Patellar Injury and Dislocation Treatment & Management
- Author: Gerard A Malanga, MD; Chief Editor: Craig C Young, MD more...
During the acute phase of a patellar injury or dislocation, the immediate goals are to reduce inflammation, relieve pain, and stop activities that place excessive loads on the patellofemoral joint. Patients with an acute patella dislocation typically have been evaluated in an emergency department, with radiographic evaluation, and have often had a consultation with an orthopedist to assess for intra-articular pathology. Acute phase management should apply the PRICE principle: protection of the injured joint, relative rest, ice, compression, and elevation to control inflammation.
A study by Maenpaa and Lehto suggested that a period of immobilization may be beneficial. In their study of 100 acute dislocations, patients were divided into 3 treatment groups: plaster cast, posterior splint, and patellar bandage/brace. At long-term follow-up, fewer redislocations were noted in the posterior splint group and the cast group than in the patellar bandage group. The first 2 groups had a period of immobility, whereas the bandage group did not. The mechanism of benefit is thought to be the time to heal the disrupted medial structures. The best outcomes were noted in the group initially treated with a posterior splint. The plaster cast group had a longer period of immobilization, and the authors suggested limiting the period of immobilization to 3 weeks to avoid muscle atrophy, knee joint restrictions, and retropatellar crepitation.
Quadriceps strengthening is initiated during the acute phase. In the event of acute patella dislocation, these should be static exercises initiated during the period of immobilization. Quadriceps electrical stimulation is an option for muscle reeducation if the patient has difficulty activating the muscle secondary to pain. Electrical stimulation may also play a role in the management of knee joint effusion. When dolor, calor, rubor, and edema resolve, the patient may progress to the recovery phase of rehabilitation.
Therapy should also include a protocol for hamstring muscle stretching. Tight hamstring muscles functionally counteract their agonist group, the quadriceps.
In the acute phase, surgical interventions are reserved for complicated dislocations with associated fractures. The most common site of cartilage injury to the patella occurs as osteochondral fractures of the medial patellar facet or cracks in the central dome of the patella. Cartilaginous injuries are also frequently seen on the lateral femoral condyle. Arthroscopy can repair or remove fracture fragments. However, acute surgical interventions are unnecessary in most cases of patellofemoral syndromes.
If conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon. Particular attention should be paid to symptoms of an intra-articular foreign body, such as clicking, locking, or persistent intra-articular knee pain. These may be signs of an occult loose body within the knee.
See the list below:
- In the acute phase, protecting the patellofemoral joint involves reducing loads by postural correction, activity modification, and shoe changes/orthotic management if pes planus is present.
- Shoe wear and orthotics can prevent excessive hip internal rotation, knee valgus, and subtalar joint pronation, all of which promote lateral patellar tracking.
- Inappropriate cartilage-wear disorders can also be resolved by these measures.
- Proper foot support helps reduce patellofemoral pain. Proper foot alignment helps correct some biomechanical causative factors due to congenital deformities.
- Conservative treatment of acute traumatic patellar dislocations in this fashion has shown good results.
- Some controversy exists regarding the effectiveness of knee braces with a patella buttress in the treatment of patellofemoral pain and redislocation. Some authors find bracing to be useful primarily for patient reassurance and believe the primary benefit is psychologic in nature. However, other authors support their use both as a pain reduction adjunct in a conservative rehabilitation program that includes quadriceps strengthening and as protection against redislocation and subluxation.
- Study results on the efficacy of bracing for patellofemoral pain are highly variable. None of the studies reviewed controlled for the amount of pressure elicited by the brace on identified muscle groups. One study identified a significantly increased sulcus angle through the entire knee flexion range secondary to the brace use. However, the gross tracking pattern did not change, and minute differences in alignment may have influenced joint mechanics to improve patellofemoral pain. Another study found no benefits when braces were worn. Neptune et al found that increasing VMO strength produces more uniform results than those achieved with brace orthotics.
- The goal of bracing is to restore proper alignment. This occurs either by mechanical inhibition of lateral patella motion with a patella buttress or, as in taping, by a change in neuromuscular recruitment secondary to muscular proprioception. A case study by Shellock et al that evaluated the use of loaded kinematic MRI to evaluate patellar positioning while the patient wore a patellar realignment brace demonstrated a reduction in lateral subluxation at 30° of flexion and a functional decrease in patient pain. Additionally, bracing unloads painful structures, keeps the joint warm, provides proprioceptive feedback, and may assist in improving knee extension neuromuscular patterning.
- Care must be used in the acute phase, because bracing may aggravate the patient’s acute condition. However, a neoprene sleeve or other knee wrap that provides external compression helps control inflammation. Many braces have a patellar cutout and lateral buttresses to help prevent lateral patellar tracking.
Patellar taping (McConnell method)
- The goals of McConnell taping are to restore proper alignment and control pain.
- With proper alignment, VMO retraining is initiated. Once taped, patients should note decreased pain when performing painful activities such as stepping down from a stool. The goal of taping is to optimize patellar positioning and facilitate better activation of the medial patellar stabilizers, particularly the VMO. The technique can be taught to patients to perform themselves. Taping is continued until appropriate patellar positioning and tracking is achieved through the rehabilitation process, which includes appropriate activation of the VMO.
- A study examined the timing of VMO and VL firing in patients with patellar pain while walking up and down stairs. The authors demonstrated that during step-up activities, the VMO in the taped knee fired earlier in the gait cycle, and the VL had no change in the cycle timing. During step-down activities, the VMO in the taped knee fired earlier and the VL fired later. The authors postulated that these timing changes very early in the gait cycle, when the knee is near full extension, may have a beneficial effect on patellofemoral mechanics and promote movement of the patella into the trochlea groove early in flexion.
- Barefoot running may reduce patellofemoral joint stress as a result of reduced joint reaction forces. Barefoot runners are more likely to use a forefoot vs a heel strike pattern in the initial loading response, which has been shown to increase ankle eccentric work and simultaneously decrease the loading on the knee joint.
