Patella Revision/Reconstruction

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CHAPTER SYNOPSIS

There are various sources of patellar morbidity that may compromise total knee arthroplasty outcomes. A careful clinical evaluation of patients with patellofemoral symptoms is used to decide the best treatment option. In addressing the patella during revision total knee arthroplasty, the surgeon faces difficult decisions and technical challenges. Several reconstructive surgical techniques have been described for the patella in revision knee arthroplasty.

IMPORTANT POINTS:

1

Etiology of Patellar Morbidity
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  Previously unresurfaced patella
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  Wear
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  Maltracking
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  Loosening
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  Fracture
2

Clinical Evaluation
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  History
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  Physical examination
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  Radiographic imaging and laboratory studies
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  Intraoperative inspection
3

Treatment Options
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  Nonoperative treatment
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  Leave the patella unrevised
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  Revision with component reimplantation
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  Resection arthroplasty with patellar reconstruction
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  Fracture fixation
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  Salvage techniques
4

Surgical Techniques
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  Reimplantation of a polyethylene button
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  Resection arthroplasty with patelloplasty
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  Bone grafting procedures
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  Revision with a trabecular metal component
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  Patellectomy
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  Extensor mechanism allograft reconstruction
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  Fracture fixation
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  Partial patellectomy with extensor mechanism repair

CLINICAL/SURGICAL PEARLS:

1

The importance of a careful clinical evaluation cannot be overstated.
2

A clear source of patellar morbidity should be identified prior to proceeding with surgery in patients with isolated patellofemoral symptoms.
3

When at least 8 to 10 mm of bone stock remains after resection, reimplantation with a cemented polyethylene is the best option.
4

When less than 8 to 10 mm of bone stock remains after resection, the surgeon should consider from one of several other reconstructive options.
5

Periprosthetic patella fractures with a stable component, minimally displaced fracture, and intact extensor mechanism should be treated nonoperatively.

CLINICAL/SURGICAL PITFALLS:

1

Plain radiographs often fail to demonstrate sources of patellar morbidity and other imaging modalities should be pursued when there is high clinical suspicion.
2

For a well-appearing patellar component in the setting of tibiofemoral revision, patellar reconstruction should be considered if poor survivorship of the existing component is predicted and sufficient bone stock remains for reimplantation.
3

Reimplantation of a polyethylene component with less than 8 to 10 mm of residual bone stock is associated with a high risk of failure.
4

When scant to no bone stock remains, reconstruction with a trabecular metal component is associated with a high rate of failure.
5

Prior to the surgical treatment of periprosthetic patella fractures, patients should be warned of the high risks of complications and suboptimal outcomes.

VIDEO AVAILABLE:

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HISTORY/INTRODUCTION/SCOPE OF THE PROBLEM

The patella is a potential source of morbidity that may compromise total knee arthroplasty (TKA) outcomes, with the possibilities of component wear, loosening, periprosthetic fracture, avascular necrosis, patellofemoral instability, and other such problems. In addressing the patella during revision TKA, the surgeon faces difficult decisions and technical challenges. Optimizing the results of revision TKA requires maintenance of a well-fixed patellar component and a well-tracking patellofemoral joint, while avoiding complications in achieving these goals. This chapter will focus on the management of the patella in revision TKA. It will discuss the etiologies of patellar morbidity, preoperative clinical evaluation, nonoperative and operative treatment options, surgical reconstructive techniques, and treatment outcomes. It will also use the current literature to provide the reader with an organized approach that can be used to guide management of the patella in revision TKA.

ETIOLOGY OF PATELLAR MORBIDITY

Pain and dysfunction resulting from a failed TKA commonly, at least in part, stem from the patellofemoral articulation. Factors related to intraoperative technique, to component design and manufacturing, and to patient characteristics and activities can all contribute to the development of patellar problems. In order to identify the patella as a cause of pain and dysfunction, the surgeon must recognize sources of patellar morbidity when evaluating patients.

Although the role of patella resurfacing in primary TKA remains an area of controversy, several prospective, randomized studies have implicated the unresurfaced patella as a source of knee pain after primary TKA. Along with changes in patellofemoral biomechanics that take place with TKA, the prolonged effects of cartilage–metal contact leads to significant cartilage erosion with time. As such, an unresurfaced patella must be considered a potential source of knee pain after arthroplasty.

