Medial patellofemoral ligament: anatomy, injury and treatment in the adolescent knee Daniel Hensler a, Petri J. Sillanpaa b, and Philip B. Schoettle c

Purpose of review Traumatic and nontraumatic patellofemoral instability (PFI) in children and adolescents is a complex problem. It is determined by a large number of mechanical and pathomorphologic conditions, mainly seen in nontraumatic dislocations. Recent findings Although conservative treatment with a short immobilization, followed by early passive motion and isometric quadriceps strengthening, can be considered in real traumatic dislocations without any cartilaginous injury, a surgical intervention should be considered in atraumatic cases. As 90% of PFI are nontraumatic and correlated with skeletal deformities, the redislocation rate is reported to be up to 80% after initial conservative treatment. To optimize the results, the causing disorder for PFI has to be considered imperatively. In addition to bony disorder, further risk factors have to be taken into consideration for determining the optimal time for surgery. As biomechanical and clinical studies have shown the importance of the medial patellofemoral complex, especially the medial patellofemoral ligament (MPFL), against patellar lateralization, the reconstruction or minimally invasive double-bundle reconstruction of the MPFL is the main surgical technique to treat PFI in children, as it can be used even in open epiphysial cartilage. Further surgical interventions correcting bone deformities, such as trochleoplasty or tibial tubercle osteotomies addressing lower limb deformities, should be performed after closure of the epiphysial cartilage. Summary It is the goal of this overview to explain the pathoanatomy of PFI, the demanding clinical and radiological examinations and treatment options. Keywords children, dislocation, medial patellofemoral ligament, patellofemoral instability, trochlear dysplasia

INTRODUCTION As reconstruction of the medial patellofemoral ligament (MPFL) has become one of the major interventions in the past years in treatment of patellofemoral instability (PFI) in the adult, it is the purpose of this review to also focus on MPFL reconstruction in the adolescent. This is especially because recent findings have shown that PFI is a complex disorder that most commonly occurs in children and adolescents, with an atraumatic cause and thus a congenital pathological anatomy in more than 90%. The precise incidence of patellar dislocation is not known, but it is estimated to be approximately 43/100,000 children [1]. Furthermore, this review cites the important articles in which the reasons for an early onset of PFI in the adolescent are explained, as the

patellofemoral joint (PFJ) has a unique morphology that is already predestined under physiological conditions for instability. After the first lateral patellar dislocation, injury to the MPFL occurs in more than 90% [2,3]. Injury to the cartilage of the medial patella facet or the lateral femur condyle, or both, appears to be significantly less [4]. These lesions,


Department of Trauma Surgery, Trauma Center Murnau, Murnau, Germany, bTampere University Hospital, Tampere, Finland and cMedical Director of Orthopedics and Sports Medicine, Isar Medical Centre, Munich, Germany Correspondence to Philip B. Schoettle, MD, PhD, Medical Director of Orthopedics and Sports Medicine, Isar Medical Centre, Sonnenstrasse 24, 80331 Munich, Germany. Tel: +49 89 149903 8200; fax: +49 89 149903 8205; e-mail: [email protected] Curr Opin Pediatr 2014, 26:70–78 DOI:10.1097/MOP.0000000000000055 Volume 26  Number 1  February 2014

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Medial patellofemoral ligament Hensler et al.

KEY POINTS  Risk factors for patellofemoral treatment are multifactorial and have to be detected before treatment.  MPFL reconstruction is one of the most important surgical interventions in children with PFI.  The femoral insertion distal to the physis is a key point in MPFL reconstruction in the adolescent.