- Compared with use of neutral running shoes, barefoot running can decrease the peak patellofemoral joint stress by up to 12%. This is accomplished through a reduction in the peak knee flexion angle during stance phase and the peak knee extension moment.
- Progression from running with neutral shoes to barefoot running should occur in intervals. An athlete who continues to use a heel strike pattern with barefoot running will experience an increase in the ground reaction forces and worsen patellofemoral joint stress.
Therapeutic theory goals of nonoperative management of patellar injury and dislocation are to improve patellar tracking. The VMO is an important medial stabilizer of the patella. Inappropriate synergy patterns between the VMO and the VL have been theorized for lateral patellar tracking. The VL is a much larger muscle than the VMO. By overpowering the VMO, the VL may contribute to lateral tracking.
The prevailing theory has been that lateral patellar tracking is associated with VMO weakness. However, research has been inconclusive for VMO weakness as a direct causative mechanism of lateral patellar tracking. A study by Mohr et al examined timing differences between the VMO and VL in patients both with and without patellofemoral pain. The authors concluded that the timing differences noted and their relationship to the gait cycle suggest overall quadriceps weakness rather than specific, focal VMO weakness. As such, Mohr et al recommended overall quadriceps strengthening as the basis of rehabilitation strengthening programs. Other authors have also noted that general quadriceps strengthening has demonstrated reductions in lateral tracking irrespective of the mechanism.
The patient should be educated about correct posture and joint preservation at this time. Supportive adjuncts such as taping and bracing are common treatment modalities. Exercises to strengthen the quadriceps muscle (focusing on VMO activation) include quadriceps-setting exercises and straight-leg raises.
Quadriceps-setting exercises are performed with the patient in the supine position. The contralateral hip and knee are flexed to approximately 45° to protect the low back, and the ipsilateral leg is kept in extension. The quadriceps muscle in the extended leg is contracted, and the contraction is held for 5 seconds. The patient then relaxes the quadriceps and repeats the contraction. (Repetitions and sets are gradually increased.) The ankle of the exercising leg must be actively dorsiflexed during the contraction.
Straight-leg raises are performed with the patient in the supine position and the contralateral hip and knee flexed to approximately 45°. The extended leg (the leg to be strengthened) is raised 8-12 inches from the table and is held at that level for 10 seconds. (Repetitions and sets are gradually increased.)
Additional strengthening exercises must be performed for the hip adductors, hip abductors, and hip flexors. Hip adductors are strengthened with the patient lying on his or her side. The leg against the exercise mat is lifted away from the mat and is held for 10 seconds, followed by relaxation. Hip abductors are strengthened with the patient lying on his or her side. The leg away from the exercise mat is lifted away from the mat and is held for 10 seconds, followed by relaxation. Hip flexors are strengthened with the patient in a seated position. Both the knee and hip are held at 90° of flexion, and the leg to be exercised is lifted off the ground and is held for 10 seconds. (Repetitions and sets are gradually increased for all exercises.)
Any physical therapy program for patellofemoral problems must address tightness of the lower-extremity musculature. Reduced flexibility of the hamstrings, hip abductors, and iliotibial band all can increase patellofemoral pain. Additionally, tight gastrocnemius muscles can increase patellofemoral pain.
Medial patellar gliding exercises may loosen lateral retinacular tightness in this stage. Medial patellar gliding exercises are performed with the leg extended. The patient manually pushes the patella medially and holds for a count of 10 seconds.
An important concept in the rehabilitation of patellar dislocation and patellofemoral pain is knee flexion. Initially, any activity that requires greater than 40-45° of knee flexion causes symptoms. Initial rehabilitation programs start with the isometric open kinetic chain exercises described earlier. Early rehabilitation programs should limit all activities that require quadriceps firing with the knee flexed greater than 45°.
Once isometric open kinetic chain exercises are tolerated without discomfort, the rehabilitation program advances to closed kinetic chain exercises (eg, mini squats, lunges, stair climbing). The rectus femoris, VMO, and VL are all strengthened by the mini squats (repetitions and sets modified to the tolerance of the patient). Earl et al found that when isometric hip adduction is performed in conjunction with mini squats, the strength in these muscles increased significantly compared with the control group performing conventional squats.
Important goals are to restore ROM in the joint, mobilize soft tissues, and strengthen the surrounding musculature. Lunges and bike riding allow strengthening through a controlled ROM. The patient becomes more active in this phase, and the clinician must screen the patient for exacerbations of symptoms. If symptoms reemerge, the optimal loading zone of the knee and the activity level must be reevaluated. The patient learns activity limits in this phase. Once pain has resolved sufficiently to complete daily activity requirements without exacerbations, the patient can advance to the final phase of rehabilitation.
Advanced rehabilitation programs progress to jogging, running, plyometrics, and sport-specific exercises. Patients must be monitored and must always follow proper technique, as well as learn to properly fire the VMO.
Surgical intervention may be appropriate in 2 different patient populations: (1) those with normal anatomy who experience recurrent dislocation or pain and (2) those with an anatomic abnormality who may benefit from surgical intervention either upon initial acute dislocation or later with recurrence of dislocation or subluxation. In general, following acute patella dislocation, patients with normal lower extremity anatomy and without radiographic indications of intra-articular injury are best served by conservative treatment.
Buchner et al compared conservative treatment with surgical repair in patients with acute patella dislocation ; patients with radiologic signs suggestive of a predisposition to redislocation were excluded from the study. Results indicated no significant difference between surgically treated and conservatively treated groups in terms of redislocation rate, reoperation rates, level of activity, or functional or subjective outcomes.
When Camanho et al compared 33 patients with acute first-time patellar dislocation who underwent conservative versus open repair of the MPFL, after a mean of 36 months, 8 patients in the conservative group had recurrent dislocations compared with none in the surgical group. Additionally the surgical group had improved functional outcome as measured by the Kujala score. Overall, the investigators evaluated the rates of recurrent dislocations, subluxations, and instability as indicated by a positive patellar apprehension test.
