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Prospective Evaluation of the Posterior Tissue Envelope and Anterior Capsule After Anterior Total Hip Arthroplasty
The Journal of Arthroplasty xxx (2019) 1e7
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Prospective Evaluation of the Posterior Tissue Envelope and Anterior Capsule After Anterior Total Hip Arthroplasty Alexander S. McLawhorn, MD, MBA a, Alexander B. Christ, MD a, Rachelle Morgenstern, MPH a, *, Alissa J. Burge, MD b, Michael M. Alexiades, MD a, Edwin P. Su, MD a a b
Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY Department of Radiology and Imaging, Hospital for Special Surgery, New York, NY
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2019 Received in revised form 24 September 2019 Accepted 26 September 2019 Available online xxx
Background: Femoral exposure for direct anterior approach (DAA) total hip arthroplasty (THA) invariably requires posterior soft tissue releases. Released posterior structures cannot be repaired. The purpose of this study is to describe the frequency and anatomic consequences of DAA THA posterior soft tissue releases and to compare the appearance of the anterior capsule between a group of patients who had capsulotomy and repair versus capsulectomy. Methods: Thirty-two DAA THA patients underwent metal artifact reduction sequence magnetic resonance imaging at discharge and 1-year follow-up. Seventeen had underwent capsulotomy and repair and 15 capsulectomy. A radiologist blinded to intraoperative data scored each metal artifact reduction sequence magnetic resonance imaging. Anterior capsular integrity, status of the piriformis and conjoint tendons, and muscle atrophy were graded. Descriptive statistics were performed to analyze results. Results: Immediately postoperatively, 75% of piriformis tendons were intact and 38% of conjoined tendons were intact. At 1 year, 97% had an intact piriformis and conjoined tendon, although many were in continuity through scar with the capsule. The posterior capsule directly contacted bone in all patients. At 1 year, none of the patients who underwent capsulotomy with repair had persistent anterior capsule defects, while 27% in the capsulectomy group had persistent defects. Conclusion: Posterior capsule and conjoined tendon releases were commonly performed during DAA THA, yet continuity with bone was frequently achieved at 1 year. In this study, capsulotomy with repair resulted in no anterior capsular defects when compared with capsulectomy. These results may support improved THA stability observed after DAA with capsular repair despite posterior soft tissue releases. Level of Evidence: Level III, prospective cohort study. © 2019 Elsevier Inc. All rights reserved.
Keywords: direct anterior total hip arthroplasty capsulotomy capsulectomy piriformis tendon conjoined tendon posterior capsule
The direct anterior approach (DAA) for total hip arthroplasty (THA) is thought to avoid release and repair of posterior soft tissue structures, and it is has been suggested that DAA THA has decreased dislocation rates relative to the standard posterolateral approach. There is no consensus in published series as to whether dislocation risk is less with one surgical approach versus another. A number of
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2019.09.045. * Reprint requests: Rachelle Morgenstern, MPH, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th Street, New York, NY 10021. https://doi.org/10.1016/j.arth.2019.09.045 0883-5403/© 2019 Elsevier Inc. All rights reserved.
studies have demonstrated that dislocation rates after DAA are similar to rates of prosthetic instability after posterior approaches [1e4]. A well-controlled study examining over 2000 matched patients from a statewide arthroplasty registry suggested that DAA does not confer a benefit in regard to dislocation [5]. Although surgeons might suppose that the direction of dislocation after the DAA would be anterior, literature suggests that posterior instability may be as common as anterior instability after the DAA [6].The technical aspects of the DAA pertaining to soft tissue management during surgery may explain findings illustrating similar dislocation rates for DAA and the posterolateral approach. Posterior capsular repair prevents instability after THA using a posterior approach, whereby the repaired posterior soft tissues serves as a scaffold for the formation of a pseudocapsule that
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becomes a biological check rein to dislocation [7e10]. During the DAA, many surgeons release posterior soft tissue structures (ie, the posterior capsule, piriformis, and conjoined tendon insertions) in order to expose the proximal femur and elevate it anteriorly to facilitate femoral canal preparation and stem insertion [11,12]. These posterior structures cannot be repaired easily through an anterior incision, and their release may predispose DAA THA to posterior instability. However, this remains unknown as there have been no studies using magnetic resonance imaging (MRI) to evaluate the frequency of short external rotator (SER) release after DAA THA. The imaging appearance and status of the posterior soft tissues of the hip after primary THA using the posterolateral approach is well documented [9,10,13]. Although the condition of the abductor muscles and tendons has been reported, the appearance of the posterior soft tissue envelope after THA through the DAA has not been studied. Currently, there is no agreement as to whether capsulotomy and repair of the anterior capsule or capsulectomy is more appropriate during DAA. Capsulectomy facilitates femoral exposure, but a persistent capsular defect may predispose to anterior dislocation. Similar to the appearance of the posterior soft tissue envelope after DAA THA, the status of the anterior capsule after capsulotomy and repair versus capsulectomy has yet to be studied [14]. To date, no study has demonstrated the consequences of posterior releases as they relate to the integrity and healing of the posterior structures, which are integral for the posterior stability, as well as whether capsulectomy results in persistent anterior soft tissue defect [7,8]. The aim of this study is to evaluate the appearance of the posterior soft tissue envelope following the DAA, immediately postsurgery and at 1-year follow-up on MRI. A secondary aim is to determine the appearance of the anterior capsule after capsulotomy and repair versus capsulectomy during the DAA, immediately postsurgery and at 1-year follow-up on MRI. Furthermore, this study is a small prospective cohort study, and thus in order to provide direction for future, larger clinical studies and power analyses, this study presents outcomes data potentially related to capsulotomy and repair versus capsulectomy. Patients and Methods This prospective cohort study was approved by our in-house institutional review board and written informed consent was obtained from all participating subjects. All surgeries and scientific investigations were performed at a single, urban specialty hospital from April 2014 through April 2018. Adult patients, aged 35 years, who underwent primary uncemented THA through the DAA for osteoarthritis without a secondary diagnosis, by either of the 2 study surgeons, were eligible for inclusion. Patients were excluded if they had diagnoses of inflammatory arthritis, previous ipsilateral hip trauma, previous surgery on the ipsilateral hip, or a contraindication for MRI. Sample size was based on signal intensity of the anterior pseudocapsule at 1 year postoperative. Forty patients consented to participate in the study, and 32 patients completed immediate postoperative and a minimum of 1-year postoperative MRI scans. Seven patients refused to return for their 1-year postoperative MRI scans; 1 patient experienced a postoperative dislocation and withdrew from the study. Metal artifact reduction sequence-MRI was performed on a 1.5-T clinical scanner (General Electric Healthcare, Waukesha, WI) using a cardiac or small body coil and the institution’s routine clinical hip arthroplasty imaging protocol, including coronal multiacquisition variable-resonance image combination selective (MAVRIC-SL) inversion recovery and MAVRIC-SL proton densityeweighted images, in addition to high-resolution axial, sagittal, and coronal proton densityeweighted fast spin echo images. This imaging algorithm provides good spatial resolution as afforded by the fast
spin echo images, and excellent suppression of metal susceptibility artifact due to inclusion of the MAVRIC-SL pulse sequences (Table 1). The modified DAA is a minimally invasive approach to hip arthroplasty that involves an incision on the front of the hip and moving muscles rather than detaching tendons to replace the joint. This surgical technique was used for all surgeries; half the patients underwent capsulotomy and repair performed by one study surgeon and half underwent anterior capsulectomy performed by the other study surgeon. In patients who had a capsulotomy, an “H-type” incision was made along the femoral neck axis and extended medially and laterally along the anterior acetabulum and intertrochanteric ridge. In patients who had a capsulectomy, the anterior capsule from the anterior acetabulum to the intertrochanteric ridge, and between the superior and inferior femoral neck, was excised. For both groups of patients, the THA then proceeded with acetabular preparation and component insertion, with fluoroscopic guidance. The femoral hook for either the Omni-Tract or the Hana table was inserted distal to vastus flare and around the posterior femur. The femur was externally rotated, hyperextended, and adducted. The proximal femur was elevated using either the table-mounted retractor or motorized jack. Posterior soft tissue releases were performed according to the surgeon’s assessment of soft tissue tension and degree of femoral elevation necessary for femoral preparation. The posterior capsule was released first, followed by releases of the SER tendons, as deemed necessary by the operating surgeon, for femoral exposure. These releases included the piriformis and conjoined tendons, but not the obturator externus. Once femoral exposure was achieved, the femur was prepared and the implant was inserted, with fluoroscopic confirmation of sizing and position. In those patients who had a capsulotomy, an anterior capsular repair was performed in a side-to-side fashion with multiple nonresorbable sutures. The anterior capsule was repaired to the residual capsular tissue on the intertrochanteric ridge. In those patients who had an anterior capsulectomy, the tensor fascia lata and satorious were allowed to drape over the hip joint and the tensor fascia lata fascia was closed (Fig. 1). All patients received the same aftercare. Patients were permitted weight-bearing as tolerated immediately after surgery, without postoperative motion restrictions. Crutches, cane, or walker were used as walking aids as patient ability dictated. Aspirin 325 mg oral twice daily was provided for venous thromboembolic prophylaxis. Prospectively, each patient was offered MRI scans during his or her initial hospitalization for THA, at 3 months after THA, and at least 1 year after THA. MAVRIC sequences were used to suppress metal artifact, following previously published protocols [15]. MRI is an accurate and reproducible test to evaluate the soft tissues around the hip after THA [9,10,14,16,17]. There is excellent intraobserver reliability in regard to grading tendinosis, and the interobserver and intraobserver reliability for grading the soft tissues around THA has been established [17,18]. The present study used MRI methods and metrics similar to those that have been employed for evaluating the soft tissues around THA performed through the posterolateral approach [9,10]. A single senior board-certified musculoskeletal radiologist, blinded to the intraoperative, interpreted all studies. Integrity of the posterior soft tissues was measured and graded as previously detailed. The distance between SER tendons and bone were measured in millimeters, scored as intact when the measurement was 0 mm, or scored as scarred when in continuity to bone through scar tissue. The posterior capsule was scored qualitatively as intact to bone, released, or in continuity to bone through scar. Atrophy of the obturator internus and piriformis was graded similar to Goutallier's classification, and atrophy was characterized as none, mild, moderate, or severe [19].
