The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 95, Issue 2

Instructional Course Lecture | January 16, 2013

Patellofemoral Instability in Skeletally Immature Athletes

William Hennrikus, MD¹; Tamara Pylawka, MD¹

¹ Department of Orthopaedics, Penn State College of Medicine, 30 Hope Drive, Hershey, PA 17033. E-mail address for W. Hennrikus: whennrikus@hmc.psu.edu

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An Instructional Course Lecture, American Academy of Orthopaedic SurgeonsLook for this and other related articles in Instructional Course Lectures, Volume 62, which will be published by the American Academy of Orthopaedic Surgeons in March 2013:“Shoulder Instability in the Young Athlete,” by Benton E. Heyworth, MD, and Mininder S. Kocher, MD, MPHPrinted with permission of the American Academy of Orthopaedic Surgeons. This article, as well as other lectures presented at the Academy's Annual Meeting, will be available in March 2013 in Instructional Course Lectures, Volume 62. The complete volume can be ordered online at www.aaos.org, or by calling 800-626-6726 (8 a.m.-5 p.m., Central time).

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. None of the authors, or their institution(s), have had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, 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.

J Bone Joint Surg Am, 2013 Jan 16;95(2):176-183

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Extract

Acute patellofemoral dislocation is the most common acute knee disorder in children and adolescents. The predisposing factors for acute patellar dislocation are multifactorial.

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Introduction

Acute patellofemoral dislocation is the most common acute knee disorder in children and adolescents. The predisposing factors for acute patellar dislocation are multifactorial.

Treatment of a first-time acute patellofemoral dislocation in the skeletally immature athlete is typically nonsurgical unless associated with substantial articular cartilage damage. In the setting of recurrent instability, surgical reconstruction is usually recommended. Patellofemoral instability is a difficult condition to treat. Surgical treatment of patellofemoral instability in the skeletally immature athlete is evolving from nonanatomic extensor mechanism surgical procedures to anatomic restorative procedures based on reconstitution of the medial patellofemoral ligament. The current goal of surgery is to restore the normal anatomy of the patellofemoral joint. Proper patient selection and attention to technical details are key to good outcomes.

Treatment of the skeletally immature athlete with an acute patellofemoral dislocation remains controversial with long-term outcomes not well understood. In children, the incidence of patellofemoral dislocation is approximately forty-three per 100,000 individuals, with a peak incidence at the age of fifteen years^1-3. The risk of acute dislocation and recurrent instability is particularly high in females from ten to seventeen years old^4,5. After a first-time dislocation, young athletes may feel a sense of giving-way, pain, or anxiety. Recurrent patellar dislocations often substantially impair their athletic performance. In 1952, MacNab reported a 15% redislocation rate following a first-time dislocation, with 33% of patients reporting pain and weakness following a dislocation⁶. Additional studies have noted a redislocation rate ranging from 20% to 44%^4,7,8. Treatment is complicated by the presence of open growth plates, which precludes utilization of osteotomies^9-11. The goal of this paper is to summarize the pathoanatomy and natural history of this patellofemoral instability in the skeletally immature athlete and to discuss both nonoperative and operative treatment options for this injury.

Anatomy and Biomechanics of the Medial Patellofemoral Ligament

The medial patellofemoral ligament is the primary restraint to patellofemoral instability at 0° to 30° of flexion and overall provides >50% of the medial restraint to the patella^12,13. The medial patellofemoral ligament is most taut in full knee extension with the quadriceps muscle contracted. The medial patellofemoral ligament aids in guiding the patella into the trochlear groove during early flexion. Once the patella is engaged in the trochlear groove, the slope of the lateral facet provides the primary resistance to lateral translation^14,15. Patellofemoral joint compression increases as flexion increases because of the increasing force vectors of the quadriceps and patellar tendons¹⁴.

Anatomically, the origin of the medial patellofemoral ligament is at the adductor tubercle on the medial femoral epicondyle near the distal femoral physis (Fig. 1). The medial patellofemoral ligament inserts on the upper two-thirds of the medial aspect of the patella and is approximately 55 mm long. The width of the patellar insertion is approximately 17 mm (range, 14 to 20 mm), and the width of the femoral origin is approximately 15 mm (range, 11 to 20 mm)¹⁶. The medial patellofemoral ligament has two origins: a transverse origin from the osseous groove between the medial epicondyle and the adductor tubercle and an oblique origin from the leading edge of the medial collateral ligament¹⁷. The site of the femoral origin of the medial patellofemoral ligament is controversial. For example, in the skeletally immature athlete with open physes, Shea et al., using radiographic analysis, suggested that the femoral origin of the medial patellofemoral ligament is 2 to 5 mm proximal to the distal femoral physis¹⁸. However, in children, ligaments originate and insert into the epiphysis so that as the patient grows, the origin of the ligament does not migrate farther from the joint. In agreement with this principle, Nelitz et al., also using radiographic analysis, suggested that the medial patellofemoral ligament origin is approximately 6 mm distal to the medial physis in the epiphysis¹⁹. Similarly, Kepler et al., using magnetic resonance imaging (MRI) analysis, demonstrated that the medial patellofemoral ligament origin was epiphyseal and approximately 5 mm distal to the medial femoral physis²⁰. Despite the debate about the exact location of the origin of the medial patellofemoral ligament, all three studies agree that the medial patellofemoral ligament origin is very near the physis; therefore, a drill-hole in this area risks physeal injury.

