7.3 Preoperative planning for total hip replacement, consent, and complications

Preoperative planning is of the utmost importance in performing total hip replacement successfully and obtaining reproducible results. For the surgeon, meticulous planning allows for efficient utilization of resources, the selection of appropriate implants, the need for any special equipment, and the anticipation of intraoperative difficulties. It shortens the learning curve when performing relatively new procedures, and achieves consistent results. Because total hip replacement is an operation aimed at improving quality of life, emphasis must be placed on prevention of complications rather than salvage afterwards.

Patients undergoing hip replacement are often elderly. The approach should be a multidisciplinary one. Patient education, attention to psychosocial needs, and early assessment of home circumstances will assure timely discharge home and increased satisfaction (Box 7.3.1).

The process begins with the careful evaluation of the whole patient (Box 7.3.2). The indication for hip replacement must be well founded and appropriate. It is important to clarify that the signs and symptoms for which treatment is sought is attributable to the hip, and not the adjacent joint or overlying soft tissues. Childhood conditions such as developmental dysplasia of the hip, slipped upper femoral epiphysis, and Perthes’ will have obvious consequences on the choice of implant due to altered anatomy, as will any previous surgery for these conditions.

The preoperative examination (Box 7.3.3) should include assessment of the patient’s gait, as well as the spine and knee. Any conditions precluding the use of crutches or walking aids will have obvious consequences. Limb-length discrepancy, both true and apparent, should be established. The true limb length is measured from the anterior superior iliac spine to the medial malleolus; apparent length is from any midline structure, e.g. the umbilicus, to the medial malleolus. The commonest reason for apparent leg-length discrepancy is abduction or adduction contractures around the hip. When there is a difference between actual and apparent leg length, pelvic obliquity should be assessed with the patient sitting and standing. Pelvic obliquity due to causes above the pelvis, e.g. lumbar scoliosis, persists in the sitting position. Conversely, obliquity due to causes in or below the pelvis, e.g. gross arthritis, post-traumatic deformity of the pelvis, infection, or muscle contracture, resolves on sitting. In addition, leg-length discrepancy due to more distal causes, such as limb fracture, poliomyelitis, infection, and physeal trauma, should be excluded.

Correcting any leg-length discrepancy optimizes muscle function and provides the patient with improved gait and increased comfort, provided the stability of the hip replacement is not compromised, and sciatic nerve function not threatened.

Patients at high risk of postoperative dislocation, e.g. due to neuromuscular problems, should be identified. This may influence the choice of implant, e.g. the use of a larger femoral head to confer greater stability.

The aim of implant positioning in hip arthroplasty is to restore the biomechanics (Box 7.3.4); templating helps to achieve this reliably and consistently. The traditional method of templating involves the use of transparent acetate templates held against hard-copy radiographs. The magnification of radiographs is generally in the region of 110–125%, and this needs to be known. Templates are usually supplied by the manufacturer.

Templating usually follows the steps of surgery, and attention is first turned to the acetabulum to determine the centre of rotation, and the cup position and size. A horizontal reference line can be drawn through the base of the teardrops, which represents the true floor of the acetabulum; it is also helpful to identify two further key anatomic landmarks—the ilioischial line and the superolateral margin of the acetabulum (Figure 7.3.1). Correct positioning and orientation of the cup is essential for the stability of the hip replacement. The cup should be sized so that it lies in 45 degrees of abduction, the medial border approximates the ilioischial line, and there is adequate lateral coverage. The inferior border of the cup is placed level with the teardrop line (Figure 7.3.2). In cemented cups there should be a 2–3-mm uniform cement mantle. The centre of rotation should be marked, and compared with the contralateral hip; templating the contralateral hip is useful in the presence of bone loss. Any osteophytes that need removal and cysts that require curettage and grafting are noted. Special care must be taken to seat the cup in the anatomically correct position in the presence of protrusio acetabuli, a lateralized acetabulum due to medial osteophytes and the dysplastic acetabulum; the use of bone graft may be required to augment any defects in these situations.

The aims of femoral templating are to restore femoral offset, optimize limb length and correctly size the stem. The anteroposterior (AP) view of the pelvis is useful to assess limb-length discrepancy. The teardrop line is used to orientate the pelvic axis; alternatively, a horizontal line drawn through the most distal part of the ischial tuberosities is also commonly used. The former is more accurate, as it lies nearer the centre of rotation of the hip joint. The vertical distance between this reference line and the most medial part of the lesser trochanters will enable measurement of any limb-length difference (Figure 7.3.3). The radiographic discrepancy should be compared with that measured clinically.