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Table 1 MRI Sample Imaging Parameters for THA at 1.5 T. Parameter
Coronal MAVRIC IR
Axial FSE
Sagittal FSE
Coronal FSE
Axial FSE
Coronal MAVRIC FSE
Imaged TR (ms) TE (ms) TI (ms) BW (kHz) NEX FOV (cm) Matrix Slice/gap (mm)
Whole pelvis 4000-6000 21-43 150 ±125 0.5 40 256 192 5/0
Whole pelvis 4500-5500 21.4-32 NA 83-100 4 32-36 512 256 5/0
Affected hip 5500-6500 23-30 NA 83-100 4-5 17-18 512 352 2.5-3/0
Affected hip 4500-5800 24-30 NA 83-100 4-5 18 512 352 4/0
Affected hip 4500-5500 24-30 NA 83-100 4-5 17-19 512 256-288 4/0
Whole pelvis 4000-6000 21-43 NA ±125 0.5 40 320-512 256-384 3-4.5/0
MRI, magnetic resonance imaging; THA, total hip arthroplasty; TR, time to repetition; TE, echo time; TI, inversion time; pBW, pixel bandwidth; NEX, number of excitations; FOV, field of view; IR, inversion recovery; PD, proton density; FSE, fast spin echo; MAVRIC-SL, multiacquisition variable resonance image combination selective; NA, not applicable.
Patient baseline demographics, clinical characteristics, and frequency of postoperative groin pain were collected. Postoperative patient-reported outcome measures, including modified Harris Hip Scores (mHHS), Hip disability and Osteoarthritis Outcome Score for Joint Replacement, and Lower Extremity Activity Scale, were collected; mHHS was also collected preoperatively. Heterotopic ossification was categorized on final follow-up radiographs according to the classification of Brooker [20,21]. MRI appearance of soft tissue repairs was summarized. Statistical analyses were conducted using SAS software version 9.4 (SAS Institute Inc, Carey, NC), with a 5% level of significance. Data were analyzed using Fisher exact tests, Wilcoxon sum rank tests, Wilcoxon signed-rank test, and where appropriate only descriptive statistics were used. Results At the time of surgery, the median (q1-q3) age of the total cohort was 61.1 (56.8-68.6) years, the median body mass index was 25.7 (23.7-27.7) kg/m2, and 78% of participants were female. Fifty-nine percent of surgeries were performed on a right hip and there were no intraoperative complications. Immediately postoperatively, 75% (24/32) of piriformis tendons were intact, 88% (28/32) had no piriformis atrophy, and for those that were released the mean distance to bone was 2.3 mm (range, 2-8). At 1year follow-up, 97% (31/32) had an intact piriformis, although 28% (9/32) were in continuity through scar with the capsule (Figs. 2 and 3). Fifty-nine percent of hips (19/32) showed no piriformis atrophy, 18% (6/32) had mild atrophy, and 22% (7/32) showed moderate atrophy.
Immediately postoperatively, 35% (11/32) of conjoined tendons were intact, 94% (30/32) showed no sign of obturator internus atrophy, and for those that were released the mean distance to bone was 4.1 mm (range, 2-10 mm). Of released conjoined tendons, at 1year follow-up, only 1 conjoined tendon was not intact while 95% (20/21) were intact through scar-in-continuity with the posterior capsule (Figs. 2 and 3). At 1-year follow-up, 34% (11/32) of patients had moderate obturator internus atrophy, 34% (11/32) had mild atrophy, and 31% (10/32) showed no atrophy. The posterior capsule directly contacted bone or was in continuity with bone through scar in all patients. Seventeen patients underwent capsulotomy with repair and 15 underwent anterior capsulectomy. Between the capsulotomy and repair and capsulectomy groups, the only significant differences in baseline characteristics were that the capsulotomy group was slightly but significantly older (P ¼ .0234) and had slightly lower body mass index (P ¼ .0246). During the study period, there was 1 reoperation for iliopsoas impingement, and 1 patient withdrew from the study after a dislocation event. At 1 year postoperatively, none of the patients who underwent capsulotomy with repair had persistent anterior capsule defects, while 27% (4/15) in the capsulectomy group had persistent defects (Fig. 4).In the total cohort, the median preoperative mHHS was 51.5 (43-59.2) points with significantly higher scores in the capsulotomy and repair versus the capsulectomy group (P ¼ .0069). Postoperative mHHS scores were significantly higher than preoperative in the total cohort (P < .0001), in the capsulotomy and repair group (P < .0001), and in the capsulectomy group (P ¼ .0001), with no significant difference between the 2 cohorts (P ¼ .358). The median postoperative Hip
Fig. 1. Repaired and detached capsules intraoperatively. Intraoperative images of a repaired capsule during a capsulotomy and repair (A) as compared to a detached capsule during a capsulotomy (B).
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Fig. 2. Intact SERs. Coronal PD image (A) in a 68-year-old woman immediately following DAA THA demonstrates somewhat hyperintense but otherwise intact conjoined tendon (white arrowhead). Coronal PD image (B) obtained 3 months following surgery demonstrates ongoing scar remodeling with decreased hyperintensity of tendon fibers (white arrowhead), with further remodeling yielding normal signal intensity of fibers (white arrowhead) at 1 year following surgery (C). SER, short external rotator; PD, proton density; DAA, direct anterior approach; THA, total hip arthroplasty.
disability and Osteoarthritis Outcome Score for Joint Replacement score and Lower Extremity Activity Scale were 100 (80.6-100) and 13 (11-14), respectively; there was no difference between the 2 subcohorts (P ¼ .892 and P ¼ .269, respectively; Table 2). Two
patients had pain at final follow-up: 1 patient reported it as 1/10 on the visual analogue scale and the other reported it as 4/10. Two patients had evidence of Brooker grade I heterotopic ossification at final follow-up. There were no differences between the
Fig. 3. Scar-remodeled SERs. Coronal (A) and axial (B) PD images in a 57-year-old woman immediately following DAA THA demonstrate discontinuity of the conjoined tendon (white arrowhead) yielding a 3-mm gap; obturator internus muscle bulk is preserved at this time point (black arrowhead). Coronal (C) and axial (D) PD images 7 months later demonstrate formation of scar in continuity with intact tissue bridging the previously visible gap (white arrowhead), although a degree of interval obturator internus atrophy is noted (black arrowhead).
