Robin West, Ryan S. Murray, and Daniel M. Dean
Introduction
Recurrent patellar instability has an incidence of 5.8 per 100,000; in individuals age 10–17 years, the incidence increases to 29 per 100,000 [1, 2]. The rate of recurrence after a single episode of patellar dislocation ranges from 15% to 69% if the initial injury is treated nonoperatively [2]. If a second patellar dislocation occurs, there is a 50% incidence of further recurrent patellar dislocations [1]. Although the rate of recurrence following primary patellar dislocation is low in some patients, many patients may continue to have pain and mechanical symptoms of instability follow- ing the initial dislocation episode [3]. Patellar dislocation can result in articular cartilage injuries, osteochondral fractures, and patellofemoral arthritis in addition to the risk of recurrent instability [1, 2, 4]. Atkin et al. found that 58% of patients had limitations in strenuous activity at 6 months following a single episode of patellar dislocation [5]. In addition, up to 55% of patients fail to return to sporting activity after a primary patellar dislocation event [5].
The etiology of patellar instability is multifactorial and is related to limb align- ment, the osseous structure of the patella and trochlea, and the integrity of the static and dynamic soft tissue constraints [4, 6]. The management of recurrent patellar instability is challenging due to the complex relationship of the predisposing factors as well as a dearth of long-term, robust, clinical outcome studies. This chapter will provide an understanding of the factors affecting recurrent patellar instability and an algorithmic approach to managing these injuries.
R. West (*)
Inova Sports Medicine, Georgetown University Medical Center, Washington, DC, USA Virginia Commonwealth University School of Medicine, Richmond, VA, USA e-mail: [email protected]
R. S. Murray · D. M. Dean
Department of Orthopedic Surgery, Georgetown University Hospital, Washington, DC, USA
Treatment
Nonoperative Management
When considering the management of patellar dislocations in general, there is strong evidence to support nonoperative management for first-time patellar disloca- tors [7]. There is a shortage of evidence indicating whether physical therapy or bracing is effective in the management of acute, first-time, patellar dislocations.
However, the aim of nonoperative treatment of a patellar dislocation is to decrease swelling, promote vastus medialis and gluteus activity, and increase knee range of motion [6]. Swelling negatively affects quadriceps function, so the faster the swell- ing is controlled and reduced, the more expedient the expected recovery.
Before making recommendations regarding treatment, plain radiographs should be performed to include a 45° flexion weight bearing, a flexion lateral, and bilateral Merchant views to assess joint space narrowing, patellar height, patellar tilt, and trochlear dysplasia (Figs. 8.1, 8.2 and 8.3). An MRI is usually performed in addition to the radiographs to better assess articular cartilage, medial patellofemoral liga- ment, and other associated findings.
Few studies have directly addressed the efficacy of various nonoperative treat- ment modalities [6]. Treatment regimens range from immediate mobilization with- out a brace to cast immobilization in extension for a period of 6 weeks, with countless variations in between. Immobilization in extension may help the medial soft tissue structures heal but can result in stiffness. Maenpaa and Lehto treated 100 patients with three modalities, cast immobilization, posterior splint, or a patella brace. The casts and splints were worn for 6 weeks, and the patients were followed an average of 13 years post injury. There was a three times higher rate of redisloca- tion in patients treated with a brace. However, cast immobilization resulted in an expected higher rate of stiffness [8].
There is also a role for nonoperative modalities, including physical therapy in patients with recurrent patellar instability. This is especially true when evaluating in-season athletes who desire to continue to participate. However, they need to be
Fig. 8.1 PA flexion weight-bearing radiograph to assess joint space narrowing, patellar height
informed as to the risks, including recurrent dislocation as well as the potential for cartilage and soft tissue damage [4]. Patients with chronic patellar instability may benefit from physical therapy which can help to regain strength, motion, and pro- prioception. Therapy should consist of a gradual progression to full range of motion and strength followed by a graduated return to play. Patellar taping such as McConnell taping may help to control excessive patellar motion during therapy and has been shown to increase quadriceps muscle torque while activating the vastus medialis earlier than the vastus lateralis with repetitive resisted flexion and exten- sion [9–11]. Hinged knee braces or lateral stabilization braces may also enhance the patient’s sense of stability and should be employed especially in the case of an in- season athlete hoping to progress through rehabilitation more aggressively [4, 6].
Muscle specific physical therapy should focus not only on the medial quadriceps but also on the gluteal muscles, which are often weak in recurrent patellar dislocators.
This weakness results in adduction and internal rotation of the femur, which may
Fig. 8.2 Lateral flexion weight-bearing radiograph to assess patellar height/
tilt, trochlear dysplasia, joint space narrowing/
spurring
Fig. 8.3 Bilateral Merchant view radiograph to assess patellar tilt, patellar subluxation, trochlear dysplasia, joint space narrowing
exacerbate patellar instability with weight-bearing activities. Strengthening the glu- teal muscles, and in some cases taping the hip, helps to promote external rotation of the femur to help address this problem [10].
