Proximal Femoral Replacement: A Solution for Total Femur Replacement

Comprehensive Introduction and Patho-Epidemiology

Definition and Evolution of Megaprostheses

Proximal femoral replacement (PFR) and total femoral replacement (TFR) represent the pinnacle of salvage limb-sparing surgery. Historically, these massive endoprosthetic reconstructions were exclusively reserved for oncologic indications, specifically primary bone sarcomas or aggressive metastatic lesions, which in the past were definitively managed with major amputations such as hip disarticulation or hemipelvectomy. However, the paradigm has shifted dramatically. Today, the non-oncologic applications for megaprostheses have expanded exponentially, primarily driven by the increasing burden of catastrophic periprosthetic bone loss encountered in complex revision total hip arthroplasty (THA).

During the past decade, remarkable advances in the field of revision hip reconstruction have been made, fundamentally altering the surgical algorithms for massive femoral defects. One of the most critical improvements has been the introduction of second-generation and third-generation modular prosthetic components. Unlike the monolithic custom-made implants of the past, contemporary modular systems provide the surgeon with an unparalleled intraoperative ability to restore precise limb length, optimize femoral offset, and achieve meticulous soft tissue tensioning. These biomechanical restorations are paramount in reducing the incidence of postoperative instability—a notorious complication that historically plagued the insertion of fixed-geometry megaprostheses.

Furthermore, the new generation of megaprostheses is engineered to provide a vastly superior biological environment for soft tissue reattachment. Advanced porous coatings, specialized trochanteric claws, and synthetic mesh sleeves (such as Trevira tubes) allow for the reapproximation of the retained host bone and abductor musculature directly to the prosthesis. This integration is critical for restoring the abductor moment arm and minimizing the debilitating Trendelenburg gait often seen in salvage hip reconstructions.

Pathogenesis of Femoral Bone Loss

Femoral bone loss is a constantly rising, predominantly complex, and technically demanding challenge in revision arthroplasty. The pathogenesis is multifactorial, often representing a culmination of mechanical, biological, and iatrogenic insults to the proximal femur. Osteolysis secondary to particulate wear debris (macrophage-mediated foreign body response) remains one of the most common culprits, leading to silent, progressive endosteal and cortical destruction. Additionally, stress-shielding with adaptive bone remodeling, particularly around stiff, fully porous-coated cylindrical stems, can lead to severe proximal femoral osteopenia and eventual structural failure of the metaphysis.

Infection plays a devastating role in the pathogenesis of bone loss. Chronic periprosthetic joint infection (PJI) necessitates aggressive surgical debridement, often resulting in the deliberate resection of compromised or sequestrated host bone to eradicate the nidus of infection. Similarly, the natural processes of aging, including severe osteoporosis, predispose the femur to catastrophic failure. Periprosthetic fractures, particularly Vancouver Type B3 fractures (where the stem is loose and the bone stock is severely inadequate), frequently necessitate the bypass of the deficient proximal segment with a modular PFR.

Finally, multiple previous failed reconstructive procedures compound the problem. The repetitive insertion and removal of implants, extraction of well-fixed cement mantles, and the use of cortical windows or extended trochanteric osteotomies inevitably compromise the structural integrity of the remaining diaphyseal bone stock. This surgical trauma not only depletes the osseous reserves but also severely damages the surrounding soft tissue envelope, adversely affecting the viability and contractile function of the critical abductor musculature.

Natural History of Severe Bone Deficiency

The natural history of untreated or inadequately treated massive femoral bone loss is characterized by progressive functional decline, intractable pain, and eventual loss of ambulatory capacity. Without definitive structural reconstruction, patients face the prospect of a flail extremity, chronic dislocation, or the necessity of a resection arthroplasty (Girdlestone procedure), which leaves the patient with a profoundly shortened limb and high energy expenditure during ambulation.

The megaprosthesis is an invaluable tool in the armamentarium of the reconstructive hip surgeon who treats patients with this extensive bone loss, particularly when other available reconstructive procedures—such as impaction allografting, long press-fit stems, or allograft-prosthesis composites (APCs)—cannot be reliably utilized. For the elderly, low-demand patient, the natural history following a successful PFR is generally favorable, offering immediate weight-bearing capability and rapid mobilization.