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Fig. 4. Anterior capsule. (A) Axial PD-weighted image (A1) in a 51-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulotomy, with band of hyperintense tissue bridging the site, related to repair (white arrowheads). Axial PD image (A2) obtained approximately 8 months following surgery demonstrates scar remodeling of the repaired capsule, with intact tissue bridging the previously visualized capsular defect (white arrowhead). (B) Axial PD-weighted image (B1) in a 60-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulectomy (white arrowheads). Axial PD image (B2) obtained approximately 5 months following surgery demonstrates scar remodeling of the capsule, with intact tissue bridging the previously visualized capsular defect (white arrowhead). (C) Axial PD-weighted image (C1) in a 61-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulectomy (white arrowheads). Axial PD image (C2) obtained approximately 8 months following surgery demonstrates persistent, although smaller, capsular defect (white arrowheads).
capsulotomy and repair versus capsulectomy groups with respect to these outcomes. Discussion Postoperative instability remains a clinically important problem after primary THA. The overall frequency of postoperative dislocation is 2%-4%, depending on the quoted series and duration of follow-up [22]. Similarly, this study found the frequency of postoperative dislocations was 3%. Studies report that instability accounts for 22.5% of revision THAs [23]. The etiology of dislocation is multifactorial, including factors under the purview of surgical technique as well as independent patient factors. Historically, the surgical approach used for THA has been associated with risk of
dislocation [24]. Recently, the DAA for THA has become increasing popular, in part due to a reported reduction in postoperative dislocation [1,4]. It is counterintuitive that instability might be reduced when posterior soft tissue structures are not infrequently released (and not repaired) for femoral exposure during the DAA, because the posterior soft tissue repair is recognized as an important barrier to short-term and long-term postoperative instability after THA performed through the posterolateral approach [9e12]. The short-term integrity of the posterior capsule and SER tendons after DAA THA has not been previously studied. Furthermore, the insertions of the piriformis and conjoined tendons onto the greater trochanter are variable, and surgeons’ ability to perform selective posterior tendon releases through a minimally invasive anterior approach to the hip has not been studied [11,25]. Therefore,
Table 2 Preoperative Clinical Characteristics and Preoperative and Postoperative PROMs According to Capsulotomy and Repair versus Capsulectomy Cohorts. Variables
Total (N ¼ 32)
Capsulotomy and Repair (N ¼ 17)
Capsulectomy (N ¼ 15)
P Value
Sex (male:female) Laterality (left:right) Age (y) Height (cm) Weight (kg) Body mass index (kg/m2) mHHS preoperative (points) mHHS follow-up (points) HOOS, JR. postoperative (points) LEAS postoperative (points)
7:25 13:19 61.1 (56.8-68.6) 165.1 (160-168.9) 69.5 (63.3-78) 25.7 (23.7-27.7) 51.5 (43-59.2) 96 (90-98) 100 (80.6-100) 13 (11-14)
2:15 9:8 67.9 165.1 66.7 25.1 59 98 100 13
5:10 4:11 60.4 165.1 75.7 26.8 45.1 95.7 100 13
.210 .166 .0234 .482 .0413 .0246 .0069 .358 .892 .269
(57.6-70.5) (160-167.6) (61.2-72.6) (23.3-26.1) (48-63) (89-99) (92-100) (11-14)
(53.8-62) (160-175.2) (63.5-108.9) (24.8-35.8) (41-53) (90-97) (77-100) (10-13)
PROMs, Patient-reported outcome measures; mHHS, modified Harris Hip Scores; HOOS, JR., Hip disability and Osteoarthritis Outcome Score for Joint Replacement; LEAS, Lower Extremity Activity Scale.
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this study sought to quantify the frequency of SER tendon releases and to describe the serial appearance of the posterior soft tissue envelope on MRI, in patients after THA through the DAA immediately following surgery and at a minimum of 1-year follow-up. Posterior capsule and conjoined tendon releases were commonly performed during DAA THA, yet continuity with bone was frequently achieved at 1-year MRI follow-up. There are several limitations to this study. A small sample size was used and patients were contributed by only 2 orthopedic surgeons. Consequently, descriptive statistics were used to report MRI appearance of soft tissue repairs but tests for significance were not appropriate. Additionally, due to the sample size no associations could be made between posterior soft tissue releases and the occurrence of THA instability. However, this is countered by the fact that the study is the first to provide a longitudinal description of the posterior soft tissue envelope after DAA with particular attention to tendon releases. A gold standard for assessing tendon releases from the anterior approach has not been established. Surgeon identification of posterior tendons through the DAA is based on their perception of the distal tendon course and insertion, whereas a radiologist may trace a tendon across serial slices in multiple planes to its muscle belly. It is probable that the radiologist’s assessment is more reliable than the surgeon’s. MAVRIC sequences do suppress a significant amount of metal artifact. Nonetheless some artifact still remains, which may obscure accurate interpretation of all anatomic features. In general, however, MRI has had an excellent track record for investigating soft tissue structures around THAs [9,10,15,16,26]. We are not aware of any study reporting a comparison between intraoperative surgical releases and postoperative imaging assessments of recorded releases. However, difficulty in identifying releases intraoperatively may be due to the substantial variability that exists in the insertion of these tendons on the greater trochanter [11,25]. Tendons may also be inadvertently damaged during femoral broaching and thus not recognized. Additionally, many DAA surgeons were classically trained as posterior approach surgeons, and tendinous anatomy of the SERs from the inside out may be unfamiliar. Ito et al [11] mapped the attachments of the piriformis and conjoined tendons in 20 cadaveric hips. While there was considerable interspecimen variability, on average the conjoined tendon inserted near the anterior aspect of the greater trochanter, approximately 5 mm superior to the saddle between the lateral femoral neck and the greater trochanter. On average, the piriformis tendon inserted in a relatively posterior and superior position to the conjoined tendon [11]. Roche et al [25] observed similar insertions in 15 cadaveric specimens. Consequently, it is not surprising that conjoined tendon was released more frequently than the piriformis tendon in this series at 65% and 25%, respectively, as the surgeon is more likely to encounter this tendon through the anterior approach and after releasing the superior band of the hip capsule. Additionally, after the capsule, the conjoined tendon provides modest restraint to femoral elevation, and its release is advocated when femoral exposure must be augmented [1,12]. During the anterior approach, access to the hip joint must be obtained through the anterior capsule. In this series, capsulotomy with repair was performed in 17 patients, and capsulectomy was performed in 15 patients. Of the patients who underwent capsular repair, none had a persistent defect on MRI at 1 year. In contrast, 27% of patients who underwent capsulectomy had a persistent defect at 1 year. While this study was underpowered to show any significant clinical differences between these 2 groups, lack of the anterior capsule is concerning and larger studies may be able to detect such differences.
