Studies suggest that total hip arthroplasty (THA) performed through direct anterior (DA) approach has better functional outcomes than other surgical approaches. The immediate to very early outcomes of DA THA are not known. A prospective, randomized study examined the very early outcome of THA performed through DA versus direct lateral approach. The functional outcomes on day 1, day 2, week 6, week 12, 6 months, and 1 year were measured. Patients receiving DA THA had significantly higher functional scores during the early period following surgery. The difference in functional scores leveled out at 6 months.
Key points
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Total hip arthroplasty (THA) performed through the direct anterior (DA) approach provides better early functional outcomes as measured by the validated functional instruments. These patients are able to return to work and gain functional independence earlier than their counterparts who receive surgery through the direct lateral approach and are subjected to the same postoperative rehabilitation protocols.
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The use of the DA approach, and the lack of need for muscle strengthening, reduces the need for physical therapy following discharge from the hospital. This difference minimizes cost, enhances functional recovery, and allows early return to driving and work.
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Performing THA through a DA approach, particularly without the proper training, may be challenging for the first few cases. Thus, there is a certain level of learning involved with this surgical approach. It is therefore paramount that surgeons unfamiliar with this approach who wish to adopt the DA approach for THA need to subject themselves to extensive cadaveric training.
Introduction
In recent years total hip arthroplasty (THA) performed through the direct anterior (DA) approach using the Hueter interval has been gaining popularity. This approach uses an internervous and intermuscular access to the hip joint and avoids violation of the abductor muscles or short rotators around the hip. Because of its minimally invasive nature, patients are expected to have a better early functional outcome, at least once the surgeon is beyond the learning curve. Numerous level 1 studies have compared the outcomes of THA performed through the DA approach with those of patients receiving THA either through direct lateral (DL) approach or posterolateral approach. In all of these studies, THA performed through the DA approach had better early functional outcome. In addition, patients receiving THA through the DA approach reported returning to daily activities, such as driving, more quickly.
Although based on available evidence, early outcomes of THA performed through the DA approach are superior to THA performed through other approaches, but a few facts still remain unknown. It is not known whether the superior outcome of THA performed through the DA approach applies to the very early time period, (ie, within hours). It is also not known by what time point in the postoperative period the functional outcome of THA done through other approaches catches up with the patients who undergo THA through a DA approach. This article addresses both of these questions and discusses a randomized, prospective study with specific objectives.
Material and methods
Following institutional review board approval, all patients with end-stage arthritis of the hip needing THA were approached and consented to participate in this randomized, prospective study. The study was also enlisted in http://www.clinicaltrials.gov . Randomization was performed using a random number generator in an electronic spread sheet. Patients were assigned to 1 of 2 groups. One group of patients received THA using the DA approach (modified Smith-Petersen), whereas others were assigned to receive THA using the DL approach (modified Hardinge) ( Fig. 1 ). The study began in February 2012 and enrollment completed in November 2013. During the period of study, 75 patients (84 hips) were recruited into the study. Throughout the same period, 47 other patients were also approached for enrollment but declined to be part of the study. The responses that eliminated participation included preference of a surgical approach (8 patients), unwillingness to participate in the follow-up data collection (3 patients), and not specifically providing a reason (36 patients). All patients undergoing conversion THA, revision THA, or complex THA that required an additional surgical approach or exposure, such as trochanteric slide or osteotomy, were also excluded.
In addition, and as a requirement of the institutional review board, the patients needed to be between the ages of 18 and 75 years, have the underlying diagnosis of osteoarthritis, able to read and comprehend English, and to sign the consent form to participate in the study. Patients with cognitive impairment or severe psychiatric illness that would preclude participation in the protocol mandated procedures were excluded. The purpose of the study and the method, including the randomization, were discussed in detail with the patients before the consent was obtained. The patients were informed that they would receive 1 of 2 surgical approaches, both of which were safe and effective. The risks of the surgical procedure were also discussed in detail with the patients.
All patients were subjected to the same preoperative and postoperative protocols for rehabilitation, pain management, and anticoagulation. There were 18 men (40.9%) and 26 (59.1%) women in the DA group, compared with 14 (35.0%) men and 26 (65%) women in the DL group.
Preoperative Protocol
The patients were evaluated in the outpatient setting. Patients were told they would be subjected to THA using either the DA or the DL approach. Patients were not advised that one was likely to provide better early outcomes than the other. The postoperative analgesia protocol was also discussed in detail; patients were told it would include oral opioid and nonopioid analgesics supplemented by intravenous medications, if needed. The patients were reassured that their pain would be well controlled. The patients were told about the benefits of early ambulation and encouraged to comply with the rehabilitation protocol, which involved assisted ambulation on the day of surgery and twice daily thereafter. Patients were told that home discharge was preferred and family members were encouraged to care for the patient at home.
Surgical Data
All patients received spinal anesthesia using 0.2 mg of DepoMorphine. Intravenous propofol, midazolam, and opioid analgesics such as morphine, fentanyl, or meperidine were administered at the discretion of the anesthesiologist. A detailed record of all intraoperative analgesics was maintained.