Cootjans et al devised the following surgical algorithm for recurrent patellar dislocations that resulted in a 87% reduction in recurrent dislocations and 66% reduction in instability at 5 year follow up :
A. Immature patient (open physis)
- Normal Q Angle – medial retinacular imbrication
- Increased Q Angle – medial retinacular imbrication + patellar tendon hemitransfer
B. Mature patient (closed physis)
- Normal Q Angle – MPFL reconstruction + medial retinacular imbrication
- Increased Q Angle – MPFL reconstruction + medial retinacular imbrication + an (antero) medial transfer of the tibial tubercle +/- tibial tuberosity distalization for patella alta +/- tracheoplasty for trochlea dysplasia
Operative choices may be classified into distal, proximal, and combined procedures. Some authors suggest that rigid, distal procedures are associated with increased rates of progressive retropatellar arthrosis but lower rates of redislocation and that dynamic proximal procedures are associated with a lower incidence of arthrosis but a higher risk of redislocation.
There are 3 types of primary procedures for medial repair, all of which attempt to recreate an appropriate physiologic mechanism at the knee joint by improving the integrity of the structures that provide medially directed forces on the patella. The techniques include (1) plication of the medial patellar retinaculum, (2) anatomic repair of the MPFL, and (3), plasty surgery of the VMO.
Anatomic and biomechanical studies have indicated that the MPFL and the VMO are the primary restraints to lateral patella translation, particularly early in flexion before full trochlear engagement. An article by Arendt et al suggested that repair or reconstruction of the MPFL needs to be a component of any surgical intervention to control lateral translation of the patella in a knee with demonstrated lateral instability or dislocation.
Multiple studies evaluated MPFL surgical reconstruction in patients with recurrent patellar dislocations. Sillanpaa et al compared the results of MPFL reconstruction by adductor magnus tenodesis (18 knees) with distal patellar realignment (ie, Roux-Goldthwait procedure) (29 knees). The authors also evaluated the development of patellofemoral osteoarthrosis for these 2 procedures at a median 10-year follow-up.
The incidence of patellar redislocation after surgery was 7% in the adductor magnus group and 14% in the Roux-Goldthwait group. Patellofemoral articular cartilage lesions were found on MRI in 22 knees (73.3%) at follow-up, including 14 knees (46.6%) with full-thickness cartilage loss, whereas radiographs revealed patellofemoral osteoarthritis in 5 patients in the Roux-Goldthwait group but in none of the patients in the adductor magnus group. Based on their findings, Sillanpaa et al concluded that "adductor magnus tenodesis is a reliable method to treat recurrent patellar dislocation. The medial patellofemoral ligament reconstruction seems to reduce the risk of osteoarthrosis compared with distal realignment surgery."
Panagopoulos et al used a single hamstring tendon graft that was passed through the medial intermuscular septum at the adductor's magnus insertion and then fixed to the superomedial pole of the patella.
Improvement in patellar position and outcomes has been reported when performing medial patellar retinaculum plication with MPFL reconstruction compared to reconstruction of the MPFL alone. MPFL with polyester suture augmentation resulted in better static patellar position, dynamic stability, and functional outcome than without augmentation in the treatment of recurrent patellar dislocation in adults.
A study by Krause et al followed 28 patients for 5 years following a VMO plasty. In this procedure, the VMO was detached from its insertion on the patella and reinserted 10-15 mm distally. Their 5-year follow-up results indicated a 7% redislocation rate. Also noted was that 83% of patients reported good or excellent satisfaction with the procedure, and 89% of the knees had little or no evidence of arthrosis. These authors reported the results as better than those for other surgical repairs, and they attributed the positive results to the minimal interference with physiologic joint mechanics and restoration of the anatomic structure of the knee.
Another study found that vastus medialis plasty (VMP) is superior to arthroscopic medial retinaculum plication for recurrent patellar dislocation in adolescents, with better results in the final patellar position, better clinical results, and fewer episodes of redislocation.
Ma et al compared medial retinaculum plasty and medial patellofemoral ligament reconstruction and found that both procedures resulted in radiographic and functional improvement with no statistical difference indicating that either procedure results in favorable outcomes.
This procedure involves making an incision of the capsule of the lateral retinaculum to divide it. Lateral release may be performed as either an open or arthroscopic procedure, and it may also include release of the distal VL.
Extending the release too far can cause medial subluxation of the patella; in fact, medial patella subluxation or dislocation is almost always iatrogenic, secondary to an overzealous lateral release. Instead, the goal of this procedure is to facilitate medial motion of the patella into the trochlear groove and/or to level a patella with a large degree of lateral patella tilt.
This procedure has come under extensive criticism, especially as a sole surgical procedure. Anatomic studies suggest that in addition to providing a laterally directed force on the patella, the lateral retinaculum also provides a posteriorly directed force, with the net force being posterolateral. This posterior force component may provide stability as the patella is directed into the trochlea early in flexion.
In a knee with soft-tissue laxity, a lateral release removes one of the forces directing the patella into the trochlea and further destabilizes the knee. Post et al suggested that this problem is accentuated in patients with a large Q-angle. In a cadaveric study by Christoforakis et al, the investigators demonstrated that a lateral retinacular release decreased the force needed to displace the patella laterally 10 mm by 16-19% at knee flexions of 0-20°. This correlates exactly with the range of flexion in which the laterally unstable knee is most at risk for lateral dislocation.
Arendt et al suggested that a lateral release should only be performed if it facilitates the recentering of the patella by other procedures or when it is specifically performed to address objective lateral patella tilt.
Combined proximal procedures
Multiple studies have examined surgical treatment that combines medial reconstruction and lateral retinaculum release.
