Traumatic Patellar Dislocation in Children and Adolescents Treatment Update and Literature Review

Abstruse

• Patellar instabilities are the most common knee pathologies during growth. Built dislocations are rare. Extensive, early soft tissue releases relocate the extensor mechanism and may enable normal development of the femoro-patellar anatomy.

• Bourgeois management is the preferred strategy after a 'first-time' traumatic dislocation. In cases with concomitant anatomical predisposing factors such as trochlear dysplasia, malalignment, malrotation or ligamentous laxity, surgical reconstruction must be considered. The same applies to recurrent dislocations with pain, a sense of instability or re-dislocations which may also lead to functional compensatory mechanisms (quadriceps-avoiding gait in human knee extension) or cartilaginous lesions with subsequent patello-femoral osteoarthritis. The decision-making procedure guiding surgical re-alignment includes analysis with standard radiographs and MRI of the trochlear groove, articulation cartilage and medial patello-femoral ligament (MPFL). Careful evaluation of dynamic and static stabilisers is essential: the medial patello-femoral ligament provides stability during the commencement 20° of flexion, and the trochlear groove thereafter.

• Excessive femoral anteversion, general ligamentous laxity with increased femoro-tibial rotation, patella alta and increased distance between the tibial tuberosity and the trochlear groove must also be taken into account and surgically corrected.

• In cases with ongoing dislocations during skeletal immaturity, soft tissue procedures must suffice: reconstruction of the medial patello-femoral ligament as a standalone procedure or in conjuction with more circuitous distal realignment of the quadriceps mechanism may lead to a permanent stable result, or at least buys time until a definitive bony procedure is performed.

Cite this commodity: Hasler CC, Studer D. Patella instability in children and adolescents. EFORT Open up Rev 2016;ane:160-166. DOI: ten.1302/2058-5241.1.000018.

Epidemiology and history

Patellar instabilities account for the most prevalent knee issues during growth. The overall incidence is around 50 in 100 000 children and adolescents per year with a tiptop at the historic period of fifteen years.^i,2 About patellae displace laterally. Medial dislocations are usually iatrogenic due to all-encompassing lateral retinacular release. After the kickoff occurrence near xl% stop up as recurrent dislocations, where two-thirds take open physes which limit the type of stabilising interventions to those which respect the integrity of the growth plates.³ A non-specific, non-contact trauma mechanism with a history of sudden 'giving way' or 'locking' under load in the stance phase, in combination with a movement of valgus–flexion–external rotation, occurs in more than 80% of primary patellar dislocations. Spontaneous patellar dislocation is common in skeletally immature girls, and locked dislocation is common in skeletally mature men.^iv Many patients report that they felt the patella displacing medially.

Clinical presentation and examination

Conscientious appreciation of the dynamics of patellar tracking and thorough orthopaedic examination to define all of the involved predisposing static factors is of paramount importance. A positive 'anticipation sign' with tenderness and quadriceps activation when pushing the patella laterally in early on flexion is characteristic for instability. Increased medio-lateral movement is quantified in dissimilar degrees of flexion. Tenderness over the medial facet and lateral condyle follows astute dislocations or in cases with chondral lesions. In contrast to general thought, the Q-angle is oft decreased in cases with patellar lateralization.⁵ Gait analysis in patients with chronic instability typically reveals quadriceps-avoiding gait with increased foot plantar-flexion, hyperextension of the knee without loading response and anterior shift of the eye of gravity (plantar-flexion–genu extension couple). A minority of patients display increased knee flexion during stance.

