So-called minimally invasive total hip arthroplasty theoretically results in less blood loss, less pain, and a shorter hospital stay when compared with total hip arthroplasty performed with use of larger incisions1-3. While there is considerable interest in less-invasive surgical techniques among patients and surgeons, the safety and efficacy of these techniques as well as the indications for their use are being debated2,4. There is concern that minimally invasive joint replacement procedures may have been promoted prematurely in the media and to patients, before the outcomes had been properly assessed in the peer-reviewed literature2,5.
In the present study, we evaluated the short-term results of primary total hip replacements that had been performed by a single surgeon with use of two small incisions and intraoperative fluoroscopic guidance. We then compared these results retrospectively with those of a historical series of hip replacements that had been performed by the same surgeon through a single small incision and a direct lateral approach without fluoroscopic guidance. Our null hypothesis was that fluoroscopically guided hip-replacement surgery performed through two small incisions is not associated with a higher risk of complications and repeat surgery when compared with a single mini-incision approach.
Materials and Methods
Between August 2003 and June 2004, eighty-nine consecutive primary total hip arthroplasties were performed in eighty-seven patients with use of the two-incision technique as described by Mears and Berger2,3. All of the procedures were performed by a single surgeon (B.S.B.), who prepared to use the two-incision technique by attending a two-day training seminar sponsored by Zimmer (Warsaw, Indiana). The training at this seminar consisted of oral lectures, written instructions, and surgery on four cadavera, performed under the direction of surgeons who were experienced with the two-incision technique. The consecutive series of two-incision procedures began with the first patient who underwent the procedure after the surgeon had completed this training.
The two-incision group was compared retrospectively with a group of ninety-six patients (ninety-six hips) in whom total hip arthroplasty had been performed by the same surgeon, between August 2002 and July 2003, with use of a single mini-incision technique through a direct lateral approach6. The surgeon had extensive experience with the direct lateral approach prior to adopting the mini-incision technique. This series of mini-incision procedures also began with the first patient in whom this procedure was performed. The surgeon had received fellowship training in total joint arthroplasty and had performed >300 total hip replacement procedures before beginning this study.
Clinical data that were obtained for the two groups of patients included age, gender, body mass index, side of involvement, intraoperative blood loss, total duration of inpatient stay (including the stay in the hospital and in the rehabilitation facility), and postoperative complications. Exclusion criteria for both groups included any previous surgical procedure on the hip joint or a preexisting hip deformity that mandated a more extensive surgical approach. Eight hips were excluded from the single mini-incision group. Five of these hips had had previous surgery related to fracture fixation, and three had deformities related to developmental dysplasia. The three dysplastic hips required additional procedures during the arthroplasty that could not be performed through a small incision. Five hips were excluded from the two-incision group. Four of these hips had had previous surgery related to trauma, and one required a complex acetabular reconstruction because of dysplasia.
Demographic data on the patients are listed in Table I. Radiographic data were obtained from a single postoperative anteroposterior radiograph of the pelvis and included the cup abduction angle, the presence of radiolucent lines between the cup and the pelvis, the amount of limb-length discrepancy, the alignment of the femoral implant, and the adequacy of fit and fill of the femoral stem. In addition to determining the mean cup abduction angle, we also defined outliers as hips with a cup abduction angle of ≤30° or ≥50°. Limb-length discrepancy was determined with use of previously described methods7, and the quality of fit and fill of the cementless femoral component was classified as good, fair, or poor8. Varus malpositioning of the femoral stem was considered to be present when the longitudinal axis of the stem was tilted in >5° of varus relative to the diaphyseal axis of the femur.
We used the two-incision surgical technique described by Mears and Berger2,3,9. The patient is placed in the supine position, and the anterior surgical approach10 is used to reach the hip joint and to implant the acetabular component. The second of the two incisions allows for the implantation of the femoral stem through an approach similar to that described for the insertion of an intramedullary femoral nail11. Because the incisions are only 1 to 2 in (2.5 to 5.1 cm) in length, respectively, intraoperative fluoroscopy is necessary to position the implants correctly9.
