Original Editors - Jeremy Luytens as part of the Vrije Universiteit Brussel's Evidence-based Practice project
- 1 Definition/Description
- 2 Clinically Relevant Anatomy
- 3 Epidemiology /Etiology
- 4 Differential Diagnosis
- 5 Diagnostic Procedures
- 6 Outcome Measures
- 7 Examination
- 8 Medical Management
- 9 Physical Therapy Management
- 10 Key Research
- 11 Resources
- 12 Clinical Bottom Line
- 13 Recent Related Research (from Pubmed)
- 14 References
A patellar dislocation is a severe acute injury where there is a shift of the patella, where the patella will leave the patellofemoral groove.
It is important to make a differentiation between acute primary patellar dislocation, which accounts for 2-3%, and habitual dislocation for recommendations with varying treatment approaches. Primary (first-time) patellar dislocation is defined as a clinical entity that usually causes a traumatic disruption of the previously uninjured medial peripatellar structures [14,15,16].
One of the common findings related to acute, primary, traumatic patellar dislocations is hemarthrosis (bleeding into joint spaces) of the knee, caused by rupture of the medial restraints of the patella. 
Clinically Relevant Anatomy
The patellofemoral joint is the portion of the knee joint between the patella and the femoral condyles. The patellofemoral articulation totally depends on the function of the quadriceps. It increases the angle of pull of the patellar tendon, improving the mechanical advantage of the quadriceps in knee extension.
The articular surfaces consist of the patella and the trochlear surface of the femoral condyles. The articular cartilage on the medial facet is thicker than on the lateral facet, with the lateral facet bigger than the medial.
The femoral condyles only project slightly in front of the shaft of the femur but project quite a distance posteriorly. The anterior aspects of both condyles are included in the articular area of the patella. The patellar articular surface is larger on the lateral femoral condyle than on the medial. There is an anterior projection on the lateral femoral condyle lateral to the patellar groove. This is the bony factor, which prevents lateral dislocation of the patella. The trochlea is on the anterior, distal end of the femur. The groove is continuous posteriorly with the intercondylar notch of the femur. The lateral facet is more prominent and has a greater radius.
The suspension and movement of the patella is provided by passive and active stabilizers.
• Passive: fascia lata, ligamentum patellae, capsule of the knee, ligamentum patellofemorale medial and lateral and ligamentum meniscopatellare medial and lateral
• Active: the four heads of the quadriceps, ligamentum patellae and the retinacullum
Athletics are often associated with patellar dislocation ( Ficat ’77, Hugston ’84 ). It is most common in females in the second decade of life.
Patellar dislocation most often result results from a non-contact injury to the knee. But apart from the traumatic component, it is also important to refer to the presence of predisposing morphological and functional patellofemoral disorders. Dominant predisposing factors need less trauma for dislocations, and vice versa. It’s etiology is regarder as multi-factorial, being associated with: reduced osseous constraint form the lateral femoral condyle; an imbalance between stronger lateral tissues, such as the lateral retinacullum and vastus lateralis, which are able to overcome weaker medial structures, especially the medial patellofemoral ligament and the distal vastus medialis; and finally biomechanical issues such as femoral and tibial rotation, and pes planus.
The typical mechanism of injury is a twist of the leg, with the femur rotating internally on a fixed foot and tibia. Valgus stress is often associated with this rotating mechanism, thereby creating a strong laterally directed force, dislocating the patella ( Hugston ’84 ). A direct blow as well to the lateral side of the knee, producing a valgus stress, as to the medial side of the knee producing a direct dislocating force can also create this injury ( Fu ’90 ).
A knee tape with a lateral reinforcement will reduce the movement of the patella so that can be used as prevention.
The patient will experience pain, instability of the knee and blocking of the knee after the trauma. After de dislocation there will be a swelling on the medial side of knee because on this side a lot of tissue will be hit.
Research shows knee-specific scales yielded higher reliability coefficients and stronger validity than did general health instruments in Assessing Acute Patellar Dislocation. The Fulkerson and Lysholm scales were the only instruments to differentiate between patients with and without recurrent subluxations/dislocations. 
MRI is necessary to examine if the tendon is partially torn, for a complete tear a lateral X-ray might be sufficient due luxation of the patella. 
A patellar dislocation can be diagnosed by using a MRI, conventional X-rays and computed tomography scans for measurement of the tuberositas tibiae-trochlea groove distance. 