A line perpendicular to the femoral shaft at the level of the tip of the greater trochanter can be used to assess the desired level of the centre of rotation of the femoral head; caution must be exercised in the presence of coxa valga and coxa vara, as the true centre of rotation will then lie above and below the tip of the trochanter respectively. The stem size is chosen next, depending on the mode of fixation—for a cemented stem a 2–3mm cement mantle is desirable. For cementless fixation, adequate endosteal contact is required, either proximally or in the diaphysis, depending on prosthetic design. Finally, the femoral template is translated proximally or distally depending on the desired limb-length correction. The amount of limb-length change produced by surgery will be the vertical distance between the centre of rotation of the femoral component and the centre of rotation of the acetabular component.

The femoral offset should restore the offset of the normal hip; this can be judged from the contralateral hip if required. The offset is the horizontal distance between the centre of rotation of the hip joint and the longitudinal axis of the femur, and there is large anatomical variation (Figure 7.3.3). Failure to reproduce the correct offset will decrease the abductor moment arm, lead to a limp, increase joint reaction force and wear, and cause instability. Once again, the change in offset produced by surgery will be the horizontal distance between the centre of the femoral head and the centre of rotation of the cup on templating. Some stem designs allow for different offsets and neck-shaft angle. In addition, the angle and level of neck osteotomy can also be altered. In this way, it may be possible to adjust for anatomic variations in offset. Finally, when the surgeon is happy with the chosen size and position of the stem, the new centre of rotation and the position of the neck cut should be marked. Templating should usually aim for the middle range of neck lengths to allow for adjustment to a shorter or longer size of head intraoperatively if required.

The lateral view of the hip helps to plan the location of the femoral opening, and assess the femoral bow and the AP canal diameter. Any excessive femoral anteversion can be detected on a true lateral view. An inaccurate femoral entry point can lead to eccentric reaming and concomitant shaft perforation.

Digital radiographic technology is increasingly being introduced into hospitals in association with Picture Archiving and Communication Systems (PACS). This has changed the traditional templating process; the central issue here is of variable magnification in the digital images. An external scale marker of known dimension attached to the patient at the time of imaging is therefore needed to assess the magnification. On-screen templating requires specific digital software, and are now commercially available, although at considerable cost. The sequence of steps involved in templating is similar to those outlined earlier. The hope is that these will make the whole process faster and more accurate, and translate to improved patient outcomes.

Informed consent is a legal requirement before any surgical procedure. Effective communication is the key to enabling patients to make informed decisions. Successfully consenting a patient to treatment revolves around three key issues: the patient must have adequate mental capacity to make the decision; have sufficient information upon which to base their decision (Box 7.3.6); and reach that decision voluntarily without undue duress.

The surgeon should pass on that information which any reasonable patient would wish to know before giving consent. In the setting of hip replacement, this should include the common risks and complications. If cardiopulmonary or systemic condition places the patient at high risk, the patient should be fully informed and guided with relatives in deciding whether to undergo surgery.

The doctor who consents should whenever possible be the one carrying out the procedure, or at least be appropriately qualified and familiar with all the details involved. The explanation given to the patient is of paramount importance and the signing of the consent form is of secondary significance. Due consideration should be given to language ability, appropriate setting, and adequate time.

A structured verbal discussion of the information has traditionally been the mode of imparting the information. Alternatively, a written information sheet may also be employed, and this may enhance patients’ comprehension and recall of information.

The increasingly litiginous environment at present may endanger the surgeon’s ability to practice. Good consenting practice is crucial both for the patient and for the surgeon. A recent review of malpractice claims of an insurance company that involved orthopaedic surgeons noted that all the claims involved elective surgery, and not a single emergency case. Poor communication was established as the critical factor linked to malpractice claims. Documentation in the surgeon’s notes that informed consent took place was associated with a decreased risk of indemnity payment; dictating even a brief description of the informed consent processes—whether part of the clinic notes or the operative notes—is deemed as more legally substantive.

Patients undergoing total hip replacement often have significant medical comorbidities, and the general risks of surgery must not be forgotten when obtaining informed consent. Cardiovascular, pulmonary, and renal complications can occur, and patients should be counselled as to these (Box 7.3.7).

Published reports of the incidence of dislocation after primary hip arthroplasty vary from 0.2–7%, the majority occurring within the first few months after surgery. Variables that influence postoperative instability can be grouped into: factors related to the surgical technique; factors related to the prosthesis; and factors related to the patient.

The surgical approach has commonly been cited as a risk factor for dislocation, with the direct lateral and anterolateral approaches reporting lower rates than the posterior approach. A recent meta-analysis, however, concluded that there was insufficient evidence in the published literature to support this claim. Others have stated that if repair of the posterior capsule and short external rotators is performed, the dislocation rate following the posterior approach is comparable to that of the lateral/anterolateral approach. Surgical experience may also affect dislocation rates, with more experienced surgeons having a lower incidence.

