Minimally invasive total hip arthroplasty

MINIMALLY INVASIVE TOTAL HIP ARTHROPLASTY GEORGE F. CHIMENTO, MD, and THOMAS P. SCULCO, MD

Total hip arthroplasty (THA) is commonly performed by using a posterior approach through an incision of 15 to 20 cm in length. A modified posterior approach allows for THA to be performed through an incision of 5 to 10 cm in length. Most patients with a Body Mass Index less than 30 who have not had a previous hip surgery are candidates for this approach; hypotensive epidural anesthesia is recommended. The incision is based over the posterior aspect of the greater trochanter, and specially designed retractors are used. The femoral component may be cemented or press fit, and a press fit monoblock acetabular component is generally used. The wotmd is closed over suction drainage. Patients receive mechanical and pharmacologic antithrombolytic prophylaxis and follow a standard postoperative rehabilitation protocol. A review of the first 1,000 patients operated on with this approach shows results comparable with THA performed through a standard length incision. There has been I deep infection (0.1%), 2 patients with sciatic neuropraxia (0.2%), 12 dislocations (1.2%), and 1 patient revised for recurrent instability (0.1%). KEY WORDS: arthroplasty, hip, minimally invasive, approach Copyright © 2001 by W.B. Saunders Company

Surgical technique for total hip arthroplasty (THA) has evolved greatly over the years. A transtrochanteric approach was the standard procedure in the early days of hip replacement surgery.~ Although this approach greatly facilitated exposure, it was not without morbidity, and nonunions of the greater trochanter were not uncommon. 2 Presently, trochanteric osteotomies are rarely performed for a routine primary total hip. Anterolateral, lateral, and posterior approaches have all been used in hip replacement surgery. Surgeons tend to choose an approach with which they are most familiar and comfortable. Many surgeons favor the posterior approach for its relative ease and simplicity. An informal survey of orthopaedic surgeons at The Hospital for Special Surgery in New York and in the New Orleans area showed that most surgeons preferred a 15 to 20-cm incision when performing THA through a posterior approach. Ease of exposure was the most c o m m o n reason given for the length of incision. Over 5 years ago, the senior author (T.P.S.) began using a modified posterior approach that enabled him to perform THA through a much smaller incision than he previously used. Originally, this procedure was performed only in very thin patients, but currently this approach is used on most nonobese patients.

PATIENT SELECTION Body mass index (BMI) or Quetelet index is a most useful and practical method to measure patients' size. 3 Weight in From the Orthopaedic and Sports Medicine Clinic, New Orleans, LA;

and the Hospital for Special Surgery, New York, NY. Address reprint requests to George F. Chimento, MD, 6050 Bullard Ave, Suite 100, New Orleans, LA 70128. Copyright © 2001 by W.B. Saunders Company 1048-6666/01/1104-0004535.00/0 doi:10.1053/otor.2001.26208

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kilograms is divided by height in meters squared (kg/m2). Although this m e t h o d does not take into account the location of the b o d y fat, it is an easy tool to use to screen patients. A BMI greater than 25 is considered overweight and greater than 30 is considered obese. Performing THA through a smaller incision was originally developed as an answer to patient concerns about the appearance of the scar. As a rule, these patients were y o u n g e r and thinner. Currently, patients whose BMI is less than 30 and who have had no previous surgery on the involved hip are candidates for a small incision. Some patients with conditions such as severe hip dysplasia would require a more standard approach. The location of b o d y fat and the overall musculature of the patient should also be considered. Patients with a large a m o u n t of trunkal obesity, regardless of BMI, w h o m carry little fat in their hip region, are candidates for a short incision. However, experience has also shown that patients w h o possess extremely muscular thighs are the most difficult patients in w h o m to gain adequate exposure. These patients may require a longer incision.