Types of dislocation

1. Congenital dislocation is a rare status. In such cases, a modest dysplastic patella is dislocated at nascency. The laterally displaced extensor machinery leads to a progressive valgus-flexion deformity which – in contrast to other built pathologies such as deficient cruciates or discoid menisci – becomes obvious at an early stage. This condition is frequently bilateral and associated with underlying general pathologies such as boom-patella syndrome. Hence, it must be differentiated from neuromuscular dislocations which occur after in life owing to loftier lateral-pulling muscle forces, for case in spastic tetraparesis. Surgical reconstruction is challenging during growth but becomes even more and then in neglected cases. Conservative handling is therefore not a valid option. Early surgery includes vastus lateralis releases combined with medial shortening and patellar tendon re-routing. In cases where the vastus approach does not provide adequate soft tissue length to let medial relocation of the patella, one may consider Z-lengthening of the quadriceps tendon or the patellar ligament dependent on the craniocaudal position of the patella. Quadriceps lengthening is used for patella alta; patellar ligament lengthening is used for patella baja.

2. In astute traumatic dislocations, the patella almost always moves laterally, acquired past a combination of knee joint flexion, valgus and external rotation of the human knee. In cases of a complete, easy to diagnose dislocation, the knee is locked in flexion. Reduction is achieved by gentle knee extension. Spontaneous reduction occurs frequently. Knee effusion and tenderness over the medial patello-femoral region and at the border of the lateral femoral condyle are typical findings. Patellar dislocations are the chief cause for knee haemarthrosis during growth, and secondary causes are ACL injuries.⁶ Osteochondral fragments are found in virtually every sixth acute dislocation (15%), mostly following spontaneous relocation of the patella.¹ They normally arise from the medial patellar facet or lateral femoral condyle when the patella hits against the lateral condyle every bit it relocates into the trochlear groove. Simultaneous femoral and patellar fragments are rare. Re-fixation can prove difficult if the bony portion is too small (< 1.5 cm) or in neglected cases. Over fourth dimension the hydrophilic cartilage of the fragment attracts fluid and hence loses its original shape. Such fragments will crave removal and eventually cartilage resurfacing. Extra-articular bony avulsions of the medial patello-femoral ligament more often occur at the patellar than at the femoral insertion⁷ (Fig. 1). Principal ligamentous repair afterwards a get-go dislocation does not give better results than conservative handling. Notwithstanding, in patients with clear anatomical predisposing factors such as malalignment and malrotation, re-alignment surgery including MPFL repair and correction of the underlying biomechanical pathologies should exist considered. Master surgery should also be considered in cases with associated osteochondral fractures.^eight,9

3. Acute constitutional dislocations happen without proportionate trauma and show few concomitant injuries, but the patient presents with multiple predisposing factors. A positive family history and general joint laxity are commonly constitute. Such dislocations most ever progress to a chronic habitual form. In practice, at first presentation of a patient lament about long-standing patellar instability and pain, it is not like shooting fish in a barrel to describe a articulate line between recurrent post-traumatic and habitual dislocations since the start of the history often remains obscure. There are more predisposing factors in habitual cases, whereas a clear commencement acute episode without previous history of patellar problems and without obvious anatomical features indicates post-traumatic recurrent dislocation. Those beginning in early childhood are usually congenital. However, at the end of the diagnostic pathway all contributing factors (ligamentous, muscular, bony, lower limb malalignment and malrotation) have to be considered and taken into the therapeutic – mostly surgical – strategy.

4. Chronic permanent dislocations are institute in patients with meaning ligamentous laxity and small patella embedded in a curt, laterally displaced extensor mechanism which acts as a knee flexor with consequent lack of agile and passive knee extension and crouching gait.

Fig. i

xiv-yr-old boy with astute showtime-time dislocation during soccer play. The MRI shows a knee effusion (haemarthrosis marked with asterisk), a shallow trochlear groove (dotted line) and an avulsion fracture of the MPFL at its patellar insertion (pointer).

Citation: EFORT Open Reviews 1, 5; 10.1302/2058-5241.one.000018

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Fig. 1

14-year-erstwhile boy with astute first-fourth dimension dislocation during soccer play. The MRI shows a knee effusion (haemarthrosis marked with asterisk), a shallow trochlear groove (dotted line) and an avulsion fracture of the MPFL at its patellar insertion (pointer).

