Current Orthopaedic Practice

A concise guide for postgraduate exams

Agarwal, Sanjeev

• Publisher: tfm Publishing Ltd
• Year: 2012
• Print ISBN: 9781903378595
• eBook ISBN: 9781908986900
• Topic: Medizin
• Subtopic: Medizinische Theorie, Praxis & Referenz

The book is intended as a concise overview of current orthopaedic practice. It will be of interest to orthopaedic surgeons in practice and to orthopaedic trainees - both specialist and basic surgical, in particular, orthopaedic specialist registrars in the UK preparing for the FRCS Orth. exam, or trainees in other countries at an equivalent stage of orthopaedic training. Medical students doing orthopaedic attachments will find it a practical reference tool. In addition, individuals involved in the care of orthopaedic patients, such as physiotherapists and nurse practitioners, will find the book useful. With increasing subspecialisation in orthopaedic surgery, it is more difficult for the specialist to keep abreast of recent changes and current trends in the management of orthopaedic conditions other than their own area of interest. This book aims to fill that void and will be an easily readable source with information that is concise and current. Emphasis is placed on the current literature and an effort has been made to provide evidence on controversial topics with annotated references incorporated into the text. These will be a useful resource for further reading. Any reader wishing to gain insight into 21st century orthopaedic surgery will find this book of interest and value.

Chapter 1 Arthroplasty

Total hip replacement

Total hip replacement (THR) is one of the most successful operative procedures in orthopaedic surgery.

Indications

The indications for THR are as follows:

•To relieve hip pain that is unresponsive to non-operative measures.

•To improve function.

The vast majority of hip replacements are performed because of osteoarthritis. Other indications include rheumatoid arthritis, post-traumatic arthritis, avascular necrosis, dysplastic hip in skeletally mature patients, failed fracture fixations and tumours.

There is an increasing trend towards THR in active patients of 50-80 years with displaced femoral neck fractures.

Contraindications

Contraindications to THR include the following:

•Active infection in the hip.

•Relative contraindications include poor abductor function, medical condition or mobility, an immature skeleton and progressive neurologic disease.

Note

Blomfeldt R, Törnkvist H, Ponzer S, et al. Comparison of internal fixation with total hip replacement for displaced femoral neck fractures. Randomised, controlled trial performed at four years. J Bone Joint Surg Am 2005; 87: 1680-8. This study looked at 102 patients with a femoral neck fracture. All were older than 70 years and had intact cognitive function. At 4 years, the mortality rate was 25% in both the internal fixation and THR groups. The THR group had a 4% complication and 4% reoperation rate. The fixation group had a 42% complication rate and 47% reoperation rate. Hip function was better in the THR group.

Assessment and investigations

Pre-operative assessment should include the following:

•A detailed history and examination to confirm that the hip joint is the source of pain.

•Full blood count, electrolytes and urine analysis to check for urinary tract infection.

•Nasal and perineal swabs for MRSA.

•Cross-matching (or autodonation) of blood.

•Electrocardiogram.

•Chest X-ray, if medically indicated.

•X-ray of: the anteroposterior (AP) view of the pelvis; an AP view of the hip performed in 20° of internal rotation for templating; and a lateral view of the hip. At some centres, a shoot-through lateral view of the hip is also taken.

Other investigations:

•Lateral C-spine flexion and extension views for patients with rheumatoid arthritis affecting C-spine stability.

•Spirometry for patients with reduced pulmonary function.

•Cardiac assessment – echocardiography.

•Vascular assessment in patients with vascular compromise.

Informed consent

The procedure should be explained to the patient, along with all the risks of surgery. These are described later in the section on complications.

Cemented femoral component design

In the early days of THR, femoral prostheses were made out of cast stainless steel. This was not strong enough to sustain prolonged physiological loading and incidences of stem fracture led to development of cold-forged implants.

Titanium stems in cement transfer more load to the cement as the titanium is less stiff, leading to early cement fatigue and failure. Hence, cemented femoral components are made of stiffer materials – cobalt chrome or stainless steel.

A broad medial border on the prosthesis reduces the load on the cement. Hence, the diamond-shaped Muller prosthesis, which had a narrow medial border, is no longer used. The Thompson prosthesis used in hemiarthroplasty is also diamond-shaped in cross-section and has a narrow medial border. Femoral components should have a broad medial border to reduce cement strain, and a broader lateral border (e.g., C stem) to load the cement in compression (Figure 1.1).

Tapered stems (e.g., the Exeter system) help to transfer the load to cement evenly. Cement is stronger in compression. The flanged Charnley stem is broader laterally and helps to load the cement in compression. The C stem (DePuy) is thicker laterally and thinner medially – known as the third taper – which loads the medial cement mantle.

Offset

The offset of the stem is the perpendicular distance between the centre of the prosthetic femoral head and the longitudinal axis of the femoral stem (Figure 1.2). A high offset produces higher stress in the femoral stem and can lead to failure of the cement or metal. The advantage of a high offset, however, is that less force is required by the abductors because of an elongated lever arm. The offset of the prosthesis selected should normally reproduce the original offset of the patient.

Figure 1.1. Diagrammatic cross-section of femoral stems to illustrate differences in design.

Figure 1.2. The offset and neck length of femoral components.

Most femoral prostheses have a high-offset option. For instance, the Charnley stem provides an offset of 40 or 45mm. In systems in which a range of stem sizes are available, the offset increases with increasing stem size. Increasing the neck length also results in a higher offset.

Implanting a femoral stem in varus alignment increases the offset. However, this is disadvantageous in cemented stems as it leads to an inadequate cement mantle in zones 3 and 7 and may lead to early failure. A cementless stem implanted in varus will be undersized and have less contact with the endosteum.

Offset can be altered during surgery by the following:

•Using a high-offset stem – this will increase offset without increasing leg length.

•Using a longer neck length – this will add to offset as well as leg length.

•Using an offset liner with a cementless socket. The centre of rotation is more laterally placed in offset compared to standard liners.

•Lateral placement of the acetabular component...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Contents
• Contributors
• Foreword
• Abbreviations
• Chapter 1: Arthroplasty
• Chapter 2: Shoulder disorders
• Chapter 3: Sports medicine
• Chapter 4: Spine and nerve injuries
• Chapter 5: Foot and ankle
• Chapter 6: Hand
• Chapter 7: Bone and soft tissue tumours
• Chapter 8: Infections
• Chapter 9: Non-union
• Chapter 10: Inflammatory joint disorders
• Chapter 11: Arthrodesis and amputations
• Chapter 12: Disorders in children
• Chapter 13: Trauma
• Chapter 14: Nerve injuries and neuromuscular disorders
• Chapter 15: Imaging
• Chapter 16: Clinical examination
• Chapter 17: Surgical approaches
• Index