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Patellar Dislocation in Skeletally Immature Athletes
Patellar Dislocation in Skeletally Immature Athletes Kevin G. Shea, MD,* Kurt Nilsson, MD,* and Jennifer Belzer, BS,† Patellar dislocations are common in skeletally immature athletes, with several anatomic factors placing athletes at risk of dislocation owing to the complex 3-dimensional motion of the patellar articulation. Although there is a paucity of prospective studies on patellar dislocations, the available evidence suggests significant redislocation rate and persistent knee dysfunction with nonoperative or operative treatment. Evaluation of the skeletally immature patient should consist of a detailed history and physical examination with radiologic testing and treatment protocols chosen judiciously. Surgical approaches should take into consideration physeal anatomy about the knee. Regardless of treatment protocol, all patients should undergo early physical therapy with gradual return to sport. Oper Tech Sports Med 14:188-196 © 2006 Elsevier Inc. All rights reserved. KEYWORDS patella, dislocation, cartilage injury, pediatric, adolescent
P
atellar dislocation is a common injury in the skeletally immature patient1 and is one of the most common causes of acute hemarthrosis in young athletes.2-5 Studies have demonstrated an annual incidence of this injury at 5.8 per 100,000, with studies in pediatric patients having a higher incidence of 43 per 100,000.6 Some studies have suggested that males and females have equal rates of dislocation,7,8 and others have demonstrated the highest rate of dislocation in girls younger than 18 years of age.9 Although seen in association with underlying diseases, these injuries are very common in the young athlete. These injuries frequently are seen with sports that involve rapid directional change or cutting.7,10
Anatomy Most dislocations occur in a lateral direction and are associated with injury to the medial retinacular tissues and the medial patellofemoral ligament. Medial and superior dislocation also can occur,11-14 and rare cases of intra-articular dislocation also have been reported.15 The patellofemoral joint is complex, and the path of the patella during knee motion is a complex combination of motion in multiple planes.16 At full extension, the patella assumes a slightly lateral relationship to
*Center for Orthopaedics and Biomechanics Research, Intermountain Orthopaedics, Boise State University, Boise, ID. †Medical College of Wisconsin, Madison, WI. Address reprint requests to Kevin G. Shea, MD, Boise State University, Center for Orthopaedics and Biomechanics Research, Intermountain Orthopaedics, 600 N Robbins Road, Suite 100, Boise, ID 83702. E-mail: kshea@ intermountainortho.com
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the femoral groove and, in this position, the patella may assume the most lateral displacement.17 During the first 30° of flexion, the patella begins to engage the femoral sulcus.12,17 In patients with patellar alta, the patella may not engage the trochlear groove until additional flexion occurs, which may contribute to patellar instability and an increased risk of patellar instability.1,7,8,18
Anatomic Risk Factors Although these injuries may be seen in association with anatomic conditions (increased genu valgum, patella alta,19-21 lower-extremity version abnormalities,22-25 trochlear dysplasia,26-31 increased quadriceps angle,32 foot pronation, patellar tilt,33,34 etc.),31,35-37 the relationship between these physical findings and patellar instability is not clearly defined.7,8,38,39 Patellar dislocations occur in otherwise-normal individuals,7,8 although soft-tissue laxity may be a significant risk factor.7,8,40 In recent studies of trochlear dysplasia, authors have attempted to define the relationship between trochlear morphology and patellar dislocation.27,24,31,41 The results of some of these studies have suggested that trochlear dysplasia may have a genetic basis,27 and other studies have suggested that the risk of dislocation may be higher in some families.9
Mechanism of Injury Several different mechanisms of injury have been proposed, including direct and indirect mechanisms.42 The indirect mechanism involves a position of internal rotation of the femur, knee valgus, and a planted foot in combination with a quadriceps contraction.8,11 The direct mechanism involves a
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Figure 1 Medial soft-tissue restraints of the knee. (Reprinted with permission from Clarke HD, Scott WN, Insall JN: Anatomy, in Insall JN, Scott WN (eds): Surgery of the Knee (ed 3, vol 1). Philadelphia, WB Saunders, 2001, p 52.)
laterally directed force to the medial aspect of the patella. Combinations of these mechanisms can occur.42
Medial Patellofemoral Ligament Although the medial retinacular tissues limit the lateral displacement of the patella, the medial patellofemoral ligament is one of the primary restraints to patellar dislocation (Figs. 1 and 2). Injury to this ligament is common during patellar dislocation.43,44 This structure originates from the adductor tubercle region of the femoral condyle, travels transversely, and attaches to the upper two-thirds of the medial patellar border.43,44,45,46 Biomechanical studies have shown this to be
Figure 3 MRI demonstrating injury to the lateral femoral condyle, with associated cartilage defect and subchondral bone contusion.
one of the main soft-tissue structures preventing lateral patellar dislocations.43-45,47-49 Other structures contribute to stability of the patella with respect to lateral subluxation, including the meniscopatellar and tibio patellar ligaments, and the dynamic contribution of the vastus medialis obliquus muscle.12,50
Osteochondral Injuries In addition to disruption of the medial restraints and the medial patellofemoral ligament that occurs during acute lateral patellar dislocation, osteochondral fractures and contusions are seen in as many as 40% to 50% of patients.10,51,52-57 During the dislocation, the osteochondral fragments may originate from the lateral femoral condyle (Fig. 3) or the medial patella facet (Fig. 4). These injuries may result from a shearing force during the patellar dislocation. In some cases, the osteochondral injury of the lateral femoral condyle may be in a more posterior region, in areas of significant weight bearing during full extension.58
Natural History Figure 2 Medial patellofemoral ligament. A right cadaveric knee medial view. The “P” is the patella tendon. The open arrow is on the patellomeniscal ligament. The curved arrow is on the patellotibial ligament, which has been reflected from the tibia. The deep surface is seen and the tibial attachment is in the forceps. The large arrow points to the medial patellofemoral ligament, which is also supported by a probe. The arrowhead is on the superficial medial collateral ligament. (Reprinted with permission from Desio et al.43)
Several studies have attempted to define the natural history of this injury in adult and skeletally immature athletes. Additional long-term studies will be necessary to assess the incidence of osteoarthritis, define subgroups that have a higher risk of secondary dislocation events, and determine the effectiveness of nonoperative and operative treatment regimens.59 Additional study in younger athletes also will help better
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Figure 4 MRI demonstrating injury to the patella, with associated subchondral bone contusion, osteocartilagenous injury to the patella, and detached osteochondral fragment (arrows).
clarify the natural history of this injury.1,9,52,55,60,61 Studies have demonstrated redislocation rates of 13% to 52% for nonsurgical treatment.10,39,52,62-64 Significant knee dysfunction may persist, even in patients that don’t have secondary dislocation episodes.7,55 Previous studies on patellar dislocation demonstrate a small number of prospective designs. These study designs may be the best to identify the natural history of this condition and to determine which patients need operative or nonoperative treatment regimens. A limited number of prospective studies have evaluated the natural history of patellar dislocations, with a specific focus on secondary dislocation and other dysfunction.9,59,65,66 In a well-designed prospective cohort study, Fithian and coworkers9 followed 189 patients for 2 to 5 years. The group with the highest risk of dislocations was females ages 10 to 17 years; 61% of dislocations occurred during sports, and 9% during dancing. The risk of recurrent patellar instability/dislocation appeared to be significantly greater in females. Young age at the time of the first dislocation also was a significant risk factor for future dislocation/subluxation events.
Evaluation Clinical Evaluation Patients with a first-time patellar dislocation may recall a specific dislocation event, which may have spontaneously reduced, or may have required a reduction at the scene of injury or the emergency room. In other cases, patients may describe a significant “pop” or other major mechanical sensation or event, although they may not realize that a dislocation occurred. The dislocation/relocation sequence may oc-
cur very quickly. The history, examination, and image evaluation will determine if patellar dislocation occurred. Athletes with a first-time patellar dislocation usually present with a significant effusion. Many patients have been evaluated in the emergency room and have been placed in a knee immobilizer and advised to use crutches. Patients may be quite uncomfortable and apprehensive, and the examiner should work to help the patient relax as much as possible, which will facilitate a more complete examination. The examination should include a thorough evaluation and look for other injuries, including ligamentous injuries such as the ACL or MCL, osteochondral injuries, meniscus tears, etc. Injuries to the medial retinacular restraints and the medial patellofemoral ligament may produce tenderness in the region of the MCL. Gentle valgus stress maneuvers with the knee near full extension, and in 30° to 45° of flexion, should help determine whether MCL injury has occurred. With regards to the examination of the patellofemoral joint, the examiner should palpate the medial retinacular structures, looking for evidence of disruption of these tissues. Significant ecchymosis or palpable defects could be evidence of major structural damage to these tissues. This palpation should be done very gently because it will not require much pressure to produce discomfort while palpating the traumatized structures. Palpation should also include the entire medial and superomedial border of the patella, and the vastus medialis. These areas may be tender because of medial retinacular avulsion, avulsion injury of the vastus medialis, and/or the presence of osteochondral injury from the medial aspect of the patella. The lateral femoral condyle should also be palpated, to look for evidence of chondral injury, as areas of tenderness may be present, suggesting underlying chondral injury. The evaluation of patellar stability, especially with regards to significant lateral laxity because of traumatized medial restraints, may be challenging in the first 1 to 15 days after the dislocation (Fig. 5). Patellar mobilization after the initial injury may be quite uncomfortable for the patient, and more information may be obtained after the knee has had several weeks of recovery and therapy. Comparison of the injured knee to the uninjured knee can provide very useful information when determining the degree of laxity of the patellofemoral joint. Many patients, especially female, may have other signs of soft-tissue laxity, or other anatomic issues that predispose them to primary and secondary dislocations events.59 Stanitski has emphasized the importance of evaluating patients for signs of soft-tissue laxity.40 Evaluating the patients for genu recurvatum, hyperextension of the elbows, and softtissue laxity of the wrist, thumbs, and fingers also may be helpful during the evaluation and subsequent treatment.
