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Hybrid total hip replacement
HYBRID TOTAL HIP REPLACEMENT WILLIAM MACAULAY, MD, and MICHAEL L. PARKS, MD
This article reviews the rationale and current knowledge regarding hybrid total hip arthroplasty. Patient selection, preoperative planning, and templating are covered in depth. The authors provide technical pearls regarding the surgical performance of hybrid total hip replacement using a posterolateral approach to the hip. Particular attention is given to acetabular component positioning, seating of the acetabular component, and formal repair of the posterior capsule and short external rotators. KEY WORDS: hip replacement, technique, review
Primary total hip arthroplasty (THA) is one of the most successful orthopedic procedures performed today. Hybrid THA (cemented femoral component and uncemented acetabulum component) is considered "state-of-the-art," as we enter the 21st century) Its effectiveness in relieving hip pain and reversing the functional loss caused by hip pathology is unparalleled. More than half of the 150,000 primary THAs performed each year in the United States are performed for primary or secondary osteoarthritis. Most of Sir John Charnley's pioneering advances in hip biomechanics, lubrication, biomaterials, prosthetic design, and operating theatre environment remain unchallenged to this day.-~He introduced these concepts into the performance of "low frictional torque arthroplasty" (LFA) at The Wrightington Centre For Hip Surgery. Although several technical improvements have been made over the past 40 years, many modifications to LFA have not withstood the test of time. With the advent of modular prosthetic femoral heads (and adjustable neck lengths), the trochanteric osteotomy has been abandoned. Also, for the active patient, cemented polyethylene acetabular cups are rarely used in the United States today. LFA was founded on the low friction principle which emphasized the use of a small diameter prosthetic head (22.225 mm) in combination with a large outer diameter socket with maximal plastic thickness. Originall}; Charnley used teflon (polytetrafluroethylene; PTFE), and in 1962 he switched to high-density polyethylene (HDPE) sockets. Charnley's choice of methacrylate as a grout for the femoral component proved serendipitous, and the material has not been significantly improved on to this day, even though the application technique has been significantly refined. Charnley's 20-year success with cemented femoral components has been reproduced in the United States with smooth femoral stems and first-generation cementing techniques. 3 This article reviewed minimum 20-year results of
From the Division of Hip and Knee Surgery, The Department of Orthopaedic Surgery, New York Presbyterian Hospital at Columbia University, New York, NY. Address reprint requests to William Macaulay, MD, Columbia University, 622 W. 168th Street, PH 1lth Floor, New York, NY 10032. Copyright ~ 2000 by W.B. Saunders Company 1048-6666/00/1002-0004510.00/0 doi: 10.1053/io.2000.5885
330 cemented prostheses placed from 1970 to 1972 in Iowa. Eighty-three patients with 98 THAs were still living and thus available for review. The mechanical failure rate for these 98 cemented femoral stems was 3%. These excellent long-term results corroborate Charnley's experience and are yet to be duplicated with uncemented femoral stems. Unfortunately, the excellent results observed on the femoral side by Charnley THAs were not equaled on the acetabular side, particularly beginning 10 to 12 years after surgery. For example, in the Iowa study mentioned previously,3 6% of cemented acetabular components required revision at 20 years. A far greater number had radiolucent lines that suggested loosening; but without adequate symptoms, they had not come to revision. This trend was noted in the United States during the 1980s--a decade now generally regarded as the decade of cement versus cementless. Many surgeons tried to avoid using cement completely (cementless THA), whereas others worked to preserve the cemented femoral component (and its excellent results) while using cementless fixation on metal-backed acetabular components--so-called hybrid THA. The early results (6.5 year average follow-up) of hybrid THA were excellent. 4 In this study of 65 consecutive, unselected standard primary hybrid total hip replacements, no sockets and no stems had loosened after a minimum 5-year follow-up. Intermediate~ and 10-year average follow-up~ studies of hybrid THA have likewise shown better than 95% excellent results without loosening.
PATIENT SELECTION It is of utmost importance to ensure that the patient's symptoms are directly attributable to the hip joint. A patient with the painful hip will generally hold his open hand over the ipsilateral inguinal region, describing the classic activity-related "groin pain" that worsens with weight-bearing. Lumbosacral pathology (which commonly refers symptoms to the hip area) must be considered and ruled out. Rarely, intrapelvic disorders such as hernia, vascular insufficiency, or intrapelvic tumor can cause hip activity-related pain. If other conditions coexist and the proportion of the pain caused by hip pathology is unclear, valuable prognostic information can be obtained with an intra-articular injection of a local anesthetic which will relieve the pain for patients with significant intra-
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articular hip pathology. On the other hand, hip pathology can frequently refer pain to the ipsilateral knee area. This finding can complicate the diagnosis because such patients may actually have apparent direct distal femoral (or even proximal tibial) bony tenderness. Like all medical personnel, the hip surgeon should take a thorough medical, family, and social history. A history of immunocompromised state, bleeding diathesis, or osteomalacia can be critical to perioperative management, implant choice, and patient selection. Information regarding the progression of hip pain and loss of function can be useful for choosing the appropriate timing of primary hybrid THA. How severe is the hip pain? How far can the patient walk? How easily can the patient negotiate stairs (with or without a banister), place socks, cut toenails, sit in a chair, get into a car, use public transportation, or engage in sexual activity? Perhaps the most useful question is: "Is your current hip situation acceptable?" The answer can be enlightening and can help guide the course of the encounter with the patient.