SURGICAL TECHNIQUE Hypotensive epidural anesthesia is r e c o m m e n d e d to decrease intraoperative blood loss. Vision is greatly enhanced by a blood-free operative field. Prophylactic antibiotics are administered. The patient is positioned in the lateral decubitus position on the operating table. The surgeon should take care to ensure that the pelvis is secured perpendicular to the table, and the b o d y is aligned axially. This will aide in proper positioning of the acetabular component. The posterior tip of the greater trochanter is identified, and a longitudinal incision is made. Two thirds of the incision is distal to the tip of the trochanter, and one third is proximal. The subcutaneous fat is dissected, and the

Operative Techniques in Orthopaedics, Vol 11, No 4 (October), 2001: pp 270-273

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Fig 1. The skin is incised and the tensor fascia is exposed. This incision measures 9.5 cm.

Fig 3. The exposure of the acetabulum. Clockwise from the top: proximal femoral retractor, Aufranc retractor, a wide bent Hohmann retractor, a Steinmann pin, and the anterior blade of a Charnley retractor.

tensor fascia is identified (Fig 1). The tensor fascia is incised in line with the skin incision. The fascial incision may be extended beyond the skin incision a short distance proximally and distally to aid exposure. A thin-bladed Charnley retractor is then placed below the level of the tensor fascia. The surgeon should take care not to injure the sciatic nerve when placing the posterior blade. While slightly extended at the hip, the leg is gently internally rotated. A thin bent Hohmaml retractor is placed along the superior portion of the femoral neck, and an Aufranc retractor is placed inferiorly. The Aufranc retractor should be positioned proximal to the quadratus femoris. The fat covering the short external rotators is swept back with a Cobb elevator. The external rotators should be visualized at this point. The external rotators with the exception of the quadratus, and posterior capsule are released from the femur in a trapezoidal fashion. The piriformis and conjoint tendon are each tagged along with the underlying capsule with a large nonabsorbable suture for later repair. The hip is then dislocated (Fig 2). The

quadratus can be swept distally with the Aufranc retractor, exposing the lesser trochanter. A femoral neck cut of the appropriate length is then made with a reciprocating saw, and the femoral head is removed. The leg is then laid on the table in extension, and the acetabulum is exposed. A proximal femoral retractor is placed over the anterior edge of the acetabulum, retracting the proximal femur anteriorly. A Steinmarm pin is then inserted into the pelvis superiorly at the 12 o'clock position. The reflected head of the rectus femoris can be partially released to aid in exposure. With the leg in extension, a wide bent Hohmann retractor is inserted into the bone along the posterior rim of the acetabulum. The surgeon must take care to avoid injuring the sciatic nerve when placing the Hohmann retractor. An Aufranc retractor is placed inferiorly, just distal to the transverse acetabular ligament. The labrum is then excised both anteriorly

Fig 2. The femoral head is dislocated and the suture tags are visible inferiorly. MINIMALLY INVASIVE TOTAL HIP ARTHROPLASTY

Fig 4. The monoblock acetabular component is implanted.

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Once these goals are met, the patient is discharged. Some patients require transfer to a rehabilitation facility before going home. The healed incision provides a satisfying cosmetic result (Fig 6).

RESULTS The minimally invasive technique has been used for over 5 years, and the first 1,000 patients have been identified from the senior surgeon's (T.P.S.) database. There has been 1 case of deep infection (0.1%) that required the removal of the components. Two cases (0.2%) of sciatic neuropraxia occurred. Both resulted from direct injury to the sciatic nerve with a retractor. One resolved completely, whereas 1 patient still exhibits some weakness (grade 4/5) in the peroneal nerve distribution. Twelve hips have dislocated (1.2%), 1 of which was revised for recurrent instability (0.1%). There have been no early failures or considerable loosening of either the femoral or acetabular components. Fig 5. The proximal femur is delivered into the field with the femoral neck retractor. The canal is to be prepared for the femoral prosthesis.

and posteriorly. At this point, the acetabulum should be well exposed (Fig 3). The pulvinar may be removed and reaming commenced. Once reaming is completed, the cup is inserted; the use of a monoblock cup facilitates this portion of the procedure (Fig 4). All retractors are then removed, and a moist lap sponge is placed to protect the acetabular component. The leg is then flexed and internally rotated. A small femoral neck retractor is positioned to elevate the proximal portion of the femur (Fig 5). The femoral canal is then prepared, and a trial femoral component is inserted. A trial reduction is performed, and if all is satisfactory, the actual femoral component is then inserted. Before the final reduction, 2 drill holes of 2.0 mm are made in the greater trochanter. The previously placed sutures through the short external rotators and capsule are passed through these holes but not tied. The hip is the reduced. The sutures through the trochanter are then tied, securing the short external rotators and the capsule to the bone. The wound is copiously irrigated, and 2 medium-sized drains are placed deep to the tensor fascia. The drains exit through the anterolateral thigh. The subcutaneous layer and skin are closed, and a dressing is applied.

