Periprosthetic patella fractures are a rare complication after primary total knee arthroplasty. The cause is multifactorial and may include trauma, osteonecrosis of the patella, excessive patellar bone resection, component malalignment, lateral retinacular release, press-fit patellar implants, osteolysis, and osteoporosis. Periprosthetic patella fractures are usually classified based on the nature of the fracture, stability of the patellar implant, integrity of the extensor mechanism, and remaining bone stock. Fractures with minimal displacement, an intact extensor mechanism, and a stable patellar component are best treated nonsurgically. Surgical treatment should be reserved for fractures with extensor mechanism disruption and patellar component loosening because of high complication rates and poor results associated with surgical treatment in these cases.
Surgical Pearls and Pitfalls
Proper classification of the fracture is important in determining the method of treatment.
Careful release of associated scar tissue, lateral retinacular release, quadriceps snip, or more extensile exposures may be necessary to gain adequate exposure.
Adequate patellar thickness should be maintained if a revision of the patellar component is considered to prevent recurrent fracture.
Robust repair of the extensor mechanism and the retinaculum after partial or total patellectomy is important in preventing extensor lag.
The need for complex procedures such as allograft reconstruction of the extensor mechanism, patellar bone reconstruction with bone graft, or the use of trabecular metal components should be identified and planned preoperatively.
A normal patellofemoral joint is essential for a well-functioning total knee arthroplasty (TKA). Patella fractures are uncommon overall, with a prevalence reported between 0.12% and 21% in resurfaced patellae and 0.05% in unresurfaced patellae; however, they are the most common periprosthetic TKA fracture. Periprosthetic patella fractures occur both intraoperatively and postoperatively but are significantly more common postoperatively and after revision arthroplasty. Improvements in surgical technique and implant design and a better understanding of knee biomechanics and implant alignment have contributed to an overall decrease in this complication.
Several factors may contribute to the etiology of periprosthetic patella fractures. Traumatic causes can be direct, such as a fall onto the knee, or indirect, secondary to an eccentric contraction of the quadriceps muscle. Many atraumatic causes, including osteonecrosis of the patella, excessive patellar bone resection, component malalignment, lateral retinacular release, press-fit patellar implants, osteolysis, osteoporosis, and thermal necrosis from cement polymerization, have been cited as predisposing to these fractures.
Periprosthetic patella fractures are usually classified based on a scheme that includes location or nature of the fracture, stability of the patellar implant (if present), and integrity of the extensor mechanism. Treatment options span a range from nonoperative observation to patellectomy with various alternatives between those extremes. Results with operative management are often discouraging for both patient and surgeon, and some loss of function appears common. As a result, decision making to optimize the outcome can be difficult.
Indications and Contraindications
Periprosthetic patella fractures may manifest with pain, effusion, extensor mechanism weakness, and episodes of instability. However, a significant percentage of these fractures are asymptomatic and are discovered only on follow-up radiographs. Ortiguera and Berry reported that 44% of their observed fractures were asymptomatic or minimally symptomatic at the time of diagnosis. Tria and colleagues found that 80% of the periprosthetic patella fractures in their patients were asymptomatic.
Treatment considerations for these fractures are primarily influenced by the integrity of the extensor mechanism, the location and nature of the fracture, the stability of the patellar implant, and the quality of the remaining patellar bone stock. Various classification schemes and treatment algorithms have been proposed for periprosthetic patella fractures based on these factors, but there is no single validated, universally accepted classification system.
Ortiguera and Berry classified periprosthetic patella fractures into three types. This scheme appropriately incorporates the factors mentioned earlier in guiding treatment decisions. Type I fractures have a stable implant and an intact extensor mechanism. Type II fractures have a disrupted extensor mechanism and a stable or loose implant. Type III fractures are those with a loose patellar implant and an intact extensor mechanism. Type III fractures are further classified based on the quality of patellar bone stock remaining, with type IIIA having reasonable remaining bone stock and type IIIB having poor bone stock. This classification has gained some credence in recent literature and clinical practice.
Based on this classification scheme and their results with 85 fractures, the authors formulated a treatment algorithm to help in clinical decision making (see “Algorithm”). Type I fractures are treated nonoperatively. Type II fractures require repair of the extensor mechanism with partial or complete patellectomy or with open reduction and internal fixation (ORIF) of the fracture. Operative treatment is recommended for type III fractures if they are sufficiently symptomatic. Type IIIA fractures may be treated with a patelloplasty with component revision or component resection arthroplasty. Type IIIB fractures can be treated with patellar component removal and patelloplasty or total patellectomy. Some Type IIIB fractures may be amenable to fixation with local bone grafting and patellar revision.