All patients received an uncemented acetabular component (Trilogy Acetabular Cup; Zimmer) with a 10° elevated rim on the cephalad and posterior aspects of the polyethylene liner. Three different femoral stem designs were used as we gained experience with this procedure. The first twenty-three arthroplasties were performed with use of a tapered femoral implant that had a circumferential layer of fiber metal at the proximal end for bone ingrowth (VerSys Fiber Metal Taper; Zimmer). The next twenty arthroplasties were performed with use of an extensively coated femoral stem (VerSys Beaded FullCoat Plus; Zimmer). The last forty-six arthroplasties were performed with use of a femoral stem with a proximal wedge-shaped design and a proximal circumferential porous coating for bone ingrowth (M/L Taper; Zimmer). Unlike the first two implants, this last implant can be inserted without reaming of the femoral canal.
Mini-Incision Direct Lateral Technique
The mini-incision direct lateral surgical technique has been described previously1,6 and is performed with use of a 7 to 12-cm-long incision over the greater trochanter. The patient is placed in the lateral decubitus position. After division of the fascia lata over the greater trochanter, the tendon and fibers of the gluteus medius muscle are split and the hip joint is exposed from an anterior direction, as originally described by Hardinge12. A similar design of uncemented acetabular component (Foundation Total Hip System; Encore Medical, Austin, Texas) as was used in the two-incision group and a femoral component that was identical in design to the Zimmer M/L Taper (Linear Hip System; Encore Medical) were implanted in all ninety-six hips.
All patients in the two-incision group were allowed to place full weight on the involved hip after surgery, with use of crutches or a walker. No precautions to prevent hip dislocation were specified, and patients were instructed to use assistive devices during walking for the first six weeks after surgery as needed. Patients in the single mini-incision group were instructed to place 50% of their body weight on the involved hip with use of crutches or a walker. Patients in this group could begin full weight-bearing four weeks after surgery and were asked to use assistive devices during walking for the first six weeks after surgery. During these six weeks, patients in the single mini-incision group were instructed to follow precautions to prevent anterior hip dislocation.
After six weeks, both groups were allowed to increase their activity level as tolerated and to discard assistive devices. No specific pain-control regimen, anti-emetic protocol, or early discharge protocol was indicated for either group. Adjusted-dose warfarin was used for prophylaxis against deep venous thrombosis in both groups.
Data were reviewed retrospectively following the approval of our institutional review board. A chart review and an examination of radiographs were performed by an investigator who was not directly involved with the surgical procedures. All statistical analyses were performed by an independent statistician who was not otherwise associated with the present study.
Data were compared between groups at a mean of eleven months (range, six to seventeen months) after the two-incision hip replacements and at a mean of twenty-two months (range, eighteen to thirty months) after the single-incision hip replacements. The Wilcoxon rank-sum test was used for the evaluation of noncategorical variables, and the Fisher exact test was used for the evaluation of categorical variables. The level of significance was set at p < 0.05.
The study groups did not differ significantly with regard to age, gender, involved side, preoperative diagnosis of hip disease, or mean body mass index (Table I). The mean operative time was 127 minutes (range, eighty-two to 225 minutes) for the two-incision technique, compared with ninety-six minutes (range, seventy-seven to 125 minutes) for the single mini-incision technique; this difference was not significant.
The mean intraoperative blood loss was significantly greater (p < 0.0001) and the length of hospital stay was significantly shorter (p < 0.0013) for the two-incision group (Table I). Two hips in the single mini-incision group sustained an intraoperative fracture of the proximal part of the femur that necessitated cable fixation during the procedure (Table II). In contrast, seven femoral fractures were encountered in the two-incision group, five of which were fixed with cables during the index procedure and two of which were discovered after surgery when the femoral stem subsided. The latter two fractures necessitated a second surgical procedure for revision of the femoral component. The difference in the number of femoral fractures between the two groups approached significance (p = 0.0547).
One femoral stem was radiographically loose in the single-incision group, compared with four stems in the two-incision group; this difference did not reach significance (p = 0.20). The loose femoral stem in the single-incision group was diagnosed nine months after surgery during a workup of the patient for pain in the ipsilateral hip. In the two-incision group, the four loose stems were diagnosed between four and seven weeks after surgery. All loose stems in both groups were revised.
Nerve complications occurred only in the two-incision group (Table II). Twenty-two patients (twenty-two hips) had at least transient numbness in the thigh (suggesting an injury of the lateral femoral cutaneous nerve) after the two-incision procedure, and nine still had residual symptoms at the time of the last recorded follow-up. One patient (one hip) in the two-incision group had an incomplete femoral nerve palsy immediately after surgery, which resolved twelve months after the procedure. In contrast, no nerve complications occurred in the single-incision group. This difference between the two groups with regard to the rate of nerve complications was significant (p < 0.0001).
