Total hip arthroplasty is one of the most common orthopaedic procedures with approximately 200,000 primary procedures being done each year in the United States. 9 Because of its very high success rate, it has been shown to be one of the most cost-effective interventions in medical care. 1,5,9,22,24,33,47 Complications, however, do occur and can be disheartening for the patient and the surgeon. Other than deep venous thrombosis, dislocation historically has been the most common complication of primary or revision total hip arthroplasty and it is the second leading cause of revision total hip replacement. 28,37,42,45 The etiology of instability after total hip arthroplasty is multifactorial. Although there are patient factors that are important, it often is technical factors that receive the most attention because the patient factors often cannot be altered.
One of the most important technical factors in avoiding instability is surgical approach. Dislocation rates of as much as 6.5% after posterior approaches have been reported. 6,16,32,43,44,49,51 To reduce the incidence of dislocation, some hip surgeons have switched to the direct lateral approach. Modifications of the direct lateral approach have yielded dislocation rates of approximately 1% for primary arthroplasties. Mallory et al 37 reported an incidence of 0.79% in a series of 1518 total hip arthroplasties. Kohn et al 30 evaluated 26 dislocations in 1238 primary total hip arthroplasties and found a statistically significant difference in dislocation rates of 3.1% for the posterior approach versus 1.2% for the transgluteal approach. Woo and Morrey, 49 in their review of 10,500 total hip arthroplasties done at the Mayo Clinic, found that the posterior approach had a 5.8% dislocation rate versus 2.3% for an anterolateral approach.
The direct lateral approach first was described by Kocher in 1903, 29 then modified by McFarland 38 who detached the gluteus medius in its entirety while maintaining its continuity with the vastus lateralis distally. Hardinge 17 additionally modified the approach to detach only the anterior portion of the gluteus medius, leaving the thicker posterior portion attached. There have been numerous modifications to this approach, including detaching a small sliver of bone with the abductor tendons. 15,19,37,40,41,48 Although the term Hardinge approach remains widely used, there are other synonyms for this approach including the anterior, anterolateral, transgluteal, abductor split, or direct lateral approach. It is the latter term that will be used in the current study.
The direct lateral approach is used almost exclusively at the authors’ institution for primary and revision total hip arthroplasties. The senior authors (CHR and RBB) began using this approach in 1985 in response to an unacceptably high dislocation rate (3%) with the posterior approach. Review of the initial experience with this approach in 712 primary total hip arthroplasties yielded a dislocation rate of 0.3%, a moderate or severe limp in 10%, and severe heterotopic ossification (Brooker 2 Grade III or IV) in 3%. 41 To additionally evaluate the dislocation rate, possible causative factors, and morbidity of the direct lateral approach, a review of primary total hip arthroplasties done between January 1, 1990 and December 31, 1999 was done.
