A Pictorial review of orthopaedic radiology: Not just screws and plates!

Shoulder Prosthesis

The image above shows a typical right total shoulder replacement which involves replacing the arthritic joint surfaces with highly polished metal ball attached to a stem, and a plastic socket.

Total shoulder arthoplasty: Total shoulder arthroplasty is indicated for patients with intact rotator cuffs and bone on bone OA. It includes polyethylene glenoid component which is radiolucent except for a few radiodense markers. If the bone is of good quality, the surgeon may use a non-cemented (press-fit) humeral component. If the bone is soft, the humeral component may be implanted with bone cement.

Shoulder resurfacing arthroplasty: Resurfacing hemiarthroplasty may be an option if the glenoid still has an intact cartilage surface, there has been no fresh fracture of the humeral neck/head or there is a desire to preserve humeral bone. Resurfacing hemiarthroplasty avoids the risks of component wear and loosening that may occur with conventional total shoulder replacements.

The image on the left shows a Left shoulder Resurfacing hemiarthroplasty- replacing just the joint surface of the humeral head with a cap-like

prosthesis without a stem.

Reverse Total shoulder replacement: This used for people who have had : 1) Completely torn rotator cuffs with severe arm weakness or 2)The effects of severe arthritis and rotator cuff tearing or 3)Had a previous shoulder replacement that failed. In the reversed design, the forces in the joint are directed through the center of the glenosphere providing inherent stability.

The image on the left shows a total reverse shoulder

replacement. The socket and metal ball are switched- a

metal ball is attached to the shoulder bone and a plastic

socket is attached to the humerus. This allows the patient to use the deltoid muscle instead of the torn rotator cuff to lift the arm.

Wires

Kirschner wires: Are unthreaded segments drilled into bone like a drill bit. K wires can be used for either temporary or final stabilization, be placed between bones, or they can be used as an intramedullary device to bridge a fracture of a small tubular bone.

The image above shows percutaneous

K wire fixation of a

distal radius fracture

with acceptable

reduction.

Cables: are used primarily as adjunctive fixation devices for fractures of the long bones.

Tension wiring: The wires take the normal muscular pull that is trying to pull the fracture fragments apart and use it in a clever way to force the bony fragments together in compression. Common applications are patellar and olecranon fractures.

The image on the left shows tension band wiring of a patellar fracture. The wire has a figure of eight appearance and has been reinforced with K-wires. The wires are placed anteriorly.

The image on the right shows cables around the proximal femur providing compression to the bone and help improve contact with the femoral prosthesis.

Hip Prosthesis

In intracapsular neck of femur fractures the blood supply to femoral head is compromised. For these displaced fractures, patients will do better if some of the hip components are replaced. In some cases, this can mean a replacement of the head of the femur (hemiarthroplasty) or both the head of the femur and acetabulum (total hip replacement).

Total hip replacement: The damaged femoral head is removed and replaced with a metal stem that is placed into the hollow femur centre. The femoral stem may be either cemented or press fit into the bone. A metal or ceramic ball is placed on the upper part of the stem replacing the removed femoral head. The damaged acetabulum is replaced with a metal socket. Screws or cement are sometimes used to hold the socket in place. A plastic, ceramic, or metal spacer is inserted between the new ball and the socket to allow for a smooth gliding surface.

Above image shows a total hip arthroplasty. This AP radiograph shows the femoral (metal, cemented) and acetabular (polyethylene cup with metal backing, cementless) components.

Hip hemiathroplasty: A hemiarthroplasty involves replacement of the articular surface of the femoral head without surgical alteration to the acetabular articular surface. This may involve replacement of the femoral head and neck (unipolar hemiarthroplasty), replacement of the femoral head and neck with an additional acetabular cup that is not attached to the pelvis (bipolar hemiarthroplasty), or replacement of the surface of the femoral head (resurfacing hemiarthroplasty).

The image on the left shows a left hemiarthroplasty. A cup is present over the femoral head but is not attached to the acetabulum. The cup also covers more of the head than a THR. There are two areas of motion, between the cup and the head and also the cup and acetabulum.

