David G. Campbell, BM Bassam A. Masri, MD Donald S. Garbuz, MD Clive P. Duncan, MD

1. ICL 7 & 8Acetabular Bone Loss During Revision Total Hip Replacement:Preoperative Investigation and Planning David G. Campbell, BM Bassam A. Masri, MD Donald S. Garbuz, MD Clive P. Duncan, MD

2. INTRODUCTION • The prevalence of hip replacements has increased dramatically, and thus, so have the number of revision total hip arthroplasty. This may be the largest iatrogenic orthopaedic problem of the late twentieth century. • When planning a revision hip procedure, it is useful to consider the acetabular and femoral components independently.

3. GENERAL CONSIDERATIONS • Prior to acetabular revision, it is imperative to devise a preoperative plan. The following factors must be considered:

4. PATIENT FACTORS • Age: patients are usually a decade or more older than at the primary operation • This results in diminished health and physiologic reserve and a greater risk of perioperative morbidity • Local complications: increased following revision hip surgery • Increased dislocation rates-2 or more times > than primary arthroplasty • Increased nerve palsies-aprox. 3 times > with revision arthroplasty

5. PATIENT FACTORS CONT • Previous skin incisions: these suggest the approach that was previously taken • Whenever possible the previous incision should be used to avoid wound edge necrosis, although unlike the knee, this is rarely a complication. • Hip range of motion: this can be an important indicator of heterotopic bone formation and joint contracture

6. Limb length discrepancies: extensive bone loss is often associated both with shortening of the limb and with decreased femoral offset. This causes a short and stiff joint and is often difficult to mobilize unless an extensive soft-tissue release is performed. • A special approach may be necessary for wider exposure of the pelvis and femur.

7. Morrey-factors associated with an increased hip dislocations • Female sex • Revision surgery • Posterior approach • Mobile hips • Decreased femoral offset • MOST IMPORTANT: Acetabular orientation

8. PREOPERATIVE INVESTIGATIONS TO RULE OUT INFECTION • Severe loss of bone stock, particularly within a short period of time, should raise the index of suspicion for occult infection. • A careful history and physical should precede any tests. • Persistent pain, despite unremarkable radiographs • Question pt regarding recent infections, such as skin infections or ulceration, UTIs, dental infections

9. Initial tests should include ESR and C-reactive protein level- if both are normal, and the Hx and PE are not suggestive of infection, no further tests are necessary. • If the ESR and/or CRP are elevated, further tests are indicated. • A hip joint aspiration, with the pt off ABX for at least 4 weeks, should then be performed. If the aspiration is negative, and the suspicion remains high, it should then be repeated under arthrography or ultrasound.

10. Other tests include various nuclear scans and if all remain inconclusive, however, the suspicion remains high, a frozen intraoperative tissue section can be obtained prior to revision surgery. • If all of these remain negative the surgeon can then proceed with the revision total hip arthroplasty.

11. ANATOMY AND RADIOLOGIC EVALUATION OF THE ACETABULUM • The hemipelvis can be thought of as an inverted “Y”, with the limbs of the letter “Y” representing the anterior and posterior columns straddling the acetabulum. • The acetabulum can be divided into 4 regions: • The roof and superior rim • The posterior column and posterior rim • The anterior column and anterior rim • The medial wall

12. RADIOGRAPHS • Judet views best enhance the acetabulum, they include: • Iliac oblique • posterior column • anterior rim • Obturator oblique • anterior column • posterior rim

13. The acetabular tear figure is a constant reference of the medial acetabular wall and is best evaluated by a standard A/P radiograph. • Despite best efforts, however, this assessment may not be entirely accurate, and the surgeon has to be prepared to deal with more severe bone defects at the time of surgery.

14. CLASSIFICATION OF ACETABULAR BONE DEFICIENCY • The AAOS currently recommends the descriptive classification of D’Antonio. • Two basic categories are used: segmental and cavitary • Segmental-any complete loss of bone in the supporting hemispheric structure of the acetabulum. • Cavitary-localized volumetric loss of bone that does not disrupt the acetabular rim.

15. ENGH AND GLASSMAN MODIFICATION OF THE AAOS CLASSIFICATION • The modified classification is simpler and consists of three categories: • Type I-mild • TypeII-moderate • Type III-severe* • *Protrusio acetabuli and pelvic discontinuity are subcategories of type III bone loss

16. CHANDLER AND PENENBERG CLASSIFICATION • This classification is based upon the anatomic division of the acetabulum into a superior wall, anterior and posterior columns, and a medial wall.