Imaging Evaluation Anteroposterior, lateral, and Merchant view radiographs can evaluate for patella alta/baja, or osteochondral fractures of the patella or intercondylar groove or lateral femoral condyle. Avulsion injuries may be seen of the medial aspect of the
Patellar dislocation in skeletally immature athletes
191 significant information with regards to the location and magnitude of soft-tissue and osteochondral injury, and the anatomy of the trochlea.43,46,76 Several MRI studies have demonstrated significant injury, which may be missed on the initial radiographic evaluation.3,40,67,55 MRI sequences also have been used in the evaluation of anatomic parameters associated with patellar dislocation, including vastus medialis insertion,77 patellar tilt,78 and sulcus angle.79 For athletes, we are obtaining MRI studies early in the evaluation process, which may allow for the identification of trochlear dysplasia, as well as evidence of significant osteochondral injuries, or intra-articular fragments. This information can be useful during the evaluation and during counseling about possible treatment options, both surgical and nonsurgical. For nonathletes or lower-demand individuals, we initially may not obtain an MRI. We counsel these patients that future knee dysfunction may warrant further imaging evaluation. Even in lower demand patients, an MRI may be obtained if we have concerns about significant osteochondral injury or intra-articular fragments.
Treatment
Figure 5 Apprehension sign. Patient anxiety caused by awareness of unpleasantness associated with patellar dislocation. (Reprinted with permission from Stanitski CL: Patellofemoral mechanism, in Stanitski CL, DeLee JC, Drez D Jr (eds): Pediatric and Adolescent Sports Medicine (vol 3). Philadelphia, WB Saunders, 1994, p 340.)
patella and may be best seen on Merchant view radiographs.42 Radiographs are limited in the ability to identify osteochondral injuries.3,55,67 In addition to radiographic evaluation for the presence of osteochondral injuries, radiographic studies have also been used to assess patellofemoral mal-alignment.68 Numerous radiographic and computerized tomographic measures of patellofemoral dysplasia have been described in the literature, including measures of congruence,69,70 sulcus angles,26 patellar tilt,33,72,73 dysplasia,27 subluxation, hyperlaxity, etc. Future studies that use dynamic measurement methods may provide more insight into normal patellofemoral mechanics.74 In our own practice, we routinely evaluate plain radiographs for the presence of patellofemoral alignment or other anomalies, or the presence of significant osteochondral injuries. Most patients come from the emergency department with films available for review. For skeletally immature subjects, the patellar height can be evaluated using the method described by Koshino and coworkers (Fig. 6).75 Although the indications for obtaining an magnetic resonance imaging (MRI) after patellar dislocation may require further clarification in the literature, the MRI can provide
Treatment protocols for patellar dislocation in athletes continue to evolve, and both operative and nonoperative modalities have been recommended for first-time dislocations. At this time, treatment recommendations based on adequate level 1 and 2 studies do not exist. For this reason, most treatment recommendations are based on level 3, 4, and 5 evidence. A recent review of Medline did not identify any randomized prospective studies on the treatment of athletes with first time dislocations. Historically, nonoperative treatment program advocated several weeks of immobilization, followed by therapy to recover motion and strength.10,63,64,80 Because of concerns that
Figure 6 Epiphyseal line midpoint method for measurement of patellar height. The average PT: FT ratio is 1.31 ⫾ 0.09 in full extension and decrease to 0.99 ⫾ 0.06 at 90° of flexion. P, patella; F, femur; T, tibia. (Reprinted with permission from Koshino and Sugimoto.75)
192 immobilization may lead to problems with arthrofibrosis, atrophy of cartilage, muscle, ligaments, and bone, several recent studies have advocated early rehabilitation programs emphasizing range of motion, strengthening, and the use of patellar buttress braces.2,8,81 A limited number of prospective studies have been conducted on patellar dislocation, with respect to comparing operative and nonoperative treatment protocols. Nikku and coworkers studied 126 patients.64 Part of the study group underwent operative treatment, and the other group was treated with nonoperative means. The patients were followed for 2 years. The subjective and objective outcome measures did not differ significantly for these groups. The follow-up period was short, as many studies have demonstrated dislocation after 2 years follow-up. A secondary study of this same patient group at 7 years follow-up did not demonstrate improved outcomes in patients that underwent surgery for primary patellar dislocation.65 Both of these studies had significant limitations, including a nonrandomized design. In a retrospective study, Buchner and coworkers evaluated 126 patients at 8.1 years of follow-up. The study evaluated 2 groups: those managed with or without surgery. The functional and subjective results were good overall, but the recurrence rate was high in both surgical and nonsurgical groups. Although this study had several limitations, including variation in surgical procedures, the authors suggested that many patients may not do better with surgery, although surgery was still indicated in some cases. There are a plethora of operative treatment protocols for the treatment of patellar dislocation, which makes review of the literature even more challenging. During the last 50 years, more than 100 operations have been described to address patellar dislocation. These procedures have ranged from lessinvasive procedures, to open or arthroscopic lateral release,41,67,82-85 to more invasive procedures, including soft-tissue repair/augmentation,86 soft-tissue proximal realignment with lateral release,87,88 medial tissue imbrications,89 tubercle osteotomy with/without soft-tissue procedure,90 thermal shrinkage of medial retinaculum and lateral release,91 transfer of the patellar tendon to the medial collateral ligament,92,93 medial patellofemoral ligament reconstruction,43,45,94,94 distal transposition of the patellar tendon in cases of patella alta.20 More extensive discussion of the plethora of surgical procedures used for patello-femoral dislocation is beyond the scope of this review.
Lateral Release Recent work by Fithian and Paxton and the International Patello-femoral Study Group96 have suggested that the indications for lateral release for the treatment of patellar dislocation/instability is very limited, and these procedure appears to be much less popular than in the past.96 Other authors also have suggested that the results of lateral release for the treatment of patellar dislocation are not predictable, and this isolated procedure is rarely indicated for this condition.97-99
K.G. Shea, K. Nilsson, and J. Belzer
Physeal Considerations in Skeletally Immature Patients The operative treatment options in skeletally immature athletes are somewhat different than those available in adults because of concerns about potential physeal injury to the distal femoral or proximal tibial physis or apophysis. Procedures that violate these structures or the surrounding perichondral ring can produce complications of altered growth, including coronal plane angular deformity, leg length discrepancy, and recurvatum.61,100 For these reasons, soft-tissue procedures are more likely to be appropriate in children or adolescents with significant growth remaining. Numerous soft-tissue procedures have been described, and these procedures range from those with extensive exposure, to those with arthroscopic or minimally invasive approaches. Reconstruction of the medial patellofemoral ligament has been described in children,101 although the close association between the distal femoral physis and the origin of this ligament warrant caution during surgical procedures in this area. Tubercle osteotomy procedures used in adults are contraindicated in those with significant growth remaining. Procedures that involve transfer of the patellar tendon, such as the Roux-Goldthwait patellar tendon transposition, may play a role in some patients with patellar dislocation.102,103 With respect to our practice, the following treatment protocols for nonoperative and operative management will be described.