PREOPERATIVE PLANNING Preoperative planning for primary hybrid THA will help in being prepared and in optimizing the construct. It is a simpler task than planning for the revision THA. Preoperative planning begins with obtaining medical history, performing the physical examination, and selecting radiographic and laboratory workup. A detailed medical history will help assess the severity of hip pain and rule out other sources such as referred pain from the spine. The thorough physical examination will yield information regarding leg length, pelvic obliquity, and neurovascular abnormality. A selective radiographic and laboratory workup will save money by eliminating unnecessary tests and by decreasing complications. Preoperative planning for the unoperated hip is simpler because there is no previous incision, altered anatomy, or hardware. Proper hip mechanics can be restored by the careful templating of high-quality radiographs. Excessive magnification should always be considered in patients with extreme body habitus. Although the radiographic magnification of the "average" patient approximates 15%, very thin patients have magnification of 12.5%, whereas obese patients can have magnification of upwards of 25%. 7 The center of rotation, offset, and leg length can be restored while also providing a construct with good range of motion that is not prone to dislocation. The principles of primary hybrid THA templating are simpler when cemented cups and uncemented femoral components are used; however, uncemented femoral components require more precision on the anteroposterior (AP) and lateral radiographs. Templating for primary hybrid THA should begin with the acetabular side, as described by Eduardo Salvati, MD (see Table 1). On the AP pelvis radiograph, a dot is placed at the inferolateral border of the teardrop and another dot at the superolateral margin of the acetabulum. The convex side of the acetabular template is then juxtaposed to these dots at approximately a 40 ° abduction angle. The projected center of rotation is marked with a dot. At this point, a decision must be made regarding leg
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TABLE 1. Preoperative Templating for Primary Hybrid Total Hip Replacement I. Position the acetabular component A. Place two dots: inferolateral teardrop and superolateral acetabulum B. Superimpose acetabular template at 40 ° abduction C. Place dot at center of rotation (COR) 13. Record probable cup size II. Leg Length/Offset Decision A. "X" at proposed COR relative to the femur II1. Position the femoral stem A. Superimpose stem template: neck length = 0 mm B. Mark neck cut C. Record stem size, + / - collar, regular vs extented offset and head size IV. Complete the templating A. Record lesser trochanter (LT) to cut distance B. Record LT to COR distance C. Record proximal/medial stem to medial cortex distance Ii). Measure and record centralizer size E. Record restrictor size IV. Doublechecks during surgery (some are optional) A. Measure LT to COR prior to neck cut B. Is the cup the anticipated size? C. Is the LT to cut measure what you expected? D. Is the broach the anticipatedsize? E. Does the trial stem have enough "play"? F. Is the medial stem to cortex distance what was anticipated? G. Is the LT to COR distance what was anticipated? H. Trial reduction to check ROM and stability Goals: To reproducibly anticipate the location of the center of rotation and confidently restore leg length and hip range of motion in a planned fashion, (Avoid skirted necks, elevated liners, stem collar which will impinge, too little offset, excessive operating room time, constrained liners, lateralization of the cup, varus or valgus stems, deficient cement mantles, liners that are too thin/heads that are too big or small, etc.) Requirements: Medical history and physical examination; selective radiography (high-quality AP pelvis and frog lateral of the affected hip); templates.
length. The preoperative information gathered from the block test and clinical examination of leg length is essential and should coincide with the relative hip length on the AP pelvis radiograph. For example, one can draw the interteardrop line (a line connecting the nadirs of the teardrops) and place a dot at this level on both femora. Then, the difference in height relative to the lesser trochanter is calculated. Usually, the arthritic side is short, and this difference should be added by placing an "X" that same distance directly above the proposed center of rotation of the templated acetabulum. The surgeon will want this templated center of the prosthetic head to fall over this "X" as well. Careful consideration must be given to lengthening more than 3 cm. Restoring equal leg lengths is not always desirable in patients with long-standing shortening because compensatory mechanisms may be established in the lumbosacral spine, knee, and ankle. Patients may perceive the reconstructed limb to be long when equalized and thus may be unhappy. The preoperative application of the block test is the best way to predict this and if in doubt, shortening is better tolerated than lengthening.
TECHNICAL PEARLS Asepsis Aseptic technique is essential for ensuring that the primary hybrid THA operative wound site is exposed to as low a bacterial load as possible. Isolator suits, a clean air laminar flow enclosure, and perioperative antibiotics should be
MACAULAYAND PARKS
used whenever possible. Isolator suits control bacterial shedding by the operative team members in the enclosure. 2 Traffic in the operating room should be kept to a minimum. Clean air filters 99.9% of particles larger than I lam (thus all bacteria). 8 Laminar flow can direct airborne particles (and bacteria) away from the wound. Anesthesia personnel and the patient's upper body should remain outside the enclosure. Frequent pulse lavage and intraoperative antibiotics can help purge those bacteria that do settle in the operative wound.8
Pelvic Positioning: The Key to Acetabular Component
Positioning
Patients should be in the lateral position on a customdesigned hip table (Medrecon, Garwood, NJ). This table has a height-adjustable pelvic holder that uses a vertical padded rest over the sacrum and a shorter concave padded rest over the pubis. This holder prevents forward/ backward rolling of the pelvis. The height adjustment feature allows the pelvis to be positioned neutrally and held snugly--thus avoiding tilting of the pelvis in all planes. This firm, neutral positioning of the pelvis reduces the guesswork involved in positioning the acetabular component in the correct abduction and anteversion. Although we prefer to position the acetabular component in 40 ° abduction and 20 ° anteversion in most cases, it will take anatomical clues to adjust the version once osteophytes are removed.
Surgical Technique We use the posterolateral approach for all primary hybrid THA cases. Many clinicians caution that this approach increases the rate of dislocation. However, dislocation will rarely occur if the components are positioned with proper version and abduction and the external rotators and posterior capsule are formally repaired. Protection of the skin edges and peri-incisional tissues (with a delicate touch, proper retractor placement, and avoidance of selfretaining retractors) is our preference during the approach. With the patient positioned as described previously, bony landmarks and the intended incision are marked with a pen. The superior, posterior, and anterior margins of the greater trochanter of the femur are marked. The curvilinear skin incision should be centered over the acetabulum where the bulk of the work is to be performed. The length of the incision will depend on the size of the patient and the depth of the surgical wound. It should be long enough to perform the operation with minimal trauma to the surrounding tissues; however, care should be taken not to make it unnecessarily long. The lower part of the incision is linear from the top of the trochanter (in-line with the femur) and centered slightly posteriorly. The upper part of the incision curves posteriorly at an angle of approximately 140 ° relative to the inferior linear portion. The incision is carried through the skin (and subcutaneous tissues in-line with the skin incision) using a large blade. A fresh No. 11 blade is used to incise the tensor and gluteal fascia in-line with the skin incision. Hemostasis is achieved using electrocautery. This fascial incision should be made directly lateral to the greater trochanter with care given not to injure the underlying vastus lateralis fascia.
