Partial Preservation of the Anterior Capsule in Total Hip Arthroplasty to Decrease the Risk of Iliopsoas Impingement

Mechanical irritation of the iliopsoas muscle resulting from a prominent acetabular cup leads to a well-known complication after total hip arthroplasty, referred to as the iliopsoas impingement.1 Clinically, patients present with persistent postoperative groin pain triggered by active flexion of the hip. Various risk factors have been identified for the development of iliopsoas impingement, including excessive anterior cup overhang, usage of larger components, higher native acetabular anteversion, female gender, younger age, or prior spine fusion.1–3 Recently, emphasis has been placed on the functional role of the hip capsule, which is compromised in anterior-based approaches.1,4 Disruption of its protective function at the iliopsoas notch appears to contribute to increased irritation of the iliopsoas muscle by the edge of the overhanging acetabular cup.1,2,4 Conventional hemispheric cups may not entirely match the natural anatomical contour of the acetabulum. Particularly, in the case of a pronounced iliopsoas notch where the cup protrudes above the anterior acetabular rim (Fig. 1A). This overhang of the component predisposes to snapping of the iliopsoas muscle, particularly the tendinous portion of the psoas major muscle, over the relatively sharp edge of the implant (Fig. 1B). To decrease the protrusion of the acetabular cup, significant anteversion is required, leading to abnormal cup positioning (Fig. 1C). However, even in cases with a well-developed iliopsoas notch, coverage of the prominent cup can be achieved by preserving the capsule below the iliopsoas muscle which ensures a solid protective layer between the iliopsoas muscle and the acetabular cup and avoids the unwanted mechanical irritation (Figs. 1D, E).FIGURE 1: A cadaveric specimen with implanted acetabular cup. With an approximate cup anteversion of 25 degrees and inclination of 40 degrees, the component overhangs at the iliopsoas notch (A). At this positioning, the tendon of the psoas major muscle is irritated by the edge of the cup (B). To assure sufficient bony coverage of the component at the iliopsoas notch, critical cup anteversion (>30 degrees) and inclination (>45 degrees) is required (C). Coverage of the acetabular cup can be achieved by sparing the capsule (asterisk) medially to the footprint of the iliocapsularis muscle (D, E). I indicates inferior; IM, iliacus muscle; L, lateral; M, medial; PMT, tendon of the psoas major muscle; S, superior; sup., superior view; tIPM, transected iliopsoas muscle; tRFM transected rectus femoris muscle.In this technical report, we describe a simple technique that partially spares the anterior capsule in total hip arthroplasty, and aims to minimize the contact between the iliopsoas muscle and the implanted acetabular cup to decrease the risk of postoperative iliopsoas impingement. TECHNIQUE The surgery is performed under general or spinal anesthesia, and the patient is placed in supine position. At our institution, we either use the direct anterior approach (DAA) or the anterolateral approach (ALA) to access the hip joint. Once the capsule is exposed, a raspatorium is used to peel off the iliocapsularis muscle from the anterior portion of the capsule (Fig. 2A). The medial border of the iliocapsularis muscle’s footprint is used as a reference line for partial capsular preservation, as the portion of the capsule lateral to this reference line is resected (Fig. 3). The capsule is opened through a quadrangular, window-like incision, starting from the aforementioned reference line to the proximal tip of the greater trochanter, continuing toward the lateral acetabular rim, and following the acetabular rim medially to meet the initial incision (Figs. 2B, 3B). The partial capsulectomy should result in a spared fine protective capsular layer underneath the tendon of the psoas major muscle. Subsequently, osteotomy of the femoral neck is performed, and the femoral head is extracted from the acetabulum. The posterolateral aspect of the capsule can be further excised to gain comfortable access to the acetabulum for reaming (Fig. 2C).FIGURE 2: Intraoperative images of the capsular management. Once the capsule is reached, raspatorium is used to peel off the iliocapsularis muscle (A). A window is created on the anterior aspect of the capsule and the femoral neck is exposed for osteotomy (B). The posterolateral portion of the capsule is excised to achieve appropriate access to the acetubulum for reaming (C). A Hohmann retractor is placed underneath the spared capsular portion and inserted by the iliopubic eminence, which