The direct anterior (DA) approach for total hip arthroplasty (THA) has become increasingly popular in North America. Advantages raised by proponents include quicker return to function,1,2 reduced length of stay (LOS), increased accuracy in component positioning,3 and absent need for immediate postoperative hip precautions.4,5 With experience, adequate exposure of both the acetabulum and femur can be achieved. However, femoral access can be more technically challenging in difficult cases compared with other approaches to the hip.6
Although the DA approach is described as muscle sparing and internervous, the surgeon may require additional soft tissue releases to adequately expose the proximal femur. Most commonly, this involves release of the conjoint tendon (the common tendon of the superior and inferior gemelli and the obturator internus) and possibly the piriformis. If the exposure remains limited, the anterior 1 to 2 cm of the tensor fascia lata (TFL) can also be released off the iliac wing. These releases facilitate the ability to instrument the femur, including insertion of broaches and trials. The obturator externus and quadratus femoris typically remain intact following these releases.
To date, the effect of conjoint tendon release has not been previously explored with regard to either postoperative pain or function. It is unknown whether these additional releases compromises patient function or pain control in the immediate postoperative period. As such, the primary goal of this study was to evaluate the LOS and inpatient pain medication requirements of patients undergoing primary DA THA on the basis of conjoint tendon release. The secondary aim of the study was to determine whether conjoint tendon release influenced postoperative functional outcome scores.
Materials and Methods
A retrospective review of a prospectively collected database of THAs performed at the authors' institution was completed to identify all cases of primary DA THAs conducted by a single surgeon between August 2012 and July 2015. Three hundred twelve primary DA THAs were done in this period. All THAs were performed for hip arthrosis. Intraoperative release of the conjoint tendon and TFL was performed at the discretion of the surgeon at the time of surgery, and this information was obtained from the operative notes. As part of the release, the posterior capsule was elevated to expose the conjoint tendon. The remainder of the data was retrieved from prospectively collected database information or from the patient's hospital records. Approval was received from the institutional review board.
Patient demographics, intraoperative complications, and hospital LOS were evaluated for all cases. Inpatient pain medication data were available for all cases beginning in April 2014, with 27 patients taking patient-controlled analgesia excluded. All narcotics used in the hospital postoperatively were converted into milligram equivalents of oral morphine sulfate and were then divided by the LOS in days to obtain a daily morphine equivalent dose (MED). Pain medication data were available for 107 cases, of which 11 were concurrent bilateral THAs. Clinical outcome scores used were the 12-Item Short Form Health Survey (SF-12) score,7 Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score,8 and Harris Hip Score (HHS).9 Hip scores were calculated according to the HHS, with a total score including pain and function scores with a maximum of 100. The SF-12 and WOMAC questionnaires were filled out by patients both preoperatively and at the 1-year follow-up visit. One-year outcome scores were evaluated for all cases.
Statistical analyses were completed to identify differences in LOS, inpatient pain medication use, and clinical outcome scores between groups using multiple linear regression. All statistical analyses were performed using Excel (Microsoft Corp, Redmond, Washington).
Three hundred twelve cases of primary DA THAs were identified, of which 29 were concurrent bilateral THAs (Figure 1). Of these, 180 (57.7%) cases included a conjoint tendon release, whereas 29 (9.3%) had an additional TFL release. Of the 29 concurrent bilateral THAs, 21 (72.4%) cases had a conjoint tendon release. Mean LOS was 1.3±1.1 days, with age (P=.002), bilateral THA (P<.001), TFL release (P=.005), and intraoperative complications (P=.002) being predictive of LOS (Figure 2). Mean daily MED narcotic use was 43.2±48.2 mg, with age being a negative predictor of narcotic use (P=.019) (Figure 3). Neither conjoint or TFL release was a predictor of narcotic use. Mean change in HHS and WOMAC scores were 43.5±19.3 and 44.2±12.8, respectively (Figures 4–5). Body mass index was a negative predictor of 1-year HHS pain (P=.002), HHS total (P=.013), and all WOMAC subcategory scores (P<.001), whereas age was a negative predictor of 1-year HHS function (P<.001) and HHS total scores (P<.001). Conjoint tendon release was not predictive of LOS, inpatient pain medication requirements, or outcome scores.
Flowchart of numbers of patients in each cohort. Abbreviations: BMI, body mass index; DA, direct anterior; THA, total hip arthroplasty.
Bar graph of length of stay in days in patients who had no conjoint release, conjoint release only, or conjoint and tensor fascia lata (TFL) release.
Bar graph of daily narcotic use in oral morphine equivalent dosing in milligrams in patients who had no conjoint release, conjoint release only, or conjoint and tensor fascia lata (TFL) release.
Bar graph of change in Harris Hip Score (HHS) in patients who had no conjoint release, conjoint release only, or conjoint and tensor fascia lata (TFL) release.
Bar graph of change in the Western Ontario and McMaster Universities Arthritis Index (WOMAC) in patients who had no conjoint release, conjoint release only, or conjoint and tensor fascia lata (TFL) release.
