Medical Apparatus: Imaging Guide to Orthopedic Devices
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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

 

Introduction

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 in 2011 almost 1 million total joint replacements were performed in the United States:

Musculoskeletal Procedures (2011)

Procedure Hospital Discharges
Total Knee Replacement (TKR or TKA) 645,062
Total Hip Replacement (THR or THA) 306,600
Partial Hip Replacement 105,506
Total Shoulder Replacement (TSR or TSA)

29,414

Partial Shoulder Replacement 15,860
Spinal Fusion 465,070

Department of Research & Scientific Affairs, American Academy of Orthopaedic Surgeons. Annual Incidence of Common Musculoskeletal Procedures and Treatment. http://www.aaos.org/research/stats/CommonProceduresTreatments-March2014.pdf. Published March 2014.

 

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.

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.

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Author contact information

Tim Hunter
Email: hunter@radiology.arizona.edu


COPYRIGHT 2013: TBH
All Rights Reserved

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