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The appropriately centered fascial incision will be rewarded with the absence of tensor or gluteal musculature lateral to the greater trochanter. Superiorly, the gluteus maximus should be divided bluntly after completing the fascial incision. The sciatic nerve is identified posteriorly and deep within the wound. The gluteal sling is located inferiorly and posteriorly and divided using electrocautery over its proximal half after being held under tension with a Hibbs retractor. Care is taken to avoid the perforating vessels immediately beneath the gluteal sling. After dividing the trochanteric bursa, the posterior border of the gluteus medius is identified, and the piriformis tendon is palpated with an index finger. A thin Hohmann retractor (bent mid-shaft at a right angle; thinbent Hohmann) is placed over the piriformis tendon and under the posterior border of the gluteus minimus muscle, which has been separated from the capsule using a Cobb elevator. Next, an Aufranc retractor is swept from the piriformis tendon, along the posterior capsule, under the femoral neck. With the appropriate amount of pressure, this maneuver exposes the piriformis and conjoined tendons, which are divided at their insertion on the greater trochanter and separately tagged with "short" No. 2 braided nonabsorbable suture. These "short" external rotators are retracted posteriorly to further protect the sciatic nerve, and the entire posterior capsule is thus exposed. A posterior capsular flap is then created by incising the capsule at its insertion on the posterior intertrochanteric crest area of the neck. For example, for a right hip, the capsule is incised posterosuperiorly toward the 10 to 11 o'clock position (along the inferior border of the gluteus minimus) back to the edge of the acetabulum, incising the labrum. A similar linear incision is made in the capsule from the lower posterior femoral neck, posteroinferiorly toward the 7 o'clock position, stopping near the tip of (but not touching) the Aufranc retractor. Particular care is given to protect the sciatic nerve. This posterior capsular flap is then tagged with two "long" No. 2 braided nonabsorbable sutures (spread by 1 to I~A cm) at its distal base and retracted posteriorly. The femoral head is gently dislocated by internal rotation and flexion of the hip, bringing the femoral head to be replaced superficially into the wound. Two tagging sutures (No. 0 absorbables) are then placed proximally within the superior half of the quadratus femoris muscle which is divided with electrocautery. Care is taken to cauterize the medial femoral circumflex artery before it is transected, and the posterior femoral neck is completely denuded of soft tissue. As a result, the proximal aspect of the lesser trochanter is visualized, and the femoral neck cut can be marked at an appropriate height above the lesser trochanter as templated preoperatively. We prefer to use a reciprocating saw for the femoral neck osteotomy. The orientation of this osteotomy should avoid flexion and extension, which can be made technically easier by placing soft goods below the knee so that the femur is parallel with the floor while the leg is kept vertical. The angle of the osteotomy relative to the long axis of the length of this osteotomy from the neck toward the greater trochanter is determined based on the proximal geometry of the implants and insertion devices. Care is taken to avoid overly thinning the greater trochanter because this will predispose it to fracture. After the
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osteotomy is made with the reciprocating saw, the wound is lavaged to remove bone debris (and its associated osteoblast and osteoinductive factors, ie, bone morphogenetic proteins) to decrease the risk of postoperative heterotopic ossification. If there are significant subchondral cysts on the pelvic side, cancellous autograft bone is removed and prepared for later insertion into these defects. The remainder of the femoral head is kept sterile, but prepared for delivery to the surgical pathology department, Attention is then focused on the acetabulum as unsterile personnel tilt the hip table 20 ° posteriorly. Exposure of the acetabulum is obtained with the hip in extension, which is critical for precise positioning of the acetabular cup. First, a "C-retractor" is placed over the anterior lip of the acetabulum, further moving the femur anteriorly. The remaining capsule and reflected head of the rectus femoris are divided at "1 o'clock" on the acetabulum (relaxing the anterior capsule more and further improving anterior exposure), and a smooth Steinman pin placed into the pelvis 2 cm above the acetabulum, improving superior and anterior visualization by retracting the gluteus minimus and medius. The Aufranc retractor is placed inferiorly adjacent and distal to the capsule enhancing inferior exposure. A "wide-bent" Hohmann retractor is then placed outside the labrum, but inside the capsule, and secured into the ischium with gentle taps with the mallet. Care is taken to avoid injuring the sciatic nerve during this maneuver. If these steps are followed, the acetabulum is clearly exposed, and acetabular preparation reaming can be performed easily. The labrum and soft tissue pulvinar within the acetabular notch can now be removed using a long-handled scalpel and a large curette, respectively. Hemispheric reaming is begun at 6 to 8 mm below the preoperatively templated size and directed medially toward the quadrilateral surface. Preoperative radiographs will help the surgeon anticipate how much medialization is necessary based on thickness of the tear drop. In cases of severe osteoarthritis, the head of the femur is lateralized relative to the tear drop with interposition of large medial osteophytes. These osteophytes must not be confused with the medial wall. If there is confusion, a drill bit is used judiciously to gauge the location of the quadrilateral plate by drilling medially. Once reaming medially has abutted the quadrilateral surface, reaming is performed at the desired version angles (40° abduction and 20 ° anteversion), preserving the medial wall. Reaming is continued with sequentially larger reamers (increasing by 2 mm increments). As the reamers increase in size, the entire surface of the acetabulum is reamed. Bleeding corticocancellous bone should comprise the entire hemisphere to receive the pressfit shell. A pressfit trial is tried when the reamer's diameter is approximately 2 mm smaller than the size that was preoperatively templated. The preoperatively templated acetabular shell is then pressfit into the socket, which has been under-reamed by 2 mm. Contained cystic defects can be filled with the cancellous autograft from the native femoral head as mentioned previously. We prefer using a cluster hole cup so that 1 or 2 screws can be inserted into the posterosuperior safe zone, ~ but we actually insert screws in less than 20% of patients. Pressfit fixation will often allow for lifting the patient's pelvis off 11 8