Prosthetic wear is another potential source of patellar morbidity. Several parameters influence the rate and pattern of wear of the patellar component. Factors that promote uniform contact forces minimize wear while those that cause contact loading lead to increased wear. Patellar and trochlear component geometries that conform to each other reduce prosthetic contact loading. Modern femoral components are designed with a concave-shaped femoral sulcus that conforms to the patellar component. Similarly, several patellar components have been designed with this conformity in mind. While central-domed patellar components eliminate the concern of rotational malalignment and the resulting patellofemoral asymmetry with the knee motion, the design is suboptimal with regards to congruency with the femoral component. The contact stresses that result from the mismatched geometries of central-domed patellar components and the trochlea of standard femoral components exceed the polyethylene strength, leading to “conforming” patterns of wear. Patellar components with concave peripheral lips have been designed to provide more patellofemoral congruity in an attempt to minimize contact loading and wear. Although these designs offer a more even distribution of compressive forces, they introduce concerns for rotational alignment and may also cause increased shear stresses at the interface of the prosthesis and bone with knee motion.

Patellofemoral maltracking caused by component malpositioning and extensor mechanism soft tissue imbalance may also cause a focalization of contact forces. Specifically, stresses are focused between the patellar component and the lateral aspect of the femoral component, resulting in an increased rate of polyethylene wear. Other component design and manufacturing features have also been associated with an increased rate of wear. Two prime examples include the metal-backed patellar component and sterilization with gamma irradiation in air.

While several patterns of patellar component wear have been observed, including scratching, delamination, and polishing, the means by which the entity causes patient symptoms are likely 2-fold. First, sufficient deterioration of the polyethylene may leave the overlaying patella uncovered, leading to osseous impingement on the femoral condyle. This effect is most likely to occur with thin patellar components subject to peripheral wear. Second, macroscopic and microscopic debris that is a byproduct of wear may lead to mechanical obstruction, osteolysis, synovitis, and local soft tissue reaction and attenuation. These processes lead to pain, mechanical symptoms, and dysfunction. It is important to note that most patients with patellar component wear remain asymptomatic.

As with the tibial and femoral components, loosening of the patellar component is another potential source of morbidity in TKA and can occur by several mechanisms. The reported incidence of patellar component loosening ranges from 1% to 3% but does not always cause symptoms. Patient factors that have been associated with the entity include weight, level of activity, and male sex. Periprosthetic fracture is the most obvious cause of patellar component loosening. Infection may cause compromise of the bone–prosthesis interface as part of the disease process or may lead to resection arthroplasty as part of the treatment. Osteolysis of the patella that results from a local inflammatory response to particulate debris typically occurs around the margin of the component or around the implant–bone or cement–bone interface, and can also result in component loosening.

Several technical factors and component features also influences the risk of patellar component loosening. Overresection of the patella, malpositioning of the patellar component, and poor cementation technique may compromise the initial fixation. Avascular necrosis, which may be related to lateral retinacular release or excessive soft tissue stripping, may cause periprosthetic fracture and fragmentation, compromising fixation strength and leading to prosthetic loosening. Patellar maltracking may cause increased forces on the bone-prosthesis interface, which may also compromise fixation. Early patellar component designs involved a large central lug, but concerns for risk of fracture with the use of this design prompted the use of smaller central lugs, which was found to provide inadequate fixation. Currently, three-pegged fixation is the most commonly used and most successful design. Metal-backed patellar components have been plagued with early failure related to component wear, fracture, and loosening. Design constraints on the thickness of the polyethylene lead to wear and delamination, causing osteolysis and loosening. With sufficient wear, the metal-backing of the component is exposed and articulates with the femoral component, creating metallic debris.

Patella fractures, another source of morbidity, are the most common type of periprosthetic fracture complicating TKA. Their etiology is usually multifactorial and related to trauma, intraoperative technical factors, component design factors, osteolysis, and avascular necrosis. Poor outcomes, including chronic pain, mechanical symptoms, stiffness, and extensor dysfunction, commonly result from fractures associated with component loosening and extensor mechanism disruption. In order to guide management, Ortiguera and Berry devised a classification for periprosthetic patella fractures based on extensor mechanism integrity, stability of component fixation, and bone stock ( Box 24-1 ).

Box 24-1

Type of Fracture	Description
I	Implant stable Extensor mechanism intact
II	Implant stable Extensor mechanism disrupted
IIIa	Implant loose Sufficient bone stock
IIIb	Implant loose Insufficient bone stock

Classification of Periprosthetic Patella Fractures

From Ortiguera CJ, Berry DJ: Patella fractures after total knee arthroplasty. J Bone Joint Surg Am 84:532–540, 2002.