In a cadaver study, significantly more anterior translation of the native femoral head was found after capsulectomy, whereas there was no difference between the intact and suture-repaired capsule [27]. Another cadaver study found that from the lateral approach capsular repair increased the force needed to dislocate the hip after hemiarthroplasty [28]. Also, experientially the tissue that forms in place of the capsulectomy is not of the same quality as the repaired capsule. While this was not specifically examined in our study, it should be taken into consideration. The posterior capsule was frequently released in both groups of patients during the femoral exposure. Although it was not directly repaired, the posterior capsule directly contacted bone or was in continuity with bone through scar in all patients at 1 year after THA. The present findings should be interpreted within the context of similar studies examining these soft tissues after the posterior approach. In a previous study by Pellicci et al, 36 patients received primary THA using the standard posterolateral approach. In these patients, the posterior capsule and SER tendons were all released during surgery and then repaired using a transosseous technique. Subsequently, patients received MRI of the operated hip during their postoperative hospital stay and at 3 months. At 3 months, the posterior capsule was intact in 90% of patients. Forty-three percent of piriformis repairs were intact, and only 57% of conjoint tendon repairs were intact based on study criteria [9]. A follow-up study performed on 22 patients from this series at a mean of 49 months after THA showed that there were progressive increases in the distances between the native tendon stumps and the greater trochanter. At 3 months, all SER tendons had retracted on average 2.5 to 2.7 cm, and these findings were associated with substantial atrophy of the piriformis and obturator internus muscles, with only 23% of muscles showing no atrophy. The authors concluded that the repair did not provide functional muscle tendon units, but they believe that it facilitated scar formation in continuity to bone between the posterior capsule and the tendons, which was observed in 96% of cases [10]. No repair was performed for released posterior structures in the present study, yet continuity with bone was achieved in nearly all patients. Furthermore, we saw a lower incidence of muscle atrophy with 40% of mild/moderate piriformis and 65% mild/moderate obturator externus. It is probable that released tendons and posterior capsule retracted minimally after the DAA, as there was otherwise minimal interruption in the posterior soft tissue envelope and adjacent fascial tethers. Possibly scar can easily bridge subcentimeter defects between the released structures and bone without an intervening scaffold. These observations may explain why posterior instability is limited after DAA despite frequent release of posterior soft tissue structures. On the other hand, the frequency with which posterior releases are performed, and large diameter femoral heads, may explain why a modern comparative study failed to identify a difference in dislocation rates between anterior and posterior approaches [5]. Conclusion Posterior capsule and conjoined tendon releases were commonly performed in this series of DAA THA, yet continuity with bone was frequently achieved at short-term follow-up. In comparison to some studies reporting a decreased incidence of instability using the DAA, the present study had a frequency of instability similar to a conventional posterior-lateral approach. Differences in sample size and patient population can affect overall instability rates and in our hands the DAA has proven to be reliable. Capsulotomy and repair consistently resulted in intact anterior capsule at final follow-up, while capsulectomy left a persistent defect in 27% of patients. Appreciation of the variability and relative
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location of tendon insertions, along with capsular repair whenever possible, is required for DAA surgeons aiming to provide soft tissueesparing THA surgery. Acknowledgments We would like to acknowledge our patients who continue to participate in clinical trials and enable us to further our understanding of and treatments for musculoskeletal diseases. Lauren Mount and Imraan Khan were early contributors to this study and we would like to acknowledge their work. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Matta JM, Shahrdar C, Ferguson T. Single-incision anterior approach for total hip arthroplasty on an orthopaedic table. Clin Orthop Relat Res 2005;441: 115e24. https://doi.org/10.1097/01.blo.0000194309.70518.cb. [2] Hallert O, Li Y, Brismar H, Lindgren U. The direct anterior approach: initial experience of a minimally invasive technique for total hip arthroplasty. J Orthop Surg Res 2012;7:17. https://doi.org/10.1186/1749-799X-7-17. [3] Sariali E, Leonard P, Mamoudy P. Dislocation after total hip arthroplasty using hueter anterior approach. J Arthroplasty 2008;23:266e72. https://doi.org/ 10.1016/j.arth.2007.04.003. [4] Kennon RE, Keggi JM, Wetmore RS, Zatorski LE, Huo MH, Keggi KJ. Total hip arthroplasty through a minimally invasive anterior surgical approach. J Bone Joint Surg Am 2003;85:39e48. https://doi.org/10.1007/s11610-006-0011-5. [5] Maratt JD, Gagnier JJ, Butler PD, Hallstrom BR, Urquhart AG, Roberts KC. No difference in dislocation seen in anterior vs posterior approach total hip arthroplasty. J Arthroplasty 2016;31:127e30. https://doi.org/10.1016/j.arth. 2016.02.071. [6] Jewett BA, Collis DK. High complication rate with anterior total hip arthroplasties on a fracture table. Clin Orthop Relat Res 2011;469:503e7. https:// doi.org/10.1007/s11999-010-1568-1. [7] Pellicci PM, Bostrom M, Poss R. Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop Relat Res 1998:224e8. https://doi.org/10.1097/00003086-199810000-00023. [8] Chiu FY, Chen CM, Chung TY, Lo WH, Tain Hsiung C. The effect of posterior capsulorrhaphy in primary total hip arthroplasty. A prospective randomized study. J Arthroplasty 2000;15:194e9. [9] Pellicci PM, Potter HG, Foo LF, Boettner F. MRI shows biologic restoration of posterior soft tissue repairs after THA. Clin Orthop Relat Res 2009;467:940e5. https://doi.org/10.1007/s11999-008-0503-1. [10] McLawhorn AS, Potter HG, Cross MB, Boettner F, Lim W, Lee Y, et al. Posterior soft tissue repair after primary THA is durable at mid-term followup: a prospective MRI study. Clin Orthop Relat Res 2015;473:3183e9. https://doi.org/ 10.1007/s11999-015-4380-0. [11] Ito Y, Matsushita I, Watanabe H, Kimura T. Anatomic mapping of short external rotators shows the limit of their preservation during total hip arthroplasty. Clin Orthop Relat Res 2012;470:1690e5. https://doi.org/ 10.1007/s11999-012-2266-y.
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[12] Matsuura M, Ohashi H, Okamoto Y, Inori F, Okajima Y. Elevation of the femur in THA through a direct anterior approach: cadaver and clinical studies. Clin Orthop Relat Res 2010;468:3201e6. https://doi.org/10.1007/s11999-0101349-x. [13] Su EP, Mahoney CR, Adler RS, Padgett DE, Pellicci PM. Integrity of repaired posterior structures after THA. Clin Orthop Relat Res 2006;447:43e7. https:// doi.org/10.1097/01.blo.0000218744.07366.29. [14] Bremer AK, Kalberer F, Pfirrmann CWA, Dora C. Soft-tissue changes in hip abductor muscles and tendons after total hip replacement: comparison between the direct anterior and the transgluteal approaches. J Bone Joint Surg Br 2011;93-B:886e9. https://doi.org/10.1302/0301-620X.93B7.25058. [15] Koch KM, Brau AC, Chen W, Gold GE, Hargreaves BA, Koff M, et al. Imaging near metal with a MAVRIC-SEMAC hybrid. Magn Reson Med 2011;65:71e82. https://doi.org/10.1002/mrm.22523. [16] Potter HG, Nestor BJ, Sofka CM, Ho ST, Peters LE, Salvati EA. Magnetic resonance imaging after total hip arthroplasty: evaluation of periprosthetic soft tissue. J Bone Joint Surg Am 2004;86:1947e54. [17] Springer I, Muller M, Hamm B, Dewey M. Intra- and interobserver variability of magnetic resonance imaging for quantitative assessment of abductor and external rotator muscle changes after total hip arthroplasty. Eur J Radiol 2012;8:928e33. https://doi.org/10.1016/j.ejrad.2011.01.113. [18] Sein ML, Walton J, Linklater J, Harris C, Dugal T, Appleyard R, et al. Reliability of MRI assessment of supraspinatus tendinopathy. Br J Sports Med 2007;41: e9. https://doi.org/10.1136/bjsm.2006.034421. [19] Goutallier D, Postel J-M, Bernageau J, Lavau L, Voisin M-C. Fatty muscle degeneration in cuff ruptures. Clin Orthop Relat Res 1994;304:78e83. https:// doi.org/10.1097/00003086-199407000-00014. [20] Lyman S, Lee YY, Franklin PD, Li W, Mayman DJ, Padgett DE. Validation of the HOOS, JR: a short-form hip replacement survey. Clin Orthop Relat Res 2016;474:1472e82. https://doi.org/10.1007/s11999-016-4718-2. [21] Brooker AF, Bowerman JW, Robinson RA, Riley LH. Ectopic ossification following total hip replacement: incidence and a method of classification. J Bone Joint Surg Am 1973;55:1629e32. https://doi.org/10.1007/978-1-44715451-8_25. [22] Malkani AL, Ong KL, Lau E, Kurtz SM, Justice BJ, Manley MT. Early- and lateterm dislocation risk after primary hip arthroplasty in the Medicare population. J Arthroplasty 2010;25:21e5. https://doi.org/10.1016/j.arth.2010.04.014. [23] Bozic KJ, Kurtz SM, Lau E, Ong K, Vail TP, Berry DJ. The epidemiology of revision total hip arthroplasty in the United States. J Bone Joint Surg Am 2009;91:128e33. https://doi.org/10.2106/JBJS.H.00155. [24] Kwon MS, Kuskowski M, Mulhall KJ, Macaulay W, Brown TE, Saleh KJ. Does surgical approach affect total hip arthroplasty dislocation rates? Clin Orthop Relat Res 2006;447:34e8. https://doi.org/10.1097/01.blo.0000218746.8 4494.df. [25] Roche JJW, Jones CDS, Khan RJK, Yates PJ. The surgical anatomy of the piriformis tendon, with particular reference to total hip replacement: a cadaver study. Bone Joint J 2013;95:764e9. https://doi.org/10.1302/0301-620X.95 B6.30727. [26] Hayter CL, Koff MF, Potter HG. Magnetic resonance imaging of the postoperative hip. J Magn Reson Imaging 2012;35:1013e25. https://doi.org/ 10.1002/jmri.23523. [27] Bakshi NK, Bayer JL, Bigelow EMR, Jameel OF, Sekiya JK. The effect of capsulectomy on hip joint biomechanics. Orthop J Sports Med 2017;5:1e6. https:// doi.org/10.1177/2325967117733433. [28] Hughes AW, Clark D, Carlino W, Gosling O, Spencer RF. Capsule repair may reduce dislocation following hip hemiarthroplasty through a direct lateral approach: a cadaver study. Bone Joint J 2015;97:141e4. https://doi.org/10.1 302/0301-620X.97B1.
