A 57-year-old man with a medical history of hypertension and hyperlipidemia presented to our clinic for consultation. He had undergone right total knee arthroplasty 3 years earlier at another institution. He has developed progressive anterior knee pain and crepitus, which has limited his ambulatory capacity. He denies having had fever, chills, or wound problems. He is able to perform a straight leg raise, although with pain.
Radiographs taken in the clinic demonstrated patellar osteolysis and radiolucencies surrounding the femoral and tibial components ( Fig. 25.1 ). Test results for serum inflammatory markers were negative. At the time of revision surgery, after removal of the polyethylene patellar button and surrounding membrane, the residual shell of bone was too thin to accept a standard cemented patellar component ( Fig. 25.2 ).
Algorithm
Management of a failed patellar component follows the tenets of revision total knee arthroplasty. Care must be taken to evaluate the cause of failure, the integrity of the patellar prosthesis and extensor mechanism, and the alignment and orientation of the femoral and tibial components. Periprosthetic infection should be ruled out, and host factors should be optimized. Findings of the intraoperative assessment of the patellar host bone bed guide the choice of surgical options. The algorithm presents an approach to the patient with a failed patellar component that requires revision arthroplasty; nonoperative options are not discussed.
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Chapter Synopsis
Management of patella bone loss during revision total knee arthroplasty (TKA) can pose significant challenges. Treatment options depend on the integrity of the extensor mechanism and the quantity and vascularity of remnant host bone. This chapter describes a case of patella bone loss managed with a porous metal patellar component.
Important Points
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Proper femoral and tibial component rotation is crucial for patellar component tracking and successful patella reconstruction.
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Viable and vascular host bone is critical for bone ingrowth and reconstruction using a porous tantalum (PT) or trabecular metal patellar component.
Clinical/Surgical Pearls
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Before patellar reconstruction, attention must be paid to proper femoral and tibial component positioning.
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The extensor mechanism must be inspected for continuity and disruptions.
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When using PT patellar components, a high-speed bur or hemispherical reamers can be used to prepare the patellar surface before implantation. The tourniquet should be deflated to confirm the presence of bleeding and viable host bone before implantation.
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At least 50% contact with host bone is needed to accept the PT implant.
Clinical/Surgical Pitfalls
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PT patellar components cannot reliably integrate with soft tissue alone.
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These components cannot bridge a fragmented patella at the time of revision TKA.
Introduction
Revision TKA may be complicated by severe patella bone loss that can preclude the use of standard cemented patellar components. Traditional approaches to the management of severe patella bone loss include patelloplasty of the remnant bony shell, patellar bone grafting, and partial or complete patellectomy.
Although patelloplasty and patellectomy are acceptable treatment options in the setting of severe bone loss, both result in inferior functional outcomes when compared with revision TKA and resurfacing of the patella. Other techniques include patellar bone grafting procedures that restore a more normal quadriceps moment arm and improve patellar bone stock and the gull-wing osteotomy. Despite these advances in surgical technique, several studies have highlighted the continued challenges of addressing the deficient patella.
Porous tantalum (PT) patellar components have been designed to allow patellar resurfacing in the setting of severe patella bone loss. The use of trabecular metal across all aspects of revision and primary arthroplasty procedures has grown in popularity and utility. Short- and medium-term results after patellar resurfacing using a trabecular metal patellar component during revision TKA in patients with marked patella bone loss have been reported. Although this technique may not be appropriate in all cases of severe patella bone loss, porous trabecular metal patellar components can be used when there is remnant viable host bone precluding the use of traditional onlay or inset patellar components. In this chapter, we present a case study in the use of a PT patellar component and a review of the indications, techniques, pearls, and pitfalls of this technique.
Indications and Contraindications
Indications for the use of a PT patellar component are a patella with residual thickness less than 10 mm in the thickest segment, with at least 50% of the dorsal cortex intact, and without a sufficient rim to contain a biconvex inset patellar component. The remaining host bone must be viable and vascular. This can be checked by débriding the remnant bone using a high-speed bur and assessing the vascularity of the remnant host bone by deflating the tourniquet and looking for punctate bleeding in the host bone.
PT patellar components are contraindicated when the remnant bone is avascular, fragmented ( Fig. 25.3 ), or insufficient (<50%) to provide enough bone–prosthesis contact. These components should not be sutured directly to the extensor mechanism.
Equipment
The equipment needed for patellar preparation includes the following items:
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High-speed bur
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Implant-specific hemispherical reamers (Zimmer, Warsaw, Ind.)