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Anatomical considerations and predisposing factors

Identifying the presence of isolated or combined pre-disposing anatomical factors and weighing upwardly their influence on patellar instability is crucial in determining the optimal, individualised treatment pathway. Many individuals (sixty%) show multiple factors.¹⁰ Finite element models of the patello-femoral joint analysing the influence of sulcus angle, Insall-Salvati ratio, tibial tubercle-trochlear groove distance and femoral anteversion in over 100 combinations showed that the sulcus bending is the most important cistron.¹¹ Apart from a routine orthopaedic appraisal of lower limb alignment and rotation, the patello-femoral joint requires careful dynamic and static examination. Patellar tracking is observed during active and passive knee joint motion in the supine position. Patellar position and tilt are assessed in the sitting patient with knees 90° flexed, with and without activation of the quadriceps muscle. The patella is carefully pushed in a lateral direction in diverse degrees of flexion. Local tenderness on palpation over the medial retinacula and on the lateral and medial patellar facets, and pain with manipulation in mediolateral and craniocaudal direction, with and without pressure level, may signal chondral lesions. The younger the child, the more oft an underlying dysplasia of the patella (flattening of the cross-section) and the condylar surfaces if found.

General ligamentous laxity based on the Beighton scale is unremarkably plant in female person patients or in individuals with a collagen disorder. Apart from its direct influence on patellar stability, it may as well indirectly bear on on the patello-femoral tracking by increasing the intra-articular range of femoro-tibial rotation, clinically evident as postero-lateral rotational instability. Care must be taken when including the tibial tuberosity-trochlear groove distance (TT-TG) in the decision-making process with regard to surgical transposition of the TT: lateralisation of the tubercle may be more than affected by human knee rotation than past its anatomical position on the tibia, particularly in habitual dislocators.¹² Also the caste of knee flexion influences TT-TG.¹³ At 120° knee flexion forces of upward to 4600 N are pulling laterally on the patella.¹⁴ Genu valgum and/or recurvatum (which indicates increased ligamentous laxity), excessive femoral anteversion and external torsion of the tibia lead to an increase of that vector. Rotational anomalies are of more than predisposing importance than axial deviations.

Patients with recurrent dislocation have rates of effectually three-fold higher of patella alta.¹⁰ Wasting of the quadriceps musculus is unremarkably nowadays afterward recurrent dislocations. Moreover, fibrosis in the vastus lateralis may be present.¹⁵ Increased Q-angle is more often than not believed to contribute to a patella-lateralising vector, and diverse surgical techniques aim at decreasing it. However, there is poor correlation betwixt clinical and radiographic measurements, and the Q-angle in dislocating knees may even exist decreased.⁵ True lateral radiographs permit nomenclature of the type and degree of trochlear dysplasia, about usually according to the principles stated by Déjour: shallow or missing sulcus (crossing sign), a flat or convex proximal sulcus or even a pace-off between trochlea and inductive cortex of the distal femur and flattening of the lateral femoral condyle^16,17 (Fig. 2). According to Insall, in patients with closed physis, standard lateral radiographs in 45° flexion determine whether there is a patella baja or alta position. In cases with open proximal tibia growth plates, the Insall reference point at the tuberosity is not reliable. Hence, in individuals who are nonetheless growing, the Caton-Deschamps alphabetize is preferred (length ratio of A. inductive proximal tibial plateau corner to well-nigh junior point of patellar articular surface to B. length of patellar articular surface). Skeletal immaturity and trochlear dysplasia are the dominating factors for patellar instability, and a CD-index > 1.45 (patella alta) provides an of import additional predictive gene^18,19 (Fig. 3). A skyline view of the patella in 30° to ninety° flexion may reveal gratuitous fragments, a shallow sulcus, patellar dysplasia and actress-articular avulsion fragments of the medial patello-femoral ligament at the patella. A CT scan allows for measurements of the bony trochlear groove angle, patellar tilt and elevation. Femoral anteversion and tibial torsion are assessed clinically or by a CT scan which however represents the 'gold standard'. Nevertheless, MRI and low-dose stereoradiography (EOS) are valuable alternatives, although the availability of the latter is limited. Ultrasound or MRI is helpful to distinguish between the cartilaginous and the osseous anatomy of the knee which is particularly important when it comes to the cess of the morphology of the trochlear groove.^20,21