An increase in the Q-angle could lead to lateral patellar dislocation or increased lateral patellofemoral contact pressures. A Q-angle decrease may not shift the patella medially, but could increase the medial tibiofemoral contact pressure by increasing the varus orientation. (35)
It is measured by drawing a line from the anterosuperior iliac spine to the centre of the patella, and a second line from the centre of the tibial tubercle to the centre of the patella. The angle where these lines intersect is regarded as the Q-angle. Traditionally, the Q-angle has been measured with subjects in supine, knee extended and with the quadriceps muscle relaxed. This is regarded as the ‘traditional’ or ‘conventional’ method of assessing Q-angle. (36)
In women, the Q angle should be less than 22 degrees. In men, the Q angle should be less than 18 degree. A typical Q angle is 12 degrees for men and 17 degrees for women. (37)
Immediately after the trauma there is an immobilization in a cylinder cast for 6 weeks and medication, supplements like glucosamine and NSAID’s that could be used to keep the knee strong. If required arthroscopy with or without retinacular repair, surgical repair of the torn retinacullum or immediate patellar realignment.
Acute primary dislocations can be managed conservatively by immobilisation with a removable knee brace, posterior splint, a cylinder cast or by surgical treatment. 
A posterior splint might be the best therapeutic option because of the low redislocation rates and knee joint restrictions. However, this recommendation is based on only one small study with significant limitations. Further investigation with modern braces and standardisation of immobilisation time is needed to find the most appropriate conservative treatment for patellar luxation.
Contemporary treatment regimens range from immediate mobilization without a brace to cast immobilization in extension for 6 weeks. In a patient who finds 6 weeks of immobilization unacceptable, a 3-week period of immobilization may be performed with the understanding that a higher redislocation rate may result. A 3-fold higher risk of redislocation was reported in those treated with immediate mobilization. 
Physical Therapy Management
An important thing is the important task of the physiotherapist: Prevention. The physiotherapist has to increase the functions after an injury, but also has to prevent re-dislocation (in this way).
Conservative treatment have included:
• Manual Therapy: Knee and Knee Mobilizations to improve the ROM of the knee
• Combination Therapy
• Strengthening exercises for quadriceps, hamstrings, adductors, muscles of the hip and lower abdomen. Important, is the use of closed kinetic chain exercises because of a greater number of advantages over the other forms of exercise.
• Stretching and flexibility training for hamstrings and quadriceps
• Proprioceptive exercises to improve the stability of the knee
Distal vastus medialis (VM) muscle strengthening doesn’t significantly improve functional outcomes compared to general quadriceps muscle strengthening following first-time patellar dislocation. 
Bracing and re-education can play an important role in the treatment and prevention of patellar dislocation.
Reassurance and behavioural modification is also commonly applied as preperation for exercises in therapy and thus to prevent redislocation of the patella. 
Other than preferences for nonoperative treatment of primary patellar dislocations have been shown in previous studies [20,21,22], patients with habitual dislocations and patellofemoral symptoms seem to be benefited from reconstructive surgery [23,24]. High-level evidence supports nonoperative treatment for first-time lateral acute patellar dislocations. Surgical intervention is often indicated for recurrent dislocations . However, according to studies , surgical treatment is associated with a higher risk of patellofemoral joint osteoarthritis. Therefore, it is of major importance to formulate one's management strategy patient oriented and to inform patients of the advantages and disadvantages of each management strategy when deciding.
Conservative treatment is still the most common treatment after primary dislocation of the patella. 
There is no statistically significant difference (p=0.091) between operatively and conservatively treated groups with regard to functional results. The same statistical outcome emerged when comparing incidences of re-dislocation (p=0.854), or other major patellar instabilities (p=0.856), between the groups. .
The results obtained should not promote a non-operative method on the basis of lower risk, but do support an individual approach based on precise diagnosis and defined criteria. .
Thus it appears that surgical and nonsurgical management of patellar dislocation tends to yield similar results in the skeletally mature and adolescents. Individual characteristics and goals should be taken into consideration when choosing an acute patellar dislocation treatment approach. Unless future studies show a more definitive benefit for surgical management, exercise and bracing should be considered initially. Exercise and bracing are less invasive and likely to be less expensive than surgery. 
Surgeon experience as well as individual patient values and preferences should primarily guide management. 
