Hemiarthroplasty Hip: Procedure, Indications, Recovery, and Risks

What is Hemiarthroplasty Hip?

Hemiarthroplasty of the hip is a surgical procedure that involves replacing only the femoral head (the "ball" part of the hip joint) with a prosthetic implant, while preserving the natural acetabulum (the "socket" part).

Understanding the Hip Joint Anatomy

The hip joint is a classic ball-and-socket synovial joint, designed for multi-directional movement and significant weight-bearing. It is formed by the articulation of the femoral head (the rounded top end of the femur, or thigh bone) and the acetabulum (a cup-shaped depression in the pelvis). Both surfaces are covered with smooth articular cartilage, which allows for frictionless movement and acts as a shock absorber. Surrounding the joint is a strong joint capsule, reinforced by ligaments, providing stability.

What is Hemiarthroplasty?

Hemiarthroplasty, often referred to as a "partial hip replacement," is an orthopedic surgical procedure where only one part of the hip joint is replaced. Unlike a total hip arthroplasty (THA), which replaces both the femoral head and the acetabulum with prosthetic components, hemiarthroplasty specifically targets the femoral component. The damaged or diseased femoral head is removed and replaced with a metal or ceramic prosthetic head, which is attached to a stem inserted into the femur. This new prosthetic head then articulates directly with the patient's native, preserved acetabulum.

When is Hemiarthroplasty Performed?

Hemiarthroplasty is primarily indicated for specific conditions, most commonly acute fractures.

• Femoral Neck Fractures: This is the most common indication, especially in older adults. When the femoral neck (the area just below the femoral head) is fractured, the blood supply to the femoral head can be compromised, leading to avascular necrosis (AVN) or non-union. Hemiarthroplasty is often preferred over internal fixation for displaced femoral neck fractures in elderly patients due to potentially faster recovery and lower re-operation rates.
• Avascular Necrosis (AVN) of the Femoral Head: In cases where the blood supply to the femoral head is severely disrupted, causing bone death, and the acetabulum is relatively healthy, hemiarthroplasty may be considered.
• Failed Internal Fixation of Femoral Neck Fractures: If an initial attempt to fix a femoral neck fracture with screws or plates fails, hemiarthroplasty can be a salvage procedure.
• Less Common for Osteoarthritis: While total hip arthroplasty is the gold standard for severe hip osteoarthritis, hemiarthroplasty might be considered in very specific, often elderly, patients with advanced femoral head osteoarthritis but relatively preserved acetabular cartilage, though this is less frequent.

The decision to perform a hemiarthroplasty is influenced by factors such as the patient's age, activity level, bone quality, and the overall condition of the acetabular cartilage.

Types of Hemiarthroplasty

There are two primary types of hemiarthroplasty, differentiated by the design of the prosthetic head:

• Unipolar Hemiarthroplasty: This involves a single prosthetic component that directly articulates with the patient's native acetabular cartilage. The femoral stem is inserted into the femur, and a single prosthetic head is attached to it.
• Bipolar Hemiarthroplasty: This design features two articulating surfaces within the prosthetic head itself. An inner metallic or ceramic head articulates with a polyethylene liner, which is housed within a larger metal outer shell. This outer shell then articulates with the patient's native acetabulum. The idea behind bipolar designs is to potentially reduce wear on the native acetabular cartilage compared to unipolar designs by distributing forces over two surfaces.

The Surgical Procedure

Hemiarthroplasty is performed under general or spinal anesthesia. The surgeon makes an incision (typically posterior, anterior, or lateral) to access the hip joint. The dislocated or fractured femoral head is carefully removed. The femoral canal is then prepared, and a prosthetic stem is cemented or press-fitted into the femur. Finally, the appropriate size of prosthetic head (unipolar or bipolar) is attached to the stem, and the new joint is reduced (put back into place). The incision is then closed.

Benefits and Advantages

Compared to total hip arthroplasty, hemiarthroplasty offers several potential advantages, particularly in the context of acute fracture management:

• Shorter Surgical Time: The procedure is generally less complex and quicker to perform, as it doesn't involve preparing and implanting an acetabular component.
• Less Blood Loss: Due to the shorter surgical time and less bone manipulation, there is typically less intraoperative blood loss.
• Preservation of Native Acetabulum: The patient's own acetabular cartilage is retained, which can theoretically reduce the risk of acetabular loosening, a common complication in total hip replacement.
• Potentially Lower Dislocation Risk: Some studies suggest a lower dislocation rate for hemiarthroplasty compared to total hip arthroplasty, particularly in the immediate post-operative period for specific approaches.
• Quicker Recovery for Specific Indications: For elderly patients with femoral neck fractures, hemiarthroplasty often allows for earlier weight-bearing and mobilization, which is crucial to prevent complications associated with prolonged bed rest.