MATERIALS AND METHODS
The technique used for the direct lateral approach at the authors’ institution is a modification of previously described approaches. 15,19,37,40,41,48 Although based on similar principles, this approach differs from the classic description by Hardinge 17 in that the patient is lateral rather than supine. The gluteus medius is split by blunt dissection rather than being incised and this portion of the approach is more anterior than in his description. Small variations of the technique exist among the authors of the current study but, for the most part, the technique is similar to that described by Frndak et al. 15
The patient is positioned in the lateral position with a lumbar spine support and a pubic support. The nonoperative hip and knee are flexed. The incision is centered over the greater trochanter and extends an equal distance proximally and distally. It can vary, depending on the size of the patient, from 12 to 15 cm. The fascia lata is divided in line with the skin incision between the gluteus maximus and tensor fascia lata muscles (Fig 1). The sciatic nerve is palpated posteriorly and a large Charnley retractor is used to retract the incised iliotibial band. The abductor muscles are palpated anteriorly and posteriorly to get a sense as to the bulk. After that, blunt dissection is used to separate the muscle fibers between the anterior ⅓ and the posterior ⅔ of the muscle. This dissection is limited to 3 cm proximal to the insertion on the trochanter to avoid injury to the inferior branch of the superior gluteal nerve. Blunt right angle retractors are used to retract the gluteus medius, exposing the fat covering the gluteus minimus, which is retracted to expose the underlying muscle and tendon. Dissection continues distally in an Omega fashion around the anterior portion of the greater trochanter (Fig 2). Care is taken to leave a small cuff of tissue on the greater trochanter to allow ease of suturing at the end of the operation. The incision is extended distally before angling posteriorly to elevate the anterior cuff of the vastus lateralis. It is important, at this point, to ensure that an adequate cuff of tissue remains in continuity between the detached abductors and the vastus lateralis. The gluteus minimus and capsule then are incised in one layer along the neck of the femur up to the labrum (Fig 3). A blunt Hohmann retractor is placed anteriorly and a second retractor is placed posteriorly around the neck of the femur. The capsule is elevated anteriorly and posteriorly. Depending on the tightness of the hip, it occasionally is necessary to cut the reflected head of the rectus femoris. With an assistant externally rotating the leg, dissection is continued distally detaching the capsule and the tendon of the gluteus minimus. The dissection is continued with the leg in external rotation and the remaining anterior capsule is elevated until the lesser trochanter can be identified. A fixed point on the ileum is used as a reference to measure leg length and offset. This is done before dislocation of the hip. With the hip externally rotated and a blunt hook placed around the neck of the femur, it is easy to dislocate the hip with adduction and external rotation. A blunt retractor then is placed behind the greater trochanter and a second blunt retractor is placed anteriorly above the lesser trochanter to aid in exposure for the osteotomy of the femoral neck. After removal of the femoral head, an important part of the exposure involves release of the capsule from the posterior aspect of the neck of the femur. With the femoral head removed, this can be done under direct vision by flexing and externally rotating the femur. By doing this, it is relatively easy for the surgeon to move the femur posteriorly to allow adequate exposure of the acetabulum (Fig 4). Exposure is completed with the placement of three blunt retractors. The labrum of the acetabulum is removed by sharp dissection and a blunt Hohmann retractor is placed around the anterior column of the acetabulum. A blunt retractor also is placed posteriorly to aid in retraction of the proximal femur. The transverse acetabular ligament inferiorly may be divided and a third blunt retractor is placed inferiorly. One of the advantages of this approach is the complete and easy exposure of the acetabulum.
After the trial and final components are inserted, stability is evaluated in extension and external rotation and in flexion and internal rotation. Any osteophytes contributing to impingement are excised. The restoration of leg length and offset is determined from the previously placed fixed pin in the ileum. Closure is done by reapproximating the deep layer consisting of the gluteus minimus and capsule. The tendinous portion of the gluteus minimus also is repaired. The anterior ⅓ of the gluteus medius and vastus lateralis falls back into place as a flap and this is sutured with a locking suture at the inferior portion of the trochanter, a running suture distally, a locking suture at the proximal portion of the trochanter, and a running suture proximally (Fig 5). Several interrupted locking sutures are used to anchor the flap to the trochanter. If the material over the trochanter seems insufficient, sutures can be passed through one or two drill holes in the trochanter. Closure is continued in the usual fashion.
Postoperatively, it is not necessary to limit weightbearing for soft tissue protection, but adduction and external rotation are avoided to protect the abductor repair. Precautions to protect against dislocation, such as avoiding excessive flexion or crossing of the legs, are encouraged for 6 weeks. Postoperative physical therapy concentrates on abductor strengthening and continues for approximately 3 months.