Fig. 2

18-year-former boy with Down syndrome and recurrent painful dislocations of his left patella. Apart from syndrome-associated ligamentous laxity equally a major predisposing gene, he displays significant trochlear dysplasia: 1) positive crossing sign (trochlear line crosses anterior femoral cortex line); 2) osseous bump (spur) at the upper border of the trochlea which misguides the patella into a lateral position when the patient is flexing his knee.

Commendation: EFORT Open Reviews 1, v; 10.1302/2058-5241.ane.000018

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Fig. 2

18-year-former male child with Down syndrome and recurrent painful dislocations of his left patella. Apart from syndrome-associated ligamentous laxity every bit a major predisposing factor, he displays significant trochlear dysplasia: one) positive crossing sign (trochlear line crosses anterior femoral cortex line); 2) osseous bump (spur) at the upper border of the trochlea which misguides the patella into a lateral position when the patient is flexing his human knee.

Citation: EFORT Open Reviews 1, v; 10.1302/2058-5241.ane.000018

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Fig. 3

12-twelvemonth-old boy with chronic habitual bilateral patellar dislocations. A concomitant predisposing gene was a moderate valgus deformity, young historic period and a trochlear dysplasia of both knees (a). The lateral view of the left articulatio genus shows the difficulty to objectify the patella position (alta, normal or baja): the growth plate with its anterior natural language (white line) has not ossified yet. Hence, there is no distinct insertion area of the patellar ligament (dotted line) and no clear osseous reference to assess the Insall alphabetize as in skeletally mature patients. The Caton-Deschamps ratio (A/B) is more than advisable only nonetheless difficult to assess in a patella which is subluxed (b). Moreover, longstanding lateralisation of the extensor machinery led to a articulatio genus flexion contracture which omits a standard lateral radiograph.

Citation: EFORT Open Reviews 1, 5; 10.1302/2058-5241.1.000018

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Fig. 3

12-year-former boy with chronic habitual bilateral patellar dislocations. A concomitant predisposing factor was a moderate valgus deformity, immature age and a trochlear dysplasia of both knees (a). The lateral view of the left human knee shows the difficulty to objectify the patella position (alta, normal or baja): the growth plate with its inductive tongue (white line) has non ossified however. Hence, at that place is no distinct insertion area of the patellar ligament (dotted line) and no articulate osseous reference to assess the Insall index equally in skeletally mature patients. The Caton-Deschamps ratio (A/B) is more advisable but still difficult to assess in a patella which is subluxed (b). Moreover, longstanding lateralisation of the extensor machinery led to a knee flexion contracture which omits a standard lateral radiograph.

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Therapeutic considerations

It is an ongoing argue whether or non to leave congenitally displaced patellae alone. Yet, once the child reaches walking age, the lateral displacement of the extensor mechanism and the flexion-valgus deformity correspond a pregnant biomechanical burden, particularly if the dislocation is part of a syndromic circuitous. A stepwise surgical à la carte approach may comprise a vastus lateralis release including the lateral ilio-tibial band, the vastus lateralis muscle and lengthening of the quadriceps (rectus snip). Also, doubling (shortening) of the medial structures over the patella including advancement of the oblique vastus medialis fibres and eventually re-routing of the lateral part of the patellar tendon with reinsertion (suture) nether the human foot anserinus is required. It aims at keeping the mostly cartilaginous, small disc-similar patella on a flat trochlea in all degrees of flexion. Isolated procedures such as all-encompassing medial transfer of the quadriceps muscle (Stanisavljevic procedure) has shown limited success rates.²² In adolescents with residual instabilities, targeted procedures such as trochleaplasties may be indicated.