Potential Risks and Complications

While generally safe, hemiarthroplasty carries potential risks inherent to any major surgery:

• Infection: Though rare, infection can occur at the surgical site, sometimes requiring further surgery.
• Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE): Blood clots can form in the legs and potentially travel to the lungs.
• Nerve or Vascular Damage: Though uncommon, surrounding nerves or blood vessels can be injured during surgery.
• Dislocation: The prosthetic head can come out of the acetabulum, particularly in the early post-operative period.
• Leg Length Discrepancy: The operated leg may feel longer or shorter, sometimes requiring a shoe lift.
• Periprosthetic Fracture: A fracture can occur around the implant, either during or after surgery.
• Acetabular Erosion: In unipolar hemiarthroplasty, the prosthetic head articulating directly with the native cartilage can lead to wear and erosion of the acetabulum over time, potentially necessitating revision to a total hip replacement.
• Component Loosening: Over time, the prosthetic femoral component can loosen from the bone.

Recovery and Rehabilitation

Recovery from hemiarthroplasty is a critical phase for successful outcomes.

• Immediate Post-Operative: Pain management is a priority. Patients are typically encouraged to begin moving the operated leg and sit up shortly after surgery.
• Early Mobilization: Weight-bearing status will be determined by the surgeon, often allowing partial or full weight-bearing with assistance (walker, crutches). Early mobilization is crucial to prevent stiffness and reduce the risk of DVT.
• Physical Therapy: A structured physical therapy program is essential. It focuses on:
  • Range of Motion (ROM): Restoring normal hip movement.
  • Strengthening: Building strength in the hip and surrounding musculature (quadriceps, hamstrings, glutes).
  • Gait Training: Re-learning how to walk safely and efficiently.
  • Balance and Proprioception: Improving stability.
• Activity Progression: Return to daily activities is gradual. Driving may be resumed when pain is controlled and the patient can safely operate pedals. Most patients will require several weeks to months to regain significant independence.

Life After Hemiarthroplasty: Exercise and Activity

For fitness enthusiasts and trainers, understanding the implications for long-term activity is key.

• Adherence to Physical Therapy: Continued adherence to prescribed exercises is paramount for maintaining strength, flexibility, and preventing complications.
• Recommended Activities:
  • Walking: Excellent for cardiovascular health and maintaining joint mobility.
  • Swimming/Aquatic Exercise: Provides resistance without impact, ideal for early rehabilitation and ongoing fitness.
  • Cycling (Stationary or Road): Low-impact, excellent for strengthening leg muscles and improving cardiovascular fitness.
  • Elliptical Trainer: Another low-impact option.
  • Light Resistance Training: Focusing on hip abductors, extensors, and core muscles is vital for stability.
• Activities to Approach with Caution or Avoid:
  • High-Impact Sports: Running, jumping, contact sports, and activities with sudden stops and starts should generally be avoided due to increased stress on the implant and native cartilage.
  • Extreme Hip Flexion: Avoid positions that bring the knee past the hip (e.g., deep squats, sitting on very low chairs) initially, depending on the surgical approach, to reduce dislocation risk.
  • Extreme Internal Rotation and Adduction: Specific movements that combine these can increase dislocation risk, especially with posterior approaches.
• Listening to Your Body: Patients should be educated to recognize signs of pain, swelling, or instability and report them to their healthcare provider. Regular follow-up appointments are important to monitor the implant and joint health.

Hemiarthroplasty vs. Total Hip Arthroplasty (Brief Comparison)

While hemiarthroplasty preserves the acetabulum, its long-term durability can be limited by the wear of the prosthetic head on the native acetabular cartilage, particularly in younger, more active individuals. For severe, chronic conditions like osteoarthritis affecting both sides of the joint, Total Hip Arthroplasty (THA) is generally preferred due to its superior long-term outcomes and lower rates of re-operation, especially in patients with a longer life expectancy. Hemiarthroplasty remains a valuable option, particularly for acute femoral neck fractures in older, less active patients, offering a quicker and less invasive solution with good short- to medium-term results.