17. PAPROSKY CLASSIFICATION • This system is designed to assess failed total hip replacements • The main parameters that are assessed are: • 1. the degree of superior migration of the cup- >2cm or not • 2. lysis of the ischium-which is indicative of column bone loss • 3. the integrity of Kohler’s line-determines if anteromedial portion can support a prosthesis • 4. the presence or absence of a teardrop-indicating whether the inferomedial is able to allow osteointegration of a porous-coated component.

18. PAPROSKY CLASSIFICATION • Three different types of defects divided into subcategories:

19. PREOPERATIVE PLANNING • It is important to be aware of the limitations of assessing the bone deficiency preoperatively. • Frequently, the bone deficiency encountered after component removal is more extensive than suggested by preoperative imaging, and it is recommended that the surgical plan include a strategy to manage an unexpectedly larger deficiency.

20. Following radiographic assessment of bone deficiency, the degree of bone loss is classified and the reconstruction is planned with reference to 5 important questions: • 1. Is there sufficient host bone to allow a standard acetabular component to achieve stability and restore the center of rotation, with or without morcellized bone grafting but without structural grafting?

21. 2. Is there segmental acetabular deficiency that will require augmentation with structural allograft, or can a high hip center be accepted? • 3. Is the bone loss so severe that stable cup support and fixation will not be achieved by a simple segmental bone graft alone? • 4. Is there pelvic discontinuity? • 5. What is the best surgical approach for this procedure?

22. CONCLUSIONS • With adequate preoperative planning, the surgeon should have an assessment of the preoperative deficiencies associated with acetabular revision, including general patient factors and anatomic deficiencies that will require attention during the reconstruction. • It is imperative to have a comprehensive assessment of these factors, particularly the nature of the bone deficiency. • This will help predict potential problems and complications before discovering them intraoperatively.

23. REVISION ARTHROPLASTY OF THE ACETABULUM IN ASSOCIATION WITH LOSS OF BONE STOCK Allan E. Gross, MD Clive P. Duncan, MD Donald Garbuz, MD Elsayed Morsi Z. Mohamed, MBBCH, MS

24. INTRODUCTION • The goals of revision arthroplasty of the hip are to relieve pain and to improve function. These goals can be accomplished by insertion of a new implant with stable fixation of the interface and restoration (or at least near restoration) of the anatomy.

25. If there is no loss of bone stock, the anatomy may be restored by simply inserting a new implant. If there is loss of bone it should be categorized as a contained or uncontained defect and dealt with accordingly. • Contained, or cavitary, defects are more easily dealt with because the skeleton, while weakened, is basically intact. • Uncontained, or segmental, defects are more of a challenge.

26. Revision of the acetabular side of a total hip arthroplasty requires that considerable resources, including a variety of implants and banked bone, be available to the treating surgeon; that the surgeon be well versed in the use of comprehensive surgical exposures and the potential complications.

27. PRINCIPLES OF BONE GRAFTING • The treatment of bone defects on the acetabular side of an arthroplasty ranges from morcellized bone graft to large structural grafts. • Bone grafts can be classified as heterogenous grafts (bone from another species), allografts (bone from the same species), and autogenous grafts (bone from another part of the same individual).

28. TYPES OF BONE GRAFTS • Autogenous grafts have the advantage of being nonimmunogenic and, being the best at inducing new bone formation. • Their main disadvantage are that the supply of available bone is limited and that the strength, shape, and form of the graft usually cannot duplicate those of the bone that originally was present at the site of the deficit.

29. Allografts, in contrast, are available in large quantity, have very good initial strength, and can be shaped to fit almost any deficit. • However, they are expensive, immunogenic, and not as effective as autogenous grafts at inducing new-bone formation. • Allograft bone can be classified as morcellized or structural, depending on how it is used.

30. MORCELLIZED BONE • Morcellized bone (fragments of cancellous bone ranging from 5-10 mm in diameter) is used as a filler scaffold in contained defects. It can undergo revascularization and remolding, and it strengthens with time. • It is designed to be inserted without cement, at least 50% of the cup to make contact with host bone and screws will probably be necessary for fixation.

31. If it is not possible for at least 50% of the cup to make contact with host bone, then a roof-reinforcement ring and a cup that is designed to be inserted with cement.

