ADVANCES IN TOTAL HIP ARTHROPLASTY
Selections from Harvard Medical School’s Advances in Arthroplasty
| INSTABILITY AFTER TOTAL HIP ARTHROPLASTY (THA): WHAT IS THE ROLE OF HEAD SIZE ?—Daniel J. Berry, MD, Professor and Chair, Department of Orthopaedic Surgery, Mayo Medical School, Rochester, MN |
| Dislocation: rate 3.1% within 90 days of THA; most commonly stated reason for revision after THA; ≥25% of all revisions; Mayo Clinic has kept registry of all THAs and subsequent dislocations since 1969 |
| Prevention of dislocation: understanding risk factors enables optimal treatment of patients at highest risk; risk factors (based on 6000 Charnley THAs performed in 1970s)—age weak risk factor; sex relatively strong, with women at higher risk; osteonecrosis (risk almost 2-fold higher); acute fracture/nonunion, mostly femoral neck fracture (1.8-fold risk); rheumatoid arthritis (modestly increased risk) |
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Surgical factors: based on >22,000 THAs |
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Operative approach: risk almost same for transtrochanteric and anterolateral; with posterior approach, risk 2.3- fold higher (cumulative dislocation risk); recent data indicate careful posterior capsular repair may reduce early dislocation rate |
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Femoral head size: advantage of larger head unproven clinically for first 25 to 30 yr of THA; stratified by approach—at 10 yr; 22-mm heads, cumulative risk 3.9%; 28-mm heads 3%; 32-mm heads 2.4%; rates higher for posterior approach (risk for 22-mm head 1.7 times that for 32-mm head; 28-mm head 1.3 times that for 32- mm head); larger head sizes—preliminary data encouraging; 3-mo follow-up of 38-mm head in 616 hips found no dislocations, indicating long-term risk relatively low |
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High-risk patients: consider combined risk factors; led to selection of 36-mm and 40-mm heads and favorable results in speaker’s examples |
| Treatment of instability: successful reoperation rate (60%-75%) lower than rate of success for any other operation in revision THA, including infection-related; new understanding of instability allows multimodal management strategy; factors include—malposition; soft-tissue laxity; impingement; often in combination; malposition—for repositioning (especially cup), rate of success ≈80%; soft-tissue laxity—for advancing trochanter (with no other problems), rate of success 80% to 90%; impingement—for removing source, rate of success 50% to 60%; summary point—for operating on specific problem seen on x-ray and found in surgery, rate of success 60% to 80% |
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Current answer to problem: optimize implant position; correct soft-tissue tension; eliminate impingement; take advantage of modern technology—large fixed head; nonconstrained bipolar implant; constrained implant; moving from first to last, options increase both stability and risk |
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Large fixed heads: provide increased motion to impingement; greater displacement to dislocation; contained by soft-tissue envelope |
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Tripolar implants: bipolar implant against fixed cup; head size >40 mm; compatible with many stems (eg, snap on to 22- , 26- , or 28-mm heads); double articulation improves stability; low interface stresses; off-the-shelf liners now provided by many manufacturers; main risk—wear |
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Constrained implants: most beneficial for substantial abductor deficiency or instability after several unsuccessful attempts to solve problem; large fixed heads (36-40 mm) insufficient to reliably solve problems; risk for dislocation—varies greatly according to series, indications, and design; results—success rate good for better designs (79 hips with no dislocation at Mayo Clinic; 32 hips with 1 dislocation, based on data from Australia; longer term data from John Callaghan support judicious use in complex cases with instability) |
| DON’T RELAX: OXIDATION IS NOT BENIGN —William H. Harris, MD, DSc, Alan Gerry Clinical Professor of Orthopaedic Surgery, Harvard Medical School, and Chief (Emeritus) of Adult Reconstruction Unit, Massachusetts General Hospital, Boston |
