Essentials of Orthopedic Surgery, third edition / 11-The Hip and Femur

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initial stability and eliminate the need for screws and screwholes in many cases.

At the present time, a “hybrid” total hip arthroplasty is recommended for the majority of patients receiving THR, which includes the use of a cemented femoral stem and a porous ingrowth acetabular component. This arthroplasty takes advantage of the excellent long-term fixation of the cemented femoral stems and the improved fixation with modern cementing as well as the very encouraging results with the use of porous ingrowth acetabular components.

Loosening appears to be primarily related to the generation of polyethylene wear debris from the articulation. Several new technologies have been developed to reduce wear from the articulation in a total hip replacement. The first new concept was to improve the polyethylene, which was accomplished by cross-linking the polymer strands within the material. Think of a polymer as a bowl of cold spaghetti. If you pull out a strand of spaghetti, you can tease the whole strand from the bowl. If you cut some of the strands and then link these shorter strands to other strands, it will make it more difficult to pull out a strand and also more difficult to pull out a long strand. This logic applies to cross-linked polyethylene. The wear rate is reduced by 10 fold and the debris produced is of much smaller particles.

However, even with cross-linking, the plastic is the weak link, and the debris produced is from the polyethylene. Two other alternatives are now available, referred to as hard-on-hard interfaces. Both metal-on-metal and ceramic-on-ceramic are currently available. By using much harder materials for the articulation, the wear rate and debris production can be reduced as much as 1000 fold. With less debris and less wear, we hope to see a much longer functional life for these articulations. These new articulations, however, also have some limitations. Metal on metal involves the use of a cobalt-chromium femoral head on a cobalt-chromium acetabular liner.

This articulation has been in clinical use for approximately 30 years. Early designs failed early as a result of design problems. The early heads were made of equal dimension to the acetabular opening. These would result in binding of the head within the acetabulum and the component would loosen. Current designs have reduced the size of the head relative to the acetabulum by a very small amount, which allows for lubrication of the interface and less friction; this eliminated the problem of acetabular loosening. However, it has been demonstrated that patients with metal- on-metal hip articulations have a very low level of metal detectable in their blood and urine. The long-term effects of this are unknown, but looking at the long-term follow-up of early implant designs there was no detrimental effect.

Ceramic on ceramic is the other hard-on-hard interface. This interface has been used in Europe for many years. Ceramic on ceramic results in the least amount of wear debris of all the currently used articulation for

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total hip arthroplasty. However, it is limited by the strength of the ceramic material. Ceramic implants can be prone to fracture. When a ceramic implant fails, it results in a catastrophic failure. The ceramic fragments are very hard and abrasive, resulting in rapid extensive wear of the metallic implants that are attached to the bones. Frequently, the metal components that are attached to the bones and the ceramic articulation all need to be removed after a fracture. For other materials, you can change only the articulation.

Currently, wear and loosening are the most worrisome complications. We are trying to address these with improvements in materials and designs. However, the current devices work so well that to determine if new technology is truly an improvement we need at least a 10-year clinical follow-up. All the new devices need to be evaluated for not only their benefits but also the real and potential limitations.

Complications

The most frequent complication after THR is thromboembolic disease, including deep venous thrombosis and pulmonary embolism. Early in the history of THR the rate of fatal pulmonary embolism was 1% to 2%. However, at that time patients were kept at bed rest for as long as 2 to 3 weeks and kept as long as 6 weeks in the hospital. Early mobilization of patients has undoubtedly contributed to the significant reduction in the rate of fatal pulmonary embolism. However, significant reduction has also occurred through the use of anticoagulant prophylaxis, regional anesthesia, shorter operating times, and less blood loss. In the United States, THR is considered a significant risk factor for thromboembolic disease (TED) and therefore the routine use of medical and/or mechanical prophylaxis has been recommended. At present, the rate of TED ranges between 5% and 20%. The rate of fatal pulmonary embolism is low, approximately

0.01%.