Total Knee Replacements

Total knee replacement: Total knee replacements (TKR) can be categorized by mechanical stability into:

•Non-constrained •Semi-constrained

•Constrained or hinged

Non-constrained or cruciate retaining prostheses are designed to use the PCL, and referred to as PCL-sparing prostheses. The components are not linked and rely on the patient's own ligaments and muscles for stability.

Semi-constrained or cruciate substituting prostheses are used when PCL retention is not possible and use a more stable prosthesis. These protheses have more inherent stability by virtue of a variety of design techniques.

The image on the left shows a semi constrained knee replacement-including placement of large central anterior tibial spine that articulates with a rectangular box-like opening between the femoral condyles component. The posterior portion of the box is formed by a transverse metal cam that prevents posterior tibial subluxation when the knee is in extension.

The image on the left shows a Non-constrained total knee prosthesis. The femoral and tibial components are independent of each other. A groove is present in the posterior aspect of the tibial prosthesis for the native PCL.

The image’s above and on the left show a rotating hinge knee replacement. Components feature a close fit between the elevated tibial spine and the intercondylar box, partially restricting varus/ valgus and rotational component movement.

Plates

Dynamic Compression plate: Plate compression is provided by eccentric placement of screws that, when tightened, draw both ends closer together compressing the fracture. Offset screws exert force on specially designed holes in the plate. Forces between the screw and plate moves bone until the screw sits properly.

Plates are used not only for stabilization, but may also be used for compression or to work as a buttress (counter-force).

The image on left shows dynamic compression plate bridging a fibualr fracture. Arrow points to a syndesmosis screw bridging tibiofibular syndesmosis. The Compression plate can be recognised by its oval screw holes with a bevelled floor.

Neutralization plates : Are designed for protecting surface fractures from axial loading, bending and rotation. They allow the primary fracture fixation to be accomplished with other devices such as lag screws.

The two images above shows a neutralization plate. A single screw is placed perpendicular to the fracture line, providing a greater compressive force on the fracture.

Constrained/hinged prostheses: are used when the knee is highly unstable and the ligaments cannot support other types of prostheses, as seen in severely damaged knees. Typically they are used in elderly patients undergoing revision arthroplasty.

Cortical screws: Cortical screws have fine threads along their shreds and are inserted into the cortical bone on both ends.

Cancellous screws: have longer threads and more pitch, making them less invasive, preserving the normal trabecula and allowing purchase to be acquired in cancelous

bone.

The two image’s on the left show medial malleolar fracture fixation with a partially threaded cancellous screw. This has coarser distal threads and a long unthreaded portion which acts as a lag screw. Left shoulder xray shows a hill sach’s defect reconstruction with two countersunk cortical screws. The screws have fine threads all along the shaft designed to anchor in cortical bone.

Dynamic hip screw: These are used for internal fixation of fractures of the femoral neck and intertrochanteric region. The screw is a large cancellous lag screw that glide freely in a metal sleeve. The sleeve is attached to a side plate that is fixed to the lateral femoral cortex with screws. The shaft of the lag screw slides down the sleeve maintaining reduction of the fracture as compression occurs.

The image on the right shows a dynamic hip screw transfixing an intertrochanteric fracture. A cannulated cancellous screw that serves as a lag screw has also been inserted to increase compression and to control rotation of the femoral head.

Screws

K Paramesparan 1, R Rajakulasingam2 1. North Hampshire Hospital NHS Foundation Trust, 2. University Hospital Birmingham NHS Foundation Trust

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2. Petscavage-Thomas J. Semin Musculoskelet Radiol. 2014 Sep;18(4):448-62. Epub 2014 Sep,

3. Nguyen VD, London J, Cone RO 3d. Ring sequestrum: radiographic characteristics of skeletal fixation pin-tract osteomyelitis.Radiology 1986;158:129-131.

4. New and Improved Orthopedic Hardware for the 21st Century: Part 1, Upper Extremity. Jonelle M. Petscavage, Alice S. Ha, Leila Khorashadi, Kiley Perrich, and Felix S. Chew.

American Journal of Roentgenology 2011 197:3, W423-W433