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ORIGINAL ARTICLE

Natural History Of The Supero-Lateral Bipartite Fragment Of The Patella In Children

Yoshikazu Oohashi1, Tomihisa Koshino2 , Yoshinori Oohashi1

1 Oohashi Orthopaedic Clinic, Fukui, Japan
2
Department of Orthopaedic Surgery, Yokohama City University,
   School of Medicine, Yokohama, Japan.

Address for Correspondence:
Yoshikazu Oohashi
Oohashi Orthopaedic Clinic, 38-20,
Ninomiya-3-choume
Fukui-City, Fukui-Ken, 910-0015, Japan.

Phone : +81 776 25 0099
E-mail :
oohashiy@lilac.ocn.ne.jp

Abstract:

The purpose of this study was to clarify the natural history of the supero-lateral bipartite fragment of the patella in children. Twenty-three patients with bipartite fragment of the patella (27 knees) under 15 years old at initial examination were followed until they were over 16 years old. Among them, spontaneous bone union of bipartite fragment was gained in 13 knees (united group) and not gained in 14 knees (non-united group). These bipartite fragments of the united group were thought to be accessory ossification centers of the patella and these of the non-united group were thought to be usual bipartite patellas. The gap between the bipartite fragment and body of patella of the united group at initial examination (median; 1 mm, range 1-2 mm) was significantly narrower than that of the non-united group (median; 3 mm, range 2-4 mm) (p<0.0001). Therefore, the development of bipartite patella may be predicted in bipartite fragments with large gap.

J.Orthopaedics 2010;7(4)e5

Keywords:

bipartite fragment; accessory ossification center; bipartite patella; natural history; bone union; children.

Introduction:

As the ossification center of the patella enlarges, the expanding margins become irregular and associated with accessory ossification centers and these are most common supero-laterally1. Bipartite patella is supposed to be developed from a failure of an accessory ossification center of the patella to unite with the main portion of the patella1-5. However, it is not clear why an accessory ossification center of the patella fail to unite with the main portion of the patella. Until now, few authors reported the differences between supero-lateral accessory ossification center and bipartite patella. Therefore, it is important to clarify the natural history of the supero-lateral bipartite fragment of the patella in children.

The purpose of this study was to clarify the natural history of the supero-lateral bipartite fragment of the patella in children. Our hypothesis was that development of bipartite patella would be predicted in bipartite fragments with large gap.

Materials and Methods:

Forty patients (46 knees) with bipartite fragment of the patella under 15 years old at initial examination were examined by the first author between 1973 and 2007. Among them, those patients who could be followed until they were over 16 years old without any interventions were included in this study. Five patients (7 knees) were lost to follow up and those patients were excluded. Fragments of 10 bipartite and 2 tripartite patellae were excised at surgery due to pain in 12 patients and those patients were also excluded. Surgical treatment was considered for those patients who had failed to respond to at least 3 months of conservative treatment, including rest and restriction of sports activities. In all those operated patients, tenderness over the supero-lateral or lateral aspect of the patella disappeared within 4 weeks after surgery and all returned to their previous sports activities at 2 months. Finally, twenty-three patients (27 knees) were included in this study. Accessory ossification center is defined as asymptomatic bipartite fragment that will unite spontaneously without any intervention until 16 years of age. Bipartite patella is defined as a bipartite fragment that will not unite spontaneously over 16 years of age. Symptomatic bipartite patella is defined as both pain at the separated fragments during or after strenuous activity and localized tenderness over the separated fragments6. Asymptomatic bipartite fragment is defined as an incidental finding when the knee is radiographed for other reasons. According to a classification for developmental anomaly of ossification type bipartite or tripartite patellae6, all bipartite fragments were supero-lateral bipartite type. In those patients, both bone union of the bipartite fragment and symptoms at initial examination and at follow-up were investigated. The gap between the bipartite fragment and the body of patella at initial examination was measured in 1-millimeter increments at the widest gap by a ruler on AP roentgenograms. All measurements were made once by the same observer (Yoshikazu Oohashi).

Statistical analysis

The measured gap between bipartite fragment and the body of patella did not follow a normal distribution; therefore, non-parametric the Wilcoxon Rank Sum test with the R program was used. All analyses were two-tailed, and p<0.05 was considered statistically significant. Differences in proportions of the bone union of bipartite fragment between symptomatic and asymptomatic bipartite fragment were analyzed using Fisher’s exact probability test with the R program. P<0.05 was considered statistically significant.