Studies have shown taping resulted in a signiﬁcantly better Lysholm score at 6 and 12 weeks post-dislocation (P=0.05), and also after 5-year follow-up (P=0.01). Knee function was better at 1-year follow-up. There were no cases of recurrent dislocation. . 1B
Tape bandage immobilization seems superior to a cylinder cast even after 5 years. .
Surgical intervention for first-time traumatic patellar dislocation is indicated in the following situations:
1) evidence on imaging or clinical examination of osteochondral fracture or major chondral injury;
2) palpable or MRI findings of substantial disruption of the MPFL (medial patellofemoral ligament)-VMO (vastus medialis obliquus)-adductor mechanism;
3) a patella laterally subluxated on the plain Mercer-Merchant view with normal alignment on the contralateral knee;
4) a patient fails to improve with nonoperative management especially in the presence of one or more predisposing factors to patellar dislocation;
5) subsequent redislocation . Surgical stabilization significantly reduced the redislocation rate of primary traumatic patellar dislocation in a young adult population than those without surgical treatment, which was addressed in a prospective, randomized, controlled study .
For surgical treatment, There are several surgical options that may be used to prevent patellar dislocation and subluxation. These procedures may be used alone or in a combination:
- Lateral release
- Medial patellofemoral ligament (MPFL) reconstruction / proximal realignment
- Distal realignment / anteromedialization (AMZ)
Release of tight lateral retinaculum (soft tissue) to allow patella to track more medially. This procedure is sometimes performed alone on patients with mild instability of the patella.
Medial patellofemoral ligament (MPFL) reconstruction
A tightening of the MPFL or a reconstruction of this ligament can be used to balance the tracking of the patella to more natural (medial) alignment. This procedure is performed in patients with more severe patellar instability. A lateral release often is performed in conjunction with this procedure. (38)
After research 93% had good/exellent results using the Fulkerson’s functional knee score: Radiographic evaluation showed significant improvements in the congruence angle by an average of 20° (P= .0006), and in the lateral patellofemoral angle by an average of 10° (P = .0003). 
Conclusion: initial acute patellofemoral dislocations should be treated with immobilization and rehabilitation, as a majority of patients will do well without surgery. MRI is necessary to assess for osteochondral lesions, because they are associated with a poor prognosis if they are not addressed.
Distal realignment / anteromedialization (AMZ)
This realignment procedure involves transferring the tibial tubercle (where the patellar tendon attaches to the tibia). The bony attachment of the tendon is moved more medially to allow the patella to track normally. This procedure is performed on patients with severe patellar instability and is used in conjunction with the lateral release and/or the MPFL reconstruction.
Following the operation you will be taken to the recovery room for observation. Once the effects of the anesthesia have worn off and your pain is under control you will be released. Initial treatment after surgery consists of pain management, physical therapy and cryotherapy (ice). (38)
add links and reviews of high quality evidence here (case studies should be added on new pages using the case study template)
Clinical Bottom Line
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Recent Related Research (from Pubmed)
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- D.L. Egmond, R. Schuitemaker. De knieregio. In: A.J.F. Mink, H.J. ter Veer, J.A.C.Th. Vorselaars. Extremiteiten manuele therapie in enge en ruime zin. 1e uitgave. Houten. Bohn Stafleu Van Loghum bv. 2006. p. 559 – 628 Level of evidence: D
- Omer Matthijs, Didi van Paridon-Edauw, Dos winkel. Hoofdstuk 2 knie. Manuele therapie van de perifere gewrichten. 1e uitgave. Houten. Bohn Stafleu Van Loghum bv. 2004. p. 220 – 235 Level of evidence: D