Haspl et al reported a small study of 17 patients who were followed for up to 26 months following plication of the medial patellar retinaculum and release of the lateral patella retinaculum. The results were deemed good by the authors, and they reported no redislocations or subluxations in that period.
Nam and Karzel reported a study of 23 patients who were followed for an average of 4.4 years after undergoing a medial reefing and arthroscopic lateral release. The authors reported 1 dislocation, 1 subluxation, and good patient satisfaction. All the patients reported the procedure was worthwhile, with 26% rating the results as excellent and 65% rating the results as good.
Maenpaa and Lehto treated 284 knees operatively with reefing of the medial capsule. In 243 of the knees, the lateral patellar retinaculum was released. The patient population mostly consisted of soccer players, gymnasts, and ice hockey players. The authors noted that the prognosis for decreased redislocation rate and subjective improvement was better if the mechanism of injury was traumatic.
Tibial tubercle transfers
Tibial tubercle transfer was first described by Hauser in 1938 with a medial and distal transplantation of the tibial tuberosity. This procedure was associated with a high rate of arthrosis, reportedly up to 71% of patients, and had a relatively high redislocation rate, reportedly 17-20%. Consequently, medial and distal transplantation of the tibial tuberosity are no longer performed.
Initially, high rates of arthrosis were thought to be secondary to the posterior movement of the tubercle inherent in the original procedure. This realignment makes use of muscular pull to maintain the patella in a central position in the trochlea. In current practice, numerous variations of this procedure are in use, and they are typically performed in conjunction with the proximal procedures described above.
Tibial tubercle transfer procedures are often performed in an effort to correct for an abnormal Q-angle. However, a large variation in norms for the Q-angle is reported in the literature. Arendt et al noted that in many patients, an exaggerated Q-angle at full extension may correct to normal at 90° of flexion, and surgical correction of those knees would lead to overmedialization of the patella mechanism.
In any case, tibial tubercle transfers are likely best avoided in patients with near-normal Q-angles. These procedures do, however, have the capability to correct patella alta, a potentially beneficial component of the corrective process.
Multiple variations of these procedures are used, in which a distal medialization of the tibial tubercle is combined with a proximal procedure, usually a medial reconstruction and a lateral release. These interventions can also correct for patella alta, with distal movement of the tibial tubercle during the medial transfer.
A study by Cossey and Paterson reported on 21 knees followed for 23 months postoperatively after having undergone a combined procedure consisting of lateral release, distal realignment of the tibial tubercle, and reconstruction of the MPFL with a graft for medial retinacular tissue. They reported no redislocations or recurrence of subluxation. The authors also reported that all patients achieved activity levels comparable to or improved from preinjury levels, a functional finding not matched in most other studies.
Mikashima et al examined the results of 20 patients who underwent an Elmslie-Trillat distal realignment compared with 20 patients who underwent the same procedure but with the addition of reconstruction of the MPFL. At 2-year follow-up, patients in the combined group all had a negative apprehension sign, whereas the distal realignment–only group demonstrated 30% with a positive apprehension sign. The combined group also demonstrated improved radiographic stability on a stress skyline view compared with the distal realignment–only group.
Other surgical treatments
More intensive joint reconstructive surgery
Procedures such as a trochleoplasty, rotational osteotomy for excessive femoral anteversion or external tibial rotation, and even patellectomy may be performed in cases in which both conservative treatment and less extensive surgery have failed.
When Nelitz et al followed 26 knees with severe trochlear dysplasia that underwent trochleoplasty and medial patellofemoral ligament reconstruction at a minimum of 2 year follow-up, patients reported no recurrent dislocations and significantly improved function.
Another study by Ntagiopoulos et al reported no dislocations with improvement in functional scores and overall satisfaction at a median follow-up of 7 years in 27 knees with severe cases of trochlear dysplasia and recurrent dislocation that underwent a sulcus-deepening trochleoplasty procedure. Additional procedures were selected based on deficiencies, including medial patellofemoral ligament reconstruction (16.1%), vastus medialis obliquus plasty (83.8%), tibial tuberosity distalization (51.6%), tibial tuberosity medialization (67.7%), and lateral retinaculum release (67.6%).
Importantly, these are extensive surgeries with significant morbidity and potentially lifelong functional deficit; as such, they are reserved for patients with severe trochlear dysplasia and anatomic variants.
In some cases, patients may benefit from arthroscopic debridement for symptomatic relief of arthrosis secondary to the patellofemoral instability.
Postsurgical rehabilitation closely follows nonoperative conservative treatment. All surgical procedures are at risk for complications such as medial tracking, arthrofibrosis, reflex sympathetic dystrophy symptoms, hemarthrosis, and rupture of the quadriceps tendon.
If the conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon.
Other Treatment (Injection, manipulation, etc.)
Bracing and taping can be continued in this phase to decrease pain and increase activity participation.
Patellar bracing and McConnell taping are viewed as temporary supportive measures whose functions are described in Acute Phase, Other treatment. They should be discontinued when functional activities are performed without pain.
The final phase of rehabilitation emphasizes developing an independence program for the patient. The patient learns how to stretch appropriately, conduct training routines, modify activity, and apply ice after activity routines. Returning the patient to the preinjured functional state often requires progressive functional activity. The rate of progression is limited by the patient’s tolerance. The patient should work toward single-leg standing, deep squatting, and jumping. Once patients are able to adjust activity routines within their optimal loading zones, they are ready to be discharged and only require routine follow-up treatment.
If the conservative management is not effective and the patient still experiences symptoms, consult an orthopedic surgeon.