Though prognosis is difficult to determine after initial acute patellofemoral dislocation, bourgeois treatment is the current best evidence strategy if significant maltracking factors and concomitant osteochondral fractures are ruled out.²³ In mixed cohorts which were not divided into subgroups with different risk patterns, the 3–v-year recurrence charge per unit varied between 35% and 70%, but the long-term functional and subjective results were satisfactory in most patients.^24,25 A positive family unit history and instability of the contralateral patella are gamble factors for recurrence. Skeletally young patients with trochlear dysplasia comport the highest gamble (69%) after non-operative handling, compared with a 62% success charge per unit if no major predisposing gene is nowadays.³

First-time dislocators are at loftier run a risk of not returning to their previous level of sports activity. At that place is no evidence regarding the superiority of one rehabilitation programme over another, but it is common sense to involve patients in a 3 to 4 month practise plan that is well-supervised by a physiotherapist through the specific functional stages: The first aim is to resolve hurting and swelling, followed by restoration of joint motion, musculus strengthening and finally sport-specific exercises with render to sports activities and prevention of further episodes of instability. The programmes starting time with isometric general quadricep-strengthening exercises, specific distal vastus medialis muscle strengthening, edifice to the level of complex dynamic stabilisation of the lower extremity including the pelvic and lateral trunk stabilisers, and include proprioceptive tasks of increasing complexity. The 'dark-green light' for a safe return to total activity should only be given when the patient is hurting-complimentary, without human knee effusion, shows a complete range of motility of the knee, and when all sport-specific functional criteria are fulfilled. Adhesive tapes and proprioceptive braces tin can support this process, and may be applied through the showtime weeks after return to total sports activities. Despite focussed rehabilitation, quadriceps weakness may persist over years. Therefore patients should be motivated to continue exercising within a personalised fitness and sports program, peculiarly if ligamentous laxity is present. In these cases, the importance of muscular competence – both forcefulness and proprioception – cannot exist overemphasised, particularly when the patient enters the process of ageing-related tissue degeneration and loss of muscle mass in later adulthood.²⁶

In cases of failed conservative treatment with established disabling instability, operative treatment should be discussed depending on the level of suffering and functional impairment. Repeated 'giving manner' may cause cartilaginous lesions and chronic hyperpression with the risk of the later development of patellofemoral osteoarthritis. The goal of surgery is perfect tracking past restoration of the local bony and non-bony anatomy, and by the correction of more than remote factors such equally torsional and centric malalignment. Many isolated or combined procedures have been described to stabilise the patella:

• In children with still open physes, astringent patellar maltracking and predisposing factors for future re-dislocations, MPFL reconstruction, lateral release and correction of any malrotation and malalignment, for example past growth guidance (temporary hemiepiphysiodesis), should be considered starting time.

• Lateral release can exist performed arthroscopically, via mini-open up surgery or through the main incision in major reconstructions. It is not indicated as an isolated procedure for recurrent dislocations. Moreover, extensive release in mild lateral instabilities can over-correct them into an iatrogenic medial dislocation. Medial, distal and anterior deportation of the tibial tuberosity is a 'no go' in the growing kid (boys upwardly to 16 years, girls upwardly to 14 years) because of the hazard of partial growth arrest with subsequent progressive, fixed knee recurvatum. Withal, the morphology of the anterior tongue of the proximal tibial physis allows lateral transposition of the non-osseous part of the distal extensor machinery as originally described by Grammont in 1985 and modified afterwards, for example past sharp autopsy of the distal patellar tendon insertion and periosteal split up along the tibial crest without affecting the growth plate.^27,28

