A 9-year-old girl was referred to the emergency department after falling from an electric scooter. The emergency physician noticed a swollen right knee and patella alta. During the clinical examination, the patient was unable to perform active knee extension. No previous medical history was known.
A lateral radiograph of the right knee demonstrated a patella alta, an irregular delineated bone fragment anterior to the femoral condyles, and a small amount of fluid in the suprapatellar recess (Figure 1).
The T1 and T2 FS weighted MR images showed periosteal stripping at the apex of the patella combined with a slack patellar tendon and a small bone fragment at the base of the patella (Figures 2 and 3). The bone fragment consists of a hypointense cortex and isointense to slightly hypointense trabecular bone (Figure 3) and is connected to the tibia by a small strand of T1 and T2 hypointense periosteum (Figures 2 and 3).
The patellar tendon is buckled and oedematous, hence the slight T2 hyperintense signal (Figure 2).
These findings confirm a patellar periosteal stripping proximally and a tibial periosteal sleeve avulsion fracture distally.
Additionally, there was a rupture of both the medial and lateral patellofemoral retinacula (Figure 4).
Sleeve fractures are characterised by the avulsion of a strand of cartilage or periosteum, with or without pieces of cortical and sometimes trabecular bone, and occur in skeletally immature patients [1,2].
Sleeve fractures from the inferior patellar pole are rare, but they are a well-recognized entity in children after trauma [1]. Even though the incidence of patellar fractures in children is only 1%, the patellar sleeve fracture is the most common type of patellar fracture in patients younger than 16, at 57% of all patellar fractures. The peak incidence is at 12.7 years old, with a male-to-female ratio of 3:1 [3].
Much more rare is the tibial periosteal sleeve fracture. It is a rare variant of the tibial tuberosity avulsion fracture and wasn’t originally included in the Watson-Jones or Ogden classifications of tibial tuberosity avulsion fractures. Several authors have now proposed to include these fractures in a modified classification [1,2].
Bifocal patellar tendon avulsion lesions are extremely rare [4]. This case depicts a patient with a combined patellar periosteal stripping and a tibial periosteal sleeve fracture.
Forced knee flexion with simultaneous forceful quadriceps muscle contraction causes a high tensile force at the patellar apex and the tibial apophysis. In children, these forces can cause avulsion fractures [1,4].
A suggestive history, combined with a joint effusion, a high-riding patella and loss of active extension, is very suggestive of a patellar tendon injury [1,4). MR imaging is required for the evaluation of the affected parts of the tendon, i.e., origin, tendon or insertion [4].
Treatment of these avulsion fractures consists of open reduction and internal fixation by an orthopaedic surgeon and suturing of the periosteum. The patient-reported outcome is excellent [1,4].
Take home message
Children with a swollen knee, a patella alta and a history of forced knee flexion who can’t perform active knee extension should be examined for a patellar tendon injury. These injuries can be suspected on plain radiography but are better recognized on MRI as bone fragments with a connected strand of periosteum. An orthopaedic surgeon can treat these fractures with an excellent patient-reported outcome.
All patient data have been completely anonymised throughout the entire manuscript and related files.
Combined patellar stripping and tibial periosteal sleeve fracture
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1. The lateral X-ray shows an elevated position of the right patella (patella alta), with a possible small avulsed bony fragment at the inferior pole of the patella (arrow indicated). The joint space is generally acceptable, but there is significant soft tissue swelling.
2. MRI images (sagittal and axial views) reveal an avulsion at the local bony attachment of the inferior pole of the patella, with noticeable soft tissue edema signal enhancement in the related region. Continuous or membranous avulsion signs are also observed at the tibial tubercle attachment (i.e., small bony fragments or soft tissue stripping at the superior rim of the tibia).
3. High-signal changes are present in the soft tissue tendon area, indicating damage to the patellar tendon and its insertion. Surrounding soft tissue swelling and effusion are consistent with traumatic injury. Overall, imaging suggests avulsive injuries at both the origin and insertion points of the patellar tendon.
Taking into account the patient’s age, history of trauma (fall from an electric scooter causing direct or indirect force), imaging findings (avulsion fractures of the inferior pole of the patella and tibial tubercle with associated periosteal or cartilage detachment), and clinical signs (patella alta, inability to actively extend the knee):
The most likely diagnosis is: Avulsion-type “sleeve” fracture of the inferior pole of the patella combined with a “sleeve” avulsion fracture of the tibial tubercle (a bidirectional patellar tendon attachment injury featuring periosteal avulsion).
According to the postoperative phase, a gradual progression of exercises is recommended (following the FITT-VP principle):
Throughout the rehabilitation process, professional guidance from a qualified therapist or physician is advised, and regular follow-ups are necessary to ensure proper bone and soft tissue healing, preventing reinjury from premature or excessive weight-bearing.
Disclaimer:
This report is based solely on the provided medical history and imaging data for reference purposes and is not a substitute for an in-person consultation or professional medical advice. Clinical decisions should be made by a specialist physician after a comprehensive evaluation of the patient’s full medical history, physical examination findings, and other pertinent tests.
Combined patellar stripping and tibial periosteal sleeve fracture
