  B

   

  C

  FIGURE 16

   

  D

   

   

   

  P ITFALLS

  • Ligament reconstruction may stretch out over time and compromise the stability of the revision TKA. A constrained implant will protect the repair, and, if future revision TKA is necessary, a less constrained implant may be used once the ligament reconstruction has healed.

     

  • A collateral ligament that was intact preoperatively and is lacerated or avulsed during surgery can be repaired primarily and a nonconstrained implant used. The repair should be protected with use of a hinged knee brace postoperatively.

  Instrumentation/ Implantation

  • Ligament reconstruction should be augmented with autogenous soft tissue such as semitendinosus or fascia lata, or with allograft (Achilles tendon).

   

   

   

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  Controversies

  • Mediolateral soft tissue imbalance with an attenuated but not disrupted collateral ligament can be treated either by release of the opposite tight collateral ligament, advancement of the loose ligament, or use of a constrained implant. However, advancement of a loose ligament is associated with risk of ligament disruption postoperatively and requires adequate soft tissue to repair, secure fixation of the reconstructed ligament, and a relatively nonobese limb that can be effectively braced postoperatively to protect the reconstruction.

   

  Soft Tissue Balancing in Revision TKA

   

• Use of a constrained implant is appropriate to protect the reconstruction from stresses during healing.

  Postoperative Care and Expected Outcomes

• Postoperative care after revision TKA with soft tissue balancing is similar to that for primary TKA.

• If flexion contracture was present preoperatively and posterior soft tissue release was required, flexion contracture may recur after surgery due to shortening of the hamstrings.

P EARLS

• Use of dynamic splinting for 1–2 hours twice daily can be helpful to minimize the development of postoperative flexion contracture.

   

  P ITFALLS

• Patients with poor pain control and limited preoperative mobility can experience recurrent stiffness. Early manipulation should be considered in this patient population to achieve adequate motion.