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Prospective Evaluation of the Posterior Tissue Envelope and Anterior Capsule After Anterior Total Hip Arthroplasty Alexander S. McLawhorn, MD, MBA a, Alexander B. Christ, MD a, Rachelle Morgenstern, MPH a, *, Alissa J. Burge, MD b, Michael M. Alexiades, MD a, Edwin P. Su, MD a a b
Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY Department of Radiology and Imaging, Hospital for Special Surgery, New York, NY
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 July 2019 Received in revised form 24 September 2019 Accepted 26 September 2019 Available online xxx
Background: Femoral exposure for direct anterior approach (DAA) total hip arthroplasty (THA) invariably requires posterior soft tissue releases. Released posterior structures cannot be repaired. The purpose of this study is to describe the frequency and anatomic consequences of DAA THA posterior soft tissue releases and to compare the appearance of the anterior capsule between a group of patients who had capsulotomy and repair versus capsulectomy. Methods: Thirty-two DAA THA patients underwent metal artifact reduction sequence magnetic resonance imaging at discharge and 1-year follow-up. Seventeen had underwent capsulotomy and repair and 15 capsulectomy. A radiologist blinded to intraoperative data scored each metal artifact reduction sequence magnetic resonance imaging. Anterior capsular integrity, status of the piriformis and conjoint tendons, and muscle atrophy were graded. Descriptive statistics were performed to analyze results. Results: Immediately postoperatively, 75% of piriformis tendons were intact and 38% of conjoined tendons were intact. At 1 year, 97% had an intact piriformis and conjoined tendon, although many were in continuity through scar with the capsule. The posterior capsule directly contacted bone in all patients. At 1 year, none of the patients who underwent capsulotomy with repair had persistent anterior capsule defects, while 27% in the capsulectomy group had persistent defects. Conclusion: Posterior capsule and conjoined tendon releases were commonly performed during DAA THA, yet continuity with bone was frequently achieved at 1 year. In this study, capsulotomy with repair resulted in no anterior capsular defects when compared with capsulectomy. These results may support improved THA stability observed after DAA with capsular repair despite posterior soft tissue releases. Level of Evidence: Level III, prospective cohort study. © 2019 Elsevier Inc. All rights reserved.
Keywords: direct anterior total hip arthroplasty capsulotomy capsulectomy piriformis tendon conjoined tendon posterior capsule
The direct anterior approach (DAA) for total hip arthroplasty (THA) is thought to avoid release and repair of posterior soft tissue structures, and it is has been suggested that DAA THA has decreased dislocation rates relative to the standard posterolateral approach. There is no consensus in published series as to whether dislocation risk is less with one surgical approach versus another. A number of
One or more of the authors of this paper have disclosed potential or pertinent conflicts of interest, which may include receipt of payment, either direct or indirect, institutional support, or association with an entity in the biomedical field which may be perceived to have potential conflict of interest with this work. For full disclosure statements refer to https://doi.org/10.1016/j.arth.2019.09.045. * Reprint requests: Rachelle Morgenstern, MPH, Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E 70th Street, New York, NY 10021. https://doi.org/10.1016/j.arth.2019.09.045 0883-5403/© 2019 Elsevier Inc. All rights reserved.
studies have demonstrated that dislocation rates after DAA are similar to rates of prosthetic instability after posterior approaches [1e4]. A well-controlled study examining over 2000 matched patients from a statewide arthroplasty registry suggested that DAA does not confer a benefit in regard to dislocation [5]. Although surgeons might suppose that the direction of dislocation after the DAA would be anterior, literature suggests that posterior instability may be as common as anterior instability after the DAA [6].The technical aspects of the DAA pertaining to soft tissue management during surgery may explain findings illustrating similar dislocation rates for DAA and the posterolateral approach. Posterior capsular repair prevents instability after THA using a posterior approach, whereby the repaired posterior soft tissues serves as a scaffold for the formation of a pseudocapsule that
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becomes a biological check rein to dislocation [7e10]. During the DAA, many surgeons release posterior soft tissue structures (ie, the posterior capsule, piriformis, and conjoined tendon insertions) in order to expose the proximal femur and elevate it anteriorly to facilitate femoral canal preparation and stem insertion [11,12]. These posterior structures cannot be repaired easily through an anterior incision, and their release may predispose DAA THA to posterior instability. However, this remains unknown as there have been no studies using magnetic resonance imaging (MRI) to evaluate the frequency of short external rotator (SER) release after DAA THA. The imaging appearance and status of the posterior soft tissues of the hip after primary THA using the posterolateral approach is well documented [9,10,13]. Although the condition of the abductor muscles and tendons has been reported, the appearance of the posterior soft tissue envelope after THA through the DAA has not been studied. Currently, there is no agreement as to whether capsulotomy and repair of the anterior capsule or capsulectomy is more appropriate during DAA. Capsulectomy facilitates femoral exposure, but a persistent capsular defect may predispose to anterior dislocation. Similar to the appearance of the posterior soft tissue envelope after DAA THA, the status of the anterior capsule after capsulotomy and repair versus capsulectomy has yet to be studied [14]. To date, no study has demonstrated the consequences of posterior releases as they relate to the integrity and healing of the posterior structures, which are integral for the posterior stability, as well as whether capsulectomy results in persistent anterior soft tissue defect [7,8]. The aim of this study is to evaluate the appearance of the posterior soft tissue envelope following the DAA, immediately postsurgery and at 1-year follow-up on MRI. A secondary aim is to determine the appearance of the anterior capsule after capsulotomy and repair versus capsulectomy during the DAA, immediately postsurgery and at 1-year follow-up on MRI. Furthermore, this study is a small prospective cohort study, and thus in order to provide direction for future, larger clinical studies and power analyses, this study presents outcomes data potentially related to capsulotomy and repair versus capsulectomy. Patients and Methods This prospective cohort study was approved by our in-house institutional review board and written informed consent was obtained from all participating subjects. All surgeries and scientific investigations were performed at a single, urban specialty hospital from April 2014 through April 2018. Adult patients, aged 35 years, who underwent primary uncemented THA through the DAA for osteoarthritis without a secondary diagnosis, by either of the 2 study surgeons, were eligible for inclusion. Patients were excluded if they had diagnoses of inflammatory arthritis, previous ipsilateral hip trauma, previous surgery on the ipsilateral hip, or a contraindication for MRI. Sample size was based on signal intensity of the anterior pseudocapsule at 1 year postoperative. Forty patients consented to participate in the study, and 32 patients completed immediate postoperative and a minimum of 1-year postoperative MRI scans. Seven patients refused to return for their 1-year postoperative MRI scans; 1 patient experienced a postoperative dislocation and withdrew from the study. Metal artifact reduction sequence-MRI was performed on a 1.5-T clinical scanner (General Electric Healthcare, Waukesha, WI) using a cardiac or small body coil and the institution’s routine clinical hip arthroplasty imaging protocol, including coronal multiacquisition variable-resonance image combination selective (MAVRIC-SL) inversion recovery and MAVRIC-SL proton densityeweighted images, in addition to high-resolution axial, sagittal, and coronal proton densityeweighted fast spin echo images. This imaging algorithm provides good spatial resolution as afforded by the fast