Nonoperative Treatment Protocol Whether surgical or nonsurgical treatment protocols are chosen, we usually start all patients on an early treatment regimen with several goals: (1) reduction of swelling; (2) early mobilization, strengthening, and proprioception to minimize weakness and associated dysfunction of all major muscle groups of the lower extremity, especially the thigh musculature; and (3) early return to sports and other exercise. Aspiration is performed on some patients, especially those with large effusions. In our experience, a very large effusion may interfere with a rehabilitation program. The effusion may prolong the period of motion recovery and also may have deleterious effect on quadriceps/hamstring activation about the knee. By the time of arrival to the clinic, most of our patients have spent 2 to 10 days in a knee immobilizer and with protected weight bearing. This treatment protocol is almost universal in primary care clinics and emergency rooms. The patients have significant quadriceps/vastus medialis obliquus atrophy, which develops rapidly post injury, especially in patient who have been placed in a knee immobilizer. Cryotherapy is used several times daily for the first several days to weeks, to help with swelling. In some cases, a short course of oral antiinflammatories also may be used, to assist with the effusion. A patella sleeve is also provided to the patient, as the swelling decreases. All of these patients are referred to a formal physical therapy program. This program emphasizes active contraction of the quadriceps and hamstrings, isometrics, straight leg raises,
Patellar dislocation in skeletally immature athletes and return to early full weight bearing. The patient is quickly advanced to riding an exercise bike, first with a light load on the injured leg. The load on the injured leg is increased as the patient is capable of assuming more demands on the lower extremity. As recovery progresses, we will encourage patients to “stand in the saddle” on the exercise bike, to place more proprioceptive/coordination demands on the knee. If the patient has access to a pool, we encourage them to swim laps with a kickboard. The kickboard program is done in both a prone and supine position, as the prone position focuses on the hip flexors and quadriceps, and the supine position focuses on the gluteals and hamstrings. Return to running activity also is managed closely, with a stepwise return to activity. Athletes will start with easy jogging and slowly increase their speed. Cutting and directional change activity is started at slow speed in a controlled noncompetitive environment, and the speed is slowly increased. The patient will then begin work on sports specific activity. An emphasis on strengthening and stretching is emphasized throughout the recovery program. For first time dislocators, our usual protocol is to have them complete their rehab program, and return to sport. The time to return to sport is 6 to 16 weeks, depending on the age of the patient, rate of progression with the PT program, presence of significant clinical signs of instability/apprehension on the examination, higher- versus lower-demand athletic activity, etc. Patients must demonstrate full range of motion, excellent strength, and evidence of coordinated lower-extremity function appropriate for their highest demand sport activity before being cleared to return to sport or unlimited activity. Patients are followed closely for future symptoms, either pain, mechanical complaints arising from the patellofemoral joint, or future subluxation events. Patients are counseled about the possibility of future problems with respect to subluxation, dislocation, cartilage problems, etc.
Operative Treatment Protocol The treatment protocols for patella dislocation continue to evolve.8 During the last 10 years, a growing number of studies have looked at the medial patellar restraints, the medial patellofemoral ligament,18,25,43-45,47,86,94,101,104-112 and the configuration of the trochlea.26,27,29,31,40 As these anatomic and clinical follow-up studies continue, we anticipate continued modification to our treatment protocols. In most cases of first time dislocation, we do not recommend surgical intervention. In cases with significant laxity and soft-tissue disruption, or significant osteochondral injury in association with intra-articular fragment, operative intervention may be discussed with the patient and family after the first dislocation event. In most cases, a rehab program will be initiated. Modification of sports activities or switching to lower risk sports can be considered, but in our experience, most young athletes and their parents are not particularly interested in changing to other sports, or giving up one sport altogether. Significant osteochondral injuries may be approached ar-
193 throscopically. Lesser injuries, those with bone contusions without significant chondral defects, or those without obvious free fragments, are observed. For larger chondral defects, free fragment removal is performed and the chondral defects may be treated with microfracture. The athlete and the family will be counseled about the significance of chondral injury and the potential for long-term problems with osteoarthritis. Although most of the osteochondral fragments are not amenable to repair, larger fragments will be repaired in an arthroscopic, mini-open, or open manner. In our experience, MRI sequences will usually identify significant free fragments or damage that may indicate early surgery. On occasion, the MRI may miss these fragments, or these fragments may detach later and lead to mechanical symptoms, and surgery may be performed at a later date. We routinely counsel patients about the possibility of future symptoms, as well as the possibility of future surgery to address these symptoms. If patients present with a history of previous dislocations and/or subluxation episodes, or those that have failed a nonoperative rehab program, athletes and their families will be counseled about surgical options. In some cases, the presence of significant soft tissue laxity or other risk factors may be an indication for surgery after a first time dislocation. Although patients are examined for anatomic factors that may predispose them to dislocations, we find that young athletes who present to our clinic do not have obvious osseous deformities such a increased Q-angles, torsional abnormalities, genu valgum, patella alta, etc. Fithian identified several historical and anatomic risk factors for predicting secondary dislocations: young age at presentation, female gender, history of previous dislocation or subluxation event, family history of dislocation/subluxation event, developmental hip dysplasia, increase quadriceps angle, and torsional malalignment.9,59 Hinton and coworkers have outlined the main indications for surgery in young athletes, and we believe that his surgical algorithm is appropriate for most patients.8 The relative indications for surgery include the following: ● ● ● ● ●
Failure to improve with nonoperative care; Concurrent osteochondral injury; Continued gross instability; Palpable disruption of the medial patellofemoral ligament and the vastus medialis obliquus; and High-level athletic demands coupled with mechanical risk factors and an initial injury mechanism not related to contact
For patients that undergo surgery, we perform a thorough examination of both knees under anesthesia. The degree of patellar laxity is assessed for both the normal and abnormal knee. In some cases, both knees will be prepped during the procedure, as this will allow comparison of both knees, to assess the appropriate tension of the retinacular tissues on the repaired side. For many of our patients with recurrent dislocation/subluxation episodes, we first evaluate the medial patellofemoral ligament structures. If the patients do not have other significant anatomic issues, these patients may undergo primary
K.G. Shea, K. Nilsson, and J. Belzer