(muscles) stabilizers. The pathological changes in any of these structures, in particular the static stabilizers, can disrupt the balance very quickly and thus lead to a PFI [11,12]. The MPFL as part of the medial soft tissue complex is the main stabilizer in lower degrees of knee flexion and resists against the lateralization force of the quadriceps. The importance of the MPFL as the strongest passive stabilizer against lateral subluxation and its rupture after initial dislocation of the patella (in more than 90% of the cases) have been cited several times [13–15,16 ]. It has been shown that in lower knee flexions (08–308) the MPFL accounts for more than 90% of medial stabilization, and therefore isolated insufficiency of the MPFL leads to increased lateralization or even dislocation of the patella between 08 and 308 [2,3,17]. Additionally, recent studies pointed out that the lateral soft tissue complex of the PFJ also significantly contributes to the patellofemoral stability against lateral dislocation of the patella [18], whereas the vastus medialis obliquus (VMO) as the most important dynamic stabilizer of the PFJ, affects the stability only in flexion of more than 608, when the fibers run perpendicularly to the mediolateral patella motion with an intact connection between the SOB and the fibres of the quadriceps tendon [19]. The patellofemoral movement and stability are, therefore, the result of very complex interactions between dynamic, passive and static stabilizers [20]. In full extension of the knee, the patella is located superior and slightly lateral of the trochlea groove. Between 108 and 308 of knee flexion, the patella starts to make contact with the trochlea and slides into the sulcus [21]. In the course of increasing knee flexion, the depth of the trochlea increases and the bony factor becomes the main stabilizer of the PFJ [22], whereas it is located in the notch in 908 of flexion and more. &&

however, are crucial while determining the treatment regimen and whether conservative or surgical procedure is necessary. Furthermore, different findings will lead to different treatment options for surgery of the MPFL in the adolescent to treat PFI and this review should help to decide about the correct treatment, and provide a detailed understanding of the relevant risk factors and the correct clinical and mandatory radiological examination.

ANATOMY AND BIOMECHANICS OF THE PATELLOFEMORAL JOINT The patella evolves within the seventh week of the embryo and emanates from a cartilaginous nucleus in the area of the patellar tendon, which increasingly grows and slowly starts to form bone between the fourth and sixth years of age [5]. In the early adolescent, the thickness of the cartilage decreases and finally the impression of deeper trochlea groove persists [6]. The MPFL plays an important role, as it is considered the main passive stabilizer of the PFJ. Warren and Marshall [7] described a three-layer structure of the medial soft tissue complex of the knee joint, where the MPFL is identified in the second layer. The MPFL has a ‘sail-like’ appearance and consists of two functional bundles, an inferior-straight bundle and a superior-oblique bundle (SOB), that originate from the medial aspect of the femur condyle, proximal to the femoral attachment of the medial collateral ligament and distal to the adductor tubercle [8]. In the young patient with open growth plate, the femoral insertion is located only slightly distal to the femoral physis (in up to 93% of the population) and therefore reconstruction of the MPFL is challenging in this patient population, especially because the femoral insertion is relatively smaller than the insertion at the patella, where the MPFL is attached to the superomedial border [8–10]. The biomechanics of the PFJ is based on a complex interaction of static (bony configuration), passive (capsule and ligaments) and dynamic

PATHOMORPHOLOGY OF PATELLOFEMORAL INSTABILITY In the extended knee positions, where the stabilizing component of the trochlea is missing, the MPFL is the only structure that can resist against the lateralizing strength of the quadriceps [22,23]. Additionally, clinical and radiological studies have shown pathological alteration of the MPFL in more than 90% after initial dislocation of the patella [3] (Fig. 1). Therefore, it can be concluded that insufficiency of the MPFL is one essential pathomorphology in PFI. However, the MPFL may also be chronically insufficient in children when the patella is pushed into a wrong position because of bony malalignment with

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FIGURE 2. Axial MRI of chronic patellofemoral instability with a dysplastic trochlea and a widened medial patellofemoral ligament, ruptured at the femoral and patellar insertion. FIGURE 1. Axial MRI with rupture of the medial patellofemoral ligament, chondral flake at the medial patella facet as well as edema at the lateral condyle after patellar dislocation.