However, it must be emphatically stated that this prosthesis will have an unacceptably high mechanical failure rate in younger, high-demand patients. In these demographics, the natural history of a megaprosthesis is marred by eventual aseptic loosening, component fracture, or bushing wear due to the massive cantilever bending forces applied to the implant interface. Therefore, in younger cohorts, alternative reconstructive options focusing on biological restoration of bone stock, such as an allograft-prosthesis composite, must be exhaustively explored before committing to a definitive megaprosthesis.

Detailed Surgical Anatomy and Biomechanics

Osteology and Musculotendinous Attachments

A profound understanding of the surgical anatomy of the proximal femur and its surrounding musculature is an absolute prerequisite for executing a successful proximal femoral or total femoral replacement. The proximal femur serves as the critical anchor point for the major muscle groups governing hip kinematics. The abductors, comprising the gluteus medius, gluteus minimus, tensor fasciae latae (TFL), and the iliotibial band, insert primarily onto the greater trochanter. The functional preservation or meticulous reattachment of these structures is the most significant determinant of postoperative gait efficiency and joint stability.

The adductor complex, including the adductor brevis, adductor longus, gracilis, and the anterior portion of the adductor magnus, originates from the pubis and ischium and inserts along the linea aspera of the posterior femur. During massive femoral resections, these insertions are inevitably detached, which can lead to a relative overpull of the abductors if not properly balanced, or conversely, severe adductor contractures if the limb is acutely shortened.

The short external rotators—the piriformis, quadratus femoris, superior gemellus, inferior gemellus, obturator internus, and obturator externus—insert into the piriformis fossa and the intertrochanteric crest. These muscles act as vital dynamic stabilizers against posterior dislocation. In revision scenarios requiring PFR, these structures are often scarred, attenuated, or previously resected, demanding meticulous capsular reconstruction or the use of constrained acetabular liners to compensate for their absence.

Neurovascular Topography

The neurovascular anatomy surrounding the hip and thigh dictates the safety corridors during extensile exposures. The abductors are innervated predominantly by the superior gluteal nerve, which exits the pelvis via the suprapiriform portion of the greater sciatic foramen, accompanied by the superior gluteal vessels. Iatrogenic injury to this nerve during proximal dissection, particularly when extending the approach proximally into the ilium, results in irreversible abductor palsy. Clinically, this manifests as a profound abductor lurch, or Trendelenburg gait, severely compromising the functional outcome of the reconstruction.

The sciatic nerve, exiting inferior to the piriformis, is at significant risk during posterior approaches, extensive scar resection, and particularly during limb lengthening procedures. When restoring limb length with a modular megaprosthesis, the sciatic nerve is highly susceptible to traction neurapraxia. The femoral nerve, located anteriorly within the femoral triangle, is less commonly injured but remains at risk during anterior capsulectomies or when managing severe intrapelvic protrusio.

Vascular considerations are equally critical. The profound femoral artery and its perforating branches lie in close proximity to the linea aspera and must be carefully ligated during the diaphyseal dissection required for TFR or extensive PFR. Preoperative distortion of this anatomy due to multiple previous surgeries, heterotopic ossification, or chronic infection necessitates extreme vigilance, and in some cases, preoperative angiography to map the displaced vessels.

Biomechanical Considerations in Proximal Femoral Replacement

The biomechanics of a proximal femoral replacement differ fundamentally from standard primary or revision THA. The resection of the proximal femur ablates the natural abductor moment arm, shifting the joint reaction forces significantly. In a normal hip, the abductor muscles exert a force approximately three times body weight to maintain a level pelvis during the single-leg stance phase of gait. When the greater trochanter is excised, the effective lever arm of the abductors is drastically reduced, requiring exponentially greater muscle force to stabilize the pelvis, which the compromised muscles are rarely able to generate.