spin echo images, and excellent suppression of metal susceptibility artifact due to inclusion of the MAVRIC-SL pulse sequences (Table 1). The modified DAA is a minimally invasive approach to hip arthroplasty that involves an incision on the front of the hip and moving muscles rather than detaching tendons to replace the joint. This surgical technique was used for all surgeries; half the patients underwent capsulotomy and repair performed by one study surgeon and half underwent anterior capsulectomy performed by the other study surgeon. In patients who had a capsulotomy, an “H-type” incision was made along the femoral neck axis and extended medially and laterally along the anterior acetabulum and intertrochanteric ridge. In patients who had a capsulectomy, the anterior capsule from the anterior acetabulum to the intertrochanteric ridge, and between the superior and inferior femoral neck, was excised. For both groups of patients, the THA then proceeded with acetabular preparation and component insertion, with fluoroscopic guidance. The femoral hook for either the Omni-Tract or the Hana table was inserted distal to vastus flare and around the posterior femur. The femur was externally rotated, hyperextended, and adducted. The proximal femur was elevated using either the table-mounted retractor or motorized jack. Posterior soft tissue releases were performed according to the surgeon’s assessment of soft tissue tension and degree of femoral elevation necessary for femoral preparation. The posterior capsule was released first, followed by releases of the SER tendons, as deemed necessary by the operating surgeon, for femoral exposure. These releases included the piriformis and conjoined tendons, but not the obturator externus. Once femoral exposure was achieved, the femur was prepared and the implant was inserted, with fluoroscopic confirmation of sizing and position. In those patients who had a capsulotomy, an anterior capsular repair was performed in a side-to-side fashion with multiple nonresorbable sutures. The anterior capsule was repaired to the residual capsular tissue on the intertrochanteric ridge. In those patients who had an anterior capsulectomy, the tensor fascia lata and satorious were allowed to drape over the hip joint and the tensor fascia lata fascia was closed (Fig. 1). All patients received the same aftercare. Patients were permitted weight-bearing as tolerated immediately after surgery, without postoperative motion restrictions. Crutches, cane, or walker were used as walking aids as patient ability dictated. Aspirin 325 mg oral twice daily was provided for venous thromboembolic prophylaxis. Prospectively, each patient was offered MRI scans during his or her initial hospitalization for THA, at 3 months after THA, and at least 1 year after THA. MAVRIC sequences were used to suppress metal artifact, following previously published protocols [15]. MRI is an accurate and reproducible test to evaluate the soft tissues around the hip after THA [9,10,14,16,17]. There is excellent intraobserver reliability in regard to grading tendinosis, and the interobserver and intraobserver reliability for grading the soft tissues around THA has been established [17,18]. The present study used MRI methods and metrics similar to those that have been employed for evaluating the soft tissues around THA performed through the posterolateral approach [9,10]. A single senior board-certified musculoskeletal radiologist, blinded to the intraoperative, interpreted all studies. Integrity of the posterior soft tissues was measured and graded as previously detailed. The distance between SER tendons and bone were measured in millimeters, scored as intact when the measurement was 0 mm, or scored as scarred when in continuity to bone through scar tissue. The posterior capsule was scored qualitatively as intact to bone, released, or in continuity to bone through scar. Atrophy of the obturator internus and piriformis was graded similar to Goutallier's classification, and atrophy was characterized as none, mild, moderate, or severe [19].
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Table 1 MRI Sample Imaging Parameters for THA at 1.5 T. Parameter
Coronal MAVRIC IR
Axial FSE
Sagittal FSE
Coronal FSE
Axial FSE
Coronal MAVRIC FSE
Imaged TR (ms) TE (ms) TI (ms) BW (kHz) NEX FOV (cm) Matrix Slice/gap (mm)
Whole pelvis 4000-6000 21-43 150 ±125 0.5 40 256 192 5/0
Whole pelvis 4500-5500 21.4-32 NA 83-100 4 32-36 512 256 5/0
Affected hip 5500-6500 23-30 NA 83-100 4-5 17-18 512 352 2.5-3/0
Affected hip 4500-5800 24-30 NA 83-100 4-5 18 512 352 4/0
Affected hip 4500-5500 24-30 NA 83-100 4-5 17-19 512 256-288 4/0
Whole pelvis 4000-6000 21-43 NA ±125 0.5 40 320-512 256-384 3-4.5/0
MRI, magnetic resonance imaging; THA, total hip arthroplasty; TR, time to repetition; TE, echo time; TI, inversion time; pBW, pixel bandwidth; NEX, number of excitations; FOV, field of view; IR, inversion recovery; PD, proton density; FSE, fast spin echo; MAVRIC-SL, multiacquisition variable resonance image combination selective; NA, not applicable.
Patient baseline demographics, clinical characteristics, and frequency of postoperative groin pain were collected. Postoperative patient-reported outcome measures, including modified Harris Hip Scores (mHHS), Hip disability and Osteoarthritis Outcome Score for Joint Replacement, and Lower Extremity Activity Scale, were collected; mHHS was also collected preoperatively. Heterotopic ossification was categorized on final follow-up radiographs according to the classification of Brooker [20,21]. MRI appearance of soft tissue repairs was summarized. Statistical analyses were conducted using SAS software version 9.4 (SAS Institute Inc, Carey, NC), with a 5% level of significance. Data were analyzed using Fisher exact tests, Wilcoxon sum rank tests, Wilcoxon signed-rank test, and where appropriate only descriptive statistics were used. Results At the time of surgery, the median (q1-q3) age of the total cohort was 61.1 (56.8-68.6) years, the median body mass index was 25.7 (23.7-27.7) kg/m2, and 78% of participants were female. Fifty-nine percent of surgeries were performed on a right hip and there were no intraoperative complications. Immediately postoperatively, 75% (24/32) of piriformis tendons were intact, 88% (28/32) had no piriformis atrophy, and for those that were released the mean distance to bone was 2.3 mm (range, 2-8). At 1year follow-up, 97% (31/32) had an intact piriformis, although 28% (9/32) were in continuity through scar with the capsule (Figs. 2 and 3). Fifty-nine percent of hips (19/32) showed no piriformis atrophy, 18% (6/32) had mild atrophy, and 22% (7/32) showed moderate atrophy.
