Muscle-tendon pain and outcome of hip-preserving surgery in patients with hip dysplasia

Role of Julie Sandell Jacobsen:
Principal investigator, including design of individual studies, application of funding, practical running of project and leading project team. The project team includes the co-authors and two project physiotherapist employed to test the project patients (Aarhus University Hospital).

Finally, two students in physiotherapy (from a talent program at VIA University College) were involved, recruiting healthy volunteers for comparative analysis. The project is part of JSJ PhD studies.

The project is supported by: 615.000 kr. from the following funds: The Danish Rheumatism Association, the Aase and Ejnar Danielsen Fund, and the Fund of Family Kjaersgaard, Sunds.

Abstract
Hip dysplasia is considered a joint disease where pain presents secondary to intraarticular lesions. Yet, previous studies indicate that this understanding may be insufficient, and it has been suggested that extra-articular structures such as muscles and tendons may play a role in relation to the development of pain in hip dysplasia.
However, muscle-tendon pain and structural abnormalities have not been investigated in patients with hip dysplasia, and there is a lack of studies reporting outcome of periacetabular osteotomy (PAO) with outcome measures considered relevant for the typical young and active patient.

A prospective case series study was conducted in 100 patients with hip dysplasia with follow-up 1 year after PAO. PAO outcome was investigated, applying the Copenhagen Hip and Groin Outcome Score (HAGOS), accelerometer-based measures of physical activity and standardised clinical examinations. Clinical examinations were used to identify muscle-tendon pain in specific anatomical regions (i.e. clinical entities). Moreover, prior to PAO, structural abnormalities in hip tendons were identified with standardised ultrasonographic examinations, while hip muscle strength was assessed with a handheld dynamometer.

Prior to PAO, the majority of patients experienced muscle-tendon pain, primarily affecting the iliopsoas (56%; CI 46 - 66) and hip abductors (42%; CI 32 - 52). Muscle-tendon pain was negatively associated with patient-reported outcome (PRO) and hip muscle strength, and abnormal ultrasonographic findings were identified in the
corresponding painful structures. However, only weak to moderate correlations between abnormal ultrasonographic findings and clinically identified pain were
found for the iliopsoas and hip abductors. One year after PAO, the proportion of patients with muscle-tendon pain had fallen by 39% points, while patients reported moderate to very high improvements across all subscales of the HAGOS. For patient-reported participation in physical activity and physical function in sport/recreation, about half of patients reported change scores lower than the minimally important change, indicating that these patients did not experience clinically relevant improvements after PAO. Moreover, despite considerable improvement in patient-reported physical activity, no changes in accelerometer-based physical activity were found.

Muscle-tendon pain and structural abnormalities were common in hip dysplasia; and 1 year after PAO, muscle-tendon pain decreased parallel with improvements in
PRO. However, the level of daily physical activity did not change after PAO. Based on these results, hip dysplasia appears to be a joint disease that is associated with
muscle-tendon pain and structural abnormalities in muscle-tendon tissue.