- G.VD. Bijl Jr., C.G. De Graaf, P.A. De Ridder. “hoofdstuk”. Actief en passief bewegen in de gewrichten der extremiteiten. De tijdsstroom. 1975. p. 126 Level of evidence: A1
- R. meeusen. 2011. Praktijkgids knieletsels. Cursus. Vrije universiteit brussel. Level of evidence: 5
- Harry B. SKinner, Robert L. Barrack, Michael S. Bedmar, George D. Clarson et al. Sports medicine. In: Shelley Reinhardt, Isabel Nogueira, Peter J. Boyle. Current diagnosis en treatment in orthopedics. 2e edition. United states of America. McGraw-Hill. 2000. p. 125 – 175 Level of evidence: A2
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- Karen S. Beeton. The knee. Manual therapy masterclass: the peripheral joints. Churchill Livingstone. Elsevier. 2003. p. 54 – 55 Level of evidence: A1
- Pierre-paul Castelyn. “hoofdstuk”. Acute knee injuries, diagnostic and treatment managment proposals. Vub University press. 2001. p. 42-43 Level of evidence: A1
- Smith TO., Davies L., Chester R., Clark A., Donell ST. CLinical outcomes of rehabilitation for patients following lateral patellar dislocation: a systematic review. Phystiotherapy. Volume 96. Issue 4. December 2010. p. 269 – 281 Level of evidence: A1
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13) Journal of otrhopaedic surgery and research.Primary traumatic patellar dislocation. Chun-Hao Tsai. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3511801
14) Atkin DM, Fithian DC, Marangi KS, Stone ML, Dobson BE, Mendelsohn C. Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med. 2000;28:472–479. [PubMed]
15) Atkin DM, Fithian DC, Marangi KS, Stone ML, Dobson BE, Mendelsohn C. Characteristics of patients with primary acute lateral patellar dislocation and their recovery within the first 6 months of injury. Am J Sports Med. 2000;28:472–479. [PubMed]
16) Kirsch MD, Fitzgerald SW, Friedman H, Rogers LF. Transient lateral patellar dislocation: diagnosis with MR imaging. AJR Am J Roentgenol. 1993;161:109–113. [PubMed]
17) http://www.physio-pedia.com/Quadriceps_tendon_tear/Differential diagnosis
18) Hohlweck J., Diagnostic and therapeutic management of primary and recurrent patellar dislocations - analysis of a nationwide survey and the current literature. Zeitschrift für Orthopädie und Unfallchirurgie. 2013 Aug;151(4):380-8. [Pubmed]
19) Picture from: www.slideshare.net/bhavinj/mri-of-patellar-disorders (Bhavin Jankharia, Doctor at Jankharia Imaging, Mumbai, India)
20) Nikku R, Nietosvaara Y, Aalto K, Kallio PE. 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. 2005;76:699–704. doi: 10.1080/17453670510041790. [PubMed] [Cross Ref] (level of evidence 1B)
21) Arendt EA, Fithian DC, Cohen E. Current concepts of lateral patella dislocation. Clin Sports Med. 2002;21:499–519. doi: 10.1016/S0278-5919(02)00031-5. [PubMed] [Cross Ref] (level of evidence 5)
22) 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;15:62–66. doi: 10.1097/01.jsm.0000157315.10756.14. [PubMed] [Cross Ref]
(level of evidence 2B)
23) Fithian DC, Paxton EW, Cohen AB. Indications in the treatment of patellar instability. J Knee Surg. 2004;17:47–56. [PubMed] (level of evidence 5)
24) Koskinen SK, Rantanen JP, Nelimarkka OI, Kujala UM. Effect of Elmslie-Trillat and Roux-Goldthwait procedures on patellofemoral relationships and symptoms in patients with patellar dislocations. Am J Knee Surg. 1998;11:167–173. [PubMed] (level of evidence 2b)
25) Hohlweck J., Diagnostic and therapeutic management of primary and recurrent patellar dislocations - analysis of a nationwide survey and the current literature. Zeitschrift für Orthopädie und Unfallchirurgie. 2013 Aug;151(4):380-8. [Pubmed] (level of evidence 4)
26) Apostolovic M., Vukomanovic B., Slavkovic N., Vuckovic V., Vukcevic M., Djuricic G., and Kocev N., Acute patellar dislocation in adolescents: operative versus nonoperative treatment. Int Orthop. 2011 Oct [PubMed] (level of evidence 2B)
27) Akkie Rood, Harm Boons, Joris Ploegmakers, William van der Stappen, Sander Koëter; Tape versus cast for non-operative treatment of primary patellar dislocation: a randomized controlled trial; Archives of Orthopaedic and Trauma Surgery; 2012 [PubMed] (level of evidence 1B)