Immediately postoperatively, 35% (11/32) of conjoined tendons were intact, 94% (30/32) showed no sign of obturator internus atrophy, and for those that were released the mean distance to bone was 4.1 mm (range, 2-10 mm). Of released conjoined tendons, at 1year follow-up, only 1 conjoined tendon was not intact while 95% (20/21) were intact through scar-in-continuity with the posterior capsule (Figs. 2 and 3). At 1-year follow-up, 34% (11/32) of patients had moderate obturator internus atrophy, 34% (11/32) had mild atrophy, and 31% (10/32) showed no atrophy. The posterior capsule directly contacted bone or was in continuity with bone through scar in all patients. Seventeen patients underwent capsulotomy with repair and 15 underwent anterior capsulectomy. Between the capsulotomy and repair and capsulectomy groups, the only significant differences in baseline characteristics were that the capsulotomy group was slightly but significantly older (P ¼ .0234) and had slightly lower body mass index (P ¼ .0246). During the study period, there was 1 reoperation for iliopsoas impingement, and 1 patient withdrew from the study after a dislocation event. At 1 year postoperatively, none of the patients who underwent capsulotomy with repair had persistent anterior capsule defects, while 27% (4/15) in the capsulectomy group had persistent defects (Fig. 4).In the total cohort, the median preoperative mHHS was 51.5 (43-59.2) points with significantly higher scores in the capsulotomy and repair versus the capsulectomy group (P ¼ .0069). Postoperative mHHS scores were significantly higher than preoperative in the total cohort (P < .0001), in the capsulotomy and repair group (P < .0001), and in the capsulectomy group (P ¼ .0001), with no significant difference between the 2 cohorts (P ¼ .358). The median postoperative Hip
Fig. 1. Repaired and detached capsules intraoperatively. Intraoperative images of a repaired capsule during a capsulotomy and repair (A) as compared to a detached capsule during a capsulotomy (B).
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Fig. 2. Intact SERs. Coronal PD image (A) in a 68-year-old woman immediately following DAA THA demonstrates somewhat hyperintense but otherwise intact conjoined tendon (white arrowhead). Coronal PD image (B) obtained 3 months following surgery demonstrates ongoing scar remodeling with decreased hyperintensity of tendon fibers (white arrowhead), with further remodeling yielding normal signal intensity of fibers (white arrowhead) at 1 year following surgery (C). SER, short external rotator; PD, proton density; DAA, direct anterior approach; THA, total hip arthroplasty.
disability and Osteoarthritis Outcome Score for Joint Replacement score and Lower Extremity Activity Scale were 100 (80.6-100) and 13 (11-14), respectively; there was no difference between the 2 subcohorts (P ¼ .892 and P ¼ .269, respectively; Table 2). Two
patients had pain at final follow-up: 1 patient reported it as 1/10 on the visual analogue scale and the other reported it as 4/10. Two patients had evidence of Brooker grade I heterotopic ossification at final follow-up. There were no differences between the
Fig. 3. Scar-remodeled SERs. Coronal (A) and axial (B) PD images in a 57-year-old woman immediately following DAA THA demonstrate discontinuity of the conjoined tendon (white arrowhead) yielding a 3-mm gap; obturator internus muscle bulk is preserved at this time point (black arrowhead). Coronal (C) and axial (D) PD images 7 months later demonstrate formation of scar in continuity with intact tissue bridging the previously visible gap (white arrowhead), although a degree of interval obturator internus atrophy is noted (black arrowhead).
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Fig. 4. Anterior capsule. (A) Axial PD-weighted image (A1) in a 51-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulotomy, with band of hyperintense tissue bridging the site, related to repair (white arrowheads). Axial PD image (A2) obtained approximately 8 months following surgery demonstrates scar remodeling of the repaired capsule, with intact tissue bridging the previously visualized capsular defect (white arrowhead). (B) Axial PD-weighted image (B1) in a 60-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulectomy (white arrowheads). Axial PD image (B2) obtained approximately 5 months following surgery demonstrates scar remodeling of the capsule, with intact tissue bridging the previously visualized capsular defect (white arrowhead). (C) Axial PD-weighted image (C1) in a 61-year-old woman immediately following DAA THA demonstrates surgical defect related to capsulectomy (white arrowheads). Axial PD image (C2) obtained approximately 8 months following surgery demonstrates persistent, although smaller, capsular defect (white arrowheads).
capsulotomy and repair versus capsulectomy groups with respect to these outcomes. Discussion Postoperative instability remains a clinically important problem after primary THA. The overall frequency of postoperative dislocation is 2%-4%, depending on the quoted series and duration of follow-up [22]. Similarly, this study found the frequency of postoperative dislocations was 3%. Studies report that instability accounts for 22.5% of revision THAs [23]. The etiology of dislocation is multifactorial, including factors under the purview of surgical technique as well as independent patient factors. Historically, the surgical approach used for THA has been associated with risk of
dislocation [24]. Recently, the DAA for THA has become increasing popular, in part due to a reported reduction in postoperative dislocation [1,4]. It is counterintuitive that instability might be reduced when posterior soft tissue structures are not infrequently released (and not repaired) for femoral exposure during the DAA, because the posterior soft tissue repair is recognized as an important barrier to short-term and long-term postoperative instability after THA performed through the posterolateral approach [9e12]. The short-term integrity of the posterior capsule and SER tendons after DAA THA has not been previously studied. Furthermore, the insertions of the piriformis and conjoined tendons onto the greater trochanter are variable, and surgeons’ ability to perform selective posterior tendon releases through a minimally invasive anterior approach to the hip has not been studied [11,25]. Therefore,
Table 2 Preoperative Clinical Characteristics and Preoperative and Postoperative PROMs According to Capsulotomy and Repair versus Capsulectomy Cohorts. Variables
Total (N ¼ 32)
Capsulotomy and Repair (N ¼ 17)
Capsulectomy (N ¼ 15)
P Value
Sex (male:female) Laterality (left:right) Age (y) Height (cm) Weight (kg) Body mass index (kg/m2) mHHS preoperative (points) mHHS follow-up (points) HOOS, JR. postoperative (points) LEAS postoperative (points)
7:25 13:19 61.1 (56.8-68.6) 165.1 (160-168.9) 69.5 (63.3-78) 25.7 (23.7-27.7) 51.5 (43-59.2) 96 (90-98) 100 (80.6-100) 13 (11-14)
2:15 9:8 67.9 165.1 66.7 25.1 59 98 100 13
5:10 4:11 60.4 165.1 75.7 26.8 45.1 95.7 100 13
.210 .166 .0234 .482 .0413 .0246 .0069 .358 .892 .269
(57.6-70.5) (160-167.6) (61.2-72.6) (23.3-26.1) (48-63) (89-99) (92-100) (11-14)
(53.8-62) (160-175.2) (63.5-108.9) (24.8-35.8) (41-53) (90-97) (77-100) (10-13)
PROMs, Patient-reported outcome measures; mHHS, modified Harris Hip Scores; HOOS, JR., Hip disability and Osteoarthritis Outcome Score for Joint Replacement; LEAS, Lower Extremity Activity Scale.
