Glossary of Orthopedic Terms


This glossary contains information on orthopedic related items. Start by clicking on a letter in the table 
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ALIF - Anterior lumbar interbody fusion. An operation for stabilization of the spine using an anterior approach. This is the standard approach for inserting cages in the lumbar disc spaces.

Antiglide plate - A hardware construct that uses weight bearing to provide dynamic compression of a fracture. It is usually employed for oblique fractures of the fibula. A plate with screws is affixed to the proximal fibula such that the tip of the distal fracture fragment is wedged between the plate and the proximal fragment. It is not necessary to place screws in the plate distal to the fracture, although an "anti-glide" screw can be placed at the apex of the fracture.

AO/ASIF - Arbeitsgemeinschaft fur Osteosynthesfragen/Association for the Study of Internal Fixation. An association founded in Germany to study and promote the use of internal fracture fixation. The association has an education program for teaching surgical methods. There are national branches of the association in several countries. In the United States, it is the Association for the Study of Internal Fixation. Several types of orthopedic hardware have been developed by AO, and they are given AO designations, e.g. an AO screw.

Arthroplasty - An operation that restore as far as possible the integrity and function of a joint. In general, an arthroplasty involves prosthetic replacement of one or both sides of a joint. A hemiarthroplasty involves replacement of only one side of a joint. A total joint arthroplasty involves replacement of both sides of a joint. A hemiarthroplasty may be unipolar of bipolar.

Austin-Moore Prosthesis - A metallic unipolar femoral prosthesis used in hip hemiarthroplasties. It was one of the earliest prosthetic devices. Femoral prostheses are sometimes referred to as Moore or Austin-Moore prostheses.


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Bipolar prosthesis - A two component prosthesis used for hemiarthroplasties in which one prosthetic component is fixed rigidly in place on one side of the joint and the second component with which the first articulates is inserted loosely on the other side of the joint. The prosthesis is named after the fixed component. Motion of the across the joint component puts less stress on bone and the articulating surfaces. As an example, one design of a femoral bipolar hemiarthroplasty consists of a prosthetic femoral head articulating with a polyethylene liner in the acetabular component. The liner is inside a metal shell and can move with respect to the shell. The shell is press fitted into the acetabulum either with or without reaming of the acetabulum. The shell can move within the acetabulum. It is important when reading x-rays of bipolar implants to be aware that the across the joint component is mobile and not to interpret a change in position of this component as necessarily indicative of loosening. See unipolar prosthesis.

Bone morphogenetic proteins - Bone morphogenetic proteins, BMPs, are a group of endogenous proteins that stimulate bone growth. Recombinant human bone morphogenetic protein two, rhBMP-2, is the only FDA approved BMP for human use. It is used with bone grafts and spinal cages for interbody fusion of vertebral bodies.


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Cancellous screw - A screw designed for placement in cancellous bone. The pullout strength of a screw is proportional to the amount of metal-bone contact. Because cancellous bone is porous, threads for cancellous bone screws have to be longer than for cortical screws to achieve the same degree of metal-bone contact and thus have the same pullout strength as cortical screws.

Cortical screw - A screw designed for placement in cortical bone. See cancellous screw.


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Dynamic compression - The compression of a fracture by weight bearing and/or muscle contraction. Fracture fixations that employ dynamic compression include dynamic hip screws, anti-glide plates, dynamized tibial and femoral nails, and tension band wiring.


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Ender nail - Also referred to as an Ender rod. A smooth, flexible rod used for intramedullary fixation of long bone fractures. The nail is used for diaphyseal fractures in patients whose epiphyseal growth plates are still open. It is inserted through the metadiaphyseal region, avoiding the epiphyseal plate so that the growth of the bone is not impaired.


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Fixate - To hold in place. Orthopedic hardware can be used to fixate bone, for example with fracture repairs. Bone can be used to fixate orthopedic hardware as with joint prostheses.

Food and Drug Administration - All implantable orthopedic hardware in the United States must be approved by the Food and Drug Administration (FDA). The FDA classification of hardware is specified in the code of federal regulations (CFR) under Title 21, part 888, Orthopedic Devices. Devices are classified by type and anatomic region. For joint replacements, the main classification areas are the degree of constraint, composition, cemented or noncemented., and a few subcategories. The classification can be found by searching the Center for Devices and Radiological Health Database at


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Gerdy's tubercle - A bony projection on the anterolateral tibial plateau between the patellar tendon and fibular head that is used as a landmark for examining or operating on the knee.


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Hardware - A generic term that encompasses all metallic implants. By extension, it also includes nonmetallic materials associated with metallic components such as polyethylene components of joint prostheses. See implants.

Hemiarthroplasty - Replacement of one side of a joint with a prosthesis. The prosthesis in a hemiarthoplasty can have a unipolar or bipolar design. In a unipolar design, the prosthetic component is on only on side of the joint. In a bipolar design, there is a prosthetic component on the other side of the joint that is not fixed in place. In a total hip arthroplasty, the across the joint component is rigidly fixed in place. See bipolar hemiarthroplasty.


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Implant - Any surgically placed, nonbiological material whose purpose is to promote healing of tissues or serve as a replacement of structures such as joints.


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Judet views - Oblique x-ray images of the hips at approximately 45 degree angles that allow visualization of the anterior and posterior columns of the acetabulum and in particular, the anterior and posterior walls of the acetabulum.


