Hip, Replacement

Article Author:
Matthew Varacallo
Article Editor:
Norman Johanson
Updated:
5/28/2018 8:39:31 AM
PubMed Link:
Hip, Replacement

Introduction

Total hip arthroplasty (THA) is one of the most cost-effective and consistently successful surgeries performed in orthopedics. THA provides reliable outcomes for patients’ suffering from end-stage degenerative hip osteoarthritis (OA), specifically pain relief, functional restoration, and overall improved quality of life. OA affects millions of Americans, and with an incidence of 88 symptomatic cases per 100,000 patients per year, this translates to hip OA claiming the top underlying diagnosis leading to THA. Other underlying diagnoses include hip osteonecrosis (ON), congenital hip disorders, and inflammatory arthritis.

The underlying diagnosis that leads to a degenerative hip is an important consideration as this has been shown to impact overall outcome. Overall, THA provides consistent short-term and long-term pain relief and positive patient-reported clinical and functional outcomes. In general, THA provides even more reliable and consistent positive results compared to its counterpart procedure, the total knee arthroplasty (TKA).

Anatomy

The hip is a ball-and-socket type diarthrodial joint. Overall hip joint stability is achieved via a dynamic interplay from osseous and soft tissue anatomic components. Osseous components include the proximal femur (head, neck, trochanters), and the acetabulum, which is formed from 3 separate ossification centers (the ilium, ischium, and pubic bones). The native acetabulum is oriented in 15 to 20 degrees of anteversion and 40 degrees of abduction. The femoral neck is oriented in 15 to 20 degrees of anteversion and is angled 125 degrees with respect to its diaphysis.

Soft tissue structures involved in hip joint stability include the labrum and joint capsule. The iliofemoral ligament (IFL) is the strongest of the 3 divisions of capsular ligaments. The IFL functions to restrict extension and external rotation of the hip. The other 2 components are the ischiofemoral and pubofemoral ligaments. The acetabular labrum is anchored at the periphery of the outer rim and functions to maintain negative joint pressure and deepen the hip socket.

Indications

The most common indication for THA includes end-stage, symptomatic hip OA. In addition, hip ON, congenital hip disorders including hip dysplasia, and inflammatory arthritic conditions are not uncommon reasons for performing THA. Hip ON, on average, presents in the younger patient population (35 to 50 years of age) and accounts for approximately 10% of annual THAs.

Contraindications

THA is contraindicated in the following clinical scenarios:

  • Local: Hip infection or sepsis
  • Remote (in other words extra-articular or outside the joint) active, ongoing infection or bacteremia
  • Severe cases of vascular dysfunction

Equipment

Historical Timeline

THA prosthetic designs have been evolving since the late 1800s when Dr. Themistocles Gluck continuously experimented with various options for joint replacements in preliminary animal experiments.  In 1890, one of Dr. Gluck’s reported 14 total joint arthroplasties included an ivory femoral head replacement in a human patient. In 1940, Dr. Austin Moore collaborated with trauma surgeon Dr. Harold Bohlman in developing the first hip hemiarthroplasty (endoprosthesis) for the treatment of displaced femoral neck fractures. In 1952, Dr. Moore developed his prestigious, “Austin Moore prosthesis” as an off-the-shelf joint replacement available worldwide. Sir John Charnley entered the scene in the 1960s when he introduced the concept of “low-friction arthroplasty” by utilizing a metallic femoral stem and small femoral head articulating with a cemented polyethylene acetabular component.

Modern Implants and Bearing Surfaces

Contemporary THA techniques have evolved into press-fit femoral and acetabular components. In general, femoral stems can be categorized into the following general designs:

  • Press-fit, proximally coated, distal taper (dual or single tapered in medial-lateral and/or anterior-posterior planes)
  • Press-fit, extensively coated, diaphyseal engaging
  • Press-fit, Modular stems: Modularity junction options include: (1) head-neck, (2) neck-stem, (3) stem-sleeve, and (4) mid-stem
  • Cemented femoral stems: Cobalt-chrome stems are the preferred material to promote cement bonding

Options for bearing surfaces include:

  • Metal-on-polyethylene (MoP): MoP has the longest track record of all bearing surfaces at the lowest cost
  • Ceramic-on-polyethylene (CoP): becoming an increasingly popular option
  • Ceramic-on-ceramic (CoC): CoC has the best wear properties of all THA bearing surfaces
  • Metal-on-metal (MoM): Although falling out of favor, MoM has historically demonstrated better wear properties from its MoP counterpart. MoM has lower linear-wear rates and decreased volume of particles generated. However, the potential for pseudotumor development as well as metallosis reactions (type-IV delayed hypersensitivity reactions) has resulted in the decline in the use of MoM. MoM is also contraindicated in pregnant women, patients with renal disease, and patients at risk of metal hypersensitivity

One THA prosthesis includes a press-fit acetabular component, neutral polyethylene liner, and either a MoP, CoP, or CoC head/liner construct depending on patient age and projected activity level. In addition, patients with poor bone quality are often considered for a cemented femoral stem option. This concept is particularly relevant in the THA treatment for active, elderly patients with displaced femoral neck fractures.

