Medical Apparatus: Imaging Guide to Orthopedic Devices

Orthopedic Devices

Fracture Fixation


Joint Arthroplasty - Introduction

Joint Arthroplasty - Shoulder

Joint Arthroplasty - Elbow

Joint Arthroplasty - Wrist and Hand

Joint Arthroplasty - Hip

Joint Arthroplasty - Knee

Joint Arthroplasty - Ankle and Foot


Joint Arthroplasty References

Fracture Fixation References




Joint Arthroplasty - Introduction

by Tim B Hunter, MD, MSc



The most frequent orthopedic procedures are everyday fracture reductions, immobilizations, and fixations. The next most important and frequently performed orthopedic procedures are joint arthroplasties in which a portion of a joint or the entire joint is replaced by a surgically placed prosthesis. The American Academy of Orthopedic Surgeons estimates from 2012-2020 that 2,244,587 knee and hip arthroplasty procedures were performed in the United States:

Athroplasty Procedures (2012-2020)

Procedure Number of Procedures
Total Knee arthropasty 1,168,826, 52.1%
Total Hip arthroplasty 775,589, 34.6%
revision knee arthroplasty 89,463, 4.0%
Hemiarthroplasty 82,594, 3.7%
Revision Hip Arthroplasty

61,214, 2.7%

Partial knee arthroplasty 61,207, 2.4%
Hip Resurfacing 5,694, 0.3%

58.5% of these patients were female, and 41.1% were male. In 0.4% of the cases the sex of the patient was not reported.

A number of overlapping terms are used when discussing joint replacement. Arthroplasty is a generic term for any joint replacement surgery designed to restore joint function. A prosthetic device (prosthesis or implant) may replace the native joint totally or partially. A total arthroplasty involves prosthetic replacement of both sides of a joint, whereas hemiarthroplasty (or hemi-arthroplasty) involves replacement of only one side of a joint. The term prosthesis is a loosely used term for an artificial substitute for a missing body part. Often, the terms prosthesis, implant, and medical device are used interchangeably.

The major indication for joint replacement is advanced degenerative osteoarthritis from everyday wear and tear and/or associated joint related trauma earlier in life. Inflammatory arthropathy, particularly rheumatoid arthritis, is a common indication for replacement of the elbow and the small joints in the hand and wrist. Infectious arthritis of any joint may cause severe joint destruction warranting joint replacement. Osteonecrosis with destruction of the femoral head or the humeral head is sometimes an indication for joint arthroplasty. Comminuted fractures which cannot be surgically fixed may also lead to joint replacement (HEALTH, 2019).

A somewhat rarer indication for joint replacement is limb sparing surgery (LSS), which is a complex operative procedure most commonly performed by oncology orthopedic surgeons for treatment of extremity sarcomas. The tumor is removed by an extensive excision, and the removed tissue is replaced with a metallic prosthesis, allograft bone, or a combination of an allograft bone metallic prosthesis. The specially designed limb sparing prosthesis is fixed to the remaining bones with bone cement or press fit into the remaining bones for later bony ingrowth. Patients with serious accidents or chronic infections sometimes may be candidates for limb sparing surgery.

The most common joints requiring replacement are the hips, total hip arthroplasty (THA), and knees, total knee arthroplasty (TKA), though total shoulder arthroplasty (TSA) is also common. Joint replacement in the elbow, wrist, hand, ankle, and feet is far less common.

The major contraindications for any joint arthroplasty are systemic infection or localized infection in the joint in question. A neuropathic joint is also a contraindication for joint arthroplasty. Joint radiography is nearly always required for preoperative evaluation of a joint being considered for replacement. Cross-sectional imaging - CT, MRI, and sometimes nuclear medicine imaging - may add additional information concerning a joint being evaluated for replacement.

Postoperative evaluation of joint arthroplasty is always initially performed with standard radiography. Cross-sectional imaging with CT or MRI may be used for additional information. The metallic constituents in most joint replacements cause a variety of artifacts on CT and MRI, but there are metal reduction imaging algorithms which permit very useful cross-sectional imaging of joint arthroplasties (Dula, 2014; Fritz, 2014; Jansen, 2014; Koff, 2014). While these algorithms may reduce many artifacts associated with metal implants, they can introduce other artifacts which may sometimes obscure pelvic structures (Han, 2014). For more information see Orthopedic medical devices and cross-sectional imaging: protocols and artifacts.

It is important to recognize the proper positioning of an implant as well as complications that may occur. The specific names of the numerous arthroplasty designs are not important per se and should not be mentioned in the radiology report, unless one is 100% sure about the name. Implants are often described as being constrained or nonconstrained (also called unconstrained). Constraint is the resistance of an implant to a particular degree of motion in a given plane, most often anterior-posterior translation or axial rotation. An implant may be described as fully constrained (very limited motion in a given direction), semiconstrained (intermediate amount of motion in a given direction), or nonconstrained (allowing full motion in a given direction).

Conformity is the geometric measure of the articulation fit between the joint components - fully conforming prostheses have full articular contact. The greater the conformity, the larger the contact area between components, and the less intrinsic stress wear. Modularity is the ability to add implant components, such as stems, augments, and wedges, to enable the orthopedic surgeon to make a custom prosthesis intra-operatively (Barrack, 1994).

A custom prosthesis is a preoperatively designed implant having features to accommodate the specific needs of the patient. Fixation of a joint implant to the skeleton is accomplished in a variety of ways using press fit stems, cerclage wires, fixation screws, and cementing with polymethyl methacrylate (PMMA). As a general rule, bone cement used with joint arthroplasty increases component fixation and is frequently used.

Bone cement has its downsides as well. It may damage the surrounding bone and leak into anatomic spaces where it can produce neurovascular injury. It also makes any needed subsequent revision arthroplasty considerably more difficult. Moreover, bone cement may lead to bone cement implantation syndrome (BCIS) (Olsen, 2014; Rassir, 2021). BCIS is characterized by hypoxia, hypotension, possible cardiovascular collapse, and even death during cemented arthroplasty. It has only been studied to much extent for hip hemiarthroplasty and total hip arthroplasty (THA) after hip fracture or hip cancer. Its incidence is largely unknown but is felt to be common during cemented arthroplasty, though severe BCIS is felt to be uncommon. If severe BCIS occurs during surgery, it is associated with an increased risk of death within 30 days of surgery (Rassir, 2021). Medically complex patients undergoing hip hemiarthroplasty appear to be at particular risk.

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Tim Hunter

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