The principal methods of prophylaxis are low-dose Coumadin, aspirin, low molecular weight heparin, and pneumatic compression stockings. Coumadin has the greatest volume of data supporting its use. Coumadin is started the evening preceding surgery or on the day of surgery. It is recommended that the therapy be continued for 6 weeks postoperatively. The medication needs to be monitored closely to keep the level within a safe range. The prothrombin time (PT) is held between 16 and 18 and the INR (international normalized ratio) at 1.25 to 1.5. It has been shown in many studies to be a safe and effective method of prophylaxis. The monitoring of

Coumadin is of particular concern. Occasionally, patients have a dramatic elevation of their PT and INR with the first dose, which will lead to a risk of postoperative bleeding and hematoma at the operative site. As the length of stay in the hospital has decreased to 3 to 4 days or less, this has made the use of Coumadin increasingly difficult; 5 to 7 days are frequently required

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to equilibrate a patient on a steady dose of Coumadin, and this is more difficult to accomplish in the outpatient setting. Currently, this is managed with the use of home nursing services and frequent monitoring.

Low molecular weight heparin formulations were developed in part to provide safe effective prophylaxis against thromboembolic disease. Subcutaneous unfractionated heparin has been used historically in the general surgical population; it has not been found to be effective in the orthopedic population. Intravenous unfractionated heparin is effective prophylaxis and treatment of thromboembolic disease. However, it requires even greater monitoring when used intravenously as it fully anticoagulates the patient immediately. If this occurs with in the first 3 days postoperatively, the incidence of wound hematoma is greater than 50%; thus, this is infrequently used in the postoperative orthopedic patient. Low molecular weight heparin is more selective in the interruption of the coagulation cascade; this results in a more controlled effect and patients do not require monitoring. The current protocols are for 2 weeks of therapy. Most studies demonstrate efficacy comparable with Coumadin for total hip replacement.

Aspirin has been used for DVT prophylaxis historically. Aspirin irreversibly inhibits platelet function and theoretically reduces the rate of formation of DVT. Few data directly support its routine use in THR; however, several studies demonstrate acceptable prophylaxis with the use of aspirin and hypotensive epidural anesthesia (HEA). HEA is an excellent anesthesia technique for THR; however, it requires careful patient monitoring and a dedicated anesthesia team. This form of anesthesia results in reduced blood loss while maintaining blood flow in the lower extremities. This approach reduces the need for transfusion postoperatively, which has been shown to increase the risk of DVT. In addition, the reduction in blood loss results in less activation of the coagulation cascade, again minimizing the risk of DVT. Although this technique has been shown to be very effective, it has not been widely applied because of concerns about the reduction of mean arterial pressure in elderly patients, which may result in stroke, renal failure, or myocardial infarction.

Dislocation of the prosthetic femoral head from the acetabular component occurs in 2% to 5% of patients after THR. As discussed previously, the incidence and direction vary with the operative approach. Postoperatively patients are instructed to not bend their replaced hip beyond 90 degrees and to keep their legs abducted and in neutral rotation. These restrictions should be followed closely for the first 6 to 8 weeks following surgery. After this time the patient should have formed a sufficient pseudocapsule to protect against dislocation. However, a replaced hip is always at greater risk for dislocation compared to a native hip joint. The majority of patients who dislocate their hip in the early postoperative period can be reduced without additional surgery and protected with a hip abduction brace for 6 weeks to allow healing of the pseudocapsule. The risk of recur-

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rent instability after an early dislocation is approximately 30%. In addition to patient compliance, the other etiologies for dislocation are component malposition, excessive soft tissue laxity, and impingement of the prosthetic or osseous structures, resulting in levering of the femoral head out of the acetabulum. If a patient recurrently dislocates, revision surgery may be indicated.

