Introduction

Fractures of the patella are rare in children, as the patellais largely cartilaginous and has greater mobility [1]. In alarge series the reported incidence of patellar fractures inchildren was less than 2% of all patellar fractures [2]. Thegrowing patella is more vulnerable to osteochondral oravulsion fractures [3]. Avulsion or sleeve fractures can oc-cur at the superior or lower pole, but superior pole frac-tures are very rare, and we could find only one publishedreport in the literature [2].

Case report

A 14-year-old girl initially presented with a history of a lat-eral dislocation of her patella after a minor injury. The dis-location reduced spontaneously, but her knee was immo-bilised in a cylinder cast for 1 month. The cast was thenremoved and she was left free to mobilise. 2 days later,she fell downstairs when the same knee gave way, and shepresented to an accident department with a painful, swollenleft knee. Examination revealed a haemarthrosis with ten-derness over the patella. Plain radiographs were initiallyinterpreted as normal and she was treated with a support

bandage. After 3 days, the case was reviewed by an expe-rienced orthopaedic surgeon who noted that the patellawas tilted anteriorly, with a small bony fragment in rela-tion to the superior pole (Fig. 1). Clinical examination

Abstract The growing patella ismore vulnerable to osteochondral oravulsion fractures. Avulsion or sleevefractures can occur at the superior orlower pole. Superior pole fracturesare very rare. A case of superior polesleeve facture of the patella is pre-sented and the treatment described.

Keywords Fracture · Patella ·Avulsion · Osteochondral · Child

KNEEKnee Surg Sports Traumatol Arthrosc(2005) 13 : 299–301

DOI 10.1007/s00167-004-0514-8

Kapil Kumar David J. Knight

Sleeve fracture of the superior pole of patella: a case report

Received: 15 June 2003 Accepted: 7 January 2004 Published online: 20 May 2004© Springer-Verlag 2004

K. Kumar (✉) · D. J. KnightDepartment of Orthopaedics, Grampian University Hospitals, Foresterhill, Aberdeen, UKe-mail: kkumar@lineone.net

K. Kumar9 Edgehill Road, Aberdeen, AB15 5JG, UK

Fig. 1 Preoperative radiograph showing the patella tilted anteriorly

confirmed disruption of the extensor mechanism, and shewas admitted for exploration. There were no signs of gen-eralised joint laxity.

At surgery she was found to have a sleeve fracture ofthe superior pole of the patella, but there was no large frag-ment of the articular cartilage, unlike a previous report [4].There was a thin shell of bone avulsed from the proximalpole of the patella by the quadriceps tendon. There was noevidence of any damage to the articular cartilage as a re-sult of this injury or of a previous episode of dislocation.The bony fragment and the quadriceps tendon were re-duced on to the patella and fixed using Ethibond suturesthrough the quadriceps tendon attached to bone anchors(Mitek) in the patella (Fig. 2). Mitek anchors provide astrong hold in bone and are inserted through a single drillhole. Postoperatively the knee was immobilised in a cylin-der cast for 6 weeks, this immobilisation being followedby physiotherapy. Four months after the original injury thepatient had regained full painless movements of the kneejoint, with normal quadriceps strength on clinical exami-nation.

Discussion

Patellar fractures are very rare in children. The immaturepatella is less subject to both impact and tensile forcesthan in adults. It is surrounded by a thick layer of cartilagethat acts as a cushion against a direct blow. Also, the rela-tive magnitude of forces generated in the extensor mecha-nism of a child’s knee is less than an adult’s knee [3].

A sleeve fracture is a common type of fracture of thepatella in skeletally-immature patients [5]. This is due totensile loading of the knee [6]. In our case, the mechanismof injury was a stumble when descending stairs, causingforced flexion of the knee. The weakness of the thighmuscles after 4 weeks immobilisation in a cylinder castprobably contributed to the stumble.

Sleeve fractures usually involve the lower pole of thepatella [5, 7, 8]. To our knowledge there has been only onepreviously reported case of a sleeve fracture of the superiorpole [4]. This was fixed with a figure-of-eight suture. Weused bone anchors to fix the quadriceps tendon fragmentto the patella. Both methods appear to have given unevent-ful healing.

This case illustrates that the diagnosis may be missedunless there is a high index of suspicion. Fractures of thepatella can be difficult to diagnose. Developmental anom-alies can be confused with fractures. The small fragmentof bone, especially in sleeve fractures, may be overlookedon plain radiographs. This is illustrated in our case, wherethe bony fragment was small and was not noticed initially.Although the bony fragment may be very small, the anteriortilt of the patella is very characteristic of this injury, andwas present in both our case and a previous one. Otherimaging such as ultrasound [6] and MRI scan [9] can beused if there is clinical suspicion and the radiographs failto show the abnormality. In this case, the clinical and ra-diographic findings were clear-cut and no further imagingwas necessary.

We conclude that it is important to be aware of the pos-sible presence of this injury in the skeletally-immature pa-tient who presents with an indirect injury to the knee. Bel-man and Neviaser [10] pointed out that it is not uncommonfor the diagnosis of patellar fracture in a child to be missedor substantially delayed. The size of fracture fragments,especially in sleeve fractures, may be underestimated in agrowing child because the patella is partly cartilaginous.

300

Fig. 2 Postoperative radiograph showing normally-placed patellawith bone anchors used to reattach the quadriceps tendon to thepatella

301

1. Zionts LE (2002) Fractures around theknee in children. J Am Acad OrthopSurg 10:345–355

2. Bostrom, A (1972) Fracture of thepatella. Acta Orthop Scand 43(Suppl):1–80

3. Sponseller PD, Beaty JH (1996) Frac-tures and dislocations about the knee.In: Rockwood CA Jr, Wilkins KE,Beaty JH (eds) Fractures in children.Lippincott-Raven, Philadelphia, pp 1232–1329

4. Bishay M (1991) Sleeve fracture ofupper pole of patella. J Bone JointSurg Br 73:339

5. Ray JM, Hendrix T (1992) Incidence,mechanism of injury and treatment offractures of the patella in children. J Trauma 32:464–467

6. Ditchfield A, Sampson MA, TaylorGR (2000) Case reports. Ultrasounddiagnosis of sleeve fracture of thepatella. Clin Radiol 55:721–722

7. Dai LY, Zhang WM (1999) Fracturesof the patella in children. Knee SurgSports Traumatol Arthrosc 7:243–245

8. Houghton GR, Ackroyd CE (1979)Sleeve fractures of the patella in chil-dren: a report of three cases. J BoneJoint Surg Br 61:165–168

9. Bates DG, Hresko MT, Jaramillo D(1994) Patellar sleeve fracture: demon-stration with MR imaging. Radiology193:825–827

10. Belman DAJ, Neviaser RJ (1973)Transverse fracture of the patella in achild. J Trauma 13:917–918

References