Kevin D. Campbell-Karn 1, *Thomas Korff 2 Ian McDermott 2 (July 2015) Can Patellofemoral Joint (PFJ) Alignment Be Assessed Clinically Using a Custom Made Calliper? The 25th Congress of the International Society of Biomechanics, Glasgow 2015
1Faculty of Life Science and Computing, London Metropolitan University, London,
2College of Health and Life Sciences, Brunel University, Uxbridge, United Kingdom
[vc_row][vc_column][vc_column_text]Introduction and Objectives: Knee problems are a common complaint among the general population with a high proportion of physical injuries being knee-related. Up to one in six knee-related conditions have been coded as a ‘patellofemoral condition’ which includes anterior knee pain. However, anterior knee pain can have several causes. One common cause is mal-alignment of the patellofemoral joint (PFJ) and is considered as an abnormal static position of the patella within the trochlear groove during knee extension and flexion. This can cause undue stress to the joint and surrounding structures, with resultant damage and potential pathology. Mal-alignment of the PFJ causes patellar kinematic abnormalities predominantly in the last 20° of knee extension mainly due to the decreased congruency as the patella rises out of the trochlear groove in this range. Clinicians currently assess the alignment of the patella via measurement of the Q-angle, functional testing and the so-called McConnell technique. The latter was developed by McConnell and has been broadly adopted by the physiotherapy community when assessing and treating alignment of the patellofemoral joint. The goal of this method is to determine the centre of the patella in relation to the femoral epicondyles and is reliant on accurate localisation of the medial and lateral borders and the femoral epicondyles. Whilst the McConnell technique may be useful within a clinical context, this subjective measurement is reported to have limited reliability. It is clear therefore that there is a need for the position of the patella in relation to the femur to be determined more objectively and reliably. Therefore the purpose of this study was to assess the suitability and reliability of a custom-made ‘patellofemoral tracking calliper’ to assess the patellar position with respect to the femur.
Methods: A calliper, which measures the medial-lateral offset of the middle of the patella with respect to the mid-point of the femoral epicondyles (Patellofemoral Tracking Calliper [PFTC]) was developed (Figure 1) and assessed for accuracy and reliability. To assess accuracy, 39 right knees were measured with the calliper and compared to the equivalent measures obtained from MRI images. For this purpose, the knee was placed in an MRI scanner with the tibiofemoral joint positioned in 30° of flexion and the rotation of the leg orientated by using a spirit level along the medial side of the foot.
The knee was supported with wedges and strapped to the MRI table in this position to prevent any deviation from the desired orientation. This position was replicated for measurements with the PFTC. During MRI analysis, the midpoint of the femoral epicondyles was defined as the half distance between the widest epicondyle points and the mid-point of the patella was defined as the half distance between the widest medial and lateral borders of the patella. This followed the same measurement methods as the PFTC, however this device used these landmarks via physical contact from the calliper arms.
Thus, both the PFTC and the MRI equivalent provided information about the superficial position for the patella with respect to the femur. To assess agreement between both methods, the Pearson product moment correlation coefficient was determined, and the Bland and Altman limits of agreement test was used to assess bias and limits of agreement.
Each calliper measure was taken three times, and the reliability of the PFTC was assessed using intra-class correlation coefficients (ICC).
Results: The patellofemoral tracking calliper was highly reliable (ICC=0.990-0.991). The limits of agreement with regards to the MRI equivalent method were ±8 mm. The Bland and Altman plot highlighted a systematic bias of 2 mm. The calliper measures correlated significantly with the MRI equivalent method (r = 0.675, p = 0.001).
Figure:
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Caption: Figure 1. Application of the Patellofemoral Tracking Calliper
Conclusion: The patellofemoral tracking calliper is a useful tool, where the reliable assessment of patella position with respect to the femur is needed. The superficial landmarks of the patella and femur require further investigation into their accuracy in providing true alignment outcome measures of the patellofemoral joint. The McConnell method for assessing alignment may have questionable methods when the anatomical shape and interaction of the joint surfaces is considered alongside the data presented here.
Disclosure of Interest: None Declared[/vc_column_text][/vc_column][/vc_row]