Wound complications occurred in two patients (two hips) in each group. All were successfully treated with irrigation and débridement and retention of the implants during the immediate postoperative period. One hip dislocation occurred in each group. A posterior dislocation occurred after trauma in a patient from the single-incision group twelve months after the index procedure. Closed reduction was successful, but the patient had recurrent dislocations. Revision surgery with use of a constrained acetabular component was ultimately performed, and the instability resolved. In the two-incision group, an anterior hip dislocation occurred in the recovery room in one patient. The patient required operative repositioning of the acetabular component because the cup was too anteverted. The malpositioning of the cup was not evident during surgery, despite the fact that fluoroscopic imaging was used.
The overall rate of complications was 42% (thirty-seven of eighty-nine) in the two-incision group, compared with 6% (six of ninety-six) in the single mini-incision group (p < 0.0001). The overall reoperation rate was 10% (nine of eighty-nine) in the two-incision group, compared with 3% (three of ninety-six) in the single-incision group, a difference that approached significance (p = 0.0731). At the time of the most recent follow-up, seven (8%) of the eighty-nine hips in the two-incision group had undergone component revision, compared with two (2%) of the ninety-six hips in the single-incision group; this difference also approached significance (p = 0.0905).
To assess the effect of surgeon experience on the rate of complications, the complication data from the first forty two-incision procedures were compared with those from the subsequent forty-nine procedures (Table III). The overall rate of complications (including all instances of thigh numbness) was 55% (twenty-two of forty) following the first forty procedures, compared with 31% (fifteen of forty-nine) following the next forty-nine procedures (p = 0.0202). The prevalence of thigh numbness was 23% (nine of forty) following the first forty procedures, compared with 27% (thirteen of forty-nine) following the next forty-nine procedures (p = 0.66). With the exclusion of thigh numbness, the prevalence of complications was 33% (thirteen of forty) for the first forty hips, compared with 4% (two of forty-nine) for the next forty-nine hips (p = 0.0004). The reoperation rate was 18% (seven of forty) for the first forty hips, compared with 4% (two of forty-nine) for the next forty-nine hips; this difference approached significance (p = 0.0725). Finally, the component revision rate was 15% (six of forty) for the first forty hips, compared with 2% (one of forty-nine) for the subsequent forty-nine hips; this difference was significant (p = 0.0425).
The radiographic results for the two-incision and single mini-incision groups are shown in Table IV. No complete radiolucent lines were noted around any acetabular component. The mean cup abduction angle was significantly greater in the two-incision group than in the single-incision group (46.4° compared with 40.8°; p < 0.0001). Importantly, the number of outliers, defined as cups with an abduction angle of ≤30° or ≥50°, was significantly greater in the two-incision group than in the single-incision group (twenty-five compared with ten; p = 0.019). The number of stems that were in >5° of varus relative to the diaphyseal axis of the femur was twice as great in the two-incision group than in the single-incision group (eight stems compared with four stems), although this difference was not significant (p = 0.15). The mean limb-length discrepancy in the two-incision group was significantly less than that in the single-incision group (0.5 mm compared with 1.4 mm; p = 0.0001), although this difference was not thought to be clinically meaningful. Finally, the number of hips that were graded as having poor fit and fill of the cementless femoral component was significantly greater in the two-incision group as compared with the single-incision group (nine stems compared with one stem; p = 0.0064).
In our hands, the so-called minimally invasive two-incision approach demonstrated strikingly higher rates of complications, repeat surgery, and radiographic malpositioning of components than have been reported in association with the use of similar techniques1-4,6,9. In a series of 100 nonconsecutive primary total hip replacements that had been performed with the two-incision approach, for example, Berger and Duwelius reported only one intraoperative femoral fracture and no other complications3. Berger also reported an identical experience in a series of total hip replacements that had been performed for selected patients with use of a single mini-incision direct lateral approach6. Those reports suggest that, in carefully selected patients, hip-replacement surgery that is performed by a very experienced surgeon with a two-incision technique or with a single mini-incision direct lateral approach can be associated with few, if any, complications.
