Thompson Hemiarthroplasty: Procedure, Indications, and Recovery

What is Thompson Hemiarthroplasty?

Thompson hemiarthroplasty is a specific type of partial hip replacement surgery where the damaged femoral head (the ball of the hip joint) is replaced with a single-piece metallic prosthetic implant, while the acetabulum (the socket of the hip joint) is left untouched.

Introduction to Hip Hemiarthroplasty

The hip joint is a crucial ball-and-socket joint, formed by the head of the femur (thigh bone) and the acetabulum of the pelvis. When severe damage occurs to the femoral head, often due to fracture or avascular necrosis, surgical intervention may be necessary to restore function and alleviate pain. Hemiarthroplasty, meaning "half joint replacement," involves replacing only one component of the joint, typically the femoral head. The Thompson hemiarthroplasty represents a foundational technique within this category.

Historical Context and Evolution

The Thompson hemiarthroplasty was developed by Dr. Fred Thompson in the mid-20th century. It emerged as an innovative solution for treating displaced femoral neck fractures, particularly in elderly patients, at a time when total hip replacement was not as refined or widely available. Its design, being a single-piece, cemented prosthesis, offered a relatively straightforward surgical approach for managing these complex injuries, significantly improving outcomes compared to non-surgical management or internal fixation alone for certain patient populations.

Anatomy and Biomechanics Involved

Understanding the hip joint's anatomy is key to appreciating the Thompson procedure. The femoral head is a spherical structure that articulates with the acetabulum, a cup-shaped depression in the pelvis. In a Thompson hemiarthroplasty, the damaged femoral head is resected (removed). A prosthetic femoral component, consisting of a stem that fits into the femoral canal and a head that articulates with the patient's native acetabulum, is then implanted.

From a biomechanical perspective, the success of this procedure relies on the new metallic femoral head articulating smoothly within the natural cartilage lining of the acetabulum. Unlike total hip arthroplasty (THA), which replaces both surfaces, the Thompson prosthesis introduces a metal-on-cartilage bearing surface. The stem of the prosthesis is typically cemented into the femoral canal, providing immediate stability and allowing for early weight-bearing.

Components of a Thompson Hemiarthroplasty

A Thompson hemiarthroplasty prosthesis is characterized by its monopolar, single-piece design. This means:

• One-piece construction: The femoral stem, neck, and head are manufactured as a single, integrated unit.
• Monopolar articulation: The prosthetic head directly articulates with the patient's native acetabular cartilage. It does not have a separate articulating component within the head itself, unlike bipolar hemiarthroplasties.
• Cemented fixation: The stem of the prosthesis is typically secured within the femoral canal using bone cement. This provides immediate stability and strong fixation, which is particularly beneficial in osteoporotic bone often found in elderly patients.

Indications for the Procedure

Thompson hemiarthroplasty is primarily indicated for:

• Displaced femoral neck fractures: This is the most common indication, especially in elderly, less active patients. These fractures disrupt the blood supply to the femoral head, leading to avascular necrosis if not treated promptly, and often do not heal well with internal fixation.
• Failed internal fixation of femoral neck fractures: When previous attempts to fix a femoral neck fracture with screws or pins have failed.
• Avascular necrosis of the femoral head: In cases where the blood supply to the femoral head is compromised, leading to bone death and collapse, and the acetabulum is still healthy.
• Certain types of pathological fractures: Fractures caused by tumors, where the patient's life expectancy or functional demands make a more extensive procedure unnecessary.

It is generally favored for patients with lower functional demands and pre-existing acetabular cartilage that is healthy or only mildly degenerated. For more active individuals or those with significant acetabular arthritis, a total hip arthroplasty is often preferred.

The Surgical Procedure

The Thompson hemiarthroplasty is typically performed under general or spinal anesthesia. The general steps involve:

1. Incision: An incision is made over the hip joint to access the femoral head.
2. Femoral Head Resection: The damaged femoral head is carefully removed.
3. Femoral Canal Preparation: The femoral canal is prepared (reamed) to accept the prosthetic stem.
4. Prosthesis Insertion: The Thompson prosthesis is inserted into the femoral canal, usually with bone cement to ensure a secure fit.
5. Reduction: The new prosthetic femoral head is reduced (placed) into the patient's natural acetabulum.
6. Closure: The surgical site is closed layer by layer.