Preparation

Nonoperative Treatment Modalities

According to the most recent American Academy of Orthopaedic Surgeons' (AAOS) Guidelines for the treatment of symptomatic osteoarthritis of the hip or knee, strong or moderately strong recommendations for nonoperative treatment was endorsed for the following modalities:

  • Weight loss programs
  • Physical activity and physical therapy programs
  • Non-steroidal anti-inflammatory medications (NSAIDs) and tramadol

Corticosteroid injections can be therapeutic and/or diagnostic for symptomatic patients. This can be particularly beneficial in patients when confounding conditions of lower back pain and lumbar spinal stenosis with or without radicular symptoms is in the clinical picture.  In addition, a cane has the ability to decrease the joint reaction forces generated in the hip. When patients present with unilateral hip pain, they should be instructed to use the cane with the contralateral upper extremity.

Other modalities for symptomatic management that were not supported but are often considered reasonable alternative treatment measures to help manage symptoms secondary to hip arthritis include but are not limited to acupuncture, viscoelastic joint injections, and glucosamine and chondroitin supplements.

Preoperative Evaluation: Clinical Examination

A comprehensive history and physical examination are required prior to considering performing a THA in any patient. Patients should be questioned about prior interventions and treatments. Prior joint replacements, arthroscopic procedures, or other surgeries around the hip should be considered as prior surgical incisions or the presence of hardware in the femur or acetabulum can significantly impact the planned surgery and/or prosthesis design utilized.  In addition, a comprehensive medical evaluation should also be performed, and medical clearance and risk stratification are recommended for all patients prior to THA consideration.

Other considerations include patient body habitus, prior functional activity and goals/expectations following surgery, the pattern of arthritic involvement, and any history of prior hip trauma. The hip should be inspected for any skin discoloration, wounds, or previous scars. The soft tissues should be examined for evidence of gross atrophy, overall symmetry, and stability. The peripheral vascular disease may warrant preoperative vascular surgery consultation.

Physical examination also includes evaluation of the mechanical axis of the limb. It is critical to ensure spine and/or knee pathology is ruled out or at least considered prior to performing any surgery around the hip. Any leg length discrepancy (LLD) should also be noted. It is critical to also consider the impact of any of the following conditions in addition to actual or apparent LLD:

  • Hyperlordotic spine conditions
  • Pelvic obliquity
  • Hip flexion contractures: The patient may not be able to stand upright
  • Trendelenburg gait or Trendelenburg sign

 Preoperative range of motion (ROM) should also be noted. Patients with end-stage arthritis more frequently present with a combination of hip adduction and flexion contractures. Any appreciable flexion contracture greater than 5 degrees and lack of flexion beyond 90 to 100 degrees should be documented. In addition, rotational arc ROM is typically limited, especially in the internal rotation. The neurovascular exam should also include the positive/negative status of a straight leg raise test.

Preoperative Evaluation: Radiographs 

Preoperative radiographs, including a standing anteroposterior (AP) pelvis plus AP/lateral of the involved hip(s), is recommended. A false profile view is considered in cases of hip dysplasia. When the surgeon is faced with cases of severe hip dysplasia, and when considering the use of customized components, we recommend obtaining a preoperative CT scan with thin (1-mm) cuts.

On imaging, the hip joint is assessed for joint space narrowing, presence of osteophytes, and presence of subchondral sclerosis and/or degenerative cysts. Particular attention is paid to the planned center of hip rotation (COR) in relation to the native COR. The surgeon should also have an idea of planned cup medialization and corresponding reaming required to ensure appropriate medialization of the acetabular implant. Finally, any appreciable LLD can also be calculated utilizing any combination of described methods.

Technique

Approaches

Any number of approaches can be utilized for the THA procedure. The three most common approaches are as follows:

Posterolateral

This is the most common approach for primary and revision THA cases. This dissection does not utilize a true internervous plane. The intermuscular interval involves blunt dissection of the gluteus maximus fibers and sharp incision of the fascia lata distally. The deep dissection involves meticulous dissection of the short external rotators and capsule. Care is taken to protect these structures as they are later repaired back to the proximal femur via trans-osseous tunnels.