the operating room table with a Kocher clamp. The holes are also beneficial to judge complete seating of the acetabular component. Some uncoverage is accepted laterally to achieve 40 ° abduction if fixation is not compromised. The desired polyethylene liner (selected based on thickness, internal diameter, wear prognosis, and posterior elevation) is inserted under direct visualization without intervening soft tissue and impacted into place. Engagement of the locking mechanism is verified, and any residual anterior or posterior osteophyte is removed at this time with an osteotome. Retractors are removed, the wound is lavaged, and attention is then focused on the femoral side. The leg is brought into 90 ° of hip internal rotation, flexion, and adduction so that the surgeon can prepare the proximal femur. The surgeon should be aware that this position twists the proximal vasculature of the lower extremity; thus, the duration of this position should be limited to decrease the risk of postoperative deep venous thrombosis. Exposure is ensured with the use of a "Stinchfield" retractor anterior to the femoral neck and an Aufranc medially adjacent to the jaws. A crown (or thin-bent Hohmann) retractor protects the abductor musculature during broaching. Soft tissue is removed from the area of the neck and posterior greater trochanter. Anterior femoral osteophytes should also be removed at this time. The femoral neck osteotomy is revised with the reciprocating saw, if necessary. A canal finder will identify the long axis of the femur. Femoral canal broaching is performed based on a prosthesis-specific protocol in the desired anteversion with sequentially larger broaches. Again, fatty exudate from the canal (with osteoinductive biological factors) is suctioned to decrease the risk of postoperative heterotopic ossification. Enough space is created for a 2-mm minimum cement column. Trial reduction can be performed with modular broaches and a head and neck assembly or with a separate trial prosthesis. The lesser trochanter to center of head distance should be measured and can be matched within 2 mm in most patients. The trial reduction ensures that soft tissue balance, range of motion, and hip joint stability has been achieved. The trials are removed and the cement restrictor is placed to the desired depth (1-1Acm distal to the tip of the prosthesis). The canal is thoroughly irrigated, cleaned of debris, and dried with vaginal packing as the cement is mixed. The canal is filled in retrograde fashion using a cement gun with polymethylmethacrylate cement of the appropriate consistency with pressurization. The femoral stem is inserted within the cement column (with associated distal or proximal centralizers) in the desired anteversion and neutral varus/valgus alignment. Excess cement is removed, and care is taken not to sink the prosthesis too deeply if it is of a collarless design. The cement is then allowed to cure. The templated modular femoral head is tapped into place on the Morse taper, and the construct is gently relocated under visualization. The posterior capsular flap and short external rotators are formally repaired by placing the "long" and "short" braided sutures through drill holes in the posterior greater trochanter with Keith needles and tying them separately. The wound is vigorously irrigated with antibiotic-laden saline to remove any remaining bone, soft tissue, or cement debris. The tensor fascia latae is repaired with interrupted No. 2 nonabsorbMACAULAYAND PARKS
able suture beginning distally. As this closure approaches the trochanteric flare, two small tubes to a self-suction drain are placed u n d e r the tensor fascia anteroinferiorly exiting 5 cm from the w o u n d edge. The surgeon m a y decide to use figure-of-eight knots over the greater trochanter. As the closure of the tensor layer a p p r o a c h e s thin fascia superiorly, absorbable No. 0 suture should be used. This s a m e suture can be used for inverted deep s u b c u t a n e o u s knots, but 2-0's should be used i m m e d i a t e l y subcutaneously. Staples are applied on the skin. We cover the w o u n d with nonstick antibacterial dressing, gauze, and two abdominal pads. This dressing is covered loosely with w r a p s with minimal elastic capacity in a hip spica fashion. Placement of the hip spica is facilitated b y using the hip table m e n t i o n e d previously.
mandatory. An assistant familiar with both h u m a n hip a n a t o m y and the surgeon's technique will help simplify the procedure. In an academic setting, the assistant(s) change on a rotational basis. The time of these rotational stints should be m a x i m i z e d for efficiency, but not be so long so as to c o m p r o m i s e the assistant diversity of training. We prefer that the surgeon stand behind the laterally positioned patient, with the first assistant on the s a m e side of the operating room table toward the foot. The last assistant stands in front of the patient toward the foot and holds the patient's leg w h e n needed. The second assistant, if available, stands opposite to the surgeon.
REFERENCES
The Operative Team The p r i m a r y T H A operative team consists of the surgeon, anesthesiologist, surgical assistant(s), scrub technician, and circulator. The team that w o r k s together m o s t often will be the most efficient, with all m e m b e r s being able to anticipate the next step of the procedure and avoid unnecessary delays. Decreasing operative time is important for minimizing the incidence of infection and v e n o u s t h r o m b o e m b o lism. Although remaining outside the enclosure, the anesthesiologist and circulator are integral parts of the operative team. The THA-efficient anesthesiologist helps minimize patient preparation and room turnover time. He or she is proficient in regional anesthesia (epidural and spinal) which can be refined with deliberate intraoperative h y p o tension 1° which will lower blood loss and not fluid overload the patient. The efficient circulator will anticipate potential delays or p r o b l e m s and will h a v e e q u i p m e n t and supplies ready on request, thereby decreasing surgical time. For the surgical technique (involving a posterolateral a p p r o a c h to the hip) outlined in this article, two or three surgical assistants are preferable. One surgical assistant is
HYBRID THR
1. National Institutes of Health Concensus Statement of Total Hip Replacement. 12:12-14, 1994 2. Charnley J: Low Friction Arthroplas~,: TheoD, and Practice. London, Churchill Livingstone, 1979 3. Schulte KR, Callahan JJ, Kelley SS, et al: The outcome of Charnley total hip arthroplas~, with cement after a minimum twenl3.,-year follow up. J Bone Joint Surg 75A:961-975, 1993 4. Harris WH: Hybrid total hip replacement: Rationale & intermediate clinical results. Clin Orthop 333:155-164, 1996 5. Berger RA, Kull LR, Rosenberg AG, et al: Hybrid total hip arthroplasty: 7- to 10-year results. Clin Orthop 333:134-146, 1996 6. Clohisy JC, Harris WH: Primary hybrid total hip replacement, performed with insertion of the acetabular component without cement and a precoat femoral component with cement. An average ten-year fo|low-up study. J BoneJoint Surg Am 81:247-255, 1999 7. Clarke IC, Gruen T, Matos M, et al: Improved methods for quantitative radiographic evaluation with particular reference to total hip arthroplasty. Clin Orthop 121:83-91, 1976 8. Lidwell OA, Lowbury EJL, Whyte W, et al: Effect of ultraclean air in operating rooms on deep joint sepsis in the joint after total hip or knee replacement: A randomized stud,,,. Br Med J 285:10-14, 1982 9. Wasielewski RC, Cooperstein LA, Kruger MP, et al: Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg 72(A):501-508, 1990 10. Sharrock NE, Mineo R, Urquhart B: Hemodynamic response to low-dose epinephrine infusion during hypotensive epidural anesthesia for total hip replacement. Reg Anesth 15:295-299, 1990