194 repair and advancement of these medial retinacular tissues. The use of supplemental tissue, such as semitendinosis autograft or allograft, may be determined preoperatively, or intraoperatively.37,95,101,104 If the medial tissues are of questionable quality/integrity, supplemental tissue may be used. Although a lateral release may be performed, it is exceptionally rare in our surgical practice to do so. The lateral retinacular tissues rarely seem to contribute to undue lateral tension of the patellofemoral restraints and, in our opinion, lateral release is rarely indicated. Lateral release is not without complications, and reports of medial patellar instability have been reported.41,96,114,115 In addition to reconstruction and/or tightening of the static medial restraints, we may also combine this with a distal advancement or repair of the damaged/avulsed vastus medialis obliquus. In addition to an anatomic reconstruction of the medial retinaculum, the medial patellofemoral ligament, and repair/ advancement of the vastus medialis oblique, additional softtissue reconstruction may be done in select cases. This may be most appropriate in patients with excessive soft-tissue laxity, previous surgery, or other factors that suggest a greater rate of surgical failure. These patients may have additional reconstruction of the patellotibial ligaments, using autograft or allograft.8,116,117 Like Hinton and coworkers, we do not routinely reconstruct the patello-tibial ligament.8 In cases with functional abnormalities of the Q angle, a tubercle transfer may be considered.52 We do this procedure in skeletally immature patients, to reduce the risk of growth disturbance in the tibia, such as recurvatum.8,61,100 Recent studies of patellofemoral sulcus dysplasia have attempted to define normal and pathologic anatomy of the patellofemoral joint.27-29,31,118 Although we have very limited experience with procedures that attempt to modify the configuration and/or depth of the sulcus, we follow these anatomic and surgical studies closely.26,119-120 These procedures would have the potential to damage the distal femoral physis and, therefore, may be best delayed until skeletal maturity. Regardless of the surgical procedure performed, a closely supervised physical therapy program is started early after surgery. The program is modified to account for patient variables, such as significant soft-tissue laxity. Prolonged immobilization is best avoided because of concerns about arthrofibrosis, cartilage atrophy, and significant muscle atrophy. With the use of a hinged knee brace, motion is progressed to allow for early recovery of motion of the knee and patellofemoral joint. Patellofemoral mobilization modalities are implemented as well, to reduce the risk of arthrofibrosis of the patellofemoral joint. Patients are slowly returned to sports specific activity using a similar protocol described in the previous section.71,113
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copy and examination under anaesthesia in the diagnosis of fresh injury haemarthrosis of the knee joint. Injury 19:21-24, 1988 Iobst CA, Stanitski CL: Acute knee injuries. Clin Sports Med 19:621635, vi, 2000 Stanitski CL: Patellar instability in the school age athlete. Instr Course Lect 47:345-350, 1998 Nietosvaara Y, Aalto K, Kallio PE: Acute patellar dislocation in children: incidence and associated osteochondral fractures. J Pediatr Orthop 14:513-515, 1994 Atkin DM, Fithian DC, Marangi KS, et al: Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med 28:472-479, 2000 Hinton RY, Sharma KM: Acute and recurrent patellar instability in the young athlete. Orthop Clin North Am 34:385-396, 2003 Fithian DC, Paxton EW, Stone ML, et al: Epidemiology and natural history of acute patellar dislocation. Am J Sports Med 32:1114-1121, 2004 Cash JD, Hughston JC: Treatment of acute patellar dislocation. Am J Sports Med 16:244-249, 1988 Bassi RS, Kumar BA: Superior dislocation of the patella; a case report and review of the literature. Emerg Med J 20:97-98, 2003 Beasley LS, Vidal AF: Traumatic patellar dislocation in children and adolescents: treatment update and literature review. Curr Opin Pediatr 16:29-36, 2004 Hughston JC, Deese M: Medial subluxation of the patella as a complication of lateral retinacular release. Am J Sports Med 16:383-388, 1988 Joseph G, Devalia K, Kantam K, et al: Superior dislocation of the patella. Case report and review of literature. Acta Orthop Belg 71:369371, 2005 Choudhary RK, Tice JW: Intra-articular dislocation of the patella with incomplete rotation—two case reports and a review of the literature. Knee 112:125-127, 2004 Stanitski CL: Patellofemoral mechanism, in DeLee JC, Drez D (eds): DeLee & Drez’s Orthopaedic Sports Medicine: Principles and Practice. Philadelphia, WB Saunders, 2003, pp 1814-1840 Senavongse W, Farahmand F, Jones J, et al: Quantitative measurement of patellofemoral joint stability: force-displacement behavior of the human patella in vitro. J Orthop Res 21:780-786, 2003 Arendt EA, Fithian DC, Cohen E: Current concepts of lateral patella dislocation. Clin Sports Med 21:499-519, 2002 Lancourt JE, Cristini JA: Patella alta and patella infera. Their etiological role in patellar dislocation, chondromalacia, and apophysitis of the tibial tubercle. J Bone Joint Surg Am 57:1112-1125, 1975 Simmons E Jr., Cameron JC: Patella alta and recurrent dislocation of the patella. Clin Orthop Relat Res 274:265-269, 1992 Singerman R, Davy DT, Goldberg VM: Effects of patella alta and patella infera on patellofemoral contact forces. J Biomech 27:1059-1065, 1994 Airanow S, Zippel H: [Femoro-tibial torsion in patellar instability. A contribution to the pathogenesis of recurrent and habitual patellar dislocations]. Beitr Orthop Traumatol 37:311-316, 1990 Cameron JC, Saha S: External tibial torsion: an underrecognized cause of recurrent patellar dislocation. Clin Orthop Relat Res 328:177-184, 1996 Elgafy H, El-Kawy S, Elsafy M, et al: Internal torsion of the distal femur as a cause of habitual dislocation of the patella: a case report and a review of causes of patellar dislocation. Am J Orthop 34:246-248, 2005 Schoettle PB, Werner CM, Romero J: Reconstruction of the medial patellofemoral ligament for painful patellar subluxation in distal torsional malalignment: a case report. Arch Orthop Trauma Surg 125: 644-648, 2005 Fucentese SF, Schottle PB, Pfirrmann CW, et al: CT changes after trochleoplasty for symptomatic trochlear dysplasia. Knee Surg Sports Traumatol Arthrosc (in press)
Patellar dislocation in skeletally immature athletes 27. Fucentese SF, von Roll A, Koch PP, et al: The patella morphology in trochlear dysplasia—a comparative MRI study. Knee 13:145-150, 2006 28. Hing CB, Shepstone L, Marshall T, et al: A laterally positioned concave trochlear groove prevents patellar dislocation. Clin Orthop Relat Res 447:187-194, 2006 29. Pfirrmann CW, Zanetti M, Romero J, et al: Femoral trochlear dysplasia: MR findings. Radiology 216:858-864, 2000 30. Remy F, Chantelot C, Fontaine C, et al: Inter- and intraobserver reproducibility in radiographic diagnosis and classification of femoral trochlear dysplasia. Surg Radiol Anat 20:285-289, 1998 31. Schottle PB, Fucentese SF, Pfirrmann C, et al: Trochleaplasty for patellar instability due to trochlear dysplasia: a minimum 2-year clinical and radiological follow-up of 19 knees. Acta Orthop 76:693-698, 2005 32. Mizuno Y, Kumagai M, Mattessich SM, et al: Q-angle influences tibiofemoral and patellofemoral kinematics. J Orthop Res 19:834-840, 2001 33. Grelsamer RP, Bazos AN, Proctor CS: Radiographic analysis of patellar tilt. J Bone Joint Surg Br 75:822-824, 1993 34. Pookarnjanamorakot C, Jaovisidha S, Apiyasawat P: The patellar tilt angle: correlation of MRI evaluation with anterior knee pain. J Med Assoc Thai 81:958-963, 1998 35. Beals RK, Eckhardt AL: Hereditary onycho-osteodysplasia (Nail-Patella syndrome). A report of nine kindreds. J Bone Joint Surg Am 51:505-516, 1969 36. Geary M, Schepsis A: Management of first-time patellar dislocations. Orthopedics 27:1058-62, 2004 37. Schottle PB, Fucentese SF, Romero J: Clinical and radiological outcome of medial patellofemoral ligament reconstruction with a semitendinosus autograft for patella instability. Knee Surg Sports Traumatol Arthrosc 13:516-521, 2005 38. Maenpaa H, Lehto MU: Patellar dislocation has predisposing factors. A roentgenographic study on lateral and tangential views in patients and healthy controls. Knee Surg Sports Traumatol Arthrosc 4:212216, 1996 39. Maenpaa H, Lehto MU: Patellofemoral osteoarthritis after patellar dislocation. Clin Orthop Relat Res 339:156-162, 1997 40. Stanitski CL: Articular hypermobility and chondral injury in patients with acute patellar dislocation. Am J Sports Med 23:146-150, 1995 41. Sherman OH, Fox JM, Sperling H, et al: Patellar instability: treatment by arthroscopic electrosurgical lateral release. Arthroscopy 3:152160, 1987 42. Bharam S, Vrahas MS, Fu FH: Knee fractures in the athlete. Orthop Clin North Am 33:565-574, 2002 43. Desio SM, Burks RT, Bachus KN: Soft tissue restraints to lateral patellar translation in the human knee. Am J Sports Med 26:59-65, 1998 44. Smirk C, Morris H: The anatomy and reconstruction of the medial patellofemoral ligament. Knee 10:221-227, 2003 45. Burks RT, Desio SM, Bachus KN, et al: Biomechanical evaluation of lateral patellar dislocations. Am J Knee Surg 11:24-31, 1998 46. Sallay PI, Poggi J, Speer KP, et al: Acute dislocation of the patella. A correlative pathoanatomic study. Am J Sports Med 24:52-60, 1996 47. Conlan T, Garth WP Jr, Lemons JE: Evaluation of the medial softtissue restraints of the extensor mechanism of the knee. J Bone Joint Surg Am 75:682-693, 1993 48. Hautamaa PV, Fithian DC, Kaufman KR, et al: Medial soft tissue restraints in lateral patellar instability and repair. Clin Orthop Relat Res 349:174-182, 1998 49. Reider B, Marshall JL, Koslin B, et al: The anterior aspect of the knee joint. J Bone Joint Surg Am 63:351-356, 1981 50. Panagiotopoulos E, Strzelczyk P, Herrmann M, et al: Cadaveric study on static medial patellar stabilizers: the dynamizing role of the vastus medialis obliquus on medial patellofemoral ligament. Knee Surg Sports Traumatol Arthrosc 14:7-12, 2006 51. Ahstrom JP Jr: Osteochondral fracture in the knee joint associated with hypermobility and dislocation of the patella. Report of eighteen cases. J Bone Joint Surg Am 47:1491-1502, 1965
