Patellofemoral instability and dysfunction are frequent symptoms in Nail patella syndrome (NPS). In this article, the first large series of NPS patients is presented in which these knee symptoms were assessed using validated outcome scores. Additionally, the need for surgical interventions, percentage of patients who received surgical treatment and patient reported outcomes are reported.

A questionnaire based survey was conducted in 139 Dutch NPS patients. Symptoms of the knees were assessed by the Knee injury and Osteoarthritis Outcome Score (KOOS) and Kujala knee score. The questionnaire addressed whether surgical intervention was currently considered, history of past surgeries, type of surgical procedures performed and results of these procedures.

Response rate was 74%. Mean KOOS (73.04) and Kujala (74.01) scores showed a wide range and variability between patients. Patellofemoral instability was present in 48.5% of patients. Surgical intervention was currently considered by 12% of patients. Their KOOS and Kujala scores were significantly lower compared to those not considering surgery and they experienced more patellar instability. Surgery was performed on 31 knees in 23 patients. KOOS and Kujala scores were lower in surgically treated versus nonoperated patients but no difference in patellar instability was present. An improvement in pain in 87% and in function in 30% of knees was reported after surgery. Patient satisfaction with the surgical results was 61% and 10% was dissatisfied. Patellar realignment procedures showed similar results, although persistent patellar instability was reported in 40% of patients, not different from nonoperated patients.

Knee symptoms in NPS patients vary widely, with patellar instability present in nearly half of the patients. Although surgical treatment appears unfavourable as surgically treated patients have lower KOOS and Kujala scores, the patient reported surgical results are generally good with a high patient satisfaction.

Level IV.