To counteract this, modern modular megaprostheses are designed to optimize lateral offset. By increasing the horizontal distance from the center of rotation to the mechanical axis of the femur, the surgeon can artificially lengthen the abductor moment arm, thereby reducing the requisite muscle force and enhancing stability. However, excessive offset must be avoided, as it exponentially increases the cantilever bending moments on the diaphyseal fixation interface, predisposing the stem to mechanical loosening or fatigue fracture.

Soft tissue tensioning is the second biomechanical pillar of PFR. Without the bony landmarks of the lesser and greater trochanters, determining the appropriate limb length and myofascial tension is highly subjective. The surgeon must balance the need for sufficient tension to prevent dislocation (often requiring slight over-lengthening of the myofascial envelope) against the risk of sciatic nerve traction palsy. The use of dual mobility articulations or constrained liners alters the biomechanical requirements for soft tissue tension, allowing for a more forgiving stability profile in the face of abductor deficiency.

Exhaustive Indications and Contraindications

Clinical Indications for Reconstruction

The decision to proceed with a proximal or total femoral replacement is typically reserved for catastrophic clinical scenarios where conventional reconstructive techniques are futile. The primary indication is massive bone loss (Paprosky Type IIIb or IV defects) where the remaining proximal bone is incapable of supporting a primary or revision diaphyseal-engaging stem. This is frequently encountered following multiple failed reconstructive procedures with the insertion and removal of implants that compromise the structural integrity of the bone stock.

In the elderly or sedentary population, PFR is the treatment of choice for severe periprosthetic fractures (Vancouver B3), deep periprosthetic joint infections (as the second stage of a two-stage exchange, or occasionally in single-stage protocols for highly selected patients), and fracture nonunions with failed multiple attempts at osteosynthesis. It is also an excellent salvage option for a failed resection arthroplasty (Girdlestone), providing immediate structural stability and restoring ambulatory potential.

When the distal bone is severely deficient—leaving less than 10 cm of viable diaphyseal bone for secure fixation of a cemented or uncemented femoral stem—a total femoral replacement (TFR) must be considered. TFR is indicated for diaphyseal lesions that extend proximally to the lesser trochanter and distally to the distal diaphyseal-metaphyseal junction, causing extensive bone destruction that precludes any form of segmental fixation.

Absolute and Relative Contraindications

The use of a megaprosthesis is not without significant risk, and strict adherence to contraindications is mandatory to prevent catastrophic failure. The presence of an active, untreated superficial or deep periprosthetic infection around the hip is an absolute contraindication to definitive implantation. Any ongoing infectious process must be managed with a thorough debridement, placement of an antibiotic-loaded cement spacer, and appropriate systemic antimicrobial therapy prior to considering reconstruction.

Relative contraindications include a lack of cooperation or cognitive capacity on the part of the patient to adhere to strict postoperative dislocation precautions and weight-bearing restrictions. Vascular insufficiency that may prevent wound healing is a profound concern; patients with a history of chronic venous stasis ulcers, previous vascular bypass surgery, or absent distal pulses must be optimized by a vascular surgeon prior to intervention.

Furthermore, the presence of significant medical comorbidities precluding the administration of prolonged anesthesia or the ability to tolerate major blood loss makes this massive surgery prohibitive. Finally, as previously noted, young patient age and high functional demand serve as strong relative contraindications due to the near certainty of eventual mechanical failure; in these patients, biological reconstruction via an allograft-prosthesis composite (APC) is preferred, despite its higher risks of junctional nonunion and infection.

Differential Diagnosis

Before committing to a massive resection and megaprosthesis, the surgeon must systematically evaluate the differential diagnosis of the patient's severe hip pathology. Assessment of the present and past medical history, physical examination results, and radiographic findings lead to a correct diagnosis in most patients. The differential includes:

• Osteomyelitis / Periprosthetic Joint Infection: Must be ruled out via aspiration, inflammatory markers (ESR, CRP), and intraoperative frozen sections.
• Metastatic Lesions: Often present with unremitting rest pain and require systemic staging.
• Primary Bone Tumors: e.g., multiple myeloma, chondrosarcoma.
• Periprosthetic Fracture: Can be subtle; requires careful radiographic scrutiny.
• Osteolysis / Aseptic Loosening: The most common non-oncologic cause of massive bone loss.
• Paget Disease: Characterized by cortical thickening, bowing, and altered trabecular patterns.
• Metabolic Bone Disease: Severe osteoporosis or osteomalacia complicating fixation.

