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Bearing Surfaces in Total Joint Replacement THE DESTRUCTIVE EFFECTS of wear and wear debris have challenged the existence of joint replacement. Charnley's initial use of polytetrafluoroethylene (Teflon) resulted in severe destructive granulomas from the Teflon debris. Highdensity polyethylene at this time continues to be the most used of all substitute bearing materials, but problems with it have now begun to emerge. Many now think that osteolysis is as much related to wear debris as it is to cement fragmentation. The term "cement disease" is considered a misnomer; it should be particle disease. Attempts are being made to improve the high-density

polyethylene as a joint surface material, changing the physical structure by altering its molecular chains. This new material seems to have superior properties when creep, oxidation, fracture, pitting, delamination, and wear are tested in the laboratory. It is unknown if this material will decrease the amount of wear debris when it is used clinically in patients. Titanium alloy should not be used as an articular surface in joint replacement. Titanium alloy loses its polished surface when articulating against polyethylene and generates particulate debris that produces osteolysis, thus making it ill-suited as a bearing surface for joint replacement. A new process of nitrogen ion bombardment of titanium is being developed and used, but its clinical usefulness is unknown. Ceramic on ceramic-bearing components also appears to generate considerable particulate debris, and caution must be exercised before this combination is used. Ceramic heads, articulating with polyethylene, have been shown to have superior wear characteristics and thus generate less particulate debris. Time will tell whether the incidence of lysis is affected by ceramic on polyethylene, thus justifying the expense of the ceramic heads. In addition to the materials chosen, the size of the femoral head is important in joint replacement. The 28-mm head, or midrange head prosthesis, seems to be the best compromise when linear wear and volumetric wear are considered. This head size, though, must be placed in proportion to the patient and the amount of polyethylene in the bearing. REFERENCES

RICHARD B. WELCH, MD GARY LEVENGOOD, MD San Francisco, California

Livermore J, Ilstrup D, Morrey B: Effect of femoral head size on wear of the polyethylene acetabular component. J Bone Joint Surg 1990; 71A:518-528 Lombardi AV Jr, Mallory TH, Vaughn BK, Drouillard P: Aseptic loosening in total hip arthroplasty secondary to osteolysis induced by wear debris from titanium-alloy modular femoral heads. J Bone Joint Surg 1989; 71A: 1337-1342 Nasser S, Campbell PA, Kilgus D, Kossovsky N, Amstutz HC: Cementless total joint arthroplasty prostheses with titanium-alloy articular surfaces. Clin Orthop 1990; 261:171-185 Schuller HM, Marti RK: Ten-year socket wear in 66 hip arthroplasties. Acta Orthop Scand 1990; 61:240-243 Willert HG, Bertram H, Bushhom GH: Osteolysis in alloarthroplasty of the hipThe role of ultra-high molecular weight polyethylene wear particles. Clin Orthop 1990; 258:95-107

Arthroscopic-assisted Reconstruction of the Anterior Cruciate Ligament RUPTURE OF THE ANTERIOR CRUCIATE LIGAMENT can lead to degenerative arthritis of the knee. Persons who participate in sports that require jumping and pivoting are at a high risk for injury leading to repeated episodes of instability, and surgical reconstruction is usually undertaken. Although no procedure can exactly replicate the kinematic and anatomic properties of the anterior cruciate ligament, intra-articular reconstruction with a strong and isometric graft offers the best hope of