Fig. 1

Anatomy of the lateral aspect of the knee and the medial patellofemoral ligament (MPFL). MCL = medial collateral ligament.

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Pathoanatomy of Patellar Instability

Clinical Findings

The pathoanatomy of patellofemoral instability is multifactorial. For example, patients who are at risk for patellofemoral instability often present with an increased Q angle (Fig. 2), ligamentous laxity, patella alta, trochlear dysplasia, external tibial torsion, and genu valgum. In addition, patients may demonstrate contractures of the iliotibial band, lateral retinaculum, and vastus lateralis muscle^19-26. The gait may have a valgus thrust, valgus and internal rotation thrust, and excessive pronation of the foot²⁴. The general core strength may be weaker, and vastus medialis oblique hypoplasia should be evaluated. Clinical examinations and/or signs that should be checked include the patellar glide test, patellar apprehension sign, tilt test, and the J sign²⁴. Common additional injuries associated with a patellar dislocation on MRI include knee effusion, tears at the femoral insertion of the medial patellofemoral ligament, medial patellar bone bruises, and increased signal in the vastus medialis muscle²³.

Fig. 2

The Q angle. ASIS = anterior superior iliac spine.

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Imaging

Radiographs of a patient with patellar instability should include anteroposterior, lateral, and Merchant views of the patella. Radiographs should be examined carefully for occult fractures. The presence of trochlear hypoplasia as well as the patellar height, patellar tilt, and patellar subluxation should be noted²¹. If a large effusion exists, further investigation may warrant an MRI examination. On the MRI examination, the tibial tuberosity-trochlear groove (TT-TG) distance (Fig. 3) and patellar tilt may be measured²⁷. MRI scans can often define where the medial patellofemoral ligament tear occurred. Sillanpää et al. reported medial patellofemoral ligament tears from the femur in 66% of patients, from the patella in 13%, and in the midsubstance in 21%²⁸. In addition, the MRI scan nicely illustrates bone bruise patterns typical of patellar dislocation at the medial patellar facet and at the lateral femoral condyle²⁹.

Fig. 3

The horizontal distance between the tibial tubercle and the center of the groove (TT-TG).

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Epidemiology and Natural History of Acute Patellar Dislocation

Adolescent females from ten to seventeen years old have the highest risk for patellar dislocation⁴. Furthermore, of the patients sustaining a first-time dislocation, 61% were participating in a sporting activity at the time of dislocation. At the five-year follow-up evaluation, both the patients with a first-time dislocation and those with subsequent subluxation-dislocation events did not present with substantial radiographic evidence of degenerative joint disease²³. Overall, the reported redislocation rate following an initial patellar dislocation has ranged from 15% to 44%^4,6-8.

Management of First-Time Patellar Dislocation

Nonoperative management of a first-time traumatic patellar dislocation in a young athlete is recommended, except when there is an osteochondral fracture, an avulsion of the vastus medialis obliquus muscle, or additional intra-articular injuries such as a meniscal tear^30-35. Nonoperative management of patients with a first-time dislocation includes rehabilitation focused on vastus medialis obliquus and gluteal muscle strengthening, as well as core strengthening^26,36. Taping and/or bracing with the goal to pull the patella away from the painful area may be considered³⁷. Activity modification and proper sports training should be emphasized. An MRI examination may be warranted to evaluate the status of the cartilage if radiographic findings are normal and a large effusion is present. Palmu et al. recently reported on a randomized clinical trial of acute patellar dislocations in children and adolescents comparing operative and nonoperative treatment³⁸. They demonstrated that primary repair of the medial patellofemoral ligament and/or medial retinacular structures did not improve long-term subjective or functional results, supporting nonoperative treatment for acute first-time patellar dislocation in children and adolescents.