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This article reviews the rationale and current knowledge regarding hybrid total hip arthroplasty. Patient selection, preoperative planning, and templating are covered in depth. The authors provide technical pearls regarding the surgical performance of hybrid total hip replacement using a posterolateral approach to the hip. Particular attention is given to acetabular component positioning, seating of the acetabular component, and formal repair of the posterior capsule and short external rotators. KEY WORDS: hip replacement, technique, review
Primary total hip arthroplasty (THA) is one of the most successful orthopedic procedures performed today. Hybrid THA (cemented femoral component and uncemented acetabulum component) is considered "state-of-the-art," as we enter the 21st century) Its effectiveness in relieving hip pain and reversing the functional loss caused by hip pathology is unparalleled. More than half of the 150,000 primary THAs performed each year in the United States are performed for primary or secondary osteoarthritis. Most of Sir John Charnley's pioneering advances in hip biomechanics, lubrication, biomaterials, prosthetic design, and operating theatre environment remain unchallenged to this day.-~He introduced these concepts into the performance of "low frictional torque arthroplasty" (LFA) at The Wrightington Centre For Hip Surgery. Although several technical improvements have been made over the past 40 years, many modifications to LFA have not withstood the test of time. With the advent of modular prosthetic femoral heads (and adjustable neck lengths), the trochanteric osteotomy has been abandoned. Also, for the active patient, cemented polyethylene acetabular cups are rarely used in the United States today. LFA was founded on the low friction principle which emphasized the use of a small diameter prosthetic head (22.225 mm) in combination with a large outer diameter socket with maximal plastic thickness. Originall}; Charnley used teflon (polytetrafluroethylene; PTFE), and in 1962 he switched to high-density polyethylene (HDPE) sockets. Charnley's choice of methacrylate as a grout for the femoral component proved serendipitous, and the material has not been significantly improved on to this day, even though the application technique has been significantly refined. Charnley's 20-year success with cemented femoral components has been reproduced in the United States with smooth femoral stems and first-generation cementing techniques. 3 This article reviewed minimum 20-year results of
From the Division of Hip and Knee Surgery, The Department of Orthopaedic Surgery, New York Presbyterian Hospital at Columbia University, New York, NY. Address reprint requests to William Macaulay, MD, Columbia University, 622 W. 168th Street, PH 1lth Floor, New York, NY 10032. Copyright ~ 2000 by W.B. Saunders Company 1048-6666/00/1002-0004510.00/0 doi: 10.1053/io.2000.5885
330 cemented prostheses placed from 1970 to 1972 in Iowa. Eighty-three patients with 98 THAs were still living and thus available for review. The mechanical failure rate for these 98 cemented femoral stems was 3%. These excellent long-term results corroborate Charnley's experience and are yet to be duplicated with uncemented femoral stems. Unfortunately, the excellent results observed on the femoral side by Charnley THAs were not equaled on the acetabular side, particularly beginning 10 to 12 years after surgery. For example, in the Iowa study mentioned previously,3 6% of cemented acetabular components required revision at 20 years. A far greater number had radiolucent lines that suggested loosening; but without adequate symptoms, they had not come to revision. This trend was noted in the United States during the 1980s--a decade now generally regarded as the decade of cement versus cementless. Many surgeons tried to avoid using cement completely (cementless THA), whereas others worked to preserve the cemented femoral component (and its excellent results) while using cementless fixation on metal-backed acetabular components--so-called hybrid THA. The early results (6.5 year average follow-up) of hybrid THA were excellent. 4 In this study of 65 consecutive, unselected standard primary hybrid total hip replacements, no sockets and no stems had loosened after a minimum 5-year follow-up. Intermediate~ and 10-year average follow-up~ studies of hybrid THA have likewise shown better than 95% excellent results without loosening.
PATIENT SELECTION It is of utmost importance to ensure that the patient's symptoms are directly attributable to the hip joint. A patient with the painful hip will generally hold his open hand over the ipsilateral inguinal region, describing the classic activity-related "groin pain" that worsens with weight-bearing. Lumbosacral pathology (which commonly refers symptoms to the hip area) must be considered and ruled out. Rarely, intrapelvic disorders such as hernia, vascular insufficiency, or intrapelvic tumor can cause hip activity-related pain. If other conditions coexist and the proportion of the pain caused by hip pathology is unclear, valuable prognostic information can be obtained with an intra-articular injection of a local anesthetic which will relieve the pain for patients with significant intra-
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articular hip pathology. On the other hand, hip pathology can frequently refer pain to the ipsilateral knee area. This finding can complicate the diagnosis because such patients may actually have apparent direct distal femoral (or even proximal tibial) bony tenderness. Like all medical personnel, the hip surgeon should take a thorough medical, family, and social history. A history of immunocompromised state, bleeding diathesis, or osteomalacia can be critical to perioperative management, implant choice, and patient selection. Information regarding the progression of hip pain and loss of function can be useful for choosing the appropriate timing of primary hybrid THA. How severe is the hip pain? How far can the patient walk? How easily can the patient negotiate stairs (with or without a banister), place socks, cut toenails, sit in a chair, get into a car, use public transportation, or engage in sexual activity? Perhaps the most useful question is: "Is your current hip situation acceptable?" The answer can be enlightening and can help guide the course of the encounter with the patient.