195 52. Cofield RH, Bryan RS: Acute dislocation of the patella: results of conservative treatment. J Trauma 17:526-531, 1977 53. Garth WP Jr., Pomphrey M Jr., Merrill K: Functional treatment of patellar dislocation in an athletic population. Am J Sports Med 24: 785-791, 1996 54. Grogan DP, Carey TP, Leffers D, Ogden JA: Avulsion fractures of the patella. J Pediatr Orthop 10:721-730, 1990 55. Hawkins RJ, Bell RH, Anisette G: Acute patellar dislocations. The natural history. Am J Sports Med 14:117-120, 1986 56. Hughston JC: Subluxation of the patella. J Bone Joint Surg Am 50: 1003-1026, 1968 57. Rorabeck CH, Bobechko WP: Acute dislocation of the patella with osteochondral fracture: a review of eighteen cases. J Bone Joint Surg Br 58:237-240, 1976 58. Mashoof AA, Scholl MD, Lahav A, et al: Osteochondral injury to the mid-lateral weight-bearing portion of the lateral femoral condyle associated with patella dislocation. Arthroscopy 21:228-232, 2005 59. Fithian DC, Paxton EW, Cohen AB: Indications in the treatment of patellar instability. J Knee Surg 17:47-56, 2004 60. Larsen E, Lauridsen F: Results of conservative treatment of patellar dislocations. Acta Orthop Belg 48:455-462, 1982 61. Macnab I: Recurrent dislocation of the patella. J Bone Joint Surg Am 34 A:957-967; passim, 1952 62. Larsen E, Lauridsen F: Conservative treatment of patellar dislocations. Influence of evident factors on the tendency to redislocation and the therapeutic result. Clin Orthop Relat Res 171:131-136, 1982 63. Maenpaa H, Lehto MU: Patellar dislocation. The long-term results of nonoperative management in 100 patients. Am J Sports Med 25:213217, 1997 64. Nikku R, Nietosvaara Y, Kallio PE, et al: Operative versus closed treatment of primary dislocation of the patella. Similar 2-year results in 125 randomized patients. Acta Orthop Scand 68:419-423, 1997 65. Nikku R, Nietosvaara Y, Aalto K, et al: Operative treatment of primary patellar dislocation does not improve medium-term outcome: a 7-year follow-up report and risk analysis of 127 randomized patients. Acta Orthop 76:699-704, 2005 66. Nikolai N: [Traumatic patellar dislocation and its sequelae.]. Monatsschr Unfallheilkd Versicherungsmed 63:215-224, 1960 67. Dainer RD, Barrack RL, Buckley SL, et al: Arthroscopic treatment of acute patellar dislocations. Arthroscopy 4:267-271, 1988 68. Murray TF, Dupont JY, Fulkerson JP: Axial and lateral radiographs in evaluating patellofemoral malalignment. Am J Sports Med 27:580584, 1999 69. Aglietti P, Insall JN, Cerulli G: Patellar pain and incongruence. I: Measurements of incongruence. Clin Orthop Relat Res 176:217-224, 1983 70. Inoue M, Shino K, Hirose H, et al: Subluxation of the patella. Computed tomography analysis of patellofemoral congruence. J Bone Joint Surg Am 70:1331-1337, 1988 71. Davies AP, Costa ML, Shepstone L, et al: The sulcus angle and malalignment of the extensor mechanism of the knee. J Bone Joint Surg Br 82:1162-1166, 2000 72. Martinez S, Korobkin M, Fondren FB, et al: Computed tomography of the normal patellofemoral joint. Invest Radiol 18:249-253, 1983 73. Martinez S, Korobkin M, Fondren FB, et al: Diagnosis of patellofemoral malalignment by computed tomography. J Comput Assist Tomogr 7:1050-1053, 1983 74. McNally EG, Ostlere SJ, Pal C, et al: Assessment of patellar maltracking using combined static and dynamic MRI. Eur Radiol 10:10511055, 2000 75. Koshino T, Sugimoto K: New measurement of patellar height in the knees of children using the epiphyseal line midpoint. J Pediatr Orthop 9:216-218, 1989 76. Pope TL Jr: MR imaging of patellar dislocation and relocation. Semin Ultrasound CT MR 22:371-382, 2001 77. Koskinen SK, Kujala UM: Patellofemoral relationships and distal insertion of the vastus medialis muscle: a magnetic resonance imaging study in nonsymptomatic subjects and in patients with patellar dislocation. Arthroscopy 8:465-468, 1992
196 78. Koskinen SK, Taimela S, Nelimarkka O, et al: Magnetic resonance imaging of patellofemoral relationships. Skeletal Radiol 22:403-410, 1993 79. Kujala UM, Osterman K, Kormano M, et al: Patellofemoral relationships in recurrent patellar dislocation. J Bone Joint Surg Br 71:788792, 1989 80. Vainionpaa S, Laasonen E, Patiala H, et al: Acute dislocation of the patella. Clinical, radiographic and operative findings in 64 consecutive cases. Acta Orthop Scand 57:331-333, 1986 81. Jarvinen M: Acute patellar dislocation— closed or operative treatment? Acta Orthop Scand 68:415-418, 1997 82. Chen SC, Ramanathan EB: The treatment of patellar instability by lateral release. J Bone Joint Surg Br 66:344-348, 1984 83. Fulkerson JP, Schutzer SF: After failure of conservative treatment for painful patellofemoral malalignment: lateral release or realignment? Orthop Clin North Am 17:283-288, 1986 84. Metcalf RW: An arthroscopic method for lateral release of subluxating or dislocating patella. Clin Orthop Relat Res 167:9-18, 1982 85. Schreiber SN: Arthroscopic lateral retinacular release using a modified superomedial portal, electrosurgery, and postoperative positioning in flexion. Orthop Rev 17:375-380, 1988 86. Ahmad CS, Stein BE, Matuz D, et al: Immediate surgical repair of the medial patellar stabilizers for acute patellar dislocation. A review of eight cases. Am J Sports Med 28:804-810, 2000 87. Brief LP: Lateral patellar instability: treatment with a combined openarthroscopic approach. Arthroscopy 9:617-623, 1993 88. Scuderi G, Cuomo F, Scott WN: Lateral release and proximal realignment for patellar subluxation and dislocation. A long-term follow-up. J Bone Joint Surg Am 70:856-861, 1988 89. Fukushima K, Horaguchi T, Okano T, et al: Patellar dislocation: arthroscopic patellar stabilization with anchor sutures. Arthroscopy 20: 761-764, 2004 90. Koskinen SK, Hurme M, Kujala UM: Restoration of patellofemoral congruity by combined lateral release and tibial tuberosity transposition as assessed by MRI analysis. Int Orthop 15:363-366, 1991 91. Coons DA, Barber FA: Thermal medial retinaculum shrinkage and lateral release for the treatment of recurrent patellar instability. Arthroscopy 22:166-171, 2006 92. Luscombe KL, Maffulli N: The three in one procedure: how I do it. Surgeon 2:32-36, 2004 93. Myers P, Williams A, Dodds R, et al: The three-in-one proximal and distal soft tissue patellar realignment procedure. Results, and its place in the management of patellofemoral instability. Am J Sports Med 27:575-579, 1999 94. Cossey AJ, Paterson R: A new technique for reconstructing the medial patellofemoral ligament. Knee 12:93-98, 2005 95. Fernandez E, Sala D, Castejon M: Reconstruction of the medial patellofemoral ligament for patellar instability using a semitendinosus autograft. Acta Orthop Belg 71:303-308, 2005 96. Fithian DC, Paxton EW, Post WR, et al: Lateral retinacular release: a survey of the International Patellofemoral Study Group. Arthroscopy 20:463-468, 2004 97. Aglietti P, Buzzi R, De Biase P, et al: Surgical treatment of recurrent dislocation of the patella. Clin Orthop Relat Res 308:8-17, 1994 98. Aglietti P, Pisaneschi A, De Biase P: Recurrent dislocation of patella: three kinds of surgical treatment. Ital J Orthop Traumatol 181:25-36, 1992 99. Dandy DJ, Desai SS: The results of arthroscopic lateral release of the extensor mechanism for recurrent dislocation of the patella after 8 years. Arthroscopy 10:540-545, 1994 100. Harrison MH: The results of a realignment operation for recurrent dislocation of the patella. J Bone Joint Surg Br 37-B:559-567, 1955
K.G. Shea, K. Nilsson, and J. Belzer 101. Deie M, Ochi M, Sumen Y, et al: Reconstruction of the medial patellofemoral ligament for the treatment of habitual or recurrent dislocation of the patella in children. J Bone Joint Surg Br 85:887-890, 2003 102. Fondren FB, Goldner JL, Bassett FH 3rd: Recurrent dislocation of the patella treated by the modified Roux-Goldthwait procedure. A prospective study of forty-seven knees. J Bone Joint Surg Am 67:9931005, 1985 103. Vahasarja V, Kinnunen P, Lanning P, et al: Operative realignment of patellar malalignment in children. J Pediatr Orthop 15:281-285, 1995 104. Deie M, Ochi M, Sumen Y, et al: A long-term follow-up study after medial patellofemoral ligament reconstruction using the transferred semitendinosus tendon for patellar dislocation. Knee Surg Sports Traumatol Arthrosc 13:522-528, 2005 105. Elias DA, White LM, Fithian DC: Acute lateral patellar dislocation at MR imaging: injury patterns of medial patellar soft-tissue restraints and osteochondral injuries of the inferomedial patella. Radiology 225: 736-743, 2002 106. Ellera Gomes JL: Medial patellofemoral ligament reconstruction for recurrent dislocation of the patella: a preliminary report. Arthroscopy 8:335-340, 1992 107. Luo ZP, Sakai N, Rand JA, et al: Tensile stress of the lateral patellofemoral ligament during knee motion. Am J Knee Surg 10:139-144, 1997 108. Mikashima Y, Kimura M, Kobayashi Y, et al: Clinical results of isolated reconstruction of the medial patellofemoral ligament for recurrent dislocation and subluxation of the patella. Acta Orthop Belg 72:65-71, 2006 109. Muneta T, Sekiya I, Tsuchiya M, et al: A technique for reconstruction of the medial patellofemoral ligament. Clin Orthop Relat Res 359: 151-155, 1999 110. Ostermeier S, Stukenborg-Colsman C, Hurschler C, et al: In vitro investigation of the effect of medial patellofemoral ligament reconstruction