Date Published: June 14, 2012
Publisher: Hindawi Publishing Corporation
Author(s): A. Gkiokas, L. G. Morassi, S. Kohl, C. Zampakides, P. Megremis, D. S. Evangelopoulos.
A retrospective study was performed on the use of bioabsorbable pins in the fixation of osteochondral fractures (OCFs) after traumatic patellar dislocation in children. Eighteen children (13 females, 5 males) aged 11 to 15 years (mean age 13.1 years) with osteochondral fracture (OCF) of the knee joint were treated at the authors’ institution. Followup ranged from 22 months to 5 years. Diagnosis was verified by X-ray and magnetic resonance imaging (MRI) of the knee and patella. In seven patients the osteochondral fragment was detached from the patella and in 11 it was detached from the lateral femoral condyle. All patients were subjected to open reduction and fixation of the lesion with bioabsorbable pins. Postoperatively, the knee was immobilized in a cast and all patients were mobilized applying a standardized protocol. Bone consolidation was successful in 17 of the 18 patients. Bioabsorbable pins reliably fix OCF in children and adolescents, demonstrating a high incidence of consolidation of the detached osteochondral fragment in short- and middle-term followup without requiring further operative procedures.
Acute patellar dislocation is a common injury in early adolescence, with an incidence ranging from 29 to 42 per 100,000 children under 16 years of age [1, 2]. The etiology is mainly traumatic, involving either direct trauma to the knee or a twisting action. Adolescents, particularly those with preexisting ligamentous laxity of the knee, are prone to patellar dislocation. Osteochondral fractures (OCFs) of the patella or femur represent a major complication following patella dislocation, its incidence varying from 5% to 39% after dislocation . The fractured fragments consist of both cartilaginous and bony parts. Certain anatomic variables may predispose to patellar lateral instability in adolescents, including patella alta, genu valgum, internal torsion of the femur, trochlear dysplasia, laxity of the medial patellofemoral ligament (MPFL), or increased Q angle . The majority of lateral patellar dislocations occur at the initial stages of flexion of the knee joint, when the patella is not fully engaged in the femoral sulcus. In this phase, the MPFL acts as the primary restraint to the patella’s lateral translation [2, 4].
Over a period of five years, 18 adolescents (5 males, 13 females; mean age 13.1 years, range 11–15 years) were treated at our institution (a level A trauma center) for osteochondral fracture following traumatic acute patellar dislocation. The mechanism of injury included either a direct blow to the patella or a twisting action. In two patients initial clinical evaluation found the patella to be dislocated with the knee flexed and swollen requiring immediate reduction. In the remaining 16 patients the patellar dislocation was reported by the patient, or caregivers, and spontaneous reduction with knee extension had occurred at the scene of injury. In all patients there was significant knee effusion, raising the suspicion of osteochondral damage secondary to traumatic patellar dislocation. Seven patients had intense hemarthroses that were treated by aspiration under local anesthesia. Thorough radiographic assessment of all 18 patients included anteroposterior, lateral, and tangential views of the knee. For the tangential view of the patella a Merchant’s view was used. In one patient, a CT scan had been performed prior to transfer to our institution from a rural hospital. In the remaining 17 patients, preoperative MRI scans of the knee were performed to confirm the diagnosis, reveal the extent of cartilage damage, and rule out rupture of cruciate or collateral ligaments. All scans revealed bone marrow edema of the lateral femoral condyle (Figure 1).
All 18 patients were subjected to open reduction and internal fixation of the osteochondral fragment. The detached fragments were primarily chondral with small bony parts and surprisingly larger than expected in the majority of the patients. Seven (38%) of the detached fragments were from the medial facet of the patella, 11 (61%) from the lateral condyle of the femur on a weight-bearing surface.
Acute patellar dislocation may result in OCF. In the past, OCFs following patellar dislocation were thought to be a rarity. In 1976 Rorabeck and Bobechko reported an incidence of 5% after acute patellar dislocation . However, several recent studies report a higher incidence of OCF after patellar dislocation, ranging from 39% to 71% [1, 11–13]. As the aforementioned studies show, the incidence of such injuries had previously been underestimated. Nevertheless, despite the higher incidence of chondral injuries, not all injuries were displaced, requiring surgical treatment.
Despite our efforts to ensure validity, the present study displays certain limitations. This is a retrospective analysis and the number of patients composing the study group is limited to draw significant conclusions. Although our results demonstrate good functional outcome for all patients for a period ranging from 22 months to five years, a longer follow-up period is required to assess long-term changes of the articular surface of the lateral condyle.
The use of biodegradable pins for treatment of OCF in 18 children and early adolescents resulted in a high rate of consolidation, restoring congruity of the articular surfaces of the knee joint with no signs of foreign body reaction or synovitis. Studies with longer followup are still required to properly assess the benefits of bioabsorbable pins in the treatment of OCF.