Patient characteristics influencing knee injury and osteoarthritis outcome scores vary with time from patellar dislocation and number of dislocations.

Objectives: Demographic characteristics of the patient population influence patient reported outcome measures (PROMs) following patellar dislocations. The time from injury and number of dislocations can also vary within the patient population. The hypothesis of the study is that characteristics of the patient population influencing Knee injury and Osteoarthritis Outcome Score (KOOS) measures of pain, function, and quality of life vary with time from patellar dislocation and number of dislocations.

Methods: Outcome scores were evaluated for subjects in four groups: within five months of a first patellar dislocation (first-time group, n ​= ​24), within five months of a recurrent dislocation (multiple group, n ​= ​15), five to twelve months after a first dislocation (post-acute group, n ​= ​14), and two years or longer after a first dislocation (two-year group, n ​= ​14). For each group, KOOS pain, physical function, and quality of life scores were compared between males and females. KOOS scores were also correlated against age, body mass index (BMI), and time since first and most recent dislocation.

Results: For the first-time dislocation group, physical function, and quality of life scores were higher for men than women (p ​< ​0.05). For the multiple dislocation group, pain and physical function improved as BMI decreased (p ​< ​0.025), while quality of life improved as age decreased (p ​= ​0.014). For the post-acute group, all three scores improved as BMI decreased (p ​< ​0.05). For the two-year group, all three scores worsened as time since first dislocation increased (p ​< ​0.01).

Conclusions: Following patellar dislocation, relationships between characteristics of the patient population and PROMs vary with time from injury and number of dislocations. In the acute phase following a first dislocation, PROMs likely reflect the traumatic injury. Based on relationships with BMI, outcomes likely reflect functional capacity of the knee in the acute phase of multiple dislocations and post-acute phase of a first dislocation. After multiple years, progressive degradation of the knee over time seems to influence PROMs.

Level of evidence: Retrospective study with more than one negative criterion (Level 4).