restoring anatomic and functional stability and preventing future degenerative changes. Traditional intra-articular reconstruction is associated with substantial morbidity from the surgical dissection necessary to expose the torn anterior cruciate ligament and then implant the substitute. In most cases, this has meant severe pain, swelling, and difficulty initiating range-of-motion exercises in the immediate postoperative period, resulting in a hospital stay of three to five days. Arthroscopic techniques have recently been used to reconstruct the anterior cruciate ligament by adding a small extracapsular incision along with routine arthroscopic portals. This procedure is often done on an outpatient basis, and usually only an overnight hospital stay is required. With diminished pain, range of motion can be regained early. The cosmetic advantage of arthroscopic-assisted reconstruction of the anterior cruciate ligament is obvious. The arthroscopic procedure begins with the use of a motorized shaver and burr to remove remnants of the torn ligament and to enlarge the intercondylar notch of the femur to prevent impingement of the graft as the knee extends. A special aiming guide allows a tunnel to be drilled into the joint at the selected tibial attachment site. Work is carried out through this tunnel while viewing arthroscopically, and the femoral attachment site is selected. A strain gauge is used to measure any shortening or elongation between the selected points. If substantial strain is found, the femoral attachment site can be altered. Once an acceptable site is located, the bony tunnel for the anterior cruciate ligament graft is drilled from within the joint, using the tibial tunnel as a working portal. The selected graft (usually autogenous tissue) is then passed through the tibial tunnel, across the joint, and positioned in the closed femoral tunnel. After the graft is securely fixed, immediate range of motion is allowed. Regardless of the method of reconstruction, all biologic grafts used to reconstruct the anterior cruciate ligament undergo revascularization that requires protection of the graft from excessive activity for several months. Despite the improved cosmetic and perioperative advantages of arthroscopic reconstruction, the long-term outcome is similar to the results achieved by open methods. RICHARD A. MARDER, MD

Sacramento, California REFERENCES

Gillquist J, Odensten M: Arthroscopic reconstruction of the anterior cruciate ligament. Arthroscopy 1988; 4:5-9 Wainer RA, Clarke TJ, Poehling GG: Arthroscopic reconstruction of the anterior cruciate ligament using allograft tendon. Arthroscopy 1988; 4:199-205

Percutaneous Discectomy PERCUTANEOUS LUMBAR DISCECIOMY is a safe and effective alternative to laminectomy in some patients who require discectomy for the treatment of herniated nucleus pulposus. Percutaneous discectomy is done under local anesthesia and fluoroscopy with the patient in the lateral decubitus or prone position. The procedure has fewer potential postoperative difficulties than laminectomy or chemonucleolysis, with no epidural scarring, allergic reactions, or serious neurologic

complications. Patient selection is extremely important. The criteria for selection should be strict and include the following: the patient must have shown no improvement after at least six weeks of conservative therapy; the primary complaint is sciatica-that is, leg pain is greater than back pain; paresthe-

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sias or hyperesthesia occurs in a specific dermatome or dermatomes; straight-leg raising is restricted, preferably less than half of normal; weakness, atrophy, sensory changes, or reflex alteration is demonstrated in a lower extremity; and the findings of computed tomography, myelography, or magnetic resonance imaging correlate with clinical findings. Absolute contraindications include causes of symptoms such as tumor, infection, spondylolisthesis, or congenital abnormalities; sequestration or a free fragment; foraminal stenosis; and severe facet arthropathy. Relative contraindications are back pain without sciatica, previous chymopapain injection at the same level, stenosis or facet arthropathy with disc protrusion, multiple levels, and internal disc derangement. These relative contraindications constitute a "gray zone" for surgeons. The procedure is done with either manual instruments, such as pituitary rongeurs, or an automated suction aspiration probe called the nucleotome. The procedure consists of inserting a cannula through a small incision down to the annulus by a posterolateral approach. This avoids entering the spinal canal and injuring its contents. The instrumentrongeur or nucleotome-is then inserted into the disc for the removal of nucleus pulposus material. Positioning of the instruments is carefully monitored by fluoroscopy throughout the procedure. The following five criteria should be met for the procedure to be considered a success: no further intervention is needed; radicular pain has moderately or totally improved; postoperative function has improved; no need for narcotic analgesics exists; and both patient and surgeon are satisfied. The percutaneous discectomy procedure is a safe and well-tolerated alternative to laminectomy with discectomy or chemonucleolysis in patients meeting the selection criteria. With these patients, it is reasonable to expect a success rate in the range of 70% to 75%. JAMES M. MORRIS, MD San Francisco, California REFERENCES Kambin P, Schaffer JL: Percutaneous lumbar discectomy-Prospective review of 100 patients and current practice. Clin Orthop 1989; 238:24-34 Morris J: Percutaneous diskectomy. Orthopedics 1988; 11:1483-1487