PREOPERATIVE PLANNING Preoperative planning for primary hybrid THA will help in being prepared and in optimizing the construct. It is a simpler task than planning for the revision THA. Preoperative planning begins with obtaining medical history, performing the physical examination, and selecting radiographic and laboratory workup. A detailed medical history will help assess the severity of hip pain and rule out other sources such as referred pain from the spine. The thorough physical examination will yield information regarding leg length, pelvic obliquity, and neurovascular abnormality. A selective radiographic and laboratory workup will save money by eliminating unnecessary tests and by decreasing complications. Preoperative planning for the unoperated hip is simpler because there is no previous incision, altered anatomy, or hardware. Proper hip mechanics can be restored by the careful templating of high-quality radiographs. Excessive magnification should always be considered in patients with extreme body habitus. Although the radiographic magnification of the "average" patient approximates 15%, very thin patients have magnification of 12.5%, whereas obese patients can have magnification of upwards of 25%. 7 The center of rotation, offset, and leg length can be restored while also providing a construct with good range of motion that is not prone to dislocation. The principles of primary hybrid THA templating are simpler when cemented cups and uncemented femoral components are used; however, uncemented femoral components require more precision on the anteroposterior (AP) and lateral radiographs. Templating for primary hybrid THA should begin with the acetabular side, as described by Eduardo Salvati, MD (see Table 1). On the AP pelvis radiograph, a dot is placed at the inferolateral border of the teardrop and another dot at the superolateral margin of the acetabulum. The convex side of the acetabular template is then juxtaposed to these dots at approximately a 40 ° abduction angle. The projected center of rotation is marked with a dot. At this point, a decision must be made regarding leg
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TABLE 1. Preoperative Templating for Primary Hybrid Total Hip Replacement I. Position the acetabular component A. Place two dots: inferolateral teardrop and superolateral acetabulum B. Superimpose acetabular template at 40 ° abduction C. Place dot at center of rotation (COR) 13. Record probable cup size II. Leg Length/Offset Decision A. "X" at proposed COR relative to the femur II1. Position the femoral stem A. Superimpose stem template: neck length = 0 mm B. Mark neck cut C. Record stem size, + / - collar, regular vs extented offset and head size IV. Complete the templating A. Record lesser trochanter (LT) to cut distance B. Record LT to COR distance C. Record proximal/medial stem to medial cortex distance Ii). Measure and record centralizer size E. Record restrictor size IV. Doublechecks during surgery (some are optional) A. Measure LT to COR prior to neck cut B. Is the cup the anticipated size? C. Is the LT to cut measure what you expected? D. Is the broach the anticipatedsize? E. Does the trial stem have enough "play"? F. Is the medial stem to cortex distance what was anticipated? G. Is the LT to COR distance what was anticipated? H. Trial reduction to check ROM and stability Goals: To reproducibly anticipate the location of the center of rotation and confidently restore leg length and hip range of motion in a planned fashion, (Avoid skirted necks, elevated liners, stem collar which will impinge, too little offset, excessive operating room time, constrained liners, lateralization of the cup, varus or valgus stems, deficient cement mantles, liners that are too thin/heads that are too big or small, etc.) Requirements: Medical history and physical examination; selective radiography (high-quality AP pelvis and frog lateral of the affected hip); templates.
length. The preoperative information gathered from the block test and clinical examination of leg length is essential and should coincide with the relative hip length on the AP pelvis radiograph. For example, one can draw the interteardrop line (a line connecting the nadirs of the teardrops) and place a dot at this level on both femora. Then, the difference in height relative to the lesser trochanter is calculated. Usually, the arthritic side is short, and this difference should be added by placing an "X" that same distance directly above the proposed center of rotation of the templated acetabulum. The surgeon will want this templated center of the prosthetic head to fall over this "X" as well. Careful consideration must be given to lengthening more than 3 cm. Restoring equal leg lengths is not always desirable in patients with long-standing shortening because compensatory mechanisms may be established in the lumbosacral spine, knee, and ankle. Patients may perceive the reconstructed limb to be long when equalized and thus may be unhappy. The preoperative application of the block test is the best way to predict this and if in doubt, shortening is better tolerated than lengthening.
TECHNICAL PEARLS Asepsis Aseptic technique is essential for ensuring that the primary hybrid THA operative wound site is exposed to as low a bacterial load as possible. Isolator suits, a clean air laminar flow enclosure, and perioperative antibiotics should be
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used whenever possible. Isolator suits control bacterial shedding by the operative team members in the enclosure. 2 Traffic in the operating room should be kept to a minimum. Clean air filters 99.9% of particles larger than I lam (thus all bacteria). 8 Laminar flow can direct airborne particles (and bacteria) away from the wound. Anesthesia personnel and the patient's upper body should remain outside the enclosure. Frequent pulse lavage and intraoperative antibiotics can help purge those bacteria that do settle in the operative wound.8
Pelvic Positioning: The Key to Acetabular Component
Positioning
Patients should be in the lateral position on a customdesigned hip table (Medrecon, Garwood, NJ). This table has a height-adjustable pelvic holder that uses a vertical padded rest over the sacrum and a shorter concave padded rest over the pubis. This holder prevents forward/ backward rolling of the pelvis. The height adjustment feature allows the pelvis to be positioned neutrally and held snugly--thus avoiding tilting of the pelvis in all planes. This firm, neutral positioning of the pelvis reduces the guesswork involved in positioning the acetabular component in the correct abduction and anteversion. Although we prefer to position the acetabular component in 40 ° abduction and 20 ° anteversion in most cases, it will take anatomical clues to adjust the version once osteophytes are removed.
Surgical Technique We use the posterolateral approach for all primary hybrid THA cases. Many clinicians caution that this approach increases the rate of dislocation. However, dislocation will rarely occur if the components are positioned with proper version and abduction and the external rotators and posterior capsule are formally repaired. Protection of the skin edges and peri-incisional tissues (with a delicate touch, proper retractor placement, and avoidance of selfretaining retractors) is our preference during the approach. With the patient positioned as described previously, bony landmarks and the intended incision are marked with a pen. The superior, posterior, and anterior margins of the greater trochanter of the femur are marked. The curvilinear skin incision should be centered over the acetabulum where the bulk of the work is to be performed. The length of the incision will depend on the size of the patient and the depth of the surgical wound. It should be long enough to perform the operation with minimal trauma to the surrounding tissues; however, care should be taken not to make it unnecessarily long. The lower part of the incision is linear from the top of the trochanter (in-line with the femur) and centered slightly posteriorly. The upper part of the incision curves posteriorly at an angle of approximately 140 ° relative to the inferior linear portion. The incision is carried through the skin (and subcutaneous tissues in-line with the skin incision) using a large blade. A fresh No. 11 blade is used to incise the tensor and gluteal fascia in-line with the skin incision. Hemostasis is achieved using electrocautery. This fascial incision should be made directly lateral to the greater trochanter with care given not to injure the underlying vastus lateralis fascia.