Results :

Spontaneous bone union of bipartite fragment was seen in 13 knees (11 patients) (united group) (Fig.1). These bipartite fragments of the united group were thought to be accessory ossification centers of the patella. The mean age at initial examination was 11.3±1.5 years (range, 7 years 9 months to 12 years 9 months). Mean age of patients with bone union of the bipartite fragment was found to be 12.9±1.2 years (range, 10 years to 14 years 7 months) (Fig.2). Mean follow-up period of patients until bone union was observed was 2.1±1.2 years (range, 8 months to 3 years 11 months). The gap between the bipartite fragment and body of patella of the united group (13 knees) at initial examination was 1-2 mm (median, 1 mm). Eight were male and 3 were female. All 13 bipartite fragments that united were asymptomatic.

Spontaneous bone union of bipartite fragment was not obtained in 14 knees (12 patients) (non-united group) at final examination at mean age of 17.9±2.6 years (range, 16 years to 24 years 1 month) (Fig.3). These bipartite fragments of the non-united group were thought to be usual bipartite patellas. The mean age at initial examination was 13.9±0.7 years (range 13 years to 15 years 5 months). Mean follow-up period was 3.9±2.8years (range, 1 year 4 months to 10 years 9 months). The gap between the bipartite fragment and body of patella (14 knees) at initial examination was 2-4 mm (median, 3 mm). All were male. Among them, ten bipartite patellae (8 patients) were symptomatic and 4 (4 patients) were asymptomatic at initial examination; however, 4 bipartite patellae (3 patients) were symptomatic and 10 bipartite patellae (9 patients) were asymptomatic at final examination.

The gap between the bipartite fragment and body of patella at initial examination of the united group was significantly narrower than that of the non-united group (p<0.0001) (Table 1). Bone union of the bipartite fragment was seen more frequently in asymptomatic bipartite fragments (13 of 17 patellae, 76%) than that seen in symptomatic bipartite fragments (0 of 10 patellae, 0%) (p<0.001).

 

                         a.                                           b.

Fig.1 Radiographs of a girl with asymptomatic supero-lateral bipartite fragment of the right knee (united group)

a. Antero-posterior radiograph showing a bipartite fragment of patient at 12 years, 7 months old. The gap between the bipartite fragment and body of the patella is 1- mm (arrow).

b Antero-posterior radiograph showing union of the bipartite fragment in the same patient at 13 years, 6 months old.

Fig.2 Frequency of bone union of the bipartite fragment noted by age.

The peak incidence is seen in 13-year-olds.

Fig.3 Radiographs of a boy with a symptomatic supero-lateral bipartite fragment of the left knee (non-united group).

a. Antero-posterior radiograph showing a bipartite fragment at 13 years, 10 months old. The gap between the bipartite fragment and body of the patella is 2-mm (arrow).

b Antero-posterior radiograph of the same patient showing a bipartite patella (arrow) at 22 years, 9 months old.

Discussion :

The most important finding of the present study was that the gap between the bipartite fragment and body of patella of the united group was significantly narrower than that of the non-united group. Furthermore, bone union of the bipartite fragment was seen more frequently in asymptomatic bipartite fragment than that seen in symptomatic bipartite fragment.

Several theories have been proposed to explain the development of bipartite patella. Ogden et al. suggested etiology involving a traumatically induced, chondroosseous disruption of the superolateral pole of the incompletely ossified patella, analogous to Sinding -Larsen-Johansson or Osgood-Schlatter’s disease7. Furthermore, van Holsbeeck et al. reported four patients with an association of a dorsal defect of the patella and a multipartite patella and they suggested a common genesis for these two ossification variants by which the traction lesion at the insertion of the vastus lateralis muscle plays an important role8 . Although Devas presented a symptomatic superolateral fragment as a result of stress fracture9 , Bourne et al. described that his evidence was not convincing [3]. Until now, the more likely explanation is that bipartite patella is a failure of an accessory center of ossification to unite with the main portion of the patella1-5 . However, it is not clear why an accessory ossification center of the patella fail to unite with the main portion of the patella. Present study may suggest that supero-lateral accessory ossification center that gap between the bipartite fragment and body of patella is greater than 2mm may remain separate and lead to bipartite patella.

A few cases have been reported in which knees that appeared normal on radiograph later developed an acute fracture of the superolateral patella10 or bipartite patella7, or late appearance of accessory ossification center3,11. Echeverria et al. reported a rare case of an acute fracture of the superolateral patella in a 17-year-old high school soccer player10. X-ray films of his same knee 10 weeks before injury were normal and they concluded that the lesion seen at this injury represent an acute fracture 10. Bourne et al. reported a case in which knee that appeared normal on radiograph later developed bipartite patella and described that delayed ossification of the accessory ossicle is a possible explanation in such case 3. Similarly, Zumstein et al. also reported a case of bilateral radiographic progression of the supero-lateral fragment of a bipartite-into a tripartite patella and they concluded etiology involving a late appearance of a third ossification center11.