With individualization as necessary based on patient comorbidities, activity, and expectations, we find this classification scheme to be useful for the treatment of periprosthetic patella fractures. We typically immobilize symptomatic type I fractures for a period of 1 to 3 weeks, followed by physical therapy to regain motion, as necessary ( Fig. 31.1 ). Those type I fractures that are clinically asymptomatic or found incidentally are treated without immobilization ( Fig. 31.2 ). Type II fractures are almost always treated surgically because they are associated with extensor mechanism disruption. The spectrum of intervention, from extensor mechanism repair with or without ORIF to partial or complete patellectomy, may be employed. Symptomatic type III fractures are typically treated with revision of the patellar component if bone stock is adequate and with total patellectomy if the bone stock is poor ( Fig. 31.3 ). Allograft reconstruction of the extensor mechanism with the graft tightly tensioned in extension is reserved for catastrophic failures of these techniques.
Examination and Imaging
The history, physical examination, and radiographic findings are used in the diagnosis of periprosthetic patella fractures. Often patients do not report a history of discrete trauma before the onset of pain. A significant number of type I fractures are asymptomatic and are diagnosed incidentally on routine follow-up radiographs.
Symptomatic patients typically present with anterior knee pain, effusion, extensor mechanism weakness, and episodes of instability. These fractures can be radiographically evaluated with anteroposterior, lateral, and skyline views. Transverse fractures usually are best seen on a lateral view, whereas vertical fractures are best evaluated on skyline views. Osteolysis and loosening of the patellar component are also best evaluated on lateral and skyline views. Occasionally a technetium-99m bone scan is necessary to differentiate an age-indeterminate fracture or to diagnose an occult fracture.
The following equipment should be readily available in the operating theater:
18- to 20-gauge stainless steel wire
4.0-mm, partially-threaded, cancellous cannulated screws
Kirschner wires (K-wires), 0.062 inch
No. 2 FiberWire braided composite suture
Patellar component from compatible manufacturer
Anatomy and Approaches
An anterior longitudinal midline skin incision with a median parapatellar retinacular incision is most often used to approach the patella. It is preferable to use the prior joint replacement surgery incision to avoid any skin bridges. The skin and subcutaneous tissues are reflected to expose the entire anterior surfaces of patella, quadriceps tendon, and patellar ligament, and the quadriceps tendon and retinacula are inspected for any tears.
Exposure of the patella can be difficult due to tethering by scar tissue in the suprapatellar pouch, in the lateral gutter, and deep to the patellar tendon. Careful release and excision of this scar tissue usually gives sufficient exposure to evert or adequately sublux the patella. Posteromedial release decreases extensor mechanism tension by allowing external rotation of the tibia. Eversion of the patella can be further facilitated by proximal extension of the incision, lateral retinacular release, and/or a quadriceps snip. Removal of the tibial polyethylene insert may also help by relaxing the extensor mechanism. Extensile exposures such as a tibial tubercle osteotomy or a V-Y quadriceps turndown may be used but are rarely required when dealing with periprosthetic patella fractures.
Open Reduction and Internal Fixation
A modified anterior tension band wiring technique, as recommended by the AO group for the fixation of transverse patella fractures, may be used for displaced fractures through the middle third of the patella. The patellar component is typically loose or attached to only one fragment and is removed. With the fracture reduced and held firmly with clamps, two 0.062-inch K-wires are drilled from inferior to superior through each fragment. The wires are placed about 5 mm deep to the anterior surface of the patella as parallel as possible and with a wide enough spread to minimize incarceration of the patellar or quadriceps tendon. A strand of 18- or 20-gauge wire is passed transversely through the quadriceps tendon attachment, deep to the protruding K-wires. The wire is then passed over the anterior surface of the reduced patella, transversely through the patellar tendon attachment and deep to the protruding K-wires, and back over the anterior patellar surface. The wire is typically placed in a figure-of-eight fashion and tightened with a tensioner. In patients with good bone stock, 4.0-mm cannulated lag screws may be used instead of K-wires, and the cerclage wire is passed through the screws ( Fig. 31.4 ).