Wu treated patients who had anterior knee pain, tenderness, quadriceps imbalance, and patellar subluxation with Chinese manipulation. The diagnosis was determined by a plain radiography protocol, and his patients were treated with a combination of manipulation and an exercise program. Although his treatment was successful in alleviating symptoms of patellofemoral dysfunction, Wu's study is limited by not having control groups that received either only manipulation or exercise alone. Future studies should take this into account. His manipulation techniques included the following:
Rolling the metacarpophalangeal joints over the VMO muscle for a deep massage effect
Circularly kneading the quadriceps with the thenar eminence
Mobilizing the patella side to side
Kneading the infrapatellar fat pad
Peripatellar rubbing with the hypothenar eminences
Torsion of the tibia on the femur
Ranging the patella into extension and flexion
Massaging the gastrocnemius
Grasping and elevating the patella
Moving the patella against the resistance of the lateral retinaculum to stretch the latter
Therapeutic ultrasonography is an option used by some healthcare professionals to treat patellofemoral pain syndrome. Of the 85 articles Brosseau et al reviewed, only 1 met preestablished criteria. The study that met preestablished criteria evaluated 53 patients and revealed that the effects of ultrasound combined with ice massage versus ice massage alone were not statistically significant. Brosseau et al concluded that more studies needed to be performed.
Bracing and taping can be of benefit for symptoms of patellofemoral dysfunction, as discussed in Acute Phase, Other treatment.
Raty HP, Kujala UM, Videman T, et al. Lifetime musculoskeletal symptoms and injuries among former elite male athletes. Int J Sports Med. 1997 Nov. 18(8):625-32. [Medline].
Thijs Y, De Clercq D, Roosen P, Witvrouw E. Gait-related intrinsic risk factors for patellofemoral pain in novice recreational runners. Br J Sports Med. 2008 Jun. 42(6):466-71. [Medline].
Hahn T, Foldspang A. Prevalent knee pain and sport. Scand J Soc Med. 1998 Mar. 26(1):44-52. [Medline].
Zhang Y, Xu L, Nevitt MC, et al. Comparison of the prevalence of knee osteoarthritis between the elderly Chinese population in Beijing and whites in the United States: The Beijing Osteoarthritis Study. Arthritis Rheum. 2001 Sep. 44(9):2065-71. [Medline]. [Full Text].
Nietosvaara Y, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. J Pediatr Orthop. 1994 Jul-Aug. 14(4):513-5. [Medline].
Andrikoula S, Tokis A, Vasiliadis HS, Georgoulis A. The extensor mechanism of the knee joint: an anatomical study. Knee Surg Sports Traumatol Arthrosc. 2006 Mar. 14(3):214-20. [Medline].
Kepler CK, Bogner EA, Hammoud S, Malcolmson G, Potter HG, Green DW. Zone of injury of the medial patellofemoral ligament after acute patellar dislocation in children and adolescents. Am J Sports Med. 2011 Jul. 39(7):1444-9. [Medline].
Escala JS, Mellado JM, Olona M, et al. Objective patellar instability: MR-based quantitative assessment of potentially associated anatomical features. Knee Surg Sports Traumatol Arthrosc. 2006 Mar. 14(3):264-72. [Medline].
Dejour H, Walch G, Nove-Josserand L, Guier C. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc. 1994. 2(1):19-26. [Medline].
Post WR, Teitge R, Amis A. Patellofemoral malalignment: looking beyond the viewbox. Clin Sports Med. 2002 Jul. 21(3):521-46, x. [Medline].
Bongers EM, van Kampen A, van Bokhoven H, Knoers NV. Human syndromes with congenital patellar anomalies and the underlying gene defects. Clin Genet. 2005 Oct. 68(4):302-19. [Medline].
Amin S, Goggins J, Niu J, et al. Occupation-related squatting, kneeling, and heavy lifting and the knee joint: a magnetic resonance imaging-based study in men. J Rheumatol. 2008 Aug. 35(8):1645-9. [Medline].
Grelsamer RP, Dubey A, Weinstein CH. Men and women have similar Q angles: a clinical and trigonometric evaluation. J Bone Joint Surg Br. 2005 Nov. 87(11):1498-501. [Medline].
Verma A, Su A, Golin AM, O'Marrah B, Amorosa JK. A screening method for knee trauma. Acad Radiol. 2001 May. 8(5):392-7. [Medline].
Stanciu C, Labelle HB, Morin B, Fassier F, Marton D. The value of computed tomography for the diagnosis of recurrent patellar subluxation in adolescents. Can J Surg. 1994 Aug. 37(4):319-23. [Medline].
Shea KP, Fulkerson JP. Preoperative computed tomography scanning and arthroscopy in predicting outcome after lateral retinacular release. Arthroscopy. 1992. 8(3):327-34. [Medline].
McNally EG, Ostlere SJ, Pal C, et al. Assessment of patellar maltracking using combined static and dynamic MRI. Eur Radiol. 2000. 10(7):1051-5. [Medline].
Guerrero P, Li X, Patel K, Brown M, Busconi B. Medial patellofemoral ligament injury patterns and associated pathology in lateral patella dislocation: an MRI study. Sports Med Arthrosc Rehabil Ther Technol. 2009 Jul 30. 1(1):17. [Medline]. [Full Text].
Brossmann J, Muhle C, Büll CC, et al. Evaluation of patellar tracking in patients with suspected patellar malalignment: cine MR imaging vs arthroscopy. AJR Am J Roentgenol. 1994 Feb. 162(2):361-7. [Medline]. [Full Text].
Watanabe A, Obata T, Ikehira H, et al. Degeneration of patellar cartilage in patients with recurrent patellar dislocation following conservative treatment: evaluation with delayed gadolinium-enhanced magnetic resonance imaging of cartilage. Osteoarthritis Cartilage. 2009 Dec. 17(12):1546-53. [Medline].
Felus J, Kowalczyk B, Lejman T. Sonographic evaluation of the injuries after traumatic patellar dislocation in adolescents. J Pediatr Orthop. 2008 Jun. 28(4):397-402. [Medline].
Maenpaa H, Lehto MU. Patellar dislocation. The long-term results of nonoperative management in 100 patients. Am J Sports Med. 1997 Mar-Apr. 25(2):213-7. [Medline].