Advantages and Disadvantages

Advantages:

• Simpler and faster surgery: Generally involves less surgical time and blood loss compared to total hip arthroplasty.
• Lower dislocation rate: The larger prosthetic head articulating with the native acetabulum may offer greater stability.
• Preserves acetabular bone stock: Does not involve reaming or replacing the acetabulum, which can be advantageous if future revisions are needed.
• Good for less active patients: Provides a reliable solution for pain and mobility in individuals with lower functional expectations.

Disadvantages:

• Potential for acetabular erosion/pain: The metal prosthetic head articulating directly with the native cartilage can lead to wear and tear of the acetabulum over time, causing pain and requiring revision surgery.
• Leg length discrepancy: Can sometimes result in a difference in leg length.
• Limited range of motion: May not restore full range of motion compared to a total hip replacement.
• Not ideal for active individuals: Due to the risk of acetabular wear and potential for pain, it's less suitable for younger, more active patients.
• Risk of loosening: While cemented, aseptic loosening can occur over time.

Post-Operative Rehabilitation and Considerations for Fitness

Rehabilitation following a Thompson hemiarthroplasty is crucial for restoring function and preventing complications.

• Early Mobilization: Patients are typically encouraged to begin moving and walking with assistance very soon after surgery, often within 24-48 hours, to prevent complications like deep vein thrombosis and muscle atrophy.
• Weight-Bearing: Due to the cemented fixation, immediate weight-bearing (as tolerated) is often permitted, though specific surgeon protocols may vary.
• Physical Therapy: A structured physical therapy program is essential. This typically includes:
  • Gait training: Learning to walk safely and efficiently.
  • Strengthening exercises: Focusing on the muscles surrounding the hip (quadriceps, hamstrings, glutes, hip abductors, core) to improve stability and power.
  • Range of motion exercises: To prevent stiffness and improve flexibility.
  • Balance and proprioception training: To reduce fall risk.
• Hip Precautions: Patients are often advised to follow certain hip precautions for several weeks or months to prevent dislocation, such as avoiding excessive hip flexion (e.g., bending past 90 degrees), adduction (crossing legs), and internal rotation.
• Long-Term Fitness:
  • Low-impact activities: Activities like walking, swimming, cycling, and elliptical training are generally encouraged.
  • Avoid high-impact activities: Running, jumping, and contact sports are typically discouraged due to the increased stress on the joint and the risk of acetabular wear or implant loosening.
  • Strength and flexibility maintenance: Continued engagement in strength training and stretching is vital for long-term joint health and functional independence.
  • Listen to your body: Any new or persistent pain should be reported to a healthcare professional.

Comparison with Other Hip Surgeries

The Thompson hemiarthroplasty is one of several surgical options for hip pathology:

• Total Hip Arthroplasty (THA): Replaces both the femoral head and the acetabulum. It offers better long-term outcomes for active patients or those with pre-existing acetabular arthritis, but is a more extensive procedure.
• Bipolar Hemiarthroplasty: Also replaces only the femoral head, but uses a two-part prosthetic head (an inner head articulates with the stem, and an outer head articulates with the acetabulum). This design aims to reduce wear on the native acetabulum by allowing motion at two interfaces.
• Internal Fixation: Involves using screws or plates to fix a fracture without replacing the joint. This is often preferred for non-displaced fractures or in younger patients where preserving the native joint is prioritized.

Conclusion

The Thompson hemiarthroplasty remains a relevant surgical option, particularly for elderly, less active individuals suffering from displaced femoral neck fractures. While newer techniques and prostheses like total hip arthroplasty and bipolar hemiarthroplasty have gained prominence, the Thompson procedure offers a simpler, effective solution for specific patient profiles. Understanding its design, indications, and the critical role of post-operative rehabilitation is essential for patients, fitness professionals, and healthcare providers to optimize outcomes and ensure a safe return to functional activity.