Proper orientation of the acetabular component is a very important factor for hip stability. Cup placement in 35–45 degrees of abduction and 15–25 degrees of anteversion has been generally accepted as ideal. Retroversion, excessive anteversion, or placement of the cup in a more vertical position can all lead to increased instability and accelerated wear. In addition, the aim should be to centre the primary arc range of the hip replacement in the middle of the patient’s functional range.

The use of larger femoral heads is another factor that may enhance postoperative stability. Larger femoral head sizes provide a more favourable head–neck ratio and therefore allow a greater arc of motion before impingement occurs. The use of constrained liners can also decrease instability rates; however, their use may be associated with increased polyethylene wear and loosening secondary to impingement.

Inadequate restoration of femoral offset results in decreased tension on the abductor musculature and subsequent instability. Preoperative templating should ensure that when the prosthetic stem is inserted, appropriate neck length and offset are restored. Restored hip mechanics confer stability via optimized abductor tension.

Finally, inherent neuromuscular disorders in the patient can affect hip stability by compromising soft tissue function. These can be grouped into central causes such as stroke, cerebellar dysfunction, Parkinson’s disease, alcohol abuse, and peripheral causes such as peripheral neuropathy and lumbar stenosis.

Most cases of dislocation can be successfully treated with closed reduction and abduction bracing. Patients who experience multiple dislocations may require revision surgery; it is then crucial to identify the cause of dislocation, as this leads to optimal results. Surgical options include revision for malpositioned components, use of constrained acetabular components, larger femoral heads, and trochanteric advancement.

The reported rate of deep infection after total hip replacement is now around 0.3–2%. Infection arises either by contamination at the time of surgery or later by haematogenous spread; the airborne route is probably responsible for most cases. The commonest organisms are Gram-positive, with Staphylococcus aureus (50–65%) and Staph. epidermidis (25–30%) accounting for the majority. The remainder consist of other bacteria, fungi, and mycobacteria.

Also important is the suppression or elimination of infection at remote sites before surgery. Dental procedures produce a bacteraemia in nearly all patients, and should be covered with antibiotics, although this remains controversial. Any chronic skin ulcers should be treated prior to hip replacement. Patients should be screened to exclude concurrent urinary tract infections, and if identified, appropriate treatment instituted.

The use of ultraclean air and prophylactic antibiotics in combination has had a dramatic reduction in the rate of sepsis. The use of prophylactic antibiotics has been of paramount importance. Cephalosporins tend to be the antibiotic of choice because of their broad-spectrum activity. A preoperative dose at induction is always administered; the evidence for the recommended duration of prophylaxis thereafter is in favour of 24h, and not for longer periods.

Evaluation of a patient with suspected infection should include the use of blood inflammatory markers, plain radiographs, bone scans, and white cell scans. The goals of treatment are the eradication of infection and restoration of function; treatment itself is usually operative.

Despite the use of thromboembolic prophylaxis for some time now, deep venous thrombosis continues to pose a significant risk after total hip replacement. In the absence of any prophylaxis, deep venous thrombosis rates are reported to be in the region of 40–60%, and the incidence of fatal pulmonary embolism about 0.5–2%; with prophylaxis, the corresponding rates are approximately 3–30% and 0.5 % respectively. Despite extensive research, the ideal agent for prophylaxis remains controversial; however there is agreement that some form of prophylaxis should be used. The results of randomized trials indicate that low-molecular-weight heparin, warfarin, and fondaparinux are the most effective agents, with or without the use of graduated compression stockings and/or intermittent pneumatic compression devices. Surgeons are concerned about bleeding associated with the use of prophylactic agents, as it can lead to haematoma formation, infection, and reoperation. Further controversy also surrounds the duration of prophylaxis; prophylaxis should, however, probably continue beyond discharge. The selection of a particular regimen depends on the experience of the surgeon and risk factors in individual patients.

Limb-length discrepancy after total hip replacement may result in impairment of abductor function, pain, and a limp; it is one of the commoner reasons for significant patient dissatisfaction in an otherwise successful arthroplasty. The amount of disparity that causes a clinically significant or functionally relevant shortening remains unclear, and published data are conflicting. This is probably due to variation in individual patients; the presence of concomitant spinal deformity, pelvic obliquity, and contractures of the contralateral limb all have an influence on the patient’s functional leg length. Psychological issues and cosmesis are also important factors in the patient’s perception of leg-length discrepancy.