Management of Recurrent Patellar Instability

Failure to improve after nonoperative treatment and repeat dislocations are the most common indications for surgical care of patellar instability in the skeletally immature athlete^35,37,39. More than 100 different types of surgical procedures for addressing recurrent patellar dislocations have been described⁴⁰. The surgical approach that is chosen is individualized for each patient and should address the existing pathoanatomy contributing to the repeat dislocations⁴⁰. Often, no single procedure corrects all patellofemoral problems⁴¹. Surgical options for patellofemoral instability in the skeletally immature athlete include proximal realignment, distal realignment, lateral release, medial patellofemoral ligament reconstruction, guided growth with tension-band plates, and combinations of the above procedures. Osteotomies of the proximal part of the tibia and distal end of the femur are not indicated in this young age group because of the risk of injury to the growth plate.

Proximal Realignment

Traditional proximal realignment techniques alter the medial-lateral patellar position through release of a tight retinaculum lateral to the patella and tensioning of loose structures medial to the patella. The classic proximal realignment procedure described by Insall includes an extensive open medial imbrication and lateral retinacular release⁴² (Fig. 4). The Insall procedure has a success rate for preventing additional episodes of patellar dislocation of approximately 90%^42,43. However, some authors have described high rates of patellofemoral pain and arthritis following this nonanatomic reconstruction⁴⁴. Nam and Karzel reported a mini-incision open medial reefing and arthroscopically-assisted lateral release as an alternative proximal realignment method with similar (90%) success in preventing subsequent patellar instability with less potential morbidity and improved cosmesis⁴⁵ (Fig. 5).

Fig. 4

The Insall technique for proximal realignment.

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Fig. 5

Arthroscopic lateral release with open medial reefing.

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Lateral Release

The role of lateral release in the treatment of patellofemoral instability has undergone reevaluation^46-48. An isolated lateral release is not recommended for the treatment of patellar instability^37,46,49. Lateral release alone does not align the patella more medially^46,50. In cases of patellofemoral instability with normal alignment and no evidence of excessive patellar tilt, medial reefing without routine lateral release can be performed⁵¹. The current indications for performing a lateral release are (1) abnormal patellar tilt by examination or imaging in the setting of anterior knee pain that has had unsuccessful conservative treatment or (2) recurrent patellofemoral instability in combination with other surgical procedures⁴⁶. Potential morbidity following lateral release includes hemarthrosis and medial instability^47,49,52. For the uncommon patients with anterolateral knee pain and symptoms of medial patellar instability after lateral release, open lateral retinacular closure surgery has been described⁵³.

Distal Realignment

Distal realignment surgical procedures in skeletally immature patients aim to modify the proximal-distal and medial-lateral positions of the patella by soft-tissue transfer distal to the inferior pole of the patella⁵⁴. Stanitski recommended that a soft-tissue realignment procedure should include releasing the abnormal tethering vector, balancing the medial vector, and aligning the quadriceps-patellar-tibial mechanism⁵⁵. Distal realignment procedures include transfer of the semitendinosus tendon to the patella^54,56,57, transfer of part or all of the patellar tendon medially to the periosteum or to the sartorius tendon^58-60, and combination procedures including distal and proximal soft-tissue transfers^58,61,62. The Galeazzi procedure (Fig. 6) includes a lateral release combined with transfer of the semitendinosus tendon to the medial patellar retinaculum or directly to the patella via an oblique drill-hole through the patella^56,57,63. Success rates for preventing subsequent patellar instability of >80% have been reported with the Galeazzi procedure⁵⁶. The modified Roux-Goldthwait procedure is a combination distal and proximal soft-tissue transfer that includes a lateral release, plication of the medial retinaculum, advancement of the vastus medialis muscle, and medial transfer of the lateral half of the patellar tendon beneath the intact medial half to the sartorius insertion^58,62 (Fig. 7). Success rates for preventing subsequent patellar instability of >80% have been reported with the modified Roux-Goldthwait procedure⁶². Most recently, Joo et al. reported excellent results in a small case series of patients treated with the “four-in-one” procedure⁶¹. The four-in-one procedure includes a lateral release, a vastus medialis muscle advancement, transfer of the semitendinosus tendon to the patella, and transfer of the lateral half of the patellar tendon to the medial tibial periosteum⁶¹. These proximal and distal realignment procedures involve shifting extensor mechanism tissue in various nonanatomic directions. Recently, the primary stabilizing role of the medial patellofemoral ligament has been emphasized as the key factor for patellar instability. The current trend in the treatment of patellofemoral instability in young athletes has evolved from nonanatomic extensor mechanism realignments to more anatomic procedures centered on reconstruction of the medial patellofemoral ligament^{12,13,39,64,65}.

Fig. 6

The Galeazzi semitendinosus tenodesis.

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Fig. 7

The modified Roux-Goldthwait procedure. A = lateral retinacular release, B = medial transfer of the lateral patellar tendon, C = advancement of the vastus medialis, and D = plication of the medial retinaculum.