On the other hand, bone union of bipartite patella in children and adolescents has been reported following procedures to reduce traction force of the vastus lateralis muscle on the bipartite fragment12-14 or after treatment with low-intensity pulsed ultrasound15 or after treatment with cast immobilization7. Adachi et al. reported arthroscopic vastus lateralis release in patients with an average age of 13.8 years, resulting in 64.7% bone union, and bone union in patients 15 years or younger was significantly better than that seen in patients over 15 years of age14. Ogden et al. also reported the incorporating the accessory center into the main patellar ossification center after cast immobilization for 3 weeks in a 12-year-old boy7. However, present study shows that it is necessary to distinguish symptomatic bipartite patella from supero-lateral accessory ossification center that unite spontaneously when such treatments are considered in children and adolescents.

According to the natural history of the symptoms of bipartite patella, few studies have been reported. In present series, among symptomatic bipartite patella under 15 years old at initial examination, only a few were symptomatic at the follow-up. Therefore, it is necessary to investigate long-term symptom amelioration.

This study has several limitations. First, the number of cases investigated in this study is small and a further randomized controlled study is needed. Second, the gap between the bipartite fragment and the body of patella was measured in 1-millimeter increments on roentgenograms by the same observer (Yoshikazu Oohashi) and all measurements were made only once. Therefore, there was not a study of inter- and intra-personal validity.

Conclusion:

Development of bipartite patella may be predicted in patients 14 years old or younger, particularly in symptomatic bipartite fragments in which the gap between the bipartite fragment and the body of patella is more than 2mm.

Reference:

  1. Ogden J.A. Radiology of postnatal skeletal development. X. Patella and tibial tuberosity. Skeletal Radiol 1984; 11: 246-257.

  2. Adams JD, Leonard RD. A developmental anomaly of the patella frequently diagnosed as fracture. Surg Gynecol Obstet 1925; 41:601-604.

  3. Bourne MH, Bianco AJ. Bipartite patella in the adolescent: Results of surgical excision. J Pediatr Orthop 1990; 10:69-73.

  4. George R. Bilateral bipartite patellae. Br J Surg 1935; 22:555-560.

  5. Oohashi Y, Noriki S, Koshino T, Fukuda M. Histopathological abnormalities in painful bipartite patellae in adolescents. The Knee 2006; 13:189-193.

  6. Oohashi Y, Koshino T, Oohashi Y Clinical features and classification of the bipartite and tripartite patella. Knee Surgery, Sports Traumatology, Arthroscopy in press. DOI 10.1007/s00167-010-1047-y.

  7. Ogden JA, McCarthy SM, Jokl P. The painful bipartite patella. J Pediatr Orthop 1982; 2:263-269.

  8. van Holsbeeck M, McCally WC. Dorsal defect of the patella: concept of its origin and relationship with bipartite and multipartite patella. Skelet Radiol 1989; 16:304-311.

  9. Devas MB. Stress fractures of the patella. J Bone Joint Surg Br 1960; 42:71-74.

  10. Echeverria T S, Bersani F A. Acute fracture simulating a symptomatic bipartite patella. Report of a case.  Am J Sports Med 1980; 8:48-50.

  11. Zumstein M, Sukthankar A, Exner G U. Tripartite patella: late appearance of a third ossification center in childhood. J Pediatr Orthop B 2006; 15:75-76.

  12. Ogata K. Painful bipartite patella. A new approach to operative treatment. J Bone Joint Surg Am 1994; 76:573-578.

  13. Mori Y, Okuno H, Iketani H, Kuroki Y. Efficacy of lateral retinacular release for painful bipartite patella. Am J Sports Med 1995; 23:13-18.

  14. Adachi N, Ochi M, Yamaguchi H, Uchio Y, Kuriwaka M. Vastus lateralis release for painful bipartite patella. Arthroscopy 2002; 18:404-411.

  15. Kumahashi N, Uchio Y, Iwasa J, Kawasaki K, Adachi N, Ochi M. Bone union of painful bipartite patella after treatment with low-intensity pulsed ultrasound: Report of two cases. The Knee 2008; 15: 50-53.

This is a peer reviewed paper 

Please cite as: Yoshikazu Oohashi: Natural History Of The Supero-Lateral Bipartite Fragment Of The Patella In Children.

J.Orthopaedics 2010;7(4)e5

URL: http://www.jortho.org/2010/7/4/e5

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