Management of extensor mechanism complications in total knee arthroplasty.

Complications involving the knee extensor mechanism and patellofemoral joint occur in 1% to 12% of patients following total knee arthroplasty and have major negative effects on patient outcomes and satisfaction. The surgeon must be aware of intraoperative, postoperative, and patient-related factors that can increase the rate of these problems. This review focuses on six of the most commonly encountered problems: patellar tendon disruption, quadriceps tendon rupture, patellar crepitus and soft-tissue impingement, periprosthetic patellar fracture, patellofemoral instability, and osteonecrosis of the patella. The goals of this report are to (1) review the relevant anatomy of the knee extensor mechanism, (2) present risk factors that may lead to extensor mechanism complications, (3) provide a diagnostic and treatment algorithm for each of the aforementioned problems, and (4) review the specific surgical techniques of Achilles tendon allograft reconstruction and synthetic mesh augmentation. Extensor mechanism disorders following total knee arthroplasty remain difficult to manage effectively. Although various surgical techniques have been used, the results in patients with a prior total knee arthroplasty are inferior to the results in the young adult without such a prior procedure. Surgical attempts at restoration of the knee extensor mechanism are usually warranted; however, the outcomes of treatment of these complications are often poor, and management of patient expectations is important. C omplications involving the knee extensor mechanism and patellofemoral joint are relatively common following total knee arthroplasty, with a reported prevalence of 1% to 12%. Although the majority of these complications occur postoperatively, the surgeon must be aware of intraoperative, postoperative, and patient-related factors that may increase the risk of an extensor mechanism complication. This review focuses on six of the most commonly encountered extensor mechanism complications: patellar tendon disruption, quadriceps tendon rupture, patellar crepitus and softtissue impingement, periprosthetic patellar fracture, patellofemoral instability, and osteonecrosis of the patella. A description of the epidemiology, risk factors, clinical presentation, and management options is presented for each of these complications. Although various surgical procedures have been attempted, the results in patients with a prior total knee arthroplasty are inferior to the results in the young adult without such a prior procedure. The goals of this report are to (1) review the relevant anatomy of the knee extensor mechanism and how it is affected by a total knee arthroplasty, (2) present risk factors that may lead to disruption of the extensor mechanism, (3) provide a diagnostic and treatment algorithm for each of the aforementioned Disclosure: None of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of any aspect of this work. One or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article. e47(1) COPYRIGHT 2014 BY THE JOURNAL OF BONE AND JOINT SURGERY, INCORPORATED J Bone Joint Surg Am. 2014;96:e47(1-9) d http://dx.doi.org/10.2106/JBJS.M.00949 complications, and (4) review the specific surgical techniques of Achilles tendon allograft reconstruction and synthetic mesh augmentation. Anatomy of the Extensor Mechanism and Risk Factors for Disruption Following Total Knee Arthroplasty The extensor mechanism of the knee consists of the quadriceps muscle group, quadriceps tendon, patella, patellar retinaculum, patellar tendon, adjacent soft tissues, and tibial tubercle. The primary blood supply to the extensor mechanism is supplied by the descending genicular, superior and inferior medial genicular, and superior and inferior lateral genicular arteries and the recurrent branch of the anterior tibial artery. Depending on the surgical approach and soft-tissue dissection, all aspects of the blood supply to the extensor mechanism may potentially be compromised during total knee arthroplasty. A medial parapatellar arthrotomy is the most common surgical approach used in total knee arthroplasty and can potentially disrupt all of the medial vessels supplying the extensor mechanism (descending genicular and superior and inferior medial genicular arteries). In addition, excision of the lateral meniscus and infrapatellar fat pad can disrupt the inferior lateral genicular artery and the recurrent branch of the anterior tibial artery, whereas a concomitant lateral parapatellar release can compromise the superior lateral genicular artery (Fig. 1). Pawar et al. performed preoperative and postoperative technetium-99m methylene diphosphate scans of seventy-two patients treated with total knee arthroplasty. Thirty-six of the patients required a lateral release intraoperatively, and the prevalence of transient patellar hypovascularity was 3.95 times higher in these patients. Disruption of the extensor mechanism vascularity also limits healing capacity after a surgical repair or reconstruction. Additional surgical factors that may increase the risk of extensor mechanism complications following total knee arthroplasty include poor patellar alignment and over-resection of the patella during patellar resurfacing; the latter increases the risk of iatrogenic damage to the quadriceps and patellar tendons, and it increases the risk of fracture if the anteroposterior dimension of the remaining bone is <12 mm5. Furthermore, prior surgical procedures such as a high tibial osteotomy or tibial tubercle osteotomy and the presence of patella baja due to infrapatellar scar tissue may increase the difficulty of exposure and the risk of iatrogenic damage to the extensor mechanism (Fig. 2). Lastly, the presence of systemic disorders, including obesity, inflammatory arthritis, diabetes mellitus, and hyperthyroidism, as well as a history of chronic corticosteroid use or multiple corticosteroid injections, may increase the risk of quadriceps and patellar tendon rupture. Patellar Tendon Rupture Prevalence Patellar tendon rupture is a relatively rare occurrence following total knee arthroplasty, affecting <1% of patients.