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Acute Patellar Dislocation in Children and Adolescents: A Randomized Clinical Trial
Sauli Palmu, BM1; Pentti E. Kallio, MD, PhD2; Simon T. Donell, FRCS(Orth), MD3; Ilkka Helenius, MD, PhD2; Yrjänä Nietosvaara, MD, PhD2
1 Rakuunantie 18 A 21, FIN-00330 Helsinki, Finland. E-mail: sauli.palmu@helsinki.fi
2 Children's Hospital, Helsinki University Central Hospital, Stenbäckinkatu 11, FIN-00290 Helsinki, Finland
3 Institute of Health, University of East Anglia, Norwich, NR4 7TJ, United Kingdom
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
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Investigation performed at Aurora Hospital, Helsinki, and Children's Hospital, Helsinki University Central Hospital, Helsinki, Finland

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Mar 01;90(3):463-470. doi: 10.2106/JBJS.G.00072
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Background: The treatment of acute patellar dislocation in children is controversial. Some investigators have advocated early repair of the medial structures, whereas others have treated this injury nonoperatively. The present report describes the long-term subjective and functional results of a randomized controlled trial of nonoperative and operative treatment of primary acute patellar dislocation in children less than sixteen years of age.

Methods: The data were gathered prospectively on a cohort of seventy-four acute patellar dislocations in seventy-one patients (fifty-one girls and twenty boys) younger than sixteen years of age. Sixty-two patients (sixty-four knees) without large (>15 mm) intra-articular fragments were randomized to nonoperative treatment (twenty-eight knees) or operative treatment (thirty-six knees). Operative treatment consisted of direct repair of the damaged medial structures if the patella was dislocatable with the patient under anesthesia (twenty-nine knees) or lateral release alone if the patella was not dislocatable with the patient under anesthesia (seven knees). All but four patients who underwent operative treatment had a concomitant lateral release. The rehabilitation protocol was the same for both groups. The patients were seen at two years, and a telephone interview was conducted at a mean of six years and again at a mean of fourteen years. Fifty-eight patients (sixty-four knees; 94%) were reviewed at the time of the most recent follow-up.

Results: At the time of the most recent follow-up, the subjective result was either good or excellent for 75% (twenty-one) of twenty-eight nonoperatively treated knees and 66% (twenty-one) of thirty-two operatively treated knees. The rates of recurrent dislocation in the two treatment groups were 71% (twenty of twenty-eight) and 67% (twenty-four of thirty-six), respectively. The first redislocation occurred within two years after the primary injury in twenty-three (52%) of the forty-four knees with recurrent dislocation. Instability of the contralateral patella was noted in thirty (48%) of the sixty-two patients. The only significant predictor for recurrence was a positive family history of patellar instability. The mode of treatment and the existence of osteochondral fractures had no clinical or significant influence on the subjective outcome, recurrent patellofemoral instability, function, or activity scores.

Conclusions: The long-term subjective and functional results after acute patellar dislocation are satisfactory in most patients. Initial operative repair of the medial structures combined with lateral release did not improve the long-term outcome, despite the very high rate of recurrent instability. A positive family history is a risk factor for recurrence and for contralateral patellofemoral instability. Routine repair of the torn medial stabilizing soft tissues is not advocated for the treatment of acute patellar dislocation in children and adolescents.

Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    Sauli A Palmu, BM
    Posted on March 19, 2008
    Dr. Palmu et al. respond to Dr. Rogers et al.
    Rakuunantie 18 A 21, FIN-00330 HELSINKI, Finland

    We want to thank Dr. Rogers et. al for their comments. We have responded to their requests point by point.

    1. This study(1) was conducted in the Aurora Hospital, which, at that time, was the only treatment center for patients with patellar dislocation under the age of 16 in the city of Helsinki. Eight of the patients were referred for tertiary opinion.

    2. Patients with previous patellar dislocations were excluded from our study as stated in the fourth paragraph of Materials and Methods –section(1). A physiotherapist gave instructions for daily thigh muscle exercises after the treatment and at 3 and 6 weeks from the injury. Performance tests were performed at two years from the injury with similar results in both study groups(2).

    3. All of the radiological measurements were performed by YN. Sulcus angle was registered in tangential views of both patellae with knees in 20° of flexion taken at admission(3). Patellar height was calculated using the Insall-Salvati method(4). Intrarater range of five repeated measurements and interrater range between five different investigators was 4° concerning the measurements of sulcus angle.

    4. General joint laxity of the patients was analyzed using the method of Carter and Wilkinson(5) at two years from the injury with similar results in both treatment groups.

    5. Q-angle, range of hip rotation, femoral neck anteversion and thigh -foot angle were measured without significant differences in the study groups.(6,7,8).


    1. Palmu S. Kallio PE, Donell ST, Helenius I, Nietosvaara Y. Acute patellar dislocation in children and adolescents: a randomized clinical trial. J Bone Joint Surg Am. 2008;90:463-470.