Since 1972, data have been collected on all arthroplasties done at the authors’ institution. The minimum data collected include Harris hip scores 18 and radiographic evaluations. The data form used to collect these data has not included complications such as dislocation. However, this information is recorded in a comments field on the evaluation form and is maintained in the arthroplasty database. Data are collected at the preoperative evaluation, surgery, and postoperative followups and are maintained on a computer network. For patients having primary total hip arthroplasty, followups routinely are scheduled for 6 weeks, 3 and 6 months, 1, 2, 3, 5, 7, 9, and 10 years, and yearly thereafter.
The arthroplasty database was used to generate demographic data and to identify patients who had primary total hip replacements done at the authors’ institution between January 1, 1990 and December 31, 1999. Patients who had a postoperative episode of instability or dislocation were identified and their charts were reviewed retrospectively. Additionally, the charts of other patients were reviewed to include any patients who may have had instability that was not recorded in the database. This group included all patients who had either captured or offset liners implanted at their primary or revision procedures. This subset of patients was reviewed to cross-check the database because it was thought that these patients might represent a group who had instability before their revision or during their procedure that required the use of modified acetabular liners. A separate search of the financial databases was done to identify additionally patients who had a billed procedure of closed reduction of a hip prosthesis. Data including age, gender, diagnosis, operative surgeon, operative approach, implants used, mechanism and direction of dislocation, time from surgery to dislocation, number of dislocations, and treatment were collected for all patients with unstable hip arthroplasties. For the current study, only those patients who had instability complicating primary total hip replacement were included.
The radiographs of all patients with instability were reviewed to determine the acetabular inclination and anteversion and as described by Woo and Morrey 49 (Figs 6, 7). Leg length restoration was measured from a line tangential to the ischial tuberosities to the medial-most aspect of the lesser trochanter and was compared with the opposite side. 49
Followup data of at least 12 months were available for 1519 primary total hip arthroplasties done at the authors’ institution between January 1, 1990 and December 31, 1999. The direct lateral approach was used in all but four patients leaving 1515 hips in 1333 patients for inclusion in this study. The average time to the latest followup in these patients was 3.3 years (range, 1–10.6 years). The four patients who were excluded had a posterior approach secondary to previous trauma involving the posterior wall or column of the acetabulum.
Six hundred ninety of the arthroplasties were done in male patients and 825 were done in female patients. The underlying diagnosis was osteoarthritis in 82% of the hips, inflammatory arthritis in 5%, avascular necrosis in 4.2%, developmental dysplasia in 3.9%, and posttraumatic arthritis in 2.4%. The other 2.5% of patients had arthroplasty for miscellaneous conditions. Sixty-three percent of the hips were cementless, 26% were hybrids, and 11% were cemented on the femoral and acetabular sides.
At the most recent followup, the average Harris hip score was 87.1 points and the range of motion (ROM) portion of this score averaged 4.5 of a possible 5.0. A cane or other assistive device was used by 28% of patients. Thirty-nine percent of the patients had arthritis in other locomotor joints or systemic illness that limited their activity.
A moderate or severe limp was seen in 11.6% of patients, 76% of whom used a cane or other assistive device. The average Harris hip score in this group was 66.4 points. There were other causes of activity limitation in 52.3% of these patients.
Brooker Grade III or IV heterotopic ossification was seen after 2.5% of the primary total hip arthroplasties. The average Harris hip score was 84.8 points and the ROM portion of this score averaged 3.89 for these arthroplasties. Forty-two percent of these patients used an assistive device for ambulation. There was no record of any of the patients having an additional surgical procedure solely to excise heterotopic ossification.
The search of the arthroplasty and financial databases and retrospective review of 75 patients who had lateralized or constrained acetabular liners implanted yielded seven patients who had instability after a primary total hip arthroplasty that was done at the authors’ institution during this study. One patient had an infection after her total hip arthroplasty and was treated with irrigation, debridement, polyethylene liner exchange, capsulectomy, and placement and removal of antibiotic-impregnated polymethylmethacrylate beads. The patient’s hip subsequently dislocated; however, this was not considered a dislocation after primary arthroplasty for the purposes of this study.