There is a growing body of evidence to support weight-bearing or closed chain exercises for rehabilitation rather than open chain exercises. It has been shown that closed chain knee extension promotes simultaneous electromyographic activity in the four different muscles of the quadriceps in asymptomatic subjects. The rectus femoris has the earliest response, while the vastus medialis obliquus has the latest and weakest response with open chain exercises, which is not optimal in rehabilita- tion of a recurrently unstable patella [12]. Closed chain exercises, however, produce more vastus activity which promotes patellar stability and allows for training of the vastus muscles as well as the gluteal muscles and core trunk muscles simultane- ously to better control limb position [13].
Despite the potential for a reasonably good response to nonoperative methods in first-time patellar dislocators, there is a significant rate of failure. Atkin et al.
reviewed their results of nonoperative management at 6 months following patellar dislocation and found that 58% of patients continued to have limitations with stren- uous activity and that 55% had not returned to sports [5]. Therefore it is generally thought that operative intervention is indicated in patients who continue to experi- ence recurrent patellar instability with or without progressive worsening osteochon- dral injury [4]. Thus, the benefit of avoiding surgery should be weighed against the risks of recurrent dislocation and further secondary injury.
Operative Management
Patients with recurrent patellar instability should be thoroughly evaluated to deter- mine the optimal surgical approach to address their pathology. More than 100 dif- ferent operations have been described for the treatment of patellar instability, and typically, a combination of procedures is necessary to achieve a satisfactory out- come. Given the multifactorial and dynamic problems associated with recurrent patellar instability, the approach to a surgical evaluation should be algorithmic in nature. A thorough algorithm to approach these patients will be discussed briefly, and the specific techniques will be covered in detail subsequently.
There are several clinical and radiographic metrics that must be incorporated into the initial evaluation of surgical treatment options for recurrent patellar instability.
First a determination of skeletal maturity should be made. For skeletally immature patients, the coronal and rotational alignment should be determined as well as any isolated or concomitant soft tissue injury to the medial patellofemoral ligament
(MPFL). In skeletally immature patients with a coronal malalignment greater than 10°, with more than a year of growth remaining, a guided growth hemiepiphysiode- sis should be done and will be covered more thoroughly in the pediatrics section. If excessive femoral anteversion (absolute value of greater than 20–25°) is present, a femoral derotational osteotomy may be considered as a component of the manage- ment of the recurrent patellar instability. Finally, in the setting of medial patello- femoral ligament disruption in the skeletally immature patient, an anatomic medial patellofemoral ligament reconstruction should be undertaken. In cases where there is a concern for potential physeal injury, a non-anatomic procedure can be pursued.
In the skeletally mature patient, important anatomic metrics including trochlear dysplasia, patella alta, patella tilt, and tibial tubercle-trochlear groove distance should be compiled to determine the best procedure(s) to address their recurrent patellar instability. A general brief overview of the indications will be outlined and again reviewed in detail in later sections. The tibial tubercle-trochlear groove dis- tance should be considered as a part of the equation, and if it is close to, or above, 20 millimeters and/or if there is a lateral patellar or trochlear chondral lesion, a tibial tubercle transfer should be considered. If there is significant patella alta, the tuber- cle may also be distalized in isolation or in combination with medialization. If Dejour Types B or D trochlear dysplasia is present, a groove deepening trochleo- plasty can be considered; however, it is important to realize that this procedure has significant potential complications including early arthritis and chondral damage and should be considered only if other well done stabilization procedures have failed. Patients with a medial patellofemoral ligament injury should undergo a medial patellofemoral ligament reconstruction in conjunction with any necessary osseous procedures. In cases of patellar tilt greater than 20° that is not flexible, but fixed, a lateral release or lengthening can be done in combination with other defini- tive procedures. Finally, in cases of rotational alignment abnormalities, such as excessive tibial external rotation or femoral anteversion, derotational osteotomies should be considered.
The subsequent sections will provide a detailed review of the various procedures to address each facet of the pathology inherent to recurrent patellar instability. It should be noted that these procedures do not always occur in isolation so a thorough review of the underlying pathology should be undertaken prior to selecting the cor- rective surgical procedure(s). Prior to performing any surgical treatment, a diagnos- tic knee arthroscopy should be performed to assess for associated meniscal, ligamentous, or articular cartilage injuries. The 70° scope placed into the superolat- eral portal gives a view of the entire patellofemoral joint and allows for excellent visualization to assess the articular cartilage of the trochlea and patella and the patellar tracking through a range of motion (Figs. 8.4 and 8.5).