The most devastating complication after THR is deep sepsis. Early postoperative infection occurs in approximately 0.3% to 0.5% of cases after primary THR. Late infection resulting from hematogenous spread can occur in 1% to 2% of patients. If detected within the first 2 weeks postoperatively, aggressive open debridement and synovectomy combined with intravenous antibiotics may be successful. However, if the infection recurs after debridement or is detected beyond 2 weeks, treatment must include removal of the prosthetic components and all cement. The prosthesis is left out for at least 6 weeks. An antibiotic-impregnated spacer may be placed at the time of debridement; this will provide a local depot of antibiotic at the site of the infection.

Recent work has demonstrated the effectiveness of a prosthesis covered in antibiotic-impregnated cement inserted at the time of the debridement to maintain the articular space and soft tissue tension and to provide stability to the soft tissues to promote healing. The success of this technique also raises the question of the role of one-stage reconstruction for an infected total hip replacement. Early data from Europe had demonstrated a success rate of 80% with this technique. However, more study is required to define the role of these techniques in the management of the infected arthroplasty. If the pathologic organisms are highly virulent and resistant to antibiotic therapy, reimplantation should be delayed for more than 12 months. Serum bactericidal titers (SBT) should be determined and a titer of at least 1 : 8 maintained during the 6-week course of therapy. During the antibiotic therapy, patients may be mobilized as tolerated with the use of a walker. Reimplantation can proceed when the wound is sterile if sufficient bone stock and soft tissue integrity remain. The use of antibioticimpregnated cement for the femoral component is recommended at the time of reimplantation. If the SBT was maintained at greater than 1 : 8 for 6 weeks, reimplantation of a new prosthesis will be successful in more than 90% of cases. Recent data have demonstrated a higher rate of recurrence for patients reimplanted without cement.

Heterotopic ossification (HO) can form around a THR in 5% to 25% of cases. Heterotopic bone is histologically bone tissue, which forms within the muscle around the hip after arthroplasty. A metaplasia occurs, forming a bone matrix that becomes calcified over the first 6 to 12 months after the surgery. Most commonly the presence of HO will not compromise the clinical result. Associated risk factors are patients with hypertrophic osteoarthritis, male, over the age of 65, HO formation after previous surgery, and ankylosing spondylitis.

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Heterotopic ossification is graded according to Brooker. Grade one consists of isolated islands of bone within the soft tissue between the femur and pelvis; grade two is bone protruding from the proximal femur or pelvis with greater than 1 cm of separation; grade three consists of bone protruding from the femur and or pelvis with less than 1 cm between the bones; and grade four is radiographic ankylosis, with no visible space between the bone protruding from the femur and pelvis. Grades one and two are rarely symptomatic. Grade three patients usually have stiffness and mild pain, and patients with grade four usually have marked stiffness and can be very symptomatic.

Patients who are at high risk for this complication can receive prophylaxis using indomethacin for 6 weeks or low-dose radiation therapy. Once HO forms the patients should be encouraged to maintain range of motion and activity, but passive stretching and passive range of motion should be avoided. Surgical intervention is indicated in patients with significant restriction of motion and pain, which occurs most commonly in patients with grade three and four HO. Surgery should be delayed until the HO is mature; this usually takes 12 to 24 months and is indicated by mature appearance on plain radiography, uptake similar to the uninvolved bone of the pelvis on a Tc 99-MDP bone scan, and normal serum alkaline phosphatase level. When the bone is mature, it can be surgically excised. Attempts to remove the bone before maturity have an increased rate of recurrence. After the bone is excised, the patient should receive prophylaxis to prevent recurrence either with indomethacin or by radiation therapy. Radiation therapy is preferred in most patients; it is usually a one-dose regimen of 700 to 800 cGy that can be administered either immediately preoperatively or within the first 2 or 3 days postoperatively. In this way, the entire treatment regimen is delivered in a controlled setting, compared to indomethacin, which is administered for 6 weeks. The rate of recurrence after excision and prophylaxis is approximately 5% to

20%.