Table: Indications and Contraindications for Megaprosthesis

Pre-Operative Planning, Templating, and Patient Positioning

Patient History and Physical Examination

Initial history taking should begin with a detailed discussion of the patient’s chief complaint. The location and nature of the patient’s pain are critical diagnostic guides. Intra-articular or acetabular pathology typically presents as deep groin pain. Conversely, thigh pain—especially severe start-up pain upon initial weight-bearing—is highly indicative of a loose femoral stem micromotion. Importantly, patients may present with severe knee pain as referred pain from hip pathology via the obturator nerve; thus, any patient with unexplained knee pain must have their hip evaluated.

A thorough review of the patient’s medical history and a complete review of systems help identify potential factors leading to perioperative complications, providing an opportunity to medically optimize the patient. Sources of potential or concurrent infection (e.g., dental abscesses, urinary tract infections) must be discovered and treated well in advance. Negative preoperative hip aspirations do not completely rule out indolent infection; therefore, the surgeon must be prepared for intraoperative tissue sampling with frozen sections, alerting the pathology department well before the surgical date.

The physical examination begins with a meticulous gait analysis. Use of ambulatory assistive devices, a limp, or a lower extremity deformity must be documented. An antalgic gait, characterized by a shortened stance phase, indicates pain with weight-bearing. A Trendelenburg gait, or abductor lurch, indicates either paralysis or loss of continuity of the abductor musculature, identified by the patient shifting their center of gravity over the affected extremity during the stance phase. Specific tests, including the Trendelenburg test, Straight Leg Raise (for radicular pain), Thomas test (for flexion contractures), and Stinchfield test, must be documented alongside precise leg-length assessments (apparent vs. functional discrepancy). Finally, a rigorous neurovascular exam and evaluation of the spine and abdomen are mandatory to exclude neuropathies, vascular claudication, or spinal stenosis.

Imaging Modalities and Diagnostic Studies

Proximal and total femur resections are massive surgical undertakings that necessitate a flawless preoperative evaluation. Imaging studies are the cornerstone for determining the extent of bone resection, the dimensions of the required prosthesis, and the proximity of scarred-in neurovascular structures. Plain radiographs (AP pelvis, AP and lateral of the entire femur) are the first-line tools to evaluate the extent and level of bone destruction.

When plain films are insufficient, CT scanning with metal artifact reduction sequences (MARS) is heavily utilized for precise 3D delineation of the remaining femoral and acetabular bone stock. MRI is less commonly used due to metallic artifact from existing implants but is invaluable for evaluating the medullary canal and the viability of the soft tissue envelope around the hip joint in oncologic cases. A three-phase technetium-99m bone scan is essential to determine the presence of metastatic bone disease or to highlight areas of active loosening/infection. Finally, angiography of the iliofemoral vessels is essential before PFR if severe distortion of the anatomy following multiple previous surgeries is suspected, ensuring the femoral vessels are not inadvertently transected during deep dissection.

Implant Selection and Templating

The importance of preoperative templating in proximal femur reconstruction cannot be overstated. These cases are technically demanding and require meticulous attention to detail. Preoperative templating on calibrated digital radiographs is essential to select the appropriate stem length, diameter, and required modular body segments. The surgeon must template the exact level of the proposed bone resection, ensuring that at least 10 cm of healthy diaphyseal bone remains for distal fixation of a PFR. If this 10 cm rule cannot be satisfied, the surgical plan must pivot to a Total Femoral Replacement.

Problems with the removal of existing hardware, specific needs for concurrent acetabular reconstruction (e.g., use of cages or augments), and the potential need for insertion of constrained liners or dual mobility constructs must be anticipated. Even with the most accurate preoperative measurements, a wide variety of prosthesis sizes, modular bodies, and stem lengths must be available in the operating room. Intraoperative adjustments and deviations from the anticipated size are commonplace. The representative of the implant manufacturer must be present in the operating room to assist with the complex modular assembly.

