Hip instability: a review of hip dysplasia and other contributing factors

Abstract

Background: Hip instability has classically been associated with developmental dysplasia of the hip (DDH) in newborns and children. However, numerous factors may contribute to hip instability in children, adolescents, and adults.

Purpose: This review aims to concisely present the literature on hip instability in patients of all ages in order to guide health care professionals in the appropriate diagnosis and treatment of the various disorders which may contribute to an unstable hip.

Methods: We reviewed the literature on the diagnosis and surgical management of hip dysplasia and other causes of hip instability.

Conclusions: Multiple intra- and extra-articular variables may contribute to hip instability, including acetabular bony coverage, femoral torsion, femoroacetabular impingement, and soft tissue laxity. Physical examination and advanced imaging studies are essential to accurately diagnose the pathology contributing to a patient's unstable hip. Conservative management, including activity modification and physical therapy, may be used as a first-line treatment in patients with intra-articular hip pathology. Patients who continue to experience symptoms of pain or instability should proceed with arthroscopic or open surgical treatment aimed at correcting the underlying pathology.

Level of evidence: V.

Keywords: developmental dysplasia of the hip; femoral anteversion; femoroacetabular impingement; hip instability; periacetabular osteotomy.

Figure 1a–c

a) Anteroposterior (AP) radiograph of a right hip with severe lateral acetabular dysplasia, superolateral migration of the femoral head, and a break in Shenton’s line (dashed white line). b) AP radiograph of a right hip with borderline acetabular dysplasia, deficient anterior acetabular coverage, and preserved lateral center edge angle. The blue shaded area indicates the small degree of overlap between the femoral head and the anterior acetabular wall. Note the flattened sourcil or acetabular roof. c) AP radiograph of a right hip with severe lateral and posterior acetabular dysplasia. The red shaded area indicates the overlap between the femoral head and the posterior acetabular wall. Note that the center of the femoral head (white dot) lies lateral to the posterior wall, indicating a positive posterior wall sign with deficient posterior coverage.

Figure 2 a–f

a) Three-dimensional reconstruction of the left hip from computed tomography (CT) images indicating excessive femoral antetorsion of 56 degrees and resultant functional undercoverage of the anterior femoral head. b) AP radiograph of the right hip in a patient with frank acetabular dysplasia and associated excessive femoral neck shaft angle of 146 degrees corresponding with coxa valga. c) Minimally invasive surgical site used to perform a derotational femoral osteotomy (DFO) measuring 4 cm in length. d) Intraoperative fluoroscopic radiograph of the right femur with intramedullary saw in place prior to performing femoral osteotomy. e) Intraoperative fluoroscopic radiograph of the right femur with intramedullary saw in place following completion of femoral osteotomy. f) Postoperative AP radiograph of the right femur with expandable intramedullary rod in place following DFO to correct for antetorsion and coxa valga deformities. Note the well-healed femoral osteotomy site with robust callus (white arrows) and slight varus angle across osteotomy to correct for coxa valga.

Figure 3 a–e

a) Model representation of a periacetabular osteotomy (PAO) indicating the rotational correction of the acetabular fragment (blue arrow) which creates normalized femoroacetabular joint contact forces (red arrow) and reduces superolaterally-directed shear forces creating symptomatic instability. b) Schematic diagram of the Birmingham Interlocking Pelvic Osteotomy (BIPO) indicating location of ilium cuts (a, b, and c) and interlocking construct following rotation of central acetabular fragment. This osteotomy is stable enough for immediate full weight-bearing and, as a result, results in less muscle atrophy and deconditioning. c) AP radiograph of a right hip with borderline acetabular dysplasia predominantly due to lateral and posterior deficiencies in coverage. Note the short and inclined acetabular roof or sourcil. d) AP radiograph of a right hip following PAO with cannulated screw fixation. Note the degree of posterolateral coverage gained by the procedure with normalization of the relationship between the anterior and posterior walls. e) AP radiograph of a right hip following screw removal from healed PAO.

Figure 4 a–f

a) AP radiograph of a pelvis in a 36-year-old female patient presenting with 6 month history of left groin pain and mechanical symptoms, having failed conservative management. She has a history of childhood developmental dysplasia of the hip (DDH) and her clinical examination is concerning for ligamentous laxity with a Beighton score of 7 as well as left hip internal rotation of 30° with the hip at 90° of flexion, despite having a large cam deformity (white arrow). Note the positive posterior wall sign with slight posterior acetabular deficiency. b) Axial CT scans of the left hip with overlapping images through the center of the femoral head, the lesser trochanter, and the distal femur. Femoral torsion measures 29° antetorsion (normal 10–20° antetorsion). c) Axial CT scan of the left hip through the center of the femoral head indicating equatorial acetabular version to be 16° anteversion (normal 15–20° anteversion). Given the posterior wall deficiency, this value underrepresents the true extent of anterior acetabular deficiency. d) Coronal proton density (PD) fat saturated (FT) image of the left hip indicating enlarged labrum (white arrow), which serves as a marker of instability. Note the large lateral cam lesion with impingement cyst in the upper femur (orange arrow). e) Arthroscopic image of the left hip demonstrating instability type “inside-out” articular cartilage flap tear (c) with preserved chondrolabral junction (red dashed line) and enlarged labrum (black asterisk). Note that this pattern of injury is not what would be expected from cam-type FAI which typically results in a break at the chondrolabral junction and an “outside-in” articular flap tear. FH = femoral head. f) Postoperative AP radiograph of the left hip demonstrating restoration of the normal femoral head-neck contour with improved offset.

Figure 5 a–f

a) AP radiograph of a pelvis in a 40-year-old male patient presenting with 12-month history of left groin pain and mechanical symptoms, having failed conservative management. His clinical examination is concerning for limited left hip internal rotation of 5° with the hip at 90° of flexion, despite have a severely dysplastic acetabulum. Note the positive posterior wall sign with posterior acetabular deficiency which, in conjunction with reduced lateral coverage, represents global acetabular deficiency. b) Axial CT scans of the left hip with overlapping images through the center of the femoral head, the lesser trochanter, and the distal femur. Femoral torsion measures 0° (normal 10–20° antetorsion), indicating relative retrotorsion, and accounting for the limited internal rotation seen on clinical exam. c) Axial CT scan of the left hip through the center of the femoral head indicating equatorial acetabular version to be 22° anteversion (normal 15–20° anteversion). Given the posterior wall deficiency, this value underrepresents the true extent of anterior acetabular deficiency. d) Three-dimensional CT reconstruction of the left hip indicating a large cam lesion in the upper femur (white arrow). e) Arthroscopic image of the left hip demonstrating enlarged and torn labrum consistent with instability. f) Arthroscopic image of the left hip demonstrating full thickness “outside-in” articular flap with a break in the chondrolabral junction consistent with cam-type FAI. The impingement is further exacerbated by the femoral retrotorsion. The pattern of intra-articular injury in this hip supports both a diagnosis of impingement and that of instability.