The surgery was performed in supine position on a regular operating table that could be flexed at the hip for the DA patients. The initial incision length was 5 cm, and the incision was lengthened as dictated by the need for surgical exposure. The only difference between the two groups was the location of the incision, which was placed laterally over the greater trochanter for the DL patients, and more anteriorly for the DA patients. The DA approach involved exposure of tensor fascia lata and division of its perimysium. The interval between sartorius and tensor fascia lata was not used in order to minimize the risk of injury to the lateral femoral cutaneous nerve. The lateral head or reflected portion of rectus was not incised but was retracted medially. Anterior capsulotomy was performed, preserving the capsule for later closure, and the femoral neck was exposed. A double osteotomy of the neck was performed and a wedge of bone from the femoral neck was removed to allow easy extraction of the remaining head. The preparation of the acetabulum and the femoral canal was then performed in the routine manner. Exposure of the femoral canal involved selected soft tissue releases on the posterior aspect of the femoral neck ensuring that the abductor mechanism and the short rotators of the hip were preserved. Modified instruments for the exposure of acetabulum and the femur were used during the DA approach, which included the use of a double offset broach handle for the femur.
The DL approach was performed by placement of the incision over the greater trochanter and division of the underlying fascia lata. The abductor mechanism was divided and the anterior one-half retracted anteriorly. Following capsulotomy, the hip was dislocated and the femoral neck was cut. Acetabular and femoral preparation was conducted in a conventional manner.
Uncemented femoral and acetabular components were used in all patients, which included a proximally coated, collarless, tapered femoral stem (ML Taper, Zimmer, Warsaw, IN) and a porous tantalum acetabular component (Continuum, Zimmer, Warsaw, IN). The type of bearing surface used was delta ceramic femoral head and highly cross-linked polyethylene (Longevity, Zimmer, Warsaw, IN) in all patients.
All surgical parameters, including estimated blood loss, operative time, intraoperative complications, and any other pertinent information, were recorded in detail. A full-time clinical coordinator was assigned to this study.
Postoperative Management
Appropriate prophylaxis for infection (Ancef [GlaxoSmithKline LLC, Middlesex, United Kingdom] preoperatively and for 24 hours postoperatively), and thromboembolism (aspirin [Bayer, Leverkusen, Germany] 81 mg twice a day for 4 weeks) was administered to all the patients according to our protocols.
Blood management included administration of 1 g of tranexamic acid intravenously before incision to all patients. Allogeneic blood transfusion was provided when necessary. Hemodynamic symptoms triggering transfusion included persistent tachycardia (heart rate >100 beats/min for at least 4 hours) and lassitude (inability to comply with physical therapy exercises). Any patients with dyspnea or chest pain were extensively evaluated. The internal medicine specialists, unaware of the status of the patients in the study, were responsible for hemoglobin management. The details of blood transfusion were recorded.
All patients received a social service consultant, who was also blinded to the surgical approach. The purpose was to discuss social circumstances and confirm the preoperatively determined disposition plan based on the degree of home support, the home layout, and the patient’s physical abilities. On occasions, patients initially assumed to be candidates for home discharge were sent to a skilled rehabilitation facility at the recommendation of the physical therapy team.
The cumulative dose and the type of analgesic medications administered during hospital stay were recorded in detail for each patient. The equianalgesic dose for all drugs was calculated. The equianalgesic conversion based on pain-relieving efficacy equivalent to 10 mg of morphine was used. Patients were placed initially on oral opioid medication (oxycodone 5 mg every 4 to 6 hours as needed) and oral nonopioid analgesics such as ketorolac were administered based on each patient’s needs and level of pain.
The patients were seen by a physical therapist a few hours after arrival on the ward and helped to sit in a chair or ambulate with assistance, if possible. Physical therapy occurred at least twice daily thereafter. The wounds were covered by a single occlusive dressing, which was kept in place for 5 to 7 days. The physical therapists were kept unaware of the type of approach that each patient had received.
Functional Outcome
The functional outcomes on day 1, day 2, week 6, week 12, 6 months, and 1 year were measured using the time-to-get-up-and-go (TUG), gait speed, chair test, Linear Analogue Scale (LASA), Harris Hip Score (HHS), and Lower Extremity Functional Score (LEFS). These tests included a timed test involving the patient standing from a seated position in a chair and walking 10 feet before turning around and returning to a seated position in the same chair without stopping (TUG). Gait speed is a timed test in which a patient walks a premeasured distance and velocity is measured. The chair test records the time required for a patient to stand from a seated position in a chair 5 consecutive times without the use of armrests for support. In addition, patients’ Functional Independence Measure subscores were recorded, which included patients’ locomotion status (complete independence, modified independence, supervision, minimal assistance, moderate assistance, maximal assistance, and total assistance), walking distance, the type of walking aid used (single-point cane, axillary crutches, rolling walker, or standard walker), return to work, and return to driving.
Follow-up
On discharge, patients were instructed to complete a daily diary that attempted to capture their functional recovery and analgesia consumption. A strict follow-up protocol was followed to closely monitor the patients recruited into this study. All patients were seen in the office and examined by an independent observer as well as the senior surgeon at or around 4 weeks postoperatively. Patients were then followed at routine intervals, which included a visit at 6 months, 1 year, and then at 2 years. Clinical examination and radiographic evaluation were performed during the follow-up. The independent blinded observer collected the data on all patients.
Statistical Analysis
Before initiation of the study a power analysis was performed by a statistician to ensure enrollment of an adequate sample size. For an effect size of 20% with alpha set to 0.05 and a power of 0.80, 40 patients were needed in each group. In addition to the required 80 subjects, 10 more patients in each group were recruited to allow for possible attrition.
Baseline and information collected at each study visit were compared between each intervention group using the Wilcoxon test for continuous variables and Fisher exact test for binary outcomes. Longitudinal analysis of outcomes was performed using a linear mixed effects model. All analyses were performed using R.3.1 (R Foundation for Statistical Computing, Vienna, Austria).
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