Anesthesia, Patient Positioning, and Setup

These procedures require an experienced operating room team. The anesthesia team must be highly skilled, as these patients are often elderly, frail, and subject to massive fluid shifts. Regional anesthesia (epidural or spinal) is preferred when feasible, as it reduces intraoperative blood loss and postoperative deep vein thrombosis risk. Invasive monitoring with arterial lines and potentially central venous catheters is warranted. The anesthesia team must be prepared for large volume blood loss; intraoperative blood salvage (cell saver) should be routinely utilized.

Patient positioning is dictated by surgeon preference and the required exposure. We place the patient in either the lateral decubitus or supine position. If the lateral decubitus position is chosen, rigid pelvic fixation with peg boards is necessary to ensure the pelvis does not roll during aggressive reaming and trialing.

Draping must be meticulous. Nonpermeable U-drapes are used to isolate the groin. Crucially, the entire extremity down to the foot must be prepped, and the knee must be included in the operative field, even in patients undergoing only proximal femoral replacement. Extension of the incision and arthrotomy of the knee to address intraoperative problems, such as distal extension of a fracture, is not uncommon. The skin is scrubbed with povidone-iodine solution for at least 10 minutes, and DuraPrep is applied before sealing the field with an iodine-impregnated incise drape (Ioban).

Step-by-Step Surgical Approach and Fixation Technique

Surgical Incision and Extensile Approaches

We utilize either a direct lateral approach (Hardinge) or a standard posterolateral approach, often incorporating a trochanteric slide osteotomy to gain wide access to the hip while preserving the continuity of the abductor-vastus lateralis myofascial sleeve. The surgeon must maintain a low threshold to extend the incision distally along the lateral aspect of the thigh as needed. Inspection of previous surgical wounds is routinely performed; planning the surgical incision is critical. Although skin flap necrosis after hip surgery is rare, utilizing previous incisions and maintaining thick fasciocutaneous flaps is optimal to avoid this devastating complication.

When extensile exposure of the entire femoral diaphysis is required, a vastus slide osteotomy or an extended trochanteric osteotomy (ETO) is employed. The vastus slide involves elevating the vastus lateralis from the linea aspera, reflecting it anteriorly as a continuous musculotendinous unit with the abductors. This provides unparalleled visualization of the anterior and lateral femur while protecting the neurovascular bundle located medially.

Soft Tissue Dissection and Bone Resection

Once the femur is exposed, the pseudocapsule is excised, and the hip is dislocated. If an existing implant is present, it is carefully extracted. In cases of severe bone loss or tumor, the proximal femur is skeletonized. The insertions of the gluteus maximus, short external rotators, and iliopsoas (at the lesser trochanter) are tagged for potential later repair, though often they must be sacrificed.

The level of femoral resection is determined based on preoperative templating and intraoperative assessment of bone viability. A transverse osteotomy is performed using an oscillating saw in healthy, bleeding diaphyseal bone. The resected segment is measured, and this measurement is used to guide the assembly of the modular prosthesis.

Trialing, Limb Length Restoration, and Soft Tissue Tensioning

Preparation of the distal femoral canal is performed using sequential flexible or rigid reamers. Depending on the bone quality and surgeon preference, the definitive stem may be fully porous-coated for diaphyseal press-fit fixation, or it may be cemented. If cementing, the canal is aggressively brushed, pulsatile lavaged, and dried. A cement restrictor is placed, and polymethylmethacrylate (PMMA) is delivered in a retrograde fashion using a cement gun and pressurized.

Before definitive implantation, extensive trialing is mandatory. The modular trial components are assembled to match the exact length of the resected bone. The hip is reduced, and stability is rigorously tested. Intraoperative monitoring of the sciatic and femoral nerves may be required in patients where extensive limb lengthening (more than 4 cm) is anticipated to restore original leg length. Soft tissue tension is evaluated by the "shuck test" and the resting position of the leg. If the hip is unstable in flexion and internal rotation (posterior approach), a larger femoral head, increased offset, or a constrained acetabular liner must be considered.

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