| FLEXION | Volume 2 · Number 5 |
Supported through an unrestricted educational grant from
CEMENT REMOVAL USING ULTRASONIC TOOLS IN REVISION TOTAL HIP ARTHROPLASTY
Paul E. Di Cesare, MD
Co-Director, Arthritis Service
Director, Cartilage & Bone Research Center
Hospital for Joint Diseases Orthopaedic Institute
New York, New York
Removal of well-fixed or loose, cemented (polymethylmethacrylate) total hip components presents many challenges to the orthopaedic surgeon. In cases of loose components with extensive bone-cement radiolucencies, extraction may not be too difficult because a well-defined soft tissue plane that has been biologically placed facilitates removal of hard cement from hard bone. In cases where well-fixed cemented components and cement need to be removed - due to infection, catastrophic polyethelene wear, revision implant mismatch, malposition with chronic dislocations, and distal cement plugs and mantles the surgeon, how ever, may face difficult challenges that may lead to increased operative time, blood loss, bone perforation, or fracture. Additionally, in cases with cemented porous implants or implants with pre-coating to bond the stem to the cement, removal of the components again may not be easy. In these situations, it is often difficult to determine the plane between hard bone and hard cement which predisposes to operative difficulties.
Removal of implants and preservation of host tissue
The goal in these revision settings is to remove the unwanted implants and cement and preserve the integrity of the normal host tissue. A new advance to aid the orthopaedic surgeon in achieving this goal has been the adaptation of ultrasound technology to develop instruments that remove cement. The ultrasonic device consists of a console to generate ultrasound power, an ultrasonic handpiece, and a variety of tool tips and extenders that are controlled by a foot switch during surgery. With the use of a piezoelectric transducer, the console converts electrical energy into mechanical energy. The mechanical energy passes through the tool tip as high frequency energy acoustic waves (20,000 to 100,000 cycles/sec or hertz). The energy from the acoustic waves is transferred from the tool tip to the cement, causing intermolecular friction that converts the hard cement into a putty. Minimal heat is generated during this process.
Tactile and audible safety indicators
The ultrasonic device comes with a vari ety of tool tips to aid in the different aspects of cement removal. Removal of cement is performed using both tactile and audible feedback to ensure host-bone integrity. The tool is capable of cutting through or perforating host bone, especially in areas of impaired integrity where the bone is thin. An audible high-pitched change in sound, or difficulty in passing the tip through an area, are both indicators that the tool tip is in contact with host bone and should be avoided. The tool tips are manufactured from tita nium alloy.
Figures 1A, 1B Use of on ultrasonic short osteotome (9.5 mm) permits the creation of three or four troughs or slices down the entire length of the cement mantle. Three troughs (Fig. 1A) are placed at 12.4, and 8 o'clock intervals, while four troughs (Fig. IB) are positioned at 12.3, 6 and 9 o'clock intervals. To cut the troughs, move distally with a side-to-side oscillating saw.
Use of flexible osteotome
For well-fixed femoral components, it is recommended that the flexible osteotome be used between the stem and cement. The implant can then be removed with a slap hammer. The remaining cement mantle usually consists of a cement tube proximally and a cement plug or mantle distally. To remove the proximal cement, the ultrasonic flat osteotome is used to develop three or four slices or troughs down the sides of the cement tube (Figs. 1A, B). It is important to maintain a side-to-side oscillating motion when using the device to widen the slice or trough. An ultrasonic tip is then used to section the cement perpendicular to the longitudinal slices. The short ultrasonic osteotome can then be used to develop a plane between the cement and host bone. A manual hand osteotome is then used to remove these large segments of proximal cement.
Figures 2A, 2B, 2C. When using ultrasound technology for cement removal in revision hip arthroplasty, assessment of bone plug position and fixation is essential for determining which bone plug classification applies. Fig. 2A shows a plug proximal to the bend in the isthmus. Fig. 2B illustrates a plug within the bend of the isthmus, or what is termed a type A plug that cannot be dislodged. Fig. 2C shows a plug distal to and wider than the bend of the isthmus.
The distal cement plug or mantle
The distal cement plug or mantle has been classified into three types: A, B, and C (Figs. 2A, B, C). Type A distal cement plug/mantle is one that is located proximal to the isthmus of the femur and is therefore more narrow distally (Fig. 2A). This is easily removed using the ultrasonic plug puller tool with the extender. The distal tip is driven straight into the center of the distal cement and the power turned off. The tool is then immediately rotated 90 degrees and held in place until the cement hardens. Once hard, the slap hammer is applied to the device and the cement plug/mantle can often be removed in its entirety. Type B distal cement plug/mantle is at the isthmus (Fig. 2B). The short osteotome must be used first to free the cement from the host bone, and the plug puller can then be used as described above.
Type C distal cement plug/mantle is distal to the isthmus; and as a result, the distal cement is larger than the more proximal cement (Fig. 2C). In this case the ultrasonic disc drill should be used to convert the solid cement into a cylinder of cement. Once a cylinder, the cement can then be removed in a similar fashion as the proximal cement mantle. Removal of acetabular cement is performed using the ultrasonic acetabular gouge to disrupt the cement-acetabular component interface. Once the acetabular component is removed, the ultrasonic short osteotome can be used to section the remaining cement into thirds to aid in removal.
