Postoperative radiograph of the hip arthroplasty: what the radiologist should know

Abstract

This pictorial review aims to provide the radiologist with simple and systematic guidelines for the radiographic evaluation of a hip prosthesis. Currently, there is a plethora of commercially available arthroplasties, making postoperative analysis not always straightforward. Knowledge of the different types of hip arthroplasty and fixating techniques is a prerequisite for correct imaging interpretation. After identification of the type of arthroplasty, meticulous and systematic analysis of the following parameters on an anteroposterior standing pelvic radiograph should be undertaken: leg length, vertical and horizontal centre of rotation, lateral acetabular inclination, and femoral stem positioning. Additional orthogonal views may be useful to evaluate acetabular anteversion. Complications can be classified in three major groups: periprosthetic lucencies, sclerosis or bone proliferation, and component failure or fracture. Teaching Points • To give an overview of the different types of currently used hip arthroplasties. • To provide a simple framework for a systematic approach to postoperative radiographs. • To discuss radiographic findings of the most common complications.

Keywords: Arthroplasty; Hip; Imaging; Postoperative complications; Radiography.

Fig. 1

Anteroposterior (AP) radiograph. Cemented unipolar hemiarthroplasty. The femoral stem with the fixed head (arrowheads) articulates with the native acetabulum (arrow)

Fig. 2

AP radiograph. Cementless bipolar hemiarthroplasty. The femoral stem with a fixed head (arrowheads) articulates with a polyethylene lined metal cup (arrow indicates position of the radiolucent polyethylene), which articulates with the native acetabulum (dotted arrow)

Fig. 3

AP radiograph. Cementless resurfacing hemiarthroplasty. Only the femoral head is replaced (arrowheads), which articulates with the native acetabulum (arrow)

Fig. 4

AP radiograph. Cementless total hip arthroplasty. In a total hip arthroplasty, both femoral head and neck (arrowheads) as well as the acetabulum (dotted arrow) are replaced. The open arrow indicates the position of the radiolucent polyethylene cup at the articulation of the prosthetic femoral head and the acetabulum

Fig. 5

AP radiograph. Cementless resurfacing total hip arthroplasty. In a resurfacing total hip arthroplasty, the femoral head (arrowheads) and acetabulum (arrow) are replaced. No radiolucent area at the femoral head—acetabulum is noted (metal—on—metal bearing surface)

Fig. 6

AP radiograph. Cemented total hip arthroplasty, single acetabular screw fixation. In a hybrid cemented arthroplasty, the femoral stem is fixed with cement (arrowheads)

Fig. 7

AP radiograph. Cemented total hip arthroplasty. In a reverse hybrid cemented arthroplasty, the acetabular cup is fixed with cement (arrowheads)

Fig. 8

AP radiograph. Cementless total hip arthroplasty. Arrowheads indicating the collar of this collared femoral stem

Fig. 9

The leg length is measured as the distance between line A (connecting the undersurface of the acetabular tear drops) and line B (through the middle of the lesser trochanter)

Fig. 10

The horizontal centre of rotation is defined as the distance between the centre of the femoral head (point C) and the lateral outline of the teardrop shadow. The vertical centre of rotation is defined as the distance between the centre of the femoral head (point C) and the transischial tuberosity line (line D)

Fig. 11

The acetabular inclination is measured by drawing a line through the medial and lateral margins of the cup (line E) and measuring the angle with the transverse pelvic axis (line D). The femoral stem positioning should be aligned with the longitudinal axis of the shaft (line F = normal, longitudinal axis of the shaft)

Fig. 12

Normal valgus positioning of the femoral stem in a resurfacing arthroplasty (line H) compared with the longitudinal axis of the femoral neck (line G)

Fig. 13

a Photograph of the patient positioning for a lateral view of the hip, the arrow indicating the direction of the x-rays. b Lateral radiograph. The acetabular anteversion is defined by the angle between the acetabular axis (line I) and the coronal plane (line J). In this patient, the angle measures approximately 25° (normal range between 5°–25°)

Fig. 14

Standardized template for radiographic assessment of periprosthetic lucency, with three acetabular zones (I–III) and seven femoral zones (1–7)