Six of 1515 hips had instability after a primary total hip arthroplasty done via a direct lateral approach during the 1990s. This yielded an instability rate of 0.4%. One patient had a primary diagnosis of osteoarthritis, two had hip dysplasia, and three had inflammatory arthritis. Three patients were men and three were women. Their average age at the time of primary surgery was 62.5 years (range, 47–88 years). There were five dislocations of the right hip and one of the left hip. Three hips were unstable posteriorly and three were unstable anteriorly. No patients had a femoral head component with a skirted neck. All six first-time dislocations occurred within the first postoperative year. Patient information is summarized in Table 1.
One of the patients had an episode of instability that she was able to reduce. This occurred as she was bending over to tie her shoe approximately 11 months after the primary surgery. She described a pop in her hip, along with immediate numbness in her leg. As she extended her hip fully, she felt her hip reduce and the paresthesia resolved. She has had no additional episodes of instability. Although there was no documented dislocation, she was included in these results because it was thought that she had experienced a posterior subluxation.
The second patient had an anterior dislocation while turning in bed 3 weeks after his primary surgery. He had a closed reduction and had no additional episodes of instability.
The third patient had noticed episodes of subluxation that could not be verified on fluoroscopic examination 4 months after her surgery. The patient’s hip dislocated posteriorly 7 months after surgery while she was gardening, requiring closed reduction with the patient under a general anesthetic. She was treated conservatively and has not had a repeat dislocation.
The fourth patient had two anterior dislocations within 1 month of surgery (Fig 8). He had revision surgery during which an anterior osteophyte that did not impinge and a satisfactorily placed acetabular shell were observed. His acetabular shell was replaced in a similar position with one that accepted a constrained liner. The patient has not had a subsequent dislocation of his hip.
The fifth patient had 12 operative procedures for treatment of developmental dysplasia of the hip, excision of heterotopic ossification, and infection before her primary total hip arthroplasty. Because of the anticipated risk of dislocation in this patient, an acetabular shell that would accept a constrained liner was used during the initial arthroplasty. The constrained liner was not used initially because of the patient’s young age. The patient experienced anterior dislocation of the hip three times within 6 months of surgery and then had revision of the acetabular liner to a constrained component. The patient has not had a repeat dislocation since the revision surgery.
The sixth patient had three posterior dislocations within the first 3 months of primary surgery. At revision, some scarring and early heterotopic ossification were observed which were not apparent on radiographs. This was thought to be impinging and contributing to the patient’s instability. Despite excision of this bone and replacement of the modular components with a +4 mm offset liner and a 32-mm head with a +17 mm neck, the patient’s hip continued to be unstable and had two more dislocations of the hip. The patient had rerevision surgery during which the acetabular shell was replaced and a constrained liner was inserted. The patient’s hip now is stable and she is functioning well.
The radiographs of these six patients were reviewed. The safe zone, as described by Lewinnek et al, 34 of 40° ± 10° for the acetabular inclination and 15° ± 10° for anteversion was used to determine acetabular malposition. The results are summarized in Table 2. Two of the six patients with instability had acetabular inclination and anteversion within the safe zone. One of these two patients had recurrent instability that required revision surgery. No patients with instability had a leg length discrepancy greater than 1 cm.