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1.6- to 2.0-mm drill
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Heavy no. 2 or no. 5 nonabsorbable Ethibond suture (Ethicon, Somerville, NJ)
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Keith needles (traditional Hewson suture passers do not reliably fit through implant suture holes)
Surgical Techniques
The knee is approached through a standard medial parapatellar approach. The femoral and tibial components are addressed as needed, with careful attention to component rotation. The rotation of the tibial base plate should be set at the junction of the middle and medial thirds of the tibial tubercle, and the femoral component rotation should be set parallel to the transepicondylar axis of the femur. Careful attention should be paid to restoration of the joint line. The femoral component should be positioned between 20 and 24 mm from the femoral epicondyles. Failure to restore the joint line and appropriate rotation results in patellar maltracking and increased stress on the extensor mechanism.
The old patellar component is removed. The extensor mechanism and the remnant host bone are carefully inspected, and all options for reconstruction should be considered. A PT patellar component may be used when the remaining bone is vascular, the residual thickness is less than 10 mm (precluding the use of traditional components), and there is sufficient intact dorsal cortex (≥50%) to provide adequate surface for support and bone ingrowth.
The steps for patellar preparation to accept a PT patellar component are as follows:
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Patellar thickness is assessed with the use of a caliper.
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Using a high-speed bur, the host bone is thoroughly débrided, and all cement or membranous debris is removed (see Fig. 25.2 ).
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The remnant bony shell is reamed using implant-specific, appropriate-diameter hemispherical reamers (Zimmer, Warsaw, Ind.) selected according to the anticipated host bone base ( Fig. 25.4 ).
FIGURE 25.4
Patellar surface after spherical reaming and preparation of the host bone bed for trabecular metal implant placement.
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Trial reductions are used with the goal of restoring normal patellar thickness (26 mm for men and 23 mm for women).
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The PT patellar component is secured to host bone Using heavy no. 2 or no. 5 nonabsorbable sutures ( Fig. 25.5 ). A drill and a suture passer or Keith needle is used to pass the sutures through bone. The sutures may be passed directly without drilling if the host bone is thin enough.
FIGURE 25.5
Intraoperative image after securing the porous tantalum patellar component to the host bone with a heavy suture.
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Sutures are tied down with knots on the dorsal surface of the patella; alternating the suturing on opposite sides of the implant may ensure adequate balancing. A patellar clamp may be used during the suturing stage.
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Intraoperative fluoroscopy may be used to verify the position of the trabecular metal implant.
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A provisional button may be used to assess a trial reduction.
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A standard three-pegged, all-polyethylene button is cemented to the trabecular metal shell to provide an articulation against the femoral trochlear component. Doughy bone cement is applied to the base and polyethylene button postholes and to cover the entire suture ring. Filling the space between the polyethylene button and the suture ring protects the sutures. The patellar clamp may be removed after the cement hardens.
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Patellar tracking is evaluated to ensure central tracking throughout the range of motion.
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The arthrotomy and superficial tissues are closed in standard fashion.
Complications
Septic and aseptic loosening can occur after any surgical procedure. Maltracking and patella instability can occur in the setting of femoral or tibial component malrotation. Failure of bone ingrowth can result in loosening ( Fig. 25.6 ) and, in some cases, erosion through the extensor mechanism. Failure to restore the joint line and appropriate component rotation results in patellar maltracking and increased stress on the extensor mechanism. Figure 25.7 shows a referred case of component compromise and malposition and a failed attempt at patella reconstruction; both issues must be addressed at the time of revision arthroplasty.
Outcomes
Our institution’s experience with PT patellar implants demonstrates that with sufficient host bone contact, these components represent a viable revision option at midterm follow-up. Nevertheless, the trabecular metal patella technique is but one of many options in the revision setting, and as for all techniques, indications and proper patient selection are essential for good outcomes. At a mean follow-up of 92 months, these components remained functional in nineteen (83%) of twenty-three patients; four patients underwent revision surgery. Evidence of radiographic fixation was seen as early as 3 months. Clinically, the mean Knee Society score was 82.7 points for pain, and the average Oxford Knee Score was 32.6 points. Although these clinical ratings systems do not directly reflect the success or failure of the implants, at last follow-up, 15 (65%) of the patients reported no or only mild anterior knee pain, five had moderate pain, and three had severe anterior knee pain. At midterm follow-up, the trabecular metal patellar components provided satisfactory function and reliable fixation in cases of severe patella bone loss precluding the use of traditional patellar components. An asymptomatic, ingrown PT patellar component in the patient described in the case study (part of the previously described cohort at our institution) is shown in Figure 25.8 .
