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Introduction

Rupture of the patellar tendon after total knee arthroplasty (TKA) is an infrequent but devastating complication. The reported prevalence of this debilitating complication is 0.17% to 2.5%. Patients are left with dramatic functional impairment from extensor lag and instability of the joint. Nonoperative management often relegates patients to the use of a brace or cast and limits their ambulatory ability, which often necessitates surgical intervention.

The cause of patellar tendon rupture is complex and often multifactorial. It is important, therefore, to identify patients who are at risk preoperatively. Risk factors include obesity, previous history of corticosteroid use, stiffness, previous extensor mechanism complications, osteolysis, previous osteotomy, and patella baja. The arthroplasty surgeon must avoid problems during primary TKA that can lead to extensor mechanism failure. For example, appropriate extensile exposures must be used when necessary to avoid damage.

Ruptures can be categorized as acute or chronic. Acute ruptures of the patellar tendon occur during surgery, in the early postoperative period, or as the result of a traumatic injury that causes immediate extensor mechanism dysfunction. Chronic ruptures often result from an injury that is neglected, and patients develop extensor mechanism dysfunction over a longer period of time.

The success of surgical intervention for rupture of the patellar tendon after TKA depends on several factors, including the type of rupture (acute or chronic), quality of the remaining host tissue, and functional demands of the patient. Meticulous surgical technique and adherence to a strict postoperative protocol are imperative for a successful outcome after repair.

Disruption of the patellar tendon after TKA can be treated by primary repair with additional augmentation or by extensor mechanism reconstruction with the use of an allograft or synthetic graft. Primary repair alone for acute or chronic ruptures typically has produced poor results. It is not recommended as the sole treatment option and should be accompanied by augmentation of the repair.

Primary repair with augmentation of the host tissue is used for treatment of acute ruptures when there is good remaining host tissue. Numerous surgical augmentation procedures using sutures, staples, wires, and autogenous tissue have been described, and surgeons should be familiar with the various techniques.

Extensor mechanism reconstruction with allograft tissue is used for the treatment of chronic patellar tendon disruption or in the acute setting when there is poor remaining host tissue to allow for an adequate primary repair with augmentation. The use of whole extensor mechanism allografts or Achilles tendon allografts has become the mainstay of extensor mechanism reconstruction. Newer techniques using synthetic graft reconstruction have become popular and have had short-term success rates comparable to those obtained with the use of allograft tissue. This chapter focuses on the surgical techniques used for allograft extensor mechanism reconstruction after rupture of the patellar tendon.

Indications and Contraindications

Physical Examination and Imaging

A thorough history and physical examination are essential for determining whether the patient is an appropriate candidate for extensor mechanism augmentation or reconstruction. Several important facts should be ascertained from the patient’s history:

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  Acute or chronic nature of the injury

  
  
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  Complications resulting from the initial operation

  
  
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  Symptoms of infection

  
  
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  Other procedures performed in the interim, such as attempts at primary repair of the patellar tendon

  
  
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  Current functional status

  
  
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  Overall health status

The physical examination should focus on the function of the extensor mechanism and the status of the soft tissue envelope. Inability of a patient to perform active knee extension or inability to do a straight leg raise indicates dysfunction of the extensor mechanism. Active and passive extension should be tested to differentiate an extensor lag from a flexion contracture. A palpable defect in the patellar tendon may be felt during the examination, along with a high-riding patella (i.e., patella alta). Underlying infection, instability, or component malrotation that may be the cause of extensor mechanism disruption must be addressed before the reconstruction. If the primary surgery was performed at another institution, it is important to obtain the outside record to determine the types of implants that are in place.

In most instances, plain radiographs are sufficient to assist in the diagnosis. The lateral radiograph may show patella alta ( Fig. 27.5 ). Evaluation of radiographs obtained before the injury can help to evaluate its extent. The position and alignment of the components should be assessed, because malposition and malrotation can be risk factors for extensor mechanism disruption, and they require revision during surgery. The component should be evaluated for loosening and periprosthetic osteolysis. The patella should be critically evaluated and the thickness of the remaining host bone assessed.

Lateral radiograph demonstrates a high-riding patella, or patella alta, which indicates disruption of the patellar tendon.

Computed tomography (CT) and magnetic resonance imaging (MRI) are useful adjuncts in the diagnosis of a patellar tendon rupture if it is not readily evident on physical examination and plain radiographs. Advances in metal artifact reduction sequences have allowed better characterization of the remaining host tissue to assist in surgical decision making.