However, Mears and colleagues reported a number of complications in a series of seventy-five consecutive patients who had undergone total hip replacement with the two-incision technique2. Sixteen patients had thigh numbness, two sustained a proximal femoral fracture, and one femoral stem subsided after surgery. Furthermore, an increased risk of complications such as nerve injuries and femoral fractures has been reported by others who have used the two-incision method13 or a single anterior incision14 to perform total hip replacement.
The complications in the present series occurred despite the fact that all procedures were performed by a surgeon who had fellowship training and whose practice was limited to joint replacement surgery. Since the prevalence of complications has been shown to be inversely related to practice volume, it is probable that the complications reported here may be even higher in the hands of surgeons with a lower-volume practice15.
A previous multicenter study indicated that the number of key complications associated with the two-incision hip replacement technique did not decrease as a function of case number for the first ten cases13. In contrast, our data suggest that the rate of key complications (femoral fracture, femoral implant loosening, and dislocation) does decrease slightly. In the present series, the rates of complications and repeat surgery were substantially higher for the first forty patients as compared with the last forty-nine. Thus, while the results improved with experience, complications continued to occur, albeit at a lower rate, suggesting that the procedure is technically difficult to master.
It is possible that the rate of complications reported here could have been reduced by adopting the two-incision approach incrementally. For example, the surgical approach described by Smith-Petersen16 and Light and Keggi10 could be learned first with use of the traditional exposure so that a surgeon could become more familiar with the anatomy of the anterior part of the thigh. Several reports have advised surgeons to attempt mini-incision total hip surgery only after thorough familiarity and experience have been obtained with the standard surgical approach2,4,6. The present data suggest that the combination of a new anatomic approach, new implants, and severely compromised surgical exposure can result in an unacceptably high prevalence of early complications following hip replacement surgery.
Injury to branches of the lateral femoral cutaneous nerve is a recognized risk associated with the various anterior approaches to the hip joint10,16,17, just as the direct lateral approach is associated with gluteal nerve injury, abductor mal-function, and postoperative limp18-20. If the lateral branches of the lateral femoral cutaneous nerve are severed during the anterior approach to the hip joint, thigh numbness can persist for two to three years16. One technique that has been suggested to avoid nerve injury is to split the fibers of the tensor fasciae latae muscle longitudinally along its anteromedial border, instead of approaching the femoral neck in the interval between the tensor fasciae latae and the sartorius muscles10. We found that careful subcutaneous dissection to avoid branches of the lateral femoral cutaneous nerve, followed by splitting the fascia of the tensor fasciae latae muscle as far laterally as possible, reduced the rate of thigh numbness; in addition, we found that symptoms, when present, resolved within a few weeks after surgery. In these instances, symptoms of thigh numbness had to be elicited by questioning and examining the patients, who did not volunteer complaints related to this complication.
The intraoperative blood loss was greater in the two-incision group, probably because of the longer duration of surgery and the femoral canal reaming that was necessary to implant the femoral stems early in our experience with this technique. We observed that blood loss appeared to be associated with canal reaming in particular, and this led us to use a tapered femoral stem that is implanted without canal reaming21.
Although not documented in the present report, the patients who did well with the two-incision approach subjectively appeared to recover faster, to shed assistive devices earlier, and to return to independent walking earlier than those in the single-incision group; others have reported similar observations9,10. Furthermore, our data indicate that the duration of hospital stay was reduced by a mean of 0.6 day and that our ability to equalize limb lengths may have been some-what better in association with the two-incision technique. Importantly, the magnitude of these results is not clinically important. Such transient gains in early recovery parameters, no matter how satisfying to the surgeon and patient, must be balanced against the higher prevalence of complications, repeat surgery, and implant malpositioning that can occur when surgical exposure is compromised during total hip replacement surgery. The present study suggests that surgeons should approach total hip surgery involving small incisions and unfamiliar anatomic approaches with great caution. We currently use a modified version of the two-incision technique for all patients who meet our criteria for an uncomplicated primary total hip replacement by employing slightly larger incisions as well as previously described methods22,23. The gains associated with less-invasive surgical methods must be weighed carefully against the possibility of adverse short-term outcomes and the potential for increased long-term failures resulting from sub-optimal implant positioning. ▪
In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from Zimmer. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Department of Orthopaedic Surgery, School of Medicine, University of Missouri, Columbia, Missouri
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