A major advantage of this approach is the avoidance of the hip abductors. Other advantages include the excellent exposure provided for both the acetabulum and the femur and the optional extensile conversion in the proximal or distal direction. Historically, some studies comparing this approach to the direct anterior (DA) approach have cited higher dislocation rates in the former approach. This remains an inconclusive and controversial as the literature has not established a definitive consensus, especially when comparing the posterior approach technique that utilizes an optimal soft tissue repair at the conclusion of the THA procedure.

Direct Anterior (DA)

The DA approach is becoming increasingly popular among THA surgeons. The internervous interval is between the tensor fascia lata (TFL) and sartorius on the superficial end, and the gluteus medius and rectus femoris (RF) on the deep side. DA THA advocates cite the theoretical decreased hip dislocation rates in the postoperative period and the avoidance of the hip abduction musculature.

The disadvantages include the learning curve associated with the approach as the literature documents the decreased complication rates after a surgeon surpasses the more than 100-case mark. Other disadvantages include increased wound complications in particularly obese patients with large panni (without the use of an abdominal binder), difficult femoral exposure, the risk of lateral femoral cutaneous nerve (LFCN) paresthesias, and a potentially higher rate of intra-operative femur fractures. Finally, many surgeons need access to a specialized operating table with appropriately trained personnel and surgical technicians to assist in the procedure. Although the latter is not always required, learning to do the procedure on a regular operating table also requires a substantial learning curve that must be considered.

Anterolateral

Compared to the other approaches, the anterolateral (AL) approach is the least commonly used approach secondary to its violation of the hip abductor mechanism. The interval exploited includes that of the TFL and gluteus medius musculature. This may lead to a postoperative limp at the tradeoff of a theoretically decreased dislocation rate.

Procedural steps

After the surgical approach is completed, the next step required prior to visualizing the acetabulum is the femoral neck osteotomy. This is most commonly with a reciprocating saw beginning at a starting point about 1-cm to 2-cm proximal to the lesser trochanter. This is continued in a proximal-lateral direction toward the base of the greater trochanter.  Once the neck osteotomy is completed, the femoral head and neck are freed of all soft tissue attachments and removed.

Acetabular visualization is accomplished with a combination of retractors. Some surgeons prefer the anterior retractor placement at the 2 o'clock (right hip) or 10 o'clock (left hip) position, in addition to bent Hohmann retractors at the 12’ o-clock (both hips) and 8’ o-clock (right hip) or 4’ o-clock (left hip) positions. A blunt Hohmann (or “No. 3”) retractor is placed in the extra-capsular position at the level of the trans-acetabular ligament (TAL). The ligamentum teres/fibrofatty pulvinar remnants are excised to expose the acetabular teardrop, followed by removal of the labrum (if present) to ensure efficient use of the acetabular reamers.

Preferred reaming methods consist of starting small (i.e., size 44) and focusing on appropriate medialization of the cup with exposure of the medial wall without protruding. Once medialization is achieved, sequential reaming in the planned position of the press-fit implanted cup becomes the major focus. Most commonly, this is in the 35 to 40 degrees of inclination and 15 to 20 degrees of anteversion range. Once all sclerotic bone is reamed and a healthy bleeding bony bed is established, the acetabular component is inserted in press-fit fashion followed by insertion of the corresponding liner.

The femur is then prepared with a ream and/or broach system-specific instrumentation. This is continued until provisional press-fit stability is achieved. Then with the trial femoral stem in place, the hip should be reduced and evaluated for stability utilizing a combination of standard or increasing neck offset trial implants. The head can also be adjusted based on the specific system used. Most implants offer a variety of “plus” and “minus” head size options to add or subtract additional length based on trial total hip stability.

One method for intraoperative THA stability parameters includes the following:

  • A shuck test is utilized to free any potential interposed soft tissue and to also evaluate stability with axial traction
  • Equal leg lengths: The patella and heels are compared to the contralateral extremity via direct palpation
  • With the hip at zero degrees of extension, the hip is externally rotated, and avoidance of posterior impingement is ensured
  • The hip should be ranged in abduction and external rotation to ensure avoidance of posterior impingement and anterior subluxation
  • The hip should be brought to 90 degrees of flexion with additional adduction and internal rotation to about 70 to 90 degrees and remain stable

Wound Closure

Attention to detail is required, and a methodical closure is unanimously advocated. A nonabsorbable, braided, sterile, surgical suture composed of ethylene terephthalate suture is used to repair the capsule and/or short external rotators to the proximal femur via two trans-osseous tunnels. One protocol includes the use of a unidirectional or bi-directional barbed suture for the deep fascial, deep fat, and deep dermal/subcutaneous layers. Staples or monocryl can be used for the skin. Some surgeons prefer using a running barbed monocryl-based suture augmented by a mesh dressing and skin glue closure. A sterile dressing is then applied and left in place without being changed for the first seven days. An abduction pillow placed and patient education about the appropriate hip flexion precautions and activity restrictions in the early postoperative period is important. Topical tranexamic acid (TXA) application prior to pulsatile saline lavage and commencement of the closure is also recommended.