and medial tibial tuberosity transfer on lateral patellar stability. Arthroscopy 22:308-319, 2006 111. Sanders TG, Morrison WB, Singleton BA, et al: Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr 25:957-962, 2001 112. Satterfield WH, Johnson DL: Arthroscopic patellar “bankart” repair after acute dislocation. Arthroscopy 21:627, 2005 113. Koeter S, Bongers EM, de Rooij J, et al: Minimal rotation aberrations cause radiographic misdiagnosis of trochlear dysplasia. Knee Surg Sports Traumatol Arthrosc 1-5, 2006 114. Nonweiler DE, DeLee JC: The diagnosis and treatment of medial subluxation of the patella after lateral retinacular release. Am J Sports Med 22:680-686, 1994 115. Teitge RA, Torga Spak R: Lateral patellofemoral ligament reconstruction. Arthroscopy 20:998-1002, 2004 116. Drez D Jr, Edwards TB, Williams CS: Results of medial patellofemoral ligament reconstruction in the treatment of patellar dislocation. Arthroscopy 17:298-306, 2001 117. Letts RM, Davidson D, Beaule P: Semitendinosus tenodesis for repair of recurrent dislocation of the patella in children. J Pediatr Orthop 19:742-747, 1999 118. van Huyssteen AL, Hendrix MR, Barnett AJ, et al: Cartilage-bone mismatch in the dysplastic trochlea. An MRI study. J Bone Joint Surg Br 88:688-691, 2006 119. Johnson AL, Probst CW, Decamp CE, et al: Comparison of trochlear block recession and trochlear wedge recession for canine patellar luxation using a cadaver model. Vet Surg 30:140-150, 2001 120. Verdonk R, Jansegers E, Stuyts B: Trochleoplasty in dysplastic knee trochlea. Knee Surg Sports Traumatol Arthrosc 13:529-533, 2005
P
atellar dislocation is a common injury in the skeletally immature patient1 and is one of the most common causes of acute hemarthrosis in young athletes.2-5 Studies have demonstrated an annual incidence of this injury at 5.8 per 100,000, with studies in pediatric patients having a higher incidence of 43 per 100,000.6 Some studies have suggested that males and females have equal rates of dislocation,7,8 and others have demonstrated the highest rate of dislocation in girls younger than 18 years of age.9 Although seen in association with underlying diseases, these injuries are very common in the young athlete. These injuries frequently are seen with sports that involve rapid directional change or cutting.7,10
Anatomy Most dislocations occur in a lateral direction and are associated with injury to the medial retinacular tissues and the medial patellofemoral ligament. Medial and superior dislocation also can occur,11-14 and rare cases of intra-articular dislocation also have been reported.15 The patellofemoral joint is complex, and the path of the patella during knee motion is a complex combination of motion in multiple planes.16 At full extension, the patella assumes a slightly lateral relationship to
*Center for Orthopaedics and Biomechanics Research, Intermountain Orthopaedics, Boise State University, Boise, ID. †Medical College of Wisconsin, Madison, WI. Address reprint requests to Kevin G. Shea, MD, Boise State University, Center for Orthopaedics and Biomechanics Research, Intermountain Orthopaedics, 600 N Robbins Road, Suite 100, Boise, ID 83702. E-mail: kshea@ intermountainortho.com
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the femoral groove and, in this position, the patella may assume the most lateral displacement.17 During the first 30° of flexion, the patella begins to engage the femoral sulcus.12,17 In patients with patellar alta, the patella may not engage the trochlear groove until additional flexion occurs, which may contribute to patellar instability and an increased risk of patellar instability.1,7,8,18
Anatomic Risk Factors Although these injuries may be seen in association with anatomic conditions (increased genu valgum, patella alta,19-21 lower-extremity version abnormalities,22-25 trochlear dysplasia,26-31 increased quadriceps angle,32 foot pronation, patellar tilt,33,34 etc.),31,35-37 the relationship between these physical findings and patellar instability is not clearly defined.7,8,38,39 Patellar dislocations occur in otherwise-normal individuals,7,8 although soft-tissue laxity may be a significant risk factor.7,8,40 In recent studies of trochlear dysplasia, authors have attempted to define the relationship between trochlear morphology and patellar dislocation.27,24,31,41 The results of some of these studies have suggested that trochlear dysplasia may have a genetic basis,27 and other studies have suggested that the risk of dislocation may be higher in some families.9
Mechanism of Injury Several different mechanisms of injury have been proposed, including direct and indirect mechanisms.42 The indirect mechanism involves a position of internal rotation of the femur, knee valgus, and a planted foot in combination with a quadriceps contraction.8,11 The direct mechanism involves a
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Figure 1 Medial soft-tissue restraints of the knee. (Reprinted with permission from Clarke HD, Scott WN, Insall JN: Anatomy, in Insall JN, Scott WN (eds): Surgery of the Knee (ed 3, vol 1). Philadelphia, WB Saunders, 2001, p 52.)
laterally directed force to the medial aspect of the patella. Combinations of these mechanisms can occur.42
Medial Patellofemoral Ligament Although the medial retinacular tissues limit the lateral displacement of the patella, the medial patellofemoral ligament is one of the primary restraints to patellar dislocation (Figs. 1 and 2). Injury to this ligament is common during patellar dislocation.43,44 This structure originates from the adductor tubercle region of the femoral condyle, travels transversely, and attaches to the upper two-thirds of the medial patellar border.43,44,45,46 Biomechanical studies have shown this to be
Figure 3 MRI demonstrating injury to the lateral femoral condyle, with associated cartilage defect and subchondral bone contusion.
one of the main soft-tissue structures preventing lateral patellar dislocations.43-45,47-49 Other structures contribute to stability of the patella with respect to lateral subluxation, including the meniscopatellar and tibio patellar ligaments, and the dynamic contribution of the vastus medialis obliquus muscle.12,50
Osteochondral Injuries In addition to disruption of the medial restraints and the medial patellofemoral ligament that occurs during acute lateral patellar dislocation, osteochondral fractures and contusions are seen in as many as 40% to 50% of patients.10,51,52-57 During the dislocation, the osteochondral fragments may originate from the lateral femoral condyle (Fig. 3) or the medial patella facet (Fig. 4). These injuries may result from a shearing force during the patellar dislocation. In some cases, the osteochondral injury of the lateral femoral condyle may be in a more posterior region, in areas of significant weight bearing during full extension.58
Natural History Figure 2 Medial patellofemoral ligament. A right cadaveric knee medial view. The “P” is the patella tendon. The open arrow is on the patellomeniscal ligament. The curved arrow is on the patellotibial ligament, which has been reflected from the tibia. The deep surface is seen and the tibial attachment is in the forceps. The large arrow points to the medial patellofemoral ligament, which is also supported by a probe. The arrowhead is on the superficial medial collateral ligament. (Reprinted with permission from Desio et al.43)
Several studies have attempted to define the natural history of this injury in adult and skeletally immature athletes. Additional long-term studies will be necessary to assess the incidence of osteoarthritis, define subgroups that have a higher risk of secondary dislocation events, and determine the effectiveness of nonoperative and operative treatment regimens.59 Additional study in younger athletes also will help better
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Figure 4 MRI demonstrating injury to the patella, with associated subchondral bone contusion, osteocartilagenous injury to the patella, and detached osteochondral fragment (arrows).
clarify the natural history of this injury.1,9,52,55,60,61 Studies have demonstrated redislocation rates of 13% to 52% for nonsurgical treatment.10,39,52,62-64 Significant knee dysfunction may persist, even in patients that don’t have secondary dislocation episodes.7,55 Previous studies on patellar dislocation demonstrate a small number of prospective designs. These study designs may be the best to identify the natural history of this condition and to determine which patients need operative or nonoperative treatment regimens. A limited number of prospective studies have evaluated the natural history of patellar dislocations, with a specific focus on secondary dislocation and other dysfunction.9,59,65,66 In a well-designed prospective cohort study, Fithian and coworkers9 followed 189 patients for 2 to 5 years. The group with the highest risk of dislocations was females ages 10 to 17 years; 61% of dislocations occurred during sports, and 9% during dancing. The risk of recurrent patellar instability/dislocation appeared to be significantly greater in females. Young age at the time of the first dislocation also was a significant risk factor for future dislocation/subluxation events.