Early results with ultra sound technology
Early results with the use of ultrasound in revision surgery have backed up the theoretical advantages of this method. Gardnier et al presented the results from a multicenter clinical study at the 1993 annual meeting of the American Academy of Orthopaedic Surgeons. Fifty-six revisions of cemented hips were performed, using either ultrasonic tools or hand tools. The mean femoral cement removal time decreased from 44 minutes using hand tools to 23 minutes when using ultrasonic tools. This correlated to a reduction from 25% to 12.5% of the surgical time for cement removal. There were no cases of femoral shaft perforations in the area of the distal cement plug when using the ultrasonic tools. The mean time for acetabular cement removal was, however, similar between groups. Mean blood loss also was noted to be less. Both early clinical experience and laboratory results have indicated that ultrasonic tools are valuable instruments in difficult orthopaedic reconstructions. The ultrasonic tools decreased the risk of femoral perforation by tactile and sound feedback, thereby preserving host-bone viability and mechanical stability. Distal cement mantles can be removed without intraoperative x-rays, and the ultrasonic instruments are relatively easy to use. These instruments are relatively expensive to purchase and are probably not cost effective for centers performing few of these procedures or in all cases of cement removal. Further clinical studies are needed to better delineate the role of this powerful new tool in orthopaedic surgery.
Paul E. Di Cesare, M.D., is Co-Director, Arthritis Service, and Director, Cartilage & Bone Research Center at Hospital for Joint Diseases Orthopaedic Institute of New York University
Medical Center, New York, New York.
| TECHNICAL HINTS |
The technique of achieving a dry acetabular bed following reaming remains a challenging problem, particularly to those cementing the cup. The time honored, pressurized medicated packs often fail to curtail the troublesome ooze that occurs. A helpful hint is to decrease the blood volume in the subchondral cancellous bone bed by applying suction to it.
Two 5 mm holes are placed - one anteriorly and the other posteriorly - 1 cm above the superolateral margin of the acetabulum. A cannula with suction is inserted into each hole prior to and during cementing. This technique should produce a better result, as viewed on postoperative x-rays.
David Shein, MD
Bronx, New York
| QUESTIONS & ANSWERS |
Can you comment on the management of thigh pain in cementless total hip arthroplasty?
Guy Frumson, MD
Thigh pain following cementless THA has a variety of etiologies. Weightbearing prior to biologic fixation or undersizing of the prosthesis results in micromotion at the bone-prosthesis interface, and the formation of fibrous ingrowth instead of osseous ingrowth. A fibrous interface allows for further micromotion and hence thigh pain. Once a fibrous interface forms, it will not convert to an osseous interface. Therefore, the prosthesis must be revised to alleviate this pain. Frequently, activity moderation can control the amount of pain and preclude the need for revision.
The onset of thigh pain in a previously painless hip has three possible etiologies: infection, trauma, or osteolysis. Late infection can cause loosening of a well-fixed prosthesis and thus cause thigh pain. Obviously, such prostheses require revision. An acute episode of trauma can disrupt an osseous prosthesis-bone interface and lead to loosening and pain. This is especially true of prostheses with small amounts of porous surface area available for bony ingrowth.
Typically, only one third of the area of available porous surface undergoes osseous integration. Thus in a prosthesis that is only 30% porous coated, only about 10% of the entire surface area of the prosthesis is biologically fixed, a relatively small area of bone that may not be strong enough to withstand traumatic loading.
Osteolysis caused by prosthetic particulate debris can also lead to disruption of the bone-prosthesis interface and lead to loosening and thigh pain. Lastly, thigh pain can be caused by micromotion of the bone relative to the prosthesis in patients with a large disparity between the modulus of elasticity of their bone and the prosthesis. This is most common in older osteoporotic patients with widened canals, requiring large prostheses to achieve fit and fill.
Joseph A. Bosco, IlL MD
Can you comment on the care of defects in total knee arthroplasty and on the use of modular components?
Steve Stout, MD
Bone defects in total knee arthroplasty can be managed by either bone graft or modular wedges or blocks, and reinforced cement. Excellent clinical results can be achieved by either of these methods with certain caveats. Bone defects in elderly patients should not be grafted and should be managed with either reinforced cement or modular components. In younger patients, care also must be exercised in selecting modular components, as fretting between components and metallic wear is at least a theoretical concern.
Joseph A. Bosco, III, MD
| EDITORIAL BOARD |
Editor for This Issue: David S. Hungerford, M.D.
Lester S. Borden, M.D.
Head of Secion of Joint Replacements
and Arthritis Surgery
Cleveland Clinic Foundation
Edward T. Habermann, M.D.
Professor and Chairman
Department of Orthopaedic Surgery
Albert Einstein College of Medicine
Orthopaedic Surgeon in Chief
Montefiore Medical Center and
Albert Einstein College of Medicine
Bronx, New York
Anthony K. Hedley, M.D.
Chairman, Department of Orthopaedic Surgery
St. Luke's Medical Center
David S. Hungerford, M.D.
Chief, Division of Arthritis Surgery
Good Samaritan Hospital
Professor, Department of Orthopaedic Surgery
The Johns Hopkins University
School of Medicine
Kenneth A. Krackow, M.D.
Professor, The Full Time Faculty
Department of Orthopaedic Surgery
State University of New York at Buffalo
Chief Department of Orthopaedic Surgery
The Buffalo General Hospital
Buffalo, New York
All rights reserved. The opinions expressed in this publication are those of the authros and do not necessarily represent those of the publisher.