Instability of a total hip arthroplasty is a severe complication, usually causing patients to lose confidence in their total hip replacement. Most hip dislocations require emergent reduction and some patients require general anesthesia for closed or open reduction. As many as 95% of dislocated total hip arthroplasties can be reduced successfully on the first attempt. 49 Reduction, however, may be complicated by loosening of the femoral or acetabular components, intraarticular foreign bodies, drain entrapment, or damage to ceramic femoral heads. 3,14,23,31,36,45 Recurrent hip dislocation may occur in 60% of patients after first time dislocations, and 15% to 40% of patients require reoperation. 35,49,51
Depending on the timing of dislocation (early or late), many factors have been associated with its etiology. As many as 85% of dislocations are reported to occur within 2 months after total hip arthroplasty. 35 It is more common in elderly people, particularly those with impaired balance and vibration sensitivity. 21,46 It occurs more commonly in women. 49 There is a correlation with history of trauma or developmental dysplasia of the hip. 37 Patients with cerebral dysfunction or excessive alcohol use also are at higher risk. 43,50 Commonly cited surgical risk factors include revision surgery and failure of the abductor mechanism. 4,16,25,34,45,49 The role of other factors such as acetabular cup malposition, excessive femoral retroversion, prostheses with smaller femoral heads, and acetabular components larger than 60 mm is less clear. 16,26,27,51 Late causes of dislocation often are associated with subsidence or loosening of a component, impingement, or with laxity of the joint pseudocapsule. 8,49
Perhaps the most commonly cited factor associated with early dislocation has been the surgical approach. In the past decade, dislocation rates of 2.3% to 6.5% have been reported after primary total hip arthroplasty using the posterior approach. 6,16,32,43,44,49–51 Recent modifications of this approach, especially repair of the posterior structures, have reduced the dislocation rate. Chiu et al 6 reported a 0% dislocation rate in 96 patients treated with posterior capsulorrhaphy in a prospective randomized trial. Pellicci et al 44 similarly reported a rate of 0.19% in 519 patients treated with an enhanced posterior repair. Notwithstanding these two reports, much of the literature dealing with the posterior approach for primary total hip arthroplasty is attendant with a significant dislocation rate. 6,16,32,43,44,49–51
In the current study, the authors identified six of 1515 hips in 1333 patients that had instability after a primary total hip arthroplasty done via a direct lateral approach. This yielded a dislocation or subluxation rate of 0.4%. This low dislocation rate is consistent with the experience of others reporting on this approach. 30,37,39,41
The associated morbidity with the direct lateral approach is relatively low. Persistent limp often is reported, 15,39–41,48 as was the case in 11.6% of these patients. The majority of these patients, however, had systemic disease or disease involving other locomotor joints. Stephenson and Freeman 48 reported a 26% incidence of a slight limp after a similar operative approach and Moskal and Mann 39 reported an 18% incidence of limp in their prospective analysis of primary arthroplasties with this approach. Frndak et al 15 had a 20% incidence of limp in their patients, but this was not attributed to the hip in any patient. Mostardi et al 40 found that the wafer technique, in which the anterior gluteus medius and minimus are removed with a small wafer of bone, did not significantly increase abduction strength over the sharp technique.
Severe heterotopic ossification (Brooker Grade III of IV) was present in 2.5% of the patients in the current series at latest evaluation. Although 42% of these patients required the use of a cane, the presence of severe heterotopic ossification did not dramatically decrease the Harris hip score or the ROM portion of this score. Prophylactic measures for heterotopic ossification are not used routinely by the authors. Radiation therapy is not readily available and nonsteroidal antiinflammatory agents are avoided because the patients receive warfarin for deep venous thrombosis prophylaxis. Frndak et al 15 reported a similar incidence of 2% (one patient) without routine use of prophylaxis.
It is unlikely that this low dislocation rate can be attributed to surgical approach alone. The direct lateral approach is only one factor in the process of achieving soft tissue balance. The approach allows anatomic restoration of the periarticular soft tissue sleeve and elimination of dead space. Other authors applying similar concepts to posterior approaches have reported similarly low dislocation rates. 6,44 Also, achievement of soft tissue balance in flexion and extension and restoration of offset and leg length are imperative. Standardized preoperative radiographs are reviewed and templated to assist with selection of appropriate implants. Intraoperatively, a caliper that measures offset and leg length from a fixed pin in the ileum to a marked location on the greater trochanter is used. This is done before initial dislocation, during trial reductions, and after the final implant is inserted. By using offset acetabular liners and femoral stems with variable offsets and neck lengths, the important parameters of length and offset are restored. This allows restoration of soft tissue tension and the abductor moment arm. Stability is determined intraoperatively in flexion, adduction, and internal rotation, and in extension and external rotation. Soft tissue contractures, particularly the hip flexors and external rotators, are released as necessary.