| Introduction: commonly believed that oxidation of conventional polyethylene in THA benign; speaker presents data that challenge this belief |
| Case 1: THA using conventional gamma-in-air sterilized polyethylene revised ll.5 yr after implantation; massive destruction at rim; liner actually spinning in shell; failure not from wear or osteolysis, but from oxidation |
| Case 2: THA using conventional gamma-in-air polyethylene revised at 14 yr because shell loose secondary to osteolysis; flange separated from polyethylene through area of severe oxidation |
| Experimental studies: hip simulator used to test stability of liners in cases of high rotational torque with larger heads, eg, 40 mm; contrasted aged conventional and aged highly cross-linked melded polyethylene; aged 5 wk at 80°C in air; results—major damage to locking mechanism in conventional liner; no damage in highly cross-linked polyethylene (no detectable free radicals); in conventional design, after 7 million cycles flange being destroyed, and after 12 million cycles complete loss of rotational stability; highly cross-linked design remained stable after 20 million cycles (no oxidation; even though somewhat weaker from start) |
| Future implications: 2 cases represent “tip of the iceberg” (expect similar results after 11-15 yr in conventional polyethylene); highly cross-linked polyethylenes—several (eg, Crossfire, X3) contain high amounts of residual free radicals; some evidence newer designs oxidize more than conventional polyethylene; anticipate increasing mechanical failure from oxidation |
| HARD-ON-HARD BEARINGS: AN OVERVIEW —B. Sonny Bal, MD, MBA, Associate Professor of Orthopaedic Surgery, University of Missouri School of Medicine, Kansas City |
| Introduction: wear of major concern, especially in younger patients; metal-polyethylene wear rate (1.2-0.5 mm/ yr); ceramic-polyethylene (0.1 mm/yr); ceramic-metal under investigation |
| Metal-metal: polished cobalt-chrome on chrome-cobalt; used in young active patients; advantages—low wear rate; strong; large-diameter heads allow modularity; very large heads with small shells maximize range of motion and stability; low wear; easier to insert in minimally invasive surgery; alternative for resurfacing; disadvantages—metal ions and particles of ongoing concern (long-term data on cancer risk unavailable); improper component orientation leads to runaway wear; impingement |
| Ceramic-ceramic: alumina on alumina; advantages—lowest wear rate of all; large heads reduce risk for impingement and ceramic breakage; inert material (stable for lifetime); ultralow wear; disadvantages—risk for fracture; noisy squeaky bearings (cause unknown); recurrent dislocation |
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Silicon nitride (Si3 N4 ): nonoxide ceramic under investigation; used in extreme environments (eg, space shuttle nozzles); increased fracture resistance; according to manufacturer, burst strength of 28-mm heads significantly higher than alumina heads; elastic modulus similar to cobalt-chrome permits use of silicon nitride on cobalt- chrome |
| Future prospects: metal head on ceramic; ceramic head on metal liner (10-fold less metal wear and ions than metal-metal; may provide greater flexibility and reduced fracture risk, compared to ceramic-ceramic) |
| HIP FRACTURES: THA FOR ALL ?—Ivan Tomek, MD, Assistant Professor of Orthopaedic Surgery, Dartmouth Medical School, Lebanon, NH |
| Introduction: cost—“hip fracture epidemic” focuses attention on cost; patient involvement—only 4% of patients wanted surgeon to make decision for them; unrealistic patient expectations lead to disappointment |
| Treatment goals and outcomes: restoring anatomy—often possible, but not with displaced fractures, significant comminution, and unstable fractures; preventing complications—high reoperation rates with osteosynthesis of displaced unstable fractures (including intratrochanteric fractures) |
| Advantages of THA: full weight-bearing; immediate mobilization, especially with cemented stem; open reduction and internal fixation (ORIF) of unstable fractures leads to high rate of complications (more pain; reduced mobility) |