The limitations to the long-term fixation of a total hip arthroplasty are loosening and wear. The primary articulation in total hip arthroplasty is a metal ball in a polyethylene socket. The rate of wear is variable; however, it is between 0.01 and 0.1 mm/year. The rate of wear is affected by the surface roughness of the femoral head, the quality of the polyethylene, the thickness of the polyethylene, the method of sterilization of the polyethylene, and stress applied to the articulation by the patient. As the implant, particularly the polyethylene liner, wears, the debris that is produced is released into the local tissues. The body has no mechanism to digest or eliminate the polyethylene debris. However, the local macrophages in the area recognize the material as a foreign substance and try to eliminate the debris. The macrophages ingest the material and try to digest it with catabolic enzymes and superoxides, which fails to alter the material. As the debris accumulates within the cell, it breaks down, releasing the polyeth-

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ylene, enzymes, and oxides into the local environment. The result is a local bone lysis that creates cysts in the bone and dissects along the fixation of the implant or cement and bone. If allowed to continue, the lysis leads to loosening. In addition, failure can occur if the polyethylene is thin at the time of implantation. Thin polyethylene results in increased stress within the polyethylene with weight-bearing and a significantly increased rate of wear, which in turn leads to failure of the polyethylene liner and the need for revision of the implant.

Loosening can also result from mechanical failure of the implant–bone interface. The cement mantle can fragment or fracture, leaving the implant loose. In noncemented fixation, the implant can also loosen because the implant never actually bonds to the bone with bone ingrowth; a fibrous tissue forms instead, and this fibrous tissue may not be sufficient to maintain stable fixation of the implant. The implant will then migrate slowly, which is best appreciated on serial radiographs. Revision will be required to provide a stable implant.

Similar to the indications for primary arthroplasty, these are elective surgeries. However, in the revision setting it is important to follow the patient closely with plain radiographs. If an accelerated pattern of bone loss is noted, revision surgery should be performed before the loss of an extensive amount of bone. The greater the loss of bone at the time of revision, the greater the difficulty in obtaining stable fixation for the revision components. This loss may also lead to a higher rate of repeated revision for aseptic loosening.

Summary

As noted initially, disorders involving the hip and femur are manifested by alteration in the patient’s ability to ambulate. These conditions can be diagnosed and treated by obtaining a careful history, thorough physical examination, and the appropriate use of radiographic studies. When the proper diagnosis is made for most nontraumatic disorders, it is usually best to begin with a nonoperative approach. If the nonoperative treatment alternatives are not successful, then operative intervention is indicated, which will result in an excellent outcome in the majority of patients.

Suggested Readings

Brooker AF, Bowerman JW, Robinson RA, Riley LH. Ectopic ossification following total hip replacement: Incidence and a method of classification. J Bone Joint Surg 1973;55(A):1629–1632.

Callaghan JJ, Templeton JE, Liu SS, et al. Results of Charnley total hip arthroplasty at a minimum of thirty years: a concise follow-up of a previous report. J Bone Joint Surg 2004;86:690–695.

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Collier JP, Sutula LC, Currier BH, et al. Overview of polyethylene as a bearing material: comparison of sterilization methods. Clin Orthop Relat Res 1996; 333:76–86.

Evans BG, Salvati EA, Huo MH, Huk OL. The rationale for cemented total hip arthroplasty. Orthop Clin N Am 1993;24(4):599–610.

Evans BG. Late complications and their management. In: Callaghan JJ, Rosenberg AG, Rubash HE, (eds) The Adult Hip. New York: Lippincott-Raven, 1998: 1149–1161.

Garvin K, Evans BG, Salvati EA, Brause B. Palacos gentamicin for the treatment of deep periprosthetic hip infections. Clin Orthop Relat Res 1994; 298:97–1054.