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K-wires - The commonly used designation for Kirschner wires. These are thin wires that used for a variety of purposes. They can act as fixation devices for small bones, as guide wires for insertion of cannulated nails, and as accessory components with external fixation devices.


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Lag screw - A screw inserted across a fracture that provides compression to the fracture. Lag screws can provide static or dynamic compression. The term "lag" refers to the function of a screw. The physical design of the screw, the type of bone the screw is inserted into, and the manner in which it is inserted determine whether a screw functions as a lag screw. In the diaphyses of long bones, cortical screws are used as lag screws while cancellous screws function as lag screws for cancellous bone fractures.


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Modular - Composed of interchangeable parts. With respect to prostheses, femoral hip prostheses are most commonly modular in design. Different types of femoral implants have interchangeable heads, necks, and/or stems. See monoblock.

Monoblock - A single structure without interchangeable parts. See modular.


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Nonself-tapping screw - A screw that requires a tapping procedure in a predrilled guide hole before the screw can be inserted. See self-tapping screw, tap.


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Osteoconductive - Refers to any structure that facilitates the formation of bone structure. Commonly used to describe the properties of various types of bone grafts and bone graft substitutes.

Osteoinductive - Any substance that stimulates bone formation. Bone morphogenetic proteins are osteoinductive.


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Pitch - The distance between threads on a screw. Cancellous bone screws have a larger pitch than cortical bone screws.

Press fit - A method for implanting orthopedic devices. For a press fit, a device is inserted without cement or hardware fixation. The geometry of adjacent structures holds the device in place. The acetabular component of a bipolar femoral prosthesis is press fitted into the acetabulum. The stem of uncemented femoral prostheses are press fitted into the medullary canal of the proximal femur. Also referred to as interference fit.


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Ream - The process of enlarging a cavity so that a prosthesis can be inserted. Reaming most commonly is performed in the femur for insertion of a femoral nail.

Reconstruction nail - A femoral intramedullary nail used to fixate femoral neck, intertrochanteric, and subtrochanteric fractures. There is a proximal hold for an interlocking femoral screw that is placed in the femoral neck or head.


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Screws - One of the most commonly used orthopedic fixation devices. Screws are designed for different uses and for placement in different types of bone. Screws can be used as single standalone devices, as components of hardware constructs (e.g. plates with screws), or as separate devices complementing other hardware (e.g. interfragmentary screws and plates with screws for fracture fixation).

Self-tapping screw - A screw that cuts its own thread holes in bone as it is screwed into place. Prior to inserting a screw in cortical bone, a guide hole is first drilled that has the same diameter as the core diameter of the screw to be inserted. For a  nonself-tapping, a tap is then inserted which cuts the thread holes for the screw. The screw is then inserted. A self-tapping screw has one or more cutting edges at the screw tip that cut the threads holes in the side of the guide hole in which the screw is inserted. Thus, a separate tapping step is eliminated shortening operative time. See nonself-tapping screw.

Stress riser - Places where stress lines from applied forces concentrate within a structure. Breakage is most likely to occur at these places. In long bones or orthopedic plates, for example, stress lines from forces applied at the ends tend to produce uniform cross sectional stress lines. Discontinuities, such as screw holes, redistribute these forces concentrating them close to the holes where fracture is most likely to occur.

Stress shielding - The removal of forces or stresses that normally act on bone. Stress shielding eventually leads to osteopenia.  A common site for stress shielding is the proximal femoral diaphysis after placement of a femoral prosthesis. The more tightly the stem of the prosthesis fits into the distal medullary canal, the greater the shift of body weight to the prosthetic stem from the proximal femoral cortex. This causes loss of the normal remodeling forces above the level at which the stem is fixated against the endosteal surface of the medullary canal resulting in osteopenia of the proximal femoral diaphysis.


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Tap, Tapping - A tap is an instrument used to create threads holes in a hole drilled in bone. Tapping is process of using a tap to create the thread holes. Tapping is used for inserting screws in cortical bone. To insert a cortical screw, a pilot hole is first drilled in the bone that has the same diameter as the core diameter of a screw. The tap is then inserted creating the thread holes for the screw. Finally the screw is inserted. The type of screw inserted is called a nonself-tapping screws. See self-tapping screw.


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Ultrahigh molecular weight polyethylene - UHMWPE. A type of highly durable polyethylene used for replacement of joint surfaces or as entire components in prosthetic joints.

Unipolar prosthesis - A prosthesis used for hemiarthroplasties with no across the joint articulating component. Hip and shoulder prostheses are often unipolar. A unipolar device can be of monoblock or modular design. See bipolar prosthesis.


Vertebroplasty - Generic term for any repair or reconstruction of a vertebral body. Titanium vertebral cages or bone allografts are common ways of replacing damaged vertebral bodies.

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Wires - The term can refer to thin diameter, fully flexible wires with minimal resistance to bending or thicker diameter wires, such as K-wires, that can be used as rigid fixation devices.


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XIP - X-ray in plaster. Refers to an x-ray study performed while the examined part is in a cast.

XOP - X-ray out of plaster. Refers to an x-ray study performed after the examined part has been removed from a cast.


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Yasargil clip - A commonly used clip for cerebral aneurysms. The clip has relatively long tongs that permit insertion around the neck of an aneurysm.


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