protects the capsule from contact with the reamer (D). The overhanging edge of the cup at the iliopsoas notch is covered by the spared anterior capsule (asterisk) (E). Once the definitive hardware is implanted, the preserved capsule (asterisk) prevents the irritation of the iliopsoas muscle by the protruding acetabular cup (F). I indicates inferior; L, lateral; M, medial; S, superior.FIGURE 3: Schematic drawing of the capsular incisions. The usual appearance of the anterior musculocapsular complex of the hip is shown (A). A quadrangular window (dotted lines) between the medial edge of the footprint of the iliocapsularis muscle, greater trochanter of the femur, and acetabular rim is created (B). After the partial resection solid portion of the articular capsule is spared underneath the psoas major muscle (C). ICM indicates iliocapsularis muscle; PMM, psoas major muscle.We first prefer to prepare the acetabulum and implant the acetabular cup. To protect the spared portion of the capsule, a Hohmann retractor is placed underneath the capsule and inserted by the bony iliopubic eminence. This retraction allows for comfortable reaming of the acetabulum and avoids fraying of the capsule in case of contact with the spinning reamer (Fig. 2D). Following the implantation of a definitive acetabular cup (Fig. 2E), the femoral canal is prepared and a femoral stem is put in place. An appropriate polyethylene liner is then installed, and a suitable prosthetic head is secured in place (Fig. 2F). Subsequently, the hip arthroplasty is reduced, and the wound is closed. This technique does not require any special postoperative care as it follows the usual regime after total hip arthoplasty. EXPECTED OUTCOMES We have used our technique in 93 primary total hip arthroplasties between February 2023 and January 2024. There were 59 (63.4%) males and 34 (36.6%) females with a mean age of 58±12.4 (range 28 to 83) years. From this cohort, all participants featured good clinical and radiological outcomes with no postoperative complications. In particular, none of the participants reported groin pain triggered by passive or active hip flexion at a mean follow-up of 7.8±4.1 months. According to the findings of Harada et al,5 there was a significant improvement in short-term pain experienced by the patients undergoing medial capsulotomy, extending from the anterior superior iliac spine to the inferomedial end of the intertrochanteric line, leaving a solid portion of the medial capsule (Fig. 4). In comparison to the hereby presented technique, Harada et al5 performed the initial capsular incision lateral to the footprint of the iliocapsularis muscle. Conversely, in this technical tip, we describe a more extensive capsular resection that spares only the iliopsoas-capsule complex and sacrifices the iliofemoral ligament. We suspect that our capsular preservation technique is adequate to control the postoperative pain as well, and additionally provides a protective layer to avoid irritation of the iliopsoas muscle at the iliopsoas notch. Nevertheless, the utility of our technique should be further verified in a large cohort analysis with long-term follow-up and compared with the capsular resection group.FIGURE 4: Schematic drawing showing the extent of capsular preservation in our technique and the technique proposed by Harada et al.5Several measures to avoid iliopsoas impingement have been reported. Optimal implantation of the acetabular cup appears as the most important contributing factor.2 However, individual anatomical features at the iliopsoas notch may restrict ideal cup placement without compromising hip stability.6 Therefore, a special anatomical cup design, respecting the natural contour of the acetabulum, may be necessary.6 Nevertheless, the preoperative selection of eligible patients for these implants may be problematic, and their associated costs and demanding implantation procedures could be prohibitive. We believe that appropriate soft-tissue management, which includes capsular-sparing techniques, appears as more cost-effective approach that maintains surgical simplicity. This encompasses both partial capsular preservation and capsular repair techniques. Furthermore, preserving the reflected head of the rectus femoris muscle during total hip arthroplasty prevents displacement of the iliopsoas tendon, and decreases the reliance on the iliopsoas muscle during hip flexion.4 COMPLICATIONS There were no complications seen while performing this technique. However, expected complications should not differ from the ones seen regularly after total hip arthroplasty. Theoretically, a higher dislocation rate could be observed in comparison with capsular reconstruction.