28) Stefancin JJ, Parker RD. First-time traumatic patellar dislocation: a systematic review. Clin Orthop Relat Res. 2007;455:93–101. [PubMed]
(level of evidence 2A)
29) Sillanpaa PJ, Mattila VM, Maenpaa H, Kiuru M, Visuri T, Pihlajamaki H. Treatment with and without initial stabilizing surgery for primary traumatic patellar dislocation. A prospective randomized study. J Bone Joint Surg Am. 2009;91:263–273. doi: 10.2106/JBJS.G.01449. [PubMed] [Cross Ref] (level of evidence 1B)
30) van Gemert et al.. Patellar dislocation: cylinder cast, splint or brace? An evidence-based review of the literature. International Journal of Emergency Medicine 2012 5.45
31) White BJ et al. Patellofemoral instability: bulletin of the NYU Hospital for Joint Diseases 2009; 67
32) David Drez, T.Bradley Edwards; Claude S. Williams: Results of medial patellofemoral ligament reconstruction in the treatment of patellar dislocation ; March 2001; Arthroscopy: The Journal of Arthroscopic and Related Surgery (level of evidence 4)
33) Peter R.Miller, Roger M.Klein. Robert A. Teitge : Medial dislocation of the patella; August 1991, Volume 20; Issue 6; pp 429-431
34) Elizabeth W. Paxton, Donald C. Fithian, Mary Lou Stone and Patricia Silva: The Reliability and Validity of Knee-Specific and General Health Instruments in Assessing Acute Patellar Dislocation Outcomes; July 2003
35) Mizuno, Y., Kumagai, M., Mattessich, S. M., Elias, J. J., Ramrattan, N., Cosgarea, A. J. and Chao, E. Y. S. (2001), Q-angle influences tibiofemoral and patellofemoral kinematics. J. Orthop. Res., 19: 834–840. doi: 10.1016/S0736-0266(01)00008-0
36) Smith TO, The reliability and validity of the Q-angle: a systematic review , Knee Surg Sports Traumatol Arthrosc. 2008 Dec;16(12):1068-79. doi: 10.1007/s00167-008-0643-6. Epub 2008 Oct 8.
37) Emami MJ, Q-angle: an invaluable parameter for evaluation of anterior knee pain, Arch Iran Med. 2007 Jan;10(1):24-6.
39) Chris S et al; Femoral Neuropathy due to patellar dislocation in a theatical and jazz dancer: a case report; Arch Phys Med Rehabil Vol 86, June 2005.
40 Neel P. Jain, MD, Najeeb Khan, MD, and Donald C. Fithian, MD; A Treatment Algorithm for Primary Patellar Dislocations ; Sports Health. 2011 March
41) Fuller J., Hammil H., Prochinske K., Druall C., “Operative vs. Nonoperative Treatment after Acute Patellar Dislocation: Which is more Effective at Reducing Recurrence in Adolescents?”. Journal of Sport Rehabilitation, © 2017 Human Kinetics, Inc. [PubMed] (level of evidence 3A)
42) Khan M. and Miller B., Cochrane in CORR®: Surgical Versus Non-surgical Interventions for Treating Patellar Dislocation (Review). Clin Orthop Relat Res. 2016 Nov [Pubmed] (level of evidence 1A)
43) Weber A.E., Nathani A., Dines J.S., Allen A.A., Shuyin-Stein B.E., Arendt E.A., Bedi A., "An algorithmic Approach to the Management of Recurrent Lateral Patellar Dislocation." (review). J Bone Joint Surg Am. 2016 Mar [Pubmed] (level of evidence 1A)
44) Smith T., Cheste R., Cross J., Hunt N., Clark a., Donnel S., Rehabilitation following first-time patellar dislocation: a randomised controlled trial of purported vastus medialis obliquus muscle versus general quadriceps strengthening exercises. 2015 Elsevier. [Pubmed] (level of evidence 1B)
45) SMITH (Toby O.), CHESTER (Rachel), CLARK (Allan), DONELL (Simon T.), STEPHENSON (Richard). A national survey of the physiotherapy management of patients following first-time patellar dislocation, in Physiotherapy, 2011, vol. 97, nr. 4, p. 327–338. [Online] http://www.sciencedirect.com.myezproxy.vub.ac.be/science/article/pii/S0031940611000265?via%3Dihub (Level of evidence: 2b)
46) SMITH (Toby O.), SONG (Fujian), DONELL (Simon T.), HING (Caroline B.). Operative versus non-operative management of patellar dislocation. A meta-analysis, in Knee Surgery, Sports Tramatology, Arthroscopy, 2011, vol. 19, nr. 6, p. 988-998. [Online] https://link-springer-com.myezproxy.vub.ac.be/article/10.1007%2Fs00167-010-1355-2 (Level of evidence: 3a)