Colvin AC, West RV. Patellar instability. J Bone Joint Surg Am. 2008 Dec. 90(12):2751-62. [Medline].
Neptune RR, Wright IC, van den Bogert AJ. The influence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running. Clin Biomech (Bristol, Avon). 2000 Oct. 15(8):611-8. [Medline].
Shellock FG, Mink JH, Deutsch AL, Molnar T. Effect of a newly designed patellar realignment brace on patellofemoral relationships. Med Sci Sports Exerc. 1995 Apr. 27(4):469-72. [Medline].
Gilleard W, McConnell J, Parsons D. The effect of patellar taping on the onset of vastus medialis obliquus and vastus lateralis muscle activity in persons with patellofemoral pain. Phys Ther. 1998 Jan. 78(1):25-32. [Medline]. [Full Text].
Arendse RE, Noakes TD, Azevedo LB, Romanov N, Schwellnus MP, Fletcher G. Reduced eccentric loading of the knee with the pose running method. Med Sci Sports Exerc. 2004 Feb. 36(2):272-7. [Medline].
Bonacci J, Vicenzino B, Spratford W, Collins P. Take your shoes off to reduce patellofemoral joint stress during running. Br J Sports Med. 2014 Mar. 48(6):425-8. [Medline].
Tam N, Astephen Wilson JL, Noakes TD, Tucker R. Barefoot running: an evaluation of current hypothesis, future research and clinical applications. Br J Sports Med. 2014 Mar. 48(5):349-55. [Medline].
Mohr KJ, Kvitne RS, Pink MM, Fideler B, Perry J. Electromyography of the quadriceps in patellofemoral pain with patellar subluxation. Clin Orthop Relat Res. 2003 Oct. 415:261-71. [Medline].
Earl JE, Schmitz RJ, Arnold BL. Activation of the VMO and VL during dynamic mini-squat exercises with and without isometric hip adduction. J Electromyogr Kinesiol. 2001 Dec. 11(6):381-6. [Medline].
Buchner M, Baudendistel B, Sabo D, Schmitt H. Acute traumatic primary patellar dislocation: long-term results comparing conservative and surgical treatment. Clin J Sport Med. 2005 Mar. 15(2):62-6. [Medline].
Camanho GL, Viegas Ade C, Bitar AC, Demange MK, Hernandez AJ. Conservative versus surgical treatment for repair of the medial patellofemoral ligament in acute dislocations of the patella. Arthroscopy. 2009 Jun. 25(6):620-5. [Medline].
Cootjans K, Dujardin J, Vandenneucker H, Bellemans J. A surgical algorithm for the treatment of recurrent patellar dislocation. Results at 5 year follow-up. Acta Orthop Belg. 2013 Jun. 79(3):318-25. [Medline].
Arendt EA, Fithian DC, Cohen E. Current concepts of lateral patella dislocation. Clin Sports Med. 2002 Jul. 21(3):499-519. [Medline].
Sillanpaa P, Mattila VM, Visuri T, Maenpaa H, Pihlajamaki H. Ligament reconstruction versus distal realignment for patellar dislocation. Clin Orthop Relat Res. 2008 Jun. 466(6):1475-84. [Medline]. [Full Text].
Panagopoulos A, van Niekerk L, Triantafillopoulos IK. MPFL reconstruction for recurrent patella dislocation: a new surgical technique and review of the literature. Int J Sports Med. 2008 May. 29(5):359-65. [Medline].
Zhao J, Huangfu X, He Y. The role of medial retinaculum plication versus medial patellofemoral ligament reconstruction in combined procedures for recurrent patellar instability in adults. Am J Sports Med. 2012 Jun. 40(6):1355-64. [Medline].
Xie G, Zhao J, Huangfu X, He Y. Medial patellofemoral ligament reconstruction using semitendinosus tendons: polyester suture augmentation versus nonaugmentation. Am J Sports Med. 2012 Jun. 40(6):1365-74. [Medline].
Krause F, Kolling C, Brantschen R, Sieber HP. [Medium-term results after m. vastus medialis obliquus-plasty for lateral patellar dislocation] [German]. Orthopade. 2006 Jan. 35(1):94-101. [Medline].
Zhao J, Huangfu X, He Y, Liu W. Recurrent patellar dislocation in adolescents: medial retinaculum plication versus vastus medialis plasty. Am J Sports Med. 2012 Jan. 40(1):123-32. [Medline].
Ma LF, Wang F, Chen BC, Wang CH, Zhou JW, Wang HY. Medial retinaculum plasty versus medial patellofemoral ligament reconstruction for recurrent patellar instability in adults: a randomized controlled trial. Arthroscopy. 2013 May. 29(5):891-7. [Medline].
Christoforakis J, Bull AM, Strachan RK, et al. Effects of lateral retinacular release on the lateral stability of the patella. Knee Surg Sports Traumatol Arthrosc. 2006 Mar. 14(3):273-7. [Medline].
Haspl M, Cicak N, Klobucar H, Pecina M. Fully arthroscopic stabilization of the patella. Arthroscopy. 2002 Jan. 18(1):E2. [Medline].
Nam EK, Karzel RP. Mini-open medial reefing and arthroscopic lateral release for the treatment of recurrent patellar dislocation: a medium-term follow-up. Am J Sports Med. 2005 Feb. 33(2):220-30. [Medline].
Maenpää H, Lehto MU. Surgery in acute patellar dislocation--evaluation of the effect of injury mechanism and family occurrence on the outcome of treatment. Br J Sports Med. 1995 Dec. 29(4):239-41. [Medline]. [Full Text].
Cossey AJ, Paterson R. A new technique for reconstructing the medial patellofemoral ligament. Knee. 2005 Apr. 12(2):93-8. [Medline].
Mikashima Y, Kimura M, Kobayashi Y, Asagumo H, Tomatsu T. Medial patellofemoral ligament reconstruction for recurrent patellar instability. Acta Orthop Belg. 2004 Dec. 70(6):545-50. [Medline].