| Disadvantages of THA: high cost to hospital, eg, increased cost of implants; in acute fractures, higher rate of displacement, complications, and mortality (10-fold increase found in Medicare data, although speaker found no significant increase) |
| Management considerations: abductor-sparing approaches allow early mobilization; preoperative planning critical (eg, digital templating off contralateral hip); large heads offer advantages |
| Speaker’s approach: involve patient in decision; stable fracture—ORIF; unstable—for young patient, discuss ORIF and leave decision to patient; choice of implant (hemiarthroplasty vs THA) depends on activity level (for patients with higher level, THA preferred) |
| SALVAGE OF FAILED ACETABULAR FRACTURES WITH THA—Dr. Berry |
| Component selection: apply principles of revision surgery; use uncemented socket augmented with screws |
| Managing bone loss: view as revision surgery; fill cavitary defect with jumbo cup and bone graft; for major segmental bone loss (posterior wall migration and failure), insert cup in normal center, using patient’s femoral head for augmentation graft |
| Nonunited fractures: pelvic discontinuity in transverse acetabular fracture; good healing potential; treatment— stabilize with posterior column plate; uncemented socket; autogenous bone graft from femoral head |
| Hardware removal: remove hardware impeding operation; trying to remove more hardware increases risk for neurovascular and soft-tissue injuries |
| Sciatic nerve: avoid if possible; if necessary to work on posterior column, identify nerve by incising gluteus maximus tendon and following proximally; flex knee to relax nerve |
| Heterotopic ossification: often present; incise if symptomatic; computed tomography to identify exact location |
| Choice of bearing surface: important because of high activity demands of patients; removing part of capsule limits stability |
| Minimizing complications: careful preoperative assessment; consider challenges of bone loss and nonunion; rule out infection; before surgery, prepare—for more blood loss, longer operative time, and difficult exposure; to assemble tools that may be required (reconstruction plates; autogenous bone graft; metal cutting and screw-removal instruments; heterotopic bone prophylaxis) |
| DEEP VENOUS THROMBOSIS (DVT): WHAT TO DO ABOUT IT— Louis M. Kwong, MD, Associate Professor of Orthopaedic Surgery, the David Geffen School of Medicine at the University of California, Los Angeles, and Chief, Orthopaedic Arthritis Service, and Vice Chair, Department of Orthopaedic Surgery, Harbor-UCLA Medical Center, Los Angeles |
| Introduction: of frequent complications after total joint arthroplasty, venous thromboembolic disease most serious; largely silent clinically; manifested as DVT and pulmonary embolism (PE); associated with 0.1% to 0.2% of fatal PEs; significant long-term morbidity; without prophylaxis—DVT develops after THA and hip fracture in ≈50% of patients, and after total knee arthroplasty in ≈60% of patients; in highest risk group, leads to ≤6% rate of fatal PE after THA, and to rate of ≈13% after hip fracture |
| First episode of DVT: goal of orthopaedist to avoid first episode; confers 30% cumulative risk for recurrent DVT, even 8 yr later; same risk conferred for post-thrombotic (phlebitic) syndrome (characterized by pain, edema, skin breakdown, and ulceration) |
| Thromboprophylactic agents: introduced in recent decades, each more effective than previous generation; dextran—1960s; unfractionated heparin—1970s; warfarin—1980s; low-molecular-weight heparins (LMWHs)—1990s; factor Xa inhibitors and thrombin inhibitors—2000s; level of risk reduction after THA—aspirin reduced rate from 50% to 41.7%; warfarin to 22.3%; LMWH to 4.7% |
| Newer agents: >6 oral agents expected in next 1 to 5 yr; fixed dose; unmonitored |
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Thrombin inhibitors: direct inhibitors—dabigatran; ximelagatran (available only in Europe); indirect inhibitor— odiparcil |
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Factor Xa inhibitors: direct inhibitor—rivaroxaban (trial found 64% reduction in risk for symptomatic venous thromboembolism after TKA); indirect inhibitor—fondaparinux (approved for clinical use) |
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American Academy of Orthopaedic Surgeons: based on risk stratification for PE and bleeding; after THA and TKA in patients at increased risk for PE and standard risk for bleeding; options—LMWH; synthetic pentasaccharide; warfarin; no dosing recommendations |
