Management of Knee Instability: Use of Hinged Implants

CASE STUDY

A 77-year-old woman suffered a ground-level fall 9 months before presentation in which she sustained a comminuted left distal femur fracture. Before the fall, she was a community ambulator without an assistive device. She had no major ongoing medical problems. She underwent open reduction and internal fixation with a lateral locked plate soon after her injury. Weight bearing was protected postoperatively. Her pain persisted, and follow-up radiographs failed to demonstrate healing. The flexion and varus deformity increased over time as weight bearing was advanced. Failure of fixation was eventually ascertained, and referral to an arthroplasty surgeon was made. On initial examination, gross varus deformity was present, and the range of motion was limited to a few degrees because of pain. The lateral incision had healed well, and the findings on neurovascular examination were within normal limits. Radiographs were obtained, including a long standing view ( Fig. 19.1 , A to C ). Distal femur fracture nonunion with failure of fixation was diagnosed. Measurements of the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) level were obtained and were within normal range. Distal femoral replacement was performed (see Fig. 19.1 , D to F ).

$FIGURE 19.1, A 77-year-old woman who presented approximately 1 year after lateral locked plating for distal femur fracture ( A to C ) underwent distal femoral replacement ( D to F ).$

Algorithm

A total knee arthroplasty constraint algorithm is provided ( PCL , posterior cruciate ligament).

Chapter Preview

In cases of knee instability, in both the primary and the revision setting, hinged implants represent a reconstruction salvage option that preserves knee motion and function.
Indications include circumstances of global knee instability secondary to ligamentous incompetence, bony deficit or fracture, or severe flexion/extension gap mismatch.
Adequate exposure is the key to minimizing complications associated with implant removal and hinge implantation, to addressing ligamentous and bony deficiencies, and to appropriately balancing the final implant.
Correct component rotation is vital to patellar tracking; it is imperative to mark the tibia and femur intraoperatively during trialing to ensure appropriate rotation of final implants.
The fixation technique used—either full cementation or hybrid fixation with diaphyseal-engaging stems—must provide adequate fixation to prevent loosening.
Video: Preferred technique for rotating hinge implantation ( ).

Introduction

Revision total knee arthroplasty (TKA) is increasingly common as the number of primary TKAs performed annually increases. Minimally constrained or unlinked constrained conventional prostheses can be used for revision TKA in most patients. However, fully constrained hinged prostheses may be necessary in the presence of knee instability secondary to severe bone loss ( Fig. 19.2 ), ligament attenuation ( Fig. 19.3 ), severe flexion/extension gap mismatch ( Fig. 19.4 ), or distal femur fracture or nonunion ( Fig. 19.5 ). Additionally, hinged prostheses may be indicated in cases of primary arthroplasty complicated by severe deformity or contracture ( Fig. 19.6 ).

FIGURE 19.2, A and B , A 48-year-old man presented 6 years after a right knee revision that became infected, requiring staged reimplantation the same year. The knee had continued to be painful and exhibited an effusion and periodic drainage at the time of presentation ( A ). He underwent radical débridement with placement of an antibiotic spacer and subsequent reimplantation with a hinged proximal tibial–replacing device ( B ).

FIGURE 19.3, A 77-year-old woman who presented 20 years after primary total knee arthroplasty had pain and instability with objective evidence of medial collateral ligament deficiency.

FIGURE 19.4, A and B , A 58-year-old man presented after revision total knee arthroplasty with 25-degree flexion contracture and anteroposterior flexion instability. This combination is consistent with flexion/extension gap imbalance.

$FIGURE 19.5, A and B , A 63-year-old woman with mental retardation and developmental delay was referred 6 months after a fall with distal femur fracture malunion.$

FIGURE 19.6, A 57-year-old woman with human immunodeficiency virus (HIV) infection presented with bilateral knee pain that was worse on the left, a valgus deformity of approximately 30 degrees, and a flexion contracture of approximately 20 degrees ( A ). Staged, hinged primary knee replacement was performed bilaterally, beginning with the left side ( B ).

The early hinged prostheses, including the Stanmore, Walldius, Guepar, and Herbert devices, were initially implanted in the primary setting and were truly fixed hinges, allowing motion in only a single plane (flexion and extension) while not allowing varus or valgus tilt, axial rotation, or distraction. This resulted in the transmission of excessive force to the bone–cement interface and early failure of the prosthesis. The use of fixed hinge prostheses therefore fell out favor as rotating hinge designs were developed. Currently, there are limited indications for fixed hinge devices. Early clinical results for rotating hinge prostheses were disappointing and led to the development of unlinked, varus-valgus constrained components. Design changes to address sources of complication, including patellofemoral maltracking, have been incorporated into the most recent generation of rotating hinge prostheses in anticipation that they would become a valuable tool for the knee reconstruction surgeon in the management of instability.

