HIP MUSCLE STRENGTH AND LOWER EXTREMITY MOVEMENT IN PATIENTS WITH ACETABULAR DYSPLASIA

Kizawa L.¹, Kataoka A.¹, Sumida H.¹, Murase T.¹, Suzuki A.¹, Yukari F.¹, Yamamoto Y.¹, Mitamura S.¹, Fujiwara S.¹, Warashina H.², Kato M.², Kitamura S.²

¹Nagoya Orthopedic Joint Replacement Clinic, Physical Therapy, Aichi, Japan, ²Nagoya Orthopedic Joint Replacement Clinic, Orthopaedic Surgery, Aichi, Japan

Background: Acetabular Dysplasia (AD) is known as a risk factor for hip osteoarthritis. Despite the need to better understanding of AD, there are no reports of muscle strength and movement patterns of the lower extremity specializing in only AD subjects.

Purpose: (1) To examine whether differences exist in hip muscle strength and lower extremity movement between patients with AD and healthy group.
(2) To investigate the effects of muscle strength on symptom and lower extremity movement in AD group.

Methods: 23 participants with AD (lateral center edge angle 20) and 20 matched controls (age 41.8±27.8, 41.5±19.5) participated in the study. In AD group, the participants who did not have any hip pain during the past week were excluded. Strength of the hip abductor (AB), hip external rotator (ER) and internal rotator (IR) were assessed using hand-held dynamometer. ER and IR were assessed with the hip flexed to 90°(ER90°, IR90°) and 0°(ER0°, IR0°). AB strength was assessed in supine position. ER90°and IR90°were assessed in sitting position with knee flexed to 90°. ER0°and IR0°were assessed in supine position with the knees flexed to 90°and the legs hanging over the edge of the table. Break tests were performed three times in each assessment. The average torques were calculated and normalized by body weight and the length of the lever arm. 2D Frontal Plane Projection Angle (FPPA), which is an angle between the line of the proximal thigh to the knee joint and the line from the knee joint to the ankle, was measured for assessing lower extremity movement. Participants performed single leg squat at least 45°of knee flexion and no greater than 60°. After performing three trials, the third one was used for analysis. Hip disability and osteoarthritis outcome score (HOOS) were used for assessing self-rated hip problems in AD group.

Results: Compared to control group, patients with AD demonstrated significant weakness in all assessed muscle strength (AB, ER90°, IR90°, ER0°, IR0°, p 0.05). No significant differences exist in FPPA between two groups. In AD group, there was a moderate correlation between AB strength and HOOS (r=0.45, p 0.05), but no relationship between muscle strength and FPPA.

Conclusion(s): Patients with AD have weakness in their hip muscles but these weaknesses does not effect on lower extremity alignment during single leg squat. Weakness of AB strength may increase hip related problems in daily life.

Implications: (1) Strengthening hip abductor muscle may help to decrease symptoms in patients with AD. (2) Hip rotator muscles play an important role in the stability for hip joint. Although clinical effects of having weak hip rotator muscles in patients with AD are still unclear, we should continue to have a focus on the function of these muscles in clinical practice.

Funding acknowledgements: None

Topic: Musculoskeletal: lower limb

Ethics approval: Approved by Research Ethics Committee of Nagoya Orthopedic Joint Replacement Clinic

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