Ligamentum patellae (Roux-Goldthwait) distal re-alignment is an pick for children. It requires acceptable tension in the medial direction and secure fixation. Muscle forces back up stability in xxx°-twoscore° knee flexion, but practice non guarantee optimal patellar tracking. Passive bony and ligamentous stabilisers are considered more than important: the patella enters the trochlea in early knee flexion guided past the medial patello-femoral ligamentous (MPFL) restraints, which tighten in knee extension and slacken with flexion. Acceptable trochlear shape and sulcus depth are major stabilisers in knee flexion greater than xx°.²⁹ Hence, MPFL reconstruction has get one of the near important surgical techniques for chronic patellar instability. This ligament has a tensile strength upwardly to 200 Due north. Information technology reaches from the medial femoral epicondyle to the superomedial border of the patella. In normal controls it is 40–60 mm long and 330 mm wide but was found to exist thinner, just xiv mm, elongated and with lack of tension in dislocators.^30,31 It is covered by the distal part of the vastus medialis obliquus muscle with fibres connecting both structures. MPFL reconstruction has mostly substituted previous medial repair with retinaculum doubling, which is not sufficient. The aforementioned holds true for first-time dislocations and primary surgical repair of the torn medial structures which does not give any ameliorate results than primary bourgeois treatment but often leaves unsightly scars or puts the infrapatellar nerve at take chances. Isolated MPFL reconstruction with a hamstring tendon graft or adductor magnus is safe and benign if the anatomy of the limb and knee is normal. If obligatory (every time) dislocations occur in patients with ligamentous laxity, a combination with more than extensive soft tissue procedures equally described above is warranted and may show higher success rates.^22,23,26

Every bit a supplement to MPFL reconstruction or soft tissue techniques, the extensor mechanism can be realigned further distally in various ways depending on the state of the physis, the often under-appreciated proximal or distal malposition of the patella (alta or baja) and the localisation of the tibial tuberosity (TT). A laterally shifted tuberosity can be a consequence of a long-continuing dislocation. Using osteotomy, the TT can be shifted medially (Hauser, Elmslie), distally (Roux, Magnussen) or ventrally (Maquet). In the unstable patello-femoral joint a scarce trochlea and high-riding patella often co-exist. A patella alta tin either exist corrected by shortening of the patellar ligament (open physis) or distalisation of the TT. Trochleoplasties are only applicable later closure of the distal femoral growth plate. Two-thirds of patients with recurrent dislocations display a trochlear dysplasia, compared with 6% in the stable accomplice.^x Surgery either elevates the upper part of the lateral femoral condyle or deepens the intercondylar sulcus. Both strategies have a high success rate in terms of prevention of further dislocations. Notwithstanding, development of anterior articulatio genus pain and patellofemoral osteoarthritis is less predictable and data well-nigh mid- and long-term outcomes are limited.³² Moreover, it is not clear to what extent and to what historic period limit a dysplastic patella and reconstructed trochlea may remodel to congruency.

Conclusions

Patellar instability during growth is a challenge since many congenital and caused factors may crusade it. Therefore conscientious cess and a thorough agreement of a patient'south anatomy, biomechanics, growth dynamics and development are crucial to ascertain a targeted surgical strategy. In cases with still open physes, osteotomies for the correction of juxta-articular bony deformities and trochlear dysplasia demand to exist delayed, and soft tissue buy-fourth dimension procedures may be indicated. Counselling regarding second-stage definitive surgery after the cease of growth is mandatory. The incidence and fourth dimension of occurrence of second-stage osteoarthritis after surgical treatment of patellar instabilities is non clear, nor is the natural history of untreated instabilities. However, recurrent dislocations in childhood lead to superficial cartilaginous point changes in MRI scans of young adults,³³ and an improvement of chondral condition at 'second-expect' arthroscopy an average of 1 yr post-operatively has been documented after MPFL repair.³⁴

Conflict of Involvement

CH has received financial support outside of the current work in the class of consultancy fees from DePuy Synthes.

Funding

No benefits in any form have been received or volition be received from a commercial party related straight or indirectly to the subject of this article.

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