Fig. 15

AP radiograph, 3 years postoperatively. Cementless bipolar hemiarthroplasty. Aseptic loosening, radiographically seen as periprosthetic lucencies in a Gruen zone 5/6 (arrows)

Fig. 16

AP radiograph. Cementless total hip arthroplasty. A < 2 mm lucency, outlined by a discrete sclerotic margin, in Gruen zone 3/4 (arrowheads): this indicates a fibrous rather than bony ingrowth, thought to provide sufficient stability

Fig. 17

a AP radiograph, 1 month postoperatively. Cementless total hip arthroplasty. Normal postoperative findings. b AP radiograph of the same patient, 3 months postoperatively. Periosteal reaction in Gruen zone 2/5/6/7 (arrows): proven case of infection

Fig. 18

a AP radiograph, 4 months postoperatively. Cemented (hybrid) total hip arthroplasty after revision with acetabular fixation screws. Normal postoperative findings. b AP radiograph of the same patient, 5 months postoperatively. Periprosthetic lucencies in Gruen zone 5/6 (arrows) and more discrete in Gruen zone 2 (arrowhead): proven case of infection

Fig. 19

AP radiograph. Cementless total hip arthroplasty. Periprosthetic lucency in the area of the greater trochanter (arrow) and some punctate densities adjacent to the lesser trochanter/ Gruen zone 7 (arrowheads), representing small metal particles: adverse reaction to metal debris

Fig. 20

Although current state-of-the art MRI with Metal Artefact Reduction Sequences allows assessment of correct position of the hip prosthesis as well as periarticular abnormalities, mature heterotopic bone formation (arrowheads in A and C) is often more readily visible on plain radiographs than on MRI due to similar signal of mature bone marrow and fatty infiltration within the gluteus musculature at the site of the hip prothesis. a AP radiograph. Cementless total hip arthroplasty. Heterotopic bone formation (arrowheads), 7 years postoperatively. b T1-weighted, coronal image (WI) of the pelvis in the same patient. c T1-weighted, coronal image (WI) of the pelvis at a more anterior location barely showing heterotopic bone formation (arrowheads). d STIR, coronal image of the pelvis in the same patient

Fig. 21

AP radiograph. Cementless bipolar hemiarthroplasty. Extensive heterotopic bone formation (arrowheads), bridging from femur to pelvis, restricting abduction

Fig. 22

AP radiograph. Cementless bipolar hemiarthroplasty. Spot welding (new bone formation originating from the endosteal surface and reaching the prosthesis) in Gruen zone 2/6 (arrowheads)

Fig. 23

AP radiograph. Cementless total hip arthroplasty. Stress shielding. Cortical hypertrophy in Gruen zone 1 (arrowheads) and adaptive atrophy in Gruen zone 6 (arrows) as different parts of reactive bone remodelling

Fig. 24

AP radiograph. Cementless bipolar hemiarthroplasty. Bone pedestal in zone 4 (arrowheads). The association with loosening remains unclear

Fig. 25

a AP radiograph, 6 months postoperatively. Cementless total hip arthroplasty. Normal postoperative findings. b AP radiograph of the same patient, 4 years postoperatively. Cranial displacement of the femoral head in the acetabular cup (arrowheads), indicating linear wear

Fig. 26

AP radiograph. Cementless bipolar hemiarthroplasty. Lateral dislocation of head and acetabular cup

Fig. 27

Vancouver classification of periprosthetic fractures. Type A fractures are peritrochanteric fractures (subtypes AG: greater trochanter and AL: lesser trochanter). Type B fractures occur around or just below the tip of the femoral stem (subtypes B1: stable stem, B2: loose stem, B3: loose implant with substantial bone loss). Type C fractures occur well below the implant (image courtesy of Hwang KT, Kim YH (2011) Treatment of periprosthetic femoral fractures after hip arthroplasty. J Korean Fract Soc 24:121–130)

Fig. 28

AP radiograph. Cementless total hip arthroplasty. Periprosthetic fracture in Gruen zone 5 (arrowheads), Vancouver type B1 fracture

Fig. 29

AP radiograph. Cementless total hip arthroplasty. Proximal prosthetic/metallic fracture through the neck of the femoral implant (arrowheads)