Rotational deformities, such as femoral (thigh bone) and tibial (leg bone) torsion, are established causes of patellofemoral (kneecap joint) pain and instability. Currently, computerized tomography (CT) remains the gold standard assessment tool for measuring the degree of rotational deformity. However, there is disagreement as to the thresholds for surgical correction as it is suggested that some individuals compensate for the deformity better than others. Gait (walking) analysis provides important information of the biomechanical parameters undertaken in the knee joint during dynamic movement. In patients with rotational deformities, several variations from normal gait patterns have previously been described by several authors. Therefore, it is questioned whether these parameters can be correlated with the static features of CT scans, in individuals with rotational deformities. This study aims to determine whether gait analysis is a useful tool in the diagnosis and treatment pathway for rotational abnormalities in patellofemoral pain or instability. A secondary aim of this study will be to assess whether gait analysis can detect a rotational deformity in the lower limb and determine whether the changes seen are proportionate to the level of deformity.

Patients to be included in this retrospective study are, adult patients, with presumed rotational deformity of the lower limb, with anterior knee pain, who have been referred to the gait laboratory for assessment, and for CT rotational profiles. Only patients who have given consent to the gait laboratory for their information to be utilised in research will be included. Two researchers will record measures of rotational deformity from the CT images. The gait laboratory assessment includes measurements of biomechanical parameters based on joint movement through the gait cycle - these parameters will be assessed and compared with CT measures for correlation. All research will be conducted at the hospital where the gait laboratory assessment has been performed.

Patellofemoral pain (PFP) is one of the most common disorders in orthopaedic clinics (Rothermich, 2015). The knee pain is said to responsible for 25-40% of annual incidence, though a true prevalence is unknown (Witvrouw, 2014)(Lankhortst et al, 2012). Patient demographics range from young, active individuals to sedentary, elderly individuals (Witvrouw, 2014).

Primary care consultations to orthopaedic and musculoskeletal clinics, from knee pain alone, are reported to account for over 100,000 appointments annually (Smith et al., 2018). This costs the UK economy around £7.4million a year through employment absenteeism, alongside additional costs for non-operative and operative treatment procedures (Smith et al., 2018)(Swan et al., 2010).

Alongside age and activity, an important variable in understanding the epidemiology of PFP is the difference in the incidence and prevalence between genders. Many epidemiologic studies have shown that females have a two-fold higher incidence rate of the disorder than males (Rothermich, 2015).

The aetiology of PFP is evasive and multifactorial. Therefore, patients presenting with this syndrome pose a challenge for the diagnosis and long-term treatment of the pain. An important part of the diagnosis for the disorder is to rule out any other possible causes such as plica syndrome, neuromas or intra-articular pathology (Rothermich, 2015). Combinations of malalignment of the lower extremities, imbalance in muscles of the hips and knee joints, and over use, are the main factors which present most often and are considered causative to the disorder (Rothermich, 2015). One main contributors to PFP is that of lower limb structural factors, such as femoral ante/retro version and tibial torsion (Snow, 2021). These factors are thought to significantly effect gait and muscular function, which results in overloading of the joint and disturbed patellofemoral mechanics (Snow, 2021).

Currently, computerised tomography (CT) is the gold standard tool used to quantify rotational deformity on the lower limb (Snow, 2021). However, CT is a static imaging modality and does not capture the 'real life' dynamic kinetics that occur through movement (Saevarsson et al., 2013). Gait analysis provides important quantitative information of the biomechanical parameters undertaken in the knee joint during dynamic movement. In patients with rotational deformities, these parameters are either heightened or decreased on activity (Arazpour et al., 2016). Therefore, it is questioned as to whether gait analysis can detect a rotational deformity in the lower limb and determine whether the changes seen are proportionate to the level of deformity. Consequently, questioning as to whether gait analysis is an appropriate tool for diagnostic and treatment pathways for PFP.

Inclusion Criteria:

• All patients who have previously undergone gait analysis for assessment of patellofemoral pain and or instability
• Have a rotational CT scan available for assessment of femoral and tibial torsion
• Signed research consent form

Exclusion Criteria:

• No available CT scan available
• No gait analysis data available
• No signed gait research consent form

Study population will include patients over 16 years of age who have previously had assessment of their gait and who have been diagnosed with suspected rotational deformity and patellofemoral pain/anterior knee pain. All genders will be accepted.