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this study sought to quantify the frequency of SER tendon releases and to describe the serial appearance of the posterior soft tissue envelope on MRI, in patients after THA through the DAA immediately following surgery and at a minimum of 1-year follow-up. Posterior capsule and conjoined tendon releases were commonly performed during DAA THA, yet continuity with bone was frequently achieved at 1-year MRI follow-up. There are several limitations to this study. A small sample size was used and patients were contributed by only 2 orthopedic surgeons. Consequently, descriptive statistics were used to report MRI appearance of soft tissue repairs but tests for significance were not appropriate. Additionally, due to the sample size no associations could be made between posterior soft tissue releases and the occurrence of THA instability. However, this is countered by the fact that the study is the first to provide a longitudinal description of the posterior soft tissue envelope after DAA with particular attention to tendon releases. A gold standard for assessing tendon releases from the anterior approach has not been established. Surgeon identification of posterior tendons through the DAA is based on their perception of the distal tendon course and insertion, whereas a radiologist may trace a tendon across serial slices in multiple planes to its muscle belly. It is probable that the radiologist’s assessment is more reliable than the surgeon’s. MAVRIC sequences do suppress a significant amount of metal artifact. Nonetheless some artifact still remains, which may obscure accurate interpretation of all anatomic features. In general, however, MRI has had an excellent track record for investigating soft tissue structures around THAs [9,10,15,16,26]. We are not aware of any study reporting a comparison between intraoperative surgical releases and postoperative imaging assessments of recorded releases. However, difficulty in identifying releases intraoperatively may be due to the substantial variability that exists in the insertion of these tendons on the greater trochanter [11,25]. Tendons may also be inadvertently damaged during femoral broaching and thus not recognized. Additionally, many DAA surgeons were classically trained as posterior approach surgeons, and tendinous anatomy of the SERs from the inside out may be unfamiliar. Ito et al [11] mapped the attachments of the piriformis and conjoined tendons in 20 cadaveric hips. While there was considerable interspecimen variability, on average the conjoined tendon inserted near the anterior aspect of the greater trochanter, approximately 5 mm superior to the saddle between the lateral femoral neck and the greater trochanter. On average, the piriformis tendon inserted in a relatively posterior and superior position to the conjoined tendon [11]. Roche et al [25] observed similar insertions in 15 cadaveric specimens. Consequently, it is not surprising that conjoined tendon was released more frequently than the piriformis tendon in this series at 65% and 25%, respectively, as the surgeon is more likely to encounter this tendon through the anterior approach and after releasing the superior band of the hip capsule. Additionally, after the capsule, the conjoined tendon provides modest restraint to femoral elevation, and its release is advocated when femoral exposure must be augmented [1,12]. During the anterior approach, access to the hip joint must be obtained through the anterior capsule. In this series, capsulotomy with repair was performed in 17 patients, and capsulectomy was performed in 15 patients. Of the patients who underwent capsular repair, none had a persistent defect on MRI at 1 year. In contrast, 27% of patients who underwent capsulectomy had a persistent defect at 1 year. While this study was underpowered to show any significant clinical differences between these 2 groups, lack of the anterior capsule is concerning and larger studies may be able to detect such differences.
In a cadaver study, significantly more anterior translation of the native femoral head was found after capsulectomy, whereas there was no difference between the intact and suture-repaired capsule [27]. Another cadaver study found that from the lateral approach capsular repair increased the force needed to dislocate the hip after hemiarthroplasty [28]. Also, experientially the tissue that forms in place of the capsulectomy is not of the same quality as the repaired capsule. While this was not specifically examined in our study, it should be taken into consideration. The posterior capsule was frequently released in both groups of patients during the femoral exposure. Although it was not directly repaired, the posterior capsule directly contacted bone or was in continuity with bone through scar in all patients at 1 year after THA. The present findings should be interpreted within the context of similar studies examining these soft tissues after the posterior approach. In a previous study by Pellicci et al, 36 patients received primary THA using the standard posterolateral approach. In these patients, the posterior capsule and SER tendons were all released during surgery and then repaired using a transosseous technique. Subsequently, patients received MRI of the operated hip during their postoperative hospital stay and at 3 months. At 3 months, the posterior capsule was intact in 90% of patients. Forty-three percent of piriformis repairs were intact, and only 57% of conjoint tendon repairs were intact based on study criteria [9]. A follow-up study performed on 22 patients from this series at a mean of 49 months after THA showed that there were progressive increases in the distances between the native tendon stumps and the greater trochanter. At 3 months, all SER tendons had retracted on average 2.5 to 2.7 cm, and these findings were associated with substantial atrophy of the piriformis and obturator internus muscles, with only 23% of muscles showing no atrophy. The authors concluded that the repair did not provide functional muscle tendon units, but they believe that it facilitated scar formation in continuity to bone between the posterior capsule and the tendons, which was observed in 96% of cases [10]. No repair was performed for released posterior structures in the present study, yet continuity with bone was achieved in nearly all patients. Furthermore, we saw a lower incidence of muscle atrophy with 40% of mild/moderate piriformis and 65% mild/moderate obturator externus. It is probable that released tendons and posterior capsule retracted minimally after the DAA, as there was otherwise minimal interruption in the posterior soft tissue envelope and adjacent fascial tethers. Possibly scar can easily bridge subcentimeter defects between the released structures and bone without an intervening scaffold. These observations may explain why posterior instability is limited after DAA despite frequent release of posterior soft tissue structures. On the other hand, the frequency with which posterior releases are performed, and large diameter femoral heads, may explain why a modern comparative study failed to identify a difference in dislocation rates between anterior and posterior approaches [5]. Conclusion Posterior capsule and conjoined tendon releases were commonly performed in this series of DAA THA, yet continuity with bone was frequently achieved at short-term follow-up. In comparison to some studies reporting a decreased incidence of instability using the DAA, the present study had a frequency of instability similar to a conventional posterior-lateral approach. Differences in sample size and patient population can affect overall instability rates and in our hands the DAA has proven to be reliable. Capsulotomy and repair consistently resulted in intact anterior capsule at final follow-up, while capsulectomy left a persistent defect in 27% of patients. Appreciation of the variability and relative
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location of tendon insertions, along with capsular repair whenever possible, is required for DAA surgeons aiming to provide soft tissueesparing THA surgery. Acknowledgments We would like to acknowledge our patients who continue to participate in clinical trials and enable us to further our understanding of and treatments for musculoskeletal diseases. Lauren Mount and Imraan Khan were early contributors to this study and we would like to acknowledge their work. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. References [1] Matta JM, Shahrdar C, Ferguson T. Single-incision anterior approach for total hip arthroplasty on an orthopaedic table. Clin Orthop Relat Res 2005;441: 115e24. https://doi.org/10.1097/01.blo.0000194309.70518.cb. [2] Hallert O, Li Y, Brismar H, Lindgren U. The direct anterior approach: initial experience of a minimally invasive technique for total hip arthroplasty. J Orthop Surg Res 2012;7:17. https://doi.org/10.1186/1749-799X-7-17. [3] Sariali E, Leonard P, Mamoudy P. Dislocation after total hip arthroplasty using hueter anterior approach. J Arthroplasty 2008;23:266e72. https://doi.org/ 10.1016/j.arth.2007.04.003. [4] Kennon RE, Keggi JM, Wetmore RS, Zatorski LE, Huo MH, Keggi KJ. Total hip arthroplasty through a minimally invasive anterior surgical approach. J Bone Joint Surg Am 2003;85:39e48. https://doi.org/10.1007/s11610-006-0011-5. [5] Maratt JD, Gagnier JJ, Butler PD, Hallstrom BR, Urquhart AG, Roberts KC. No difference in dislocation seen in anterior vs posterior approach total hip arthroplasty. J Arthroplasty 2016;31:127e30. https://doi.org/10.1016/j.arth. 2016.02.071. [6] Jewett BA, Collis DK. High complication rate with anterior total hip arthroplasties on a fracture table. Clin Orthop Relat Res 2011;469:503e7. https:// doi.org/10.1007/s11999-010-1568-1. [7] Pellicci PM, Bostrom M, Poss R. Posterior approach to total hip replacement using enhanced posterior soft tissue repair. Clin Orthop Relat Res 1998:224e8. https://doi.org/10.1097/00003086-199810000-00023. [8] Chiu FY, Chen CM, Chung TY, Lo WH, Tain Hsiung C. The effect of posterior capsulorrhaphy in primary total hip arthroplasty. A prospective randomized study. J Arthroplasty 2000;15:194e9. [9] Pellicci PM, Potter HG, Foo LF, Boettner F. MRI shows biologic restoration of posterior soft tissue repairs after THA. Clin Orthop Relat Res 2009;467:940e5. https://doi.org/10.1007/s11999-008-0503-1. [10] McLawhorn AS, Potter HG, Cross MB, Boettner F, Lim W, Lee Y, et al. Posterior soft tissue repair after primary THA is durable at mid-term followup: a prospective MRI study. Clin Orthop Relat Res 2015;473:3183e9. https://doi.org/ 10.1007/s11999-015-4380-0. [11] Ito Y, Matsushita I, Watanabe H, Kimura T. Anatomic mapping of short external rotators shows the limit of their preservation during total hip arthroplasty. Clin Orthop Relat Res 2012;470:1690e5. https://doi.org/ 10.1007/s11999-012-2266-y.
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