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International Surgical Thrombosis Forum: options—LMWH (dosing according to manufacturer); fondaparinux (fixed dose postoperatively); pneumatic compression |
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American College of Chest Physicians: options—LMWH (started pre- or postoperatively at high-risk dose; or started postoperatively at 50% of high-risk dose); warfarin (dose adjusted to international normalized ratio 2.0- 3.0); fondaparinux (unmonitored fixed dose started postoperatively) |
| Aspirin: inhibits platelet aggregation; nonselective cyclooxygenase 1 and 2 inhibitor; risk for upper gastrointestinal bleeding; effective for arterial thrombosis; no trial for efficacy in venous thrombosis |
Suggested Reading
Amstutz HC et al: Metal-on-metal hip resurfacing: what have we learned? Instr Course Lect 56:149, 2007; Berend KR et al: Acute hip arthroplas-ty for the treatment of intertrochanteric fractures in the elderly. J Surg Orthop Adv 14:185, 2005; Berry DJ et al: Effect of femoral head diameter and operative approach on risk of dislocation after primary total hip arthroplasty. J Bone Joint Surg Am 87:2456, 2005; Berry DJ et al: The cumulative long-term risk of dislocation after primary Charnley total hip arthroplasty. J Bone Joint Surg Am 86-A:9, 2004; Colwell CW Jr, Annenberg Center for Health Sciences and Quadrant Medical Education: Thromboprophylaxis in orthopedic surgery. Am J Orthop Suppl:1, 2006; Parker MJ et al: Replacement arthroplasty versus internal fixation for extracapsular hip fractures in adults. Cochrane Database Syst Rev:CD000086, 2006; Pritchett JW et al: Total hip replacement after central fracture dislocation of the acetabulum. Orthop Rev 20:607, 1991; Sanchez-Sotelo J et al: Epidemiology of instability after total hip replacement. Orthop Clin North Am 32:543, 2001; von Knoch M et al: Late dislocation after total hip arthroplasty. J Bone Joint Surg Am 84-A:1949, 2002; Wannomae KK et al: In vivo oxidation of retrieved cross-linked ultra-high-molecular-weight polyethylene acetabular components with residual free radicals. J Arthroplasty 21:1005, 2006; Weber M et al: Total hip arthroplasty after operative treatment of an acetabular fracture. J Bone Joint Surg Am 80:1295, 1998.
Educational Objectives
| The goal of this program is to improve performance in total hip arthroplasty (THA). After hearing and assimilating this program, the clinician will be better able to: |
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1. Avoid instability by using larger femoral head sizes. |
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2. Recognize the risk for oxidation in polyethylene liners. |
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3. Compare the properties of different bearing surfaces. |
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4. Salvage failed acetabular fractures by performing THA. |
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5. Employ effective thromboprophylaxis to avoid deep venous thrombosis and pulmonary embolism. |
Faculty Disclosure
In adherence to ACCME Standards for Commercial Support, Audio-Digest requires all faculty and planning committee members to disclose relevant financial relationships within the past 12 months that might create any personal conflicts of interest. Any identified conflicts were resolved to ensure that this educational activity promotes quality in health care and not a proprietary business or commercial interest. For this program, the following has been disclosed: Dr. Harris — Zimmer (royalties to Massachusetts General Hospital and speaker; research support); Dr. Kwong — Zimmer (consultant); Atelias; Bristol Myers Squibb; Pfizer (research grant). Drs. Berry, Bal, and Tomek, and the planning committee, reported nothing to disclose.
Acknowledgements
Drs. Berry, Harris, Bal, Tomek, and Kwong were recorded at Advances in Arthroplasty, sponsored by Harvard Medical School, September 26-29, 2007, in Cambridge, MA. The Audio-Digest Foundation thanks the speakers and Harvard Medical School for their cooperation in the production of this program.
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