Indications and Contraindications

The use of a hinged knee prosthesis is indicated in cases of severe knee instability. In the nononcologic setting, this may result from segmental bone loss secondary to infection, trauma, or osteolysis or from collateral ligament attenuation associated with multiple revisions or sepsis and radical débridement. Extreme imbalance of the flexion and extension gaps may also necessitate the use of a hinged prosthesis. If the flexion space is very wide, the tibia has a tendency to fall away from the femur and, although a constrained unlinked prosthesis may provide adequate varus-valgus stability, dislocation may occur. Additionally, patients with an extremely stiff knee encountered in both primary and revision situations may require stripping of the entire ligamentous complex from the distal femur to allow for correction of the deformity and adequate exposure, thus necessitating either a constrained condylar prosthesis or a rotating hinge.

Implantation of a hinged prosthesis is contraindicated in the circumstance of known infection in the involved knee or ipsilateral hip. Impending infection based on soft tissue compromise or poor capacity for wound healing is a relative contraindication. Staged or simultaneous plastic surgery procedures (e.g., soft tissue expansion, muscle transfers) may be indicated before proceeding with reconstruction. If inadequate bone stock is present for component fixation, as in the case of ipsilateral long-stemmed hip components, total femoral replacement including a hinged knee prosthesis should be considered.

Equipment

These complex cases require preoperative planning to ensure that prosthetic parts are available along with potentially necessary bone graft and metal augments. Recent weight-bearing anteroposterior, lateral, and Merchant radiographic views of the knee are necessary for preoperative planning and intraoperative reference. Hip-to-ankle views may also be helpful to plan the level of resection or if ipsilateral hardware or prostheses are present that may interfere with fixation.

Numerous prosthetic options exist. They may be broadly divided into two categories: (1) segmental replacement hinges that allow for replacement of large bone defects that have resulted in collateral ligament insufficiency ( Fig. 19.7 ) and (2) condylar-type resurfacing hinges that are designed for cases in which bone stock is adequate for use of a less constrained device but complete medial or lateral ligament incompetence, flexion/extension gap mismatch, or both necessitate the use of a hinged device. In general, a condylar-type resurfacing hinge is preferable because load is distributed through the condyles rather than principally through the hinge or axle.

FIGURE 19.7, A segmental distal femoral replacement hinge is shown after cementation of the femoral component ( A ) and after linkage to the tibial component ( B ).

Certain design features are important to the success of contemporary hinged devices and should be considered when selecting a prosthesis. These factors include side-specific femoral components with an anatomic trochlear groove to prevent patellar instability or maltracking and the ability to revise the hinge or bearing, parts that are more prone to failure. Availability of the full range of augments, prostheses, and stem options should be verified and familiarity with different body, stem, and extension segments should be gained preoperatively, because unanticipated scenarios may be encountered.

Additionally, equipment to remove prior implants should be available. This includes a thin-bladed oscillating saw, thin or flexible osteotomes, high-speed burs, small drills, an ultrasonic device designed for cement removal, and a component removal slap hammer. Also, component-specific screwdrivers should be available if stemmed components are being extracted in order to remove the tibial baseplate or condylar portion of the femoral component separate from the stem and gain access to metaphyseal cement, which can be a particular problem in the presence of offset femoral or tibial stems. A high-speed metal-cutting wheel may also be useful in the setting of well-fixed stemmed, cemented components. Antibiotic-impregnated cement should be used in these revision cases.

Surgical Techniques

The patient is positioned supine on a standard operating table. A well-padded, thigh-high, nonsterile tourniquet is placed. Before skin preparation and draping, all prior incisions are marked and the incision to be used is identified. Draping is completed with an impervious stockinette and extremity drape. The stockinette is incised and the knee exposed; an iodophor-impregnated adhesive drape is placed over the skin. A leg holder boot is placed and secured with Coban wrap, but a stabilizing plate that attaches to the table is not used. Before skin preparation, the lowest occluding pressure is ascertained and the tourniquet is pre-set to this level. An Ace wrap is used to exsanguinate the extremity, and the tourniquet is insufflated.

Step 1: Exposure

The incision is made with attention to excise any areas of skin compromise or hypertrophic scar formation. Any acceptable prior incision is incorporated in this incision, maximizing the skin bridge between the new incision and any prior incision. Ideally, the incision should pass over the medial third of the patella and extend distally to at least the level of the tubercle. In the revision setting, the incision often must be extended proximally and distally to gain adequate exposure. We do not favor a minimally invasive approach when implanting a hinged device and believe that the proximal extent of the incision should approach tissue not previously incised so that normal tissue planes can be identified and these layers propagated distally. This ensures maximal thickness of medial and lateral skin flaps and facilitates closure.

A medial parapatellar arthrotomy is made in the standard fashion. To facilitate exposure, a scalpel or electrocautery device is used to excise fibrotic scar from the suprapatellar region, to reestablish the medial and lateral gutters, and to remove remnants of the infrapatellar fat pad and peripatellar scar. Subperiosteal dissection is then carried medially around the proximal tibia to the posteromedial corner, elevating the fibers of the deep medial collateral ligament (MCL) from their tibial insertion. The tibia is incrementally externally rotated and the knee is flexed to deliver the tibia as the release is continued to include the insertion of the semimembranosus. At this point, exposure should be adequate without too much tension on the extensor mechanism for component removal. If it is not, extensile exposure techniques may be employed. We prefer a quadriceps snip as an initial maneuver. Usually, however, the underlying ligamentous laxity present in these patients precludes the need for use of these techniques.

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