Achieving Reliable Collar-Calcar Contact in Anterior Total Hip Arthroplasty: Surgical Technique

Total hip arthroplasty (THA) continues to grow in popularity due to its consistent success in treating end-stage osteoarthritis.1 Alongside this growth, advancements in implant technology have expanded the options available to surgeons. Among these, collared, cementless femoral stems have become increasingly favored due to several biomechanical and clinical advantages over other press-fit designs.2 This implant design helps redistribute forces to the calcar, which has been shown to enhance the stability of the femoral component under both axial and torsional loads when compared with collarless alternatives.3 As a result, it increases the torsional load required to cause a periprosthetic fracture.3 These properties are particularly valuable for surgeons using the anterior approach to THA, where periprosthetic fracture remains a primary concern. In addition, the presence of a collar has been shown to reduce rates of femoral stem subsidence—a potential contributor to implant failure across all surgical approaches.4 However, these benefits depend heavily on proper implantation technique, specifically adequate collar-calcar contact. Although manufacturers of collared implants prioritize achieving secure metaphyseal press fit rather than flush collar-calcar contact in their technique guides, emerging data indicate that the degree of collar-calcar contact in an appropriately press-fit stem can enhance the performance of modern collared designs. Lamb et al5 conducted a biomechanical study showing that collared implants with sufficient collar-calcar contact required greater force to cause a periprosthetic fracture compared with specimens with collar-calcar separation at implantation. Similarly, Jeon et al2 found that perfect collar-calcar contact reduces subsidence and enhances implant stability. However, they caution that imperfect contact can lead to lateral tilting of the implant, resulting in varus deformity and potentially increasing the risk of periprosthetic fracture. Taken together, these biomechanical studies suggest the clinical advantages observed using collared implants, including reduced subsidence and lower periprosthetic fracture risk, are maximized with flush collar-calcar contact. However, because clinical studies have not directly compared flush versus nonflush seating in collared implants, the specific contribution of achieving truly flush contact to long-term outcomes remains understudied and represents an important area for future investigation. Therefore, these findings highlight that achieving flush collar-calcar contact may be as critical as the implant design itself in realizing biomechanical benefits. Despite this importance, studies report wide variability in achieving adequate contact, with success rates estimated to be 63.9%.4 This raises questions about whether the proposed biomechanical advantages of collared stems are consistently realized in clinical practice. At our institution, we have routinely used collared stems in anterior approach THA, achieving complete collar-calcar contact in >90% of cases, according to currently unpublished data. Given our success, we aim to share our technique for reliably achieving collar-calcar contact using a representative case. This report highlights the technical steps and pearls that contribute to optimal outcomes when using collared stems during anterior approach THA. The patient was informed that data from their case would be used for publication and provided informed consent. TECHNIQUE This was a 67-year-old female with pertinent past medical history significant for factor V Leiden, type 2 diabetes mellitus, and obstructive sleep apnea. She suffered from several years of progressive right hip pain, which radiated to the knee and was worse with ambulation, decreased range of motion about the hip, an antalgic gait, and hip radiographs consistent with osteoarthritis. She initially managed pain conservatively and upon clinical presentation felt that she exhausted conservative measures and elected to undergo a right primary total hip arthroplasty. Preoperative TemplatingFIGURE 1: Preoperative AP pelvis and template demonstrating femoral stem and acetabular cup position with a measured femoral neck resection planned at 17 mm.Before surgery, we strongly endorse having a standardized protocol for preoperative templating with an AP pelvis XR. Here, we demonstrate this patient’s template. First, a trans-tear drop line is drawn with lines down to the top of the lesser trochanter to determine leg lengths. This patient had a discrepancy of 2 mm, the right longer than the left. Then, we place the acetabular component of choice with the inferior aspect of the cup being at the inferior portion of the tear drop, the medial aspect abutting the medial wall of the acetabulum and ∼40 degrees of inclination. Then, the femoral stem is placed in the canal and sized with attention being paid to adjustments in leg length, offset, and varus/valgus alignment. Here, a size 7 femoral stem with +1.5 femoral head and a 52 mm acetabular cup were determined to be the appropriate size. One can see this leaves a relatively high femoral neck cut 17 mm from the top of the lesser trochanter. This higher initial neck cut is intentional and crucial for this technique. Positioning the planned cut slightly proximal to the final target allows for intraoperative adjustment to ensure flush collar seating against the calcar. We then have this template to reference when looking at our intraoperative fluoroscopic images (Fig. 1). Surgical Procedure The patient underwent spinal anesthesia and was positioned supine on a Hana table. A standard anterior approach was performed through a longitudinal incision centered over the anterior superior iliac spine and extended distally over the tensor fascia lata (TFL). The intermuscular interval between the TFL and sartorius was developed with careful identification and protection of the lateral femoral cutaneous nerve. The TFL was retracted laterally and the rectus femoris medially to expose the anterior hip capsule. A partial capsulectomy was performed to facilitate visualization of the femoral head and acetabulum. Once adequate exposure was achieved, intraoperative fluoroscopy was utilized to guide the femoral neck resection (Fig. 2). Fluoroscopic images were obtained until the electrocautery tip aligned with the level of the templated neck cut. It is critical that the AP pelvis obtained intraoperatively closely resembles the templated AP pelvis in terms of inlet/outlet and rotation so that you are reproducing what was templated preoperatively. A marking was made on the femoral neck with electrocautery