Evaluation Clinical Evaluation Patients with a first-time patellar dislocation may recall a specific dislocation event, which may have spontaneously reduced, or may have required a reduction at the scene of injury or the emergency room. In other cases, patients may describe a significant “pop” or other major mechanical sensation or event, although they may not realize that a dislocation occurred. The dislocation/relocation sequence may oc-
cur very quickly. The history, examination, and image evaluation will determine if patellar dislocation occurred. Athletes with a first-time patellar dislocation usually present with a significant effusion. Many patients have been evaluated in the emergency room and have been placed in a knee immobilizer and advised to use crutches. Patients may be quite uncomfortable and apprehensive, and the examiner should work to help the patient relax as much as possible, which will facilitate a more complete examination. The examination should include a thorough evaluation and look for other injuries, including ligamentous injuries such as the ACL or MCL, osteochondral injuries, meniscus tears, etc. Injuries to the medial retinacular restraints and the medial patellofemoral ligament may produce tenderness in the region of the MCL. Gentle valgus stress maneuvers with the knee near full extension, and in 30° to 45° of flexion, should help determine whether MCL injury has occurred. With regards to the examination of the patellofemoral joint, the examiner should palpate the medial retinacular structures, looking for evidence of disruption of these tissues. Significant ecchymosis or palpable defects could be evidence of major structural damage to these tissues. This palpation should be done very gently because it will not require much pressure to produce discomfort while palpating the traumatized structures. Palpation should also include the entire medial and superomedial border of the patella, and the vastus medialis. These areas may be tender because of medial retinacular avulsion, avulsion injury of the vastus medialis, and/or the presence of osteochondral injury from the medial aspect of the patella. The lateral femoral condyle should also be palpated, to look for evidence of chondral injury, as areas of tenderness may be present, suggesting underlying chondral injury. The evaluation of patellar stability, especially with regards to significant lateral laxity because of traumatized medial restraints, may be challenging in the first 1 to 15 days after the dislocation (Fig. 5). Patellar mobilization after the initial injury may be quite uncomfortable for the patient, and more information may be obtained after the knee has had several weeks of recovery and therapy. Comparison of the injured knee to the uninjured knee can provide very useful information when determining the degree of laxity of the patellofemoral joint. Many patients, especially female, may have other signs of soft-tissue laxity, or other anatomic issues that predispose them to primary and secondary dislocations events.59 Stanitski has emphasized the importance of evaluating patients for signs of soft-tissue laxity.40 Evaluating the patients for genu recurvatum, hyperextension of the elbows, and softtissue laxity of the wrist, thumbs, and fingers also may be helpful during the evaluation and subsequent treatment.
Imaging Evaluation Anteroposterior, lateral, and Merchant view radiographs can evaluate for patella alta/baja, or osteochondral fractures of the patella or intercondylar groove or lateral femoral condyle. Avulsion injuries may be seen of the medial aspect of the
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191 significant information with regards to the location and magnitude of soft-tissue and osteochondral injury, and the anatomy of the trochlea.43,46,76 Several MRI studies have demonstrated significant injury, which may be missed on the initial radiographic evaluation.3,40,67,55 MRI sequences also have been used in the evaluation of anatomic parameters associated with patellar dislocation, including vastus medialis insertion,77 patellar tilt,78 and sulcus angle.79 For athletes, we are obtaining MRI studies early in the evaluation process, which may allow for the identification of trochlear dysplasia, as well as evidence of significant osteochondral injuries, or intra-articular fragments. This information can be useful during the evaluation and during counseling about possible treatment options, both surgical and nonsurgical. For nonathletes or lower-demand individuals, we initially may not obtain an MRI. We counsel these patients that future knee dysfunction may warrant further imaging evaluation. Even in lower demand patients, an MRI may be obtained if we have concerns about significant osteochondral injury or intra-articular fragments.
Treatment
Figure 5 Apprehension sign. Patient anxiety caused by awareness of unpleasantness associated with patellar dislocation. (Reprinted with permission from Stanitski CL: Patellofemoral mechanism, in Stanitski CL, DeLee JC, Drez D Jr (eds): Pediatric and Adolescent Sports Medicine (vol 3). Philadelphia, WB Saunders, 1994, p 340.)
patella and may be best seen on Merchant view radiographs.42 Radiographs are limited in the ability to identify osteochondral injuries.3,55,67 In addition to radiographic evaluation for the presence of osteochondral injuries, radiographic studies have also been used to assess patellofemoral mal-alignment.68 Numerous radiographic and computerized tomographic measures of patellofemoral dysplasia have been described in the literature, including measures of congruence,69,70 sulcus angles,26 patellar tilt,33,72,73 dysplasia,27 subluxation, hyperlaxity, etc. Future studies that use dynamic measurement methods may provide more insight into normal patellofemoral mechanics.74 In our own practice, we routinely evaluate plain radiographs for the presence of patellofemoral alignment or other anomalies, or the presence of significant osteochondral injuries. Most patients come from the emergency department with films available for review. For skeletally immature subjects, the patellar height can be evaluated using the method described by Koshino and coworkers (Fig. 6).75 Although the indications for obtaining an magnetic resonance imaging (MRI) after patellar dislocation may require further clarification in the literature, the MRI can provide
Treatment protocols for patellar dislocation in athletes continue to evolve, and both operative and nonoperative modalities have been recommended for first-time dislocations. At this time, treatment recommendations based on adequate level 1 and 2 studies do not exist. For this reason, most treatment recommendations are based on level 3, 4, and 5 evidence. A recent review of Medline did not identify any randomized prospective studies on the treatment of athletes with first time dislocations. Historically, nonoperative treatment program advocated several weeks of immobilization, followed by therapy to recover motion and strength.10,63,64,80 Because of concerns that
Figure 6 Epiphyseal line midpoint method for measurement of patellar height. The average PT: FT ratio is 1.31 ⫾ 0.09 in full extension and decrease to 0.99 ⫾ 0.06 at 90° of flexion. P, patella; F, femur; T, tibia. (Reprinted with permission from Koshino and Sugimoto.75)
192 immobilization may lead to problems with arthrofibrosis, atrophy of cartilage, muscle, ligaments, and bone, several recent studies have advocated early rehabilitation programs emphasizing range of motion, strengthening, and the use of patellar buttress braces.2,8,81 A limited number of prospective studies have been conducted on patellar dislocation, with respect to comparing operative and nonoperative treatment protocols. Nikku and coworkers studied 126 patients.64 Part of the study group underwent operative treatment, and the other group was treated with nonoperative means. The patients were followed for 2 years. The subjective and objective outcome measures did not differ significantly for these groups. The follow-up period was short, as many studies have demonstrated dislocation after 2 years follow-up. A secondary study of this same patient group at 7 years follow-up did not demonstrate improved outcomes in patients that underwent surgery for primary patellar dislocation.65 Both of these studies had significant limitations, including a nonrandomized design. In a retrospective study, Buchner and coworkers evaluated 126 patients at 8.1 years of follow-up. The study evaluated 2 groups: those managed with or without surgery. The functional and subjective results were good overall, but the recurrence rate was high in both surgical and nonsurgical groups. Although this study had several limitations, including variation in surgical procedures, the authors suggested that many patients may not do better with surgery, although surgery was still indicated in some cases. There are a plethora of operative treatment protocols for the treatment of patellar dislocation, which makes review of the literature even more challenging. During the last 50 years, more than 100 operations have been described to address patellar dislocation. These procedures have ranged from lessinvasive procedures, to open or arthroscopic lateral release,41,67,82-85 to more invasive procedures, including soft-tissue repair/augmentation,86 soft-tissue proximal realignment with lateral release,87,88 medial tissue imbrications,89 tubercle osteotomy with/without soft-tissue procedure,90 thermal shrinkage of medial retinaculum and lateral release,91 transfer of the patellar tendon to the medial collateral ligament,92,93 medial patellofemoral ligament reconstruction,43,45,94,94 distal transposition of the patellar tendon in cases of patella alta.20 More extensive discussion of the plethora of surgical procedures used for patello-femoral dislocation is beyond the scope of this review.
Lateral Release Recent work by Fithian and Paxton and the International Patello-femoral Study Group96 have suggested that the indications for lateral release for the treatment of patellar dislocation/instability is very limited, and these procedure appears to be much less popular than in the past.96 Other authors also have suggested that the results of lateral release for the treatment of patellar dislocation are not predictable, and this isolated procedure is rarely indicated for this condition.97-99
K.G. Shea, K. Nilsson, and J. Belzer
Physeal Considerations in Skeletally Immature Patients The operative treatment options in skeletally immature athletes are somewhat different than those available in adults because of concerns about potential physeal injury to the distal femoral or proximal tibial physis or apophysis. Procedures that violate these structures or the surrounding perichondral ring can produce complications of altered growth, including coronal plane angular deformity, leg length discrepancy, and recurvatum.61,100 For these reasons, soft-tissue procedures are more likely to be appropriate in children or adolescents with significant growth remaining. Numerous soft-tissue procedures have been described, and these procedures range from those with extensive exposure, to those with arthroscopic or minimally invasive approaches. Reconstruction of the medial patellofemoral ligament has been described in children,101 although the close association between the distal femoral physis and the origin of this ligament warrant caution during surgical procedures in this area. Tubercle osteotomy procedures used in adults are contraindicated in those with significant growth remaining. Procedures that involve transfer of the patellar tendon, such as the Roux-Goldthwait patellar tendon transposition, may play a role in some patients with patellar dislocation.102,103 With respect to our practice, the following treatment protocols for nonoperative and operative management will be described.
