Focal lesions of the patella

Giant cell tumour of the patella with local recurrence: successful management with excision, curettage and artificial bone grafting

Primary patellar neoplasms are rare, comprising 0.12% of primary bone tumours; thus, no standardised treatment related to staging exists. 70%-90% of primary patellar neoplasms are benign or intermediate with giant cell tumour (GCT) being the most common. GCTs are locally aggressive, have a high recurrence rate and metastasise in 1%-2%. We report the case of a 23-year-old man with histologically confirmed recurrent GCT of the patella to demonstrate that aggressive surgical management options described in the literature, such as patellectomy with or without complex reconstruction, may be excessive and cause patients undue morbidity. Initially, the patient underwent intralesional curettage with excellent recovery, but presented again with a local recurrence within a year. A further definitive operation was performed which included excision of the inferior pole followed by curettage of the patellar body and artificial bone grafting. The patient made a good recovery and at 5-year follow-up has maintained good function.

Association of trochlear dysplasia with degenerative abnormalities in the knee: data from the Osteoarthritis Initiative

OBJECTIVE

To evaluate trochlear morphology as a potential risk factor for patellofemoral osteoarthritis, determined by morphological and quantitative measurements of cartilage degeneration using 3-T magnetic resonance imaging (MRI) of the knee.

MATERIALS AND METHODS

MRI of the right knees of 304 randomly selected subjects, aged 45-60 years, from the Osteoarthritis Initiative (OAI) progression cohort were screened for trochlear dysplasia, defined by an abnormal trochlear depth. Out of 304 subjects, n = 85 demonstrated a shallow trochlea (depth ≤3 mm; 28 %). In these, and also in a random sample of controls with normal trochlear depth (n = 50), the facet ratio and the sulcus angle were calculated and knee structural abnormalities were assessed by using a modified Whole Organ MR Imaging Score (WORMS). Cartilage segmentation was performed and T2 relaxation times and patellar cartilage volume were determined. ANOVA and multivariate regression models were used for statistical analysis of the association of MRI structural measures and trochlear morphology.

RESULTS

Knees with a shallow trochlea showed higher patellofemoral degeneration (WORMS mean ± standard deviation, 11.2 ± 0.5 versus 5.7 ± 0.6; multivariate regression, P < 0.001) and lower patellar cartilage volume than controls (900 ± 664 mm(3) versus 1,671 ± 671 mm(3); P < 0.001). Knees with an abnormal medial-to-lateral facet ratio (<0.4) showed increased patellofemoral WORMS scores (12.3 ± 0.9 versus 8.3 ± 0.5; P < 0.001). Knees with an abnormal sulcus angle (>170°) also showed increased WORMS scores (12.2 ± 1.1 versus 8.6 ± 0.6; P = 0.003). T2 values at the patella were significantly lower in the dysplasia group with a shallow trochlea. However, significance was lost after adjustment for cartilage volume (P = 0.673).

CONCLUSION

Trochlear dysplasia, defined by a shallow trochlea, was associated with higher WORMS scores and lower cartilage volume, indicating more advanced osteoarthritis at the patellofemoral joint.

Ewing's sarcoma of the patella

Ewing's sarcoma is a relatively rare malignancy, occurring mainly between 4 and 25 years of age. It usually arises from the pelvis, followed by the femur, tibia, and remainder of both the long bones of the extremities and flat bones of the axial skeleton. To the best of our knowledge, Ewing's sarcoma of the patella has never been reported previously. Patellar tumors occur infrequently and represent an uncommon etiology of anterior knee pain. We describe the rare case of a 41-year-old man who presented with a 3-4 month history of escalating right anterior knee pain and swelling. Imaging demonstrated an aggressive patellar tumor with an adjacent soft tissue mass. The diagnosis of Ewing's sarcoma was confirmed by pathology. Physicians should be aware of atypical locations for Ewing's sarcoma and, conversely, of rare tumors arising in the patella and accounting for anterior knee pain. Early recognition of such malignancies allows prompt initiation of treatment, hence improving prognosis.

Magnetic resonance imaging of anatomical variations in the knee. Part 2: miscellaneous

Magnetic resonance imaging is the modality of choice for investigation of internal derangement of the knee. The reporting radiologist must be familiar with both normal anatomy and anatomical variants within the knee, in order to avoid mis-diagnosis, over-investigation and unnecessary intervention. This article reviews the recognised anatomical variants of the non-ligamentous/musculotendinous structures of the knee, their anatomy, incidence and typical appearances on MRI.