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There are two important elements to measure: range of motion and muscle performance. In the lumbar spine, the spinal range of motion is difficult to separate from hip range of motion. Pelvic rotation must be separated from lumbar motion. The current American Medical Association guidelines recommend the use of two inclinometers to identify true lumbar range and the range of the thoracic or cervical spine. An array of computerized devices to measure range and strength has entered the marketplace. The most accurate measurements can be obtained when the equipment can isolate spinal segments as well as stabilize the pelvis. One system collects data simultaneously along three axesflexion-extension, rotation, and lateral bend. This device monitors both speed and strength. Strength screening can be accomplished on the equipment at variable speeds. At present, there is no evidence that exercise training at various speeds offers an advantage for muscle strengthening. The controlling of speed during testing is known as isokinesis. If speed is controlled by the equipment when the patient is tested, high-impact forces occur as the patient tries to make the machine move faster. Isokinetic testing is dynamic testing, and thus gravity and inertia must be controlled for. Comparisons among populations of patients are not always accurate and reliable. In addition to the variable-axes and the speed-controlled equipment, a third method of measuring range and muscle performance of the spine is available. This equipment measures isometric strength at various equidistant points along the arc of available range. To evaluate spinal function only, the spine is isolated from the pelvis and extremities when the patient sits in the equipment. Strength training through slow variable-resistance exercise in a concentric and an eccentric mode is also available. Function measured in this manner is the most accurate, and strength training is the most efficient. Range and muscle strength can now be tested with commercially available computerized equipment. Valid results are variable for most equipment, but experience has shown that measuring function rather than documenting pain allows the best opportunity for an efficient rehabilitation program.

VERT MOONEY, MD San Diego, California

Objective Measurements for Rehabilitation After Back Injury

REFERENCES

WE NEED OBJECrIVE MEASUREMENTS of spinal function after back injury to know if a patient is improving with treatment or has reached a plateau. Once a plateau has been reached with an exercise program, the level of impairment can be identified and job readiness established.

Gomez T, Beach G, Cooke C, et al: Normative data base for trunk range of motion, strength, velocity, and endurance on the Isostation B-200 Lumbar Dynamometer. Spine 1991; 16:15-21 Graves JE, Pollock ML, Carpenter DM, et al: Quantitative assessment of full range of motion isometric lumbar extension strength. Spine 1990; 15:289-294 Sapega AA: Current concepts reviewed: Muscle performance evaluation in orthopaedic practice. J Bone Joint Surg 1990; 72A: 1562-1574

ADVISORY PANEL TO THE SECTION ON ORTHOPEDICS WILLIAM C. MCMASTER,

MD

Advisory Panel Chair CMA Council on Scientific Affairs Representative Orange

RICHARD B. WELCH, MD

MICHAEL W. ABDALLA, MD

ROBERT SZABO,

CMA Section Chair San Francisco

Immediate Past Panel Chair Orange

Section Editor

WILLIAM P. BUNNELL,

ROBERT A. BAIRD, MD University of California, Irvine GERALD FINERMAN, MD University of California, Los Angeles

SANFORD H. ANZEL,

MD

Loma Linda University

CMA Section Secretary Orange

JAMES V. LUCK, JR,

MD

MD

CMA Section Assistant Secretary Los Angeles

STUART B. GOODMAN, MD Stanford University

MD

University of California, Davis

WAYNE H. AKESON, MD University of California, San Diego JAMES M. MORRIS, MD University of California, San Francisco AUGUSTO SARMIENTO, MD University of Southern California ROBERT HART Medical Student Representative University of California, San Diego

Percutaneous discectomy.

172 EPITOMES-ORTHOPEDICS Bearing Surfaces in Total Joint Replacement THE DESTRUCTIVE EFFECTS of wear and wear debris have challenged the existence o...
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