Nonoperative Treatment Protocol Whether surgical or nonsurgical treatment protocols are chosen, we usually start all patients on an early treatment regimen with several goals: (1) reduction of swelling; (2) early mobilization, strengthening, and proprioception to minimize weakness and associated dysfunction of all major muscle groups of the lower extremity, especially the thigh musculature; and (3) early return to sports and other exercise. Aspiration is performed on some patients, especially those with large effusions. In our experience, a very large effusion may interfere with a rehabilitation program. The effusion may prolong the period of motion recovery and also may have deleterious effect on quadriceps/hamstring activation about the knee. By the time of arrival to the clinic, most of our patients have spent 2 to 10 days in a knee immobilizer and with protected weight bearing. This treatment protocol is almost universal in primary care clinics and emergency rooms. The patients have significant quadriceps/vastus medialis obliquus atrophy, which develops rapidly post injury, especially in patient who have been placed in a knee immobilizer. Cryotherapy is used several times daily for the first several days to weeks, to help with swelling. In some cases, a short course of oral antiinflammatories also may be used, to assist with the effusion. A patella sleeve is also provided to the patient, as the swelling decreases. All of these patients are referred to a formal physical therapy program. This program emphasizes active contraction of the quadriceps and hamstrings, isometrics, straight leg raises,
Patellar dislocation in skeletally immature athletes and return to early full weight bearing. The patient is quickly advanced to riding an exercise bike, first with a light load on the injured leg. The load on the injured leg is increased as the patient is capable of assuming more demands on the lower extremity. As recovery progresses, we will encourage patients to “stand in the saddle” on the exercise bike, to place more proprioceptive/coordination demands on the knee. If the patient has access to a pool, we encourage them to swim laps with a kickboard. The kickboard program is done in both a prone and supine position, as the prone position focuses on the hip flexors and quadriceps, and the supine position focuses on the gluteals and hamstrings. Return to running activity also is managed closely, with a stepwise return to activity. Athletes will start with easy jogging and slowly increase their speed. Cutting and directional change activity is started at slow speed in a controlled noncompetitive environment, and the speed is slowly increased. The patient will then begin work on sports specific activity. An emphasis on strengthening and stretching is emphasized throughout the recovery program. For first time dislocators, our usual protocol is to have them complete their rehab program, and return to sport. The time to return to sport is 6 to 16 weeks, depending on the age of the patient, rate of progression with the PT program, presence of significant clinical signs of instability/apprehension on the examination, higher- versus lower-demand athletic activity, etc. Patients must demonstrate full range of motion, excellent strength, and evidence of coordinated lower-extremity function appropriate for their highest demand sport activity before being cleared to return to sport or unlimited activity. Patients are followed closely for future symptoms, either pain, mechanical complaints arising from the patellofemoral joint, or future subluxation events. Patients are counseled about the possibility of future problems with respect to subluxation, dislocation, cartilage problems, etc.
Operative Treatment Protocol The treatment protocols for patella dislocation continue to evolve.8 During the last 10 years, a growing number of studies have looked at the medial patellar restraints, the medial patellofemoral ligament,18,25,43-45,47,86,94,101,104-112 and the configuration of the trochlea.26,27,29,31,40 As these anatomic and clinical follow-up studies continue, we anticipate continued modification to our treatment protocols. In most cases of first time dislocation, we do not recommend surgical intervention. In cases with significant laxity and soft-tissue disruption, or significant osteochondral injury in association with intra-articular fragment, operative intervention may be discussed with the patient and family after the first dislocation event. In most cases, a rehab program will be initiated. Modification of sports activities or switching to lower risk sports can be considered, but in our experience, most young athletes and their parents are not particularly interested in changing to other sports, or giving up one sport altogether. Significant osteochondral injuries may be approached ar-
193 throscopically. Lesser injuries, those with bone contusions without significant chondral defects, or those without obvious free fragments, are observed. For larger chondral defects, free fragment removal is performed and the chondral defects may be treated with microfracture. The athlete and the family will be counseled about the significance of chondral injury and the potential for long-term problems with osteoarthritis. Although most of the osteochondral fragments are not amenable to repair, larger fragments will be repaired in an arthroscopic, mini-open, or open manner. In our experience, MRI sequences will usually identify significant free fragments or damage that may indicate early surgery. On occasion, the MRI may miss these fragments, or these fragments may detach later and lead to mechanical symptoms, and surgery may be performed at a later date. We routinely counsel patients about the possibility of future symptoms, as well as the possibility of future surgery to address these symptoms. If patients present with a history of previous dislocations and/or subluxation episodes, or those that have failed a nonoperative rehab program, athletes and their families will be counseled about surgical options. In some cases, the presence of significant soft tissue laxity or other risk factors may be an indication for surgery after a first time dislocation. Although patients are examined for anatomic factors that may predispose them to dislocations, we find that young athletes who present to our clinic do not have obvious osseous deformities such a increased Q-angles, torsional abnormalities, genu valgum, patella alta, etc. Fithian identified several historical and anatomic risk factors for predicting secondary dislocations: young age at presentation, female gender, history of previous dislocation or subluxation event, family history of dislocation/subluxation event, developmental hip dysplasia, increase quadriceps angle, and torsional malalignment.9,59 Hinton and coworkers have outlined the main indications for surgery in young athletes, and we believe that his surgical algorithm is appropriate for most patients.8 The relative indications for surgery include the following: ● ● ● ● ●
Failure to improve with nonoperative care; Concurrent osteochondral injury; Continued gross instability; Palpable disruption of the medial patellofemoral ligament and the vastus medialis obliquus; and High-level athletic demands coupled with mechanical risk factors and an initial injury mechanism not related to contact
For patients that undergo surgery, we perform a thorough examination of both knees under anesthesia. The degree of patellar laxity is assessed for both the normal and abnormal knee. In some cases, both knees will be prepped during the procedure, as this will allow comparison of both knees, to assess the appropriate tension of the retinacular tissues on the repaired side. For many of our patients with recurrent dislocation/subluxation episodes, we first evaluate the medial patellofemoral ligament structures. If the patients do not have other significant anatomic issues, these patients may undergo primary
K.G. Shea, K. Nilsson, and J. Belzer
194 repair and advancement of these medial retinacular tissues. The use of supplemental tissue, such as semitendinosis autograft or allograft, may be determined preoperatively, or intraoperatively.37,95,101,104 If the medial tissues are of questionable quality/integrity, supplemental tissue may be used. Although a lateral release may be performed, it is exceptionally rare in our surgical practice to do so. The lateral retinacular tissues rarely seem to contribute to undue lateral tension of the patellofemoral restraints and, in our opinion, lateral release is rarely indicated. Lateral release is not without complications, and reports of medial patellar instability have been reported.41,96,114,115 In addition to reconstruction and/or tightening of the static medial restraints, we may also combine this with a distal advancement or repair of the damaged/avulsed vastus medialis obliquus. In addition to an anatomic reconstruction of the medial retinaculum, the medial patellofemoral ligament, and repair/ advancement of the vastus medialis oblique, additional softtissue reconstruction may be done in select cases. This may be most appropriate in patients with excessive soft-tissue laxity, previous surgery, or other factors that suggest a greater rate of surgical failure. These patients may have additional reconstruction of the patellotibial ligaments, using autograft or allograft.8,116,117 Like Hinton and coworkers, we do not routinely reconstruct the patello-tibial ligament.8 In cases with functional abnormalities of the Q angle, a tubercle transfer may be considered.52 We do this procedure in skeletally immature patients, to reduce the risk of growth disturbance in the tibia, such as recurvatum.8,61,100 Recent studies of patellofemoral sulcus dysplasia have attempted to define normal and pathologic anatomy of the patellofemoral joint.27-29,31,118 Although we have very limited experience with procedures that attempt to modify the configuration and/or depth of the sulcus, we follow these anatomic and surgical studies closely.26,119-120 These procedures would have the potential to damage the distal femoral physis and, therefore, may be best delayed until skeletal maturity. Regardless of the surgical procedure performed, a closely supervised physical therapy program is started early after surgery. The program is modified to account for patient variables, such as significant soft-tissue laxity. Prolonged immobilization is best avoided because of concerns about arthrofibrosis, cartilage atrophy, and significant muscle atrophy. With the use of a hinged knee brace, motion is progressed to allow for early recovery of motion of the knee and patellofemoral joint. Patellofemoral mobilization modalities are implemented as well, to reduce the risk of arthrofibrosis of the patellofemoral joint. Patients are slowly returned to sports specific activity using a similar protocol described in the previous section.71,113
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