DISCUSSION The goal of this article is not to encourage surgeons to perform all their total hips through a 5-cm incision. Each surgeon should use an incision that provides adequate exposure and enables him or her to perform the operation well. However, when conditions warrant use of a minimally invasive procedure, the modified posterior approach described previously should enable the surgeon to use this technique without excessive difficulty. With most procedures in orthopaedics, there is a learning curve involved. Hypotensive epidural anesthesia, which has been shown to decrease blood loss,4 is instrumental in providing a dry surgical field. A skilled assistant is also necessary because initial retractor positioning and maintenance of the position is of the utmost importance. The smaller size retractors designed for this procedure allow for less crowding and freer movement in the operative field (Fig 7A, B).

AFTERCARE Mechanical foot pumps and pharmacologic antithrombotic prophylaxis are used in the postoperative period. Patients receive antibiotics for 24 hours postoperatively. The drains are pulled on the first postoperative day, and the wound checked on the second. Pain is initially controlled through a patient-controlled epidural pump. Most patients are switched to oral analgesics on the second or third postoperative day. Physical therapy is instituted on the first postoperative day. The major goals of therapy are to enable the patient to independently transfer, ambulate with a walker, ambulate with a cane, and negotiate stairs.

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Fig 6. A healed incision. CHIMENTO AND SCULCO

Fig 7. (A) From top to bottom: A proximal femoral retractor, thin bent Hohmann retractor, and a wide bent Hohmann retractor. (B) A specially designed femoral neck retractor (Implex Corp, Allendale, NJ) (top) compared with a standard size femoral neck retractor (bottom).

M o d u l a r acetabular c o m p o n e n t s h a v e been used with this technique, but inserting the liner can be difficult through a small incision. A m o n o b l o c k c o m p o n e n t eliminates the need for liner insertion. Surgeon experience is crucial here, because a poorly seated m o n o b l o c k c o m p o nent cannot be secured with screws. A retrospective review b y Crockett et aP was presented at the American A c a d e m y of O r t h o p a e d i c Surgeons Annual Meeting in 1998. Fourty-two patients using the minimally invasive a p p r o a c h c o m p a r e d with a control p o p u lation of 42 "traditional length" incisions s h o w e d that T H A could be p e r f o r m e d safely and effectively with this approach. There was no difference in operative time or complications between the small and standard incision g r o u p s in this study. 5 The use of this tecl'mique is not for all patients, but it is safe and effective w h e n used for the p r o p e r indications. A

MINIMALLY INVASIVE TOTAL HIP ARTHROPLASTY

r a n d o m i z e d prospective c o m p a r e the minimally standard length incision sion length affects short

s t u d y is currently u n d e r w a y to invasive a p p r o a c h with a m o r e and to investigate whether incirecovery after THA.

REFERENCES 1. Charnley J, Ferrera A: Transplantation of the greater trochanter in arthroplasty of the hip. J Bone Joint Surg Br 46: 191-197, 1964 2. Amstutz HC, Maki S: Complications of trochanteric osteotomy in total hip replacement. J Bone Joint Surg Am 60: 214-216, 1978 3. Bray GA: Overweight is risking fate. Definition, classification, prevalence and risks. Ann N Y Acad Sci 499:14-28, 1987 4. Sharrock NA, Salvati EA: Hypotensive epidural anesthesia for total hip arthroplasty: A review. Acta Orthop Scand 67:91-107, 1996 5. Crockett HC, Wright JM, Bonner KF, et al: Mini-incision for total hip arthroplasB,. Scientific Exhibit. American Association of Orthopaedic Surgeons, Annual Meeting, New Orleans, LA, 1998

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