In terms of intraoperative complications, 3 calcar fractures (2 with a conjoint release, 1 with no releases), 2 greater tro-chanter fractures (1 who had a conjoint release, 1 with no release), and 1 anterior femoral cortex fracture (no releases) occurred, as well as 1 broken drill bit during acetabular cup fixation.
Postoperative complications included 2 superficial wound infections treated with antibiotics (1 with conjoint release, 1 with no releases), 1 wound breakdown requiring revision of the incision (conjoint and TFL release), 1 hematoma requiring irrigation and debridement (conjoint and TFL release), 2 persistently draining wounds ultimately going on to a stage I revision (both conjoint release), 4 periprosthetic fractures secondary to fall (2 with a conjoint release, 2 with no releases), 1 myocardial infarction (conjoint release), 1 pulmonary embolus (no releases), and 1 deep venous thrombosis (conjoint release). Two patients received blood transfusions in hospital. There were no dislocations.
The direct anterior approach for THA has been advocated as an internervous, muscle sparing approach. However, more than half of patients in this cohort received a formal conjoint release, which is not an insignificant proportion. This is in keeping with a study by Meneghini et al,10 which found that 50% of their cadavers required piriformis or conjoint release to mobilize the femur during a Smith-Peterson approach. This may indicate that conjoint tendon releases are required in a substantive number of DA THA patients to enable appropriate access to the femur to enable safe femoral component instrumentation and implant insertion.
Although this release may be required in a large number of patients, conjoint release did not affect LOS, pain, or patient reported outcomes. If this is the case, then a low threshold for conjoint release to improve visualization, or even doing a conjoint release as a routine step in the uncomplicated DA THA, should be considered. Intraoperative proximal femoral fracture has been one concern with the DA approach, which has been noted to occur at a higher rate than that seen in other approaches.11 This may be in the form of femoral perforation or calcar fracture due to poor femoral exposure or greater tro-chanter fracture from excessive tension on the femoral elevation hook. As such, by improving exposure and anterior mobility of the femur, conjoint release may reduce the risk of proximal femoral fracture.
Even without formal release, the conjoint tendon may be compromised. Cadaveric studies have shown considerable variation in the attachments of the conjoint tendon.12 The anterosuperior nature of the conjoint attachment may result in damage to the tendon during capsular release or femoral rasping even if preserved by the surgical dissection. If this is indeed the case, then it may be preferable to formally release the conjoint and benefit from the improved exposure rather than leave it in situ and compromise the tendon later in the procedure. This potential for collateral damage done to the conjoint tendon may also explain the lack of difference in pain and outcome between cases of formal conjoint release and attempted preservation.
In contrast, release of the tensor fascia lata from the iliac crest was associated with an increased LOS. However, it did not predict inpatient narcotic requirements in this patient population. It could reflect collateral damage done to the TFL during those cases where a formal TFL release was not done, with resultant pain. Meneghini et al10 found that the TFL was damaged in all specimens undergoing a Smith-Peterson approach, with a mean of 31.2% of the surface area injured. Similarly, De Anta-Díaz et al13 found a significantly lower mean thickness of the TFL in patients with THA done via direct anterior approach as compared to a lateral approach, which may reflect TFL damage.
Regarding overall narcotic use, the current authors' mean numbers were higher than those seen in other studies,14–16 with the mean daily MED narcotic use in those studies being approximately 30 to 35 mg after conversion. However, this likely reflects the fact that the current data represent only inpatient narcotic use, which for most of the authors' patients involved postoperative days 0 to 2 as the authors had a short mean LOS. This is in contrast to other studies that assessed overall narcotic use up to postoperative day 3 or 4. Given that analgesic consumption is typically greatest in this period, this would explain the higher mean numbers seen in this study.
In terms of complications, intraoperative fractures of the proximal femur occurred in 6 (1.9%) cases. This is consistent with numbers seen in the literature, which range from 0.84% to 3%.17–19 No significant difference was seen with conjoint or TFL release. However, given that the decision to do a conjoint release was made intraoperatively, those patients receiving a conjoint release presumably had a more difficult femoral exposure and therefore may have been more at risk for intraoperative fracture. No dislocations occurred in any of the authors' patients, despite concerns in the literature with conjoint release. However, in those patients where there is greater risk for dislocation, the decision to do a conjoint release should be done on a case-by-case basis depending on the intraoperative exposure achieved without it.
Certain limitations of this study should be noted. First, it was retrospective and nonrandomized, with conjoint and TFL release being at the discretion of the operating surgeon. Second, a surrogate measure of pain was used as opposed to a validated measure such as visual analog scale. Third, the authors did not include shorter-term outcomes in this study. As such, the authors may not have been able to catch any short-term impacts, if they existed, on function with conjoint or TFL release. Finally, the ceiling effect of the outcome measures used may not allow a small difference to be seen.
This is the first study to look at the impact of conjoint tendon release in DA THA. Conjoint tendon release does not appear to affect postoperative pain, LOS, or 1-year functional outcomes in primary DA THA. The effect of intraoperative release of other soft tissues is uncertain because TFL release was associated with increased LOS but not postoperative pain. Given that conjoint release improves femoral exposure and mobilization, intraoperative thresholds for conjoint release should be low.
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