Nelitz M, Dreyhaupt J, Lippacher S. Combined trochleoplasty and medial patellofemoral ligament reconstruction for recurrent patellar dislocations in severe trochlear dysplasia: a minimum 2-year follow-up study. Am J Sports Med. 2013 May. 41(5):1005-12. [Medline].
Ntagiopoulos PG, Byn P, Dejour D. Midterm results of comprehensive surgical reconstruction including sulcus-deepening trochleoplasty in recurrent patellar dislocations with high-grade trochlear dysplasia. Am J Sports Med. 2013 May. 41(5):998-1004. [Medline].
Wu LS. Evaluation and manipulative therapy of patellar malalignment: a clinical review and preliminary report. J Manipulative Physiol Ther. 1991 Sep. 14(7):428-35. [Medline].
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. 2000 Jul-Aug. 28(4):472-9. [Medline].
Hinton RY, Sharma KM. Acute and recurrent patellar instability in the young athlete. Orthop Clin North Am. 2003 Jul. 34(3):385-96. [Medline].
Cash JD, Hughston JC. Treatment of acute patellar dislocation. Am J Sports Med. 1988 May-Jun. 16(3):244-9. [Medline].
Altman AR, Davis IS. Barefoot running: biomechanics and implications for running injuries. Curr Sports Med Rep. 2012 Sep-Oct. 11(5):244-50. [Medline].
Andrish J. The management of recurrent patellar dislocation. Orthop Clin North Am. 2008 Jul. 39(3):313-27, vi. [Medline].
Beaconsfield T, Pintore E, Maffulli N, Petri GJ. Radiological measurements in patellofemoral disorders. A review. Clin Orthop Relat Res. 1994 Nov. 308:18-28. [Medline].
Beasley LS, Vidal AF. Traumatic patellar dislocation in children and adolescents: treatment update and literature review. Curr Opin Pediatr. 2004 Feb. 16(1):29-36. [Medline].
BenGal S, Lowe J, Mann G, Finsterbush A, Matan Y. The role of the knee brace in the prevention of anterior knee pain syndrome. Am J Sports Med. 1997 Jan-Feb. 25(1):118-22. [Medline].
Bensahel H, Souchet P, Pennecot GF, Mazda K. The unstable patella in children. J Pediatr Orthop B. 2000 Oct. 9(4):265-70. [Medline].
Boden BP, Pearsall AW, Garrett WE Jr, Feagin JA Jr. Patellofemoral Instability: Evaluation and Management. J Am Acad Orthop Surg. 1997 Jan. 5(1):47-57. [Medline].
Brody LT, Thein JM. Nonoperative treatment for patellofemoral pain. J Orthop Sports Phys Ther. 1998 Nov. 28(5):336-44. [Medline].
Bui KL, Ilaslan H, Parker RD, Sundaram M. Knee dislocations: a magnetic resonance imaging study correlated with clinical and operative findings. Skeletal Radiol. 2008 Jul. 37(7):653-61. [Medline].
Burgess KE, Pearson SJ, Onambele GL. Patellar tendon properties with fluctuating menstrual cycle hormones. J Strength Cond Res. 2009 Nov 13. epub ahead of print. [Medline].
Chapman MW, ed. Chapman's Orthopaedic Surgery. 3rd ed. Baltimore, Md: Lippincott Williams & Wilkins; 1993. Vol 2:
Christiansen SE, Jakobsen BW, Lund B, Lind M. Isolated repair of the medial patellofemoral ligament in primary dislocation of the patella: a prospective randomized study. Arthroscopy. 2008 Aug. 24(8):881-7. [Medline].
Connolly JF. Fractures and Dislocations: Closed Management. Philadelphia, Pa: WB Saunders Co; 1995.
Csintalan RP, Latt LD, Fornalski S, Raiszadeh K, Inacio MC, Fithian DC. Medial patellofemoral ligament (MPFL) reconstruction for the treatment of patellofemoral instability. J Knee Surg. 2014 Apr. 27(2):139-46. [Medline].
Eckstein F, Adam C, Sittek H, et al. Non-invasive determination of cartilage thickness throughout joint surfaces using magnetic resonance imaging. J Biomech. 1997 Mar. 30(3):285-9. [Medline].
Eckstein F, Schnier M, Haubner M, et al. Accuracy of cartilage volume and thickness measurements with magnetic resonance imaging. Clin Orthop Relat Res. 1998 Jul. 352:137-48. [Medline].
Elias DA, White LM. Imaging of patellofemoral disorders. Clin Radiol. 2004 Jul. 59(7):543-57. [Medline].
Fithian DC, Paxton EW, Cohen AB. Indications in the treatment of patellar instability. J Knee Surg. 2004 Jan. 17(1):47-56. [Medline].
Fulkerson JP. Alternatives to patellofemoral arthroplasty. Clin Orthop Relat Res. 2005 Jul. 436:76-80. [Medline].
Gagliardi JA, Chung EM, Chandnani VP, et al. Detection and staging of chondromalacia patellae: relative efficacies of conventional MR imaging, MR arthrography, and CT arthrography. AJR Am J Roentgenol. 1994 Sep. 163(3):629-36. [Medline]. [Full Text].
Grelsamer RP, Klein JR. The biomechanics of the patellofemoral joint. J Orthop Sports Phys Ther. 1998 Nov. 28(5):286-98. [Medline].
Grood ES, Suntay WJ, Noyes FR, Butler DL. Biomechanics of the knee-extension exercise. Effect of cutting the anterior cruciate ligament. J Bone Joint Surg Am. 1984 Jun. 66(5):725-34. [Medline].
Handelberg F, Shahabpour M, Casteleyn PP. Chondral lesions of the patella evaluated with computed tomography, magnetic resonance imaging, and arthroscopy. Arthroscopy. 1990. 6(1):24-9. [Medline].