Preoperative radiographic templating, as outlined previously, should be used to minimize the possibility of creating a significant leg-length discrepancy. A method of intraoperative assessment of leg length is also essential. A variety of methods are available: iliac fixation pins, intraoperative calipers, and computer-assisted navigation have all been described. Leg length can be compared by assessing the equivalence of knee joints and the malleoli. Measurement of distances from the tip of the greater trochanter to the centre of the femoral head, and the distance from the lesser trochanter to the centre of the femoral head should be compared to preoperative measurements. The toggle or ‘shuck’ test, in which the hip is distracted in the neutral position, also indicates length restoration; in general no more than 2mm of distraction should be possible.

Leg-length inequality may respond to the use of a shoe raise; persistent symptoms or significant patient dissatisfaction may necessitate revision surgery.

The overall incidence of nerve injury associated with total hip replacement is 1–2%. Sciatic nerve injuries are by far the commonest, accounting for about 80%, followed by femoral, with obturator and superior gluteal nerve injuries accounting for a very small number. The posterior approach to the hip is traditionally associated with injury to the sciatic nerve, but the lateral approach may also be responsible. The aetiology of injury is usually unknown in a significant proportion of the cases. Out of the known causes, traction, compression, haematoma, constriction by suture, and heat from cement polymerization are generally responsible. Traction injury may be from intraoperative manoeuvres including dislocation and reduction, or from leg lengthening. Lengthening of greater than 4cm is generally accepted as a risk factor for nerve injury.

The majority of injury to the sciatic nerve affects the peroneal division; it is at increased risk of damage because it is tethered at both the sciatic notch and the head of the fibula, and is also located more laterally than the tibial division. For the femoral nerve, mechanisms of injury are similar to those that can lead to sciatic nerve palsy, and include direct injury from retractor placement, leg lengthening, and extruded cement. Obturator nerve injury is rare, and is usually due to cement extrusion, and anteroinferior quadrant screw placement. Injury to the superior gluteal nerve is a complication of the anterolateral or direct lateral approach to the hip.

If the postoperative clinical evidence points to injury of a nerve at the time of surgery, then that nerve must be explored. Loss of motor and sensory function, and in particular pain and numbness in the distribution of a nerve, should alert the surgeon to the possibility of its damage. Electromyography and nerve conduction studies are useful adjuncts in the diagnosis; however, they should not delay surgical exploration. Prompt diagnosis and early exploration is associated with a better outcome.

Vascular complications after total hip replacement are rare—reported rates in the literature are in the order of 0.1–0.2%. They can either be perioperative, presenting with obvious haemorrhage, or late, causing pain or ischaemia due to a pseudoaneurysm. The commonly affected vessels are the common femoral, the external iliac, and the obturator. Vessels may be injured by direct mechanisms (scalpel, retractor, or reamer) or indirectly from a stretching injury, particularly in patients with atherosclerosis.

The use of screws to augment acetabular stability has also caused concern with regards to vascular injury. The quadrant system as described by Wasielewski and colleagues has become popular as a guide to safe screw placement (Figure 7.3.4). The acetabulum is divided into quadrants by two lines; the first from the anterior superior iliac spine extending distally through the centreof the acetabulum, and a second line perpendicular to, and bisecting, the first line. The anterosuperior quadrant risks external iliac injury, and the anteroinferior quadrant risks injury to the obturator vessels. The posterosuperior and posteroinferior quadrants are the safest for screw placement, and generally have the best bone quality.

The reported incidence of periprosthetic fractures after total hip replacement varies, being in the region of 1–3% with cementless femoral stem implantation; the incidence is much lower using cemented stems. Fractures to the acetabulum occur much less frequently than occur in the femur. A recent report from the Swedish National Hip Arthroplasty Register found the accumulated incidence for primary hip replacements to be about 0.4%.

The surgeon must keep in mind patient factors that increase the chance of fracture, including age, female gender, and osteoporosis. Routine follow-up of patients after total hip replacement is critical in identifying those at high risk of fracture.

In conclusion, careful preoperative planning ensures that the goals of total hip replacement are consistently and reliably achieved—the anatomical aims of restoring the centre of rotation, leg length and offset, as well as maximizing patient satisfaction. It ensures that the appropriate implants are available, shortens the learning curve for the surgeon, and minimizes the incidence of complications. Digital templating is gaining in popularity, and holds promise for the future.

The process of obtaining informed consent is an important component of the whole process, both for the surgeon and for the patient. Due attention must be given to the provision of adequate information to the patient, and appropriate documentation.

Finally, a comprehensive knowledge of the aetiology and treatment of complications associated with hip arthroplasty is necessary for safe practice. A hip replacement is an elective procedure that is very good at improving a patient’s quality of life; the patient rightly has very high expectations. A meticulous approach will ensure the surgeon anticipates potential complications and minimizes them.