a resulting, permanent strain on the medial soft tissue complex. This configuration can lead to early and chronic PFI already in the young patient (Fig. 2). The underlying disorder can be either a dysplasia of the trochlea or a malalignment (valgus or rotational deformity of the lower limb), which are both congenital pathomorphologies and can lead to an early and persistent pathological, lateralized shift and tilt of the patella, with the conclusion that, when the MPFL cannot be developed physiologically, an early insufficiency of the MPFL occurs [24]. The persistent traction on the MPFL results in a stretched and insufficient passive stabilizer. Accordingly, a dysplasia of the trochlea is evident in 96% of patients with chronic PFI and therefore can be considered as one of the main risk factors for PFI [25–27]. In addition to the dysplasia that affects the PFJ directly, internal rotation and valgus deformity of the lower limb are considered to be important factors of chronic insufficiency of the MPFL and an early onset of PFI. This clarifies in summary why disorders of the static stabilizers are the most common causes of the PFI [11,28]. It needs to be assumed that a sufficient MPFL cannot be developed and therefore the main stabilizer in low knee flexion 72

angles is missing, if these disorders are already present in childhood.

RISK FACTORS FOR PATELLOFEMORAL INSTABILITY Dysplasia of the trochlea is a congenital, hereditary disease, and therefore a positive family history as well as subluxation or dislocation of the contralateral side in the past has to be interpreted as risk factors for redislocations. Additionally, age of the patient at time of primary dislocation plays a significant role (>14 years). Although mild dysplasias of the trochlea (type A and B) often lead to PFI after adolescence, when the growth plates are closed, severe deformities of the axis of the lower limb can result in persistent subluxation of the patella in early childhood. Dislocation in the past without traumatic cause also increases the risk of redislocations in the future [27,29–32].

CLINICAL EVALUATION A first traumatic dislocation of the patella in a young patient is a dramatic and painful injury [32]. Most commonly, these injuries occur in contact sports such as soccer, handball or American football with direct trauma to the patella from medial and a resulting lateral force or motions of the lower limb Volume 26  Number 1  February 2014

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Medial patellofemoral ligament Hensler et al.

with significant internal rotation and valgus stress on the lower extremity (as happens in skiing sports). The first reduction may be under anesthesia; the knee is extended, whereas the patella must be manually held in the lateral dislocation position to prevent cartilage damage, which can occur if the patella reduces in higher knee flexion angles [27,30]. However, the number of atraumatic patellar dislocations in children/adolescents, as well as the number of subluxations with minimally traumatic genesis, where spontaneous reduction of the patella occurs in almost 100% and which are not even recognized as a dislocation, are higher when compared with traumatic patellar dislocations. The typical patients with a nontraumatic PFI at a young age are described as obese young girls who appear with general joint laxity. These patients suffer from congenital valgus deformity or trochlear dysplasia, which seems to be an X-linked heritage [33,34]. Therefore, the patient’s history is important to elicit the mechanism of injury in order to distinguish between traumatic and nontraumatic injury, whereas the above-mentioned risk factors need to be clarified [11,27,32].

DIAGNOSIS AND TREATMENT AFTER FIRST-TIME TRAUMATIC DISLOCATION Following medical history, a comprehensive inspection of the injured joint is mandatory. As it must be assumed that the medial patellofemoral complex including the VMO is torn, special attention should be paid to any swelling in this area. Furthermore, an osteochondral flake fracture at the patellar or trochlear site can lead to a massive hemarthrosis, which in some cases is the only sign of a previous patellar dislocation. In this initial stage, further clinical examination is not necessary, as it is painful and might even lead to redislocation. Radiological diagnostics include plain radiographs of the knee in three planes in order to identify any bony lesions and to determine the status of the epiphyseal plates. Additional axial radiographs in 308, 608 and 908 of knee flexion do not provide further information because of potential projection of the notch, in contrast to MRI [15,35]. In contrast, MRI is indicated in PFI, with a sensitivity of 85% and specificity of 70% [15,35], as it helps to determine the MPFL, locations of its rupture, the patella tilt and shift as well as additional lesions of the cartilage. Recent literature describes the main location of the MPFL rupture after initial dislocation to be at the patellar site, which is important for the surgical reconstruction of the MPFL [10]. Overall, the MRI shows up all eventual risk factors [36 ]. &&

The initial treatment for acute PFI consists of immobilization of the knee in 208 flexion (brace) in order to allow the MPFL to heal in a position where the physiological load is the highest. Additionally, cooling and anti-inflammatory medication is needed. Eventual additional treatment is decided as follows.

