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 ).
Chapter Preview
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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.
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Indications include circumstances of global knee instability secondary to ligamentous incompetence, bony deficit or fracture, or severe flexion/extension gap mismatch.
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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.
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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.
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The fixation technique used—either full cementation or hybrid fixation with diaphyseal-engaging stems—must provide adequate fixation to prevent loosening.
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Video: Preferred technique for rotating hinge implantation
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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 ).
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.
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.
Step 2: Prosthesis and Hardware Removal
Exposure of the bone–cement–implant interface is mandatory for successful removal of the implant with preservation of bone stock. All synovium and osteophytic overgrowth should be removed. Mason and Fehring have discussed the removal of well-fixed components in detail. We apply similar techniques and begin with the femur. When the device to be removed has been cemented, the prosthesis–cement interface should be violated using both a reciprocating saw and thin osteotomes. To minimize bone loss and the risk of condyle fracture, care should be taken to disrupt the interface not only anteriorly but also at the chamfers and posterior condyles. Firestone and Krackow proposed a technique using a Gigli saw that may be helpful in the case of uncemented components. A retrodriver and mallet are used to remove the femoral component once the interface has been disrupted.
Cemented all-polyethylene tibial components can be removed with the use of a reciprocating saw to violate the interface and sever the stem from the remainder of the component. Osteotomes and the high-speed burr can be used to remove the stem portion of the component. A reciprocating saw and osteotomes are used to disrupt the interface in the case of cemented metal-backed tibial components, which are ultimately removed with the use of a retrodriver and mallet. Cementless tibial components are dealt with in much the same way after screw removal.
Removal of stemmed tibial and femoral components requires similar work at the interface. If components cannot be removed easily once the interface is disrupted and force is applied with either a retrodriver and mallet or a backslap device—and especially in the case of offset femoral or tibial components—removal of the tibial baseplate or condylar portion of the femoral prosthesis may facilitate access to metaphyseal cement impeding stem removal. This removal may require the use of manufacturer-specific tools. Once access to the metaphyseal cement is obtained, disruption with flexible osteotomes and a high-speed burr or reciprocating saw may proceed. If removal is not achieved, an anterior femoral osteotomy or tibial tubercle osteotomy may be required for better access to the bone–cement–implant interface.
The patella does not always require revision. If revision is deemed necessary, all-polyethylene patellae may be removed with an oscillating saw used to disrupt the prosthesis–cement interface. The surgeon may proceed through the patellar pegs and later remove them with an osteotome or high-speed burr. Metal-backed, cementless patellae may be removed with the use of a thin osteotome at the interface.
If a lateral plate is present in the context of revision to constrained or hinged components, it can often be removed without making an additional lateral incision. If preservation of ligaments and revision with less-constrained components is planned, an additional lateral incision should be considered.
Step 3: Débridement of Bone and Soft Tissues
Once the components have been removed, the remaining polymethylmethacrylate and fibrinous material must be débrided. This may be accomplished with the use of hand tools, high-speed burrs, or ultrasound. Additionally, remaining periarticular scar tissue, especially in the posterior recess of the knee, should be thoroughly excised.
Step 4: Assessment of Bone Stock
Once débridement is complete, bone stock must be assessed. The first issue to address is whether bone stock is adequate for the use of a condylar-type resurfacing hinge or whether a segmental replacement hinge is required. If a resurfacing hinge is to be used, then the symmetry of bone loss on both the femoral and tibial sides should be assessed and the potential need for metal augmentation, cones, and bone graft addressed.
Step 5: Assessment of Ligamentous Competence
The status of the MCL and the lateral collateral ligament (LCL) must be determined, as well as the competence of the bone to which they are attached. The status of these ligaments and the function of the extensor mechanism should have been thoroughly evaluated preoperatively but must be redetermined at this point as a final decision regarding prosthetic selection is made.
Step 6: Implant Selection
The selection of the appropriate implant is based on the assessment of bone stock and ligamentous competence as indicated in the Algorithm. Bone stock deficiencies are dealt with by incorporation of stems, metallic augments, metaphyseal or diaphyseal cones, and bone graft, whereas ligamentous deficiency is handled with varying degrees of constraint. With an intact MCL and LCL, unconstrained components may be used except in the situation of severe flexion/extension gap imbalance. If balance cannot be obtained, a constrained device, and in certain cases a hinge, may be indicated. If the collateral ligaments are deficient, a linked or unlinked constrained device should be used, depending on the balance of the flexion and extension gaps. If significant imbalance is present, a linked device should be used. By using the Algorithm, the surgeon can correctly identify and properly reconstruct even the most complex bony and ligamentous deficiencies.
Step 7: Preparation of Bone Stock for Prosthesis Implantation
Preparation begins on the tibial side and proceeds to the femur and, finally, the patella. Tibial preparation, after implant removal and adequate débridement of cement and fibrinous tissue, continues by ensuring appropriate alignment of tibial resection ( Fig. 19.8 ). This should be perpendicular to the mechanical axis of the tibia with neutral slope. If it is not, an extramedullary tibial resection guide should be used to re-cut. Reaming of the canal to ascertain desired stem diameter and length should then be performed. The trial is placed after alignment and reaming are complete. Placement of the trial device will make it clear whether stem offset is needed. The trial should be modified until an appropriate fit is obtained. Attention is then turned to the femur. Reaming is first performed to ascertain stem diameter and length. A trial femur is then placed. Decisions regarding distal femoral, chamfer, or posterior condylar re-cuts, use of augments, and offset are made based on the fit of this trial. After appropriate fit is obtained, trial polyethylene is placed.
