Classification and Treatment of Patella Fractures

Algorithm

The following is a classification scheme and treatment algorithm for periprosthetic patella fractures:

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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.

Introduction

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.

Equipment

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