DIAGNOSIS AND TREATMENT OF CHRONIC PATELLOFEMORAL INSTABILITY OR FAILED CONSERVATIVE TREATMENT As mentioned above, proper medical history is crucial in adolescents or children with PFI. Especially in young patients under the age of 14 years, it has to emanate from a high-grade and complex instability with underlying severe disorder of the static stabilizers. Therefore, the inspection of the lower limb with the patient in a standing position is crucial, with the main focus on potential valgus deformity. The investigation of the ‘J-sign’ will be done in a sitting position with active extension out of the hanging leg to detect at which point the patella shifts laterally. Otherwise, when the knee is flexed, it needs to be detected whether the patella emerges into the trochlear groove regularly or delayed (reversed J-sign), which indicates a longer lateralization of the patella (the patella ‘rides’ onto the lateral femoral condyle). The apprehension sign is performed with the patient in a supine position. The patella is manually lateralized by the examiner and the test is positive if the patient indicates fear of redislocation. It is important to execute this test in full extension and 308, 608 and 908 of knee flexion in order to be aware of the characteristics of the PFI. This examination can suggest whether passive factors (MFPL, main stabilizer between 08 and 308 of knee flexion) or static factors (trochlear dysplasia leads to an PFI between 308 and 508, further osseous disorders such as valgus or rotational deformities to an PFI on flexion angles of more than 508) are pathological [22]. An additional examination of an eventual femoral malrotation (especially internal rotation) can be easily performed in prone position: the knee is flexed at 908 and functions as an index. Internal rotation of the lower limb is passively conducted and the angle between the neutral position and the endpoint after internal rotation is measured. Similarly to the acute setting of PFI, plain X-rays and MRI have to be performed accordingly. Additional computer tomography (CT) imaging is necessary to diagnose potential rotational deformities or malalignment [37] (Fig. 3).

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FIGURE 3. Rotational CT scan for determining femoral rotation.

TREATMENT OPTIONS We divide options into conservative and surgical treatment depending on the underlying risk factors.

Conservative treatment Recent literature describes unsatisfactory results after conservative treatment of PFI; however, greater epidemiological data on the treatment of PFI in children and adolescents are still missing. These studies investigate one treatment option without a control group. According to the recent publications, redislocation can occur in up to 44% after conservative treatment. Therefore, it is mandatory to clarify the cause of PFI, and, after exclusion of underlying disorders of the static factors and additional injuries (such as flake fractures), conservative treatment is an option [38,39 ,40 ]. After reposition of the patella, the patient is encouraged to make frequent use of cold to control postoperative pain and swelling. The patient ambulates with crutches using weight bearing as tolerated with the knee brace locked in 208 of knee flexion for the first week, which furthermore helps in optimal healing of the torn MPFL by minimizing strain on the ligament [41]. During the first 2–3 weeks, flexion/extension 608 208 0 will be allowed and the brace locked accordingly. As range of motion improves, biceps femoris strengthening can be progressed to include limited arc (from 60 to 208) nonweightbearing (open chain) knee flexion exercises and low-level weightbearing (closed chain) exercises. Within weeks 4–6 the range of motion is increased (908 108 0) in order to maintain &


sufficient knee movement with optimal healing of the MPFL. Full extension still needs to be avoided, as, in the lower knee flexion angle, strain on the MPFL amplifies. After 6 weeks, the apprehension test should be negative throughout the full range of motion. In a stable PFJ after 6 weeks, emphasis is placed on activations of the thigh muscles, such as being able to perform a full sustained isometric contraction of the quadriceps that results in superior migration of the patella with the knee at the end range of full passive extension. Gait training is performed as necessary to ensure that the individual uses a normal heel–toe gait and does not walk with a flexed knee during the midstance of gait. Tape dressings of the patella are discussed controversially, as they can reduce the pain and allow earlier activation of the quadriceps, but medialization of the patella can be ensured. In the scenario of ongoing PFI including positive apprehension test, the inability of the MPFL can be attributed to an increased tilt and shift of the patella because of slight disorders of the static factors or insufficient compliance of the patient, and surgical intervention with regard to open growth plates needs to be discussed.