CLINICAL EVALUATION

There are two situations that raise the possibility of patella revision or reconstruction as a treatment option in symptomatic patients with TKA. First, patients presenting with isolated anterior knee pain and with a negative workup related to the tibial and femoral components are evaluated to search for an identifiable cause of the patellofemoral symptoms. If such a source is identified, revision surgery is considered. Second, patients requiring a revision of the tibial and/or femoral component have their patella evaluated and appropriate actions may be taken if an intraoperative source of patellar morbidity is identified.

In revision TKA, establishing a firm preoperative diagnosis is essential for optimizing outcomes. In the absence of a clear etiology of patient symptoms, the chances of successful surgical interventions are limited. Often, a thorough history is the most important element of the evaluation. Information should be gathered from the preoperative, perioperative, and postoperative periods of the index procedure from the patients themselves and from all available records.

The diagnosis that led to the primary TKA as well as history of prior injury or surgery to the knee is collected. A history of deformity, instability, and stiffness prior to the index procedure is obtained and, when available, initial radiographs are reviewed. Obtaining the operative note describing the details of the index procedure is essential in order to determine the implant design and sizes, whether the patella was resurfaced, and whether soft tissue releases, including a lateral release, was required for balancing. Perioperative complications, including fracture, hematoma, persistent drainage, infection, thrombophlebitis, persistent swelling, and stiffness are noted. Procedures undertaken on the same knee after the index procedure, such as irrigation and debridement, fracture fixation, or manipulation under anesthesia, are documented.

Details of the postoperative symptoms are also important to gather. The patients are questioned regarding the location, quality, severity, and temporal nature of the symptoms, as well as alleviating and aggravating factors. If the patient did not experience pain relief from the index procedure, one must consider other anatomic origins, such as hip and lumbar spine pathology. Associated symptoms such as stiffness, instability, mechanical symptoms, and dysesthesias are identified. Patients are questioned regarding the temporal nature of the symptoms in order to distinguish those who had experienced an asymptomatic interval from those whose symptoms began immediately after the index procedure. Patients with an asymptomatic interval are more likely to suffer from diagnoses such as hematogenous infection or component loosening while those whose symptoms began at the time of the index procedure are more likely to suffer from diagnoses related to technical errors, such as instability or maltracking.

Physical examination proceeds in an organized manner. It is important to perform a general musculoskeletal examination, particularly of the spine and ipsilateral hip, in order to identify other sources of symptoms. The patient is asked to demonstrate ambulation and the lower limb alignment and gait pattern are observed. The skin is examined to identify signs of infection, reflex sympathetic dystrophy, peripheral neuropathy, and vascular disease. Active and passive range of motion is documented and associated pain, weakness, crepitus, and loss of motion are noted. Tibiofemoral stability is tested in the coronal and sagittal planes in 0, 30, and 90 degrees of flexion. The knee is carefully palpated for an effusion and to localize areas of tenderness.

A detailed examination of the patellofemoral joint can reveal important clues. The overall alignment of the limb is noted and compared to the contralateral side and the clinical Q angle is measured. The tracking of the patella is observed with full passive and active range of motion. Patellar apprehension with laterally directed pressure supports the diagnosis of patellofemoral maltracking or instability. Anterior grinding, squeaking, or popping with range of motion is consistent with a loose or damaged patellar component. Finally, the function of the extensor mechanism is evaluated and weakness, an extensor lag, or complete dysfunction is noted.

Imaging studies are also an important part of the clinical picture used in determining the etiology of patient symptoms. Weight-bearing plain radiographs should be compared to all available previous studies, and are used to assess for malalignment, wear, osteolysis, loosening, fracture, and extensor mechanism disruption. Scrutinizing the position of the limb at the time of imaging cannot be understated, as signs of pathology are often difficult to visualize. To that end, fluoroscopy is often a valuable tool for imaging the knee in multiple angles at one time in order to identify signs of pathology.

Evaluation of the patellofemoral joint with plain radiographs can be challenging. Berend et al. reported on radiographic features associated with patellar component loosening. In order of average chronological progression, these features included bone–cement radiolucency, increased bone density, trabecular collapse, fragmentation and fracture, and lateral subluxation of the patella on the component ( Fig. 24-1 ). When the patient presents with tibiofemoral failure, it is important to inspect the radiographs for these signs of patellar component failure. While the sunrise view often demonstrates signs of maltracking, component malrotation and malposition are often difficult to assess. Computed tomography is suggested to evaluate these factors when maltracking is suspected.