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Medial Patellofemoral Ligament Reconstruction

The goal of soft-tissue reconstruction of the medial patellofemoral ligament is to reestablish the normal checkrein against lateral motion and create a tether to help restore normal passive motion of the patella, including allowing the patella to glide laterally about 9 mm. Medial patellofemoral ligament reconstruction is recommended for patients with repeat dislocation, whereas medial patellofemoral ligament repair is utilized more often for patients with a first-time dislocation in whom concomitant injuries are also being addressed. Reconstruction is advocated over repair in patients with repeat dislocation because the chronically injured medial retinacular tissues are insufficient to establish a checkrein against lateral dislocation. Various graft choices have been utilized for medial patellofemoral ligament reconstruction including hamstrings⁶⁶, patellar tendon⁶⁷, quadriceps^68,69, and adductor magnus⁷⁰. Allograft can be considered if the patient has hyperlaxity.

Techniques that avoid injury to the growth plate should be utilized in the skeletally immature athlete. Two techniques in particular are safe and effective in this young athletic population. Noyes and Albright reported using an 8 × 70-mm strip of the medial part of the quadriceps tendon to reconstruct the medial patellofemoral ligament⁶⁸ (Fig. 8). The quadriceps graft is left attached to the superomedial border of the patella. The free end of the graft is passed between the synovium and the retinaculum to the medial femoral epicondyle and is sutured to the medial intermuscular septum. The remaining medial retinaculum is imbricated when the quadriceps tendon harvest site is closed. The graft is tensioned at 30° to 45° of knee flexion to allow for lateral patellar movement of up to 25% of the patellar width. They add a lateral release if tightness of the tissues prevents normal medial patellar translation with or without abnormal patellar tilting. Femoral or patellar drill-holes are not utilized in this technique, so the risk of patellar fracture or injury to the distal femoral physis is reduced⁶⁸.

Fig. 8

Medial patellofemoral ligament reconstruction with use of the medial one-third of the quadriceps tendon.

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Sillanpää et al. reported a technique using the adductor magnus tendon autograft that can also be of value when treating skeletally immature athletes with patellofemoral instability⁷⁰. The medial two-thirds of the adductor tendon are harvested while leaving the distal insertion intact. A 12-cm strip of the medial aspect of the adductor magnus tendon is transferred via a tunnel between the capsule and the retinaculum and is fixed to the medial patellar margin with two suture anchors. The graft is tensioned at 30° of knee flexion with care to avoid overtightening by allowing lateral patellar glide similar to the contralateral knee⁷⁰. Lateral release is not added to the procedure except in cases in which the patella cannot be medialized to the neutral position in the trochlear groove. The adductor magnus tendon reconstruction also avoids drill-holes and minimizes the risk of a fracture or injury to the distal femoral physis.

Guided Growth

In young athletes, genu valgum of >10° has been associated with patellofemoral instability and anterior knee pain^71-73. Extraphyseal tension-band plating can be performed as a safe and minimally invasive technique to correct abnormal valgus in skeletally immature patients^71-75. So-called guided growth to correct the genu valgum with the utilization of a tension-band plate across the distal femoral medial physis can gradually correct the angular deformity to neutral. Guided growth is considered for patients with >10° of valgus and at least twelve months of growth remaining. Guided growth is typically not recommended before eight years of age because until this age spontaneous correction of idiopathic genu valgum may occur^71,76. The tension-band plates are removed when alignment is corrected. If rebound growth causes recurrent deformity, guided growth can be repeated safely⁷¹. The speed of correction decreases with increasing age as the physis grows at a slower rate as the patient approaches skeletal maturity^71,73. Correction of approximately 0.7° per month in the femur and 0.3° per month in the tibia can be expected^71,74.

Rehabilitation

The goal of the rehabilitation phase is to protect the patellar reconstruction while knee motion and strength are regained. Rehabilitation protocols vary by surgeon. Most surgeons utilize a brace for three to six weeks and allow a gradual increase in motion during this time. Utilization of ice packs and ice massage may be helpful. Partial weight-bearing is allowed postoperatively and is progressed to full weight-bearing over four to six weeks. Initial isometric exercises are supplemented with proprioceptive exercises, closed kinetic chain exercises, and lastly, open chain exercises. Most patients can be expected to be able to jog by three to four months and return to full sporting activities by about four to six months.

Complications

Potential complications of the treatment of patellofemoral instability in the skeletally immature athlete include recurrent instability, patellofemoral pain, osteoarthritis, knee stiffness, wound infection, patellar fracture, medial instability, neuroma, and growth plate injury^10,60,77,78. Patients should be adequately counseled preoperatively regarding potential complications.

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Topics

patella ; athlete ; medial patellofemoral ligament

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William Hennrikus, Tamara Pylawka; Patellofemoral Instability in Skeletally Immature Athletes. The Journal of Bone & Joint Surgery. 2013 Jan;95(2):176-183.

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