Surgical interventions On the contrary, if the above-mentioned risk factors or disorders of the static factors are present at the first dislocation, or if the patient already represents with chronic PFI, flake fractures are diagnosed or conservative treatment has failed, surgical treatment is indicated (Fig. 4).


FIGURE 4. Patellar flake fracture after first-time patella dislocation. Volume 26  Number 1  February 2014

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Medial patellofemoral ligament Hensler et al.

Therefore, different surgical techniques are present depending on the underlying disorder and the status of the growth plates [42 ,43–46]. The MPFL, as it is the main soft-tissue stabilizer of the patella, should be reconstructed in order to stabilize pediatric PFI respectively to adult PFI. The goal of the reconstructed MPFL graft is in any case to allow the patella to enter the trochlea smoothly in early flexion, without medial patella facet overload in deeper flexion. Though several techniques can be used to reconstruct the MPFL, overconstraining of the graft must be avoided. In general, the patella should enter the trochlea from the lateral side, and, at 308, knee flexion should be centered or in a slightly lateral position, not medial in the groove. When the patella is manually displaced laterally at 08 of knee flexion, there should be laxity in the system with a firm end point (check rein). At 308 of knee flexion, a firm point against patella lateralization should exist, while crepitation must not appear in the whole range of motion. Furthermore, especially in children with open physes, MPFL reconstructions offer additional complexities regarding the femoral graft fixation. As in other reconstructions, such as anterior cruciate ligament reconstruction, one has to avoid tunnel placement or screw fixation at or tangential to the distal femoral physis. Avoiding transverse patella tunnels and screw fixation within patella tunnels is ideal. These include the adductor magnus tendon transfer, the adductor sling technique and the medial collateral ligament sling technique. But also anchor fixation at the femur or femoral tunnel placement with respect to the femoral physis is possible when using ongoing fluoroscopy. Some of these techniques will be described in the following. &

and the adductor magnus tendon is identified (Fig. 1) [46]. A graft harvester is used to harvest the adductor magnus tendon, keeping the distal insertion intact. Graft length is determined by measuring the distance from the adductor tubercle to the medial edge of the patella; usually 14–18 cm is required for two bundles. The free end of the graft is sewn with a whipstitch, using an absorbable suture. The distal insertion of the adductor magnus tendon is dissected free of adjacent tissues for ease in turning of the tendon 908 toward the patella; this turn is done on the most distal portion of the tendon possible (Fig. 2). The free end of the graft is passed through a tunnel created deep to the distal VMO and superficial to the joint capsule. The patellar insertion of the graft is then made at the proximal twothirds of the medial patella. Thus, the free end of the graft emerges deep to the distal VMO in the periosteal region of the most proximal part of the medial patellar margin. This recreates the proximal MPFL bundle. The distal bundle runs back to the adductor tubercle (Fig. 2). Suture anchors are placed in the medial patellar margin at the turning points of the looped graft. Thirty degrees of flexion position is used to fix the free end of the distal bundle near to the adductor tubercle with two periosteal sutures (Figs. 5 and 6) [47].

Primary fixation/suture of the medial patellofemoral ligament After initial, traumatic dislocation of the patella, the MPFL can be sutured (intratendineous rupture of the MPFL) or can be fixed to its femoral insertion site with suture anchors (clear diagnosis of an isolated rupture of the MPFL at the femoral site). Prior to any

Surgical technique of medial patellofemoral ligament Depending on the size of the knee and the situation of the growth plate, different techniques for MPFL reconstruction can be used. However, in every technique, the femoral fixation is the key point, as it has been shown that it is distal to the physis. By respecting this insertion, the proximalization of the femoral insertion while growing is avoided [42 ]. &

Adductor magnus transfer This technique is a double-bundle MPFL reconstruction technique, which can be used in skeletally immature patients [47]. After blunt dissection in the subcutaneous tissue, the adductor tubercle is palpated. The superficial overlying fascia is incised,

FIGURE 5. The adductor magnus tendon in a cadaver specimen (marked with ink). The adductor magnus tendon is harvested and turned 908 toward the patella, to reconstruct medial patellofemoral ligament; this turn is done on the most distal portion of the tendon possible. Reproduced with permission from [47]. AM, adductor magnus; VMO, vastus medialis obliquus.