to delineate the planned resection level (Fig. 2). This mark is deliberately placed 1 to 2 mm proximal to the final desired position, creating a small buffer that allows the calcar cut to be fine-tuned intraoperatively so the collar achieves maximal contact on the prepared calcar surface. Resection was then performed with cobra retractors on both the inferior and superior femoral neck for protection posteriorly.FIGURE 2: Intraoperative fluoroscopic images demonstrating the bovie overlying the femoral neck ∼17 mm from the lesser trochanter, trial femoral broach in place with final acetabular component and screw in place, and final components in place with the collar seated flush on the calcar.Following resection and extraction of the femoral head, the acetabulum was sequentially reamed. A 52 mm acetabular shell was implanted and impacted to the medial wall of the acetabulum with ∼40 degrees of lateral inclination and 20 degrees of anteversion, confirmed under fluoroscopy. Once optimal positioning was verified, a single 30 mm screw was placed in the posterior-superior quadrant, and the polyethylene liner was inserted. Attention was then directed to the femur. Gross traction and maximal external rotation facilitated exposure of the proximal femur. The femoral canal was broached sequentially until achieving an axial depth that achieves rotational stability. Given that the initial femoral neck cut was intentionally conservative relative to our template (high), the final broach was then seated slightly below the existing calcar level to our templated depth (Fig. 3). A calcar planar instrument was then used (Fig. 3), and excess calcar bone was removed until the resected surface was flush with the broach, allowing for the collar of the definitive implant to rest evenly on the calcar and negate potential off-axis cuts (Fig. 2). We do not attempt to further advance the broach after calcar planing as this may increase risk of intraoperative fracture. Instead, we reconfirm adequate press fit of the broach with torsional testing, ensuring the broach and femur move as one unit without appreciable micromotion. Trial components were placed, and direct visualization confirmed that the collar sat flush with the calcar. While we primarily confirm flush collar-calcar contact through direct visualization, intraoperative fluoroscopy may be used. We would recommend internally rotating the femur until version is neutralized to obtain a true AP femur, which best evaluates collar-calcar contact. Intraoperative fluoroscopy was reintroduced to assess leg length and offset.FIGURE 3: Intraoperative photographs showing the broach seated below the level of the femoral neck cut once rotational stability was achieved and the calcar planning instrument removing excess bone to ensure the femoral neck cut is flush with the broach.Final components were implanted, and leg length and offset were reassessed to ensure symmetry and stability (Fig. 2). Hemostasis was achieved, and the wound was closed in a layered fashion. The patient has been followed up through 1 year thus far and has experienced excellent results. Importantly, her 1-year postoperative radiographs demonstrate excellent fixation with a lack of subsidence. EXPECTED OUTCOMES By adhering to this systematic approach—accurate implant sizing, high femoral neck cut templating, and calcar planar following broach stability—our institution has achieved >90% collar-calcar contact in anterior approach THA using collared stems, markedly surpassing previously reported contact rates of ∼60%.4 This technique is important to review and consider as it offers a reproducible method to maximize the effectiveness of collared implants by getting the collar flush on the calcar to hopefully help mitigate subsidence and periprosthetic femur fractures. COMPLICATIONS Inability to achieve flush contact between the collar and the calcar may undermine the implant’s advantages, thereby lowering the load to failure and increasing the risk of subsidence. This can occur due to undercutting the neck, undersized templating, and not leaving room for intraoperative corrections. This report presents a reliable technique to optimize collar-calcar engagement by combining accurate preoperative templating with a high femoral neck cut and intraoperative calcar planning. The key principle is to template the neck cut ∼1 to 2 mm proximal to the desired final collar position. This intentional overcut creates a margin for intraoperative adjustment, allowing the surgeon to correct for minor angular deviations that might otherwise prevent proper collar seating. Equally important during preoperative planning is accurate templating of the implant size. Undersized templating may lead to intraoperative upsizing, which can result in the final stem seating higher than expected—above the calcar—and thus compromise collar contact. Proper preoperative estimation of both the implant size and neck cut location is therefore essential to ensure the collar will engage flush with the calcar after final implant placement. The rationale for the high neck cut stems from the technical challenge of aligning the cut perfectly with the implant’s coronal and sagittal geometry. Attempting to match the collar position precisely on the initial cut leaves no room for correction. By starting slightly high, the surgeon preserves bone stock that can be shaped intraoperatively with a calcar planar tool to achieve optimal implant-calcar congruity. During femoral preparation, the broach is advanced past the high neck cut and achieves rotational stability in the metaphysis. Once this is confirmed, a dedicated calcar planning instrument—attached to the broach handle and sharing the same geometry—is used to contour the calcar precisely to the shape of the implant collar. This ensures flush, full-surface contact and restores the biomechanical advantage intended by the collared stem design. In rare cases, despite appropriate broach positioning and use of the calcar planing instrument, the collar may still remain slightly proud after achieving metaphyseal stability. When this occurred, we avoided further forceful broach advancement or stem downsizing to reduce the risk of intraoperative fracture. Instead, when proper alignment and press fit were confirmed, a small initial collar-calcar gap was accepted. Conversely, in cases where an undersized stem was prematurely stopped by the calcar before achieving adequate metaphyseal press fit, we elected to upsize the broach and femoral component to ensure reliable fixation, even if this resulted in less than perfect collar-calcar contact. Surgeons must be diligent and careful with the calcar planar, as improper utilization can lead to an incidental calcar fracture.