Healy WL, Lo TCM, DeSimone AA, Rask B, Pfeifer BA. Single-dose irradiation for the prevention of heterotopic ossification after total hip arthroplasty: a comparison of doses of five hundred and fifty and seven hundred centigray. J Bone Joint Surg 1995;77A:590–595.

Hoagland FT, Steinbach LS. Primary osteoarthritis of the hip: etiology and epidemiology. J Am Acad Orthop Surg 2001;9:5.

Jazarawi LM, Kummer FJ, DiCesare PE. Alternative bearing surfaces for total joint arthroplasty. J Am Acad Orthop Surg 1998;6:198–203.

Steinberg ME. Early diagnosis, evaluation and staging of osteonecrosis. Instruct Course Lect 1994;43:513–518.

Trousdale RT, Ekkernkamp A, Ganz R, Wallrichs SL. Periacetabular and intertrochanteric osteotomy for the treatment of osteoarthrosis in dysplastic hips. J Bone Joint Surg 1995;77A:73–85.

Wedge JH, Cummiskey DJ. Primary arthroplasty of the hip in patients who are less than twenty-one years old. J Bone Joint Surg 1994;76A:1732–1742.

Wiklund I, Romanus BA. Comparison of quality of life before and after arthroplasty in patients who had arthrosis of the hip joint. J Bone Joint Surg 1991; 73A:765–769.

Willert HG, Bertram H, Buchhorn GH. Osteolysis in alloarthroplasty of the hip, the role of ultra-high molecular weight polyethylene wear particles. Clin Orthop 1990;258:95–107.

Woo RYG, Morrey BF. Dislocation after total hip arthroplasty. J Bone Joint Surg 1982;64A(9):1295-1306.

Questions

Note: Answers are provided at the end of the book before the index.

11-1. The femoral head receives 80% of its blood supply from:

a.Artery of the ligamentum teres

b.Obturator artery

c.Superior gluteal artery

d.Small vessels within the synovial retinaculum

e.Internal iliac artery

11-2. The primary internal rotator of the hip is the: a. Iliopsoas

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b.Rectus femoris

c.Gluteus medius

d.Gluteus maximus

e.Piriformis

11-3. Osteotomy of the hip joint is contraindicated in which of the following conditions:

a.Osteoarthritis

b.Rheumatoid arthritis

c.Developmental dysplasia of the hip

d.Avascular necrosis of the femoral head

e.Coxa vara

11-4. The most frequent complication of total hip arthroplasty is:

a.Loosening

b.Fracture

c.Infection

d.Deep venous thrombosis

e.Dislocation

11-5. Dislocation after total hip replacement can result from:

a.Impingement on an anterior osteophyte

b.Soft tissue laxity

c.Malposition of the components

d.Poor patient compliance

e.All the above

11-6. Patients with high risk for developing heterotopic ossification after a total hip replacement can be treated with which of the following treatments to reduce the risk?

a.Coumadin

b.Antibiotics

c.Calcium channel blockers

d.Radiation therapy

e.Chemotherapy

11-7. Fractures of the femoral neck can commonly result in which complication?

a.Infection

b.Avascular necrosis of the femoral head

c.Rheumatoid arthritis

d.Lengthening of the leg

e.Dislocation of the hip

11-8. During the anterior approach to the hip for a total hip replacement, which muscle is partially detached from the greater trochanter?

a.Gluteus medius

b.Gluteus maximus

c.Tensor fascia lata

d.Piriformis

e.Quadratus femoris

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11-9. Deep periprosthetic infection after total hip replacement is:

a.An easy complication to treat

b.Can be managed without surgery with antibiotics alone

c.A devastating complication requiring several surgeries and long courses of intravenous antibiotics

d.Associated with good range of motion

e.Less frequent in patients taking oral corticosteroids

11-10. A coxalgic gait pattern has which two components?

a.Increased stance phase and abductor lurch

b.Decreased stance phase and adductor lurch

c.Normal stance phase and swing phase

d.Decreased stance phase and abductor lurch

e.Increased stance phase and late toe-off