JBJS -- Letters to the Editor for Palmu et al., 90 (3) 463-470

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Letters to the Editor to:

Scientific Articles:
Sauli Palmu, Pentti E. Kallio, Simon T. Donell, Ilkka Helenius, and Yrjänä Nietosvaara
Acute Patellar Dislocation in Children and Adolescents: A Randomized Clinical Trial
J Bone Joint Surg Am 2008; 90: 463-470 [Abstract] [Full text] [PDF]

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Electronic letters published:

Dr. Palmu et al. respond to Dr. Rogers et al.: Sauli A Palmu, BM, Yrjänä Nietosvaara (20 March 2008)

Acute Patellar Dislocation in Children and Adolescents: Benedict A Rogers, Charline Roslee, Nick J Little (11 March 2008)

Dr. Palmu et al. respond to Dr. Rogers et al. 20 March 2008

Sauli A Palmu, BM
Rakuunantie 18 A 21, FIN-00330 HELSINKI, Finland,
Yrjänä Nietosvaara
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Re: Dr. Palmu et al. respond to Dr. Rogers et al.

sauli.palmu{at}helsinki.fi Sauli A Palmu, BM, et al.

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).
References:
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.

Acute Patellar Dislocation in Children and Adolescents 11 March 2008

Benedict A Rogers,
Specialist Registrar
St Peter's Hospital, Chertsey, UK,
Charline Roslee, Nick J Little
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Re: Acute Patellar Dislocation in Children and Adolescents

benedictrogers{at}hotmail.com Benedict A Rogers, et al.

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?
References:
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.