Handelberg F, Shahabpour M, Van Betten F, et al. CT arthrography and MRI of the patella. Acta Orthop Belg. 1989. 55(3):331-8. [Medline].
Hawkins RJ, Bell RH, Anisette G. Acute patellar dislocations. The natural history. Am J Sports Med. 1986 Mar-Apr. 14(2):117-20. [Medline].
Holmes SW Jr, Clancy WG Jr. Clinical classification of patellofemoral pain and dysfunction. J Orthop Sports Phys Ther. 1998 Nov. 28(5):299-306. [Medline].
Ireland ML, Chang JL. Acute fracture bipartite patella: case report and literature review. Med Sci Sports Exerc. 1995 Mar. 27(3):299-302. [Medline].
Kapur S, Wissman RD, Robertson M, et al. Acute knee dislocation: review of an elusive entity. Curr Probl Diagn Radiol. 2009 Nov-Dec. 38(6):237-50. [Medline].
Leblanc JM. Patellar complications in total knee arthroplasty. A literature review. Orthop Rev. 1989 Mar. 18(3):296-304. [Medline].
Levine J. Chondromalacia patellae. Physician Sportsmed. 1979. 7:41-9.
Lindberg U, Lysholm J, Gillquist J. The correlation between arthroscopic findings and the patellofemoral pain syndrome. Arthroscopy. 1986. 2(2):103-7. [Medline].
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. 1996. 4(4):212-6. [Medline].
Mangine RE, Eifert-Mangine M, Burch D, Becker BL, Farag L. Postoperative management of the patellofemoral patient. J Orthop Sports Phys Ther. 1998 Nov. 28(5):323-35. [Medline].
Miller MD, Hinkin DT, Wisnowski JW. The efficacy of orthotics for anterior knee pain in military trainees. A preliminary report. Am J Knee Surg. 1997 Winter. 10(1):10-3. [Medline].
Miller PR, Klein RM, Teitge RA. Medial dislocation of the patella. Skeletal Radiol. 1991. 20(6):429-31. [Medline].
Moore KL. Clinically Oriented Anatomy. 3rd ed. Baltimore, Md: Lippincott Williams & Wilkins; 1992.
Mow VC, Ateshian GA, Ratcliffe A. Anatomic form and biomechanical properties of articular cartilage of the knee joint. J Biomech Eng. 1991. 113(2):198-207.
Nietosvaara Y, Paukku R, Palmu S, Donell ST. Acute patellar dislocation in children and adolescents. Surgical technique. J Bone Joint Surg Am. 2009 Mar 1. 91 Suppl 2 Pt 1:139-45. [Medline].
Nissen CW, Cullen MC, Hewett TE, Noyes FR. Physical and arthroscopic examination techniques of the patellofemoral joint. J Orthop Sports Phys Ther. 1998 Nov. 28(5):277-85. [Medline].
Nomura E, Inoue M, Kurimura M. Chondral and osteochondral injuries associated with acute patellar dislocation. Arthroscopy. 2003 Sep. 19(7):717-21. [Medline].
Powers CM. Rehabilitation of patellofemoral joint disorders: a critical review. J Orthop Sports Phys Ther. 1998 Nov. 28(5):345-54. [Medline].
Powers CM, Shellock FG, Beering TV, et al. Effect of bracing on patellar kinematics in patients with patellofemoral joint pain. Med Sci Sports Exerc. 1999 Dec. 31(12):1714-20. [Medline].
Rauschning W, Nordesjo LO, Nordgren B. Isokinetic knee extension strength and pain before and after correction of recurrent patellar dislocation. Arch Orthop Trauma Surg. 1983. 102(2):102-6. [Medline].
Sanders TG, Morrison WB, Singleton BA, Miller MD, Cornum KG. Medial patellofemoral ligament injury following acute transient dislocation of the patella: MR findings with surgical correlation in 14 patients. J Comput Assist Tomogr. 2001 Nov-Dec. 25(6):957-62. [Medline].
Schonholtz GJ, Zahn MG, Magee CM. Lateral retinacular release of the patella. Arthroscopy. 1987. 3(4):269-72. [Medline].
Shellock FG. Effect of a patella-stabilizing brace on lateral subluxation of the patella: assessment using kinematic MRI. Am J Knee Surg. 2000 Summer. 13(3):137-42. [Medline].
Shellock FG. Patellofemoral joint abnormalities in athletes: evaluation by kinematic magnetic resonance imaging. Top Magn Reson Imaging. 1991 Sep. 3(4):71-95. [Medline].
Sillanpaa PJ, Peltola E, Mattila VM, et al. Femoral avulsion of the medial patellofemoral ligament after primary traumatic patellar dislocation predicts subsequent instability in men: a mean 7-year nonoperative follow-up study. Am J Sports Med. 2009 Aug. 37(8):1513-21. [Medline].
Sobhy MH, Mahran MA, Kamel EM. Midterm results of combined patellofemoral and patellotibial ligaments reconstruction in recurrent patellar dislocation. Eur J Orthop Surg Traumatol. 2013 May. 23(4):465-70. [Medline].
Tecklenburg K, Dejour D, Hoser C, Fink C. Bony and cartilaginous anatomy of the patellofemoral joint. Knee Surg Sports Traumatol Arthrosc. 2006 Mar. 14(3):235-40. [Medline].
Wessel LM, Scholz S, Rusch M. Characteristic pattern and management of intra-articular knee lesions in different pediatric age groups. J Pediatr Orthop. 2001 Jan-Feb. 21(1):14-9. [Medline].
White BJ, Sherman OH. Patellofemoral instability. Bull NYU Hosp Jt Dis. 2009. 67(1):22-9. [Medline].
Williams DS 3rd, Green DH, Wurzinger B. Changes in lower extremity movement and power absorption during forefoot striking and barefoot running. Int J Sports Phys Ther. 2012 Oct. 7(5):525-32. [Medline]. [Full Text].