32. STRUCTURAL GRAFTS • The advantages of structural grafts include the potential to restore the anatomy and to provide structural support for the implant • Disadvantages include revascularization and remolding that can lead to resorption, collapse, or both, and often weaken with time. • A structural graft is indicated for the treatment of an uncontained defect when it is necessary to restore the anatomy and limb length and provide support for the implant.

33. SIMULATED STRUCTURAL GRAFT • This term is used when bone from another anatomic region and is shaped to fit the deficit. • e.g.-the distal aspect of the femur can be sculpted to duplicate an acetabulum, or a femoral head can be sculpted to the desired shape.

34. ANATOMIC STRUCTURAL GRAFT • This term is used when the bone is from the same anatomic part as that being duplicated. • e.g.-an acetabular allograft can be used, in whole or in part, to replace an acetabular defect. • These grafts have been found easier to shape than simulated grafts.

35. STRUCTURAL ALLOGRAFTS • These grafts may fail because of resorption or fragmentation. It is therefore important to use an implant that extends from host bone to host bone, thereby bridging and protecting the graft. • It is important to use morcellized autogenous graft for bone grafting of the host bone-allograft junctions.

36. CLASSIFICATION OF BONE DEFECTS • Gross et al developed a simple, functional system for the classification of bone defects associated with loose hip implants. • These defects can usually be classified by plain radiograph but the final decision depends of intraoperative findings.

37. SURGICAL TECHNIQUE • Approach-a contained defect can be reconstructed through a conventional approach. • For a structural defect, it is preferred to have access to the anterior and posterior columns; therefore, a transtrochanteric approach or trochanteric slide is implemented.

38. The acetabulum is prepared after the hip has been dislocated. • After the cement and the component are removed, the defect is defined whether it is cavitary or segmental and then which type of reconstruction is necessary.

39. TYPE-I DEFECTS • Morcellized bone is compacted into the cavitary defect by reverse reaming. A porous-coated implant can be inserted without cement if it is possible for at least 50% of the cup to make contact with host bone. Screws are usually needed for fixation.

40. TYPE-I DEFECTS CONT. • If it is not possible for at least 50% of the cup to make contact with bleeding host bone, a roof-reinforcement ring is impacted superomedially and is held with 2 or 3 cancellous bone screws that are directed into the dome. the cup is then cemented into the ring.

41. TYPE-IIA DEFECTS • Structural acetabular allografts are used for the treatment of type-IIA segmental defects, which involve <50% of the acetabulum. • Because at least 50% of the cup will be in contact with host bone, the cup can be inserted with or without cement.

42. TYPE-IIB DEFECTS • Type-IIB segmental defects involve at least 50% of the acetabulum, and may be associated with pelvic discontinuity. • An acetabular allograft involving at least 50% of the acetabulum is fashioned to fit the defect with 6.5mm cancellous screws.

43. TYPE-IIB DEFECTS CONT. • Cavitary defects are filled with morcellized bone and a Burch-Schneider reconstruction ring extends from the ilium to the ischium used to protect the graft. • If fixation of the screws is not adequate, the cup must be inserted with cement.

44. OVERVIEW • In summary, cavitary defects are treated with impacted, morcellized allograft bone. If at least 50% of the cup will be in contact with host bone, the cup can be inserted without cement with screw fixation. • Otherwise, a roof-reinforcement ring should be used and inserted with cement.

45. OVERVIEW CONT. • If a segmental defect cannot be treated by placement of the cup at a high hip center, a structural allograft is used. • It is attempted to make contact between at least 50% of the cup and host bone so that a minor column or shelf graft can be used. • If it is not possible, a major column graft is used. Under these circumstances, the graft should be protected with a reconstruction ring and the cup should be cemented.

46. RESULTS • Success was defined as an increase of at least 20 points in the Harris hip score, a stable cup, and no need for an additional operation. • Hips revised with morcellized grafts only had a 90% success rate • Hips revised with a minor column had an 86% success rate • Use of major column allograft had a 55% success rate

47. CONCLUSIONS • The use of morcellized bone grafts for the treatment of cavitary defects and structural grafts that support <50% of the cup provide reproducible, encouraging results. • Structural grafts that support >50% of the cup are associated with a more guarded prognosis. • It is imperative that techniques be developed to improve the performance of large grafts rather than abandon their use.