Soft Tissue Pathology in Hip Dysplasia Before and After Periacetabular Osteotomy

Introduction

In hip dysplasia the acetabulum presents as shallow and oblique with insufficient coverage of the femoral head. Deformity of the femoral neck and head is common with bilateral affection in 54%. The lack of congruence between the acetabulum and femoral head compromise the passive stability of the hip joint resulting in increased increased stress on the acetabular labrum, joint capsule and the muscles acting close to the hip joint. The increased stress on soft tissue results in acetabular labrum injury in 49-94% of the patients with hip dysplasia scheduled for joint preserving surgery. Left untreated hip dysplasia may lead to development of early osteoarthritis; however, the osteoarthritic process can be prevented or delayed with the Periacetabular osteotomy (PAO).

Soft tissue injury is present in hip dysplasia, and pathology of the iliopsoas muscle has been found in 18-50%. The muscles acting close to the hip joint including the deep fibers of the iliopsoas and the iliocapsularis muscle are together with the acetabular labrum and joint capsule able to increase the dynamic stabilisation of the femoral head in the dysplastic and shallow acetabulum. The hip joint is beside the iliopsoas further stabilised by the adductors and the gluteus medius muscle. Sustained hip pain and immobilisation has a negative impact on the iliopsoas, psoas and the hip adductors in terms of atrophy and decreased hip muscle strength. In an experimental study design it was found that decreased force contribution from the gluteal muscles during hip extension and the iliopsoas muscle during hip flexion resulted in an increase in the anterior hip joint force. The increased anterior hip joint force may contribute to anterior hip pain, subtle hip instability and the development of anterior acetabular labral tears.

Patients with hip dysplasia are less physical active prior to PAO mainly due to groin pain. A decreased physical activity level is likely to have a negative impact on the muscles acting close to the hip joint with a possible increased risk of sustaining further acetabular labrum injury and/or overuse related to soft tissue pathology. After surgery, the risk of overuse related soft tissue pathology might be further increased due to surgery impact on muscles and tendons. If it is possible to demonstrate pathology of the hip muscles and tendons applying clinical tests, muscle strength tests, and ultrasonography, as it has been found in sports-active people with groin pain, it will make sense to plan and test a specific training program focusing on the pathological soft tissue pathology.

The overall aim of this research project is to examine soft tissue pathology in 100 patients with hip dysplasia prior to and one year after PAO.

Material and methods

Design Prospective cohort study on 100 patients with symptomatic and radiologically verified hip dysplasia with one year of follow-up.

Inclusion

1. Diagnosis of hip dysplasia with a Wiberg´s Center-Edge (CE) angle \<25 degrees, and planned PAO surgery at Aarhus University Hospital

Exclusion

1. Osteoarthritis grade ≥2 using Tönnis' classification
2. Other hip conditions as Calvé Perthes and epiphysiolysis
3. Surgery due to discus disease and spondylodesis and joint preserving and alloplastic surgery at the hip, knee or angle region
4. Neurological and/or rheumatological conditions affecting the function of the hip joint
5. Tenotomy of the iliopsoas tendon
6. BMI > 40
7. Cross-over sign (retroversion of the acetabulum)

Primary outcomes measures

1. Soft tissue pathology of abnormal clinical entities of the iliopsoas, adductors, rectus abdominis, gluteus medius and hamstrings using a standardized and reliable examination protocol
2. Soft tissue pathology of the iliopsoas, adductors, rectus abdominis, gluteus medius and hamstrings using a standardized ultrasonography protocol
3. Hip related health measured with the reliable Copenhagen Hip and Groin Outcome Score (HAGOS) validated on patients with groin pain
4. Physical activity measured with triaxial accelerometers during a period of 7 days on the following categories: rest, standing, walking, sit to stand (STS), cycling and running

Secondary outcome measures

1. Isometric hip muscle strength of the hip flexors, hip abductors, hip adductors and hip extensors using a reliable standardized method
2. Subjective visual analogue scale (VAS) at rest and during hip muscle strength tests
3. Pain location registered on a pain-drawing
4. Presence of internal snapping hip examined with a standardized examination test and ultrasonography
5. Presence of intra-articular pathology examined with the Flexion/Abduction/External Rotation (FABER) and Flexion/Adduction/Internal Rotation (FADDIR) tests and ultrasonography of the hip joint
6. Presence of lumbar and thoracic back pathology examined with the reliable Spine Springing Tests of the spinous process and processus transversi and of the sacrum
7. Conjoint tendon pathology examined with palpation of the pubic tubercle and ultrasonography of the pubic tubercle

Procedure

Patients are included from the division of hip surgery at Aarhus University Hospital using the listed inclusion and exclusion criteria's. The patients complete the HAGOS questionnaire after informed written consent. Wiberg's center-edge (CE) angle, Tönnis' acetabular index (AI) angle, and osteoarthritis grade are measured on anteroposterior radiographs after inclusion and after surgery by the surgeon. Information from the hospital charts is used to record age, gender, unilateral or bilateral involvement and other pathologies. Baseline characteristics are registered using standardized questions including data on BMI, duration of pain and intake of analgesia. Pain is afterwards measured on 100 mm visual analogue scale (VAS) resting in sitting and lying, and furthermore registered on a pain drawing. Preferred physical activity and hours spend on primary and overall physical activity is registered using standardized questions.

Ultrasonography is carried out first with an ultrasound scanner (Noblus, Hitachi-Aloka Medical, Zug, Switzerland) using an 18 Megahertz (MHz) linear transducer.Then the standardized examination protocol of abnormal clinical entities is carried out. Examination of pain at the conjoint tendon, presence of lumbar and thoracic back pathology, examination of intra-articular pathology and evaluation of internal snapping hip follow this. The hip muscle strength is then carried out, and finally the physical activity sensor is attached, and the patients are informed on how to monitor duration of physical activity.

One year postoperative the following examination is carried out in the listed order: HAGOS, baseline characteristics, pain on a VAS scale, pain on a pain drawing, hours of physical activity, ultrasonography, abnormal clinical entities, pain at the conjoint tendon, presence of lumbar and thoracic back pathology, examination of intra-articular pathology, evaluation of internal snapping hip, hip muscle strength. Finally the physical activity sensor is attached and the patient informed.

Statistics

Stata 11 is used for statistic calculations, and results are presented as significant if p\<0.05.

Sample size

The present study is a descriptive study aiming to describe musculotendinous pathology in patients with hip dysplasia. This means that a power calculation is not feasible. On an annual basis approximately 140 periacetabular osteotomies is carried out on Aarhus University Hospital.

Allowing a lack of participation of 25 % it seems possible to include 100 patients during a period of one year. Based on this, a convenience sample of 100 patients is included to describe musculotendinous pathology in patients with hip dysplasia.

Ethics

The study was presented to the local research ethics the 14th of January 2014. The Committee waived the request of ethic approval, since the study according to Danish law does not require approval owing the observational design (Request 5/2014). All participants provided written consent prior to inclusion, and approval has been obtained from the Danish Data Protection Agency (Reference number: 1-16-02-47-14).

Economy and publicising

Financial support will be applied to internal and external funds. Both positive and negative results will be published in international journals and presented at conferences.