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The appropriately centered fascial incision will be rewarded with the absence of tensor or gluteal musculature lateral to the greater trochanter. Superiorly, the gluteus maximus should be divided bluntly after completing the fascial incision. The sciatic nerve is identified posteriorly and deep within the wound. The gluteal sling is located inferiorly and posteriorly and divided using electrocautery over its proximal half after being held under tension with a Hibbs retractor. Care is taken to avoid the perforating vessels immediately beneath the gluteal sling. After dividing the trochanteric bursa, the posterior border of the gluteus medius is identified, and the piriformis tendon is palpated with an index finger. A thin Hohmann retractor (bent mid-shaft at a right angle; thinbent Hohmann) is placed over the piriformis tendon and under the posterior border of the gluteus minimus muscle, which has been separated from the capsule using a Cobb elevator. Next, an Aufranc retractor is swept from the piriformis tendon, along the posterior capsule, under the femoral neck. With the appropriate amount of pressure, this maneuver exposes the piriformis and conjoined tendons, which are divided at their insertion on the greater trochanter and separately tagged with "short" No. 2 braided nonabsorbable suture. These "short" external rotators are retracted posteriorly to further protect the sciatic nerve, and the entire posterior capsule is thus exposed. A posterior capsular flap is then created by incising the capsule at its insertion on the posterior intertrochanteric crest area of the neck. For example, for a right hip, the capsule is incised posterosuperiorly toward the 10 to 11 o'clock position (along the inferior border of the gluteus minimus) back to the edge of the acetabulum, incising the labrum. A similar linear incision is made in the capsule from the lower posterior femoral neck, posteroinferiorly toward the 7 o'clock position, stopping near the tip of (but not touching) the Aufranc retractor. Particular care is given to protect the sciatic nerve. This posterior capsular flap is then tagged with two "long" No. 2 braided nonabsorbable sutures (spread by 1 to I~A cm) at its distal base and retracted posteriorly. The femoral head is gently dislocated by internal rotation and flexion of the hip, bringing the femoral head to be replaced superficially into the wound. Two tagging sutures (No. 0 absorbables) are then placed proximally within the superior half of the quadratus femoris muscle which is divided with electrocautery. Care is taken to cauterize the medial femoral circumflex artery before it is transected, and the posterior femoral neck is completely denuded of soft tissue. As a result, the proximal aspect of the lesser trochanter is visualized, and the femoral neck cut can be marked at an appropriate height above the lesser trochanter as templated preoperatively. We prefer to use a reciprocating saw for the femoral neck osteotomy. The orientation of this osteotomy should avoid flexion and extension, which can be made technically easier by placing soft goods below the knee so that the femur is parallel with the floor while the leg is kept vertical. The angle of the osteotomy relative to the long axis of the length of this osteotomy from the neck toward the greater trochanter is determined based on the proximal geometry of the implants and insertion devices. Care is taken to avoid overly thinning the greater trochanter because this will predispose it to fracture. After the
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osteotomy is made with the reciprocating saw, the wound is lavaged to remove bone debris (and its associated osteoblast and osteoinductive factors, ie, bone morphogenetic proteins) to decrease the risk of postoperative heterotopic ossification. If there are significant subchondral cysts on the pelvic side, cancellous autograft bone is removed and prepared for later insertion into these defects. The remainder of the femoral head is kept sterile, but prepared for delivery to the surgical pathology department, Attention is then focused on the acetabulum as unsterile personnel tilt the hip table 20 ° posteriorly. Exposure of the acetabulum is obtained with the hip in extension, which is critical for precise positioning of the acetabular cup. First, a "C-retractor" is placed over the anterior lip of the acetabulum, further moving the femur anteriorly. The remaining capsule and reflected head of the rectus femoris are divided at "1 o'clock" on the acetabulum (relaxing the anterior capsule more and further improving anterior exposure), and a smooth Steinman pin placed into the pelvis 2 cm above the acetabulum, improving superior and anterior visualization by retracting the gluteus minimus and medius. The Aufranc retractor is placed inferiorly adjacent and distal to the capsule enhancing inferior exposure. A "wide-bent" Hohmann retractor is then placed outside the labrum, but inside the capsule, and secured into the ischium with gentle taps with the mallet. Care is taken to avoid injuring the sciatic nerve during this maneuver. If these steps are followed, the acetabulum is clearly exposed, and acetabular preparation reaming can be performed easily. The labrum and soft tissue pulvinar within the acetabular notch can now be removed using a long-handled scalpel and a large curette, respectively. Hemispheric reaming is begun at 6 to 8 mm below the preoperatively templated size and directed medially toward the quadrilateral surface. Preoperative radiographs will help the surgeon anticipate how much medialization is necessary based on thickness of the tear drop. In cases of severe osteoarthritis, the head of the femur is lateralized relative to the tear drop with interposition of large medial osteophytes. These osteophytes must not be confused with the medial wall. If there is confusion, a drill bit is used judiciously to gauge the location of the quadrilateral plate by drilling medially. Once reaming medially has abutted the quadrilateral surface, reaming is performed at the desired version angles (40° abduction and 20 ° anteversion), preserving the medial wall. Reaming is continued with sequentially larger reamers (increasing by 2 mm increments). As the reamers increase in size, the entire surface of the acetabulum is reamed. Bleeding corticocancellous bone should comprise the entire hemisphere to receive the pressfit shell. A pressfit trial is tried when the reamer's diameter is approximately 2 mm smaller than the size that was preoperatively templated. The preoperatively templated acetabular shell is then pressfit into the socket, which has been under-reamed by 2 mm. Contained cystic defects can be filled with the cancellous autograft from the native femoral head as mentioned previously. We prefer using a cluster hole cup so that 1 or 2 screws can be inserted into the posterosuperior safe zone, ~ but we actually insert screws in less than 20% of patients. Pressfit fixation will often allow for lifting the patient's pelvis off 11 8