Complications

The following are some major complications following THA.

THA Dislocation

About 70% of THA dislocations occur within the first month following index surgery. The overall incidence is about 1% to 3%. Risk factors include:

  • Prior hip surgery (most significant independent risk factor for dislocation)
  • Elderly age (older than 70 years)
  • Component malpositioning: Excessive anteversion results in anterior dislocation and excessive retroversion results in posterior dislocation
  • Neuromuscular conditions/disorders (for example, Parkinson disease)
  • Drug/alcohol abuse

Recurrent THA dislocations often result in revision THA surgery with component revision.

THA Periprosthetic Fracture

THA periprosthetic fractures (PPFs) are increasing in incidence with the overall increased incidence of procedures in younger patient populations.

Intraoperative fractures can occur and involve either the acetabulum and/or femur. Acetabular fractures occur in 0.4% of press-fit acetabular implant components, most often during component impaction. Risk factors include underreaming more than 2 mm, poor patient bone quality, and dysplastic conditions. Intraoperative femur fractures occur in up to 5% of primary THA cases as reported in some series. Risk factors include technical errors, press-fit implants, poor patient bone quality, and revision surgery.

Treatment of fractures surrounding the femoral stem is reliably managed using the Vancouver classification system.

THA Aseptic Loosening

As in its counterpart TKA procedure, aseptic loosening is the result of a confluence of steps involving particulate debris formation, prosthesis micromotion, and macrophage activated osteolysis. Treatment requires serial imaging and radiographs and/or CT imaging for preoperative planning. Persistent pain requires revision THA surgery.

Wound Complications

The THA postoperative wound complication spectrum ranges from superficial surgical infections (SSIs) such as cellulitis, superficial dehiscence, and/or delayed wound healing, to deep infections resulting in full-thickness necrosis. Deep infections result in returns to the operating room for irrigation, debridement (incision and drainage) and depending on the timing of the infection, may require explant of THA components.

THA Prosthetic Joint Infection (PJI)

The incidence of prosthetic total hip infection (THA PJI) following primary THA is approximately 1% to 2% as reported in the literature.  Risk factors include patient-specific lifestyle factors (morbid obesity, smoking, intravenous [IV] drug use and abuse, alcohol abuse, and poor oral hygiene). Other risk factors include patients with a past medical history consisting of uncontrolled diabetes, chronic renal and/or liver disease, malnutrition, and HIV (CD4 counts less than 400).

The most common offending bacterial organisms in the acute setting include Staphylococcus aureus, Staphylococcus epidermidis, and in chronic THA PJI cases, coagulase-negative Staphylococcus bacteria.  Treatment in the acute setting (less than 3 weeks after index surgery) can be limited to I and D, polyethylene exchange, and retention of components. This is commonly referred to as the “I and D, head/liner exchange” treatment modality. In addition, IV antibiotics are utilized for up to 4 to 6 weeks duration. Outcomes vary and are often influenced by multiple intraoperative, patient-related factors, and offending bacterial organism, but studies site a 55% successful outcome rate.

More aggressive treatments, especially in the setting of presentation beyond the acute (3- to 4-week time mark) includes a 1 or 2-stage revision THA procedure with interval antibiotic spacer placement. The surgeon must ensure and document evidence of infection eradication.

Other Complications and Considerations

Other potential THA complications include the following:

  • Sciatic nerve palsy
  • Leg Length Discrepancy (LLD)
  • Iliopsoas impingement
  • Heterotopic ossification
  • Vascular injury

Clinical Significance

THA is one of the most successful and cost-effective procedures in all of orthopedics. The procedure is most commonly performed on patients suffering from debilitating, end-stage arthritic conditions of the hip. Once considered a procedure limited to the elderly, low-demand patients, THA is becoming an increasingly popular procedure performed in younger patient populations.

The literature, in general, cites superior satisfaction rates in THA patient populations. Outcomes in THA are overall considered to be even more reliable and predictable compared to the general TKA patient populations. Success following THA results in significant improvements in patient-reported pain and functional outcome scores in the short- and long-term postoperative periods. Although the overall longevity of the THA prosthesis is influenced by a multitude of patient-related and prosthetic technicality factors, in general, the lifespan is expected for about 15 to 20 years.

Clinicians are encouraged to ensure that surgical candidates have first exhausted all nonoperative treatment modalities mentioned earlier in this review. As the rates of surgical procedures in the young and elderly populations continue to increase, orthopedic surgeons can expect excellent outcomes in the appropriately indicated patient populations.