    2. Nietosvaara Y. Acute Patellar Dislocation in children and adolescents. Academic dissertation. Helsinki, University of Helsinki; 1996.

    3. Laurin CA, Dussault R, Levesque HP. The tangential X-ray investigation of the patellofemoral joint: X-ray technique, diagnostic criteria and their interpretation. Clin Orthop Relat Res. 1979;144:16-26.

    4. Insall J, Salvati E. Patella position in the normal knee joint. Radiology 1971;101:101-4.

    5. Carter C, Wilkinson W. Persistent joint laxity and congenital dislocation of the hip. J Bone Joint Surg 1964;46B:40-5.

    6. Woodland LH, Francis RS. Parameters and comparisons of the quadriceps angle of college-aged men and women in the supine and standing positions. Am J Sports Med 1992;20:208-11.

    7. Staheli LT. Rotational problems of the lower extremities. Orthop Clin North Am 1987;18:503-12.

    8. Ruwe PA, Gage JR, Ozonoff MB, Deluca PA. Clinical determination of femoral anteversion. A comparison with established techniques. J Bone Joint Surg 1992;74A:820-30.

    Benedict A Rogers
    Posted on March 06, 2008
    Acute Patellar Dislocation in Children and Adolescents
    St Peter's Hospital, Chertsey, UK

    To The Editor:

    We read with interest the March 2008 paper by Palmu et al.(1) entitled “Acute Patellar Dislocation in Children and Adolescents: A randomized Clinical Trial” and would like to make the following points.

    1. The study details 74 cases of acute patella dislocations over a two-year period. In comparison to the study by Nietosvaara et al.(2), this is a large number for a two year study from Helsinki, a city that currently has a total population of circa 550,000. Were any of the cases referred to the author's center for tertiary opinion and management?

    2. As cited in the introduction, nonoperative treatment, entailing a period of rest followed by physiotherapy, is advocated for acute patellar dislocation(3-5). Despite the methods detailing the demographic and radiographic characteristics of both patient cohorts examined in this study, there is no quantification of the number of previous acute patellar dislocations experienced or the amount of physiotherapy received. More specifically, since the patella is a mobile structure, the dynamic soft tissue constraint provided by the extensor mechanism is thought to be crucial for its stability. A quantification of quadriceps strength would be informative for both patient cohorts studied.

    3. The Insall-Salvati ratio used to assess patella height in this study, whilst have the theoretical advantages of measuring the patellar tendon length directly, has poor inter-observer correlation(6). How and by whom was the measurement of the sulcus angle and the Insall-Salvati ratio measured? Was adequate inter- and intra- observer agreement achieved?

    4. Ligamentous hyperlaxity is a well known predisposing factor to acute patellar dislocation and patellofemoral instability in children and adolescents(7). Ligamentous hyperlaxity can be assessed using Beighton score(8) and comparison of the degree of hypermobility in this study would be useful.

    5. Tibio – femoral alignment is known to alter patellofemoral mechanics. External tibial torsion(9) and a high Q-angle(10) are associated with recurrent lateral patella dislocation. Was there any reason for these not being assessed in the two patient groups studied?


    1. Palmu, Kallio PE, Donell ST, Helenius I, Nietosvaara Y. Acute patellar dislocation in children and adolescents: a randomized clinical trial. J.Bone Joint Surg.Am 2008;90:463-470.

    2. Nietosvaara, Aalto K, Kallio PE. Acute patellar dislocation in children: incidence and associated osteochondral fractures. J.Pediatr.Orthop 1994;14:513-515.

    3. Beasley, Vidal AF. Traumatic patellar dislocation in children and adolescents: treatment update and literature review. Curr.Opin.Pediatr. 2004;16:29-36.

    4. Buchner, 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.

    5. Cash, Hughston JC. Treatment of acute patellar dislocation. Am J.Sports Med. 1988;16:244-249.

    6. Rogers, Thornton-Bott P, Cannon SR, Briggs TW. Interobserver variation in the measurement of patellar height after total knee arthroplasty. J Bone Joint Surg Br. 2006;88:484-488.

    7. Arendt, Fithian DC, Cohen E. Current concepts of lateral patella dislocation. Clin Sports Med. 2002; 21:499-519.

    8. Beighton, de PA, Danks D, Finidori G, Gedde-Dahl T, Goodman R, Hall JG, Hollister DW, Horton W, McKusick VA, International Nosology of Heritable Disorders of Connective Tissue, Berlin, 1986. Am J.Med.Genet. 1988; 29:581-594.

    9. Cameron, Saha S. External tibial torsion: an underrecognized cause of recurrent patellar dislocation. Clin Orthop Relat Res. 1996;177-184.

    10. Mizuno, Kumagai M, Mattessich SM, Elias JJ, Ramrattan N, Cosgarea AJ, Chao EY. Q-angle influences tibiofemoral and patellofemoral kinematics. J.Orthop Res. 2001; 19:834-840.

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