the operating room table with a Kocher clamp. The holes are also beneficial to judge complete seating of the acetabular component. Some uncoverage is accepted laterally to achieve 40 ° abduction if fixation is not compromised. The desired polyethylene liner (selected based on thickness, internal diameter, wear prognosis, and posterior elevation) is inserted under direct visualization without intervening soft tissue and impacted into place. Engagement of the locking mechanism is verified, and any residual anterior or posterior osteophyte is removed at this time with an osteotome. Retractors are removed, the wound is lavaged, and attention is then focused on the femoral side. The leg is brought into 90 ° of hip internal rotation, flexion, and adduction so that the surgeon can prepare the proximal femur. The surgeon should be aware that this position twists the proximal vasculature of the lower extremity; thus, the duration of this position should be limited to decrease the risk of postoperative deep venous thrombosis. Exposure is ensured with the use of a "Stinchfield" retractor anterior to the femoral neck and an Aufranc medially adjacent to the jaws. A crown (or thin-bent Hohmann) retractor protects the abductor musculature during broaching. Soft tissue is removed from the area of the neck and posterior greater trochanter. Anterior femoral osteophytes should also be removed at this time. The femoral neck osteotomy is revised with the reciprocating saw, if necessary. A canal finder will identify the long axis of the femur. Femoral canal broaching is performed based on a prosthesis-specific protocol in the desired anteversion with sequentially larger broaches. Again, fatty exudate from the canal (with osteoinductive biological factors) is suctioned to decrease the risk of postoperative heterotopic ossification. Enough space is created for a 2-mm minimum cement column. Trial reduction can be performed with modular broaches and a head and neck assembly or with a separate trial prosthesis. The lesser trochanter to center of head distance should be measured and can be matched within 2 mm in most patients. The trial reduction ensures that soft tissue balance, range of motion, and hip joint stability has been achieved. The trials are removed and the cement restrictor is placed to the desired depth (1-1Acm distal to the tip of the prosthesis). The canal is thoroughly irrigated, cleaned of debris, and dried with vaginal packing as the cement is mixed. The canal is filled in retrograde fashion using a cement gun with polymethylmethacrylate cement of the appropriate consistency with pressurization. The femoral stem is inserted within the cement column (with associated distal or proximal centralizers) in the desired anteversion and neutral varus/valgus alignment. Excess cement is removed, and care is taken not to sink the prosthesis too deeply if it is of a collarless design. The cement is then allowed to cure. The templated modular femoral head is tapped into place on the Morse taper, and the construct is gently relocated under visualization. The posterior capsular flap and short external rotators are formally repaired by placing the "long" and "short" braided sutures through drill holes in the posterior greater trochanter with Keith needles and tying them separately. The wound is vigorously irrigated with antibiotic-laden saline to remove any remaining bone, soft tissue, or cement debris. The tensor fascia latae is repaired with interrupted No. 2 nonabsorbMACAULAYAND PARKS
able suture beginning distally. As this closure approaches the trochanteric flare, two small tubes to a self-suction drain are placed u n d e r the tensor fascia anteroinferiorly exiting 5 cm from the w o u n d edge. The surgeon m a y decide to use figure-of-eight knots over the greater trochanter. As the closure of the tensor layer a p p r o a c h e s thin fascia superiorly, absorbable No. 0 suture should be used. This s a m e suture can be used for inverted deep s u b c u t a n e o u s knots, but 2-0's should be used i m m e d i a t e l y subcutaneously. Staples are applied on the skin. We cover the w o u n d with nonstick antibacterial dressing, gauze, and two abdominal pads. This dressing is covered loosely with w r a p s with minimal elastic capacity in a hip spica fashion. Placement of the hip spica is facilitated b y using the hip table m e n t i o n e d previously.
mandatory. An assistant familiar with both h u m a n hip a n a t o m y and the surgeon's technique will help simplify the procedure. In an academic setting, the assistant(s) change on a rotational basis. The time of these rotational stints should be m a x i m i z e d for efficiency, but not be so long so as to c o m p r o m i s e the assistant diversity of training. We prefer that the surgeon stand behind the laterally positioned patient, with the first assistant on the s a m e side of the operating room table toward the foot. The last assistant stands in front of the patient toward the foot and holds the patient's leg w h e n needed. The second assistant, if available, stands opposite to the surgeon.
REFERENCES
The Operative Team The p r i m a r y T H A operative team consists of the surgeon, anesthesiologist, surgical assistant(s), scrub technician, and circulator. The team that w o r k s together m o s t often will be the most efficient, with all m e m b e r s being able to anticipate the next step of the procedure and avoid unnecessary delays. Decreasing operative time is important for minimizing the incidence of infection and v e n o u s t h r o m b o e m b o lism. Although remaining outside the enclosure, the anesthesiologist and circulator are integral parts of the operative team. The THA-efficient anesthesiologist helps minimize patient preparation and room turnover time. He or she is proficient in regional anesthesia (epidural and spinal) which can be refined with deliberate intraoperative h y p o tension 1° which will lower blood loss and not fluid overload the patient. The efficient circulator will anticipate potential delays or p r o b l e m s and will h a v e e q u i p m e n t and supplies ready on request, thereby decreasing surgical time. For the surgical technique (involving a posterolateral a p p r o a c h to the hip) outlined in this article, two or three surgical assistants are preferable. One surgical assistant is
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1. National Institutes of Health Concensus Statement of Total Hip Replacement. 12:12-14, 1994 2. Charnley J: Low Friction Arthroplas~,: TheoD, and Practice. London, Churchill Livingstone, 1979 3. Schulte KR, Callahan JJ, Kelley SS, et al: The outcome of Charnley total hip arthroplas~, with cement after a minimum twenl3.,-year follow up. J Bone Joint Surg 75A:961-975, 1993 4. Harris WH: Hybrid total hip replacement: Rationale & intermediate clinical results. Clin Orthop 333:155-164, 1996 5. Berger RA, Kull LR, Rosenberg AG, et al: Hybrid total hip arthroplasty: 7- to 10-year results. Clin Orthop 333:134-146, 1996 6. Clohisy JC, Harris WH: Primary hybrid total hip replacement, performed with insertion of the acetabular component without cement and a precoat femoral component with cement. An average ten-year fo|low-up study. J BoneJoint Surg Am 81:247-255, 1999 7. Clarke IC, Gruen T, Matos M, et al: Improved methods for quantitative radiographic evaluation with particular reference to total hip arthroplasty. Clin Orthop 121:83-91, 1976 8. Lidwell OA, Lowbury EJL, Whyte W, et al: Effect of ultraclean air in operating rooms on deep joint sepsis in the joint after total hip or knee replacement: A randomized stud,,,. Br Med J 285:10-14, 1982 9. Wasielewski RC, Cooperstein LA, Kruger MP, et al: Acetabular anatomy and the transacetabular fixation of screws in total hip arthroplasty. J Bone Joint Surg 72(A):501-508, 1990 10. Sharrock NE, Mineo R, Urquhart B: Hemodynamic response to low-dose epinephrine infusion during hypotensive epidural anesthesia for total hip replacement. Reg Anesth 15:295-299, 1990
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