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FIGURE 7. Suture anchor at the femoral condyle for suturing a medial patellofemoral ligament rupture at the femoral insertion side.

those cases surgical procedures that address the passive stabilizers should be used. Indication for reconstruction of the MPFL in aperture fixation technique with an autologous gracilis transplant includes PFI or insufficiency of the MPFL. The reconstruction is performed with a free gracilis autograft, fixed anatomically at the medial patellar edge at two FIGURE 6. The medial patellofemoral ligament graft is fixed with suture anchors at the medial patellar margin, and the distal bundle is fixed near to the adductor tubercle with periosteal sutures. Reproduced with permission from [47].

surgical intervention, MRI is mandatory in order to identify the location of the MPFL rupture and to perform the fixation according to the location (intratendineous suture, refixation with suture anchors) (Fig. 7). For example, medial reefing of the capsular can be performed arthroscopically with biodegradable sutures if the rupture was located close to the patellar insertion site of the MPFL, but medial patellar periost has to be sutured as well (Fig. 8).

Reconstruction of the medial patellofemoral ligament with an autologous gracilis graft The main problem of reconstructive techniques in children is the open growth plate, and therefore in 76

FIGURE 8. Arthroscopic reefing of a patellar side ruptured medial patellofemoral soft tissue complex. Volume 26  Number 1  February 2014

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Medial patellofemoral ligament Hensler et al.

universally agreed upon treatment algorithm published. Conservative treatment of patella dislocation is only successful in a minority of patients. Surgical treatment for PFI requires an individual plan that often includes surgical reconstruction of the patella femoral ligament. Acknowledgements None. Conflicts of interest There are no conflicts of interest.

FIGURE 9. Medial patellofemoral ligament reconstruction in a patient with open growth plates. Seeing both planes, the plate has not been injured.

points to achieve an anatomical double-bundle reconstruction [45]. Therefore, two small knotless anchors (3.5 mm) are used to insert the two free ends in the patella simulating an aperture fixation. In cases of a too small patella, there can be inserted two resorbable suture anchors into the medial patellar edge, where the graft is tied with two knots [48]. According to the anatomical situation, the graft is shuttled under the vastus medialis and above the capsule toward the femoral insertion in the area of the adductor tubercle. The most demanding part in the adolescent MPFL reconstruction with a free graft is the femoral fixation, as it is overlapping with the growth plate in lots of cases. Using the fluoroscope, the correct insertion point is identified (Schoettle insertion point) [45]. This point can be in the area of the growth plate and, if so, the overdrilling with the final drill diameter has to be performed under ongoing fluoroscopic ap-view to avoid tangential harm to the epiphysis. However, recent studies have shown that an ossification does not occur with the graft in the tunnel, and, even if it did, the medial ossification would lead to a slight variszation of the operated extremity, which would lower the tendency to a subluxation [42 ]. The fixation of the graft is performed with an interference screw of the bone tunnel diameter. If one wants to avoid the tunnel drilling, another suture anchor can be used at the insertion point, clarifying that there is no connection to the growth plate (Fig. 9). &

CONCLUSION The PFI of the adolescent is influenced by pathoanatomy and risk factors, and, currently, there is no

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Volume 26  Number 1  February 2014

Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.

Medial patellofemoral ligament: anatomy, injury and treatment in the adolescent knee.

Traumatic and nontraumatic patellofemoral instability (PFI) in children and adolescents is a complex problem. It is determined by a large number of me...
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