Periacetabular osteophytes that contribute to impingement routinely are excised. Additionally, femoral stems that have a neck geometry and taper designed to avoid impingement are used. Whenever possible, skirted necks on modular femoral heads are avoided and 28-mm rather than smaller femoral heads are used. Use of an acetabular liner with an elevated rim varies among the authors, but there has been no difference in dislocation rates with its use at this institution. Cobb et al 7 reported that posteriorly lipped liners significantly lower the dislocation rate, although the long-term effects on wear and loosening from impingement are unknown.
The treatment of the dislocated total hip arthroplasty often focuses on the mechanical or technical aspects of the procedure. Daly and Morrey 10 classified the causes of instability as malrotation of the components, disruption of the abductor mechanism, impingement, or multiple or unknown. Similarly, Dorr and Wan 11 and Dorr et al 12 classified causes as positional, component malposition, soft tissue imbalance, or component malposition and soft tissue imbalance. Many of these factors, however, often are difficult to evaluate. Woo and Morrey 49 were unable to correlate position of the components or myofascial tension with instability. Although the safe zone was well described by Lewinnek et al, 34 they acknowledge no significant correlation between the cup orientation angle and posterior dislocation and no correlation between the inclination and dislocation. In the current study, two of six patients with instability had acetabular anteversion and inclination within the safe zone and one of these patients required revision surgery for recurrent dislocation. One patient had anterior instability and one patient had posterior instability. Of the three hips with excessive anteversion, one dislocated posteriorly. Both hips with excessive anteversion and inclination dislocated anteriorly. The significance of these observations is unknown. Although the patients had some of the reported risk factors (confusion, advanced age, female gender, previous surgery), no one significant factor in this small group was determined.
The authors acknowledge that there may be some inherent weaknesses in the collection of the data that cause this dislocation rate to be erroneously low. First, the complication of dislocation was not one of the specific items collected in a prospective fashion for the database. Although this information often was recorded and included, there was opportunity for omission. An attempt to minimize this error was made by reviewing the accounting database and the charts of a select group of 75 patients who were thought to have been at risk for instability.
A complete chart review of all 1515 hips may identify additional patients with instability, but there is a possibility that some patients with dislocations may have had them reduced at their local emergency rooms and the authors were not notified. This is a weakness with any retrospective review of dislocation rates and it probably would not significantly change the results. Even if the database and chart review had captured only ½ of the patients with instability, the rate still would be less than 1%.
Although there may be an underreporting of the true dislocation rate in the current series, similar inaccuracies probably occur in all large reports of dislocation rates. Hedlundh et al 20 reported that their registry missed ½ of dislocations when compared with a manual retrospective review. Fender et al 13 reported a higher overall complication rate than those reported by individual surgeons or specialist centers. They thought that their data probably were more indicative of the true rate given the added accuracy of their regional registry combined with a radiographic review. They stressed the importance of establishment of a national registry for surveillance of patients with total hip arthroplasties. A province-wide arthroplasty registry that will increase the accuracy of the data from the authors’ region is in the process of being created.
The dislocation rate of 0.4% shows that what once was considered one of the most common complications after total hip arthroplasty almost can be eliminated with the use of the direct lateral approach and soft tissue balancing. Given the dramatic benefit of this approach, the authors think that the risks of limp or heterotopic ossification are acceptable and they continue to recommend its use.
The authors thank Jeff Guerin for assistance and management of the database.
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Richard A. Brand, MD; and John R. Moreland, MD, Guest Editors